Gasification fine slag dewatering and drying method and system based on fluidized bed dryer

Abstract

The application provides a gasification fine slag dewatering and drying method and system based on a fluidized bed dryer, which can dewater and dry high-water-content gasification fine slag, has high energy utilization rate and causes less waste of water resources. The method comprises the following steps: 1) performing flash evaporation concentration, sedimentation and filtration dewatering on coal gasification black water in a black water treatment unit; 2) sending the gasification fine slag to be treated into a fine slag preheater to perform heat exchange with a heat medium; 3) performing heat exchange between the preheated gasification fine slag and superheated steam in a fluidized bed dryer to obtain dried gasification fine slag and secondary steam; 4) sending the secondary steam into a secondary steam dust removal unit to perform dust removal treatment, and then sending the secondary steam into the fine slag preheater; 5) sending the secondary steam output from the fine slag preheater into a steam preheater to perform heat exchange, and obtaining preheated secondary steam; 6) sending the preheated secondary steam into a steam superheater to perform superheating treatment, and obtaining superheated steam; and sending the superheated steam into the fluidized bed dryer.

Description

TECHNICAL FIELD

[0001] The present application relates to a dewatering and drying technology of gasification fine slag, in particular to a gasification fine slag dewatering and drying method and system based on a fluidized bed dryer. BACKGROUND

[0002] A large amount of gasification ash is discharged by the coal chemical industry in China every year. With the increasingly strict requirements for harmless treatment of solid waste in China, harmless and resource utilization of 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 entrained with part of the unreacted carbon and ash into black water. At present, the general treatment method for the gasification fine slag is to dewater by a vacuum filter and then transported to a landfill site for landfill. Due to the high moisture content of the gasification fine slag filter cake, leakage exists in the vehicle during the transportation process, which not only causes environmental pollution and freezing in winter, but also wastes water resources because the moisture is not recycled. At the same time, the gasification fine slag contains 30-40% residual carbon, which has considerable recycling value (such as being sent to 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 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, etc. Therefore, it has strong adhesion and adsorption performance to water molecules; In addition, in the process of coal chemical black water sedimentation, flocculants such as polyacrylamide need to be added, and after the flocculants and fine slag particles in the black water coagulate into a group, a flocculated colloidal structure is formed, which has strong water holding capacity, thereby causing the gasification fine slag to be difficult to dewater. Due to its structural characteristics and water holding characteristics, the gasification fine slag is obviously different from other particles such as raw coal (such as lignite) and other materials, and it is difficult to directly apply or learn from the dewatering treatment process of other materials such as lignite. In production practice, it is found that the dewatering effect of conventional dewatering equipment (vacuum filter dewatering machine, horizontal screw centrifuge, plate and frame filter dewatering machine, etc.) on gasification fine slag is poor. 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 greater than 60%. This is 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, 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 dewatered gasification fine slag can only be reduced to about 40%, and the dewatering effect is poor.

[0005] The heating dewatering technology uses dry media such as hot air, hot flue gas and steam to evaporate and dry the gasification fine slag to reduce the moisture of the gasification fine slag. Common heating dewatering equipment includes rotary dryers, disc dryers, etc. However, the existing heating dewatering method has the problems of high energy consumption, low energy efficiency ratio, large equipment investment, and difficult routine maintenance and repair work.

[0006] Patent application CN201710321402 discloses a coal gasification system fine slag slurry dewatering and drying method, which comprises the following steps: (a) the fine slag slurry generated by the coal gasification system is pre-dewatered by a pre-dewatering and thickening device to obtain thickened 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 thickened fine slag slurry and the hot air are simultaneously fed into a spray dryer, the thickened fine slag slurry and the hot air are directly contacted and heat- and mass-transferred in the spray dryer, and the dried fine slag is obtained after most of the water is removed through the bottom. However, this method uses hot air as a heat source, the heat capacity of air is relatively small, the required amount of hot air is large, the heat efficiency of waste heat for heating air is low, and the efficiency of the gasification fine slag drying system is relatively low; meanwhile, a large amount of water vapor is mixed with air in the drying process, the residual heat energy cannot be recovered, resulting in a large amount of energy waste, and the wet drying tail gas at the outlet of the spray dryer contains a large amount of air, the heat exchange efficiency coefficient of air and circulating water is low, a large amount of cooling water is required in the tail gas condenser to cool the tail gas, causing high condensation load of the wet drying tail gas condenser, and the exhaust gas emission is also relatively high. In addition, a large amount of air and water vapor mixed tail gas is generated at the outlet of the dryer through this process, and this tail gas is usually directly discharged, which results in heat waste; or the tail gas needs to be cooled and then gas-liquid separated, and then discharged, which also causes heat waste; and if the hot air is expected to be recycled, the water content in the air needs to be reduced by deep dewatering of the tail gas, so that the hot air can be reused, however, a large amount of cooling water needs to be used for heat exchange to realize gas-liquid separation, and a large amount of heat needs to be input to the separated air again, causing cold and hot phenomena.

[0007] Patent application CN201910913874.9 discloses a gasification ash drying device and method of four-nozzle water-coal gas flow bed; comprising a feeding unit connected with the gasification ash, a high-temperature gas supply unit, a gasification ash drying unit, the high-temperature gas in the high-temperature gas supply unit is connected with the tail gas treatment unit through the gasification ash drying unit, and the bottom of the gasification ash drying unit is provided with a gasification ash recovery unit; the feeding unit comprises a gasification coarse slag storage tank connected with a stirrer through a first weighing belt conveyor, and a gasification filter cake crusher connected with the stirrer through a second weighing belt conveyor; the high-temperature gas supply unit comprises a hot blast furnace connected with a natural gas storage tank; the gasification ash drying unit comprises a waste heat roller dryer connected with a three-return dryer through a hot air interface feeding device. This technology has problems of large consumption of natural gas, high energy consumption, low filling rate of the roller dryer, large equipment investment, etc.

[0008] A drying system of a centrifuge matched with a dryer for treating coal gasification fine slag is introduced in the document "Application of drying system in coal gasification fine slag treatment". In order to overcome the limited dewatering capacity of the vacuum belt filter, the fine slag can only be dewatered to 60% of the moisture content, which leads to the problems of frequent blockage of the conveying belt and the coal bunker discharge port when the fine slag is mixed with the power coal and sent to the boiler. The document proposes a drying process of using a centrifuge matched with a dryer. The black water (10% of the solid content) after flocculation and sedimentation is separated by the centrifuge to obtain the fine slag with about 50% of the moisture content. Then the single-shaft disc dryer is used to reduce the moisture content of the fine slag to about 30%, and then the fine slag is sent to the thermal power plant for mixing with the power coal. The system has the problems of low heat transfer efficiency, slow water evaporation speed, and small equipment processing capacity. SUMMARY

[0009] Therefore, the present application provides a gasification fine slag dewatering and drying method and system based on a fluidized bed dryer. The present application can efficiently realize the dewatering and drying of the gasification fine slag without introducing air, and the secondary steam formed during the drying process can be directly recycled in the system. The water resources and energy can be fully and reasonably reused, the energy utilization rate is high, the water resource waste is small, and the system safety is good.

[0010] In order to achieve the purpose, the present application provides the following technical solutions:

[0011] In one aspect, the present application provides a gasification fine slag dewatering and drying method based on a fluidized bed dryer, which comprises:

[0012] 1) Flash evaporation, sedimentation and filtration dewatering of the coal gasification black water in a black water treatment unit to obtain flash evaporation gas and fine slag to be treated; preferably, the particle size of the fine slag to be treated meets the following requirements: 0-10wt% of particles with a particle size <45μm, 10-30wt% of particles with a particle size of 45-125μm, 45-80wt% of particles with a particle size of 125-500μm, and 0-15wt% of particles with a particle size >500μm;

[0013] 2) The fine slag to be treated is sent to a fine slag preheater to exchange heat with a heat medium to obtain preheated fine slag;

[0014] 3) The preheated fine slag is sent to a fluidized bed dryer to exchange heat with superheated steam directly to obtain dried fine slag and secondary steam;

[0015] 4) The secondary steam obtained in step 3) is sent to a secondary steam dust removal unit for dust removal treatment to obtain dust-removed secondary steam, which is then sent to the fine slag preheater in step 2) as the heat medium.

[0016] 5) sending the secondary steam outputted from the fine slag preheater in step 2) into a steam preheater to exchange heat with the flash steam outputted from the black water treatment unit in step 1), to obtain preheated secondary steam;

[0017] 6) sending the preheated secondary steam obtained in step 5) into a steam superheater to perform superheating treatment, to obtain superheated steam; and sending the superheated steam into the fluidized bed dryer in step 3) to exchange heat with the preheated gasified fine slag.

[0018] In some preferable embodiments, in step 3), the superheated steam inlet of the fluidized bed dryer is arranged at the bottom of the fluidized bed dryer; preferably, in step 3), the middle or upper part of the fluidized bed dryer is provided with a gasified fine slag inlet for the gasified fine slag to be treated to pass in.

[0019] Further preferably, the inner cavity of the fluidized bed dryer is provided with a gas distributor and a plurality of partitions, the gas distributor is located above the superheated steam inlet, a plurality of distribution holes for the superheated steam to pass through are arranged on the gas distributor; the plurality of partitions are arranged above the gas distributor and separate the space above the gas distributor into a plurality of areas, and each of the areas corresponds to at least one of the distribution holes.

[0020] More preferably, the gasified fine slag inlet of the fluidized bed dryer is located above the partitions.

[0021] In some preferable embodiments, in step 6), the temperature of the superheated steam is 160-190°C, and the pressure of the superheated steam is 0.2-0.3 MPa.

[0022] In some preferable embodiments, in step 3), the temperature of the secondary steam is 130-150°C, and the pressure of the secondary steam is 0.2-0.3 MPa.

[0023] In some embodiments, in step 1), the water content of the gasified fine slag to be treated is 40-70 wt%.

[0024] In some preferable embodiments, in step 6), the superheating medium used in the steam superheater is coal gasification black water from a coal gasification system; after the superheating treatment of the preheated secondary steam in step 6), the coal gasification black water is sent into the black water treatment unit in step 1) for treatment.

[0025] In some preferable embodiments, in step 6), the superheating medium used in the steam superheater is crude synthesis gas from a coal gasification system.

[0026] In some embodiments, in step 1), the flash concentration comprises successively performing high-pressure flash and vacuum flash on the coal gasification black water, and preferably, before performing the vacuum flash, further comprising performing low-pressure flash on the coal gasification black water; preferably, the flash steam used in the steam preheater in step 5) is high-pressure flash steam obtained from the high-pressure flash;

[0027] In some embodiments, in step 1), the settling is performed in a settling tank.

[0028] In some embodiments, in step 4), the dust removal treatment comprises preliminarily removing dust from the secondary steam obtained in step 3) by passing through a cyclone separator, and then washing and removing dust in a steam washing tower; preferably, the washing water obtained by washing and removing dust in the steam washing tower is fed into the settling tank.

[0029] Preferably, in step 5), further comprising feeding the flash steam output from the steam preheater into a flash steam separation tank for vapor-liquid separation, and feeding the condensed liquid obtained by the separation into the steam washing tower as washing liquid.

[0030] 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 the steam preheater in step 5); preferably, part of the condensed liquid obtained by the separation in the secondary steam separation tank is fed into a grey water tank or the steam washing tower as washing liquid.

[0031] The present application also provides a dewatering and drying system capable of implementing the gasification fine slag dewatering and drying method described above, the dewatering and drying system comprising:

[0032] a black water treatment unit for performing flash concentration, settling and filter dewatering on coal gasification black water, and obtaining flash steam and gasification fine slag to be treated;

[0033] a fine slag preheater for preheating the gasification fine slag to be treated using a heat medium;

[0034] a fluidized bed dryer for directly contacting the gasification fine slag output from the fine slag preheater with superheated steam for heat exchange, so as to obtain dried gasification fine slag and secondary steam;

[0035] a secondary steam dust removal unit for performing dust removal treatment on the secondary steam output from the fluidized bed dryer; the secondary steam dust removal unit is connected with the fine slag preheater, so as to feed the secondary steam subjected to the dust removal treatment to the fine slag preheater as the heat medium;

[0036] a steam preheater for performing heat exchange between the secondary steam output from the fine slag preheater and the flash steam from the black water treatment unit, so as to obtain preheated secondary steam.

[0037] a steam superheater for superheating the secondary steam treated by the steam preheater to obtain superheated steam; the steam superheater is connected to the fluidized bed dryer to supply the superheated steam to the fluidized bed dryer;

[0038] Preferably, the superheated medium inlet of the steam superheater is connected to a coal gasification black water delivery pipeline of a coal gasification system, and the superheated medium outlet of the steam superheater is connected to the black water treatment unit through a pipeline; or, the superheated medium inlet of the steam superheater is connected to a raw syngas outlet of a coal gasification system through a raw syngas delivery pipeline.

[0039] In some preferred embodiments, the bottom of the fluidized bed dryer is provided with a superheated steam inlet; preferably, the middle or upper part of the fluidized bed dryer is provided with a gasification fine slag inlet for the passage of the gasification fine slag to be treated.

[0040] Further preferably, the inner cavity of the fluidized bed dryer is provided with a gas distributor and a plurality of partitions; the gas distributor is located above the superheated steam inlet, and a plurality of distribution holes for the passage of the superheated steam are formed in the gas distributor; the plurality of partitions are arranged above the gas distributor and divide the space above the gas distributor into a plurality of areas, and each of the areas corresponds to at least one of the distribution holes.

[0041] More preferably, the gasification fine slag inlet is located above the partitions.

[0042] In some embodiments, the black water treatment unit comprises a flash concentration unit and a sedimentation filtration unit.

[0043] The flash concentration unit is used for flashing and concentrating the coal gasification black water to obtain the flash steam and concentrated black water.

[0044] The sedimentation filtration unit is used for sedimentation and filtration dehydration of the concentrated black water to obtain the gasification fine slag to be treated.

[0045] Preferably, the flash concentration unit comprises a high-pressure flash tower and a vacuum flash tower connected in series; further preferably, a low-pressure flash tower is further connected in series between the high-pressure flash tower and the vacuum flash tower; preferably, the flash steam outlet of the high-pressure flash tower is connected to the flash steam inlet of the steam preheater.

[0046] Preferably, the settling filtration unit comprises a settling tank for settling the concentrated black water output by the flash 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; preferably, the filter dewatering device is a vacuum belt filter or a plate-and-frame filter.

[0047] In some embodiments, the secondary steam dedusting unit comprises a cyclone separator and a steam scrubbing tower.

[0048] The cyclone separator is connected with the fluidized bed dryer and used for preliminarily dedusting the secondary steam output by the fluidized bed dryer.

[0049] The gas inlet of the steam scrubbing tower is connected with the cyclone separator, and the gas outlet of the steam scrubbing tower is connected with the heat medium inlet of the fine slag preheater; the steam scrubbing tower is used for washing and dedusting the preliminarily dedusted secondary steam with a washing liquid to obtain washing water and dedusted secondary steam.

[0050] Preferably, the washing water outlet of the steam scrubbing tower is connected with the settling tank.

[0051] In some embodiments, the flash gas outlet of the steam preheater is connected with a flash steam separation tank, which is used for vapor-liquid separation of the flash gas output by the steam preheater and obtaining condensate; preferably, the condensate outlet of the flash steam separation tank is connected with the washing liquid inlet of the steam scrubbing tower.

[0052] In some embodiments, 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 obtaining 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 scrubbing tower.

[0053] The technical scheme provided by the present application has the following beneficial effects:

[0054] The method and system provided by the present application use superheated steam to directly contact with the fine gasification slag in the fluidized bed dryer for heat exchange and removal of most of the water in the fine slag to obtain fine gasification 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 fine gasification slag, saves transportation and processing costs, improves the plant environment, and improves the water resource utilization efficiency of coal gasification.

[0055] Meanwhile, the secondary steam output from the fluidized bed dryer is recycled in the process system, is used for preheating the gasification fine slag to be treated after dust removal, so that the residual heat is fully utilized, then is heat-exchanged with the flash steam (so that the residual heat of the flash steam is reasonably utilized), and is superheated to form superheated steam, and the superheated steam is returned to the fluidized bed dryer for recycling, so that the heat of the secondary steam is reasonably and fully recycled, and the waste of water resources is reduced. In addition, the scheme does not need to introduce hot air, is safe, and is energy-saving and environment-friendly. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 a schematic diagram of a dehydration and drying system of gasification fine slag in an embodiment;

[0057] Figure 2 a schematic diagram of a dehydration and drying system of gasification fine slag in another embodiment. DETAILED DESCRIPTION

[0058] In order to facilitate the understanding of the present application, the present application will be further described below in conjunction with examples. It should be understood that the following examples are only for better understanding of the present application, and do not mean that the present application is limited to the following examples only.

[0059] 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. The terms "first", "second", etc. are used only for descriptive purposes and should not be construed as indicating or implying relative importance.

[0060] In the examples, the specific experimental steps or conditions not noted can be operated according to the corresponding conventional experimental steps or conditions in the technical field. The reagents or instruments not noted by the manufacturer are all conventional products that can be obtained by purchase.

[0061] The present application provides a gasification fine slag dehydration and drying method based on a fluidized bed dryer, which mainly comprises the following steps:

[0062] 1) The coal gasification black water is subjected to flash evaporation concentration, sedimentation and filtration dehydration in a black water treatment unit, to obtain flash steam and gasification fine slag to be treated;

[0063] 2) The gasification fine slag to be treated is sent into a fine slag preheater to perform heat exchange with a heat medium, to obtain preheated gasification fine slag;

[0064] 3) The preheated gasification fine slag is sent into a fluidized bed dryer to perform heat exchange with superheated steam directly, to obtain dried gasification fine slag and secondary steam;

[0065] 4) The secondary steam obtained in step 3) is sent to a secondary steam dust removal unit for dust removal treatment, and the dust-removed secondary steam is then sent to the fine slag preheater in step 2) as a heat medium for heat exchange with the gasified fine slag to be treated;

[0066] 5) The secondary steam output from the fine slag preheater in step 2) is sent to a steam preheater, so that the used secondary steam in the fine slag preheater is heat-exchanged with the flash steam output from the black water treatment unit in step 1), thereby obtaining preheated secondary steam;

[0067] 6) The preheated secondary steam obtained in step 5) is sent to a steam superheater for heat exchange with a superheating medium, so that the aforementioned preheated secondary steam is subjected to superheating treatment to obtain superheated steam; the superheated steam is sent to the fluidized bed dryer in step 3) for heat exchange with the preheated gasified fine slag, so that the gasified fine slag is dehydrated and dried to obtain dried gasified fine slag, and secondary steam is obtained again.

[0068] The present application, by the above method, does not need to introduce air, nor to heat the air to realize the drying of the gasified fine slag; the present application uses superheated steam to directly contact with the gasified fine slag in the fluidized bed dryer for heat exchange, so that the water in the gasified fine slag is vaporized and separated to form new steam, which is mixed with the surrounding superheated steam flow to become secondary steam; as the secondary steam is discharged from the fluidized bed dryer, the water is also continuously carried away, thereby removing most of the water in the fine slag to obtain gasified fine slag with low water content. Not only the current environmental protection and fine slag resource utilization needs are met, but also the amount of fine slag to be transported is greatly reduced; at the same time, the secondary steam output from the fluidized bed dryer 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 amount of superheated steam), and then after heat exchange with the flash steam, it is superheated to form superheated steam, which is returned to the fluidized bed dryer 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.

[0069] In the present application, superheated steam is used as the drying medium in the fluidized bed dryer, which has a large specific heat capacity. Compared with the drying medium of hot air, flue gas and the like in the prior art, the present application has lower energy consumption, a large convective heat transfer coefficient, smaller water migration resistance, higher heat transfer efficiency, and can achieve higher drying efficiency and energy utilization rate. Moreover, no air or other gas is introduced into the system, and the secondary steam output from the fluidized bed dryer only needs simple dust removal treatment to be directly reused in the system, with fewer intermediate links and less energy loss. Furthermore, the present application does not involve the contact of hot air with the fine gasification 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.

[0070] Preferably, in step 1) of the present application, the particle size of the obtained fine gasification slag to be treated meets the following requirements: the particles with a particle size < 45 μm account for 0-10 wt%, the particles with a particle size of 45-125 μm account for 10-30 wt%, the particles with a particle size of 125-500 μm account for 45-80 wt%, and the particles with a particle size > 500 μm account for 0-15 wt%.

[0071] The present inventors have found that for fine gasification slag with a particle size meeting the above requirements, the method of the present application has better dewatering and drying effect, which can on the one hand improve the dewatering and drying effect of the fine gasification slag in the fluidized bed dryer, and on the other hand can achieve more uniform and sufficient fluidization in the fluidized bed dryer, thereby enabling more sufficient heat exchange with the superheated steam and improving the drying efficiency. Preferably, in step 3), the superheated steam inlet of the fluidized bed dryer is arranged at the bottom of the fluidized bed dryer, i.e. the superheated steam enters the fluidized bed dryer from the superheated steam inlet at the bottom of the fluidized bed dryer. Further preferably, in step 3), the middle or upper part of the fluidized bed dryer is provided with a fine gasification slag inlet for the fine gasification slag to be treated to pass into the fluidized bed dryer, i.e. the fine gasification slag to be treated passes into the fluidized bed dryer from the middle or upper part of the fluidized bed dryer.

[0072] In a preferred embodiment, the inner cavity of the fluidized bed dryer is provided with a gas distributor and a plurality of partitions, the gas distributor is located above the superheated steam inlet, and a plurality of distribution holes for the superheated steam to pass through are formed in the gas distributor. The plurality of partitions are arranged above the gas distributor and separate the space above the gas distributor into a plurality of regions, and each region corresponds to at least one distribution hole of the gas distributor. By using this preferred mode, more uniform and sufficient fluidization of the fine gasification slag can be achieved in the fluidized bed dryer, and accumulation and other phenomena are less likely to occur, which is conducive to more uniform contact between the superheated steam and the fine gasification slag to be treated and uniform and efficient heat transfer, thereby improving the energy utilization efficiency and the drying efficiency.

[0073] Further preferably, the gasification fine slag inlet of the fluidized bed dryer is located above the partition.

[0074] In some embodiments, the temperature of the superheated steam obtained from the steam superheater in step 6) is 160-190°C, and the pressure of the superheated steam is 0.2-0.3 Mpa; and the temperature of the secondary steam output from the fluidized bed dryer in step 3) is 130-150°C, and the pressure of the secondary steam is 0.2-0.3 Mpa.

[0075] In some embodiments, the water content of the gasification fine slag to be treated obtained from the black water treatment unit in step 1) is 40-70 wt%, and the dewatering and drying by the method of the present application can obtain dried gasification fine slag with a water content of 30% or less, for example, gasification fine slag with a water content of 10-30%, or gasification fine slag with a water content of 15-25%.

[0076] In the present application, the superheating medium required for the superheating treatment of the aforementioned preheated secondary steam in step 6) 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, for example, black water from the quench chamber of the gasifier and / or black water from the raw synthesis gas washing tower for washing the raw synthesis gas. The coal gasification black water from the coal gasification system is first subjected to heat exchange with the preheated secondary steam in the steam superheater, 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 synthesis gas from the coal gasification system, for example, raw synthesis gas from the gasifier after dust removal by the raw synthesis gas washing tower.

[0077] In some specific embodiments, the flash concentration in step 1) specifically includes first sending the coal gasification black water into a high-pressure flash tower for high-pressure flashing, and then sending it into a vacuum flash tower for vacuum flashing; in some embodiments, the coal gasification black water can also be sent into a low-pressure flash tower for low-pressure flashing before being sent into the vacuum flash tower. As for high-pressure flashing, low-pressure flashing and vacuum flashing, they are all conventional operations for flash treatment of coal gasification black water in the art, and will not be described here. The flash concentration described above obtains flash steam and concentrated black water. Preferably, the flash steam required in the steam preheater of step 5) comes from the high-pressure flash steam generated in the aforementioned high-pressure flashing process, i.e., the high-pressure flash steam is used for preheating the secondary steam.

[0078] In some embodiments, in step 1), the settling in the settling tank is performed, i.e. the concentrated black water obtained from the flash concentration is sent to the settling tank for settling to obtain the slurry and the supernatant (i.e. the grey water). During the settling, a flocculant can be added to promote the settling of the solids, which is a routine operation in the art and will not be described in detail. Specifically, the supernatant is sent to the downstream grey water tank. The slurry obtained from the settling (e.g. with a solid content of 10-20 wt%) is subjected to filtration and dewatering, e.g. using a vacuum belt filter or a plate and frame filter, to obtain the fine gasification slag to be treated, which still has a high water content, e.g. a water content of 40-70 wt%. The filtrate obtained from 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.

[0079] In some embodiments, in step 4), the dust removal treatment of the secondary steam output from the fluidized bed dryer specifically comprises: first subjecting the secondary steam to cyclone separation in a cyclone separator to obtain a preliminary dust removal, and then sending the secondary steam to a steam scrubbing tower for washing and dust removal with a washing liquid. In the steam scrubbing tower, the washing liquid is specifically brought into countercurrent contact with the secondary steam to wash the ash carried in the secondary steam and ensure the purity of the secondary steam. The washing liquid used is mainly the condensate water generated in the process, and can also be the grey water from the grey water tank, as will be described later. Preferably, the washing water obtained by washing and dust removal of the secondary steam in the steam scrubbing tower is sent to the settling tank. Through the above-mentioned preferred dust removal treatment, the secondary steam can be deeply dust-removed, and the dust content in the secondary steam can be <10 mg / m 3 .

[0080] Preferably, in step 5), the flash steam output from the steam preheater is also sent to a flash steam separation tank for vapor-liquid separation, and the condensate obtained from the separation is sent to the steam scrubbing tower as a washing liquid; the separated steam continues to be processed downstream, e.g. for sulfur recovery treatment, etc.

[0081] Preferably, in step 2), the secondary steam used as a heat medium in the fine slag preheater is output after heat exchange with the fine gasification slag, and is first sent to a secondary steam separation tank for vapor-liquid separation, and then sent to the steam preheater in step 5) for heat exchange with the flash steam. Preferably, part of the condensate obtained from the secondary steam separation tank is sent to the grey water tank or to the steam scrubbing tower as a washing liquid.

[0082] In the present application, superheated steam is used as the drying medium, which has higher specific heat capacity (1.968 kJ / (kg·K)) and stronger heat exchange capacity compared with low-temperature flue gas and hot air. Through the method of the present application, good dewatering and drying effect of gasified fine slag can be achieved with smaller flow of superheated steam. In the present application, superheated steam and gasified fine slag are directly contacted and exchanged in the fluidized bed dryer, so that the temperature distribution is more uniform and the processing capacity is larger. The present application uses secondary steam 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.

[0083] The second aspect of the present application provides a gasified fine slag dewatering and drying system based on a fluidized bed dryer, which can be used to implement the above-mentioned gasified fine slag dewatering and drying method.

[0084] Referring to Figure 1 The dewatering and drying system of the present application mainly includes a black water treatment unit 100, a fine slag preheater, a fluidized bed dryer, a secondary steam dust removal unit, a steam preheater, and a steam superheater.

[0085] The black water treatment unit 100 is used for flash evaporation concentration, sedimentation, and filtration dewatering of coal gasification black water, thereby obtaining flash steam and gasified fine slag to be treated;

[0086] The fine slag preheater is used for preheating the gasified fine slag to be treated using a heat medium, thereby obtaining preheated gasified fine slag;

[0087] The fluidized bed dryer is used for directly contacting and heat exchanging the gasified fine slag output by the fine slag preheater with superheated steam, 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;

[0088] The secondary steam dust removal unit is used for dust removal treatment of the secondary steam output by the fluidized bed dryer, thereby obtaining dust-removed secondary steam; the secondary steam dust removal unit is connected with the fine slag preheater to deliver the dust-removed secondary steam as a heat medium to the fine slag preheater, thereby being used for preheating the gasified fine slag to be treated;

[0089] The steam preheater is used for heat exchanging the secondary steam output by the fine slag preheater with the flash steam from the black water treatment unit, thereby obtaining preheated secondary steam;

[0090] The steam superheater is used for superheating treatment of the secondary steam treated by the steam preheater (i.e., preheated secondary steam), thereby obtaining superheated steam; the steam superheater is connected with the fluidized bed dryer to supply superheated steam to the fluidized bed dryer, i.e., the required superheated steam of the fluidized bed dryer is supplied by the steam superheater.

[0091] By means of the above system, the gasified fine slag is dehydrated and dried, the superheated steam is used to efficiently, safely and environmentally dry and dehydrate the gasified fine slag, there is no explosion risk of contact between hot air and dry gasified fine slag with high carbon content, and the energy utilization rate is higher. Moreover, no air is introduced into the system, the secondary steam flow generated in the drying and dehydration process is mainly steam, which can be recycled without complicated intermediate treatment links. The secondary steam is first dedusted in the present application, then enters the fine slag preheater to preheat the gasified fine slag, then enters the steam preheater to preheat by heat exchange with flash steam, and then enters the steam superheater to be superheated, to obtain superheated steam for recycling in the fluidized bed dryer. The ingenious design of the whole 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, so that water resources can be efficiently and fully utilized.

[0092] In some preferred embodiments, referring to Figure 1 , the superheated medium inlet of the steam superheater is connected with the coal gasification black water conveying pipeline of the coal gasification system, and the superheated medium outlet of the steam superheater is connected with the black water treatment unit through a pipeline; that is, the required superheated medium in the steam superheater is the coal gasification black water of the coal gasification system, which first exchanges heat with the preheated secondary steam in the steam superheater, and then enters the black water treatment unit for further treatment. Figure 2 For Figure 1 , a variant of the dehydration and drying system is shown, which is another embodiment. The main difference between this embodiment and Figure 1 is that the superheated medium inlet of the steam superheater is connected with the crude synthesis gas outlet of the coal gasification system through a crude synthesis gas conveying pipeline, that is, the required superheated medium in the steam superheater is the crude synthesis gas of the coal gasification system; specifically, the crude synthesis gas generated by the gasifier is washed in the crude synthesis gas washing tower to obtain the crude gas, which is used as the aforementioned superheated medium and introduced into the steam superheater.

[0093] Preferably, the bottom of the fluidized bed dryer is provided with a superheated steam inlet, that is, the superheated steam enters the fluidized bed dryer from the bottom of the fluidized bed dryer to exchange heat with the gasified fine slag to be treated. Preferably, the middle or upper part of the fluidized bed dryer is provided with a gasified fine slag inlet for the gasified fine slag to be treated to enter.

[0094] Preferably, as shown in Figure 2As shown, the inner cavity of the fluidized bed dryer is provided with a gas distributor 1 and a plurality of partitions 2. The gas distributor 1 is located above the superheated steam inlet, and a plurality of distribution holes for the superheated steam are formed in the gas distributor 1. The plurality of partitions 2 are arranged above the gas distributor 1 and divide the space above the gas distributor 1 into a plurality of regions, and each region corresponds to at least one distribution hole; preferably, the structure is beneficial to more uniform contact of the superheated steam with the fine gasification slag to be treated, and the fine gasification slag to be treated can be more uniformly fluidized in the fluidized bed dryer, and is not prone to accumulation and other phenomena, which is beneficial to improving the heat transfer efficiency and improving the drying efficiency. More preferably, the fine gasification slag inlet of the fluidized bed dryer is located above the partition.

[0095] In some embodiments, as shown in Figure 1 As shown, the black water treatment unit 100 specifically includes a flash concentration unit 101 and a sedimentation and filtration unit 102. The flash concentration unit 101 is used to flash and concentrate the coal gasification black water, thereby obtaining flash gas and concentrated black water; the sedimentation and filtration unit 102 is used to sediment and filter the concentrated black water to remove water, thereby obtaining the fine gasification slag to be treated.

[0096] Further specifically, the flash concentration unit 101 includes a high-pressure flash tower and a vacuum flash tower connected in series; in some embodiments, a low-pressure flash tower is further connected between the high-pressure flash tower and the vacuum flash tower; preferably, the flash gas outlet of the high-pressure flash tower is connected with the flash gas inlet of the steam preheater, that is, the flash gas in the steam preheater is derived from the high-pressure flash gas output by the high-pressure flash tower.

[0097] Further specifically, the sedimentation and filtration unit 102 includes a sedimentation tank and a filter dewatering device. The sedimentation tank is used to sediment the concentrated black water output by the flash unit, thereby obtaining a slurry; the filter dewatering device is used to filter and dewater the slurry obtained by the sedimentation treatment, thereby obtaining the fine gasification slag to be treated; preferably, the filter dewatering device specifically adopts a vacuum belt filter or a plate-and-frame filter. As shown in Figure 1 As shown, the sedimentation and filtration unit specifically further includes a grey water tank for receiving the supernatant (i.e. grey water) in the sedimentation tank and the filtrate obtained by the filter dewatering 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.

[0098] In some specific embodiments, as shown in Figure 1The secondary steam dust removal unit comprises a cyclone separator and a steam washing tower. The cyclone separator is connected with the fluidized bed dryer and used to perform cyclone separation on the secondary steam output by the fluidized bed dryer, so that the secondary steam is preliminarily dust removed, and the solid particles separated by the cyclone separator are discharged and returned to the fluidized bed dryer. The steam washing tower is connected with the cyclone separator at an air inlet, and connected with the heat medium inlet of the fine slag preheater at an air outlet. The steam washing tower receives the preliminarily dust removed secondary steam from the cyclone separator, and the preliminarily dust removed secondary steam is washed by washing liquid in the steam washing tower, so that washing water and dust removed secondary steam are obtained. Preferably, the washing water outlet of the steam washing tower is connected with the settling tank.

[0099] In some embodiments, the flash steam outlet of the steam preheater is connected with a flash steam separation tank, which is used to perform vapor-liquid separation on the flash steam output by the steam preheater and obtain condensate; preferably, the condensate outlet of the flash steam separation tank is connected with the washing liquid inlet of the steam washing tower, so that the condensate separated in the flash steam separation tank can be sent to the steam washing tower for use as washing liquid. Further, the flash steam output by the flash steam separation tank enters a downstream unit such as a sulfur recovery unit for further treatment.

[0100] In some embodiments, the secondary steam outlet of the fine slag preheater is connected with a secondary steam separation tank through a pipeline, which is used to perform vapor-liquid separation on the secondary steam output by the fine slag preheater and obtain condensate; the vapor phase outlet of the secondary steam separation tank is connected with 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 condensate outlet of the secondary steam separation tank is connected with the 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, so that the condensate separated in the secondary steam separation tank can enter the grey water tank for reuse, or be used as washing liquid.

[0101] The application will be further described below by application cases.

[0102] Example 1

[0103] The schematic diagram of the dewatering and drying system used in this example is shown in Figure 1 The following description is not repeated hereinafter for the dewatering and drying system and the dewatering and drying method, which can be referred to the foregoing description.

[0104] The coal gasification black water used in this example is black water from the quenching chamber of a gasifier and black water from a raw synthesis gas washing tower. In this example, the dewatering and drying of the gasification fine slag comprises the following processing links:

[0105] 1) Flash concentration, settling and filtration:

[0106] 1.1) Flash concentration: The coal gasification black water is sent to 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 sent to a vacuum flash tower, and is further flashed at -0.5 MPa to obtain concentrated black water;

[0107] 1.2) Sedimentation:

[0108] The concentrated black water obtained in step 1.1) is sent to 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 (80 wt% anionic polyacrylamide and 20 wt% coagulant (polyaluminum)).

[0109] 1.3) Filtration and dewatering:

[0110] 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 with a water content of 60 wt% to be treated. The filtrate is pumped to the ash water tank. The particle size of the gasification fine slurry is as follows: particles with a particle size of <45 μm account for 3 wt%, particles with a particle size of 45-125 μm account for 24 wt%, particles with a particle size of 125-500 μm account for 62 wt%, and particles with a particle size of >500 μm account for 11 wt%.

[0111] 2) Fine slurry preheating:

[0112] 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. 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 is sent to the ash water tank.

[0113] 3) Drying and dewatering:

[0114] The aforementioned preheated gasification fine slurry is sent to a fluidized bed dryer, and is directly contacted with superheated steam in the fluidized bed dryer. The gasification fine slurry is heated, and the water in the gasification fine slurry is vaporized to 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 by an induced draft fan provided in the fluidized bed dryer, and the water is continuously carried away, so that most of the water in the fine slurry is removed, and dry gasification fine slurry with a water content of 20% is obtained.

[0115] 4) Secondary steam dust removal:

[0116] The secondary steam discharged from the fluidized bed dryer is first separated from most of the solids by a cyclone separator. The preliminarily dedusted secondary steam is then introduced into a steam scrubber tower, in which the secondary steam is further dedusted by washing with condensate from the flash steam separation tank as washing liquid. The final dedusted secondary steam contains <10 mg / m 3 The washing water at the bottom of the steam scrubber tower is transported into a settling tank. The dedusted secondary steam obtained in this step is introduced into the fine slag preheater of step 2) as a heating medium for preheating the gasification fine slag.

[0117] 5) Secondary steam preheating

[0118] The secondary steam separated from the liquid in the secondary steam separation tank in step 2) is introduced into a steam preheater to exchange heat with high-pressure flash steam from the high-pressure flash tower, thereby obtaining preheated secondary steam.

[0119] 6) Secondary steam superheating

[0120] The preheated secondary steam exchanges heat with coal gasification black water (superheating medium, temperature: 210°C, pressure: 4.0 MPa) from the coal gasification system in a steam superheater, thereby forming new superheated steam. The superheated steam is recycled to the fluidized bed dryer in step 3) (at the initial stage of system operation, fresh superheated steam introduced from outside the system can be used in step 3). After the system is operated and superheated steam is generated in the steam superheater, the superheated steam generated in the steam superheater is used in step 3). The coal gasification black water from the coal gasification system exchanges heat in the steam superheater and is then introduced into the high-pressure flash tower in step 1.1) for treatment.

[0121] Example 2

[0122] The schematic diagram of the dewatering and drying system used in this example is shown in Figure 2 The following description of the dewatering and drying system and the dewatering and drying method is not particularly described below and can be referred to the foregoing description.

[0123] The coal gasification black water used in this example is black water from the quenching chamber of the gasifier and black water from the crude synthetic gas scrubber tower. In this example, the dewatering and drying of the gasification fine slag includes the following treatment steps:

[0124] 1) Flash concentration, settling and filtration

[0125] 1.1) Flash concentration: The coal gasification black water is sent to 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 sent to 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 sent to a vacuum flash tower, and is further flashed at -0.5 MPa to obtain concentrated black water.

[0126] 1.2) Sedimentation:

[0127] The concentrated black water obtained in step 1.1) is sent to 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 (poly-iron)). The slurry containing 20% solids is settled at the bottom of the sedimentation tank, and the supernatant of the sedimentation tank is sent to an ash water tank.

[0128] 1.3) Filtration and dewatering:

[0129] The slurry settled at the bottom of the sedimentation tank is sent to a filtration and dewatering device (vacuum belt filter) by a slurry pump for filtration and dewatering to obtain gasification fine slag to be treated containing 60 wt% water. 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 15 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 4 wt%.

[0130] 2) Fine slag preheating:

[0131] The aforementioned gasification fine slag to be treated is sent to 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 sent to a secondary steam separation tank for vapor-liquid separation. The condensed liquid separated is sent to the ash water tank.

[0132] 3) Drying and dewatering:

[0133] The aforementioned preheated gasification fine slag is sent to a fluidized bed dryer, and is directly contacted with superheated steam in the fluidized bed dryer. 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. The secondary steam is discharged from the fluidized bed dryer by an induced draft fan provided in the fluidized bed dryer. The water is continuously carried away, so that most of the water in the fine slag is removed, and dry gasification fine slag containing 15% water is obtained.

[0134] 4) Secondary steam dust removal:

[0135] The secondary steam discharged from the fluidized bed dryer is first separated from most of the solids by a cyclone separator, and the preliminarily dedusted secondary steam is then introduced into a steam scrubbing tower, in which the secondary steam is further dedusted by washing with condensate from the flash steam separation tank as washing liquid, and the finally obtained 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 introduced into the fine slag preheater of step 2) as a heating medium for preheating the gasification fine slag.

[0136] 5) Secondary steam preheating:

[0137] The secondary steam subjected to vapor-liquid separation in the secondary steam separation tank in step 2) is introduced into a steam preheater to exchange heat with high-pressure flash steam from the high-pressure flash tower, thereby obtaining preheated secondary steam.

[0138] 6) Secondary steam superheating:

[0139] The preheated secondary steam exchanges heat with the raw synthesis gas from the raw synthesis gas scrubbing tower (superheating medium, pressure 4.0 MPa, temperature 210°C), thereby forming new superheated steam; the superheated steam is recycled to the fluidized bed dryer 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 during system operation, the superheated steam generated in the steam superheater is used in step 3).

[0140] Examples 3-8

[0141] Example 3-5 is performed with reference to Example 2, and Examples 6-8 are performed with reference to Example 1, and the process parameters and experimental results of Examples 3-8 are shown in Table 1.

[0142] Table 1

[0143]

[0144]

[0145] As can be seen from the above examples, the dehydration and drying system and method of the present application can dry and dehydrate the gasification fine slag with high water content to a water content of less than 30%, and the energy and water resources in the entire process can be reasonably and fully utilized, the additional input energy required in the entire process is small, the water resources are recycled, the waste of water resources can be greatly reduced, and hot air does not need to be introduced in the treatment process, which is not only environmentally friendly but also safe. By using the scheme of the present application, the problems of poor effect, high energy consumption, large waste of water resources, and serious environmental pollution in the existing gasification fine slag dehydration treatment can be effectively solved.

[0146] It is readily understood that the above-described embodiments are only illustrative of the application and not intended to limit the scope of the application. Other variations and modifications can be made to the embodiments described and illustrated herein, without departing from the spirit of the application, the scope of which is defined by the appended claims.

Claims

1. A method for dehydrating and drying gasified fine slag based on a fluidized bed dryer, characterized in that, The method includes: 1) The coal gasification black water is concentrated by flash evaporation, settled and dehydrated by filtration in the black water treatment unit to obtain flash steam and gasification fine residue to be treated; 2) The gasification slag to be processed is fed into the slag preheater to exchange heat with the heat medium to obtain preheated gasification slag. 3) The preheated gasified fine slag is fed into a fluidized bed dryer to directly contact superheated steam for heat exchange, resulting in dried gasified fine slag and secondary steam. The superheated steam inlet of the fluidized bed dryer is located at the bottom of the dryer, and the middle or upper part of the dryer has a gasified fine slag inlet for the gasified fine slag to be processed. The inner cavity of the dryer is equipped with a gas distributor and multiple baffles. The gas distributor is located above the superheated steam inlet and has multiple distribution holes for the superheated steam to pass through. The multiple baffles are located above the gas distributor and divide the space above the gas distributor into multiple regions, and each region corresponds to at least one of the distribution holes. 4) The secondary steam obtained in step 3) is sent to the secondary steam dust removal unit for dust removal treatment to obtain dust-removed secondary steam, and then sent to the fine slag preheater in step 2) as the heat medium. 5) The secondary steam output from the fine slag preheater in step 2) is fed into the steam preheater to exchange heat with the flash steam output from the black water treatment unit in step 1) to obtain preheated secondary steam. 6) The preheated secondary steam obtained in step 5) is fed into a steam superheater for superheating treatment to obtain superheated steam; the superheated steam is fed into the fluidized bed dryer in step 3) for heat exchange with the preheated gasified fine slag.

2. The method for dehydrating and drying gasified fine residue according to claim 1, characterized in that, The particle size of the gasification slag to be treated meets the following requirements: particles with a particle size <45μm account for 0wt%-10wt%, particles with a particle size of 45μm-125μm account for 10wt%-30wt%, particles with a particle size of 125μm-500μm account for 45wt%-80wt%, and particles with a particle size >500μm account for 0wt%-15wt%.

3. The method for dehydrating and drying gasified fine residue according to claim 1, characterized in that, The gasified fine residue inlet of the fluidized bed dryer is located above the partition.

4. The method for dehydrating and drying gasified fine residue according to claim 1, characterized in that, In step 6), the temperature of the superheated steam is 160℃-190℃, and the pressure of the superheated steam is 0.2Mpa-0.3Mpa; And / or, in step 3), the temperature of the secondary steam is 130℃-150℃, and the pressure of the secondary steam is 0.2Mpa-0.3Mpa; And / or, in step 1), the water content of the gasification slag to be treated is 40wt%-70wt%.

5. The method for dehydrating and drying gasified fine residue according to any one of claims 1-4, characterized in that, In step 6), the superheating medium used in the steam superheater is coal gasification black water from the coal gasification system; after the preheated secondary steam is superheated in step 6), the coal gasification black water from the coal gasification system is sent to the black water treatment unit in step 1) for further treatment. Alternatively, in step 6), the superheating medium used in the steam superheater is crude syngas from the coal gasification system.

6. The method for dehydrating and drying gasified fine residue according to any one of claims 1-4, characterized in that, In step 1), the flash concentration includes performing high-pressure flash evaporation and vacuum flash evaporation on the coal gasification black water. In step 1), the settling takes place in a settling tank; In step 4), the dust removal process includes first passing the secondary steam obtained in step 3) through a cyclone separator for preliminary dust removal, and then sending it into a steam scrubbing tower for washing and dust removal.

7. The method for dehydrating and drying gasified fine residue according to claim 6, characterized in that, Prior to the vacuum flash evaporation, a low-pressure flash evaporation operation is also performed on the coal gasification black water.

8. The method for dehydrating and drying gasified fine residue according to claim 6, characterized in that, The flash steam used in the steam preheater in step 5) comes from the high-pressure flash steam obtained by the high-pressure flash evaporation.

9. The method for dehydrating and drying gasified fine residue according to claim 6, characterized in that, The washing water obtained from the washing and dust removal process in the steam scrubbing tower is sent to the settling tank.

10. The method for dehydrating and drying gasified fine residue according to claim 6, characterized in that, Step 5) further includes sending the flash steam output from the steam preheater into a flash steam separator for vapor-liquid separation, and sending the separated condensate into the steam scrubbing tower as washing liquid.

11. The method for dehydrating and drying gasified fine residue according to claim 6, characterized in that, In step 2), the secondary steam output from the fine slag preheater is first sent to a secondary steam separator for vapor-liquid separation, and then sent to the steam preheater in step 5).

12. The method for dehydrating and drying gasified fine residue according to claim 6, characterized in that, A portion of the condensate separated in the secondary steam separator is sent to the ash water tank or to the steam scrubbing tower as washing liquid.

13. A dehydration and drying system capable of implementing the gasification fine residue dehydration and drying method according to any one of claims 1-12, characterized in that, The dehydration and drying system includes: The black water treatment unit is used to flash concentrate, settle, and filter dewater the black water from coal gasification, and to obtain flash steam and gasification slag to be treated. A fine slag preheater is used to preheat the gasified fine slag to be treated using a heat medium. A fluidized bed dryer is used to directly contact the gasified fine slag output from the fine slag preheater with superheated steam for heat exchange, thereby obtaining dried gasified fine slag and secondary steam. The fluidized bed dryer has a superheated steam inlet at its bottom and a gasified fine slag inlet in its middle or upper part for the gasified fine slag to be processed. The inner cavity of the fluidized bed dryer is equipped with a gas distributor and multiple baffles. The gas distributor is located above the superheated steam inlet and has multiple distribution holes for the superheated steam to pass through. The multiple baffles are located above the gas distributor and divide the space above the gas distributor into multiple regions, each region corresponding to at least one of the distribution holes. A secondary steam dust removal unit is used to remove dust from the secondary steam output from the fluidized bed dryer; the secondary steam dust removal unit is connected to the fine slag preheater so that the dust-removed secondary steam is used as the heat medium to be transported to the fine slag preheater. A steam preheater is used to exchange heat between the secondary steam output from the fine slag preheater and the flash steam from the black water treatment unit to obtain preheated secondary steam. A steam superheater is used to superheat secondary steam that has been treated by the steam preheater to obtain superheated steam; the steam superheater is connected to the fluidized bed dryer to supply the superheated steam to the fluidized bed dryer.

14. The dehydration and drying system according to claim 13, characterized in that, The superheated medium inlet of the steam superheater is connected to the coal gasification black water conveying pipeline of the coal gasification system, and the superheated medium outlet of the steam superheater is connected to the black water treatment unit through a pipeline; or, the superheated medium inlet of the steam superheater is connected to the crude syngas outlet of the coal gasification system through a crude syngas conveying pipeline.

15. The dehydration and drying system according to claim 13, characterized in that, The gasification fine residue inlet is located above the partition.

16. The dehydration and drying system according to any one of claims 13-15, characterized in that, The black water treatment unit includes a flash evaporation concentration unit and a sedimentation filtration unit; The flash evaporation and concentration unit is used to flash evaporate and concentrate the coal gasification black water to obtain flash steam and concentrated black water; The sedimentation and filtration unit is used to settle and filter the concentrated black water to obtain the gasified fine residue to be treated.

17. The dehydration and drying system according to claim 16, characterized in that, The flash concentration unit includes a high-pressure flash tower and a vacuum flash tower connected in series.

18. The dehydration and drying system according to claim 17, characterized in that, A low-pressure flash tower is connected in series between the high-pressure flash tower and the vacuum flash tower.

19. The dehydration and drying system according to claim 17, characterized in that, The flash steam outlet of the high-pressure flash tower is connected to the flash steam inlet of the steam preheater.

20. The dehydration and drying system according to claim 16, characterized in that, The settling and filtration unit includes a settling tank and a filtration and dewatering device. The settling tank is used to settle the concentrated black water output from the flash concentration unit, and the filtration and dewatering device is used to filter and dewater the slurry obtained after the settling treatment to obtain the gasification fine slag to be treated.

21. The dehydration and drying system according to claim 20, characterized in that, The filtration and dehydration device is a vacuum belt filter or a plate and frame filter.

22. The dehydration and drying system according to claim 20, characterized in that, The secondary steam dust removal unit includes a cyclone separator and a steam scrubbing tower; The cyclone separator is connected to the fluidized bed dryer and is used to perform preliminary dust removal on the secondary steam output from the fluidized bed dryer. The inlet of the steam scrubbing tower is connected to the cyclone separator, and the outlet of the steam scrubbing tower is connected to the heat medium inlet of the fine slag preheater. The steam scrubbing tower is used to wash the secondary steam that has undergone preliminary dust removal with a washing liquid to obtain washing water and dust-removed secondary steam.

23. The dehydration and drying system according to claim 22, characterized in that, The washing water outlet of the steam scrubbing tower is connected to the settling tank.

24. The dehydration and drying system according to claim 22, characterized in that, The flash steam outlet of the steam preheater is connected to a flash steam separator for vapor-liquid separation of the flash steam output from the steam preheater to obtain condensate. And / or, the secondary steam outlet of the fine slag preheater is connected to a secondary steam separator via a pipeline for vapor-liquid separation of the secondary steam output from the fine slag preheater to obtain condensate; the vapor phase outlet of the secondary steam separator is connected to the secondary steam inlet of the steam preheater.

25. The dehydration and drying system according to claim 24, characterized in that, The condensate outlet of the flash vapor separator is connected to the washing liquid inlet of the steam scrubbing tower; And / or, the condensate outlet of the secondary steam separator is connected to the ash water tank, or the condensate outlet of the secondary steam separator is connected to the washing liquid inlet of the steam scrubbing tower.

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