GB920681A - Removal of hydrogen sulphide from gases - Google Patents

Abstract

Hydrogen sulphide is extracted from a gaseous mixture (e.g coal gas or coke-oven gas) by contacting the mixture with iron oxide disposed in a plurality of containers through which the mixture is passed in sequence, the order in which the mixture passes through the containers being changed at intervals so that the mixture always enters first into a container wherein the iron oxide has suffered no substantial reduction (preferably not more than 10%) in its ability to combine with and remove the hydrogen sulphide from the mixture. The interval between changes in sequence may be 1/3 -8 hrs., preferably 4 hrs. or less, while the number of containers in the sequence may be 6-12. The iron oxide is converted by the hydrogen sulphide to ferric sulphide but, if oxygen (e.g. in the form of air) is introduced with the gases entering the first or second container in the sequence, reaction takes place between the ferric sulphide and the oxygen to reproduce ferric oxide and to form elementary sulphur. The iron oxide charge in the containers may contain, in addition to the oxide, sawdust and possibly some sodium carbonate, this mixture being moistened to a predetermined level. Initially, fresh iron oxide may be employed in the containers, but this may be replaced at intervals with a mixture of fresh and partly spent oxide. If desired, the direction of flow of gas through the containers may be changed at intervals. According to a modification of the process, the order of the sequence is changed at intervals so that each container takes the first position in turn and the direction of flow of gas through the containers is reversed at intervals, it being arranged that the intervals between changes in the order of sequence and between reversing the direction of flow of the gas are such that the average water content of the iron oxide in each of the containers in the sequence does not fall substantially below its initial value. Usually the initial water content of the iron oxide is of the order of 35%. However, it may be desirable for the final water content of the oxide to be of the order of 10% or less, in which case the water content may be allowed to fall gradually over the latter portion of the active life of the oxide. Apparatus for carrying out the process of the invention is described.