The targeted removal of carbon dioxide from the atmosphere is regarded as a central approach for achieving greenhouse gas neutrality in the European Union by the year 2050. As well as the planned planting of forests, agricultural soils are playing an increasingly significant role as an important carbon sink in the climate protection debate, as they store around four times as much carbon as surface vegetation.
The objective of carbon farming is to improve the quality of arable soils, thus trapping more CO2 in the soil and counteracting climate change. Farmers who implement this concept in the long term add more carbon to their soils than they release – experts refer to this as negative emissions. Enrichment with biochar is considered to be one of the most important carbon capture and storage (CCS) technologies in this context. At EnergyDecentral 2022, its potential will be discussed both at the stands and in the international technical programme.
Ecologically sound soils
Biochar is a solid with a high content of elementary carbon previously originating from atmospheric carbon dioxide that was absorbed by the plants during their growth phase. To produce it, organic material is carbonised with the aid of heat and pressure with the exclusion of oxygen. A large part of the carbon is thereby bound in molecular structures that remain stable in soils over a period of many centuries and are only released again very slowly. In the long term, around 30 to 50 percent of the carbon contained in plants could therefore be removed from the atmosphere.
According to a study conducted by the Stiftung Wissenschaft und Politik (SWP; German Foundation for Science and Politics), global application could bind between 0.5 and two billion tonnes of CO2 per annum, representing significant potential.
“There are millions of tonnes of timber in Germany's forests. Unused, they are exposed to the elements and therefore release carbon. This incredible volume could be processed to make very good biochar. Besides the necessary technical plants, we also need the backing and understanding of politicians as regards what biochar is really capable of in order to achieve this”, says Dr Susanne Veser, Chairwoman of the German Biochar Association.
Marcus Vagt, EnergyDecentral's Project Manager, also sees clear advantages for carbon farming. “Effective climate protection demands the implementation of easily scalable processes for the targeted removal of CO₂ from the atmosphere. That is already possible today with biochar”, he confirms.
Depending on input and method, roughly 3.2 tonnes of CO₂ are stored per tonne of biochar. With respect to EnergyDecentral, it can be seen that biochar is being produced in efficient high-tech plants today. During carbonisation, called pyrolysis, plant residues such as green waste, waste wood or waste products from food production are thermally treated in a low-oxygen environment.
From biogenic residual substances to fuel
One example of this is thermo-catalytic reforming (TCR), which has been developed at the Fraunhofer UMSICHT Institute. In this process, the residual biomass is transformed into synthesis gas with a very high hydrogen content - up to 50 percent- carbonisate and pyrolysis oil with a petroleum-like consistency, which has a high calorific value and very low acid values and is comparable to vegetable oils. It can either be refined together with mineral crude oil in refineries known as co-processing or further processed on its own to form products such as petrol and diesel. The resulting products are climate-neutral. The energy required is generated from the residual substances used, with the result that hardly any CO2 emissions occur during the process.
The TCR technology has been developed for a containerised, compact plant design. It therefore represents a decentralised solution for recycling diverse types of biogenic residual substances. In a first stage, the biomass is gently broken down into biochar and volatile components in a screw reactor in the absence of oxygen at medium temperatures below 500 degrees Celsius. The formation of tar and other pollutants is prevented through optimised process conditions in the various reactor zones. In the second stage, the coal and vapours are catalytically refined at temperatures of up to 700 degree Celsius in a post-reformer in order to improve the gas yield and the product quality. The vapours are then cooled. During condensation, oil and process water are separated. The remaining gas is cleaned.
Optimising biogas plants with biochar
Depending on input material, the biochar or carbonisate that is produced in this way reveals a high content of nutrients and can be used, for instance, for fertiliser application. “The carbonisate enables improved aeration and allows sandy soils to absorb water better”, explains Fabian Stenzel, head of the responsible department at Fraunhofer UMSICHT in Sulzbach-Rosenberg. The biochar can be spread on arable land in pulverised form, where it acts as a vehicle for nutrients and provides a habitat for microorganisms. The new EU fertilising product regulation that came into effect in mid-July 2022 is also likely to ensure additional momentum in agricultural use. Alongside chemically untreated wood, it also permits additional output materials for biochar. Marcus Vagt welcomes these adjustments, stating “This change makes an important contribution to cycle-based decarbonisation, because it enables farmers as well as food and feed producers or other industries that generate biomass to transform their residues into a CO2 store.”
Biochar can also be put to economically and ecologically beneficial use in biogas plants, for example, prior to its ultimate function as a soil improver. Firstly, its spongy structure offers a very good surface for bacterial colonisation – and more bacteria lead to more turnover in the process as a whole and therefore to more biogas. Secondly, biochar is able to adsorb pollutants due to its surface properties. The background to this is that an excessively high ammonium concentration inhibits the activity of the microorganisms that produce methane in the fermenter. Biochar effectively binds ammonium, with the result that more methane can be obtained from the substrate. Later on, the ammonia nitrogen is available again with the biochar in the digestate fertiliser, as it is washed out less extensively. The gas yield can be increased by up to ten percent depending on biochar type, grain size and output materials.
Carbon farming on the advance
As one of the most important methods of fostering sustainable agriculture, carbon farming is now also increasingly shifting into the focus of the European Union. The E.U. launched its carbon farming initiative, with which previously completed pilot projects are to be extended throughout the entire E.U., back in December 2021. The E.U. is intending to introduce a corresponding regulation by the end of 2022. The aim is to encourage farmers to change their working practices and to use carbon-rich fertilisers as well as cultivating crops and trees that are able to absorb more CO2 from the atmosphere. Farmers who are operating sustainably would therefore be given an incentive to use carbon farming as a business model – and could sell emissions certificates for the amount of carbon that they bind in their land. But which specific measures are suitable for binding carbon in the soil and forming humus? How can the effects be documented in terms of CO2 certificate trading?
EnergyDecentral 2022 aims to provide the answers to these questions in its expert talks. Verification specialist BELOW2, an organisation that is concentrated on documenting and reviewing CO2 offsetting projects according to strict scientific standards and therefore offers climate protection solutions that solely evaluate the CO2 effect, will also be taking part. “Together with customers, we define which projects best match their compensation objective. In close coordination, we then develop specific proposals for an individually tailored strategy and evaluate this in terms of cost-effectiveness and the degree of CO2 reduction”, explains Oliver T. Hellriegel, one of the three founders of BELOW2. For Hellriegel, one of the central drivers in the scientific analysis of technological CO2 avoidance or sink projects is the vast potential slumbering in the domestic farming industry. He is convinced that the region also needs to play a central role in compensation in addition to transparency and protection against falsification. “Improved fertilisation methods, accessing renewable energies and the use of alternative cultivation and harvesting methods are putting agriculture at the forefront of the climate change movement although it hasn't been talked about a great deal so far”, says Hellriegel. Visitors can find out more about this at EnergyDecentral, the leading trade fair for decentralized energy supply, 15 -18 November in Hanover, Germany.
