Reducing carbon dioxide emissions when using methane-hydrogen fuel

Abstract

AIM. To determine optimal modes for methane decarbonization, as well as to assess CO2 emissions during subsequent combustion of the pyrolysis gas, including together with the natural gas in various ratios.METHODS. The processes of thermochemical conversion of methane into hydrogen and condensed carbon in a reactor with external heating of the walls were considered. The thermal energy required for gas pyrolysis is obtained by burning a mixture of air and part of the pyrolysis gas, which is free from solid carbon particles. When performing numerical studies of pyrolysis processes, a kinetic model of one-dimensional flow of the reacting mixture was used with an external supply of thermal energy through the walls of an axisymmetric channel (tubular reactor).RESULTS. The mechanism of chemical interaction during the thermal decomposition of methane was developed, taking into account the formation of condensed carbon in the temperature range from 1000 to 1200 °C. The main energy indicators and the composition of pyrolysis gas were determined at various values of the pyrolysis temperature and the degree of carbon conversion.CONCLUSION. Carbon dioxide emissions from the combustion of pyrolysis gas, including together with the natural gas, were assessed. When developing pyrolysis technologies and applying them on an industrial scale, it is advisable to use part of the resulting pyrolysis gas with a high hydrogen content to provide thermal energy for the processes of thermal decomposition of the feedstock. According to the calculations, the share of this part reaches ≈ 35% of the total amount of pyrolysis gas. This approach, as opposed to burning the natural gas for this purpose, significantly reduces CO2 emissions. The combustion of the resulting pyrolysis gas, even without removing residual hydrocarbons, is characterized by currently quite acceptable CO2 emission factors of ≈ 7-25 t CO2/TJ.