Employing aliens to capture carbon

By Kobus Venter

(Extracted from a Green Times article published on 20 February, 2014: http://thegreentimes.co.za/employing-aliens-to-fight-carbon/)

Imagine turning thirsty alien invasive trees into biochar. Biochar is charcoal created by pyrolysis of biomass. This differs from charcoal only in the sense that its primary use is not for fuel, but for biosequestration or atmospheric carbon capture. If created under specific conditions it can also be suitable as a soil amendment.

The beginnings of biochar

The first attempts at making large volumes of charcoal in ancient times had little to do with creating fuel and more with increasing the fertility of the soil. These soils are known as terra-preta soils, which are fertile, black charcoal-rich soil found in scattered tracts throughout the Amazon basin, dating back 450 to 8,000 B.C.

In the humid tropics most of the nutrients remain in the plant growth. The little organic matter that does reach the forest floor decomposes rapidly. Combined with high rainfall means that most nutrients leache away into the soil unutilised. The terra-preta charcoal, called biochar, attracts certain fungi and microorganisms and allow the charcoal to absorb and retain nutrients that keep the soil fertile for hundreds of years.

micropore structure charcoal biochar

The basis of all charcoal and biochar production is pyrolysis: essentially, breaking wood down into its chemical constituents by heat, with little or no oxygen. Today, popular methods of producing biochar include Top-down open burns, so-called TLUD (Top-lit updraft gasifiers) designs and Closed retorts (whereby feedstock is contained and heated within an enclosed chamber).

The quality of biochar can be informally determined by feel: Good biochar is light and rigid but easily crushed, finely grained, not greasy to the touch, washes off with plain water and lastly has a characteristic metallic ring to it when dropped.

Biochar has a high carbon content (typically over 80%) and adsorption capacity which is a function of the internal surface area. The greater the surface area the higher the absorption capacity and the better biochar will retain moisture and soluble organic matter. Activated carbon however does not make good biochar.

3-drum Biochar Retort

Vuthisa Technologies have developed a retort called the ‘3-drum Biochar Retort’ to make large quantities of biochar in batch type burns. The system comprises of an outer drum containing three 210 L oil drums, serving as the retorts, based on their Trans-Portable Kiln technology.

Lower quality feedstock is loaded into the outer drum and lit. This heat is transferred to the contents of the retorts until carbonised.

Carbon capture

In a world dependent on fossil energy, it is easy to see the carbon capture benefits of biochar as offsets against current and future fossil fuel emissions. Many scientists believe there is already an unsafe excess of carbon dioxide in the atmosphere, this obligates the nations that caused the excess to abate it.

Charcoal has the potential to sequester gigatonnes of atmospheric carbon per annum, making it the most potent engine of atmospheric cleansing we possess. Approximately 8 percent of all atmospheric CO2 is absorbed by plants each year. If just a small proportion of the carbon captured by plants can be pyrolysed and transformed into charcoal, humanity’s prospects will be much brighter, for this will buy us time as we struggle to make the transition to a low emissions economy.

Anything from 3 to 9 tons per hectare of biochar (crushed into a powder form) can be mixed into the soil. Typically the biochar is first inoculated and conditioned with soil microbes and usually first mixed with compost before being placed into the soil.

Benefits of adding biochar to soil

As a soil additive, biochar ground down into powder form and mixed with compost offers numerous potential benefits:

Unlike fertilizers, biochar has an extremely long life in soils and is not susceptible to biological decay.
Biochar attracts microbes and beneficial fungi (such as mycorrhizae) and holds on to nutrients that are put into the soil.
Biochar helps conserve nutrients by storing them within its matrix, making the nutrients available when the crop needs them.
Clayey and poorly aggregated soils become less compacted and provide better aeration.
Sandy soils acquire additional bulk moisture storage capacity.

Feedstock

The first step in ensuring the successful implementation of the ‘Vuthisa Biochar Initiative’ was to secure the feedstock for the charcoal kilns. Vuthisa Technologies secured a tender from the Government’s Natural Resource Management Programme (NRM), Land User Incentive (LUI) initiative to eradicate Invasive Alien Plant Species (IAPs) within the Sisonke District Municipality, encompassing some 10,000 km2 from Underberg/Ixopo to Kokstad.

The harvesting contract commenced on 1 December 2013 and expires on 31 March, 2016 and in this time period 580 ha of invasive plant species will be harvested and the stumps treated to prevent re-emergence.

Aiming for 25% conversion efficiency

The first goal of the ‘Vuthisa Biochar Initiative’ is to achieve a minimum of 25% wood to biochar conversion efficiency. Current efficiencies of conventional charcoal producing kilns are less than 15%. Using more efficient methods to produce charcoal has the potential to save approximately 100 MtCO2 per year in Sub-Saharan Africa (see here for more information).

As the plant matter decomposes or ferments, predominantly methane gas is released. Venting un-burnt methane into the atmosphere contributes 26 more times to the Greenhouse effect than CO2 alone. To avoid this Vuthisa will utilise this gas to provide the heat into the retorts and to maintain the biochar forming process within the retorts. They plan to produce 150 tons of Biochar in the next two years and envisage that 20% of this will be bought by fertiliser companies. This could result in at least 30 tons of carbon being sequestered back into the soil.

It is hoped that this project will show at demonstration level that it is profitable to make biochar from forest waste and that it is a viable product. Other goals include securing additional funding to start biochar trials and fully investigate the agri-commercial development of biochar products for use by subsistence farmers.

A little help from our friends

Vuthisa Technologies secured funding from the Energy and Environment Partnership, Southern and East Africa (EEP-S&EA), sponsored by the Ministry of Finland to start their demonstration project using their internally developed biochar kilns. The project will be implemented over a 20-month period. Now the dilemma is that they have to raise 50% of the capital for the venture, which up to this point has been self-funded.

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