Refuse incineration fly ash fixed bed ultra-low water consumption desalination system and method

Abstract

The invention relates to a waste incineration fly ash desalting treatment technology, and aims to provide a waste incineration fly ash fixed bed ultra-low water consumption desalting system and a waste incineration fly ash fixed bed ultra-low water consumption desalting method. The system comprises: a fly ash pretreatment unit for performing gradient heating on waste incineration fly ash under an anaerobic condition, sequentially completing dioxin thermal decomposition and fly ash sintering modification treatment, and performing crushing and screening treatment to obtain coarse-grain fly ash; the fixed bed desalination unit is used for carrying out washing desalination treatment on the coarse-grained fly ash filled in the fixed bed filler column in a bottom water inlet and top water outlet manner; on the basis of the characteristic that the content of chloride ions in the packed column is distributed along the way, cutting off the primary-section fly ash subjected to washing desalination, discharging the primary-section fly ash from the bottom, and supplementing new coarse-grain fly ash from the top; and the wastewater treatment unit is used for collecting the fixed bed desalination wastewater and carrying out evaporation concentration and fractional crystallization treatment to obtain a solid salt product. According to the invention, the mass transfer efficiency can be obviously improved, and efficient desalination is realized through sectional unloading; the method has a remarkable industrial application value.

Description

Technical Field

[0001] The invention relates to a waste incineration fly ash desalination treatment technology, and in particular to a waste incineration fly ash water washing, filtering and desalination method. Background Art

[0002] With the continuous increase in the proportion of incineration treatment of municipal solid waste, the amount of fly ash produced has shown a significant upward trend. As a hazardous waste, fly ash has a high toxicity characteristic. The high concentration of soluble chloride salts contained in it not only poses a pollution threat to the environment, but also seriously limits the resource utilization of fly ash. Therefore, it is urgent to carry out harmless treatment. At present, the water washing method has become the mainstream technology for fly ash desalination treatment due to its advantages such as simple process, low equipment investment and stable operation. However, the existing water washing process is essentially a simple combination of multiple batch treatment units, the system is complex, and a large water-ash ratio (usually ≥3:1) is required, which produces a large amount of low-concentration brine, which significantly increases the energy consumption of the subsequent evaporation and crystallization process; at the same time, the combination of multi-stage countercurrent water washing and plate and frame filter press is not only time-consuming, but also energy-intensive. In addition, some chloride ions still remain in the fly ash after water washing, and the desalination effect does not reach the ideal level.

[0003] Fixed bed continuous elution technology has been widely used in industrial separation processes due to its high mass transfer efficiency. However, due to the small particle size of fly ash, strong water absorption and certain gelling properties, direct use of this technology will lead to clogging of the fixed bed. Patent document CN118808282A discloses a fly ash diafiltration desalination method, which is carried out by mixing fly ash with diafiltration auxiliary materials such as river sand and using a series of fly ash cleaning columns for diafiltration desalination. However, due to the small particles and poor permeability of fly ash, this method has significant defects in practical applications. First, the design of the series cleaning column makes the material produce huge resistance when passing through each module, and the pressure loss caused by multiple modules in series is unacceptable; secondly, in order to recover the diafiltration auxiliary materials, additional clean water washing and screening steps are required, which not only increases the water consumption and energy consumption of the process, but also brings difficulties to the disposal of polluted water. Similarly, other methods that use auxiliary materials to improve the performance of fly ash water washing columns are also difficult to overcome the outlet blockage problem, and the density difference between the auxiliary materials and the fly ash is easy to cause fluidization stratification and aggravate the blockage. More importantly, auxiliary materials often need to be disposed of together with fly ash after being mixed, which substantially increases the amount of hazardous waste to be handled.

[0004] Based on the above background, the purpose of the present invention is to provide a new type of low-energy consumption and high-efficiency desalination system and method to solve the technical problems in the prior art such as complex process flow, numerous operating steps, high energy consumption and large water consumption, so as to achieve efficient desalination of fly ash. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a fixed-bed desalination system and method for municipal solid waste incineration fly ash with ultra-low water consumption.

[0006] To solve the technical problem, the solution of the present invention is as follows:

[0007] Provide a fixed-bed desalination system for municipal solid waste incineration fly ash with ultra-low water consumption, comprising:

[0008] A fly ash pretreatment unit, which is suitable for heating the municipal solid waste incineration fly ash at a gradient temperature under an anaerobic condition to complete the thermal decomposition of dioxin and the sintering modification treatment of fly ash in sequence; after being crushed and screened, the pretreated coarse fly ash is obtained.

[0009] A fixed-bed desalination unit, which is suitable for washing and desalinating the coarse fly ash filled in the fixed-bed packing column in a way of water inlet at the bottom and water outlet at the top; and based on the characteristics of the distribution of chloride ion content along the packing column, the initial-stage fly ash after washing and desalination is cut off and discharged from the bottom, and then new coarse fly ash is supplemented from the top.

[0010] A wastewater treatment unit, which is suitable for collecting the fixed-bed desalination wastewater and obtaining solid salt products after evaporation concentration and stepwise crystallization treatment.

[0011] As a preferred embodiment of the present invention, the fly ash pretreatment unit includes a heat treatment furnace, a crusher and a vibrating screening device connected in sequence; the heat treatment furnace is a multi-stage rotary kiln structure and is provided with a partition temperature control device for forming two temperature ranges of thermal decomposition first and then sintering in the inner cavity of the heat treatment furnace; the crusher is a double-rotor hammer crusher for crushing the sintered fly ash lumps after heating; the vibrating screening device is a standard vibrating screen for screening coarse fly ash.

[0012] As a preferred embodiment of the present invention, the fixed-bed desalination unit includes a fixed-bed packing column, which is provided with a discharge port, a water inlet and a water flow distributor in sequence at its lower end, a feed port, a water outlet and a water flow distributor in sequence at its upper end, and a pneumatic truncation device in its middle and lower part; wherein, the feed port and the discharge port are provided with electric gate valves; the water flow distributor is connected with a pneumatic pulling device and can perform lateral displacement according to the needs of feeding and discharging operations; the pneumatic truncation device adopts a double-layer valve plate design and an on-line conductivity meter is arranged above it.

[0013] As a preferred embodiment of the present invention, the water flow distributor is composed of a perforated plate and a polypropylene filter screen, and the aperture of the filter screen is smaller than the particle size of the coarse fly ash; the distance between the pneumatic truncation device and the discharge port is 20% - 40% of the total height of the packing column, and a buffer zone is directly arranged between the two valve plates of the pneumatic truncation device.

[0014] As a preferred embodiment of the present invention, the wastewater treatment unit includes a brine collection tank, a multi-effect evaporator, and a stepwise crystallization device connected in sequence; the multi-effect evaporator is provided with a condensate outlet and a concentrated liquid outlet.

[0015] As a preferred embodiment of the present invention, the connection between the units is achieved in the following manner: between the heat treatment furnace, crusher, and vibrating screening device in the fly ash pretreatment unit, they are connected through a fly ash conveying channel; the vibrating screening device is connected to the upper feed port of the packing column in the fixed bed desalination unit through a fly ash conveying channel, the water outlet at the upper end of the packing column is connected to the brine collection tank through a pipeline, and the water inlet at the lower end of the packing column is sequentially connected to a filter and a water pump through a pipeline; the brine collection tank, multi-effect evaporator, and stepwise crystallization device in the wastewater treatment unit are connected in sequence through pipelines, and the condensate outlet of the multi-effect evaporator is connected to the water inlet at the lower end of the packing column through a pipeline; the flue gas discharge pipe of the heat treatment furnace is connected to a heat exchanger and then to a tail gas treatment device, and the multi-effect evaporator and the stepwise crystallization device are respectively connected to the heat exchanger through a medium circulation loop.

[0016] The present invention further provides a method for desalination of municipal solid waste incineration fly ash with ultra-low water consumption in a fixed bed, which uses the device described in the foregoing claims. The method includes:

[0017] (1) Fly ash pretreatment: Feed the original municipal solid waste incineration fly ash into a heat treatment furnace protected by a nitrogen atmosphere. The heat treatment furnace adopts a multi-stage rotary kiln structure and is heated in a zone temperature control manner; after feeding, thermal decomposition is first carried out to eliminate dioxin-like toxic substances; then fly ash sintering is carried out to complete sintering modification; the treated material is crushed and screened, and coarse fly ash within a preset particle size range is collected.

[0018] (2) Loading coarse fly ash: Uniformly fill the pretreated coarse fly ash into the fixed bed packing column, and seal the upper and lower ends of the packing column with water distributors to ensure uniform water distribution and prevent fly ash loss.

[0019] (3) Water washing desalination: Use a feed water pump to pump water upward from the bottom of the packing column to fully contact with the fly ash for countercurrent washing; the washed salt-containing wastewater is discharged to the brine collection tank; use an on-line conductivity meter to monitor the change of the salt concentration in the fly ash in the initial section of the packing column in real time. When the conductivity of the effluent water drops below 1.5 S / m, it indicates that the fly ash in this section has completed desalination.

[0020] (4) Sectional unloading: Close the feed water pump, start the pneumatic cutoff device to separate the fly ash in the packing column; laterally move the water distributor at the bottom, open the electric gate valve at the discharge port, and unload the desalinated fly ash; close the electric gate valve at the discharge port and restore the water distributor.

[0021] (5) Supplementary coarse fly ash: Close the pneumatic cutoff device to restore the connected state in the packing column. The original filled fly ash falls and forms a cavity at the top. Transversely move the water distributor at the top, open the electric gate valve of the feed inlet, add new pretreated fly ash into the cavity to keep the bed height constant, and restore the water distributor after completion. Repeat steps (3)-(5) to achieve continuous operation;

[0022] (6) Evaporation and salt separation: Feed the salt-containing wastewater in the brine collection tank into a multi-effect evaporator for concentration and crystallization, and the condensed water is recycled as washing water; The mixed salt concentrate obtained by evaporation and crystallization is then sent to a fractional crystallization device for fractional crystallization to obtain industrial-grade chloride salt products.

[0023] As a preferred embodiment of the present invention, the temperature during low-temperature thermal decomposition is 300-400 °C, and the time is 30-60 minutes; The temperature during high-temperature sintering is 550-600 °C, and the time is 12-20 minutes; The particle size range of the coarsely screened and collected fly ash is 50-120 mesh.

[0024] As a preferred embodiment of the present invention, the influent flow rate in the fixed-bed packing column is controlled during water washing and desalting, and the specific flow rate is calculated and determined by the following formula:

[0025]

[0026] In the formula: Q is the influent flow rate (L / min); ε is the porosity of the fixed bed, and the value range is 0.35-0.45, which is specifically determined according to actual measurement; A is the cross-sectional area of the packing column, and H is the bed height; t c is the contact time, in minutes, and the value range is 10-120 minutes (specifically selected according to the length-diameter ratio).

[0027] As a preferred embodiment of the present invention, clean water is used during water washing and desalting, or polluted water containing F - , microplastics is used for desalting to achieve co-removal of pollutants by utilizing the adsorption effect of fly ash; The waste heat dissipated during the cooling process of sintered fly ash is used for preheating in the low-temperature thermal decomposition process through a heat exchanger, or as the heat source for the multi-effect evaporator and the fractional crystallization device; The fixed-bed packing column adopts a cylinder-cone combination, where the inner diameter of the cylinder part is 500-1000 mm, and the length-diameter ratio is 3-8; The lower end of the cylinder is connected to the cone to ensure uniform water flow. The outlet inclination angle of the contracted cone is designed to be 50-70° to avoid forming dead zones and guide the discharge of materials; The filter screen of the distributor is made of temperature-resistant and corrosion-resistant polypropylene material to ensure stable structure during long-term water washing.

[0028] Description of the invention principle:

[0029] During long-term in-depth research, the applicant found that at medium and low temperatures (550 - 600 °C), the chlorides in fly ash will melt, and at the same time, aluminosilicates will be formed, eventually forming a hard sintered block. If combined with a common low-temperature thermal decomposition process (300 - 400 °C), medium and low-temperature sintering of fly ash can be achieved under low energy consumption conditions, thereby significantly reducing the gelling properties and water absorption of fly ash; at the same time, increasing its particle size to make it suitable as a fixed-bed filler. On this basis, the present invention proposes an innovative solution: using the physical and chemical properties of fly ash at medium and low temperatures to convert the original fly ash into a coarse-grained fly ash material suitable for fixed-bed fillers, and realizing continuous desalination treatment of fly ash based on the characteristics of efficient mass transfer in the fixed bed. The specific technical principle is as follows:

[0030] (1) Mechanism of fly ash thermal modification and dioxin synergistic degradation:

[0031] The fly ash thermal modification process is mainly divided into two stages. In the first stage, combined with the fly ash low-temperature thermal decomposition process, in a nitrogen atmosphere, after the original fly ash is introduced into the heat treatment furnace, in the temperature range of 300 - 400 °C, through reactions such as catalytic dechlorination and oxidative ring opening, the dioxin toxicity equivalent is reduced by more than 99%; in the second stage, the temperature is raised to 550 - 600 °C for sintering modification. Under this temperature condition, two key physical and chemical change processes occur in the fly ash. First, the chlorides in the fly ash (mainly NaCl, KCl) reach the melting point and melt, and the molten chlorides form a liquid phase on the particle surface, promoting the initial bonding between fly ash particles. At the same time, the silicon, calcium, and aluminum components in the fly ash undergo sintering, and small particles agglomerate, significantly reducing the specific surface area of the fly ash and weakening its surface activity and gelling properties; the hydrophobicity of the sintered particles inhibits the water absorption of the fly ash, effectively overcoming the disadvantages of the original fly ash being prone to caking and hardening. In addition, through the cascade reuse of waste heat in the low-temperature section, the heating consumption in the medium-temperature section is reduced, and the waste heat dissipated during the cooling of the sintered fly ash can also be used for preheating in the low-temperature section, and the comprehensive energy consumption is significantly lower than that of traditional high-temperature sintering, taking into account both environmental and economic effects.

[0032] (2) Mechanism of fly ash desalination column water washing:

[0033] In the process of washing and desalting fly ash in a fixed-bed packed column mode, the along-flow distribution of chloride content after the packed column passes water once is an obvious three-segment distribution including a desalting section, a mutation section, and a stable section. This is because in the initial stage of water washing, the soluble chlorides in the fly ash will quickly dissolve in water in the form of single salts, causing the washing liquid to quickly reach a nearly saturated or saturated state. This situation makes it so that in the subsequent sections, only a small amount of fly ash can continue to be desalted, and it will also make the washing liquid at the outlet saturated or supersaturated. When washing and desalting fly ash in a fixed-bed packed column mode, three effects are mainly considered, namely the adsorption effect, the dissolution rate, and the diffusion effect. Experimental studies have found that the adsorption effect and the dissolution rate have relatively little influence on the along-flow distribution of chloride ions, while the diffusion effect has a greater influence. As time goes by, the diffusion effect will gradually flatten the along-flow distribution curve of chloride ions in the packed column. In view of this, if the fly ash water-washing column that has completed desalting can be cut off and unloaded in time, this characteristic of the along-flow distribution can be utilized to the maximum extent, thereby effectively saving water consumption.

[0034] (3) Fixed-bed mass transfer and co-removal mechanism of pollutants:

[0035] The modified fly ash as a fixed-bed packing can maintain a stable void structure in the bed layer. This process adopts an upward flow regime, and clear water is pumped into the bottom of the fixed bed by a water pump to achieve countercurrent contact with the modified fly ash particles. This countercurrent design not only provides a greater mass transfer driving force, but also the upward water flow can moderately disturb the bed layer to form a more sufficient mass transfer contact interface. Since the packing surface is hydrophobic and the pore structure is stable, the upward water flow can be evenly distributed in the voids of the bed layer, effectively avoiding the agglomeration of fly ash in the traditional water washing process, thereby significantly improving the mass transfer efficiency.

[0036] The entire water passing and desalting process maintains a slow flow rate (Reynolds number Re << 1, belonging to the laminar flow state, and the influence of inertial force can be ignored). According to Darcy's law, combined with parameters such as permeability (K), cross-sectional area (A), pressure drop (ΔP), fluid viscosity (μ), and flow path length (L), the volume flow rate (Q) or the corresponding apparent flow velocity (v) can be calculated. The flow rate should be set appropriately, neither too fast to damage the fixed bed layer structure nor too slow to prolong the contact time and affect the desalting efficiency and effect. Specifically, the simplified formula given in this method can be referred to. In addition, the segmented design of the fixed bed ensures the continuous progress of the water washing process and realizes efficient desalting.

[0037] In the process of washing and desalting, the modified fly ash can not only achieve efficient removal of chlorides, but also show a co-removal effect on other pollutants in water (such as F - , microplastics, etc.). This is because the sintered particles formed during the modification process have a certain adsorption activity and can fix these pollutants through physical adsorption and chemical precipitation, thereby realizing the co-treatment of pollutants.

[0038] Compared with the prior art, the present invention has the following remarkable advantages:

[0039] 1. The present invention converts fly ash into coarse-grained materials with a relatively large particle size (120 - 50 mesh) through low-temperature sintering, overcoming the inherent defects of fly ash such as its gelling property and strong water absorption, thereby realizing the stable operation of continuous water washing and desalination in a fixed bed, and effectively reducing the energy consumption and water consumption in the treatment process.

[0040] 2. The innovative process adopted by the present invention significantly improves the mass transfer efficiency, and the desalination rate is greatly increased compared with traditional water washing methods. At the same time, the water consumption can be reduced by more than 85%, realizing the efficient utilization of resources;

[0041] 3. The present invention discharges materials in a segmented manner for the water washing and desalination mechanism of the packing column, achieving efficient desalination.

[0042] 4. The present invention significantly reduces the generation amount of the washing liquid, and the obtained washing liquid is in a saturated or supersaturated state. This characteristic significantly reduces the energy consumption of the subsequent evaporation and salt extraction process by about 90%, having good economic benefits;

[0043] 5. The present invention is not only applicable to the treatment of conventional pollutants, but also can realize the co-disposal of physical and chemical polluted wastewater. This process has the characteristics of high reaction efficiency and good treatment effect, and can improve the water washing effect at the same time, having significant industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Structural diagrams of each part designed for the present invention.

[0045] Figure 2 Structural diagram of the fly ash water washing fixed bed packing column designed for the present invention.

[0046] Figure 3 Process flow diagram of the efficient water washing and desalination method of the present invention.

[0047] Among them, Figure 2 Each label represents: 1 feed inlet; 2 water outlet; 3 perforated plate; 4 filter screen; 5 conductivity meter; 6 pneumatic cut-off device; 7 filter screen; 8 perforated plate; 9 water inlet; 10 discharge outlet; 11 water pump; 12 brine collection tank; 13 vacuum pump. DETAILED DESCRIPTION OF THE INVENTION

[0048] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0049] As Figure 1As shown in the figure, the ultra-low water consumption desalination system for municipal solid waste incineration fly ash in a fixed bed of the present invention includes a fly ash pretreatment unit, a fixed bed desalination unit, and a wastewater treatment unit. Among them, the fly ash pretreatment unit is suitable for heating the municipal solid waste incineration fly ash at a gradient temperature under an anaerobic condition to sequentially complete the thermal decomposition of dioxins and the sintering modification treatment of fly ash; after being crushed and screened, the pretreated coarse fly ash is obtained; the fixed bed desalination unit is suitable for washing and desalinating the coarse fly ash filled in the fixed bed packing column in a way of water inlet at the bottom and water outlet at the top; and based on the characteristics of the along-way distribution of chloride ion content in the packing column, the initial-stage fly ash after washing and desalination is cut off and discharged from the bottom, and then new coarse fly ash is supplemented from the top; the wastewater treatment unit is suitable for collecting the fixed bed desalination wastewater, and obtaining solid salt products after evaporation concentration and step-by-step crystallization treatment.

[0050] The fly ash pretreatment unit includes a heat treatment furnace, a crusher, and a vibrating screening device connected in sequence; the heat treatment furnace is of a multi-stage rotary kiln structure and is provided with a partition temperature control device for forming two temperature ranges of thermal decomposition first and then sintering in the inner cavity of the heat treatment furnace; the involvement of partition temperature control and two-step treatment can ensure the continuity of the heat treatment process and improve the efficiency of fly ash pretreatment. The crusher is a double-rotor hammer crusher for crushing the sintered fly ash lumps after heating; the vibrating screening device is a standard vibrating screen for screening coarse fly ash of 50 - 120 mesh (particle size 0.125 - 0.3 mm).

[0051] The fixed bed desalination unit includes a fixed bed packing column, which is sequentially provided with a discharge port, a water inlet, and a water flow distributor at its lower end, and sequentially provided with a feed port, a water outlet, and a water flow distributor at its upper end, and is provided with a pneumatic truncation device in its middle and lower part; among them, the feed port and the discharge port are provided with electric gate valves; the water flow distributor is connected to a pneumatic pulling device and can perform lateral displacement according to the requirements of feeding and discharging operations; the pneumatic truncation device adopts a double-layer valve plate design and is provided with an on-line conductivity meter above it. The water flow distributor is composed of a perforated plate and a filter screen, and the aperture of the filter screen is smaller than the particle size of the coarse fly ash.

[0052] The wastewater treatment unit includes a brine collection tank, a multi-effect evaporator, and a step-by-step crystallization device connected in sequence; the multi-effect evaporator is provided with a condensate outlet and a concentrated liquid outlet; the step-by-step crystallization device is used for separating and obtaining products such as industrial-grade potassium chloride and sodium chloride.

[0053] The connection of each unit is achieved in the following manner: between the heat treatment furnace, crusher, and vibrating screening device in the fly ash pretreatment unit, they are connected through a fly ash conveying channel; the vibrating screening device is connected to the upper feed port of the packing column in the fixed bed desalination unit through a fly ash conveying channel, the water outlet at the upper end of the packing column is connected to the brine collection tank through a pipeline, and the water inlet at the lower end of the packing column is sequentially connected to a filter and a water pump through pipelines; the brine collection tank, multi-effect evaporator, and fractional crystallization device in the wastewater treatment unit are sequentially connected through pipelines, and the condensate outlet of the multi-effect evaporator is connected to the water inlet at the lower end of the packing column through a pipeline; the flue gas discharge pipe of the heat treatment furnace is connected to a heat exchanger and then to a tail gas treatment device, and the multi-effect evaporator and fractional crystallization device are respectively connected to the heat exchanger through a medium circulation loop.

[0054] The fixed bed packing column for fly ash washing has a structure as Figure 2 shown. The fixed bed packing column adopts a cylinder-conical combination. The inner diameter of the cylindrical part is 500 - 1000 mm, and the length-diameter ratio is 3 - 8. The lower end of the cylinder is connected to the cone to ensure uniform water flow. The outlet inclination angle of the contracting cone is designed to be 50 - 70° to avoid the formation of dead zones and guide the discharge of materials. At the upper end of the fixed bed packing column, there are successively a feed port 1, a water outlet 2, and a water distributor (composed of a perforated plate 3 and a filter screen 4). At the outlet of the contracting cone, there are successively a water distributor (composed of a perforated plate 8 and a filter screen 7), a water inlet 9, and a discharge port 10. In the middle and lower part of the inner cavity of the fixed bed packing column, there is a pneumatic cut-off device 6, which is 20% - 40% of the total height of the packing column away from the discharge port 10; the pneumatic cut-off device 6 adopts a double-layer valve plate design with a spacing of 50 mm to ensure the support of the upper-side packing, and a buffer zone is directly arranged between the two layers of valve plates. During the washing operation, the valve plates are in the retracted state, enabling the continuous washing operation of the loaded coarse-grained fly ash. The perforated plates 3 and 8 are made of stainless steel, and the filter screens 4 and 7 are made of temperature-resistant and corrosion-resistant polypropylene material to ensure stable structure during long-term washing. The aperture of the filter screen is 140 - 200 meshes (0.075 - 0.106 mm) to prevent the loss of fly ash. An electrical conductivity meter 5 is arranged above the pneumatic cut-off device 6 to determine the salt concentration in the lower section by measuring the electrical conductivity of water in real time. The measurement range is 0 - 50 S / m, and the accuracy is ±0.5%. When the electrical conductivity value is stably lower than 1.5 S / m for about 3 minutes, it is regarded that the lower section at the cut-off has completed desalination; at this time, the cut-off device can be started to separate the desalination column and discharge the desalinated fly ash in the lower section. The water pump 11 is connected to the water inlet 9 through a pipeline to provide power for the upward transportation of water; the water outlet 2 is connected to the brine collection tank 12 through a pipeline to collect the washing liquid into the brine collection tank 12; the air inlet of the vacuum pump 12 is connected to the brine collection tank 12 through a vacuum rubber hose; during the washing process, starting the vacuum pump can create a negative pressure environment and improve the water permeability.

[0055] As Figure 3As shown in the figure, the method for desalination of incineration fly ash in a fixed bed according to the present invention mainly includes the following steps:

[0056] (1) Fly ash pretreatment: Feed the original municipal solid waste incineration fly ash into a heat treatment furnace protected by a nitrogen atmosphere. The heat treatment furnace adopts a multi-stage rotary kiln structure and is heated in a zone temperature control mode. The fly ash material gradually moves from the low-temperature area to the high-temperature area inside the rotary kiln. After the original fly ash is fed, it first undergoes low-temperature thermal decomposition in the temperature range of 300 - 400 °C for 30 - 60 minutes to effectively decompose dioxin-like toxic substances; then it gradually moves to the temperature range of 550 - 600 °C for 12 - 20 minutes for high-temperature sintering to complete the sintering modification of the fly ash. Feed the sintered material into a double-rotor hammer crusher (PCX0706) for crushing to refine the particle size; then feed the crushed modified fly ash particles into a vibrating screening device (standard vibrating screen) for screening, and collect the particles in the particle size range of 50 - 120 mesh as the raw material for subsequent use.

[0057] (2) Loading of coarse fly ash: Uniformly fill the pretreated coarse fly ash into the fixed bed packing column, and seal the upper and lower ends of the packing column with water distributors to ensure uniform water distribution and prevent fly ash loss.

[0058] (3) Continuous water washing desalination: Start the vacuum pump to create a negative pressure environment, and pump clean water or polluted water from the bottom water inlet of the fixed bed upward at a flow rate of Q through the water inlet pump to fully contact with the fly ash for countercurrent washing; monitor the chloride ion concentration at the cut-off point in real time through an on-line conductivity meter. When the conductivity drops below 1.5 S / m, it indicates that the fly ash in the lower section of the cut-off position has been desalinated; when eluting salts, clean water can be used, or polluted water containing F - and microplastics can be used for desalination to achieve co-removal of pollutants by utilizing the adsorption effect of fly ash.

[0059] (4) Sectional discharging: Close the water inlet pump, start the pneumatic cut-off device to separate the fly ash in the packing column; horizontally move the bottom water distributor, open the electric gate valve at the discharge port, and discharge the desalinated fly ash; close the electric gate valve at the discharge port and restore the water distributor;

[0060] (5) Supplementary feeding of coarse fly ash: Close the pneumatic cut-off device to restore the communication state in the packing column, and the original filled fly ash falls and forms a cavity at the top; horizontally move the top water distributor, open the electric gate valve at the feed port, add new pretreated fly ash into the cavity to keep the bed height constant, and restore the water distributor after completion; repeat steps (3) - (5) to achieve continuous operation;

[0061] (6) Evaporation and salt separation: The salt-containing wastewater in the brine collection tank is sent to a multi-effect evaporator for concentration and crystallization, and the condensed water is recycled as washing water; the mixed salt concentrate obtained by evaporation and crystallization is then sent to a fractional crystallization device for fractional crystallization to obtain industrial-grade chloride salt products.

[0062] In the present invention, the waste heat dissipated during the cooling process of sintered fly ash can be used through a heat exchanger for preheating in the low-temperature thermal decomposition process, or as the heat source for the multi-effect evaporator and the fractional crystallization device.

[0063] The following specific examples are used to further illustrate the application of the present invention.

[0064] Example 1

[0065] (1) Fly ash pretreatment: The original fly ash is placed in a heat treatment furnace with a multi-stage rotary kiln structure under the protection of a nitrogen atmosphere for thermal modification treatment. First, low-temperature thermal decomposition is carried out in the 300 °C temperature range in the front section of the rotary kiln for 60 minutes to effectively decompose dioxin-like toxic substances; based on the furnace body structure and the principle of rotational discharging, the fly ash material gradually moves to the 600 °C temperature range in the rear section of the rotary kiln for 12 minutes of high-temperature sintering to complete the sintering modification of the fly ash. The sintered material is sent to a double-rotor hammer crusher (PCX0706) for crushing to refine the particle size, and then the modified fly ash particles after crushing treatment are sent to a vibrating screening device (standard vibrating screen) for screening, and the particles in the particle size range of 50-120 meshes are collected as the raw materials for subsequent utilization;

[0066] (2) Fixed bed filling: The pretreated coarse fly ash is uniformly filled into a fixed bed packing column (the inner diameter of the cylindrical part is 500 mm, the length-diameter ratio is 8, the outlet inclination angle of the conical body is designed to be 50°, and the void fraction of the fixed bed is 0.35), and a water flow distributor is used to ensure uniform water distribution, and a filter screen is used to prevent the loss of fly ash particles;

[0067] (3) Water washing and desalination: Use a feed pump to pump water upward from the bottom of the packing column to fully contact with the fly ash for countercurrent washing; the salt-containing wastewater after washing is discharged to the brine collection tank; use an on-line conductivity meter to monitor the change of the salt concentration in the fly ash in the initial section of the packing column in real time. When the effluent conductivity drops below 1.5 S / m, it indicates that the fly ash in this section has completed desalination;

[0068] (4) Sectional discharging: After detecting that the fly ash in the lower section has completed desalination, turn off the feed pump, start the pneumatic cutoff device to divide the fixed bed into upper and lower sections, open the bottom discharge port, and discharge the desalinated fly ash;

[0069] (5) Continuous feeding: Close the discharge port, close the pneumatic cutoff device, add new pretreated fly ash to the top of the fixed bed to keep the bed height constant; repeat steps (3)-(4) to achieve continuous operation;

[0070] (6) Evaporation and salt separation: The collected salt-containing wastewater is sent to a multi-effect evaporator and a distributed crystallization device for concentration and crystallization. The evaporated condensate is returned to the water pump through a pipeline and used as cleaning water; the mixed salt obtained by evaporation and crystallization is subjected to fractional crystallization, and the prepared NaCl meets the secondary standard of industrial salt in GB / T 5462, and the KCl meets the qualified product standard in GB / T 6549.

[0071] In this embodiment, the comprehensive liquid-solid ratio is 0.58, and the chlorine content of the fly ash after desalination is reduced from 27.8% to 1.24%, meeting the standard of "Technical Specification for Pollution Control of Municipal Solid Waste Incineration Fly Ash" (HJ 1134-2020).

[0072] Example 2

[0073] (1) Fly ash pretreatment: The raw fly ash is placed in a heat treatment furnace with a multi-stage rotary kiln structure under the protection of a nitrogen atmosphere for thermal modification treatment. First, it undergoes low-temperature thermal decomposition at a temperature range of 400°C in the front section of the rotary kiln for 30 minutes to effectively decompose dioxin-like toxic substances; based on the rotation of the furnace body structure, the fly ash material gradually moves to the 550°C temperature range in the rear section of the rotary kiln for 20 minutes of high-temperature sintering to complete the sintering modification of the fly ash. The sintered material is sent to a double-rotor hammer crusher (PCX0706) for crushing to refine the particle size, and then the modified fly ash particles after crushing are sent to a vibrating screening device (standard vibrating screen) for screening, and the particles in the particle size range of 50-120 mesh are collected as raw materials for subsequent use;

[0074] (2) Fixed bed filling: The pretreated coarse fly ash is evenly filled into a fixed bed packing column (the inner diameter of the cylindrical part is 1000 mm, the length-diameter ratio is 3, the outlet inclination angle of the conical body is designed to be 70°, and the void fraction of the fixed bed is 0.45). The water flow distributor is used to ensure uniform water flow distribution, and the filter screen prevents the loss of fly ash particles;

[0075] (3) Continuous water washing and desalination: Start the vacuum pump to create a negative pressure environment, and pump the contaminated water (F - polluted water (F - concentration 56 mg / L) is transported upward from the bottom water inlet of the fixed bed at a flow rate of 33 L / min to fully contact with the fly ash for countercurrent washing; the chloride ion concentration at the cut-off point is monitored in real time through an on-line conductivity meter. When the conductivity drops below 1.5 S / m, it indicates that the fly ash in the lower section of the cut-off position has completed desalination;

[0076] (4) Sectional discharging: After detecting that the fly ash in the lower section has completed desalination, turn off the inlet water pump, start the pneumatic cut-off device to divide the fixed bed into upper and lower sections, open the bottom discharge port, and discharge the desalinated fly ash;

[0077] (5) Continuous feeding: Close the discharge port and the pneumatic cutoff device, and add new pretreated fly ash to the top of the fixed bed to keep the bed height constant; repeat steps (3)-(4) to achieve continuous operation;

[0078] (6) Evaporation and salt separation: Feed the collected salt-containing wastewater into a multi-effect evaporator and a distributed crystallization device for concentration and crystallization. The evaporated condensate is piped back to the water pump and used as washing water; the mixed salt obtained by evaporation and crystallization is subjected to fractional crystallization, and the prepared NaCl meets the secondary standard of industrial salt in GB / T 5462, and the KCl meets the qualified product standard in GB / T 6549.

[0079] In this example, the comprehensive liquid-solid ratio is 0.76, F - The concentration drops to 4 mg / L, and the chlorine content of the fly ash after desalination decreases from 31.6% to 0.96%, meeting the standard of "Technical Specification for Pollution Control of Municipal Solid Waste Incineration Fly Ash" (HJ1134-2020).

[0080] Example 3

[0081] (1) Fly ash pretreatment: Place the original fly ash in a heat treatment furnace with a multi-stage rotary kiln structure under the protection of a nitrogen atmosphere for thermal modification treatment. First, perform low-temperature thermal decomposition in the 350 °C temperature range in the front section of the rotary kiln for 45 minutes to effectively decompose dioxin-like toxic substances; based on the rotation of the furnace body structure, the fly ash material gradually moves to the 580 °C temperature range in the rear section of the rotary kiln for 16 minutes of high-temperature sintering to complete the sintering modification of the fly ash. Feed the sintered material into a double-rotor hammer crusher (PCX0706) for crushing to refine the particle size, and then feed the crushed modified fly ash particles into a vibrating screening device (standard vibrating screen) for screening, and collect the particles in the particle size range of 50-120 mesh as the raw material for subsequent use;

[0082] (2) Fixed bed filling: Uniformly fill the pretreated coarse fly ash into the fixed bed packing column (the inner diameter of the cylindrical part is 700 mm, the length-diameter ratio is 6, the outlet inclination angle of the conical body is designed to be 60°, and the void fraction of the fixed bed is 0.40), and ensure uniform water distribution through the water distributor, and use the filter screen to prevent the loss of fly ash particles;

[0083] (3) Continuous water washing and desalination: Start the vacuum pump to create a negative pressure environment, and pump the microplastic-polluted water from the bottom water inlet of the fixed bed upward at a flow rate of 12 L / min through the water inlet pump to fully contact with the fly ash for countercurrent washing; continuously monitor the chloride ion concentration at the cutoff point through an on-line conductivity meter. When the conductivity drops below 1.5 S / m, it indicates that the fly ash in the lower section of the cutoff position has been desalinated;

[0084] (4) Sectional discharging: After detecting that the fly ash in the lower section has completed desalination, close the feed water pump, start the pneumatic cutoff device to divide the fixed bed into upper and lower sections, open the bottom discharge port, and discharge the desalinated fly ash.

[0085] (5) Continuous feeding: Close the discharge port, close the pneumatic cutoff device, add new pretreated fly ash to the top of the fixed bed to keep the bed height constant; repeat steps (3)-(4) to achieve continuous operation.

[0086] (6) Evaporation and salt separation: Feed the collected salt-containing wastewater into a multi-effect evaporator and a distributed crystallization device for concentration and crystallization. The evaporated condensate is piped back to the water pump and used as washing water; the mixed salt obtained by evaporation and crystallization is subjected to fractional crystallization, and the prepared NaCl meets the secondary standard of industrial salt in GB / T 5462, and the KCl meets the qualified product standard of GB / T 6549.

[0087] In this embodiment, the comprehensive liquid-solid ratio is 0.59, microplastics are not detected in the salt-containing wastewater, and the chlorine content of the fly ash after desalination is reduced from 27.3% to 1.38%, meeting the standard of the Technical Specification for Pollution Control of Municipal Solid Waste Incineration Fly Ash (HJ 1134-2020).

[0088] The fixed-bed ultra-low water consumption desalination system and method for municipal solid waste incineration fly ash provided by the present invention have significant energy-saving and environmental protection advantages. This technology innovatively integrates the fly ash desalination process with waste heat utilization technology, converts fly ash into coarse fly ash materials through low-temperature thermal decomposition and medium-low temperature sintering processes, and utilizes the physical and chemical properties of modified fly ash. It not only solves the problem of easy blockage of fly ash used as fixed-bed filler in traditional technologies, but also realizes the efficient water washing desalination of fly ash and the synergistic removal of various pollutants. In terms of energy efficiency, through optimizing equipment configuration, the system energy consumption is reduced by more than 85%; in terms of water resource utilization, combined with the characteristics of the distribution of the salt content of the fly ash fixed bed along the process, a fixed-bed sectional continuous water washing process is adopted, reducing the water consumption by more than 90%. In addition, this method scientifically plans the fly ash resource utilization path: the washing liquid can be converted into industrial salt products after treatment, and the modified fly ash can be used for the synergistic removal of pollutants such as microplastics, realizing zero waste residue and wastewater discharge in the whole process, achieving the greening and resource utilization of fly ash treatment, and greatly reducing the fly ash disposal cost. The equipment involved in the present invention is simple to transform, has low operating costs, can be seamlessly connected with existing municipal solid waste incineration power plant facilities, and has significant commercial application value and environmental protection promotion significance.

[0089] Obviously, those skilled in the art can make subsequent various applications, supplements, modifications and variations to the present invention without departing from the spirit and scope of the present invention. If various applications, supplements, modifications and variations based on the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these applications, supplements, modifications and variations.

Claims

1. A fixed-bed desalination system for municipal solid waste incineration fly ash with ultra-low water consumption, characterized in that, Including: A fly ash pretreatment unit, which is suitable for heating the fly ash from waste incineration at a gradient temperature under an oxygen-free condition to sequentially complete the thermal decomposition of dioxins and the sintering modification treatment of fly ash; After being further crushed and screened, the pretreated coarse-grained fly ash is obtained; A fixed-bed desalination unit, which is suitable for washing and desalinating the coarse-grained fly ash filled in the fixed-bed packing column in a way of bottom water inlet and top water outlet; and based on the characteristics of the distribution of chloride ion content along the fixed-bed packing column, the initial-stage fly ash that has completed the washing and desalination is cut off and discharged from the bottom, and then new coarse-grained fly ash is supplemented from the top; A wastewater treatment unit, which is suitable for collecting the fixed-bed desalination wastewater and obtaining solid salt products after evaporation concentration and stepwise crystallization treatment.

2. The system according to claim 1, wherein The fly ash pretreatment unit includes a heat treatment furnace, a crusher and a vibrating screening device connected in sequence; the heat treatment furnace is a multi-stage rotary kiln structure and is provided with a partition temperature control device for forming two temperature ranges of first thermal decomposition and then sintering in the inner cavity of the heat treatment furnace; the crusher is a double-rotor hammer crusher for crushing the sintered fly ash lumps after heating; the vibrating screening device is a standard vibrating screen for screening coarse-grained fly ash.

3. The system according to claim 1, wherein The fixed-bed desalination unit includes a fixed-bed packing column, which is sequentially provided with a discharge port, a water inlet and a water distributor at its lower end, and sequentially provided with a feed port, a water outlet and a water distributor at its upper end, and is provided with a pneumatic cutoff device in its middle and lower part; among them, the feed port and the discharge port are provided with electric gate valves; the water distributor is connected to a pneumatic pulling device and can perform lateral displacement according to the needs of feeding and discharging operations; the pneumatic cutoff device adopts a double-layer valve plate design, and an on-line conductivity meter is provided above it.

4. The system according to claim 3, wherein The water distributor is composed of a perforated plate and a polypropylene filter screen, and the aperture of the filter screen is smaller than the particle size of the coarse-grained fly ash; the distance between the pneumatic cutoff device and the discharge port is 20% - 40% of the total height of the packing column, and a buffer zone is directly arranged between the two valve plates of the pneumatic cutoff device.

5. The system according to claim 1, wherein The wastewater treatment unit includes a brine collection tank, a multi-effect evaporator and a stepwise crystallization device connected in sequence; the multi-effect evaporator is provided with a condensate outlet and a concentrated liquid outlet.

6. The system according to claim 1, wherein The connection between the units is realized in the following way: between the heat treatment furnace, the crusher and the vibrating screening device in the fly ash pretreatment unit, they are connected through a fly ash conveying channel; the vibrating screening device is connected to the upper feed port of the fixed-bed packing column in the fixed-bed desalination unit through a fly ash conveying channel, the water outlet at the upper end of the packing column is connected to the brine collection tank through a pipeline, and the water inlet at the lower end of the packing column is sequentially connected to a filter and a water pump through a pipeline; the brine collection tank, the multi-effect evaporator and the stepwise crystallization device in the wastewater treatment unit are connected in sequence through pipelines, and the condensate outlet of the multi-effect evaporator is connected to the water inlet at the lower end of the packing column through a pipeline; the flue gas discharge pipe of the heat treatment furnace is connected to a heat exchanger and then connected to a tail gas treatment device, and the multi-effect evaporator and the stepwise crystallization device are respectively connected to the heat exchanger through a medium circulation loop.

7. An ultra-low water consumption desalination method for waste incineration fly ash in a fixed bed, characterized in that, The method uses the device described in any one of claims 1 to 6, and the method includes: (1) Fly ash pretreatment: Feed the original municipal solid waste incineration fly ash into a heat treatment furnace protected by a nitrogen atmosphere. The heat treatment furnace adopts a multi-stage rotary kiln structure and is heated by a zone temperature control method. After feeding, thermal decomposition is carried out first to eliminate dioxin-like toxic substances. Then fly ash sintering is carried out to complete sintering modification. The material after heat treatment is crushed and screened to collect coarse fly ash within a preset particle size range. (2) Loading coarse fly ash: Uniformly fill the pretreated coarse fly ash into a fixed bed packing column. The upper and lower ends of the packing column are blocked by a water distributor to ensure uniform water distribution and prevent fly ash loss. (3) Washing and desalting: Use a feed pump to convey water upward from the bottom of the packing column to fully contact with the fly ash for countercurrent washing. The salt-containing wastewater after washing is discharged into a brine collection tank. Use an on-line conductivity meter to monitor the change of salt concentration in the fly ash in the initial section of the packing column in real time. When the conductivity of the effluent water drops below 1.5 S / m, it indicates that the fly ash in this section has completed desalting. (4) Sectional discharging: Close the feed pump and start the pneumatic cut-off device to separate the fly ash in the packing column. Transversely move the water distributor at the bottom, open the electric gate valve at the discharge port, and discharge the desalted fly ash. Close the electric gate valve at the discharge port and restore the water distributor. (5) Supplementary feeding of coarse fly ash: Close the pneumatic cut-off device to restore the connection state in the packing column. The original filled fly ash falls and forms a cavity at the top. Transversely move the water distributor at the top, open the electric gate valve at the feed port, add new pretreated fly ash into the cavity to keep the bed height constant, and restore the water distributor after completion. Repeat steps (3)-(5) to achieve continuous operation. (6) Evaporation and salt separation: Feed the salt-containing wastewater in the brine collection tank into a multi-effect evaporator for concentration and crystallization. The condensed water is recycled as washing water. The mixed salt concentrate obtained by evaporation and crystallization is then sent to a fractional crystallization device for fractional crystallization to obtain industrial-grade chloride salt products.

8. The method according to claim 7, wherein The temperature during the low-temperature thermal decomposition is 300 - 400 °C, and the time is 30 - 60 minutes. The temperature during the high-temperature sintering is 550 - 600 °C, and the time is 12 - 20 minutes. The particle size range of the coarse fly ash collected by screening is 50 - 120 mesh.

9. The method according to claim 7, wherein During washing and desalting, control the water flow rate in the fixed bed packing column. The specific flow rate is calculated and determined by the following formula: Where: Q is the influent flow rate, L / min; ε is the porosity of the fixed bed, with a value range of 0.35 to 0.45, specifically determined according to actual measurements; A is the cross-sectional area of the packing column, H is the bed height; t c is the contact time, in minutes, with a value range of 10 to 120 minutes.

10. The method according to claim 7, wherein During water washing and desalination, clean water or polluted water containing F - , and microplastics is used for desalination to achieve the co-removal of pollutants by utilizing the fly ash adsorption effect; The waste heat dissipated during the cooling process of the sintered fly ash is used for preheating in the low-temperature thermal decomposition process through a heat exchanger, or as the heat source for the multi-effect evaporator and the fractional crystallization device. The fixed bed packing column adopts a cylinder-cone combination. The inner diameter of the cylinder part is 500 - 1000 mm, and the length-diameter ratio is 3 - 8. The cylinder is connected to a cone at the lower end to ensure uniform water flow. The outlet inclination angle of the cone body contraction is designed to be 50 - 70° to avoid the formation of dead zones and guide the discharge of materials. The filter screen of the distributor is made of temperature-resistant and corrosion-resistant polypropylene material to ensure stable structure during long-term washing.

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