NEWS RELEASE NOVEMBER 2015
Reducing the Negative Impact of Coal Firing at Minimum Cost
Coal-fired power plants emit a variety of pollutants. Some are more harmful than others. The best way to minimize the harm from coal-fired power plant emissions is to assign a monetary value to each ton of each pollutant and then develop a program to minimize the total.
Hundreds of thousands of people are dying each year as a result of fine particles in the ambient air. Some of this particulate is fine flyash emitted from power plants. Much of this particulate is sulfates and nitrates formed by reaction of SO2 and NOx with ammonia and other chemicals in the air. This is partially attributable to the SO2 and NOx emissions from power plants.
China has recognized the problem and has spent more than any other nation to reduce power plant emissions. Even so there is more that can be done. Other nations such as India are building new coal-fired power plants without the efficient controls now being applied in China. Options for countries are:
- Build new coal-fired power plants with limited controls.
- Build new coal-fired power plants with the most efficient controls.
- Upgrade existing coal-fired power plants with the most efficient controls.
- Replace coal-fired power plants with wind, solar or LNG-fueled gas turbines.
The economics are different depending on the location and economy. Turkey needs electricity to bring up its standard of living. It has its own coal supply. It plans to add 80 more coal-fired power plants and eliminate the expensive and uncertain gas supply from Russia. Some environmental groups argue that a better choice would be investment in solar and wind. The less proven economics of this option are offset by the global warming benefits according to the environmental groups. A more certain route is “clean and economic coal.” In general, all the pollutants except a portion of the CO2 can be eliminated economically.
Pollutants vary in their harm impact. The US EPA has assigned a dollar value for each ton of each type of pollutant which is emitted. Each pound of mercury has been priced at up to $60 million/ ton, whereas CO2 has been priced at $50/ton. Due to the health problems associated with fine particulate its price tag is $50,000/ton. EPA generates these harm factors in justifying the cost of control technology.
The price tag for each pollutant is certainly debatable. Many would assign higher values to CO2. Since the impact is longer term, an analogy can be made to inheritance. A wealthy person who has money to leave to his grandchildren will place a higher value on a legacy than will a Syrian refugee who rightly wonders whether he will have grandchildren.
Pollutants such as fine particulate should be considered at least as harmful in developing countries as in the developed because there is no way to avoid their impact. The following table is a harm index based in part on EPA costs.
Harm Index (Relative)
Coal-fired power plants generate 250 tons/yr of particulate per MW. Efficiency of capture ranges from less than 98 percent to more than 99.5 percent. So emissions to the atmosphere range from 5 tons per year/MW to 1.25 tons per year/MW or less.
There are presently 2.1 million MW of coal-fired power generation. The difference between efficient particulate control and inefficient control is more than 3 tons/MW or 6 million tons per year. At $50,000/ton, the harm differential is valued at $300 billion/yr. The annual depreciated cost to install and operate the more efficient controls is less than $15 billion/yr.
One approach to reducing particulate also reduces CO2. A small amount of sorbent is injected ahead of the air pre heater. This reduces the acid dew point and allows extension of the air pre heater, the extracted heat (350oF to 250oF) decreases CO2/MW by 1 or 2 percent. The colder temperature entering the precipitator can result in a 50 percent reduction in emissions. The capital costs are small and the small amount of sorbent needed is not a significant operating cost. So the value in reduced harm outweighs the cost by an order of magnitude.
Mercury reduction can be accomplished very economically where scrubbers are in place. The Chinese have scrubbers on most of their power plants. If they added bromine with the coal and re-emission prevention chemicals in the scrubbers, they could eliminate 20 tons of mercury per year. The value would be $1.2 billion/yr. The cost would be less than $75 million/yr. W.L Gore has a mercury module which can be installed downstream of both wet and dry scrubbers. It can achieve high removal efficiencies at modest cost.
SO2 scrubbers are required in most countries but not all. Efficiency requirements are typically 90 percent but often 98 percent. Lime wet scrubbers would achieve 99 percent removal. Sodium scrubbers using a double alkali process would also achieve 99 percent removal. Recent dry scrubber developments make this option capable of 95 percent efficiency using lime.
The SO2 generated in coal-fired boilers is over 100 million tons per year. At least 40 million tons escapes through the stacks. So the potential harm saving is $80 billion/yr. The depreciated costs would be less than $15 billion/yr.
The benefits from NOx reduction are similar. Selective catalytic reduction (SCR) systems can also assist in mercury removal. The new catalytic filters promise particulate, SO2 and NOx removal all in one device.
The potential for revenue generation from byproducts is substantial. Flyash and gypsum are already major revenue generators. Extraction of rare earths from coal flyash with an in situ process may be the best option for this byproduct. Ultrapure gypsum to compete with precipitated calcium carbonate for paper coatings is another option. Hydrochloric and sulfuric acid are already being produced by some plants. Continuing development of byproducts is very likely to increase the value of reduced harm vs. the cost.
The McIlvaine Company continually analyzes the costs and benefits in: