AU2013251229B2

AU2013251229B2 - Gasification system for solid fuel

Info

Publication number: AU2013251229B2
Application number: AU2013251229A
Authority: AU
Inventors: Takuya Ishiga; Fumihiko Kiso; Fumihiko Nagaremori; Akinori Suetsugu
Original assignee: Mitsubishi Power Ltd
Current assignee: Mitsubishi Power Ltd
Priority date: 2012-11-08
Filing date: 2013-10-31
Publication date: 2016-04-21
Anticipated expiration: 2033-10-31
Also published as: JP2014095004A; AU2013251229A1; JP6057674B2; CN103805280B; CN103805280A

Abstract

An object is to suppress energy efficiency reduction due to fuel drying and to effectively utilize steam generated through fuel drying in a gasification system using lignite or 5 another high-moisture solid fuel. A high-moisture solid fuel having a high moisture content is dried upstream from a gasifier. The high-moisture solid fuel after drying is fed to the gasifier to thereby prevent temperature fall in the gasifier. A steam-containing gas evolved through fuel drying is fed to 10 downstream from the gasifier, cools the syngas, and accelerates the shift reaction. Examples of the fuel-drying heat source include steam generated through heat recovery downstream from the shift reactor; plant exhaust heat derived typically from steam used for regenerative heating of a CO 2 15 absorbing liquid in a CO 2 regeneration tower; and CO 2 adiabatically compressed after being recovered from the syngas. CO CD co Co Uj co U') -j C) 0 Q0 C, co --------- ui Ul) to co co co C) C) co C) m ui -Jo 0 C-) 0 CMI) C) Cw) C14 C', C 'C ' U') co cq U-1 cq co to U') cn: cli co cli co U') 0-0

Description

Australian Patents Act 1990 - Regulation 3.2 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention Title Gasification system for solid fuel The following statement is a full description of this invention, including the best method of performing it known to me/us:- The present invention relates to a gasification system using lignite or another solid fuel having a high moisture content and to a system that less suffers from energy efficiency reduction due to drying of the solid fuel. 5 Lignite and other high-moisture solid fuels are increasingly used in an amount reaching about one half of the total amount of coal to be used. Lignite has a high moisture content of from about 30% to about 65%. This moisture content is 5 to 10 times that of bituminous coal which has been used in a large amount for power generation in 10 Japan. Lignite has a net heating value per unit weight of from about 40% to about 70% of that of bituminous coal and has a combustion temperature lower than that of bituminous coal by several hundreds of degrees when used at an equivalent oxygen amount. In a coal gasifier, coal is partially burnt (gasified) to 15 evolve a syngas mainly containing CO and H:; the syngas is recovered; and ash contained in the coal is heated and melted into a fused slag and thereby separated from the syngas. The coal gasifier should have its internal temperature raised to the ash melting point (1200*C to 16000C) or higher. If lignite is charged as intact into the 20 gasifier, the high moisture content and low net heating value thereof may prevent the temperature rise in the gasifier, and this may impede ash 2 melting in the gasifier and thereby impede the gasification operation. To raise the gasifier internal temperature, lignite should be dried to have a lower moisture content and to have a higher net heating value before being charged into 5 the gasifier. In addition, the gasification system requires such lignite drying as to less consume energy and to effectively utilize generated steam (water vapor), for higher energy efficiency of the gasification system as a whole. Typically, 10 Patent Literature 1(Japanese Unexamined Patent Application Publication No. 2011-214562) discloses a lignite drying system employing a fluidized bed for lignite drying. In this system, generated steam is used in three ways as follows: (1) the steam is recycled into the fluidized bed and used as 15 a lignite fluidizing gas and as a heat source for direct heating; (2) steam newly generated through heat recovery from the steam is used as a heat source for indirect heating of lignite in the fluidized bed; and 20 (3) the steam is used as steam for shift reaction in a shift reactor. Patent Literature 2 (PCT International Publication WO 2011-129192) discloses a coal gasification system which includes a dryer arranged upstream from a coal gasification 25 reactor (gasifier). The dryer dries subbituminous coal or lignite having a predetermined moisture content to give a l iu iuneosen;,aRI'oriND CtCiW fli(n 1 docelI H.r in moisture-controlled coal. The system gives the moisture-controlled coal having a predetermined moisture content and thereby efficiently gasifies tar/char without feeding steam to the gasifier. The invention provides a solid-fuel gasification system comprising: 5 a dryer that dries a high-moisture solid fuel having a moisture content reaching 30 to 65 percent by weight; a pulverizing equipment that pulverizes the high-moisture solid fuel after drying: a hopper that stores the high-moisture solid fuel after pulverization: a fuel feed line; 10 a gasifier; a syngas cooling unit; a dust removal equipment; a water washing tower; a desulfurization equipment; 15 two or more CO shift reactors; and a CO 2 recovery device, wherein the hopper includes a lock hopper and a feed hopper; the solid-fuel gasification system further comprising a syngas feed line that feeds a syngas at the upstream side of the two or more CO shift reactors or heat of reaction of the 20 syngas to the dryer, wherein heat of reaction generated at the upstream side of the two or more CO shift reactors is used as a drying heat source in the dryer, and a steam-containing gas evolved in the dryer is supplied to at least one of the syngas cooling unit and the CO shift reactor. 25 A gasification system in which lignite or another high-moisture solid fuel is dried before being fed into a gasifier requires such fuel drying as to less consume energy and to effectively utilize generated steam, for higher energy efficiency of the system as a whole.

-3A Initially, exemplary provisional calculations of energy consumption in fuel drying are performed as follows. Assume that a high-moisture solid fuel having a moisture content of50 percent by weight is dried in an amount of 1500 t/d (containing water in an amount of 750 t/ld) into a high-moisture solid fuel having a moisture content of25 percent by weight in an amount 5 of 1000 t/d (containing II igutmto Rono~G M 7 I dccu2la 1112111 3B water in an amount of 250 t/d), and the solid fuel after drying is charged into a gasifier. In this case, the total heating value of the fuel after drying and the heat quantity required for fuel drying are indicated in Tables 1 and 2, respectively. 5 The provisional calculation in Table 2 is performed on the assumption that moisture (water) in the fuel is present as a liquid at 20*C, and the term "fuel drying" is defined as heating water in a liquid state at 20*C to steam (water vapor) 4 at 100'C. As is known from (4) (in gigajoule per day) in Table 1 and (10) in Table 2, the heat quantity necessary for fuel drying reaches about 7% of the total heating value of the fuel after 5 drying. A fuel-drying heat source for use herein has only to have a temperature of 100'C or higher, and exhaust heat generated in the gasification system is effectively used as the heat source. A gasification system, when including a device for recovering CO 2 from a syngas, is possibly a system 10 where the recovered CO 2 is heated to be used as a fuel-drying heat source. However, Patent Literature 1 does not refer to such a gasification system that dries the fuel with exhaust heat of the gasification system or recovered C0 2 . [Table 1] 15 TABLE 1 Exemplary Provisional Calculation of Total Heating Value of Fuel After Drying (1000 t/d) Item Unit Value Remarks (1) Amount of fuel after drying t/d 1000 1500 t/d before drying (2) Total moisture content percent by 25 50 percent by weight before weight drying (3) Net heating value kJ/kg 18600 (4) Total heating value of fuel after GJ/d 18600 (1) x (3) drying [Table 2] 20 TABLE2 Exemplary Provisional Calculation of Heat Quantity Necessary for Fuel Drying (fuel before drying 1500 t/d (moisture content 50 percent by weight is dried into fuel after drying 1000 t/d (moisture content 25 percent by weight) Item Unit Value Remarks (5) Evaporated water amount t/d 500 from (1) and (2) (6) Temperature before drying 0 C 20 liquid 5 (7) Temperature after drying 0 C 100 steam (8) Specific heat of water kJ/kg 4.2 (9) Latent heat of vaporization kJ/kg 2256 (10) Heat quantity necessary for fuel GJ/d 1296 water at 20 0 C is converted into steam at drying 100 0 C A possible effective utilization of steam generated through fuel drying is the use of the steam as steam for power generation, as a fluidizing medium or a drying heat source in fuel drying, or steam to be used in the gasification system. 5 The steam generated through fuel drying, when having a temperature of 100'C at normal atmospheric pressure, has a temperature and a pressure significantly lower than the temperature (500'C or higher) and the pressure (20 MPa or greater) of steam to be used typically in thermal power 10 generation, resulting in poor energy efficiency. If the steam is used as a fluidizing medium or a drying heat source in fuel drying, the entire generated steam should be ultimately recovered as water, and this requires extra waste-water treatment equipment. 15 For these reasons, in a preferred gasification system, steam generated through fuel drying is used as steam for use in the gasification system and treated in an existing water treatment equipment. Specifically, the steam generated through fuel drying is advantageously used for syngas cooling 20 and for CO shift reaction. Patent Literature 1 describes a system of using steam generated through fuel drying as steam for CO shift reaction in the CO shift reactor, but fails to teach a system of charging 6 the steam into a syngas cooling unit. Patent Literature 2 discloses a novel coal gasification system that decomposes char with water (moisture) contained in the moisture controlled coal. Specifically, it is effective for char 5 decomposition to feed steam from a steam nozzle and to make the inside atmosphere of the pyrolytic gasification reactor steam enriched; but, with an increasing amount of the steam, the inside temperature of the gasification reactor falls down to reduce the reaction rate, and such a large amount of steam to be fed requires 10 certain facilities. Patent Literature 2, however, lacks a description about a gasification system that suitably feeds steam to a gasification reactor and treats steam discharged in a drying process typically of lignite. According to embodiments of the present invention, steam 15 generated through fuel drying is mixed with a high-temperature syngas in a syngas cooling unit arranged downstream from the gasifier so as to achieve both syngas cooling and CO shift reaction acceleration. Such syngas cooling unit is most promising for the use of the steam generated through fuel drying because the steam at 100*C has only to 20 be pressurized before being charged into the syngas cooling unit. Specifically, a solid fuel having a high moisture content is dried upstream from a gasifier, and the dried solid fuel is then fed to the gasifier. Independently, a steam-containing gas evolved through fuel drying is fed to downstream from the gasifier and mixed 25 with a syngas to cool the syngas and to accelerate the CO shift reaction. Excess steam-containing gas is fed as shift-reaction steam to the shift reactor. Exhaust heat generated in the gasification system is used as a fuel-drying heat source. When the system includes a device for 30 recovering CO from a syngas, the heat source for use herein is exemplified by the syngas heated in the CO shift reactor; steam generated in a heat recovery unit downstream from the CO shift Higku~iimslRw o nbDC um 758 doce-2OiIld20)I 7 reactor; and steam used for regenerative heating of a CO absorbing liquid in a CO 2 regeneration tower. The recovered CO: is adiabatically compressed, the resulting high-temperature CO- is used as a heat source to dry the fuel, and the solid fuel after drying is 5 fed to the gasifier with the CO 2 . The fuel drying is mainly performed in a dryer (drying equipment), but a fuel stored in a lock hopper with pressurization may be dried. The fuel may be stored in the lock hopper for a duration of at least 20 minutes. The fuel is pressurized by charging 10 a feed vehicle into the lock hopper. Accordingly, the fuel can be dried in the lock hopper by charging the CO 2 warmed through the adiabatic compression into the lock hopper. According to embodiments of the present invention, steam generated through fuel drying is mixed with a syngas downstream from 15 the gasifier to cool the syngas and to accelerate a CO shift reaction upstream process from the shift reactor. This reduces the size of the syngas cooling unit and the amount of the shift-reaction steam to be used in the CO shift reactor. In addition, embodiments of the present invention employ plant exhaust heat, which has not been 20 utilized, as a fuel-drying heat source in the dryer and thereby less suffers from energy efficiency reduction due to fuel drying. The plant exhaust heat is exemplified by excess steam generated in the heat recovery unit arranged downstream from the CO shift reactor; and steam after being used for regenerative heating of the CO: absorbing 25 liquid in the CO 2 regeneration tower. The present invention will now be described, by way of non limiting example only, with reference to the accompanying drawings as briefly described below. Fig. 1 is a system diagram illustrating a solid-fuel 30 gasification system according to First Embodiment of the present invention.

Fig. 2 is a system diagram illustrating a solid-fuel gasification system according to Second Embodiment of the present invention. Fig. 3 is a system diagram illustrating a solid-fuel 5 gasification system according to Third Embodiment of the present invention. Fig. 4 is a system diagram illustrating a solid-fuel gasification system according to Fourth Embodiment of the present invention. 10 Solid-fuel gasification systems according to embodiments of the present invention will be illustrated with reference to several examples (embodiments) below. [First Embodiment] Fig. 1 is a system diagram illustrating a solid-fuel 15 gasification system according to First Embodiment of the present invention. The solid-fuel gasification system according to First Embodiment includes a dryer for a high-moisture solid fuel, a shift reactor, and a CO2 recovery device. The system employs, as a heat source for the dryer, a syngas warmed through a shift reaction; and 20 CO 2 derived from part of the recovered CO warmed by adiabatic compression. A high-moisture solid fuel 1 such as lignite has a high moisture content reaching 30 to 65 percent by weight, which is as much as 5 to 10 times that of bituminous coal. The bituminous coal 25 is widely used for power generation in Japan. The high-moisture solid fuel 1 such as lignite also has a low heating value per unit weight and is difficult to be directly charged into a gasifier 16. This is because such a large amount of moisture suppresses rise of the gasifier internal temperature, and this impedes ash melting and 30 stable discharge of fused slag.

I ignilwtrnosc enNRrotblIDCCtG 1167511_ I dccs-211' 112111i1 9 To prevent this, the high-moisture solid fuel 1 is initially dried in a dryer 2 and pulverized in pulverizing equipment 3. Thereafter the pulverized fuel is stored in a 10 lock hopper 4, transferred via a transfer valve 6 to a feed hopper 5, and fed via a feed pipe 10 to the gasifier GF, as with customary gasification systems typically for bituminous coal. 5 The gasifier GF includes a gasifier unit 16 and a syngas cooling unit 18. Oxygen 15 is also fed to the gasifier unit 16, which oxygen has been separated from air 11 in an air separation unit 13. The high-moisture solid fuel 1 is gasified in the gasifier to evolve a high-temperature syngas 17. 10 Simultaneously with this, ash in the fuel is melted (fused) in a high temperature atmosphere in the gasifier and separated as a fused slag from the syngas 17. The syngas 17 may have a temperature reaching 1000'C or higher at the outlet of the gasifier unit 16, entrains char 20, and is cooled down to a 15 temperature of lower than 400'C in the syngas cooling unit 18. The syngas 17 is dedusted by a dust removal equipment 19 arranged downstream from the syngas cooling unit 18. The recovered char 20 is charged again into, and gasified again in, the gasifier 16. 20 The syngas 17 dedusted by the dust removal equipment 19 is cooled down to about 100 C, from which halogen-containing substances and fine dust are removed, in a water washing tower 33 and is desulfurized in a desulfurization tower 34. The syngas 35 at a temperature of about 40'C after desulfurization 25 is heated to 200'C or higher by a syngas heat exchanger 36 and a syngas heater 37 and fed to a shift reactor. The term "shift 11 reaction" refers to a reaction represented by Formula (1) . The reaction, when proceeding rightward, is an exothermic reaction. Formula (1) is expressed as follows: CO + H 2 0 - C02 + H 2 (1) 5 The shift reaction actively proceeds at 1000'C or higher in the absence of a catalyst, but can actively proceed even at 500'C or lower in the presence of a shift catalyst. The heating temperature of the syngas 35 after desulfurization is determined by the activating temperature of the catalyst 10 loaded in the shift reactor. In general, the shift reactor is arranged in a number of two or more, recovers the heat of shift reaction downstream from the shift reactor, thereby maintains the inside temperature of the shift reactor within a predetermined range, 15 and protects the shift catalyst. The exemplary system according to First Embodiment employs two shift reactors arranged in series, i.e., a first shift reactor 38 and a second shift reactor 54 when seen from upstream. A syngas 41 emitted after the shift reaction from the 20 second shift reactor 54 mainly contains CO 2 and hydrogen and has a temperature of 200'C or higher. The syngas 41 is cooled in the syngas heat exchanger 36 and fed to a CO 2 recovery device. The syngas 41 after the shift reaction is brought into contact with a CO 2 absorbing liquid in a CO 2 absorption tower 42 to 25 remove CO 2 therefrom. A syngas 43 after CO 2 absorption mainly contains hydrogen and is usable as a power generation fuel, 12 as well as a raw material typically for methanol, DME (dimethyl ether), and ammonia. The CO 2 absorbing liquid 47, which has absorbed CO 2 in the

CO

2 absorption tower 42, is heated to 100'C or higher by a heat 5 exchanger 44 and a heater 45 and fed to a CO 2 regeneration tower 46. The CO 2 absorbing liquid 47 after absorption of CO 2 can be reused (recycled) by allowing the same to release CO 2 in the CO 2 regeneration tower 46.

CO

2 101 recovered in the CO 2 regeneration tower 46 is 10 separated into two portions, i.e., recycled CO 2 102 and pooled

CO

2 103. The flow rate of the recycled CO 2 102 is regulated by a recycled-CO 2 flow-rate control valve 51. Of the recycled

CO

2 102, CO 2 exhausted from the gasification system (symbols *b, *c, and *e) is preferably mixed with the pooled CO 2 103 15 and stored typically in the ground. The absorbing liquid should be kept warm to maintain a high CO 2 recovery percentage in the CO 2 regeneration tower 46. In a preferred embodiment for this purpose, part of the absorbing liquid is extracted as a CO 2 absorbing liquid 48 for 20 regenerative heating, reheated to 100'C or higher by a CO 2 absorbing liquid heater 49, and returned to the CO 2 regeneration tower 46. Steam at a low temperature of from about 150'C to about 300'C is suitable as a heat source for the regenerative heating, and this is referred to as steam 50 25 for CO 2 absorbing liquid regenerative heating. First Embodiment illustratively employs chemical 13 absorption using an absorbing liquid to recover CO 2 from the syngas 41 after the shift reaction. However, the CO 2 recovery can be performed by any other CO 2 recovery procedure such as physical absorption, chemical absorption, adsorption, 5 membrane separation, or cryogenic separation. Next, the high-moisture solid fuel after drying in the dryer 2 desirably has a moisture content of 25 percent by weight or less, though the moisture content may vary depending on the fuel properties and condition. The solid fuel, when dried to 10 a moisture content of this level, can be pulverized by a handling (treatment) as with bituminous coal. The moisture content after drying is preferably determined according to the coal type in consideration of pulverizability and gasifier internal temperature. 15 Moisture contained in lignite is probably present as a liquid and adsorbed by particles. To dry the moisture in lignite, water in a liquid state is heated to 100'C and thereby evaporated into steam. Independently, lignite is distinctively more pyrophoric than bituminous coal is, and has 20 a risk of spontaneous combustion at a temperature of 150'C or higher in an air atmosphere. Accordingly, the drying heat source should have a temperature of 100'C or higher, and the dryer 2 is evacuated with a non-oxidizing gas and sealed so as to reduce the oxygen concentration. The non-oxidizing gas 25 for use in this embodiment is exemplified by CO 2 , nitrogen, steam, and argon, of which CO 2 or steam is preferred because 14 the use of a high-temperature gas is advantageous. A large amount of steam is generated in the dryer 2, as indicated in Table 2. The use of this steam eliminates the need of a steam generation process by heat recovery as in 5 customary gasification systems typically for bituminous coal. The use of heat in this process as a drying heat source allows the gasification system to less suffer from energy efficiency reduction due to fuel drying. In the illustrated gasification system according to First 10 Embodiment, the steam generated in the dryer 2 is compressed by a compressor 28 to have a high pressure as with that of the gasifier unit 16, then used for cooling of the syngas 17 generated in the gasifier unit 16, and also used as a shift-reaction steam 40. 15 In the customary gasification systems, such shift-reaction steam 40 is mainly generated downstream from the shift reactor by the action of shift reaction heat as a heat source. However, when a steam-containing gas 27 can be used as the shift-reaction steam 40, there is an excess heat 20 typically downstream from the first shift reactor 38, where the heat is derived from a syngas 53 warmed by the shift reaction. Accordingly, in a preferred embodiment, the high-temperature syngas 53 is fed to the dryer 2, and the 25 sensible heat thereof is used as the drying heat source, which high-temperature syngas 53 has been obtained through the shift 15 reaction. The high-temperature syngas 53 has a temperature of 200'C or higher and is suitable as the drying heat source. This temperature may vary depending on the activating temperature of the shift reaction catalyst and/or on how the 5 catalyst is loaded. Exemplary procedures for cooling the syngas 17 in the syngas cooling unit 18 include: (a) heat exchange typically to steam in a heat-exchanger tube; (b) spraying of spray water 32; and 10 (c) mixing with the steam-containing gas 29 in the syngas cooling unit. The gasification system for the high-moisture solid fuel 1 can employ the procedure (c), and this enables reduction in size of the syngas cooling unit 18 and in amount (flow rate) 15 of the spray water 32. When the syngas 17 at 1000'C or higher is mixed with the steam-containing gas in the syngas cooling unit 18 as in the procedure (c), the shift reaction represented by Formula (1) proceeds even in the absence of a catalyst. This reduces the amount of the shift-reaction steam 40 20 to be charged into a downstream shift reactor. In addition, useful hydrogen is also recovered from the steam-containing gas 27 generated through drying of the high-moisture solid fuel 1. Thus, the moisture in the high-moisture solid fuel 1 is effectively utilized. The flow rate of the steam-containing 25 gas in the syngas cooling unit 18 in the procedure (c) is limited by the gas composition in the downstream water washing tower 16 33 and/or by the flow rate of the spray water in the procedure (b), and this requires a flow-rate control valve 31 to be arranged. In contrast, the whole quantity of the steam-containing 5 gas 27 can be utilized as the steam-containing gas 30 to be fed to the shift reactor, as in the case illustrated in Table 2. This is because the shift-reaction steam 40 is operated at a stoichiometric ratio or more (may be operated at a ratio about two times the stoichiometric ratio). This eliminates 10 the need of a flow-rate control valve, and the system has only to include a steam-containing gas heater 39 for heating the gas up to a temperature suitable for the shift reaction. The system according to First Embodiment employs part of the CO 2 recovered in the system as an inert gas for feeding 15 the post-drying high-moisture solid fuel and char 20. Specifically, part of the recovered CO 2 101 is separated as recycled CO 2 102, subjected to adiabatic compression in a CO 2 compressor 52 to increase the pressure and temperature thereof and to give compressed CO 2 104, and the compressed CO 2 104 is 20 fed to the dryer 2. The compressed CO 2 104 is fed so as to use its sensible heat as a drying heat source in the dryer 2. Typically, CO 2 at room temperature and normal atmospheric pressure, when compressed to a pressure of 10 MPa, can be raised in temperature to about 100'C. 25 Part of CO 2 discharged from the dryer 2 is fed as a feed vehicle to the lock hopper 4 and the feed hopper 5 for the 17 post-drying high-moisture solid fuel, as well as to the char lock hopper 21 and the char feed hopper 22, and thereby fed to the gasifier GF. The flow rate of CO 2 used as the feed vehicle is controlled by a feed vehicle CO 2 flow-rate control 5 valve 60. As is described above, the system according to First Embodiment uses the steam-containing gas evolved through drying of the high-moisture solid fuel for cooling of the high-temperature syngas evolved in the dryer. This can not 10 only reduce the size of the syngas cooling unit, but also recover hydrogen from moisture in the fuel due to acceleration of the shift reaction even in the absence of a catalyst, and, in addition, reduce the amount of steam in the downstream shift reactor. 15 The system also fully utilizes the residual steam-containing gas as the shift-reaction steam in the shift reactor and can significantly reduce the amount of shift-reaction steam to be fed from outside of the system. In addition, the system employs, as the heat source for 20 heating the high-moisture solid fuel, the sensible heat of the syngas warmed by the shift reaction and serving as the heat source; and the sensible heat of CO 2 derived from part of the recovered CO 2 and warmed by adiabatic compression. The system can therefore serve as a gasification system which less suffers 25 from energy efficiency reduction due to fuel drying and effectively utilizes the moisture in the high-moisture solid 18 fuel. [Second Embodiment] Fig. 2 depicts a system diagram illustrating a solid-fuel gasification system according to Second Embodiment of the 5 present invention. The system according to Second Embodiment differs from the system according to First Embodiment illustrated in Fig. 1 in how to use the sensible heat of the high-temperature syngas 53 obtained through the shift reaction and in the drying heat source for the dryer 2. These 10 differences will be illustrated below. The system according to Second Embodiment further includes a shift heat exchanger 55 that recovers the sensible heat of the high-temperature syngas 53 obtained through the shift reaction and discharged from the first shift reactor 38. 15 The shift heat exchanger 55 heats steam up to 200'C or higher by the action of the sensible heat and feeds back the heated steam to the dryer 2 as steam 56 for drying the high-moisture solid fuel 1; and to the first shift reactor 38 and the second shift reactor 54 as the shift-reaction steam 40, respectively. 20 The flow rate of the shift-reaction steam 40 is regulated by a shift-reaction steam flow-rate control valve 57 according to the flow rate of the steam-containing gas 30 to be fed from the dryer 2 to the shift reactors. The drying steam 56 heated up to 200'C or higher is 25 introduced into the dryer 2 and dries the high-moisture solid fuel 1 by the action of its sensible heat. The system 19 illustrated in Fig. 2 employs indirect heat exchanging from the drying steam 56 for heating of the high-moisture solid fuel 1. However, the system may employ direct heat exchanging in which part or all of the drying steam 56 is fed to the dryer 5 2. The drying steam 56 discharged from the dryer 2 is mixed with makeup steam 58 and heated again up to 200'C or higher in the shift heat exchanger 55. The makeup steam 58 is fed from outside of the system and is controlled in flow rate by 10 a makeup-steam flow-rate control valve 59. As is described above, the system heats steam by the sensible heat of the syngas warmed through the shift reaction, and uses the heated steam as the heat source for drying the high-moisture solid fuel and as the shift-reaction steam. The 15 system can therefore serve as a gasification system that less suffers from energy efficiency reduction due to fuel drying and effectively utilizes moisture in the high-moisture solid fuel. [Third Embodiment] 20 Fig. 3 depicts a system diagram illustrating a solid-fuel gasification system according to Third Embodiment of the present invention. The gasification system according to Third Embodiment differs from the system according to Second Embodiment illustrated in Fig. 2 in that the drying steam 56 25 is also used as a heating heat source for the regenerative-heating CO 2 absorbing liquid 48.

20 The drying steam 56 is heated up to 200'C or higher in the shift heat exchanger 55 and fed to the CO 2 absorbing liquid heater 49. This heats the regenerative-heating CO 2 absorbing liquid 48 up to l00'Cor higher. The drying steam56 discharged 5 from the heater 49 is fed to the dryer 2 while being maintained at 100'C or higher and serves as a drying heat source for the high-moisture solid fuel 1. The temperature of the drying steam 56 at the inlet of the dryer 2 herein is lower than, and the sensible heat of the 10 drying steam 56 to be usable in the dryer 2 is smaller in amount than, those in Second Embodiment. To ensure a heat source in the dryer 2 without using external heat, three actions as follows may be possible. Action 1 is to increase the flow rate of the adiabatically 15 compressed CO 2 104. Action 2 is to increase the flow rate of the drying steam 56. The shift-reaction steam 40 is used at a flow rate of from about 1.5 to about 2 times the stoichiometric ratio. The flow rate of the drying steam 56 can be increased if the shift 20 catalyst can be improved to reduce the flow rate of the shift-reaction steam 40. Action 3 is to increase the heat transfer efficiency by charging a high-temperature non-oxidizing gas directly into the dryer 2. Steam and CO 2 are promising as the 25 high-temperature non-oxidizing gas. Action 3 will be illustrated in detail in Fourth Embodiment.

21 As is described above, the system according to this embodiment heats steam by the action of the sensible heat of the syngas warmed through the shift reaction and employs the heated steam as the heat sources for drying of the high-moisture 5 solid fuel and for reheating of the CO 2 absorbing liquid; and as the shift-reaction steam. The system can therefore serve as a gasification system that less suffers from energy efficiency reduction due to fuel drying and effectively utilizes moisture in the high-moisture solid fuel. 10 [Fourth Embodiment] Fig. 4 depicts a system diagram illustrating a solid-fuel gasification system according to Fourth Embodiment of the present invention. The system according to Fourth Embodiment differs from the system according to Third Embodiment 15 illustrated in Fig. 3 in that the adiabatically compressed CO 2 104 is fed to hoppers for storing and feeding the post-drying high-moisture solid fuel to thereby further dry and preheat the post-drying high-moisture solid fuel. Specifically, the compressed CO 2 104 is fed not only to 20 the dryer 2, but also to the lock hopper 4 and the feed hopper 5. The lock hopper 4 stores and pressurizes the post-drying high-moisture solid fuel; whereas the feed hopper 5 stores the pressurized post-drying high-moisture solid fuel to be fed. The stand-by time from the pressurization of the fuel in the 25 lock hopper 4 to the transfer to the feed hopper 5 may be at least 20 to 30 minutes. The high-moisture solid fuel can be 22 further dried by feeding the high-temperature compressed CO 2 104, which also serves as a feed vehicle, into the lock hopper 4 to pressurize the inside. This process, i.e., feeding of

CO

2 also to the feed hopper 5 and using of the same as a feed 5 vehicle to the gasifier, enables preheating of the high-moisture solid fuel. The lock hopper 4 discharges CO 2 and a steam-containing gas (*b) via a lock hopper pressure equalization valve 7 and a pressure control valve 9. The CO 2 and the steam-containing 10 gas (*b) are preferably used for cooling of the syngas 17 in the syngas cooling unit 18. The CO 2 and the steam-containing gas (*b) include particulate solids. The solids are preferably recovered by the existing dust removal equipment 19. 15 In addition, a high-temperature non-oxidizing gas 61 is fed into the dryer 2 to accelerate the heating of the high-moisture solid fuel 1. The high-temperature non-oxidizing gas 61 is preferably steam or CO 2 . The steam-containing gas 27 generated in and discharged 20 from the dryer 2 can contain particulate solids. The solids, if fed to the shift reactor, may reduce the shift reactivity and impair the shift catalyst. To prevent this, dust removal equipment 62 is provided to remove dust from the steam-containing gas to be fed to the shift reactor, and thereby 25 the dustable solid 63 is recovered. The dustable solid 63 may be fed from the char lock hopper 21 with the char 20 to the in'kgui nmo. ntNRPonfbDCC\(6756Idoc%.20/lo2OI$ 23 gasifier 16. As is described above, the system feeds the adiabatically compressed CO: and dries the high-moisture solid fuel with fully utilizing the pressurization and standby time. This enables size 5 reduction of the dryer. The system feeds the adiabatically compressed CO, also to the feed hopper so as to preheat the high moisture solid fuel and the feed vehicle. This can be one of actions to suppress gasifier internal temperature fall which might occur in high-moisture solid fuel gasifiers. 10 Embodiments of the present invention are applicable to gasification systems for high-moisture solid-fuels such as lignite. 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 15 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. The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is 20 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 endeavor to which this specification relates. 25 While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not by way of limitation. It will be apparent to a person skilled in the relevant art that various changes in form and detail can be made therein without departing from 30 the spirit and scope of the invention. Thus, the present invention should not be limited by any of the above described exemplary embodiments.

Claims

1. A solid-fuel gasification system comprising: a dryer that dries a high-moisture solid fuel having a moisture content reaching 30 to 65 percent by weight; 5 a pulverizing equipment that pulverizes the high-moisture solid fuel after drying; a hopper that stores the high-moisture solid fuel after pulverization: a fuel feed line; a gasifier; a syngas cooling unit; 10 a dust removal equipment; a water washing tower; a desulfurization equipment; two or more CO shift reactors; and a CO 2 recovery device, 15 wherein the hopper includes a lock hopper and a feed hopper; the solid-fuel gasification system further comprising a syngas feed line that feeds a syngas at the upstream side of the two or more CO shift reactors or heat of reaction of the syngas to the dryer, wherein heat of reaction generated at the upstream side of the two or more CO shift 20 reactors is used as a drying heat source in the dryer, and a steam-containing gas evolved in the dryer is supplied to at least one of the syngas cooling unit and the CO shift reactor.

2. The solid-fuel gasification system according to claim 1, further the feed line of heat of reaction comprising: 25 a heat recovery unit arranged downstream from upstream side CO shift reactor of the two or more CO shift reactors; and a steam feed line that feeds steam generated in the heat recovery unit to the dryer. wherein heat of reaction generated at the upstream side CO shift reactor of the two or more CO shift reactors is used as a drying heat source in the dryer. Hi.gu1I~nciNlem e t RIobhDCMG Wi1X's4b7 docs-I<KI2!*II - 25

3. The solid-fuel gasification system according to claim 1 or claim 2, wherein: the CO 2 recovery device includes a CO2 regeneration tower; the CO2 regeneration tower includes a regenerative heating unit that heats part of a CO 2 absorbing liquid; and 5 the solid-fuel gasification system further comprises: a steam feed line that feeds steam to the dryer, the steam obtained after heating the CO 2 absorbing liquid in the regenerative heating unit; and a steam feed device that uses the steam as a drying heat source in the dryer, the steam obtained after heating the CO 2 absorbing liquid in the regenerative heating unit. 10

4. The solid-fuel gasification system comprising: according to any one of claims I to 3, further comprising: a compressor that compresses CO 2 recovered by the CO 2 recovery device; a CO-feed line that feeds compressed CO 2 to the dryer: a feed device that uses sensible heat of the compressed CO 2 as a heat source for the 15 high-moisture solid fuel drying; and a CO-feed line that feeds the compressed CO 2 to the lock hopper and the feed hopper respectively; wherein the compressed CO 2 is used as a feed vehicle for a dried high-moisture solid fuel to the gasifier and used as a heat source for preheating the dried high-moisture solid fuel 20 after drying.

5. The solid-fuel gasification system according to claim 4, wherein a steam-containing gas evolved in the lock hopper and the feed hopper is mixed with a syngas downstream from the gasifier, the syngas evolved in the gasifier.