GB695812A - Improvements in or relating to methods and apparatus for the recovery of condensableconstituents from hot gaseous mixtures - Google Patents

Abstract

<PICT:0695812/III/1> <PICT:0695812/III/2> <PICT:0695812/III/3> In the removal of a condensable constituent, e.g. water vapour, from a hot gaseous mixture, the gas is conducted along a confined course and is contacted countercurrently at two separate points with different sectors of a circulating stream of a solid granular adsorbent for the constituent in a manner forming a sequence of shallow, fluidized beds, the hot gas mixture being cooled at a third point, intermediate of the two separate points along its confined course. As applied to the drying of hot combustion gases in the isolation of nitrogen oxides from the combustion gases of a nitrogen fixation furnace, the gases are passed in countercurrent to a solid drying agent, e.g. silica gel, in tower 21, then through cooled catalyst chambers 131, 132 where nitric oxide is oxidized to nitrogen dioxide and finally in countercurrent to a solid adsorbent for the nitrogen dioxide, e.g. silica or titania gel or carbon, in tower 140. The tower 21 is divided into three processing chambers, viz. a drying chamber 24, a desorbing chamber 25 and an adsorbent cooling chamber 26, the chambers being separated by valve mechanism 28 (Fig. 3) which is adapted to pass solids but prevent admixture of gases between the chambers. Solids enter the tower at 39 from hopper 38 and leave at 41 when they are recirculated to the hopper by airlift circuit 44. The chambers are divided into compartments by perforated plates 30 on which shallow fluidized beds are formed, the adsorbent moving from one compartment to the next below through downspouts 32 which are provided with closure means 34 (Fig. 3) adapted to open under a certain weight of adsorbent. The hot combustion gases enter chamber 25 at 20 wherein they strip the adsorbent of moisture and leave the chamber at 77. They are then passed through the upper chamber 79 of a tower 80 where they are showered with cooling liquid, e.g. water or brine. The cooling water is gas-cooled in lower chamber 88 and recirculated to the upper chamber through line 98. Cooled combustion gases are then passed through conduit 99 to the adsorbent chamber 24, which is provided with heat exchange coils 105, the gases in the upper part being cooled to a lower temperature. Cooling of the adsorbent in lower chamber 26 is effected by a gaseous medium. Operation of tower 140 is similar in principle to that of tower 21. It is divided into two chambers, viz. an upper chamber 142 in which the gases are cooled and nitrogen dioxide is adsorbed and a lower chamber 143 in which the adsorbent is stripped of nitrogen dioxide by contact with a hot gas, e.g. hot nitrogen dioxide, the chambers being separated by a modified valve mechanism 145 (Fig. 5).