Biomass Emits Double The CO2 Of Gas
February 26, 2015
By Paul Homewood
As we all know, burning coal and gas to produce electricity is BAD, but burning wood is GOOD.
But what do the actual figures tell us?
I asked DECC to supply comparative figures CO2 produced/MWh, for coal, gas and biomass (specifically wood pellets). I specifically requested that the biomass figures should purely relate to emissions from the power stations, and not to include “whole life” calculations. This was their reply:
1) We have identified a calculation of the biologically derived CO2 emitted from a typical power station converted to biomass combustion. The calculation assumed that 47% of the dry weight of the wood pellet is carbon and that large biomass conversions are typically 35.5% efficient at converting the energy content of the wood pellets into electricity.
These assumptions would need to be amended for specific biomass fuels, and power station operating conditions. Also the value below is higher than the true value of CO2 emissions as no allowance was made for the carbon retained in the ash at the power station.
The value calculated was 920 kg CO2/MWh of electricity generated.
We do not routinely estimate the emissions of biogenic carbon dioxide (CO2) from combustion of wood pellets when calculating the national emissions total. In reporting emissions the UK follows the requirements of IPCC guidelines on International Greenhouse Gas reporting. In order to avoid double counting of emissions and removals, the reporting convention is that the CO2 contained within biological materials, such as wood pellets, which are to be burnt for energy purposes, such as electricity generation, is accounted for by the harvesting country. This emission is reported by countries included under the forest management sector.
2) The quantity of CO2 emitted by fuel use in the pellet making process depends on a range of factors such as how the fuels are used to dry the biomass before pelletisation. As examples;
• saw mill offcuts require no additional drying before pelletisation,
• natural forest-side drying can reduce timber moisture content from 50% to 25% without requiring energy,
• the CO2 released in generating the electricity used in pelletising will normally have the typical CO2 impact of the electricity network of the country in which it is located.
3) The BEAC report and spreadsheet referred to above contain values for the comparable emissions of carbon dioxide from typical coal and natural gas fired power stations of 1018 and 437 kg CO2 equivalent/ MWh electricity generated respectively.
So, on a straight comparison, we get:
| CO2
kg/MWh | | Coal | 1018 | | Gas | 437 | | Bio | 920 |
While bio is slightly better than coal, it is emitting more than double the CO2 of gas.
None of these figures account for the emissions involved in processing or transporting wood pellets. Equally of course, they don’t include these for fossil fuels, although it seems reasonable that the add on emissions for gas would not be as great.
The only logic to biomass is that forests are replanted to compensate for the extra CO2 produced, but, even if this is true, it would take decades to happen.
In any event, if the forests were left where they were, how much CO2 would simply have been sequestrated into the soil? Or if the wood had been used for other purposes, such as building material, there would be no extra emissions at all.
Given that we are supposed to only have a few years left to save the planet, would it not be more sensible to be burning gas?
The only conclusion is that the whole biomass farrago has been no more than a gimmick, with a veneer of “sustainability”. The clue lies in DECC’s statement:
In reporting emissions the UK follows the requirements of IPCC guidelines on International Greenhouse Gas reporting. In order to avoid double counting of emissions and removals, the reporting convention is that the CO2 contained within biological materials, such as wood pellets, which are to be burnt for energy purposes, such as electricity generation, is accounted for by the harvesting country. This emission is reported by countries included under the forest management sector.
In other words, you can burn as many trees as you like, as long as they are not your own. Without this edict, biomass would be dead in the water.
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