Experimental measurements of straw drying using flue gases

In many European countries, notably in Poland, there is a significant demand for space heating. This could be largely satisfied by biomass, primarily in rural areas, where biomass is locally available, mainly as agricultural residues. In Poland, this is mainly straw, which is often burnt uselessly in the fields, although it may become an environment friendly fuel for heating the rural holdings, if burnt in dedicated biomass boilers. One of the main problems of the energy use of biomass is the bulk density as well as the calorific value. One of the most important factors influencing the biomass calorific value is humidity. The higher humidity of the biomass, the lower the calorific value. It should be mentioned that there is a lower and upper limit of humidity, which should not be exceeded in energy use of biomass. This has a negative effect on the biomass combustion process and biomass boiler construction elements. This paper presents experimental results of the heat and mass transfer in a round bale of straw during straw drying in three different configurations. The experimental measurements were made in a specialized stand of straw driers. Flue gasses from straw combustion in biomass boiler were used as a drying agent. Measurements were made of the humidity and temperature inside the cylindrical straw bale during the drying process. Moreover, the temperature, humidity and flow of the drying agent were measured. In addition, a thermographic analysis of the straw bale surface was made to determine the best method of straw drying in the form of round bales. Finally, the best configuration of straw drying was chosen. It is possible to get a better fuel in a very short time and more energy production during straw combustion in biomass boilers.