Thermodynamic optimisation and computational analysis of irreversibilities in a small-scale wood-fired circulating fluidised bed adiabatic combustor

Abstract

An analysis of irreversibilities generated due to combustion in an adiabatic combustor burning wood was conducted. This was done for a reactant mixture varying from a rich to a lean mixture. A non-adiabatic non-premixed combustion model of a numerical code was used to simulate the combustion process where the solid fuel was modelled by using the ultimate analysis data. The entropy generation rates due to the combustion and frictional pressure drop processes were computed to eventually arrive at the irreversibilities generated. It was found that the entropy generation rate due to frictional pressure drop was negligible when compared to that due to combustion. It was also found that a minimum in irreversibilities generated was achieved when the Air-Fuel mass ratio was 4.9, which corresponds to an equivalence ratio of 1.64, which are lower than the respective Air-Fuel mass ratio and equivalence ratio for complete combustion with theoretical amount of air of 8.02 and 1.

Minimum entropy generation due to heat transfer and fluid friction in a parabolic trough receiver with non-uniform heat flux at different rim angles and concentration ratios

“…Several researchers have applied the entropy generation minimisation method to the analysis and optimisation of engineering systems [8,22,23] as well as to heat transfer and fluid flow problems [24][25][26][27]. Moreover, the entropy generation minimisation method has been shown to be applicable to a wide range of engineering systems such as small-scale wood fired circulating fluidised bed adiabatic combustor as demonstrated in the study by Baloyi et al [28], analysis of exergy recovery from the exhaust cooling in a DI diesel engine as demonstrated by Ghazikhani et al [29] and in characterising the effects of fuel additives on exergy parameters of engines [30] and many others.…”

Gas-phase transport and entropy generation during transient combustion of single biomass particle in varying oxygen and nitrogen atmospheres

“…The effects of coal particle diameter, coal composition and the free stream gas phase temperature on temporal variations of process irreversibilities were investigated [33]. The exergetic behaviour of a small scale wood-fired fluidised bed burner under steady state was examined by Baloyi et al [34]. This study was primarily focused on the influences of air fuel ratio upon the irreversibility of an adiabatic combustor.…”

“…This study was primarily focused on the influences of air fuel ratio upon the irreversibility of an adiabatic combustor. The authors showed that there is an optimal air fuel ratio, which results in the minimisation of the entropy generation [34]. Further to the significant role of direct biomass combustion in the current and future energy systems, thermochemical conversion of biomass through gasification is becoming a key technology for syngas and hydrogen production [35] [36].…”

Exergy Analysis of Solid Fuel-Fired Heat and Power Plants: A Review

“…The generation of entropy occurs mainly in the combustion process, which prompted Baloyi et al [72] to examine the change in its rate as a function of the air to fuel (AF) ratio in an adiabatic combustor, using wood as the source of fuel. They showed that the entropy generation rate reaches a minimum at an AF of 4.9 and equivalence ratio of 1.64.…”