A wastewater evaporation and concentration and zero wastewater discharge process using a gas-liquid premixing device

Abstract

The present invention belongs to the field of zero discharge of industrial wastewater, and provides a wastewater evaporation and concentration process and a zero wastewater discharge process using a gas-liquid premixing device. According to the characteristics of wastewater evaporation, a gas-liquid premixing device is adopted to quickly complete the mixing and contact of wastewater and flue gas before the flue gas enters the evaporation tower. This enables the subsequent evaporation tower to be used only as a dedicated demister tower (hereinafter referred to as "demister tower" for short). The hot flue gas first enters the gas-liquid premixing device, and the impact force is generated by the forward nozzle, so that the wastewater slurry and the hot flue gas produce a rapid mixing effect similar to that of Venturi. In this way, both the full mixing of the hot flue gas and the wastewater slurry is realized, and the flue gas is pushed to a certain extent, resulting in: (1) the system flue gas resistance drops from 1-2 kPa to 0.4-0.6 kPa; the power consumption of the induced draft fan is reduced by 30-50%; (2) the liquid-gas ratio of the circulation pump drops from 5-10 L / m<supgt;3< / supgt; to 2.5-4, significantly reducing the energy consumption of the process of evaporating wastewater with the waste heat of the flue gas.

Description

Technical Field

[0001] The present invention belongs to the field of industrial wastewater zero-discharge processes, and particularly relates to a process method and device for wastewater evaporation concentration and zero-discharge that utilize the waste heat of flue gas as a heat source and adopt a gas-liquid premixing device. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and it is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] The process of using the waste heat of flue gas for wastewater evaporation and zero-discharge has been relatively mature. Especially in the thermal power industry, by adopting a wastewater evaporation tower or a similar device and the method of counter-phase spraying, continuous evaporation and concentration of wastewater are achieved, so that wastewater reduction and zero-discharge have become a relatively popular process.

[0004] However, the above-mentioned concentration and zero-discharge processes generally imitate the spraying process of wet flue gas desulfurization, and thus also bring the problem of relatively high energy consumption. Due to the existence of the evaporation tower and the large-flow spraying layer, in order for the corresponding induced draft fan to overcome the resistance of the spraying layer, the rated boost pressure must be maintained between 1.5 and 2 kPa; moreover, the flow rate of the circulation pump is also relatively large, and the overall liquid-gas ratio is between 5 and 10 L / m 3 between.

[0005] After analysis by the inventor, the main reason for the relatively high energy consumption of the induced draft fan is caused by the gas-liquid counter-phase contact. Because the downwardly sprayed slurry generates a relatively large downward pressure (air pump pressure), it forms a certain resistance to the flow of flue gas; while the main reason for the relatively large flow rate of the circulation pump is that in order to cover the entire flow cross-section of the evaporation tower, the flow rate of the circulation pump must have sufficient spraying coverage, so the flow rate of the circulation pump is relatively large.

[0006] The currently commonly used process scheme for using the waste heat of flue gas for wastewater evaporation simply imitates the wet flue gas desulfurization tower, thus resulting in relatively high power energy consumption during operation, and the energy consumption level for evaporating 1 ton of wastewater is about 40 - 60 degrees of electricity. This has significantly reduced the energy-saving advantage of the "process of using the waste heat of flue gas for wastewater evaporation and zero-discharge" compared to other wastewater zero-discharge processes such as triple-effect evaporation and vacuum flashing. Summary of the Invention

[0007] To solve the above problems, the present invention provides a "wastewater evaporation and concentration and zero wastewater discharge process using a gas-liquid pre-mixing device" with relatively low energy consumption and easy implementation. According to the characteristics of wastewater evaporation, the present invention adopts a gas-liquid pre-mixing device to quickly complete the mixing and contact of wastewater and flue gas before the flue gas enters the evaporation tower. This enables the subsequent evaporation tower to be used only as a dedicated demister tower (hereinafter referred to as "demister tower" for short). The hot flue gas first enters the gas-liquid pre-mixing device, and the impact force is generated by the forward nozzles, so that the wastewater slurry and the hot flue gas have a rapid mixing effect similar to that of a Venturi, which not only realizes the full mixing of the hot flue gas and the wastewater slurry, but also can generate a driving force for the flue gas to a certain extent, resulting in: (1) the system flue gas resistance drops from between 1 and 2 kPa to between 0.4 and 0.6 kPa; the power consumption of the induced draft fan is reduced by 30 to 50%; (2) the liquid-gas ratio of the circulation pump drops from between 5 and 10 L / m 3 to between 2.5 and 4, thus significantly reducing the energy consumption of the process of evaporating wastewater with flue gas waste heat.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] In the first aspect of the present invention, a gas-liquid pre-mixing device is provided, including a Venturi-shaped air duct and forward nozzles; a multi-layer forward nozzle array is arranged in the Venturi-shaped air duct, and the included angle between the jet direction of the forward nozzles and the flue gas flow direction is controlled between 0 and 45°. Each layer of the forward nozzle array is formed by arranging a plurality of forward nozzles in a ring shape, and the liquid inlets of the nozzles are respectively connected to the liquid outlet of the wastewater injection pump through pipes; the liquid inlet of the wastewater injection pump is connected to the suction pipe, and the suction pipe extends into the slurry pool of the demister tower.

[0010] A gas-liquid pre-mixing device with a similar Venturi shape is adopted to quickly mix the wastewater with the low-temperature hot flue gas; the forward flow injection is adopted, and the flue gas flow is promoted by the forward flow injection, so as to cancel the large-flow circulation pump and greatly save the power consumption.

[0011] In the second aspect of the present invention, a system for wastewater evaporation and concentration and zero wastewater discharge using a gas-liquid pre-mixing device is provided, including: a hot flue gas inlet air duct, the above-mentioned gas-liquid pre-mixing device, a demister tower, and a filter press;

[0012] The above-mentioned gas-liquid pre-mixing device is arranged on the hot flue gas inlet air duct, the air outlet of the gas-liquid pre-mixing device is connected to the inlet of the gas-liquid mixing buffer zone of the demister tower, the demister tower is divided into a gas-liquid mixing buffer zone and a demisting zone from bottom to top, two layers of demisters are arranged at the top of the demister tower, a slurry pool is arranged at the bottom of the demister tower, the liquid outlet of the slurry pool is connected to the liquid inlet of the filter press, and the filtrate outlet of the filter press is connected to the liquid inlet of the slurry pool.

[0013] This technical solution of the present invention for evaporating industrial wastewater using waste heat from flue gas has a relatively simple system. Since the large-flow circulation pump and spray layer are omitted, the operating energy consumption of the system is further reduced, having certain technical competitive advantages and practical value.

[0014] The principle of energy consumption reduction in the above system is based on: canceling the large-flow wastewater evaporation circulation pump and the relatively complex spray layer structure in the tower, and replacing them with a small wastewater injection pump (group). A forward nozzle (group) of a gas-liquid premixing device with a Venturi-like shape is used to inject the flue gas forward, converting the flue gas resistance caused by the traditional liquid spray layer into the driving force of the forward-injected flue gas, thereby greatly reducing the flue gas resistance. In addition, the original evaporation tower is only used as a buffer space and a demister tower (demister tower), using fresh wastewater as the flushing water for the demister, while preventing the deposition of the demister, realizing the continuous injection of wastewater; in addition, a plate and frame filter press is used to control the concentration of the wastewater slurry at the bottom of the evaporation tower, so as to maintain the long-term stable operation of the wastewater evaporation system.

[0015] In the third aspect of the present invention, a process for wastewater evaporation concentration and zero wastewater discharge using a gas-liquid premixing device is provided, and the above system is used to treat the flue gas;

[0016] The hot flue gas is introduced into the gas-liquid premixing device. The wastewater injection pump pumps out the concentrated wastewater slurry from the bottom slurry pool of the demister tower, and then sprays it out through the forward nozzle for gas-liquid mixing, and pushes the flue gas into the buffer zone of the demister tower;

[0017] After the flue gas flows through the lower demister and the upper demister in the buffer zone of the demister tower, it returns to the main flue through the flue gas outlet duct;

[0018] Fresh wastewater from outside is introduced into the wastewater feed pipe to intermittently flush the lower demister and the upper demister, and the flushed wastewater enters the slurry pool of the demister tower;

[0019] The concentrated wastewater in the slurry pool of the demister tower is introduced into the plate and frame filter press for filtration operation. The solid residue filtered out is discharged, and the filtrate returns to the bottom slurry pool of the demister tower again, and so on in a cycle.

[0020] Advantages of the present invention

[0021] (1) Adopting a gas-liquid premixing device with a Venturi-like shape to quickly mix wastewater with low-temperature hot flue gas;

[0022] (2) Using forward flow injection, using the forward flow injection to drive the flue gas flow, thereby canceling the large-flow circulation pump and greatly saving power consumption.

[0023] (3) The complex spray layer in the demister tower is canceled, and the system has high reliability.

[0024] (4) The system is relatively simple and easy to operate and maintain.

[0025] The technical solution of adopting a gas-liquid pre-mixing device and using the waste heat of flue gas to evaporate wastewater proposed in the present invention is applicable to zero-discharge projects of wastewater in many industries such as metallurgy and electric power; BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings forming a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0027] Figure 1 is the process flow chart of the present invention;

[0028] Figure 2 is a schematic diagram of the forward nozzle arrangement of the gas-liquid pre-mixing device;

[0029] Among them, (1) hot flue gas inlet air duct; (2) induced draft fan; (3) gas-liquid pre-mixing device; (4) demister tower slurry pond; (5) demister tower buffer zone; (6) lower demister; (7) upper demister; (8) flue gas outlet air duct; (9) wastewater feed pipeline; (10) small wastewater injection pump (group); (11) forward nozzle (group) of the gas-liquid pre-mixing device; (12) plate and frame filter press feed pump; (13) plate and frame filter press. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0031] In the first aspect, the present invention adopts a "gas-liquid pre-mixing device" in a shape similar to a Venturi in front of the inlet flue, and 1 to 3 layers of forward nozzles are arranged inside it. By spraying wastewater liquid forward through the nozzles, gas-liquid mixing can be achieved and a certain flue gas driving force can be formed.

[0032] In the present application, the gas-liquid pre-mixing device refers to a special air duct in the shape of a Venturi, and the specific dimensions of the flue can be proportionally enlarged according to the dimensions specified in the national standard GB / T2624-2006.

[0033] To achieve the desired mixing effect, the present application has studied the flow rate of the flue gas. In some embodiments with better effects, the inlet flue gas velocity is between 12 and 15 m / s; the outlet wind speed is between 8 and 10 m / s, and the residence time is between 0.5 and 1.5 seconds. Due to the high wind speed, the hot flue gas can rapidly tear the wastewater injection liquid, forming countless fine particles that mix with the flue gas, enabling the wastewater to quickly complete evaporation. At the same time, the hot flue gas cools down and enters the saturated state.

[0034] In some embodiments, the external shape of the gas-liquid pre-mixing device is circular, square or rectangular, and the size can be adjusted according to the actual situation on the project site;

[0035] In some embodiments, the gas-liquid pre-mixing device has a smooth transition to reduce the flue gas resistance;

[0036] In some embodiments, an insulating layer with a sufficient thickness is provided outside the gas-liquid pre-mixing device. The insulating material is rock wool or aluminosilicate insulating material, and the thickness is not less than 50 mm;

[0037] In some embodiments, a plurality of forward nozzles (groups) are arranged outside the gas-liquid pre-mixing device. The nozzles (groups) are located in the diverging pipe section of the venturi-shaped air duct. The injection speed of the nozzles is controlled between 5 and 15.0 m / s, and the total injection flow rate is designed according to the liquid-gas ratio L / Q = 3.0 - 4.0 L / Nm 3 to obtain a better mixing effect.

[0038] To obtain a better mixing effect, the flow rate of the nozzles is analyzed. In some embodiments with better effects, the nozzles of the gas-liquid pre-mixing device are solid cone atomizing nozzles, and; the flow rate of each nozzle is 1 - 10.0 m 3 / h, the inlet pressure is 0.05 - 0.07 MPa, and the atomization particle size is controlled within the range of 50 - 100 um to obtain the desired atomization effect.

[0039] In some embodiments, the injection angle of the nozzles relative to the flue gas flow direction is controlled within the range of 0 - 45°;

[0040] In some embodiments, the nozzles are arranged in multiple layers to ensure the gas-liquid mixing effect, preferably 3 - 5 layers, with 6 - 8 nozzles in each layer;

[0041] In some embodiments, the pipes of the nozzles are made of SiC / hard plastic / alloy materials; the type is solid cone; the injection expansion angle is controlled within the range of 75 - 120°;

[0042] The small wastewater injection pump adopts the "one in use and one standby" method;

[0043] In some embodiments, the small wastewater injection pump is of the non-clogging and slurry pump type, and the impeller can withstand the reverse impact of water hammer;

[0044] In some embodiments, the small wastewater injection pump is made of corrosion-resistant alloy material / full rubber lining material / full plastic lining material, etc.;

[0045] In some embodiments, the suction pipe of the small wastewater injection pump extends into the slurry pool of the demister tower. The lower part thereof is of a porous type, which can not only suck the slurry and prevent large-diameter debris from blocking the inlet pipe of the circulation pump, but also realize upward extraction of the slurry, thereby eliminating the agitator;

[0046] In the second aspect, the traditional evaporation tower is transformed into a buffer tower and a demister tower (hereinafter referred to as the demister tower). The tower is divided into two parts: a gas-liquid mixing buffer zone and a demisting zone. The so-called gas-liquid buffer zone means that after the large-flow circulation pump spray layer is cancelled in the tower, a certain space in the tower is reserved as the buffer space for gas-liquid contact after the front-end gas-liquid premixing device, ensuring sufficient contact time and space for gas-liquid mixing, preventing local hot flue gas from rushing upward into contact with the demister body, thereby ensuring the stable operation of the system; the so-called demisting zone refers to the area where two layers of demisters are configured at the top of the tower, and its function is to completely remove the droplets entrained in the flue gas and whose temperature has dropped to the saturation temperature (50-60 °C) to prevent these high-salt droplets from escaping.

[0047] In some embodiments, the demister tower is a circular vertical tower;

[0048] In some embodiments, the demister tower is provided with corresponding manholes, observation holes and their corresponding platforms;

[0049] In some embodiments, the demister tower is made of carbon steel with a phosphating coating, the wall thickness is not less than 10 mm, and it meets the corresponding structural strength design requirements;

[0050] In order to ensure sufficient contact time and space for gas-liquid mixing in the demister tower, prevent local hot flue gas from rushing upward into contact with the demister body, and thus ensure the stable operation of the system, this application has studied the flow rate of the flue gas. After verification, the lower part of the demister tower is the buffer zone, the flue gas flow rate is controlled within 2-4 m / s, and the flue gas residence time is controlled within the range of 2-3 seconds, which can achieve the expected mixing effect and the system operates stably.

[0051] This application has optimized the residence time of the flue gas in the demister. In some embodiments, the upper part of the demister tower is the demisting zone, and the flue gas residence time is controlled within the range of 1-2 seconds; two-stage demisters are provided therein; to completely remove the droplets entrained in the flue gas and whose temperature has dropped to the saturation temperature (50-60 °C) to prevent these high-salt droplets from escaping.

[0052] In some embodiments, the demister adopts a flat type, a roof type demister or a high-efficiency special demister, and the removal rate of fog droplets is as high as 99.0 - 99.9% or more;

[0053] In some embodiments, the demister blades are made of corrosion-resistant materials such as PP / FRP, and the thickness is controlled between 1 - 5 mm;

[0054] In some embodiments, the demister is provided with a demister flushing water system. The flushing water uses fresh wastewater, and a demister flushing water pump, pipelines and valves are configured; the wastewater after flushing directly enters the slurry tank at the bottom of the demister tower as evaporation makeup water to maintain the stability of the evaporation liquid level.

[0055] In the third aspect, since the desulfurized wastewater contains a large amount of dissolved salts, when concentrated to a certain stage, these dissolved salts continuously precipitate due to supersaturation, and at this time the slurry density will reach a relatively high level. Therefore, to ensure continuous and stable long-term operation, these precipitated salts must be removed from the slurry. In one or more embodiments of the inventor, the plate and frame filter press system consists of a feed pump, a filter press, a filter pump, and a filter water tank; the density of the wastewater slurry at the bottom of the demister tower is between 1.1 - 1.3 g / cm 3 ; the filter cake after filtration will be continuously discharged from the system to ensure the stable operation of the system;

[0056] Among them, the plate and frame filter press uses a filter cloth with an appropriate pore size, which can effectively filter the crystal precipitated substances of dissolved salts.

[0057] In some embodiments, the plate and frame filter press adopts an automatic plate return mechanism to reduce the operation intensity;

[0058] In some embodiments, the processing capacity of the plate and frame filter press is in the range of 1.2 - 2.0 times the total amount of precipitated crystal salts;

[0059] In some embodiments, the plate and frame filter press is arranged at a high position, and a slag storage bin is arranged below it to facilitate the outward transportation of filter residues;

[0060] In some embodiments, the feed pump of the plate and frame filter press adopts a non-clogging slurry pump type, and the head is controlled in the range of 50 - 100 m to meet the feeding requirements of the filter press; the flow rate is designed according to the total amount of salt substances brought in by the wastewater, the concentration of the slurry tank and a margin of 20 - 50%;

[0061] In some embodiments, the feed pump can also be connected from the outlet pipeline of the circulation pump. In this way, it is beneficial for the feed pump to reduce the rated head;

[0062] In some embodiments, expansion joints are arranged before and after the feed pump;

[0063] In some embodiments, the feed pump adopts a structure design with a ceramic lining or plastic lining to adapt to high-salt corrosion conditions;

[0064] The following further elaborates on the present invention with reference to specific embodiments. It should be noted that the specific embodiments are interpretations rather than limitations of the present invention.

[0065] Embodiment 1

[0066] The process flow of the present invention is described as follows:

[0067] (I) Flue gas system process: Hot flue gas at 80 - 200 °C passes through the inlet air duct 1, is boosted by the induced draft fan 2 and introduced into the gas-liquid premixing device 3. Driven by the injection of the forward nozzle 11, it enters the demister tower buffer zone 5, and then passes through the lower demister 6 and the upper demister 7, and returns to the main flue through the flue gas extraction duct 9.

[0068] Among them, the hot flue gas at 80 - 200 °C is connected to the inlet of the gas-liquid premixing device 3 of the present invention; the outlet of the gas-liquid premixing device 3 is connected to the inlet of the demister tower; the outlet saturated humid flue gas is connected to the top outlet of the demister tower of the present invention;

[0069] (II) Wastewater injection process: The small wastewater injection pump (group) 10 pumps the concentrated wastewater slurry from the bottom slurry pool 4 of the demister tower through the pipeline extending deep into the tower, and then sprays it through the forward nozzle 11 to drive the flue gas into the demister tower buffer zone 5, thus completing the wastewater evaporation process.

[0070] Among them, the inlet of the small wastewater injection pump (group) 10 is connected to the bottom slurry pool 4 of the demister tower, and its outlet is connected to the forward nozzle 11;

[0071] (III) Wastewater replenishment and demister flushing process: The incoming fresh wastewater passes through the incoming pipeline and the wastewater feed pipeline 9 to intermittently flush the lower demister 6 and the upper demister 7. The wastewater after flushing enters the demister tower slurry pool 4 to supplement the consumption of wastewater evaporation.

[0072] (IV) Plate and frame filter press process: The filter press feed pump 12 pumps out the concentrated wastewater from the demister tower slurry pool 4 and conducts a filtration operation in the plate and frame filter press 13. The solid residues filtered out are discharged externally, and the filtrate returns to the bottom slurry pool 4 of the demister tower again. Through repeated operations like this, the slurry density in the bottom slurry pool 4 of the demister tower is always maintained within the control range.

[0073] For details, see the appendix Figure 1 。

[0074] Embodiment 2

[0075] A gas-liquid premixing device 3, a venturi-shaped air duct, and a forward nozzle 11; a multi-layer forward nozzle 11 array is arranged in the venturi-shaped air duct, and the included angle between the jet direction of the forward nozzle 11 and the flue gas flow direction is controlled within 0 to 45°. Each layer of the forward nozzle 11 array is formed by arranging a plurality of forward nozzles 11 in a circular pattern. The liquid inlets of the forward nozzles 11 are respectively connected to the liquid outlet of the waste water injection pump 10 through pipes; the liquid inlet of the waste water injection pump 10 is connected to the suction pipe, and the suction pipe extends into the slurry pool 4 of the demister tower.

[0076] The jet velocity of the forward nozzle 11 is 5 to 15.0 m / s, and the total jet flow rate is based on a liquid-gas ratio of L / Q = 3.0 to 4.0 L / Nm 3 。

[0077] The forward nozzle 11 adopts a solid cone atomizing nozzle, and the flow rate of each nozzle is 1 to 10.0 m 3 / h, the inlet pressure is 0.05 to 0.07 MPa, and the atomization particle size is controlled within 50 to 100 um.

[0078] The pipes of the forward nozzle 11 are made of SiC, hard plastic or alloy materials, and the jet expansion angle is in the range of 75 to 120°.

[0079] The waste water injection pump 10 adopts a "one in use and one standby" mode.

[0080] The suction pipe extends into the slurry pool 5 inside the demister tower, and its lower part adopts a porous type.

[0081] A waste water evaporation concentration and waste water zero discharge system using the gas-liquid premixing device 3, including: a hot flue gas inlet air duct, the above-mentioned gas-liquid premixing device 3, a demister tower, and a filter press 13;

[0082] The above-mentioned gas-liquid premixing device 3 is arranged on the hot flue gas inlet air duct. The air outlet of the gas-liquid premixing device 3 is connected to the inlet of the gas-liquid buffer zone 5 of the demister tower. The demister tower is divided into a gas-liquid mixing buffer zone 5 and a demisting zone from bottom to top. The top of the demister tower is equipped with two layers of demisters (the lower demister 6 and the upper demister 7). The bottom of the demister tower is provided with a slurry pool 5. The liquid outlet of the slurry pool 5 is connected to the liquid inlet of the filter press 13, and the filtrate outlet of the filter press 13 is connected to the liquid inlet of the slurry pool 5.

[0083] The demister is provided with a demisting flushing water system;

[0084] The flue gas outlet air duct 9 at the top of the demister tower is connected to the main flue.

[0085] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A system for wastewater evaporation and concentration and zero discharge of wastewater using a gas-liquid pre-mixing device, characterized in that, Including: Hot flue gas inlet air duct, gas-liquid pre-mixing device, demister tower, filter press; A gas-liquid pre-mixing device is arranged on the hot flue gas inlet air duct. The air outlet of the gas-liquid pre-mixing device is connected to the inlet of the gas-liquid buffer zone of the demister tower. The demister tower is divided into a gas-liquid mixing buffer zone and a demister zone from bottom to top. Two layers of demisters are configured at the top of the demister tower. A slurry pool is arranged at the bottom of the demister tower. The liquid outlet of the slurry pool is connected to the inlet of the filter press. The filtrate outlet of the filter press is connected to the inlet of the slurry pool; The demister is provided with a demister flushing water system; the flushing water uses fresh wastewater, and a demister flushing water pump, pipelines and valves are configured; the wastewater after flushing directly enters the slurry pool at the bottom of the demister tower as evaporation makeup water to maintain the stability of the evaporation liquid level; The gas-liquid pre-mixing device includes a venturi-shaped air duct and forward nozzles; a multi-layer forward nozzle array is arranged in the venturi-shaped air duct. The included angle between the jet direction of the forward nozzles and the flue gas flow direction is controlled within 0-45°. Each layer of the forward nozzle array is formed by a plurality of forward nozzles arranged in a ring. The liquid inlets of the forward nozzles are respectively connected to the liquid outlet of the wastewater injection pump through pipelines; the liquid inlet of the wastewater injection pump is connected to a suction pipe, and the suction pipe extends into the slurry pool of the demister tower; The inlet flue gas velocity is between 12 and 15 m / s; the outlet air velocity is between 8 and 10 m / s, and the residence time is between 0.5 and 1.5 seconds; The nozzle is located in the divergent section of the Venturi-shaped air duct. The injection speed of the nozzle is 5 to 15.0 m / s, and the total injection flow rate is based on a liquid-gas ratio of L / Q = 3.0 to 4.0 L / Nm 3 ; The nozzle adopts a solid cone atomizing nozzle, and the flow rate of each nozzle is 1 to 10.0 m 3 / h, the inlet pressure is 0.05 to 0.07 MPa, and the atomization particle size is controlled within 50 to 100 um; The suction pipe extends into the slurry pool inside the demister tower, and its lower part adopts a porous type.

2. The system for wastewater evaporation and concentration and zero wastewater discharge using a gas-liquid pre-mixing device according to claim 1, characterized in that The flue gas extraction air duct at the top of the demister tower is connected to the main flue.

3. The wastewater evaporation and concentration and wastewater zero-discharge system using the gas-liquid premixing device as described in claim 1, characterized in that, The pipelines of the nozzles are made of SiC, hard plastic or alloy materials, and the jet expansion angle is within the range of 75-120°.

4. The wastewater evaporation and concentration and zero wastewater discharge system using the gas-liquid premixing device according to claim 1, characterized in that, The wastewater injection pump adopts a "one in use and one standby" method.

5. A process for wastewater evaporation and concentration and zero discharge of wastewater using a gas-liquid premixing device, characterized in that, Using the system according to any one of claims 1-4 to treat flue gas; Introduce the hot flue gas into the gas-liquid pre-mixing device. The wastewater injection pump pumps out the concentrated wastewater slurry from the bottom slurry pool of the demister tower, and then sprays it out through the forward nozzles for gas-liquid mixing and pushes the flue gas into the buffer zone of the demister tower; After the flue gas flows through the lower demister and the upper demister from the buffer zone of the demister tower, it returns to the main flue through the flue gas extraction air duct; Introduce the external fresh wastewater into the wastewater feed pipeline to intermittently flush the lower demister and the upper demister, and the wastewater after flushing enters the slurry pool of the demister tower; Introduce the concentrated wastewater in the slurry pool of the demister tower into the plate and frame filter press for filtration operation. The solid residues filtered out are discharged externally, and the filtrate returns to the bottom slurry pool of the demister tower again, and so on in a cycle.

6. The process for wastewater evaporation and concentration and zero discharge of wastewater using the gas-liquid premixing device as described in claim 5, characterized in that, The density of the waste water slurry at the bottom of the demister tower is between 1.1 and 1.3 g / cm 3 3

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