Patent GB-615641-A (GB)
Title: Method and apparatus for recovering ammonia from ammonia-containing gases
IPC: C01C1/12
Filed: 1946-02-13
Abstract: <PICT:0615641/III/1> Ammonia is continuously absorbed by contacting an ammonia-containing gas with an aqueous acid solution containing crystals of the ammonium salt, withdrawing supersaturated solution from the gas absorption zone at a rate such that new crystals form in the absence of said crystals of the salt, disupersaturating the withdrawn solution by passing it in contact with relatively large crystals of the salt, separating the solution therefrom and returning it to the absorption zone.  In one embodiment, Fig. 1, the gas, e.g. coke oven gas, is passed through a moisture collector 36, pipe 32 and a cracker pipe 40 into a saturator 10 containing a solution, e.g. 3-8 per cent sulphuric acid, which is caused to flow upwardly to an elevation near the surface whence it is withdrawn into a suction head 56 and returned through pipes 64, 68 and distributor 74 to the bottom of the saturator to form a classification zone in which the rate of flow, correlated with the proportions of the saturator, maintains an even gradation of crystal size with crystals less than 0.8 mm. at the top.  Large crystals are withdrawn through suction heads 82 to a settling cone 90, the overflow from which is returned through pipe 134 to the saturator while the crystals are filtered at 98. Filter cake, after being dried by hot air from a blower 100 and heater 102, is discharged on to a conveyor while the filtrate, communicating with the low pressure side of a blower 104 through a receiver 106 and moisture collector 108 which drain into a pressure equalizer 116, is returned to the cone 90 or to <PICT:0615641/III/2> a mother liquor tank 132.  Saturator solution is also continuously withdrawn through an overflow pipe 52, located where the upward velocity of the solution is zero, into a tar skimmer 142 and returned through the mother liquor tank to the saturator, water and acid being added through pipes 158 and 160 to desaturate the solution in the tar skimmer.  Acid or mother liquor and steam or hot water may be sprayed through nozzles 154 and 156 respectively into the saturator. Degasification of the saturator solution, which is at a temperature between 30 and 115 DEG  C. may be effected by withdrawing it over a large area so that the upward velocity of entrained bubbles exceeds the downward velocity of the solution. The saturator shown in Fig. 1 contains a cracker pipe 40 formed of an inverted frustro-conical top section 44 which is provided with a plurality of uniformly spaced vertical slots 46, and a cup-shaped suction head 56 provided with an adjustable weir and vanes to inhibit surging and whirlpool action, whereas the saturator in Fig. 4 differs mainly in that (a) the cracker pipe 40 has a ring of orifices 184 at the top of which is positioned an annular plate 194 having vertical radial fins forming radial channels and united to a frustro-conical section 196 intersecting the bottom section 44 to which is attached an extension or ring 186, an adjustable ring 190 and an inverted frustro-conical section 188; (b) the suction head 56a is shaped as an inverted cone having an upstanding ring 202 with an adjustable weir 58a, the space between ring 202 and upper edge 204 being covered by a plate 206.  In Figs. 5-9 (not shown), suction heads, cup-shaped, cone-shaped or cone-shaped with a plurality of inverted oblique hollow cones, are located entirely within the saturators, propellers being used to circulate the solution, and in Figs. 6, 7 and 9 (not shown), the cracker pipe discharges in the middle of the saturator inside the suction head.