Table of Contents. List of Tables. Table Acidic Waste Water Quality Characteristics List of Figures

Transcription

1 Table of Contents 5.0 PROJECT DESCRIPTION Project Facilities Existing Facilities General Description Utilities Material Handling and Blending Concentrate Drying Flash Smelting Furnace (FSF) Peirce-Smith Converter (PSC) Metallurgical Off-Gas Handling Acid Plant Effluent Treatment Plant Slag Treatment Plant Electrical Supply and Distribution Instrumentation and Controls Building Services (Control Room and MCC Rooms) Project Diagrams and Process Flowsheets Drawings and Block Flow Diagram Plant Layout Existing Plant Plant Layout for Base Case List of Tables Table Acidic Waste Water Quality Characteristics List of Figures Figure Aerial View of New Smelter and Acid Plan Page i

2 Project Description

3 5.0 PROJECT DESCRIPTION The current smelter modernization project and planned investment scope relates solely to those areas within the Bor smelter and concentrator complex from receipt of road and rail delivered concentrates up to the production of the primary blister copper product and sulphuric acid and steam by-products for export from the complex. Investment in or changes to the existing anode plant and refinery facilities are not included in the current project. The project is planned to be built on the site of the existing TIR plant and Cadastral parcels in the industrial complex. All works will be carried out within the industrial complex with no expansion of existing boundaries and no temporary engagement of areas not belonging to the smelter. The new smelter project will involve closure of the old roaster / reverberatory furnace technologies and installation of new primary smelting by FSF technology. The existing copper smelter is to be modified to treat up to 400,000 tpa of copper concentrates using the Outotec FSF technology. The new production capacity will be equivalent to about 80,000 tpa of fine copper. The modernization will also incorporate the installation of a new modern gas collection for the FSF and a single operating PSC, with sulphur dioxide in the process gases fixed to sulphuric acid in a new sulphuric acid plant. The new sulphuric acid plant will treat the gases from the new FSF and modernized PSC gas handling operations. Liquid effluent from the smelter wet gas cleaning scrubbers will be treated in an effluent treatment plant. 5.1 Project Facilities The following discussion provides a detailed description of the following facility components: Existing Facilities - General Description & Status; Utliities for the Proposed New Smelter and Acid Plant; Materials Handling and Blending System; Concentrate Drying; Flash Smelting Furnace (FSF); Peirce-Smith Converter (PSC; Page 1

4 Metallurgical Off-Gas Handling; Acid Plant; Effluent Treatment; Slag Treatment Plant; Electrical Supply and Distribution; Instrumentation and Controls; and Building Services Existing Facilities General Description EIA Study New Smelter and Sulphuric Acid Plant Project The primary smelting plant uses a process of partial roasting of blended copper concentrate feed to yield a calcine which is fed to a reverberatory smelting furnace (reverb). While there are two similar lines comprising individual roaster and reverb furnaces, only one line is in operation as there is a shortage of concentrate feed. Over time, the nonoperating second line has degraded and been used as a source of parts. Reverb matte grading around 40% copper is currently processed in a single (hot) operating PSC with a second similar unit available on (cold) standby. Two additional converters are installed but these together with its associated plant have been closed down for many years. Blister grade copper produced in the batch operated converter is transferred to a single rotary, fire-refining anode furnace for subsequent casting into anodes on a single casting wheel. Anodes are processed to cathode in one of two electrolytic refining tank-houses. A second casting wheel associated with a further two anode furnaces is also installed but has remained shut down for many years due to the reduced throughput and lack of investment / rehabilitation. The main (strong) sulphur dioxide-bearing process off gases from the single operating roaster are cooled and partially de-dusted in a hot dry electrostatic precipitator (ESP) prior to ducting and mixing with converter gases. The converter process gases are collected via a hood and cooled in a water-cooled chamber and prior to partial de-dusting in a single ESP unit. An Induced Draught (ID) fan transfers the converter gas to a mixing chamber where it is combined with the roaster gases. Page 2

5 These mixed gases pass to a single operating acid plant (No. 2) for cleaning and cooling prior to conversion and fixation of the contained sulphur dioxide as sulphuric acid. The main process plant currently in operation was seen to be in a reasonable if rundown condition noting, however, that throughput remains substantially below the original plant capacity of about t/y copper. Current copper production is about tpa. Reverb gases pass via an ESP and fan system to an independent Reverb stack where they are currently vented to atmosphere without any sulphur fixation. The second roaster/reverb smelting line is in very poor condition such that substantial refurbishment and major investment would be required if it were ever intended to restart. With regard to the gas treatment aspects, the No. 1 acid plant, which is of similar design and capacity to the currently operating No. 2 acid plant, is in a state of major disrepair and has been substantially cannibalised to maintain operation of the No. 2 plant. A more modern and approximately of 50% larger capacity No.3 acid plant is also in a state of major disrepair and its refurbishment is not considered economically viable Utilities Process Description Plant Air and Instrument Air Plant air and instrument air will be provided by existing plant and equipment. Air receivers will be installed as necessary to maintain integrity of supply e.g. high pressure atomising air supply to the PSC evaporative cooling chamber water sprays. Plant Water The existing river water supply will provide plant water and will be treated as necessary to produce potable water and demineralised water using existing facilities. Potable Water Potable water will be used for emergency showers, eyewash and ablution facilities. Demineralised Water The existing smelter demineralised water plant will provide demineralised water for boiler feed water. Page 3

6 Steam (New) Saturated high-pressure steam (6 MPa) will be provided by the FSF waste heat boiler. Saturated low-pressure steam (2 MPa) will be provided by the sulphuric acid plant heat recovery system. Oxygen Supply (New) An over-the-fence oxygen supply will be required and must be capable of supplying 10,000 Nm3/h of technical oxygen at 150 kpa(g) during normal operation. The major portion of this oxygen will be required for enrichment of the FSF process air during operation. In addition, a smaller portion of high pressure oxygen at 1,500 kpa(g) will be required for matte and slag tapping of the furnace. A further portion of the oxygen will be required for blowing enriched air on both slag and copper blow stages of the PSC operation. Oxygen of minimum purity of 95% O2 by volume will be required. Equipment Description Water Treatment, Water and Fire Water Branches from relevant water tie-in points will run to delivery points in the following areas: Plant water for new conveying system for blending beds: wet concentrate feed system areas: slag cooling water tank; Firemain water for new conveying system for blending beds and wet concentrate feed system areas; Demineralised water for PSC primary cooling water system jacket cooling water tank; and Demineralised water to PSC Nº3 and Nº4 spray water tanks; No provision for secondary cooling water pipes has been made for this area. Page 4

7 Oxygen Distribution A pipe rack for low and high pressure oxygen will run from tie-in points at the over-thefence oxygen plant to delivery points in the FSF area for low pressure oxygen (40 kpa) and high pressure oxygen (1,500 kpa), and additionally for low pressure oxygen (150 kpa) to a tie-in point with low pressure blast air ducts for PSC converter Nº3 and Nº4. Air Supply and Distribution Branches for plant and instrument air from the relevant tie-in points will run to delivery points in the following areas: Plant and instrument for new conveying system for blending beds and wet concentrate feed system areas; Plant air for spray cooling system air receivers in cooling chamber; Instrument air for valves in converter gas handling system; and Plant and instrument air for slag cooling pits. Steam and Condensate Handling and Distribution No provision has been made for steam and condensate distribution. Fuel Storage and Distribution No provision has been made for heavy fuel oil and diesel storage and distribution Material Handling and Blending Process Description Material Off-Loading (Existing) Concentrates containing typically 10% moisture and fluxes delivered by rail will be offloaded using a rail tippler of 40t capacity. A weigh scale is under-fitted to the discharge belt conveyor. A ground hopper will be used for receiving concentrates and fluxes delivered by road. The ground hopper is suitable for both end and side-tipping vehicles. A weighbridge, remote from the ground hopper, is situated adjacent to the smelter site entrance for weighing road deliveries. Page 5

8 Material Storage (Existing) After off-loading, materials will be transferred by a series of conveyors and discharged into concrete bunkers in a covered storage area. Each concentrate type can be stored in discrete stockpiles for subsequent reclaim. Up to t of concentrate will be stored in this area. Up to 3 520t of silica flux will also be stored in the covered storage area. Concentrates and fluxes will discharge onto a material transfer conveyor. Charge Blending (Existing) The material transfer conveyor will transport the charge materials to the blending beds tripper conveyor where they will be discharged along the length of the bed to promote homogeneity of the FSF charge. There will be two blending beds, each of nominal capacity t, equivalent to about ten days supply at the nominal smelting rate. One bed will be built up while the other bed is in the process of being drawn down, providing the charge for the FSF. Material Transfer Material will be reclaimed from the blending beds by means of an existing front end loader. The front end loader will discharge the blend via an existing single hopper onto the blending beds existing reclaim conveyor. The blended concentrates will be transferred by a series of existing conveyors to a new diverter which directs the feed a new reversible conveyor that will feed three new day bins, two for storing blended furnace feed, each of capacity 400t, and one 40t capacity for storing flux. The concentrates and fluxes will be drawn from the day bins using weigh feeders, at prescribed rates, and fed via a new feed belt conveyor to a steam dryer. Equipment Description Concentrate and Silica Blend Conveying Blended copper concentrate will be transferred from the blending beds to blended concentrate bins using existing front end loaders and hopper / feeders as reclaiming units. Existing belt conveyors 1036, 1037 and 1038 will be used to transfer blend concentrate to day bins via a new diverter chute in the existing transferring tower. Three new belt conveyors will transfer the material to the feed day bins. Belt conveyor parallel to existing conveyor 1039 will run from the diverter chute to a new belt conveyor in a 90º Page 6

9 arrangement to deliver the material to a reversible belt conveyor which feed both blended concentrate day bins. Blended concentrate conveying capacity will be 240 t/h. Silica flux will be transferred from the material storage building using existing reclaimers. Existing belt conveyors will be used to transfer silica flux to day bins via a new diverter chute in the existing transferring tower. A belt conveyor will run from the diverter chute to a silica trimming bin. Silica flux conveying capacity will be 150 t/h. Blended Concentrate and Trimming Silica Blend Storage Two day bins for blended concentrate storage and one day bin for trimming silica flux storage will be provided. Each bin will be equipped with bar and knife valves. Blended concentrate day bins will be 400t each and the Silica flux day bin 40t. Wet Concentrate Feed System Three belt feeders fitted with belt scales will draw blended concentrate and silica flux from the day bins. Blended concentrate belt feeders will be treated at 80 t/h each and the Silica flux belt feeder 5 t/h. Feed materials from the belt feeders will be collected on the inclined belt conveyor and delivered to vibrating screen, for lump removal in the feed. Lumps will be collected in a tote bin and will be recycled to the blending plant. Screen undersize material will be transferred by a series of two belt conveyors arranged and a pipe conveyor which will feed the steam dryer feed belt conveyor. Vibrating screen and steam dryer feed conveying system rating will be 80 t/h Concentrate Drying Process Description The drying process will comprise a single rotary steam dryer for indirect heating using saturated steam of feed that contains approximately 10% moisture. The FSF blended Page 7

10 feed mixture from the raw materials handling area will be dried to less than 0.3% free moisture by weight. Steam at about 2 MPa pressure and 212oC will flow through steam heating elements and condense on the inner surface. The heat released will be conducted through the element wall and into the wet feed mixture bed. As the temperature of the wet material rises, moisture will vaporise, diffuse through the material bed and evaporate into the dryer freeboard. The driving force of this phenomenon is the vapour pressure gradient, firstly inside the material bed and secondly, between the material bed and the ambient air. The humid air will be continuously drawn from the dryer and be discharged to atmosphere through the gas collection system. Gas collection will consist of a bag filter and exhaust fan. The exhaust fan will be equipped with a variable speed drive for draught control. Description The dryer will use indirect heating by medium pressure saturated steam as the energy source. The steam manifold will be located at the end of the dryer. From the manifold steam will be divided into several steam-pipe heating elements located in the direction of the drum axis. The whole steam-pipe heating element system will rotate along with the dryer shell. The elements will be designed to allow the steam to flow freely in the pipes and the condensed water will be collected in the manifold. The condensate will be removed via a siphon pipe through the rotary joint. The dryer will be supported by two riding rings, each rolling on support rollers. The drum will be slightly tilted downwards and thrust rollers will be installed to prevent the drum creeping off the support rollers. The feed-hole, located in the centre of the feed-plate, will allow the belt feeder to bring the wet feed mixture into the dryer and also allows the entry of purge air that will remove the evaporated moisture. At the discharge end there will be a weir plate that allows the dry product to flow out of the drum and will control drum filling. The shell of the dryer will be made from mild steel plate. The inside of the drum will be lined with a stainless steel plate to prevent corrosion and moist concentrate sticking to the shell. At the discharge end, the warm air carrying the vaporized water and a small amount of dust will be drawn from the drum by an exhaust fan via a bag filter to stack. The new Page 8

11 purge air flowing into the dryer through the feed-end hole continuously replaces the removed air. The dryer product together with dust collected in the bag filter will be stored in a dried FSF blended feed bin below the steam dryer. The dried product will be discharged into a pneumatic conveyor tank and be conveyed by means of two parallel dense-phase pneumatic conveyors to a FSF feed bin located above the FSF loss-in-weight feed system. Normally, both pneumatic conveyors will operate. Dry compressed air will be used for conveying. The FSF feed bin will be equipped with a bag filter for cleaning the conveying air and a fan for exhausting it to atmosphere Flash Smelting Furnace (FSF) Process Description The dry charge mixture, together with the oxygen-enriched process air, will form a homogeneous suspension that reacts in the reaction shaft. The suspension heats up, ignites and burns rapidly to form a matte and slag in the settler. The main shaft reactions that will occur are: 4CuFeS2 + 61/2O2 = (2Cu2S + FeS) + 3FeO + 5SO2 2FeS2 + 5O2 = 2FeO + 4SO2 Corresponding reaction equations can be written for the other sulphide minerals that form the concentrate mixture. These oxidation reactions will produce energy for smelting the reaction products. Page 9

12 The degree of oxidation or matte grade will be controlled by the total oxygen / feed mixture ratio, the oxygen coefficient. By increasing the oxygen coefficient, a greater part of iron sulphide will be oxidised, resulting in a higher copper content of matte. The matte grade will be selected for optimising the smelter operations as a whole. It can be changed when required by adjusting the oxygen coefficient. The furnace temperature and furnace heat balance will be controlled by the degree of oxygen enrichment of the reaction air and modulation of the fuel sent to the various burners. Generally the normal range of oxygen enrichment is 40-60% O2, depending on the feed mixture composition, the condition of the furnace and the feed rate. The reactions taking place in the reaction shaft will be mainly exothermic. The concentrate in consideration at Bor is particularly hot, so oxygen enrichment at the lower end of the typical range will be applied. The process will be operated with as high oxygen enrichment as the reaction shaft heat balance will allow. The middle fuel oil burner in the middle oxygen lance can be used for maintaining the heat balance in the reaction shaft if needed, and will ensure that the feed mixture be properly ignited. Smaller size particles will ignite readily and consume most of the oxygen in the process air. The smallest fraction will be over-oxidised; producing magnetite that partially dissolves in the slag. Larger sized particles will heat more slowly and experience lower residence time in the reaction shaft, resulting in under-oxidation Page 10

13 In the settler, the molten as well as solid smelting products will separate from the gas stream. The reactions will still continue in the bath below the reaction shaft when the over and under-oxidised particles react with each other producing matte, slag and sulphur dioxide gas. The slag forming reactions between the oxidic reaction products and silica flux will be completed in the bath. The main reactions will be as follows: 2FeO + SiO2 = 2FeO.SiO2 (fayalite). Because matte and slag are insoluble in each other, they separate in the furnace settler. The matte droplets will be denser than slag and settle by gravity through the slag to form a distinct layer on the furnace bottom. The less dense slag layer will float on the matte layer. Some technical oxygen will be blown into the settler, close to the uptake shaft, to ensure flue dust post-combustion and sulphatizing reactions proceed. There will be five nozzles to distribute and mix the technical oxygen evenly to the furnace off-gas. Flue dust sulphatizing reactions will be completed in the waste heat boiler by the sulphatizing air feed. Burners are also present in the settler to maintain the settler heat balance. A matte grade of 62% Cu has been selected, but can be adjusted based on operational requirements. The main factors affecting the selection of matte grade will be: Raw materials; Converting capacity; Volumetric capacity of acid plant; and Oxygen plant capacity. Equipment Description FSF Feed Systems The gravimetric feed systems for the FSF feed (concentrate and silica flux) and flue dust will consist of the following: A material fluidisation cone at the feed mixture / dust bin bottom hopper; Slide gate valve; Dome valve; Page 11

14 Dosing bin; Agitators; Screw feeder; and Bin venting system. The bottom cone of the bin will be provided with aeration nozzles to fluidise the material to aid discharge. The feed mixture bin and the dosing bin are provided with load cells. The dosing bin is filled batch-wise with a dome valve. The dried feed mixture is fed from the dosing bin to an air slide conveyor via a screw feeder. The FSF feed systems consist of gravimetric loss-in-weight feeders for both the feed mixture and recycled flue dust. The concentrate will be fed from the dosing bin to the concentrate burner via the screw feeder system and the air slide conveyor. The operation of the gravimetric feed system will be based on the continuous weighing of the material in the dosing bin, calculation of the actual feed rate and control of the rate according to a set point by the speed of the screw feeder. The dosing bin will be filled batch-wise and the screw feeder speed programme-controlled. The dosing bin outlet will be provided with agitators to fluidise the material and provide constant feeding. The dosing bin aeration will be carried out with the venting duct and valve system. One valve will be open during normal feeding (dosing bin emptying) to let the compensation air flow into the dosing bin for accurate weighing. The other valve will be opened during the dosing bin filling period to let the exhaust air flow into the feed mixture bin. The exhaust gas from the bin will be cleaned in a bag filter and blown to atmosphere by an air fan. The air slide conveyor for the furnace dry charge mixture will be a slightly downwardstilted air-assisted gravity conveyor using dried plant air. Flue Dust Feed to FSF Flue dusts from the FSF off-gas handling will be re-circulated back to the process via a separate FSF flue dust feed system. Recycled flue dust will be pneumatically conveyed Page 12

15 into the dust bin by dense phase pneumatic conveyors. An equivalent loss-in-weight feed system will weigh the flue dust and convey it to a slide conveyor. The gravimetric system for flue dust corresponds to that of the dried feed mixture with dosing and screw feeder. The screw feeder will feed the flue dust to a draglink conveyor which will convey the total FSF charge to a concentrate burner located in the centre of the reaction shaft roof. Concentrate Burner The concentrate burner will be provided with a central jet distributor for distributing the dry charge and oxygen enriched process air as an even suspension into the reaction shaft. The spread of the air-concentrate suspension will be controlled by adjusting the flow rate of the suspension air. Plant air will be used to supply the distribution air for the central jet distributor. The distribution air will cool the jet distributor; the shell around the jet distributor will be water-cooled. Oxygen-enriched process air will be blown into the air chamber of the concentrate burner. Process air velocity will be controlled at the air chamber discharge opening. A part of the oxygen demand for smelting, referred to as middle oxygen, will be fed as technical oxygen through the middle lance of the central jet distributor. The middle oxygen lance will be used to control the smelting reactions in the middle zone of the reaction shaft. The concentrate burner will be equipped with step-less process air velocity control to maintain the required process air velocity at the air chamber discharge opening, over the range of operating conditions. In the central jet distributor a fuel oil lance will provide additional heat to the concentrate suspension. The middle fuel will be burned with technical oxygen emanating from the middle oxygen lance. Flash Smelting Furnace Structure The FSF consists of three main sections: a vertical reaction shaft; a horizontal settler; and a vertical uptake shaft. The reaction shaft is a refractory-lined cylindrical-shaped tower suspended from a rigid furnace steel frame. The refractory lining will be thermally protected with copper cooling elements installed between the brick layers. The main smelting reactions take place in the reaction shaft. Molten products and off-gas are then led to the horizontal settler. Page 13

16 The settler is a rectangular, refractory-lined vessel. The steel casing will be retained by vertical buck-stays and horizontal beams that surround the casing and will be connected to each other by spring-loaded tie-rods. The structure will allow thermal movements during heating and cooling against preset inward-force spring loads. Copper cooling elements will be used to cool the refractory lining of the settler walls and part of the settler roof. In the furnace settler, matte and slag layers will be formed that separate into two distinct layers. The process off-gas is conducted to the uptake shaft. The uptake shaft is a vertical, refractory-lined cylindrical structure at the opposite end of the settler. The uptake shaft will be suspended from the rigid steel frame surrounding the furnace. The connections between the settler and uptake shaft, as well as the uptake shaft and waste heat boiler, will be cooled by copper cooling elements. The dustcontaining off-gas will be conducted via the uptake shaft to the waste heat boiler. Matte and Slag Tap Holes Matte tap holes will be located at the sidewall and reaction shaft end wall of the settler. The tap holes will be equipped with water cooled copper plates. The holes will be opened manually using oxygen lances and closed with clay cones / stoppers. Matte will be periodically tapped through the tap holes and laundered to ladles for transfer by aisle crane to PSCs. The matte launders will be constructed of steel plate and lined with refractory. Slag will be tapped through the tap holes at the uptake end of the settler. The tap holes will be equipped with water-cooled copper plates. The tap holes will be opened manually using oxygen lances and closed with clay cones / stoppers. Slag will be laundered to dedicated slag ladles that will be transferred to the slag cooling area by carrier. The slag launders will be constructed from water cooled copper. FSF Burners The settler will be provided with four roof- and six wall- fuel-oil burners. Each settler burner will have a design capacity of 300kg/h of fuel oil. Auxiliary fuel oil burners will be available to ensure the furnace heat balance. Product target temperatures will be maintained during normal operation and also during feed interruptions or during heat up of the furnace after relining. Because of the batch nature of the PSC operations, FSF matte tapping will be intermittent. Fuel oil burners will be provided for the matte launders to maintain launder temperature and aid matte flow. Page 14

17 Process Air and Combustion Air Fans Two process air fans will supply process air to the concentrate burner, one in operation and one on standby. Two combustion air fans will supply combustion air to the fuel burners and sulphatising air to the waste heat boiler. Each fan will be provided with inlet guide vanes and be equipped with frequency converter drives. The combustion air fans will be also connected to emergency power. FSF Cooling Water System The FSF will consist of a primary closed-circuit cooling-water system. The heat from this circuit will be removed in plate heat exchangers that will be cooled by secondary cooling water. The secondary cooling water will be cooled open-circuit in a cooling tower(s). Primary Cooling Water System The primary cooling water system will comprise: jacket cooling water tank; circulation pumps; heat exchangers; supply lines with distribution headers; collection headers; and return lines. Primary cooling water will pumped from the jacket cooling water tank via plate heat exchangers and through cooling water headers to the FSF cooling elements. There will be three electric jacket cooling water pumps; two will normally be in operation at any one time. There will be two standby diesel pumps. The electric pumps will be connected to the emergency power supply. In case of a power failure, emergency power will be connected automatically in about 20 seconds. If the emergency power cannot be started within about 2 minutes, the diesel pumps will be started automatically. FSF cooling elements will be fitted at various locations in the brick lining. Water cooled copper blocks are situated at the following locations: Reaction shaft walls; Settler walls and roof; Settler and reaction shaft junction; Settler and uptake shaft junction; and Uptake shaft and waste heat boiler junction. Page 15

18 Tap-hole blocks and slag launders will also be of water-cooled copper construction. The concentrate burner cooling water supply will also be connected to the furnace closedcircuit cooling-water system. Warmed cooling water from the cooling elements and other water cooled equipment will be conducted to the collection headers and jacket cooling water tank for re-circulation. A small bleed / make-up will be needed to maintain cooling-water quality in the primary cooling water circuit. All electric primary circuit cooling-water pumps will be connected to the smelter emergency power system Peirce-Smith Converter (PSC) Process Description Converter Operation There will be two PSCs with nominal capacity 120t of blister copper. One converter will be hot and in operation at any one time with the second unit on cold standby / maintenance. There will be up to three converter charges (batches) per day producing a blister copper for subsequent fire refining in anode furnaces. About 160t of FSF matte will be ladled on demand to form each converter charge in a series of slag blows. There will be up to five slag blows before the final slag skim. The slag bowing will be followed by copper blows which are essentially continuous except for short interruptions to add copper scrap coolant. The typical blowing rate on slag and copper blows will be 33,000 Nm3/h and 36,000 Nm3/h respectively. Oxygen enrichment of the blast air typically will be 26% on a slag blow and 22.5% on a copper blow. Silica flux will be added to form a low melting point liquid fayalite type slag with FeO and Fe3O4. Silica will be stored in a bin adjacent to the converter hood; the fluxing rate will be nominally 1t per minute for blows other than the first when bank flux is being consumed. Temperature control during a slag blow will be effected by the addition of reverts. This is important for both bath temperature control and maximising production and recovery by the recycling of secondary materials. Crushed reverts will be stored in a bin adjacent to the silica flux bin and will be charged via the flux charging system. The converter is skimmed clean of slag as far as possible when almost all the FeS has been converted to iron oxide. The slag will be discharged into aisle ladles transferred by Page 16

19 electric (EOT) overhead travelling cranes and then decanted into new large transfer ladles that will be despatched by mobile slag carrier to the slag cooling area. Any matte that has settled out of this slag is not added to the transfer ladles but will be returned to the converter. The rate of temperature rise during a copper blow will be only about one third of that on a slag blow; however, the temperature rise is sufficient to require cooling by the addition of recycled solid copper such as anode casting scrap and refinery tank house scrap anode returns. At the completion of the copper blow the blister copper produced will be low in sulphur and oxygen: generally within the ranges ppm sulphur and 1,000-8,000 ppm oxygen. It will be transferred by EOT crane to the existing anode fire-refining furnaces. As a second converter is not available to receive the final slag, and the copper content is too high to send it to the transfer ladle, the converter will have to be banked so that the blister can be removed from under the slag, ad the slag left in the vessel as a heel for the following charge. Banking is achieved by adding coarse flux adjacent to the mouth of the converter when it is in the skim position to solidify a bank of slag that act as an underflow weir for blister. The bank, which is high silica, is well preheated so the coarse flux is readily taken into the slag during the first slag blow of the following charge. Equipment Description No physical modifications to the converters themselves are planned except for minor improvements related to improving labyrinth-type sealing at the hood to apron plate interface. The operating cycle will change due to the higher matte grade Metallurgical Off-Gas Handling Process Description FSF Off-Gas System The off-gas from the FSF uptake shaft enters the WHB radiant section where it will be cooled to form steam by indirect heat exchange with boiler feed water flowing in the membrane tube wall. The partially-cooled off-gas enters the convection section at a temperature of about 750oC where it will be further cooled along the length of this section by indirect heat exchange to form steam with boiler feed water flowing in pendant tube-banks suspended in the gas flow. Page 17

20 Flue dust suspended in the off-gas will consist of mechanically entrained dust; vaporised / condensed elements of the dry charge; and highly volatilised gaseous fumes of the dry charge impurity components. During cooling, the oxide flue dust will tend to form sulphates according to the following reaction-type which is highly exothermic: MeO + SO2 + 1/2O2 = MeSO4 The dust mass will increase due to the above reaction. As the stickiness of poorly sulphated dust is high, sulphating will be performed in a controlled manner in the radiant section to optimize dust physical characteristics. Part of the oxygen needed will be pre-mixed into the off-gas stream by injecting technical oxygen through nozzles into the FSF settler. The degree of sulphating of the entrained dust will be controlled by combustion air blown through nozzles at the inlet to the radiant section. Part of the sulphated dust will settle in the WHB dust hoppers and the remainder will be recovered downstream in an ESP. The oxygen content of the process off-gas will be controlled to balance the required degree of sulphation of dust against the need to minimise SO3 gas formation. Off-gas at about 350oC will exit the WHB and be ducted to a hot ESP for removal of the remaining entrained dust. In the ESP, the dust particles will be electrically charged by the corona of discharge electrodes and migrate under the influence of a strong electric field to collection electrodes where they will be deposited. The discharge and collection electrodes will be rapped by hammers and the dust will move vertically down the collection electrodes until it drops off at the bottom into dust collection hoppers. All the dust from the flash smelting process collected in the WHB and ESP will be recirculated to the FSF. The de-dusted off-gas containing typically 150 mg/nm3 residual dust will be ducted to an induced draught fan. This fan will discharge the cleaned off-gas to the wet gas cleaning plant whilst maintaining the required FSF settler freeboard pressure at about -50 to - 100Pa. PSC Off-Gas System Gas Collection Hood Converter off-gas will be collected in closely fitting hoods mounted above each converter mouth. Air dilution of the off-gas by ambient air ingress of typically around 110% of the equivalent volume of process off-gas takes place and will pre-cool the primary off-gas. Page 18

21 The air gap is necessary to prevent to hood being welded to the vessel by splash. The ingress air will reduce the amount of water subsequently required for evaporative cooling. The dilution air enters via the side seals, back-flap and front of the hood. Certain panels in the hood will be cooled by a dedicated closed circuit cooling water system common to both modernised converters. Heat energy will be removed from this closed circuit by indirect heat exchange with cooling tower water. Evaporative Cooling Chamber (ECC) The off-gas exits the converter hood at a temperature in the range oC and enters a horizontal ECC where it will be cooled by an evaporative spray cooling technique to about 350oC. The sonic-type spray equipment will have the capability to rapidly control the outlet temperature of the spray chamber over a wide range of gas enthalpies to cater for variations in converting conditions, blowing rates and hood dilution air ingress. In order to ensure complete evaporation, thus ensuring a dry dust hopper during operation, it will be necessary to generate a water spray consisting of fine droplets, normally less than 200 microns in size. The purpose of the spray atomisation system will be to provide sufficient air quantity and pressure for efficient atomisation of water at the spray nozzles, thereby ensuring complete evaporation of water and rapid cooling of the converter off-gas. Dust fall-out in the chamber will be removed by a draglink conveyor, collected and returned to the smelting process. Each converter will have its own dedicated gas collection hood and horizontal evaporative cooling chamber. The cooled off-gas from the outlet of the horizontal cooling chamber will be ducted to a common converter manifold via high velocity ducts into a wet gas scrubber. After wet scrubbing (described in the acid plant section), wet scrubbed converter gas will be mixed together with wet scrubbed FSF off-gas in a mixing chamber before ducting to the wet ESPs and sulphuric acid plant. Equipment Description FSF Off-Gas System Waste Heat Boiler The FSF waste heat boiler (WHB) is a forced-circulation type boiler that will consist of radiant and convection sections. The WHB will produce saturated steam at 6 MPa pressure. The heat exchange area will be maximised by the installation of tube screens in the radiant section and by banks of pendants in the convection section. Page 19

22 WHB main auxiliary equipment will consist of: steam drum; silencer; blow down tank; circulation water pumps; and mechanical dust rapping system with spring hammers. There will be three circulation water pumps: two electric pumps and one steam turbine pump (standby) located close to the boiler. The electric pumps will be connected to the emergency power supply. Dry Electrostatic Precipitator The cooled off-gas from the FSF WHB will be drawn through a single four or five field dry ESP. The ESP will have inlet and outlet plenums and dust collection hoppers and be thermally insulated to prevent heat losses and minimise corrosion. The gas flow will be evenly distributed by baffle plates in the ESP. The dust collection plates and discharge electrodes will be suspended vertically in the chamber and will be automatically and sequentially rapped by hammers located out of the gas stream. The dust hoppers will be provided with air-lock valves to prevent ingress of air. Dust collected in the ESP will be transported via drag link conveyors and pneumatic handling systems that feed the recycle dust bin. Transformer / rectifier sets will be mounted on the ESP roof. Induced Draught Fan The cooled and cleaned off-gas will be ducted to an induced draught fan rated at 47,800 Nm3/h that controls the draught in the FSF settler freeboard. Secondary Gas Handling The matte and slag launders, matte ladle and slag pot areas, and all tap hole openings will be fitted with gas hoods for the collection of fugitive emissions. The FSF area ventilation gases will be collected and ducted to a bag house and the cleaned gas discharged to atmosphere via a gas fan and stack. Recycled Dust The WHB and ESP dust hoppers will be fitted with drag link conveyors for transporting the flue dust. Large dust lumps from the WHB will be crushed in a roller crusher. The crushed dust will be conveyed together with ESP dust by drag link conveyors. A dense phase pneumatic conveying system will transfer the dust to the flue dust bin above the FSF reaction shaft. All the dust produced from the flash smelting process will be re-circulated to the FSF via the dust loss-in-weight feeder. Page 20

23 During short stoppages of the dust conveying system, flue dusts from the WHB and ESP can be by-passed to the dust buckets from the dust hoppers of the drag-link conveyors. This dust will be re-circulated to the bedding plant. PSC Off-Gas System Gas Collection Hood The PSC off-gas collection hoods will be panelled chambers mounted over the converter mouths that capture the primary off-gas. They will fit as closely as practicable to the converters to limit infiltration air, and will use labyrinth seals to further minimize inleakage. The material of each air-cooled hood panel will be cast steel. Water-cooled panels will be fabricated from steel plate. The panels will be bolted together with a compressible gasket material that will ensure air-tight joints between the panels. There will be a common single water-cooling system for each of the two hoods. The water cooling tank, pumps and heat exchanger will be located at ground level. A closed loop system will use demineralised water (chemically dosed to prevent corrosion) as the cooling medium. The heat will be removed in a plate heat exchanger array by indirect exchange with water supplied from an open circuit cooling tower. Each hood will be provided with a sliding door at the front to enclose the mouth when the converter is blowing and to allow the addition of matte and solid materials or the pouring of slag and blister copper when open. A moveable flap at the back of the hood will seal when the converter is in stack or, by partial opening, will allow limited control of hood air dilution. It will fully open to allow accretions from the hood uptake to drop out. Provision will be made for the addition of flux and reverts through the side of the hood. Evaporative Cooling Chamber (ECC) The ECCs will be horizontal rectangular chambers connected to the exit of the converter hoods by an expansion joint. The chambers will be approximately 4m wide by 5m high. The front portion (about one-third) of the chambers will be made of cast steel panels and the rear of the chamber from fabricated steel panels. The lower portions of the chambers will be single trough hoppers with a drag link conveyor. Dust collected in the ECC will be transported via a drag link cross-conveyor to a tote bin. This will be manually transported by forklift truck to the bedding plant. Page 21

24 The hood off-gas will be cooled by an evaporative spray cooling system that will include HP water pumps; air receiver; a valve rack and controls; piping and lances. Hoists will be provided to raise and lower the position of the lances in the chambers. The gas outlet of each ECC will connect via high velocity ductwork to a common manifold that connects to the inlet of a wet gas scrubber. The high velocity ducts will each be fitted with a butterfly damper for converter hood draught control and a vertically acting isolation valve. The gas outlet of each ECC will connect via high velocity ductwork to a common manifold that connects to the inlet of a wet gas scrubber. The high velocity duct of each converter will be fitted with a butterfly damper for converter hood draught control and a vertically acting isolation valve Acid Plant The gas flow to the sulphuric acid plant will vary considerably. The flow of FSF off-gas will present a base-line (almost constant) primary gas flow to the acid plant for a nominal 7,920 hours per year. The converter operation is, however, a batch process with a single converter blowing or not at any one time. The in-stack time is estimated to be 42%, sending gas to the acid plant for 3,350 hours each year. Thus for a minimum of 4,570 hours per year, the gas feed to the acid plant will comprise FSF gas only. There will be occasions where only converter gas will be going to the acid plant, but these are upset conditions and should not amount to more than a few hundred hours per year. The feed gas from the copper smelter contains dust, metallic fume, halides and sulphur trioxide. These materials must be removed from the gas before entering the drying section of the acid plant. Process Description The process described includes the following systems: Wet gas cleaning; Contact & absorption; Strong acid circulation; Preheater system; Steam generation; Acid sampling; and Page 22

25 Cooling water. Wet Gas Cleaning System FSF Wet Gas Cleaning This wet gas scrubber can have many physical configurations, but all share the common purpose of bringing the gas into intimate contact with scrubber solution to simultaneously cool and clean the gas. Vaporization of water from the solution will bring the solution and the gas to or near to the adiabatic saturation temperature, which for the case of FSF gas that has passed a waste heat boiler and Hot ESP, will be around 55 to 60oC. The pressure drop in the gas phase across the scrubber is not highly dependent on the scrubber configuration for a given target gas cleaning efficiency, and will be in the order of 5 kpa of water gauge during normal flow conditions. Both Venturi based and DynaWave based technologies are described below. Suspended particles in the gas phase, as well as some fume that condenses while the gas is cooling, will be captured in the liquid phase. In addition, any SO3 in the gas will also report to the solution, increasing the solution acidity. The saturated gases will proceed to gas cooling. Gas cooling is required to lower the moisture content of the gas so that the acid plant water balance can be maintained. To make sulphuric acid, H2SO4, there can not be more molecules of H2O than SO2, so the volumetric concentration of water must be lower than that of SO2. As the SO2 content of the gas is high, no cooling is required to achieve the necessary ratio. Nonetheless, to give an adequate operating envelope of the acid plant, cooling to under 45oC is recommended. Cooling will be effected by passing the gas through a pack bed tower with cooled recirculating scrubber liquor. The liquor will be cooled in a plate heat exchanger with open circuit cooling tower water to remove the heat. Solids accumulate in the scrubber liquor, which can be tolerated to varying levels depending on the scrubber technology selected. A blowdown will be required so as not to exceed the maximum permissible solid loading. The blowdown is usually equivalent to the quantity of water condensed from the gas phase in the cooling tower plus any fresh water that is used to flush the wet ESPs. However, for scrubbing technologies that can only tolerate low amount of solids, especially if applied to gases that have little moisture as is the case for FSF gas cooled in a waste heat boiler, make-up water may need to be added to control scrubber liquor solids percentage. There are also instances where the acidity of the liquor must be controlled by make-up water addition, or solubility of problematic minor elements such as selenium maintained by dilution. The blowdown typically referred to as weak acid bleed or weak acid effluent is sent to an effluent treatment plant for further treatment before discharge. Page 23

26 PSC Wet Gas Cleaning Similar to the wet gas scrubber described above, this device can have many physical configurations. For the case where PSC gas will be collected in tight fitting hoods and sent directly to wet scrubbing, the adiabatic saturation temperature will be around 70oC. The pressure drop in the gas phase across the scrubber will be in the order of 6 to 7.5 kpa of water gauge during normal flow conditions to account for the increased cleaning duty required in the absence of a Hot ESP. The saturated gases will be cooled to around 30 to 33oC so that a sufficiently low moisture content to respect the water balance on the rare occasions when the acid plant is treating only converter gas is achieved. Weak acid bleed will be sent to an effluent treatment plant for further treatment before discharge. Venturi Based Gas Cleaning System This technology will consist of a Quench Tower (QT), a Venturi Scrubber (RFS), a Gas Cooling Tower (GCT), an SO2 Stripper and three sets (2 in operation, and 1 stand-by) of Wet Electrostatic Precipitators (WESP) in parallel, with each set of WESP including a primary WESP and a secondary WESP. The off-gas coming from the FSF Hot Gas ID Fan or from the PSC Manifold will enter via a hot gas duct to the gas cleaning system at the specially designed vertical gas inlet nozzle. The gas will enter the cross-current zone of the scrubber and passes through the hot/cold zone. This cooling will reduce thermal stress of the brick lining. Circulating weak acid will be injected co-currently through spray nozzles made of corrosion and erosion resistant alloy. The gas will be quenched and saturated by means of circulating liquid sprayed from nozzles each independently supplied with scrubbing liquid located in the Quench Tower head. Adiabatic cooling to saturation temperature will be achieved in this zone of the scrubber. The high turbulence between the gas and the particles in this section are Page 24

27 important for partial dust removal from the gas. The removal efficiency partially depends on the particle size and the retention time. The sprayed water droplets will move through the flue gas, covering the entire cross section of the Quench Tower. Depending on gas enthalpy, the saturation temperature will typically be between C. As the circulating liquid in the Quench Tower will be a weak acid and the outlet gas temperature will be influenced by its concentration. Simultaneous to cooling, a portion of the impurities will be scrubbed from the raw gas, and transferred to the scrubbing liquid. To keep the arsenic and other impurities in solution and to avoid its crystallization, process water will be added via spray nozzles also located at the QT head. The scrubbing liquid will be drained from the QT and collected in a separate pump tank. Two separate and independent acid recirculation circuits are typical, each consisting of a pump, piping and related spray nozzles. Both circuits will be in continuous operation. In the case of failure of one pump, a third standby will enable continuous operation. Additionally, an emergency spray system, connected to the process water network, will supply fresh water from the Emergency Water System or Process Water system to the spray nozzles, initiated by a temperature control device located at the gas outlet of the QT and/or low pressure of the circulating liquid. Due to the evaporation loss in the QT, at least an equivalent amount of liquid must be added. The overflow from the gas cooling tower will be directed to the pump tank of the Radial Flow Scrubber and from there via the overflow to the pump tank of the QT. This overflow will be produced by means of condensation in the gas cooling tower. Page 25

28 Either to keep the concentration of impurities such as solids, arsenic, chlorine and fluorine below a desired maximum level or to keep the total liquid level in the range of the hydraulic design of the plant, a constant weak acid stream will be withdrawn, which will be pumped to the effluent SO2 Stripping Tower. The QT shell will be made from carbon steel protected from corrosive media with a soft rubber lining. The complete QT shell will be lined with acid resistant bricks upon which a layer of carbon bricks is applied for protection against hydrofluoric acid. The inlet elbow of the QT will be covered by one layer of heat resistant bricks for thermal protection and a layer of acid resistant bricks on the gas side. This design ensures strong protection and thus a long lifetime of the rubber lining. After the quench tower, the gases will pass through the Venturi flow scrubber. One particular manufacturer offers an adjustable pressure drop scrubber developed for conditions in off highly variable gas flowrate. For this device, the scrubbing zone is formed by two rings between which the gas and the scrubbing liquid flow radially from inside to the outside. The maximum relative velocity between gas and scrubbing liquid, which is the main criteria for scrubbing, is located at the narrowest point between the two rings. The cross section of the scrubbing zone may be modified by adjusting the lower ring. This enables a constant differential pressure and consequently a uniform scrubbing efficiency to be maintained even in the case of fluctuating gas volumes. The scrubbing zone is controlled as a function of the differential pressure. By adjusting the scrubbing zone, the gas flowrate can be changed by a ratio of up to 1:10 while maintaining a constant pressure drop. This feature permits optimum adjustment to varying modes of operation. It is especially suitable for batch processes in converters. The collecting efficiency of the scrubber can be defined as required, irrespective of fluctuating raw gas loads; and Even for critical substances like As, Se or Pb, high collecting efficiencies are achieved. Since radial flow scrubbers can be adjusted as required for the respective collecting efficiency the scrubber can be operated at optimum differential pressure which conserves energy. Page 26

29 Table Pressure drop of Venturi Scrubber and Radial Flow Scrubber at varying gas flow rate PSCs have two operating modes, full flowrate during blowing and no flowrate when on stand-by. During blowing, the variation in flow between that experienced with clean tuyeres as opposed to dirty tuyeres is a function of the diligence of the converter operator, and is not typically large. The difference in off-gas volume arriving at the scrubber between the slag blow and copper blow is about 6%, also a small change. As a consequence, the amount of movement made by the variable throat to achieve constant scrubber efficiency is small. Similarly, the off-gas flowrate from a FSF is relatively constant so the throat adjustments are very minor. As a consequence, the minor advantage of tuning the throat to modulate the pressure drop is normally outweighed by the cost of maintaining the system, so the throat is set at a constant setting that provides satisfactory performance during regular operation. The impurity loading in the gas also drops with flowrate, so the need to maintain scrubber efficiency at lower flows is unnecessary. When there is no flow, the scrubber throat setting is irrelevant. For these reasons, variable throat control has only been briefly adopted. If the plant were to be designed to mix the FSF and PSCV gases before a single scrubber, variable throat Page 27

30 would hold some benefit, but to date, furnace gas and converter gases have generally been scrubbed separately due to the difficulty of maintaining close draft control at the furnace with a system that has to handle the intermittent converter gas flow as well. The off-gas which will be adiabatically cooled in the scrubber passes through the packed cooling tower where it is cooled. The condensate accumulating in the cooling tower will be conducted to the scrubber circuit in order to make up for evaporation losses. The gas outlet of the cooling tower will not typically be equipped with a droplet separator because the irrigation system will be based on a weir trough system so that large weak acid droplets will be produced. These large droplets will not be carried to the top of the low gas velocity Cooling Tower. The packed cooling tower will be chemically resistant against H2SO4 and other impurities found in the gas stream such as chlorine. The shell of the Cooling Tower will be made of FRP with a chemical resistant barrier. Acidic waste water from the gas cleaning system will be pumped from the QT circulating system to an SO2 stripping tower. The packed stripping tower shell will be made of FRP with a chemical resistant barrier. For stripping, ambient air will pass through stripping tower in counter current to the liquid. Due to the lower pressure in the gas duct upstream of the Cooling Tower, a fan will not be needed. The air flow rate will be controlled by dampers located at the stripping tower inlet air flanges. The dissolved SO2 in the acidic waste water will be reduced to 100 ppm or less. The stripped weak acid will be pumped to the effluent treatment plant by a horizontal centrifugal pump (one in operation and one on stand by). Six WESPs will be arranged in three trains, each consisting of two stages. Two WESP trains will be in operation while one train serves as standby. All parts in contact with the gas stream will be either homogeneously lead lined steel or PP and FRP with chemical resistant liner / barrier. Page 28

31 DynaWave Based Gas Cleaning System The DynaWave Scrubbing System will consist of a Reverse Jet scrubber followed by a gas cooling tower. The gas first will enter the primary scrubber where it will be quenched and scrubbed with a counter-current spray of weak acid passing through large bore spray nozzles. Dust, fume and mist particles will be scrubbed from the gas and at the same time, the gas will be cooled by evaporation of water from the weak acid. The weak acid will be circulating through the scrubber without cooling. From the primary scrubber, the gas will flow to a packed cooling tower. The inlet barrel of the primary scrubber will be protected against high temperature by the presence of a weir bowl. The weir bowl will provide a uniform liquid film flowing down the inside wall of the inlet barrel. This will prevent the inlet barrel from coming in contact with the high inlet temperature gas. Liquid will be circulated back to the weir bowl via a recirculation pump. Because the gas will be fully quenched after the first froth zone, all downstream equipment can be made out of FRP. Emergency spray nozzles will be included in the system to protect the FRP disengagement vessel from excessively high temperatures resulting from failure of the circulation pump. Low liquid flow to the Reverse Jet or high-high temperature in the vessel will activate the emergency spray nozzles to quench the hot inlet gas. In the packed cooling tower, the gas will pass through random plastic packing where it will be cooled by counter-current contact with a circulating weak acid stream. The gas will be sub-cooled and water will be condensed out of the gas stream. The condensation also enhances mist and fume particle growth and subsequent downstream removal. The condensed water will be cross-flowed from the Gas Cooling Tower to the Scrubber. Weak acid will be removed from the scrubber based on the acid concentration and will be sent to effluent stripping tower for removal and return of dissolved SO 2 to the process before discharge to the effluent treatment plant. Page 29

32 The amount of solids in the liquid will be limited to 10% or lower by the water balance of the system. The WESPs will be the final stage of gas cleaning to remove the remaining impurities from the feed gas and will provide an optically clear gas to the Drying Tower. The saturated gas enters the bottom of the first precipitator and passes up through the precipitator tubes which have a high-voltage discharge electrode suspended down each vertical axis. The mist droplets and particulate contained in the gas will receive a negative electric charge from the discharge electrode and will be attached to the inside wall of the collecting tubes, which will be earthed. The droplets agglomerate and drain to the bottom of the precipitator and discharges via drain pipes will be assisted by a periodic wash down spraying system. The gas from the first precipitator will exit the top and enter the top of the second precipitator where it in turn will flow from top to bottom. The cleaned gas then will exit the secondary precipitator. Gas Conversion and Absorption Process gas from the WESPs in the gas cleaning system will enter the bottom of the drying tower and pass upwards through a layer of packing counter-current to a flow of recirculated 96% H 2 SO 4. The acid will remove water from the gas stream. After the gas leaves the main packing, it will pass through a layer of spray eliminator packing and then through a mesh pad which will remove entrained acid mist. Dilution air will be added at the inlet to the drying tower, if necessary, to adjust the gas strength to the contact section at the levels required for further processing. The dried and essentially mist free gas leaving the drying tower will enter the suction side of the SO 2 blower. The blower will be of the single stage centrifugal type with a cast iron casing, driven by an electric motor through a gear increaser. Gases from the discharge of the blower will pass through the shell side of the cold and hot gas-to-gas exchangers in series prior to entering the first pass of the converter. The purpose of these exchangers will be to raise the temperature of the gases to the proper Page 30

33 operating temperature to effect conversion of SO 2 to SO 3 in the converter. Temperature control on each exchanger will be by a series of bypass ducts and valves. Since the reaction of SO 2 and O 2 to produce SO 3 is exothermic, the gas temperature must be reduced following each pass of the converter in order to permit further conversion. Gases leaving the first pass of the converter will enter the tube side of the hot gas-to-gas exchanger. The cooled gases leaving this unit will enter the second pass of the converter. The heat generated in the second pass of the converter will be removed by passing the gas through the tube side of the hot interpass gas-to-gas exchanger prior to entering the third pass of the converter. The temperature of the gases exiting the third pass will be reduced by passing the gas through the tube side of the cold interpass gas-to-gas exchanger and through the tubes of a waste heat boiler prior to entering the interpass absorbing tower. In the interpass absorbing tower, the SO 3 component of the gas steam will be absorbed in a recirculated flow of 98.5% H 2 SO 4 as it passes up through the main packing in the tower. After the gas leaves the main packing, it will pass through a layer of spray eliminator packing and a Brownian movement candle type mist eliminator prior to exiting the tower. The gas from the interpass tower will then pass through the shell side of the cold interpass gas-to-gas exchanger and the shell side of the hot interpass gas-to-gas exchanger in series in order to achieve the strike temperature prior to entering the fourth and final pass of the converter. In the fourth pass of the converter, the final conversion of SO 2 to SO 3 will take place. Once again, the hot gases from this pass must be cooled to a suitable temperature for SO 3 absorption in the final absorbing tower. To this end, the gases will pass through the tube side of the cold gas-to-gas exchanger and through the tubes of a waste heat boiler prior to entering the final absorbing tower. Page 31

34 In the final absorbing tower, the SO 3 component of the gas steam will be absorbed in a recirculated flow of 98.5% H 2 SO 4 as it passes up through the main packing in the tower. After the gas leaves the main packing, it will pass through a layer of spray eliminator packing and a Brownian movement candle type mist eliminator prior to exiting the tower. The gases are discharged to atmosphere via the process gas exit stack. Preheater System An external source of heat must be provided during initial plant start-up in order to obtain proper operating temperatures in the converter and when low strength gas from the smelter is below the autothermal point. This will be supplied by the preheater system which will consist of a fuel fired furnace and gas-to-gas heat exchanger. The furnace will operate on diesel fuel to produce products of combustion which pass through the shell side of the preheater exchanger, counter-current to a flow of either process gas or air on the tube side. Products of combustion from the exchanger will be discharged to atmosphere via the preheater stack. Heated process gases or air from the exchanger will be delivered to the converter. Strong Acid Circulation 96% H 2 SO 4 circulation acid for the drying tower circuit will be provided from a horizontal, cylindrical, acid brick lined pump tank. One duty circulation pump, together with an installed spare, will be supplied for this service. The duty pump will deliver acid to the tower via the drying acid cooler. Acid from the drying tower will flow by gravity to the pump tank. A side stream of 96% acid from the drying tower pump tank will be taken to the absorbing tower circuit as required to control the level in the drying acid pump tank. 98.5% H 2 SO 4 circulation acid for the two absorbing towers will be provided from the interpass and final absorbing acid pump tank. This tank will be similar in design to the drying acid pump tank. One duty and one installed spare pump will be provided for this service. Acid from the tanks will be cooled in the absorbing acid cooler prior to entering the two absorbing towers. Acid from the tower outlets will flow by gravity back to the Page 32

35 pump tank. Strength control in the absorbing acid circuit will be maintained by the addition of fresh water to the pump tank. A side stream of acid from the outlet of the absorbing acid cooler will be directed to the drying acid pump tank on strength control from the drying acid loop. Steam Generation System Deaerated boiler feed water, from outside of the acid plant battery limits, will be provided to the steam generation system, which includes a steam drum, an interpass absorption tower low pressure boiler and a final absorption tower low pressure boiler, to generate 2 MPa steam for export from the acid plant. This steam will be suitable for use at the steam dryer without being let down. Acid Sample System An acid sample system will be provided for each of the two acid loops (drying and final absorbing) in the acid plant. These consist of three conductivity analysers, one for the drying acid circuit and two for the absorbing acid circuit. A manual sampling station will also be provided to allow samples of drying, absorbing and product acid to be tested. Water Cooling Tower The Cooling Tower will be used for cooling treated water returning from the acid plant. Water will be circulating in a closed loop (open to atmosphere at the cooling tower), via cooling water circulating pumps (i.e. open, recirculation mode). The Cooling Tower will be modular, including 3-cell design, with partitions to allow isolation and maintenance of any cell while the other cells remain in operation. Air will be drawn through each cell by an induced draft fan at the top of the cell. Overall heat rejection to the atmosphere will be accomplished using control of the air mass passing through the tower, by varying the speed of one or more fans. Conductivity elements will be provided in the return cooling water system to detect leaks. Equipment Description Page 33

36 SNC-Lavalin has considered proprietary equipment, as specified below. Patented Converter with Gas Distribution and Internal Heat Exchangers SNC-Lavalin Fenco s patented design catenary plate converter is successfully operating at Kingisepp in Russia. Compared to the conventional Staid design with multi-column supports, SNC- Lavalin Fenco s new converter, which has no internal support columns, uses less materials, allows faster erection, and requires much less welding. In addition, this converter can house two internal gas-gas heat exchangers, which significantly reduces the amount of ducting, making construction simpler and requiring maintenance. The shell and tube exchangers will be designed to optimize surface area, vessel physical size and overall shell and tubeside pressure drop. The material of construction throughout for the hot and hot interpass gas exchangers will be 304 stainless steel. The use of stainless steel for these units is required to ensure structural integrity at the high operating temperatures involved and better corrosion resistance. The gas exchangers, which will be mounted internally in the converter, will be enclosed with an internal shell, supported on grade foundations. The use of legs is preferable to support with grillage beams as the underside of the exchanger can be easily insulated and inspected without difficulty. Page 34

37 Furthermore, the first pass of conversion will be, in this particular converter, at the top, with the advantage of less stress on the hottest exterior shell, it also will allow easier access for periodically catalyst screening. Catalyst The catalyst will be an industry standard based on a balance of the following properties: high activity, low pressure drop, long life, and high hardness (resistance to screen loss). Mist Eliminators Selection of the type of mist eliminator will be a function of the tower duty. For the drying tower, the acid mist is generated "mechanically" (i.e. by entrainment of acid droplets from the top of the packing), a simple mesh pad will provide suitable mist removal to ensure minimal carryover. It will be also less susceptible to plugging by solids in the event of upsets in the upstream process. For the absorbing towers where fine acid mist is "chemically" generated, the use of a mist collection device that relies on the principle of Brownian movement is necessary. An "ES" type mist eliminator candles is considered for use in the interpass and final absorbing towers where a high level of mist will be generated. The re-entrainment of collected mist in the discharge gases will be virtually eliminated with the bi-component design, which will ensure that high collection efficiency for these elements will be maintained over the whole operating range. Acid Distributors The strong acid towers will use the well proven trough and Downcomers type acid distribution system. This is an "above the packing" type of acid distributor fabricated from high silica austenitic corrosive-resistant alloy material (HSA Alloy). The system will Page 35

38 employ a number of "troughs" into which will be cast slots. "Downcomers" are fitted into the slots and distribute acid from the troughs by gravity to the packing. The bottoms of the Downcomers will be buried in the packing to a depth of about 200 mm. Comparing with traditional cast iron, HSA alloy materials has much higher corrosion resistance. Its light weight makes it easier to handle. The use of HSA alloy allows for higher point loadings than that of a conventional distributor (10 points/m 2 ) and a savings in tower height. Trough and Downcomer type distributors will offer accessibility for maintenance while at the same time will not be as prone to plugging as pipe type distributors. As well, any debris (i.e.: packing chips, brick chips etc.) will settle out in the troughs and is easily removed during yearly turnarounds. The use of this type of distributor will also reduce the generation of acid mist in the towers reducing loading on the associated mist eliminators. Strong acid will be delivered to the troughs through HSA alloy piping inside the towers. Equal distribution to the troughs will be assured by a series of orifice plates located in distribution "tees" in the tower. The orifice plates will be fabricated of HSA to ensure long trouble free life for this important function. HSA Alloy Material HSA alloy material and Sandvik s alloy belong to the same family of alloys, but do not have the same chemistry. HSA alloy welds more easily than Sandvik s alloy and has much higher corrosion resistance. HSA alloy has no sulphate formation, due to its low iron content. This also reduces the amount of iron in acid. It is also light weight, easier and less expensive for installation. Mondi Material Mondi, a special alloy of ductile iron with unique metallurgy was developed by Monsanto, to handle 92-99% acid at temperatures up to 149 C. It has been the industry standard Page 36

39 for reliable performance in sulphuric acid plants since Mondi piping is used worldwide in recirculation systems for drying and absorbing towers. Its corrosion rate is about mm per year. The benefits include the reduced maintenance with a service life up to four times the life of standard metallurgy ductile iron; its durable construction provides safe, trouble-free operation; and it is cost-effective. Its excellent ductility can better handle the high earthquake forces Pump Tanks and Pumps The single pump tank for drying tower and a common pump tank for the interpass absorption and final absorption towers will be of the horizontal dished head type. This design ensures that the internal brick lining will be kept in compression. All vertical acid pumps considered for the project are of the Lewis submerged type. Lewis is considered to be the industry standard for this application. Furthermore, the use of submerged pumps provides a high degree of safety for the plant. In addition to the Lewis standard, the pumps also will incorporate a number of quality options. To protect the pump shafts from corrosion due to build up of static electric charges a shaft grounding brush kit was costed. The kit will consist of a graphite brush grounded back to the pump base and to earth via the tank shell. The pumps will be provided with a protective Teflon shaft cover and cap nut with O-ring fasteners. Strong Acid Cooling The strong acid coolers will be of the plate and frame or anodically protected shell and tube type from proven suppliers. Elevated Strong Acid Towers Nearly 20 years ago it was demonstrated that packed towers could operate efficiently at much higher velocities than were Page 37

40 then practised in the industry. As a result the gas velocities were increased by using three inch "Intalox" type packing exclusively and by raising the acid distributors above the packing level. The towers will incorporate this technology in packing design. The packing will be supported on a layer of grid blocks which in turn will be supported on ceramic beams. In SNC-Lavalin's experience this type of packing support system is the best for this application. Tower bottoms are dished to ensure the acid brick lining in this area is held in compression over the entire floor area. Holding bricks in compression will prevent brick heaving in the towers. Dished bottom floors are now SNC-Lavalin's standard for all strong acid towers. Due to high operating temperatures, the gas inlet nozzles for the absorbing tower as well as the brick lining below the packing will be provided as high temperature type "H" brick. Interpass and final absorption tower will be designed with nozzles for NO x removal if required. Gas Cooling and Cleaning System In this study, SNC-Lavalin has based the estimate upon the front end gas cooling and cleaning system using the DynaWave based gas cleaning system, which consists of a primary scrubber, a gas cooling tower, a SO 2 stripper and six sets of WESP s. The gas cleaning plant will be designed to minimize pressure drop in those parts of the plant (such as quench tower, cooling tower and gas ducts) which are not relevant for the removal of impurities. The Blower The blower considered should for this study was a heavy duty type with a cast casing and forged/fabricated impeller and inlet guide vanes. It will be driven by an electric motor. The compressor vendor will be responsible for the engineering to ensure the Page 38

41 motor and compressor train are compatible from a vibration, and operational standpoint. The unit torsional analysis will be done by the compressor vendor. In addition to the equipment for the compressor, suitable instrumentation for the unit has been incorporated. This instrumentation will monitor critical functions providing alarms and shutdown signals when any part of the compressor operates outside preset limits. This will include vibration as well as the installation of thermocouples or RTD's in critical bearings and motor windings. A forced lubrication system will be provided for the compressor train. This will consist of a cooler, dual filters, auxiliary lube oil pump and associated controls/alarms. The main lube oil pump will be mounted on the idle end of the gearbox to ensure that lube oil is supplied as long as the blower is operating. An auxiliary motor-driven pump will also be provided to ensure that oil is available for start-up and rundown if pressure is lost from the main lube oil pump Effluent Treatment Plant Water Sources and Characteristics Acidic waste waters from the copper smelter will be generated at the: FSF gas scrubber and gas cooling tower; PSC gas cleaning scrubber, cooling tower; and Wet electrostatic mist precipitators (ESPs). Hot flue gases from the copper smelter flash furnace are cleaned and cooled in the plant s FSF primary scrubber and gas cooling tower. The weak acid bleed generated is stripped in the FSF effluent stripper before being pumped to the effluent treatment plant raw waste water storage tank. ESP effluent flushing pumps will transfer spent flushing water to the PSC circulating pumps for recycle in the PSC gas cleaning scrubber. The bleed from the scrubber is Page 39

42 used in the PSC effluent stripper and pumped via the weak acid effluent pumps to the effluent treatment plant raw waste water storage tank. Copper concentrates have been categorized into three blends, High Blend, Normal Blend and Low Blend. Based on preliminary projections, processing of the High Blend concentrates will generate the highest acid content waste water. Refer to the tables in Appendices 1.0 and 2.0 summarizing quantity and quality projections for the acidic waste water generated at the FSF and PSC gas cleaning and cooling operations. The combined waste water will be very acidic containing up to 20 per cent sulphuric acid, carry a very high dust load comprised of heavy metal- and non-metal oxides, and include a significant amount of dissolved heavy metals, specifically Bi, Cu, Fe, Zn and As, and others including Co, Ni, Pb, and Sb; a trace amount of Hg may also be expected. Based on the projected acid content, the ph of the waste water was determined to be negative, i.e., less than 0 (standard ph units). The temperature of the acidic waste effluents is projected to be 66 oc and 72oC for respective FSF and PSC gas cleaning operations, and approximately 66oC for the combined waste stream in the raw waste water storage tank. Generation of acidic waste water effluents from the smelter operations is not continuous during the 24-hour day. Daily total flows were projected for processing of the various ore blends, as shown in the tables in Appendices 1.0 and 2.0, and these values were then used to derive the average hourly flow rates for the individual waste water streams and the combined total effluent. The waste streams are pumped to the waste water storage tank at the effluent treatment plant, which serves to balance peak flow rates at a design treatment rate of10 m3/h. A summary of the combined acidic waste water effluent from the smelter is presented in the following table. Page 40

43 Table Acidic Waste Water Quality Characteristics Combined Effluent FSF and PSC Gas Cleaning Scrubbers Parameter Units Value Slurry Flow Rate m 3 /d m 3 /h 7.37 Physical-Chemical Suspended Solids Tonnage t/d 8.25 t/h 0.34 Slurry Density t/m Slurry Weight t/d Solids Content %wt 4.66 Acid Content (H 2 SO 4 ) %wt (S.G. = 1.1 at 66 o C) Kg/h 1,586.4 Sulphur Dioxide Gas (in solution) mg/l 50 ph (calculated) st. units <0.64 Temperature o C 66 Major Ions Aluminum Oxide, Al 2 O 3 mg/l 260 Calcium Oxide, CaO mg/l 40 Magnesium Oxide, MgO mg/l 0 Silica, SiO 2 mg/l 3,580 Sulphide, S 2- mg/l 434 Heavy Metals Aluminum, Al mg/l - Antimony, Sb mg/l 90 Arsenic, As mg/l 181 Bismuth, Bi mg/l 2,200 Cobalt, Co mg/l 180 Copper, Cu mg/l 735 Iron, Fe (total) mg/l 3,810 Lead, Pb mg/l 288 Mercury, Hg mg/l 1.0 to 2.7 Nickel, Ni mg/l 20 Zinc, Zn mg/l 1,590 Note: Waste water quality characteristics are preliminary and must be confirmed. Page 41

44 Process Description The process flow sheet for the conceptual design of the effluent treatment plant is included at the end of this section. The Effluent Treatment Plant is designed to treat contaminated process flows from the copper smelter and converter gas cleaning and cooling operations. Bleed streams from the respective scrubbers, FSF and PSC, will be pumped to the effluent treatment plant raw waste water storage tank for balancing of peak rates of flow at the design treatment plant rate of 10 m3/h. The effluent treatment plant is a modification of the High Density Sludge (HDS) process for neutralization and precipitation of heavy metals. The HDS process relies on sludge recycle from the clarifier to a lime / sludge mix tank or directly to the neutralization reactor to enhance the precipitation reaction and minimize / prevent gypsum scaling. The amount of sludge normally recycled is based on the ratio of the recycled solids to the solids precipitated from the feed solution. The sludge recycle ratio can vary from as low as 0.5:1 to a high of 25:1, depending upon the amount of solids precipitated and the sludge solids concentration in the neutralization reactors. For typical weak acid mine drainage, the sludge recycle ratio is critical to control the level of scale formation (primarily caused by precipitation of calcium sulphate and hydration to form gypsum), and to optimize the chemical reactions in the neutralization / precipitation reactors. In the case of the RTB Bor smelter, however, sludge recycle should not be required because of the high solids concentration that will result from the neutralization of the acidic waste water and the precipitation of metal hydroxides. Therefore, a lime / sludge mix tank has not been provided and no clarifier sludge recycle pumps are included to return sludge solids to the neutralization reactor. These can be easily retrofitted later by the owner if determined to be necessary. Unit operations of the effluent treatment plant process include: Flow / quality equalization in a raw waste water storage tank; Page 42

45 Neutralization of acidity using lime and precipitation of calcium sulphate down to its solubility level; Air oxidation and precipitation of metals as metal hydroxides by sparging air and adding lime to the reaction tanks to elevate the ph to 7.2 in reactor #1 and to about 9.5 to 10 in reactor #2 to precipitate metal hydroxides down to their solubility product levels; Co-precipitation of arsenic (As), and perhaps cadmium (Cd) and selenium (Se), if present, with ferric hydroxide; it is expected that sufficient dissolved ferrous/ferric sulphate will be present in the feed water to sustain the ferric hydroxide arsenic coprecipitation reaction; but until this can be confirmed experimentally, commercially available ferric sulphate solution will be supplied and added to reactor #1 to ensure arsenic precipitation will occur. At this time, no specific treatment is included for the precipitation of trace levels of mercury (Hg) and lead (Pb); there is evidence to suggest that these metals may be removed by hydroxide precipitation and co-precipitation with ferric hydroxide; this will need to be confirmed experimentally. If these metals cannot be treated by ph adjustment to regulated concentrations, consideration will be given to the addition of a separate sulphide precipitation step to the flow sheet; calcium poly-sulphite or similar reagent would be needed for the precipitation of mercury and lead sulphides; also, sodium hypochlorite would be dosed to the effluent from the sulphide treatment reactor to oxidize any hydrogen sulphide that may form during the sulphite treatment step; The effluent from reactor #2 will discharge to the clarifier via a de-aeration tank for the separation of solids from the liquid phase of the treated solution; A flocculent will be added to the outlet of the de-aeration tank and/or to the inlet well of the clarifier to improve floc formation and settling of solids; and Discharge of the clarified effluent to a polishing pond (provided by others) before discharging the treated effluent to the receiving tailings pond; the polishing pond has two purposes, one is to achieve quality equalization of the effluent, and the other, to provide Page 43

46 a storage reservoir and pump well to house water reuse pumps, should an opportunity for re-using the water exist. Slaked lime will be prepared using quicklime in a paste slaker. Quicklime, CaO, shall be delivered in bulk by truck trailer. On-site storage of quicklime will be in a 300 tonne capacity lime silo equipped with baghouse and vibrating cone to ensure uniform feeding of the product. A volumetric screw feeder will feed dry lime to the lime slaker. Two feeders and two slakers shall be provided, one system for each lime silo. Slaked lime slurry will be transferred to a slaked lime storage tank sized for eight hours retention at the design consumption rate. The tank is equipped with an agitator and two lime slurry feed pumps, one duty and one standby. Using ph control loops, lime slurry will be added automatically to the neutralization / oxidation tank (reactor #1) and to the precipitation tank (reactor #2) to maintain the desired ph in each tank. Chemical reaction tanks are sized for 60 minutes retention at the maximum design feed rate to the reactor of 25 m3/h. Ferric sulphate solution will be stored in a bulk chemical storage tank, transferred to a day tank and dosed via metering pump to reactor #1. Two process air blowers are provided to sparge air into the neutralization / oxidation tank through a sparge cone located at the base of the tank, beneath a high shear, gas dispersing impeller. The cone has a serrated edge to assist in uniformly distributing the air below the impeller. An agitator with a high efficiency pitched blade turbine gas dispersion impeller distributes the air bubbles and promotes vigorous mixing of the tank contents to ensure rapid transfer of oxygen into solution and the oxidation of ferrous iron to its ferric state. At this point, all the ferric iron precipitates and some non-hydroxide forming trace metals are also removed by co-precipitation. Reactor #1 effluent discharges by gravity to the second reactor tank of equal size to the first tank, referred to as reactor #2. Hydrated lime slurry is added to raise the ph to between 9.5 and 10.0 to precipitate any remaining iron and other heavy metals such as copper, nickel and zinc. Page 44

47 Air is added to continue the oxidation process, as necessary. Vigorous mixing of the tank contents is achieved by an agitator fitted with a high shear, gas dispersing impeller. This promotes the continuation of the oxidation process and intimate contact of the reactants. The tank capacity provides 60 minutes of hydraulic residence time based on the maximum design feed rate of 25 m3/h. Following chemical treatment, the slurry is discharged by gravity to the clarifier for separation of solids. The clarifier is a conventional, high rate, clarifier equipped with a bottom rake mechanism and rake lift. The clarifier is sized for a maximum design solids loading rate of 290 kg/m2-d. A flocculent is added to the outlet of the clarifier feed tank, and at the inlet to the clarifier feed well to increase particle size through flocculation and improve the settling characteristics of the solids in the clarifier. An inventory of sludge is maintained in the clarifier. To maintain a daily balance in the sludge inventory, the amount of new solids produced by the process is pumped continuously, or on an intermittent basis, to the tailings transfer pump box in the mill for codisposal with tailings in the tailings pond. The sludge that is produced can vary in density; a probable operational range is 20 to 35 %wt. Clarified overflow is discharged by gravity to the polishing pond Slag Treatment Plant Process Description Molten slag from the FSF and PSCs will be transferred to slag cooling pits to allow the slag to harden and for copper minerals to crystallise. The slag will be transferred by slag hauler in 15 m3 steel ladles to the slag cooling area. The pits will be filled on rotating cycles to optimise their usage. At any given time, there is likely to be pouring of molten slag, air cooling, water cooling, dozer-ripping, excavation, and preparation of pits for the next cycle. After pouring into pits, the slag will be allowed to cool for eight hours. This will be followed by variable periods of water cooling and additional air cooling for a period of two to three days. Page 45

48 Normal water demand will be about 120 m3/h, with a design maximum of 160 m3/h. The timing of the water applications will be dependant on smelter demand. Total cooling time will be 72 hours, but when variations in slag make occur, cooling periods will be adjusted as required. The cooled slag will be ripped out of the beds using ripper bulldozers. The slag will be pushed into heaps and loaded onto a grizzly / feed hopper in the slag concentrator by means of a front end loader or truck. Oversize slag will be broken on the grizzly using a hydraulic hammer. The screened slag will be stored in 50t hopper that feeds a static grizzly of aperture 100 mm square to produce a feed for a 150 t/h primary jaw crusher. The jaw crusher top size feed will be 350 mm and the top size product 150mm. An electro-magnet will be provided for the removal of tramp iron upstream of the cone crushers. A two-stage secondary crushing circuit will be used to give higher utilisation and improved product quality compared to a single cone crusher. The first stage crusher product top size will be 70 mm; the second stage product top size will be 40 mm. The final product / mill feed top size will be 25 mm. The existing mill circuit of one rod and one ball will be more than adequate to process nominally 800 t/d of slag. The existing flotation circuit will need to be modified / re-built to provide a new rougherscavenger circuit for slag flotation based upon Tank-Cell technology. The existing conventional cells will be used as cleaners. Concentrate from the Bor Slag concentrator will be combined with that from the Bor Ore concentrator and be processed through the existing de-watering facility; this will be adequate for the proposed future requirements. Page 46

49 Tails from the Bor Slag concentrator will be combined with those from the Bor Ore concentrator and will be pumped to the existing tailings dam. Equipment Description There will be 30 slag cooling pits, each will measure 8.1 m long by 4.4 m wide. Slag from one ladle will typically form a layer 0.5 m to 0.6 m thick. The slag pits will be arranged in large blocks. Each block will be separated by areas sufficiently large for vehicular access. The cooling pits will be unlined and constructed of crushed slag to create berms around each pit. A water spray system will be employed for cooling the slag. A mm water main will deliver water to 18 spray nozzles that run down the centre of each block of cooling pits. Ripper bulldozers will rip the slag out of the beds and load it onto a feed hopper fitted with a stationary grizzly. A hydraulic hammer will be used to break up the slag. The free opening of the grizzly will be 300 mm square. The hopper below the grizzly will be of 50t capacity and the slag discharged via an apron feeder to a static grizzly of 100 mm square aperture. The screened slag will be fed to a 0.9 m by 0.6 m primary jaw crusher of capacity 150 t/h. An electromagnet will be installed on a sacrificial conveyor downstream of the jaw crusher for the removal of tramp iron. A 150 t/h capacity standard crusher feed conveyor will feed a HP300 standard cone crusher. A crusher product conveyor and two recycle conveyors, each of capacity 314 t/h, will feed an 8m2 short-head crusher double-deck feed screen of 25 mm aperture. The screen oversize will feed a HP300 short-head crusher of capacity 150 t/h. The final product will be conveyed to the mill grinding circuit by the final product delivery conveyor of capacity 150 t/h. Page 47

50 A grinding circuit power consumption of about 40 kwh/t slag will be required for slow cooled smelter slag. A slag grinding circuit comprising one (existing) primary rod mill and one (existing) secondary ball mill with a combined pinion power of kw will be suitable for the nominal plant throughput of 800 t/d slag at 75% equipment utilisation. The existing flotation circuit is in a very poor condition. Adequate finances are indicated in the Bor Business Plan to re-build the existing plant. It is however proposed to build a new rougher-scavenger circuit for slag flotation based upon Tank-Cell technology, and to use the existing conventional cells as cleaners. The dewatering facilities required for the slag will utilise the existing process plant circuits which are more than adequate for the proposed throughput. Slag tailing will be discharged to the common RTB Bor concentrator tailing disposal facility Electrical Supply and Distribution The electrical system for the Smelter and Slag Concentrator will be powered from 110 kv incoming line. The emergency power will be supplied from the emergency power generators dimensioned to supply necessary power also in starting situation. Emergency power diesel generator of 5.25 kv will provide power for feeding vital process equipment and UPS system of Smelter area. Automatic switchover to emergency system in case of main power failure is included. Smelter Uninterruptible Power Supply System (UPS), rated for at least 20 min. of operation, will supply Process Control System, motor control circuits, PLCs and vital part of the instrumentation. Power factor compensation and harmonic filtering will be provided on 5.25 kv level. Earthing system will be provided and will include protective and technical earthing. Page 48

51 Motor Control Centers (MCCs) of the Smelter is powered from 5.25/0.4 kv distribution transformers and will be located in electrical rooms of the corresponding area. The following equipment is included in the electrification scope of Smelter: 110 kv incomer bay; 110/5.25 kv main transformer; High and medium voltage cables; Medium voltage distribution and motor control switchgears; Distribution transformers; Capacitor banks for reactive power compensation; Emergency power machines; AC-busbar bridges between distribution transformers and MCCs; Motor Control Centers; Local control switches for each motor unless other specified; Uninterrupted Power Supply (UPS) system; Low voltage power and control cables; Cable racks and conduits; Earthings; Power outlet panels; and Detail design and documentation of above mentioned items. Switchgears will be of metal-clad type. Live parts of the switchgears protected against contact of persons, control compartments completely separated from the high voltage parts. Circuit breakers of incomer, feeder and starter sections will be motor charged type placed in a draw-out truck. Page 49

52 In order to prevent harmful resonances with network impedances all capacitor banks shall be equipped with filter coils in series with capacitors. Smelter will be provided with a 2200 kva 5.25 kv emergency power unit. Copper or aluminum armored power cables of 1000 V with minimum cross-section of 2.5 mm2 has been considered. Coating and insulation material is PEX or corresponding suitable for plant environment. Cables will be normally installed on cable trays in the process area. Cables on process area where is the risk of mechanical damage are protected with protection pipes or with open rigid conduit system. Earthing net of the plant consists of earthing rods and loops, and nets of copper conductors around and under the buildings as well as steel reinforcement of concrete foundations Instrumentation and Controls Instrumentation and control system for the plant and support services must be designed to provide the operating staff with a clear presentation of the process status and total plant operation at all times. The control system requirements are developed to include the following: Process and Instrumentation Diagrams; Instrument List; Control Logic Narratives; Motor Logic Narratives; Instrument Loop Diagrams; Installation Details (field instrumentation only); Local Instrument Panels (LIP) Arrangements; Instrument Location Drawings; Page 50

53 Junction Box Layouts; Cable List; Input/Output List; and Instrument Specifications data sheets. The degree of automation as shown on the Process and Instrumentation Diagrams (P&ID s) is consistent with the operation philosophy. The instrumentation and controls for the plant will consist of: Distributed Control System (DCS); Analytical Instrumentation; and Field-Mounted Instrumentation. Control rooms are required for operation. Operators will have the capability to safely operate, monitor, and shut down the process and critical equipment from the control room with minimal field operator assistance. Matte, slag and product acid quality and emissions standards will be maintained within specification limits by means of controls provided in the control room. Distributed Control System A scalable, modular Distributed Control System (DCS) has been considered for continuous process control, process variable indication, status indication of discrete variables, interlock shutdown logic, alarms, trends and historical data acquisition for operation. The DCS will consist of field process controllers, PC based operator console/engineering workstation (HMI), redundant communications network, configuration and documentation software, and operator interface software, and two operator workstations. The field process controller will consist of a primary process controller module, redundant process controller module, module power supplies, I/O modules, communications modules, module racks and bulk power supplies. All components associated with the field process controller will be installed in the DCS vendor s standard Page 51

54 NEMA 12 cabinet. Terminal strips will be provided in the cabinet for connections between I/O modules and field devices. The cabinet will be located in the electrical building. The field process controller equipment operating environment will be maintained within the DCS vendor specifications by the electrical building HVAC system. Redundancy is provided for the process controller module, module power supplies. Redundancy has not been considered for I/O modules. A dual, redundant local control network will be provided for communications between the process controllers and the operator engineering workstations. The local control network will support a 10 baset Ethernet physical layer. Data throughput on the control network will be at least 5 M bits/sec. If one side of the network should fail, communications will continue, uninterrupted, on the remaining side of the network. Configuration of the DCS will be performed per RTB standards and per the DCS vendor's recommendations. Dynamic graphics displays will be provided for access to operations. Dynamic graphics displays will be configured to represent each of the P&ID s and implement process controls as shown on the P&ID s. Vendor s standard historical data collection services will be provided and include trending for all dynamic process variables. Provisions for any long term archiving of historical trending data will be made by RTB. Interlocks The safety interlocks will be designed to protect process equipment and personnel. Control Valves Control valves have been considered as shown on the P&ID's. Control valves will be provided with pneumatic positioners mounted on the valve yoke or body. Control valves will be specified and selected based on the service conditions, process variables, and suitability for the application. The piping specifications will generally be used to determine control valve body and trim materials. Page 52

55 Damper Operators Operators for control butterfly dampers in large gas ducts will be provided with spring return piston and cylinder actuators for fail open or fail closed operation. Operators for control butterfly dampers in large gas ducts will be provided with double acting piston and cylinder actuators for fail last operation. Operators for gate valves in large gas ducts will be provided with double acting piston and cylinder actuators with volume tanks for fail closed operation. All damper operators will be provided with pneumatic positioners mounted on the operator assembly. Process Analyzers A process analyzer system will be provided for process gas discharge at blower and stack gas emissions monitoring. The process gas will consist of an SO 2 infrared analyzer and O 2 paramagnetic detector. The stack gas analyzer will be an ultraviolet type SO 2 analyzer. Electrodeless type toroidal conductivity analyzers will be used for measurement of strong acid concentration in the combination acid pump tank. Contact electrode type insertion conductivity analyzers will be used for measurement of conductivity in water and condensate. Field-Mounted Instrumentation The process flow, level, pressure, temperature and open/close loop control functions will be executed by the DCS and associated pneumatically operated control valves and dampers, equipped with positioners and/or solenoid valves limit switches etc., as required. The rotating equipment within the plant will be operated manually from local stop/start push button with ON lamp stations, with status indication and overload trips monitored and alarmed by the DCS. The field transmitters will be 4-20 ma + HART type. Page 53

56 Digital contact devices connected to the DCS will be rated at 120 VAC including solenoid valves, powered from individual starter circuits or uninterruptable power supply (UPS). Electrically operated devices will be FM approved. The instrumentation and control wiring will be run in separate cable trays, terminating in the DCS I/O cabinets, located in the control building Building Services (Control Room and MCC Rooms) Heating, Ventilating and Air Conditioning Heating, ventilating and air conditioning design was considered using guideline fundamentals set out by ASHRAE codes including all relevant SNC-Lavalin standards, specifications and good engineering practices. Heating systems was sized based on the local winter design temperatures as indicated in the Climatic Data and Interior Design Conditions for the specific area. Air conditioning systems was sized based on the local summer design temperatures as indicated in the Climatic Data and Interior Design Conditions for the specific area. Ventilation will be provided by supplying air to or removing air from a space for the purpose of controlling air contaminant levels, humidity or temperature within the space. It will be sized for the space based on the amount of contaminants or heat dissipation by the equipment. All heating, ventilating and air conditioning systems will be specified for heavy duty industrial service and the materials used in the construction of these systems will be suitable for corrosive service. Blower Building and Compressor room During winter operation, heating requirements will be satisfied by equipment heat emissions and electric space heaters Page 54

57 Thermostatically controlled electric unit heaters will maintain internal design temperatures. The units will be sized based on building heat losses at winter design temperature for the site location. Wall exhaust fans and air intake louvers with manually operated dampers will be provided for summer ventilation. Electrical Rooms Ventilation, pressurization and air conditioning will be provided by packaged air conditioning units complete with air distribution ducting and air outlets. The areas will be maintained under a positive pressure of 25 Pa relative to their surroundings. Control Room and Washrooms Ventilation, air conditioning and make-up air will be provided by air conditioning units with distribution ducting and air outlets. The Control room will be maintained under a positive pressure relative to their surroundings. Washroom ventilation will be provided by ducted exhaust with make-up air infiltrated from the Control room air conditioning system. Thermostatically controlled electric perimeter heaters will be provided for winter operation. Fire Protection Fire protection was considered to be tied to the existing facility to conform with the requirements of the project designated Risk Management Consultant, FM Global and NFPA. The Blower building and the Compressor room will have full coverage of all areas with fire hose cabinets, supplemented with portable hand held fire extinguishers. Fire hose cabinets will be located so that all interior areas of the buildings are within reach of a fire hose stream. Page 55

58 No fire fighting systems were included but can be provided if requested by a Risk Management Consultant. Electrical Room and Control room will be equipped with ionization type smoke detectors supplemented with hand held clean gas fire extinguishers. Portable hand held fire extinguishers will be provided at all exits and as required based on the process operations in each area. Wet type sprinkler system for water cooling tower has been included. Plumbing and Drainage Plumbing, sanitary drainage will be tied-up by RTB by utilizing the existing sanitary system of the running metallurgical plant. Potable water will be provided from the existing supplied main for tie-in to the Battery limit. The domestic hot water in the Control room washroom will be provided by electric domestic hot water system. The volume of hot water provided by the system will be sufficient to satisfy the daily requirements. 5.2 Project Diagrams and Process Flowsheets This section presents a series of project diagrams that show the facilities discussed in sections through (see end of section) Figure provides an aerial photo of the smelter and acid plant areas. Page 56

59 New Smelter Area New Acid Plant Area Figure Aerial View of Area for New Smelter and Acid Plant RTB Bor Bor Complex

60 5.3 Drawings and Block Flow Diagram Plant Layout Existing Plant A simplified plant layout for the existing Bor Smelter plant is provided on drawing D-AD-PLA Rev A Plant Layout for Base Case. The layout for the Base Case Modernisation as shown on drawing number D-AD-PLA Rev A,.shows the new Roaster and Electric Furnace in the location at present occupied by the existing No.2 Roaster and Reverberatory Furnace. The new Electro-Static Precipitators (ESP s) are located as close as possible to the new Roaster and Electric Furnace. To facilitate this layout the existing plant in the area would be demolished, and the site cleared. The orientation of the new Electric Furnace is east- west, with the west end wall facing the Converter Aisle, where matte would be discharged via launders into ladles in the Converter Aisle. Slag returned from the converters by ladle to the Electric Furnace, would also enter the Electric Furnace at the west end wall via a launder. Slag from the new Electric Furnace would exit via launders at the east end of the Electric Furnace into the existing slag car system, the routing of which would require some modification. The concentrate feed system to the existing No. 2 Roaster would require modification to feed the new Roaster. Gas ducts from the new plant would tie into the existing system discharging to a new Gas Mixing vessel, prior to discharge to the refurbished and modernized acid plants. The new ESP to the Converters to be located alongside the existing ESP. The benefit of this proposed layout is that the majority of construction work can be carried out with almost no interference to existing Line 1 operations, and production would continue uninterrupted during construction. Page 58

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