Photosynthesis is nature’s way of extracting carbon from the atmosphere. It leads to biomass in the form of plants which contain carbon. When the plant dies and decays, that carbon is returned to the atmosphere as CO2 and some methane gas. If we could convert the biomass before it decays to a char material, then the carbon is effectively taken out of the cycle and can be stored easily and cheaply for centuries as solid charcoal. Charcoal remains are regularly found in archaeological dig sites dating back thousands of years. Thus, conversion of biomass to biochar and subsequent storage of the char in the shallow ground could offer a much cheaper alternative to abating carbon emissions from fossil fuel burning.
This idea has been explored, but appears to excite little attention compared to carbon capture and storage being considered for trials on large power plant. The only technology involved is the conversion of the biomass to char which is conventionally carried out by slow pyrolysis (heating in the absence of air).
In practice this is usually carried out without any external fuel being supplied. The volatiles and hydrogen in the biomass provide the heat for pyrolysis. The thermochemistry is complex and needs further investigation if yields of biochar are to be optimised. However, it is possible that the pyrolysis could offer some net heat output in addition to capturing carbon. Is this a more valuable option than simply burning biomass to displace fossil fuel? The product (solid charcoal) is certainly easier to store than compressed CO2 gas.There is evidence to suggest that charcoal can be also be applied as a soil improver whihch would aid crop growth and further assist the natural carbon cycle and crop yields.
Estimates of char yield have been carried out in a student postgraduate project at Warwick University. Softwood grows at a rate of 11 tonnes per hectare p.a. Eleven tonnes of softwood can yield around 2.3 tonnes of biochar, which is equivalent to 8.5 tonnes of CO2. At these yields approximately 1/3 of the U.K. Forestry Commission land would be needed to offset emissions from a 1GWe power plant. Not a viable option on any large scale in the UK you would conclude. However, researchers in Canada have concluded that worldwide and in Canada, there is sufficient biomass to make a global impact on atmospheric CO2 levels.
For further information on this latest work please cite : Matovic D, Biochar as a viable carbon sequestration option: Global and Canadian perspective, Energy (2010) – article in press currently, but can be viewed at www.elsevier.com/locate/energy.
Biochar from other sources such as agricultural and manufacturing waste could offer a better alternative in the UK than incineration because of the added value of landfill avoidance. Zerontec Energy Consultancy would be interested in hearing the views from readers on this topic. Does this offer the potential for a funded projects?
– interested readers please contact info@zerontec.com
