GB349238A - A process for producing sulphuric acid from waste gases containing hydrogen sulphide and carbonic acid - Google Patents

Abstract

A process for producing sulphuric acid from gases containing very diluted hydrogen sulphide mixed with inert gases such as carbonic acid, particularly waste gases from ammonia saturators, comprises converting the hydrogen sulphide with air in an indirectly heated furnace into sulphur dioxide, drying the gases first by indirect cooling and then with sulphuric acid, adding a considerable excess, such as two to three times the theoretical amount, or dried air, oxidizing to sulphur trioxide in a contact furnace, and absorbing the sulphur trioxide by the sulphuric acid used in the drying <PICT:0349238/III/1> <PICT:0349238/III/2> process and circulating in a cyclic path. Air produced by the Linde process or oxygen may be used in place of atmospheric air and the process may be carried out at ordinary, increased, or reduced pressure. Hydrogen sulphide gases and air are mixed in a vessel 1 and pass into an indirectly heated furnace 6 filled with bauxite, thence through an indirect cooler 9 into a vessel 13, sulphuric acid being sprayed from the pipe 17 with nozzle 16. Additional sulphuric is supplied from a container 27 when required and condensate from the cooler 9 can be introduced by a pipe 20. The dried gas mixed with air introduced by a pipe 24 and dried by the acid in the vessel 13 passes to a contact furnace 23 filled with platinized asbestos and maintained at 400-450 DEG C. The SO3-containing gas passes to a second absorption vessel 31 containing sulphuric acid and having a nozzle 37 for spraying acid from the tank 27 or the collecting vessel 34. The gas is then led out through a pipe 48 having a suction device 49. Other suction devices may be inserted in the pipe 22 or elsewhere. The vessels 13, 31 may be connected in parallel, the gas passing from furnace 6 to one vessel, then through furnace 23 to the other, an air supply pipe being supplied for vessel 31. The acid level is maintained constant in the collector 34 and gas only led to it when one of the vessels 13, 31 is to be cleaned or repaired. An additional cooler may be arranged between the furnace 23 and the following absorption vessel. Ammonia, pyridine, or other nitrogen compounds may be removed from the H2S gases by warm sulphuric acid, preferably before burning. If atmospheric oxygen is used in the combustion, a temperature of at least about 700 DEG C. is maintained in the furnace, to prevent formation of nitrogen oxides, by adjusting the air input. The combustion products may be used to preheat the initial gas and air. The combustion tube may comprise two parts, the first heated externally and the second embedded in a heat insulating material, so that the heat can be cut off as soon as the required temperature is obtained. The sulphur trioxide furnace may be gas heated, the flue gases from the burners 58, 59 passing by pipes 64 to the lowest chamber of a preheater 54. This comprises a number of superposed columns, each containing two chambers, each of which communicates by pipes 55 or 56 with the column below. The SO2-containing gases descend through one series of chambers, being preheated by flue gases ascending through the adjacent chambers. The reacting gases pass through heating tubes 62, arranged between the rows of burners, which tubes may be filled with a catalyst such as platinized asbestos. The tubes 64 are connected with a thermostat controlling the gas supply so that overheating of the reacting gases is prevented.