Can Biomass Conversion of Coal Plants be a Game-Changer?
Biomass has been frequently touted as a viable alternative for coal. But the reality is that there is a lot of variation in the carbon intensities of biomass resources. The true carbon intensity of a biomass resource depends on a number of factors, namely the chemical constituents of the resource, and the state of the biomass before it was harvested as a resource.
Biomass resources can only be said to be carbon neutral if new trees planted absorb enough carbon dioxide to negate the emissions from burning, processing, and transporting the harvested wood. For example, the emission intensity of biomass from forest residue is very low, at just 52 kg/MWh – far lower than natural gas (437 kg/MWh) and coal (1,018 kg/MWh). Biomass from specially grown forests produces fewer emissions than coal (481 kg/MWh), but more than natural gas. However, biomass from older-growth forests produces a whopping 2,629 kg/MWh due to the huge level of CO2 absorbed by the trees over their long lives.
If an appropriate resource is used, wood pellets can be substituted (partly or completely) for coal in coal-fired power plants to reduce plant carbon emissions. This is particularly relevant in light of the Clean Power Plan, which will require steep emission reductions from existing coal power plants.
Obviously, harnessing biomass resources from old-growth forests doesn’t make sense – but that doesn’t mean that it never happens. There are dangers associated with overpromising on biomass electricity supply, as demonstrated by the case of Drax Power. The company operates a power plant in the U.K. fueled by both biomass and coal, and has faced criticism for allowing old-growth wood into their plant, a move that investigators believe was done to keep the three biomass boilers running at full capacity.
The company denies the allegations, stating that they only source from forests that produce more wood than is harvested, and from forest residues. If this is true, then the biomass component of the Drax power plant can achieve carbon-neutral operation. However, clearly there needs to be high levels of accountability with regards to the source of biomass inputs to ensure that biomass plants do indeed run sustainably. Accountability is particularly important when producers receive carbon credits for the emission reductions associated with shifting to biomass.
One challenge in the shift away from coal will be securing adequate biomass resources. Thanks to the Drax power plant, the U.K. is now the world’s largest wood pellet importer, sourcing most of its inputs from the U.S. The Drax power plant requires the equivalent of a forest four-times the size of Rhode Island, or more than all of the annual wood harvested from all U.K. forests. Clearly, the sustainable sourcing of carbon neutral biomass resources will be challenge, but if done correctly, biomass could be game-changer, particularly if it replaces coal.
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501Carbon uses agricultural waste products for its bioenergy project inputs. Carbon neutrality can be guaranteed with our projects because the energy inputs would otherwise be left to decompose or be burned in open fires. Moreover, our goal is to produce energy and fertilizer from the agricultural waste inputs, providing even more carbon benefits than energy production alone.
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