The kinetic model of wood pyrolysis under pressure is discussed in the present paper taking into account the diffusion of the resulting gas-phase products (i.e. heavy hydrocarbons) and their decomposition reactions. This model is based on a simplified mechanism of wood pyrolysis, including two parallel chemical reactions, viz. the primary decomposition reaction of  wood biomass with the formation of solid and gaseous components and the thermal decomposition reaction in the biomass pores of hydrocarbons formed in the primary process. The model takes into account the diffusion processes of the primary pyrolysis products from the resulting pores and thermal decomposition in the pores of these products. Based on the developed model, a computer program for calculating the main parameters of the pyrolysis process under pressure was created and the mass yield of solid pyrolysis products under various conditions was calculated. The calculation took into account the main parameters that affect the yield of solid wood biomass products, viz. temperature and pyrolysis pressure, particle sizes, porosity, etc. The calculations demonstrated that the increase of the pressure at which the pyrolysis of wood biomass is carried out causes an increase of the formation of the amount of solid products, which corresponds to the available experimental data. It was established that at a pressure of 1 atm when a sample size is of 0.025 m, the maximum yield of solid products is observed at the temperature of 600 °C. As the pressure increases the maximum yield increases, while the temperature at which the maximum is reached decreases. So, at a pressure of 10 atm when a particle size is of 0.025 m, the maximum yield of solid products is observed at the temperature of about 500 °C, and it is higher than that at 1 atm by 1.18 times. It was also determined that the temperature of the maximum yield of charcoal decreases with increasing sizes of pyrolyzable samples. Thus, when a sample size is of 0.5 m, this temperature is about 400 °C at 10 atm.

ВЛИЯНИЕ ДАВЛЕНИЯ ГАЗОВОЙ СРЕДЫ НА ОБРАЗОВАНИЕ ДРЕВЕСНОГО УГЛЯ В ПРОЦЕССЕ ПИРОЛИЗА РАСТИТЕЛЬНОЙ БИОМАССЫ Аннотация. Приводятся результаты экспериментального исследования влияния давления на образование древесного угля в процессе пиролиза древесины, осуществленного на лабораторном стенде при давлениях 1, 3, 5, 7 атм и температуре 400 °С. В качестве исходного сырья использована березовая древесина в виде щепы размером частиц 17 ç 8 ç 6 мм. Влажность сырья составляла 14,2 мас.%, плотность-506,4 кг/м 3 , зольность-0,23 мас.%. Установлено, что повышение давления от 1 до 7 атм приводит к увеличению выхода древесного угля от ~ 25 мас.% до ~ 32 мас.%. Содержание углерода при этом возрастает от 89,1 до 96,4 мас.%. Также экспериментально исследовано влияние искусственного ухудшения условий выхода летучих компонентов парогазовой смеси из реакционной зоны на образование древесного угля и содержание углерода. Полученные данные позволяют предположить, что ухудшение условия выхода из реакционной зоны летучих компонентов приводит к их разложению с образованием углерода, отлагающегося в порах пиролизуемого материала и на его внешней поверхности. Представлены экспериментальные данные, свидетельствующие о том, что компоненты пиролизной смолы разлагаются в присутствии древесного угля с отложением образующегося углерода на его поверхности. На протекание этого процесса указывает различие в массах одинаковых образцов древесного угля, выдерживаемых при температуре 600 °С при отсутствии и наличии пиролизной смолы: конечная масса образца, выдерживаемого в присутствии пиролизной смолы, превышает массу образца, выдерживаемого при ее отсутствии. Эти результаты дают косвенное доказательство правильности предположения о разложении компонентов пиролизной смолы в порах и на поверхности пиролизуемого материала при задержке выхода продуктов пиролиза из реакционной зоны. Результаты настоящего исследования представляют интерес для специалистов, разрабатывающих пиролизное оборудование. Ключевые слова: пиролиз, давление, древесный уголь, содержание углерода, вторичные процессы Для цитирования: Влияние давления газовой среды на образование древесного угля в процессе пиролиза растительной биомассы / С. В. Василевич [и др.] // Вес. Нац. акад. навук Беларусі.

The paper describes methods for producing charcoal (highly porous carbon materials) based on plant (wood) raw materials, and the equipment used to implement these processes, the use of activated carbons. The paper describes results of an experimental study of the effect of pressure on the formation of charcoal in the pyrolysis of birch chips. The experimental investigation was carried out at pressures of 0.1, 0.3, 0.5, 0.7 MPa. To investigate the effect of pressure on the pyrolysis process, a laboratory bench was designed and constructed. It was found that increasing the pressure from 0.1 MPa to 0.7 MPa increases the yield of charcoal from 25.1 to 32.4% by weight (relative to the dry weight of the starting material) and the carbon content from 89.1% by weight at 0.1 MPa to 96.4% by weight at 0.7 MPa. The calorific value of charcoal decreases from 34.86 MJ/kg at a pressure of 0.1 MPa to 30.23 MJ/kg at a pressure of 0.7 MPa. This is due to the release of oxygen-containing components, which have a higher calorific value than pure carbon, from the porous coal structure. Reduction of the charcoal heat combustion with a decrease in the amount of oxygen-containing components confirms conclusion that their calorific value exceeds the calorific value of pure carbon.

The paper discusses the results of an experimental study of the thermal decomposition of pyrolytic wood tar in a homogeneous process, as well as in the presence of a number of mineral substances: potassium sulfate, magnesium sulfate, monopotassium phosphate and the mineral residue of the production of potassium salts. The experiments were carried out on a laboratory setup under isothermal conditions at temperatures of 300, 350, and 400 °C by two methods providing two-phase and three-phase contact with the catalyst, respectively. It has been established that the rate of decomposition of pyrolysis tar under the studied conditions obeys the laws described by the Avrami–Erofeev equation with a variable exponent n. The area of change of this indicator in various experiments includes values from 0.415 to 1.238. The mean n value calculated for all study options was 0.694 (95 % CI 0.605 to 0.783), and the median value was 0.639. It has been found that the decomposition rate of the pyrolysis tar increases when MOX particles, potassium sulfate, and magnesium sulfate are introduced into the reaction zone. No effect of monopotassium phosphate on the rate of decomposition of the pyrolysis tar was not found. It is shown that in the case of tailings of potassium salts production an increase in the rate of decomposition of pyrolysis tar is due to the catalytic effect of this substance. The most likely reason for the positive effect of potassium sulfate, as well as magnesium sulfate on the rate of decomposition of pyrolysis tar, is apparently also the catalytic effect of these substances. The Arrhenius parameters of the homogeneous process of thermal decomposition of the pyrolysis tar and the decomposition process in the presence of tailings of potassium salts production, as well as potassium and magnesium sulfates, were determined. According to the data obtained, the activation energy of the homogeneous process was 29.6 kJ/mol, and the pre-exponential factor was 3.15·101 min–1, respectively. The Arrhenius parameters of the decomposition of pyrolysis tar in the presence of tailings of potassium salts production, according to the data of the performed studies, were 23.0 kJ/mol and 1.82·101 min–1. The paper also determined the Arrhenius parameters of the decomposition of pyrolysis tar in the presence of K2SO4 and MgSO4. According to estimates, the activation energy in the presence of these substances was about 50–60 kJ/mol. The research results presented in the article can be used in the design of heat generating equipment, which includes a system for cleaning products of thermochemical conversion of vegetable raw materials.

A method is presented for obtaining activated carbons (highly porous carbon materials) based on plant (wood) raw materials using a developed and manufactured experimental setup, consisting of a steam generator, a superheater, a pyrolysis and activation chamber and a cooler with a heat exchanger with forced convection. The analysis of the features of chemical and physical activation of charcoal, obtained by pyrolysis of wood raw materials, is carried out, and a conclusion is made about the advantage of physical activation, based on the use of water vapor as an activating agent. A description of the results of experimental studies carried out using the developed installation is given. These results confirm the conclusions of other studies that excessive pressure increases the mass yield of solid products formed during the thermochemical conversion of plant biomass. It was found that an increase in pressure, at which pyrolysis occurs, leads to an increase in the carbon content in charcoal. So, with an increase in pressure at which pyrolysis was carried out, from 1 to 8 atm, the carbon content in charcoal increased from 88.3 to 93.7 wt.%. Data on the efficiency of physical activation of solid products of pyrolysis of woody biomass using water vapor are presented and a conclusion is made that this direction is promising in the development of the foundations for the production of highly porous carbon materials.