GB807885A - Improvements in and relating to chemical processes - Google Patents

Abstract

In a chemical process in which fluids are required to be compressed for use and circulation therein, and from which residual gases, at pressure higher than atmospheric, are exhausted by passing them through one or more gas turbines driving machines for compressing and circulating fluids to provide at least part of the energy required, the one or more gas turbines are adapted to be supplied with operating gas from at least one freepiston gas generator, for starting the process and for providing the balance of energy subsequently required. In the oxidation of ammonia at 2-10 atmospheres, air at 20 DEG C. and 75 per cent saturated enters compressor 3 through filter 4 and passes to mixer 11. Liquid ammonia enters evaporator 6 at 6a and the gas is raised to 100 DEG C. in lowpressure steam preheater 8 and filtered in 9 before entering mixer 11. The gas mixture passes through filter 12, through platinum-rhodium catalyst gauzes 15 in converter/cooler 13, and immediately through water cooling tubes to reduce the temperature from 825 DEG C. to 250 DEG C. The cooling water is fed through feed water heater 25 to steam and water drum 16, whence steam at 205 DEG C. is withdrawn through 16c. The cooled mixture, with air from compressor 3 added through pipe 21, passes through oxidation vessel 23, residual gas reheater 24 and feed water heater 25 to cooler condenser 26 at 120 DEG C. Water is condensed in 26, which has earthenware packing 27, 28, and unpacked oxidation spaces 29, 30, and weak HNO3 formed is recycled through pump 40 and cooler 41 to the top of 26. Part of the recycled HNO3 is passed through heating coil 42b of the ammonia evaporator and part into absorption <PICT:0807885/III/1> tower 31 at 44. The gas mixture at 41 DEG C. passes to absorption tower 31 and is washed with cooled condensate or water treated to remove mineral impurities from 33 to absorb nitrogen oxides. The HNO3 (60 per cent) is withdrawn to earthenware packed bleacher 36 down which it passes countercurrent to air from compressor 3 and pipe 37. The HNO3 is removed at 39 and the air passes into the gases passing to the absorber. The residual gases from 31 flow through heater 24 and at 105 DEG C. to intermediate stage of multi-stage gas turbine 2, which drives compressor 3. The main portion of operating gases for the turbine are supplied from free-piston gas generator 1 and gas receiver 1a and the turbine is exhausted through stack 47. It is stated that temperature, or pressure, or both of the residual gases may be adjusted before use in the turbine, and the residual gases may heat exchange with the gases from the free-piston gas generator in place of, or in addition to, exchange with the process gases.