Development and analysis of a mathematical model of methanogenesis during thermal destruction of organic matter, taking into account inhibiting additives

THE RELEVANCE. Peat is a promising renewable energy source; however, its thermal processing is associated with unstable combustible gas emissions and the risk of uncontrolled oxidation. Furthermore, drained peat lands serve as a source of greenhouse gases (methane, carbon dioxide), requiring the development of methods for controlling the gas evolution process. THE

Purpose

To develop and numerically implement a mathematical model of peat thermal decomposition that takes into account biological methanogenesis, the death of methanogenic bacteria, the pyrolysis stages, and the introduction of an inhibitor to suppress undesirable oxidation reactions.

Methods

The model is based on a system of differential equations for heat and mass transfer in a two-temperature porous medium. Pyrolysis kinetics are described using the Friedman method and the Kissinger equation. A modified Arrhenius equation and the Gompertz sigmoidal model are used to describe the biological stage. Experimental verification was carried out on peat samples from the Lyuk-Kolen-Egan deposit, determining moisture content, ash content, and mass loss upon heating to 800°C.

Results

The temperature ranges of the main stages were determined: drying (20-150°C), bacterial death and methane release (70-110°C), decomposition of hemicellulose and cellulose (200-450°C), and coke carbonization (>500°C). The introduction of an inhibitor at 300°C helps suppress oxidation, which is confirmed by stabilization of the kinetic parameters. The discrepancy between the calculated and experimental data for mass loss does not exceed 5%.

Conclusion

The developed model adequately describes the process of thermal destruction of peat and can be used to optimize pyrolysis modes in order to increase the yield of combustible gases and reduce greenhouse gas emissions.