Impact of differences in combustion conditions of rape straw on the amount of flue gases and fly ash properties
Czech University of Life Sciences Prague, Faculty of Engineering, Department of Technological Equipment of Buildings, Kamýcká 129, CZ165 21 Prague, Czech Republic
The rising trend of biomass energy usage as a renewable energy source raises issues with combustion waste products, mostly bottom ash and its potential for further use. Rape straw was selected as a fuel sample for experiments because of the fact, that this crop figures among the 10 most important crops in the world and its straw is frequently used as a source of renewable energy. The rape straw was processed in pelletizing line LSP 1800 of the company ATEA PRAHA Ltd. into pellets with diameter of 8 mm and length 15 to 30 mm. Composition of bottom ash arising during the energy utilization of biomass is primarily dependent on the composition of input raw material and next on the combustion technology. Therefore, the aim of this article is to clarify the influence of excess air amount on the composition of end products in combustion of rape straw pellets in three combustion modes (low, optimal and high excess air).
The last part of study were combustion tests and measurements on a laboratory hot-air stove – KNP from the company KOVO NOVAK. Excess air coefficient values ranged between 3.31 and 6.77. The average net calorific value of the original rape straw sample was about 15.95 MJ kg-1. Input raw material may not have always been completely combusted in the device, and therefore the ash could contain elevated amounts of hazardous elements. These substances are a limiting factor for application of the ash into soil. Overall, ash from biomass not only offers a wide range of potential applications thanks to its physical and chemical properties, but also returns some of the nutrients back to the soil closing the nutrient cycle and reducing the landfill of such material. And last but not least it enables cost reduction in agricultural production spent on mineral fertilizers.