PURPOSE: To reduce the amount of alkali to be used by enhancing the removal ratio of hydrochloric acid gas, by treating hydrochloric acid gas and ammonia gas generated in a thermal decomposition furnace in a high temp. absorbing part and the next stage low temp. absorbing part by utilizing ammonia as carrier gas.
CONSTITUTION: Hydrochloric acid gas and ammonia gas generated in a thermal decomposition furnace 2 is sent to a high temp. absorbing tower 4 of which the operation temp. is set to 85°C or more and the pH is set to 7 or more to fix both of them as an ammonium chloride solution. In the next step, the treated gas is sent to a low temp. absorbing tower 8 of which the operation temp. is set to 55°C or less and the pH is set to 7 or more to fix excessive ammonia as an ammonium carbonate solution which is, in turn, returned to the high temp. absorbing tower. Alkali is added to the ammonium chloride solution and the ammonium carbonate solution from the high temp. absorbing tower 4 in a pH control tank 13 to send both of them to a first evaporation boiler 15 and, further, a second evaporation boiler 17. Steam containing ammonia generated in the first evaporation boiler 15 is returned to the thermal decomposition furnace 2 as fluidizing gas through a pipeline 18 and the steam heater 3 of the high temp. absorbing tower 4.
KAMIJIYOU YASUHIKO
IGARASHI MISAO
KAGAYAMA MASAMI
OOUCHI KENJI
TAKAHASHI KANEYUKI
