Carbon dioxide removal (CDR)

A guide to biochar as a scalable carbon dioxide removal technology

biochar carbon removal process

Biochar as a carbon dioxide removal technology

The production and sequestration of Biochar (BC) may be described as a Pyrogenic Carbon Capture & Storage (PyCCS) carbon dioxide removal (CDR) solution. More specifically it is a ‘pre-combustion’ method of Carbon Capture & Storage (CCS) as distinct to the more usual ‘post combustion’ methods. A BC+CCS could be proposed, but this configuration is rarely considered. Biochar is seen as a fundamentally different approach to carbon dioxide (CO2) reduction and removal as it involves deliberately extracting, before combustion, a solid energy rich carbon product from plant material – biomass – to prevent this carbon returning to the atmosphere.

While the ‘renewable’ energy market has been paying a premium for combusting biomass to generate ‘green’ energy – electricity and heat – there has not been widespread interest in converting biomass to ‘biochar’. However, with the CO2 Removal Certificate market starting to pay better prices for not burning this material there is a dramatic shift happening to the commercial opportunities.

This is particularly the case where the cost of renewable electricity from wind and solar has fallen rapidly with respect to traditional renewables, like hydro and biomass, and below the cost of conventional fossil and nuclear power options. Here, the consumption of plant carbon for energy purposes is less attractive and the use for sequestration is enhanced by a number of potential non-energy multiplier benefits from biochar, such as in soil improvement.

From a CO2 perspective biochar is not a ‘complete’ solution. There is an inevitable release of CO2 as part of the pyrolysis process which usually involves burning some (or all) of the by-product pyrolytic gases and liquids. There are proposals in the market to address this, for instance, through ‘thermolysis’ where the pyrolysis kiln is electrically heated (with renewable energy) and the CO2 release is chemically re-combined into liquid carbon products, or to manufacture ‘green’ hydrogen, to produce a zero CO2 biochar option.

This is a new platform from which ‘bio-refining’ is likely to become more widespread, however, the technology is immature commercially. In the meantime there is a pressing need to address the CO2 question with technologies that are available, and potentially, viable today.

In the CapChar proposal it is only materials that were destined to return to the atmosphere as a result of natural aerobic/anaerobic processes that are considered as potential feedstocks. As this would result in all of the carbon returning as greenhouse gases – CO2 and CH4 – reducing this by only partial conversion into CO2 is beneficial to carbon mitigation by avoiding full CO2 emission.

Biochar - A today solution

In comparison with other carbon removal technologies biochar offers an immediate, cost effective and permanent solution.

Immediate – there are a number of biochar systems available on the market, essentially as development of conventional combustion and pyrolysis technologies, offering the possibility of biochar production.

In China, producers of gasifier equipment have already progressed through batch carbonisers to continuous carbonisers. These are generally high volume, high throughput machines designed for agricultural residues (to address the issue of crop burning pollution).

In both situations the arrival of suitable economic incentives is all that is required to switch carbon away from the energy market, and this is already happening in China.

Cost Effective – soil sequestration of pyrolysed carbon is a relatively inexpensive option compared to other carbon removal techniques. As biochar often has independent value the premium needed for its adoption is already within the range of current market prices on CO2 exchanges. This potentially minimises the support for carbon capture needed from the public, in terms of price paid for carbon mitigation, and the volume of support needed from Government to stimulate the development of biochar solutions.

Permanent – there is compelling evidence, linked to the discovery of black Terra Preta soils in the amazonian region, that carbon char endures within most soils. Carbon in a condensed ring form is not consumed by the natural soil processes. It will break up and become embedded in the soil as a carbon dense phase, but is not subject to the normal decay processes of un-pyrolysed carbon. Functionally, it appears to be compatible with the more usual forms of soil organic matter (SOM) and techniques for measuring the recalcitrance of this carbon fraction are in development.

Biochar vs Afforestation vs Bioenergy Carbon Capture & Storage (BECCS) vs Direct Air Capture (DAC) vs Enhanced Weathering

Below is a table highlighting the differences between the current available carbon dioxide removal technologies.

carbon removal biochar versus