Modelling and Simulation of Solid Particle Combustion
Overview
Increasing the worldwide energy demand will require the operation of conventional power plants in the next decades until technical development enables the supply mainly by renewable sources at minimum emissions. Therefore, optimizing the existing power plants in order to achieve high efficiency and low pollutant emissions is necessary.
Based on the reports of the international energy agency, coal remains firmly in place as the largest source of power with a share of 38% of the overall power generation [1]. To reduce CO2 emissions from coal fired power plants, carbon capture and storage (CCS) techniques can be applied. Oxy-fuel combustion is one of the most promising approaches for CCS to sequestrate and reduce CO2 emissions from coal combustion. Another option for reducing CO2 emissions that is applicable to the conventional coal fired powerplants is to use alternative solid fuels such as biomasses. Using biomasses coupled with oxyfuel combustion can even lead to negative CO2 emissions which can be a promising solution for carbon capture. However, to develop oxy-fuel technology in solid combustion, computational modeling of solid combustion under oxy-fuel condition is indispensable to improve our understanding of the underlying physical processes.
For simulating a solid fuel-powered powerplant in large scales, understanding the physics of solid fuels combustion in particle scale is necessary. Since solid fuel combustion is a transient and multiphase phenomenon, simulations require detailed models to describe the behavior of these fuels under combustion conditions. The aim of our research team is to study this transient behavior in different conditions and provide accurate models for improving the large scales application. Therefore, modelling the combustion of single solid particles and jets streams in both laminar and turbulent conditions are the focus of this project.
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Methods
Mass, momentum, and energy transfers between a solid particle and its surrounding gas can be either particle-resolved or modeled by an Euler-Lagrange approach or the point particle approximation. In the particle-resolved approach, the particle-gas interface and the boundary layer are chemically and spatially resolved. In the point-particle approximation or Euler-Lagrange approach, particles are tracked as Lagrangian points and the exchange of the mass, momentum, and energy between the gas phase and particles correspond to source terms in the conservation equations. The Euler-Lagrange models are typically used for system scale simulations that are used for relevant applications like furnaces.
The transient behavior in solid particles includes different stages of combustion. By exposing to external energy in high temperatures, because of bond breaking in its internal structure, the particle loses part of its mass by releasing volatile gas species to its surrounding, which react with the oxidizer and create a gas flame around the particle, which is called a volatile flame. After the devolatilization finishes, the remaining solid part in the particle, which is referred to as char, reacts via surface reactions with the surrounding gas. The surface reactions will completely burn the particle and non-reactive ash matter is produced [2,3].
Single particle combustion [2]
This combustion behavior is affected by the particle-particle interactions in jets or streams and leads to change in the ignition time, combustion duration, and the shape of the flame [3,4].
Particle jet combustion [4]
References
[1] IEA (2018), Coal 2018, IEA, Paris www.iea.org/reports/coal-2018
[2] S. Farazi, A. Attili, S. Kang, H. Pitsch, Numerical study of coal particle ignition in air and oxy-atmosphere, Proceedings of the Combustion Institute 37 (2019) 2867–2874.
[3] S. Farazi, J. Hinrichs, M. Davidovic, T. Falkenstein, M. Bode, S. Kang, A. Attili, H. Pitsch, numerical investigation of coal particle stream ignition in oxy-atmosphere, Fuel 241 (2019) 477-487.
[4] P. Farmand, C. Schumann, A. Attili, H. Pitsch , Direct numerical simulation of solid fuel ignition and combustion in laminar and turbulent conditions, 3rd Oxyflame International Workshop (2020)