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

Abstract

According to the gasification fine slag dewatering and drying method and system based on the spray dryer, gasification fine slag with high water content can be dewatered and dried, the energy utilization rate is high, and waste of water resources is little. The method comprises the following steps: 1) carrying out flash evaporation concentration, sedimentation and filtration dehydration on the coal gasification black water in the black water treatment unit; (2) gasified fine slag to be treated is fed into a fine slag preheater to be subjected to heat exchange with a heating medium; 3) spraying the preheated gasified fine slag and superheated steam into a spray dryer for heat exchange to obtain dried gasified fine slag and secondary steam; 4) feeding the secondary steam into a secondary steam dust removal unit for dust removal treatment, and then feeding the secondary steam into a fine slag preheater; (5) the secondary steam output by the fine slag preheater is fed into a steam preheater for heat exchange, and preheated secondary steam is obtained; (6) the preheated secondary steam is fed into a steam superheater to be subjected to superheating treatment, and superheated steam is obtained; the superheated steam is fed into a spray dryer.

Description

Technical Field

[0001] The invention relates to a dehydration and drying technology for gasified fine slag, and in particular to a dehydration and drying method and a dehydration and drying system for gasified fine slag based on a spray dryer. Background Art

[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 harmlessness and resource utilization of gasification fine slag are important factors restricting the sustainable development of coal chemical industry.

[0003] Gasification fine slag is the raw coal gas carrying part of the unreacted carbon and ash into black water after washing, and then forms a filter cake through flash evaporation, concentration, flocculation sedimentation and filtration dehydration. At present, the general treatment method for gasification fine slag is to dehydrate it through a vacuum filter and then transport it to a landfill for landfill. Due to the high moisture content of the gasification fine slag filter cake, the vehicle leaks during the transportation process, which not only causes environmental pollution and winter icing, but also causes water resource waste if its moisture is not recycled. At the same time, the gasification fine slag contains 30-40% residual carbon, which has a very considerable recycling value (for example, it is sent to the boiler and gasifier for mixed combustion). However, due to the high moisture content of the fine slag, it not only reduces the calorific value of the gasification fine slag, but also easily causes adhesion, blocking, corrosion and other problems, which seriously affects the harmless treatment and resource utilization of the gasification fine slag.

[0004] Since gasification fine slag has the characteristics of rich pore structure, large specific surface area and small particle size, it has strong adhesion and adsorption properties for water molecules; in addition, flocculants such as polyacrylamide need to be added during the sedimentation of coal chemical black water. After the flocculants and fine slag particles in the black water are condensed into agglomerates, a flocculated colloidal structure will be formed. This structure has a strong water holding capacity, which makes it difficult to dehydrate the gasification fine slag. Gasification fine slag is significantly different from other particles such as raw coal (such as lignite) due to its structural characteristics and water holding characteristics. It is difficult to remove moisture, and it is difficult to directly apply or learn from the dehydration treatment process of other materials such as lignite. In production practice, it is found that conventional dehydration equipment (vacuum filtration dehydrator, horizontal screw centrifuge, plate and frame filtration dehydrator, etc.) has poor dehydration effect on gasification fine slag. The vacuum belt filter is the most commonly used equipment for dehydration of coal gasification fine slag. However, after dehydration by the vacuum belt filter, the water content of the gasification fine slag is still greater than 60%. This is because when the water content of the gasification fine slag filter cake is reduced to about 60%, the filter cake will crack, resulting in the inability of vacuum filtration to further dehydrate the filter cake. In addition, the vacuum belt filter also has problems such as short filter cloth life, large amount of filter cloth washing water, large filtrate turbidity and poor operating environment hygiene. Compared with the vacuum belt filter, the horizontal screw centrifuge has the advantages of small footprint, high dehydration efficiency, fully enclosed continuous feeding and environmental friendliness. However, after dehydration by the horizontal screw centrifuge, the water content of the gasification fine slag is still about 40-50%. The plate and frame filter press can only remove some of the free water between the gasification fine slag particles and some of the water in the pores. However, since there is no phase change during the dehydration process, the water content in the gasification fine slag after dehydration can only be reduced to about 40%, and the dehydration effect is not good.

[0005] Heating dehydration technology uses hot air, hot flue gas and steam as drying media to reduce the moisture content of gasified fine slag by evaporating and drying the gasified fine slag. Common heating dehydration equipment includes rotary dryers, disc dryers, etc. However, the existing heating dehydration method has high energy consumption and low energy efficiency. At the same time, there are problems such as large equipment investment and difficulty in daily maintenance and repair.

[0006] Patent application CN201710321402 discloses a method for dehydrating and drying fine slag slurry in a coal gasification system, which comprises 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, and the concentrated fine slag slurry and the hot air are in direct contact with each other in the spray dryer for heat and mass transfer, and after most of the water is removed, it flows out through the bottom to become dry fine slag. However, this method uses hot air as the heat source, the heat capacity of air is relatively small, the required amount of hot air is large, the thermal efficiency of waste heat heating air is low, and the efficiency of the gasification fine slag drying system is low; at the same time, a large amount of water vapor is mixed with the air during the drying process, and the remaining heat energy cannot be recovered, resulting in a large amount of energy waste. At the same time, the wet drying exhaust gas at the outlet of the spray dryer contains a large amount of air, and the heat exchange efficiency coefficient of 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 of the wet drying exhaust gas condenser and a relatively high exhaust gas emission. In addition, a large amount of exhaust gas mixed with air and water vapor is generated at the dryer outlet through this process. Usually, this exhaust gas will be discharged directly, which will result in heat waste; or the exhaust gas needs to be cooled and then separated into gas and liquid before being discharged, which also causes heat waste; and if it is desired to recycle the hot air, the exhaust gas must first be deeply dehydrated to reduce the moisture content in the air before it can be reused. However, this will require a large amount of cooling water to exchange heat with the exhaust gas to achieve gas-liquid separation, and a large amount of heat will need to be input again to heat the separated air, resulting in a cold and hot phenomenon.

[0007] Patent application CN201910913874.9 discloses a gasification ash drying device and method of a four-nozzle water-gas entrained bed; including a feeding unit connected to the gasification ash, a high-temperature gas supply unit, a gasification ash drying unit, and the high-temperature gas in the high-temperature gas supply unit is connected to the tail gas treatment unit through the gasification ash drying unit, and a gasification ash recovery unit is provided at the bottom of the gasification ash drying unit; the feeding unit includes a gasification coarse slag storage tank connected to the agitator through a first weighing belt conveyor, and a gasification filter cake crusher is connected to the agitator through 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, and the waste heat drum dryer is connected to the feed port of the three-return dryer through a hot air interface feeding device. This technology has problems such as consuming a large amount of natural gas, excessive energy consumption, low drum dryer filling rate, and large equipment investment.

[0008] The document "Application of Drying System in Treatment of Coal Gasification Fine Slag" introduces a drying system of a centrifuge equipped with a dryer for treating coal gasification fine slag. In order to overcome the limited dehydration capacity of the vacuum belt filter, the fine slag can only be dehydrated to a water content of 60% by mass, which leads to the frequent blockage of the conveyor belt and the coal bunker discharge port after the coal gasification fine slag is mixed with thermal coal and sent to the boiler; the document proposes a drying process using a centrifuge equipped with a dryer, firstly separating the black water (solid content of 10%) after flocculation and sedimentation by a centrifuge to obtain fine slag with a water content of about 50%, and then using a single-axis disc dryer to reduce the water content of the fine slag to about 30%, and then sending it to the thermal power plant for mixing with thermal coal. The system has problems such as low heat transfer efficiency, slow water evaporation rate, and small equipment processing capacity. Summary of the invention

[0009] In view of this, the present invention provides a dehydration and drying method and a dehydration and drying system for gasified fine slag based on a spray dryer. The scheme of the present invention is used to dehydrate and dry gasified fine slag with a high water content. Not only can the dehydration and drying of the gasified fine slag be efficiently achieved without introducing air, but the secondary steam formed in the drying process can be directly recycled in the system, and the water resources and energy of the system can be fully and reasonably reused, the energy utilization rate is high, the waste of water resources is small, and the system safety is good.

[0010] To achieve the purpose, the present invention provides the following technical solutions:

[0011] A first aspect of the present invention provides a method for dehydrating and drying gasified fine slag, the method comprising:

[0012] 1) flash evaporation, concentration, sedimentation and filtration and dehydration of coal gasification black water in a black water treatment unit to obtain flash gas and gasification fine slag to be treated; preferably, the particle size of the gasification fine slag to be treated meets the following requirements: particles with a particle size of <20 μm account for 25-35wt%, particles with a particle size of <45 μm account for 65-75wt%, and particles with a particle size of <100 μm account for 85-95wt%;

[0013] 2) sending the gasified fine slag to be treated into a fine slag preheater for heat exchange with a heat medium to obtain preheated gasified fine slag;

[0014] 3) spraying the preheated gasified fine slag and superheated steam into a spray dryer so that the two are in direct contact for heat exchange, thereby obtaining dry gasified fine slag and secondary steam;

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

[0016] 5) sending the secondary steam output from the fine slag preheater in step 2) into a steam preheater to perform heat exchange 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 sent to a steam superheater for superheating to obtain superheated steam; the superheated steam is sent to 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 gasified fine slag to be treated is 40-70 wt %.

[0021] In some preferred embodiments, the superheated medium used in the steam superheater is coal gasification black water from a coal gasification system; the coal gasification black water from a coal gasification system is sent to the black water treatment unit in step 1) for treatment after the preheated secondary steam is superheated in step 6).

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

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

[0024] Wherein, the gasified fine slag is sprayed in through the middle feed channel of the feed nozzle, and the superheated steam is sprayed in through the central feed channel and the outer ring feed channel of the feed nozzle, and 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 aspect ratio of the feed nozzle is 3-10:1, more preferably 5-7:1.

[0026] In some embodiments, in step 1), the flash concentration comprises successively performing high-pressure flash evaporation and vacuum flash evaporation on the coal gasification black water, and preferably, before performing the vacuum flash evaporation, the operation of performing 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 embodiments, in step 1), the settling is performed in a settling tank;

[0028] In some embodiments, in step 4), the dust removal treatment includes first passing the secondary steam obtained in step 3) through a cyclone separator for preliminary dust removal, and then sending the secondary steam into a steam washing tower for washing and dust removal; preferably, the washing water obtained by washing and dust removal in the steam washing tower is sent to the sedimentation tank;

[0029] Preferably, step 5) further comprises sending the flash gas output from the steam preheater into a flash gas separation tank for vapor-liquid separation, and sending the separated condensate into the steam washing tower for use as washing liquid;

[0030] Preferably, in step 2), the secondary steam output from the fine slag preheater is first sent to a secondary steam separation tank for vapor-liquid separation, and then sent to the steam preheater in step 5); preferably, part of the condensate separated in the secondary steam separation tank is sent to a gray water tank or to the steam washing tower for use as washing liquid.

[0031] A second aspect of the present invention provides a dehydration and drying system capable of implementing the above-mentioned dehydration and drying method for gasified fine slag, the dehydration and drying system comprising:

[0032] A black water treatment unit is used to flash condense, settle and filter the coal gasification black water to dehydrate it, and obtain flash gas and gasification fine slag to be treated;

[0033] A fine slag preheater, used for preheating the gasified fine slag to be treated using a heat medium;

[0034] A spray dryer, used for directly contacting the gasified fine slag outputted from the fine slag preheater with superheated steam for heat exchange, so as to obtain dry gasified fine slag and secondary steam;

[0035] A secondary steam dust removal unit is used to perform dust removal on the secondary steam output from the spray dryer; the secondary steam dust removal unit is connected to the fine slag preheater to transport the secondary steam that has undergone the dust removal treatment as the heat medium to the fine slag preheater;

[0036] a steam preheater, used for performing heat exchange between the secondary steam outputted from the fine slag preheater and the flash steam from the black water treatment unit to obtain preheated secondary steam;

[0037] a steam superheater, used for superheating the secondary steam 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 delivery 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 raw gas outlet of the coal gasification system through a raw gas delivery pipeline.

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

[0040] The feed nozzle comprises a central feed channel for introducing the superheated steam, an intermediate feed channel arranged around the periphery of the central feed channel for introducing the gasified fine slag, and an outer ring feed channel arranged around the periphery of the intermediate feed channel for introducing the superheated steam;

[0041] Preferably, the aspect 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 concentration unit is used to flash and concentrate the coal gasification black water to obtain the flash gas and concentrated black water;

[0044] The sedimentation and filtration unit is used to sediment and filter and dehydrate the concentrated black water to obtain the gasified 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 in sequence. Further preferably, a low-pressure flash tower is connected in series between the high-pressure flash tower and the vacuum flash tower. Preferably, the flash gas outlet of the high-pressure flash tower is connected to the flash gas inlet of the steam preheater.

[0046] Preferably, the sedimentation and filtration unit comprises a sedimentation tank and a filtration and dehydration device, the sedimentation tank is used to perform sedimentation treatment on the concentrated black water output by the flash evaporation unit, and the filtration and dehydration device is used to filter and dehydrate the slurry obtained by the sedimentation treatment to obtain the gasified fine slag to be treated; preferably, the filtration and dehydration 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 scrubber;

[0048] The cyclone separator is connected to the spray dryer and is used for preliminary dust removal of the secondary steam output by the spray dryer;

[0049] The air inlet of the steam washing tower is connected to the cyclone separator, and the air outlet of the steam washing tower is connected to the heat medium inlet of the fine slag preheater. The steam washing tower is used to wash and dedust the secondary steam that has undergone the preliminary dust removal with washing liquid to obtain washing water and secondary steam after dust removal.

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

[0051] In some embodiments, the flash gas outlet of the steam preheater is connected to a flash gas separation tank, which is used to separate the flash gas output by the steam preheater into vapor and liquid and obtain condensate; preferably, the condensate outlet of the flash gas separation tank is connected to the washing liquid inlet of the steam washing tower;

[0052] And / or, the secondary steam outlet of the fine slag preheater is connected to the secondary steam separation tank through a pipeline, so as 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 to the secondary steam inlet of the steam preheater; preferably, the condensate outlet of the secondary steam separation tank is connected to the ash water tank, or the condensate outlet of the secondary steam separation tank is connected to the washing liquid inlet of the steam washing tower.

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

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

[0055] At the same time, the secondary steam output from the spray dryer of the present invention is recycled in the process system. After dust removal, it is first used to preheat the gasified fine slag to be treated, so that the remaining heat can be fully utilized, and then after heat exchange with flash steam (so that the remaining heat of flash steam can be reasonably utilized), it is superheated to form superheated steam, and the superheated steam is returned to the spray dryer for reuse, so that not only the heat of the secondary steam is reasonably and fully reused, but also the waste of water resources is reduced. In addition, the scheme of the present invention does not need to introduce hot air, has good safety, and is energy-saving and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0057] Figure 2 A schematic diagram of a dehydration and drying system for gasified fine slag in another embodiment;

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

[0059] Figure 4 for Figure 3 Schematic diagram of the feed channel structure of the feed nozzle. DETAILED DESCRIPTION

[0060] In order to facilitate the understanding of the present invention, the present invention will be further described below in conjunction with examples. It should be understood that the following examples are only for a better understanding of the present invention and do not mean that the present invention is limited to the following examples.

[0061] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The term "and / or" as may be used herein includes any and all combinations of one or more of the related listed items. The terms "first", "second", etc. are used for descriptive purposes only and are not to 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 the art can be used. The reagents or instruments used without specifying the manufacturer are all conventional products that can be purchased commercially.

[0063] The present invention provides a method for dehydrating and drying gasified fine slag based on a spray dryer, the method mainly comprising the following steps:

[0064] 1) The coal gasification black water is flash-evaporated, concentrated, settled, filtered and dehydrated in a black water treatment unit to obtain flash gas and gasification fine slag to be treated;

[0065] 2) sending the gasified fine slag to be treated into a fine slag preheater for heat exchange with a heat medium to obtain preheated gasified fine slag;

[0066] 3) spraying the preheated gasified fine slag and superheated steam into a spray dryer so that the two are in direct contact for heat exchange, thereby obtaining dry gasified fine slag and secondary steam;

[0067] 4) sending the secondary steam obtained in step 3) to a secondary steam dust removal unit for dust removal to obtain dust-removed secondary steam, and then sending the dust-removed secondary steam to the fine slag preheater in step 2) to use it as a heat medium for heat exchange with the gasified fine slag to be treated;

[0068] 5) sending the secondary steam output from the fine slag preheater in step 2) into a steam preheater, so that the secondary steam used 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;

[0069] 6) The preheated secondary steam obtained in step 5) is sent to a steam superheater to exchange heat with a 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, so that the gasified fine slag is dehydrated and dried to obtain dry gasified fine slag, and secondary steam is obtained again.

[0070] The present invention uses the above method to achieve the drying of gasified fine slag without introducing air or heating the air; the present invention uses superheated steam to directly contact the gasified fine slag in a spray dryer for heat exchange, so that the moisture in the gasified fine slag is heated and vaporized to form new steam, and the steam is mixed with the surrounding superheated steam airflow to form secondary steam. As the secondary steam is discharged from the spray dryer, the moisture is also continuously carried away, thereby removing most of the moisture in the fine slag and obtaining gasified fine slag with a low moisture content. It not only meets the current needs of environmental protection and resource utilization of fine slag, but also can greatly reduce the amount of fine slag to be transported; at the same time, the secondary steam output from the spray dryer is recycled in the process system, and after dust removal, it is first used to preheat the gasified fine slag to be treated (it can increase the initial temperature of the gasified fine slag and is conducive to obtaining a good drying and dehydration effect while reducing the amount of superheated steam), and then it is superheated to form superheated steam after heat exchange with flash steam, and the superheated steam is returned to the spray 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.

[0071] In the present invention, superheated steam is used as the drying medium in the spray dryer. It has the characteristics of large specific heat capacity. Compared with the drying medium such as hot air and flue gas used in the prior art, it has lower energy consumption, large convective heat transfer coefficient, small moisture migration resistance, and high heat transfer efficiency, and can achieve higher drying efficiency and energy utilization. Moreover, no other gases such as air are introduced into the system. The secondary steam output by the spray dryer only needs simple dust removal treatment to be directly reused in the system. The intermediate links required for recycling are few, and the energy loss is small. Furthermore, the present invention does not involve the contact between hot air and gasified fine slag, and only uses superheated steam as the drying medium. It has high safety and can avoid the hidden danger of fine slag with high carbon residue content exploding in the air atmosphere during the drying process.

[0072] Preferably, in step 1) of the present invention, the particle size of the gasified fine slag to be treated meets the following requirements: particles with a particle size of <20 μm account for 25-35wt%, particles with a particle size of <45 μm account for 65-75wt%, and particles with a particle size of <100 μm account for 85-95wt%. Specifically, for example, particles with a particle size of <20 μm account for 30wt%, particles with a particle size of <45 μm account for 70wt%, and particles with a particle size of <100 μm account for 90wt%. The inventors have found that for gasified fine slag with a particle size that meets the above requirements, the dehydration and drying effect of the method of the present invention is better. On the one hand, it can be more fully and evenly contacted with superheated steam in the spray dryer, improve the heat exchange efficiency, improve the dehydration and drying effect of the gasified fine slag, and facilitate the acquisition of dry gasified fine slag with a low water content; on the other hand, it can also effectively avoid the 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 0.2-0.3Mpa; in step 3), the secondary steam output in the spray dryer has a temperature of 130-150°C, and the pressure of the secondary steam is 0.2-0.3Mpa.

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

[0075] In the present invention, in step 6), the superheated medium required for superheating the aforementioned preheated secondary steam in the steam superheater is preferably a waste heat resource of the coal gasification system. In a preferred embodiment, the waste heat resource is coal gasification black water from the coal gasification system, such as black water from the gasifier quenching chamber and / or black water from the raw gas washing tower used for washing raw synthesis gas. The coal gasification black water from the coal gasification system is first heat exchanged 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 coal gas from the coal gasification system, such as raw synthesis gas from the gasifier that has been washed and dusted by the raw gas washing tower.

[0076] Preferably, in step 3), the preheated gasified fine slag and superheated steam are simultaneously sprayed into the spray dryer through a feed nozzle; wherein the feed nozzle comprises three channels, see Figure 3 , 4, respectively, a central feed channel 201 located in the center, an intermediate feed channel 202 arranged around the periphery of the central feed channel 201, and an outer ring feed channel 203 arranged around the periphery of the intermediate feed channel 202. The gasified fine slag is sprayed in through the intermediate feed channel 202, and the superheated steam is sprayed in through the central feed channel 201 and the outer ring feed channel 203. The above-mentioned preferred nozzle feeding method can make the gasified fine slag be wrapped and preheated by superheated steam before entering the spray dryer, thereby increasing the initial temperature, thereby utilizing the efficient drying and dehydration in the spray dryer, which is conducive to reducing the amount of superheated steam. Preferably, the aspect ratio of the feed nozzle is 3-10:1, more preferably 5-7:1; the use of a feed nozzle with a preferred aspect ratio is conducive to more fully utilizing the heat carried by the superheated steam, so that the gasified fine slag to be treated can be well preheated and heated by the superheated steam in a wrapped manner during the feeding process, which is conducive to 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, before sending it into the vacuum flash tower, it is also possible to add a step of sending the coal gasification black water into a low-pressure flash tower for low-pressure flash evaporation. High-pressure flash evaporation, low-pressure flash evaporation and vacuum flash evaporation are all conventional operations for flash evaporation of coal gasification black water in the field, which will not be elaborated. Flash steam and concentrated black water are obtained by the above-mentioned flash concentration. Preferably, the flash steam required in the steam preheater of step 5) comes from the high-pressure flash steam generated in the above-mentioned 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 is carried out in a sedimentation tank, that is, the concentrated black water obtained by flash concentration is sent to a sedimentation tank for sedimentation to obtain a slurry and a supernatant (i.e., gray water). During the sedimentation process, a flocculant can be added to promote solid sedimentation, which is a conventional operation in the field and will not be described in detail. Specifically, the supernatant is sent to the downstream gray water tank. The slurry obtained by sedimentation (solid content, for example, 10-20wt%) is filtered and dehydrated, for example, by using a vacuum belt filter or a plate and frame filter, and the gasified fine slag to be treated is obtained by filtration and dehydration, and the water content of the gasified fine slag is still relatively high, for example, the water content is between 40-70wt%. The filtrate obtained by filtration and dehydration is sent to the gray water tank. The water in the gray 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 spray dryer specifically includes: firstly passing the secondary steam through a cyclone separator for cyclone separation to obtain preliminary dust removal, and then sending the secondary steam into a steam washing tower for washing and dust removal with a washing liquid. In the steam washing tower, the washing liquid is specifically brought into countercurrent contact with the secondary steam to wash the ash carried in the secondary steam to ensure the purity of the secondary steam. The washing liquid used mainly comes from the condensed water generated in the process, as described in the subsequent description. Preferably, the washing water obtained by washing and dust removal of the secondary steam in the steam washing tower is sent to a sedimentation 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 reduced to <10 mg / m 3 .

[0080] Preferably, step 5) further includes sending the flash gas output from the steam preheater into a flash gas separation tank for gas-liquid separation, and sending the separated condensate into a steam washing tower for use as washing liquid; the separated steam continues to enter downstream processing, such as sulfur recovery processing, etc.

[0081] Preferably, in step 2), after the secondary steam used as heat medium in the fine slag preheater is heat-exchanged with the gasified fine slag, it is output and first sent to the secondary steam separation tank for vapor-liquid separation, and then sent to the steam preheater of step 5) for heat exchange with the flash gas. Preferably, part of the condensate separated in the secondary steam separation tank is sent to the gray water tank or to the steam washing tower for use as washing liquid.

[0082] In the present invention, superheated steam is used as the drying medium. Compared with low-temperature flue gas and hot air, superheated steam has a higher specific heat capacity (1.968 kJ / (kg·K)) and a stronger heat exchange capacity. Through the method of the present invention, a good dehydration and drying effect of gasified fine slag can be achieved with a smaller superheated steam flow rate. In the present invention, superheated steam and gasified fine slag are directly contacted for heat exchange in a spray dryer, the temperature distribution is more uniform, and the processing capacity is greater. The present invention uses secondary steam to preheat the gasified fine slag to be treated, which can effectively recycle 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 dehydration and drying system for gasified fine slag based on a spray dryer, which can be used to implement the dehydration and drying method for gasified fine slag as described above.

[0084] See also 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] The black water treatment unit 100 is used to flash condense, settle and filter the coal gasification black water to obtain flash gas and gasification fine slag to be treated;

[0086] A fine slag preheater, used for preheating 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 the 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 perform dust removal treatment on the secondary steam outputted 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 being used to preheat the gasified fine slag to be treated;

[0089] A steam preheater, used for performing heat exchange between the secondary steam outputted from the fine slag preheater and the flash steam from the black water treatment unit, thereby obtaining preheated secondary steam;

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

[0091] By using the above system to dehydrate and dry the gasified fine slag, the superheated steam can be used to dry and dehydrate the gasified fine slag efficiently, safely and environmentally friendly. There is no explosion hazard caused by the contact between hot air and the dry gasified fine slag with high carbon content, and the energy utilization rate is higher. Moreover, no air is introduced into the system, and a secondary steam airflow mainly composed of steam is generated during the drying and dehydration process, which can be recycled without going through a complicated intermediate processing link. The present invention first removes dust from the secondary steam, then enters the fine slag preheater to preheat the gasified fine slag, then enters the steam preheater to exchange heat with the flash gas for preheating, and then enters the steam superheater for superheating to obtain superheated steam for circulation in the spray dryer. The ingenious design of the entire system and the organic integration of each processing device unit enable the energy of the secondary steam to be more fully and reasonably utilized, and can greatly reduce the waste of water resources, so that water resources can be efficiently and fully utilized.

[0092] In some preferred embodiments, see Figure 1The superheated medium inlet of the steam superheater is connected to the coal gasification black water delivery 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, and 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 A variation of the dehydration and drying system shown in FIG. Figure 1 The main difference is that the superheating medium inlet of the steam superheater is connected to the raw gas outlet of the coal gasification system through a raw gas transmission pipeline, that is, the superheating medium required in the steam superheater is the raw gas of the coal gasification system; specifically, Figure 2 As shown, the synthesis gas produced by the gasifier enters the raw gas washing tower for washing and dust removal, and the raw gas obtained is passed into the steam superheater as the aforementioned superheated medium; in this embodiment, the black water in the gasifier quenching chamber and the black water in the raw gas washing tower are no longer passed into the steam superheater, but directly enter the black water flash unit for treatment.

[0093] In a preferred embodiment, Figure 3 As shown, the spray dryer is provided with a feed nozzle 200, through which the gasified fine slag to be treated and the superheated steam are sprayed into the spray dryer together. Figure 4 As shown, the feed nozzle includes a central feed channel 201, an intermediate feed channel 202 and an outer ring feed channel 203, and the three are in a sleeve-type structure as a whole, wherein the central feed channel 201 is located in the center, the intermediate feed channel 202 is arranged around the periphery of the central feed channel 201, and the outer ring feed channel 203 is arranged around the periphery of the intermediate feed channel 202, wherein the central feed channel 201 and the outer ring feed channel 203 are used to pass superheated steam, and the intermediate feed channel 202 is used to pass gasified fine slag. The feed nozzle adopting this preferred structure can make the gasified fine slag be wrapped by superheated steam during the feeding process, fully exchange heat with the superheated steam to increase its initial temperature, which is beneficial to improve the drying and dehydration effect after entering the spray dryer later, and is beneficial to reduce the consumption of superheated steam. More preferably, the aspect ratio of the feed nozzle is 3-10:1.

[0094] In some embodiments, Figure 1 As shown, the black water treatment unit 100 specifically includes a flash evaporation concentration unit 101 and a sedimentation filtration unit 102. The flash evaporation concentration unit 101 is used to flash and concentrate the coal gasification black water to obtain flash gas and concentrated black water; the sedimentation filtration unit 102 is used to sediment and filter the concentrated black water to obtain gasification fine slag to be treated.

[0095] More specifically, the flash concentration unit 101 comprises a high-pressure flash tower and a vacuum flash tower connected in series in sequence; 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 comes from the high-pressure flash steam output by the high-pressure flash tower.

[0096] More specifically, the sedimentation and filtration unit 102 includes a sedimentation tank and a filtering and dehydrating device. The sedimentation tank is used to perform sedimentation treatment on the concentrated black water outputted from the flash evaporation unit, thereby obtaining a slurry; the filtering and dehydrating device is used to perform filtering and dehydrating on the slurry obtained after the sedimentation treatment, thereby obtaining the gasified fine slag to be treated; preferably, the filtering and dehydrating device specifically adopts a vacuum belt filter or a plate and frame filter. Figure 1 As shown, the sedimentation and filtration unit specifically also includes an ash water tank for receiving the supernatant in the sedimentation tank and the filtrate obtained by the filtration and dehydration device. The ash water in the ash water tank can be recycled to the coal gasification system, for example, recycled to the washing tower of the coal gasification system.

[0097] In some specific embodiments, participating Figure 1 The secondary steam dust removal unit includes a cyclone separator and a steam washing tower. The cyclone separator is connected to the spray dryer and is used to perform cyclone separation on the secondary steam output by the spray dryer so as to obtain preliminary dust removal. The air inlet of the steam washing tower is connected to the cyclone separator, and the air outlet of the steam washing tower is connected to the heat medium inlet of the fine slag preheater. The steam washing tower receives the secondary steam that has undergone preliminary dust removal from the cyclone separator. The secondary steam that has undergone preliminary dust removal is washed and dust removed by washing liquid in the steam washing tower, thereby obtaining washing water and secondary steam that has undergone dust removal. Preferably, the washing water outlet of the steam washing tower is connected to the sedimentation tank.

[0098] In some embodiments, the flash gas outlet of the steam preheater is connected to a flash gas separation tank, which is used to separate the flash gas output by the steam preheater into gas and liquid and obtain condensate; preferably, the condensate outlet of the flash gas separation tank is connected to the washing liquid inlet of the steam scrubber, so that the condensate separated in the flash gas separation tank can be sent to the steam scrubber for use as washing liquid. Furthermore, the flash gas output by the flash gas separation tank 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 the 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 to the secondary steam inlet of the steam preheater, so that the secondary steam after vapor-liquid separation can enter the steam preheater for preheating. Preferably, the condensate outlet of the secondary steam separation tank is connected to the gray water tank, or the condensate outlet of the secondary steam separation tank is connected to the washing liquid inlet of the steam washing tower, so that the condensate separated by the secondary steam separation tank enters the gray water tank for reuse, or is used as washing liquid.

[0100] The solution of the present invention is further illustrated below through application cases.

[0101] Example 1

[0102] The schematic diagram of the dehydration and drying system used in this embodiment is shown in Figure 1 Regarding the dehydration and drying system and the dehydration and drying method not specifically described below, please refer to the previous description and will not be repeated one by one.

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

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

[0105] 1.1) Flash concentration: send the coal gasification black water into a high-pressure flash tower, and at a pressure of 0.6MPa, some soluble gases are flashed and released from 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 0.1MPa, the soluble gases in the black water are further flashed and released in the low-pressure flash tower; the black water at the bottom of the low-pressure flash tower enters a vacuum flash tower, and is further flashed at -0.5MPa to obtain concentrated black water;

[0106] 1.2) Sedimentation:

[0107] The concentrated black water obtained in step 1.1) is sent to a sedimentation tank for gravity sedimentation solid-liquid separation, and a flocculant (composed of 80wt% anionic polyacrylamide and 20wt% coagulant (polyaluminum)) is added to accelerate the sedimentation of solids in the black water; a slurry with a solid content of 20wt% is precipitated at the bottom of the sedimentation tank (flow rate: 5000kg / h, temperature: 60°C, water content 80wt%), and the supernatant of the sedimentation tank is sent to a gray water tank;

[0108] 1.3) Filtration and dehydration:

[0109] The slurry settled out from the bottom of the sedimentation tank is sent to the filtering and dehydrating device (plate and frame filter press) through the slurry pump for filtering and dehydration to obtain the gasification fine slag with a water content of 50wt% (flow rate: 2000kg / h, temperature: 60℃), and the filtrate (flow rate: 3000kg / h, temperature: 60℃) is sent to the ash water tank by the water pump. The particle size of the gasification fine slag is as follows: particles with a particle size of <20μm account for about 30wt%, particles with a particle size of <45μm account for about 70wt%, and particles with a particle size of <100μm account for about 90wt%.

[0110] 2) Preheating of fine slag:

[0111] The gasified fine slag to be treated is sent to the fine slag preheater for indirect heat exchange with the heat medium to obtain preheated gasified fine slag; after the secondary steam is generated during the operation of the system, the heat medium is the dust-removed secondary steam output from the steam scrubber. During the preheating process, the secondary steam is cooled and condensed, and sent to the secondary steam separation tank for vapor-liquid separation, and the separated condensate (flow rate: 750kg / h) is sent to the ash water tank.

[0112] 3) Drying and dehydration:

[0113] The preheated gasified fine slag and superheated steam are fed through the feed nozzle (the nozzle structure diagram is shown in FIG. Figure 3 , 4 The superheated steam is sprayed into the spray dryer, and the superheated steam and the gasified fine slag are in direct contact in the spray dryer. The gasified fine slag is heated, and the moisture in the gasified fine slag is vaporized and precipitated to form new steam, which is mixed with the surrounding superheated steam airflow to form secondary steam (temperature 144°C, 0.3MPa, flow rate: 22250kg / h). The secondary steam is discharged from the spray dryer through the induced draft fan equipped with the spray dryer, and the moisture is continuously carried away, thereby removing most of the moisture in the fine slag, and obtaining dry gasified fine slag with a moisture content of 20% (output 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-free secondary steam then enters a steam scrubber, where the condensate from the flash steam separation tank is used as a wash liquid to wash the secondary steam for further dust removal. The dust content in the final dust-free secondary steam is less than 10 mg / m 3 The washing water at the bottom of the steam washing tower is transported to the sedimentation tank; the secondary steam obtained from the dust removal in this link is sent to the fine slag preheater in the above step 2) as a heat medium for preheating the gasified fine slag.

[0116] 5) Secondary steam preheating:

[0117] The secondary steam (temperature 144°C, pressure: 0.3MPa, flow rate: 21500kg / h) that has undergone vapor-liquid separation in the secondary steam separation tank in step 2) is sent to a 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] The preheated secondary steam (temperature 154°C, pressure: 0.3MPa, flow rate: 21500kg / h) is heat exchanged with black water (temperature: 220°C, pressure: 4.0MPa, flow rate 120000kg / h) from the gasifier quenching chamber in the steam superheater to form new superheated steam (temperature 190°C, pressure: 0.3MPa, flow rate: 21500kg / h); the superheated steam is circulated and sent to the spray dryer in step 3) (in the initial stage of system operation, step 3) can use fresh superheated steam introduced from outside the system. During the operation of the system, after superheated steam is generated in the steam superheater, the superheated steam generated in the steam superheater is used in step 3). The black water in the gasifier quenching chamber is heat exchanged in the steam superheater and sent to the high-pressure flash tower in step 1.1) for treatment.

[0120] Example 2

[0121] The schematic diagram of the dehydration and drying system used in this embodiment is shown in Figure 2 Regarding the dehydration and drying system and the dehydration and drying method not specifically described below, please refer to the previous description and will not be repeated one by one.

[0122] The coal gasification black water used in this embodiment is the black water from the gasification furnace quenching chamber and the black water from the raw coal gas washing tower. In this embodiment, the dehydration and drying of gasification fine slag includes the following processing steps:

[0123] 1) Flash concentration, sedimentation and filtration

[0124] 1.1) Flash concentration: The black water from the gasifier quenching chamber and the black water from the raw gas washing tower are sent to the high-pressure flash tower. At a pressure of 0.6MPa, part of the soluble gas is flashed and released from the black water. The black water at the bottom of the high-pressure flash tower enters the low-pressure flash tower; at a pressure of 0.1MPa, the soluble gas in the black water is further flashed and released in the low-pressure flash tower; the black water at the bottom of the low-pressure flash tower enters the vacuum flash tower and is further flashed at -0.5MPa to obtain concentrated black water;

[0125] 1.2) Sedimentation:

[0126] The concentrated black water obtained in step 1.1) is sent to a sedimentation tank for gravity sedimentation solid-liquid separation, and a flocculant (composed of 85wt% anionic polyacrylamide and 15wt% coagulant (polyferric)) is added to accelerate the sedimentation of solids in the black water; a slurry with a solid content of 20% is precipitated at the bottom of the sedimentation tank (flow rate: 5000kg / h, temperature: 60°C, water content 80%), and the supernatant of the sedimentation tank is sent to a gray water tank;

[0127] 1.3) Filtration and dehydration:

[0128] The slurry settled out from the bottom of the sedimentation tank is sent to the filtering and dehydrating device (vacuum belt filter) through the slurry pump for filtering and dehydration to obtain gasified fine slag with a water content of 60wt% (flow rate: 2500kg / h, temperature: 60℃), and the filtrate is sent back to the ash water tank by the water pump. The particle size of the gasified fine slag is as follows: particles with a particle size of <20μm account for about 30wt%, particles with a particle size of <45μm account for about 70wt%, and particles with a particle size of <100μm account for about 90wt%.

[0129] 2) Preheating of fine slag:

[0130] The gasified fine slag to be treated is sent to the fine slag preheater for indirect heat exchange with the heat medium to obtain preheated gasified fine slag; after the secondary steam is generated during the operation of the system, the heat medium is the dust-removed secondary steam output from the steam scrubber. During the preheating process, the secondary steam is cooled and condensed, and sent to the secondary steam separation tank for vapor-liquid separation, and the separated condensate (flow rate: 1250kg / h) is sent to the ash water tank;

[0131] 3) Drying and dehydration:

[0132] The preheated gasified fine slag and superheated steam are simultaneously passed through the feed nozzle (the nozzle structure diagram is shown in FIG. Figure 3 , 4 As shown in the figure, the aspect ratio is 7:1) and sprayed into the spray dryer. The superheated steam directly contacts the gasified fine slag in the spray dryer, and the gasified fine slag is heated, so that the moisture in the gasified fine slag is vaporized by heat to form new steam, and is mixed with the surrounding superheated steam airflow to form secondary steam (temperature 144°C, 0.3MPa, 36450kg / h). The secondary steam is discharged from the spray dryer through the induced draft fan equipped with the spray dryer, and the moisture is continuously carried away, thereby removing most of the moisture in the fine slag, and obtaining dry gasified fine slag with a moisture content of 20% (output 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-free secondary steam then enters a steam scrubber, where the condensate from the flash steam separation tank is used as a wash liquid to wash the secondary steam for further dust removal. The dust content in the final dust-free secondary steam is less than 10 mg / m 3 The washing water at the bottom of the steam washing tower is transported to the sedimentation tank; the secondary steam obtained from the dust removal in this link is sent to the fine slag preheater in the above step 2) as a heat medium for preheating the gasified fine slag.

[0135] 5) Secondary steam preheating:

[0136] The secondary steam (temperature 144°C, pressure: 0.3MPa, flow rate: 35200kg / h) that has undergone vapor-liquid separation in the secondary steam separation tank 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.

[0137] 6) Secondary steam superheating:

[0138] The preheated secondary steam (temperature 150°C, pressure: 0.30MPa, flow rate: 35200kg / h) is heat exchanged with the crude gas from the crude gas washing tower (pressure 4.0MPa, temperature 220°C, flow rate, 24100kg / h) to form new superheated steam (temperature 190°C, 0.3MPa, 35200kg / h); the superheated steam is circulated to the spray dryer in step 3) (in the initial stage of system operation, step 3) can use fresh superheated steam introduced from outside the system. During the operation of the system, after superheated steam is generated in the steam superheater, the superheated steam generated in the steam superheater is used in step 3)).

[0139] In this embodiment, the gray water in the gray water tank is used as washing water for the raw gas washing tower.

[0140] Embodiment 3-9

[0141] The process parameters and experimental results of Examples 3-9 are shown in Table 1.

[0142] Table 1

[0143]

[0144] From the above embodiments, it can be seen that the dehydration and drying system and method of the present invention can dry and dehydrate gasified fine slag with high water content to a water content of less than 30%, and the energy and water resources of the entire process can be reasonably fully utilized, the entire process requires less additional energy input, and water resources are recycled, which can greatly reduce the waste of water resources. There is no need to introduce hot air during the treatment process, which is not only environmentally friendly but also safe. The scheme of the present invention can effectively solve the problems of poor effect, high energy consumption, large waste of water resources, and serious environmental pollution in the existing gasified fine slag dehydration treatment.

[0145] It is easy to understand that the above embodiments are only examples for clear explanation and do not mean that the present invention is limited thereto. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the present invention.

Claims

1. A method for dehydrating and drying gasified fine slag based on a spray dryer, characterized in that: The method comprises: 1) flash evaporation, concentration, sedimentation and filtration and dehydration of coal gasification black water in a black water treatment unit to obtain flash gas and gasification fine slag to be treated; preferably, the particle size of the gasification fine slag to be treated meets the following requirements: particles with a particle size of <20 μm account for 25-35wt%, particles with a particle size of <45 μm account for 65-75wt%, and particles with a particle size of <100 μm account for 85-95wt%; 2) sending the gasified fine slag to be treated into a fine slag preheater for heat exchange with a heat medium to obtain preheated gasified fine slag; 3) spraying the preheated gasified fine slag and superheated steam into a spray dryer so that the two are in direct contact for heat exchange, thereby obtaining dry gasified fine slag and secondary steam; 4) sending the secondary steam obtained in step 3) to a secondary steam dust removal unit for dust removal to obtain dust-removed secondary steam, which is then sent to the fine slag preheater in step 2) for use as the heat medium; 5) sending the secondary steam output from the fine slag preheater in step 2) into a steam preheater to perform heat exchange 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 sent to a steam superheater for superheating to obtain superheated steam; the superheated steam is sent to the spray dryer in step 3) for heat exchange with the preheated gasified fine slag.

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

3. The method for dehydrating and drying gasified fine slag according to claim 1, characterized in that: In step 6), the superheated medium used in the steam superheater is coal gasification black water from a coal gasification system; the coal gasification black water from a coal gasification system is sent to the black water treatment unit in step 1) for treatment after the preheated secondary steam is subjected to the superheating treatment in step 6); Alternatively, in step 6), the superheated medium used in the steam superheater is raw coal gas from a coal gasification system.

4. The method for dehydrating and drying gasified fine slag according to claim 1, characterized in that: In step 3), the preheated gasified fine slag and the superheated steam are simultaneously sprayed into the spray dryer through a feed nozzle; Wherein, the gasified fine slag is sprayed in through the middle feed channel of the feed nozzle, and the superheated steam is sprayed in through the central feed channel and the outer ring feed channel of the feed nozzle, and 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; Preferably, the aspect ratio of the feed nozzle is 3-10:1, more preferably 5-7:

1.

5. The method for dehydrating and drying gasified fine slag according to any one of claims 1 to 4, characterized in that: In step 1), the flash concentration comprises successively performing high-pressure flash evaporation and vacuum flash evaporation on the coal gasification black water, and preferably, before performing the vacuum flash evaporation, the process further comprises performing low-pressure flash evaporation on the coal gasification black water; 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; In step 1), the sedimentation is carried out in a sedimentation tank; In step 4), the dust removal treatment 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 washing tower for washing and dust removal; preferably, the washing water obtained by washing and dust removal in the steam washing tower is sent to the sedimentation tank; Preferably, step 5) further comprises sending the flash gas output from the steam preheater into a flash gas separation tank for vapor-liquid separation, and sending the separated condensate into the steam washing tower for use as washing liquid; Preferably, in step 2), the secondary steam output from the fine slag preheater is first sent to a secondary steam separation tank for vapor-liquid separation, and then sent to the steam preheater in step 5); preferably, part of the condensate separated in the secondary steam separation tank is sent to a gray water tank or to the steam washing tower for use as washing liquid.

6. A dehydration and drying system capable of implementing the gasification fine slag dehydration and drying method according to any one of claims 1 to 5, characterized in that: The dehydration and drying system comprises: A black water treatment unit is used to flash condense, settle and filter the coal gasification black water to dehydrate it, and obtain flash gas and gasification fine slag to be treated; A fine slag preheater, used for preheating the gasified fine slag to be treated using a heat medium; A spray dryer, used for directly contacting the gasified fine slag outputted from the fine slag preheater with superheated steam for heat exchange, so as to obtain dry gasified fine slag and secondary steam; A secondary steam dust removal unit is used to perform dust removal on the secondary steam output from the spray dryer; the secondary steam dust removal unit is connected to the fine slag preheater to transport the secondary steam that has undergone the dust removal treatment as the heat medium to the fine slag preheater; a steam preheater, used for performing heat exchange between the secondary steam outputted from the fine slag preheater and the flash steam from the black water treatment unit to obtain preheated secondary steam; a steam superheater, used for superheating the secondary steam 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; Preferably, the superheated medium inlet of the steam superheater is connected to the coal gasification black water delivery 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 raw gas outlet of the coal gasification system through a raw gas delivery pipeline.

7. The dehydration and drying system according to claim 6, characterized in that: The spray dryer is provided with a feed nozzle for spraying the gasified fine slag and the superheated steam into the spray dryer; The feed nozzle comprises a central feed channel for introducing the superheated steam, an intermediate feed channel arranged around the periphery of the central feed channel for introducing the gasified fine slag, and an outer ring feed channel arranged around the periphery of the intermediate feed channel for introducing the superheated steam; Preferably, the aspect ratio of the feed nozzle is 3-10:

1.

8. The dehydration and drying system according to claim 6 or 7, characterized in that: The black water treatment unit includes a flash concentration unit and a sedimentation filtration unit; The flash concentration unit is used to flash and concentrate the coal gasification black water to obtain the flash gas and concentrated black water; The sedimentation and filtration unit is used to sediment and filter and dehydrate the concentrated black water to obtain the gasified fine slag to be treated; Preferably, the flash concentration unit comprises a high-pressure flash tower and a vacuum flash tower connected in series in sequence. Further preferably, a low-pressure flash tower is connected in series between the high-pressure flash tower and the vacuum flash tower. Preferably, the flash gas outlet of the high-pressure flash tower is connected to the flash gas inlet of the steam preheater. Preferably, the sedimentation and filtration unit comprises a sedimentation tank and a filtration and dehydration device, the sedimentation tank is used to perform sedimentation treatment on the concentrated black water output by the flash evaporation unit, and the filtration and dehydration device is used to filter and dehydrate the slurry obtained by the sedimentation treatment to obtain the gasified fine slag to be treated; preferably, the filtration and dehydration device is a vacuum belt filter or a plate and frame filter.

9. The dehydration and drying system for gasified fine slag according to claim 8, characterized in that: The secondary steam dust removal unit includes a cyclone separator and a steam scrubber; The cyclone separator is connected to the spray dryer and is used for preliminary dust removal of the secondary steam output by the spray dryer; The air inlet of the steam washing tower is connected to the cyclone separator, the air outlet of the steam washing tower is connected to the heat medium inlet of the fine slag preheater, and the steam washing tower is used to wash and dedust the secondary steam after the preliminary dedusting with washing liquid to obtain washing water and dedusted secondary steam; Preferably, the washing water outlet of the steam washing tower is connected to the settling tank.

10. The dehydration and drying system for gasified fine slag according to claim 9, characterized in that: The flash steam outlet of the steam preheater is connected to a flash steam separation tank, which is used to separate the flash steam output by the steam preheater into vapor and liquid and obtain condensate; preferably, the condensate outlet of the flash steam separation tank is connected to the washing liquid inlet of the steam washing tower; And / or, the secondary steam outlet of the fine slag preheater is connected to the secondary steam separation tank through a pipeline, so as 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 to the secondary steam inlet of the steam preheater; preferably, the condensate outlet of the secondary steam separation tank is connected to the ash water tank, or the condensate outlet of the secondary steam separation tank is connected to the washing liquid inlet of the steam washing tower.

Images