A combination of coal and biomass for power generation with CO2 capture capability represents an effective method for curtailing carbon emissions, according to a report by the McIlvaine Group (www.mcilvainecompany.com). With such a system, McIlvaine says more carbon would be extracted from the atmosphere than returned to it, and the resulting waste streams could be reused, limiting the threat of hazards similar to last month’s coal ash spill from the Tennessee Valley Authority (www.tva.gov) dump in East Tennessee.



McIlvaine says the best global-warming reducer would be a 100 percent biomass boiler with 90 percent CO2 capture, yet the company acknowledges there is not enough biomass to meet the world’s electricity needs in this fashion. However, McIlvaine believes a combination of coal and biomass would be sufficient.

In Europe, for example, McIlvaine says coal-fired boilers are required to co-fire biomass. The company cites Doosan Babcock (www.doosanbabcock.com), which it says has successfully supplied systems that fire pulverized coal with 20 percent biomass. Meanwhile, McIlvaine says Foster Wheeler (www.fwc.com) has developed circulating fluid bed technology, which enables unlimited quantities of biomass to be mixed with coal. McIlvaine also notes that the United Kingdom is growing and pelletizing straw to use as boiler fuel, which actually takes CO2 out of the atmosphere as the straw grows. If the CO2 it releases when combusted is captured and sequestered, McIlvaine says this process is a very effective CO2 reducer.

McIlvaine says the waste stream can also be effectively used by industry, such as for heating and cooling of buildings and in making ethanol. The flyash replaces cement, which McIlvaine says saves one ton of CO2 for every ton of flyash used. Other byproducts are gypsum for wallboard, sulfuric acid, sulfur, ammonium sulfate fertilizer, calcium chloride, and hydrochloric acid.

According to McIlvaine, the newest coal-fired power plants use 30 percent less coal than the older designs. Further, McIlvaine says Enel (www.enel.com) contracted with Aquatech (www.aquatech.com) to provide zero liquid discharge technology for the wastewater at three of its plants in Italy.

Given the current state of technology development for clean energy alternatives, McIlvaine says the coal-biomass combination with CO2 capture is clearly the best option from the perspective of greenhouse gases. With this technology universally applied, McIlvaine says the CO2 in the atmosphere would steadily drop from the present level of 385 ppm.

However, McIlvaine says currently there is not enough biomass now and a program to create it will take time and money. CO2 capture and sequestration is presently costly, but McIlvaine believes the technology may become more affordable with developments underway.

McIlvaine says the investment in coal/biomass, solar, wind and other alternative energies has to take into account the total eco-efficiency considerations. The environmental burden has to be weighed against the cost. As such, McIlvaine has created a universal environmental burden index, which can factor with costs to determine the best options. Coal-fired power plants emit 2.1 lbs of CO2/kWh, according to the McIlvaine index. The total environmental burden from coal-fired power plants including CO2, NOx, particulate, toxics, and SO2 is 5.46 equivalent lbs/kW-hr.

New coal-fired power plants would cost $2500/kW to build with a useful life of 25 years, according to McIlvaine, which estimates the depreciation on these plants to be $.0125/kWh. If the plants were only operated for 15 years, the depreciation would rise to only $0.02/kWh. Hence, McIlvaine believes even if new coal-fired plants were operated for less than their useful life, they could be very cost effective.

Meanwhile, McIlvaine asserts that solar, wind, nuclear and coal-fired power plants with carbon sequestration will be more costly than super-critical coal-fired power plants, if widely applied.

As such, McIlvaine says new ultra-super-critical plants with a 25-year life are obviously the most eco-efficient solution. Even if these plants are only operated for 15 years, McIlvaine says they are still 22 percent more eco-efficient than retrofitting the old coal plants. As a result, McIlvaine says new coal plants with carbon sequestration and biomass co-firing provide the most environmental burden reduction but at more than twice the cost of electricity.

If existing coal-fired power plants in the United States were to be replaced with ultra-supercritical, carbon-ready power plants with biomass co-firing, McIlvaine predicts the advantages would be:
• $600 billion economic stimulus with no increase in electricity cost,
• 30% reduction in coal consumption,
• More than 30% CO2 and 70% total environmental burden reduction,
• Meets the goal of 20% greenhouse gas reduction by 2020.
• These plants would be carbon capture ready and could be fitted with co-firing and CO2 capture at a later date.
• Investment would be fully realized by 2038-44 and replaced by even newer technology to meet the 80 percent reduction of greenhouse gases in 2050.

For more information on the McIlvaine eco-efficiency analysis and implications for energy choices, click here.