A low-temperature flue gas evaporation and crystallization system for desulfurization wastewater

Abstract

This invention relates to the field of low-temperature flue gas evaporation for treating high-salt wastewater, and discloses a low-temperature flue gas evaporation crystallization system for desulfurization wastewater. The system includes a low-temperature flue gas main pipe, an outlet connected to a desulfurization tower, and an outlet connected to a clean flue gas discharge pipe. One end of the clean flue gas discharge pipe is connected to a low-temperature flue gas evaporator via a wet flue gas pipe, on which a clean and wet flue gas blower is installed. The low-temperature flue gas main pipe is connected to the lower part of one end of the low-temperature flue gas evaporator via an inlet pipe, on which a low-temperature dry flue gas blower is installed. This invention achieves one-time treatment of desulfurization wastewater by low-temperature flue gas waste heat, evaporation and concentration to crystallization for salt production, with low energy consumption. The evaporated water is used as makeup water for the desulfurization tower, realizing water resource recovery and utilization. This invention also has advantages such as no large circulating water volume, no salt mist carried by flue gas, achieving evaporation crystallization within the low-temperature evaporation device, and low energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of low-temperature flue gas evaporation and high-salt wastewater treatment technology, specifically a low-temperature flue gas evaporation and crystallization system for desulfurization wastewater. Background Technology

[0002] Power plant wastewater, including reverse osmosis concentrate, desulfurization wastewater, and circulating cooling tower wastewater, all contain high concentrations of salt. Zero discharge of high-salinity water is one of the development goals of water treatment. Evaporation crystallization is the main final treatment method, often employing MVR evaporation crystallization and multi-effect flash evaporation processes. These processes utilize steam heat or electricity as the heat source for wastewater evaporation, resulting in complex systems with high energy consumption.

[0003] To reduce energy consumption in water treatment, engineers utilize the waste heat from flue gas generated by coal-fired boilers in power plants to treat desulfurization wastewater. The main processes employed fall into two categories: one involves atomizing the desulfurization wastewater and feeding it before a dry flue gas dust collector, which then collects the evaporated crystallization products along with fly ash; the other utilizes the low-temperature flue gas between the dry dust collector and the desulfurization tower, employing methods such as spray thickening towers, liquid column flow, and membrane flow to treat the desulfurization wastewater.

[0004] Patent application number 201621125928.3 discloses a concentration tower for reducing and concentrating desulfurization wastewater. This concentration tower includes a wastewater tank, a wastewater inlet, a wastewater circulation pump, a spray device, an oxidation air system, a demister, a flue gas inlet, a flue gas outlet, and a wastewater outlet. The wastewater tank is located at the bottom of the concentration tower. Wastewater enters the wastewater tank from the wastewater inlet on the side of the concentration tower and is then pumped into the spray device at the top of the concentration tower by the wastewater circulation pump. The concentrated water falls into the lower wastewater tank, forming a water circulation system. Hot flue gas is drawn from the main flue and enters the tower from the lower part, exiting from the top of the tower back into the main flue. This concentration tower replaces the pretreatment (water softening, membrane concentration, etc.) part of existing zero-discharge desulfurization wastewater technologies, reducing investment and operating costs.

[0005] However, this patent has problems such as large spray circulation water volume, the phenomenon of flue gas carrying salt mist droplets requiring the addition of a demister, the need for a large amount of cleaning water to clean the demister during operation, the increase in cleaning water will increase the amount of flue gas required for heating, high salt water operating environment has high requirements for equipment, and large workload for operation and maintenance.

[0006] Patent application number 201720093233.X discloses a wastewater concentration system based on liquid column evaporation using waste heat from flue gas: flue gas enters the wastewater sprayed by liquid column nozzles perpendicular or intersecting the flue gas from the flue gas inlet of the evaporation tower for heat and mass transfer. The wastewater absorbs heat and evaporates to produce water vapor, which enters the flue gas and flows out through the flue gas outlet of the evaporation tower into the desulfurization tower. The liquid column nozzles are connected to the wastewater storage tank. The evaporation tower is connected to the wastewater storage tank. The evaporated wastewater enters the wastewater storage tank to achieve wastewater recycling and concentration.

[0007] This patent adopts a columnar flow mode, which optimizes the problem of flue gas carrying salt back to the desulfurization tower in the patent application number: 201621125928.3. However, it is obvious that the liquid column formed by spraying has the problem of fluid boundary breakage and the columnar flow field cannot be stably maintained. Therefore, in order to reduce the flue gas carrying, the columnar flow formed by the pressure nozzle will be very short, which will result in a small heat exchange area between the water and the flue gas, thus reducing the heat exchange efficiency.

[0008] Application No. 201810017272.0 describes a fluoroplastic falling film evaporator that utilizes waste heat from flue gas to concentrate desulfurization wastewater. It employs the principle of falling film evaporation within the tube and uses a tubular heat exchange concentration method. The desulfurization wastewater inside the heat exchange tube forms a falling film and is concentrated by evaporation through heating with flue gas outside the tube.

[0009] Although the falling film tube heat exchanger improves the heat transfer coefficient on the water side through the falling film evaporation process, it still has problems such as not being able to solve the heat transfer coefficient on the flue gas side where the thermal resistance is the greatest.

[0010] To further optimize the treatment of desulfurization wastewater with low-temperature flue gas, this invention provides a low-temperature flue gas evaporation and crystallization system for desulfurization wastewater. Summary of the Invention

[0011] In view of the above situation and to overcome the shortcomings of the prior art, the present invention provides a low-temperature flue gas evaporation and crystallization system for desulfurization wastewater, which effectively solves the problems mentioned in the background.

[0012] To achieve the above objectives, the present invention provides the following technical solution: a low-temperature flue gas evaporation and crystallization system for desulfurization wastewater, comprising a low-temperature flue gas main pipe, an output end of which is connected to a desulfurization tower, an output end of which is connected to a clean flue gas discharge pipe, one end of which is connected to a low-temperature flue gas evaporator via a wet flue gas pipe, a clean and wet flue gas blower on the wet flue gas pipe, the low-temperature flue gas main pipe being connected to the lower part of one end of the low-temperature flue gas evaporator via an input pipe, a low-temperature dry flue gas blower on the input pipe, and one side of the upper part of the low-temperature flue gas evaporator being connected to the low-temperature flue gas main pipe via an output pipe;

[0013] The upper side of the low-temperature flue gas evaporator is connected to a water inlet pipe, and the water inlet pipe is equipped with a flocculation tank, a sedimentation tank, a multi-media filter and a filtered water tank in sequence.

[0014] Preferably, the low-temperature flue gas evaporator includes an evaporation tower body, a hopper connected to the lower end of the evaporation tower body, a low-temperature dry flue gas inlet on one side of the lower part of the evaporation tower body, an evaporation flue gas outlet on one side of the upper part of the evaporation tower body, a clean and wet flue gas distribution chamber connected to the upper side inside the evaporation tower body, a clean and wet flue gas inlet connected to one end of the clean and wet flue gas distribution chamber, a membrane flow guide pipe uniformly connected to the lower end of the clean and wet flue gas distribution chamber, and a microporous ceramic tube connected to the lower end of the membrane flow guide pipe.

[0015] Preferably, a desulfurization wastewater distribution plate is connected to the upper side of the evaporation tower body. The desulfurization wastewater distribution plate is located below the clean and wet flue gas distribution chamber. The lower end of the desulfurization wastewater distribution plate is evenly provided with openings. A membrane flow distribution short pipe is welded to the lower end of the opening. The number of membrane flow distribution short pipes is the same as that of membrane flow guide pipes. The membrane flow guide pipes pass concentrically through the membrane flow distribution short pipes.

[0016] Preferably, the inner diameter of the membrane flow distribution tube is larger than the outer diameter of the membrane flow guide tube.

[0017] Preferably, the membrane flow guide tube and the microporous ceramic tube have the same outer diameter, and the membrane flow guide tube and the microporous ceramic tube are connected by threads, wherein the lower end of the membrane flow guide tube is provided with internal threads, and the upper connecting end of the microporous ceramic tube is provided with external threads.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] (1) This invention uses low-temperature hot dry flue gas extracted from the outlet of the dry electrostatic precipitator of a coal-fired boiler before entering the desulfurization tower as a heat source to meet the temperature rise and heat consumption required for the evaporation process when the desulfurization wastewater is evaporated and concentrated to a crystallized state. The desulfurization wastewater entering the low-temperature flue gas evaporator is treated by flocculation, sedimentation and filtration to remove particulate matter. The evaporation and concentration process of the desulfurization wastewater is mainly carried out on the surface of the water film of the vertical tube bundle in the low-temperature flue gas evaporator. The crystallization process is realized on the surface of the microporous ceramic tube at the bottom of the vertical tube bundle. The vertical tube bundle is filled with clean wet flue gas after wet desulfurization and dust removal. The clean wet flue gas forms a dynamic protective layer of bubbles and water vapor on the outer surface of the microporous ceramic tube through the micropores on the wall of the microporous ceramic tube, preventing the crystallization product from staying and scaling on the outer surface of the microporous ceramic tube in the crystallization zone. The crystallization product falls into the hopper at the bottom of the low-temperature flue gas evaporator and is collected and discharged. This invention system realizes the one-time treatment of desulfurization wastewater evaporation and concentration to crystallization and salt production by low-temperature flue gas waste heat. The energy consumption is low, and the evaporated water is used as makeup water for the desulfurization tower to realize water resource recycling.

[0020] (2) The invention also has the advantages of no large circulating water volume, no salt mist droplet flue gas carrying problem, realizing evaporation and crystallization in low temperature evaporation device, and low energy consumption. Attached Figure Description

[0021] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0022] In the attached diagram:

[0023] Figure 1 This is a system diagram of the present invention;

[0024] Figure 2 This is a schematic diagram of the structure of the low-temperature flue gas evaporator of the present invention;

[0025] In the diagram: 1. Low-temperature flue gas main pipe; 2. Desulfurization tower; 3. Clean flue gas discharge pipe; 4. Wet flue gas pipe; 5. Low-temperature flue gas evaporator; 501. Evaporation tower body; 502. Hopper; 503. Low-temperature dry flue gas inlet; 504. Evaporation flue gas outlet; 505. Clean and wet flue gas distribution chamber; 506. Clean and wet flue gas inlet; 507. Membrane flow guide pipe; 508. Microporous ceramic tube; 509. Desulfurization wastewater distribution plate; 510. Membrane flow distribution short pipe; 6. Clean and wet flue gas forced draft fan; 7. Input pipe; 8. Output pipe; 9. Water inlet pipe; 10. Flocculation tank; 11. Sedimentation tank; 12. Multi-media filter; 13. Filtered water tank; 14. Low-temperature dry flue gas forced draft fan. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0027] Example 1, by Figures 1-2 The present invention includes a low-temperature flue gas main pipe 1, a desulfurization tower 2 connected to the output end of the low-temperature flue gas main pipe 1, a clean flue gas discharge pipe 3 connected to the output end of the desulfurization tower 2, a low-temperature flue gas evaporator 5 connected to one end of the clean flue gas discharge pipe 3 through a wet flue gas pipe 4, a clean and wet flue gas blower 6 provided on the wet flue gas pipe 4, a low-temperature flue gas main pipe 1 connected to the lower part of one end of the low-temperature flue gas evaporator 5 through an input pipe 7, a low-temperature dry flue gas blower 14 provided on the input pipe 7, and a low-temperature flue gas evaporator 5 connected to the low-temperature flue gas main pipe 1 through an output pipe 8 on one side of the upper part of the low-temperature flue gas evaporator 5.

[0028] The upper side of the low-temperature flue gas evaporator 5 is connected to a water inlet pipe 9, and the water inlet pipe 9 is sequentially equipped with a flocculation tank 10, a sedimentation tank 11, a multi-media filter 12, and a filtered water tank 13.

[0029] Specifically, the low-temperature flue gas evaporator 5 includes an evaporation tower body 501, a hopper 502 connected to the lower end of the evaporation tower body 501, a low-temperature dry flue gas inlet 503 on one side of the lower part of the evaporation tower body 501, an evaporation flue gas outlet 504 on one side of the upper part of the evaporation tower body 501, a clean and wet flue gas distribution chamber 505 connected to the upper side inside the evaporation tower body 501, a clean and wet flue gas inlet 506 connected to one end of the clean and wet flue gas distribution chamber 505, a membrane flow guide pipe 507 uniformly connected to the lower end of the clean and wet flue gas distribution chamber 505, and a microporous ceramic tube 508 connected to the lower end of the membrane flow guide pipe 507.

[0030] Inside the evaporator body 501, a desulfurization wastewater distribution plate 509 is connected to the upper side. The desulfurization wastewater distribution plate 509 is located below the clean and wet flue gas distribution chamber 505. The lower end of the desulfurization wastewater distribution plate 509 is evenly provided with openings. A membrane flow distribution short pipe 510 is welded to the lower end of the opening. The number of membrane flow distribution short pipes 510 and membrane flow guide pipes 507 is the same. The membrane flow guide pipes 507 pass concentrically through the membrane flow distribution short pipes 510.

[0031] In this device, the flange height of the 504 desulfurization wastewater distribution plate must ensure that the liquid holding height is 7-10cm without overflow;

[0032] The inner diameter of the membrane flow distribution tube 510 is larger than the outer diameter of the membrane flow guide tube 507;

[0033] The membrane flow guide tube 507 and the microporous ceramic tube 508 have the same outer diameter, and the membrane flow guide tube 507 and the microporous ceramic tube 508 are connected by threads. The lower end of the membrane flow guide tube 507 is provided with internal threads, and the upper connecting end of the microporous ceramic tube 508 is provided with external threads.

[0034] The microporous ceramic tube 508 is an ultrafiltration microporous ceramic tube, which belongs to the tubular membrane type. The outer tube wall needs to be polished before membrane fabrication. The average pore diameter of the micropores is 20nm; the porosity is greater than 30%. One end of the tubular membrane is closed and the other end is externally threaded. The externally threaded end is connected to the membrane flow guide tube 507.

[0035] The membrane flow guide tube 507 and the microporous ceramic tube 508 together form the site for wastewater concentration and evaporation crystallization. The membrane flow guide tube 507 can be a corrosion-resistant metal tube with a polished outer wall, or a composite plastic tube with good hydrophilicity that can adapt to temperatures below 80 degrees Celsius. Depending on the length of the heat exchange tube, the outer wall of the membrane flow guide tube 507 can be a smooth tube for short sections, while for long sections, it should be designed with annular grooves. The annular grooves are distributed at intervals of 300mm-500mm along the length of the tube, and the groove width is 5mm-10mm. The accumulation and outflow of water in the groove structure has a "redistribution" effect on the water film on the outer wall of the tube, which is conducive to the uniform distribution of the water film.

[0036] Working principle: Low-temperature hot dry flue gas in the low-temperature flue gas main pipe 1 is transported to the low-temperature flue gas evaporator 5 through the input pipe 7 by the low-temperature dry flue gas blower 14. After the desulfurization wastewater is pretreated by the flocculation tank 10, the sedimentation tank 11 and the multi-media filter 12 to remove the influence of turbidity, it enters the desulfurization wastewater distribution plate 509 in the evaporation tower body 501. The liquid level of the desulfurization wastewater distribution plate 509 is controlled at a height of 7-10cm. The potential energy formed by this liquid level provides the initial power for the formation of the water film.

[0037] The desulfurization wastewater in the distribution plate 509 flows down the membrane flow guide pipe 507 in a membrane-like manner through the annular gap between the membrane flow distribution short pipe 510 and the membrane flow guide pipe 507. The outer surface of the membrane flow guide pipe 507 is used to optimize the uniformity and continuity of the water film by employing polishing technology, annular groove redistribution technology, or hydrophilic material technology.

[0038] The water film on the outer wall of the membrane flow guide tube 507 exchanges heat with the flue gas for evaporation and concentration. The water film gradually becomes thinner and forms a crystal product after flowing to the outer surface of the microporous ceramic tube 508.

[0039] The low-temperature hot dry flue gas input into the low-temperature flue gas evaporator 5 flows in the opposite direction to the wastewater. It first passes through the lower crystallization zone, which is conducive to the further crystallization and precipitation of the concentrate. Then, the wet flue gas carrying the wastewater vapor returns to the low-temperature flue gas main pipe 1 through the upper output pipe of the low-temperature flue gas evaporator 5 and enters the desulfurization tower 2.

[0040] Then, the clean and wet flue gas is sent to the induced draft fan 6 from the clean and wet flue gas after desulfurization and wet dust removal through the wet flue gas pipe 4 into the clean and wet flue gas distribution chamber 505. It then enters the microporous ceramic tube 508 through the membrane flow guide pipe 507. Under a certain pressure, a wetting layer composed of moisture and flue gas bubbles will be formed on the outer surface of the microporous ceramic tube 508, preventing the crystallization products from scaling on the outer wall of the microporous ceramic tube 508. The precipitated crystallization products fall into the hopper 502 and can be discharged by screw conveyor or pneumatic conveying.

[0041] This invention utilizes low-temperature hot dry flue gas extracted from the outlet of a dry electrostatic precipitator in a coal-fired boiler before it enters the desulfurization tower as a heat source. This satisfies the temperature rise and heat consumption required for the evaporation and concentration of desulfurization wastewater to a crystallized state. The desulfurization wastewater entering the low-temperature flue gas evaporator 5 undergoes flocculation, sedimentation, and filtration processes to remove particulate matter. The evaporation and concentration process of the desulfurization wastewater mainly takes place on the surface of the water film in the vertical tube bundle within the low-temperature flue gas evaporator 5. The crystallization process is achieved on the surface of the microporous ceramic tube 508 at the bottom of the vertical tube bundle. The interior of the vertical tube bundle is filled with clean, wet flue gas that has undergone wet desulfurization and dust removal. The micropores on the wall of the microporous ceramic tube 508 form a dynamic protective layer of bubbles and water vapor on the outer surface, preventing the crystallization products from remaining and forming scale on the outer surface of the microporous ceramic tube 508 in the crystallization zone. The crystallization products fall into the hopper 502 at the bottom of the low-temperature flue gas evaporator 5 and are collected and discharged. The system of this invention realizes the one-time treatment of desulfurization wastewater by low-temperature flue gas waste heat evaporation and concentration to crystallization and salt production. It has low energy consumption, and the evaporated water is used as makeup water for the desulfurization tower to realize water resource recycling. At the same time, it has the advantages of no large circulating water volume, no salt mist flue gas carrying problem, realization of evaporation and crystallization in the low-temperature evaporation device, and low energy consumption.

Claims

1. A low-temperature flue gas evaporation and crystallization system for desulfurization wastewater, comprising a low-temperature flue gas main pipe (1), characterized in that: The output end of the low-temperature flue gas main pipe (1) is connected to the desulfurization tower (2), the output end of the desulfurization tower (2) is connected to the clean flue gas discharge pipe (3), one end of the clean flue gas discharge pipe (3) is connected to the low-temperature flue gas evaporator (5) through the wet flue gas pipe (4), the wet flue gas pipe (4) is equipped with a clean wet flue gas blower (6), the low-temperature flue gas main pipe (1) is connected to the lower part of one end of the low-temperature flue gas evaporator (5) through the input pipe (7), the input pipe (7) is equipped with a low-temperature dry flue gas blower (14), the upper side of the low-temperature flue gas evaporator (5) is connected to the low-temperature flue gas main pipe (1) through the output pipe (8); The upper side of the low-temperature flue gas evaporator (5) is connected to a water inlet pipe (9), and the water inlet pipe (9) is provided with a flocculation tank (10), a sedimentation tank (11), a multi-media filter (12) and a filtered water tank (13) in sequence. The low-temperature flue gas evaporator (5) includes an evaporation tower body (501), a hopper (502) connected to the lower end of the evaporation tower body (501), a low-temperature dry flue gas inlet (503) on one side of the lower part of the evaporation tower body (501), an evaporation flue gas discharge port (504) on one side of the upper part of the evaporation tower body (501), a clean and wet flue gas distribution chamber (505) connected to the upper side inside the evaporation tower body (501), a clean and wet flue gas inlet (506) connected to one end of the clean and wet flue gas distribution chamber (505), a membrane flow guide pipe (507) uniformly connected to the lower end of the clean and wet flue gas distribution chamber (505), and a microporous ceramic tube (508) connected to the lower end of the membrane flow guide pipe (507). The upper side of the evaporator body (501) is connected to a desulfurization wastewater distribution plate (509). The desulfurization wastewater distribution plate (509) is located below the clean and wet flue gas distribution chamber (505). The lower end of the desulfurization wastewater distribution plate (509) is evenly provided with openings. A membrane flow distribution short pipe (510) is welded to the lower end of the opening. The number of membrane flow distribution short pipes (510) is the same as that of membrane flow guide pipes (507). The membrane flow guide pipes (507) pass concentrically through the membrane flow distribution short pipes (510).

2. The low-temperature flue gas evaporation and crystallization system for desulfurization wastewater according to claim 1, characterized in that: The inner diameter of the membrane flow distribution tube (510) is larger than the outer diameter of the membrane flow guide tube (507).

3. The low-temperature flue gas evaporation and crystallization system for desulfurization wastewater according to claim 1, characterized in that: The membrane flow guide tube (507) and the microporous ceramic tube (508) have the same outer diameter, and the membrane flow guide tube (507) and the microporous ceramic tube (508) are connected by threads, wherein the lower end of the membrane flow guide tube (507) is provided with internal threads, and the upper connecting end of the microporous ceramic tube (508) is provided with external threads.

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