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Biomass burning impacts: the debate continues

By Dave Elliott
The seemingly endless debate on the impacts of burning biomass continues. At one extreme there are those who see almost all use of biomass as suspect. More specifically there are objections to using whole trees or stem wood, especially if imported so that the source is less sure. One claim is that this can produce more carbon emissions net than would be produced from burning coal, and depletes biogenic carbon stores.

It’s actually a complex issue, since forests are managed for a variety of purposes. As a new EU report on ‘Biogenic Carbon and Forest Bioenergy’ from Forest Research notes:
‘Typically, forest bioenergy is produced as a complementary co-product of wood material/fibre products. It is unusual for forest bioenergy to be the sole product from harvested wood’. However it says EU forest bioenergy is likely to increase significantly, so that ‘it will be necessary to intensify management of EU forests in order to increase removals of primary wood and/or import more wood into the EU and/or mobilise the availability of sources of other woody biomass.’ But it claims ‘A requirement to produce forest bioenergy seems unlikely to become the principal driver of forest management unless demand for forest bioenergy becomes very intense’. In particular is suggest that ‘demand for forest bioenergy seems likely to be met through increased extraction of harvest residues including poor-quality stemwood and trees, the use of sawmill co-products and recovered waste wood. Some small roundwood may be used as a source of bioenergy. It is less likely that forest bioenergy will involve consumption of wood suitable for high value applications, such as sawlogs typically used for the manufacture of sawn timber’.

Having set the scene it notes that, given this complex and changing pattern of sourcing, ‘Biogenic carbon can make a very variable contribution to the GHG emissions associated with forest bioenergy. Consequent GHG emissions can vary from negligible levels to very significant levels (similar to or greater than GHG emissions of fossil energy sources)’, although ‘in some specific cases, forest bioenergy use may be associated with net carbon sequestration’ e.g. when the replanting or rotation rate is high.

Nevertheless ‘There is widespread recognition in the research literature that increasing the levels of wood harvesting in existing forest areas will, in most cases, lead to reductions in the overall levels of forest carbon stocks compared with the carbon stocks in the forests under previous levels of harvesting. Where the additional harvesting is used to supply bioenergy as the sole product, then such forest bioenergy will typically involve high associated GHG emissions (i.e. compared with fossil energy sources) for many decades.’

It is this that groups like Friends of the Earth (FoE) and Biofuelwatch focus on, claiming that this is now what is happening- to feed giant biomass combustion plants like Drax with wood pellets from North America, some of which are allegedly made from stemwood. Even so that doesn’t necessarily mean they are against the use of all biomass. For example FoE’s new report ‘Felled for Fuel’ focuses on, and objects to, ‘burning trees for electricity’. Instead it wants the government to ‘refocus support for bioenergy on the use of feedstocks such as agricultural and forestry wastes and biogas from sewage, food waste and other organic wastes’ and also to limit the use of the available sustainable biomass ‘to modern combined heat and power (CHP) plants which would ensure the most efficient use of these limited feedstocks, making use of the energy for heat as well as generating electricity’.

FoE does see overall biomass use as being constrained though by more careful assessment of sources and their bio-impacts. It calls for ‘the government’s ambitions for bioenergy to be scaled down and capped at a level that ensures supplies can be
sourced sustainably and domestically’. That raises many issues. Some see bio-conversion of big old coal plants as a useful stop gap, but if that’s not on, then others look to specially grown energy crops as a viable new source, in addition to wastes. And to the use of wood for heat production at the local level. It’s a broad ranging debate.

DECC’s new, long awaited, Bio-carbon Calculator may help clear the air a bit in relation to large scale biomass conversion plants. DECC uses it to assess a range of scenarios for the net carbon balance that would be associated with North American biomass used in the UK, with different land use changes assumed. It concludes that ‘in 2020 it may be possible to meet the UK’s demand for solid biomass for electricity using biomass feedstocks from North America that result in electricity with GHG intensities lower than 200 kg CO2e/MWh, when fully accounting for changes in land carbon stock changes. However, there are other bioenergy scenarios that could lead to high GHG intensities (e.g. greater than electricity from coal, when analysed over 40 or 100 years) but would be found to have GHG intensities less than 200 kg CO2e/MWh by the Renewable Energy Directive LCA methodology’.

So it can produce more emissions than coal, but also, done right, with proper choice and regulation of sources, it can be fine. The Renewable Energy Association agreed: ‘Anyone using biomass in accordance with the guidelines set out by the UK government would be lower-carbon than other fuels.’

However DECC says the energy input requirement of biomass electricity generated from North American wood used by the UK could be significantly greater than other electricity generating technologies, such as coal, natural gas, nuclear and wind. That may limit its use. But DECC says Energy Input Requirements can be cut e.g. by reducing transport distances and the moisture content of the biomass. So overall it sees some projects as viable.

Will that end the debate? Unlikely! FoE said it was vital to have tougher regulation and clearly it’s not convinced that stem wood isn’t being used. But at least the various stakeholders are almost now on the same analytical page, or ought to be, in relation to biomass conversion! How they then decide to respond in terms of strategic development priorities is another matter. Interestingly, DECC won an appeal against a Judicial Review ruling that required it to reinstate a large DRAX biomass conversion project which it had turned down. So it won’t now happen. And DECC has also said, in its allocation statement for future CfD rounds (limiting them to £205m p.a.), that it was‘ not at present intending to release a further budget for biomass conversion’, i.e. after the current ‘early’ CfD round. Clearly biomass conversion is something of a hot potato!

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  1. I don’t see any “dollar” figures, the ultimate driver in any scenario. It’s hard to imagine the price of small roundwood (pulp) becoming equal to the value of an oak log suitable for furniture, flooring, trim,…., simply for the purpose of meetimg a government imposed restriction on carbon. (?)

  2. Muddy

    The logging industry cannot be trusted to simply use ‘waste’ wood. This ‘waste’ has been the main driver of the clearfelling of vast areas of forest globally for woodchips to make a cheap short lived paper product. These ‘waste’ trees had captured and stored carbon for hundreds of years. Not so renewable when the regrowth that’s coaxed back is cut down again in 30-40 years time. Any biomass derived from native forests must be considered a major contributor to climate chaos.

  3. Vailhem

    Why burn? Why not gasify?

    If via anaerobic digestion, the remaining pulp can be used as a building material or for paper production. ..saving trees!

    If via pyrolysis then the remaining biochar can be used as a soil-building material or for a building material … helping plants grow!

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