Polytechnik

Durability: the decisive factor for carbon sequestration

One of the central questions in the discussion about biocarbon is the stability of the bound carbon. How long does this carbon remain bound before it returns to the atmosphere as CO₂? As a rule, a stability of at least 100 years is assumed. But what factors influence this durability?

Temperature and residence time as influencing factors

The biomass is ‘roasted’ in a special thermal reactor. The details of the thermal treatment (i.e. the processing temperature and the residence time in the reactor) have a decisive influence on the structure of the biocarbon. At higher temperatures and longer residence times (‘dark roasting’), biocarbon with a high carbon content (Cfix) and few volatile components is produced. Biocarbon with a high Cfix value is more stable and reactive, which increases its long-term stability. Temperatures above 500 °C result in Cfix values of over 80%, making it particularly suitable for long-term CO₂ sequestration.

Different technologies for producing biocarbon

There are market-ready processes for producing biocarbon based on different temperatures. Each of these technologies produces biocarbon with different C-fixation content and different chemical properties, which are crucial for its subsequent application.

The future of biocarbon: a sustainable means of reducing CO₂?

The debate about biocarbon as a sustainable means of CO₂ avoidance, as well as CO₂ capture and storage, is in full swing. Since biocarbon is produced from biomass and agricultural residues that bind atmospheric CO₂, it offers enormous potential for CO₂ reduction. As a versatile material, biocarbon is proving to be a real all-rounder, depending on where and how it is used.

Option A: Fire up the biocarbon as an energy source!
Biocarbon can replace fossil coal and be burned to generate energy. This may sound surprising at first. But using biocarbon reduces the consumption of fossil coal, thereby saving CO₂. Biocarbon can serve as a substitute in various areas:

• Industry heats up: In metallurgy, for example in the production of steel, biocarbon can be used as a reducing agent. This helps to reduce CO₂ emissions.
• Power plants in transition: Biocarbon can be burned in combined heat and power plants, cement plants and even in coal-fired power plants instead of fossil coal. This is a step towards a more climate-friendly energy supply.
• Barbecuing with a clear conscience: Biocarbon briquettes are a great alternative to charcoal and conventional briquettes.

Option B: Biocarbon as a long-term CO₂ store – the soil makes it possible!
However, the really exciting application of biocarbon is the long-term storage of CO₂. And this works best when it is not burned, but added to the soil. Why?

• Soil improvement with a climate effect: Biocarbon improves the soil’s ability to store water and nutrients. This makes the soil more fertile and at the same time ensures that CO₂ is bound in the long term.
• Sustainable construction with biocarbon: Concrete, asphalt and bricks can be mixed with biocarbon. This stores carbon in building materials and reduces the ecological footprint of construction.
• Compost turbo with biocarbon: Adding biocarbon to compost not only reduces methane emissions, but also ensures that the carbon in the compost is stabilised and stored in the soil in the long term.

What will prevail: biocarbon as an energy source or as a CO₂ store? That depends entirely on what we want to achieve. Do we need a short-term alternative to fossil fuels, or do we want to remove CO₂ from the atmosphere in the long term? The answer to this question will largely determine the future of biocarbon. It remains exciting to see which of these promising approaches will prevail.

Harald Fuchs, Head of BU Torrefaction & Carbonisation

* Terms such as biochar, charcoal, carbonised or torrefied biomass and plant charcoal are ubiquitous in industry, the media and science. But do they all mean the same thing? To avoid confusion, we use the umbrella term ‘biocarbon’ in this article.