CFD analysis of municipal solid waste combustion using detailed chemical kinetic modelling
Nitrogen oxides (NO x ) emissions from the combustion of municipal solid waste (MSW) in waste-to-energy (WtE) facilities are receiving renewed attention to reduce their output further. While NO x emissions are currently 60% below allowed limits, further reductions will decrease the air pollution control (APC) system burden and reduce consumption of NH3. This work combines the incorporation of the GRI 3.0 mechanism as a detailed chemical kinetic model (DCKM) into a custom three-dimensional (3D) computational fluid dynamics (CFD) model fully to understand the NO x chemistry in the above-bed burnout zones. Specifically, thermal, prompt and fuel NO formation mechanisms were evaluated for the system and a parametric study was utilized to determine the effect of varying fuel nitrogen conversion intermediates between HCN, NH3 and NO directly. Simulation results indicate that the fuel nitrogen mechanism accounts for 92% of the total NO produced in the system with thermal and prompt mechanisms accounting for the remaining 8%. Results also show a 5% variation in final NO concentration between HCN and NH3 inlet conditions, demonstrating that the fuel nitrogen intermediate assumed is not significant. Furthermore, the conversion ratio of fuel nitrogen to NO was 0.33, revealing that the majority of fuel nitrogen forms N2.
Surrogate model for improved simulations of small-scale sludge incineration plants
Abstract Although various modelling approaches exist for the simulation of solid fuel combustion, no specific model has been developed for the accurate description of gas-phase combustion in small-scale combustion devices. This is particularly limiting in scenarios when volatile-rich, complex and incompletely described solid fuels such as sewage sludge are used. To address this issue, an accurate description of combustion from the fuel bed onwards is required as well as an improved description of emitted volatiles. This paper introduces an innovative surrogate-based combustion model that combines data on sludge devolatilisation and measured combustion characteristics to offer a new surrogate composition. The composition includes heavy hydrocarbon species to accurately describe combustion evolution. A sensitivity analysis revealed that H2 contributes significantly to combustion evolution, while the most robust surrogate composition is obtained when ethanol is used as a leading representative of heavier hydrocarbons. The model can be used to produce suitable surrogates for the main sludge combustion interval, offering the required improvement in fuel descriptions and accuracy of simulations in the vicinity of the fuel bed. Hence, this model is particularly suitable for the optimisation of temperature, heat release rate, and concentration field in combustion chambers with limited volumes.
Techno-economic analysis of chemical looping combustion with humid air turbine power cycle
Abstract Power generation from fossil fuel-fired power plant is the largest single source of CO2 emission. CO2 emission contributes to climate change. On the other hand, renewable energy is hindered by complex constraints in dealing with large scale application and high price. Power generation from fossil fuels with CO2 capture is therefore necessary to meet the increasing energy demand, and reduce the emission of CO2. This paper presents a process simulation and economic analysis of the chemical looping combustion (CLC) integrated with humid air turbine (HAT) cycle for natural gas-fired power plant with CO2 capture. The study shows that the CLC–HAT including CO2 capture has a thermal efficiency of 57% at oxidizing temperature of 1200 °C and reducer inlet temperature of 530 °C. The economic evaluation shows that the 50 MWth plant with a projected lifetime of 30 years will have a payback period of 7 years and 6 years for conventional HAT and CLC–HAT cycles respectively. The analysis indicates that CLC–HAT process has a high potential to be commercialised.