DIESEL HYDRODESULPHURISATION UNIT CHAPTER 4.0 DETAILED PROCESS AND UTILITY DESCRIPTION

Transcription

1 CHAPTER 4.0 DETAILED PROCESS AND UTILITY DESCRIPTION 4.1 FEED SECTION ( Refer. P-&ID ) Feed Pumping Section The Diesel feed is supplied from different sources, namely Storage, CDU, VDU, Visbreaker Unit and FCCU so as to have required blend of Feeds as per Feed specification. These blends are controlled by FV-0101, FV- 0102, FV-0103, FV-0104 and FV-0106 to have desired feed flow rates. A Selector switch HS-0102 is used to select the source stream for feed. To enhance the pressure of Feed from FCC Unit, TCO Booster Pumps P- 125 A/B is installed online to have the desired pressure at Feed Filter inlet. The filtered diesel from GN-105 then goes to the Feed Surge Drum V-101. The control valve PV-0116 controls the pressure especially during filter backwash to ensure required pressure of 3.0 Kg/cm 2 g at the backwash inlet. The pressure in V-101 is maintained by split range pressure control using fuel gas. This system consists of two pressure control valves. PV-0103 A controls fuel gas flow into the surge drum and PV-0103B purges fuel gas from surge drum to flare. If the surge drum pressure exceeds set point pressure (~2.0 kg/cm2 g) P-V0103B opens and releases fuel gas to flare line. Similarly if the pressure falls below set point pressure, P-V0103A opens and pressurizes the surge drum. The diesel from V-101 is pumped by feed pump P-101 A/B. It is a multistage centrifugal pump of EBARA make. The controller FIC-0105 maintains constant flow through flow control valve FV This corresponds to a fairly steady draw out from the surge drum, which acts as a buffer vessel. The surge drum has two level control loops LIC-0102 in cascade with FIC-0101/FIC-0108 for feed surge drum level and LIC01016 for draining sour water from boot section. During normal operation feed is pumped through a series of heat exchangers for heat economy before entering into reaction section. During Startup reaction section is bypassed and feed is directly routed to the stripper C101 through bypass control valve HV At this point main flow control valve FV-0105 and SDV-0102 are shut. Antifouling chemical is added to feed during normal operation while DMDS addition facility is provided for catalyst sulphiding. CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 1/19

2 4.1.2 Feed Filtration Section DIESEL HYDRODESULPHURISATION UNIT The feed filter is of semiautomatic, self cleaning, internal backwashing, type capable of removing solid particles of 25 microns or larger. The filter system consists of three banks of filter elements that are configured and designed to back wash sequentially and independently. Main features of the filter are: Process Fluid : Diesel Flow Rate Normal, M 3 /Hr: : 125 Description of filter element : Each element consists of twenty eight 1 diameter x 36 length tubes mounted on a common flange Back Wash Rate, M 3 / Hr : 80 instantaneous Filtration cycle, Hr : 1.5 to 3 The system is configured to operate continuously with all filter banks in parallel filtration mode and utilizes a small amount of the filtered diesel to clean / regenerate the filter media (i.e. internal backwash). During normal filtration, diesel enters the inlet header and distributes evenly to all nineteen individual filter elements. The diesel is filtered from the outside to the inside of each filter tube. During the filtration cycle, particulate material collects on the filter element media causing the differential pressure across the system to increase. When the differential pressure reaches 1 Kg/cm 2, particulate layer has been formed. The particulate cake requires a removal before densifying or compacting, which can take place due to, excessive differential pressure. It may be noted that dense cake is difficult to dislodge from filter media. The differential pressure switch signals the master controller to begin the backwashing sequence. This happens normally every 1.5 to 3.0 hours, but depending upon feed quality it can be less or higher. The filter system is configured to operate one element at a time during backwashing. In other words, the back wash process is accomplished one housing at a time, filtered at a design flow rate, while continuing to deliver clean diesel to Feed Surge Drum V-101. Each element is supplied with two station ON/OFF valves at the inlet and a backwash drain valve. The backwash sequence begins by automatic closing the inlet station valve on the first element on the master filter bank, thus stopping flow to this single element. The backwash drain valve is then opened in a precisely controlled manner, allowing clean filtered diesel to backflow through the element in reverse direction. This quick blast of filtered diesel- provides a hydro shock that removes all particulate from the filter media and carries it to the backwash drain header. The time required CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 2/19

3 to complete the backwash cycle for one element is approximately 10 seconds. Once the backwash drain valve for element number 1 is closed completely, the inlet element valve is reopened automatically, returning the element to filtration service. To get efficient backwash, a pressure control loop PIC-0116 has been provided in the feed filter outlet line. Control valve PV-0116 maintains feed filter outlet pressure at 3 kg/cm²g which is required for efficient backwash cycle. The fluid required for backwash is taken from upstream of Control Valve PV-0116 on feed filter outlet line. The backwash fluid is collected in a backwash tank V-122 having normal vent floating with the flare header. Backwash transfer pumps P-130 A/B are provided to pump the backwash fluid to the slop header. In case of process upset, both the pumps can be run simultaneously. Interlock UC-37 gets actuated on LSHH0108 on backwash tank and stops the feed filter operation. Interlock UC-38 (LSLL-0109) and UC-39 (LSH-0110) will start / stop the backwash transfer pumps accordingly. For detailed operation instructions, refer vendor s operating manual. 4.2 FEED PRE-HEATING SECTION (Refer P-&ID DHDS 1102) For energy conservation, the reactor feed is preheated by the reactor effluent in a series of heat exchangers. The reactor feed consists of mixture of diesel pumped by P-101 A/B and hydrogen from recycle gas compressor KACF-102. This mixture is first heated in shell side of 1 st feed effluent heat exchangers EE-101 A/B/C/D/E. The feed then passes to the shell side of 2 nd feed effluent heat exchanger EE-102 A/B and then into reactor heater FF-101 for final heating prior to reactor RB-101. The feed temperature profile in typically C in 1 st feed effluent heat exchangers and C in the 2 nd feed effluent heat exchanger. The reactor effluent is used to preheat two streams viz. the reactor feed and the stripper feed. The reactor effluent is thus split into 2 streams one into tube side of stripper feed pre-heater E-103 A/B and other into tube side of 2 nd feed effluent heat exchanger. The split flows are controlled by TV-0705 which controls the stripper feed temperature. The rest of reactor effluent flow is diverted into 2 nd stage. The control valve TV-0705 which actually engineers the split is a special 3 way valve placed downstream of both heat exchangers E102 A/B & E103 A/B. Both the exchangers tube side CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 3/19

4 outlets are mixed in this control valve and the combined stream flows into tube side of 1 st feed effluent heat exchangers E101 E/D/C/B/A countercurrent to reactor feed. The temperature profile in E103 A/B is C, in E102 A/B is C and over E101 E/D/C/B/A is C. The shell side temperature profile in E103 A/B is C. The reactor effluent from E101A is sent to separation section for final cooling in a battery of air coolers EALP-101 A/B/C/D. Ammonium salts which was formed as a byproduct of reaction have a tendency to crystallize on the tube surface as the reactor effluent cools down. To dissolve these wash water point is provided between E-101C & E-101D. This stream is however only operated intermittently, the main connection being before EALP-101 A/B/C/D. During regeneration, the main stream is nitrogen/air with trace oxygen from recycle gas compressor system. The heat exchangers E-101 A/B/C/D/E are totally bypassed. The feed system is isolated at this point. The Part of stream is diverted to E-102 A/B, preheated by reactor effluent and recombined with main stream. The effluent temperature is controlled by TIC-0208 in E-102 A/B outlet which in turn engineers the split through a 3 way valve TV The mixed feed stream is then sent to reactor heater FFV-101. The reactor effluent stream from E-102 A/B is directly sent to air cooler EALP-101 A/B/C/D/E and then to separation section. 4.3 FIRED HEATER SECTION (Refer P-&ID & 1122) Required temperature at the reactor inlet is achieved by heating feedstock, which comes under preheated condition from series of feed/effluent exchanger in fired heater. Vertical cylindrical type fired heater is used with radiation, convection and air preheater (APH) sections. Feed entering the reactor heater FF-101 is split into four passes. The first section is convection where the coldest oil is heated and then it enters the radiation section. The temperature profile is C. The feed then enters the reactor RB-101. Four numbers burners are located at heater floor, vertically up. They are low NO x forced draft, fuel gas/oil fired type. They are provided with selfinspiriting, continuously burning gas pilots. Each group of burners are provided with two (1 working + 1 standby) mains operated portable high energy ignition system comprising of permanently installed transformer assembly, spark igniter, lamps and push buttons. The portable igniter is provided with a stop collar for correct positioning of the igniter tip with respect to pilot tip. The burner has two combustion zones primary and secondary. In Primary zone gas is fired at sub-stoichiometric excess air levels and combustion is completed in secondary zone. The total excess CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 4/19

5 air level is thus restricted to 5% typically and the NOx levels are also minimized. The fuel gas/oil train consists of strainers, SDV-1502 / SVD-1053 and pressure control valve P-V1501/P-V1503 which regulates the gas flow to the burner. The combustion airflow to all the burners is kept identical by means of a specially designed distribution header. This ensures uniform heat release from the burners. The reactor inlet temperature is controlled by signal from TIC-0305 to PIC-1501 / PIC-1053 under cascade control. The combustion air is supplied by two forced draft fans. Each fan is designed to handle the total air flow to the burners, however for safety reasons both fans will be operating at 50 % of the required flow. In the event of tripping of one fan, the other will automatically take the full load and the tripped fan will be isolated by shutting off of the fan damper. The fan capacity is regulated by a variable frequency drive which alters the RPM. Air preheater is provided above convection section. Combustion air is passed through the coils to preheat the same. This ensures the heater economy and also stabilizes the flame in the burner. For continuous measurement of temperature in fired heater box, thermocouples are provided across the length. For measurement of tube metal temperature 3 Nos. tube skin thermocouples are provided for each pass. A damper is provided at top of APH to regulate the draft in the furnace. Draft gauges are provided for pressure measurement at burner level in the arch and above and below the damper. Stack is also provided with plugged connections for NO x, SO 2 analyzer points. Snuffing steam (LP- steam) connections are provided to extinguish a fire caused by tube rupture or for purging the heater. Lancing steam (MP- steam) is provided for soot blowing of deposits outside the coil on top of convection section. Decoking of tubes needs to be done when coke build up occurs due to the very high temperature service, inside the tubes. 4.4 REACTOR SECTION ( Refer P-&ID ) In this section the feed from FF-101 is fed to the 1 st HDS reactor RB-101. Desulfurization reactions takes place leading to H 2 S formation and Hydrogen consumption. Denitrification reactions lead to NH 3 formation and hydrogen consumption while the hydrogenation reactions lead to hydrogen consumption. The reactor RB-101 consists of two catalytic beds in series. First bed consists of a catalyst support grid on which alumina balls are distributed. The catalyst is uniformly loaded over the alumina balls support. On the top another layer of alumina balls is provided. Feed enters from a central inlet distributor, which is pipe with a perforated tray. The spray falls on a CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 5/19

6 distributor tray, which is of chimney type. Three thermocouples are provided for measuring temperature profile. Due to HDS reaction, which is exothermic in nature, the fluid temperature rises. Since the equilibrium point reduces, the temperature is reduced by introduction of quench hydrogen stream between the two catalyst beds. The amount of quench hydrogen is determined by the 2 nd catalyst bed temperature through TIC-0315 and cascading through FIC The feed from 1 st bed is collected over a mixing tray and redistributed vide 2 nd distributor tray into 2 nd catalyst bed. The construction and operation of 2 nd bed is similar to 1 st bed except the catalyst support plate which is reactor bottom itself. The outlet from 2 nd bed is a special outlet collector consisting of wire mesh and slots to prevent elutriation of catalyst / balls with reaction effluent. The bed is provided with four thermocouples. Catalyst withdrawal is possible from 1 st bed via 3 pipes which are connected from 1 st bed to 2 nd bed. The 2 nd bed catalyst withdrawal is possible through two draw off nozzles mounted on bottom dished end. Catalyst withdrawal from both beds which are interconnected is by self draining principle when the bottom withdrawal nozzles are opened up. The reactor effluent is sent for heat recovery to the feed preheating section. Bed pressure drops are measured by two differential pressure indicators PDT-0306 & PDT The reactor temperature profile is C. The reactor pressure profile is 56.6 to 60 Kg/cm2 g. Future expansion for deep DHDS through a 2 nd HDS reactor RB-102 with single bed catalyst is possible. Ammonia injection facility is provided at reactor outlet for catalyst regeneration. CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 6/19

7 4.5 COMPRESSOR SECTION Recycle Gas Compression Section : ( Refer P-&ID DHDS 1106) An increase in hydrogen partial pressure results in a decrease of coke deposits on the catalyst. The hydrotreatment reaction being enhanced. Hence, to maintain adequate level of hydrogen partial pressure at each point in the reactor, Recycle Gas Compressor is used. Normally the recycle gas comes from H.P-. Amine Absorber CC-102 after removal of H 2 S. In Cold Separator VV-103 out of 3 phases collected the gas phase goes to H.P-.Amine Absorber C-102 knockout drum VV-104. The outlet stream partially goes to H.P-.Amine Absorber C-102 where H 2 S is removed. The other part of the stream by passes the absorber C-102 and is directly routed to Recycle K.O. Drum. This by pass valve HV-0602 allows for control H 2 S concentration in recycle gas which should be maintained within the range of 0.1 to 1.0 mol. percent (typically 0.5%) which is monitored at discharge of KACF-102 by H2/H2S analyzers. Recycle gas compressor is a steam turbine driven centrifugal type two stage compressor which develops pressure from 49.4 Kg/cm2.g to 70.1Kg/cm2g. M.P-. Steam is used to drive the steam turbine. LP- steam and condensate produced from the discharge from steam turbine is condensed in condensate tank and sent to condensate header. The discharge from recycle gas compressor goes for the following: H2 Recycle : The feed is pumped under flow control by feed pump P- 101A/B to be joined by the recycle line of KACF-102. This ensures an adequate Hydrogen partial pressure at the entry of the reactor train. The mixed stream is heated first of all in heat exchanger E-101A/B/C/D/E then in E-102 A/B & finally in reactor feed heater FF-101 to the required inlet temp. Quench Line : Quenches coming from recycle gas compressor discharge is added at the inlet of bed under temperature & flow control cascade to control the reactor bed temperature. The temperature in reactor will decide & control the flow rate of Quenching. Antisurge Line : An unstable operating condition due to changes in many conditions such as flow rate, pressure & molecular wt. of gas causes a rapid pulsations in the flow, is known as surge. No system is immune to sudden upsets at one time or another. CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 7/19

8 Typically, surge is prevented by circulating some of the flow or by blowing off the excess flow. To overcome & control the surges, an antisurge control valve UV-0602 with antisurge system is installed on recycle gas compressor KACF-102. For further details, refer vendor s operating manual and other documents Makeup Hydrogen Compression Section (Refer P-&ID DHDS 1104). H 2 gas coming from HGU unit at pressure 19.5 Kg/cm 2 g is sent to H 2 Makeup K.O. drum VV-102. It is then compressed by Makeup gas compressor KARP-101 A/B which is reciprocating type compressor, to pressure 49.7 Kg/cm 2 g. H2 coming from CRU is passed through VV-107 chlorine guard for removing chlorine from Hydrogen. It contains adsorbent for removal of chlorine. PDI-0402 indicates differential pressure across the pot. Pressure control loop PIC-0409 has been provided on H2 line from CRU. It maintains uniform supply pressure of 20 kg/cm²g to Makeup Compressor. Safety valve PSV-0407 A/B has been provided to release the over pressure above 24 kg/cm²g. The Makeup gas flow rate to the reaction section is controlled by means of spill back water cooler E-105 to Makeup K.O. Drum VV-102. The Makeup gas joins the recycle H 2 stream at upstream of recycle K.O. Drum VV-105 which goes to recycle gas compressor KACF-102. Pressure control in the reaction section is achieved by action on the Makeup compressor spill back flow control (FIC-0403)/pressure control (PIC-0504) cascade. The H.P-. gas purge is available at the vapor phase discharge of H.P-. amine absorber C-102 to control the build up of heavies in hydrogen gas recycle stream. Normally, this flow is zero. For further details, refer vendor s operating manual and other documents. 4.6 SEPARATION SECTION ( Refer P-&ID DHDS 1105) In this section the reactor effluents from E-101 A enters the Effluent Air Cooler EALP-101 A/B/C/D. As the reactor effluent may form ammonium salt deposits and cause corrosion, wash water is injected by Washing Water Pump P-102 A/B at upstream of EALP-101 A/B/C/D. The flow rate CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 8/19

9 of wash water is controlled by flow control valve FV The reactor effluents gets cooled to C in Effluent Air cooler EALP-101 A/B/C/D. The reactor effluents gets further cooled in Effluent Water train Cooler E104 to C. The resultant stream gets collected in Cold separator VV-103. In Cold Separator V-103 the three phases namely sour gas, hydrocarbon and sour water get separated. The gas phase containing H 2 S, H 2 and lighter HC goes to HP- Amine Absorber K.O. Drum VV-104 in the HP- Amine Absorption Section. The hydrocarbon phase from VV-103 containing HC and H 2 S ( small %) is sent to E-106. A level control LIC-0506 of the VV-103 in cascade with flow control FIC The level of boot is controlled by LIC-0509, operates on split range. For 0 to 50% of the level, signal goes to algorithm LY-0502 which also receives signal from LIC For level range of 0 to 100%, the signal goes to selector switch HS LV-0509B is selected for normal operation, whereas LV-0509 A is selected for catalyst regeneration case. LIC-0509 control sour water flow to 1. ToVV-106 by LV-0502 through algorithem LY To stripper unit (OSBL) by LV-0509 B 3. LIC-0509 also controls flow of spent caustic to ETP- (OSBL) by LV-0509A during catalyst regeneration. VV-106 level is controlled by LIC The signal from LIC-0502 and LIC-0509 goes to algorithm LY The signal from LY-0502 controls functions of LV If necessary the Boiler Feed Water can be used for make up of wash water in VV STRIPPING SECTION (Refer P-&ID ) The HC Liquid from cold separator VV-103 is stripped with M.P.Steam to remove H 2 S and Lighter Hydrocarbons i.e. Wild Naphtha in Stripper C The hydrocarbon liquid or Stripper feed from VV-103 is preheated with hydrotreated diesel pumped from Stripper bottom by hydrotreated diesel CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 9/19

10 pump P-104 A/B in a train of Stripper Feed/Bottom Exchangers E-106 A/B/C on shell side. The stripper fed is heated from 53 o C to C in exchangers E-106 A/B/C, while the hydrotreated diesel losses its temperature from 260 o C to 109 o C flowing in counter current manner. The stripper feed further exchanges heat with partial effluent stream from reactor as described in Section 4.2. The resultant stripper feed at 263 o C is fed into Stripper C-101. M.P. Steam is fed into the bottom of column under flow control FIC to strip off lighter hydrocarbons and H 2 S from the feed. The Hydrotreated Diesel from the column bottom containing traces of water is cooled to 109 o C in train of heat exchangers E106 A/B/C as mentioned before. The hydrotreated diesel from E-106 A is then cooled in Hydro Treated Diesel Air Cooler EALP-103 A/B/C/D to 65 o C. Further cooling is achieved in Hydrotreated Diesel Water Cooler E-108. The hydrotreated Diesel is filtered through Coalescer prefilter. It consists of cartridges made of Pleated Synthetic Fibres. Coalescer is used to separate water from finished product i.e. gas oil. Coalescer contains internals having inherent property of adsorbing the water molecules. The accumulated water molecules forms a separate layer and gets collected in the boot of the coalescer and gets drained by level control loop LIC Coalescer package also includes coalescer prefilter. Coalescer prefilter is cartridge type filter, which can retain the particles above 10 Microns. The allowable pressure drop across the coalescer package including prefilter, pipes and fittings is 2 kg/cm². Differential pressure across the coalescer prefilter and coalescer are indicated by PDI and PDI respectively. For detailed operating instructions, please refer vendor s operating manual. The hydrotreated diesel is sent under level control LIC-0702 of stripper bottom by control valve LV-0702 to storage area of offsets. The gas at the top of column containing Lighter hydrocarbons, H 2 S and water is cooled from C to 65 o C in Stripper / Stabilizer Air Condenser EALP-102 A/B/C and further to 40 o C in Stripper / Stabilized trim Condenser E107. To prevent corrosion in the lines, corrosion inhibitor from Corrosion Inhibitor Pump PA-MT-113 is injected into the line coming from C-101 and going to EA-LP-102. The resultant condensed hydrocarbon liquid and water along with HC gas enters the Stripper/Stabilizer Reflux Drum VV-108. The gaseous stream is sent to L.P-. sour gas K.O. Drum VV-110 in L.P-. Amine Absorption Section. The CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 10/19

11 water which gets collected in the boot of VV-108 is sent under level control LIC of VV-108 boot by control valve LV-0708 to the water line coming from boot of VV-109. The Hydrocarbon stream is withdrawn from VV-108 drum and pumped by Stripper Reflux Pump P-103 A/B. Part of the Hydrocarbon Liquid is taken as Wild Naphtha under control LIC-0706 in cascade with FIC-0703 of drum by control valve FV-0703 and remaining is refluxed back to stripper C-101 under flow control FIC on reflux line by control valve FV Naphtha product is sent to storage. 4.8 HP AMINE ABSORPTION SECTION(Refer P-&ID ) H.P. Amine Absorption System The gaseous stream from (Separation Section) Cold Separator V-103 is routed to Amine Absorber K.O. Drum VV-104 in the recycle compression section. The Sour H.P gaseous stream from VV-104 partly enters the bottom of the H.P-. Amine absorption column C-102. The other part is bypassed and is directly routed to the recycle K.O. drum VV-105 in the recycle compression section. This is achieved by operating the control valve HV-0601 from the DCS panel, based on readings of AI-0601 B which indicates the H 2 S concentration of the recycle gas compressor KA- CF-102 outlet. In H.P-.Amine Absorber C-102, the gas is washed by Lean Amine entering from the top of the column. H 2 S from gas gets absorbed in L.P-. Amine. The nearly H 2 S free gas is recycled back to the Recycle K.O. drum VV-105. A gas purge by control valve PV-0504 is available to control the built up of heavier in the hydrogen gas recycle stream. Control valve PV is provided for the purpose, Normally this flow is zero. The Rich Amine from bottom of the H.P-.Amine Absorber C-102 is fed under level control, i.e. LIC-0902 by control valve LV-0902, to the bottom of L.P-. Amine Absorber C-103. Lean Amine is received from ARU. It is consumed in H.P-. Amine Absorber C-102 and L.P-. Amine Absorber C-103. Lean Amine is first fed to the Lean Amine Heater E-117 from where it goes to LP- Amine Absorber and H.P-. Amine Surge Drum VV-112. The temperature of Lean Amine (for H.P-.Amine Absorber C-102) is controlled by three way valve TDV which mixes hot lean amine with normal lean amine. The control valve TDV-0902 is actuated by measuring T between the sour HP- gas inlet and lean amine inlet to the H.P-.Amine Absorber C-102. The outlet temperature of the Lean Amine CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 11/19

12 from lean amine heater E-117 is controlled by control valve TV-1007 on the condensate line, which is actuated by TIC-1007 which indicates temperature at the inlet of Lean Amine to Lean Amine Heater. A part of the heated Lean Amine goes to inlet of Three way control valve TDV in the L.P-. Amine Absorption section. The lean Amine is pumped from H.P-. Amine surge drum by H.P-. Amine Circulation P-ump P-107 A/B into the H.P-.Amine Absorber C-102 under flow control by control valve FV The control valve FV-0902 is actuated by FT-0902 in the lean amine inlet to HP- amine absorber in cascade with LIC on VV-112 HP amine surge drum Anti Foaming System The Anti foaming solution is required to prevent foaming of solution in the Absorbers. The Antifoaming solution is prepared in 10 % D.M. Water in H.D.S Antifoaming tank TT-103. It is pumped by Antifoaming Pump PA-MT- 120 from TT-103 and injected into Lean Amine near P-107 A/B suction and near Lean Amine inlet into L.P-.Amine Absorber C-103 in L.P-. Amine Absorption section. 4.9 L.P- AMINE ABSORPTION SECTION(Refer P-&ID ) L.P-. Amine Absorption System The gaseous hydrocarbons (LP- Sour Gas) from Stripper / Stabilizer reflux drum VV-108 is fed into L.P-.Sour Gas K.O. Drum to remove moisture from the gas. The Hydrocarbon gas is then fed into the L.P-. Amine Absorption column C-103. In L.P-.Amine Absorber C-103 the gas is washed by Lean mine fed from the top. H 2 S from gas gets absorbed in Lean Amine. The H 2 S free HC gas or sweet fuel gas from the top of L.P-.Amine Absorber C-103 is sent to Sweet Fuel Gas K.O. Drum VV-115 to knock out any liquid traces in the gas. The sweet fuel gas is then sent to fuel gas header by pressure control PIC-0705 measured at top of Stripper Reflux drum by control valve PV This maintains the pressure in Stripper Reflux Drum. L.P-.Amine Absorber C-103 also receives Rich amine from H.P-.Amine Absorber C-102 in H.P-. Amine Absorption section. The Rich amine from bottom of L.P-.Amine Absorber C-103 is sent under Level Control of column bottom i.e. LIC-1004 by control valve LV-1004 to ARU in offsites. Lean Amine from ARU is fed to the L.P-.Amine Absorber C-103 at the top. The temperature of lean Amine to the C-103 is controlled by control loop, TDIC-1002 which measures the T between LP- sour gas at C- CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 12/19

13 103 inlet and Lean Amine flow to C-103. This controller regulates a three way control valve TDV-1002 which mixes Lean Amine from ARU and heated Lean Amine from Lean Amine Heater. The outlet of TDV-1002 temperature is fed under flow control i.e. FIC-1002 by Control Valve FV (measured at Lean Amine inlet into column) into the L.P-.Amine Absorber C-103 top HDS Amine Sump Drum System The amine drains from HP- Lean Amine Circulation Pump P-107 A/B, HP- Amine Absorber C-101 and HP- Amine Surge Drum VV-112 from HP- Amine Absorption Sections enters Amine Sump Drum TT-110 by the main Amine Drain header. Similarly the amine drains from L.P-.Amine Absorber C-103 is routed to TT-110. The Amine Layer which is heavy and settles in the first boot leg of TT-110, is pumped by Amine Sump Drum Pump P-118 into the Rich Amine line going from L.P-.Amine Absorber C-103 to ARU, The lighter hydrocarbons which overflow from weir in the first section of vessel into the second boot leg (in second section) is pumped by Amine Sump Drum HC pump P-119 to the slop header. UC-13 starts Amine Sump Drum Pump P-118 on actuation of LAHH 1010 of the first boot section and stops on actuation of level indication LALL UC-14 starts HDS Amine Sump Drum HC Pump P-119 for High High Level indicated by LAHH-1013 of second boot section of TT-110 and stops for Low Low Level LALL The tank is maintained under positive pressure of fuel gas. The system consists of two valves, PV-1011 & PV CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 13/19

14 4.10 CHEMICAL INJECTION SYSTEM A) DMDS: (Refer P-&ID DHDS 1114) DMDS is available in drums from which it is unloaded by portable drum unloading pump P-129 A/B. DMDS is required for injecting the feed pump suction at 1% wt. rate in recirculating gas oil for fresh or regenerated catalyst sulfiding. DMDS will be received in barrels. Metering pump PA-MT-109 is used to transfer DMDS to suction line of P-101 A/B. B) Anti Foaming : (Refer P-&ID DHDS 1109) The 10% diluted solution of Anti Foaming in D.M. water is required to be injected at suction of H.P-. Lean Amine Pump P-107 A/B & into the feed to C-103 feed at 20 wt. ppm of pure product compared to each stream. Drum unloading pump P-129 A/B is used for transferring antifoaming agent from the drums. HDS antifoaming tank TT-103 is having mixer MM-103 for preparing the solution of antifoaming agent in DM water. The solution is transferred by metering pump PA- 120 A/B. The tank is fitted with calibrated gauge glass for flowrate control. C) Corrosion Inhibitor Unloading (Refer.P-&ID DHDS 1114) The Corrosion inhibitor is required to be injected in vapors from Stripper going to stripper / stabilizer air condenser EA-LP-102. A diluted solution of 10% in stabilised Naphtha at 6 wt. ppm of pure product compared to the total column overhead is injected. Corrosion inhibitor is also mixed with the vapour from Naphtha stabilizer C-105, which mixes with the vapour from C-101 stripper before going to EA-LP-102 stripper / stabilizer air condenser. Corrosion inhibitor tank is fitted with mixer (agitator) MM-102 and calibrated gauge glass for flow control and solution preparation. Corrosion inhibitor is received in drums. Drum unloading pump P- 129 A/B used for unloading it to the tank. Corrosion inhibitor pumps PA-MT-113 are used for transferring solution of corrosion inhibitor in naphtha. CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 14/19

15 D) Anti Fouling : (Refer P-&ID DHDS 1114) The Anti Fouling is required to be injected at the feed pump suction. This solution is diluted to 10% in naphtha. As for other chemicals, antifouling agent is transferred from drum by portable drum unloading pump P-129 A/B. The solution antifouling agent in naphtha is prepared with the help of antifouling mixer MM-101. Antifouling solution is transferred using metering pump PA-MT Calibrated gauge glass on tank is used while preparation of solution and controlling the flow rate. E) Ammonia Unloading (Refer P-&ID DHDS 1114) Ammonia is required for catalyst regeneration cycle. Ammonia tank is elevated at adequate elevation so as to get sufficient suction pressure for pump PA-MT-112 to avoid cavitation problem. A platform is provided for installation of this tank on it and to meet the required elevation. Ammonia ton container is located on the platform at adequate elevation so as to have good gravity flow during unloading. 1 lines have been provided for vapour equalization and ammonia unloading. Ton container will be lifted from the ground by means of chain pulley block mounted on monorail on top platform. Suitable rubber belts and metal hooks shall be used for connecting it to chain pulley block. After lifting it up, necessary piping connections shall be made to connect it with the ammonia tank TT-107. Globe valve shall be used to equalize the pressure between ammonia tank TT-107 and ton container. Once pressure is equalized, ammonia unloading may be started by controlled opening of another globe valve on unloading line. Once ammonia unloading is over, all isolation valves shall be closed. Trapped ammonia between two isolation valves is released to the atmosphere through seal pot having 400 mm of water seal. After depressurization, ton container may be disconnected. Ammonia seal pot has provision for cleaning purpose. Once regeneration cycle is over, empty ton container may be brought down and sent back for refilling. It is recommended to keep filled ton container under the shed in safe area and shall be brought to the plant in a planned manner only when it is needed for regeneration. CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 15/19

16 4.11 OILY WATER SEWER (OWS) (Refer P-&ID DHDS 1124) The Oily Water Sewer collects oily waste from pump drains equipment in process units mainly during shutdown. Each pipe from drain points are routed to the nearest manholes through a pipe seal of 150 mm. These manhole are interconnected. These manholes are provided in following cases to have uniform distribution of flow. * When there is change in direction * Two or more lines are joined * There is change in pipe size CONTAMINATED RAINWATER SEWER (CRWS) (Refer P-&ID DHDS 1124) This sewer will carry floor wash/contaminated rainwater and process drains from equipments from various process units. Uncontaminated and segregated areas will be drained through open ditches that are located at outer periphery of unit battery unit with by pass to storm sewer or CRWS. Contaminated surface area will be suitably divided into catch basin areas. The maximum coverage for catch basin typically is less than 150m 2. As far as possible, it is done in square configuration for good distribution of flow. Each catch basin is connected to a manhole. Slope of pavement is sufficient to maintain normal velocity CLOSED BLOWDOWN (CBD) SYSTEM (Refer P-&IDDHDS 1121) Draining facilities on DHDS unit is provided by laying two separate headers of 6 and 4 on either side of pipe rack. Drain points from each equipments are terminated on these underground header. Thus, the whole system is closed where there is no discharge to open atmosphere. Two main headers at the end is combined to discharge hydrocarbon drain into underground CBD drum, VV-118. From this through submersible pump P-122, effluent is discharged to slops header intermittently. Temperature in CBD tank is maintained by cooling water circulation through internal coil if necessary. Any hydrocarbon vapour generated during draining to CBD tank is taken to flare AMINE DRAIN (AD) (Refer P-&ID DHDS 1121 and 1110) Amine drain header receives drains from H.P-. Amine Absorber C-102, H.P-. Amine Surge drum VV-112, H.P-. Lean amine circulation Pumps P- 107 A/B, Rich Amine Pumps P-123 A/B and L.P-. Amine Absorber C-103. The amine header is connected to amine sump drum TT-110. HDS amine sump drum TT-110 is having two boots separated by a vertical weir. The HC liquid being lighter than the amine floats as a top CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 16/19

17 layer. The weir allows top layer of HC liquid to overflow and is collected in other compartment. HDS amine sump drum HC pump P-119 is used to transfer collected HC liquid to slop header. Collected amine is transferred to Amine Recovery Unit by Amine sump drum Pump P-118. Both the pumps P-118 and 119 operate and stop automatically in accordance with the high high and low low level switches COOLING WATER, SERVICE WATER, POTABLE & DM WATER (Refer P-&ID DHDS 1116) Flow totalizer cum recorder FI(QR) indicates and records DM water flow rate. DM water is used for condensing the steam in direct contact in VV-21 condensate drum. It is also used for preparing solution with various chemicals and other process application. Service water is used for hose stations, pumps, etc. FI(QR)-1602 measurers, totalize and record the flow rates. Low pressure will be indicated by annunciation of PAL tapping is provided on all utility hose station. Cooling water supply and return headers are connected by 12 line for flushing. FI-1601, PI-1605 and TI-1605 indicates important parameters. As line size is 18, annubar is provided for flow measurements. Sample point AP- 1 is used for drawing the sample for chemical analysis. Potable water is used for drinking purpose for operational staff. It is also used for safety showers and eyewash. Galvanised pipe is used for the potable water STEAM, CONDENSATE AND BFW SYSTEM (Refer P-&ID DHDS 1117). M.P-.Steam (12 to 15 kg/cm2g) and L.P-.Steam (5 to 10 kg.cm2g) are used in DHDS Plant. Steam is in superheated form and desuperheater is not required for the application. L.P-.Steam is required also used for Utility Hose Stations. Condensate+Steam from E-117 and E-110 flows to VV-121 Condensate drum. Condensate drum operates at atmospheric pressure. Condensate+Steam condenses in direct contact with the DM water spraying inside the Drum. Condensate is pumped to the Battery Limit by Condensate P-umps P-124 A/B under level control LIC The CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 17/19

18 pressure of L.P-.Steam is further reduced to 1.5 kg/cm2g by pressure control PIC This further depressurised steam is used for steam tracings. Condensate header also receives condensate from Surface Condenser of Recycle Compressor Package. M.P-.Steam is used for atomising fuel oil for Reactor Heater, in Stripper, in Ejector for Startup and intermittent operations like Soot Blowing, Purging, Decoking etc. BFW is consumed in Washing Water Drum V V-106. Steam traps have been provided at various places for efficient removal of condensate from the System P-LANT AIR, INSTRUMENT AIR AND NITROGEN SYSTEM (Refer P-&ID DHDS 1118) Plant Air is used for Utility Hose Stations, Reactor Heater and Makeup Compressor Area. In addition to supply Instrument air to all Instruments, it also supplies to HT motors of Makeup Gas Compressor KARP-101 A/B. The dew point of Instrument Air shall be 40 o C. Nitrogen is used wherever inert gas purging is required from Maintenance point of View. Various Pressure, Flow and Temperature measurement instruments are provided to monitor the operating conditions FUEL GAS AND FUEL OIL (Refer P-&ID 1119) Fuel gas has two way flows. Annubar FE-1902 measures flow in either direction. Pressure Safety Valves PSV A/B release pressure above 6.2 kg/cm2g. Liquid from fuel gas is remove in VV-120 Fuel Gas K.O.Drum before it is sent to Reactor Heater FF-101. Gas from L.P-.Amine absorber is sweet fuel gas from which liquid, if any, is removed in VV-115 Sweet Fuel Gas K.O.Drum before sending it to the header. Fuel Oil supply lines are steam traced to maintain the temperature required for use for Reactor Heater FF FLARE SYSTEM (Refer P-&ID 1120) Flare header receives hydrocarbons from various PSVs and Equipment of CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 18/19

19 the Plant. All lines are connected to the header from the top at an angle of 45 o C in the direction of flow. A 2 Utility Connection is also provided on Flare header. Flare gas knockout drum VV-119 removes any liquid carry over in the flare gas. The level in the drum is maintained by opening and closing of on off valve SDV-2001 on actuation of High Level Alarm LAH-2003 and Low Low Level alarm LALL CHAPTER-4 DETAILED PROCESS AND UTILITY DESCRIPTION 19/19