Beneficiation of High Sodium Fly Ash

Transcription

1 Beneficiation of High Sodium Fly Ash MEGA Symposium August 20, 2014 Authored by Michael Atwell, Solvay Chemicals, Inc. Rasik Raythatha, Solvay Chemicals Inc. Keith Day, Beneficiate North America

2 The Agenda Drivers for Sodium Dry Sorbent Injection Impacts of sodium in fly ash disposal Options for stabilization Test set up Test results Next steps 2

3 Drivers for Sodium DSI Applications Utility MATS HCl, SO 3 for mercury removal Industrial Boiler MACT HCl Regional Haze SO 2 CSAPR SO 2 SO 2 NAAQS Consent Orders mainly SO 2, some SO 3 3

4 Sodium Sorbent Application Trona is generally used for SO 3, HCl and moderate SO 2 control. Sodium Bicarbonate is generally used for moderate to high levels of SO 2 control. Residual sodium in the form of sodium sulfate, sodium chloride and sodium carbonate will be retained with the fly ash 4

5 Impacts of sodium in fly ash SO 2 and HCl control with sodium sorbents generally results in more than 2% sodium in the ash. Disposal in a land fill or mine reclamation is typical Landfills vary greatly and for many cases ash containing sodium can be disposed of with no issue. Arsenic and selenium are the leachable elements most under scrutiny from fly ash leachate. 5

6 Selenium and Arsenic Selenium and Arsenic are covered under the proposed Effluent Limitation Guidelines (ELG) Arsenic - 8ug/L single day and 6 ug/l on a 30 day rolling average. Selenium - 16ug/L for a single day and 10ug/L on a 30 day rolling average. The U.S. hazardous waste toxicity characteristic (TC) limit Arsenic - 5 mg/l Selenium - 1 mg/l. Fly ashes that exceed these limits would be classified as hazardous wastes and be more expensive to land fill. In these cases it could be cost effective to treat the ash to avoid the hazardous classification and reduce disposal costs. 6

7 Pozzolanic Reactions Pozzolanic reactions form cement that binds material in a hard water resistant material Class C fly ash readily forms pozzolanic reactions Typical of ash from PRB coal Has a high calcium content Class F fly ash does not generate pozzolanic reactions Typical of ash from bituminous coal Low calcium content and high carbon content Inducing pozzolanic reactions can be enhanced by adding calcium or silicate 7

8 Ash Stabilization Sodium Silicate Readily available form of soluble silica Soluble silicate is very reactive and can promote pozzolanic reactions. It is widely available as a 40% solution Lime Kiln Dust (LKD) A generally available source of reactive calcium from the lime manufacturing process A mix of calcium oxide, silica and inert materials Other calcium materials such as cement kiln dust (CKD) would likely perform similarly to LKD. 8

9 Ash samples PRB ash samples from a sorbent test Sodium levels 11% and 21% Baseline ash with no sorbent added. Bituminous ash mixed with spent sorbent A relatively pure spent trona was obtained from a customer who adds trona after an ESP and collects it in a baghouse. This was blended with bituminous fly ash at similar sodium levels as the PRB fly ash. The selenium level of the spent sodium sorbent was 0.28mg/L compared with <0.02ppm in trona. 9

10 Experimental Method Samples were sent to Beneficiate North America (BNA) to prepare the samples for baseline and stabilization testing. Ash samples were combined with LKD or SS and 15% water and mixed together for 60 seconds using a Lancaster Products K-Lab High-Intensive Mixer. Samples were sent for SPLP tests to Energy Laboratories in Casper WY to measure leachable metals. 10

11 PRB Test Results Base Line 11

12 PRB Test Results 12 % Sodium 12

13 PRB Test Results 21% Sodium 13

14 Bituminous Test Results Base Line 14

15 Bituminous Test Results 12% Sodium 15

16 Bituminous Test Results 21% Sodium 16

17 Test Summary The addition of silica in the form of aqueous sodium silicate in PRB ash showed reduced leaching of selenium and arsenic. The addition of a liquid stream to the fly ash disposal system is low capital and easier to retrofit than dry powders. The cost for sodium silicate is about $0.25 per pound depending on freight For bituminous ash low in calcium, the addition of LKD was very effective in stabilizing metals. Cement Kiln Dust (CKD) or other calcium materials could also be effective. 17

18 Next Steps Testing fly ash from utilities with leachate concerns Further testing of combinations of LKD and sodium silicate Look at the effects of mixing and water content Prepare for changing regulations affecting coal ash 18

19 All technical advice and recommendations provided, if any, are intended for use by persons having the appropriate education and skill. Solvay Chemicals, Inc. and its affiliates shall not be liable for any use or nonuse of such advice and/or recommendations. Users of our products are solely responsible for the design, construction and operation of their own facilities. Mike Wood, SOLVAir Business Manager Michael Atwell, Market Development Manager Marco Riccio, Technical Development Engineer