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In Latvia approximately of 14.6% of unfarmed agricultural land can be used for herbaceous energy crop growing. Herbaceous energy crops would be as the main basis for solid biofuel production in agricultural ecosystem in future. Herbaceous energy crops as hemp (Cannabis sativa) are grown in recent years and can be used for solid biofuel production. Experimentally stated hemp stalk material ultimate tensile strength the medium value is 85 ± 9 N mm-2. The main conditioning operation before preparation of herbaceous biomass compositions for solid biofuel production is shredding. Therefore hemp stalks were used for cutting experiments. Cutting using different types of knives mechanisms had been investigated. Specific shear cutting energy for hemp samples were within 0.02 – 0.04 J mm-2. Hemp stalk material density was determined using AutoCAD software for cross-section area calculation. Density values are 325 ± 18 kg m-3 for hemp stalks. Specific cutting energy per mass unit was calculated on basis of experimentally estimated values of cutting energy and density.

Abstract. Herbaceous biomass potential is considered as a valuable local renewable energy resource in Latvia. Cereal crop straw (mainly wheat straw), common reeds, rape straw and reed canary grass are the most prospective stalk materials for solid biofuel production. The main biomass conditioning operation in solid biofuel production technology is shredding. Hammer mills are the essential equipment for this operation. Hammers and their articulation are rapidly wearing during hammer mill lifetime. It is recommended to design hammers so that collisions with biomass particles are applied in the hammer centre of percussion. Then the hammer articulation hole is less wearing, unbalance and vibration of the hammer mill rotor are avoided. The main objective of this paper is to determine compliance with this rule for different size rectangular style manufactured hammers. Calculations were made using the Mathcad program for four different size hammers. Only for one size hammer positioning of articulation partly accomplished the mentioned recommended condition of the hammer centre of percussion. The recommended positions and sizes of articulation holes were determined for the mentioned four size hammers. If the hammer design accomplishes the recommended condition of the hammer centre of percussion, it is possible for collisions with particles during milling in different points of the hammer. Then some impact forces in the hammer articulation hole will appear. Therefore, it can be concluded that, if the centre of percussion is designed at the end part of the hammer, the impact forces in hammer articulation would be minimized. The results of calculation in compliance of four sizes of manufactured hammers with the condition of the centre of percussion at the end point of the hammer show that only one hammer size partly satisfies this condition. This shows that the hammer mill hammer design so that interaction between the hammer and material occur at the percussion centre of the hammer is still actual. The sizes of articulation holes have to be also calculated in accordance with the pin shaft strength conditions. Changing the size of the articulation holes the articulation position must be changed.Keywords: hammer mill hammers, centre of percussion. IntroductionHammer mills are the essential equipment for herbaceous biomass shredding before compacting as solid biofuel. Hammers are the main working tools of the hammer mill and are rapidly wearing during the hammer mill lifetime. The percussion interaction between the hammer and material produce additional perturbations generating irregularities [1] during the work. This leads to the consideration of the hammer design so that interaction between the hammer and material occur at the percussion centre of the hammer [2; 3], then the percussions in the articulation are eliminated and so the work of the machine is not disturbed.The main aim of this paper is to determine compliance with this rule for different size rectangular style existing manufactured hammers. The articulation hole...

The main task of this investigation is evaluation of patented (LV 14604 B) biomass briquetting mechanism. Theoretical relationship between necessary drive force and resistance force during pressing in die was determined. Briquettes from grinded common reed (Phragmites Australis) or common reed-peat mixture were produced with designed experimental briquetting press. Density of common reed briquettes depending on the size of particles was stated. Density of briquettes obtained during compacting was from 826.3±16.4 to 934.5±35.1 kg m-3. The minimum of density 826.3±16.4 kg m-3 had briquettes with particles from 6 mm grinding screen, but maximum density 934.5±35.1 kg m-3 had briquettes, when particles from 1.5 mm grinding screen had been used. Compositions of reed particles with peat allow obtaining briquettes density > 1000 kg m-3 if peat proportion in mixture is 30%. Results of theoretical and experimental investigation show that the designed pressing mechanism can be recommended for mobile biomass briquetter design.

The paper present experimental investigation results of common reeds (Phragmites australis) particle compacting in closed die. Common reeds are important natural biomass resource in Latvia. Compacting of biomass is very complicated process for solid biofuel production and there are many factors influencing to this process. The quality parameters of compacted biomass are described by European countries standards for solid biofuel. Density is the most important quality parameter of biomass compacting. The paper present results of common reeds particles compacting mechanism in closed die. Maximum pressure 212 MPa had been achieved in compacting. For compacting process evaluation has been determined pressing energy and density of briquettes. The minimum of density 0.87 g cm-3 have briquettes with particle size 12 – 13 mm, but maximum density 1.03 – 1.04 g cm-3 two particle sizes < 0.5 mm and 32 – 33 mm briquettes. Maximum value of energy consumption for compacting (~172 kJ kg-1) has been obtained for reed particle size 32 – 33 mm, minimum value (~53 kJ kg-1) for particle size less than 0.5 mm.