Impact of Natural Binder on Pellet Quality

Production of energy pellets from waste straw is a good way to manage the straw surplus and to increase profitability of the agricultural enterprises. The present paper covers the results of the tests of the hardness of pellet made from a mixture of rape straw with an addition of wheat flour as a natural binder. The samples of raw material for the production of pellet included 0.0%, 4.1% and 7.8 % of wheat flour, which was determined according to dry matter. The average relative humidity of the raw material samples was: 11.6 %, 22.3% and 30.7%. The measurement of the pellet hardness was performed with the aid of the Kahl method. The influence was found of wheat flour contents and the relative humidity of the mixture on the increased hardness of pellet. INTRODUCTION The management of straw resources is an important problem for farms. In the sustainable agriculture, the part of the straw can be plowed after harvesting, thereby enriching the humus layer of the soil. The remaining part can be converted into fuel pellets for boilers. Instead of purchase fuel, for example coal, farmers can produce own fuel, improving this way farms economic performance and at the same time producing source of "green energy". In the recent years, the production and use of pellet from biomass as a fuel has considerably increased. Those boilers with maintenance-free mechanical fuel supply and automatic ignition which are used for its combustion, and which offer the possibility of continuous heating work, require good quality fuel granulate. These requirements are related not only to its thermochemical properties but also to mechanical properties. Fuel granulate needs to be durable and it should not suffer from damage during transport, handling and storing. The problem of the quality of fuel pellet is particularly important when it is used in boilers in individual heating of flats because large heating plants have considerably more advanced systems of fuel supply and process control. To improve the mechanical properties of pellet, apart from the selection of technical parameters for the pelletisation process, binding agents are used that increase pellet hardness (e.g., Obernberger & Thek, 2004; Razuan et al., 2011; Emadi et al., 2017). Pellet additions can also be used to improve its combustible properties (e.g., Chyc, 2012, Tarasov et al., 2013). Many types of materials which can be used to bind biomass together in energy pellet are commonly used in feed industry as the elements of granulate for livestocks. They perform there nutritional functions, but they also act as binders and enhance the structure of pellet (e.g., Gehring et al., 2009; Obidziński & Hejft, 2012). An excess of straw from agricultural production is a favorable factor for its use as a raw material in the production of pellet biofuel. For this reason, research is conducted to invent formulae for good quality energy pellet from this raw material (e.g., Döring, 2013; Lu et al., 2014). The purpose of the research was the strength assessment of pellet from rape straw that is made solely from straw with an addition of wheat flour, with different humidity degrees of the of raw material and with various contents of flour.