Patent ID: 8603427

Claim:
An ammonia recovery method for recovering ammonia from an ammonia-containing wastewater from a gasification furnace, the ammonia recovery method comprising: a first step of, with a CO 2 .H 2 S stripper maintained to have a pressure higher than atmospheric pressure, from the ammonia-containing wastewater, discharging CO 2 and H 2 S in a form of gas having a low moisture concentration from a tower top portion of the CO 2 .H 2 S stripper while discharging an ammonia-containing solution from a tower bottom portion of the CO 2 .H 2 S stripper; a second step of introducing the ammonia-containing solution obtained after the first step into an ammonia stripper which is maintained to have a lower pressure than that of the CO 2 .H 2 S stripper, and thereby discharging a gas rich in ammonia containing a small amount of H 2 S and CO 2 from a tower top portion of the ammonia stripper while discharging water usable as industrial water from a tower bottom portion of the ammonia stripper; and a third step of introducing the ammonia rich gas obtained after the second step into a washing tower which is maintained to have a lower pressure than that of the ammonia stripper, and thereby discharging a wastewater containing a Na compound from a tower bottom portion of the washing tower while discharging a H 2 S-free gas rich in ammonia from a tower top portion of the washing tower; wherein the washing tower includes a water washing tower located above and a NaOH washing tower located below which are coupled to each other, and the third step includes: a NaOH washing step in which the gas rich in ammonia obtained after the second step is introduced into the NaOH washing tower so as to absorb H 2 S and CO 2 with NaOH contained in a circulation water in the NaOH washing tower and to then send a resultant gas to the water washing tower while discharging a wastewater containing a Na compound from a tower bottom portion of the NaOH washing tower; and a water washing step in which a make-up water is supplied to the H 2 S-free gas rich in ammonia subjected to the washing in the NaOH washing step so as to wash dispersion of droplets of NaOH with the make-up water, the water washing step being carried out in the water washing tower maintained to have a lower pressure than that of the ammonia stripper.