Environmental Control in General Galvanizing paper presented to LATINGALVA Cartagena, September Contents. Emission regulations 8/23/2010

Transcription

1 Environmental Control in General Galvanizing paper presented to LATINGALVA Cartagena, September 2010 Rob White International Zinc Association Contents ISO Emissions from a HDG plant Some typical emission numbers Emission regulations Key process changes Examples Emission regulations 1

2 ISO series The ISO series provides for: A commitment to prevention of pollution and continual improvement Compliance to environmental legislation Management and knowledge of the company s impacts upon the environment Third party certification of a company s environmental management system ISO does not Specify environmental performance beyond legal compliance and indirectly to continual improvement. Guarantee good environmental performance, although this may be viewed as an eventual target Auditing & Evaluation Environmental performance Evaluation ISO key activities Environmental Auditing 14010, , Management Systems Product Analysis Life Cycle Assessment 14040, 14041, Environmental Labeling 14020, 14020, , 14023,

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4 Degreasing bath - emissions Liquid and sludge -0 to 5.4 kg/tonne Oily sludge kg/tonne Discarded degreasing bath -1 to 2 kg/tonne Acid pickling bath Emissions to air -1 to 5 mg/m³ Acid for recycling; ph = 1 to 2 Fe = 140 to 170 g Fe/ton ZnCl2 = < 50g/l Rinsing Water - 7litre/tonne Fluxing Sludge - 5kg/tonne 4

5 Zinc kettle Ash = kg/tonne Dross = 3 10 kg/tonne Zinc Ammonium Chloride fumes = kg/tonne Air emissions Dust = mg/m 3 Zinc = 2 20 mg/m 3 Hydrogen Chloride = 1 2 mg/m 3 Typical consumption values Consumption Towers General Tube & Pipe Zn kg/tonne kg/tonne kg/tonne Ash production 6 10 kg/tonne 6 10 kg/tonne 6 10 kg/tonne Dross production 4 5 kg/tonne 4 5 kg/tonne 4 5 kg/tonne Dust production kg/tonne Typical composition Zinc Ammonium Chloride Fume Ammonium Chloride (NH 4 Cl) 68.0% Zinc Oxide (ZnO) 15.8% Zinc Chloride (ZnCl 2 ) 3.6% Ammonium (NH 3 ) 1.0% Oil &/or Carbon 1.4% to 2.8% Water Vapour 2.5% 5

6 Pollution from fuels Fuel Particulates SOx NOx Natural Gas LPG Light Fuel Oil Heavy Fuel Oil Inputs: Estimating emissions particulates Plant 5 tonnes steel/hour, 5% pickup/hour, operating 3000 hours per year, 80% particulate removal Assumption - 2.5kg particulates/tonne zinc consumed (USEPA) Emission 5 x 5% x 3000 x 2.5 x (1 80/100) = 375kg year Similar calculations can be made for: Particulate emissions from materials handling, eg. Ash Fugitive emissions NH 4 OH, HCl, etc. Disposal volumes Na OH, HCl, Cr 2 O 3 Liquid leaks acids, water, oil Site Run-off water, contaminants 6

7 Key areas for improvement Water usage Procedures Chemicals use (acidic degreasers, biological degreasers) Wastewater treatment Air emissions Air Regulations dust particles 15mg/m 3 (10 Ireland) total chloride (as HCl) 30 mg/m 3 Water oil 5mg/l suspended solids 20mg/l zinc 2mg/l Typical Chinese water (max 40 m 3 /day) ph: 6-9 chemical oxygen demand(cod) 110 mg/l suspended solids 100 mg/l total copper 1.0 mg/l total zinc 3.0 mg/l total cadmium 0.1 mg/l total chromium 1.5 mg/l hexavalent chromium 0.5 mg/l total lead 1.0mg/l total nickel 1.0mg/l petroleum 15 mg/l. 7

8 Typical Chinese air (max m 3 /day) the smoke and dust concentration is 150 mg/m 3 the fume blackness is level one (Greenman level). Benchmark emissions to air using BAT Kettle emissions 15mg/m 3 use low fuming flux Stack emissions (where extraction used) 10mg/m 3, no persistent visible emissions Total chloride (from pickling) 30mg/m 3 8

9 Benchmark emissions to water using BAT Total hydrocarbon oil 5mg/l Total suspended solids 20mg/l Zinc 2mg/l Examples using Best Available Technology Jigging Practice Water rinsing Degreasing Management Pickling Management Flux Management Fume extraction Alloy use Waste Water Treatment Emission controls Low fume chemicals (covered by others) Counter-current rinsing Control of acid concentration Flux regeneration Fume extraction and collection Water treatment 9

10 Counter-current rinsing The formula of water consumption by cascade rinsing is: C o /C n = (Q/V) n = F Q = water flow (l/h), V = drag-out (l/h), n = number of rinsing tanks F = dilution factor, C o C n = concentration of process bath = concentration of rinse water in tank number n At F = 1000 the water consumption is 31 litre per litre drag-out at 2-stage cascade rinsing and 9.6 litre per litre drag-out at 3-stage cascade rinsing. Acid strength control 10

11 Flux regeneration Pure Flux Solution Filter Press Flux Bath ZnCl 2 + NH 4Cl Hydrogen peroxide Ammonia Filter cakes for waste collection company Reaction Tank Sludge Thickener Sludge Storage Tank Step 1. Flux regeneration ferrous salts oxidised to ferric salts Step 2. precipitation at ph 4.5 Step 3. acid reacts with ammonia to form ammonium chloride (flux component) Step 4. acid produces zinc chloride from either residues or from added pickling acid 11

12 Advantages of flux treatment Decrease in zinc pick-up from 9.5 to < 7 % Higher production rate -increase of over 10 % Lower production of zinc ash Lower production of fume Lower dross production from 8 t/2 wks to 2 t/6 wks Higher quality product Fume treatment - processes Extraction depends upon waste gas flow Peripheral = 1800m 3 per m 2 of bath/hour Hood = 1000m 3 per m 2 of bath/hour Dust removal venturi bags water Typical achievable fume reductions 12

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15 Percentage of kettles having an enclosure North America (2007) Water treatment Holding tank Reaction tank Chemical additions/ph changes Precipitation tank Neutralisation Polishing Final tank 15

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17 Example 1 process controls BEFORE PROJECT IMPLEMENTATION AFTERPROJECT IMPLEMENTATION CONSUMPTION CONSUMPTION OUTPUTS WATER HCl ACID CHEMICALS WATER HCl ACID CHEMICALS Low acid pickling 36kg/ tonne 30kg/ tonne technology( 6 tanks) steel steel Rinse cascade 1.5m m 3 system (2 tanks) /tonne / tonne steel Steel Flux purification & Zinc chloride regeneration system consumption: 0; ammonium Zinc chloride: chloride: 1kg/tonne 1.5kg/tonne steel; steel, ammonium ammonia chloride: solution: 2.25kg/tonne 1kg/tonne steel steel; Electric power: 2kwh/hr Example 1 -costs Before project implementation Costs (USD) Total Annual Costs $446,325 After project implementation Costs (USD) Total Annual Costs $261,313 Annual Cost Saving $185,012 Initial investment costs of the proposed system Flux purification & regeneration system $64,342 Installation of anti-collision layers to tanks $85,714 Total initial investment costs: $150,056 Example 2 water recycling BEFOREPROJECTIMPLEMENTATION AFTERPROJECT IMPLEMENTATION CONSUMPTION CONSUMPTION OUTPUTS Wastewater treatment system Water usage: 1.2 m 3 /kon steel Water usage: 0.6 m 3 /kon steel Wastwater damped: 1.2 m 3 /kon steel Wastwater damped: 0.6 m 3 /kon steel Electrical power: 1.5kw/hr Electrical power: 2.0kw/hr 17

18 Example 2 -costs Before project implementation Costs (USD) Total Annual Costs $29,142 After project implementation Costs (USD) Total Annual Costs $17,257 Annual Cost Saving $11,885 Initial investment costs of the proposed system Total initial investment costs: $40,769 Example 3 fume control BEFORE PROJECT IMPLEMENTATION AFTER PROJECT OUTPUTS CONSUMPTION IMPLEMENTATION CONSUMPTION Zinc fume capture & filter system None Electric power: 80KWh/hr Before project implementation Costs (USD) Total Annual Costs $0 After project implementation Costs (USD) Total Annual Costs $60,880 Annual Cost Saving -$60,880 Initial investment costs of the proposed system Total initial investment costs: $266,131 Conclusions Technology is available to reduce environmental impact of HDG processes Simple water management can result in zero discharge Fume capture can make the plant and outside air quality acceptable Process changes can reduce waste Costs can be contained and even be cash positive. Irrespective pollution should be minimised 18