Gas purification apparatus and gas purification method

1. A gas purification apparatus configured to purify gas including COS, H 2 O, CO2, and H 2 S, the apparatus comprising:

a COS treatment device comprising a COS conversion catalyst and configured to degrade COS in the gas by hydrolyzing;

H 2 O adjustment means configured to adjust a concentration of H 2 O in the gas to be introduced into the COS treatment device;

a coal drying device configured to dry coal by removing moisture from the coal;

a gasification furnace configured to gasify the dried coal;

at least two water washing devices in the flowing direction of the gas configured to treat the gas discharged from the COS treatment device with water; and

at least two waste water treatment devices, each disposed with one of the at least two water washing devices, the at least two waste water treatment devices configured to treat waste water drained from the at least two water washing devices;

wherein the H 2 O adjustment means is configured to mix water from one of the at least two waste water treatment devices which is disposed downstream from another of the at least two waste water treatment devices in view of the gas flow, with the gas to be introduced into the COS treatment device.

2. The gas purification apparatus according to claim 1 ,

wherein the H 2 O adjustment means is means configured to adjust the concentration of H 2 O so that a pressure equilibrium constant K P expressed by the following expression (1) becomes 1≦K P ≦20:

[Expression 1]

K P =( P H2S ×P CO2 )/( P COS ×P H2O )  (1)

where P COS is a partial pressure of COS in the gas, P H2O is a partial pressure of H 2 O in the gas, P CO2 is a partial pressure of CO 2 in the gas, and P H2S is a partial pressure of H 2 S in the gas.

3. The gas purification apparatus according to claim 1 , wherein the H 2 O adjustment means is further configured to mix steam with the gas to be introduced into the COS treatment device.

4. A gas purification method for purifying gas including COS, H 2 O, CO 2 , and H 2 S, the method comprising:

an H 2 O adjustment step of adjusting a concentration of H 2 O in the gas;

a COS treatment step of degrading COS in the gas of which the concentration of H 2 O has been adjusted by hydrolyzing by using a COS conversion catalyst;

a coal drying step of drying coal by removing moisture from the coal;

a gasification step of gasifying the dried coal;

at least two water washing steps of water washing the gas obtained by degrading COS; and

at least two waste water treatment steps of treating waste water, each waste water treatment step treating waste water discharged from one of the at least two water washing steps;

wherein the H 2 O adjustment step is a step of mixing the water treated in one of the at least two waste water treatment steps which is after another of the at least two waste water treatment steps, with the gas before the COS treatment step.

5. The gas purification method according to claim 4 ,

wherein the H 2 O adjustment step is a step of adjusting the concentration of H 2 O so that a pressure equilibrium constant K P expressed by the following expression (1) becomes 1≦K P ≦20:

[Expression 2]

K P =( P H2S ×P CO2 )/( P COS ×P H2O )  (1)

where P COS is a partial pressure of COS in the gas, P H2O is a partial pressure of H 2 O in the gas, P CO2 is a partial pressure of CO 2 in the gas, and P H2S is a partial pressure of H 2 S in the gas.

6. The gas purification method according to claim 4 , wherein the H 2 O adjustment step is a step of further including mixing steam with the gas before the COS treatment step.

7. The gas purification apparatus according to claim 2 , wherein the H 2 O adjustment means is further configured to mix steam with the gas to be introduced into the COS treatment device.

8. The gas purification method according to claim 5 , wherein the H 2 O adjustment step is a step of further including mixing steam with the gas before the COS treatment step.