A method and system for dewatering gasified fine slag

Abstract

The application provides a gasification fine slag dewatering method and system, which can realize dewatering and drying of the gasification fine slag without introducing air, and the secondary steam formed in the drying process can be directly recycled in the system. The method comprises the following steps: 1) flash evaporation, concentration, sedimentation and filtration dewatering of coal gasification black water to obtain flash steam and gasification fine slag to be treated; 2) preheating of the gasification fine slag to be treated in a fine slag preheater; 3) heat exchange of the preheated gasification fine slag with superheated steam in a superheated steam drying device to obtain dried gasification fine slag and secondary steam; 4) dust removal treatment of the secondary steam, and then the secondary steam is sent into the fine slag preheater; 5) superheating treatment of the secondary steam output from the fine slag preheater to obtain superheated steam, and the superheated steam is sent into the superheated steam drying device in step 3).

Description

TECHNICAL FIELD

[0001] The present application relates to a dewatering drying technology of gasification fine slag, and particularly relates to a gasification fine slag dewatering method and system. BACKGROUND

[0002] Harmless and resource utilization of the gasification fine slag is an important factor restricting the sustainable development of coal chemical industry.

[0003] The gasification fine slag is formed by the flash evaporation, concentration, flocculation, sedimentation and filtration dewatering of the filter cake after the water washing of the coarse coal gas entraining part of unreacted carbon and ash into the black water. At present, the general treatment method for the gasification fine slag is to dewater through a vacuum filter and then to be transported to a landfill site for landfill. Since the gasification fine slag filter cake has high moisture, the leakage exists in the vehicle during the transportation process, which not only causes environmental pollution and freezing in winter, but also causes the waste of water resources without recycling the moisture. Meanwhile, the gasification fine slag contains 30-40% residual carbon, which has considerable recycling value (for example, being sent into a boiler and a gasification furnace for blending combustion), but due to the high moisture content of the fine slag, not only the calorific value of the gasification fine slag is reduced, but also the problems such as sticking, jamming and corrosion are easily caused, which seriously affects the harmless treatment and resource utilization of the gasification fine slag.

[0004] Due to the gasification fine slag has rich pore structure, large specific surface area and small particle size and other characteristics, so it has strong adhesion and adsorption performance to water molecules; In addition, in the process of coal chemical black water settlement, polyacrylamide and other flocculants need to be added, and after the flocculants and fine slag particles in the black water coagulate into groups, a flocculation state of colloidal structure will be formed, which has strong water holding capacity, thereby causing the gasification fine slag to be difficult to dewater. The gasification fine slag is obviously different from other particles such as raw coal (such as lignite) due to its structural characteristics and water holding characteristics, and it is difficult to remove water, and it is difficult to directly apply or learn from the dewatering process of other materials such as lignite. In production practice, it is found that the conventional dewatering equipment (vacuum filter dewatering machine, horizontal screw centrifuge, plate and frame filter dewatering machine, etc.) has poor dewatering treatment effect on gasification fine slag. The vacuum belt filter is the most commonly used equipment for dewatering treatment of coal gasification fine slag, but the moisture content of the gasification fine slag after dewatering by the vacuum belt filter is still more than 60%, because when the moisture content of the gasification fine slag filter cake is reduced to about 60%, the filter cake will crack, thereby causing the vacuum filtration to be unable to further dewater the filter cake. In addition, the vacuum belt filter also has the problems of short service life of filter cloth, large amount of filter cloth washing water, large turbidity of filtrate and poor operating environment, etc. Compared with the vacuum belt filter, the horizontal screw centrifuge has the advantages of small occupied area, high dewatering efficiency, fully enclosed continuous feeding and environmental friendliness, but after dewatering treatment by the horizontal screw centrifuge, the moisture content of the gasification fine slag is still about 40-50%. The plate and frame filter press can only remove part of the free water and part of the pore water between the gasification fine slag particles, but due to the absence of phase change during dewatering, the moisture content of the gasification fine slag after dewatering can only be reduced to about 40%, and the dewatering effect is poor.

[0005] Patent application CN201710321402 discloses a method for dehydrating and drying fine slag slurry from a coal gasification system, comprising the following steps: (a) the fine slag slurry generated by the coal gasification system is pre-dehydrated by a pre-dehydration and concentration device to obtain a concentrated fine slag slurry; (b) the waste heat resources generated by the coal gasification system are heat-exchanged with air, and the air is heated into hot air; (c) the concentrated fine slag slurry and the hot air are simultaneously fed into a spray dryer, where the concentrated fine slag slurry and the hot air directly contact each other for heat and mass transfer, and after removing most of the moisture, the slurry flows out from the bottom to become dried fine slag. However, this method uses hot air as a heat source. Air has a relatively small heat capacity, requiring a large amount of hot air. The waste heat heating of the air has low thermal efficiency, resulting in low efficiency of the gasification fine slag drying system. At the same time, a large amount of water vapor mixes with the air during the drying process, and the remaining heat energy cannot be recovered, leading to a large waste of energy. In addition, the wet drying exhaust gas at the outlet of the spray dryer contains a large amount of air, and the heat exchange efficiency coefficient between air and circulating water is low. A large amount of cooling water is required in the exhaust gas condenser to cool the exhaust gas, resulting in a high condensation load in the wet drying exhaust gas condenser and a relatively high exhaust gas emission. Furthermore, the process generates a large amount of exhaust gas mixed with air and water vapor at the dryer outlet. This exhaust gas is usually discharged directly, resulting in heat waste. Alternatively, the exhaust gas needs to be cooled before gas-liquid separation and then discharged, which also results in heat waste. If it is desired to recycle the hot air, the exhaust gas must first undergo deep dehydration to reduce the moisture content in the air before it can be reused. However, this requires a large amount of cooling water to exchange heat with the exhaust gas to achieve gas-liquid separation. At the same time, a large amount of heat needs to be input again to heat the separated air, resulting in a cooling and heating phenomenon.

[0006] Patent application CN201910913874.9 discloses a gasification ash drying device and method using a four-nozzle water-gas fluidized bed. It includes a feeding unit connected to the gasified ash, a high-temperature gas supply unit, and a gasification ash drying unit. The high-temperature gas in the high-temperature gas supply unit is connected to a tail gas treatment unit via the gasification ash drying unit. A gasification ash recovery unit is located at the bottom of the gasification ash drying unit. The feeding unit includes a gasification coarse slag storage tank connected to a stirrer via a first weighing belt conveyor, and a gasification filter cake crusher connected to the stirrer via a second weighing belt conveyor. The high-temperature gas supply unit includes a hot air furnace connected to a natural gas storage tank. The gasification ash drying unit includes a waste heat drum dryer, which is connected to the inlet of a three-pass rotary dryer via a hot air interface feeding device. This technology suffers from problems such as consuming large amounts of natural gas, high energy consumption, low drum dryer filling rate, and high equipment investment. Summary of the Invention

[0007] The present application provides a kind of gasification fine slag dewatering method and system, using the scheme of the present application to the high water content gasification fine slag is carried out dehydration drying, not only can realize the dehydration drying of gasification fine slag in the case where air is not introduced, and the secondary steam formed in drying process can be directly recycled in system, system water resources and energy can be fully and reasonably reused, energy utilization rate is high, water resource waste is less, system safety is good.

[0008] To achieve its purpose, the present application provides the following technical solutions:

[0009] The present application provides a kind of gasification fine slag dewatering method, the method comprises:

[0010] 1) coal gasification black water is carried out flash evaporation concentration, settlement and filtration dehydration in black water treatment unit, to obtain flash evaporation gas and the gasification fine slag to be processed;

[0011] 2) the gasification fine slag to be processed is sent into fine slag preheater and is preheated using heat medium, to obtain preheated gasification fine slag;

[0012] 3) the preheated gasification fine slag is sent into superheated steam drying device and is directly contacted with superheated steam to carry out heat exchange, to obtain dried gasification fine slag and secondary steam;

[0013] 4) the secondary steam obtained in step 3) is carried out dust removal treatment, to obtain dust removal secondary steam, then it is sent into the fine slag preheater of step 2) and is used as the heat medium;

[0014] 5) the secondary steam output from the fine slag preheater in step 2) is carried out superheating treatment, to obtain superheated steam;The superheated steam is sent into the superheated steam drying device of step 3) and is used for heat exchange with the preheated gasification fine slag.

[0015] In some embodiments, in step 5), the temperature of the superheated steam is 160-190 DEG C, and the pressure of the superheated steam is 0.2-0.3 Mpa.

[0016] In some embodiments, in step 3), the temperature of the secondary steam is 130-150 DEG C, and the pressure of the secondary steam is 0.2-0.3 Mpa.

[0017] In some embodiments, in step 1), the water content of the gasification fine slag to be processed is 40-70 wt%.

[0018] Preferably, in step 5), the superheating medium used for superheating treatment is coal gasification black water from coal gasification system;The coal gasification black water from coal gasification system is sent into the black water treatment unit in step 1) for treatment after carrying out the superheating treatment on the secondary steam in step 5).

[0019] Alternatively, in step 5), the superheating medium used in the superheating treatment is the crude coal gas from the coal gasification system.

[0020] In some embodiments, in step 1), the flash concentration includes sequentially performing high-pressure flash and vacuum flash on the coal gasification black water, and preferably, before the vacuum flash, the coal gasification black water is further subjected to low-pressure flash.

[0021] Further, in step 1), the sedimentation is performed in a sedimentation tank.

[0022] In some embodiments, in step 4), the dust removal treatment includes preliminarily removing dust from the secondary steam obtained in step 3) by using a cyclone separator, and then washing and removing dust from the secondary steam in a steam washing tower; preferably, the washing water obtained by washing and removing dust in the steam washing tower is fed into the sedimentation tank.

[0023] Preferably, in step 2), the secondary steam output from the fine slag preheater is first fed into a secondary steam separation tank for vapor-liquid separation, and then fed into step 5) for the superheating treatment; part of the condensate obtained by separation in the secondary steam separation tank is fed into a grey water tank or into the steam washing tower as washing liquid.

[0024] In some embodiments, in step 5), before the superheating treatment of the secondary steam output from the fine slag preheater, the secondary steam output from the fine slag preheater is first fed into a steam preheater for heat exchange with the flash steam obtained from the black water treatment unit in step 1); preferably, the flash steam used in the steam preheater is high-pressure flash steam obtained from the high-pressure flash.

[0025] Preferably, in step 5), the flash steam output from the steam preheater is further fed into a flash steam separation tank for vapor-liquid separation, and the condensate obtained by separation is fed into the steam washing tower as washing liquid.

[0026] The present application also provides a system capable of implementing the gasification fine slag dewatering method described above, and the system comprises:

[0027] a black water treatment unit for performing flash concentration, sedimentation and filtration dewatering on coal gasification black water, and obtaining flash steam and gasification fine slag to be treated;

[0028] a fine slag preheater for preheating the gasification fine slag to be treated by using a heat medium to obtain preheated gasification fine slag;

[0029] a superheated steam drying device for directly contacting the preheated gasification fine slag with superheated steam for heat exchange to obtain dried gasification fine slag and secondary steam;

[0030] a secondary steam dust removal unit for dust removal treatment of the secondary steam output by the superheated steam drying device; the secondary steam dust removal unit is connected with the fine slag preheater to deliver the secondary steam subjected to the dust removal treatment to the fine slag preheater as the heat medium;

[0031] a steam superheater for superheating treatment of the secondary steam output by the fine slag preheater to obtain superheated steam; the steam superheater is connected with the superheated steam drying device to supply the superheated steam to the superheated steam drying device;

[0032] Preferably, a superheating medium inlet of the steam superheater is connected with a coal gasification black water delivery pipeline of a coal gasification system, and a superheating medium outlet of the steam superheater is connected with the black water treatment unit through a pipeline; or, the superheating medium inlet of the steam superheater is connected with a raw coal gas outlet of the coal gasification system through a raw coal gas delivery pipeline.

[0033] In some embodiments, the black water treatment unit comprises a flash concentration unit and a sedimentation filtration unit;

[0034] The flash concentration unit is used for flash concentration of the coal gasification black water to obtain the flash steam and the concentrated black water;

[0035] The sedimentation filtration unit is used for sedimentation and filtration dewatering of the concentrated black water to obtain the gasification fine slag to be treated;

[0036] Preferably, the flash concentration unit comprises a high-pressure flash tower and a vacuum flash tower connected in series, and further preferably, a low-pressure flash tower is further connected in series between the high-pressure flash tower and the vacuum flash tower.

[0037] Preferably, the sedimentation filtration unit comprises a sedimentation tank for sedimentation treatment of the concentrated black water output by the flash concentration unit, and a filtration dewatering device for filtration dewatering of the slag slurry obtained through the sedimentation treatment to obtain the gasification fine slag to be treated.

[0038] In some embodiments, the system further comprises a steam preheater for heat exchange of the secondary steam output by the fine slag preheater with the flash steam from the black water treatment unit to obtain preheated secondary steam.

[0039] Preferably, a flash steam outlet of the high-pressure flash tower is connected with a flash steam inlet of the steam preheater.

[0040] In some embodiments, the secondary steam dust removal unit comprises a cyclone separator and a steam washing tower.

[0041] The cyclone separator is connected with the superheated steam drying device, and is used for primary dust removal of secondary steam output by the superheated steam drying device.

[0042] The gas inlet of the steam washing tower is connected with the cyclone separator, and the gas outlet of the steam washing tower is connected with the heat medium inlet of the fine slag preheater.

[0043] Preferably, the steam washing tower is connected with the settling tank.

[0044] In some embodiments, the flash steam outlet of the steam preheater is connected with a flash steam separation tank, which is used for vapor-liquid separation of the flash steam output by the steam preheater and obtains condensate; the condensate outlet of the flash steam separation tank is connected with the washing liquid inlet of the steam washing tower.

[0045] In addition, the secondary steam outlet of the fine slag preheater is connected with a secondary steam separation tank through a pipeline, which is used for vapor-liquid separation of the secondary steam output by the fine slag preheater and obtains condensate; the vapor phase outlet of the secondary steam separation tank is connected with the secondary steam inlet of the steam preheater; preferably, the condensate outlet of the secondary steam separation tank is connected with a grey water tank, or the condensate outlet of the secondary steam separation tank is connected with the washing liquid inlet of the steam washing tower.

[0046] The technical scheme provided by the present application has the following beneficial effects:

[0047] The method and system provided by the present application directly contact the gasified fine slag with superheated steam in the superheated steam drying device for heat exchange to remove most of the water in the fine slag, and obtain gasified fine slag with low water content, which not only meets the current environmental protection and fine slag resource utilization requirements, but also improves the energy density of the gasified fine slag, saves transportation and processing costs, improves the plant environment, and improves the water resource utilization efficiency of coal gasification.

[0048] Meanwhile, the secondary steam output from the superheated steam drying device in the present application is recycled in the process system, and is used for preheating the gasified fine slag to be treated after dust removal, so that the waste heat is fully utilized, and then the heat is formed into superheated steam, which is returned to the superheated steam drying device for reuse. In this way, not only the heat of the secondary steam is reasonably and fully reused, but also the waste of water resources is reduced. In addition, the present application scheme does not need to introduce hot air, has good safety, and is energy-saving and environmentally friendly. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 It is a schematic diagram of a dehydration and drying system for gasified fine slag in an embodiment;

[0050] Figure 2 Figure 1 is a schematic diagram of a dewatering and drying system for gasification fine slag according to an embodiment of the present application.

[0051] Figure 3 Figure 1 is a schematic diagram of a dewatering and drying system for gasification fine slag according to an embodiment of the present application. DETAILED DESCRIPTION

[0052] In order to facilitate the understanding of the present application, the present application will be further described in conjunction with the embodiments. It should be understood that the following embodiments are only for better understanding of the present application, and do not mean that the present application is limited to the following embodiments.

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0054] Where no specific experimental procedures or conditions are indicated in the embodiments, the procedures or conditions can be performed according to the corresponding conventional experimental procedures in the art. Where no manufacturer of the reagents or instruments is indicated, the reagents or instruments are conventional products that can be obtained commercially.

[0055] The present application provides a gasification fine slag dewatering method, which mainly comprises:

[0056] 1) Flashing, concentrating, settling and filtering dewatering of coal gasification black water in a black water treatment unit to obtain flash gas and gasification fine slag to be treated;

[0057] 2) Preheating the gasification fine slag to be treated in a fine slag preheater with a heat medium to obtain preheated gasification fine slag;

[0058] 3) Directly contacting the preheated gasification fine slag with superheated steam in a superheated steam drying device for heat exchange to obtain dried gasification fine slag and secondary steam;

[0059] 4) Dust removal treatment of the secondary steam obtained in step 3) to obtain dust-removed secondary steam, which is then sent to the fine slag preheater in step 2) to be used as a heat medium for heat exchange with the gasification fine slag to be treated;

[0060] 5) Superheating treatment of the secondary steam output from the fine slag preheater in step 2) to obtain superheated steam; the superheated steam is then sent to the superheated steam drying device in step 3) to be used for heat exchange with the preheated gasification fine slag, so that the gasification fine slag is dewatered and dried to obtain dried gasification fine slag, and secondary steam is obtained again.

[0061] The present application realizes drying of the gasified fine slag without introducing air or heating the air; the superheated steam is used to directly contact the gasified fine slag in the superheated steam drying device to exchange heat, so that the moisture in the gasified fine slag is vaporized to form new steam, which is mixed with the surrounding superheated steam flow to become secondary steam, and as the secondary steam is discharged from the superheated steam drying device, the moisture is also continuously carried away, so that most of the moisture in the fine slag is removed, and the gasified fine slag with low moisture content is obtained. Not only the current environmental protection and fine slag resource utilization requirements are met, but also the transportation amount of the fine slag is greatly reduced; at the same time, the secondary steam output from the superheated steam drying device is recycled in the process system, and after dust removal, it is first used to preheat the gasified fine slag to be treated (which can increase the initial temperature of the gasified fine slag and is beneficial to obtaining good drying and dehydration effect under the condition of reducing the use amount of superheated steam), and then is superheated to form superheated steam, which is returned to the superheated steam drying device for reuse. In this way, not only the heat of the secondary steam is reasonably and fully reused, but also the waste of water resources is reduced.

[0062] In the present application, superheated steam is used as the drying medium in the superheated steam drying device, which has a large specific heat capacity. Compared with the drying medium such as hot air and flue gas in the prior art, the energy consumption is lower, the convective heat transfer coefficient is larger, the water migration resistance is smaller, the heat transfer efficiency is higher, and higher drying efficiency and energy utilization rate can be achieved. Moreover, no air or other gases are introduced into the system, and the secondary steam output from the superheated steam drying device only needs simple dust removal treatment to be directly reused in the system, so that the intermediate links required for recycling are less and the energy loss is less. Further, the present application does not involve the contact of hot air with the gasified fine slag, and only uses superheated steam as the drying medium, which is safe and can avoid the risk of explosion of fine slag with high residual carbon content in an air atmosphere during the drying process.

[0063] In some embodiments, the temperature of the superheated steam obtained by heat treatment in step 5) is 160-190℃, and the pressure of the superheated steam is 0.2-0.3Mpa; in step 3), the temperature of the secondary steam output from the superheated steam drying device is 130-150℃, and the pressure of the secondary steam is 0.2-0.3Mpa.

[0064] In some embodiments, the water content of the gasified fine slag to be treated obtained in the black water treatment unit in step 1) is 40-70wt%, and the water content can be further reduced by the dehydration and drying method of the present application, for example, the dried gasified fine slag can be reduced to below 30%, for example, in some embodiments, the gasified fine slag with a water content of 10-30% can be obtained, or for example, in some embodiments, the gasified fine slag with a water content of 15-20% can be obtained.

[0065] In the present application, in step 5), the superheating medium used for superheating the secondary steam is preferably a waste heat resource of the coal gasification system. In a preferred embodiment, the waste heat resource is coal gasification black water from the coal gasification system, such as black water from the quench chamber of the gasifier and / or black water from the raw gas scrubbing tower used for scrubbing the raw synthesis gas. The coal gasification black water from the coal gasification system is first used as the superheating medium to superheat the secondary steam, and then enters the black water treatment unit of step 1) for further treatment. In another preferred embodiment, the aforementioned waste heat resource is raw gas from the coal gasification system, such as raw synthesis gas from the gasifier which is scrubbed for dust removal by the raw gas scrubbing tower.

[0066] In some embodiments, the flash concentration in step 1) specifically comprises first sending the coal gasification black water into a high-pressure flash tower for high-pressure flash evaporation, and then sending the coal gasification black water into a vacuum flash tower for vacuum flash evaporation. In some embodiments, the coal gasification black water can be further sent into a low-pressure flash tower for low-pressure flash evaporation before being sent into the vacuum flash tower. The high-pressure flash evaporation, low-pressure flash evaporation and vacuum flash evaporation are all conventional operations for flash evaporation of coal gasification black water in the art, and will not be described here. The flash evaporation and concentration of the coal gasification black water are achieved by the above-mentioned flash concentration.

[0067] In some embodiments, the settling in step 1) is performed in a settling tank, i.e. the concentrated black water obtained by the flash concentration is sent into the settling tank for settling to obtain slurry and supernatant (i.e. grey water). During the settling process, a flocculant can be added to promote the settling of solids, which is a conventional operation in the art and will not be described here. Specifically, the supernatant is sent to a downstream grey water tank. The slurry obtained by the settling (e.g. with a solid content of 10-20 wt%) is subjected to filtration and dewatering, such as filtration using a vacuum belt filter or a plate-and-frame filter or centrifugal dewatering, to obtain the gasification fine slurry to be treated, which still has a high water content, e.g. a water content of 40-70 wt%. The filtrate obtained by the filtration and dewatering is sent to the grey water tank. The water in the grey water tank can be reused in the coal gasification system.

[0068] In some embodiments, the dust removal treatment of the secondary steam output by the superheated steam drying device in step 4) specifically comprises: first subjecting the secondary steam to cyclone separation by a cyclone separator to obtain primary dust removal, and then sending the secondary steam into a steam scrubbing tower for washing and dust removal using a washing liquid. In the steam scrubbing tower, the washing liquid is specifically brought into countercurrent contact with the secondary steam to wash and remove the ash carried by the secondary steam, so as to ensure the purity of the secondary steam. The washing liquid used is mainly condensate water generated in the process, as will be described later. Preferably, the washing water obtained by the washing and dust removal of the secondary steam in the steam scrubbing tower is sent to a settling tank. Through the above-mentioned preferred dust removal treatment, the secondary steam can be deeply dedusted, and the dust content in the secondary steam can be <10 mg / m 3 .

[0069] Preferably, in step 2), the secondary steam used as the heat medium in the fine slag preheater is output after heat exchange with the gasified fine slag, and is first sent to a secondary steam separation tank for vapor-liquid separation, and then is sent to step 5) for superheating treatment. Preferably, part of the condensed liquid separated in the secondary steam separation tank is sent to a grey water tank or is sent to a steam washing tower for use as a washing liquid.

[0070] In some embodiments, in step 5), before the superheating treatment of the secondary steam output from the fine slag preheater, the secondary steam output from the fine slag preheater is first sent to a steam preheater to exchange heat with the flash steam obtained from the black water treatment unit in step 1); preferably, the flash steam used in the steam preheater is high-pressure flash steam obtained from the high-pressure flashing. Preferably, in step 5), the flash steam after heat exchange with the secondary steam in the steam preheater is sent to a flash steam separation tank for vapor-liquid separation, and the condensed liquid separated is sent to a steam washing tower for use as a washing liquid; the separated steam continues to be processed downstream, for example, for sulfur recovery treatment, etc.

[0071] In the present application, the superheated steam is used as the drying medium, which has a higher specific heat capacity (1.968 kJ / (kg·K)) and stronger heat exchange capacity compared with low-temperature flue gas and hot air. Meanwhile, the gasified fine slag to be treated is directly contacted with the superheated steam in the superheated steam drying device for heat exchange, which can effectively remove water from the gasified fine slag and reduce the water content. The secondary steam is used to preheat the gasified fine slag to be treated, which can effectively recover and utilize the energy of the secondary steam, improve the initial temperature of the gasified fine slag, and improve the drying effect.

[0072] The present application also provides a system capable of implementing the gasified fine slag dewatering method described above. Referring to Figure 1 The dewatering and drying system of the present application mainly comprises a black water treatment unit 100, a fine slag preheater, a superheated steam drying device, a secondary steam dust removal unit, and a steam superheater.

[0073] The black water treatment unit 100 is used for flash evaporation concentration, sedimentation, and filtration dewatering of the coal gasification black water, thereby obtaining flash steam and gasified fine slag to be treated;

[0074] The fine slag preheater is used for preheating treatment of the gasified fine slag to be treated using a heat medium, thereby obtaining preheated gasified fine slag;

[0075] The superheated steam drying device is used for directly contacting the gasified fine slag output from the fine slag preheater with superheated steam for heat exchange, so that the water in the gasified fine slag is removed and vaporized into steam to form secondary steam with the surrounding superheated steam, thereby obtaining dried gasified fine slag and secondary steam;

[0076] A secondary steam dust removal unit is used to remove dust from the secondary steam output by the superheated steam drying device, thereby obtaining dust-removed secondary steam; the secondary steam dust removal unit is connected to the fine slag preheater to deliver the dust-removed secondary steam as a heat medium to the fine slag preheater, thereby being used to preheat the gasified fine slag to be treated;

[0077] A steam superheater is used to superheat the secondary steam output by the fine slag preheater, thereby obtaining superheated steam; the steam superheater is connected to the superheated steam drying device to supply superheated steam to the superheated steam drying device, i.e., the superheated steam required by the superheated steam drying device is supplied by the steam superheater.

[0078] Through the above system, the gasified fine slag is dehydrated and dried, and the gasified fine slag can be efficiently, safely and environmentally dried by using superheated steam. There is no explosion risk of hot air contacting high-carbon-content dried gasified fine slag, and the energy utilization rate is higher. Moreover, no air is introduced into the system, and the secondary steam flow generated during the drying and dehydration process is mainly steam, which can be recycled without complex intermediate treatment links. The present application first removes dust from the secondary steam, then preheats the gasified fine slag in the fine slag preheater, and then superheats it in the steam superheater to obtain superheated steam for recycling in the superheated steam drying device. The ingenious design of the entire system and the organic integration of each treatment device unit enable the energy of the secondary steam to be more fully and reasonably utilized, and the waste of water resources can be greatly reduced, enabling efficient and sufficient use of water resources.

[0079] In some preferred embodiments, referring to Figure 1 , the superheating medium inlet of the steam superheater is connected to the coal gasification black water delivery pipeline of the coal gasification system, and the superheating medium outlet of the steam superheater is connected to the black water treatment unit through a pipeline; that is, the superheating medium required in the steam superheater is the coal gasification black water of the coal gasification system, which is first heat-exchanged with the secondary steam in the steam superheater and then enters the black water treatment unit for further treatment. Figure 2 As shown in the dehydration and drying system of Figure 1 , this is another embodiment, which is different from Figure 1 in that the superheating medium inlet of the steam superheater is connected to the crude gas outlet of the coal gasification system through a crude gas delivery pipeline, i.e., the superheating medium required in the steam superheater is the crude gas of the coal gasification system; specifically, as shown in Figure 2 , the synthesis gas generated by the gasifier is washed in the crude gas washing tower to obtain crude gas as the aforementioned superheating medium, which is introduced into the steam superheater; in this embodiment, the black water of the quenching chamber of the gasifier and the black water of the crude gas washing tower are no longer introduced into the steam superheater, but directly introduced into the black water flash unit for treatment.

[0080] As shown in Figure 1 some embodiments, the black water treatment unit 100 specifically comprises a flash concentration unit 101 and a sedimentation filtration unit 102. The flash concentration unit 101 is configured to perform flash and concentration on the coal gasification black water, thereby obtaining flash gas and concentrated black water; the sedimentation filtration unit 102 is configured to perform sedimentation and filtration dehydration on the concentrated black water, thereby obtaining the gasification fine slag to be treated.

[0081] As shown in Figure 3 some embodiments, the flash concentration unit 101 comprises a high-pressure flash tower and a vacuum flash tower connected in series. As shown in Figure 1 , 2 some embodiments, a low-pressure flash tower is further connected between the high-pressure flash tower and the vacuum flash tower.

[0082] Further specifically, the sedimentation filtration unit 102 comprises a sedimentation tank and a filtration dehydration device. The sedimentation tank is configured to perform sedimentation treatment on the concentrated black water output by the flash concentration unit 101, thereby obtaining a slurry; the filtration dehydration device is configured to perform filtration dehydration on the slurry obtained by the sedimentation treatment, thereby obtaining the gasification fine slag to be treated. Preferably, the filtration dehydration device specifically adopts a vacuum belt filter, a plate-and-frame filter or a centrifugal dehydrator. As shown in Figure 1 the sedimentation filtration unit 100 further specifically comprises a grey water tank configured to receive supernatant in the sedimentation tank and filtrate obtained by the filtration dehydration device. The grey water in the grey water tank can be reused in the coal gasification system, for example, reused in the scrubbing tower of the coal gasification system.

[0083] As shown in Figure 1 some preferred embodiments, the system of the present application can further comprise a steam preheater configured to perform heat exchange between the secondary steam output by the fine slag preheater and the flash gas from the black water treatment unit, thereby obtaining preheated secondary steam. Preferably, the flash gas outlet of the high-pressure flash tower is connected with the flash gas inlet of the steam preheater, i.e., the flash gas in the steam preheater is derived from the high-pressure flash gas output by the high-pressure flash tower.

[0084] In some specific embodiments, referring to Figure 1 the secondary steam dedusting unit comprises a cyclone separator and a steam scrubbing tower. The cyclone separator is connected with the superheated steam drying device and is configured to perform cyclone separation on the secondary steam output by the superheated steam drying device, thereby obtaining primary dedusting. The gas inlet of the steam scrubbing tower is connected with the cyclone separator, the gas outlet of the steam scrubbing tower is connected with the heat medium inlet of the fine slag preheater, and the steam scrubbing tower receives the primary dedusted secondary steam from the cyclone separator. The primary dedusted secondary steam is washed by the washing liquid in the steam scrubbing tower, thereby obtaining washing water and dedusted secondary steam. Preferably, the washing water outlet of the steam scrubbing tower is connected with the sedimentation tank.

[0085] In some embodiments, preferably, the flash steam outlet of the steam preheater is connected to a flash steam separation tank for vapor-liquid separation of the flash steam that has been heat exchanged in the steam preheater and to obtain condensed liquid; preferably, the condensed liquid outlet of the flash steam separation tank is connected to the scrubbing liquid inlet of the steam scrubber, so that the condensed liquid separated from the flash steam separation tank can be sent into the steam scrubber for use as scrubbing liquid. Further, the flash steam output from the flash steam separation tank enters a downstream unit, such as a sulfur recovery unit, for further treatment.

[0086] In some preferred embodiments, the secondary steam outlet of the fine slag preheater is connected to a secondary steam separation tank via a pipeline for vapor-liquid separation of the secondary steam that has been heat exchanged in the fine slag preheater and to obtain condensed liquid; the vapor phase outlet of the secondary steam separation tank is connected to the secondary steam inlet of the steam preheater, so that the vapor-liquid separated secondary steam can enter the steam preheater for preheating treatment. Preferably, the condensed liquid outlet of the secondary steam separation tank is connected to a grey water tank, or the condensed liquid outlet of the secondary steam separation tank is connected to the scrubbing liquid inlet of the steam scrubber, so that the condensed liquid separated from the secondary steam separation tank can enter the grey water tank for reuse, or be used as scrubbing liquid.

[0087] In the system of the present application, the superheated steam drying device can employ a device conventional in the art, which can realize the function of direct contact heat exchange between superheated steam and the gasified fine slag to be treated, such as but not limited to a spray dryer, a fluidized bed dryer, a rotary dryer, a disc dryer, etc. In some embodiments, the superheated steam drying device employs a spray dryer; the superheated steam and the gasified fine slag to be treated are sprayed into the dryer via a feed spray head, which can employ a feed spray head type conventional in the art, as long as it can realize the function of spraying the superheated steam and the gasified fine slag to be treated, such as various conventional spray heads, such as a spiral spray head, etc. There is no particular limitation on the specific selection of the feed spray head.

[0088] The present application is further described below by way of application examples.

[0089] Example 1

[0090] The schematic diagram of the gasified fine slag dewatering system employed in this example is shown in Figure 1 , and the following description of the gasified fine slag dewatering system and method is not particularly described herein, and will not be described one by one.

[0091] The coal gasification black water employed in this example is the black water from the quenching chamber of a gasifier. In this example, the dewatering and drying of the gasified fine slag includes the following treatment steps:

[0092] 1) Flash concentration, sedimentation and filtration:

[0093] 1.1) Flash concentration: The coal gasification black water is sent into a high pressure flash tower, and part of the soluble gas is released from the black water by flash evaporation at a pressure of 0.5 MPa. The black water at the bottom of the high pressure flash tower is sent into a low pressure flash tower. The soluble gas in the black water is further released by flash evaporation at a pressure of 0.1 MPa in the low pressure flash tower. The black water at the bottom of the low pressure flash tower is sent into a vacuum flash tower, and is further flashed at -0.5 MPa to obtain concentrated black water.

[0094] 1.2) Sedimentation:

[0095] The concentrated black water obtained in step 1.1) is sent into a sedimentation tank for gravity sedimentation and solid-liquid separation, and the sedimentation of the solids in the black water is accelerated by adding a flocculating agent (consisting of 90 wt% anionic polyacrylamide and 10 wt% coagulant (polyaluminum)).

[0096] 1.3) Filtration and dewatering:

[0097] The slurry settled at the bottom of the sedimentation tank is sent to a filtration and dewatering device (vacuum belt filter press) by a slurry pump for filtration and dewatering to obtain gasification fine slurry to be treated (flow rate: 500 kg / h, temperature: 60°C) with a water content of 60 wt%, and the filtrate (flow rate: 1500 kg / h, temperature: 60°C) is pumped to the ash water tank. The particle size of the gasification fine slurry is as follows: particles with a particle size of <20 μm account for about 32 wt%, particles with a particle size of <45 μm account for about 71 wt%, and particles with a particle size of <100 μm account for about 89 wt%.

[0098] 2) Fine slurry preheating:

[0099] The aforementioned gasification fine slurry to be treated is sent to a fine slurry preheater for indirect heat exchange with a heating medium to obtain preheated gasification fine slurry. The heating medium is the dust-removed secondary steam output from the steam washing tower after the system is operated. In the preheating process, the secondary steam is cooled and condensed, and is sent to a secondary steam separation tank for vapor-liquid separation. The condensed liquid separated (flow rate: 250 kg / h) is sent to the ash water tank.

[0100] 3) Drying and dewatering:

[0101] The preheated gasification fine slag and superheated steam are fed into the spray dryer through the feed nozzle (a spiral nozzle with a length-diameter ratio of 5:1). The superheated steam directly contacts the gasification fine slag in the superheated steam drying device. The gasification fine slag is heated, and the water in the gasification fine slag is vaporized to form new steam, which is mixed with the surrounding superheated steam flow to become secondary steam (temperature 144°C, pressure 0.3 MPa, flow rate 7290 kg / h). The secondary steam is discharged from the superheated steam drying device by the induced draft fan of the superheated steam drying device. The water is continuously carried away, thereby removing most of the water from the fine slag, and obtaining dried gasification fine slag with a water content of 20% (yield 250 kg / h).

[0102] 4) Secondary steam dust removal:

[0103] The secondary steam discharged from the superheated steam drying device is first separated from most of the solids by a cyclone separator. The preliminarily dedusted secondary steam is then introduced into a steam scrubbing tower. The secondary steam is further dedusted by washing with condensate from the flash steam separation tank as washing liquid in the steam scrubbing tower. The final dedusted secondary steam contains <10 mg / m 3 The washing water at the bottom of the steam scrubbing tower is transported into a settling tank. The dedusted secondary steam obtained in this step is fed into the fine slag preheater in step 2) as a heating medium for preheating the gasification fine slag.

[0104] 5) Secondary steam preheating:

[0105] The secondary steam (temperature 144°C, pressure 0.3 MPa, flow rate 7040 kg / h) separated from the gas-liquid mixture in the secondary steam separation tank in step 2) is fed into a steam preheater to exchange heat with the high-pressure flash steam from the high-pressure flash tower, thereby obtaining preheated secondary steam.

[0106] 6) Secondary steam superheating:

[0107] The preheated secondary steam (temperature 154°C, pressure 0.3 MPa, flow rate 7040 kg / h) exchanges heat with the black water (temperature 220°C, pressure 4.0 MPa, flow rate 39300 kg / h) from the quench chamber of the gasification furnace in a steam superheater, thereby forming new superheated steam (temperature 190°C, pressure 0.3 MPa, flow rate 7040 kg / h). The superheated steam is circulated to the superheated steam drying device in step 3). In the initial stage of system operation, fresh superheated steam is introduced from outside the system in step 3). During system operation, the superheated steam generated in the steam superheater is used in step 3). The black water from the quench chamber of the gasification furnace is fed into the high-pressure flash tower in step 1.1) after heat exchange in the steam superheater.

[0108] Example 2

[0109] The schematic diagram of the dewatering and drying system used in this example is shown in Figure 1. Figure 2 The following description is made with reference to the above-mentioned schematic diagram, and the description of the gasification fine slag dewatering system and method is not particularly described below.

[0110] The coal gasification black water used in this example is the black water from the quenching chamber of the gasifier and the black water from the raw gas washing tower. The dewatering and drying of the gasification fine slag in this example includes the following processing steps:

[0111] 1) Flash concentration, sedimentation and filtration

[0112] 1.1) Flash concentration: The coal gasification black water is fed into a high-pressure flash tower, and part of the soluble gas is released from the black water at a pressure of 0.6 MPa. The black water at the bottom of the high-pressure flash tower is fed into a low-pressure flash tower. The soluble gas in the black water is further released in the low-pressure flash tower at a pressure of 0.1 MPa. The black water at the bottom of the low-pressure flash tower is fed into a vacuum flash tower, and is further flashed at -0.5 MPa to obtain concentrated black water.

[0113] 1.2) Sedimentation:

[0114] The concentrated black water obtained in step 1.1) is fed into a sedimentation tank for gravity sedimentation and solid-liquid separation, and the sedimentation of the solids in the black water is accelerated by adding a flocculating agent (consisting of 85 wt% anionic polyacrylamide and 15 wt% coagulant (polyferric)).

[0115] 1.3) Filtration and dewatering:

[0116] The slurry settled at the bottom of the sedimentation tank is pumped to a filtration and dewatering device (plate and frame filter) for filtration and dewatering, and the gasification fine slag with a water content of 50 wt% is obtained. The filtrate is pumped back to the ash water tank. The particle size of the gasification fine slag is as follows: particles with a particle size of <45 μm account for 5 wt%, particles with a particle size of 45-125 μm account for 16 wt%, particles with a particle size of 125-500 μm account for 76 wt%, and particles with a particle size of >500 μm account for 3 wt%.

[0117] 2) Fine slag preheating:

[0118] The aforementioned gasification fine slag to be treated is fed into a fine slag preheater for indirect heat exchange with a heating medium to obtain preheated gasification fine slag. The heating medium is the dust-removed secondary steam output from the steam washing tower. In the preheating process, the secondary steam is cooled and condensed, and is fed into a secondary steam separation tank for vapor-liquid separation. The condensed liquid separated is fed into the ash water tank.

[0119] 3) drying and dewatering:

[0120] The preheated gasified fine slag is sent into the superheated steam drying device (specifically, a fluidized bed dryer), and in the superheated steam drying device, the gasified fine slag is directly contacted with superheated steam, so that the gasified fine slag is heated, water in the gasified fine slag is vaporized to form new steam, and the new steam is mixed with the surrounding superheated steam flow to become secondary steam. The secondary steam is discharged from the fluidized bed dryer by an induced draft fan provided in the superheated steam drying device, and water is continuously carried away, so that most of the water in the fine slag is removed, and dried gasified fine slag with a water content of 15% is obtained.

[0121] 4) dust removal of secondary steam:

[0122] The secondary steam discharged from the superheated steam drying device is first separated from most of the solids by a cyclone separator, and the preliminarily dust-removed secondary steam is then introduced into a steam scrubbing tower. In the steam scrubbing tower, the secondary steam is washed with condensate from the flash steam separator as washing liquid to further remove dust. The finally obtained dust-removed secondary steam contains <10 mg / m 3 of dust. The washing water at the bottom of the steam scrubbing tower is transported into a settling tank. The dust-removed secondary steam obtained in this step is sent to the fine slag preheater in step 2) as a heat medium for preheating the gasified fine slag.

[0123] 5) preheating of secondary steam:

[0124] The secondary steam subjected to vapor-liquid separation in the secondary steam separation tank in step 2) is sent to a steam preheater, and heat-exchanged with high-pressure flash steam from the high-pressure flash tower to obtain preheated secondary steam.

[0125] 6) superheating of secondary steam:

[0126] The preheated secondary steam is heat-exchanged with the raw coal gas from the coal gas scrubbing tower (superheating medium, pressure 4.0 MPa, temperature 210°C) to form new superheated steam. The superheated steam is circulated to the superheated steam drying device in step 3) (in the initial stage of system operation, fresh superheated steam introduced from outside the system can be used in step 3), and after the superheated steam is generated in the steam superheater during the operation of the system, the superheated steam generated in the steam superheater is used in step 3).

[0127] Example 3

[0128] The schematic diagram of the dewatering and drying system used in this example is shown in Figure 2 , and the following description of the gasified fine slag dewatering system and method is not particularly described, and will not be described one by one.

[0129] The coal gasification black water used in this embodiment is the black water from the quenching chamber of the gasifier and the black water from the raw gas washing tower. In this embodiment, the dewatering and drying of the gasification fine slag includes the following processing steps:

[0130] 1) flash concentration, sedimentation and filtration

[0131] 1.1) flash concentration: the coal gasification black water is fed into a high-pressure flash tower, and part of the soluble gas is released from the black water at a pressure of 0.5 MPa. The black water at the bottom of the high-pressure flash tower is fed into a low-pressure flash tower. The soluble gas in the black water is further released in the low-pressure flash tower at a pressure of 0.08 MPa. The black water at the bottom of the low-pressure flash tower is fed into a vacuum flash tower, and is further flashed at -0.5 MPa to obtain concentrated black water;

[0132] 1.2) sedimentation:

[0133] The concentrated black water obtained in step 1.1) is fed into a sedimentation tank for gravity sedimentation and solid-liquid separation, and the sedimentation of the solids in the black water is accelerated by adding a flocculating agent (consisting of 80 wt% anionic polyacrylamide and 20 wt% coagulant (polyaluminum)).

[0134] 1.3) filtration and dewatering:

[0135] The slurry settled out at the bottom of the sedimentation tank is pumped to a filtration and dewatering device (vacuum belt filter) by a slurry pump for filtration and dewatering to obtain fine gasification slag to be treated with a water content of 60 wt%. The filtrate is pumped back to the ash water tank. The particle size of the fine gasification slag is as follows: particles with a particle size of <20 μm account for about 33 wt%, particles with a particle size of <45 μm account for about 72 wt%, and particles with a particle size of <100 μm account for about 91 wt%.

[0136] 2) fine slag preheating:

[0137] The aforementioned fine gasification slag to be treated is fed into a fine slag preheater for indirect heat exchange with a heating medium to obtain preheated fine gasification slag. The heating medium is the dust-free secondary steam output from the steam washing tower after the system is operated. In the preheating process, the secondary steam is cooled and condensed, and is fed into a secondary steam separation tank for vapor-liquid separation. The condensed liquid separated out is fed into the ash water tank.

[0138] 3) drying and dewatering:

[0139] The preheated gasification fine slag and superheated steam are fed into the spray dryer through the feed nozzle (a spiral nozzle with a length-diameter ratio of 5:1) together, and in the superheated steam drying device, the gasification fine slag is heated to make the water in the gasification fine slag vaporize and form new steam, which is mixed with the surrounding superheated steam flow to become secondary steam. The secondary steam is discharged from the fluidized bed dryer through the induced draft fan of the superheated steam drying device, and the water is continuously carried away, so that most of the water in the fine slag is removed, and dry gasification fine slag with a water content of 10% is obtained.

[0140] 4) Secondary steam dust removal:

[0141] The secondary steam discharged from the superheated steam drying device is first separated from most of the solids through a cyclone separator, and the preliminarily dust-removed secondary steam is then introduced into a steam washing tower. In the steam washing tower, the condensed liquid from the flash gas separation tank is used as a washing liquid to wash the secondary steam to further remove dust, and the finally obtained dust-removed secondary steam contains <10 mg / m 3 of dust. The washing water at the bottom of the steam washing tower is transported into a settling tank. The dust-removed secondary steam obtained in this step is sent to the fine slag preheater in step 2) as a heating medium for preheating the gasification fine slag.

[0142] 5) Secondary steam preheating:

[0143] The secondary steam that has been subjected to vapor-liquid separation in the secondary steam separation tank in step 2) is sent to a steam preheater and exchanged with high-pressure flash gas from the high-pressure flash tower to obtain preheated secondary steam.

[0144] 6) Secondary steam superheating:

[0145] The preheated secondary steam is exchanged with the raw coal gas (superheating medium, pressure 4.0 MPa, temperature 210°C) from the raw coal gas washing tower to form new superheated steam. The superheated steam is circulated to the superheated steam drying device in step 3) (in the initial stage of system operation, step 3) can use fresh superheated steam introduced from outside the system, and during system operation, after the superheated steam is generated in the steam superheater, the superheated steam generated in the steam superheater is used in step 3).

[0146] Table 1

[0147] Item Example 1 Example 2 Example 3 Superheated steam temperature, °C 190 190 180 Superheated steam pressure, MPa 0.3 0.3 0.3 Superheated steam flow rate, kg / h 7040 4225 10000 Slurry moisture content, % 90 80 80 Slurry flow rate, kg / h 2000 1000 1000 Moisture content of gasification fine slag to be treated, % 60 50 60 Flow rate of gasification fine slag to be treated, Kg / h 500 400 500 Moisture content of dried gasification fine slag, % 20 15 10 Yield of dried gasification fine slag, kg / h 250 235 222 Secondary steam temperature, °C 144 144 144 Secondary steam pressure, MPa 0.3 0.3 0.3 Secondary steam flow rate, kg / h 7290 6107 10278 Step 2) amount of condensed liquid, kg / h 250 165 278

[0148] Note: If there is a discrepancy between the data listed in Table 1 and the description of the previous examples, the data listed in Table 1 shall prevail.

[0149] From the above examples, it can be seen that the dehydration drying system and method can effectively reduce the water content in the gasified fine slag, and the energy and water resources in the whole process can be reasonably and fully utilized, the additional energy required by the whole process is small, the water resources are recycled, the waste of water resources can be greatly reduced, hot air is not introduced in the treatment process, and the environment is protected and the safety is good.

[0150] It is easily understood that the above examples are only examples for clearly illustrating the present application, and do not mean that the present application is limited to this. Other different forms of changes or variations can be made on the basis of the above description for those skilled in the art. Here, all the embodiments cannot be exhausted, and the obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for dewatering gasified fine slag, characterized by, The method comprises: 1) flash concentration, sedimentation and filtration dehydration of coal gasification black water in a black water treatment unit to obtain flash gas and gasification fine slag to be treated; the flash concentration comprises high-pressure flash and vacuum flash of the coal gasification black water in sequence; 2) preheating of the gasification fine slag to be treated in a fine slag preheater by a heat medium to obtain preheated gasification fine slag; 3) direct contact of the preheated gasification fine slag with superheated steam in a superheated steam drying device to obtain dried gasification fine slag and secondary steam; 4) dust removal treatment of the secondary steam obtained in step 3) to obtain dust-removed secondary steam, which is then sent to the fine slag preheater in step 2) to be used as the heat medium; the dust removal treatment comprises preliminary dust removal of the secondary steam obtained in step 3) by a cyclone separator, and then washing and dust removal in a steam washing tower; 5) steam and liquid separation of the secondary steam output from the fine slag preheater in step 2) in a secondary steam separation tank, and then heat exchange of the steam with high-pressure flash gas obtained by the high-pressure flash of the black water treatment unit in step 1) in a steam preheater, and then superheating treatment to obtain superheated steam; the superheated steam is sent to the superheated steam drying device in step 3) to be used for heat exchange with the preheated gasification fine slag; the superheating medium for the superheating treatment is coal gasification black water from a coal gasification system or is raw coal gas from the coal gasification system; the flash gas output from the steam preheater is sent to a flash gas separation tank for steam and liquid separation, and the condensed liquid obtained by the separation is sent to the steam washing tower to be used as washing liquid.

2. The method of dewatering gasified fine coal slurry according to claim 1, wherein In step 5), the temperature of the superheated steam is 160-190℃, and the pressure of the superheated steam is 0.2-0.3Mpa; and / or, in step 3), the temperature of the secondary steam is 130-150℃, and the pressure of the secondary steam is 0.2-0.3Mpa; and / or, in step 1), the water content of the gasification fine slag to be treated is 40-70wt%.

3. The method of dewatering gasified fine coal slurry according to claim 1, wherein The coal gasification black water from the coal gasification system is sent to the black water treatment unit in step 1) after the superheating treatment of the secondary steam in step 5).

4. The dewatering method of gasified fine sludge according to any one of claims 1 to 3, characterized by, In step 1), the operation of low-pressure flash of the coal gasification black water is further included before the vacuum flash; and / or, in step 1), the sedimentation is carried out in a sedimentation tank; and / or, in step 4), the washing water obtained by washing and dust removal in the steam washing tower is sent to the sedimentation tank.

5. The method of dewatering gasified fine coal slurry according to claim 4, wherein Part of the condensed liquid obtained by separation in the secondary steam separation tank is sent to a grey water tank or to the steam washing tower to be used as washing liquid.

6. A system capable of carrying out the dewatering method of fine gasification sludge according to any one of claims 1 to 5, characterized in that, The system comprises: The black water treatment unit is used for flash evaporation concentration, sedimentation and filtration dehydration of coal gasification black water, and obtains flash steam and gasification fine slag to be treated; the black water treatment unit comprises a flash evaporation concentration unit, which is used for flash evaporation and concentration of the coal gasification black water to obtain the flash steam and concentrated black water, and the flash evaporation concentration unit comprises a high-pressure flash tower and a vacuum flash tower connected in series; the flash steam outlet of the high-pressure flash tower is connected with the flash steam inlet of the steam preheater; The fine slag preheater is used for preheating treatment of the gasification fine slag to be treated by using a heat medium to obtain preheated gasification fine slag; the secondary steam outlet of the fine slag preheater is connected with a secondary steam separation tank through a pipeline, which is used for vapor-liquid separation of the secondary steam output by the fine slag preheater and obtains condensed liquid; the vapor phase outlet of the secondary steam separation tank is connected with the secondary steam inlet of the steam preheater; The steam preheater is used for heat exchange between the secondary steam output by the fine slag preheater after vapor-liquid separation in the secondary steam separation tank and the flash steam from the black water treatment unit, so as to obtain preheated secondary steam; the flash steam outlet of the steam preheater is connected with a flash steam separation tank, which is used for vapor-liquid separation of the flash steam output by the steam preheater and obtains condensed liquid; the condensed liquid outlet of the flash steam separation tank is connected with the washing liquid inlet of the steam washing tower; The superheated steam drying device is used for heat exchange between the preheated gasification fine slag and superheated steam to obtain dried gasification fine slag and secondary steam; The secondary steam dust removal unit is used for dust removal treatment of the secondary steam output by the superheated steam drying device; the secondary steam dust removal unit is connected with the fine slag preheater to deliver the secondary steam subjected to the dust removal treatment to the fine slag preheater as the heat medium; the secondary steam dust removal unit comprises a cyclone separator and a steam washing tower; the cyclone separator is connected with the superheated steam drying device and is used for primary dust removal of the secondary steam output by the superheated steam drying device; the steam washing tower is connected with the cyclone separator at the gas inlet, and is connected with the heat medium inlet of the fine slag preheater at the gas outlet, and is used for washing dust removal of the secondary steam subjected to the primary dust removal by using washing liquid to obtain washing water and dust-removed secondary steam; The steam superheater is used for superheating treatment of the secondary steam output by the fine slag preheater to obtain superheated steam; the steam superheater is connected with the superheated steam drying device to supply the superheated steam to the superheated steam drying device; The superheating medium inlet of the steam superheater is connected with a coal gasification black water delivery pipeline of a coal gasification system, and the superheating medium outlet of the steam superheater is connected with the black water treatment unit through a pipeline; or, the superheating medium inlet of the steam superheater is connected with a crude coal gas outlet of a coal gasification system through a crude coal gas delivery pipeline.

7. The dewatering drying system of claim 6, wherein, The black water treatment unit comprises a sedimentation and filtration unit; The sedimentation and filtration unit is used for sedimentation and filtration dehydration of the concentrated black water to obtain the gasification fine slag to be treated.

8. The dewatering drying system of claim 7, wherein, A low-pressure flash tower is further connected in series between the high-pressure flash tower and the vacuum flash tower.

9. The dewatering drying system of claim 7, wherein, The settling filtration unit comprises a settling tank for settling the concentrated black water output by the flash concentration unit, and a filter dewatering device for filtering and dewatering the slurry obtained by the settling to obtain the fine gasification slag to be treated.

10. The system of claim 7, wherein, The scrubbing water outlet of the steam scrubbing tower is connected with the settling tank.

11. The system of claim 6, wherein, The condensate outlet of the secondary steam separation tank is connected with a grey water tank, or the condensate outlet of the secondary steam separation tank is connected with the scrubbing liquid inlet of the steam scrubbing tower.

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