Patent GB-794105-A (GB)
Title: Process and apparatus for treating ammoniacal gas liquor
IPC: C10K1/10
Filed: 1954-10-04
Abstract: In a distillation of ammoniacal gas liquor, the liquor is heated under pressure and <PICT:0794105/III/1> <PICT:0794105/III/2> then introduced via an expansion valve into a lower section of a fractionating column which is maintained at a pressure in the range of 5 to 35 atmospheres, and a vapour fraction rich in ammonia is withdrawn from the side of the column.  A temperaturegradient of 25 DEG  to 185 DEG  C. is preferably maintained between the top of the column and the sump by injecting water into the top of the column. Hydrogen sulphide and carbon dioxide are withdrawn from the upper part of the column; and hot water is withdrawn from the sump.  The relation of the height of the column to its diameter should be in the range 12 to 20.  Crude coke-oven gas is charged into the lowest stage of washer 1 (Fig. 1), the two lower stages of which are supplied from pipe 17 with cold dilute ammonia water, obtained as described later. Water from the base of column 10 is sprayed from pipe 18 into the upper stages of washer 1.  The gas leaving washer 1 has been freed of a large proportion of its H2S content.  The gas is now introduced into the lowest stage of washer 2, the lower stages of which are supplied with dilute ammonia water while degasified water is introduced into the upper stages.  The bulk of the NH3 and CO2 are removed from the gas in washer 2.  The wash liquids from washers 1 and 2 are united in receiver 4; and, in order to increase the CO2 content thereof, liquor from producer-gas washer 3 is added.  Liquor from receiver 4 is pumped through heat-exchanger 6 to the lower tube-bank in furnace 8 where it is heated to about 240 DEG  C. under a pressure of about 40 atmos.  The hot liquor then passes through expansion valve 9 into column 10, which is supplied with steam through valve 13, and is maintained at a pressure of about 10 atmos. Hot water is discharged from the base of the column, flows through heat-exchanger 6, and is then used to drive pump 5.  The water is next cooled and aerated in tower 11, and then flows to distributer 14.  Some of the water is pumped through the upper tube-bank in furnace 8; and the steam formed therein is supplied to column 10 through the valve 13. Some of the cool water from receiver 14 is pumped up and sprayed into the top of the column in order to keep it at about 20 DEG  C. The upper part of the column (see Fig. 2) contains five bubble-cap trays 25 forming chambers in which are mounted cooling-coils supplied with fresh water.  Below the lowest bubble-trays is a cooling-coil 26.  The temperatures in the column just above and just below coil 26 are 85 DEG  and 96 DEG  C. respectively.  The central portion of the column contains fourteen chambers 27, separated by perforated plates, each chamber being partially packed with Raschig rings of stoneware.  The hot liquor from furnace 8 enters the column at chamber 28; and steam is introduced into the two chambers below.  Mixtures of H2S and CO2 are withdrawn from the column through outlets 31 and 32.  The gas withdrawn through outlet 31 is rich in CO2, and some of this gas may be supplied to the lowest chamber of the column.  Ammonia vapour escapes from the column through automatic expansion-valve 34 if the temperature rises above a desired value; and this causes the temperature to fall.  Ammonia vapour, containing a trace of CO2, is withdrawn via outlet 33 at a temperature of about 185 DEG  C., and may, after cooling and drying, readily be condensed. Some of this vapour is dissolved in water from receiver 14 to make dilute ammonia water.