DIN 51718 Testing of Solid Fuels - Determination of Water Content and Moisture Level of Analysis Sample

The standard “DIN 51718 Testing of solid fuels - Determination of water content and moisture content of the analytical sample”, published by the German Institute for Standardization (DIN), describes standardized procedures for determining the water content and moisture content of analytical samples in solid fuels.

Moisture content is one of the most important quality parameters for solid fuels. It directly affects:

Calorific value (heating value),
Mass calculations,
Converting analytical results to reference conditions (e.g., dry, water-free and ash-free basis),
Storage behavior, transport, and combustion efficiency.

Therefore, accurate moisture content determination is crucial for coal trading, power plants, coke production, biochar certification, biomass fuels, and fuel quality control.

This standard applies to solid fuels such as:

hard coal
Brown coal / lignite
coke
Briquettes
Peat
Other similar solid fuels (including in practice some biofuels and biochar)

The DIN 51718 standard defines three main methods for determining total water content, selected based on fuel type, particle size, expected moisture level, and required precision:

Method A: Two-stage drying (generally the reference method for coals):
First stage: Gentle pre-drying at approximately 40 degrees (to remove surface/free moisture without decomposition).
Second stage: Final drying (hygroscopic moisture) to a constant mass at approximately 106 degrees.

This method is particularly suitable for hard coal and coke to prevent oxidation or loss of volatile matter.

Method B: Direct drying at high temperature:
Single-stage drying at 105–110 degrees (typical oven drying until constant mass is achieved).
It is commonly used for many solid fuels where there is no particular sensitivity to temperature.
Method C: Alternative / simplified procedure (depending on the example)
Used in special situations (e.g., very wet fuels or quick routine checks).

To ensure reproducibility, the precise temperature, drying time, sample mass (approximately 1-50 g depending on the stage), crucible type, cooling in the dryer, and calculation formula (percentage of water content) were precisely defined.

The calculation method is standard. Results are generally reported as received or converted to other bases.

The DIN 51718 standard is technically very similar to (and is generally considered equivalent in practice to) the following standards:

ISO 589 Hard coal - Determination of total moisture (two-stage method)
CEN/TS 14774 series: Solid biofuels – Determination of moisture content (oven drying method)

Many laboratories and certification systems (e.g., European biochar certification, global biochar C-Sink standards) explicitly recognize the DIN 51718 standard (specifically Method A) as an accepted or equivalent procedure alongside its ISO versions.

Current practical applications of this standard are as follows:

Coal and coke laboratories
Biomass and wood pellet quality control.
Biochar production and certification (often referring to the DIN 51718 standard for dry matter/moisture content)
Fuel inspection at the power plant
Research and development in the field of solid fuel processing.

In short, the DIN 51718 standard outlines a method for determining the water (moisture) content of solid mineral fuels such as coal and coke. Moisture content is one of the most important parameters affecting fuel quality, calorific value, storage behavior, and combustion efficiency.

The DIN 51718 standard primarily applies to the following:

hard coal
Lignite (brown coal)
Kok
Briquettes
Other solid mineral fuels

This standard defines procedures for determining total moisture or analytical moisture content by controlled drying under specified conditions. The determination is based on:

Weighing a prepared fuel sample.
Drying under controlled humidity and temperature conditions.
Re-weighing the dried sample.
Calculated as mass loss.

Moisture content is expressed as a percentage of the original sample mass.

The steps of this method are generally as follows:

Sample preparation (crushing and homogenization)
Weighing the test sample
Oven drying (typically around 105 degrees under atmospheric conditions)
Cooling in the desiccator
Last weigh-in
Humidity calculation

Moisture content determination is considered important for the following reasons:

Calorific value correction: Water does not contribute to combustion energy. Higher humidity reduces the effective heat value.
Storage and transport: Excessive moisture:
It increases transportation costs.
It promotes biological degradation (especially in lignite).
Increases the risk of spontaneous heating.
Process control: Power plants and industrial boilers require consistent fuel quality for stable combustion.

The DIN 51718 standard is widely used in the following areas:

power generation plants
Coal trading and quality control laboratories
Coke production facilities
cement plants
steel industry

The DIN 51718 standard is part of the broader DIN 51700 series of standards covering the testing of solid fuels. Technically, it is compatible with the following international standards:

ISO 589 Hard coal - Total moisture determination
ASTM D3173 Standard test method for determining moisture content in coal analysis samples.

Although the methods are similar, there are minor differences in drying temperature, sample preparation, or reporting principles.

Accurate moisture determination allows for the following:

Fair trade practices
Reliable energy performance calculations
Compliance with legal regulations
Optimized combustion efficiency

In conclusion, the DIN 51718 standard remains a fundamental standard in fuel analysis, providing reliable and comparable moisture values for solid fuels. Even though newer biofuel-specific norms exist, it is still widely cited and used today. Since moisture directly affects energy value, handling behavior, and industrial performance, this standard plays a crucial role in fuel testing laboratories and energy production industries.

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 51718 standard.