GB739145A - Improvements in or relating to process and apparatus for recovery of ammonia from anammonia containing gas - Google Patents

Abstract

Apparatus for absorbing ammonia from coke oven gas in sulphuric acid and crystallizing ammonium sulphate comprises a crystallizer A, an absorber B, a mist precipitator C and a vacuum evaporator D all arranged about a <PICT:0739145/III/1> <PICT:0739145/III/2> common vertical axis. The absorber which surrounds the crystallizer has a gas inlet 22 and outlet 24 and a ring of spray heads 82 communicating through short pipes 80 with the top of the crystallizer. From the absorber, gas passes through a riser E and a tangential inlet 30 into the mist separator whence it flows through a central pipe 44 to an outlet 52. A pump P1 withdraws liquid collecting at the base of the absorber and from the evaporator through a pipe 58, returning it to the crystallizer from beneath and through a perforated deflector 70, whence it rises as a desupersaturated solution to an outlet 62 and thence past a throttling valve 65 to the evaporator. Supersaturation follows and on return to the crystallizer the current in rising clarifies the crystals, a slurry of the larger sizes being withdrawn through a suction head 76. Make-up acid is admitted through a pipe 95 into a tar skimmer 94 to which overflow from the absorber is directed through a pipe 90. Surplus liquid collecting in a tank 86 is drawn on to supply a spray head 106 in riser E. In one modification the absorber is disposed round the lower part of the mist separator and above the crystallizer; in another it extends below and surrounds the base of the crystallizer and the spray heads are downwardly inclined to direct liquid from an annular manifold on to the vessel walls. In a third embodiment the separator and evaporator are omitted but a centrifugal separator may be inserted in the outlet line. A further construction provides a trough round the separator outlet 44 with a pipe leading the moisture to the floor whence it drains to the absorber. Another arrangement locates the separator between the crystallizer situated above it and the absorber which surrounds its lower end.