• Analysis of Biochar
    For Use as a Fuel
    At Celignis Biomass Lab


Biochar is produced through the process of pyrolysis, which involves heating biomass in the absence of oxygen. The properties of biochar can vary depending on the feedstock used, the temperature and duration of the pyrolysis process, and other factors.

Biochar can potentially be used in a wide variety of applications, including: as a soil amendment, a component of biobased materials, and in pollution remediation.

Biochar also often has several properties that make suitable as a fuel source. For example, it typically has higher carbon contents and hydrogen contents and lower oxygen contents than the starting feedstock, which result in it having a greater calorific value. Biochar can also usually be compressed at higher densities than the starting feedstock which, coupled with the increased carbon content and calorific values, leads to a fuel with a significantly greater energy density.

The pyrolysis process will also remove the moisture from the feedstock producing a biochar with a very low water content. Furthermore, biochar is typically more stable and resistant to decomposition than the original biomass, which means it can be stored for longer periods of time without losing its fuel properties.

However, it is important to note that not all types of biomass are appropriate for producing biochar suitable for us as a combustible fuel. Factors such as the chemical composition and the content and composition of ash can all affect the properties of the resulting biochar. Additionally, the pyrolysis process itself can impact the quality of the biochar, so careful control of temperature, duration, and other factors is necessary to produce biochar with optimal fuel properties.

Celignis Analyses to Evaluate Biochar as a Fuel

Ultimate Analysis of Biochar

The ultimate analysis of biochar will provide the mass concentrations of the major elements (carbon, oxygen, hydrogen, nitrogen and sulphur) in the sample. The process of pyrolysis typically removes oxygen-containing compounds as non-condensible volatile gases, leaving the resulting biochar with a relatively greater carbon content.

Typically carbon, hydrogen, nitrogen, and sulphur can be determined in the same analytical method and the oxygen content can then be calculated as the remaining mass after the ash content has been considered.

We use an Elementar MACRO Cube unit for the ultimate analysis of samples. It allows for large sample sizes (e.g. around 40mg) to be used than many other elemental analysers, allowing us to improve the precision in the analysis of biochar samples.

Below are listed the Celignis analysis packages that include the ultimate analysis of biochar.

Differentiation Between Inorganic Carbon and Organic Carbon in Biochar

Carbon can be present in both the organic and inorganic form in biochar. Organic carbon refers to carbon that is bound to hydrogen atoms and found in living, or once-living, biomass. Inorganic carbon, on the other hand, refers to carbon that is instead associated with ash cations rather than with the biological polymers of the plant. In biochar, inorganic carbon is typically found as carbonates, e.g. calcium carbonate.

It is important to differentiate between the two forms of carbon in biochar given that organic carbon is preferred when considering biochar as a tool for cabron sequestration, plant growth promotion, and combustion.

The Dumas analysis of a biochar sample, as described in the section above, will provide data on total carbon content of the biochar. However, we can also undertake a carbon analysis of the biochar ash in order to determine the inorganic carbon content. This can then be subtracted from the total carbon content in order to determine the organic carbon content of the biochar sample.

The European Biochar Certificate (EBC), an organisation set up to ensure the quality and safety of biochar produced in Europe, sets an upper threshold of 0.7 for the stoichometric ratio between hydrogen and organic carbon in biochar.

At Celignis we check as to whether the ratio for biochar samples is above or below this threshold value and provide the results in a PASS/FAIL table included as part of our pdf reports. An example table is provided below.

Below are listed the Celignis analysis packages that include the inorganic and organic carbon contents of biochar.

Analysis of the Content and Composition of Ash in Biochar

Ash is generally considered to be the residue remaining after the material has been incinerated. It therefore has no energy value and is therefore of no direct value when considering biochar as a fuel. Indeed, high ash-contents can cause problems in many thermochemical processes (e.g. pyrolysis, gasification, and combustion).

The major cations present in biochar ashes are Calcium, Potassium and Magnesium. Other elements such as Manganese, Sulphur and Phosphorus are present in minor amounts. Trace constituents (such as Al, Fe, Zn, Cu, Ti, Pb, Ni, V, Co, Ag and Mo) are also found in many substrates. The anions that are usually present are Chloride, Carbonate, Sulphate and Silicate.

With biochars produced from waste feedstocks (municipal solid wastes in particular), ashes are often more abundant and more diverse.

At Celignis with our elemental analysis methods we are able to characerise a wide range of major and minor analytes present in biochar ash. Click here to see our relevant analysis packages.

Below are listed the Celignis analysis packages that determine ash composition.

Ash Melting Behaviour of Biochar

Ash melting, also known as ash fusion and ash softening, can lead to slagging, fouling and corrosion in boilers which may reduce conversion efficiency. We can determine the ash melting behaviour of biochar using our Carbolite CAF G5 BIO ash melting furnace. It can record the following temperatures:

Ash Shrinkage Starting Temperature (SST) - This occurs when the area of the test piece of biomass ash falls below 95% of the original test piece area.

Ash Deformation Temperature (DT) - The temperature at which the first signs of rounding of the edges of the test piece occurs due to melting.

Ash Hemisphere Temperature (HT) - When the test piece of biomass ash forms a hemisphere (i.e. the height becomes equal to half the base diameter).

Ash Flow Temperature (FT) - The temperature at which the biomass ash is spread out over the supporting tile in a layer, the height of which is half of the test piece at the hemisphere temperature.

Below are listed the Celignis analysis packages that determine the ash melting behaviour (ash fusion temperature) of biochar.

Calorific Value of Biochar

Calorific value, also known as heating value, is one of the most important properties to consider when evaluating biochar for use as a fuel.

There are several units of measurement. The caloric, or higher heating value (HHV), is independent of moisture content and reliant on the chemical composition of the material. A linear relationship exists between the heat of combustion and the carbon content of the substrate while oxygen, nitrogen and inorganic elements tend to reduce the value.

The Lower Heating Value (LHV), or effective heating value, is perhaps more relevant than the HHV in practical operations. It considers not only the energy required to vaporise the moisture of the biochar but also that necessary to vaporise the water generated when the hydrogen and oxygen elements of the biochar combine. Hydrogen content then becomes a reducing factor in the heating value.

We determine the heating value of biochar directly, by combusting the sample in a bomb calorimeter. Alternatively, it can be indrectly calculated based on the ultimate analysis of the biochar, however these values are less reliable than direct measurements and their accuracies are dependent on the robustness of the mathematical formula to cover different types of biochars.

The heating value can be reported on a dry or wet basis. The wet-basis value considers the moisture content of the biomass and reduces the heating value to incorporate the latent heat of condensation.

At Celignis we use a Parr 6200 bomb calorimeter to directly determine the gross calorific value (higher heating value) of samples. The data from ultimate analysis are then used to calculate the net calorific value (lower heating value).

Below are listed the Celignis analysis packages that determine the calorific value (or heating value) of biochar.

Volatile Matter and Fixed Carbon Contents of Biochar

Fixed carbon refers to the portion of the biochar that remains (excluding ash) after it has been heated to a high temperature (900 oC for a period of 7 minutes). The material that is lost during this treatment is termed the volatile matter. Fixed carbon is a measure of the biochar's carbon content and represents the fraction of the original feedstock material that has been converted into a stable, carbon-rich form during the pyrolysis process.

Fixed carbon is generally considered to be a desirable property of biochar, as it represents a potentially stable form of carbon that can be used for carbon sequestration or soil improvement. The volatile matter content of biochar can affect its physical properties, such as its porosity and density, as well as its chemical properties, such as its ability to release nutrients or affect soil pH. Generally, biochar with a lower volatile matter content is preferred for applications such as soil amendment, as it is less likely to release harmful compounds or affect soil fertility.

In general, fuels with a higher fixed carbon content and a lower volatile matter content are preferred for combustion applications, as they tend to be more efficient and produce fewer emissions. However, the optimal balance between fixed carbon and volatile matter content can vary depending on the specific application and combustion technology being used.

The volatile matter and fixed carbon contents of biochar are generally quite different from those of the starting feedstock material. During the pyrolysis process that produces biochar, the feedstock material is heated to a high temperature in the absence of oxygen, which causes it to decompose and release gases, liquids, and other volatile compounds. As a result, the volatile matter content of biochar is typically much lower than that of the starting feedstock material. For example, wood chips may have a volatile matter content of around 80%, while the volatile matter content of biochar produced from those same wood chips may be only 20-30%.

Correspondingly, the fixed carbon content of biochar is typically much higher than that of the starting feedstock material. This is because during the pyrolysis process, some of the carbon in the feedstock material is converted into a stable form that is resistant to decomposition. This stable carbon makes up the fixed carbon content of the biochar.

Below are listed the Celignis analysis packages that determine the fixed carbon and volatile matter contents of biochar.

Additional Information on Analysis of Biochar as a Fuel

Feel free to get in touch with us if you have any questions about our analytical services for evaluating biochar for use as a fuel. Relevant members of the Celignis biochar team will be happy to assist. Those team members with the most experience with undertaking these tests and interpreting the resulting data are listed below.

Sajna KV

Bioanalysis Developer


Our Biomass Detective! Designs, tests, optimizes and validates robust analytical methods for properties of relevance to the various biochar market applications.

Dan Hayes

Celignis CEO And Founder

PhD (Analytical Chemistry)

Dreamer and achiever. Took Celignis from a concept in a research project to being the bioeconomy's premier provider of analytical and bioprocessing expertise.

Other Celignis Tests and Services for Biochar

Global Recognition as Biomass and Biochar Experts

Celignis provides valued services to over 1000 clients. We understand how the focus of biochar projects can differ between countries and have advised a global network of clients. We also have customs-exemptions for samples sent to us allowing us to quickly get to work no matter where our clients are based.

Further Info...

Feedstock Evaluation

Our analysis packages can screen biochar feedstocks. We can estimate biochar yield and quality using feedstock chemical composition and can estimate biochar composition using the ultimate and major/minor elements analyses of the feedstock. With TGA analysis we can also monitor feedstock behaviour under pyrolysis conditions.

Further Info...

Biochar Production

We can produce biochar samples from your feedstocks using a wide range of temperatures, heating rates, and residence times. We can formulate a Design of Experiments (DoE) to study the effects of varying process parameters on biochar yield and quality and can optimise these outputs according to your desired biochar market applications.

Further Info...

Biochar Analysis

We have an extensive array of analysis packages to evaluate the suitability of biochar for a range of applications. These analyses cover properties relevant to combustion, soil amendment, feed, and biomaterials. Our reports compare the results against internationally-recognised limits for using the biochar in specific end-products.

Further Info...

Soil Amendment & Plant Growth Trials

We can test biochar for several properties (e.g. water holding capacity, electrical conductivity etc.) relevant to its use in soil amendment. We can also grow plants in biochar-amended soils and assess the impacts of this approach on germination, plant growth, plant health, and soil biology.

Further Info...

Analysis of PAHs in Biochar

Polycyclic aromatic hydrocarbons can be formed during the pyrolysis of biomass and accumulate in biochar, leading to potential risks to the environment. We can accurately quantify a range of different PAHs and determine if their concentrations exceed regulatory limits. We can also develop strategies to reduce the amount of PAHs in biochar.

Further Info...

Surface Area and Porosity of Biochar

The suitable markets for a biochar are often greatly dependent on its surface area and pore size-distrubtion. We provide detailed reports on biochar surface area and porosity and can provide guidance on the implications of the results. We can also work on strategies to increase the surface area and modify the pore-size distribution of biochar.

Further Info...

Thermogravimetric Analysis of Biochar

TGA is a powerful analytical technique for the study of biochars because it allows us to examine the thermal stability of the material as a function of temperature. The thermal stability of biochars is an important factor to consider when evaluating their potential use as a soil amendment or for carbon sequestration.

Further Info...

Biochar Upgrading

There are several different methods (covering physical, chemical and biologial routes) by which we can upgrade your biochar in order to increase its value and make it more suitable for the desired market applications. We are able to fully characterise the changes in physicochemical properties associated with upgrading.

Further Info...

Biochar for Carbon Sequestration

Biochar's efficacy as a means for sequestering carbon depends on a range of factors (e.g. feedstock and pyrolysis conditions). We can undertake a range of analytical tests to help you determine the stability of your biochar's carbon. We can also suggest alternative approaches to improve carbon sequestration potential.

Further Info...

Technoeconomic Analyses of Biochar Projects

Our TEA experts work with you to evaluate the economic prospects of your biochar facility, considering various scale, technology, and feedstock options. We apply accurate costing models to determine CAPEX/OPEX of simulated and pilot scale processes which are then used to determine key economic indicators (e.g. IRR, NPV).

Further Info...

Research Project Collaborations

Celignis is active in a number of important research projects focused on biomass valorisation. Biochar is a key component in some of these ongoing projects as well as in several prior projects. We are open to participating in future collaborative research projects where our extensive infrastructure and expertise in biochar can be leveraged.

Further Info...