Kinetic modelling of a claus sulphur plant utilizing gas-fluidized bed reactors
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AbstractA kinetic model of a gas-fluidized bed Claus reactor has been developed using the Modified Bubble Assemblage Model of Mori and Wen, to predict whether equilibrium conversions could be approached. The model accounts for the effect of the grid region and gas-bypassing in the form of bubbles that grow in size as they rise through the bed. Using the reactor model, a two reactor gas-fluidized bed Claus sulphur plant was simulated. Operation of the downstream reactor is assumed to be at temperatures below the sulphur dewpoint. The upstream reactor operates at an elevated temperature to regenerate sulphur laden catalyst which is recycled from the downstream reactor. The simulation results predicted that a two reactor fluidized bed Claus plant is capable of achieving an overall recovery efficiency of 97.1%. This is the same as the recovery efficiency which is attainable with a conventional three stage fixed bed Claus plant, but considerably less than the overall equilibrium conversion efficiency of 99.45%. cs 2 conversion is predicted to be essentially complete. The results indicate that the effect of gas-bypassing, particularly in the downstream sub-dewpoint reactor, is significant in limiting the overall conversion capabilities of the process. The optimum process configuration for a fluidized bed Claus plant is a small diameter, high velocity (0.5 m/s) upstream reactor and a large diameter, low velocity (0.1 m/s) downstream reactor. This is in contrast to the uniform size reactors which are used in all three stages of a conventional fixed bed Claus plant. For a 200 tonne per day (sulphur inlet) fluidized bed Claus plant, the upstream reactor has a diameter of about 5 metres and a fluidized bed height of 1.6 metres. The downstream reactor has a diameter of about 10 metres and a fluidized bed height of 1.3 metres. Total reactor volume for the two reactor fluidized bed process is significantly less than for a conventional three stage fixed bed Claus plant of equivalent capacity. For a 200 t/d plant, the total catalyst required is 80 tonnes (15 tonnes in the upstream reactor and 65 tonnes in the downstream reactor), compared with 120 to 150 tonnes for a typical three stage fixed bed Claus plant. Overall pressure drop is 29 kPa which is about 25% less than that for a conventional Claus plant. Finally, the fluidized bed process offers the advantage of truly continuous operation below the sulphur dewpoint temperature, since catalyst can be readily circulated between reactors. Catalyst circulation rates are extremely low compared with the holdup volume of catalyst in each reactor. Catalyst residence times were calculated to be 6 and 27 hours in the upstream and downstream reactors respectively.
Bibliography: p. 54-57.
CitationBirkholz, R. K. (1986). Kinetic modelling of a claus sulphur plant utilizing gas-fluidized bed reactors (Unpublished master's thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/13823
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