Method for optimizing water quality of coal gasification grey water of entrained-flow bed

Abstract

The invention belongs to the technical field of entrained-flow bed coal gasification processes, and particularly relates to an entrained-flow bed coal gasification grey water quality optimization method which comprises the following steps: (1) performing multi-stage flash evaporation on black water to be treated to obtain multi-stage concentrated black water; (2) adding a flocculating agent into the multi-stage concentrated black water to settle, and enabling the obtained supernatant liquid as overflow grey water to enter a filtration-adsorption system; (3) preparing a filter aid mixed solution in advance; before the filter is put into use, the filter aid mixed solution is introduced into the filter for precoating, and after precoating and filtering, the filter aid forms a filter aid filtering base layer on filter cloth of the filter; after the pre-coating process of the filter aid is finished, the overflow grey water is introduced into a filter for filtration-adsorption treatment; and (4) adding a dispersing agent into the obtained ash water filtrate to prepare recycled ash water, and feeding the recycled ash water into a washing tower and a gasification furnace for cyclic utilization. The method can effectively improve the water quality of the recycled grey water under the condition of reducing the dosage of the flocculating agent and the dispersing agent, and prolongs the operation period of a water system.

Description

Technical Field

[0001] The invention belongs to the technical field of entrained-bed coal gasification technology, and in particular relates to a method for optimizing the water quality of entrained-bed coal gasification ash water. Background Art

[0002] The water system is an indispensable part of the fluidized-bed coal gasification process. Its main function is to purify the black water from the gasifier and the scrubber into relatively clean gray water through multi-stage flash evaporation, flocculation sedimentation and clarification. The water system is recycled after the deoxygenation process. It can be described as the "blood" of the coal gasification device. Whether the water system operates normally or not is the key to whether the coal gasification device can operate stably for a long period of time. It also directly affects the service life of each major equipment.

[0003] At present, the water system processes of different entrained-bed coal gasification processes are similar. Taking the widely used Texaco water-coal slurry gasification technology as an example, a brief overview of the water treatment system is given. Figure 1 As shown, the process flow is:

[0004] The black water at the bottom of the gasifier 1 and the washing tower 3 enters the high-pressure flash tank 6 for primary flash evaporation after the black water angle valve depressurization treatment, the concentrated black water enters the low-pressure flash tank 7 for secondary flash evaporation, and the concentrated black water enters the vacuum flash tank 8 for tertiary flash evaporation. At this time, most of the acid gases in the black water are removed and the black water is further concentrated; the concentrated black water after the tertiary flash evaporation is pumped into the clarification tank 9, and the coal powder particles, calcium and magnesium ions, etc. contained in the black water entering the clarification tank 9 are precipitated by adding flocculants, and the upper clear liquid (ash water) in the clarification tank 9 is added with dispersants and then overflows into the ash water tank 10. The ash water in the ash water tank 10 is divided into two paths: one path of ash water (circulating ash water) is sent to the deaerator 5 by the low-pressure ash water pump 11, and after heating and deoxygenation, it is circulated by the high-pressure ash water pump 4 in turn into the washing tower 3 and sent to the gasifier 1 through the quenching water pump 2; the other path of ash water is transported to the lock bucket washing water tank to wash the lock bucket. In order to prevent the accumulation of suspended matter, scaling ions, corrosive ions, COD, ammonia nitrogen, etc. in the circulating grey water from causing equipment / pipeline corrosion, scaling, and water quality deterioration, the other grey water can be sent to sewage treatment after cooling through a heat exchanger, and desalted water is added to the circulating grey water to maintain the balance of the water system. The black water concentrate at the bottom of the clarifier 9 is sent to the plate and frame filter 13 (or horizontal screw centrifuge) by the underflow pump 12 for solid-liquid separation, and the filter cake is discharged from the system. The filtrate can be returned to the grey water tank 10 after being pressurized by the pump.

[0005] The grey water obtained after treatment by the water system of the existing coal gasification device generally has water quality problems such as high hardness, high suspended solids, high ammonia nitrogen, and high COD. The scaling, blockage, wear and leakage caused by this are industry problems and have become the key factors restricting the long-term stable operation of the coal gasification device. For example, the grey water quality index data obtained after the typical entrained-flow coal gasification black water is treated by the water system of the existing coal gasification device is shown in Table 1.

[0006] Table 1 Main water quality indicators of treated grey water

[0007]

[0008] The hardness of grey water is Ca 2+ Mg 2+ The content of Ca in gray water 2+ Mg 2+ It mainly comes from the dissolution of ash components in the raw coal during the quenching process, and a small amount comes from supplementary water. Part of the suspended matter in the ash water comes from ash components such as SiO2, Fe2O3, and Al2O3 in the raw coal. After these substances are burned in the gasifier, a small amount of unburned carbon enters the black water with the gas washing water. In addition, after the high-temperature and high-pressure black water is flashed, as the inorganic acid gas evaporates in large quantities, the soluble Ca(HCO3)2 and Mg(HCO3)2 become insoluble CaCO3 and MgCO3, and then suspend and deposit in the entire gasification ash water system (causing scaling). The COD in the ash water mainly comes from hydrocarbons generated during the gasification reaction, and a small amount comes from oil substances entering from the outside, such as conversion condensate. The ammonia nitrogen in the ash water is ammonia nitrogen. NH3 is mainly produced by a trace amount of ammoniation reaction between H2 and N2 under the conditions of high temperature and iron medium in the gasifier system. A small amount of NH3 will be generated during the gasification reaction and the conversion process. NH3 is easily soluble in water to form NH 4+ , resulting in high ammonia nitrogen and alkalinity in the grey water. The total phosphorus index in the grey water roughly reflects the dispersing performance of the dispersant added to the grey water.

[0009] Since the existing gasification water system treatment process mainly relies on adding flocculants to the black water after flash evaporation to discharge some scale sediments, unburned ember carbon-ash particles (i.e., gasification fine slag), etc. from the bottom of the clarification tank, the clarification separation process is a rough separation process, and some sediments and unburned ember carbon-ash particles still overflow from the clarification tank as suspended matter into the ash water tank. After adding dispersants, some ash water can be recycled, and the water quality of the ash water in the system can be adjusted by discharging some ash water and adding desalted water. However, under high hardness conditions, the dispersion effect of adding dispersants to the ash water tank is poor, the consumption of dispersants is large, and the operating cost of the treatment process is high; in addition, under high alkalinity, high hardness, and high suspended matter conditions, the scale of equipment and pipelines needs to be removed regularly, and the maintenance cost is high. When the coal quality fluctuates or the process fluctuates, resulting in the accumulation of hardness, alkalinity, and suspended matter in the water system, the water quality deteriorates, and the amount of ash water discharged cannot be increased indefinitely, which will cause the equipment / pipeline in the system to scale and block, and then cause the gasification system to shut down.

[0010] In view of the above problems, some improvements have been made in this field.

[0011] Patent document CN10529380A discloses a method for treating coal gasification ash water, which aims to solve the problem of excessively high residual carbon content of gasification fine slag and a large amount of suspended particles in the recycled ash water in the prior art. The technical scheme is as follows: the black water from the gasifier and the scrubber enters the concentrator after 2-stage or 3-stage flash evaporation and concentration; under the action of stirring, the black water in the concentrator is divided into two layers, the upper floating bead slurry overflows, and enters the ash water circulation system or sedimentation tank after separating the floating beads; the lower concentrated black water enters the residual carbon separator, the residual carbon is floated out, and the tailings slurry of the lower layer of the flotation separator enters the sedimentation tank; the upper clear liquid of the sedimentation tank enters the ash water circulation system, and the lower turbid liquid of the sedimentation tank enters the filter for dehydration to obtain the filter cake (gasification fine slag). In this technical scheme, the ash water from the concentrator and the sedimentation tank overflows, which is still a rough separation process, and the water quality indicators such as suspended matter (carbon-ash particles, scale precipitation suspended matter) and COD in the obtained ash water have not been fundamentally improved.

[0012] Patent document CN106673270A discloses a treatment method for reducing hardness, saving water and reducing emissions in a coal gasification black ash water system. The technical solution is as follows: (1) After the black water generated by the coal gasification system is treated by flocculation and sedimentation in a sedimentation tank, the overflowing ash water enters the ash water tank; after the ash water in the ash water tank is treated by scale inhibition and dispersion, a part of it is recycled back to the coal gasification system, and the discharged part is cooled by a cooling device to a water temperature not exceeding 35°C; (2) The cooled ash water enters an electrodialysis device, and most of the calcium, magnesium, bicarbonate and chloride ions are removed by electrodialysis. The generated fresh water is reused as replenishment water or used in other systems; part or all of the generated concentrated water is returned to the sedimentation tank; the sedimentation tank is provided with a dosing device for flocculants and hardness reducing agents, and the ash water tank is provided with a dosing device for scale inhibition and dispersant. This technical solution does not effectively improve the water quality of the recycled ash water.

[0013] Patent document CN112010450A discloses a system and method for treating coal gasification ash water, which aims to solve the problems of large flash evaporation equipment volume, high civil engineering cost, high energy consumption in the prior art, as well as the problems of the precision of solid-liquid separation and energy recycling in the process of treating coal gasification ash water under high temperature and high pressure conditions. The technical scheme is as follows: adopting a general scheme of mixed flocculation, solid-liquid separation, indirect cooling and recycling, that is, reducing the difficulty of solid-liquid separation by pre-treatment of ash water flocculation; then improving the precision of solid-liquid separation by combining a cyclone separator and a high-pressure cross-flow filter in series solid-liquid separation; and reducing heat consumption by combining a high-temperature and high-pressure cooler with a medium-temperature and high-pressure cooler in cooling; completing energy recycling by ash water circulation equipment and gas-liquid separation equipment. This technical solution adds flocculants to the pretreatment area for flocculation, and then uses a hydrocyclone to preliminarily separate solid particles in the black water under high temperature and high pressure conditions, and then uses a high-pressure tubular membrane cross-flow filter to further filter the solid particles. However, when flocculants are added to high-temperature and high-pressure black water, the flocculants are easily inactivated; the black water entering the hydrocyclone has a high solid content, and the hydrocyclone will be severely worn; and the tubular membrane filter equipment is expensive.

[0014] In view of this, it is worthwhile to continue to study and explore methods to effectively improve the quality of recycled grey water. Summary of the invention

[0015] The purpose of the present invention is to provide a method for optimizing the water quality of fluidized-bed coal gasification ash water in response to the problems existing in the existing process of improving the water quality of recycled ash water. By utilizing the water quality characteristics of the ash water and the characteristics of the filtering device to perform "filtration + adsorption" on the overflow ash water of the clarification tank, the water quality of the recycled ash water can be effectively improved while reducing the amount of flocculant and dispersant used, thereby extending the operating period of the water system and ensuring the long-term stable operation of the gasification system and the device.

[0016] In order to achieve the above object, the present invention provides the following technical solutions:

[0017] A method for optimizing the water quality of entrained-bed coal gasification ash water comprises the following steps:

[0018] (1) Flash process

[0019] The black water from the gasifier and the scrubber is subjected to multi-stage flash evaporation to obtain multi-stage concentrated black water;

[0020] (2) Flocculation and sedimentation process

[0021] The multi-stage concentrated black water obtained as above is passed into a clarification tank, and a flocculant is added for sedimentation; after flocculation and sedimentation, a black water concentrate is obtained at the bottom of the clarification tank, and the upper clear liquid overflowing from the top of the clarification tank is used as overflow gray water;

[0022] After the black water concentrate at the bottom of the clarifier is filtered to remove part of the water, a filter cake is obtained and sent out of the device; the overflow gray water at the top of the clarifier enters the filtration-adsorption system for treatment;

[0023] (3) Treatment process of filtration-adsorption system

[0024] ①Filter aid pre-coating process:

[0025] Mix the filter aid with desalted water in advance to prepare a filter aid mixed solution;

[0026] Before the filter is put into use, the filter aid mixture is passed into the filter for pre-coating. After pre-coating and filtration, the filter aid forms a filter aid filtration base layer on the filter cloth of the filter.

[0027] ②Filtration-adsorption process:

[0028] After the pre-coating process of the filter aid is completed, the overflow ash water overflowing from the top of the clarification tank is passed into the inlet valve of the filter; in the filter, the gasified fine slag in the overflow ash water is accumulated on the filter base of the filter aid to form a gasified fine slag filter layer and the overflow ash water is filtered-adsorbed at the same time; after the treatment is completed, the remaining liquid in the filter is returned to the clarification tank, and the filter cake obtained by the filtration-adsorption treatment is discharged from the system;

[0029] (4) Grey water circulation process

[0030] The ash water filtrate obtained by the filtration-adsorption treatment enters the ash water tank, and a dispersant is added thereto to obtain recycled ash water; a portion of the recycled ash water is discharged from the system, and the remaining recycled ash water is mixed with external desalted water and enters the deaerator for deoxygenation treatment, and then is sent to the scrubber and gasifier for recycling.

[0031] According to the optimization method provided by the present invention, the multi-stage flash evaporation in step (1) can be, for example, but not limited to, a secondary flash evaporation, a tertiary flash evaporation, a quaternary flash evaporation, etc. In some embodiments, in step (1), the black water to be treated is passed into a high-pressure flash evaporation tank for primary flash evaporation, the primary concentrated black water is passed into a low-pressure flash evaporation tank for secondary flash evaporation, and the secondary concentrated black water is then passed into a vacuum flash evaporation tank for tertiary flash evaporation to obtain tertiary concentrated black water.

[0032] The flash evaporation process steps and process conditions are conventional choices in the art and will not be described here. In some embodiments, the process conditions of the first-stage flash evaporation are: 0.8-1 MPaG (e.g., 0.85 MPaG), 175-180°C (e.g., 176°C); the process conditions of the second-stage flash evaporation are: 0.15-0.2 MPaG (e.g., 0.18 MPaG), 125-130°C (e.g., 129°C); the process conditions of the third-stage flash evaporation are: -0.1 MPaG--0.05 MPaG (e.g., -0.07 MPaG), 60-70°C (e.g., 68°C).

[0033] According to the optimization method provided by the present invention, in some embodiments, in step (2), the flocculant is selected from cationic polyacrylamide (CPAM).

[0034] In some embodiments, based on the mass of the multi-stage concentrated black water, the amount of the flocculant used is 1-5 ppm, for example, 2 ppm, 3 ppm, 4 ppm.

[0035] In some embodiments, in step (2), the overflow gray water entering the filtration-adsorption system accounts for 50-100wt% (e.g., 55wt%, 60wt%, 70wt%, 80wt%, 90wt%) of the total mass of the overflow gray water. That is, the overflow gray water can all enter the filtration-adsorption system for treatment; or, a portion of the overflow gray water enters the gray water tank, and the other portion of the overflow gray water enters the filtration-adsorption system for treatment.

[0036] According to the optimization method provided by the present invention, in some embodiments, in step (3), the filter aid is selected from one or more of perlite particles, diatomaceous earth particles and activated carbon particles, and its particle size is 100 mesh to 400 mesh (for example, 120 mesh, 150 mesh, 200 mesh, 300 mesh, 350 mesh).

[0037] In some embodiments, based on the total mass of the filter aid mixture, the content of the filter aid in the filter aid mixture is 1-10wt%, for example, 2wt%, 4wt%, 5wt%, 6wt%, 8wt%.

[0038] The desalted water in the filter aid mixed solution is a solution well known to those skilled in the art and will not be described in detail here.

[0039] In some embodiments, in one filtration-adsorption cycle, the mass ratio of the filter aid to the gasified fine slag contained in the overflow ash water is 1:(5-20), for example, 1:6, 1:10, 1:12, 1:18, preferably 1:(8-15). When the amount of filter aid is large, it will increase the cost of raw materials and generate more solid waste requiring post-treatment; when the amount of filter aid is small, the filter base layer formed is not enough to block the fine-particle gasified fine slag, resulting in a decrease in the filtration-adsorption effect.

[0040] In some embodiments, in step (3), the filter aid pre-coating time is 1-10 min, for example, 2 min, 4 min, 5 min, 6 min, 8 min.

[0041] In some embodiments, the filter aid filter substrate has a thickness of 1-3 mm (eg, 1.5 mm, 2.5 mm), preferably 2-3 mm.

[0042] In some embodiments, the filter is provided with a filter cloth and a filter rod.

[0043] In some embodiments, the filter cloth is a polymer material, preferably PP, PE, PA, PPS, or PTFE; the pore size of the filter cloth is 20-50 μm (e.g., 22 μm, 25 μm, 30 μm, 35 μm, 40 μm, or 45 μm).

[0044] In some embodiments, the outer diameter of the filter rod is 100-150 mm (eg, 110 mm, 120 mm, 140 mm), and the number of the filter rods is 200-1000 (eg, 250, 400, 500, 800).

[0045] In some embodiments, the total filtration area of ​​the filter is 100-600m 2 (For example, 200m 2 、400m 2 、500m 2 、550m 2 ).

[0046] In some embodiments, in step (3), the thickness of the gasified fine slag filter layer formed outside the filter aid filter base layer is 10-25 mm (e.g., 12 mm, 16 mm, 18 mm, 20 mm, 24 mm), preferably 15-25 mm. That is, the formed filtration-adsorption layer includes the filter aid filter base layer and the gasified fine slag filter layer located thereon. After the gasified fine slag filter layer on the filter base layer is formed, the adsorption performance of the gasified fine slag layer can be used to adsorb COD, scale precipitation suspended solids, etc., reduce the hardness of the filtrate, and improve water quality indicators.

[0047] In step (3), the filter used can be a candle filter; the candle filter has the characteristics of automatic control, closed material input and output, high filtering accuracy, easy maintenance, safety and reliability. Two filters A / B can be provided and set to be one open and one standby. For example, before filter A is put into use, the filter aid pre-coating pump is started, and the filter aid mixture enters filter A through the filter aid pre-coating pipeline. After the filter aid mixture is filtered, the obtained filtrate returns to the filter aid pre-coating tank, and the filtrate is observed at the same time. When the filtrate is clear, the filter aid pre-coating pump is stopped, and the filter aid pre-coating process is completed. The filter aid in the filter aid mixture has formed a filter cloth protective layer (i.e., filter aid filtration base layer) on the filter cloth of filter A; the filter cloth pre-coating process can set a certain operation time according to operating experience. After the filter cloth pre-coating process is completed, 50% to 100% of the overflow gray water is passed into the pre-coated filter A, and the overflow gray water passed is filtered. When the filter cloth pressure difference of filter A reaches the set value -1, the filter cloth pre-coating operation of filter B is carried out, and the operation is the same as the filter cloth pre-coating process of filter A; when the filter cloth pressure difference of filter A reaches the set value -2, the inlet valve of filter B is opened, and the inlet valve of filter A is closed at the same time, and filter B starts to filter the overflow gray water, and the gray water filtrate obtained by filtration enters the gray water tank 10. When the filter cloth pressure difference of filter B reaches the corresponding set value, filter A is pre-coated, filter B returns the feed liquid, the filter cake is blown dry and unloaded. The above operations are all automatically controlled, and the switching of filter A / B repeats the above operation process.

[0048] According to the optimization method provided by the present invention, in some embodiments, in step (4), the dispersant is selected from aminotrimethylenephosphonic acid (ATMP) and / or polyacrylic acid (PAA).

[0049] In some embodiments, based on the mass of the grey water filtrate, the amount of the dispersant is 50-150 ppm, for example, 60 ppm, 80 ppm, 100 ppm, 120 ppm, 140 ppm.

[0050] In the present invention, the structure of the filter and the particle characteristics of the gasified fine slag contained in the ash water are cleverly utilized to interact with the filter aid to form a gasified fine slag filter layer with filtering-adsorption effects, so that the overflow ash water from the top of the clarification tank can be "filtered-adsorbed" to further improve the water quality. In the gasified fine slag filter layer, the role of the filter aid is, on the one hand, to reduce the filtration resistance, increase the filtration speed, and improve the filtration accuracy; on the other hand, because the coal powder particles, COD organic matter, etc. contained in the overflow ash water have a certain viscosity, pre-coating the filter aid on the filter cloth can protect the filter cloth and prevent the filter cloth from being adhered to by sticky substances in the ash water, making it easier to discharge the filter cake on the filter cloth completely and extending the service life of the filter cloth.

[0051] By forming a 2-3 mm filter aid filter base layer outside the filter cloth and a 15-25 mm gasification fine slag filter layer outside the filter base layer, this process does not introduce additional adsorbents, but fully utilizes the characteristics of the ash water composition to be improved and its interaction with the filter aids to achieve "filtration-adsorption" of overflow ash water, so as to better adsorb impurities such as COD and scaling sediments, while improving the water quality of recycled ash water and extending the operating cycle of the device and shortening the cleaning cycle; in addition, in the process of forming the filtration-adsorption layer, the filter aid serves as the filtration base layer, which makes it easier to completely unload the obtained filter cake and discharge it from the system when the filtration-adsorption step is completed, without causing sticky substances to clog the filter cloth, thereby further extending the operating cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 The schematic diagram of the water system treatment process in the existing entrained-flow coal gasification process is shown;

[0053] Figure 2 A schematic diagram of a process flow for optimizing the quality of ash water from entrained-flow coal gasification according to some embodiments of the present invention is shown;

[0054] Figure 3 The SEM of the gasified fine slag filter layer in Example 1 is shown.

[0055] In the above figure, the descriptions of the reference numerals are as follows:

[0056] 1-gasifier; 2-quenching water pump; 3-washing tower; 4-high-pressure ash water pump; 5-deaerator; 6-high-pressure flash tank; 7-low-pressure flash tank; 8-vacuum flash tank; 9-clarifier; 10-ash water tank; 11-low-pressure ash water pump; 12-underflow pump; 13-plate and frame filter; 14-filter aid tank; 15-filter aid pre-coating tank; 16-filter aid pre-coating pump; 17-ash water pressure pump; 18-ash water filter. DETAILED DESCRIPTION

[0057] In order to understand the technical features and contents of the present invention in detail, the preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described in the embodiments, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described here.

[0058] Source of raw materials:

[0059] The water quality indicators of the untreated 1# black water and untreated 2# black water generated by the coal gasification system are shown in Table 2 below:

[0060] Table 2 Water quality indicators of black water to be treated

[0061]

[0062] The raw materials such as flocculants, diatomaceous earth, perlite particles, dispersants, etc. involved in various embodiments and comparative examples are all conventional products that can be purchased on the market.

[0063] Example 1

[0064] Through the optimization method of entrained bed coal gasification ash water quality, refer to Figure 2 As shown, the following steps are included:

[0065] (1) Three-stage flash process

[0066] The treatment object is the 1# black water shown in Table 2. The large black water from the gasifier 1 and the small black water from the washing tower 3 are depressurized by the black water angle valve and enter the high-pressure flash tank 6 for primary flash evaporation. The primary concentrated black water enters the low-pressure flash tank 7 for secondary flash evaporation. The secondary concentrated black water and slag flushing water enter the vacuum flash tank 8 for tertiary flash evaporation. At this time, most of the acid gas in the black water is removed, and the black water is further concentrated to obtain tertiary concentrated black water; wherein:

[0067] The process conditions for the first-stage flash evaporation are: 0.85MPaG, 176°C; the process conditions for the second-stage flash evaporation are: 0.18MPaG, 129°C; the process conditions for the third-stage flash evaporation are: -0.07MPaG, 68°C.

[0068] (2) Flocculation and sedimentation process

[0069] The three-stage concentrated black water is pumped into the clarification tank 9, and solids and calcium and magnesium ions contained in the black water are precipitated by adding a flocculant, and the flocculant is cationic polyacrylamide (CPAM), and the addition amount is 1.4ppm (based on the concentrated black water flow rate); after flocculation and precipitation, the black water concentrate at the bottom of the clarification tank 9 is sent to the plate and frame filter 13 through the underflow pump 12 to remove part of the water, and the resulting filter cake is sent out of the device; the upper clear liquid (overflow gray water) overflowing from the top of the clarification tank 9 is all sent to the filtration-adsorption system for treatment;

[0070] The scale of the gasifier 1 is 1500 tons / day, and the flow rate of overflow ash water from the top of the clarification tank 9 corresponding to a single gasifier is 170 t / h. The particle content in the overflow ash water is 0.146% (before entering the filtration-adsorption system for treatment).

[0071] (3) Treatment process using filtration-adsorption system

[0072] ①Filter aid pre-coating process:

[0073] Diatomaceous earth is pre-added as a filter aid in the filter aid tank 14, and its particle size is 250 meshes; when the liquid level of the filter aid pre-coating tank 15 is at a low level, desalted water is injected, and the filter aid tank 14 is controlled to add the filter aid therein to the filter aid pre-coating tank 15, and stirred to make the filter aid uniformly dispersed to form a filter aid mixed liquid; in the mixed liquid, the filter aid content is 2wt%;

[0074] Before the filter 18A is put into use, the filter aid pre-coating pump 16 connected to the filter aid pre-coating tank 15 is started, and the filter aid mixed liquid in the filter aid pre-coating tank 15 is pumped into the filter 18A through the filter aid pre-coating pipeline for pre-coating, and the filtrate after pre-coating filtration is returned to the filter aid pre-coating tank 15, and the filtrate is observed at the same time. When the filtrate is clear, the filter aid pre-coating pump 16 is turned off, and the filter aid pre-coating process is completed. The filter aid has formed a filter cloth protective layer on the filter cloth of the filter 18A (that is, the pre-coated filter aid layer serves as the filter base layer), and the filter aid pre-coating process on the filter cloth lasts for about 3 minutes.

[0075] ②Filtration-adsorption process:

[0076] After the pre-coating process of the filter aid is completed, the inlet valves of the gray water pressure pump 17 and the filter 18A connected to the gray water pressure pump 17 are opened, and all the overflow gray water from the top of the clarification tank 9 is pumped to the inlet valve of the filter 18A, so that 100% of the overflow gray water enters the filter 18A, and the filter 18A begins to filter the overflow gray water. During the filtration, the gasified fine slag in the overflow gray water accumulates on the filter aid filter base layer to form a gasified fine slag filter layer; that is, while forming a filter-adsorption layer (which includes the filter aid filter base layer and the gasified fine slag filter layer) in the filter 18A, the overflow gray water is filtered-adsorbed; wherein, the SEM characterization of the gasified fine slag filter layer is shown in Figure 3 (a), 3(b), 3(c);

[0077] The gasification fine slag in the overflow ash water contains fine particles and large particles of different particle sizes, and its particle distribution is as follows:

[0078]

[0079] Filters 18A / 18B are set to be one open and one standby; when the filter cloth pressure difference of filter 18A reaches the set value of 0.28MPa, the filter aid pre-coating process of filter 18B is carried out, and the operation is the same as that of filter 18A described above; when the filter cloth pressure difference of filter 18A reaches the set value of 0.3MPa, the inlet valve of filter 18B connected to the gray water pressure pump 17 is opened and all the overflow gray water from the top of the clarification tank 9 is pumped to the inlet valve of filter 18B, and the inlet valve of filter 18A is closed at the same time; filter 18B starts to filter and adsorb the overflow gray water, and the operation process is the same as that of filter 18A described above;

[0080] When the filter cloth pressure difference of filter 18B reaches the set value (same as filter 18A), filter 18A is pre-coated, and filter 18B returns the liquid, blows the filter cake and discharges the material; the above operations are all automatically controlled, and the switching of filters 18A / 18B repeats the above operation process; filter 18A / 18B continues to perform filtering operations under pressure for a period of time, and when the liquid level of filter 18A / 18B drops to 10%, the remaining liquid in filter 18A / 18B is returned to clarification tank 9, and the filter cake obtained by filtration is blown dry from the outside of the filter cake with compressed air, and the filter cake is discharged from the inside of the filter cake by frequent opening and closing of compressed air, and the unloaded filter cake is combined with the filter cake obtained by filtering the black water concentrate obtained at the bottom of the clarification tank 9 through the plate and frame filter 13 and then output outside the system;

[0081] When the system is running stably, the water quality index of the filter outlet water is shown in Table 3, and its particle content is reduced to 0.015%.

[0082] Among them, in one filtration-adsorption cycle, the mass ratio of the amount of filter aid to the gasified fine slag contained in the overflow ash water is 1:12.5, and a 2mm filter aid filter base layer is formed outside the filter cloth of the filter 18A / 18B;

[0083] Filter 18A / 18B is a candle filter, one is open and one is standby. The filter cloth set in filter 18A / 18B is made of PP material, the pore size of the filter cloth is 30μm, the outer diameter of the filter rod is 100mm, the number of filter rods is 400, and the total filtration area is 250m 2 ;

[0084] A 20mm gasified fine slag filter layer is formed outside the filter aid filter base layer. The filtration-adsorption time of a single filter is 6 to 7 hours. The filter aid as the filter base layer makes it easier to completely discharge the obtained filter cake when the filtration step is completed without causing sticky substances to clog the filter cloth, which can further extend the operation cycle.

[0085] Table 3 Main water quality indicators of filter effluent (gray water obtained after treatment)

[0086]

[0087] (4) Grey water circulation

[0088] After the overflow grey water passes through the filtration-adsorption of the gasified fine slag filter layer in the filter 18A / 18B, the obtained grey water filtrate enters the grey water tank 10 through the grey water filtrate pipeline. When the grey water filtrate enters the grey water tank 10, a dispersant is added to the grey water filtrate pipeline. The dispersant is aminotrimethylenephosphonic acid (ATMP), and the addition amount is 75 ppm (based on the mass of the grey water filtrate).

[0089] The recycled ash water obtained after the ash water filtrate and the dispersant are evenly mixed in the ash water tank 10 is pressurized by the low-pressure ash water pump 11. In order to prevent the accumulation of corrosive ions and salts in the circulating recycled ash water to cause pipeline corrosion and scaling, part of the recycled ash water (discharge rate is 45t / h) is discharged to the sewage treatment device, and the remaining recycled ash water enters the deaerator 5 together with external desalted water for deoxygenation treatment, and is then pressurized by the high-pressure ash water pump 4 and circulated into the washing tower 3 and sent to the gasification furnace 1 through the quenching water pump 2 for recycling.

[0090] After adding the filtration-adsorption system, the amount of ash water discharged is reduced, and the scaling cleaning cycle of equipment and pipelines in the ash water treatment system can be extended to more than 2 years.

[0091] Example 2

[0092] Through the optimization method of entrained bed coal gasification ash water quality, refer to Figure 2 As shown, the following steps are included:

[0093] (1) Three-stage flash process

[0094] Refer to step (1) of Example 1, except that the treatment object is 2# black water shown in Table 2.

[0095] (2) Flocculation and sedimentation process

[0096] The three-stage concentrated black water is pumped into the clarification tank 9, and solids and calcium and magnesium ions contained in the black water are precipitated by adding a flocculant. The flocculant is cationic polyacrylamide (CPAM), and the addition amount is 1.8ppm (based on the concentrated black water flow rate). After flocculation and precipitation, the black water concentrate at the bottom of the clarification tank 9 is sent to the plate and frame filter 13 through the underflow pump 12 to remove part of the water, and the resulting filter cake is sent out of the device. The upper clear liquid (overflow gray water) overflowing from the top of the clarification tank 9 is all sent to the filtration-adsorption system for treatment.

[0097] The scale of the gasifier 1 is 2000 tons / day, and the flow rate of overflow ash water from the top of the clarification tank 9 corresponding to a single gasifier is 220 t / h. The particle content in the overflow ash water is 0.12% (without filtration-adsorption system treatment).

[0098] (3) Treatment process using filtration-adsorption system

[0099] ①Filter aid pre-coating process:

[0100] Perlite particles are pre-added as filter aids in the filter aid tank 14, and the particle size is 325 meshes; when the liquid level of the filter aid pre-coating tank 15 is at a low level, desalted water is injected, and the filter aid tank 14 is controlled to add the filter aid therein to the filter aid pre-coating tank 15, and stirred to make the filter aid uniformly dispersed to form a filter aid mixed solution; the content of the filter aid in the mixed solution is 2wt%;

[0101] Before the filter 18A is put into use, the filter aid pre-coating pump 16 connected to the filter aid pre-coating tank 15 is started, and the filter aid mixed liquid in the filter aid pre-coating tank 15 is pumped into the filter 18A through the filter aid pre-coating pipeline for pre-coating, and the filtrate after pre-coating filtration is returned to the filter aid pre-coating tank 15, and the filtrate is observed at the same time. When the filtrate is clear, the filter aid pre-coating pump 16 is turned off, and the filter aid pre-coating process is completed. The filter aid has formed a filter cloth protective layer on the filter cloth of the filter 18A (that is, the pre-coated filter aid layer serves as the filter base layer), and the filter aid pre-coating process on the filter cloth lasts for about 5 minutes.

[0102] ②Filtration-adsorption process:

[0103] After the filter aid pre-coating process is completed, the gray water pressure pump 17 and the inlet valve of the filter 18A connected to the gray water pressure pump 17 are opened, and all the overflow gray water from the top of the clarification tank 9 is pumped to the inlet valve of the filter 18A, so that 100% of the overflow gray water enters the filter 18A, and the filter 18A begins to filter the overflow gray water. During the filtration, the gasified fine slag in the overflow gray water accumulates on the filter aid filter base layer to form a gasified fine slag filter layer; that is, while forming a filter-adsorption layer (which includes the filter aid filter base layer and the gasified fine slag filter layer) in the filter 18A, the overflow gray water is filtered-adsorbed;

[0104] The gasification fine slag in the overflow ash water contains fine particles and large particles of different particle sizes, and its particle distribution is as follows:

[0105]

[0106] Filters 18A / 18B are set to be one open and one standby; when the filter cloth pressure difference of filter 18A reaches the set value of 0.28MPa, the filter aid pre-coating process of filter 18B is carried out, and the operation is the same as that of filter 18A described above; when the filter cloth pressure difference of filter 18A reaches the set value of 0.3MPa, the inlet valve of filter 18B connected to the gray water pressure pump 17 is opened and all the overflow gray water from the top of the clarification tank 9 is pumped to the inlet valve of filter 18B, and the inlet valve of filter 18A is closed at the same time; filter 18B starts to filter and adsorb the overflow gray water, and the operation process is the same as that of filter 18A described above;

[0107] When the filter cloth pressure difference of filter 18B reaches the set value (same as filter 18A), filter 18A is pre-coated, and filter 18B returns the liquid, blows the filter cake and discharges the material; the above operations are all automatically controlled, and the switching of filters 18A / 18B repeats the above operation process; filter 18A / 18B continues to perform filtering operations under pressure for a period of time, and when the liquid level of filter 18A / 18B drops to 10%, the remaining liquid in filter 18A / 18B is returned to clarification tank 9, and the filter cake obtained by filtration is blown dry from the outside of the filter cake with compressed air, and the filter cake is discharged from the inside of the filter cake by frequent opening and closing of compressed air, and the unloaded filter cake is combined with the filter cake obtained by filtering the black water concentrate obtained at the bottom of the clarification tank 9 through the plate and frame filter 13 and then output outside the system;

[0108] When the system is running stably, the water quality index of the filter outlet water is shown in Table 4, and its particle content is reduced to 0.011%.

[0109] In one filtration-adsorption cycle, the mass ratio of the amount of filter aid to the gasified fine slag contained in the overflow ash water is 1:8.5, and a 3 mm filter aid filter base layer is formed outside the filter cloth of the filter 18A / 18B;

[0110] Filter 18A / 18B is a candle filter, one is open and one is standby. The filter cloth set in filter 18A / 18B is made of PA material, the pore size of the filter cloth is 25μm, the outer diameter of the filter rod is 100mm, the number of filter rods is 320, and the total filtration area is 200m 2 ;

[0111] A 20mm gasified fine slag filter layer is formed outside the filter aid filter base layer. The filtration-adsorption time of a single filter is 6 to 7 hours. The filter aid as the filter base layer makes it easier to completely discharge the obtained filter cake when the filtration step is completed without causing sticky substances to clog the filter cloth, which can further extend the operation cycle.

[0112] Table 4 Main water quality indicators of filter effluent (gray water obtained after treatment)

[0113]

[0114] (4) Grey water circulation

[0115] After the overflow grey water passes through the filtration-adsorption of the gasified fine slag filter layer in the filter 18A / 18B, the obtained grey water filtrate enters the grey water tank 10 through the grey water filtrate pipeline. When the grey water filtrate enters the grey water tank 10, a dispersant is added to the grey water filtrate pipeline. The dispersant is aminotrimethylenephosphonic acid (ATMP), and the addition amount is 80 ppm (based on the mass of the grey water filtrate).

[0116] The recycled ash water obtained after the ash water filtrate and the dispersant are evenly mixed in the ash water tank 10 is pressurized by the low-pressure ash water pump 11. In order to prevent the accumulation of corrosive ions and salts in the circulating recycled ash water to cause pipeline corrosion and scaling, part of the recycled ash water (discharge rate is 50t / h) is discharged to the sewage treatment device, and the remaining recycled ash water enters the deaerator 5 together with external desalted water for deoxygenation treatment, and is then pressurized by the high-pressure ash water pump 4 and circulated into the washing tower 3 and sent to the gasification furnace 1 through the quenching water pump 2 for recycling.

[0117] After adding the filtration-adsorption system, the amount of ash water discharged is reduced, and the scaling cleaning cycle of equipment and pipelines in the ash water treatment system can be extended to more than 2 years.

[0118] Example 3

[0119] Through the optimization method of entrained bed coal gasification ash water quality, refer to Figure 2 As shown, the following steps are included:

[0120] (1) Three-stage flash process

[0121] The treatment object is 1# black water shown in Table 2, and refer to step (1) of Example 1.

[0122] (2) Flocculation and sedimentation process

[0123] The three-stage concentrated black water is pumped into the clarification tank 9, and solids and calcium and magnesium ions contained in the black water are precipitated by adding a flocculant. The flocculant is cationic polyacrylamide (CPAM), and the addition amount is 2.0ppm (based on the concentrated black water flow rate). After flocculation and precipitation, the black water concentrate at the bottom of the clarification tank 9 is sent to the plate and frame filter 13 through the underflow pump 12 to remove part of the water, and the resulting filter cake is sent out of the device. 50wt% of the upper clear liquid (overflow gray water) overflowing from the top of the clarification tank 9 is passed into the filtration-adsorption system for treatment, and the other 50wt% of the upper clear liquid (overflow gray water) enters the gray water tank 10.

[0124] The scale of the gasifier 1 is 1500 tons / day, and the overflow ash water flow rate of the top of the clarification tank 9 corresponding to a single gasifier is 170 t / h, and the particle content in the overflow ash water is 0.146% (before entering the filtration-adsorption system for treatment).

[0125] (3) Treatment process using filtration-adsorption system

[0126] ①Filter aid pre-coating process:

[0127] Diatomaceous earth is pre-added as a filter aid in the filter aid tank 14, and its particle size is 250 meshes; when the liquid level of the filter aid pre-coating tank 15 is at a low level, desalted water is injected, and the filter aid tank 14 is controlled to add the filter aid therein to the filter aid pre-coating tank 15, and stirred to make the filter aid uniformly dispersed to form a filter aid mixed liquid; in the mixed liquid, the filter aid content is 2wt%;

[0128] Before the filter 18A is put into use, the filter aid pre-coating pump 16 connected to the filter aid pre-coating tank 15 is started, and the filter aid mixed liquid in the filter aid pre-coating tank 15 is pumped into the filter 18A through the filter aid pre-coating pipeline for pre-coating, and the filtrate after pre-coating filtration is returned to the filter aid pre-coating tank 15, and the filtrate is observed at the same time. When the filtrate is clear, the filter aid pre-coating pump 16 is turned off, and the filter aid pre-coating process is completed. The filter aid has formed a filter cloth protective layer on the filter cloth of the filter 18A (that is, the pre-coated filter aid layer serves as the filter base layer), and the filter aid pre-coating process on the filter cloth lasts for about 3 minutes.

[0129] ②Filtration-adsorption process:

[0130] After the filter aid pre-coating process is completed, the gray water pressure pump 17 and the inlet valve of the filter 18A connected to the gray water pressure pump 17 are opened, and all the overflow gray water from the top of the clarification tank 9 is pumped to the inlet valve of the filter 18A, so that 50% of the overflow gray water enters the filter 18A, and the filter 18A starts to filter the overflow gray water. During the filtration, the gasified fine slag in the overflow gray water accumulates on the filter aid filter base layer to form a gasified fine slag filter layer; that is, while forming a filter-adsorption layer (which includes the filter aid filter base layer and the gasified fine slag filter layer) in the filter 18A, the overflow gray water is filtered-adsorbed;

[0131] Filters 18A / 18B are set up in one open and one standby mode; when the filter cloth pressure difference of filter 18A reaches the set value of 0.28MPa, the filter aid pre-coating process of filter 18B is carried out, and the operation is the same as that of filter 18A described above; when the filter cloth pressure difference of filter 18A reaches the set value of 0.3MPa, the inlet valve of filter 18B connected to the gray water pressure pump 17 is opened and 50% of the overflow gray water from the top of the clarification tank 9 is pumped to the inlet valve of filter 18B, and the inlet valve of filter 18A is closed at the same time; filter 18B starts to filter and adsorb the overflow gray water, and the operation process is the same as that of filter 18A described above;

[0132] When the filter cloth pressure difference of filter 18B reaches the set value (same as filter 18A), filter 18A is pre-coated, and filter 18B returns the liquid, blows the filter cake and discharges the material; the above operations are all automatically controlled, and the switching of filters 18A / 18B repeats the above operation process; filter 18A / 18B continues to perform filtering operations under pressure for a period of time, and when the liquid level of filter 18A / 18B drops to 10%, the remaining liquid in filter 18A / 18B is returned to clarification tank 9, and the filter cake obtained by filtration is blown dry from the outside of the filter cake with compressed air, and the filter cake is discharged from the inside of the filter cake by frequent opening and closing of compressed air, and the unloaded filter cake is combined with the filter cake obtained by filtering the black water concentrate obtained at the bottom of the clarification tank 9 through the plate and frame filter 13 and then output outside the system;

[0133] When the system is running stably, the water quality index of the filter outlet water is shown in Table 5, and its particle content is reduced to 0.071%.

[0134] Among them, in one filtration-adsorption cycle, the mass ratio of the amount of filter aid to the gasified fine slag contained in the overflow ash water is 1:12.5, and a 2mm filter aid filter base layer is formed outside the filter cloth of the filter 18A / 18B;

[0135] Filter 18A / 18B is a candle filter, one is open and one is standby. The filter cloth set in filter 18A / 18B is made of PP material, the pore size of the filter cloth is 30μm, the outer diameter of the filter rod is 100mm, the number of filter rods is 400, and the total filtration area is 250m 2 ;

[0136] A 20mm gasified fine slag filter layer is formed outside the filter aid filter base layer. The filtration-adsorption time of a single filter is 13 to 14 hours. The filter aid as the filter base layer makes it easier to completely discharge the obtained filter cake when the filtration step is completed without causing sticky substances to clog the filter cloth, which can further extend the operation cycle.

[0137] Table 5 Main water quality indicators of filter effluent (gray water obtained after treatment)

[0138]

[0139]

[0140] (4) Grey water circulation

[0141] After the overflow gray water passes through the filtration-adsorption of the gasified fine slag filter layer in the filter 18A / 18B, the obtained gray water filtrate enters the gray water tank 10 through the gray water filtrate pipeline and is mixed with the 50wt% supernatant (gray water) that has been introduced. When the gray water filtrate enters the gray water tank 10, a dispersant is added to the gray water filtrate pipeline. The dispersant is aminotrimethylenephosphonic acid (ATMP), and the addition amount is 85ppm (based on the mass of the gray water filtrate);

[0142] The recycled ash water obtained after the ash water filtrate and the dispersant are evenly mixed in the ash water tank 10 is pressurized by the low-pressure ash water pump 11. In order to prevent the accumulation of corrosive ions and salts in the circulating recycled ash water to cause pipeline corrosion and scaling, part of the recycled ash water (discharge rate is 54t / h) is discharged to the sewage treatment device, and the remaining recycled ash water enters the deaerator 5 together with external desalted water for deoxygenation treatment, and is then pressurized by the high-pressure ash water pump 4 and circulated into the washing tower 3 and sent to the gasification furnace 1 through the quenching water pump 2 for recycling.

[0143] After adding the filtration-adsorption system, the amount of ash water discharged is reduced, and the scaling cleaning cycle of equipment and pipelines in the ash water treatment system can be extended by 1 to 2 years.

[0144] Example 4

[0145] Through the optimization method of entrained bed coal gasification ash water quality, refer to Figure 2 As shown, the following steps are included:

[0146] (1) Three-stage flash process

[0147] The treatment object is 1# black water shown in Table 2, and refer to step (1) of Example 1.

[0148] (2) Flocculation and sedimentation process

[0149] The three-stage concentrated black water is pumped into the clarification tank 9, and solids and calcium and magnesium ions contained in the black water are precipitated by adding a flocculant, and the flocculant is cationic polyacrylamide (CPAM), and the addition amount is 1.4ppm (based on the concentrated black water flow rate); after flocculation and precipitation, the black water concentrate at the bottom of the clarification tank 9 is sent to the plate and frame filter 13 through the underflow pump 12 to remove part of the water, and the resulting filter cake is sent out of the device; the upper clear liquid (overflow gray water) overflowing from the top of the clarification tank 9 is all sent to the filtration-adsorption system for treatment;

[0150] The scale of the gasifier 1 is 1500 tons / day, and the flow rate of overflow ash water from the top of the clarification tank 9 corresponding to a single gasifier is 170 t / h. The particle content in the overflow ash water is 0.146% (before entering the filtration-adsorption system for treatment).

[0151] (3) Treatment process using filtration-adsorption system

[0152] ①Filter aid pre-coating process:

[0153] Diatomaceous earth is pre-added as a filter aid in the filter aid tank 14, and its particle size is 250 meshes; when the liquid level of the filter aid pre-coating tank 15 is at a low level, desalted water is injected, and the filter aid tank 14 is controlled to add the filter aid therein to the filter aid pre-coating tank 15, and stirred to make the filter aid uniformly dispersed to form a filter aid mixed liquid; in the mixed liquid, the filter aid content is 2wt%;

[0154] Before the filter 18A is put into use, the filter aid pre-coating pump 16 connected to the filter aid pre-coating tank 15 is started, and the filter aid mixed liquid in the filter aid pre-coating tank 15 is pumped into the filter 18A through the filter aid pre-coating pipeline for pre-coating, and the filtrate after pre-coating filtration is returned to the filter aid pre-coating tank 15, and the filtrate is observed at the same time. When the filtrate is clear, the filter aid pre-coating pump 16 is turned off, and the filter aid pre-coating process is completed. The filter aid has formed a filter cloth protective layer on the filter cloth of the filter 18A (that is, the pre-coated filter aid layer serves as the filter base layer), and the filter aid pre-coating process on the filter cloth lasts for about 3 minutes.

[0155] ②Filtration-adsorption process:

[0156] After the filter aid pre-coating process is completed, the gray water pressure pump 17 and the inlet valve of the filter 18A connected to the gray water pressure pump 17 are opened, and all the overflow gray water from the top of the clarification tank 9 is pumped to the inlet valve of the filter 18A, so that 100% of the overflow gray water enters the filter 18A, and the filter 18A begins to filter the overflow gray water. During the filtration, the gasified fine slag in the overflow gray water accumulates on the filter aid filter base layer to form a gasified fine slag filter layer; that is, while forming a filter-adsorption layer (which includes the filter aid filter base layer and the gasified fine slag filter layer) in the filter 18A, the overflow gray water is filtered-adsorbed;

[0157] Filters 18A / 18B are set to be one open and one standby; when the filter cloth pressure difference of filter 18A reaches the set value of 0.28MPa, the filter aid pre-coating process of filter 18B is carried out, and the operation is the same as that of filter 18A described above; when the filter cloth pressure difference of filter 18A reaches the set value of 0.3MPa, the inlet valve of filter 18B connected to the gray water pressure pump 17 is opened and all the overflow gray water from the top of the clarification tank 9 is pumped to the inlet valve of filter 18B, and the inlet valve of filter 18A is closed at the same time; filter 18B starts to filter and adsorb the overflow gray water, and the operation process is the same as that of filter 18A described above;

[0158] When the filter cloth pressure difference of filter 18B reaches the set value (same as filter 18A), filter 18A is pre-coated, and filter 18B returns the liquid, blows the filter cake and discharges the material; the above operations are all automatically controlled, and the switching of filters 18A / 18B repeats the above operation process; filter 18A / 18B continues to perform filtering operations under pressure for a period of time, and when the liquid level of filter 18A / 18B drops to 10%, the remaining liquid in filter 18A / 18B is returned to clarification tank 9, and the filter cake obtained by filtration is blown dry from the outside of the filter cake with compressed air, and the filter cake is discharged from the inside of the filter cake by frequent opening and closing of compressed air, and the unloaded filter cake is combined with the filter cake obtained by filtering the black water concentrate obtained at the bottom of the clarification tank 9 through the plate and frame filter 13 and then output outside the system;

[0159] When the system is running stably, the water quality index of the filter outlet water is shown in Table 6, and its particle content is reduced to 0.012%.

[0160] In one filtration-adsorption cycle, the mass ratio of the amount of filter aid to the gasified fine slag contained in the overflow ash water is 1:10, and a 2.5 mm filter aid filter base layer is formed outside the filter cloth of the filter 18A / 18B;

[0161] Filter 18A / 18B is a candle filter, one is open and one is standby. The filter cloth set in filter 18A / 18B is made of PP material, the pore size of the filter cloth is 30μm, the outer diameter of the filter rod is 100mm, the number of filter rods is 400, and the total filtration area is 250m 2 ;

[0162] A 20mm gasified fine slag filter layer is formed outside the filter aid filter base layer. The filtration-adsorption time of a single filter is 6 to 7 hours. The filter aid as the filter base layer makes it easier to completely discharge the obtained filter cake when the filtration step is completed without causing sticky substances to clog the filter cloth, which can further extend the operation cycle.

[0163] Table 6 Main water quality indicators of filter effluent (gray water obtained after treatment)

[0164]

[0165] (4) Grey water circulation

[0166] After the overflow grey water passes through the filtration-adsorption of the gasified fine slag filter layer in the filter 18A / 18B, the obtained grey water filtrate enters the grey water tank 10 through the grey water filtrate pipeline. When the grey water filtrate enters the grey water tank 10, a dispersant is added to the grey water filtrate pipeline. The dispersant is aminotrimethylenephosphonic acid (ATMP), and the addition amount is 75 ppm (based on the mass of the grey water filtrate).

[0167] The recycled ash water obtained after the ash water filtrate and the dispersant are evenly mixed in the ash water tank 10 is pressurized by the low-pressure ash water pump 11. In order to prevent the accumulation of corrosive ions and salts in the circulating recycled ash water to cause pipeline corrosion and scaling, part of the recycled ash water (discharge rate is 45t / h) is discharged to the sewage treatment device, and the remaining recycled ash water enters the deaerator 5 together with external desalted water for deoxygenation treatment, and is then pressurized by the high-pressure ash water pump 4 and circulated into the washing tower 3 and sent to the gasification furnace 1 through the quenching water pump 2 for recycling.

[0168] After adding the filtration-adsorption system, the amount of ash water discharged is reduced, and the scaling cleaning cycle of equipment and pipelines in the ash water treatment system can be extended to more than 2 years.

[0169] Comparative Example 1

[0170] Using traditional methods (such as Figure 1 The process flow shown in Table 2 is used to treat the 1# black water, including the following steps:

[0171] (1) Three-stage flash process

[0172] The process steps are the same as in Example 1.

[0173] (2) Flocculation and sedimentation process

[0174] The three-stage concentrated black water is pumped into the clarification tank 9, and solids and calcium and magnesium ions contained in the black water are precipitated by adding a flocculant, and the flocculant is cationic polyacrylamide (CPAM), and the addition amount is 2.2ppm (based on the concentrated black water flow rate); after flocculation and precipitation, the black water concentrate at the bottom of the clarification tank 9 is sent to the plate and frame filter 13 through the underflow pump 12 to remove part of the water, and the resulting filter cake is sent out of the device;

[0175] The supernatant (overflow grey water) overflowing from the top of the clarification tank 9 enters the grey water tank 10, and a dispersant is added to the grey water tank 10, and the amount of the dispersant added is 90 ppm;

[0176] Among them, the scale of the gasifier 1 is 1500 tons / day, and the flow rate of overflow ash water from the top of the clarifier 9 corresponding to a single gasifier is 170t / h, and the particle content in the overflow ash water is 0.146%;

[0177] The water quality index of the recycled grey water discharged from the grey water tank 10 after adding dispersant for treatment is shown in 1# grey water in Table 1.

[0178] (3) Grey water circulation

[0179] The recycled ash water discharged from the ash water tank 10 is pressurized by the low-pressure ash water pump 11. In order to prevent the accumulation of corrosive ions and salts in the circulating recycled ash water to cause pipeline corrosion and scaling, part of the recycled ash water is discharged to the sewage treatment device with a discharge capacity of 60 t / h. The remaining recycled ash water enters the deaerator 5 together with external desalted water for deoxygenation treatment, and is then pressurized by the high-pressure ash water pump 4 and circulated into the washing tower 3 and into the gasification furnace 1 through the quenching water pump 2 for recycling.

[0180] In the recycled ash water obtained after treatment using the conventional method of this comparative example, the concentrations of COD, calcium and magnesium ions that are prone to scaling, etc. are still relatively high. In order to maintain the water quality, a large amount of dispersants, flocculants and other agents are added in subsequent processes, and a large amount of ash water is discharged, which increases the load of the subsequent water treatment system. The scaling of equipment and pipelines is frequent, and the water treatment system needs to be stopped for cleaning for as short as half a year and as long as a year, which seriously affects the long-term stable operation of the gasification device.

[0181] Comparative Example 2

[0182] Using traditional methods (such as Figure 1 The process flow shown in Table 2) is used to treat the 2# black water shown in Table 2, comprising the following steps:

[0183] (1) Three-stage flash process

[0184] The process operation is the same as in Example 1.

[0185] (2) Flocculation and sedimentation process

[0186] The three-stage concentrated black water is pumped into the clarification tank 9, and solids and calcium and magnesium ions contained in the black water are precipitated by adding a flocculant, and the flocculant is cationic polyacrylamide (CPAM), and the addition amount is 2.7ppm (based on the flow rate of the concentrated black water). After flocculation and precipitation, the black water concentrate at the bottom of the clarification tank 9 is sent to the plate and frame filter 13 through the underflow pump 12 to remove part of the water, and the resulting filter cake is sent out of the device;

[0187] The supernatant (overflow gray water) overflowing from the top of the clarification tank 9 enters the gray water tank 10, and a dispersant is added to the gray water tank 10, and the amount of the dispersant added is 95ppm;

[0188] The scale of the gasifier 1 is 2000 tons / day, and the flow rate of overflow ash water from the top of the clarifier 9 corresponding to a single gasifier is 220 t / h, and the particle content in the overflow ash water is 0.12%;

[0189] The water quality index of the recycled grey water discharged from the grey water tank 10 after adding dispersant for treatment is shown in 2# grey water in Table 1.

[0190] (3) Grey water circulation

[0191] The recycled ash water discharged from the ash water tank 10 is pressurized by the low-pressure ash water pump 11. In order to prevent the accumulation of corrosive ions and salts in the circulating recycled ash water and cause pipeline corrosion and scaling, part of the recycled ash water is discharged to the sewage treatment device with a discharge capacity of 75 t / h. The remaining recycled ash water enters the deaerator 5 together with external desalted water for deoxygenation treatment, and is then pressurized by the high-pressure ash water pump 4 and circulated into the washing tower 3 and into the gasification furnace 1 through the quenching water pump 2 for recycling.

[0192] In the recycled ash water obtained after treatment using the conventional method of this comparative example, the concentrations of COD, calcium and magnesium ions that are prone to scaling, etc. are still relatively high. In order to maintain the water quality, a large amount of dispersants, flocculants and other agents are added in subsequent processes, and a large amount of ash water is discharged, which increases the load of the subsequent water treatment system. The scaling of equipment and pipelines is frequent, and the water treatment system needs to be stopped for cleaning for as short as half a year and as long as a year, which seriously affects the long-term stable operation of the gasification device.

[0193] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for optimizing the quality of ash water from entrained-bed coal gasification, characterized in that: The steps include: (1) Flash process The black water from the gasifier and the scrubber is subjected to multi-stage flash evaporation to obtain multi-stage concentrated black water; (2) Flocculation and sedimentation process The multi-stage concentrated black water obtained as above is passed into a clarification tank, and a flocculant is added for sedimentation; After flocculation and sedimentation, the black water concentrate is obtained at the bottom of the clarification tank, and the supernatant overflowing from the top of the clarification tank is used as overflow gray water; After the black water concentrate at the bottom of the clarifier is filtered to remove part of the water, a filter cake is obtained and sent out of the device; the overflow gray water at the top of the clarifier enters the filtration-adsorption system for treatment; (3) Treatment process of filtration-adsorption system ①Filter aid pre-coating process: Mix the filter aid with desalted water in advance to prepare a filter aid mixed solution; Before the filter is put into use, the filter aid mixture is passed into the filter for pre-coating. After pre-coating and filtration, the filter aid forms a filter aid filtration base layer on the filter cloth of the filter. ②Filtration-adsorption process: After the pre-coating process of the filter aid is completed, the overflow ash water overflowing from the top of the clarification tank is passed into the inlet valve of the filter; in the filter, the gasified fine slag in the overflow ash water is accumulated on the filter base of the filter aid to form a gasified fine slag filter layer and the overflow ash water is filtered-adsorbed at the same time; after the treatment is completed, the remaining liquid in the filter is returned to the clarification tank, and the filter cake obtained by the filtration-adsorption treatment is discharged from the system; (4) Grey water circulation process The ash water filtrate obtained by the filtration-adsorption treatment enters the ash water tank, and a dispersant is added thereto to obtain recycled ash water; a portion of the recycled ash water is discharged from the system, and the remaining recycled ash water is mixed with external desalted water and enters the deaerator for deoxygenation treatment, and then is sent to the scrubber and gasifier for recycling.

2. The optimization method according to claim 1, characterized in that: In step (1), the black water to be treated is passed into a high-pressure flash tank for primary flash evaporation, the primary concentrated black water is passed into a low-pressure flash tank for secondary flash evaporation, and the secondary concentrated black water is passed into a vacuum flash tank for tertiary flash evaporation to obtain tertiary concentrated black water.

3. The optimization method according to claim 1, characterized in that: In step (2), the flocculant is selected from cationic polyacrylamide; Based on the mass of the multi-stage concentrated black water, the dosage of the flocculant is 1-5 ppm.

4. The optimization method according to claim 1, characterized in that: In step (2), the overflow grey water entering the filtration-adsorption system accounts for 50-100 wt % of the total mass of the overflow grey water.

5. The optimization method according to claim 1, characterized in that: In step (3), the filter aid is selected from one or more of perlite particles, diatomaceous earth particles and activated carbon particles, and its particle size is 100 mesh to 400 mesh; Based on the total mass of the filter aid mixed liquid, the content of the filter aid in the filter aid mixed liquid is 1-10wt%; The mass ratio of the filter aid to the gasified fine slag contained in the overflow ash water is 1:(5-20), preferably 1:(8-15).

6. The optimization method according to claim 1, characterized in that: In step (3), the filter aid pre-coating time is 1-10 minutes; The thickness of the filter aid filter base layer is 1-3 mm, preferably 2-3 mm.

7. The optimization method according to claim 1, characterized in that: In step (3), the filter is provided with a filter cloth and a filter rod; The filter cloth is made of polymer material, preferably PP, PE, PA, PPS, PTFE; the pore size of the filter cloth is 20-50 μm; The outer diameter of the filter rod is 100-150 mm, and the number of the filter rods is 200-1000.

8. The optimization method according to claim 7, characterized in that: The total filtration area of ​​the filter is 100-600m 2 .

9. The optimization method according to claim 1, characterized in that: In step (3), the thickness of the gasified fine slag filter layer formed outside the filter aid filter base layer is 10-25 mm, preferably 15-25 mm.

10. The optimization method according to claim 1, characterized in that: In step (4), the dispersant is selected from aminotrimethylenephosphonic acid (ATMP) and / or polyacrylic acid (PAA); Based on the mass of the gray water filtrate, the dosage of the dispersant is 50-150 ppm.

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