Gasification fine slag dewatering and drying method and system based on a spray dryer

Abstract

The present application provides a kind of gasification fine slag dewatering drying method and dewatering drying system based on spray dryer, can carry out dewatering drying to high water content gasification fine slag, energy utilization is high, and water resource waste is less.The method comprises:1) the coal gasification black water is concentrated in black water treatment unit by flash evaporation, settlement and filtration dehydration;2) the gasification fine slag to be treated is sent into fine slag preheater and exchanges heat with heat medium;3) the preheated gasification fine slag and superheated steam are sprayed into spray dryer to exchange heat, and dry gasification fine slag and secondary steam are obtained;4) the secondary steam is sent into secondary steam dust removal unit for dust removal treatment, and then it is sent into fine slag preheater;5) the secondary steam output from fine slag preheater is sent into steam preheater to exchange heat, and preheated secondary steam is obtained;6) the preheated secondary steam is sent into steam superheater for superheating treatment, and superheated steam is obtained;the superheated steam is sent into spray dryer.

Description

Technical Field

[0001] This invention relates to dehydration and drying technology for gasification fine residue, specifically to a dehydration and drying method and system for gasification fine residue based on a spray dryer. Background Technology

[0002] my country's coal chemical industry discharges a large amount of gasification ash every year. As my country's requirements for the harmless treatment of solid waste become increasingly stringent, the harmless treatment and resource utilization of gasification fine slag are important factors restricting the sustainable development of the coal chemical industry.

[0003] Gasification slag is formed from unreacted carbon and ash carried by crude coal gas, which is washed into black water, then flash-distilled, concentrated, flocculated, settled, and dehydrated to form a filter cake. Currently, the common method for treating gasification slag is to dehydrate it using a vacuum filter before transporting it to a landfill. Due to the high moisture content of the gasification slag filter cake, leakage during transport not only causes environmental pollution and winter icing, but also wastes water resources because the moisture is not recycled. Furthermore, while gasification slag contains 30-40% residual carbon, possessing considerable recycling value (e.g., for co-firing in boilers and gasifiers), the high moisture content reduces its calorific value and makes it prone to adhesion, blockage, and corrosion, severely impacting its harmless treatment and resource utilization.

[0004] Due to its abundant pore structure, large specific surface area, and small particle size, gasification fine slag exhibits strong adhesion and adsorption properties for water molecules. Furthermore, flocculants such as polyacrylamide are added during the sedimentation of black water in coal chemical processes. These flocculants, when agglomerated with the fine slag particles in the black water, form a flocculated colloidal structure with strong water-holding capacity, making dewatering of the gasification fine slag challenging. Because of its structural characteristics and water-holding properties, gasification fine slag differs significantly from other particles, such as raw coal (e.g., lignite), making moisture removal difficult and hindering the direct application or reference of dewatering processes used for other materials like lignite. In production practice, conventional dewatering equipment (vacuum filtration dewatering machines, horizontal screw centrifuges, plate and frame filter dewatering machines, etc.) has proven ineffective in dewatering gasification fine slag. Vacuum belt filters are the most commonly used equipment for dewatering fine gasification slag. However, even after dewatering, the moisture content of the gasification slag remains above 60%. This is because when the moisture content of the filter cake drops to around 60%, cracks form, preventing further dewatering by vacuum filtration. Furthermore, vacuum belt filters suffer from short filter cloth lifespan, high water consumption for filter cloth rinsing, high turbidity of the filtrate, and poor operating hygiene. Compared to vacuum belt filters, horizontal screw centrifuges offer advantages such as smaller footprint, higher dewatering efficiency, fully enclosed continuous feeding, and environmental friendliness. However, even after dewatering by a horizontal screw centrifuge, the moisture content of the gasification slag remains around 40-50%. Plate and frame filter presses can only remove some of the free water between gasification slag particles and some water within the pores. However, because no phase change occurs during dewatering, the moisture content of the gasification slag can only be reduced to around 40%, resulting in poor dewatering performance.

[0005] Heating dehydration technology utilizes drying media such as hot air, hot flue gas, and steam to reduce the moisture content of gasified fine slag through evaporation and drying. Common heating dehydration equipment includes rotary dryers and disc dryers. However, existing heating dehydration methods have high energy consumption, low energy efficiency, and also suffer from problems such as high equipment investment and difficulty in daily maintenance and repair.

[0006] 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.

[0007] 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.

[0008] The literature "Application of Drying System in Coal Gasification Fine Slag Treatment" introduces a centrifuge-equipped dryer system for treating coal gasification fine slag. To overcome the limited dehydration capacity of vacuum belt filter media, which can only dehydrate the fine slag to a moisture content of 60%, leading to frequent blockages in the conveyor belt and coal bunker discharge port when the coal gasification fine slag is blended with thermal coal and sent to the boiler, this literature proposes a drying process using a centrifuge-equipped dryer. First, the black water (10% solids content) after flocculation and sedimentation is separated by a centrifuge to obtain fine slag with a moisture content of approximately 50%. Then, a single-shaft disc dryer is used to reduce the moisture content of the fine slag to approximately 30%, before it is sent to a thermal power plant and blended with thermal coal. This system suffers from low heat transfer efficiency, slow moisture evaporation rate, and small equipment capacity. Summary of the Invention

[0009] In view of this, the present invention provides a method and system for dehydrating and drying gasified fine slag based on a spray dryer. The method of the present invention can be used to dehydrate and dry gasified fine slag with high water content. It can not only achieve efficient dehydration and drying of gasified fine slag without the need to introduce air, but also the secondary steam generated during the drying process can be directly recycled within the system. The system's water resources and energy can be fully and rationally reused, resulting in high energy utilization, low water waste, and good system safety.

[0010] To achieve its objective, the present invention provides the following technical solution:

[0011] The first aspect of this invention provides a method for dehydrating and drying gasification fine residue, the method comprising:

[0012] 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; preferably, the particle size of the gasification fine residue to be treated meets the following requirements: particles with a particle size <20μm account for 25-35wt%, particles with a particle size <45μm account for 65-75wt%, and particles with a particle size <100μm account for 85-95wt%;

[0013] 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.

[0014] 3) The preheated gasified fine slag and superheated steam are injected into a spray dryer so that they come into direct contact and exchange heat to obtain dried gasified fine slag and secondary steam.

[0015] 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.

[0016] 5) The secondary steam output from the fine slag preheater in step 2) is sent 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.

[0017] 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 spray dryer in step 3) for heat exchange with the preheated gasified fine slag.

[0018] In some preferred 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;

[0019] In some preferred 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.

[0020] In some embodiments, in step 1), the water content of the gasification slag to be treated is 40-70 wt%.

[0021] In some preferred embodiments, 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.

[0022] In some preferred embodiments, in step 6), the superheating medium used in the steam superheater is crude coal gas from the coal gasification system.

[0023] In a preferred embodiment, the preheated gasified fine slag and the superheated steam are simultaneously injected into the spray dryer through a feed nozzle;

[0024] Among them, the gasified fine slag is injected through the middle feed channel of the feed nozzle, and the superheated steam is injected through the central feed channel and the outer ring feed channel of the feed nozzle. The middle feed channel is arranged around the periphery of the central feed channel, and the outer ring feed channel is arranged around the periphery of the middle feed channel.

[0025] Preferably, the length-to-diameter ratio of the feed nozzle is 3-10:1, more preferably 5-7:1.

[0026] In some embodiments, in step 1), the flash concentration includes performing high-pressure flash evaporation and vacuum flash evaporation on the coal gasification black water sequentially. Preferably, before performing the vacuum flash evaporation, the operation of low-pressure flash evaporation on the coal gasification black water is also included. Preferably, 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.

[0027] In some implementations, in step 1), the settling is carried out in a settling tank;

[0028] In some embodiments, 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 to a steam scrubbing tower for washing and dust removal; preferably, the washing water obtained from washing and dust removal in the steam scrubbing tower is sent to the settling tank.

[0029] Preferably, 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;

[0030] Preferably, 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); preferably, a portion of the condensate separated in the secondary steam separator is sent to an ash water tank or to the steam scrubbing tower as washing liquid.

[0031] A second aspect of the present invention provides a dehydration and drying system capable of implementing the dehydration and drying method for gasification fine residue described above, the dehydration and drying system comprising:

[0032] 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.

[0033] A fine slag preheater is used to preheat the gasified fine slag to be treated using a heat medium.

[0034] A spray dryer is used to directly contact the gasified fine slag output from the fine slag preheater with superheated steam for heat exchange, so as to obtain dried gasified fine slag and secondary steam.

[0035] A secondary steam dust removal unit is used to remove dust from the secondary steam output from the spray 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.

[0036] 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.

[0037] 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 spray dryer to supply the superheated steam to the spray dryer.

[0038] Preferably, 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 gas outlet of the coal gasification system through a crude gas conveying pipeline.

[0039] In some preferred embodiments, the spray dryer is provided with a feed nozzle for injecting the gasified fines and the superheated steam into the spray dryer;

[0040] The feed nozzle includes a central feed channel for introducing the superheated steam, an intermediate feed channel surrounding the central feed channel for introducing the gasified fine slag, and an outer ring feed channel surrounding the intermediate feed channel for introducing the superheated steam.

[0041] Preferably, the length-to-diameter ratio of the feed nozzle is 3-10:1.

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

[0043] 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;

[0044] The sedimentation and filtration unit is used to settle and filter the concentrated black water to obtain the gasification fine residue to be treated.

[0045] Preferably, the flash concentration unit includes a high-pressure flash tower and a vacuum flash tower connected in series; more preferably, a low-pressure flash tower is 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 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 evaporation 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. Preferably, the filtration and dewatering device is a vacuum belt filter or a plate and frame filter.

[0047] In some embodiments, the secondary steam dust removal unit includes a cyclone separator and a steam scrubbing tower;

[0048] The cyclone separator is connected to the spray dryer and is used to perform preliminary dust removal on the secondary steam output by the spray dryer.

[0049] 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.

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

[0051] In some embodiments, 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; preferably, the condensate outlet of the flash steam separator is connected to the washing liquid inlet of the steam scrubbing tower.

[0052] 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; preferably, the condensate outlet of the secondary steam separator is connected to an ash water tank, or the condensate outlet of the secondary steam separator is connected to the washing liquid inlet of the steam scrubbing tower.

[0053] The technical solution provided by this invention has the following beneficial effects:

[0054] The method and system provided by this invention use superheated steam to directly contact the gasified fine slag in a spray dryer to exchange heat and remove most of the moisture from the fine slag, obtaining gasified fine slag with low moisture content. This not only meets the current requirements for environmental protection and the resource utilization of fine slag, but also increases the energy density of the gasified fine slag, saves transportation and processing costs, improves the plant environment, and increases the water resource utilization efficiency of coal gasification.

[0055] Meanwhile, the secondary steam output from the spray dryer of this invention is recycled within the process system. After dust removal, it is first used to preheat the gasified fine slag to be treated, making full use of the residual heat. Then, after heat exchange with flash steam (making reasonable use of the flash steam's residual heat), it is superheated to form superheated steam, which is returned to the spray dryer for reuse. This not only makes reasonable and full use of the heat of the secondary steam, but also reduces the waste of water resources. In addition, the present invention does not require the introduction of hot air, has good safety, and is energy-saving and environmentally friendly. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of a dehydration and drying system for gasified fine residue in one embodiment;

[0057] Figure 2 This is a schematic diagram of a dehydration and drying system for gasified fine residue in another embodiment.

[0058] Figure 3 This is a schematic diagram of a feed nozzle in one embodiment;

[0059] Figure 4 for Figure 3 A schematic diagram of the feeding channel structure of the feeding nozzle. Detailed Implementation

[0060] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0061] 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 invention pertains. The term "and / or" as used herein may include any and all combinations of one or more of the associated listed items. The terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0062] Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in this technical field can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0063] This invention provides a method for dehydrating and drying gasified fine residue based on a spray dryer, which mainly includes the following steps:

[0064] 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;

[0065] 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.

[0066] 3) The preheated gasified fine slag and superheated steam are injected into a spray dryer so that they come into direct contact and exchange heat to obtain dried gasified fine slag and secondary steam.

[0067] 4) The secondary steam obtained in step 3) is sent to the secondary steam dust removal unit for dust removal treatment to obtain dust removal secondary steam. Then, the dust removal secondary steam is sent to the fine slag preheater in step 2) and used as a heat medium for heat exchange with the gasified fine slag to be treated.

[0068] 5) The secondary steam output from the fine slag preheater in step 2) is fed into the steam preheater, so that the secondary steam used in the fine slag preheater exchanges heat with the flash steam output from the black water treatment unit in step 1), thereby obtaining preheated secondary steam.

[0069] 6) The preheated secondary steam obtained in step 5) is sent to a steam superheater to exchange heat with the superheated medium, thereby superheating the preheated secondary steam to obtain superheated steam; the superheated steam is sent to the spray dryer in step 3) to exchange heat with the preheated gasified fine slag, thereby dehydrating and drying the gasified fine slag to obtain dry gasified fine slag, and then obtaining secondary steam again.

[0070] This invention achieves the drying of gasified fine slag without the need to introduce or heat the air, using the above-described method. The invention utilizes superheated steam in a spray dryer to directly contact the gasified fine slag for heat exchange, causing the moisture in the slag to vaporize and precipitate, forming new steam. This steam mixes with the surrounding superheated steam flow to become secondary steam. As the secondary steam exits the spray dryer, moisture is continuously carried away, thereby removing most of the moisture from the fine slag and obtaining gasified fine slag with low moisture content. This not only meets the current needs for environmental protection and the resource utilization of fine slag, but also significantly reduces the amount of fine slag that needs to be transported. At the same time, the secondary steam output from the spray dryer is recycled within the process system. 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 facilitate good drying and dehydration effect with reduced superheated steam usage). Then, after heat exchange with flash steam, it is superheated to form superheated steam, which is returned to the spray dryer for reuse. In this way, not only is the heat of the secondary steam rationally and fully reused, but water resources are also reduced.

[0071] In this invention, superheated steam is used as the drying medium in the spray dryer. Superheated steam has a high specific heat capacity, resulting in lower energy consumption compared to existing technologies that use hot air or flue gas. It also boasts a high convective heat transfer coefficient, low moisture migration resistance, and high heat transfer efficiency, achieving higher drying efficiency and energy utilization. Furthermore, since no other gases, such as air, are introduced into the system, the secondary steam output from the spray dryer can be directly reused within the system after simple dust removal, minimizing intermediate steps required for recycling and reducing energy loss. Moreover, this invention avoids contact between hot air and gasified fine slag, using only superheated steam as the drying medium, ensuring high safety and preventing the potential explosion of fine slag with high residual carbon content in the air atmosphere during the drying process.

[0072] Preferably, in step 1) of the present invention, the particle size of the gasification slag to be treated meets the following requirements: particles <20μm account for 25-35wt%, particles <45μm account for 65-75wt%, and particles <100μm account for 85-95wt%. Specifically, for example, particles <20μm account for 30wt%, particles <45μm account for 70wt%, and particles <100μm account for 90wt%. The inventors have found that for gasification slag with particle size meeting the above requirements, the method of the present invention provides better dehydration and drying effects. On the one hand, it allows for more thorough and uniform contact with superheated steam in the spray dryer, improving heat exchange efficiency and enhancing the dehydration and drying effect of the gasification slag, thus facilitating the acquisition of dried gasification slag with lower water content. On the other hand, it effectively avoids clogging of the feed nozzle of the spray dryer.

[0073] In some embodiments, in step 6), the temperature of the superheated steam obtained by the steam superheater is 160-190°C and the pressure of the superheated steam is 0.2-0.3 MPa; in step 3), the temperature of the secondary steam output from the spray dryer is 130-150°C and the pressure of the secondary steam is 0.2-0.3 MPa.

[0074] In some embodiments, in step 1), the water content of the gasification slag to be treated obtained in the black water treatment unit is 40-70 wt%. By dehydrating and drying by the method of the present invention, a dried gasification slag with a water content of less than 30% can be obtained, for example, a gasification slag with a water content of 10-30% or a gasification slag with a water content of 15-20%.

[0075] In this invention, in step 6), the superheating medium required for superheating the preheated secondary steam in the steam superheater is preferably waste heat from the coal gasification system. In one preferred embodiment, this waste heat is black water from the coal gasification system, such as black water from the gasifier quench chamber and / or black water from the crude gas scrubbing tower used for washing crude syngas. The black water from the coal gasification system is first heat-exchanged with the preheated secondary steam in the steam superheater before entering the black water treatment unit in step 1) for further processing. In another preferred embodiment, the aforementioned waste heat is crude gas from the coal gasification system, such as crude syngas from the gasifier that has been scrubbed and dust-removed in the crude gas scrubbing tower.

[0076] Preferably, in step 3), the preheated gasified fine slag and superheated steam are simultaneously injected into the spray dryer through a feed nozzle; wherein the feed nozzle includes three channels, see [reference needed]. Figure 3 , 4The feed nozzles are a central feed channel 201, an intermediate feed channel 202 surrounding the central feed channel 201, and an outer ring feed channel 203 surrounding the intermediate feed channel 202. Gasified fine slag is injected through the intermediate feed channel 202, while superheated steam is injected through the central feed channel 201 and the outer ring feed channel 203. This preferred nozzle feeding method allows the gasified fine slag to be preheated by superheated steam before entering the spray dryer, increasing its initial temperature and enabling efficient drying and dehydration within the spray dryer, thus reducing the amount of superheated steam used. Preferably, the length-to-diameter ratio of the feed nozzle is 3-10:1, more preferably 5-7:1. Using a feed nozzle with a preferred length-to-diameter ratio allows for more efficient utilization of the heat carried by the superheated steam, ensuring that the gasified fine slag is well preheated by superheated steam during feeding, further improving the drying and dehydration effect.

[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 flash evaporation, and then sending it into a vacuum flash tower for vacuum flash evaporation; in some embodiments, a step of sending the coal gasification black water into a low-pressure flash tower for low-pressure flash evaporation can be added before sending it into the vacuum flash tower. High-pressure flash evaporation, low-pressure flash evaporation, and vacuum flash evaporation are all conventional operations in the art for flash treatment of coal gasification black water, and will not be elaborated upon. Through the above flash concentration, flash steam and concentrated black water are obtained. Preferably, the flash steam required in the steam preheater in step 5) comes from the high-pressure flash steam generated during the above high-pressure flash evaporation process, that is, the high-pressure flash steam is used to preheat the secondary steam.

[0078] In some specific embodiments, in step 1), sedimentation takes place in a sedimentation tank, whereby the concentrated black water obtained from flash evaporation is sent to the sedimentation tank for sedimentation to obtain slurry and supernatant (i.e., ash water). During sedimentation, flocculants can be added to promote solid sedimentation; this is a conventional practice in the art and will not be elaborated upon. Specifically, the supernatant is sent to a downstream ash water tank. The sedimentation slurry (solid content, for example, 10-20 wt%) is filtered and dewatered, for example using a vacuum belt filter or a plate and frame filter. The filtration and dewatering yields the gasification fine slag to be treated, which still has a high moisture content, for example, between 40-70 wt%. The filtrate obtained from filtration and dewatering is sent to the ash water tank. The water in the ash water tank can be reused in the coal gasification system.

[0079] In some embodiments, step 4), the dust removal treatment of the secondary steam output from the spray dryer specifically includes: first, passing the secondary steam through a cyclone separator for cyclone separation to achieve preliminary dust removal, and then sending it to a steam scrubbing tower for washing and dust removal with a washing liquid. Specifically, in the steam scrubbing tower, the washing liquid and secondary steam are brought into countercurrent contact to wash away the ash carried in the secondary steam, ensuring the purity of the secondary steam. The washing liquid used mainly comes from the condensate generated within the process, as detailed later. Preferably, the washing water obtained from 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, deep dust removal of the secondary steam can be achieved, reducing the dust content in the secondary steam to <10mg / m³. 3 .

[0080] Preferably, 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 a steam scrubbing tower as washing liquid; the separated steam continues to enter downstream processing, such as sulfur recovery treatment.

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

[0082] In this invention, superheated steam is used as the drying medium. Compared with low-temperature flue gas and hot air, it has a higher specific heat capacity (1.968 kJ / (kg·K)) and a stronger heat exchange capacity. The method of this invention achieves good dehydration and drying effects on gasified fine slag with a relatively small superheated steam flow rate. In this invention, the superheated steam and gasified fine slag directly contact each other for heat exchange in the spray dryer, resulting in a more uniform temperature distribution and greater processing capacity. This invention uses secondary steam to preheat the gasified fine slag to be treated, which can effectively recover and utilize the energy of the secondary steam, increase the initial temperature of the gasified fine slag, and improve the drying effect.

[0083] A second aspect of the present invention provides a gasification fine residue dehydration and drying system based on a spray dryer, which can be used to implement the gasification fine residue dehydration and drying method described above.

[0084] See Figure 1 The dehydration and drying system of the present invention mainly includes: a black water treatment unit 100, a fine slag preheater, a spray dryer, a secondary steam dust removal unit, a steam preheater, and a steam superheater.

[0085] Among them, the black water treatment unit 100 is used to flash concentrate, settle and filter dewater the coal gasification black water to obtain flash steam and gasification fine residue to be treated.

[0086] A fine slag preheater is used to preheat the gasified fine slag to be treated using a heat medium, thereby obtaining preheated gasified fine slag.

[0087] A spray dryer is used to directly contact the gasified fine slag output from the fine slag preheater with superheated steam for heat exchange, so that the moisture in the gasified fine slag is removed. The moisture is vaporized into steam and forms secondary steam together with the surrounding superheated steam, thereby obtaining dry gasified fine slag and secondary steam.

[0088] The secondary steam dust removal unit is used to remove dust from the secondary steam output from the spray dryer, thereby obtaining dust-removed secondary steam. The secondary steam dust removal unit is connected to the fine slag preheater to transport the dust-removed secondary steam as a heat medium to the fine slag preheater, thereby preheating the gasified fine slag to be processed.

[0089] 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.

[0090] A steam superheater is used to superheat secondary steam (i.e., preheated secondary steam) that has been treated by a steam preheater to obtain superheated steam. The steam superheater is connected to a spray dryer to supply superheated steam to the spray dryer, that is, the superheated steam required by the spray dryer is supplied by the steam superheater.

[0091] The above system dehydrates and dries gasified fine slag using superheated steam in a highly efficient, safe, and environmentally friendly manner. It eliminates the risk of explosion from contact between hot air and the high-carbon-content gasified fine slag, and boasts higher energy utilization. Furthermore, the system does not introduce air; the drying process generates a secondary steam stream, primarily composed of steam, which can be recycled without complex intermediate processing. This invention first removes dust from the secondary steam, then preheats the gasified fine slag in a fine slag preheater, followed by heat exchange with flash steam in a steam preheater, and finally superheats it in a steam superheater to obtain superheated steam for recycling in the spray dryer. The ingenious design of the entire system and the organic integration of each processing unit ensure more efficient and rational utilization of the secondary steam's energy, significantly reducing water waste and promoting efficient and full utilization of water resources.

[0092] In some preferred embodiments, see Figure 1The 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; that is, the superheated medium required in the steam superheater is the coal gasification black water of the coal gasification system. The coal gasification black water 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 The variation of the dehydration and drying system shown is another implementation method, which is similar to... Figure 1 The main difference lies in the fact that the superheating medium inlet of the steam superheater is connected to the crude gas outlet of the coal gasification system via a crude gas transmission pipeline; that is, the superheating medium required in the steam superheater is the crude gas from the coal gasification system. Specifically, for example... Figure 2 As shown, the syngas generated by the gasifier enters the crude gas scrubbing tower for washing and dust removal. The resulting crude gas is then used as the superheating medium and fed into the steam superheater. In this embodiment, the black water from the gasifier quench chamber and the black water from the crude gas scrubbing tower are no longer fed into the steam superheater, but are directly fed into the black water flash evaporation unit for processing.

[0093] In a preferred embodiment, such as Figure 3 As shown, the spray dryer is equipped with a feed nozzle 200, through which the gasified fine slag to be treated and superheated steam are sprayed into the spray dryer together. Specifically, as... Figure 4 As shown, the feed nozzle includes a central feed channel 201, a middle feed channel 202, and an outer ring feed channel 203, which together form a sleeve-like structure. The central feed channel 201 is located at the center, the middle feed channel 202 surrounds the central feed channel 201, and the outer ring feed channel 203 surrounds the middle feed channel 202. The central feed channel 201 and the outer ring feed channel 203 are used to introduce superheated steam, while the middle feed channel 202 is used to introduce gasified fine slag. This preferred feed nozzle structure allows the gasified fine slag to be enveloped by superheated steam during the feeding process, enabling sufficient heat exchange and raising its initial temperature. This facilitates improved drying and dehydration effects after entering the spray dryer and reduces the consumption of superheated steam. More preferably, the length-to-diameter ratio of the feed nozzle is 3-10:1.

[0094] In some implementations, such as Figure 1 As shown, the black water treatment unit 100 specifically includes a flash concentration unit 101 and a settling and filtration unit 102. The flash concentration unit 101 is used to flash and concentrate the coal gasification black water to obtain flash steam and concentrated black water; the settling and filtration unit 102 is used to settle and filter the concentrated black water to obtain gasification fine slag to be treated.

[0095] More 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 also 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, that is, the flash steam in the steam preheater originates from the high-pressure flash steam output from the high-pressure flash tower.

[0096] More specifically, the settling and filtration unit 102 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 evaporation unit to obtain a slurry; the filtration and dewatering device is used to filter and dewater the slurry obtained after settling to obtain the gasified fine slag to be treated; preferably, the filtration and dewatering device is a vacuum belt filter or a plate and frame filter. Figure 1 As shown, the settling and filtration unit also includes an ash water tank for receiving the supernatant in the settling tank and the filtrate obtained from the filtration and dewatering device. The ash water in the ash water tank can be reused in the coal gasification system, for example, in the scrubbing tower of the coal gasification system.

[0097] In some specific implementations, participants Figure 1 The secondary steam dust removal unit includes a cyclone separator and a steam scrubbing tower. The cyclone separator is connected to a spray dryer to perform cyclone separation on the secondary steam output from the spray dryer, thus achieving preliminary dust removal. 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 receives the pre-dust-removed secondary steam from the cyclone separator, which is then washed with a washing liquid in the steam scrubbing tower to obtain washing water and dust-removed secondary steam. Preferably, the washing water outlet of the steam scrubbing tower is connected to a settling tank.

[0098] In some embodiments, 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. Preferably, the condensate outlet of the flash steam separator is connected to the washing liquid inlet of a steam scrubbing tower, so that the condensate separated in the flash steam separator can be sent to the steam scrubbing tower for use as washing liquid. Further, the flash steam output from the flash steam separator enters a downstream unit, such as a sulfur recovery unit, for further processing.

[0099] In some embodiments, 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, allowing the vapor-liquid separated secondary steam to enter the steam preheater for preheating. Preferably, the condensate outlet of the secondary steam separator is connected to an ash water tank, or the condensate outlet of the secondary steam separator is connected to the washing liquid inlet of a steam scrubbing tower, so that the condensate separated by the secondary steam separator can be reused in the ash water tank or used as washing liquid.

[0100] The following application examples further illustrate the solution of this invention.

[0101] Example 1

[0102] See the schematic diagram of the dehydration and drying system used in this embodiment. Figure 1 Unless otherwise specified, all other descriptions of the dehydration and drying system and methods in the following text will refer to the preceding descriptions and will not be repeated here.

[0103] The black water used in this embodiment is from the quench chamber of the gasifier. In this embodiment, the dehydration and drying of the gasification slag includes the following steps:

[0104] 1) Flash concentration, sedimentation, and filtration:

[0105] 1.1) Flash Concentration: The black water from coal gasification is fed into a high-pressure flash distillation tower. Under a pressure of 0.6 MPa, some soluble gases are flashed out of the black water. The black water at the bottom of the high-pressure flash distillation tower enters a low-pressure flash distillation tower. Under a pressure of 0.1 MPa, the soluble gases in the black water are further flashed out in the low-pressure flash distillation tower. The black water at the bottom of the low-pressure flash distillation tower enters a vacuum flash distillation tower, where it is further flashed at -0.5 MPa to obtain concentrated black water.

[0106] 1.2) Settlement:

[0107] The concentrated black water obtained in step 1.1) is sent to a settling tank for gravity settling and solid-liquid separation. The settling of solids in the black water is accelerated by adding a flocculant (composed of 80 wt% anionic polyacrylamide and 20 wt% coagulant (polyaluminum)). A slurry with a solid content of 20 wt% (flow rate: 5000 kg / h, temperature: 60℃, water content 80 wt%) settles out at the bottom of the settling tank. The supernatant of the settling tank is sent to the ash water tank.

[0108] 1.3) Filtration and dehydration:

[0109] The slurry settled at the bottom of the settling tank is pumped to a filtration and dewatering device (plate and frame filter press) for filtration and dewatering, yielding a gasification fine slag with a water content of 50 wt% (flow rate: 2000 kg / h, temperature: 60℃). The filtrate (flow rate: 3000 kg / h, temperature: 60℃) is pumped to an ash water tank. The particle size distribution of the gasification fine slag is as follows: particles <20 μm account for approximately 30 wt%, particles <45 μm account for approximately 70 wt%, and particles <100 μm account for approximately 90 wt%.

[0110] 2) Preheating of fine slag:

[0111] The aforementioned gasified fine slag to be treated is sent to a fine slag preheater for indirect heat exchange with a heat medium to obtain preheated gasified fine slag. After secondary steam is generated during system operation, the heat medium is the dust-removing secondary steam output from the steam scrubbing tower. During this preheating process, the secondary steam cools and condenses, and is sent to a secondary steam separator for vapor-liquid separation. The separated condensate (flow rate: 750 kg / h) is sent to an ash water tank.

[0112] 3) Drying and dehydration:

[0113] The aforementioned preheated gasified fine slag and superheated steam are fed through a feed nozzle (see schematic diagram of nozzle structure). Figure 3 , 4 As shown, superheated steam (with a length-to-diameter ratio of 5:1) is sprayed into the spray dryer. The superheated steam directly contacts the gasified fine slag within the dryer, heating it and causing the moisture in the slag to vaporize and precipitate, forming new steam. This steam mixes with the surrounding superheated steam flow to become secondary steam (temperature 144℃, 0.3MPa, flow rate: 22250kg / h). The secondary steam is then discharged from the spray dryer by a blower equipped with the dryer, continuously carrying away moisture, thus removing most of the moisture from the fine slag and obtaining dry gasified fine slag with a moisture content of 20% (yield 1250kg / h).

[0114] 4) Secondary steam dust removal:

[0115] The secondary steam discharged from the spray dryer first passes through a cyclone separator to separate most of the solids from the secondary steam. The preliminarily dust-removed secondary steam then enters a steam scrubbing tower. In the steam scrubbing tower, the secondary steam is further scrubbed with condensate from the flash steam separator to remove dust. The final dust-removed secondary steam has a dust content of <10 mg / m³. 3 The washing water at the bottom of the steam scrubbing tower is transported into the settling tank; the secondary steam obtained from dust removal in this step is sent to the fine slag preheater in step 2) above as a heat medium for preheating and gasifying the fine slag.

[0116] 5) Secondary steam preheating:

[0117] The secondary steam (temperature: 144℃, pressure: 0.3MPa, flow rate: 21500kg / h) that underwent vapor-liquid separation in the secondary steam separator in step 2) is sent to the steam preheater to exchange heat with the high-pressure flash steam from the high-pressure flash tower to obtain preheated secondary steam.

[0118] 6) Secondary steam superheating:

[0119] Preheated secondary steam (temperature: 154℃, pressure: 0.3MPa, flow rate: 21500kg / h) and black water from the gasifier quench chamber (temperature: 220℃, pressure: 4.0MPa, flow rate: 120000kg / h) exchange heat in a steam superheater to form new superheated steam (temperature: 190℃, pressure: 0.3MPa, flow rate: 21500kg / h). This superheated steam is circulated to the spray 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. During system operation, after superheated steam is generated in the steam superheater, superheated steam generated in the steam superheater is used in step 3). The black water from the gasifier quench chamber, after heat exchange in the steam superheater, is sent to the high-pressure flash evaporator in step 1.1) for treatment.

[0120] Example 2

[0121] See the schematic diagram of the dehydration and drying system used in this embodiment. Figure 2 Unless otherwise specified, all other descriptions of the dehydration and drying system and methods in the following text will refer to the preceding descriptions and will not be repeated here.

[0122] The black water used in this embodiment comes from the quench chamber of the gasifier and from the crude gas scrubbing tower. In this embodiment, the dehydration and drying of the gasification fine slag includes the following steps:

[0123] 1) Flash concentration, sedimentation and filtration

[0124] 1.1) Flash Concentration: Black water from the gasifier quench chamber and black water from the crude gas scrubbing tower are fed into a high-pressure flash tower. At a pressure of 0.6 MPa, some soluble gases are flashed out of the black water. The black water at the bottom of the high-pressure flash tower enters a low-pressure flash tower. At a pressure of 0.1 MPa, the soluble gases in the black water are further flashed out in the low-pressure flash tower. The black water at the bottom of the low-pressure flash tower enters a vacuum flash tower, where it is further flashed at -0.5 MPa to obtain concentrated black water.

[0125] 1.2) Settlement:

[0126] The concentrated black water obtained in step 1.1) is sent to a settling tank for gravity settling and solid-liquid separation. The settling of solids in the black water is accelerated by adding a flocculant (composed of 85 wt% anionic polyacrylamide and 15 wt% coagulant (polyferric sulfate)). A slurry with a solid content of 20% (flow rate: 5000 kg / h, temperature: 60℃, water content 80%) settles out at the bottom of the settling tank. The supernatant of the settling tank is sent to the ash water tank.

[0127] 1.3) Filtration and dehydration:

[0128] The slurry settled at the bottom of the settling tank is pumped to a filtration and dewatering device (vacuum belt filter) for filtration and dewatering, yielding gasification fine slag with a water content of 60 wt% (flow rate: 2500 kg / h, temperature: 60℃). The filtrate is pumped back to the ash water tank. The particle size distribution of this gasification fine slag is as follows: particles <20 μm account for approximately 30 wt%, particles <45 μm account for approximately 70 wt%, and particles <100 μm account for approximately 90 wt%.

[0129] 2) Preheating of fine slag:

[0130] The aforementioned gasified fine slag to be treated is sent to a fine slag preheater for indirect heat exchange with a heat medium to obtain preheated gasified fine slag. After secondary steam is generated during system operation, the heat medium is the dust-removing secondary steam output from the steam scrubbing tower. During this preheating process, the secondary steam cools and condenses, and is sent to a secondary steam separator for vapor-liquid separation. The separated condensate (flow rate: 1250 kg / h) is sent to an ash water tank.

[0131] 3) Drying and dehydration:

[0132] The aforementioned preheated gasified fine slag and superheated steam are simultaneously passed through a feed nozzle (see schematic diagram of the nozzle structure). Figure 3 , 4 As shown, the superheated steam (7:1 aspect ratio) is sprayed into the spray dryer. The superheated steam comes into direct contact with the gasified fine slag inside the spray dryer. The gasified fine slag is heated, causing the moisture in the gasified fine slag to vaporize and precipitate out to form new steam. This steam mixes with the surrounding superheated steam flow to become secondary steam (temperature 144℃, 0.3MPa, 36450kg / h). The secondary steam is discharged from the spray dryer by the induced draft fan equipped with the spray dryer. The moisture is continuously carried away, thereby removing most of the moisture from the fine slag and obtaining dry gasified fine slag with a moisture content of 20% (yield 1250kg / h).

[0133] 4) Secondary steam dust removal:

[0134] The secondary steam discharged from the spray dryer first passes through a cyclone separator to separate most of the solids from the secondary steam. The preliminarily dust-removed secondary steam then enters a steam scrubbing tower. In the steam scrubbing tower, the secondary steam is further scrubbed with condensate from the flash steam separator to remove dust. The final dust-removed secondary steam has a dust content of <10 mg / m³. 3 The washing water at the bottom of the steam scrubbing tower is transported into the settling tank; the secondary steam obtained from dust removal in this step is sent to the fine slag preheater in step 2) above as a heat medium for preheating and gasifying the fine slag.

[0135] 5) Secondary steam preheating:

[0136] The secondary steam (temperature: 144℃, pressure: 0.3MPa, flow rate: 35200kg / h) that underwent vapor-liquid separation in the secondary steam separator in step 2) is sent into the steam preheater to exchange heat with the high-pressure flash steam from the high-pressure flash tower to obtain preheated secondary steam.

[0137] 6) Secondary steam superheating:

[0138] The preheated secondary steam (temperature: 150℃, pressure: 0.30MPa, flow rate: 35200kg / h) is exchanged with the crude coal gas (pressure: 4.0MPa, temperature: 220℃, flow rate: 24100kg / h) from the crude coal gas scrubbing tower to form new superheated steam (temperature: 190℃, 0.3MPa, 35200kg / h). This superheated steam is circulated to the spray 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. During system operation, after superheated steam is generated in the steam superheater, superheated steam generated in the steam superheater is used in step 3).

[0139] In this embodiment, the ash water in the ash water tank is used as the washing water for the crude gas scrubbing tower.

[0140] Examples 3-9

[0141] All procedures were carried out in accordance with Example 1. The process parameters and experimental results of Examples 3-9 are shown in Table 1.

[0142] Table 1

[0143]

[0144] As can be seen from the above embodiments, the dehydration and drying system and method of the present invention can dry and dehydrate gasification fine slag with high moisture content to a moisture content of less than 30%. Furthermore, the entire process allows for the rational and full utilization of energy and water resources. The process requires minimal additional energy input, and water resources are recycled, significantly reducing water waste. The process does not require the introduction of hot air, making it both environmentally friendly and safe. The solution of the present invention effectively solves the problems of poor performance, high energy consumption, large water waste, and serious environmental pollution associated with existing gasification fine slag dehydration treatment methods.

[0145] It is readily understood that the above embodiments are merely illustrative examples for clear explanation and do not imply that the invention is limited thereto. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method of dewatering and drying gasified fine slag based on a spray dryer, 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 particle size of the gasification fine slag to be treated meets the following requirements: 25-35wt% of particles with a particle size <20μm, 65-75wt% of particles with a particle size <45μm, and 85-95wt% of particles with a particle size <100μm; the flash concentration comprises high-pressure flash and vacuum flash of the coal gasification black water in sequence; 2) heat exchange of the gasification fine slag to be treated with a heat medium in a fine slag preheater to obtain preheated gasification fine slag; 3) direct contact of the preheated gasification fine slag and superheated steam in a spray dryer to obtain dried gasification fine slag and secondary steam; 4) dust removal treatment of the secondary steam obtained in step 3) in a secondary steam dust removal unit to obtain dust-removed secondary steam, which is then used as the heat medium in the fine slag preheater in step 2); the dust removal treatment comprises preliminary dust removal of the secondary steam obtained in step 3) through a cyclone separator, and then washing and dust removal of the secondary steam in a steam washing tower; 5) heat exchange of the secondary steam output from the fine slag preheater in step 2) with high-pressure flash gas obtained in the high-pressure flash of the black water treatment unit in step 1) in a steam preheater to obtain preheated secondary steam; flash gas output from the steam preheater is sent to a flash gas separation tank for vapor-liquid separation, and the condensate obtained by the separation is sent to the steam washing tower as washing liquid; 6) superheating treatment of the preheated secondary steam obtained in step 5) in a steam superheater to obtain superheated steam; the superheated steam is sent to the spray dryer in step 3) for heat exchange with the preheated gasification fine slag; the superheating medium used in the steam superheater is coal gasification black water from a coal gasification system or raw coal gas from the coal gasification system; after the superheating treatment of the preheated secondary steam 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 treatment.

2. The dewatering and drying method of gasifying fine sludge according to claim 1, characterized by, In step 6), the temperature of the superheated steam is 160-190℃, and the pressure of the superheated steam is 0.2-0.3Mpa; In step 3), the temperature of the secondary steam is 130-150℃, and the pressure of the secondary steam is 0.2-0.3Mpa; In step 1), the water content of the gasification fine slag to be treated is 40-70wt%.

3. The dewatering and drying method of gasifying fine sludge according to claim 1, characterized by, In step 3), the preheated gasification fine slag and the superheated steam are simultaneously sprayed into the spray dryer through a feed spray head; wherein the gasification fine slag is sprayed through a middle feed channel of the feed spray head, the superheated steam is sprayed through a center feed channel and an outer ring feed channel of the feed spray head, and the middle feed channel is arranged on the periphery of the center feed channel, and the outer ring feed channel is arranged on the periphery of the middle feed channel.

4. The dewatering and drying method of gasifying fine sludge according to claim 3, characterized by, The length-diameter ratio of the feed spray head is 3-10:

1.

5. The dewatering and drying method of gasifying fine sludge according to claim 4, characterized by, The length-diameter ratio of the feed inlet nozzle is 5-7:

1.

6. The dewatering and drying method of gasifying fine sludge according to any one of claims 1 to 5, characterized by, In step 1), before the vacuum flash evaporation, the coal gasification black water is subjected to low-pressure flash evaporation; In step 1), the sedimentation is carried out in a sedimentation tank; In step 4), the washing water obtained by washing and dedusting in the steam washing tower is fed into the sedimentation tank.

7. The dewatering and drying method of gasifying fine sludge according to claim 6, characterized by, 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).

8. The dewatering and drying method of gasifying fine sludge according to claim 7, characterized by, Part of the condensate separated in the secondary steam separation tank is fed into a grey water tank or into the steam washing tower as washing liquid.

9. A dewatering and drying system capable of carrying out the dewatering and drying method of fine sludge according to any one of claims 1 to 8, characterized in that, The dewatering and drying system comprises: a black water treatment unit for flash evaporation concentration, sedimentation and filtration dewatering of coal gasification black water, and obtaining flash steam and gasification fine slag to be treated; the black water treatment unit comprises a flash evaporation concentration unit for flash evaporation and concentration of the coal gasification black water to obtain the flash steam and concentrated black water; 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; a fine slag preheater for preheating the gasification fine slag to be treated using a heat medium; a spray dryer for directly contacting the gasification fine slag output from the fine slag preheater with superheated steam for heat exchange to obtain dried gasification fine slag and secondary steam; a secondary steam dedusting unit for dedusting the secondary steam output from the spray dryer; the secondary steam dedusting unit is connected with the fine slag preheater to deliver the dedusted secondary steam as the heat medium to the fine slag preheater; the secondary steam dedusting unit comprises a cyclone separator and a steam washing tower; a steam preheater for heat exchanging the secondary steam output from the fine slag preheater with the flash steam from the black water treatment unit to obtain preheated secondary steam; the flash steam outlet of the steam preheater is connected with a flash steam separation tank for vapor-liquid separation of the flash steam output from the steam preheater and obtaining condensate; the condensate outlet of the flash steam separation tank is connected with the washing liquid inlet of the steam washing tower; a steam superheater for superheating the secondary steam treated by the steam preheater to obtain superheated steam; the steam superheater is connected with the spray dryer to supply the superheated steam to the spray dryer; 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.

10. The dewatering drying system of claim 9, wherein, The spray dryer is provided with a feed inlet nozzle for spraying the gasification fine slag and the superheated steam into the spray dryer; The feed nozzle comprises a central feed channel for passing the superheated steam, a middle feed channel for passing the gasified fine slag arranged around the periphery of the central feed channel, and an outer ring feed channel for passing the superheated steam arranged around the periphery of the middle feed channel.

11. The dewatering drying system of claim 10, wherein, The length-diameter ratio of the feed nozzle is 3-10:

1.

12. The dewatering and drying system of any of claims 9-11, wherein, The black water treatment unit comprises a sedimentation filtration unit. The sedimentation filtration unit is used for sedimentation and filtration dewatering of the concentrated black water to obtain the gasified fine slag to be treated.

13. The dewatering drying system of claim 12, wherein, A low-pressure flash tower is further connected in series between the high-pressure flash tower and the vacuum flash tower.

14. The dewatering drying system of claim 12, wherein, The sedimentation filtration unit comprises a sedimentation tank for sedimentation treatment of the concentrated black water output by the flash unit, and a filtration dewatering device for filtration dewatering of the slag slurry obtained by the sedimentation treatment to obtain the gasified fine slag to be treated.

15. The dewatering drying system of claim 14, wherein, The filtration dewatering device is a vacuum belt filter or a plate-and-frame filter.

16. The dewatering and drying system according to claim 12, wherein The cyclone separator is connected with the spray dryer and used for primary dust removal of secondary steam output by the spray dryer. An air inlet of the steam washing tower is connected with the cyclone separator, and an air outlet of the steam washing tower is connected with a heat medium inlet of the fine slag preheater, and the steam washing tower is used for washing and dust removal of the secondary steam subjected to the primary dust removal with a washing liquid to obtain washing water and dust-removed secondary steam.

17. The dewatering drying system of claim 16, wherein, A washing water outlet of the steam washing tower is connected with the sedimentation tank.

18. The dewatering and drying system according to claim 16, wherein A secondary steam outlet of the fine slag preheater is connected with a secondary steam separation tank through a pipeline, and used for vapor-liquid separation of the secondary steam output by the fine slag preheater to obtain condensed liquid; and a vapor phase outlet of the secondary steam separation tank is connected with a secondary steam inlet of the steam preheater.

19. The dewatering drying system of claim 18, wherein, A condensed liquid outlet of the secondary steam separation tank is connected with a grey water tank, or the condensed liquid outlet of the secondary steam separation tank is connected with a washing liquid inlet of the steam washing tower.

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