Method and system for dehydrating, drying and recycling gasified fine slag

Abstract

According to the gasification fine slag dewatering, drying and recycling method and system provided by the invention, by adopting the scheme, gasification fine slag with high water content can be dewatered and dried and can be used as fuel for resource utilization. The method comprises the following steps: 1) treating coal gasification black water in a black water treatment unit to obtain flash steam and gasification fine slag to be treated; 2) feeding the gasified fine slag to be treated into a fine slag preheater, and preheating by using a heating medium; (3) the preheated gasified fine slag is fed into a drying device to be subjected to heat exchange with superheated steam, and dried gasified fine slag and secondary steam are obtained; (4) the secondary steam is subjected to dust removal treatment, and the obtained secondary steam subjected to dust removal is fed into a fine slag preheater to serve as the heating medium; (5) the secondary steam output by the fine slag preheater is subjected to superheat treatment, and superheated steam is obtained; feeding the superheated steam into a drying device for heat exchange; and 6) feeding the dried gasified fine slag as fuel into a combustion unit for use.

Description

Technical Field

[0001] The invention relates to the technical field of gasification fine slag treatment, and in particular to a method and system for dehydrating, drying and recycling gasification fine slag. Background Art

[0002] With the rapid development of my country's coal chemical industry, the annual emission of gasification ash is increasing day by day, and its large-scale disposal and resource utilization are imminent. Gasification ash is mainly divided into gasification coarse slag and gasification fine slag. Gasification coarse slag is the large ash particles discharged from the ash lock bucket under the gasifier by gravity after the coal is captured by the furnace wall after hitting the gasifier, forming liquid slag. Gasification coarse slag usually has a low carbon content. Because its composition is similar to boiler ash, it can be used as a blending raw material for roads and building materials; gasification fine slag is fine mineral particles and unreacted carbon particles entrained out of the gasifier by synthesis gas. The loss on ignition of gasification fine slag is too large, exceeding national standards and industry standards, and the high residual carbon content hinders the gelling reaction between gasification fine slag and cement or lime, which seriously limits its application in building materials, construction and other fields.

[0003] Gasification ash has not yet been applied on a large scale industrially due to its large output, low utilization rate and high processing cost. Landfill is its main treatment method, which not only causes serious waste of land resources and environmental pollution, but also wastes a large amount of inorganic minerals and carbon resources in gasification ash. It is not in line with the current trend of "carbon peak and carbon neutrality" and is not conducive to the sustainable development of my country's coal chemical enterprises.

[0004] With the construction of ecological civilization and the implementation of the "solid waste resource" strategy in my country, the resource utilization of gasification ash is currently a hot topic. Since the gasification fine slag contains 20-40% residual carbon, it has a very considerable recycling value (sent to the boiler and gasifier for mixed combustion), but 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.

[0005] Since gasification fine slag has 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.

[0006] The 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 heating dehydration method consumes a lot of energy and has a low energy efficiency ratio. At the same time, there are problems such as large equipment investment and difficulty in daily maintenance and repair. In addition, the fine slag with high carbon residue after drying also has the risk of explosion in the air atmosphere.

[0007] 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.

[0008] How to achieve safe and energy-saving dehydration and drying of gasification fine slag and facilitate resource utilization of gasification fine slag is still one of the technical difficulties that urgently needs to be broken through in this field. Summary of the invention

[0009] The present invention provides a method and system for dehydrating, drying and recycling gasified fine slag. By adopting the scheme of the present invention, gasified fine slag with high water content can be dehydrated and dried and utilized as fuel for resource utilization, thereby fully utilizing the carbon resources in the gasified fine slag and solving the problem of difficulty in treating the gasified fine slag. Moreover, the present invention does not need to introduce hot air during the dehydration and drying process, and the secondary steam formed during the drying process can also be directly recycled in the system, so that 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] In one aspect, the present invention provides a method for dehydrating, drying and recycling gasified fine slag, the method comprising the following steps:

[0012] 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;

[0013] 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;

[0014] 3) sending the preheated gasified fine slag into a drying device to exchange heat with superheated steam to obtain dried gasified fine slag and secondary steam;

[0015] 4) performing dust removal treatment on the secondary steam obtained in step 3), and sending the obtained dust-removed secondary steam into the fine slag preheater in step 2) to be used as the heat medium;

[0016] 5) superheating the secondary steam output from the fine slag preheater to obtain superheated steam; sending the superheated steam to the drying device in step 3) for heat exchange;

[0017] 6) The dried gasified fine slag is sent to a combustion unit for use as fuel.

[0018] In some embodiments, in step 6), the combustion unit includes a coal-fired boiler or a gasifier;

[0019] Preferably, the combustion unit comprises a coal-fired boiler capable of generating superheated steam, and the superheated steam generated in the coal-fired boiler is fed into the drying device of step 3);

[0020] Preferably, the ash obtained after the gasified fine slag is burned in the combustion unit is used as an admixture in the field of building materials or construction;

[0021] Preferably, in step 6), the dried gasification fine slag is mixed with coal powder before use.

[0022] In some embodiments, 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 used to superheat the secondary steam in step 5) and then is sent to the black water treatment unit in step 1) for treatment; or, in step 5), the superheated medium used for the superheating treatment is raw coal gas from a coal gasification system.

[0023] Preferably, in step 3), the preheated gasified fine slag and the superheated steam are in direct contact for heat exchange in the drying device.

[0024] 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;

[0025] In step 1), the sedimentation is carried out in a sedimentation tank;

[0026] 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;

[0027] 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.

[0028] 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 for heat exchange with the high-pressure flash steam obtained by the high-pressure flash evaporation;

[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] The present invention also provides a system capable of implementing the above-mentioned method for dehydrating, drying and recycling gasified fine slag, the system comprising:

[0031] 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;

[0032] A fine slag preheater, used for preheating the gasified fine slag to be treated using a heat medium to obtain preheated gasified fine slag;

[0033] A drying device, used for exchanging heat between the preheated gasified fine slag and superheated steam to obtain dry gasified fine slag and secondary steam;

[0034] A secondary steam dust removal unit is used to perform dust removal on the secondary steam output by the 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;

[0035] A steam superheater, used for superheating the secondary steam outputted from the fine slag preheater to obtain superheated steam; the superheated steam outlet of the steam superheater is connected to the drying device;

[0036] A combustion unit, the combustion unit being connected to the drying device and used for using the dried gasified fine slag as fuel;

[0037] 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 coal gas outlet of the coal gasification system through a raw coal gas delivery pipeline;

[0038] Preferably, the drying device is a device that enables the preheated gasified fine slag to directly contact and exchange heat with the superheated steam.

[0039] In some embodiments, the combustion unit includes a coal-fired boiler or a gasifier; preferably, the combustion unit includes a coal-fired boiler capable of generating superheated steam, and the superheated steam outlet of the coal-fired boiler is connected to the drying device; preferably, the combustion unit also includes a fuel mixing device for mixing the dried gasified fine slag with coal powder.

[0040] In some embodiments, the black water treatment unit includes a flash evaporation concentration unit and a sedimentation filtration unit; the flash evaporation concentration unit is used to flash and concentrate the coal gasification black water to obtain the flash gas and concentrated black water; the sedimentation filtration unit is used to sediment and filter and dehydrate the concentrated black water to obtain the gasification fine slag to be treated;

[0041] 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;

[0042] 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.

[0043] In some embodiments, the system further comprises a steam preheater for performing heat exchange between the secondary steam outputted by the fine slag preheater and the high-pressure flash steam outputted by the high-pressure flash tower to obtain preheated secondary steam;

[0044] The secondary steam dust removal unit comprises a cyclone separator and a steam washing tower, wherein the cyclone separator is used to perform preliminary dust removal on the secondary steam output by the drying device, and the steam washing tower is used to wash and remove dust from the secondary steam that has undergone the preliminary dust removal with a washing liquid to obtain washing water and the secondary steam after dust removal; the washing water outlet of the steam washing tower is connected to the sedimentation tank;

[0045] The flash steam outlet of the steam preheater is connected to a flash steam separation tank for separating the flash steam output by the steam preheater into vapor and liquid and obtaining condensate; the condensate outlet of the flash steam separation tank is connected to the washing liquid inlet of the steam washing tower.

[0046] In some embodiments, the secondary steam outlet of the fine slag preheater is connected to a secondary steam separation tank through a pipeline, so as to separate the secondary steam outputted from the fine slag preheater into vapor and liquid and obtain condensate; the vapor phase outlet of the secondary steam separation tank is connected to the secondary steam inlet of the steam preheater;

[0047] 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.

[0048] The technical solution provided by the present invention has the following beneficial effects:

[0049] The method and system provided by the present invention remove most of the moisture in the gasified fine slag by heat exchange with superheated steam in a drying device, 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, improves the energy density of gasified fine slag, but also saves transportation and processing costs, improves the plant environment, and improves the water resource utilization efficiency of coal gasification.

[0050] At the same time, the secondary steam output from the drying device 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 is fully utilized, and then it is heated to form superheated steam, which is returned to the drying device for reuse. In this way, not only the heat of the secondary steam is reasonably and fully reused, but also the waste of water resources is reduced. In addition, the scheme of the present invention does not need to introduce hot air, has good safety, and is energy-saving and environmentally friendly.

[0051] The present invention dehydrates and dries the gasified fine slag and then sends it to a combustion unit for combustion as fuel. The released heat can be used in a coal-fired boiler to produce superheated steam, or can be used for blending in a gasifier, so that the carbon resources in the gasified fine slag can be fully utilized and the problem of difficulty in handling the gasified fine slag can be solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 A schematic diagram of a gasification fine slag dehydration, drying and recycling system in one embodiment;

[0053] Figure 2 Schematic diagram of a gasification fine slag dehydration, drying and recycling system in another embodiment. DETAILED DESCRIPTION

[0054] 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.

[0055] 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.

[0056] 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.

[0057] The present invention provides a method for dehydrating, drying and recycling gasified fine slag, which mainly comprises the following steps:

[0058] 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;

[0059] 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;

[0060] 3) sending the preheated gasified fine slag into a drying device to exchange heat with superheated steam to obtain dried gasified fine slag and secondary steam;

[0061] 4) performing dust removal treatment on the secondary steam obtained in step 3), and sending the obtained dust-free secondary steam into the fine slag preheater in step 2) as the heat medium for heat exchange with the gasified fine slag to be treated;

[0062] 5) superheating the secondary steam output from the fine slag preheater to obtain superheated steam; sending the superheated steam to the drying device in step 3) for the heat exchange, so that the gasified fine slag can be dehydrated and dried to obtain dry gasified fine slag, and obtain secondary steam again.

[0063] 6) The dried gasified fine slag is fed into the combustion unit as fuel for use. The residual carbon contained in the gasified fine slag is fully utilized in the combustion unit.

[0064] The present invention uses the above method, and does not need to introduce air or heat the air to achieve the drying of gasified fine slag; the present invention uses superheated steam to perform heat exchange with gasified fine slag in the drying device, 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 at the same time, thereby removing most of the moisture in the fine slag and obtaining gasified fine slag with low moisture content. Not only does it meet the current needs of environmental protection and fine slag resource utilization, but it can also greatly reduce the amount of fine slag to be transported; at the same time, the secondary steam output from the 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 under the condition of reducing the amount of superheated steam), and then it is superheated to form superheated steam, and the superheated steam is returned to the 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. The water content of the dried gasification fine slag obtained through the above process can be greatly reduced, which can meet the combustion requirements and can be sent to the combustion unit for combustion and further utilization.

[0065] In the present invention, superheated steam is used as the drying medium in the 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 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 fine slag with high carbon residue exploding in the air atmosphere during the drying process.

[0066] 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.

[0067] 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.

[0068] In the present invention, the moisture content of the obtained gasified fine slag is greatly reduced, and it has an improved energy density, which can greatly reduce the impact of co-firing on the boiler combustion system. In step 6), the combustion unit includes a coal-fired boiler or a gasifier, that is, the dried gasified fine slag can be sent to the coal-fired boiler for combustion, or sent to the gasifier for co-firing, so that the carbon resources in the gasified fine slag are fully utilized. The ash obtained after the gasified fine slag is burned in the combustion unit (such as a coal-fired boiler) can be used as an admixture in the field of building materials or construction, for example, as an admixture for cement, etc., which can further reduce the difficulty and cost of handling the gasified fine slag and improve its utilization value.

[0069] Preferably, the combustion unit in step 6) includes a coal-fired boiler capable of generating superheated steam, that is, the dried gasified fine slag is fed into the coal-fired boiler for combustion, and the heat is used to heat and generate superheated steam. The superheated steam generated in the coal-fired boiler is fed into the drying device in step 3) for heat exchange with the gasified fine slag to be treated. In step 6), the dried gasified fine slag is mixed with coal powder for use.

[0070] 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.

[0071] In the present invention, preferably, in step 3), the preheated gasified fine slag and the superheated steam are in direct contact and heat exchange in the drying device.

[0072] 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 also includes 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 described in detail. Flash gas and concentrated black water are obtained through the above-mentioned flash concentration.

[0073] In some specific embodiments, in step 1), sedimentation is carried out in a sedimentation tank, and a slurry and a supernatant (i.e., ash water) are obtained by sedimentation. During the sedimentation process, a flocculant can be added to promote solid sedimentation, which is a conventional operation in the art and will not be described in detail. Specifically, the supernatant is sent to the downstream ash 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 ash water tank. The water in the ash water tank can be reused in the coal gasification system.

[0074] In some embodiments, in step 4), the dust removal treatment of the secondary steam output by the 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 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 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 <10 mg / m 3 .

[0075] Preferably, in the fine slag preheater of step 2), the secondary steam used as the heat medium is output and sent to the secondary steam separation tank for vapor-liquid separation after heat exchange with the gasified fine slag, and then sent to step 5) for superheating treatment. 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.

[0076] Preferably, 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 is first sent to the steam preheater for heat exchange with the high-pressure flash steam obtained from the high-pressure flash tower. Preferably, in step 5), the high-pressure flash steam after heat exchange with the secondary steam in the steam preheater is sent to the flash steam separation tank for vapor-liquid separation, and the condensate obtained by separation is sent to the steam washing tower for use as washing liquid; the separated steam continues to enter the downstream treatment, such as sulfur recovery treatment, etc.

[0077] In the present invention, superheated steam is used as the drying medium, which has a higher specific heat capacity (1.968 kJ / (kg·K)) and a stronger heat exchange capacity compared with low-temperature flue gas and hot air; at the same time, the present invention exchanges heat between the gasified fine slag to be treated and the superheated steam in the drying device, which can effectively remove the water in the gasified fine slag, reduce its water content, improve energy density, and facilitate use as fuel in the combustion unit. 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.

[0078] The present invention also provides a system capable of implementing the above-mentioned gasification fine slag dehydration, drying and recycling method, see Figure 1 The system mainly includes: a black water treatment unit, a fine slag preheater, a drying device, a secondary steam dust removal unit, a steam superheater and a combustion unit.

[0079] The black water treatment unit is used to flash condense, settle and filter the coal gasification black water to obtain flash gas and gasification fine slag to be treated;

[0080] A fine slag preheater, used for preheating the gasified fine slag to be treated using a heat medium, thereby obtaining preheated gasified fine slag;

[0081] A superheated steam drying device is used to contact the preheated gasified fine slag with superheated steam for heat exchange, so that the moisture in the gasified fine slag is removed, the moisture is vaporized into steam and forms secondary steam together with the surrounding superheated steam, thereby obtaining dry gasified fine slag and secondary steam;

[0082] The secondary steam dust removal unit is used to perform dust removal on the secondary steam output by the 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;

[0083] A steam superheater is used to superheat the secondary steam output from the fine slag preheater to obtain superheated steam; the steam superheater is connected to the drying device to supply superheated steam to the drying device;

[0084] A combustion unit is connected to the drying device and is used to use the dried gasified fine slag as fuel, so that the carbon resources in the dried gasified fine slag are fully utilized.

[0085] The gasified fine slag is dehydrated, dried and reused by the above system, and the gasified fine slag is dried and dehydrated efficiently, safely and environmentally friendly by using superheated steam. There is no explosion hazard caused by the contact between hot air and dry gasified fine slag with high carbon content, and the energy utilization rate is higher. Moreover, no air is introduced into the system, and the secondary steam airflow mainly composed of steam is generated during the drying and dehydration process, which can be recycled without going through a complex 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, and then enters the steam superheater to be superheated, and obtains superheated steam for circulation in the superheated steam drying device. The ingenious design of the whole 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. At the same time, the dried gasified fine slag is sent to the combustion unit as fuel for continued use, which can make full use of the carbon resources therein, and is conducive to solving the problem of difficulty in treating the gasified fine slag.

[0086] In some preferred embodiments, see Figure 1The superheated medium inlet of the steam superheater is connected to the raw coal gas outlet of the coal gasification system through a raw coal gas transmission pipeline, that is, the superheated medium required in the steam superheater is the raw coal gas of the coal gasification system; specifically, Figure 1 As shown, the synthesis gas produced by the gasifier enters the raw gas scrubber for scrubbing and dust removal, and the raw gas obtained is used as the above-mentioned superheated medium and passed into the steam superheater. As another embodiment, see Figure 2 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.

[0087] In the present invention, the combustion unit includes a coal-fired boiler or a gasifier; Figure 1 The coal-fired unit shown specifically includes a coal-fired boiler. Figure 1 As shown, the coal-fired boiler in the combustion unit is a coal-fired boiler capable of producing superheated steam, and the superheated steam outlet of the coal-fired boiler is connected to the drying device to supply fresh superheated steam to the drying device. Figure 1 As shown, the combustion unit also includes a fuel blending device, in which the dried gasified fine slag obtained by the drying device is blended with coal powder and then sent to the coal-fired boiler for combustion. The ash obtained after the combustion of the gasified fine slag can be further utilized as a blending material in the field of building materials or construction.

[0088] In some embodiments, the black water treatment unit specifically includes a flash evaporation and concentration unit and a sedimentation and filtration unit. The flash evaporation and concentration unit is used to flash and concentrate the coal gasification black water to obtain flash gas and concentrated black water; the sedimentation and filtration unit is used to sediment and filter the concentrated black water to obtain gasification fine slag to be treated. Figure 1 The flash concentration unit comprises a high-pressure flash tower and a vacuum flash tower connected in series; in some embodiments, Figure 2 As shown, a low-pressure flash tower can be connected in series between the high-pressure flash tower and the vacuum flash tower.

[0089] Specifically, Figure 1 As shown, the sedimentation and filtration unit 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 by 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 or a plate and frame filter or a centrifugal dehydrator. Figure 1As 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.

[0090] In some preferred embodiments, the system of the present invention also includes a steam preheater for exchanging heat between the secondary steam output from the fine slag preheater and the high-pressure flash steam output from the high-pressure flash tower of the black water treatment unit before entering the steam superheater, thereby obtaining preheated secondary steam.

[0091] 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 drying device and is used to perform cyclone separation on the secondary steam output by the drying device 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.

[0092] In some embodiments, 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 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 from the flash gas separation tank enters a downstream unit such as a sulfur recovery unit for further processing.

[0093] 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 separate the secondary steam that has undergone heat exchange in the fine slag preheater into vapor and liquid and obtain condensate; the vapor phase outlet of the secondary steam separation tank is connected to the secondary steam inlet of the steam preheater, that is, the secondary steam after vapor-liquid separation can enter the steam preheater for preheating treatment. 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.

[0094] In the system of the present invention, the drying device can be a conventional device in the art, preferably a drying device that can achieve direct contact heat exchange between superheated steam and the gasified fine slag to be treated, such as but not limited to a spray dryer, a fluidized bed dryer, a rotary dryer, a disc dryer, etc.

[0095] The solution of the present invention is further illustrated below through application cases.

[0096] Example 1

[0097] Taking the coal gas methanol plant with an annual output of 1.8 million tons as an example, the water-coal slurry fluidized bed process is used to produce 120,000 tons of wet-based gasification fine slag (water content of 60%) per year. At present, the gasification fine slag is mainly transported to the slag field for landfill treatment by truck, and the transportation and landfill treatment costs 6 million yuan per year. The indicators of the coal used in the power boiler of the methanol plant are: ash content (received basis) is 14.37%, total water content is 21%, and the low calorific value is 19.85MJ / kg. The industrial analysis, calorific value and composition results of the gasification fine slag are as follows:

[0098] Table 1 Industrial analysis and ignition loss of gasification fine slag (water content 60%)

[0099]

[0100] The method and system of the present invention are used to dehydrate and dry the coal gasification black water of the manufacturer for reuse. Figure 1 As shown, the system and method not specifically described can be referred to the above description, and will not be described one by one. In this embodiment, the drying, dehydration and reuse of gasified fine slag includes the following processing steps:

[0101] 1) Flash concentration, sedimentation and filtration

[0102] 1.1) Flash concentration:

[0103] The black water from the quenching chamber of the gasifier and the black water from the raw gas scrubber enter the high-pressure flash tower, and part of the soluble gas is flashed and released from the black water at a pressure of 0.6 MPa. The black water at the bottom of the high-pressure flash tower enters the vacuum flash tower, and is further flashed at -0.5 MPa to obtain concentrated black water.

[0104] 1.2) Sedimentation:

[0105] The concentrated black water obtained in step 1.1) is sent to a sedimentation tank for gravity sedimentation solid-liquid separation, and a composite flocculant (85wt% anionic polyacrylamide and 15wt% coagulant (polyaluminum)) is added to accelerate the solid sedimentation in the black water; a slurry with a solid content of 20wt% is precipitated at the bottom of the sedimentation tank (flow rate: 30t / h, temperature: 60°C, water content 80wt%), and the supernatant of the sedimentation tank enters the gray water tank;

[0106] 1.3) Filtration and dehydration:

[0107] The slurry at the bottom of the sedimentation tank in step 1.2) is pumped to a filtration and dehydration device (vacuum belt filter) for filtration and dehydration to obtain gasified fine slag with a water content of 60wt% to be treated (flow rate: 15t / h, temperature: 60°C), and the filtrate is pumped back to the ash water tank by a water pump.

[0108] 2) Preheating of fine slag:

[0109] 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: 7.5t / h) is sent to the ash water tank.

[0110] 3) Drying and dehydration:

[0111] The preheated gasified fine slag and filtered steam are simultaneously fed into the drying device (fluidized bed dryer). The superheated steam directly contacts the gasified fine slag in the drying device, and the gasified fine slag is heated, so that 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, 226.2t / h). The secondary steam is discharged from the drying device by the induced draft fan equipped with the 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 7.5t / h).

[0112] Table 2 Industrial analysis and ignition loss of dried gasified fine slag (water content 20%)

[0113]

[0114] 4) Secondary steam dust removal:

[0115] The secondary steam discharged from the 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.

[0116] 5) Secondary steam preheating:

[0117] The secondary steam (temperature 144°C, pressure: 0.3MPa, flow rate: 218.7kg / 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.

[0118] 6) Secondary steam superheating:

[0119] The preheated secondary steam (temperature 150°C, pressure: 0.30MPa, flow rate: 218.7kg / h) is heat exchanged with the raw gas from the raw gas washing tower to form new superheated steam (temperature 190°C, 0.3MPa, 218.7kg / h); the superheated steam is circulated to the drying device of 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 introduced into step 3)).

[0120] 7) Boiler blending:

[0121] The dried gasified fine slag (7.5 t / h, 20% water content) obtained in step 3) is transported to the coal blending device, and the coal powder is mixed with the gasified fine slag and then sent to the coal-fired boiler for combustion treatment, so as to make full use of the residual carbon resources in the gasified fine slag. The superheated steam produced in the coal-fired boiler can be used as fresh superheated steam and sent to the drying device for use.

[0122] The above method can save 22,400 tons of coal per year (the residual carbon conversion rate in fine slag is 92%). According to the local average price of fuel coal of 380 yuan per ton, the annual coal cost can be saved by 8.512 million yuan. The ash produced by the gasification fine slag boiler can be used as a raw material for cement blending, thus saving 6 million yuan per year in transportation and landfill treatment of gasification fine slag.

[0123] In this embodiment, the gray water in the gray water tank is used as washing water for the raw gas washing tower.

[0124] 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, drying and recycling gasification fine slag, characterized in that: The method comprises the following steps: 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 drying device to exchange heat with superheated steam to obtain dried gasified fine slag and secondary steam; 4) performing dust removal treatment on the secondary steam obtained in step 3), and sending the obtained dust-removed 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 to obtain superheated steam; sending the superheated steam to the drying device in step 3) for heat exchange; 6) The dried gasified fine slag is sent to a combustion unit for use as fuel.

2. The method for dehydrating, drying and recycling gasified fine slag according to claim 1, characterized in that: In step 6), the combustion unit includes a coal-fired boiler or a gasifier; Preferably, the combustion unit comprises a coal-fired boiler capable of generating superheated steam, and the superheated steam generated in the coal-fired boiler is fed into the drying device of step 3); Preferably, the ash obtained after the gasified fine slag is burned in the combustion unit is used as an admixture in the field of building materials or construction; Preferably, in step 6), the dried gasification fine slag is mixed with coal powder before use.

3. The method for dehydrating, drying and recycling gasified fine slag according to claim 1, characterized in that: In step 5), the superheated medium used in 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); or, in step 5), the superheated medium used in the superheating treatment is raw coal gas from a coal gasification system; And / or, in step 3), the preheated gasified fine slag and the superheated steam are directly contacted and heat exchanged in the drying device.

4. The method for dehydrating, drying and recycling 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. 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, 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, drying and recycling gasified fine slag according to claim 4, characterized in that: 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 high-pressure flash steam obtained by 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 method for dehydrating, drying and recycling gasified fine slag 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 drying device, used for exchanging heat between the preheated gasified fine slag and superheated steam 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 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 superheated steam outlet of the steam superheater is connected to the drying device; A combustion unit, the combustion unit being connected to the drying device and used for using the dried gasified fine slag as fuel; 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 coal gas outlet of the coal gasification system through a raw coal gas delivery pipeline; Preferably, the drying device is a device capable of directly contacting the preheated gasified fine slag with the superheated steam for heat exchange.

7. The system according to claim 6, characterized in that The combustion unit comprises a coal-fired boiler or a gasifier; preferably, the combustion unit comprises a coal-fired boiler capable of generating superheated steam, and the superheated steam outlet of the coal-fired boiler is connected to the drying device; preferably, the combustion unit also comprises a fuel blending device for blending the dried gasified fine slag with coal powder.

8. The system according to claim 6 or 7, characterized in that: The black water treatment unit includes a flash evaporation and concentration unit and a sedimentation and filtration unit; the flash evaporation and 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 gasification 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.

9. The system according to claim 8, characterized in that The system further comprises a steam preheater for performing heat exchange between the secondary steam outputted by the fine slag preheater and the high-pressure flash steam outputted by the high-pressure flash tower to obtain preheated secondary steam; The secondary steam dust removal unit comprises a cyclone separator and a steam washing tower, wherein the cyclone separator is used to perform preliminary dust removal on the secondary steam output by the drying device, and the steam washing tower is used to wash and remove dust from the secondary steam that has undergone the preliminary dust removal with a washing liquid to obtain washing water and the secondary steam after dust removal; the washing water outlet of the steam washing tower is connected to the sedimentation tank; The flash steam outlet of the steam preheater is connected to a flash steam separation tank for separating the flash steam output by the steam preheater into vapor and liquid and obtaining condensate; the condensate outlet of the flash steam separation tank is connected to the washing liquid inlet of the steam washing tower.

10. The system according to claim 9, characterized in that The secondary steam outlet of the fine slag preheater is connected to the secondary steam separation tank through a pipeline, which is used to separate the secondary steam output by the fine slag preheater into vapor and liquid 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 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.

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