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

Abstract

The present application relates to waste incineration fly ash desalination treatment technology, aiming at providing a waste incineration fly ash fixed bed ultra-low water consumption desalination system and method. The system comprises: a fly ash pretreatment unit, which is used for gradient heating of waste incineration fly ash under anaerobic conditions, sequentially completing dioxin thermal decomposition and fly ash sintering modification treatment, and obtaining coarse fly ash after crushing and screening treatment; a fixed bed desalination unit, which is used for water washing desalination treatment of coarse fly ash filled in the fixed bed filler column in the mode of water inlet at the bottom and water outlet at the top; and based on the chloride ion content distribution characteristics along the filler column, the initial stage fly ash after water washing desalination is cut off and discharged from the bottom, and new coarse fly ash is supplemented from the top; and a wastewater treatment unit, which is used for collecting fixed bed desalination wastewater, obtaining solid salt products after evaporation concentration and step-by-step crystallization treatment. The present application can significantly improve the mass transfer efficiency, and the segmented discharge realizes efficient desalination; and has significant industrial application value.

Description

TECHNICAL FIELD

[0001] The present application relates to a waste incineration fly ash desalination treatment technology, in particular to a method for washing and filtering fly ash to remove salt. BACKGROUND

[0002] With the continuous increase of municipal solid waste incineration ratio, the amount of fly ash is increasing significantly. As a hazardous waste, fly ash has high toxicity characteristics, and the high concentration of soluble chloride salt contained therein not only poses a pollution threat to the environment, but also seriously limits the resource utilization of fly ash, so it needs to be treated harmlessly. At present, the washing method has become the mainstream technology for fly ash desalination treatment due to its simple process, low equipment investment and stable operation. However, the existing washing process is essentially a simple combination of multiple batch units, which is complex and requires a large water-to-ash ratio (usually ≥ 3:1), resulting in a large amount of low-concentration brine and significantly increasing the energy consumption of the subsequent evaporation crystallization process. At the same time, the combination of multi-stage countercurrent washing and plate and frame pressure filtration not only takes a long time, but also consumes a lot of energy. In addition, some chloride ions remain in the fly ash after washing, and the desalination effect is not ideal.

[0003] The 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, strong water absorption and certain gelation characteristics of fly ash, direct use of this technology will cause the fixed bed to be blocked. Patent document CN118808282A discloses a method for desalination of fly ash by percolation, which mixes fly ash with river sand and other percolation auxiliary materials and uses a series of fly ash washing columns for percolation desalination. However, due to the small particle size and poor permeability of fly ash, this method has significant defects in practical application. First, the design of the series of washing columns causes a large resistance when the material passes through each module, and the pressure loss caused by the series connection of multiple modules is unacceptable. Second, in order to recover the percolation auxiliary materials, additional steps of water flushing and screening are required, which not only increases the water consumption and energy consumption of the process, but also brings difficulties to the disposal of contaminated water. Similarly, other methods that use auxiliary materials to improve the performance of fly ash water washing column also have difficulty in overcoming the outlet blockage problem, and the density difference between the auxiliary materials and fly ash easily causes fluidized stratification and aggravates the blockage. More importantly, the auxiliary materials and fly ash need to be disposed together after mixing, which essentially increases the amount of hazardous waste to be treated.

[0004] Based on the above background, the purpose of the present application is to provide a new low-energy high-efficiency desalination system and method to solve the technical problems of complex process flow, multiple operation steps, high energy consumption and large water consumption in the prior art, and to realize efficient desalination of fly ash. SUMMARY

[0005] The technical problem solved by the present application is to overcome the deficiencies in the prior art and provide a garbage incineration fly ash fixed bed ultra-low water consumption desalination system and method.

[0006] To solve the technical problem, the solution of the present application is:

[0007] The present application provides a garbage incineration fly ash fixed bed ultra-low water consumption desalination system, comprising:

[0008] A fly ash pretreatment unit is suitable for gradient heating of garbage incineration fly ash under anaerobic conditions, sequentially completing dioxin thermal decomposition and fly ash sintering modification treatment; after crushing and screening treatment, coarse particle fly ash after pretreatment is obtained;

[0009] A fixed bed desalination unit is suitable for water washing desalination treatment of coarse particle fly ash filled in the fixed bed filler column in a way of water inlet at the bottom and water outlet at the top; and based on the chlorine ion content distribution characteristics along the filler column, the initial stage fly ash completing water washing desalination is cut off and discharged from the bottom, and then new coarse particle fly ash is supplemented from the top;

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

[0011] As a preferred scheme of the present application, the fly ash pretreatment unit comprises a heat treatment furnace, a crusher and a vibrating screening device connected in sequence; the heat treatment furnace is a multi-section rotary kiln structure, and is provided with a partition temperature control device for forming two temperature intervals 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 sintered fly ash agglomerates after heating; and the vibrating screening device is a standard vibrating screen for screening coarse particle fly ash.

[0012] As a preferred scheme of the present application, the fixed bed desalination unit comprises a fixed bed filler column, which is provided with a discharge port, a water inlet and a water flow distributor in sequence at the lower end, is provided with a feed inlet, a water outlet and a water flow distributor in sequence at the upper end, and is provided with a pneumatic cutting device in the lower part; wherein the feed inlet and the discharge port are provided with electric gate valves; the water flow distributor is connected with a pneumatic pulling device and can be laterally displaced according to the needs of feeding and discharging operation; the pneumatic cutting device adopts a double-layer valve plate design, and an online conductivity meter is arranged above the pneumatic cutting device.

[0013] As a preferred scheme of the present application, the water flow distributor is composed of a perforated plate and a polypropylene filter screen, and the pore size of the filter screen is smaller than the particle size of the coarse particle fly ash; the distance between the pneumatic cutting device and the discharge port is 20% to 40% of the total height of the filler column, and a buffer zone is directly arranged between the two layers of valve plates in the pneumatic cutting device.

[0014] As a preferred scheme of the present application, the wastewater treatment unit comprises a brine collection tank, a multi-effect evaporator and a fractional crystallization device connected in sequence; the multi-effect evaporator is provided with a condensed water outlet and a concentrated liquid outlet.

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

[0016] The present application further provides a waste incineration fly ash fixed bed ultra-low water consumption desalination method, which uses the device as claimed in the preceding claims, and the method comprises the following steps:

[0017] (1) fly ash pretreatment: raw waste incineration fly ash is sent into a thermal treatment furnace protected by a nitrogen atmosphere, the thermal treatment furnace adopts a multi-section rotary kiln structure and is heated in a partition temperature control mode; after feeding, thermal decomposition is first performed to eliminate dioxin toxic substances; then fly ash sintering is performed to complete sintering modification; the material after thermal treatment is crushed and screened to collect coarse fly ash of a preset particle size range;

[0018] (2) loading coarse fly ash: the coarse fly ash after pretreatment is uniformly filled in a fixed bed filler column, and the filler column is blocked at the upper and lower ends with water flow distributors to ensure uniform water distribution and prevent fly ash loss;

[0019] (3) water washing and desalination: a water inlet pump is used to feed water upward from the bottom of the filler column to realize countercurrent washing by fully contacting with the fly ash; the salt-containing wastewater after washing is discharged to a brine collection tank; an online conductivity meter is used to monitor the salt concentration change of the fly ash in the initial section of the filler column in real time, and when the water outlet conductivity is reduced to below 1.5 S / m, it indicates that the fly ash in the section has completed desalination;

[0020] (4) section unloading: the water inlet pump is closed, the pneumatic cutting device is started to separate the fly ash in the filler column; the water flow distributor at the bottom is moved horizontally, the electric gate valve of the discharge outlet is opened, and the fly ash that has completed desalination is unloaded; the electric gate valve of the discharge outlet is closed, and the water flow distributor is restored.

[0021] (5)Supplement coarse fly ash: close the pneumatic cutoff device to restore the packing column to a connected state, the original fly ash falls and forms a cavity at the top; move the water flow distributor at the top, open the electric gate valve of the feed inlet, add new pretreated fly ash to the cavity to maintain a constant height of the bed, and restore the water flow distributor after the supplement is completed; repeat steps (3)-(5) to realize continuous operation;

[0022] (6) Evaporation and salting: send the salt-containing wastewater in the saltwater collection pool to a multi-effect evaporator for concentration and crystallization, and the condensed water is reused as cleaning water; the mixed salt concentrate obtained by evaporation and crystallization is sent to a step-by-step crystallization device for step-by-step crystallization to obtain industrial-grade chlorinated salt products.

[0023] As a preferred scheme of the present application, the temperature during low-temperature thermal decomposition is 300-400℃, and the time is 30-60 minutes; the temperature during high-temperature sintering is 550-600℃, and the time is 12-20 minutes; the particle size range of the collected coarse fly ash is 50-120 mesh.

[0024] As a preferred scheme of the present application, the water flow rate in the fixed bed packing column is controlled during water washing and desalination, and the specific flow rate is determined by calculation according to the following formula:

[0025]

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

[0027] As a preferred scheme of the present application, clean water is used during water washing and desalination, or contaminated water containing F - , microplastics is used for desalination to realize the simultaneous removal of pollutants by fly ash adsorption; the waste heat dissipated during the cooling process of sintered fly ash is used as a heat source for preheating in the low-temperature thermal decomposition process through a heat exchanger, or for multi-effect evaporators and step-by-step crystallization devices; the fixed bed packing column adopts a cylindrical-conical combination, wherein the inner diameter of the cylindrical part is 500-1000mm, and the aspect ratio is 3-8; the cylindrical part is connected to the conical part at the lower end to ensure uniform water flow, and the outlet angle of the conical body is designed to be 50-70° to avoid forming a dead zone and guide the discharge of materials; the filter screen of the distributor is made of temperature-resistant and corrosion-resistant polypropylene material to ensure structural stability during long-term water washing.

[0028] Invention principle description:

[0029] The applicant finds in long-term and in-depth research that under the condition of medium and low temperature (550-600 DEG C), the chloride salt in fly ash can melt, and at the same time, silicate and aluminate are generated, and finally, sintered block with hard texture is formed. If the common low-temperature thermal decomposition process (300-400 DEG C) is combined, the medium and low temperature sintering of fly ash can be realized under the condition of lower energy consumption, so that the cementation property and water absorption of fly ash are significantly reduced; at the same time, the particle size is increased, so that it has the condition of being used as fixed bed filler. On this basis, the application puts forward an innovative scheme: the original fly ash is converted into coarse-grained fly ash material suitable for fixed bed filler by using the physical and chemical properties of fly ash under the condition of medium and low temperature, and the continuous desalination treatment of fly ash is realized based on the characteristics of high efficient mass transfer of fixed bed. The specific technical principle is as follows:

[0030] (1) Fly ash thermal modification and dioxin synergistic degradation mechanism:

[0031] The fly ash thermal modification process mainly includes two stages. In the first stage, the low-temperature thermal decomposition process of fly ash is combined, under the nitrogen atmosphere, after the original fly ash is put into the heat treatment furnace, under the temperature range of 300-400 DEG C, through catalytic dechlorination and oxidative ring opening reaction, the dioxin toxic equivalent is reduced by more than 99%; the second stage is sintering modification by heating to 550-600 DEG C. Under this temperature condition, two key physical and chemical change processes of fly ash occur. First, the chloride salt (mainly NaCl and KCl) in fly ash reaches the melting point and melts, and the molten chloride salt forms a liquid phase on the surface of the particle, which promotes the initial bonding between fly ash particles. At the same time, the silicon, calcium and aluminum components in fly ash sinter, small particles are aggregated, and the specific surface area of fly ash is significantly reduced, so that the surface activity and cementation property are weakened; the hydrophobicity of sintered particles inhibits the water absorption of fly ash, and effectively overcomes the shortcomings of easy agglomeration and easy hardening of the original fly ash. In addition, the process reduces the heating consumption of the medium temperature section by using the low-temperature section waste heat for cascade utilization, and the sintered fly ash cooling dissipation waste heat can also be used for preheating in the low-temperature section. The comprehensive energy consumption is significantly reduced compared with the traditional high-temperature sintering, which takes into account the environmental and economic effects.

[0032] (2) Fly ash desalination column water washing mechanism:

[0033] In the process of water washing and desalination of fly ash in the fixed bed column mode, the chloride ion content along the column after the first water passing is a clear three-section distribution including desalination section, mutation section and stable section. This is because in the initial stage of water washing, the soluble chloride salt in fly ash will rapidly dissolve in water in the form of single salt, resulting in the rapid saturation of the water washing liquid. This situation will make only a small amount of fly ash continue to desalinate in the subsequent section, and also make the water washing liquid at the outlet be saturated or supersaturated. When fly ash is water washed and desalinated in the fixed bed column mode, three effects are mainly considered, which are adsorption effect, dissolution rate and diffusion effect. Experimental study shows that the adsorption effect and dissolution rate have relatively small influence on the chloride ion distribution along the column, and the diffusion effect has greater influence. With the extension of time, the diffusion effect will gradually flatten the chloride ion distribution curve along the column. In view of this, if the fly ash water washing column that has completed desalination can be cut off and unloaded in time, the along-path distribution characteristics can be maximally utilized, thereby effectively saving water consumption.

[0034] (3) Fixed bed mass transfer and pollutant synergistic removal mechanism:

[0035] The modified fly ash can maintain a stable void structure in the bed. In this process, the water is pumped from the bottom of the fixed bed to realize countercurrent contact with the modified fly ash particles through the self-flowing mode from bottom to top. This countercurrent design not only provides greater mass transfer driving force, but also the upward flow can moderately disturb the bed to form a more sufficient mass transfer contact interface. Because the surface of the filler is hydrophobic and the pore structure is stable, the upward flow can be uniformly distributed in the bed void, effectively avoiding the fly ash agglomeration phenomenon in the traditional water washing process, thereby significantly improving the mass transfer efficiency.

[0036] The whole water passing desalination process maintains a slow flow rate (Re << 1, belonging to laminar flow state, and the inertial force can be ignored), and the volume flow rate (Q) or the corresponding superficial velocity (v) can be calculated according to Darcy's law, combined with the permeability (K), cross-sectional area (A), pressure drop (ΔP), fluid viscosity (μ) and flow path length (L) and other parameters. The flow rate should be properly set, neither too fast to destroy the fixed bed structure, nor too slow to prolong the contact time and affect the desalination efficiency and effect. The specific formula is given in this method. In addition, the segmented design of the fixed bed ensures the continuous water washing process and realizes efficient desalination.

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

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

[0039] 1、 The present application converts fly ash into coarse-grained material with large particle size (120-50 mesh) through low-temperature sintering, overcomes the inherent defects of fly ash such as strong gelation and water absorption, and realizes stable operation of continuous water washing desalination of fixed bed, effectively reducing the energy consumption and water consumption of the treatment process.

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

[0041] 3、 The present application realizes efficient desalination by segmenting the discharge of the packing column according to the water washing desalination mechanism.

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

[0043] 5、 The present application is not only suitable for conventional pollutant treatment, but also can realize the collaborative disposal of physical and chemical contaminated wastewater. The process has the characteristics of high reaction efficiency and good treatment effect, and can improve the water washing effect, and has remarkable industrial application value. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The system structure diagram of each part designed for the present application.

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

[0046] Figure 3 The process flow chart of the efficient water washing desalination method of the present application.

[0047] Among them, Figure 2 The various marks in the figure represent: 1 inlet; 2 water outlet; 3 perforated plate; 4 filter screen; 5 conductivity meter; 6 pneumatic cutoff device; 7 filter screen; 8 perforated plate; 9 water inlet; 10 discharge port; 11 water pump; 12 salt water collection tank; 13 vacuum pump. DETAILED DESCRIPTION

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

[0049] As Figure 1As shown, the waste incineration fly ash fixed bed ultra-low water consumption desalination system of the present application comprises a fly ash pretreatment unit, a fixed bed desalination unit and a wastewater treatment unit. The fly ash pretreatment unit is suitable for gradient heating of waste incineration fly ash under anaerobic conditions, sequentially completing dioxin thermal decomposition and fly ash sintering modification treatment; after crushing and screening treatment, the pretreated coarse fly ash is obtained; the fixed bed desalination unit is suitable for water washing and desalination treatment of coarse fly ash filled in the fixed bed filler column in the way of water inlet at the bottom and water outlet at the top; and based on the chloride ion content distribution characteristics along the filler column, the initial stage fly ash completing water 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 fixed bed desalination wastewater, and after evaporation concentration and step crystallization treatment, solid salt products are obtained.

[0050] The fly ash pretreatment unit comprises a heat treatment furnace, a crusher and a vibrating screening device connected in sequence; the heat treatment furnace is a multi-section rotary kiln structure, and is provided with a partition temperature control device for forming two temperature intervals of thermal decomposition first and then sintering in the inner cavity of the heat treatment furnace; the 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 sintered fly ash agglomerates 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 comprises a fixed bed filler column, which is provided with a discharge port, a water inlet and a water flow distributor at the lower end in sequence, and is provided with a feed inlet, a water outlet and a water flow distributor at the upper end in sequence, and is provided with a pneumatic cutting device at the lower part; wherein the feed inlet and the discharge port are provided with electric gate valves; the water flow distributor is connected with a pneumatic pulling device and can be laterally displaced according to the needs of feeding and discharging operation; the pneumatic cutting device adopts a double-layer valve plate design, and an online conductivity meter is arranged above it. The water flow distributor is composed of a perforated plate and a filter screen, and the pore size of the filter screen is smaller than the particle size of the coarse fly ash.

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

[0053] The units are connected by the following ways: the thermal treatment furnace in the fly ash pretreatment unit, the crusher and the vibrating screening device are connected through the fly ash conveying channel; the vibrating screening device is connected to the upper end inlet of the filler column of the fixed bed desalination unit through the fly ash conveying channel, the water outlet at the upper end of the filler column is connected to the salt water collecting pool through a pipeline, and the water inlet at the lower end of the filler column is connected to the filter and the water pump through a pipeline in sequence; the salt water collecting pool, the multi-effect evaporator and the step crystallization device in the wastewater treatment unit are connected through pipelines in sequence, and the condensate water outlet of the multi-effect evaporator is connected to the water inlet at the lower end of the filler column through a pipeline; the flue gas discharge pipe of the thermal treatment furnace is connected to the heat exchanger and then to the tail gas treatment device, and the multi-effect evaporator and the step crystallization device are connected to the heat exchanger through a medium circulation loop respectively.

[0054] The fixed bed filler column for fly ash water washing has the structure as shown in Figure 2 The fixed bed filler 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 lower end connects to the cone for ensuring uniform water passing, and the outlet angle of the cone body contraction is designed to be 50-70° to avoid forming a dead zone and guide the discharge of the material. The upper end of the fixed bed filler column is sequentially provided with an inlet 1, a water outlet 2 and a water flow distributor (composed of a porous plate 3 and a filter screen 4), and at the outlet of the cone body contraction, a water flow distributor (composed of a porous plate 8 and a filter screen 7), an inlet 9 and an outlet 10 are sequentially provided. A pneumatic cutting device 6 is arranged in the inner cavity of the fixed bed filler column at the lower part, and the distance from the outlet 10 is 20%-40% of the total height of the filler column; the pneumatic cutting device 6 adopts a double-layer valve plate design with a spacing of 50 mm to ensure the support of the upper filler, and a buffer zone is directly arranged between the two layers of valve plates. During the water washing operation, the valve plate is in a retracted state, so that the packed coarse fly ash can maintain continuous water washing operation. The porous 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, so as to ensure the structural stability during long-term water washing. The filter screen has a mesh size of 140-200 meshes (0.075-0.106 mm) to avoid fly ash loss. An electric conductivity meter 5 is arranged above the pneumatic cutting device 6, the salt concentration of the lower section is determined by real-time measurement of the electric conductivity of the water, the measurement range is 0-50 S / m, and the accuracy is ±0.5%. When the electric conductivity value is stably lower than 1.5 S / m for about 3 minutes, it is considered that the lower section of the cutting part has completed desalination; at this time, the cutting device can be started to separate the desalination column and discharge the lower section desalination fly ash. A water pump 11 is connected to the inlet 9 through a pipeline to provide power for the upward water conveying; the water outlet 2 is connected to the salt water collecting pool 12 through a pipeline to collect the water washing liquid into the salt water collecting pool 12; the air inlet of the vacuum pump 12 is connected to the salt water collecting pool 12 through a vacuum rubber hose; during the water washing process, the vacuum pump can create a negative pressure environment to improve the water passing property.

[0055] As shown in Figure 3As shown, the fly ash fixed bed desalination method of the present application mainly comprises the following steps:

[0056] (1) Fly ash pretreatment: raw waste incineration fly ash is sent into a heat treatment furnace protected by a nitrogen atmosphere, the heat treatment furnace adopts a multi-section rotary kiln structure and is heated in a partition temperature control mode, and the fly ash material gradually moves from a low temperature zone to a high temperature zone inside the rotary kiln. After the raw fly ash is fed, it is first subjected to low-temperature thermal decomposition at a temperature interval of 300-400℃ for 30-60 minutes to effectively decompose dioxin toxic substances; then it is gradually moved to a temperature interval of 550-600℃ for 12-20 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 and particle size refinement; and the modified fly ash particles after crushing are sent to a vibrating sieve separation device (standard vibrating sieve) for sieving, and particles with a particle size in the range of 50-120 meshes are collected as raw materials for subsequent use.

[0057] (2) Loading coarse fly ash: the pretreated coarse fly ash is uniformly filled in the fixed bed filler column, and the water distributor is blocked at the upper and lower ends of the filler column to ensure uniform distribution of water flow and prevent fly ash loss.

[0058] (3) Continuous water washing and desalination: start the vacuum pump to create a negative pressure environment, and use the water inlet pump to send clean water or contaminated water from the water inlet at the bottom of the fixed bed to the top at a flow rate of Q to realize countercurrent washing by fully contacting with the fly ash; the online conductivity meter is used for real-time monitoring of the chloride ion concentration at the cutoff position, and when the conductivity is reduced to below 1.5 S / m, it indicates that the fly ash in the lower section of the cutoff position has completed desalination; clean water or contaminated water containing F - , microplastics can be used for desalination to realize the simultaneous removal of pollutants by fly ash adsorption.

[0059] (4) Sectional unloading: close the water inlet pump, start the pneumatic cutoff device to separate the fly ash in the filler column, move the water flow distributor at the bottom, open the electric gate valve at the discharge port, and unload the fly ash that has completed desalination; close the electric gate valve at the discharge port and restore the water flow distributor;

[0060] (5) Supplement coarse fly ash: close the pneumatic cutoff device to restore the communication state in the filler column, the original filled fly ash falls and forms a cavity at the top; move the water flow distributor at the top, open the electric gate valve at the feed port, add new pretreated fly ash to the cavity to maintain a constant height of the bed layer, and restore the water flow distributor after the supplement is completed; repeat steps (3)-(5) to realize continuous operation;

[0061] (6) Evaporation and salt separation: the salt-containing wastewater in the saltwater collection tank is sent to a multi-effect evaporator for concentration and crystallization, and the condensed water is reused as cleaning water; the mixed salt concentrate obtained by evaporation and crystallization is sent to a step-by-step crystallization device for step-by-step crystallization to obtain industrial-grade chlorinated salt products.

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

[0063] The application of the present application is further illustrated by specific examples below.

[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℃ temperature range of the front section of the rotary kiln for 60 minutes to effectively decompose dioxin toxic substances; based on the furnace structure and rotating discharge principle, the fly ash material gradually moves to the 600℃ temperature range of 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, and the particle size is refined. The modified fly ash particles after crushing are sent to a vibrating screen separation device (standard vibrating screen) for screening, and the particles with a particle size of 50-120 mesh are collected as raw materials for subsequent use;

[0066] (2) Fixed bed filling: the pretreated coarse fly ash is uniformly filled into a fixed bed filler column (cylindrical part with an inner diameter of 500mm, length-diameter ratio of 8, conical outlet inclination angle of 50°, fixed bed void ratio of 0.35) to ensure uniform water distribution through a water distribution device, and a filter screen is used to prevent fly ash particles from being lost;

[0067] (3) Water washing and desalination: water is pumped from the bottom of the filler column to the top by a water inlet pump to fully contact with the fly ash for countercurrent washing; the salt-containing wastewater after washing is discharged to a saltwater collection tank; the change in salt concentration of the fly ash in the initial section of the filler column is monitored in real time by an online conductivity meter, and when the conductivity of the outlet water decreases to below 1.5S / m, it indicates that the fly ash in this section has completed desalination;

[0068] (4) Sectional unloading: after detecting that the fly ash in the lower section has completed desalination, the water inlet pump is turned off, the pneumatic cutting device is started to divide the fixed bed into two sections, the bottom discharge port is opened, and the desalted fly ash is unloaded;

[0069] (5) Continuous feeding: the discharge port is closed, the pneumatic cutting device is closed, and new pretreated fly ash is added to the top of the fixed bed to maintain a constant height of the bed; steps (3)-(4) are repeated to realize 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 step-by-step crystallization to obtain NaCl that meets the GB / T5462 industrial salt secondary standard and KCl that meets the GB / T6549 qualified product standard.

[0071] In this embodiment, the comprehensive liquid-solid ratio is 0.58, and the chlorine content of the desalted fly ash is reduced from 27.8% to 1.24%, which meets the standard of "Domestic Waste Incineration Fly Ash Pollution Control Technical Specification" (HJ1134-2020).

[0072] Example 2

[0073] (1) Fly ash pretreatment: The original fly ash is placed in a heat treatment furnace with a multi-stage rotary kiln structure under nitrogen atmosphere protection for heat modification treatment. First, low-temperature thermal decomposition is carried out in the 400°C temperature range of the front section of the rotary kiln for 30 minutes to effectively decompose dioxin toxic substances. Based on the rotation of the furnace body structure, the fly ash material gradually moves to the 550°C temperature range of 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, and the particle size is refined. The modified fly ash particles after crushing are sent to a vibrating sieve separation device (standard vibrating screen) for sieving, and the particles in the 50-120 mesh size range are collected as raw materials for subsequent use.

[0074] (2) Fixed bed filling: The pretreated coarse fly ash is uniformly filled into the fixed bed filler column (cylindrical part inner diameter 1000mm, length-diameter ratio 3, conical outlet inclination angle design 70°, fixed bed void ratio 0.45), and the water flow distributor ensures uniform distribution of water flow, and the filter screen prevents fly ash particle loss.

[0075] (3) Continuous water washing and desalination: Start the vacuum pump to create a negative pressure environment, and use the water inlet pump to send the F - contaminated water (F - concentration 56mg / L) from the bottom inlet of the fixed bed at a flow rate of 33L / min to fully contact with the fly ash to achieve countercurrent washing. The online conductivity meter is used to monitor the chloride ion concentration at the cutoff point in real time. When the conductivity decreases to below 1.5S / m, it indicates that the fly ash in the lower section has completed desalination.

[0076] (4) Sectional unloading: After detecting that the fly ash in the lower section has completed desalination, the water inlet pump is turned off, the pneumatic cutoff device is started to divide the fixed bed into upper and lower sections, the bottom discharge port is opened, and the desalted fly ash is unloaded.

[0077] (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 maintain a constant height of the bed; repeat steps (3)-(4) to achieve continuous operation;

[0078] (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 step-by-step crystallization to obtain NaCl that meets the GB / T5462 industrial salt secondary standard and KCl that meets the GB / T6549 qualified product standard.

[0079] In this embodiment, the comprehensive liquid-solid ratio is 0.76, F - The concentration is reduced to 4 mg / L, and the chlorine content of the desalted fly ash is reduced from 31.6% to 0.96%, which meets the standard of "Domestic Waste Incineration Fly Ash Pollution Control Technology Standard" (HJ1134-2020).

[0080] Example 3

[0081] (1) Fly ash pretreatment: the original fly ash is placed in a heat treatment furnace with a multi-stage rotary kiln structure under nitrogen atmosphere protection for heat modification treatment. First, low-temperature thermal decomposition is carried out in the 350°C temperature range of the front section of the rotary kiln for 45 minutes to effectively decompose dioxin toxic substances; based on the rotation of the furnace body structure, the fly ash material gradually moves to the 580°C temperature range of the rear section of the rotary kiln for 16 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, and the particle size is refined. The modified fly ash particles after crushing are sent to a vibrating screen separation device (standard vibrating screen) for screening, and the particles in the 50-120 mesh size range are collected as raw materials for subsequent use;

[0082] (2) Fixed bed filling: the pretreated coarse fly ash is uniformly filled into the fixed bed filler column (the cylindrical part has an inner diameter of 700 mm, a length-diameter ratio of 6, and a conical outlet inclination angle of 60°, and the fixed bed voidage is 0.40). The water flow distributor ensures uniform distribution of water flow, and the filter screen prevents fly ash particles from being lost;

[0083] (3) Continuous water washing and desalination: start the vacuum pump to create a negative pressure environment, and use the water inlet pump to send the microplastic-containing water at a flow rate of 12 L / min from the water inlet at the bottom of the fixed bed to the top to fully contact with the fly ash and achieve countercurrent washing. The online conductivity meter is used to monitor the chloride ion concentration at the cutoff point in real time. When the conductivity is reduced to below 1.5 S / m, it indicates that the fly ash in the lower section below the cutoff point has completed desalination.

[0084] (4) Subsection unloading: after detecting that the lower section fly ash is desalted, the water inlet pump is closed, the pneumatic cutting device is started to divide the fixed bed into upper and lower sections, the bottom discharge port is opened, and the desalted fly ash is unloaded;

[0085] (5) Continuous feeding: the discharge port is closed, the pneumatic cutting device is closed, new pretreated fly ash is added to the top of the fixed bed to keep the bed height constant, and steps (3)-(4) are repeated to realize continuous operation;

[0086] (6) Evaporation and desalination: 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, and the mixed salt obtained by evaporation and crystallization is subjected to step-by-step crystallization to obtain NaCl that meets the GB / T5462 industrial salt secondary standard and KCl that meets the GB / T6549 qualified product standard.

[0087] In this embodiment, the comprehensive liquid-solid ratio is 0.59, no microplastics are detected in the salt-containing wastewater, and the chlorine content of the desalted fly ash is reduced from 27.3% to 1.38%, meeting the standard of “Domestic Waste Incineration Fly Ash Pollution Control Technical Specification” (HJ1134-2020).

[0088] The garbage incineration fly ash fixed bed ultra-low water consumption desalination system and method provided by the application have significant energy-saving and environmental protection advantages. The technical innovation is to deeply integrate the fly ash desalination process and waste heat utilization technology, convert the fly ash into coarse-grained fly ash material through low-temperature thermal decomposition and medium-low temperature sintering process, and utilize the modified fly ash material properties to not only solve the problem of easy clogging of fly ash used as fixed bed filler in traditional technology, but also realize efficient water washing desalination of fly ash and simultaneous removal of various pollutants. In terms of energy efficiency, by optimizing the equipment configuration, the system energy consumption is reduced by more than 85%; in terms of water resource utilization, combined with the fly ash fixed bed water washing salt content along the way distribution characteristics, the fixed bed segmented continuous water washing process is adopted, so that the water consumption is reduced by more than 90%. In addition, the method scientifically plans the fly ash resource utilization path: the water washing liquid can be converted into industrial salt products after treatment, and the modified fly ash can be used for simultaneous removal of microplastics and other pollutants, realizing no waste residue and wastewater discharge in the whole process, achieving greenization and resource utilization of fly ash treatment, and greatly reducing the fly ash disposal cost. The equipment modification involved in the application is simple, the operation cost is low, and the application can be seamlessly connected with the existing garbage incineration power plant facilities, which has significant commercial application value and environmental protection promotion significance.

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

Claims

1. A fixed bed ultra-low water consumption desalination system for waste incineration fly ash, characterized in that, The system comprises: a fly ash pretreatment unit comprising a heat treatment furnace, a crusher and a vibrating screening device connected in sequence; the fly ash pretreatment unit is suitable for gradient heating of waste incineration fly ash under anaerobic conditions, and sequentially completes thermal decomposition of dioxin and sintering modification treatment of fly ash; after crushing and screening, coarse-grained fly ash after pretreatment is obtained; the heat treatment furnace is a multi-section rotary kiln structure, and is provided with a partition temperature control device for forming two temperature intervals 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 sintered fly ash clumps after heating; and the vibrating screening device is a standard vibrating screen for screening coarse-grained fly ash; a fixed-bed desalination unit comprising a fixed-bed filler column, which is suitable for water washing and desalination treatment of coarse-grained fly ash filled in the fixed-bed filler column in a manner of water inlet at the bottom and water outlet at the top; and based on the content distribution characteristics of chloride ions in the filler column, the initial section of fly ash after water washing and desalination is cut off and discharged from the bottom, and then new coarse-grained fly ash is supplemented from the top; a discharge port, a water inlet and a water flow distributor are sequentially arranged at the lower end of the fixed-bed filler column, a feed inlet, a water outlet and a water flow distributor are sequentially arranged at the upper end of the fixed-bed filler column, and a pneumatic cutting device is arranged in the lower part of the fixed-bed filler column; the feed inlet and the discharge port are provided with electric gate valves; the water flow distributor is connected with a pneumatic pulling device and can be laterally displaced according to the needs of feeding and discharging operations; the pneumatic cutting device adopts a double-layer valve plate design, and an online conductivity meter is arranged above the pneumatic cutting device; a wastewater treatment unit comprising a brine collection tank, a multi-effect evaporator and a step crystallization device connected in sequence, which is suitable for collecting fixed-bed desalination wastewater, and obtaining a solid salt product after evaporation and concentration and step crystallization treatment; the multi-effect evaporator is provided with a condensed water outlet and a concentrated liquid outlet; the units are connected through the following modes: the heat treatment furnace, the crusher and the vibrating screening device in the fly ash pretreatment unit are connected through a fly ash conveying channel; the vibrating screening device is connected to the feed inlet at the upper end of the filler column of the fixed-bed desalination unit through the fly ash conveying channel, the water outlet at the upper end of the filler column is connected to the brine collection tank through a pipeline, and the water inlet at the lower end of the filler column is connected to a filter and a water pump through a pipeline in sequence; the brine collection tank, the multi-effect evaporator and the step crystallization device in the wastewater treatment unit are connected through pipelines in sequence, and the condensed water outlet of the multi-effect evaporator is connected to the water inlet at the lower end of the filler column through a pipeline; the flue gas discharge pipe of the heat treatment furnace is connected to the heat exchanger and then to the tail gas treatment device, and the multi-effect evaporator and the step crystallization device are connected to the heat exchanger through medium circulation loops.

2. The system of claim 1, wherein, The water flow distributor is composed of a porous plate and a polypropylene filter screen, and the pore size of the filter screen is smaller than the particle size of the coarse-grained fly ash; the distance between the pneumatic cutting device and the discharge port is 20% to 40% of the total height of the filler column, and a buffer zone is directly arranged between the two layers of valve plates in the pneumatic cutting device.

3. A method for desalination of MSWI fly ash in a fixed bed with ultra-low water consumption, characterized in that, The system is used for water washing and desalination treatment, and specifically comprises: (1) Fly ash pretreatment: The original waste incineration fly ash is sent into a heat treatment furnace protected by nitrogen atmosphere, the heat treatment furnace adopts a multi-section rotary kiln structure and is heated in a partition temperature control mode; after feeding, the fly ash is first subjected to thermal decomposition to eliminate dioxin toxic substances; then the fly ash is sintered to complete sintering modification; the material after heat treatment is crushed and sieved to collect coarse fly ash of a preset particle size range; (2) Coarse fly ash loading: The pretreated coarse fly ash is uniformly filled in a fixed bed filler column, the upper and lower ends of the filler column are sealed with water distributors to ensure uniform water distribution and prevent fly ash loss; (3) Water washing desalination: The water is pumped from the bottom of the filler column to the top to fully contact the fly ash for countercurrent washing; the salt-containing wastewater after washing is discharged into a saltwater collection tank; the online conductivity meter is used to monitor the salt concentration change of the fly ash in the initial section of the filler column in real time, and when the water conductivity decreases to below 1.5 S / m, it indicates that the fly ash in this section has completed desalination; (4) Sectional unloading: Close the water pump, start the pneumatic cutting device to separate the fly ash in the filler column; move the water distributor at the bottom, open the electric gate valve at the discharge port, and unload the desalted fly ash; close the electric gate valve at the discharge port and restore the water distributor; (5) Coarse fly ash replenishment: Close the pneumatic cutting device to restore the communication state in the filler column, the original filled fly ash falls and forms a cavity at the top; move the water distributor at the top, open the electric gate valve at the inlet, add new pretreated fly ash to the cavity to maintain a constant height of the bed, and restore the water distributor after replenishment; repeat steps (3)-(5) to realize continuous operation; (6) Evaporation and salt separation: The salt-containing wastewater in the saltwater collection tank is sent to a multi-effect evaporator for concentration and crystallization, and the condensate is reused as cleaning water; the mixed salt concentrate obtained by evaporation and crystallization is sent to a step crystallization device for step crystallization to obtain industrial-grade chlorinated salt products.

4. The method of claim 3, wherein, The temperature during thermal decomposition is 300-400℃, and the time is 30-60 minutes; the sintering temperature is 550-600℃, and the time is 12-20 minutes; the particle size range of the coarse fly ash collected by sieving is 50-120 mesh.

5. The method of claim 3, wherein, The water flow rate in the fixed bed filler column is controlled during water washing desalination, and the specific flow rate is determined by calculation as follows: ； In the formula: Q is the water flow rate, L / min; ε is the fixed bed porosity, the value range is 0.35-0.45, and is determined according to the actual measurement; A is the cross-sectional area of the filler column, and H is the bed height; t c is the contact time, unit: minute, the value range is 10-120 minutes.

6. The method of claim 3, wherein, Water washing desalination uses clean water, or uses F - contaminated water of microplastics to realize the synergistic removal of pollutants by fly ash adsorption. The waste heat dissipated during the sintered fly ash cooling process is used as the heat source for the preheating of the thermal decomposition process through a heat exchanger, or for the multi-effect evaporator and the step crystallization device; The fixed bed filler column adopts a cylindrical-conical combination, wherein the inner diameter of the cylindrical part is 500-1000mm, and the length-diameter ratio is 3-8; the lower end of the cylinder connects to a cone for uniform water flow, and the outlet angle of the conical body is designed to be 50-70° to avoid forming a dead zone and guide the discharge of the material; The filter screen of the water distributor is made of temperature-resistant and corrosion-resistant polypropylene material to ensure structural stability during long-term water washing.

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