IMMOBILIZATION OF TOXIC HEAVY METALS IN MSW RESIDUE ASH

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1 IMMOBILIZATION OF TOXIC HEAVY METALS IN MSW RESIDUE ASH Anil K. Mehrotra, M.S., P.E., BCEE Hampton/NASA Steam Plant April

2 MSW Incineration Technologies: Mass Burn and RDF Two major technologies are in use. Both technologies deploy a variety of boiler and stoker designs and configurations. 1. Mass Burn refuse is unloaded from trucks either directly into the refuse storage pit (Hampton/NASA Plant), or on tipping floor and then pushed into storage pit. Refuse is then fed to boilers in as-received condition, without any pre-processing. Only bulky items are removed from feed piles, as possible. 2. Refuse-derived Fuel (RDF) Refuse is processed before use as fuel. Various pre-processing steps are employed: Shredder, trommel, hammer mill, screening, hand-picking of metals and glass from moving conveyors (SPSA, Portsmouth) 2

3 Mass Burn: trash processing involves fluffing and mixing Hampton plant: Outside View As-received trash pile. 3

4 ASH DISPOSAL REGULATIONS, AND TEST METHODS EPA/RCRA REGULATIONS EPA determined MSW residue ash as hazardous waste and defined toxicity limits of various elements before disposal Resource Conservation and Recovery Act (RCRA) Subtitle D regulations govern sampling, treatment and disposal guidelines Toxicity Characteristics Leaching Procedure (TCLP) Test Method 1311 is used to test ash 4

5 CHARACTERISTICS OF MSW RESIDUE ASH IT IS HAZARDOUS Contains heavy metals New air emission standards have led to improvements in: - Flue gas treatment technologies dry, wet, semi-dry scrubbers (SDA)/flue gas desulfurization (FGD) product - Air pollution control (APC) technologies particulate collection equipment (ESP/Bag houses) generate fly ash (FA) At the same time it has increased the amounts and potential for toxicity of heavy metals in APC residues Scrubber/FGD product and fly ash (FA) constitute 12-15% of total ash generated from incineration process Bulk of the residue ash is bottom ash (BA) from boiler furnace and furnace siftings BA, Scrubber/FGD product, and FA are taken together as combined ash (CA) before disposal to landfill 5

6 Approach to select a suitable treatment method Scrutinize the effectiveness of various fly ash chemical treatment methods currently available to stabilize and immobilize heavy metals. Apply results of study to identify a more costeffective and environmentally safer method of treatment of CA To optimize the quantitative and qualitative injection of identified chemical treatment and process controls in the fly ash downstream To examine effect of identified treatment method during variations in the mass flux rate of residue wastes generated and during upstream process changes in operational status of one/all boilers 6

7 Treatment process comparisons 1. Soluble phosphate is an effective stabilization agent for divalent heavy metals (Ca 2+, Zn 2+, Pb 2+, Cu 2+, and Cd 2+ ) in waste materials such as scrubber residues. Other treatment processes: According to solubility of each stabilized heavy metal compound in water, the order in stabilization capacity is: 2. Liquid chelate (EDTA) most effective, but costliest option 3. Sulfide process very effective, less costly, easily injected 4. Carbonate process less effective 5. Sodium Hydroxide cheapest process, but least effective 7

8 MATERIALS AND METHODS: Hampton Plant A. PRIOR TREATMENTS (a) Treatment with a proprietary technology (b) Switch over to cost-effective dolomitic lime fines technology (2008) 8

9 MATERIALS AND METHODS: Hampton Plant B. RECENT TRIALS Following methods were tried but these proved only partially successful and with no repeatability - 1. Utilized alkalinity of boiler process water added to fly ash for its conditioning to eliminate any treatment of residue ash (2015) 2. Increased injection rate of high calcium hydrated lime slurry in SDA for flue gas treatment and monitored its effect on mobility of heavy metals in combined ash Replaced hydrated lime injection in SDA either with: 3. Dolometic hydrated lime, or with 4. Type S dolometic Super Hydrate 9

10 RECENT TRIALS (cont.) 5. Aqueous Sodium sulfide process Five trial tests by injecting sodium sulfide Na 2 S 39% aqueous solution in fly ash conditioning system combined with existing boiler process water (3/2016) Continue tests and establish and quantitative and qualitative optimization of sodium sulfide treatment process. 21 compliance tests (5/2016 8/2016) All test proved successful in immobilizing the toxic heavy metals within the regulatory limits. The level of controlling the leachability of heavy metals Cd and Pb with use of aqueous sodium sulfide was comparable or better than with use of dolomite lime as shown in cumulative results of two methods. 10

11 Summary of results of 28 tests with dolomite use, ending 12/2015 RT: Regulatory Threshold METAL AVERAGE mg/l UCL mg/l UCL: Upper Confidence Limit RT mg/l %RT Arsenic As % Barium Ba % Cadmium Cd % Chromium Cr % Lead Pb % Mercury Hg % Selenium Se % Silver Ag % Sample points for all 8 metals

12 Results of 5 trial tests with sodium sulfide treatment Results shown are of TCLP test from treatment of FGD and Fly ash residues (combined ash) with injection of gallons per day aqueous sodium sulfide 12

13 Cumulative results of 21 tests with sodium sulfide treatment: 5/016-8/

14 Sodium Sulfide Injection System Installation: Hampton plant Diagram showing permanent chemical injection arrangement Chemical System Installation at Hampton Plant 14 Technician checking the installation of chemical injection to fly ash A parallel boiler hot process water injection is sent to fly ash

15 Estimated cost savings with use of sodium 12.5gpd Leachability control for Cd is about same, and is somewhat better for Pb with use of sodium sulfide compared to dolomite Ease of operation and $150,000 per year in cost savings by switching over to sodium sulfide. A. Costs for chemicals + shipping and labor: Dolomite: Material costs/mo. Labor/mo. Total Costs/year $16, $ $199, Sodium Sulfide $4, Nil $54, Savings in cost of chemicals and labor: $145,339.40/yr B. Savings in maintenance costs (Est., $400/mo.) $4,800/yr C. Estimated Total savings $150,

Cost of residue ash treatment $ COST and PERCENTAGE The annual cost of residue waste treatment which is estimated at about $55,000. It is less than 1% of the facility s operating budget.

16 Cost of residue ash treatment $ COST and PERCENTAGE The annual cost of residue waste treatment which is estimated at about $55,000. It is less than 1% of the facility s operating budget. Dolomite silo and screw feeder are now redundant A measured quantity of liquid treatment chemical is directly injected into the fly ash conditioning screw. From metering pump installed inside 16

Avoided labor and safety hazards Doing away with use of dolomite treatment chemical avoided operator hours involved in feeding 1 ton supersacks into a silo every 12 hours.

17 Avoided labor and safety hazards Doing away with use of dolomite treatment chemical avoided operator hours involved in feeding 1 ton supersacks into a silo every 12 hours. It was a 2-man operation involving one operator lifting the super-sack using a heavy fork lift and another operator climbing over a platform and guiding and slitting open the bag to drop the lime into silo. The operation had slip hazards and other weather related elements associated with it. 17

18 Acknowledgements John MacDonald Plant Manager Hampton/NASA Steam Plant For his consistent support and encouragement in conducting this research. And All the staff of the Steam Plant facility for their help in conducting the tests and setting up the treatment system Sandeep Kumar, PhD Associate Professor, Dept. of Civil and Environmental Engineering, Old Dominion University And Prof. Ben Stuart, PhD Chair, Dept. of Civil and Environmental Engineering Old Dominion University For their mentorship and technical guidance 18

19 Questions 19

NeuStream -DR: Improving the effectiveness of DSI while substantially reducing the chemical cost

NeuStream -DR: Improving the effectiveness of DSI while substantially reducing the chemical cost J.P. Feve, V.P. Business Development, jpfeve@neustream.com Do Not Distribute w/o NSG Permission Stack Current