I was recently made aware of an article published in "Scientific American", discussing trends towards mitigation of CO2 emissions by substituting coal for forest biomass - particularly wood pellets - which I found less than useful.
There are in general quite a lot of misconceptions floating around on this issue, particularly the drive for biomass-for-coal substitution plans in Europe involving transportation of forest biomass over long distances. The arch-example is the English Drax power plant, converting 2,000 MW installed capacity to burn 7.0 million metric tons of wood pellets per year (according to Scientific American - in my book probably it should read more like 9.0 million tons, but never mind that for the moment).
IS WOOD BIOMASS CARBON NEUTRAL?
A tree extracts CO2 from the atmosphere while it grows, stores carbon in maturity and releases CO2 as it dies off or is burnt. In northern boreal forests this takes place over a very long term cycle of nearly 100 years. In commercial and sustainably managed southern pine plantations the cycle is reduced to around 15 years, and in the case of commercial eucalyptus plantations for energy use, 5 years.
If the harvesting of wood for energy purposes is equal to or lower than the regrowth cycle, the process is carbon neutral. If not, it is not. If the wood biomass is converted to pellets for the purpose of long distance transport economies, then the process is decidedly not carbon neutral. Let us look at the particular case of Drax.
To produce 7,000,000 ton pellets one needs 14,000,000 ton green wood. Let us assume that all this wood comes either from waste or sustainably managed plantations, or a combination of both. It requires close to 500 kWh energy to produce one ton pellets, mainly expended on evaporating water to reduce wood moisture content. Further assuming that this energy is generated with natural gas and not coal, we are still ending up with emitting around 1.5 million ton/a CO2, plus another 600,000 ton/a CO2 emitted from the ships bringing the pellets to England, plus whatever CO2 is emitted from fuel that is expended to bring the pellets to the port of embarcation.
Admittedly, from the point of view of England this may look like a brilliant ecological move, because were Drax to continue burning coal, the CO2 emissions would be something like 9.5 million ton/a. But this begs a question: Is CO2 emission a world problem or a national problem? It is obviously a world problem, in as much as CO2 accumulation in the atmosphere is not confined by national borders.
That being the case, and if our goal is to mitigate world CO2 emissions from fossil fuels, then why not place the power plant right inside sutainably managed forests, minimizing transport and avoiding alltogether the costly and wasteful conversion to wood pellets?
This is particularly the case for sub-Saharan Africa, which is both short on electricity and long on deforestation caused by scavenging of fuel wood. In European energy circles there has been serious consideration given to establishing very large forest plantations in Africa in order to supply European power plants with wood pellets.
When such reestablished and sustainably managed biomass resources can be converted to CO2 neutral electric power right at home, what could be more absurd than going to the trouble and expense to bring it all the way to Europe?
