PURPOSE: To considerably reduce the amount of steam used and inexpensively manufacture ammonium sulfate by utilizing the sensible heat of coke oven gas generated from a coke oven as a heat source for depositing ammonium sulfate crystals.

CONSTITUTION: Coke oven gas 2 generated from coke oven 1 is fed to dry main 3 to flash aq. ammonia 4 circulating through tar decanter 9 and tank 10, and it is cooled with primary cooler 5 using seawater. After raising the pressure of gas 2 with blower 6, gas 2 is fed to ammonium sulfate saturator 8 through coke oven gas desulfurizer 7 to remove NH3. Mother liquor 12 of ammonium sulfate which has absorbed NH3 in saturator 8 is charged into evaporator 17 through crystal vessel 14, and water is evaporated to deposit crystals, which are then granulated in vessel 14. Mother liquor of ammonium sulfate after crystallizing ammonium sulfate is introduced into heat exchanger 22 through tar separating vessel 18, heat exchanged for the sensible heat of part of aq. ammonia 4 circulating from tank 10, and returned to saturator 8 through heater 20.