CHANGES IN THERMOPHYSICAL CHARACTERISTICS OF BIOMASS WITH DIFFERENT MINERALIZATION AMOUNT DURING ITS SLOW PYROLYSIS

Abstract

The work relevance is caused by the need to study the changes of biomass thermophysical characteristics in its thermal transformation in relation to the design of technological equipment and energy use. The main aim of the research is to study the thermophysical characteristics during slow pyrolysis of biomass with different mineralization amount. Objects: biomass resources with different amount of mineralization ­– straw (Ad=2,8 %), nonconforming wheat bran (Ad=6,9 %), lowland peat of the Sukhovsky deposit (Ad=22,8 %). Methods. Thermotechnical characteristics of biomass samples and their carbon residue are determined according to certified methods (GOST R 54186-2010 (EN 14774-1: 2009), GOST R 56881-2016 (E1755-01), GOST 11305-2013, 11306-2013, GOST 32990-2014 (EN 15148: 2009)); values of the calorific value were determined using the ABK-1 calorimeter (RET, Russia) in accordance with GOST 147-2013 (ISO 1928-2009); elemental analysis of organic part was carried out on a Vario Micro Cube (Elementar, Germany) device; thermal processing was carried out by differential thermal analysis and physical experiment; the thermophysical characteristics of the biomass and its carbon residue were measured by laser flash method using the thermal conductivity analyzer Discovery Laser Flash 1 (DLF-1); the true density was measured using an automatic gas pycnometer Ultrapyc-1200e (Quantachrome Instruments, USA); the carbon residue structure was studied by scanning microscopy VEGA 3 SBU electron microscope (TESCAN, Czech Republic). Results. Straw and bran pyrolysis proceeds in two stages, differing in the average rate of decomposition – (0,38…0,41) %·°C–1 and 0,09 %·°C–1 respectively. Peat decomposition occurs in the whole temperature range (220–500 °C) with an average decomposition rate of 0,11 %·°C–1. It was found that the thermal conductivity of carbon residue from straw and bran, which have a relatively low ash content for biomass, does not significantly change up to 400 °C, after which this value increases. The heat capacity of these samples increases with the temperature of their production to 300 °C, after which it sharply decreases. The carbon residue obtained at 500 °C has a higher heat capacity value compared to the residue obtained at 400 °C. These changes can be explained by decomposition of biomass organic part components – cellulose and lignin. The heat capacity and the thermal conductivity of sukhovsky peat carbon balance, have a high mineralization amount (Ad=22,8 %), decrease in all temperature range, due to the inorganic components share increase in result of organic part decomposition, which is confirmed by the solid phase density increase.

Keywords

• biomass
• pyrolysis
• thermophysical characteristics
• differential thermal analysis
• true values