A fly ash filtration desalination method

Abstract

The present invention discloses a fly ash diafiltration desalination method, including the steps of fly ash pretreatment, fly ash cleaning column filling, diafiltration desalination, filtration separation and concentrated brine post-treatment, etc., wherein mixed fly ash is filled into a group of fly ash cleaning columns that are sequentially connected in series through a water pipe, and clean water is used to achieve continuous diafiltration desalination by diafiltration through the series of fly ash cleaning columns. In the present invention, each fly ash cleaning column and its supporting equipment form a desalination module, and each desalination module uses a pumping method to press water from bottom to top into the cleaning column filled with fly ash, and the water passes through the gaps between the fly ash particles in a diafiltration manner, fully contacts the fly ash particles, and dissolves the salt in the fly ash and takes it out. The salt water produced by the system has a high salt concentration, and the energy consumption and cost required for subsequent evaporation and salt extraction are low. There is no need for the filter press in the multi-stage stirring water washing intermediate process of the prior art, which further reduces energy consumption and saves equipment investment.

Description

Technical Field

[0001] The invention belongs to the technology of waste incineration fly ash treatment, and in particular relates to a fly ash infiltration desalination method. Background Art

[0002] The fly ash from the incineration of domestic waste has a high salt content. According to the existing pollution control technical specifications, desalination is required during the comprehensive utilization process. The existing fly ash water washing and desalination technology mainly uses a stirring device to mix and stir the fly ash and water, and then uses a plate and frame filter press to separate the solid and liquid to allow the water to remove the salt in the fly ash. However, in order to make the fly ash slurry fluid, the water-ash ratio of the stirring method is generally greater than 3, because the fly ash particles are small and the water requirement is high, otherwise the actual operation will be difficult. The high water volume results in a low salt concentration in the brine. Generally, the salt content of fly ash is 20-40%. Calculated at a water-ash ratio of 3, even if it is completely desalinated, the concentration of the brine produced is only 7-13%, which is much lower than the saturated salt concentration (about 35%). The low salt concentration requires a high amount of water to be evaporated for subsequent evaporation and salt extraction, and high energy consumption, resulting in high costs for fly ash water washing and desalination treatment. In order to ensure the desalination effect, the existing stirring technology requires multi-stage countercurrent water washing, and plate and frame filter pressing after each stage of water washing. The mainstream technology at this stage is three-stage countercurrent water washing, which requires at least three plate and frame filter pressings. The filter pressing has high energy consumption and is time-consuming.

[0003] For example, CN117680468A discloses a method and system for wet grinding pretreatment of waste incineration fly ash, which includes three steps: wet grinding fly ash pretreatment, fly ash water washing and water washing residual liquid treatment. The solid-liquid mixture after wet grinding is centrifugally filtered, the fly ash solid particles after centrifugal filtration are circulated and washed, and the circulated water-washed fly ash solid particles are centrifugally dehydrated. However, the circulated water washing of the system consumes a large amount of water to maintain the fluidity of the slurry, and the centrifugal dehydration and filtration require a large amount of energy. CN116900021A discloses a method and system for washing and desalting fly ash from hazardous waste incineration, which includes: premixing fly ash with water, then performing a primary countercurrent water washing, and filtering to obtain a primary mud cake and a primary filtrate; wherein the primary mud cake is subjected to a secondary countercurrent water washing, and filtering to obtain a secondary mud cake and a secondary filtrate; the secondary mud cake can be flexibly landfilled; the secondary filtrate is used as a primary countercurrent water washing liquid and a premixed material for a primary countercurrent water washing; if the salt concentration in the primary filtrate is lower than the set concentration, it is used as premixing water and mixed with the screened fly ash; if the salt concentration in the primary filtrate is not lower than the set concentration, it is evaporated after water treatment to obtain crystalline salt, and rigidly landfilled. The patent achieves salt separation through multi-stage water washing and filtering. CN117138944A discloses a fly ash harmless treatment method and application thereof, wherein fly ash, water, heavy metal chelating agent and frother are mixed and then floated to obtain heavy metal chelate, clean fly ash and waste liquid; wherein the frother comprises a first frother and a second frother, and the heavy metal chelating agent comprises a first heavy metal chelating agent and a second heavy metal chelating agent; a calcium and magnesium precipitating agent is added to the waste liquid, and calcium and magnesium impurities and brine are obtained after solid-liquid separation; finally, the brine is evaporated to obtain sodium chloride and potassium chloride.

[0004] The above fly ash desalination systems and methods require stirring or filter pressing operations, have low desalination efficiency, large water requirements, and high energy consumption for subsequent salt concentration, resulting in high desalination costs and being unable to meet the actual needs of large-scale low-cost treatment of fly ash. Summary of the invention

[0005] Purpose of the invention: The technical problem to be solved by the present invention is to provide a fly ash filtration desalination method in view of the shortcomings of the prior art, which realizes the continuous desalination of fly ash through the filtration desalination mode and the form of modular series cleaning columns, reduces water consumption and energy consumption, and thus greatly reduces the fly ash treatment cost.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A fly ash filtration desalination method comprises the following steps:

[0008] S1. Fly ash pretreatment: mixing the fly ash to be treated with the infiltration auxiliary material to obtain mixed fly ash;

[0009] S2. Filling the fly ash cleaning column: filling the mixed fly ash in step S1 into a group of fly ash cleaning columns which are sequentially connected in series on the water pipe, wherein a water inlet is provided at the bottom of each fly ash cleaning column, a water outlet is provided at the top of the fly ash cleaning column, and a structure is provided between the water inlet and the water outlet and the mixed fly ash to evenly distribute the water flow and prevent fine fly ash from clogging the pipe with the water flow;

[0010] S3, filtration desalination: the front end of the fly ash cleaning columns connected in series is connected to the clean water tank through a water pipe, and the rear end is connected to the salt water tank through a water pipe. Each cleaning column is placed vertically, and clean water is continuously injected into each fly ash cleaning column from bottom to top through a water pump. The water passes through the gaps between the fly ash particles in a percolation manner, fully contacts with the fly ash particles, dissolves the salt in the fly ash and collects it in the salt water tank; when the salt concentration of the effluent from the last fly ash cleaning column is lower than the set salt concentration value of the salt water, a new fly ash cleaning column to be treated is connected at the rear end as the last column in series, and the effluent is connected to the salt water tank, thereby ensuring a higher salt water concentration; when the salt concentration of the effluent from the first fly ash cleaning column is lower than the set clean water salt concentration value, it is considered that the fly ash cleaning column has completed desalination, the fly ash cleaning column that has completed desalination is removed, and the clean water tank is connected to the bottom of the next fly ash cleaning column;

[0011] S4, filtration and separation: the fly ash cleaning column that has completed desalination replaced in step S3 is rinsed with clean water, and the filtration auxiliary material and the desalinated fly ash slurry are separated by screening according to the significant difference in particle size; the desalinated fly ash slurry is further filtered to obtain a desalinated fly ash product, and the filtrate obtained by filtration can be used as clean water for rinsing the fly ash cleaning column or introduced into a clean water tank for repeated use; the separated filtration auxiliary material is directly or after drying reused in the fly ash pretreatment of step S1.

[0012] Specifically, in step S1, the particle size of the infiltration auxiliary material should be between 0.5 and 4 mm, and can be river sand or glass beads. The fly ash and the infiltration auxiliary material are mixed in a mass ratio of (2-6): (8-4). Because the untreated fly ash from the incineration of domestic waste is fine, too dense, and has poor permeability, a large pressure is required to allow water to pass through during infiltration, which will increase the treatment cost. In addition, the overly dense fly ash will form a preferential channel during infiltration, and water cannot evenly contact all the fly ash. In order to solve the above problems and improve the permeability of fly ash, the fly ash is mixed with coarse particles with good permeability such as glass beads or single-graded river sand without fine particles (medium sand or coarse sand, with a particle size range of 0.5-4 mm, and a ratio of the maximum particle size to the minimum particle size not exceeding 2). The proportion of sand or glass beads is not less than 40% of the weight of the mixture. Too much sand or glass beads will reduce the fly ash treatment efficiency. The preferred ratio is 50-70%.

[0013] Further, in step S2, the fly ash cleaning column includes a shell, a plunger, an inlet pipe, an outlet pipe and a filter layer; the plunger is a pair, respectively arranged at the two ends of the shell; the inlet pipe is arranged at the bottom of the shell and passes through the plunger below; the outlet pipe is arranged at the top of the shell and passes through the plunger above; the filter layers are respectively arranged on the inner sides of the plungers at both ends, and the fly ash to be treated is filled between the filter layers at both ends; the inner diameter of the fly ash cleaning column is 50-1000mm, preferably, 100-300 mm, and the aspect ratio is 1-20, preferably 3-10.

[0014] Furthermore, a salt concentration sensor is also provided on the outlet pipe for desalination quality control. Preferably, a conductivity sensor or a chloride ion selective electrode is used as the salt concentration sensor. By setting the two thresholds of the salt water value and the clean water value, the access timing of the cleaning column to be processed and the disassembly timing of the cleaning column that has completed desalination are indicated. During operation, when the salinity of the effluent from the front cleaning column close to the clean water tank reaches the clean water value, the fly ash cleaning column is disconnected from the system, disassembled and enters the next process link, or when the salt concentration of the effluent from the rear cleaning column close to the salt water tank is about to be lower than the salt water value, a new fly ash cleaning column to be processed is added. By regulating the size of the salt water value and the clean water value, the quality of the two products, namely salt water and desalinated fly ash, can be controlled respectively.

[0015] Furthermore, the filter layer comprises a filter membrane, a fine sand core and a coarse sand core which are arranged in sequence from the inside to the outside; the filter membrane is arranged between the fine sand core and the fly ash.

[0016] Furthermore, the water inlet pipe and the water outlet pipe are respectively connected with a water distributor, which is a porous plate water distributor or a side-mounted water distributor with more than three claws, and is arranged on the outside of the filter layer to evenly distribute water on the one hand and prevent clogging on the other.

[0017] Preferably, the filter membrane is selected from any one of glass fiber filter membrane, cellulose filter membrane and polyethersulfone filter membrane. The filter membrane can absorb some heavy metal elements in fly ash on the one hand, and prevent fine fly ash particles from entering the water pipe and causing blockage accidents on the other hand.

[0018] Preferably, the filter membrane is coated on the surface of the fine sand core in contact with the fly ash.

[0019] Furthermore, the sides of the fine sand core and the coarse sand core are sleeved with O-rings, and the filter membrane is coated on the surface of the fine sand core and fixed and sealed by the O-rings.

[0020] Preferably, a pressure gauge for monitoring water pressure is installed on the pipe at the water inlet of each fly ash cleaning column, so as to detect blockage points according to the data of the pressure detection gauge, short-circuit the corresponding cleaning column in time and remind the operator to replace and refill the problematic cleaning column in time.

[0021] Furthermore, a water pump is provided on the pipeline between the clean water tank and the fly ash cleaning column.

[0022] Specifically, in step S3, the contact time tc is controlled to be between 5 and 600 min. A shorter contact time is preferably selected for a cleaning column with a smaller length-to-diameter ratio, but generally not less than 10 min, and a longer contact time is preferably selected for a cleaning column with a larger length-to-diameter ratio, generally not exceeding 120 min. The inlet flow rate is calculated by the following formula: ;

[0023] in, ;

[0024] Q water inlet flow, unit L / min;

[0025] Vp is the pore volume of the mixed fly ash in the cleaning column, in L;

[0026] t c Contact time, in min;

[0027] m FA The mass of fly ash loaded in the cleaning column, in kg;

[0028] m Sand The filling mass of the filtration auxiliary material in the cleaning column, in kg;

[0029] ρ ture，FA True density of fly ash, in kg / L;

[0030] ρ ture，Sand True density of the filtration auxiliary material, in kg / L;

[0031] V material The volume occupied by mixed fly ash in the wash column.

[0032] Furthermore, the process of the present invention also includes step S5, wherein the concentrated brine collected in the brine pool in step S3 is subjected to impurity removal to remove calcium, magnesium and heavy metals, and then evaporated to separate the salt to obtain potassium chloride and sodium chloride industrial salt products, and the evaporated water can be returned to the clean water pool for reuse as clean water. Beneficial Effects

[0033] (1) In the present invention, each diafiltration desalination module uses a pumping method to press water from bottom to top into a cleaning column filled with fly ash. The water passes through the gaps between the fly ash particles in a diafiltration manner, fully contacts the fly ash particles, and dissolves the salt in the fly ash. In this system, the fly ash layer does not need to have fluidity, and the gap space between the fly ash particles is small. There is little residual water in each module. By increasing the salt concentration of the outlet water, saturated concentrated brine can be achieved, and ultra-low water consumption desalination with a water-ash ratio of less than 0.5 can be achieved (compared to the stirring water washing water-ash ratio of about 3). In order to save water while ensuring the desalination effect, the present invention adopts a multi-stage direct series connection method for diafiltration desalination, directly using the permeate of the previous module as the inlet water for the subsequent module, and no pressure filtration dehydration is required in the middle, which greatly saves dehydration energy and time, and achieves approximately continuous desalination. Each module is equipped with a salt concentration sensor to monitor the salinity of the outlet water. The module newly loaded with fly ash is connected to the outlet end, and the salt concentration sensor is used to ensure that the outlet water quality is close to saturated concentrated brine, thereby reducing the energy consumption of subsequent industrial salt evaporation and crystallization. The module close to the water inlet end can be disconnected from the system and the desalinated fly ash can be recovered after the sensor confirms that the salinity of the outlet water meets the standard and the desalination is completed.

[0034] (2) The cleaning column of the present invention is provided with a multi-filter layer structure inside, and the inlet and outlet water pipes are respectively arranged on the outer surface of the filter layer through a water distributor, which can evenly distribute water and prevent clogging on the other hand; the filter layer structure includes a filter membrane, a fine sand core and a coarse sand core, and the multi-layer filter structure can prevent fly ash particles from penetrating into the pipeline and causing clogging. At the same time, the modular multi-filter layer structure without powder or particles is also convenient for disassembly, assembly and replacement.

[0035] (3) The fly ash infiltration desalination method of the present invention is energy-saving and low-cost, saves the filter pressing in the multi-stage water washing process, reduces energy consumption, and saves equipment investment. The spatial layout is flexible, and stirring and filter pressing equipment that takes up a lot of space and is difficult to move is not used. The module size is adjustable and each module can be flexibly connected or short-circuited. The water inlet and outlet positions can be adjusted at any time according to the module setting, which can ensure full utilization of the space. The desalination quality is high. Since each module can be flexibly connected or short-circuited, the desalination quality of each module can be guaranteed by sensors, and the outlet water can be guaranteed to be close to saturated brine, which is difficult to achieve using the stirring water washing method. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more clear.

[0037] Figure 1 It is an overall flow chart of the fly ash infiltration desalination method of the present invention.

[0038] Figure 2 It is a schematic diagram of the overall structure of the fly ash infiltration desalination system of the present invention.

[0039] Figure 3 It is a schematic structural diagram of the fly ash cleaning column of the present invention.

[0040] Figure 4 It is a partial enlarged schematic diagram of the filter layer in the fly ash cleaning column of the present invention.

[0041] Wherein, each reference numeral represents:

[0042] 100-clean water tank; 200-salt water tank; 300-fly ash cleaning column; 301-water inlet; 302-water outlet; 400-water pump; 500-fly ash;

[0043] 10-housing; 20-plunger; 30-water inlet pipe; 40-water outlet pipe; 50-filter layer; 51-filter membrane; 52-fine sand core; 53-coarse sand core; 54-O-ring; 60-conductivity sensor; 70-water distributor. DETAILED DESCRIPTION

[0044] The present invention can be better understood with reference to the following examples.

[0045] like Figure 1 As shown, the fly ash filtration desalination method of the present invention mainly comprises the following steps:

[0046] S1. Fly ash pretreatment: mixing the domestic waste incineration fly ash to be treated with the infiltration auxiliary material in a uniform proportion to obtain mixed fly ash;

[0047] S2. Filling the fly ash cleaning column: Fill the mixed fly ash in step S1 into a group of fly ash cleaning columns 300 connected in series on the water pipe. The bottom of each fly ash cleaning column 300 is provided with a water inlet 301, and the top of the fly ash cleaning column is provided with a water outlet 302;

[0048] S3, filtration desalination: the front end of the fly ash washing columns 300 connected in series is connected to the clean water tank 100 through a water pipe, and the rear end is connected to the salt water tank 200 through a water pipe. Each washing column is placed vertically, and clean water is continuously injected into each fly ash washing column 300 from bottom to top through a water pump. The water passes through the gaps between the fly ash particles in a percolation manner, fully contacts with the fly ash particles, dissolves the salt in the fly ash and collects it in the salt water tank 200; the salt concentration of the outlet water is measured by a salt concentration sensor set at the outlet. When the salt concentration of the outlet water of the last fly ash washing column is lower than the set salt concentration value of the salt water, a new fly ash washing column to be treated is connected at the rear end as the last column in series, and the outlet water is connected to the salt water tank 200, thereby ensuring a higher salt water concentration; when the salt concentration of the outlet water of the first fly ash washing column is lower than the set salt concentration value of the clean water, it is considered that the fly ash washing column has completed desalination, and the fly ash washing column that has completed desalination is removed, and the clean water tank 100 is connected to the bottom of the next fly ash washing column;

[0049] S4, filtration and separation: the fly ash cleaning column that has completed desalination and is replaced in step S3 is rinsed with clean water, and the filtration auxiliary material and the desalinated fly ash slurry are separated by screening according to the significant difference in particle size; the desalinated fly ash slurry is further filtered to obtain a desalinated fly ash product, and the filtrate obtained by filtration can be used as clean water for rinsing the fly ash cleaning column or introduced into the clean water tank 100 for repeated use; the separated filtration auxiliary material is directly or after drying reused in the fly ash pretreatment in step S1.

[0050] like Figure 2 As shown, a processing system of the fly ash infiltration desalination method of the present invention is provided, comprising a group of fly ash cleaning columns 300 connected in series on a water pipe, each fly ash cleaning column 300 is filled with fly ash 500 to be treated; a water inlet 301 is provided at the bottom of the fly ash cleaning column 300, and a water outlet 302 is provided at the top of the fly ash cleaning column; the front ends of the fly ash cleaning columns 300 connected in series are connected to a clean water tank 100 through a water pipe, and the rear ends are connected to a salt water tank 200 through a water pipe; the clean water tank 100 can be connected to the bottom water inlet of any fly ash cleaning column 300 through a pipeline, so as to facilitate the replacement of the fly ash cleaning column.

[0051] Combination Figure 3 As shown, the fly ash cleaning column 300 of the present invention includes a shell 10, a plunger 20, an inlet pipe 30, an outlet pipe 40 and a filter layer 50; the plungers 20 are a pair, which are respectively arranged at the two ends of the shell 10; the inlet pipe 30 is arranged at the bottom of the shell 10 and passes through the plunger 20 below; the outlet pipe 40 is arranged at the top of the shell 10 and passes through the plunger 20 above; the filter layers 50 are respectively arranged on the inner sides of the plungers 20 at both ends, and the fly ash 500 to be treated is filled between the filter layers 50 at both ends.

[0052] A salt concentration sensor 60 is also provided on the outlet pipe 40 of each fly ash cleaning column 300, and the outlet water concentration and the degree of desalination are guaranteed by the reading of the salt concentration sensor 60. In the following embodiments, the salt concentration sensor is a conductivity sensor, which is used after calibration and internalization with salt water of different standard salt concentrations.

[0053] Combination Figure 4 As shown, the filter layer 50 of each fly ash cleaning column 300 includes a filter membrane 51, a fine sand core 52 and a coarse sand core 53 which are sequentially arranged from the inside to the outside; the filter membrane 51 is arranged between the fine sand core 52 and the fly ash.

[0054] The water inlet pipe 30 and the water outlet pipe 40 are respectively connected with a water distributor 70, which is arranged on the outer surface of the coarse sand core 53, so as to evenly distribute water on the one hand and prevent clogging on the other hand.

[0055] In the following embodiments, the filter membrane 51 is a water-based glass fiber filter membrane.

[0056] The filter membrane 51 is coated on the surface of the fine sand core 52 in contact with the fly ash. The sides of the fine sand core 52 and the coarse sand core 53 are sleeved with O-type sealing rings 54, and the filter membrane 51 is coated on the surface of the fine sand core 52 and fixed and sealed by the O-type sealing rings 54.

[0057] In the present invention, a pressure gauge for monitoring water pressure is also installed on the pipe of the water inlet of each fly ash cleaning column.

[0058] A water pump 400 is provided on the pipeline between the clean water tank 100 and the fly ash cleaning column 300 . Example 1

[0059] Laboratory test:

[0060] (1) Fly ash (chlorine content 26.1%) and 3 mm diameter glass beads were mixed in a mass ratio of 3:7 to improve the permeability of fly ash.

[0061] (2) The inner diameter of each fly ash cleaning column is 50 mm, and the aspect ratio is 6; the fly ash and glass bead mixture in step (1) is filled into the fly ash cleaning column, and a filter membrane 51, a fine sand core 52 and a coarse sand core 53 are arranged in sequence from the inside to the outside at both ends of the fly ash cleaning column.

[0062] (3) Use Teflon tube and quick-release manual connection, and only install conductivity sensors at the outlets of the first and last cleaning columns, without pressure sensors.

[0063] (4) A 10 L glass container filled with tap water is used as the clean water tank 100, and the clean water tank 100 is connected to the bottom water inlet 301 of the first fly ash cleaning column through a pipe. Then the outlet water 302 at the top of the first fly ash cleaning column is connected to the next fly ash cleaning column through a pipe, thereby connecting six fly ash cleaning columns in series in sequence; a 30 L plastic barrel is used as the salt water tank 200, and the top water outlet of the last fly ash cleaning column is connected to the salt water tank 200 through a pipe.

[0064] (5) The water flow rate entering the fly ash cleaning column is set at 2.84 ml / min to ensure sufficient contact time and to ensure that the salt concentration of the effluent is ≥32%.

[0065] (7) When the conductivity sensor on the first fly ash cleaning column shows that the water conductivity is lower than 0.5 S / m, the cleaning column is removed and cleaned with tap water. The fly ash and glass beads are sieved through a 2 mm mesh sieve and filtered to obtain desalinated fly ash. The filtered water is circulated as cleaning water for three times and then enters the clean water tank for use as clean water.

[0066] Through the above desalination process, the chlorine content of the desalted fly ash can be reduced to 0.84%. Example 2

[0067] Take a waste incineration plant as an example:

[0068] (1) Fly ash (chlorine content 31.1%) produced by waste incineration was mixed evenly with river sand (particle size 2-4 mm) in a mass ratio of 4:6, and the river sand was used to improve the permeability of the fly ash.

[0069] (2) The inner diameter of each fly ash cleaning column is 500 mm, and the length-to-diameter ratio is 1.5. The fly ash cleaning columns are set on two rows of long column racks, and the two rows of column racks are placed back to back. The fly ash cleaning columns are connected in series in sequence using soft PVC water pipes and quick-release manual connections. Fifteen fly ash cleaning columns are connected in series.

[0070] (3) From the bottom of the fly ash cleaning column, the fine sand core 52 covered with the filter membrane 51 (glass fiber filter membrane) and sealed with the O-ring 54 and the coarse sand core 53 sealed with the O-ring 54 are sequentially loaded, and the above-mentioned filter components are pushed into the fly ash cleaning column by the plunger 20. A layer of geotextile is set on the filter membrane 51 for protection, and the fly ash and river sand in step (1) are filled into each fly ash cleaning column. Then, the geotextile, filter membrane 51 (glass fiber filter membrane), fine sand core 52 and coarse sand core 53 are sequentially set from the inside to the outside at the upper end of the fly ash cleaning column, and the O-ring 54 is used to seal it. The lifting, installation and removal of the cleaning column are assisted by a crane. A modular conductivity sensor is set at the outlet of each fly ash cleaning column. A porous plate water distributor 70 is used at the water inlet pipe 30 and the water outlet pipe 40 respectively.

[0071] The clean water tank 100 is connected to the bottom water inlet 301 of the first fly ash cleaning column through a pipe, and then the outlet water 302 at the top of the first fly ash cleaning column is connected to the next fly ash cleaning column through a pipe, so that the fly ash cleaning columns are connected in series in sequence; the top water outlet of the last fly ash cleaning column is connected to the brine tank 200 through a pipe.

[0072] (4) Use industrial water for cleaning and set the water inlet flow rate to 4.5 L / min. This will shorten the cleaning time while ensuring sufficient contact time and ensure that the salt concentration of the effluent is 25%~35%.

[0073] (5) When the conductivity sensor on the first fly ash cleaning column shows that the water conductivity is less than 1.5 S / m, the cleaning column is removed and cleaned with tap water. The fly ash and river sand are sieved through a 2 mm mesh sieve and then filtered to obtain desalinated fly ash. The filtered water is recycled three times and then enters the tap water container for reuse as clean water. The river sand is reused after a simple drying.

[0074] At the same time, after the first cleaned cleaning column is dismantled within the same time period, a new fly ash cleaning column filled with fly ash to be cleaned is replaced as the last column in series for continuous cleaning.

[0075] In this embodiment, the chlorine content of the fly ash after desalination is reduced to 1.25%. Example 3

[0076] Based on Example 2, fly ash is processed using automated equipment:

[0077] (1) The fine sand core 52, the coarse sand core 53, the water distributor 70, the plunger 20, and the water outlet 302 are integrated into a modular configuration. The lower plunger is integrated with a pressure sensor at the water inlet, and the upper plunger is integrated with a conductivity sensor 60 at the water outlet. Each sensor can be distinguished and identified by the control system and connected to the control system for individual calibration.

[0078] (2) Each fly ash cleaning column has an inner diameter of 200 mm and an aspect ratio of 6. It is automatically loaded. Fly ash and river sand are automatically weighed and mixed in proportion from the silo and then transported to the loading area for automatic loading under manual inspection.

[0079] (3) The cleaning column is installed on a circular rotatable bracket. Each column position on the bracket has an indicator light to show the position and status of the cleaning column in the series system. The cleaning column is automatically installed and removed by a robotic arm, and the inlet and outlet water is controlled by the control system through a magnetic control valve. No human intervention is required during the cleaning process.

[0080] (4) After cleaning, the disassembled cleaning column enters the filter press workshop, where it is manually disassembled and cleaned with high-pressure water. The fly ash and river sand form a slurry that is introduced into the screening equipment through a water tank. After automatic wet screening, the river sand enters the drying area for reuse; the fly ash slurry enters the plate and frame filter press, where desalinated fly ash is obtained after filtration, and the filtered water is reused.

[0081] In this embodiment, the connection time of the new cleaning column and the cleaning end point are controlled by conductivity, and the chlorine content of the fly ash after desalination is reduced to 1.2%. Comparative Example

[0082] In Example 2, fly ash generated by garbage incineration is used as the treatment object. The more advanced three-stage countercurrent water washing in the prior art is adopted. Water and fly ash flow in the opposite direction. The desalted fly ash (chlorine content 27.6%) is stirred and mixed with the secondary water washing liquid, and then filtered and dehydrated to obtain a third-stage filter cake and a third-stage water washing liquid. The third-stage water washing liquid is the brine to be concentrated; the third-stage filter cake is stirred and mixed with the primary water washing liquid, and then filtered and dehydrated to obtain a second-stage filter cake and a second-stage water washing liquid; the secondary filter cake is stirred and mixed with clean water, and then filtered and dehydrated to obtain a first-stage filter cake and a first-stage water washing liquid. The first-stage filter cake is the desalted fly ash. The water-ash ratio of each stage of water washing is 3.

[0083] The salt concentration of the brine to be concentrated after the three-stage water washing is 13-16%, which is much lower than the brine obtained by this method.

[0084] The chlorine content of desalted fly ash was reduced to 1.62%.

[0085] The present invention provides a fly ash filtration desalination method and method. There are many methods and ways to implement the technical solution. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims

1. A fly ash filtration desalination method, characterized in that: The steps include: S1. Fly ash pretreatment: mixing the fly ash to be treated with the infiltration auxiliary material to obtain mixed fly ash; S2, filling the fly ash cleaning column: the mixed fly ash in step S1 is filled into a group of fly ash cleaning columns (300) which are sequentially connected in series on the water pipe, wherein a water inlet (301) is provided at the bottom of each fly ash cleaning column (300), a water outlet (302) is provided at the top of the fly ash cleaning column, and a structure is provided between the water inlet (301) and the water outlet (302) and the mixed fly ash to evenly distribute the water flow and prevent fine fly ash from clogging the pipe with the water flow; S3, filtration desalination: the front ends of the fly ash cleaning columns (300) connected in series are connected to the clean water tank (100) through water pipes, and the rear ends are connected to the salt water tank (200) through water pipes. Each cleaning column is placed vertically, and clean water is continuously injected into each fly ash cleaning column (300) from bottom to top through a water pump. The water passes through the gaps between the fly ash particles in a filtration manner, fully contacts the fly ash particles, dissolves the salt in the fly ash and is collected in the salt water tank (200). When the salt concentration of the effluent from the last fly ash cleaning column is lower than the set salt concentration value of the salt water, a new fly ash cleaning column to be treated is connected at the rear end as the last column in the series, and the effluent is connected to the salt water tank (200), thereby ensuring a higher salt water concentration. When the salt concentration of the effluent from the first fly ash cleaning column is lower than the set salt concentration value of the clean water, the fly ash cleaning column that has completed desalination is removed, and the pipeline of the clean water tank (100) is connected to the bottom of the next fly ash cleaning column. S4, filtration and separation: the fly ash cleaning column that has completed desalination, which was replaced in step S3, is rinsed with clean water, and the filtration auxiliary material and the desalinated fly ash slurry are separated by screening; the desalinated fly ash slurry is further filtered to obtain a desalinated fly ash product, and the filtrate obtained by filtration is used as clean water for rinsing the fly ash cleaning column or introduced into a clean water tank (100) for repeated use; the separated filtration auxiliary material is directly or after drying reused in the fly ash pretreatment in step S1; In step S2, the inner diameter of the fly ash cleaning column is 50-1000 mm, and the aspect ratio is 1-20. The fly ash cleaning column (300) comprises a shell (10), a plunger (20), an inlet pipe (30), an outlet pipe (40), and a filter layer (50); the plungers (20) are a pair, and are respectively arranged at two ends of the shell (10); the inlet pipe (30) is arranged at the bottom of the shell (10) and passes through the plunger (20) at the bottom; the outlet pipe (40) is arranged at the top of the shell (10) and passes through the plunger (20) at the top; the filter layers (50) are respectively arranged on the inner sides of the plungers (20) at the two ends, and the mixed fly ash (500) to be treated is filled between the filter layers (50) at the two ends; The filter layer (50) comprises a filter membrane (51), a fine sand core (52) and a coarse sand core (53) which are arranged in sequence from the inside to the outside; the filter membrane (51) is arranged between the fine sand core (52) and the fly ash; The water inlet pipe (30) and the water outlet pipe (40) are respectively connected to a water distributor (70), and the water distributor (70) is a porous plate water distributor or a side-mounted water distributor with more than three claws, and is arranged outside the filter layer (50).

2. The fly ash infiltration desalination method according to claim 1, characterized in that: In step S1, the particle size of the infiltration auxiliary material is between 0.5 mm and 4 mm, and the material is river sand or glass beads. The fly ash and the infiltration auxiliary material are mixed in a mass ratio of (2-6): (8-4).

3. The fly ash infiltration desalination method according to claim 1, characterized in that: The water outlet pipe (40) is also provided with a salt concentration sensor (60) for monitoring the salt concentration of the water outlet from each cleaning column. The salt concentration sensor (60) is a conductivity sensor or a chloride ion selective electrode.

4. The fly ash infiltration desalination method according to claim 1, characterized in that: The filter membrane (51) is selected from any one of a glass fiber filter membrane, a cellulose filter membrane, and a polyethersulfone filter membrane; the filter membrane (51) is coated on the surface of the fine sand core (52) in contact with the fly ash.

5. The fly ash infiltration desalination method according to claim 4, characterized in that: O-type sealing rings (54) are sleeved on the side surfaces of the fine sand core (52) and the coarse sand core (53); the filter membrane (51) is coated on the surface of the fine sand core (52) and is fixed and sealed by the O-type sealing ring (54).

6. The fly ash infiltration desalination method according to claim 1, characterized in that: In step S3, the contact time t is controlled c 5-600 min; the water inlet flow rate is calculated by the following formula: ； in, ; Q water inlet flow, unit L / min; Vp is the pore volume of the mixed fly ash in the cleaning column, in L; t c Contact time, in min; m FA The mass of fly ash loaded in the cleaning column, in kg; m Sand The filling mass of the filtration auxiliary material in the cleaning column, in kg; True density of fly ash, in kg / L; True density of the filtration auxiliary material, in kg / L; The volume occupied by mixed fly ash in the wash column.

7. The fly ash infiltration desalination method according to claim 1, characterized in that: The method further comprises step S5, wherein the concentrated brine collected in the brine pool (200) in step S3 is evaporated and salted after removing impurities to obtain potassium chloride and sodium chloride products, and the evaporated water is returned to the clean water pool for reuse as clean water.

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