A method and system for dewatering and drying gasified fine slag for reuse

Abstract

The present application provides a kind of gasification fine slag dewatering drying recycling method and system, using the scheme of the present application, can carry out dewatering drying to high water content gasification fine slag and be used as fuel and be used as resource.The method comprises the following steps: 1) coal gasification black water is treated in black water treatment unit, and flash gas and the gasification fine slag to be treated are obtained;2) the gasification fine slag to be treated is sent into fine slag preheater and is preheated with heat medium;3) the preheated gasification fine slag is sent into drying device and exchanges heat with superheated steam, and dry gasification fine slag and secondary steam are obtained;4) secondary steam is treated by dust removal, and the obtained dust removal secondary steam is sent into fine slag preheater and used as the heat medium;5) the secondary steam output from fine slag preheater is superheated, and superheated steam is obtained;superheated steam is sent into drying device for the heat exchange;6) dry gasification fine slag is sent into combustion unit as fuel and used.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gasification fine slag treatment, and particularly relates to a gasification fine slag dewatering and drying recycling method and system. BACKGROUND

[0002] With the rapid development of coal chemical industry in China, the annual emission of gasification ash is increasing, and its large-scale disposal and resource utilization is imminent. Gasification ash is mainly divided into gasification coarse slag and gasification fine slag. Gasification coarse slag is a large particle ash discharged from the gasification furnace under the action of gravity after the coal is impacted on the gasification furnace and the liquid ash slag is formed. Gasification coarse slag usually has low carbon content, and can be used as a mixed raw material for roads and building materials because of its similar composition to boiler ash; gasification fine slag is a fine mineral particle and unreacted carbon particle carried out of the gasification furnace by synthetic gas. The ignition loss of gasification fine slag is too large to meet the national and industry standards, and the high residual carbon content hinders the cementation reaction between gasification fine slag and cement or lime, which seriously limits its application in the fields of building materials, construction, etc.

[0003] Gasification ash has not been widely used in large-scale industrial applications due to its large output, low utilization rate and high treatment cost. Landfill is the main disposal method, which not only causes serious land resource waste and environmental pollution problems, but also wastes a large amount of inorganic minerals and carbon resources in gasification ash, which is not in line with the current trend of "carbon peak and carbon neutralization", and is not conducive to the sustainable development of China's coal chemical enterprises.

[0004] With the implementation of China's ecological civilization construction and "solid waste resourceization" strategy, the resource utilization of gasification ash is currently a hot topic. Gasification fine slag contains 20-40% of residual carbon, which has considerable recycling value (mixed burning into boilers and gasification furnaces), but due to the high moisture content of fine slag, it not only reduces the calorific value of gasification fine slag, but also easily causes problems such as sticking, jamming and corrosion, which seriously affects the harmless treatment and resource utilization of gasification fine slag.

[0005] Due to the characteristics of gasification fine slag such as rich pore structure, large specific surface area and small particle size, it has strong adhesion and adsorption performance to water molecules; in addition, flocculants such as polyacrylamide need to be added in the coal chemical black water sedimentation process, and the flocculants and fine slag particles in the black water coagulate into a group to form a flocculated colloidal structure, which has strong water holding capacity, thereby causing difficulty in dewatering gasification fine slag. Due to the structural characteristics and water holding characteristics of gasification fine slag, it is obviously different from other particles such as raw coal (such as lignite), and it is difficult to directly apply or learn from the dewatering treatment process of other materials such as lignite.

[0006] The heating dewatering technology uses dry medium such as hot air, hot flue gas and steam to reduce the moisture of the gasified fine slag by evaporating the dry gasified fine slag. Common heating dewatering equipment includes rotary dryers, disc dryers and the like. However, the heating dewatering method consumes a large amount of energy and has a low energy efficiency ratio. Meanwhile, the method has problems such as large equipment investment and difficult routine maintenance and repair work. In addition, the fine slag with a high residual carbon content after drying has an explosive hazard in an air atmosphere.

[0007] Patent application CN201710321402 discloses a coal gasification system fine slag slurry dewatering and drying method, which comprises the following steps: (a) the fine slag slurry generated by the coal gasification system is subjected to pre-dewatering by a pre-dewatering and thickening device to obtain thickened fine slag slurry; (b) the waste heat resources generated by the coal gasification system are subjected to heat exchange with air, and the air is heated into hot air; (c) the thickened fine slag slurry and the hot air are simultaneously fed into a spray dryer, the thickened fine slag slurry and the hot air are directly contacted and heat transferred in the spray dryer, and the fine slag is obtained after most of the water is removed through the bottom. However, the method uses hot air as a heat source, the heat capacity of air is relatively small, a large amount of hot air is required, the heat efficiency of the waste heat for heating air is low, and the efficiency of the gasified fine slag drying system is relatively low. Meanwhile, a large amount of water vapor is mixed with air in the drying process, the waste heat energy cannot be recovered, a large amount of energy is wasted, the wet drying tail gas at the outlet of the spray dryer contains a large amount of air, the heat exchange efficiency coefficient of the air and the circulating water is low, a large amount of cooling water is required to cool the tail gas in the tail gas condenser, the condensation load of the wet drying tail gas condenser is high, and the exhaust gas emission is also relatively high. In addition, a large amount of tail gas mixed with air and water vapor is generated at the outlet of the dryer through the process, the tail gas is usually directly discharged, so that heat is wasted; or the tail gas needs to be cooled and then subjected to gas-liquid separation, and then discharged, which also causes heat waste; and if the hot air is expected to be recycled, the water content in the air needs to be reduced by deep dewatering of the tail gas, so that the hot air can be reused, however, a large amount of cooling water needs to be used to exchange heat to realize gas-liquid separation, and a large amount of heat needs to be input to the separated air again, which causes the phenomenon of cold and heat.

[0008] How to realize safe, energy-saving dewatering and drying of the gasified fine slag and facilitate the resource utilization of the gasified fine slag is still one of the technical difficulties to be broken through in the field. SUMMARY

[0009] The present application provides a kind of gasification fine slag dewatering drying recycling method and system, using the scheme of the present application, high water content gasification fine slag can be dewatered and dried and used as fuel for resource utilization, carbon resources in gasification fine slag are fully utilized, and the problems such as difficulty in gasification fine slag processing are solved;And the present application does not need to introduce hot air in the dewatering drying process, the secondary steam formed in the drying process can also be directly recycled in the system, the system water resources and energy can be fully and reasonably reused, the energy utilization rate is high, water resource waste is less, and the system safety is good.

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

[0011] The present application provides a kind of gasification fine slag dewatering drying recycling method, the method includes the following steps:

[0012] 1) coal gasification black water is concentrated by flash evaporation, settled and filtered in a black water treatment unit, to obtain flash evaporation gas and gasification fine slag to be treated;

[0013] 2) the gasification fine slag to be treated is sent to a fine slag preheater for preheating with a heat medium, to obtain preheated gasification fine slag;

[0014] 3) the preheated gasification fine slag is sent to a drying device for heat exchange with superheated steam, to obtain dried gasification fine slag and secondary steam;

[0015] 4) the secondary steam obtained in step 3) is subjected to dust removal treatment, and the dust-removed secondary steam is sent to the fine slag preheater in step 2) for use as the heat medium;

[0016] 5) the secondary steam output from the fine slag preheater is subjected to superheating treatment to obtain superheated steam, which is sent to the drying device in step 3) for the heat exchange;

[0017] 6) the dried gasification fine slag is sent to a combustion unit as fuel.

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

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

[0020] Preferably, the ash obtained after the gasification fine slag is burned in the combustion unit is used as building material or admixture in the construction field.

[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 superheating medium used in the superheating treatment is coal gasification black water from a coal gasification system; the coal gasification black water from the coal gasification system is sent into the black water treatment unit in step 1) for treatment after the superheating treatment of the secondary steam in step 5); or, in step 5), the superheating medium used in the superheating treatment is coal gasification raw gas from a coal gasification system.

[0023] Preferably, in step 3), the preheated gasification fine slag and the superheated steam are directly contacted and heat-exchanged in the drying device.

[0024] In some embodiments, in step 1), the flash concentration includes sequentially performing high-pressure flash evaporation and vacuum flash evaporation on the coal gasification black water, and preferably, before the vacuum flash evaporation, the operation of low-pressure flash evaporation on the coal gasification black water is further included;

[0025] In step 1), the sedimentation is performed in a sedimentation tank.

[0026] In step 4), the dust removal treatment includes preliminarily removing dust from the secondary steam obtained in step 3) by a cyclone separator, and then washing and removing dust from the secondary steam in a steam washing tower; preferably, the washing water obtained by washing and removing dust in the steam washing tower is sent into the sedimentation tank.

[0027] Preferably, in step 2), the secondary steam output from the fine slag preheater is sent into a secondary steam separation tank for vapor-liquid separation, and then sent into step 5) for the superheating treatment; part of the condensate separated in the secondary steam separation tank is sent into a grey water tank or into the steam washing tower for use as washing liquid.

[0028] In some embodiments, in step 5), before the superheating treatment of the secondary steam output from the fine slag preheater, the secondary steam output from the fine slag preheater is sent into a steam preheater for heat exchange with the high-pressure flash gas obtained by high-pressure flash evaporation;

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

[0030] The present application also provides a system capable of implementing the gasification fine slag dewatering and drying recycling method described above, and the system comprises:

[0031] a black water treatment unit for performing flash concentration, sedimentation and filtration dewatering on coal gasification black water, and obtaining flash gas and gasification fine slag to be treated;

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

[0033] a drying device for exchanging heat between the preheated fine slag and superheated steam to obtain dried fine slag and secondary steam;

[0034] a secondary steam dust removal unit for dust removal of the secondary steam output from the drying device; the secondary steam dust removal unit is connected with the fine slag preheater to deliver the dust-removed secondary steam to the fine slag preheater as the heat medium;

[0035] a steam superheater for superheating the secondary steam output from the fine slag preheater to obtain superheated steam; the superheated steam outlet of the steam superheater is connected with the drying device;

[0036] a combustion unit connected with the drying device for using the dried fine slag as fuel;

[0037] Preferably, the superheated medium inlet of the steam superheater is connected with a coal gasification black water delivery pipeline of a coal gasification system, and the superheated medium outlet of the steam superheater is connected with the black water treatment unit through a pipeline; or, the superheated medium inlet of the steam superheater is connected with a raw coal gas outlet of a coal gasification system through a raw coal gas delivery pipeline.

[0038] Preferably, the drying device is a device capable of directly contacting and exchanging heat between the preheated fine slag and the superheated steam.

[0039] In some embodiments, 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 with the drying device; preferably, the combustion unit further comprises a fuel blending device for blending the dried fine slag with coal powder.

[0040] In some embodiments, the black water treatment unit comprises a flash concentration unit and a sedimentation filtration unit; the flash concentration unit is used for flashing and concentrating the coal gasification black water to obtain the flash gas and concentrated black water; the sedimentation filtration unit is used for sedimentation and filtration dehydration of the concentrated black water to obtain the 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; further preferably, a low-pressure flash tower is further connected in series between the high-pressure flash tower and the vacuum flash tower.

[0042] Preferably, the settling filtration unit comprises a settling tank for settling treatment of the concentrated black water output by the flash concentration unit, and a filter dewatering device for filter dewatering of the slurry obtained by the settling treatment to obtain the fine gasification slag to be treated.

[0043] In some embodiments, the system further comprises a steam preheater for heat exchange of the secondary steam output by the fine slag preheater with the high-pressure flash gas output by the high-pressure flash tower to obtain preheated secondary steam.

[0044] The secondary steam dust removal unit comprises a cyclone separator for primary dust removal of the secondary steam output by the drying device, and a steam scrubbing tower for scrubbing dust removal of the secondary steam subjected to the primary dust removal with a washing liquid to obtain washing water and dust-removed secondary steam; the washing water outlet of the steam scrubbing tower is connected with the settling tank.

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

[0046] In some embodiments, the secondary steam outlet of the fine slag preheater is connected with a secondary steam separation tank through a pipeline for vapor-liquid separation of the secondary steam output by the fine slag preheater and obtaining condensate; the vapor phase outlet of the secondary steam separation tank is connected with the secondary steam inlet of the steam preheater.

[0047] Preferably, the condensate outlet of the secondary steam separation tank is connected with a grey water tank, or the condensate outlet of the secondary steam separation tank is connected with the washing liquid inlet of the steam scrubbing tower.

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

[0049] The method and system provided by the present application can heat exchange the fine gasification slag to be treated with superheated steam in the drying device to remove most of the water in the fine slag, so that the fine gasification slag with low water content can be obtained, which not only meets the current environmental protection and fine slag resource utilization requirements, improves the energy density of the fine gasification slag, but also saves transportation and treatment costs, improves the plant environment, and improves the water resource utilization efficiency of coal gasification.

[0050] Meanwhile, the secondary steam output from the drying device is recycled in the process system, is used to preheat the gasified fine slag to be treated after dust removal, so that the remaining heat is fully utilized, and then is formed into superheated steam, and the superheated steam is returned to the drying device for recycling, so that the heat of the secondary steam is reasonably and fully reused, and the waste of water resources is reduced. In addition, the scheme does not need to introduce hot air, is safe, and is energy-saving and environment-friendly.

[0051] The gasified fine slag is sent to a combustion unit for combustion after dehydration and drying, the released heat can be used to manufacture superheated steam in a coal-fired boiler, or can be used for blending combustion in a gasification furnace, so that the carbon resources in the gasified fine slag can be fully utilized, and the problem of difficult treatment of the gasified fine slag is solved. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 It is a schematic diagram of a gasified fine slag dehydration and drying recycling system in an embodiment;

[0053] Figure 2 It is a schematic diagram of a gasified fine slag dehydration and drying recycling system in another embodiment. DETAILED DESCRIPTION

[0054] In order to facilitate the understanding of the present application, the present application will be further described below in conjunction with examples. It should be understood that the following examples are only for better understanding of the present application, and do not mean that the present application is limited to the following examples only.

[0055] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The term "and / or" as can be used herein includes any and all combinations of one or more of the associated listed items.

[0056] If the specific experimental steps or conditions are not specified in the examples, the operation or conditions can be carried out according to the corresponding conventional experimental steps in the technical field. If the reagents or instruments used are not specified by the manufacturer, they are conventional products that can be obtained by purchase.

[0057] The present application provides a gasified fine slag dehydration and drying recycling method, mainly comprising the following steps:

[0058] 1) The coal gasification black water is subjected to flash evaporation concentration, sedimentation and filtration dehydration in a black water treatment unit, to obtain flash steam and gasified fine slag to be treated;

[0059] 2) The gasified fine slag to be treated is sent into a fine slag preheater for preheating by a heat medium, to obtain preheated gasified fine slag;

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

[0061] 4) the secondary steam obtained in step 3) is subjected to dust removal treatment, and the obtained dust-removed secondary steam is sent into the fine slag preheater in step 2) to be used as the heat medium to exchange heat with the gasified fine slag to be treated;

[0062] 5) the secondary steam output from the fine slag preheater is subjected to superheating treatment to obtain superheated steam; the superheated steam is sent into the drying device in step 3) to be used for the heat exchange, so that the gasified fine slag is dehydrated and dried to obtain dried gasified fine slag, and secondary steam is obtained again.

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

[0064] By the above method, the present application does not need to introduce air or heat the air to realize the drying of the gasified fine slag; the present application uses superheated steam to exchange heat with the gasified fine slag in the drying device, so that the water in the gasified fine slag is vaporized to form new steam, which is mixed with the surrounding superheated steam flow to become secondary steam; as the secondary steam is discharged from the superheated steam drying device, the water is also continuously carried away, so that most of the water in the fine slag is removed, and the gasified fine slag with low water content is obtained. Not only the current environmental protection and resource utilization of the fine slag are met, but also the transportation amount of the fine slag is greatly reduced; 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 (which can increase the initial temperature of the gasified fine slag, and is beneficial to obtaining good drying and dehydration effect under the condition of reducing the use amount of superheated steam), and then is superheated 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. The dried gasified fine slag obtained through the above process has a greatly reduced water content, can meet the combustion demand, and is sent into a combustion unit for further utilization.

[0065] In the present application, superheated steam is used as the drying medium in the drying device, which has a large specific heat capacity. Compared with the drying medium of hot air, flue gas and the like in the prior art, the present application has lower energy consumption, a larger convective heat transfer coefficient, smaller water migration resistance, higher heat transfer efficiency, and can achieve higher drying efficiency and energy utilization rate. Moreover, no other gas such as air is introduced into the system, and the secondary steam output by the drying device only needs simple dust removal treatment to be directly reused in the system, and the intermediate links required for recycling are less, and the energy loss is less. Further, the present application does not involve the contact of hot air with the fine slag, and only uses superheated steam as the drying medium, which is safe and can avoid the risk of explosion of fine slag with high residual carbon content in the air atmosphere during the drying process.

[0066] In some embodiments, in step 5), the temperature of the superheated steam obtained by heat treatment is 160-190℃, and the pressure of the superheated steam is 0.2-0.3Mpa; in step 3), the temperature of the secondary steam output in the superheated steam drying device is 130-150℃, and the pressure of the secondary steam is 0.2-0.3Mpa.

[0067] In some embodiments, in step 1), the water content of the fine slag obtained by the black water treatment unit is 40-70wt%, and the water content can be further reduced by the method of the present application, for example, the dried fine slag can be reduced to below 30%, for example, in some embodiments, the water content of the fine slag can be reduced to 10-30%, or for example, in some embodiments, the water content of the fine slag can be reduced to 15-20%.

[0068] In the present application, the water content of the obtained fine slag is greatly reduced, and the energy density is improved, which can greatly reduce the influence of blending combustion on the boiler combustion system. In step 6), the combustion unit includes a coal-fired boiler or a gasification furnace, i.e., the dried fine slag can be sent into the coal-fired boiler for combustion, or into the gasification furnace for blending combustion, so that the carbon resources in the fine slag can be fully utilized. The ash obtained after the fine slag is burned in the combustion unit (such as a coal-fired boiler) can be used as a blending material in the building material or construction field, for example, as a blending material for cement, etc., which can further reduce the processing difficulty and cost of the fine slag and improve its utilization value.

[0069] Preferably, the combustion unit in step 6) includes a coal-fired boiler capable of producing superheated steam, i.e., the dried fine slag is sent into the coal-fired boiler for combustion, and the heat thereof is used to heat the production of superheated steam. The superheated steam produced in the coal-fired boiler is sent to the drying device in step 3) for heat exchange with the fine slag to be treated. In step 6), the dried fine slag is blended with coal powder for use.

[0070] In the present application, in step 5), the superheating 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 quench chamber of the gasifier and / or black water from the raw gas scrubbing tower used for washing the raw synthesis gas. The coal gasification black water from the coal gasification system is first used as the superheating 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 gas from the coal gasification system, such as raw synthesis gas from the gasifier which is scrubbed for dust removal by the raw gas scrubbing tower.

[0071] In the present application, preferably, in step 3), the preheated gasification fine slag and the superheated steam are directly contacted and heat exchanged in the drying device.

[0072] In some embodiments, the flash concentration in step 1) specifically comprises the following steps: the coal gasification black water is first sent into a high-pressure flash tower for high-pressure flashing, and then sent into a vacuum flash tower for vacuum flashing. In some embodiments, before being sent into the vacuum flash tower, the coal gasification black water is further sent into a low-pressure flash tower for low-pressure flashing. As to the high-pressure flashing, the low-pressure flashing and the vacuum flashing, they are all conventional operations for flash treatment of coal gasification black water in the art, and thus will not be described here. Through the above-mentioned flash concentration, flash steam and concentrated black water are obtained.

[0073] In some embodiments, in step 1), the settling is performed in a settling tank, and through the settling, slag slurry and supernatant (i.e. grey water) are obtained. During the settling, a flocculating agent can be added to promote the settling of solids, which is a conventional operation in the art and thus will not be described here. Specifically, the supernatant is sent to a downstream grey water tank. The slag slurry obtained by the settling (solid content is for example 10-20 wt%) is subjected to filtration dewatering, for example using a vacuum belt filter or a plate-and-frame filter or a centrifugal dewatering machine for filtration, and the filtration dewatering obtains gasification fine slag to be treated, which still has a relatively high water content, for example a water content of 40-70 wt%. The filtrate obtained by the filtration dewatering is sent into the grey water tank. The water in the grey water tank can be reused in the coal gasification system.

[0074] In some embodiments, the dust removal treatment of the secondary steam output from the drying device in step 4) specifically comprises: first subjecting the secondary steam to cyclone separation by a cyclone separator to obtain primary dust removal, and then sending the secondary steam into a steam washing tower for washing and dust removal by 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 and ensure the purity of the secondary steam. The washing liquid used is mainly the condensate water generated in the process, as described later. Preferably, the washing water obtained by washing and dust removal of the secondary steam in the steam washing tower is sent into a settling tank. Through the above-mentioned preferred dust removal treatment, the secondary steam can be deeply dust-removed, and the dust content in the secondary steam can be less than 10 mg / m 3 .

[0075] Preferably, in the fine slag preheater of step 2), the secondary steam used as a heat medium is output after heat exchange with the gasified fine slag, and is first sent into a secondary steam separation tank for vapor-liquid separation, and then sent into step 5) for superheating treatment. Preferably, part of the condensate separated in the secondary steam separation tank is sent into a grey water tank or into the steam washing tower to be used as a washing liquid.

[0076] Preferably, in step 5), before the superheating treatment of the secondary steam output from the fine slag preheater, the secondary steam output from the fine slag preheater is first sent into a steam preheater to exchange heat 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 into a flash steam separation tank for vapor-liquid separation, and the condensate separated is sent into the steam washing tower to be used as a washing liquid; the separated steam continues to be processed downstream, such as sulfur recovery treatment, etc.

[0077] In the present application, the superheated steam is used as a drying medium, which has a higher specific heat capacity (1.968 kJ / (kg·K)) and stronger heat exchange capacity compared with low-temperature flue gas and hot air. Meanwhile, the present application exchanges heat between the gasified fine slag to be treated and the superheated steam in the drying device, which can effectively remove water from the gasified fine slag, reduce the water content, improve the energy density, and facilitate the use of the gasified fine slag as fuel in the combustion unit. The present application uses secondary steam to preheat the gasified fine slag to be treated, which can effectively recover and utilize the energy of the secondary steam, improve the initial temperature of the gasified fine slag, and improve the drying effect.

[0078] The present application also provides a system capable of implementing the gasified fine slag dewatering and drying recycling method described above, as shown in Figure 1 , which mainly comprises: 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 for flash evaporation concentration, sedimentation and filtration dehydration of the coal gasification black water, so as to obtain flash evaporation gas and gasification fine slag to be treated;

[0080] The fine slag preheater is used for preheating treatment of the gasification fine slag to be treated by using the heat medium, so as to obtain preheated gasification fine slag;

[0081] The superheated steam drying device is used for heat exchange between the preheated gasification fine slag and the superheated steam, so that the water in the gasification fine slag is removed and vaporized into steam to form secondary steam with the surrounding superheated steam, so as to obtain dried gasification fine slag and secondary steam;

[0082] The secondary steam dust removal unit is used for dust removal treatment of the secondary steam output by the drying device, so as to obtain dust-removed secondary steam; the secondary steam dust removal unit is connected with the fine slag preheater, so that the dust-removed secondary steam is used as the heat medium to be delivered to the fine slag preheater, thereby being used for preheating the gasification fine slag to be treated;

[0083] The steam superheater is used for superheating treatment of the secondary steam output by the fine slag preheater, so as to obtain superheated steam; the steam superheater is connected with the drying device to supply the superheated steam to the drying device;

[0084] The combustion unit is connected with the drying device, and is used for using the dried gasification fine slag as fuel, so that the carbon resources in the dried gasification fine slag are fully utilized.

[0085] The above system is used for dehydration and drying treatment of the gasification fine slag and recycling, and the superheated steam is used for efficient, safe and environmentally friendly dehydration and drying of the gasification fine slag, and there is no explosion risk of contact between the hot air and the high-carbon-content dried gasification fine slag, and the energy utilization rate is higher. Moreover, no air is introduced into the system, and the secondary steam gas flow generated in the dehydration and drying process is mainly steam, which can be recycled without complex intermediate treatment links. The secondary steam is first dust-removed, then preheated in the fine slag preheater, and then superheated in the steam superheater, so as to obtain the superheated steam for recycling in the superheated steam drying device. The ingenious design of the whole system and the organic integration of the treatment device units make the energy of the secondary steam be more fully and reasonably utilized, and the waste of water resources is greatly reduced, so that the water resources are efficiently and fully utilized. At the same time, the dried gasification fine slag is sent to the combustion unit as fuel for further utilization, so that the carbon resources in the gasification fine slag can be fully utilized, which is conducive to solving the problem of difficult treatment of the gasification fine slag.

[0086] In some preferred embodiments, see Figure 1The superheated medium inlet of the steam superheater is connected with the crude coal gas outlet of the coal gasification system through a crude coal gas conveying pipeline, that is, the required superheated medium in the steam superheater is the crude coal gas of the coal gasification system; specifically, as shown in Figure 1 , the crude coal gas produced by the gasifier is washed and dedusted in the crude coal gas washing tower, and the obtained crude coal gas is used as the aforementioned superheated medium and is introduced into the steam superheater. As another embodiment, referring to Figure 2 , the superheated medium inlet of the steam superheater is connected with the coal gasification black water conveying pipeline of the coal gasification system, and the superheated medium outlet of the steam superheater is connected with the black water treatment unit through a pipeline; that is, the required superheated medium in the steam superheater is the coal gasification black water of the coal gasification system, which is first subjected to heat exchange with the secondary steam in the steam superheater and then enters the black water treatment unit for further treatment.

[0087] In the present application, the combustion unit includes a coal-fired boiler or a gasifier; Figure 1 The coal-fired unit specifically includes a coal-fired boiler. Preferably, as shown in Figure 1 , 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 with the drying device to supply fresh superheated steam to the drying device. Further, as shown in Figure 1 , the combustion unit further includes a fuel blending device, in which the dried gasification fine slag obtained from the drying device is blended with coal powder, and then is sent into the coal-fired boiler for combustion. The ash obtained after the combustion of the gasification 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 concentration unit and a sedimentation and filtration unit. The flash concentration unit is used for flash concentration of the coal gasification black water, so as to obtain flash gas and concentrated black water; the sedimentation and filtration unit is used for sedimentation and filtration dehydration of the concentrated black water, so as to obtain the gasification fine slag to be treated. Specifically, referring to Figure 1 , the flash concentration unit includes a high-pressure flash tower and a vacuum flash tower connected in series; in some embodiments, as shown in Figure 2 , a low-pressure flash tower can also be connected in series between the high-pressure flash tower and the vacuum flash tower.

[0089] Specifically, as shown in Figure 1 , the sedimentation and filtration unit includes a sedimentation tank and a filtration dehydration device. The sedimentation tank is used for sedimentation treatment of the concentrated black water output from the flash concentration unit, so as to obtain a slurry; the filtration dehydration device is used for filtration dehydration of the slurry obtained by the sedimentation treatment, so as to obtain the gasification fine slag to be treated. Preferably, the filtration dehydration device specifically adopts a vacuum belt filter, a plate and frame filter or a centrifugal dehydrator. As shown in Figure 1As shown, the settling filtration unit further comprises a grey water tank for receiving the supernatant in the settling tank and the filtrate from the filtration dewatering device, and the grey water in the grey water tank can be reused in the coal gasification system, for example, reused in the scrubbing tower of the coal gasification system.

[0090] In some preferred embodiments, the system of the present application further comprises a steam preheater for exchanging heat between the secondary steam outputted from the fine slurry preheater and the high pressure flash steam outputted from the high pressure flash tower of the black water treatment unit, before the secondary steam enters the steam superheater, so as to obtain preheated secondary steam.

[0091] In some embodiments, referring to Figure 1 , the secondary steam dedusting unit comprises a cyclone separator and a steam scrubbing tower. The cyclone separator is connected with the drying device for cyclone separation of the secondary steam outputted from the drying device, so as to obtain primary dedusting. The steam scrubbing tower is connected with the cyclone separator at the gas inlet and connected with the heat medium inlet of the fine slurry preheater at the gas outlet. The steam scrubbing tower receives the primary dedusted secondary steam from the cyclone separator, and the primary dedusted secondary steam is washed by the washing liquid in the steam scrubbing tower, so as to obtain washing water and dedusted secondary steam. Preferably, the washing water outlet of the steam scrubbing tower is connected with the settling tank.

[0092] In some embodiments, the flash steam outlet of the steam preheater is connected with a flash steam separation tank for vapor-liquid separation of the flash steam which has been exchanged heat in the steam preheater and obtaining condensate. Preferably, the condensate outlet of the flash steam separation tank is connected with the washing liquid inlet of the steam scrubbing tower, so that the condensate separated from the flash steam separation tank can be sent into the steam scrubbing tower as washing liquid. Further, the flash steam outputted from the flash steam separation tank enters a downstream unit such as a sulfur recovery unit for further treatment.

[0093] In some embodiments, the secondary steam outlet of the fine slurry preheater is connected with a secondary steam separation tank through a pipeline for vapor-liquid separation of the secondary steam which has been exchanged heat in the fine slurry preheater and obtaining condensate. The vapor phase outlet of the secondary steam separation tank is connected with the secondary steam inlet of the steam preheater, so that the vapor-liquid separated secondary steam can enter the steam preheater for preheating treatment. Preferably, the condensate outlet of the secondary steam separation tank is connected with the grey water tank, or the condensate outlet of the secondary steam separation tank is connected with the washing liquid inlet of the steam scrubbing tower, so that the condensate separated from the secondary steam separation tank can be reused in the grey water tank or used as washing liquid.

[0094] In the system of the present application, the drying device can be implemented by conventional devices in the art, and preferably a drying device capable of realizing direct contact heat exchange between the superheated steam and the gasification fine slurry 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 application scheme is further described below by using application cases.

[0096] Example 1

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

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

[0099]

[0100] The gasification black water of the plant is dehydrated and dried for reuse by using the method and system of the application. The system used is shown in FIG. 1, and the system and method are not particularly described herein, and can be referred to the foregoing description, which will not be described one by one. In this embodiment, the gasification fine slag drying and dehydration reuse includes the following processing links: Figure 1 1) flash concentration, sedimentation and filtration

[0101] 1.1) flash concentration:

[0102] The black water from the quenching chamber of the gasification furnace and the black water from the coarse coal gas washing tower enter the high-pressure flash tower, and part of the soluble gas is released from the black water under 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 under a pressure of -0.5 MPa to obtain concentrated black water.

[0103] 1.2) sedimentation:

[0104] The concentrated black water obtained in step 1.1) is sent to the sedimentation tank for gravity sedimentation and solid-liquid separation, and a composite flocculating agent (85wt% anionic polyacrylamide and 15wt% coagulant (polyaluminum)) is added to accelerate and promote the sedimentation of the solids in the black water. The slurry containing 20wt% solids (flow rate: 30t / h, temperature: 60℃, water content: 80wt%) is settled at the bottom of the sedimentation tank, and the supernatant of the sedimentation tank enters the grey water tank.

[0105] 1.3) filtration and dehydration:

[0106]

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

[0108] 2) Fine slag preheating:

[0109] The aforementioned gasification fine slag to be treated is sent to a fine slag preheater for indirect heat exchange with a heat medium, to obtain the preheated gasification fine slag; after the system is operated and secondary steam is generated, the heat medium is the dust-removed secondary steam output from the steam scrubbing tower. In the preheating process, the secondary steam is cooled and condensed, and is sent to a secondary steam separation tank for vapor-liquid separation, and the separated condensed liquid (flow rate: 7.5 t / h) is sent to the ash water tank.

[0110] 3) Drying and dewatering:

[0111] The aforementioned preheated gasification fine slag and filter steam are simultaneously sent to a drying device (fluidized bed dryer), and the superheated steam directly contacts the gasification fine slag in the drying device, the gasification fine slag is heated, the water in the gasification fine slag is vaporized and separated to form new steam, and is mixed with the surrounding superheated steam flow to become secondary steam (temperature 144°C, 0.3 MPa, 226.2 t / h). The secondary steam is discharged from the drying device by using the induced draft fan of the drying device, and the water is continuously carried away, so that most of the water in the fine slag is removed, and the dried gasification fine slag (output 7.5 t / h) with a water content of 20% is obtained.

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

[0113]

[0114] 4) Secondary steam dust removal:

[0115] The secondary steam discharged from the drying device is first separated from most of the solids by a cyclone separator, and the preliminarily dust-removed secondary steam is then introduced into a steam scrubbing tower, where the condensed liquid from the flash steam separation tank is used as a washing liquid to wash the secondary steam to further remove dust, and the finally obtained dust-removed secondary steam contains <10 mg / m 3 of dust. The washing water at the bottom of the steam scrubbing tower is pumped into the settling tank; the dust-removed secondary steam obtained in this step is sent to the fine slag preheater in step 2) as a heat medium for preheating the gasification fine slag.

[0116] 5) Secondary steam preheating:

[0117] The secondary steam (temperature 144℃, pressure: 0.3MPa, flow rate: 218.7kg / h) which has been vapor-liquid separated 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℃, pressure: 0.30MPa, flow rate: 218.7kg / h) exchanges heat with the raw coal gas from the raw coal gas washing tower, to form new superheated steam (temperature 190℃, 0.3MPa, 218.7kg / h); the superheated steam is recycled to the drying device in step 3) (at the initial stage of system operation, step 3) can use fresh superheated steam introduced from outside the system, and during system operation, after superheated steam is generated in the steam superheater, the superheated steam generated in the steam superheater is introduced in step 3).

[0120] 7) Boiler blending:

[0121] The dried gasification fine slag (7.5t / h, moisture content 20%) obtained in step 3) is sent to the coal blending device, the coal powder and the gasification fine slag are mixed and then sent to the coal-fired boiler for combustion treatment, to fully utilize the residual carbon resources in the gasification fine slag. The superheated steam produced in the coal-fired boiler can be used as fresh superheated steam in the drying device.

[0122] By using the above method, 2.24 million tons of coal can be saved per year (the conversion rate of residual carbon in the fine slag is 92%), and according to the average price of fuel coal in the local area, 851.2 million yuan of coal costs can be saved per year. The ash produced by the gasification fine slag boiler blending can be used as a blending raw material for cement, so 600 million yuan of gasification fine slag transportation and landfill treatment can be saved per year.

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

[0124] It is easily understood that the above embodiment is only an example for clear illustration, and does not mean that the present application is limited to this. Based on the above description, other different forms of changes or variations can also be made by those skilled in the art. Here, it is not necessary and impossible to exhaust all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for dewatering and drying gasified fine slag for reuse, characterized by, The method comprises the following steps: 1) flash concentration, sedimentation and filtration dehydration of coal gasification black water in a black water treatment unit to obtain flash gas and gasification fine slag to be treated; the flash concentration comprises high-pressure flash and vacuum flash of the coal gasification black water in sequence; 2) preheating of the gasification fine slag to be treated in a fine slag preheater by a heat medium to obtain preheated gasification fine slag; 3) direct contact of the preheated gasification fine slag with superheated steam in a drying device to obtain dried gasification fine slag and secondary steam; 4) dust removal treatment of the secondary steam obtained in step 3) and feeding of the obtained dust-removed secondary steam into the fine slag preheater in step 2) as the heat medium; the dust removal treatment comprises preliminary dust removal of the secondary steam obtained in step 3) by a cyclone separator and then washing and dust removal in a steam washing tower; 5) feeding of the secondary steam output from the fine slag preheater into a secondary steam separation tank for vapor-liquid separation, then into a steam preheater for heat exchange with high-pressure flash gas obtained by high-pressure flash, and then superheating treatment to obtain superheated steam; feeding of the superheated steam into the drying device in step 3) for the heat exchange; the superheating medium for the superheating treatment is coal gasification black water from a coal gasification system or is raw coal gas from the coal gasification system; feeding of flash gas output from the steam preheater into a flash gas separation tank for vapor-liquid separation and feeding of condensed liquid obtained by the separation into the steam washing tower as washing liquid; 6) feeding of the dried gasification fine slag into a combustion unit as fuel.

2. The method of dewatering and drying gasified fine slag for reuse according to claim 1, characterized by, In step 6), the combustion unit comprises a coal-fired boiler or a gasifier.

3. The method of dewatering and drying gasified fine slag for reuse according to claim 2, characterized by, 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 in step 3).

4. The method of dewatering and drying gasified fine slag for reuse according to claim 2, characterized by, The ash obtained after the gasification fine slag is combusted in the combustion unit is used as building material or admixture in the field of building and construction.

5. The method of dewatering and drying gasified fine slag for reuse according to claim 2, wherein In step 6), the dried gasification fine slag is mixed with coal powder and then used.

6. The method of dewatering and drying gasified fine slag for reuse according to claim 1, wherein The coal gasification black water from the coal gasification system is fed into the black water treatment unit in step 1) after the superheating treatment of the secondary steam in step 5).

7. The gasification fine slag dehydration and drying recycling method according to any one of claims 1-6, wherein, in step 1), before the vacuum flash, a low-pressure flash of the coal gasification black water is further performed; In step 1), the sedimentation is performed in a sedimentation tank; In step 4), washing water obtained by washing and dust removal in the steam washing tower is fed into the sedimentation tank. Part of the condensed liquid obtained by separation in the secondary steam separation tank is fed into an ash water tank or into the steam washing tower as washing liquid.

8. The method of dewatering and drying gasified fine slag for reuse according to claim 7, characterized by, The system comprises:

9. A system capable of carrying out the method of dewatering and drying of gasified fine sludge for reuse according to any one of claims 1 to 8, characterized in that, ​ The black water treatment unit is used for flash evaporation concentration, sedimentation and filtration dehydration of coal gasification black water, and obtains flash evaporation gas and gasification fine slag to be treated; the black water treatment unit comprises a flash evaporation concentration unit, which is used for flash evaporation and concentration of the coal gasification black water to obtain the flash evaporation gas and concentrated black water; the flash evaporation concentration unit comprises a high-pressure flash evaporation tower and a vacuum flash evaporation tower connected in series; The fine slag preheater is used for preheating treatment of the gasification fine slag to be treated by using a heat medium to obtain preheated gasification fine slag; a secondary steam outlet of the fine slag preheater is connected with a secondary steam separation tank through a pipeline, and is used for vapor-liquid separation of secondary steam output by the fine slag preheater to obtain condensed liquid; The drying device is used for heat exchange between the preheated gasification fine slag and superheated steam to obtain dried gasification fine slag and secondary steam; The secondary steam dust removal unit is used for dust removal treatment of the secondary steam output by the drying device; the secondary steam dust removal unit is connected with the fine slag preheater to deliver the secondary steam subjected to the dust removal treatment to the fine slag preheater as the heat medium; the secondary steam dust removal unit comprises a cyclone separator and a steam washing tower, the cyclone separator is used for primary dust removal of the secondary steam output by the drying device, and the steam washing tower is used for washing dust removal of the secondary steam subjected to the primary dust removal by using a washing liquid to obtain washing water and dust-removed secondary steam; The steam preheater is used for heat exchange between the secondary steam output by the fine slag preheater after vapor-liquid separation in the secondary steam separation tank and high-pressure flash evaporation gas output by the high-pressure flash evaporation tower to obtain preheated secondary steam; a flash evaporation gas outlet of the steam preheater is connected with a flash evaporation separation tank, which is used for vapor-liquid separation of flash evaporation gas output by the steam preheater to obtain condensed liquid; a condensed liquid outlet of the flash evaporation separation tank is connected with a washing liquid inlet of the steam washing tower; The steam superheater is used for superheating treatment of the preheated secondary steam obtained by heat exchange of the secondary steam output by the fine slag preheater in the steam preheater to obtain superheated steam; a superheated steam outlet of the steam superheater is connected with the drying device; The combustion unit is connected with the drying device, and is used for using the dried gasification fine slag as fuel; a superheating medium inlet of the steam superheater is connected with a coal gasification black water delivery pipeline of a coal gasification system, and a superheating medium outlet of the steam superheater is connected with the black water treatment unit through a pipeline; or, the superheating medium inlet of the steam superheater is connected with a crude coal gas outlet of the coal gasification system through a crude coal gas delivery pipeline; The drying device is a device capable of directly contacting and exchanging heat between the preheated gasification fine slag and the superheated steam.

10. The system of claim 9, wherein, The combustion unit comprises a coal-fired boiler or a gasification furnace.

11. The system of claim 10, wherein, The combustion unit comprises a coal-fired boiler capable of generating superheated steam, and a superheated steam outlet of the coal-fired boiler is connected with the drying device.

12. The system of claim 10, wherein, The combustion unit further comprises a fuel blending device used for blending the dried gasification fine slag with coal powder.

13. The system according to claim 9 or 10, characterized in that, the black water treatment unit comprises a sedimentation and filtration unit, which is used for sedimentation and filtration dewatering of the concentrated black water to obtain the fine gasification slag to be treated.

14. The system of claim 13, wherein, a low-pressure flash tower is further connected in series between the high-pressure flash tower and the vacuum flash tower.

15. The system of claim 13, wherein, the sedimentation and filtration unit comprises a sedimentation tank and a filtration dewatering device, the sedimentation tank is used for sedimentation treatment of the concentrated black water output by the flash concentration unit, and the filtration dewatering device is used for filtration dewatering of the slag slurry obtained by the sedimentation treatment to obtain the fine gasification slag to be treated.

16. The system according to claim 13, characterized in that, the washing water outlet of the steam washing tower is connected with the sedimentation tank.

17. The system of claim 16, wherein, the vapor phase outlet of the secondary steam separation tank is connected with the secondary steam inlet of the steam preheater.

18. The system of claim 17, wherein, the condensate outlet of the secondary steam separation tank is connected with the ash water tank, or the condensate outlet of the secondary steam separation tank is connected with the washing liquid inlet of the steam washing tower.

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