Power Plants Try Burning Wood With Coal to Cut Carbon Emissions. Matt Wald. New York Times. November 3, 2013.
There are many difficulties to burning wood in coal plants:
- Pound for pound, wood only produces 66% as much energy as coal, and takes up about 5 times as much space
- Coal power plants aren’t built to handle fuel that can rot and grow fungus
- Coal plants are finely engineered to burn one particular kind of coal, i.e. anthracite, bituminous, subbituminous, or lignite
- It’s hard to find enough wood
- Wood doesn’t come in predictable sizes. If the chunks are too large the feeder system can’t handle it
- Coal is pulverized before burning, but often this equipment can’t pulverize wood. When it is possible, the mix can be no more than five percent wood
- Up to fifteen percent of the fuel can be wood if it’s blown into holes cut in the boiler in confetti sized pieces, but that’s expensive (in both money and energy to convert the boiler and shred the wood that finely).
- Europe has tried heating wood in a chamber outside of a coal plant and pumping the resulting carbon monoxide and hydrogen fuel into the coal boiler, but that is even more expensive than the holey-boiler-confetti-wood kluge.
Although some think burning wood in coal plants is “renewable”, they’re forgetting that the next generation of trees needs good soil containing the carbon and minerals of the previous trees. Forests are not a “renewable” resource at an industrial scale because trees can only convert sunlight into tree mass at 2.25 to 2.75 percent per year in the United States. It’s also arguable that burning trees is carbon neutral given all the carbon dioxide released.
Nate Hagens, in his excellent 2007 article Home Heating in the USA: A Comparison of Forests with Fossil Fuels points out that if Americans depended only on wood to heat their homes, it would only take an average of 4 years “before the United States would resemble Easter Island”. (1)
(1) Of the 532 Trillion BTUs that could be generated annually from forest growth, approximately 55% or 297 Trillion BTUs, would end up as ‘actual heat’. Natural Gas and Heating Oils collectively generated 5,074 Trillion BTUs of ‘actual heat’. Thus, this analysis indicates that we could sustainably replace 297 / 5,074 Trillion BTUs or 5.8% of fossil fuel home heating use with home heating from wood. Alternatively, the entire United States forest stock of hardwoods contains 364 billion cubic feet of wood, or 2.84 billion cords which would throw off 24,024 Trillion BTUs (note, this is only 24% of the total annual energy usage of the country). So the good news is if we were really cold and sans fossil fuels, we could chop down trees for at least 4 years before the US would resemble Easter Island (24,024/5,074= 4.74 years).