Saturday, November 1, 2008

Do wood burning power plants pollute?

Wood burning power plants are often seen as "soft" energy sources that are environmentally friendly, non polluting, and carbon neutral. But some wood burning plants also supplement their wood burning by burning natural gas during the summer, when gas is cheaper. Thus we have a generating plant that uses "soft" energy sources part of the time, and fossil fuels part of the time. They typically produces a modest amount of electricity, and mine the soil as they do so. Logging residues would be better uses by returning them to the soil, rather than burning them, this would prolong soil fertility of heavily logged forests. There are not many such plants, and it would take thousands of such small scale generating facilities to make a significant contribution to the national power needs.

Although wood burning technology is often seen as clean, in fact it produces more air pollution than natural gas. The primary pollutant is nitrogen oxide, a smog producing gas. Other pollutants include carbon monoxide, Volatile Organic Compounds, and 10 micrometers or less particulate matter.

In addition, we have to count some of the air pollution produced by logging and hauling the wood from the forrest to the power plant. Trucks hauling wood products to power plants emit CO2 from fossil fuels. Although the conventional argument is that burning wood does not increase the amount of CO2 in the atmosphere, this fails to assess the impact of wood removal on soil fertility which in turn diminishes the soils ability ability to support new biomass. Hence the CO2 neutral argument for wood burning plants is not true.


David Doty said...

Actually, it's worse than you indicate. Unless only dead trees are harvested, which is not normal logging practice, wood burning results in as much net CO2 release over the short term (several decades) as coal burning. (The carbon content of wood is ~70% that of coal, but so is its energy content.) The carbon in living trees normally remains sequestered there for many decades. When new trees are planted, they don't take CO2 out of the atmosphere at near the rate of mature trees for the first two or more decades. Of course, we have an abundant source of dead pines in the U.S. Northwest for about the next 5 years because of the pine beetle blight.

There are more sound insights on this, cellulosic ethanol, and other biofuels here:
David Doty

Woodnyet said...

Please visit our discussion forum on wood burning hazards.

Anonymous said...

It is pretty much established beyond doubt that biomass-fired electricity causes more harm to health and the environment than nuclear power. The European Commission funded the ExternE study to look into the “external costs” of different modes of generation. Wind was best. Nuclear and hydro came a close second. PV was somewhat worse, and biomass was about as bad as natural gas.

The health impact from pollution is stark – it is not a marginal difference – biomass causes more than ten times as many fatalities as nuclear (or hydro, or wind).

According to diag 3 in the above, the number of deaths per TWh of electricity is as follows:

Coal 25
Biomass 12
Gas 5
Nuclear, Wind, Hydro <1

On this basis there is no doubt in my mind that biomass should be the least favoured form of renewable energy.



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