Capturing energy from ventilation air methane a preliminary design for a new approach

Abstract

The greenhouse gas (GHG) radiative forcing factor of methane is often quoted as 23 times as potent as carbon dioxide on a 100-year time horizon; thus, any reduction in atmospheric methane would be globally beneficial. The capture or use of ventilation air methane (VAM) is challenging because it is a high volume low concentration methane source. This results in the routine discharge of methane into the atmosphere.A review of VAM mitigation technologies is provided and the main disadvantages of the existing technologies are discussed. In the proposed VamTurBurner© system, the heat from the combustion chamber is transferred to the preheating zone either by a heat exchanger or by redirecting the combustion products to mix with the ventilation air stream from a coalmine. Gas turbines (GT) are used to produce electricity with the exhaust gases directed to mix with the incoming ventilation airflow. The turbulence introduced by the GT exhaust assists with mixing of the incoming ventilation airflow and the return flow of combustion products from the combustion chamber. The combustion products are a source of heat, which increases the temperature of the incoming ventilation air to a value high enough for the methane to undergo flameless combustion upon encountering the igniters.The high temperature combustion products enter a multi-generation system. The multi-generation system is based on mature engineering technology such as heat exchangers and steam turbines. The residual heat provides additional heat based products such as industrial scale drying, chilling by an absorption chiller or simply hot water.The VamTurBurner© uses the energy from the GT, igniters and VAM to provide clean efficient energy while mitigating the atmospheric emissions of methane. The opportunity to collect carbon credits may improve the economics. Since the VAM is a free energy source, the output of the system is greater than the purchased energy.

The combustion mitigation of methane as a non-CO 2 greenhouse gas

“…Presently the availability of technology, combustion based or otherwise, to mitigate methane at the very low, but ubiquitous levels below 0.5%, without the use of an additional fuel is non-existent; thus, a forward focus on such technology would be of great benefit to the industry and provide a significant impact on the GHG emissions on a global scale [136]. There are two classes of combustion based systems in operation at present where the VAM is either used as a primary or secondary fuel.…”

“…When VAM is the primary fuel in systems such as lean-burn or recuperative gas turbines, thermal or catalytic flow reversal reactors and regenerative thermal oxidation, the VAM is the only required fuel except in cases where the systems requires start-up energy or the methane concentration falls below the design specifications [7,136]. When VAM is used as a secondary fuel a portion of the designed intake air is replaced with the air containing the VAM.…”

“…The burner design also needs to be optimised. The VamTurBurner© is a recently proposed methane mitigation system [130,136] for the mitigation of VAM. The principles of flameless combustion for lean premixed fuels are exploited, such that a lean fuel air mixture will ignite and undergo flameless combustion in the presence of an ignition source given an initial temperature that is reasonably close to the ignition temperature.…”

Numerical Investigations of the Influencing Factors on a Rotary Regenerator-Type Catalytic Combustion Reactor

“…However, not all the VAM is used to provide energy production in the TFRR and CFRR system, because some of the energy is stored directly by the reactor to attain autothermal operation. For TFRR and CFRR, the necessary amount of methane to sustain a reaction is 0.12% and 0.45%, respectively, and providing additional fuel or electrical heating is necessary on the conditions of lower VAM concentrations [10]. Moreover, how to use TFRR and CFRR to produce electricity continuously is an intractable problem, as the methane concentration is mutative overtime.…”

“…A system for the utilization and mitigation of VAM, named VamTurBurner©, was presented [10,14]. A gas turbine with natural gas as the fuel is used to produce electricity and preheat the incoming ventilation air directly to overcome the catalytic ignition temperature of methane.…”