The challenge of designing a Fischer-Tropsch reactor

Abstract

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.

The Fischer-Tropsch process converts synthesis gas, a mixture of carbon monoxide and hydrogen, to a spectrum of predominantly hydrocarbon products. The reaction is catalysed by cobalt, iron, nickel or ruthenium at elevated temperatures and pressures. In our studies of this system we developed a thermo-kinetic model of the reactor. One of the main challenges for the design of this type of reactor is the exothermicity of the reaction. Heat removal is critical to avoid catalyst deactivation and damage. To assess the heat removal it was therefore necessary to develop a descriptive model of the reactor. The overall process design we are developing is based on the results of an application of our process synthesis methodologies. These methods involved initially the definition and description of the fundamental processes taking place which are reaction and heat transfer. Thus in order to achieve an optimised design we needed to consider not only the reaction rate but also the rate of heat removal. Ideally, one would prefer a highly active catalyst to increase production per unit volume. However, the advantage of a highly active catalyst is offset by the necessity to equivalently enhance the heat removal to avoid damaging or destroying the catalyst. This requires the reactor designs to accommodate a trade-off between unit volume production rate and heat removal. This paper will address the issues involved in the thermodynamics, mass and heat transfer aspects of the Fischer-Tropsch reactor. This is further complicated by the high number of components and the multiple phases involved in the reactor. However due to the sensitivity of some information for commercial purposes in our research centre, relative values have been assigned to critical variables. This however does not compromise the quality of work.