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Thermodynamic Assessment of Heat Recovery from a Fluidized-Bed Ventilation Air Methane Abatement Unit

Nadaraju, Francis J., Maddocks, Andrew R., Zanganeh, Jafar, Moghtaderi, Behdad
Energy & fuels 2018 v.32 no.4 pp. 4579-4585
air, carbon dioxide, coal, computer software, emissions, energy, fluidized beds, global warming, greenhouse gases, heat recovery, methane, mining, power generation, temperature, trapping
Methane, a greenhouse gas, is the second largest contributor to global warming after carbon dioxide and is 25 times more effective at trapping heat in the atmosphere than carbon dioxide. In 2015, fugitive emissions of methane from Australian underground coal mines were reported at 25 million tonnes of carbon dioxide equivalent. Ventilation air methane (VAM) is present in low concentrations (below 1.0 vol %), and its abatement and use as an energy source are a challenge for the coal mining industry. This paper examines the recovery of heat from a fluidized-bed VAM abatement unit and utilization in power generation via the Brayton cycle. The objective of the study was to determine the minimum methane concentration required to maintain autothermal operations and produce sufficient power to operate a fluidized-bed plant without supplementary power or fuel. Four configurations were studied and simulated using Aspen Plus software. For direct heat recovery, the minimum methane concentration increased with an increase in both the reactor outlet temperature and compressor outlet pressure. The minimum methane concentration for the indirect heat recovery configurations decreased when both the reactor outlet temperature and compressor outlet pressure increased. For all configurations, the minimum methane concentration was limited by the maximum reactor inlet temperature of 600 °C (to prevent autoignition of methane upstream of the reactor).