Downside of coal

One of the common criticisms regarding renewables vs. coal is that the latter is cheap – a misguided perception, based, among other things, on not pricing in externalities like pollution.

A typical 500 MW coal plant generates 3.7 billion tons of carbon dioxide, as much as cutting
down 100 million trees. In 2004, coal accounted for around half of the electricity produced in the U.S. but produced roughly 83% of the resulting carbon dioxide emissions from electric power generation. Coal-fired power plants emit twice as much CO2 per KWH as any other form of power generation. According to the Union of Concerned Scientists, one 500 MW coal plant produces as much emissions as 600,000 cars.

Additional pollutants emitted by coal power plants include sulphur dioxide, nitrogen dioxide, as well as carbon monoxide, arsenic, lead mercury and cadmium. A coal plant can even generate uranium and thorium.

Should the cost of CO2 emissions be included using a conservative $20 per ton of CO2 emission, the price of coal would increase by 2-4X. Two technologies could help reduce the carbon footprint of coal – Integrated Gasification Combined Cycle (IGCC) and Carbon Capture and Storage (CCS).

IGCC technology involves two major processes:
• The gasification of coal, a process in which coal is reacted with steam and oxygen to form syngas, a combination of carbon monoxide and hydrogen. The syngas is then cleaned to remove pollutants.
• A combined cycle process to generate electricity. The produced syngas is then used as the main fuel for a gas turbine (which produces electricity), while the waste heat generated by the gas turbine is used to power an second, steam turbine (additional electricity production), thus increasing the energy efficiency of the plant as a whole.

In theory, IGCC produces less solid waste, lower emission levels (as a result of better efficiencies) as compared to pulverized coal. Aside from consistency and reliability issues, the key question is whether the capital costs of IGCC will be able to fall as projected with learning and increased economies of scale in manufacturing, engineering and so forth.

CCS brings its own host of problems and cost issues. In 2005, carbon dioxide emissions were at least 27.9 billion metric tons. Sequestering just 10% of the world’s fossil-fuel combustion CO2 would require an industry whose throughput would have to be 1.3 times that of the oil industry. Moreover, both the sheer scale and cost of the project remain unknown, as are the safety and operating reliability conditions.

Another approach could be to convert coal to an environmentally friendlier fuel, such as natural gas. Advantages of such a process include the ability to use the transportation infrastructure in place.

Source: V. Khosla