Gasification fine slag dehydration method and system

Abstract

According to the gasification fine slag dewatering method and system, high-water-content gasification fine slag is dewatered and dried by adopting the scheme, dewatering and drying of the gasification fine slag can be achieved under the condition that air does not need to be introduced, and secondary steam formed in the drying process can be directly recycled in the system. The method comprises the following steps: 1) carrying out flash evaporation concentration, sedimentation and filtration dehydration on the coal gasification black water to obtain flash evaporation gas and gasification fine slag to be treated; 2) feeding gasified fine slag to be treated into a fine slag preheater for preheating; (3) the preheated gasified fine slag is fed into a superheated steam drying device to be subjected to heat exchange with superheated steam, and dried gasified fine slag and secondary steam are obtained; (4) secondary steam is subjected to dust removal treatment, and then the secondary steam is fed into the fine slag preheater; (5) the secondary steam output by the fine slag preheater is subjected to superheat treatment, and superheated steam is obtained; and feeding the superheated steam into the superheated steam drying device in the step (3).

Description

Technical Field

[0001] The invention relates to a dehydration and drying technology for gasification fine slag, and in particular to a dehydration method and system for gasification fine slag. Background Art

[0002] 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] 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.

[0006] 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. Summary of the invention

[0007] The present invention provides a method and system for dehydrating gasified fine slag. 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 achieved without introducing air, but the secondary steam formed during 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 water resource waste is small, and the system safety is good.

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

[0009] In one aspect, the present invention provides a method for dehydrating gasified fine slag, the method comprising:

[0010] 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;

[0011] 2) sending the gasified fine slag to be treated into a fine slag preheater for preheating with a heat medium to obtain preheated gasified fine slag;

[0012] 3) sending the preheated gasified fine slag into a superheated steam drying device to directly contact with the superheated steam for heat exchange, thereby obtaining dried gasified fine slag and secondary steam;

[0013] 4) performing dust removal treatment on the secondary steam obtained in step 3) to obtain dust-removed secondary steam, and then feeding the secondary steam into the fine slag preheater in step 2) to be used as the heat medium;

[0014] 5) superheating the secondary steam output from the fine slag preheater in step 2) to obtain superheated steam; sending the superheated steam to the superheated steam drying device in step 3) for heat exchange with the preheated gasified fine slag.

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

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

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

[0018] Preferably, in step 5), the superheated medium used for the superheating treatment 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 secondary steam is subjected to the superheating treatment in step 5);

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

[0020] 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. Preferably, before performing the vacuum flash evaporation, the process further comprises performing low-pressure flash evaporation on the coal gasification black water.

[0021] Furthermore, in step 1), the sedimentation is carried out in a sedimentation tank.

[0022] 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 from the washing and dust removal in the steam washing tower is sent to the sedimentation tank.

[0023] 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 step 5) for the superheating treatment; 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.

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

[0025] 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;

[0026] The present invention also provides a system capable of implementing the above-mentioned gasification fine slag dehydration method, the system comprising:

[0027] 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;

[0028] A fine slag preheater, used for preheating the gasified fine slag to be treated using a heat medium to obtain preheated gasified fine slag;

[0029] A superheated steam drying device, used for directly contacting the preheated gasified fine slag with superheated steam for heat exchange, so as to obtain dry gasified fine slag and secondary steam;

[0030] A secondary steam dust removal unit is used to perform dust removal on the secondary steam output by the superheated steam drying device; 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;

[0031] a steam superheater, used for superheating the secondary steam outputted from the fine slag preheater to obtain superheated steam; the steam superheater is connected to the superheated steam drying device to supply the superheated steam to the superheated steam drying device;

[0032] 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.

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

[0034] The flash concentration unit is used to flash and concentrate the coal gasification black water to obtain the flash gas and concentrated black water;

[0035] 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;

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

[0037] Preferably, the sedimentation filtration unit comprises a sedimentation tank and a filtering and dehydrating device, the sedimentation tank is used to perform sedimentation treatment on the concentrated black water output by the flash concentration unit, and the filtering and dehydrating device is used to filter and dehydrate the slurry obtained by the sedimentation treatment to obtain the gasified fine slag to be treated.

[0038] In some embodiments, the system further comprises a steam preheater 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;

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

[0040] In some embodiments, the secondary steam dust removal unit includes a cyclone separator and a steam scrubber;

[0041] The cyclone separator is connected to the superheated steam drying device and is used for performing preliminary dust removal on the secondary steam output by the superheated steam drying device;

[0042] 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;

[0043] Preferably, the washing water outlet of the steam washing tower is connected to the settling tank.

[0044] In some embodiments, 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; the condensate outlet of the flash steam separation tank is connected to the washing liquid inlet of the steam washing tower;

[0045] 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.

[0046] The technical solution provided by the present invention has the following beneficial effects:

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

[0048] At the same time, the secondary steam output from the superheated steam drying device of the present invention is recycled in the process system, and is first used to preheat the gasified fine slag to be treated after dust removal, so that the remaining heat is fully utilized, and then the superheated steam is formed through heat, and the superheated steam is returned to the superheated steam drying device 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

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

[0050] Figure 2 A schematic diagram of a dehydration and drying system for gasified fine slag in another embodiment;

[0051] Figure 3 Schematic diagram of a dehydration and drying system for gasified fine slag in another embodiment. DETAILED DESCRIPTION

[0052] 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.

[0053] 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 invention belongs. The term "and / or" as may be used herein includes any and all combinations of one or more of the associated listed items.

[0054] 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.

[0055] The present invention provides a method for dehydrating gasified fine slag, which mainly comprises:

[0056] 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;

[0057] 2) sending the gasified fine slag to be treated into a fine slag preheater for preheating with a heat medium to obtain preheated gasified fine slag;

[0058] 3) sending the preheated gasified fine slag into a superheated steam drying device to directly contact with the superheated steam for heat exchange, thereby obtaining dried gasified fine slag and secondary steam;

[0059] 4) subjecting the secondary steam obtained in step 3) to dedusting to obtain dedusted secondary steam, which is then fed into the fine slag preheater in step 2) as a heat medium for heat exchange with the gasified fine slag to be treated;

[0060] 5) superheating the secondary steam output from the fine slag preheater in step 2) to obtain superheated steam; the superheated steam is then sent to the superheated steam drying device in step 3) for heat exchange 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.

[0061] 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 superheated steam drying device 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 superheated steam drying device, 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 transported; at the same time, the secondary steam output from the superheated steam drying device is recycled in the process system, and after dust removal, it is first used to preheat the gasified fine slag to be treated (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, and the superheated steam is returned to the superheated steam drying device for reuse. In this way, not only the heat of the secondary steam is reasonably and fully reused, but also the waste of water resources is reduced.

[0062] In the present invention, superheated steam is used as the drying medium in the superheated steam drying device. 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 superheated steam drying device only needs simple dust removal treatment to be directly reused in the system. The recycling requires fewer intermediate links and less energy loss. 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 explosion of fine slag with high carbon residue in the air atmosphere during the drying process.

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

[0064] 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%. The water content can be further reduced by dehydration and drying through the method of the present invention, for example, the water content can be reduced to less than 30% of the dry gasified fine slag. For example, in some embodiments, gasified fine slag with a water content of 10-30% can be obtained, or for example, in some embodiments, gasified fine slag with a water content of 15-20% can be obtained.

[0065] In the present invention, in step 5), the superheated medium used for superheating the secondary steam is preferably a waste heat resource of the coal gasification system. In a preferred embodiment, the waste heat resource is coal gasification black water from the coal gasification system, such as black water from the quenching chamber of the gasifier 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 used as a superheated medium to superheat the secondary steam, and then enters the black water treatment unit of step 1) for further treatment. In another preferred embodiment, the aforementioned waste heat resource is raw coal gas from the coal gasification system, such as raw synthesis gas from the gasifier that has been washed and dusted by a raw gas washing tower.

[0066] 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 art, and will not be elaborated on. Flash gas and concentrated black water are obtained by the above-mentioned flash concentration.

[0067] 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 or a centrifugal dehydrator for filtration, 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.

[0068] In some embodiments, in step 4), the dust removal treatment of the secondary steam output by the superheated steam drying device specifically includes: firstly subjecting the secondary steam to cyclone separation through a cyclone separator to obtain preliminary dust removal, and then sending the secondary steam to a steam washing tower for washing and dust removal with a washing liquid. In the steam washing tower, the washing liquid is specifically contacted with the secondary steam in countercurrent 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 detail 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 <10mg / m 3 .

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

[0070] In some embodiments, in step 5), before the secondary steam output from the fine slag preheater is subjected to superheating treatment, the secondary steam output from the fine slag preheater may be sent to a steam preheater to perform heat exchange with the flash steam obtained from the black water treatment unit in step 1); preferably, the flash steam used in the steam preheater is the high-pressure flash steam obtained from the high-pressure flash distillation. Preferably, in step 5), the flash steam after heat exchange with the secondary steam in the steam preheater is sent to a flash steam separation tank for vapor-liquid separation, and the condensate obtained by separation is sent to a steam scrubber for use as a washing liquid; the separated steam continues to enter downstream processing, such as sulfur recovery processing, etc.

[0071] 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. At the same time, the present invention directly contacts the gasified fine slag to be treated with superheated steam in the superheated steam drying device for heat exchange, which can effectively remove water from the gasified fine slag and reduce its water content. 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.

[0072] The present invention also provides a system capable of implementing the above-mentioned gasification fine slag dehydration method. Figure 1 The dehydration and drying system of the present invention mainly includes: a black water treatment unit 100, a fine slag preheater, a superheated steam drying device, a secondary steam dust removal unit and a steam superheater.

[0073] The black water treatment unit 100 is used to flash condense, settle and filter the coal gasification black water to obtain flash gas and gasification fine slag to be treated;

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

[0075] The superheated steam drying device is used 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;

[0076] A secondary steam dust removal unit is used to perform dust removal on the secondary steam outputted from the superheated steam drying device, thereby obtaining dust-removed secondary steam; the secondary steam dust removal unit is connected to the fine slag preheater to 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;

[0077] The steam superheater is used to superheat the secondary steam output by the fine slag preheater to obtain superheated steam; the steam superheater is connected to the superheated steam drying device to supply superheated steam to the superheated steam drying device, that is, the superheated steam required by the superheated steam drying device is supplied by the steam superheater.

[0078] 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 a 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, and then enters the fine slag preheater to preheat the gasified fine slag, and then enters the steam superheater to be superheated, and obtains superheated steam that is circulated in the superheated steam drying device. 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.

[0079] In some preferred embodiments, see Figure 1 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; 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 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.

[0080] 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.

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

[0082] More specifically, the sedimentation and filtration unit 102 includes a sedimentation tank and a filtration and dehydration device. The sedimentation tank is used to perform sedimentation treatment on the concentrated black water output from the flash concentration unit to obtain a slurry; the filtration and dehydration device is used to filter and dehydrate the slurry obtained after the sedimentation treatment to obtain the gasified fine slag to be treated. Preferably, the filtration and dehydration device specifically adopts a vacuum belt filter, a plate and frame filter, or a centrifugal dehydrator. 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.

[0083] In some preferred embodiments, Figure 1 As shown, the system of the present invention may further include a steam preheater for heat exchanging the secondary steam output by the fine slag preheater with the flash steam from the black water treatment unit, thereby obtaining preheated secondary steam. 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 is derived from the high-pressure flash steam output by the high-pressure flash tower.

[0084] In some specific embodiments, see Figure 1 The secondary steam dust removal unit includes a cyclone separator and a steam washing tower. The cyclone separator is connected to the superheated steam drying device, and is used to perform cyclone separation on the secondary steam output by the superheated steam drying device, so that it can be preliminarily dust-free. 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-free by washing liquid in the steam washing tower, thereby obtaining washing water and secondary steam after dust removal. Preferably, the washing water outlet of the steam washing tower is connected to the sedimentation tank.

[0085] In some specific embodiments, preferably, the flash gas outlet of the steam preheater is connected to the flash gas separation tank, which is used to separate the flash gas that has undergone heat exchange in 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 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 from the flash gas separation tank enters a downstream unit such as a sulfur recovery unit for further processing.

[0086] In some preferred 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 that has undergone heat exchange in 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.

[0087] In the system of the present invention, the superheated steam drying device can adopt conventional devices in the art, which can realize the function of direct contact heat exchange between superheated steam and gasified fine slag to be treated, such as but not limited to spray dryers, fluidized bed dryers, rotary dryers, disc dryers, etc. In some embodiments, the superheated steam drying device adopts a spray dryer; the superheated steam and the gasified fine slag to be treated are sprayed into the dryer through a feed nozzle, and the feed nozzle can adopt conventional feed nozzle types in the art, as long as it can realize the function of spraying superheated steam and gasified fine slag to be treated, such as various conventional nozzles such as spiral nozzles, and there is no special restriction on the specific selection of the feed nozzle.

[0088] The solution of the present invention is further illustrated below through application cases.

[0089] Example 1

[0090] The schematic diagram of the gasification fine slag dehydration system used in this embodiment is shown in Figure 1 Regarding the gasification fine slag dehydration system and method not specifically described below, please refer to the previous description and will not be described one by one.

[0091] 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:

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

[0093] 1.1) Flash concentration: send the coal gasification black water into a high-pressure flash tower, and at a pressure of 0.5MPa, 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;

[0094] 1.2) Sedimentation:

[0095] 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 90wt% anionic polyacrylamide and 10wt% coagulant (polyaluminum)) is added to accelerate the sedimentation of solids in the black water; a slurry with a solid content of 10wt% is precipitated at the bottom of the sedimentation tank (flow rate: 2000kg / h, temperature: 60°C, water content 90wt%), and the supernatant of the sedimentation tank is sent to a gray water tank;

[0096] 1.3) Filtration and dehydration:

[0097] The slurry settled out from the bottom of the sedimentation tank is sent to the filtering and dehydrating device (vacuum belt filter press) through the slurry pump for filtering and dehydration to obtain the gasification fine slag with a water content of 60wt% (flow rate: 500kg / h, temperature: 60℃), and the filtrate (flow rate: 1500kg / 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 32wt%, particles with a particle size of <45μm account for about 71wt%, and particles with a particle size of <100μm account for about 89wt%.

[0098] 2) Preheating of fine slag:

[0099] 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: 250kg / h) is sent to the ash water tank.

[0100] 3) Drying and dehydration:

[0101] The above-mentioned preheated gasified fine slag and superheated steam are fed into the spray dryer together through the feed nozzle (using a spiral nozzle, with a length-to-diameter ratio of 5:1). The superheated steam and the gasified fine slag are in direct contact in the superheated steam drying device, 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, flow rate: 7290kg / h). The secondary steam is discharged from the superheated steam drying device through the induced draft fan equipped with the superheated steam drying device, 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 250kg / h);

[0102] 4) Secondary steam dust removal:

[0103] The secondary steam discharged from the superheated steam drying device 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.

[0104] 5) Secondary steam preheating:

[0105] The secondary steam (temperature 144°C, pressure: 0.3MPa, flow rate: 7040kg / 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.

[0106] 6) Secondary steam superheating:

[0107] The preheated secondary steam (temperature 154°C, pressure: 0.3MPa, flow rate: 7040kg / h) is heat exchanged with black water (temperature: 220°C, pressure: 4.0MPa, flow rate 39300kg / h) from the gasifier quenching chamber in the steam superheater to form new superheated steam (temperature 190°C, pressure: 0.3MPa, flow rate: 7040kg / h); the superheated steam is circulated and sent to the superheated steam drying device in step 3) (in the initial stage of system operation, step 3) can use fresh superheated steam introduced from outside the system. 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.

[0108] Example 2

[0109] The schematic diagram of the dehydration and drying system used in this embodiment is shown in Figure 2 Regarding the gasification fine slag dehydration system and method not specifically described below, please refer to the previous description and will not be described one by one.

[0110] 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:

[0111] 1) Flash concentration, sedimentation and filtration

[0112] 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;

[0113] 1.2) Sedimentation:

[0114] 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, and the supernatant of the sedimentation tank is sent to a gray water tank;

[0115] 1.3) Filtration and dehydration:

[0116] The slurry settled out from the bottom of the sedimentation tank is sent to the filtering and dehydrating device (plate and frame filter) through the slurry pump for filtering and dehydration to obtain the gasified fine slag with a water content of 50wt% to be treated, 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 <45μm account for 5wt%, particles with a particle size of 45-125μm account for 16wt%, particles with a particle size of 125-500μm account for 76wt%, and particles with a particle size of >500μm account for 3wt%.

[0117] 2) Preheating of fine slag:

[0118] 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 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 is sent to the secondary steam separation tank for vapor-liquid separation, and the separated condensate is sent to the ash water tank;

[0119] 3) Drying and dehydration:

[0120] The preheated gasified fine slag is sent to a superheated steam drying device (specifically a fluidized bed dryer), and is directly in contact with the superheated steam in the superheated steam drying device. The gasified fine slag is heated, and 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. The secondary steam is discharged from the fluidized bed dryer through an induced draft fan equipped with the superheated steam drying device, 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 15%;

[0121] 4) Secondary steam dust removal:

[0122] The secondary steam discharged from the superheated steam drying device 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 separator 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.

[0123] 5) Secondary steam preheating:

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

[0125] 6) Secondary steam superheating:

[0126] The preheated secondary steam is heat exchanged with the raw coal gas (superheated medium, pressure 4.0MPa, temperature 210°C) from the gas washing tower to form new superheated steam; the superheated steam is circulated and sent to the superheated steam drying device in step 3) (in the initial stage of system operation, step 3) can use fresh superheated steam introduced from outside the system. 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)).

[0127] Example 3

[0128] The schematic diagram of the dehydration and drying system used in this embodiment is shown in Figure 2 Regarding the gasification fine slag dehydration system and method not specifically described below, please refer to the previous description and will not be described one by one.

[0129] 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:

[0130] 1) Flash concentration, sedimentation and filtration

[0131] 1.1) Flash concentration: send the coal gasification black water into a high-pressure flash tower, and at a pressure of 0.5MPa, 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 0.08MPa, the soluble gases in the black water are further flashed and released in a 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;

[0132] 1.2) Sedimentation:

[0133] 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 20% is precipitated at the bottom of the sedimentation tank, and the supernatant of the sedimentation tank is sent to a gray water tank;

[0134] 1.3) Filtration and dehydration:

[0135] The slurry settled at 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 the gasified fine slag with a water content of 60wt% to be treated, 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 33wt%, particles with a particle size of <45μm account for about 72wt%, and particles with a particle size of <100μm account for about 91wt%.

[0136] 2) Preheating of fine slag:

[0137] 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 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 is sent to the secondary steam separation tank for vapor-liquid separation, and the separated condensate is sent to the ash water tank;

[0138] 3) Drying and dehydration:

[0139] The preheated gasified fine slag and superheated steam are fed into the spray dryer together through a feed nozzle (using a spiral nozzle with a length-to-diameter ratio of 5:1). The gasified fine slag is directly in contact with the superheated steam in the superheated steam drying device, 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. The secondary steam is discharged from the fluidized bed dryer through the induced draft fan equipped with the superheated steam drying device, 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 10%;

[0140] 4) Secondary steam dust removal:

[0141] The secondary steam discharged from the superheated steam drying device 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 gas 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.

[0142] 5) Secondary steam preheating:

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

[0144] 6) Secondary steam superheating:

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

[0146] Table 1

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

[0148] Note: If there is any inconsistency between the data listed in Table 1 and the description of the previous embodiment, the data listed in Table 1 shall prevail.

[0149] It can be seen from the above embodiments that the dehydration and drying system and method of the present invention can effectively reduce the water content in the gasification fine slag, 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.

[0150] 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 gasified fine slag, characterized in that: The method comprises: 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; 2) sending the gasified fine slag to be treated into a fine slag preheater for preheating with a heat medium to obtain preheated gasified fine slag; 3) sending the preheated gasified fine slag into a superheated steam drying device to directly contact with the superheated steam for heat exchange, thereby obtaining dried gasified fine slag and secondary steam; 4) performing dust removal treatment on the secondary steam obtained in step 3) to obtain dust-removed secondary steam, and then feeding the secondary steam into the fine slag preheater in step 2) to be used as the heat medium; 5) superheating the secondary steam output from the fine slag preheater in step 2) to obtain superheated steam; sending the superheated steam to the superheated steam drying device in step 3) for heat exchange with the preheated gasified fine slag.

2. The method for dehydrating gasified fine slag according to claim 1, characterized in that: In step 5), 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 gasified fine slag according to claim 1, characterized in that: In step 5), the superheated medium used for the superheating treatment is coal gasification black water from the coal gasification system; the coal gasification black water from the coal gasification system is sent to the black water treatment unit in step 1) for treatment after the secondary steam is subjected to the superheating treatment in step 5); Alternatively, in step 5), the superheated medium used in the superheating treatment is raw coal gas from a coal gasification system.

4. The method for dehydrating gasified fine slag according to any one of claims 1 to 3, 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. Preferably, before performing the vacuum flash evaporation, the process further comprises performing low-pressure flash evaporation on the coal gasification black water. And / or, in step 1), the sedimentation is carried out in a sedimentation tank; And / or, 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; 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 step 5) for the superheating treatment; 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.

5. The method for dehydrating gasified fine slag according to claim 4, characterized in that: In step 5), before the secondary steam outputted from the fine slag preheater is subjected to the superheating treatment, the secondary steam outputted from the fine slag preheater is first sent to a steam preheater to perform heat exchange with the flash steam obtained from the black water treatment unit in step 1); preferably, the flash steam used in the steam preheater is the high-pressure flash steam obtained from the high-pressure flash evaporation; 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.

6. A system capable of implementing the gasification fine slag dehydration method according to any one of claims 1 to 5, characterized in that: The 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 to obtain preheated gasified fine slag; A superheated steam drying device, used for directly contacting the preheated gasified fine slag 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 by the superheated steam drying device; 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 superheater, used for superheating the secondary steam outputted from the fine slag preheater to obtain superheated steam; the steam superheater is connected to the superheated steam drying device to supply the superheated steam to the superheated steam drying device; 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, 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, and further preferably, a low-pressure flash tower is connected in series between the high-pressure flash tower and the vacuum flash tower; Preferably, the sedimentation filtration unit comprises a sedimentation tank and a filtering and dehydrating device, the sedimentation tank is used to perform sedimentation treatment on the concentrated black water output by the flash concentration unit, and the filtering and dehydrating device is used to filter and dehydrate the slurry obtained by the sedimentation treatment to obtain the gasified fine slag to be treated.

8. The system according to claim 7, characterized in that The system further comprises a steam preheater 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; Preferably, the flash gas outlet of the high-pressure flash tower is connected to the flash gas inlet of the steam preheater.

9. The system according to claim 7, characterized in that The secondary steam dust removal unit includes a cyclone separator and a steam scrubber; The cyclone separator is connected to the superheated steam drying device and is used for performing preliminary dust removal on the secondary steam output by the superheated steam drying device; 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 system according to claim 8, 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; 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