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Low temperature Claus reactor studies Besher, Elmarghani M.


A small-scale fluidized bed reactor (0.1m ID, 0.86m high) was used to carry out the Claus reaction 2H₂S + SO₂ ⇌3/X Sx + 2H₂O at low temperatures (100 to 150°C) where elemental sulphur condensed on the catalyst particles (Kaiser alumina S-501, 195µm mean particle size). The experimental apparatus was similar to that described by Bonsu and Meisen (1985). The feed gas consisted of pure nitrogen mixed with H₂S and SO₂ in the ratio of 2 to 1. The H₂S concentration was varied from 200 to 1300 ppm. The feed gas flow rate ranged from approximately 1.4 to 5.6 m³/h. The corresponding U/Umf ranges were approximately 2.2 to 8.8. The bed heights varied from 0.12 to 0.38m. It was found that the experimental conversion efficiencies ranged from 60 to 96% and that they were less than those predicted thermodynamically. The conversion efficiency was found to increase with H₂S concentration and catalyst bed height; it decreased with gas flow rate. Contrary to thermodynamic predictions, the conversion efficiency increased with temperature. These results suggest that thermodynamic equilibrium was not achieved in the reactor. The decline in conversion due to catalyst fouling was measured as a function of catalyst sulphur content. The experimental results could be interpreted by means of a bubbling bed model. New analytical expressions for predicting the overall conversion and the concentration profiles were developed for reactions of order n. For the Claus reaction, where n=1.5, good agreement was found between the model predictions and experimental values. The model properly discribed the observed behavior resulting from changes in feed concentration, bed temperature, U/Umf and static bed height. The bubbling bed model was used to predict the effect of particle size on conversion for various operating gas velocities and bed dimensions. The model predictions showed that the canversion improved with decreasing particle size and that the improvement depended on U/Umf. The bubbling bed model was modified for conditions where condensed sulphur fouled the catalyst. A catalyst deactivation function, derived from first principles and based on catalyst sulphur content, was incorporated into the rate expression. The modified model predicted the the experimental measurements well and conclusions are drawn regarding the continuous operation of fluidized bed Claus reactor operating under sulphur condensing conditions. A general procedure is presented to demonstrate the applicability of the bubbling bed model in the design of large scale reactors; examples for specific conditions are given. Attrition tests were performed on the catalyst at U/Umf=5.1 and room temperatures. It was found that most of the attrition occurred in the first few hours when the catalyst particles were rough. The overall test results indicated that attrition of the catalyst was negligibly small thereby suggesting the suitability of the Kaiser S-501 catalyst for long term use in fluidized bed Claus reactors.

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