Design and Control of the Dry Methane Reforming Process

The much lower cost of natural gas and the desire to reduce carbon dioxide emissions have stimulated interest in the dry methane reforming process in which these two gases react to produce synthesis gas. The ratio of hydrogen to carbon monoxide in the resulting synthesis gas is close to unity, which makes it suitable for feeding to the Fischer-Tropsch process to produce liquid transportation fuel. The dry methane reforming reaction is favored by low pressure, but high pressure synthesis gas is required in the downstream process. Higher reactor pressures reduce compression costs of the synthesis gas. However, higher pressures also require a higher reactor temperature to achieve high methane conversion. When a maximum reactor temperature limitation is encountered, high methane conversion can be maintained by operating with a higher than stoichiometric CO2-to-CH4 ratio. But this means an excess of carbon dioxide must be fed to the reactor and subsequently recycled, which imposes additional compression costs. These competing effects produce interesting design trade-offs, which are explored in this paper. The dynamic control of the process is also studied. The dominant issue is the modeling of the reactor, which is a fired furnace with combustion of fuel providing the endothermic heat of the syngas reaction. Dynamic modeling is achieved by using a tubular process reactor in which the heat flux is determined by the heat generated in a fuel-air combustion reactor.