GB1096313A - Ammonia converters - Google Patents

Abstract

<PICT:1096313/C1/1> In reacting a mixture of nitrogen and hydrogen in the presence of a catalyst to form ammonia, by utilizing an ammonia converter which comprises a pressure vessel containing a catalyst bed and a heat exchanger, and has a gas flow system equipped with a by-pass line so that gases may be introduced directly into the catalyst bed without passing through the heat exchanger, the by-pass line is fitted with a heater external to the pressure vessel so that on start up, gas heated in the external heater may be passed directly to the catalyst bed to bring it to reaction temperature, and subsequently the heater may be switched off or disconnected from the by-pass circuit when cool gas mixture may be passed through the same by-pass inlet directly to the catalyst bed so as to control its temperature. Preferably the external heater is heated by means of combustion products from a burner or by electrical means. In the Figure, pressure vessel 12 has lid 13 sealed with high-pressure seal 14. Catalyst basket 15 supported in vessel 12 by tube plate 16 resting on projection 17 has a domed cover 18 secured to the basket forming a chamber 20 and cooling tubes 21 extend through the catalyst bed and open at their upper end into the chamber 20. Bore 22 in the centre of cover 13 has sealed into it a pipe 23 carrying via branch 25 the main supply of nitrogen and hydrogen; a by-pass inlet 26 which extends through 23, 22 and the dome 18 into the chamber 20 connected at its upper end to branch 32; and a pyrometer sheath 33 containing several thermocouples. On start up, gas compressed by piston 41 is passed through valve 44, heated by heater 45 and passed directly to above the catalyst bed, to emerge from the bed via one side of heat exchanger 34 by-pass condensing system 35 by means of valve 52 and be recycled to valve 44 and heater 45; the cycle being continued until the operating temperature of 300-500 DEG C. is reached. The heater 45 is shut off and the main gas stream is passed via valve 49, branch 25 and pipe 23 to above the basket 15 when it circulates round the basket and enters heat exchanger 34 from the bottom. The gas is preheated in passing through 34 and through tubes 21. It then passes through the catalyst bed where it reacts, the reaction products leaving via the other side of exchanger 34 to condenser 35 where ammonia is condensed and removed via 38, the unreacted gases being recycled via line 40. The temperature of the catalyst bed is controlled by passing part of the main gas stream through valve 44 and pipe 26 directly to chamber 20 above the catalyst, and it may also be controlled by passing part of the main gas stream via valve 48 and line 46 directly to the ends of cooling tubes 21.