Coal-fired power plants can add PVC scrap to their coal and make byproduct hydrochloric acid.The result would be elimination of mercury both from coal-fired stacks as well as from the obsolesced chlorine manufacturing facilities.There would also be greenhouse gas benefits and elimination of the environmental problems associated with disposing of millions of tons of waste PVC.These are the conclusions from a study appearing in the McIlvaine Company online service, Power Plant Air Quality Decisions.
By adding up to 0.3 percent PVC scrap on the coal belt and installing a chloride pre-scrubber, all the following advantages would be obtained:
- Remove 95 percent of the mercury.
By controlling the chlorine through PVC additions to the coal and by recirculating some hydrochloric acid from the pre-scrubber, the chlorine content in the gas reaching the SCR is optimized.This results in full oxidation of the mercury.The chloride pre-scrubber will then remove more than 90 percent of the mercury.The down stream SO2 scrubber will remove an additional five percent, resulting in more than 95 percent mercury capture.
- Remove mercury in a concentrated form.
The water to the chloride pre-scrubber is recirculated quickly, resulting in a 30 percent hydrochloric acid solution.At equilibrium a bleed stream of acid is stripped of mercury and other contaminants, resulting in salable acid and concentrated mercury.
- Eliminate heavy metal and chloride wastewater treatment.
Capture of the metals and the chlorine in the pre-scrubber eliminates the need for gypsum washing and wastewater treatment of the wash water.
- Use less expensive alloys in SO2 scrubber and downstream duct.
With removal of the chlorides, less expensive materials can be used in the SO2 scrubber and outlet duct.This can result in a net capital cost reduction.
- Produce significant quantities of a very valuable byproduct - hydrochloric acid.
Coal-fired plants could produce 1 to 2 million tons/yr of hydrochloric acid worth $100 million to $400 million.
- Convert hydrochloric acid to calcium chloride and offer to states to reduce fugitive road dust making the coal plant a net particulate reducer.
Fugitive dust contributes to ten times as much particulate as coal-fired power plants.Fugitive dust is effectively eliminated with calcium chloride spraying which makes the roads dense and moisture absorbing.States cannot presently afford the addition of this expensive chemical.Utilities could produce it at a very low cost.Its use in the county where the plant is operating would reduce dust by more than the particulate emitted from the power plant stacks.
- Reduce average fuel cost and greenhouse gases.
The world is trying to rid itself of 300 million tons of PVC.Instead of shipping millions of tons per year overseas, it could be used in U.S.coal-fired power plants.With its high Btu content and low cost, it would reduce net fuel costs. Greenhouse gas reduction would result both from the substitution of PVC for coal and the shut down of energy intensive chlorine manufacturing facilities.
- Reduce operational risks with a two scrubber system as opposed to alternative methods for mercury removal.
Pre-scrubbers are used in a number of U.S. coal-fired power plants and in incinerators and coal-fired power plants in Europe and Asia.The two scrubber approach is safer operationally than the single scrubber approach.The only new twist is recirculating rather than discharging the scrubbing liquor.However, this is being done in a number of European waste incinerators which make hydrochloric acid. Therefore this is not something new and untried.
- Reduce mercury and other hazardous air pollutant emissions associated with chlorine production and landfill of PVC.
Chlorine production is the largest source of mercury emissions after coal-fired boilers.Manufacture of hydrochloric acid in coal-fired boilers could reduce mercury emissions by several tons per year from chlorine production.PVC is often discharged to landfills, resulting in major dioxin emissions from landfill fires.
For more information on Power Plant Air Quality Decisions click here or contact: McIlvaine Company editor@mcilvainecompany.com
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