AU2020288027B2

AU2020288027B2 - Carbon-based fuel gasification system

Info

Publication number: AU2020288027B2
Application number: AU2020288027A
Authority: AU
Inventors: Hayato Hattori; Fumihiko Kiso; Takeshi Kumagai
Original assignee: Mitsubishi Power Ltd
Current assignee: Mitsubishi Power Ltd
Priority date: 2019-06-05
Filing date: 2020-06-04
Publication date: 2023-04-06
Anticipated expiration: 2040-06-04
Also published as: JP7258663B2; JP2020200353A; WO2020246561A1; AU2020288027A1

Abstract

A water spray apparatus 3 sprays water over product gas on a downstream side of a gasifier 1. A dedusting device 4 removes unreacted coal from the product gas on a downstream side of the water spray apparatus 3. A first washing tower 5 removes halogen in the product gas on a downstream side of the dedusting device 4. A shift reactor 6 converts a water vapor and carbon monoxide in the product gas into hydrogen and carbon dioxide by the shift reaction on a downstream side of the first washing tower 5. A second washing tower 7 removes ammonia from the product gas on a downstream side of the shift reactor 6. An absorption tower 8 removes hydrogen sulfide and carbon dioxide from the product gas on a downstream side of the second washing tower 7. A drained water supply pipe 9 supplies drained water from the second washing tower 7 to the water spray apparatus 3. The water spray apparatus 3 sprays the drained water supplied from the drained water supply pipe 9.

Description

TECHNICAL FIELD

[0001] The present invention relates to a carbon-based fuel gasification system to produce gas composed of mainly hydrogen from carbon-based fuel. BACKGROUND

[0002] Patent Literature 1 discloses a system which produces gas composed of mainly hydrogen through partial oxidation of coal and a subsequent shift reaction process, followed by a C02 separation process. In this system, coal and oxygen are fed to a gasifier, where partial oxidation reaction thereof produces gasification gas composed of mainly CO and hydrogen. The produced gasification gas is fed to a water scrubber and has impurities such as heavy metals and hydrogen halides removed. The product gas washed in the water scrubber is fed to a shift reactor while being heated through a heat exchanger and a gas heater to a reaction temperature of a shift catalyst. Water vapor is supplied at an inlet to the shift reactor, and the shift catalyst charged in the shift reactor facilitates a CO-shift reaction. The gas discharged from the shift reactor is cooled through a heat exchanger, and moisture in the gas is condensed and removed by a knockout drum. The gas with moisture removed is fed to an absorber and has H 2S and C02 removed by an absorption liquid. The gas with H 2S and C02 removed is composed of mainly H 2 , which is used as a fuel for gas turbines in power generation plants and the like. PATENT LITERATURE

[0003] Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2017 48087

[0004] In order to prepare the water vapor to be supplied to the shift reactor (water vapor necessary for shift reaction), the system of Patent Literature 1 requires inclusion of a heat recovery section composed of a large number of tubular heat exchangers. In addition, since the heat recovery section cannot be directly supplied with industrial water, the system also requires a facility for producing pure water.

[0005] In addition, it is conceivable that the system includes a second water scrubber to remove ammonia from the gas, between the shift reactor and the knockout drum. Inclusion of the second water scrubber can remove ammonia from produced gas, but this

I requires a facility for treating wastewater of the second water scrubber.

[0006] Furthermore, such pure water production and wastewater treatment involve an increase in energy consumption, making it difficult to improve the heat efficiency of the whole system.

[0007] It is desired to address or ameliorate one or more disadvantages or limitations associated with the prior art, or to at least provide a useful alternative. In view of the above, in some embodiments the present invention may provide a carbon-based fuel gasification system that allows for less facility burden and higher heat efficiency.

SUMMARY

[0008] In one embodiment, the present invention provides a gasification system for carbon-based fuel, comprising: a gasifier which gasifies carbon-based fuel with an oxidant to provide a product gas composed of mainly carbon monoxide and hydrogen; a water spray apparatus which sprays water onto the product gas downstream from the gasifier; a dedusting apparatus which removes unreacted coal from the product gas downstream from the water spray apparatus; a first water scrubber which removes halogen from the product gas downstream from the dedusting apparatus; a shift reactor which converts water vapor and carbon monoxide in the product gas into hydrogen and carbon dioxide through a shift reaction downstream from the first water scrubber; a second water scrubber which removes ammonia from the product gas downstream from the shift reactor; an absorber which removes hydrogen sulfide and carbon dioxide from the product gas downstream from the second water scrubber; and a wastewater supply tube which supplies wastewater of the second water scrubber to the water spray apparatus, wherein the water spray apparatus sprays wastewater supplied from the wastewater supply tube.

[0051] According to at least some embodiments of the present invention, it is possible to reduce the facility burden of the system and improve the heat efficiency thereof.

BRIEF DESCRIPTION OF DRAWINGS

[0052] Preferred embodiments of the present invention are hereinafter described, by way of example only, with reference to the accompanying drawings, in which:

[Fig. 1] Fig. 1 is a block diagram illustrating the outline of a gasification system of the present invention.

[Fig. 2] Fig. 2 is a system configuration diagram of a gasification system of a first embodiment of the present invention.

[Fig. 3] Fig. 3 is a block diagram concerning control in the first embodiment.

[Fig. 4] Fig. 4 is a system configuration diagram of a gasification system of a second embodiment of the present invention.

[Fig. 5] Fig. 5 is a block diagram concerning control in the second embodiment. DETAILED DESCRIPTION

[0009] As described above, in a first aspect the present invention provides a carbon based gasification system, including a gasifier, a water spray apparatus, a dedusting apparatus, a first water scrubber, a shift reactor, a second water scrubber, an absorber, and a wastewater supply tube. The gasifier gasifies a carbon-based fuel with an oxidant to provide product gas composed of mainly carbon monoxide and hydrogen. The water spray apparatus sprays water onto the product gas downstream from the gasifier. The dedusting apparatus removes unreacted coal from the product gas downstream from the water spray apparatus. The first water scrubber removes halogen from the product gas downstream from the dedusting apparatus. The shift reactor, downstream from the first water scrubber, converts water vapor and carbon monoxide in the product gas into hydrogen and carbon dioxide through a shift reaction. The second water scrubber removes ammonia from the product gas downstream from the shift reactor. The absorber removes hydrogen sulfide and carbon dioxide from the product gas downstream from the second water scrubber. The wastewater supply tube supplies wastewater of the second water scrubber to the water spray apparatus. The water spray apparatus sprays the wastewater supplied from the wastewater supply tube.

[0010] In the aforementioned configuration, the product gas flows from the gasifier to the dedusting apparatus, first water scrubber, shift reactor, and second water scrubber sequentially. The wastewater of the second water scrubber contains ammonia and is supplied to the water spray apparatus through the wastewater supply tube. The wastewater is then sprayed as direct quench water onto the product gas downstream from the gasifier and upstream from the dedusting apparatus. Since the product gas is hot downstream from the gasifier, ammonia contained in the direct quench water is partially decomposed by heat. In the dedusting apparatus and first water scrubber, unreacted coal and halogen in the product gas are removed, respectively. In the shift reactor, water vapor and carbon monoxide in the product gas are converted into hydrogen and carbon dioxide through the shift reaction. In the second water scrubber, washing water flows down from above the inlet of the product gas (from the top) to below the same (toward the bottom), and ammonia contained in the product gas is removed by the washing water. In the absorber, hydrogen sulfide and carbon dioxide in the product gas are removed, thus producing gas composed of mainly hydrogen (H2 ).

[0011] As described above, the product gas is not supplied with water vapor but is directly supplied with wastewater of the second water scrubber. It is therefore unnecessary to provide a heat recovery section to prepare water vapor and a facility to produce pure water to be supplied to the heat recovery section as well as a facility to treat wastewater of the second water scrubber. This can reduce the facility burden and improve the heat efficiency of the whole system.

[0012] A second aspect of the present invention is the gasification system of the first aspect, including a cooler, a knockout drum, and a recovered water supply tube.

[0013] The cooler is provided between the second water scrubber and the absorber and cools the product gas downstream from the second water scrubber. The knockout drum is provided between the cooler and the absorber and condenses and removes moisture in the product gas downstream from the cooler. The recovered water supply tube recovers moisture removed from the product gas by the knockout drum and supplies the same to the second water scrubber.

[0014] In the aforementioned configuration, the product gas is supplied to the absorber after having moisture removed by the knockout drum. This prevents the absorption liquid of the absorber from decreasing in concentration (from diluting due to moisture in the product gas). Furthermore, since the moisture removed from the product gas is supplied to the second water scrubber through the recovered water supply tube, it is possible to reduce the amount of water supplied to the second water scrubber from outside of the system (the use of industrial water).

[0015] Furthermore, the cooler for cooling the product gas flowing into the knockout drum is not provided upstream from the second water scrubber but provided downstream, and the hot product gas before cooled by the cooler flows into the second water scrubber. The wastewater of the second water scrubber used as direct quench water is heated by the hot product gas, resulting in less thermal shock at collision of droplets of direct quench water sprayed from the water spray apparatus with a wall surface (a wall surface defining the passage space for the product gas).

[0016] A third aspect of the present invention is the gasification system of the first or second aspect, in which the water spray apparatus includes plural nozzles in layers arranged from upstream to downstream and sprays wastewater supplied from the wastewater supply tube through the plural nozzles in layers.

[0017] In the aforementioned configuration, direct quench water is sprayed in a multi layered manner, and the temperature of the product gas therefore is less likely to drop rapidly than with a single layer spray. The thermal decomposition rate (equilibrium thermal decomposition rate) of ammonia increases with temperature of the product gas. The multi-layered spray facilitates keeping a gas temperature environment suitable for thermal decomposition of ammonia (a temperature environment not lower than the thermal decomposition temperature of ammonia), leading to a stable operation.

[0018] A fourth aspect of the present invention is the gasification system of the third aspect, in which the water spray apparatus includes a gas temperature detector and a spray amount controller. The gas temperature detector which detects the temperature of the product gas lowered by water spray from the nozzle in a first layer at the upstream end, as a gas temperature after water spray in the first layer. The spray amount controller which controls the amount of water sprayed from the nozzle in the first layer such that the detected gas temperature after water spray in the first layer be a given first-layer target temperature that is not lower than thermal decomposition temperature of ammonia.

[0019] In the aforementioned configuration, the gas temperature between the first and second layers is adjusted to the thermal decomposition temperature of ammonia or higher, thus making it possible to continuously maintain the suitable gas temperature environment.

[0020] A fifth aspect of the present invention is the gasification system of the fourth aspect, in which the gas temperature detector detects the temperature of the product gas flowing into the dedusting apparatus as a dedusting inflow temperature. The spray amount controller controls the amount of water sprayed from the nozzle in the last layer such that the detected dedusting inflow temperature be a given target inflow temperature which is not lower than the dew point and not higher than an upper operating temperature limit of the dedusting apparatus.

[0021] In the aforementioned configuration, dedusting inflow temperature (for example, gas temperature at the inlet to the dedusting apparatus) is maintained at temperatures not lower than the dew point and not higher than the upper operating temperature limit of the dedusting apparatus. This can prevent condensation of moisture in the dedusting apparatus and thereby prevent char particles from aggregating and growing into lumps in the dedusting apparatus. Furthermore, since the dedusting inflow temperature does not exceed the upper operating temperature limit (maximum operating temperature) of the dedusting apparatus, it is possible to avoid wearing and wall thinning of the dedusting apparatus due to excessively high temperature.

[0022] The gas temperature detector may detect the temperature of the product gas which was lowered by water spray from the nozzle in each layer other than the first and last layers, as gas temperature after water spray in each layer. The spray amount controller may control the amount of water sprayed from the nozzle in each layer such that the detected gas temperature after water spray in the layer of interest be a target temperature for the layer which is set not lower than the target temperature for the previous layer between a first-layer target temperature and a target inflow temperature.

[0023] The gas temperature detector that detects the temperature of the product gas which was lowered by water spray from the nozzle in each layer other than the last layer, may be a thermometer corresponding to the layer. In this case, the thermometer to detect the gas temperature after water spray in the N-th layer is preferably positioned between the water spray position of the nozzle in the N-th layer (the water spray position in the layer of interest) and the water spray position of the nozzle in the (N+1)-th layer (the water spray position in the subsequent layer) and is more preferably positioned immediately before the water spray position in the subsequent layer.

[0024] A sixth aspect of the present invention is the gasification system of the first to fifth aspects, including a wastewater tank which is provided in the middle of the wastewater supply tube and is able to temporarily reserve wastewater of the second water scrubber.

[0025] In the aforementioned configuration, the wastewater tank receives wastewater supplied from the second water scrubber and reserves the same as direct quench water to be sprayed downstream from the gasifier. Even if there is a difference in amount between supply and use of wastewater (direct quench water), supply of wastewater of the second water scrubber to the water spray apparatus and the amount of direct quench water sprayed from the water spray apparatus are controlled independently within the capacity of the wastewater tank.

[0026] A seventh aspect of the present invention is the gasification system of the sixth aspect, including a washing water supply tube, a reserved washing water amount detector, a washing water supply controller, a tank water amount detector, and a wastewater supply controller.

[0027] The washing water supply tube supplies to the second water scrubber, washing water that flows down in the second water scrubber to remove ammonia from the product gas. The reserved washing water amount detector detects an amount of washing water which has flowed down in the second water scrubber and accumulated in the bottom of the second water scrubber, as a reserved washing water amount. The washing water supply controller controls supply of washing water from the washing water supply tube to the second water scrubber such that the detected reserved washing water amount be maintained at a given predetermined reserved washing water amount.

[0028] The tank water amount detector detects the amount of wastewater reserved in the wastewater tank as a tank water amount. The wastewater supply controller controls supply of wastewater from the wastewater supply tube to the wastewater tank such that the detected tank water amount not fall below a given lower tank water amount limit.

[0029] In the aforementioned configuration, when wastewater reserved in the wastewater tank is sprayed as direct quench water and the amount of wastewater reserved in the wastewater tank (the tank water amount) falls below the lower tank water amount limit, the wastewater supply controller supplies wastewater of the second water scrubber to the wastewater tank such that the tank water amount reach the lower tank water amount limit. When wastewater is supplied from the second water scrubber to the wastewater tank and the amount of washing water reserved in the bottom of the second water scrubber (the reserved washing water amount) decreases (decreases in water level) below the predetermined reserved washing water amount, the washing water supply controller supplies washing water to the second water scrubber such that the reserved washing water amount reach the predetermined reserved washing water amount. On the other hand, when the reserved washing water amount in the second water scrubber is not less than the predetermined reserved washing water amount, the washing water supply controller does not supply washing water to the second water scrubber.

[0030] The reserved washing water amount in the second water scrubber is thus maintained at the predetermined reserved washing water amount. If the wastewater supply controller is composed of a water pump, the water pump can be prevented from incorporating air or prevented from running dry. Furthermore, the predetermined reserved washing water amount may be set such that the inlet of the product gas to the second water scrubber not be submerged underwater. This prevents the inlet of the product gas from being submerged underwater.

[0031] Furthermore, the amount of wastewater reserved in the wastewater tank (the tank water amount) is maintained at not less than the lower tank water amount limit. If wastewater (direct quench water) is supplied from the wastewater tank to the water spray apparatus using a water pump, the water pump can be prevented from incorporating air or prevented from running dry.

[0032] An eighth aspect of the present invention is the gasification system of the seventh aspect, including a supplied washing water amount detector, a washing water circulation supply tube, and a washing water circulation supply controller.

[0033] The supplied washing water amount detector detects the amount of washing water supplied from the washing water supply tube to the second water scrubber, as a supplied washing water amount. The washing water circulation supply tube is able to supply part of wastewater intended to be supplied from the second water scrubber to the water spray apparatus, to the second water scrubber as washing water to remove ammonia from the product gas. When the detected supplied washing water amount is less than a given predetermined supplied washing water amount, the washing water circulation supply controller controls supply of washing water from the washing water circulation supply tube to the second water scrubber such that the amount of washing water flowing down in the second water scrubber be not less than the predetermined supplied washing water amount.

[0034] In the aforementioned configuration, when the reserved washing water amount in the second water scrubber is not less than the predetermined reserved washing water amount, the washing water supply controller does not supply washing water from the washing water supply tube to the second water scrubber. The amount of washing water supplied from the washing water supply tube to the second water scrubber (the supplied washing water amount) is therefore less than the predetermined supplied washing water amount. When the supplied washing water amount is less than the predetermined supplied washing water amount, the washing water circulation supply controller supplies washing water from the washing water circulation supply tube to the second water scrubber such that the amount of washing water flowing down in the second water scrubber be not less than the predetermined supplied washing water amount.

[0035] Even if any washing water is not supplied from the washing water supply tube to the second water scrubber, the amount of washing water flowing down in the second water scrubber can be maintained at not less than the predetermined supplied washing water amount. This prevents any decrease in ammonia removal rate in the second water scrubber.

[0036] A ninth aspect of the present invention is the gasification system of the sixth aspect, including a washing water supply tube, a gas amount detector, a washing water supply controller, a reserved washing water amount detector, and a wastewater supply controller.

[0037] The washing water supply tube supplies to the second water scrubber, washing water that flows down in the second water scrubber to remove ammonia from the product gas. The gas amount detector detects the amount of product gas flowing from the second water scrubber to the absorber as a product gas amount. The washing water supply controller controls supply of washing water from the washing water supply tube to the second water scrubber depending on the detected product gas amount.

[0038] The reserved washing water detector detects the amount of washing water which has flowed down in the second water scrubber and accumulated in the bottom of the second water scrubber, as a reserved washing water amount. The wastewater supply controller controls supply of wastewater from the wastewater supply tube to the wastewater tank such that the detected reserved washing water amount be maintained at a given predetermined reserved washing water amount.

[0039]

In the aforementioned configuration, the washing water supply controller increases or decreases the amount of washing water supplied from the washing water supply tube to the second water scrubber (the supplied washing water amount) depending on an increase or decrease in amount of product gas flowing from the second water scrubber to the absorber (the product gas amount). The wastewater supply controller controls supply of wastewater from the wastewater supply tube to the wastewater tank such that the reserved washing water amount in the second water scrubber be maintained at the predetermined reserved washing water amount.

[0040] Since the supplied washing water amount depends on the amount of product gas flowing in the second water scrubber, it is possible to remove ammonia from the product gas efficiently and surely.

[0041] Furthermore, the detected reserved washing water amount in the second water scrubber is maintained at the given predetermined reserved washing water amount. If the wastewater supply controller is composed of a water pump, the water pump can be prevented from incorporating air or prevented from running dry. In addition, the predetermined reserved washing water amount is set such that the inlet of the product gas to the second water scrubber not be submerged underwater. This prevents the inlet of the product gas from being submerged underwater.

[0042] A tenth aspect of the present invention is the gasification system of the ninth aspect, including a tank water amount detector, a washing water circulation supply tube, and a washing water circulation supply controller.

[0043] The tank water amount detector detects the amount of wastewater reserved in the wastewater tank as a tank water amount. The washing water circulation supply tube can supply part of wastewater intended to be supplied from the second water scrubber to the waste spray apparatus, to the second water scrubber as washing water to remove ammonia from the product gas. The washing water circulation supply controller controls supply of washing water from the washing water circulation supply tube to the second water scrubber.

[0044] When the detected tank water amount exceeds a given upper tank water amount limit, the washing water supply controller stops supply of washing water from the washing water supply tube to the second water scrubber; the wastewater supply controller stops supply of wastewater from the wastewater supply tube to the wastewater tank; and the washing water circulation supply controller controls supply of washing water from the washing water circulation supply tube to the second water scrubber depending on the detected product gas amount.

[0045] In the aforementioned configuration, when the amount of wastewater reserved in the wastewater tank (the tank water amount) increases and exceeds the upper tank water amount limit, the wastewater supply controller stops supply of wastewater from the wastewater supply tube to the wastewater tank. The tank water amount of the wastewater tank therefore can be adjusted so as not to exceed the upper tank water amount limit. Furthermore, the washing water supply controller stops supply of washing water from the washing water supply tube to the second water scrubber, so that the reserved washing water amount in the second water scrubber can be prevented from excessively increasing (for example, increasing and exceeding an upper reserved washing water limit which is not less than the predetermined reserved washing water amount and with which the inlet of the product gas is not submerged underwater).

[0046] When the tank water amount of the wastewater tank exceeds the upper tank water amount limit and the washing water supply controller stops supply of washing water from the washing water supply tube to the second water scrubber, the washing water circulation supply controller supplies washing water from the washing water circulation supply tube to the second water scrubber such that the amount of washing water flowing down in the second water scrubber be not less than the predetermined supplied washing water amount.

[0047] Even if any washing water is not supplied from the washing water supply tube to the second water scrubber, therefore, the amount of washing water flowing down in the second water scrubber can be maintained at not less than the predetermined supplied washing water amount. This prevents any decrease in ammonia removal rate in the second water scrubber.

[0048] An eleventh aspect of the present invention is the gasification system of the ninth aspect, including a spray water replenishing tube, a tank water amount detector, and a tank water amount controller.

[0049] The spray water replenishing tube is able to supply water to the wastewater tank, separately from the wastewater supply tube. The tank water amount detector detects the amount of wastewater reserved in the wastewater tank as a tank water amount. The tank water amount controller controls supply of water from the spray water replenishing tube to the wastewater tank such that the detected tank water amount not fall below a given lower tank water amount limit.

[0050] In the aforementioned configuration, the amount of wastewater reserved in the wastewater tank (the tank water amount) is maintained at not less than the lower tank water amount limit. If wastewater (direct quench water) is supplied from the wastewater tank to the water spray apparatus using a water pump, the water pump can be prevented from incorporating air or prevented from running dry.

[0053] A general description of a gasification system of some embodiments of the present invention is described with reference to Fig. 1.

[0054] As illustrated in Fig. 1, the gasification system of the present invention is generally composed of a gasifier 1, a water spray section 2, a water spray apparatus (a direct quench apparatus) 3, a dedusting apparatus (a dedusting facility) 4, a first water scrubber 5, a shift reactor 6, a second water scrubber 7, an absorber 8, and a wastewater supply tube 9.

[0055] The gasifier 1 gasifies carbon-based fuel (for example, coal) with an oxidant to provide product gas composed of mainly carbon monoxide and hydrogen. The water spray section 2 is a space continuously extending from the gasifier 1 vertically upward and is located downstream from the gasifier 1. The water spray apparatus 3 sprays water onto the product gas flowing upward in the water spray section 2. The dedusting apparatus 4 removes unreacted coal (char) from the product gas downstream from the water spray apparatus 3. The first water scrubber 5 removes halogen and the like from the product gas downstream from the dedusting apparatus 4.

[0056] The shift reactor 6 converts water vapor and carbon monoxide in the product gas into hydrogen and carbon dioxide through a shift reaction expressed as Formula (1) below. The second water scrubber 7 removes ammonia and the like from the product gas downstream from the shift reactor 6. The absorber 8 removes hydrogen sulfide and carbon dioxide from the product gas downstream from the second water scrubber 7.

[0057] The wastewater supply tube 9 connects the water spray apparatus 3 to the second water scrubber 7 and supplies wastewater of the second water scrubber 7 to the water spray apparatus 3 as direct quench water. The water spray apparatus 3 sprays the wastewater (direct quench water) supplied from the wastewater supply tube 9. The sprayed wastewater is heated by the hot product gas, so that moisture in the wastewater turns into water vapor. The product gas containing water vapor is supplied to the shift reactor 6 downstream.

[0058] CO + H 2 0 - C02 + H 2 ... (1)

[0059] In such a manner, the product gas is directly supplied with wastewater of the second water scrubber 7, instead of water vapor. This eliminates the need for a heat recovery section to prepare water vapor and a facility to produce pure water to be supplied to the heat recovery section as well as the need for a facility to treat wastewater of the second water scrubber 7. It is therefore possible to reduce the facility burden and improve the heat efficiency of the whole system.

[0060] Wastewater (washing water) of the first water scrubber 5 is treated by a wastewater treatment apparatus (a wastewater treatment facility) 10 and is circulated and supplied to the first water scrubber 5.

[0061]

[First Embodiment] Next, a gasification system of a first embodiment of the present invention is described with reference to Fig. 2.

[0062] This gasification system includes: a gasifier 1 that is supplied with crushed coal (carbon-based fuel, solid fuel) and oxygen and gasifies the supplied coal; a water spray section 2 that extends continuously from the gasifier 1 vertically upward and in which gas (product gas) generated in the gasifier 1 flows upward; and a water spray apparatus 3 that sprays water (direct quench water) onto the product gas flowing in the water spray section 2.

[0063] The gasification system includes: a dedusting apparatus 4 (a cyclone 45 and a char filter 11) that removes dust (unreacted coal and the like) from the product gas onto which direct quench water was sprayed in the water spray section 2; a first water scrubber that washes the product gas with char removed, with water to remove halogen and the like; plural (three in the first embodiment) shift reactors 6 that cause shift reaction of the product gas washed with water in the first water scrubber 5; a second water scrubber 7 that washes the shift-reacted product gas with water to remove ammonia and the like; a cooler 12 that cools the product gas washed with water in the second water scrubber 7; a knockout drum 13 that condenses and removes moisture in the cooled product gas; an absorber 8 that removes hydrogen sulfide and carbon dioxide from the product gas with moisture removed; a regeneration tower 14 that regenerates absorption liquid that has absorbed hydrogen sulfide and carbon dioxide; and the like. The product gas flowing out of the absorber 8 is gas composed of mainly hydrogen and is partially supplied to a turbine 60.

[0064] The second water scrubber 7 and water spray apparatus 3 are connected by the wastewater supply tube 9, and wastewater of the second water scrubber 7 is supplied to the water spray apparatus 3 as direct quench water. In the middle of the wastewater supply tube 9, a wastewater tank 21 is provided, which is able to temporarily reserve wastewater of the second water scrubber 7. The wastewater tank 21 is connected to a spray water replenishing tube 31 that supplies water (industrial water) to the wastewater tank 21, separately from the wastewater supply tube 9. The spray water replenishing tube 31 is provided with a valve 32. The wastewater tank 21 is provided with a level sensor (a tank water amount detector) 40 that detects an amount of wastewater reserved in the wastewater tank 21, as a tank water amount.

[0065] The second water scrubber 7 and knockout drum 13 are connected by a recovered water supply tube 41. The recovered water supply tube 41 recovers moisture removed from the product gas in the knockout drum 13 and supplies the same to the second water scrubber 7.

[0066] As illustrated in Fig. 3, a control apparatus for the gasification system includes a spray amount control section 50, a wastewater supply control section 51, a washing water supply control section 52, and a washing water circulation supply control section 53.

[0067] Next, the detailed configuration of the gasification system of Fig. 2 is described together with the operation thereof. Coal is crushed by a crusher and is stored in a lock hopper, which is not illustrated. Coal pressurized to a given pressure in the lock hopper is transferred to a feed hopper through a transfer valve and is then fed to the gasifier 1 through a fuel feed tube and a fuel burner while being accompanied by carrier gas.

[0068] The gas for transferring and carrying coal is inert gas such as N 2 or CO 2 . In the first embodiment, part of C02 treated in the regeneration tower 14 is extracted and recovered for use as carrier gas (see * in Fig. 2).

[0069] Coal fed through the fuel burner (not illustrated) to the gasifier 1 is mixed with oxygen also fed through the fuel burner to be partially combusted and gasified, thus generating hot product gas. The product gas is composed of mainly CO and H 2

. Oxygen to be fed to the gasifier 1 is produced by an air separator (not illustrated). Air is pressurized by a compressor (not illustrated) and is supplied to the air separator to be separated into nitrogen and oxygen. The first embodiment employs this separated oxygen. The hot product gas is supplied to the water spray section 2 while direct quench water is sprayed from the water spray apparatus 3 onto the product gas.

[0070] The water spray apparatus 3 includes nozzles 22, 23, and 24 in layers arranged from upstream to downstream. In the first embodiment, the first nozzle 22 in the first layer at the upstream end, the second nozzle 23 in the second layer, and the third nozzle 24 in the third layer at the downstream end are provided. Wastewater supplied from the wastewater supply tube 9 is sprayed from the individual nozzles 22, 23, and 24.

[0071] The water spray apparatus 3 is provided with, as a gas temperature detector: a first gas temperature sensor 25 that detects the temperature of the product gas lowered by water spray from the first nozzle 22 as a gas temperature after water spray in the first layer; a second gas temperature sensor 26 that detects the temperature of the product gas lowered by water spray from the second nozzle 23 as a gas temperature after water spray in the second layer; and a dedusting inlet gas temperature sensor 27 that detects the temperature of the product gas flowing into the dedusting apparatus 4 (the cyclone 45) as a dedusting inflow temperature. The first gas temperature sensor 25 detects the gas temperature immediately before the water spray position of the second nozzle 23. The second gas temperature sensor 26 detects the gas temperature immediately before the water spray position of the third nozzle 24. The amount of water sprayed from each nozzle 22, 23, and 24 is increased or decreased by opening or closing of the corresponding valve (a first spray amount regulation valve 28, a second spray amount regulation valve 29, and a third spray amount regulation valve 30).

[0072] As illustrated in Figs. 2 and 3, opening and closing of each valve 28, 29, and 30 is controlled by the spray amount control section 50. In other words, the valves 28, 29, and 30 and the spray amount control section 50 constitute a spray amount controller configured to control the amount of water sprayed in each layer.

[0073] The spray amount control section 50 controls the amount of water sprayed from the first nozzle 22 (the first spray amount regulation valve 28) such that the gas temperature after water spray in the first layer detected by the first gas temperature sensor be a given first-layer target temperature which is not lower than the thermal decomposition temperature of ammonia. Gas temperature and the thermal decomposition rate of ammonia after spray of direct quench water have a relationship in which the thermal decomposition rate increases with the gas temperature. The thermal decomposition temperature of ammonia can be determined based on such a relationship.

[0074] The spray amount control section 50 controls the amount of water sprayed from the third nozzle 24 (the third spray amount regulation valve 30) such that the dedusting inflow temperature detected by the dedusting inlet gas temperature sensor 27 be a given target inflow temperature which is not lower than the dew point and not higher than the upper operating temperature limit of the dedusting apparatus 4 (the cyclone 45).

[0075] The spray amount control section 50 furthermore controls the amount of water sprayed from the second nozzle 23 (the second spray amount regulation valve 29) such that the gas temperature after water spray in the second layer detected by the second gas temperature sensor 26 be a second-layer target temperature set between the first-layer target temperature and the target inflow temperature.

[0076] The product gas flowing out of the water spray section 2 is separated from the accompanied unreacted coal (char) by the cyclone 45 and char filter 11. Theseparated char is reserved in a char lock hopper 15 and is appropriately transferred to a char feed hopper 16 to be fed again to the gasifier 1.

[0077] After flowing out of the char filter 11, the product gas has halogen substances (chlorine and the like) and small particles removed in the first water scrubber 5. The product gas is then heated by a heat exchanger 17 to the reaction temperature of a shift catalyst and is sequentially fed to the three shift reactors 6 arranged in series. Since the shift reaction is an exothermic reaction, the product gas flowing out of the shift reactors 6 is cooled by heat exchangers 18, 19, and 20. The product gas then has ammonia removed in the second water scrubber 7 and is cooled in the cooler 12 to be fed to the knockout drum 13.

[0078] In the second water scrubber 7, the product gas flows into the tower through a gas inlet at an intermediate height and flows out through a gas outlet at the top. The washing water is supplied from the tower top above the gas inlet, flows down in the tower, and accumulates in the tower bottom below the gas inlet. The lower end of the second water scrubber 7 is connected to the wastewater tank 21 through the wastewater supply tube9. The wastewater supply tube 9 is provided with a water pump 33 and a valve 34. The water pump 33 and valve 34 constitute, in conjunction with the wastewater supply control section 51, a wastewater supply controller configured to control supply of wastewater from the wastewater supply tube 9 to the wastewater tank 21.

[0079] The tower top of the second water scrubber 7 is connected to a washing water supply tube 35 that supplies washing water to the second water scrubber 7. The washing water supply tube 35 is provided with a valve 36. The valve 36 constitutes, in conjunction with the washing water supply control section 52, a washing water supply controller configured to control supply of washing water to the second water scrubber 7.

[0080] To the upstream end of the wastewater supply tube 9, a washing water circulation supply tube 37 is connected as a branch, which allows part of wastewater intended to be supplied from the second water scrubber 7 to the wastewater tank 21 to be again supplied to the tower top of the second water scrubber 7 as washing water. The washing water circulation supply tube 37 is provided with a water pump 38. The water pump 38 constitutes, in conjunction with the washing water circulation supply control section 53, a washing water circulation supply controller configured to control circulation supply of washing water from the washing water circulation supply tube 37 to the second water scrubber 7.

[0081] The second water scrubber 7 is provided with a level sensor (a reserved washing water amount detector) 46 that detects the amount of washing water having flowed down in the tower and accumulated in the tower bottom, as a reserved washing water amount. The washing water supply tube 35 is provided with a flow rate sensor (a supplied washing water amount detector) 39 that detects the amount of washing water supplied from the washing water supply tube 35 to the second water scrubber 7, as a supplied washing water amount.

[0082] The washing water supply control section 52 controls supply of washing water from the washing water supply tube 35 to the second water scrubber 7 such that the reserved washing water amount in the second water scrubber 7 detected by the level sensor 46 be maintained at a given predetermined reserved washing water amount. The wastewater supply control section 51 controls supply of wastewater from the wastewater supply tube 9 to the wastewater tank 21 such that the tank water amount of the wastewater tank 21 detected by the level sensor 40 not fall below a given lower tank water amount limit. When the supplied washing water amount to the second water scrubber 7 detected by the flow rate sensor 39 falls below a given predetermined supplied washing water amount, the washing water circulation supply control section 53 controls circulation supply of washing water from the washing water circulation supply tube 37 to the second water scrubber 7 such that the amount of washing water flowing down in the second water scrubber 7 be not less than the predetermined supplied washing water amount.

[0083] According to the first embodiment, direct quench water is sprayed in a multi layered manner, and the temperature of the product gas is therefore less likely to drop rapidly than with a single-layer spray. Since the thermal decomposition rate of ammonia increases with the temperature of the product gas, the multi-layered spray facilitates keeping a gas temperature environment suitable for thermal decomposition of ammonia (a temperature environment not lower than the thermal decomposition temperature of ammonia), leading to a stable operation.

[0084] The gas temperature between the first and second layers in the multi-layered spray is adjusted to the thermal decomposition temperature of ammonia or higher, thus making it possible to continuously maintain the suitable gas temperature environment.

[0085] The temperature of the product gas at the inlet to the cyclone 45 (the dedusting inflow temperature) is maintained at temperatures not lower than the dew point and not higher than the upper operating temperature limit of the cyclone 45. This can prevent condensation of moisture in the cyclone 45 and thereby prevent char particles from aggregating and growing into lumps in the cyclone 45. Furthermore, the dedusting inflow temperature does not exceed the upper operating temperature limit (maximum operating temperature) of the cyclone 45, and it is therefore possible to avoid wearing and wall thinning of the cyclone 45 due to excessively high temperature.

[0086]

The wastewater tank 21 receives wastewater supplied from the second water scrubber 7 and reserves the same as direct quench water to be sprayed downstream from the gasifier 1. Even if there is a difference in amount between supply and use of wastewater (direct quench water), supply of wastewater from the second water scrubber 7 to the water spray apparatus 3 and the amount of direct quench water sprayed from the water spray apparatus 3 can be independently controlled within the capacity of the wastewater tank 21.

[0087] When wastewater reserved in the wastewater tank 21 is sprayed as direct quench water and the amount of wastewater reserved in the wastewater tank 21 (the tank water amount) falls below the lower tank water amount limit, the wastewater supply control section 51 supplies wastewater from the second water scrubber 7 to the wastewater tank 21 such that the tank water amount reach the lower tank water amount limit. When wastewater is supplied from the second water scrubber 7 to the wastewater tank 21 and the amount of washing water accumulated in the bottom of the second water scrubber 7 (the reserved washing water amount) falls (falls in water level) below the predetermined reserved washing water amount, the washing water supply control section 52 supplies washing water to the second water scrubber 7 such that the reserved washing water amount reach the predetermined reserved washing water amount. On the other hand, when the reserved washing water amount in the second water scrubber 7 is not less than the predetermined reserved washing water amount, the washing water supply control section 52 does not supply washing water to the second water scrubber 7.

[0088] The reserved washing water amount in the second water scrubber 7 is thus maintained at the predetermined reserved washing water amount, so that the water pump 33 can be prevented from incorporating air or prevented from running dry. Furthermore, the predetermined reserved washing water amount is set such that the inlet (the gas inlet) of the product gas to the second water scrubber 7 not be submerged underwater. This prevents the inlet of the product gas from being submerged underwater.

[0089] The amount of wastewater reserved in the wastewater tank 21 (the tank water amount) is maintained at not less than the lower tank water amount limit, so that the water pump (not illustrated) that feeds wastewater (direct quench water) from the wastewater tank 21 to the water spray apparatus 3 can be prevented from incorporating air or prevented from running dry.

[0090]

When the reserved washing water amount in the second water scrubber 7 is not less than the predetermined reserved washing water amount, the washing water supply control section 52 does not supply washing water from the washing water supply tube 35 to the second water scrubber 7. The amount of washing water supplied from the washing water supply tube 35 to the second water scrubber 7 (the supplied washing water amount) is therefore less than the predetermined supplied washing water amount. When the supplied washing water amount falls below the predetermined supplied washing water amount, the washing water circulation supply control section 53 supplies washing water from the washing water circulation supply tube 37 to the second water scrubber 7 such that the amount of washing water flowing down in the second water scrubber 7 be not less than the predetermined supplied washing water amount.

[0091] Even if any washing water is not supplied from the washing water supply tube to the second water scrubber 7, the amount of washing water flowing down in the second water scrubber 7 can be maintained at not less than the predetermined supplied washing water amount. This prevents any decrease in ammonia removal rate in the second water scrubber 7.

[0092] The product gas is supplied to the absorber 8 after having moisture removed by the knockout drum 13. This prevents the absorption liquid of the absorber 8 from decreasing in concentration (from diluting due to moisture in the product gas). Furthermore, since the moisture removed from the product gas is supplied to the second water scrubber 7 through the recovered water supply tube 41, it is possible to reduce the amount of water supplied to the second water scrubber 7 from outside of the system (the use of industrial water).

[0093] Furthermore, the cooler 12 for cooling the product gas flowing into the knockout drum 13 is not provided upstream from the second water scrubber 7 but provided downstream, so that the hot product gas before cooled by the cooler 12 flows into the second water scrubber 7. The wastewater in the second water scrubber 7 used as direct quench water is heated by the hot product gas, thus resulting in less thermal shock at collision of droplets of direct quench water sprayed from the water spray apparatus 3 with the inner wall surface defining the water spray section 2.

[0094]

[Second Embodiment] Next, a gasification system of a second embodiment of the present invention is described with reference to Figs. 4 and 5. The second embodiment is different from the first embodiment in terms of control. The same configurations as those of the first embodiment are given the same reference numerals, and the description thereof is omitted.

[0095] As illustrated in Figs. 4 and 5, the gasification system of the second embodiment includes a flow rate sensor (a gas amount detector) 42 that detects the amount of product gas flowing from the knockout drum 13 to the absorber 8 as a product gas amount. The control apparatus includes a tank water amount control section 54. The tank water amount control section 54 and valve 32 constitute a tank water amount controller configured to control supply of water from the spray water replenishing tube 31 to the wastewater tank 21.

[0096] The washing water supply control section 52 controls supply of washing water from the washing water supply tube 35 to the second water scrubber 7 depending on the product gas amount detected by the flow rate sensor 42. The wastewater supply control section 51 controls supply of wastewater from the wastewater supply tube 9 to the wastewater tank 21 such that the reserved washing water amount detected by the level sensor 46 be maintained at a given predetermined reserved washing water amount.

[0097] When the tank water amount of the wastewater tank 21 detected by the level sensor 40 exceeds a given upper tank water amount limit, the washing water supply control section 52 stops supply of washing water from the washing water supply tube 35 to the second water scrubber 7; the wastewater supply control section 51 stops supply of wastewater from the wastewater supply tube 9 to the wastewater tank 21; and the washing water circulation supply control section 53 controls circulation supply of washing water from the washing water circulation supply tube 37 to the second water scrubber 7 depending on the product gas amount detected by the flow rate sensor 42.

[0098] The tank water amount control section 54 controls supply of water from the spray water replenishing tube 31 to the wastewater tank 21 such that the tank water amount detected by the level sensor 40 not fall below a given lower tank water amount limit.

[0099] According to the second embodiment, the washing water supply control section 52 increases or decreases the amount of washing water supplied from the washing water supply tube 35 to the second water scrubber 7 (the supplied washing water amount) depending on an increase or decrease in the amount of product gas flowing from the second water scrubber 7 to the absorber 8 through the knockout drum 13 (the product gas amount). The wastewater supply control section 51 controls supply of wastewater from the wastewater supply tube 9 to the wastewater tank 21 such that the reserved washing water amount in the second water scrubber 7 be maintained at the predetermined reserved washing water amount.

[0100] Since the amount of washing water supplied to the second water scrubber 7 depends on the amount of product gas flowing in the second water scrubber 7 in such a manner, it is possible to remove ammonia from the product gas efficiently and surely.

[0101] Furthermore, since the reserved washing water amount in the second water scrubber 7 is maintained at the predetermined reserved washing water amount, the water pump 33 can be prevented from incorporating air or prevented from running dry. In addition, the predetermined reserved washing water amount is set such that the inlet of the product gas to the second water scrubber 7 be not submerged underwater. This prevents the inlet of the product gas from being submerged underwater.

[0102] When the amount of wastewater reserved in the wastewater tank 21 (the tank water amount) increases and exceeds the upper tank water amount limit, the wastewater supply control section 51 stops supply of wastewater from the wastewater supply tube 9 to the wastewater tank 21. The tank water amount of the wastewater tank 21 therefore can be adjusted so as not to exceed the upper tank water amount limit. Furthermore,the washing water supply control section 52 stops supply of washing water from the washing water supply tube 35 to the second water scrubber 7, so that the reserved washing water amount in the second water scrubber 7 can be prevented from excessively increasing (for example, increasing and exceeding an upper reserved washing water limit which is not less than the predetermined reserved washing water amount and with which the inlet of the product gas is not submerged underwater).

[0103] When the tank water amount of the wastewater tank 21 exceeds the upper tank water amount limit and the washing water supply control section 52 stops supply of washing water from the washing water supply tube 35 to the second water scrubber 7, the washing water circulation supply control section 53 supplies washing water from the washing water circulation supply tube 37 to the second water scrubber 7 such that the amount of washing water flowing down in the second water scrubber 7 be not less than a predetermined supplied washing water amount.

[0104] Even if any washing water is not supplied from the washing water supply tube to the second water scrubber 7, therefore, the amount of washing water flowing down in the second water scrubber 7 can be maintained at not less than the predetermined supplied washing water amount. This prevents any decrease in ammonia removal rate in the second water scrubber 7.

[0105] The amount of wastewater reserved in the wastewater tank 21 (the tank water amount) can be maintained at not less than the lower tank water amount limit. If wastewater (direct quench water) is supplied from the wastewater tank 21 to the water spray apparatus 3 using a water pump (not illustrated), the water pump can be prevented from incorporating air or prevented from running dry.

[0106] The present invention is not limited to the above embodiments and modifications described by way of example and, in addition to the above-described embodiments and the like, can be variously changed in accordance with the design and the like without departing from the technical idea according to the present invention.

[0106a] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0106b] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates. REFERENCE SIGNS LIST

[0107] 1 GASIFIER 2 WATER SPRAY SECTION 3 WATER SPRAY APPARATUS 4 DEDUSTING APPARATUS (DEDUSTING FACILITY) FIRST WATER SCRUBBER

6 SHIFT REACTOR 7 SECOND WATER SCRUBBER 8 ABSORBER 9 WASTEWATER SUPPLY TUBE WASTEWATER TREATMENT APPARATUS (WASTEWATER TREATMENT FACILITY) 11 CHAR FILTER 12 COOLER 13 KNOCKOUTDRUM 14 REGENERATION TOWER 21 WASTEWATER TANK FIRST GAS TEMPERATURE SENSOR (GAS TEMPERATURE DETECTOR) 26 SECOND GAS TEMPERATURE SENSOR (GAS TEMPERATURE DETECTOR) 27 DEDUSTING INLET GAS TEMPERATURE SENSOR (GAS TEMPERATUREDETECTOR) 28 FIRST SPRAY AMOUNT REGULATION VALVE (SPRAY AMOUNT CONTROLLER) 29 SECOND SPRAY AMOUNT REGULATION VALVE (SPRAY AMOUNT CONTROLLER) THIRD SPRAY AMOUNT REGULATION VALVE (SPRAY AMOUNT CONTROLLER) 32 VALVE (TANK WATER AMOUNT CONTROLLER) 33 WATER PUMP (WASTEWATER SUPPLY CONTROLLER) 34 VALVE (WASTEWATER SUPPLY CONTROLLER) 36 VALVE (WASHING WATER SUPPLY CONTROLLER) 38 WATER PUMP (WASHING WATER CIRCULATION SUPPLY CONTROLLER) 39 FLOW RATE SENSOR (SUPPLIED WASHING WATER AMOUNT DETECTOR) LEVEL SENOR (TANK WATER AMOUNT DETECTOR) 42 FLOW RATE SENSOR (GAS AMOUNT DETECTOR) 46 LEVEL SENSOR (RESERVED WASHING WATER AMOUNT DETECTOR) SPRAY AMOUNT CONTROL SECTION (SPRAY AMOUNT CONTROLLER) 51 WASTEWATER SUPPLY CONTROL SECTION (WASTEWATER SUPPLY

CONTROLLER) 52 WASHING WATER SUPPLY CONTROL SECTION (WASHING WATER SUPPLY CONTROLLER) 53 WASHING WATER CIRCULATION SUPPLY CONTROL SECTION (WASHING WATER CIRCULATION SUPPLY CONTROLLER) 54 TANK WATER AMOUNT CONTROL SECTION (TANK WATER AMOUNT CONTROLLER) TURBINE

24a

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

[Claim 1] A gasification system for carbon-based fuel, comprising: a gasifier which gasifies carbon-based fuel with an oxidant to provide a product gas composed of mainly carbon monoxide and hydrogen; a water spray apparatus which sprays water onto the product gas downstream from the gasifier; a dedusting apparatus which removes unreacted coal from the product gas downstream from the water spray apparatus; a first water scrubber which removes halogen from the product gas downstream from the dedusting apparatus; a shift reactor which converts water vapor and carbon monoxide in the product gas into hydrogen and carbon dioxide through a shift reaction downstream from the first water scrubber; a second water scrubber which removes ammonia from the product gas downstream from the shift reactor; an absorber which removes hydrogen sulfide and carbon dioxide from the product gas downstream from the second water scrubber; and a wastewater supply tube which supplies wastewater of the second water scrubber to the water spray apparatus, wherein the water spray apparatus sprays wastewater supplied from the wastewater supply tube.
[Claim 2] The gasification system for carbon-based fuel according to claim 1, further comprising: a cooler which is provided between the second water scrubber and the absorber and cools the product gas downstream from the second water scrubber; a knockout drum which is provided between the cooler and the absorber and condenses and removes moisture in the product gas downstream from the cooler; and a recovered water supply tube which recovers the moisture removed from the product gas by the knockout drum and supplies the recovered moisture to the second water scrubber.
[Claim 3] The gasification system for carbon-based fuel according to claim 1 or 2, wherein the water spray apparatus includes plural nozzles in layers arranged from upstream to downstream and sprays wastewater supplied from the wastewater supply tube through the plural nozzles in layers.
[Claim 4] The gasification system for carbon-based fuel according to claim 3, wherein the water spray apparatus includes: a gas temperature detector which detects the temperature of the product gas lowered by water spray from the nozzle in a first layer at the upstream end, as a gas temperature after water spray in the first layer; and a spray amount controller which controls the amount of water sprayed from the nozzle in the first layer such that the detected gas temperature after water spray in the first layer be a given first-layer target temperature that is not lower than thermal decomposition temperature of ammonia.
[Claim 5] The gasification system for carbon-based fuel according to claim 4, wherein the gas temperature detector detects the temperature of the product gas flowing into the dedusting apparatus as a dedusting inflow temperature, and the spray amount controller controls the amount of water sprayed from the nozzle in the last layer such that the detected dedusting inflow temperature be a given target inflow temperature which is not lower than the dew point and not higher than an upper operating temperature limit of the dedusting apparatus.
[Claim 6] The gasification system for carbon-based fuel according to any one of claims 1 to 5, further comprising a wastewater tank which is provided in the middle of the wastewater supply tube and is able to temporarily reserve wastewater of the second water scrubber.
[Claim 7] The gasification system for carbon-based fuel according to claim 6, further comprising: a washing water supply tube which supplies to the second water scrubber, washing water that flows down in the second water scrubber to remove ammonia from the product gas; a reserved washing water amount detector which detects the amount of washing water having flowed down in the second water scrubber and accumulated in the bottom of the second water scrubber, as a reserved washing water amount; a washing water supply controller which controls supply of washing water from the washing water supply tube to the second water scrubber such that the detected reserved washing water amount be maintained at a given predetermined reserved washing water amount; a tank water amount detector which detects the amount of wastewater reserved in the wastewater tank, as a tank water amount; and a wastewater supply controller which controls supply of wastewater from the wastewater supply tube to the wastewater tank such that the detected tank water amount not fall below a given lower tank water amount limit.
[Claim 8] The gasification system for carbon-based fuel according to claim 7, further comprising: a supplied washing water amount detector which detects the amount of washing water supplied from the washing water supply tube to the second water scrubber as a supplied washing water amount; a washing water circulation supply tube which supplies part of wastewater intended to be supplied from the second water scrubber to the water spray apparatus, to the second water scrubber as washing water to remove ammonia from the product gas; and a washing water circulation supply controller which, when the detected supplied washing water amount is less than a given predetermined supplied washing water amount, controls supply of washing water from the washing water circulation supply tube to the second water scrubber such that the amount of washing water flowing down in the second water scrubber be not less than the predetermined supplied washing water amount.
[Claim 9] The gasification system for carbon-based fuel according to claim 6, the gasification system comprising: a washing water supply tube which supplies to the second water scrubber, washing water that flows down in the second water scrubber to remove ammonia from the product gas; a gas amount detector which detects the amount of product gas flowing from the second water scrubber to the absorber, as a product gas amount; a washing water supply controller which controls supply of washing water from the washing water supply tube to the second water scrubber depending on the detected product gas amount; a reserved washing water amount detector which detects the amount of washing water having flowed down in the second water scrubber and accumulated in the bottom of the second water scrubber, as a reserved washing water amount; and a wastewater supply controller which controls supply of wastewater from the wastewater supply tube to the wastewater tank such that the detected reserved washing water amount be maintained at a given predetermined reserved washing water amount.
[Claim 10] The gasification system for carbon-based fuel according to claim 9, comprising: a tank water amount detector which detects an amount of wastewater reserved in the wastewater tank, as a tank water amount; a washing water circulation supply tube which is able to supply part of wastewater intended to be supplied from the second water scrubber to the water spray apparatus, to the second water scrubber as washing water to remove ammonia from the product gas; and a washing water circulation supply controller which controls supply of washing water from the washing water circulation supply tube to the second water scrubber, wherein when the detected tank water amount exceeds a given upper tank water amount limit, the washing water supply controller stops supply of washing water from the washing water supply tube to the second water scrubber; the wastewater supply controller stops supply of wastewater from the wastewater supply tube to the wastewater tank; and the washing water circulation supply controller controls supply of washing water from the washing water circulation supply tube to the second water scrubber, depending on the detected product gas amount.
[Claim 11] The gasification system for carbon-based fuel according to claim 9, further comprising: a spray water replenishing tube which is able to supply water to the wastewater tank separately from the wastewater supply tube; a tank water amount detector which detects the amount of wastewater reserved in the wastewater tank as a tank water amount; and a tank water amount controller which controls supply of water from the spray water replenishing tube to the wastewater tank such that the detected tank water amount not fall below a given lower tank water amount limit.