By Bob McIlvaine, McIlvaine Co.
Presently 52 percent of electric power in the United States is generated by coal. The U.S. has coal reserves per capita which far exceed any other country. Energy security and world competitiveness are greatly enhanced by the use of coal. The potential for coal to provide electricity for transportation has environmental advantages.
On the other hand the emissions of air pollutants from U.S. coal plants are substantial. The recent fly ash pond failure at Tennessee Valley Authority’s Kingston plant in Tennessee draws attention to the water pollution from coal as well. The potential advantages and disadvantages have had a polarizing influence.
Those opposed to coal plants advocate elimination of any new coal plants and retirement of existing coal plants as fast as possible. Those favoring coal are attempting to site new coal plants without linking these initiatives to reductions in emissions from existing plants.
Another polarizing aspect is the lack of clarity about the life of a coal plant. The decision to build a new plant is assumed to be a decision about a pollution stream for 50 years.
A new approach is needed to eliminate the political polarization and find the best energy policy for the U.S. The approach needs to be holistic. Any decisions about new coal plants must be tied to decisions about existing plants. Plant life as short as 15 years also has to be considered. As I will explain later, such a curtailed lifespan for a coal plant could be economically feasible. With this holistic approach much of the polarization will disappear.
President Obama has said he wants the United States to commit to reducing its greenhouse gas emissions to 1990 levels by 2020 and by 80 percent in 2050, mainly through a $150 billion, 10-year program to develop renewable forms of energy. However, replacement of existing coal plants with new ones is by far the best initial investment to achieve these goals.
If all the existing coal-fired power plants are replaced by new ultra-supercritical plants, there would be a reduction in coal use and greenhouse gases of 30 percent. So the U.S. could easily meet the 2020 goals. If coal plants co-fire 15 percent biomass, the total reduction would be 45 percent. If the waste heat is efficiently utilized (ethanol production or other combined heat and power applications) there is another 20 percent gain.
This is even before you consider the use of electricity to replace gasoline in cars or carbon capture and sequestration. When you add it all together there is a strong case that coal can contribute to a big reduction in CO2. It can be part of the solution and not the problem.
But even though a strong argument can be made for new coal plants based just on greenhouse gases, a stronger argument can be made based on environmental burden.
The key to obtaining the support of the environmental industry is to convince them that the construction of a new coal-fired power plant does not mean that this plant will be operating in 2050. The U.S. could build a whole fleet of new coal-fired power plants and retire them in 30 or 40 years or less. If new coal-fired power plants are conceived as temporary replacements for the old dirty plants rather than as a way to perpetuate coal, then the environmentalists should see that this is a great solution.
Nuclear, solar, wind and biomass can all play a role in meeting goals for greenhouse gas reduction economically. The role of each can be determined by the eco-efficiency defined as the cost divided by the environmental and societal burden reduction.
Some technologies are not yet eco-efficient but may become so in the future. Some technologies are eco-efficient for narrow use but not yet eco-efficient for widespread use. Different values for environmental and societal burdens will create debate over the eco-efficiency of various alternatives.
By any standard the most eco-efficient option is replacement of old coal plants with new ones. Replacement of 320,000 MW of existing coal-fired plants with new ultra supercritical plants would:
- Achieve the goal of 20 percent greenhouse gas reduction by 2020
- Result in an 80 percent air environmental burden reduction from the coal-fired power segment and a 51 percent reduction in the air environmental burden from all stacks in the U.S.
- Be accomplished using existing technology at a cost comparable to operating an old coal plant due to the 30 percent fuel savings which offsets the increased depreciation
- The $600 billion investment would create a big economic stimulus to the U.S. economy.
Determination of the environmental burden is essential to making any good decision about the options. CO2 and air pollutants have been ranked in an environmental burden index (Table 1, page 38). If CO2 is $20/ton and NOX allowances are $2000/ton, then one ton of NOX has a burden of 100-times CO2.
Various toxic air pollutants have been ranked based on the EPA Lesser Quantity Emission Rate (LQER). When the environmental burden index is multiplied by the tons of emissions, the U.S. air environmental burden from coal is 4.5 billion tons. Replacing all the coal-fired plants with ultra supercritical boilers using best available control technology (BACT) would reduce the air burden from 4.5 to 1.5 billion tons or a 66 percent reduction. This does not include the additional benefits of byproducts, waste, net utilization and co-firing of biomass.
Under a modest coal scenario, new supercritical power plants with BACT would replace all 320,000 MW of existing coal-fired power plants in the 2010-2019 period. These new power plants would be retired in the 2036 to 2044 time frame. There would be a huge reduction in the environmental burden from coal starting as early as 2013. With electricity demand growing at 1 percent a year, coal’s share would drop below 40 percent by 2035 and then fall to zero by 2045. At that point there would have to be the equivalent of 462,000 MW of baseload capacity from other sources.
Since wind operates at less than 20 percent capacity, you would need 2.3 million MW of wind capacity to provide the equivalent of 462,000 MW of baseload capacity. The chances that the industry can achieve this, or even 25 percent of this, are very slim. Nuclear and solar also have supply limitations in addition to concern about costs and other issues, so even a modest coal scenario seems unrealistic. The point is that even with this low forecast for coal, there would still be the full benefit of replacing all the existing coal-fired power plants with new ones.
This leaves all the options on the table for reducing CO2 emissions 80 percent by 2050. There will be very large new generation requirements. Even with optimistic contributions from wind, solar and nuclear it will be difficult to meet the generation requirements without some reliance on coal. But this is a decision that does not need to be made now. Replacing the old coal-fired power plants with new efficient ones is an immediate win-win initiative for the nation regardless of the long-range solution.
If burning coal and biomass provided the energy source for electricity and the CO2 from the combustion was captured, there would be more carbon extracted from the atmosphere than returned to it. The best global warming reducer would be a 100 percent biomass boiler with 90 percent CO2 capture. But there is not enough biomass to generate the electricity the world needs. However, a combination of coal and biomass would be sufficient. Co-firing, co-generation and electric cars driven by coal also produce lower CO2.
In Europe coal-fired boilers are required to co-fire biomass. Doosan Babcock has successfully supplied systems that fire pulverized coal with 20 percent biomass. With Foster Wheeler circulating fluid bed technology, unlimited quantities of biomass can be mixed with coal. The UK is growing and pelletizing straw to use as boiler fuel. This biomass takes CO2 out of the atmosphere as it grows. If the CO2 it releases when combusted is captured and sequestered, then this process is a very effective CO2 reducer.
There are other advantages of the coal/biomass combination. The waste steam can be effectively used by industry and, in the case of New York City, for heating and cooling buildings. Great Rivers Energy is using the waste steam to make ethanol. The fly ash produced replaces cement and saves one ton of CO2 for every ton of fly ash used. Other byproducts are gypsum for wallboard, sulfuric acid, sulfur, ammonium sulfate fertilizer, calcium chloride and hydrochloric acid.
Coal/biomass-fired power plants with CO2 capture will be very clean. Pollutants such as NOX and SOX have to be reduced to below 10 ppm prior to entering the CO2 scrubber. These trace amounts are further captured in the CO2 scrubber solution or sequestered. Alstom and other suppliers are building full-scale CO2 capture systems.
Coal can be clean in all respects. ENEL contracted with Aquatech to provide zero liquid discharge technology for the wastewater at three of its plants in Italy. The TVA ash pond dam break that made headlines recently represents old technology, not the new design where ash is a useful product.
Co-firing coal and biomass, combined with capturing CO2 is clearly the best option for reducing greenhouse gases. With this technology universally applied, CO2 in the atmosphere would steadily drop from the present level of 385 ppm. The question is how fast could this technology be implemented in the U.S. and at what cost?
The short answer is that there is not enough biomass now and there is never likely to be enough biomass to fully replace coal. CO2 capture and sequestration is presently costly but may become less so with developments underway.
Replacing old coal plants with new ones is the lowest cost per unit for reducing CO2. Coal-fired power plants emit 2.1 lbs of CO2/kWh. The total environmental burden from coal-fired power plants including CO2, NOX, particulate, toxics, and SO2 is 5.46 equivalent lbs/kWh (see Table 3, above).
New coal-fired power plants would cost $2,500/kW to build. Assuming they operate 8,000 hours per year for 25 years the useful life would be 200,000 hours and the depreciation would be $0.0125/kWh. If the plants were operated for 15 years the depreciation would rise to only $0.02/kWh. So even if new coal-fired power plants were operated for less than their useful life they could be very cost effective.
Without new coal plants there will be expensive retrofitting of existing plants with SO2, NOX and mercury reduction systems. This will increase electricity costs but will substantially reduce emissions. However, the cost of burden reduction is greater than building a new coal plant even for just a 15-year life span.
Solar, wind, nuclear and coal-fired power plants with carbon capture will be much more costly than supercritical coal-fired power plants without carbon capture. New ultra-supercritical plants with a 25-year life are obviously the most eco-efficient. Even if these plants are only operated for 15 years, they will still be 22 percent more eco-efficient than retrofitting the old coal-fired power plants. New coal-fired power plants with carbon sequestration and biomass co-firing provide the most environmental burden reduction, but at more than twice the cost of electricity.
From both an environmental and economic perspective, replacement of all existing coal plants with new coal plants should be the short-term solution. Fifteen years after the plant commences operation another decision can be made as to adding carbon capture or replacing it with a renewable energy-based generator.
Author: Bob McIlvaine is president of McIlvaine Co. which he founded in 1974. The company analyzes markets and technology for coal, wind, solar and biomass technologies for power generation. It also supplies utilities with a decision tree system on power plant air quality.