Coal power will continue to be a cornerstone of the world energy system for the foreseeable future. However, additional measures are needed to minimize CO2 emissions from the power generation sector by employing new technologies including clean coal, biomass co-firing at a higher rate and carbon capture and storage (CCS). This paper presents a review of the opportunities and challenges surrounding the development of computational fluid dynamics (CFD) models for coal/biomass combustion, and discusses the historical and recent advances in specific areas relating to the modelling of char oxidation, radiative heat transfer, pollutant formation, ash problems, and the impact of turbulence, combustion kinetics and transient calculations. This review also provides a coherent near-term and long-term specific CFD sub-models development strategy and a discussion on the integration of CFD into power plant process modelling for efficient and more accurate simulations of heat transfer and pollutant emissions for a safe, flexible and efficient operation of future power generation systems.

Oxy-coal combustion is one of the leading technologies for carbon capture and storage. This paper presents a review of the opportunities and challenges surrounding the development of oxy-coal combustion models and discusses historical and recent advances in specific areas related to computational fluid dynamics (CFD), including char oxidation, radiation, pollutant formation and removal (Hg, NOx and SOx), and the impact of turbulence. CFD can be used to assess and optimise full-scale retrofit designs and to provide data on matching air-fired heat duties. In addition, CFD can also be used to improve combustion efficiency and identify potential reductions in corrosion, slagging, fouling and trace pollutant emissions. Transient simulations are becoming more computationally affordable for coal combustion, providing opportunities for model development. High concentrations of CO2 and H2O in oxy-coal can influence chemical kinetic rates, burnout and ash properties. The modelling can be improved by incorporating detailed kinetic mechanisms of gasification reactions. In addition, pollutant formation and removal mechanisms must be understood during oxy-coal firing to aid the selection of flue-gas cleaning strategies. Radiative heat transfer using spectral models for gaseous properties may be necessary in oxy-coal modelling because CO2 and H2O molecules have strong emission bands. Finally this review provides a coherent near-term and long-term oxy-coal specific CFD sub-models development strategy to simulate the complex oxy-coal combustion processes, heat transfer and pollutant emissions in power generation systems.

Oxygen enriched combustion of coal under different oxidant concentrations and staging levels has been performed in a 20kW down fired pilot scale combustion test facility. The introduction of oxygen resulted in additional reduction of NO emissions as compared to simple air staged configuration. In comparison to air staged combustion, oxygen enriched air staged combustion at the 31% level of staging resulted in approximately 7%, 20% and 35% NO reduction for 28%, 30% and 35% overall oxygen concentration, respectively. Experimental evidence has also indicated that oxygen enrichment does appear to reduce NO levels along with improvement of carbon burnouts. The provision of oxygen has also resulted in operation of the test facility under lowered stoichiometric ratios. The advantages attributable to oxygen enriched combustion also included enrichment of CO2 concentration in the flue gas to reduce the cost of CO2 scrubbing and capture. The present work provides data associated to oxygen enriched combustion technology, which can be considered a compromise between conventional air-firing combustion and the emerging oxy-fuel combustion systems.

Large eddy simulations (LES) are used in a CFD model to simulate air- and oxy-fired pulverised coal combustion in a 0.5MWth combustion test facility. Simulations are carried out using two different burners, namely, a triple-staged low-NOx wall fired burner and an IFRF Aerodynamically Air-Staged Burner (AASB). Non-gray radiation is considered in order to deal with the spectral nature of absorption and emission by high levels of combustion products in oxy-fuel combustion. Predictions using LES are compared with Reynolds-averaged Navier–Stokes (RANS) calculations using variants of the k-ε model for turbulence and against available experimental measurements. The results suggest that LES can offer improvements over RANS in predicting recirculation zones and flame properties of the pulverised combustion systems investigated. Flame flickering frequencies from the LES simulations are calculated and validated against available measurements. The work presented demonstrates the potential importance of using LES turbulence models for coal combustion.