Biomass gasification is a modern method of thermochemical conversion in which solid organic material is converted into a high-energy gas. For this process to be effective, it is important to select the correct parameters for the feedstock. What should you take into account?
Moisture
Water as a reactant
In many methods of using biomass for energy, moisture is seen as an obstacle, but it plays a specific role in gasification. The advantage of these processes is that they do not require completely dry feedstock. This is because the water in the fuel (or added steam) acts as a reactant during the gasification process, contributing to the formation of synthesis gas rich in hydrogen and carbon monoxide.
Particle size
The key to uniformity
To ensure efficient heat and mass transfer during the process, biomass is most often processed into wood chips.
- Optimal dimensions: Wood chips between 20 and 30 mm in length are best.
- The risk of large pieces: If the wood chips are too long or too thick, the heat and chemicals cannot penetrate evenly to the centre, resulting in incomplete decomposition of the material.
Type of wood
Hardwood or softwood?
In Slovakia, we have a wide range of tree species available, with deciduous trees accounting for the largest proportion (60.2 per cent), particularly beech.
- Conifers (spruce, pine): They contain more lignin (25–36 per cent) than deciduous trees (15–25 per cent). Lignin is important because, during thermal decomposition, it contributes more to the formation of charcoal than other polymers, thereby protecting the remainder of the material from too rapid a degradation.
- Waste utilisation: Residual wood, forest waste or sawdust that is unsuitable for more demanding industrial processing is ideal for use as a fuel.
What is not recommended?
When selecting biomass, you should bear in mind several factors that could damage the equipment:
- High ash content: Biomass from annual plants or fast-growing trees tends to have a higher ash content. This ash contains alkali metals and chlorine, which cause corrosion of equipment during combustion.
- Excessive bark content: The bark contains high levels of extractives, which may cause deposits to form on processing equipment.
- Storm-damaged timber without analysis: When storm-damaged timber is stored for long periods, it rots and its quality deteriorates, which has a negative impact on energy production efficiency.
By selecting high-quality, properly prepared biomass, you will ensure the stability of the gasification process and maximise the energy yield of your plant.
An illustrative image created using artificial intelligence (ChatGPT).
