Ventilation air methane (VAM) emissions are a significant contributor to fugitive greenhouse gas emissions at underground coal mines. The stone dust looping (SDL) process is a novel technology developed at The University of Newcastle, Australia, for VAM abatement. The SDL process is a cyclic process in which calcium oxide (CaO) is first obtained from the calcination of limestone (CaCO 3 ). CaO is then used to simultaneously oxidize VAM (methane concentrations of 0.1− 1 vol % in air) and capture carbon dioxide (CO 2 ) produced to form CaCO 3 . The two cycles can be performed in a single reactor, or the process can be performed continuously in dual interconnected reactors. Preliminary experiments on the SDL process have previously been performed at laboratory scale. In this study, further laboratory-scale studies were conducted in conjunction with pilot-scale SDL investigations in a single 1 m 3 /s fluidized bed reactor. The effect of inventory size (1−2 tonnes of CaCO 3 ), operating temperature (565−700 °C), and flow rate (1−1.7 m 3 /s) on methane conversion was investigated. At temperatures of 600 °C and above, >99.5% methane conversion was achieved for all inventory sizes and flow rates examined. At temperatures of 565 and 575 °C, 41 and 70% methane conversions were achieved, respectively. VAM fluctuation experiments were performed, and it was shown that a fluid bed can act as a thermal mass to reduce fluctuations in the bed temperature as the VAM concentration changes.
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).
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