How the gasifier works — Production of biochar

how a gasifier produces biochar

Have you ever wondered how a gasifier that produces biochar works?
Look no further, this article gives you a good general overview of the
entire process—detailing how a typical gasifier processes.¹

A gasifier that produces biochar is a device that utilises a process called gasification to convert biomass (such as wood, agricultural waste, or other organic materials) into valuable products like biochar, combustible syngas (a mixture of carbon monoxide, hydrogen, and other gaseous products), and heat. The process involves several stages, which can be described as follows:

Key Concepts


The biomass feedstock is first dried to remove excess moisture. This is typically achieved by preheating the biomass using the heat generated from the gasifier itself.


As the biomass is heated in the absence of oxygen, it undergoes thermal decomposition, breaking down into simpler compounds. This stage produces bio-oil, gases, and solid char. The bio-oil and gases are collectively known as volatile matter, while the solid char is the precursor to biochar.


A controlled amount of oxygen (or air) is introduced into the gasifier. This oxidizes a portion of the volatile matter and char, releasing heat and producing carbon dioxide and water vapor. The heat generated in this stage drives the pyrolysis and gasification processes.


The remaining char and volatile matter react with limited oxygen and steam at high temperatures. This results in the production of syngas, which are composed mainly of hydrogen, carbon monoxide, methane, and other gases. The solid residue left behind is the biochar.

Syngas cooling and cleaning

The syngas is cooled and cleaned to remove any impurities, like tars and particulates. After cleaning, the syngas can be used for power generation, heating, or as a feedstock for producing chemicals.

Biochar collection

The biochar, which is rich in carbon and has numerous agricultural and environmental applications, is collected from the gasifier. It can be used as a soil amendment, carbon sequestration agent, or for other purposes.

In-depth process outline:

Feedstock preparation

The biomass feedstock is dried and sometimes pre-processed (e.g., chipped, shredded, or pelletized) to ensure consistent size and moisture content. This helps to facilitate smooth and efficient gasification.

Gasification process

The prepared biomass is fed into the gasifier, where it undergoes a series of thermochemical reactions under controlled temperature and oxygen-limited conditions. This usually occurs in a range of 400-1000°C (750-1830°F). The primary reactions are:

a. Pyrolysis: The biomass decomposes into volatile gases, tar, and solid char under high temperatures with little or no oxygen present. The volatile gases and tar can be further processed into syngas, while the solid char becomes the desired biochar.

b. Combustion: Some of the biomass and char react with a limited supply of oxygen, producing heat and carbon dioxide. This heat is used to maintain the gasification process temperature.

c. Reduction: The remaining char reacts with carbon dioxide and water vapour (steam) present in the system, producing carbon monoxide, hydrogen, and additional biochar. These gases are collectively known as syngas.

Gas and biochar separation

The syngas and biochar produced during gasification are separated. The syngas is typically cooled and cleaned to remove particulates, tar, and other contaminants before being used as fuel for power generation or other applications. The biochar is collected separately for further processing or use.

Biochar processing

Biochar may be further processed, such as by grinding, pelletising, or activating, to improve its properties for specific applications, such as soil amendment, carbon sequestration, or water filtration.

Energy utilisation

The syngas produced during gasification can be used for various energy applications, such as electricity generation, heating, or as a fuel for internal combustion engines or gas turbines. This helps to offset fossil fuel consumption and reduce greenhouse gas emissions.

In summary, a gasifier that produces biochar works by heating biomass in a controlled, oxygen-limited environment, causing it to break down into simpler compounds. The process results in the production of biochar, syngas, and heat, all of which have various applications in
agriculture, energy, and environmental management.

¹ This article is informational and does not describe the specific process of the CNI gasifier. Many gasifiers operate with differing principles of operation and design. The information contained herein serves merely to provide interested readers with a general overview of the gasification process that a gasifier makes possible.

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*Editor’s note: The content in this article is mainly AI-generated and is for general informational purposes only. Whilst the content herein has been screened, certain inaccuracies which may not be apparent, might necessitate further corroboration and fact-checking. The content has however, been enriched—with additional facts and citable sources provided, in a bid to corroborate some of the primary statements being made, thus providing reasonable additional credibility to the information herein.

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