DIN 51721 Testing of Solid Fuels - Determination of Carbon and Hydrogen Content - Radmacher-Hoverath Method

The standard “DIN 51721 Testing of solid fuels - Determination of carbon and hydrogen content - Radmacher-Hoverath method,” published by the German Institute for Standardization (DIN), describes a test method for determining the carbon and hydrogen content of solid fuels, particularly solid mineral fuels such as coal and related materials. This standard defines a classic analytical procedure known as the Radmacher-Hoverath method. This method is used to accurately measure elemental carbon and hydrogen in solid fuels. These values ​​are necessary for:

• Calculation of the elemental composition of fuels.
• Determining net/gross calorific value correlations (typically used in conjunction with standards such as DIN 51900 for bomb calorimetry)
• Calculation of emission factors (e.g., carbon dioxide emission factors per unit of energy required for greenhouse gas reporting)
• Fuel quality control, coal/biomass research, and international equivalency (generally cross-referenced with ASTM D5291 standard)

The Radmacher-Hoverath method includes the following:

• A carefully weighed sample of ground and dried solid fuel is burned in a stream of oxygen at a high temperature.
• Carbon oxidizes to carbon dioxide, and hydrogen oxidizes to water.
• These combustion products are absorbed by suitable reactants (e.g., carbon dioxide in soda asbestos or a similar absorbent, water in a desiccant such as magnesium perchlorate).
• The increase in the mass of the absorber tubes is measured gravimetrically.
• Carbon and hydrogen percentages are calculated from the mass increases (appropriate corrections are made for carbonate carbon dioxide, if any; however, the DIN 51726 standard can be used for separate carbonate correction).

This method is a macro or semi-macro gravimetric technique and was one of the standard classical wet chemical methods before modern element analyzers became widespread.

This method is frequently used in coal analysis laboratories across Europe. It is referenced in German emission factor inventories for fossil fuels (along with methods such as the DIN 51732 standard for sulfur or the DIN 51700 series of standards for other parameters). In international testing, it is often used in conjunction with the “ASTM D5291 Instrumental CHN analysis” standard. It is still applicable to biomass, waste-derived fuels, and some solid recovered fuels where classical methods are necessary or preferred.

Although faster instrumental techniques are becoming more common in routine testing, this standard remains an important reference in fuel chemistry, coal/oil analysis, and environmental reporting.

In short, the DIN 51721 standard provides a method for determining the carbon and hydrogen content of solid fuels. This method is widely used in coal testing laboratories and fuel analysis to support energy assessments, combustion calculations, and environmental evaluations.

The DIN 51721 standard primarily applies to the following:

• hard coal
• Lignite (brown coal)
• Kok
• Solid recovered fuels and similar carbonaceous materials

This standard describes a laboratory analytical method for measuring the total carbon and hydrogen in a fuel sample.

Determining the carbon and hydrogen content is important for the following:

• Calorific value calculations
• Combustion system design
• Emission estimate (carbon dioxide, water)
• Elemental (final) analysis of fuels

While carbon makes the largest contribution to energy release, hydrogen significantly affects the heat output and water vapor production during combustion.

The DIN 51721 standard is based on the principle of complete combustion of a fuel sample in an oxygen-rich atmosphere. The basic steps of the method are as follows:

• Sample preparation: The fuel is finely ground and dried. A precise mass is weighed.
• Combustion: The sample is burned at a high temperature in a combustion tube. Carbon is converted into carbon dioxide. Hydrogen is converted into water.
• Absorption and measurement: Carbon dioxide is absorbed into a suitable chemical absorbent. Water is absorbed into a moisture trap. The increase in the mass of the absorbents is measured gravimetrically.
• Calculation: Carbon content is calculated from the mass of carbon dioxide formed. Hydrogen content is calculated from the mass of water formed.

Typical equipment used in tests includes:

• High-temperature combustion furnace
• Oxygen supply system
• Absorption tubes for carbon dioxide and water.
• Analytical balance (high precision)

Modern laboratories may use automated CHN (carbon, hydrogen, nitrogen) analyzers, but the principle remains the same.

The DIN 51721 standard specifies the following:

• Sample size
• Combustion conditions
• Acceptable deviation limits
• Repeatability requirements

Strict procedural control ensures reliable and repeatable results.

The international equivalents of the DIN 51721 standard are as follows:

• ISO 29541 Solid mineral fuels - Determination of total carbon and hydrogen.
• ASTM D5373 CHN elemental analysis

The DIN 51721 standard is considered important for the following reasons:

• It provides a standardized methodology for fuel characterization.
• It supports quality control in the energy sector.
• It ensures consistent laboratory reporting.
• It contributes to environmental emission calculations.

Accurate carbon and hydrogen determination directly affects the following:

• Boiler efficiency calculations
• Carbon footprint assessments
• Fuel trading specifications

In conclusion, the DIN 51721 standard contains a fundamental procedure for the elemental analysis of solid fuels, particularly for the determination of carbon and hydrogen through combustion and gravimetric measurement. It plays a significant role in fuel quality control, combustion engineering, and environmental monitoring.

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting them in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services in accordance with the DIN 51721 standard.