By Dave Elliott
Not everyone backs biomass, given the emission/biodiversity/land-use issues, but biomass does offer a range of flexible green fuel options, biogas especially. The World Bioenergy Association (WBA) says bioenergy already contributes over 14% to the global energy mix, and its use is bound to expand. So what are the options? (more…)
By Dave Elliott
Is the truth out there? An extended Xmas Whimsy
It’s usual for there to be a spread of viewpoints on most issues, and it’s always worth looking at a range views, including ‘outlier’ ones! On that, this is fun: www.xonitek.com/press-room/company-news/the-stone-age-didnt-end-because-they-ran-out-of-stones/
However at times you can get weary of obsessive time wasters and yearn for clarity! Sadly that may not be easy to achieve.
‘Contemporary interest in biochar is, first and foremost, driven by its potential role as a response to the problem of climate change, through the long-term storage of carbon in soils in a stable form.’ With that preamble in mind, and noting that it could also reduced the use of fertilisers, the Biochar Research Group at Edinburgh University was commissioned by DEFRA to review the potential of biochar. and in particular to look at some major uncertainties surrounding its impacts upon soils and crops, its overall performance and its costs compared to other carbon mitigation options. As the preamble put it ‘whilst biochar might improve productivity, is this effect really understood well enough that we can factor-in a long-term enhancement of the carbon sink in vegetation and soils?’
As I indicated in an earlier blog, there were also uncertainties as to whether it would be as effective in terms of carbon dioxide gas abatement as other ways of using biomass, including use simply as a carbon-neutral fuel, offsetting fossil-fuel emissions. There were also concerns that if it did prove effective, the result might be vast biomass plantation undermining biodiversity and competing with food production.
The final report on Pyrolysis-Biochar Systems (‘PBS’) from the project has now emerged. It says that it provides ‘preliminary evidence that PBS are an efficient way to abate carbon, and tend to out-compete alternative ways of using the same biomass (in terms of carbon abated per tonne of feedstock, or in terms of abatement per hectare of land).’ It suggests that you can get abatement of 1.0–1.4 t CO2eq per oven dry tonne feedstock used in slow pyrolysis. ‘Expressed in terms of delivered energy PBS abates 1.5-2.0 kg of CO2eq/ kWh, which compares with average carbon emission factor (CEF) of 0.5 kgCO2eq/ kWh for the national electricity grid in 2008, and current CEF for many biomass feedstocks of 0.05–0.30 kgCO2eq/kWh. Expressed in terms of land-use, PBS might abate approximately 7–30 t CO2eq/ha/yr using dedicated feedstocks compared with typical biofuel abatement of between 1–7 t CO2eq /ha/yr.’
And so it concludes, provided the Carbon Stability Factor (the proportion of total carbon in freshly produced biochar, that remains fixed as recalcitrant carbon over a defined time period), remains above 0.45, ‘PBS will out-perform direct combustion of biomass at 33% efficiency in terms of carbon abatement, even if there is no beneficial indirect impact of biochar on soil greenhouse-gas (GHG) fluxes, or accumulation of carbon in soil organic matter’. But it says there is also ‘an, in principle, credible case that biochar deployment in UK soil will produce agronomic gains (and possibly suppress GHG emissions)’ so it’s doubly blessed, though, perhaps inevitably, the report says that more research is needed to be sure.
There are also some other caveats (e.g. on costs, which it puts at maybe £42/t CO2). It says that: ‘Biochar is, currently, an expensive way of abating carbon, although the costs would likely come down with investment’. It notes that: ‘There has been relatively little attention to the logistics of PBS, even though this is likely to be very important to the economic and practical viability. The issues raised include the need for (and cost of) storage, the acceptability of truck movements, and how economies of scale in producing and distributing biochar might be achieved. Biochar is currently expensive to produce due to feedstock, capital and operational costs. Extensive PBS implies an extensive infrastructure, involving pyrolysis units probably at a range of scales that will take some time to be built and operated, especially given the current lack of dominant design.’
Nevertheless it says ‘Biochar could, however, increase quite significantly the opportunities for carbon abatement in the agriculture and land-use sectors. In the UK the availability of land is unlikely to present an absolute barrier to biochar deployment, although the land potentially providing the highest returns from biochar addition (such as horticulture) is relatively small in extent. The supply and cost of biochar also depends upon the extent to which organic waste feedstocks could be utilised. There are some ‘niche’ areas where PBS could have particular advantages over alternative ways of dealing with organic residues, even within current economic conditions.’
The Centre for Alternative Technology came to similar conclusions in its ‘Zero Carbon Britain 2030’ study: see my earlier blog. They saw biochar playing a key role.
Although the Edinburgh study does highlight some potential problems and unknowns (e.g. on cost and how long carbon will stay trapped), it calls for more pilot projects and it does look like biochar, if sensibly managed, could be a winner. However, somewhat oddly, DECCs new ‘2050 Pathways’ report only sees biochar as playing a fairly limited role, as one possible geo-sequestration option – perhaps trapping 1Mt CO2 p.a. in the UK by 2050.
By contrast a US study, ‘Sustainable biochar to mitigate global climate change’ is very positive. Biochar could it says offset 1.8 bn tonnes of carbon emissions annually, in its most successful scenario – around 12% of current global greenhouse-gas emissions – without endangering food security, habitat or soil conservation.
The DEFRA/Edinburgh Biochar report is at: http://randd.defra.gov.uk/Document.aspx?Document=SP0576_9141_FRP.pdf
There is one way we
could save ourselves, and that is through the massive burial of charcoal.
Converting biomass into
charcoal type char which can be used to improve soil fertility, while also
trapping carbon dioxide, certainly has major attractions. But a key issue is whether, in net
climate terms, the loss of (some)
biomass for direct conversion to energy is balanced by the gain from CO2
entrapment and extra CO2 absorption by more fertile soils – especially if the
combustion route also used geo-sequestration i.e. CCS?
parametric study of bio-sequestration by Malcolm Fowles at the Open University,
suggested that from a global warming perspective we should displace coal with
biomass if the latter’s conversion efficiency is much over 30%. Otherwise we
should sequester carbon from biomass rather than generate energy.
this was only a preliminary study and he felt that a more comprehensive
analysis might shift the balance more towards bio-sequestration. He did not
include carbon savings from hydrogen and other pyrolysis products, or crucially
from reduced soil emissions- that’s hard to assess after all. And costs were not included in his
model, although qualitatively and intuitively he felt bio-sequestration should
be cheaper than geo-sequestration by CO2 capture and storage. (Fowles, M. (2007), “Black carbon sequestration as an
alternative to bio-energy”, Biomass and Bioenergy 31: 426–432, doi:10.1016/j.biombioe.2007.01.012).
Clearly though there are lot
of unknowns – for example as to the permanence of bio-sequestration – how long
will the carbon stay trapped in the soil? Some say thousand of years, based on historical examples of charcoal
use. But then that was in traditional “no til” agricultural contexts: farming methods would now have to change
if we wanted to avoid releasing the stored carbon.
are also strong views about the likely impact if biochar production was adopted
on a wide scale. While some see it
as a major way to deal with climate problems, the fear of vast agri-business
plantations worries some people, Guardian correspondent George Monbiot
especially, although even he accepts that there could be niche uses. http://www.guardian.co.uk/environment/2009/mar/24/george-monbiot-climate-change-biochar.
can be produced by pyrolysis at around 500 degrees C, either slowly (over days,
the traditional approach e.g. in kilns), which results in about equal amounts
of biochar (about 35% of the original biomass), liquid and gaseous fuels; or
rapidly (e.g. flash pyrolysis, in
seconds), which gives less biochar (about 15% converted) less gaseous products, but more liquid “bio-oil”
products (about 75%). In addition there is high temperature (800 °C)
gasification, which typically, over hours, yields a low proportion of solids
(only about 10% biochar), but a high proportion of gaseous products (about
with fast pyrolysis or gassifiation the processing throughputs can be larger,
but slow pyrolysis gives you more biochar in the mix. For example, BEST Energy
in Australia, have developed a slow pyrolysis approach called Argichar, in
25 and 70% by weight of the dry feed material is converted to a high-carbon
char material, while also generating
syngas: see www.ecovoice.com.au/enews/enews-47/Images%2047/Brief%20BEST%20pyrolysis%20and%20Agrichar%202007.pdf.
How much carbon
sequestration might be achieved? Globally, according to Professor Tim
Lenton, from UEA: “Biochar has the potential to sequester
almost 400 billion tonnes of carbon by 2100 and to lower atmospheric carbon
dioxide concentrations by 37 parts per million.” How does that
compare to other approaches, like Carbon Capture and Storage? Biochar production removes CO2 from the
air, while CCS aims to remove it from the exhaust gases of power plants – in
large quantities. According to Bruce Tofield, from the Low Carbon Innovation
Centre, UEA: “In the UK biochar
might yield a few million tonnes CO2 saving with current biomass
sources – CCS needs to aim for over 100 m tonnes.”
However, that doesn’t mean
turning biomass into biochar is a bad idea, and some environmenalists are quite
enthusiastic. In The Renewable World, a new book from the World Future
Council, Herbie Girardet and Miguel Mendonca (Green Books) are very keen on
techniques for improving soil fertility and biological carbon dioxide absorption,
and talk of “carbon farming”. They
note that “by pyrolysing one tonne of organic material which contains about
half a tonne of carbon, about half a tonne of CO2 can be removed from the
atmosphere and stored in the soil, while the other half can be used as carbon
neutral fuel”. However they add that “a major question that needs an urgent answer is how enough organic matter
can be made available to produce significant amounts of biochar. Opponents
argue that farming communities in developing countries may be forced to produce
fast-growing tree monocultures on precious agricultural land to produce biochar
to counter climate change for which they are not even responsible”. But
they point to sewage as an example of a less contentious feedstock.
are no doubt many other niche sources of biomass like this, as well as novel
sources like algae, although there may also be competing uses (e.g. sewage gas
is one of the cheapest renewable energy sources for electricity generation). But then we are back with the question
of which is most effective at reducing carbon dioxide?
Royal Society’s recent review of Geoengineering commented: “It remains questionable
whether pyrolysing the biomass and burying the char has a greater impact on
atmospheric greenhouse gas levels than simply burning the biomass in a power
plant and displacing carbon-intensive
coal plants.” It concludes: “Biomass
for sequestration could be a signiﬁcant small-scale contributor to a
geoengineering approach to enhancing the global terrestrial carbon sink, and it
could, under the right circumstances,
also be a benign agricultural practice. However, unless the sustainable
sequestration rate exceeds around 1 GtC/yr, it is unlikely that it could make a
large contribution. As is the case with biofuels, there is also the signiﬁcant
risk that inappropriately applied incentives to encourage biochar might
increase the cost and reduce the availability of food crops, if growing biomass
feedstocks becomes more proﬁtable than growing food.”
That is a point picked up by
James Bruges in the new Schumacher society report The Biochar Debate (Green Books). He argues for a global
Carbon Maintenance Fund, rather than just awarding carbon credits. But that is rather going ahead of
ourselves. First we have to see if the biochar option makes sense. The Royal
Society pointed out that so far there was not enough research on the topic. Defra has commissioned the UK
Biochar Research Centre (UKBRC) to review the impacts of biochar. Hopefully
that will provide some answers.