COMPARISON OF GRINDING AND LIBERATION PROCESSES FOR STALKY BIOMASS MATERIALS AS A PREREQUISITE FOR PRODUCTION OF ENERGY PELLETS WITH HIGH CALORIFIC VALUE

摘要

Pelletising biomass, especially straw and stalky materials, requires a product specific size reductionand liberation. However, moisture content plays an important role in palletising and also affects theenergetic properties of the biomass. The paper illustrates the characteristics of the mentioned typeof biomass and specifies the necessities for production of energy pellets. Defined requirements forbiomass energy pellets will be shown based on relevant standards.The work focuses on a comparative investigation of the straw fibres after grinding with hammer/impact mill and after the liberation of the straw fibres with twin-screw extruder (two differentcommunition units). A traditional hammer mill as well as an hydrothermal process taking place in atwin-screw extruder were utilised. Results of the grinding and liberation of rye and wheat straw fibresare discussed based on a detailed particle characterisation (particle size and shape distribution).Besides high calorific value the main pellet quality parameters are mechanical stability, abrasionresistance and further combustion technical characteristics.The particle size distribution displayed optimum characteristics for the combustion processes to becarried out in a furnace. The durability of the pellets produced from straw fibres liberated with twinscrewextruder was comparatively better then that prepared with the straw fibres after grinding withimpact mill. Particle size distribution, abrasion values and the strength characteristics showed a goodcorrelation with each. The high presence of N and S would result in high NOx and SOx emissions,where as the high concentrations of Cl would corrode the furnace. These chemical properties of thestraw would restrict its usage in small scale furnaces.