Coal-fired plants can become major producers of hydrochloric acid and calcium chloride. Emissions, including mercury, are reduced and those from hydrochloric acid manufacture are eliminated. The net cost of electricity goes down instead of up. These are the conclusions reached by the McIlvaine Company in its online Power Plant Air Quality Decisions service.
Power plants emit more than 90% of the hydrogen chloride (HCl) escaping in the U.S. If this HCl were converted to hydrochloric acid, it would produce as much as 1 million tons per year of acid having a value of $200 million.
Installing a chloride prescrubber ahead of the conventional limestone scrubbing system captures and concentrates the HCl. The scrubber also will capture more than 90% of the mercury. The diluted acid is recirculated until the system reaches equilibrium, when a steady stream of dirty acid can be removed and cleaned. The mercury is concentrated in a solid form for disposal, and the cleaned acid can be sold or converted to calcium chloride.
The calcium chloride could be used on unpaved local roads to reduce dust clouds. Unpaved roads near plants emit 10 times more dust than power plant stacks, but the high cost of the chemical has prevented states from treating roads. If power plants provided calcium chloride at affordable prices, they would become net reducers of dust in their vicinity.
This isnt untried technology, according to Bob McIlvaine, company spokesman. Chloride pre-scrubbers are used at the Philadelphia Electric Eddystone and Cromby plants as well as many other coal-fired plants, says McIlvaine. However, only some waste incinerator operators in Europe recirculate the scrubber solution and build up the acid concentration. The cost for the prescrubber is more than offset by reductions in the SO[-]2[-] scrubber and the wastewater treatment, so when the sales value of the acid is included, the cost of electricity is reduced.
There are two reasons why now is the time to implement the technology, McIlvaine says. First, there is a need to remove the mercury and concern that the capture does not result in transfer to the water or the gypsum. Secondly, there are now materials of construction to [cost-effectively] handle the highly acidic conditions. There is also the knowledge to take advantage of materials savings in the downstream portion of the plant once the chlorides have been removed.
This and other air quality issues facing power plants are continually covered in Power Plant Air Quality Decisions. For more information, see www.mcilvainecompany.com/brochures/energy.html#44i.