CN118543241A - A method and device for purifying tail gas produced by denitration catalyst production - Google Patents

Abstract

The invention relates to the technical field of tail gas purification, in particular to a purification method and a device for tail gas produced by a denitration catalyst, wherein the device comprises a catalytic oxidation reactor, an inlet of the catalytic oxidation reactor is connected with a high-temperature oil removal tail gas pipeline of a resistance furnace or a tunnel kiln, an outlet of the catalytic oxidation reactor is connected with a top inlet of a Venturi quenching absorber, and an outlet of the Venturi quenching absorber is connected with a tail gas inlet of a cyclone plate spray demister; the roasting tail gas pipeline of the resistance furnace or the tunnel kiln is connected with the top inlet of the Venturi quenching absorber; the tail gas outlet of the cyclone plate spray mist eliminator is connected with the inlet of the filler tower, the outlet of the filler tower is connected with the inlet of the wet electrostatic mist eliminator, and the outlet of the wet electrostatic mist eliminator is connected with the induced draft fan. The device organically integrates the purification processes of the tail gas of two procedures of catalyst production, effectively plays a role in the synergistic treatment of ammonia removal and oil removal, saves investment and occupied space, and effectively realizes the standard reaching and even ultra-clean emission of the tail gas.

Description

A method and device for purifying tail gas produced by denitration catalyst production

Technical Field

The present invention relates to the technical field of tail gas purification, and in particular to a method and device for purifying tail gas produced by a denitration catalyst.

Background Art

Nitrogen oxides NOx are one of the main components of air pollution, mainly from flue gas emissions from coal-fired power plants, steel mills, waste incineration power plants, etc. At present, SCR denitrification technology has been widely used due to its maturity, stability and high denitrification rate. It uses NH ₃ as a reducing agent, and under the action of SCR denitrification catalyst, selectively catalytically reduces NOx to N _2. SCR catalyst is the core of denitrification, and SCR plate catalyst composed of vanadium, tungsten and titanium is one of the common denitrification catalysts.

The production and preparation process of SCR plate-type denitrification catalyst is shown in Figure 1. The stainless steel mesh belt, as the support of the plate-type catalyst, is first unrolled and then placed in a resistance furnace/tunnel kiln for high-temperature degreasing. Only after high-temperature degreasing can the mesh belt meet the requirements of catalyst raw materials being rolled and attached to it; the catalyst materials after roll forming are attached to the mesh plate, and then cut and packed into small catalyst modules, and then placed in a resistance furnace/tunnel kiln for catalyst roasting; the small catalyst modules after roasting are then assembled into plate-type catalyst unit modules and stored in the warehouse for sale. Among them, the two production processes of high-temperature degreasing of the stainless steel mesh plate and catalyst roasting need to be carried out in the resistance furnace/tunnel kiln.

(1) Exhaust gas purification process of stainless steel mesh belt high temperature oil removal process

During the production process of the mesh plate factory, there are oil stains and water stains on the surface of the stainless steel mesh belt. Before the catalyst raw material is rolled, it needs to pass through the resistance furnace/tunnel kiln to remove the oil and water stains on the surface of the steel belt at high temperature. The oil stains on the mesh belt are mainly mechanical lubricating oil, which will evaporate at 300~550℃. In the resistance furnace/tunnel kiln, the mesh belt is heated and degreased at high temperature according to the set program heating curve. The heating temperature is 550℃~600℃. The exhaust gas generated is mainly composed of air and some oil mist (VOCs). Direct discharge will cause environmental pollution. The exhaust gas from the mesh belt high-temperature degreasing process needs to be purified.

The common method for purifying high-temperature exhaust gas from stainless steel mesh belts is water washing. Water washing is a cheap and widely used method for removing oil mist. The high-temperature exhaust gas is cooled and the oil mist is captured by washing in a spray tower. In the spray tower, water is sprayed into droplets through a nozzle. When the exhaust gas passes through the water mist space, the oil mist collides, intercepts and condenses with the water mist, and the oil mist falls with the water droplets, thereby achieving condensation and capture of the oil mist. However, this purification process has problems:

a) The spray tower has the problem of insufficient cooling of high-temperature tail gas, which affects the effective capture and condensation of oil mist. This is because the tail gas temperature is high, and a large amount of oil mist is not fully wetted and is still carried into the environment in the gas phase or aerosol state, which is not conducive to the condensation and capture of oil mist;

b) The demister installed at the outlet of the spray tower usually adopts a baffle or a wire mesh demister, which is a mechanical demister. This type of demister has limited effect on oil mist separation. The tail gas after demistering will still carry some fine droplets and be discharged into the atmosphere;

c) Oil mist has high viscosity and is mostly insoluble in water. After running for a period of time, oil stains adhere to the spray tower, including the tower wall, packing, demister, outlet pipe and induced draft fan blades, resulting in the spray tower/packing tower and induced draft fan being unable to operate stably for a long time and having to be cleaned manually;

d) The oil in the liquid storage tank at the bottom of the spray tower cannot be discharged in time, resulting in the continuous accumulation of oil content in the circulating water of the spray tower, making it difficult to recycle the circulating water.

(2) Tail gas purification process of catalyst calcination process

The catalyst roasting process is to place the mesh belt with the catalyst raw materials on the resistance furnace/tunnel kiln to roast the catalyst according to the set program heating curve. The roasting temperature is generally 600℃~650℃. The tail gas generated during the roasting process is mainly composed of air, ammonia, a small amount of _SO2 and dust. Direct discharge will cause environmental pollution, and the catalyst roasting tail gas needs to be purified.

The water washing method for removing ammonia is a tail gas purification method that utilizes the property of ammonia being extremely soluble in water. It is still the ammonia purification process adopted by most companies due to its low price, small investment, simple process, and mature technology, namely: direct cooling/waste heat recovery + spray tower, that is, the catalyst roasting tail gas is directly cooled in the cooler before entering the spray tower, or a water-cooled heat exchanger is set up for waste heat recovery to reduce the tail gas temperature, and then enters the spray tower to absorb ammonia and then discharge it after meeting the standards. The problems with this purification process are as follows:

a) If a heat exchanger is used for tail gas cooling and waste heat recovery, although most of the heat of high-temperature tail gas can be recovered, the heat exchanger has a serious problem of sticking and blocking. This is because the ammonia and sulfur dioxide released during the catalyst roasting process (300~650℃) are synthesized into ammonium bisulfate (ABS) (synthesis temperature range is 150~280℃) during the cooling process of the heat exchanger. These crystalline salts not only corrode the pipelines of the heat exchanger equipment, but also adhere to the pipelines. It is difficult to clean the general soot blower, and it can only be cleaned manually after the furnace is shut down, which affects the stability of catalyst production.

b) If the exhaust gas is cooled directly, although there is no problem of heat exchanger clogging, there is a problem of insufficient cooling of the high-temperature exhaust gas, which is not conducive to the absorption of ammonia by the spray tower. This is because the solubility of ammonia decreases rapidly with the increase of exhaust gas temperature, that is, the higher the exhaust gas temperature, the less conducive it is to the absorption of ammonia. Therefore, in order to ensure the efficient absorption of ammonia in the exhaust gas by water, the temperature of the spray tower should be as low as possible.

c) The demisting effect of the exhaust gas after water washing in the spray tower is limited. The exhaust gas after demisting carries a large number of tiny droplets, which appear as white smoke when discharged into the atmosphere. Especially when the ambient temperature is low and the diffusion is poor in a windless environment, the white smoke will trail and have an adverse effect on the surrounding environment.

Although there are differences in the pollutant composition of the tail gas from mesh belt high temperature oil removal and catalyst roasting, that is, the pollutant of the tail gas from mesh belt high temperature oil removal is oil mist; the tail gas pollutant from catalyst roasting is mainly ammonia, but these two processes also have the following similarities:

a) The same type of resistance furnace/tunnel kiln can be selected to meet the catalyst production needs; the high-temperature exhaust gas temperature is 550-650℃, and most of the exhaust gas components are air;

b) The exhaust gas flow rates from the two processes are similar;

c) The exhaust gases from both processes can be purified by water washing.

Based on the above commonalities, it is necessary to consider adopting a set of tail gas purification treatment devices and purification methods in this field to simultaneously meet the purification treatment of high-temperature oil removal tail gas and catalyst roasting tail gas. This will not only save equipment investment and floor space, but also the tail gas purification treatment of these two processes in one purification device can also play the advantages of synergistic treatment. This is because the ammonia in the catalyst roasting tail gas is absorbed by the spray tower to form a circulating spray ammonia solution, which can dissolve and clean the oil stains adhered to the equipment caused by the high-temperature oil removal tail gas. The principle is that the ammonia solution can undergo a saponification reaction with the oil stains to generate higher fatty acid sodium that can be soluble in water, which can effectively reduce the oil stain adhesion pollution.

Summary of the invention

In view of the above-mentioned problems existing in the purification of tail gas from the production of denitrification catalysts, the present invention provides a method and device for purifying tail gas from the production of denitrification catalysts. The method can not only solve the problems existing in the purification of tail gas from the production of catalysts, such as: blockage of the heat exchanger, insufficient quenching, low capture efficiency, poor demisting effect, white smoke tailing, and difficulty in recycling the circulating spray water, but also can achieve the coordinated treatment of the two tail gases of high-temperature oil removal and catalyst roasting in the same set of tail gas purification devices, saving the investment cost and floor space of the equipment, and ultimately achieving the purpose of energy conservation and emission reduction. However, there is currently no efficient purification treatment device for the production of denitrification catalysts that can absorb ammonia and remove oil mist on the market. Therefore, the present invention, on the basis of fully considering the adsorption characteristics of ammonia and the capture characteristics of oil mist, realizes the coordinated treatment and efficient and stable operation of the tail gas purification device.

In order to solve the above technical problems, this application provides the following technical solutions:

A device for purifying tail gas produced by a denitration catalyst, comprising a catalytic oxidation reactor, wherein the inlet of the catalytic oxidation reactor is connected to a high-temperature deoiling tail gas pipeline of an electric resistance furnace or a tunnel kiln, the outlet of the catalytic oxidation reactor is connected to a top inlet of a venturi quenching absorber, the outlet of the venturi quenching absorber is connected to a tail gas inlet of a cyclone plate spray demister, and a liquid storage tank A is provided below the venturi quenching absorber and the cyclone plate spray demister; the roasting tail gas pipeline of the electric resistance furnace or the tunnel kiln is connected to the top inlet of the venturi quenching absorber;

The tail gas outlet of the cyclone plate spray demister is connected to the inlet of the packing tower, the outlet of the packing tower is connected to the inlet of the wet electrostatic demister, and the outlet of the wet electrostatic demister is connected to the induced draft fan; a liquid storage tank B is provided below the packing tower and the wet electrostatic demister;

The high-temperature deoiling tail gas pipeline, the roasting tail gas pipeline, the top inlet of the Venturi quench absorber, the upper inlet of the cyclone plate spray demister, the side inlet of the packed tower, and the side inlet of the wet electrostatic demister are all connected to the process water pipeline for cooling the tail gas, replenishing spray water or flushing equipment; the liquid storage tank A is connected to the circulating pump A, and the outlet of the circulating pump A is respectively connected to the annular nozzle and throat nozzle of the Venturi quench absorber and the inlet of the first layer of cyclone plate spray device of the cyclone plate spray demister; the liquid storage tank B is connected to the circulating pump B, and the outlet of the circulating pump B is connected to the cooling water heat exchanger, and the outlet of the cooling water heat exchanger is connected to the inlet of the spray device of the packed tower, and the heat exchange inlet and heat exchange outlet of the cooling water heat exchanger are both connected to the process water pipeline.

Wherein, the high-temperature deoiling tail gas pipeline and the roasting tail gas pipeline are both provided with cut-off valves.

The venturi quench absorber is arranged vertically, and comprises a convergent pipe, a throat and a divergent pipe from top to bottom. An annular nozzle is provided at the top of the convergent pipe, and throat nozzles are evenly distributed at the lower part of the convergent pipe near the throat.

Among them, the annular nozzle includes a water inlet, which is connected to a water distribution ring pipe. A plurality of water spray holes are evenly distributed on the wall surface of the water distribution ring pipe. A guide ring pipe is arranged inside the water distribution ring pipe. The guide ring pipe is an integrated structure composed of a semicircular ring and an inclined plate, and its cross-section is "q"-shaped. The semicircular ring is located inside the water distribution ring pipe, and the lower part of the inclined plate extends obliquely along the annular gap at the lower part of the water distribution ring pipe. A connecting flange is arranged on the outer side of the annular nozzle.

Among them, the distance between the throat nozzle and the throat is 100-200mm; the number of the throat nozzles is multiple, evenly distributed along the circumference, and is a single-fluid hollow cone structure with an atomization angle of 90°~150°; the throat velocity of the throat is 35~60m/s; the length of the throat is 1-3 times the diameter of the throat.

The cyclone plate spray demister is a multi-tube design with multiple cyclones installed inside, each of which is composed of three layers of cyclone plates and a connected cylinder;

The three layers of swirl plates are respectively a first layer of swirl plate located at the bottom, a second layer of swirl plate located at the middle and upper part, and a third layer of swirl plate located at the top. A first layer of swirl plate spray device is provided above the first layer of swirl plate; a flushing device is provided on the top of the swirl plate spray demister.

The swirl plate includes a swirl plate blind plate located in the center, and a plurality of swirl plate blades arranged in a spiral are arranged on the outer side of the swirl plate blind plate;

The swirl plate is divided into an inward plate and an outward plate. The inward plate has a centripetal velocity component when the airflow passes through the blade, and the inward plate trajectory is longer; the outward plate has an outward velocity component when the airflow passes through the blade, and the droplets are thrown outward to the wall. The outward plate trajectory is shorter, and the time for the droplets to reach the wall is shorter, which is conducive to the separation of gas and liquid;

The first layer of swirl plates are inward plates, and the second layer of swirl plates and the third layer of swirl plates are outward plates;

The swirl plate adopts an elevation angle of 22°~30° and a radial angle <55°; the number of blades is 8~18; the diameter Dm of the swirl plate blind plate and the diameter Dx of the swirl plate blades satisfy Dm≥0.35Dx.

Among them, the flushing water pressure of the packed tower is 0.15~0.2Mpa, and the flushing coverage is 100%~300%; the wet electrostatic precipitator adopts a honeycomb type.

Wherein, the liquid storage tank A and the liquid storage tank B are both provided with overflow baffles, oil discharge ports and liquid level meters.

The method for purifying tail gas produced by a denitration catalyst of the present invention is as follows: the high-temperature tail gas discharged from a resistance furnace or a tunnel kiln is 550-650° C. When the tail gas from the mesh belt high-temperature oil removal process is discharged, the shut-off valve of the high-temperature oil removal tail gas pipeline is opened, and the shut-off valve of the roasting tail gas pipeline is closed. The tail gas is first cooled to 200-400° C. by cooling water, and then enters a catalytic oxidation reactor to degrade most of the oil mist. The tail gas is then pre-treated by a venturi quench absorber to remove most of the oil mist and reduce the tail gas to below 70° C. The tail gas coming out of the venturi quench absorber passes through a cyclone plate spray demister to spray, absorb and separate the oil mist for demisting; then the tail gas enters a packed tower for further deep ammonia and oil removal, and the tail gas temperature is further reduced to 50-60° C. Finally, the tail gas is deeply demisted by a wet electrostatic demister, and the clean tail gas is discharged into the atmosphere through a chimney through an induced draft fan;

When the exhaust is from the catalyst roasting process, close the shut-off valve of the high-temperature de-oiling exhaust pipeline, open the shut-off valve of the roasting exhaust pipeline, and the exhaust gas is cooled to 200-400°C by cooling water before directly entering the Venturi quench absorber, and then enters the cyclone plate spray demister, packed tower, and wet electrostatic demister for purification.

The spray water of the venturi quench absorber and the cyclone plate spray demister converges into the liquid storage tank A, and the spray water of the packing tower and the wet electrostatic demister converges into the liquid storage tank B; after sedimentation, clarification and sewage discharge, the liquid storage tanks A and B are pressurized by the circulating pumps A and B; among them, the circulating pump A is pressurized and sprayed into the venturi quench absorber and the cyclone plate spray demister again through the nozzle, and the circulating pump B is pressurized and enters the packing tower to realize the recycling of the spray water;

In the packed tower, when the tail gas is cooled from 70℃ to 50~60℃, a large amount of water vapor in the tail gas will condense and flow into the liquid storage tank B. The condensed water is pumped to the liquid storage tank A to achieve the cascade reuse of water.

The cooling water heat exchanger removes system heat by continuously cooling the circulating water in the liquid storage tank B to ensure that the packed tower operates within the temperature range required by the process.

Compared with the prior art, the method and device for purifying tail gas produced by denitration catalyst of the present invention have at least the following beneficial effects:

(1) The method of the present invention organically integrates the tail gas purification processes of the two steps of catalyst production, effectively plays the role of integrated synergistic treatment of ammonia removal and oil removal, saves investment and floor space, and effectively achieves standard or even ultra-clean tail gas emissions.

(2) The design of the catalytic oxidation reactor fully utilizes the high temperature of the exhaust gas from the high-temperature oil removal process and completes the oxidation reaction without external heat. This allows the exhaust gas to be degraded and most of the oil mist to be removed before entering the water washing purification equipment, thereby reducing the risk of oil stains adhering to and clogging subsequent equipment and alleviating the purification pressure of subsequent equipment. This saves energy and reduces consumption while also improving the stability and reliability of equipment operation.

(3) The design of the Venturi quench absorption tower, especially the design of the first-layer annular nozzle and the second-layer throat nozzle, not only achieves the multi-effect exhaust gas purification treatment of ammonia removal, oil removal and cooling, but also realizes continuous flushing and high-temperature protection of the equipment wall, greatly reducing the risk of oil adhesion and equipment overheating.

(4) The cyclone plate spray demister adopts a multi-tube design. Each cyclone is composed of three layers of cyclone plates and a connected cylinder. The first layer of cyclone plates is designed as an inward plate and is equipped with a spray device to absorb ammonia and capture oil mist. The second and third layers are outward plates to perform the function of mist separation. The two layers of outward cyclone plates can achieve graded capture of droplets of different particle sizes, ensuring efficient mist removal under low operating resistance, improving the mixing and mist removal efficiency of the equipment, avoiding the problem of oil blockage in the downstream equipment packed tower, and creating conditions for deep purification of exhaust gas by the packed tower equipment.

(5) The design of the packed tower further achieves deep removal of ammonia and oil mist in the exhaust gas, which can reduce the ammonia concentration in the exhaust gas to a very low value; the reasonable design of the baffle demister at the outlet of the packed tower can effectively reduce the sticking of oil pollution and perform preliminary removal and separation of droplets; acid can be added to the packed tower for chemical absorption of ammonia (the acid can be a phosphoric acid solution) to enhance the absorption of ammonia.

(6) The wet electrostatic precipitator effectively removes fine droplets in the exhaust gas, eliminates the adverse effects of white smoke on the surrounding environment, and ensures that pollutants are discharged in compliance with standards. The wet electrostatic precipitator adopts a honeycomb type, which not only has high demisting efficiency and compact structure, but also has good flame retardancy, effectively avoiding the potential safety hazards of flammable oil mist in the exhaust gas.

(7) The design of the liquid storage tank and circulating pump increases the circulation rate of the spray water in the tower, improves the heat transfer and mass transfer and capture efficiency, and realizes system recycling, energy saving and water saving. The liquid storage tank is equipped with an overflow baffle, an oil discharge port and a liquid level gauge; when the oil in the liquid storage tank accumulates to a certain level, the liquid level gauge automatically opens the oil discharge port, ensuring that all the oil above the overflow baffle of the liquid storage tank can flow to the side of the oil discharge port, realizing the timely and effective discharge of floating oil. The condensate of the packed tower converges to the liquid storage tank B and can be pumped to the liquid storage tank A to realize the cascade reuse of circulating water.

(8) The design of the cooling water heat exchanger can ensure that the system heat is removed, so that the outlet exhaust temperature of the packed tower is below 50~60℃, ensuring the deep removal of ammonia and oil mist in the packed tower.

The method and device for purifying tail gas produced by the denitration catalyst of the present invention will be further described below in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a production flow chart of plate-type denitrification catalyst.

FIG. 2 is a schematic diagram of the structure of a device for purifying tail gas produced by a denitration catalyst according to the present invention.

FIG. 3 is a flow chart of a method for purifying tail gas produced by a denitration catalyst according to the present invention.

Figure 4 is a schematic diagram of the structure of the Venturi quench absorber.

Figure 5 is a schematic diagram of the annular nozzle structure.

Figure 6 is a schematic diagram of the throat nozzle arrangement (i.e., the "A-A" view in Figure 4).

Figure 7 is a schematic diagram of a swirl plate spray demister.

Fig. 8 is a view taken along the line "B-B" in Fig. 7 .

FIG. 9 is a schematic diagram of the inner plate of the swirl plate.

FIG. 10 is a schematic diagram of the outward plate of the swirl plate.

Among them, 1-resistance furnace or tunnel kiln; 2-catalytic oxidation reactor; 3-Venturi quench absorber; 4-swirl plate spray demister; 5-packing tower; 51-baffle demister; 52-packing tower spray device; 6-wet electrostatic demister; 71-liquid storage tank A; 72-liquid storage tank B; 711-overflow baffle; 712-oil discharge port; 713-liquid level gauge; 8-cooling water heat exchanger; 91-circulating pump A; 92-circulating pump B; 10-induced draft fan; 11-shut-off valve;

31-converging tube; 32-throat; 33-expanding tube; 34-annular nozzle; 35-throat nozzle;

341-water inlet; 342-water distribution ring pipe; 343-water spray hole; 344-annular gap; 345-flow guide ring pipe; 346-connecting flange;

41-exhaust gas inlet; 42-first layer swirl plate; 43-first layer swirl plate spray device; 44-second layer swirl plate; 45-swirl cylinder; 46-third layer swirl plate; 47-flushing device; 48-exhaust gas outlet; 441-swirl plate blades; 442-swirl plate blind plate.

DETAILED DESCRIPTION

As shown in FIG2-10, a purification device for tail gas produced by a denitration catalyst comprises a catalytic oxidation reactor 2, the inlet of the catalytic oxidation reactor 2 is connected to the high-temperature de-oiling tail gas pipeline of the resistance furnace or tunnel kiln 1, the outlet of the catalytic oxidation reactor 2 is connected to the top inlet of the venturi quenching absorber 3, the outlet of the venturi quenching absorber 3 is connected to the tail gas inlet 41 of the cyclone plate spray demister 4, and a liquid storage tank A71 is provided below the venturi quenching absorber 3 and the cyclone plate spray demister 4; the roasting tail gas pipeline of the resistance furnace or tunnel kiln 1 is connected to the top inlet of the venturi quenching absorber 3. Among them, the high-temperature de-oiling tail gas and the roasting tail gas can be discharged from the resistance furnace, or can be discharged from the tunnel kiln.

The tail gas outlet 48 of the cyclone plate spray demister 4 is connected to the inlet of the packing tower 5, the outlet of the packing tower 5 is connected to the inlet of the wet electrostatic demister 6, and the outlet of the wet electrostatic demister 6 is connected to the induced draft fan 10; a liquid storage tank B72 is provided below the packing tower 5 and the wet electrostatic demister 6;

The high-temperature de-oiling tail gas pipeline, the roasting tail gas pipeline, the top inlet of the Venturi quench absorber 3, the upper inlet of the cyclone plate spray demister 4, the side inlet of the packed tower 5, and the side inlet of the wet electrostatic demister 6 are all connected to the process water pipeline for cooling the tail gas, replenishing spray water or flushing equipment; the liquid storage tank A71 is connected to the circulation pump A91, and the outlet of the circulation pump A91 is respectively connected to the annular nozzle 34 and the throat nozzle 35 of the Venturi quench absorber 3 and the inlet of the first layer cyclone plate spray device 43 of the cyclone plate spray demister 4; the liquid storage tank B72 is connected to the circulation pump B92, and the outlet of the circulation pump B92 is connected to the cooling water heat exchanger 8, and the outlet of the cooling water heat exchanger 8 is connected to the inlet of the packed tower spray device (52), and the heat exchange inlet and heat exchange outlet of the cooling water heat exchanger 8 are both connected to the process water pipeline.

As shown in FIG. 2 , both the high-temperature deoiling tail gas pipeline and the roasting tail gas pipeline are provided with a shut-off valve 11 .

The following is a detailed introduction to the main components of this device:

(1) Catalytic oxidation reactor

The existing methods for treating tail gas oil mist (i.e. VOCs) mainly include: adsorption, condensation, photocatalytic oxidation, plasma, direct combustion, and catalytic oxidation. The adsorption method uses porous media materials for adsorption, such as activated carbon, porous silica, and porous resin to adsorb VOCs. It is suitable for the removal of low-concentration VOCs. This method requires regeneration, high energy consumption, large equipment, and easy to produce secondary pollution. The condensation method usually uses cheap water as the condensation medium (i.e., water washing method), condenses the oil mist into liquid, and then captures and recovers it. This method has low investment, simple equipment, and high recovery purity, but low purification efficiency and limited scope of application. It is often matched with other processes to achieve ultra-low emission requirements. Photocatalytic oxidation method is to use photocatalyst (usually _TiO2 ) to catalytically degrade oil mist under specific wavelength light (usually ultraviolet light). Although this method has low energy consumption, it has low efficiency (30%-50%) and easy deactivation of catalysts. Plasma method uses high-voltage pulse discharge to generate high-energy active particles to degrade oil mist. This method has high energy consumption and is prone to secondary pollution. Direct combustion method is to burn directly at high temperature (≥800℃), with high removal efficiency and wide application range, but high energy consumption. A large amount of fuel gas needs to be burned in the incinerator, and the flue gas after combustion brings new secondary pollution problems such as nitrogen oxides and dioxins. Catalytic oxidation method is to use catalysts to degrade oil mist at a certain temperature (200~400℃), with high purification efficiency, low processing temperature, energy saving and economy, and no secondary pollution problems.

Catalytic oxidation is a typical gas-solid phase catalytic reaction. With the help of catalysts, the activation energy of the reaction is reduced, so that it can be flamelessly burned at a relatively low temperature (200℃~400℃), producing _CO2 and _H2O , and releasing a large amount of heat. Because of its low oxidation reaction temperature, it greatly inhibits the generation of NOx during the oxidation process. Compared with the traditional direct combustion method, the advantages of catalytic oxidation are: (1) low reaction temperature and low energy consumption; (2) high purification efficiency, with a removal efficiency of more than 80%; (3) wide adaptability to oxygen concentration range, low noise, no secondary pollution, and simple operation. The catalysts of catalytic oxidation are mainly platinum-based, manganese-based, cobalt-based, _and copper-based; the catalyst carriers are mainly _Al2O3 , _ZrO2 , _SiO2 , etc.

Since the tail gas of the high-temperature oil removal process contains a high amount of oil mist, it is generally difficult to achieve the requirements of ultra-low emissions through a single treatment method. The present invention makes full use of the existing tail gas temperature characteristics of the high-temperature oil removal process (600~650℃), and organically combines the catalytic oxidation method and the condensation method (water washing method) for use, as shown in Figure 3. The advantage of this design is that most of the oil mist has been degraded and removed before the tail gas enters the water washing equipment, reducing the risk of oil stains adhering to and blocking subsequent equipment, reducing the purification pressure of subsequent water washing equipment, improving the stability of equipment operation, and saving energy and reducing consumption. Before the tail gas enters the catalytic oxidation reactor, the tail gas is cooled by a certain amount of water spray and adjusted to the optimal reaction temperature zone (200℃~400℃) required by the catalyst, and the purpose of low-cost and high-efficiency degradation of oil mist can be achieved without additional heating equipment.

When the exhaust is the tail gas from the catalyst roasting process, the tail gas is first cooled to 200~400℃ by cooling water, and then directly enters the Venturi quench absorber and subsequent equipment for purification, and the catalytic oxidation reactor is bypassed by switching the cut-off valve. This is because the tail gas from the catalyst roasting process contains a small amount of sulfur dioxide and smoke, which will re-synthesize ammonium bisulfate (ABS) during the cooling process, causing poisoning and deactivation of the catalyst in the catalytic oxidation reactor.

(2) Venturi quench absorber

As shown in Fig. 4, the venturi quench absorber 3 is arranged vertically to prevent the captured oil paste from clogging the venturi throat. From top to bottom, there are a reducer 31, a throat 32 and a divergent tube 33. The top of the reducer 31 is provided with an annular nozzle 34, and the lower part of the reducer 31 near the throat is evenly distributed with throat nozzles 35.

During operation, high-temperature exhaust gas enters the device from the top, and is first cooled initially by the high-speed jet spray sprayed by the annular nozzle 34 set at the top of the Venturi quench absorber; then it enters the convergent tube 31, where the exhaust gas is gradually accelerated and mixed; when the exhaust gas is about to enter the throat 32, the exhaust gas velocity reaches the highest value, and the throat nozzle 35 set at the throat sprays a high-speed jet spray downward, which is impacted and broken by the high-speed exhaust gas at the throat, and instantly atomized into fine water droplets of 100-200 microns, and fills the entire throat. At this time, the three phases of gas, liquid and solid are strongly mixed to form a high-efficiency turbulent zone, the exhaust gas is completely saturated with water and cooled below 70°C, ammonia is absorbed, and oil droplets are wetted and captured by water, achieving the effect of removing ammonia and oil in a very short time; the high-speed exhaust gas passing through the throat, then passes through the divergent tube 33, the velocity gradually decreases, and the particles condense and settle by gravity, and then enters the cyclone plate spray demister for further purification.

As shown in Figure 5, the annular nozzle 34 includes a water inlet 341, which is connected to a water distribution ring pipe 342. A plurality of water spray holes 343 are evenly distributed on the wall surface of the water distribution ring pipe 342. A guide ring pipe 345 is provided in the water distribution ring pipe 342. The guide ring pipe 345 is an integrated structure composed of a semicircular ring and an inclined plate, and its cross-section is "q"-shaped. The semicircular ring is located in the water distribution ring pipe 342, and the lower part of the inclined plate extends obliquely along the annular gap 344 at the lower part of the water distribution ring pipe 342. A connecting flange 346 is provided on the outer side of the annular nozzle 34.

Since the top of the Venturi is the entrance of high-temperature flue gas, it is the highest temperature point in the exhaust gas purification system (600~650℃), and the oil mist is easy to stick and clog on the equipment wall after the temperature drops, especially the problem of sticking and clogging at the throat with a small diameter is particularly prominent. Therefore, the annular nozzle designed by the present invention not only plays a role in spraying and cooling the high-temperature exhaust gas, but also prevents the oil mist from sticking to the wall, achieving the effect of timely flushing. When the Venturi quenching absorber is working, the circulating water pump sends the circulating cooling water from the liquid storage tank B to the water distribution ring pipe through the water inlet of the annular nozzle, and multiple water inlets (2~6) are set so that the water distribution ring pipe can obtain uniform water inlet pressure. A part of the circulating water is sprayed in through the water spray hole, which has a preliminary cooling effect on the high temperature; the other part of the circulating water flows down evenly along the inner wall of the tapered pipe through the annular gap, forming a layer of water film, which realizes the cooling of the equipment wall and also flushes the wall. The water distribution ring pipe fully wraps the top of the equipment, so that the top of the Venturi with the highest temperature is completely cooled and protected. The water spray hole is located in the middle of the water distribution ring pipe, and holes are opened on the ring pipe at equal intervals. The opening shape is a flat structure. The water mist spray surface formed by the multiple flat spray holes after spraying is in a 90° horizontal cross flow with the incoming exhaust gas, which is conducive to the full mixing of the exhaust gas and the circulating cooling water; the annular gap is located at the bottom of the water distribution ring pipe, and holes are opened along the ring pipe. The opening shape is a narrow and long gap structure, so that under a small water volume, the upper part of the Venturi is completely covered by the water flow; the annular nozzle is provided with a guide ring pipe, which consists of a semicircular ring and an inclined plate. The purpose of the semicircular ring is to guide the circulating cooling water, reduce the flow resistance, avoid the cooling water flow short circuit, and make the wall of the water distribution ring pipe fully cooled; the inclined plate has the following functions: (1) to support the annular nozzle; (2) to form a guide structure together with the annular gap to cool the reducer 31 and the throat 32; (3) to be welded or flanged with the reducer 31 to complete the assembly of the equipment components. The connecting flange 346 of the annular nozzle facilitates the connection of the Venturi quench absorber to the upstream flue.

As shown in FIG6 , the distance between the throat nozzle 35 and the throat 32 is 100-200 mm, because if the nozzle is too far from the throat, the high-speed exhaust gas injection effect on the throat is weakened, and the exhaust gas cannot be densely injected at the throat; but if the nozzle is too close to the throat, the throat resistance of the exhaust gas will be significantly increased due to the excessively dense injection of the throat, and even the throat liquid seal phenomenon will occur, causing the equipment to fail to work normally. According to the capacity of the equipment, the number of throat nozzles 35 is multiple, evenly distributed along the circumference, and is a single-fluid hollow cone structure. The atomization angle is preferably 90°~150° (the cone top angle formed by the nozzle spray). In this way, a good atomization coverage can be maintained with a small number of nozzles. The downward projection surface of the injection surface formed by the confluence of multiple nozzles can cover the entire throat, so that all the exhaust gas flowing through the throat is covered and moistened by the spray water, avoiding the exhaust gas short circuit phenomenon.

The design of the venturi throat is also one of the important parameters, and factors such as cooling, ammonia absorption, oil mist capture and energy consumption should be considered comprehensively. The size of the throat diameter determines the size of the throat speed. Generally, the higher the throat speed, the higher the relative movement speed of gas and liquid, the higher the heat transfer and mass transfer capture efficiency, and the higher the oil removal and ammonia removal efficiency. However, too high a speed not only brings high energy consumption, but also causes impact vibration of the equipment. Therefore, it is necessary to select a suitable throat speed (v0) and throat diameter (D0). Generally, a throat speed greater than 35m/s can achieve good absorption of ammonia and wetting and capture of oil mist. Therefore, the venturi throat speed of the present invention is selected to be 35~60m/s. The length of the throat (L0) affects the mixing time of the throat gas and liquid. Generally, it is designed to be 1-3 times of D0 to ensure good mixing of gas and liquid. The design of the convergent tube takes into account factors such as operating resistance and equipment length. The generally designed exhaust gas inlet velocity is 15~25m/s, and the contraction angle is 10~12.5°. The design of the divergent tube takes into account factors such as droplet sedimentation, equipment length, and operating resistance. The generally designed exhaust gas outlet velocity is 15~25m/s, and the contraction angle is 3~5°.

(3) Cyclone plate spray demister

The exhaust gas passes through the Venturi quench absorber for preliminary cooling and oil and ammonia removal, and then enters the swirl plate spray demister for further oil and ammonia removal.

As shown in Figure 7, the swirl plate spray demister 4 is a multi-tube design with multiple swirls installed inside, each swirl consists of three layers of swirl plates and a connected cylinder; the three layers of swirl plates are respectively a first layer of swirl plate 42 located at the bottom, a second layer of swirl plate 44 located in the upper middle part, and a third layer of swirl plate 46 located at the top, and a first layer of swirl plate spray device 43 is provided above the first layer of swirl plate 42; a flushing device 47 is provided on the top of the swirl plate spray demister 4.

The tail gas enters the cyclone plate spray demister from the lower tail gas inlet and is discharged from the upper tail gas outlet. The tail gas is divided into multiple airflows and enters the cyclone. The cyclone plate in the cyclone makes the tail gas form a centrifugal force that rotates upward, strengthens the mixing and separation of the gas and liquid phases, and makes the tail gas fully mixed and separated. The cyclone plate spray demister is a multi-tube design. This is because the calculation formula of centrifugal force shows that the centrifugal force on the droplet particles of a certain mass is inversely proportional to the rotation radius. The larger the radius, the smaller the centrifugal force and the worse the effect. That is, the smaller the diameter of the cyclone plate, the higher the efficiency. The multi-tube design can significantly improve the mixing and demisting efficiency of the equipment.

The swirl plate has the advantages of simple structure, low manufacturing cost, small size, high efficiency, and not easy to clog. As shown in Figure 8, the swirl plate includes a swirl plate blind plate 442 located in the center, and a plurality of swirl plate blades 441 arranged in a spiral are provided on the outer side of the swirl plate blind plate 442.

The main structural parameters of the swirl plate are: number of blades m, blade diameter Dx, blind plate diameter Dm, blade inclination angle а, and radial angle β. When the gas passes through the swirl blade, a rotating airflow is formed, and the centrifugal force generated makes the gas and liquid phases fully mixed or separated; according to the different radial angles β (the angle between the radius of the swirl plate and the blade slit line), the swirl plate can be divided into an inward plate and an outward plate. As shown in Figure 9-10, the inward plate has an inward centripetal component velocity after the airflow passes through the blade, and the inward plate trajectory is longer, which is usually used for mass transfer and absorption; the outward plate is the opposite. When the airflow passes through the blade, there is an outward component velocity, and the droplets are thrown outward to the wall. The outward plate trajectory is shorter, and the time for the droplets to reach the wall is shorter, which is conducive to the separation of gas and liquid, and is usually used as a separation demister.

The first swirl plate 42 is an inward plate and is provided with a spray device. The exhaust gas passes through the first swirl plate and rotates upward inward at a certain elevation angle, and is continuously mixed with the circulating spray liquid to achieve ammonia absorption and oil mist capture. The second swirl plate 44 plays a role in mist removal and separation. The airflow moves upward in an outward rotation under the guidance of the swirl plate blades. The droplets are quickly thrown to the wall and gradually condensed into large droplets, which flow downward along the wall and converge into the liquid storage tank. The third swirl plate 46 is designed as an outward plate to capture and separate smaller droplets that cannot be captured by the second layer.

The design of two layers of outward swirl plates can achieve graded capture of droplets of different particle sizes. Through the reasonable design of the blind plate diameter, the number of blades, the elevation angle, and the swirl speed (such as a smaller swirl speed in the first stage and a larger speed in the second stage), the droplets on the swirl plates of different layers can be captured and removed step by step from large to small, ensuring efficient dust removal and mist removal under low operating resistance. The cylinder between the second and third layers of the cyclone is designed in the form of a Venturi, the purpose of which is to further accelerate the exhaust gas after high-speed swirl through the Venturi contraction to enhance mixing and condensation, which is conducive to the removal of droplets.

Generally, the efficiency and pressure drop of the swirl plate increase with the increase of gas flow rate, number of blades, elevation angle and radial angle. When the elevation angle exceeds 30° or the radial angle is greater than 55°, the pressure drop increases sharply. Therefore, the swirl plate should be designed with an elevation angle of 22°~30° and a radial angle of <55°. The number of blades should not be too large, preferably m=8~18, to prevent the oil mist in the exhaust gas from blocking the blades. The blind plate diameter Dm should not be too small, and it should be Dm≥0.35Dx with the blade diameter Dx.

The speed passing through the swirl plate cannot be too high. If the gas swirl velocity is too high, the separated droplets will break into smaller droplets, and the liquid film on the wall or blades will be torn and carried out of the outward swirl plate again by the high-speed airflow, resulting in a decrease in the demisting separation efficiency and the occurrence of "secondary entrainment" of droplets. Therefore, the air flow velocity should be ≤4.0m/s.

The flushing device installed on the top of the swirl plate spray demister can flush the wall surface and swirl plate of the swirl plate spray demister regularly or irregularly to prevent oil stains from adhering and ensure the stable operation of the demister.

(4) Packed tower

The packed tower is mainly used to deeply remove ammonia and oil mist from the tail gas, which can reduce the concentration of pollutants to a very low value. According to different emission requirements, the packed tower can adopt a single-stage or multi-stage packing method. The tail gas of the packed tower adopts a countercurrent arrangement, and the tail gas enters from the bottom of the tower and is discharged from the top of the tower; the circulating water is sprayed from the top of the tower through the spray device 52, and after the filler and the tail gas are fully contacted, it converges to the liquid storage tank B at the bottom, and then is sent to the nozzle at the top of the tower through the circulating pump B to achieve continuous spraying and recycling. When the physical absorption of ammonia by circulating water still cannot achieve ultra-low emissions, acid can be added to the packed tower for chemical absorption of ammonia (the acid can be a phosphoric acid solution) to enhance the absorption of ammonia.

A mechanical demister is arranged at the outlet of the packed tower, in the form of: swirl plate type, wire mesh type, baffle plate type, etc. Since the tail gas contains oil mist, it is easy to get stuck, so a baffle plate type mechanical demister is used, which has the advantages of not easy to get stuck, small resistance (generally less than 100Pa per stage), and allows a higher flue gas flow rate. The baffle demister 51 is arranged at the top of the packed tower, and relies on gravity and inertial impact to capture small droplets. Selecting the appropriate spacing of the baffle blades, flushing water pressure, and flushing coverage can effectively prevent the oil from sticking to the baffle blades. If the blade spacing is too large, the demisting efficiency is low, and the tail gas carries water seriously. If the spacing is too small, the pressure loss increases, and the blades are easily blocked by oil. Therefore, on the basis of fully considering the demisting efficiency, pressure loss and clogging problems, the blade spacing design selection is preferably 40~50mm. If the flushing water pressure is too low, the flushing effect is poor, and the oil is difficult to wash away; if the flushing water pressure is too high, not only the tail gas carries water seriously, but also the life of the baffle is reduced.

The flushing water pressure of packed tower 5 is 0.15~0.2Mpa. In order to ensure that the demister section is fully flushed, the flushing coverage (the coverage of the demister section by the flushing water) is 100%~300%.

(5) Wet electrostatic mist eliminator

Mechanical demisters have a good demisting effect on larger particles and droplets. Usually, droplets with a diameter greater than 50μm can be separated by gravity sedimentation; droplets larger than 5μm can be separated by inertial collision and centrifugal force; while mechanical demisters cannot effectively remove fine particles such as ammonia, oil mist, dust, SO ₃ , aerosols, mercury and other heavy metals. Wet electrostatic demisters rely on the action of high-voltage electrostatic fields to collect various fine droplets to the dust collecting pole, forming a liquid film on the inner wall, which flows into the liquid storage tank B under the action of gravity. Due to the presence of water, after the oil mist and ammonia are wetted by water, the specific resistance decreases, making it easier to electrostatically capture, and the demisting rate is as high as more than 90%, which greatly reduces the opacity (turbidity) of the exhaust smoke, and the white smoke problem is well solved.

There are two main forms of wet electrostatic precipitators: honeycomb and rectangular. The present invention adopts the honeycomb type because the honeycomb type not only has the characteristics of high demisting efficiency, compact structure and good conductivity, but also has good flame retardancy. Even if an arc is drawn in the electric field, the precipitation electrode will not be ignited, effectively avoiding the possible safety hazards of flammable oil mist in the exhaust gas. In order to prevent corrosion from ammonia water and oil stains, the equipment is made of fiberglass. A flushing water device is provided on the top of the wet electrostatic precipitator to flush the electrodes at regular intervals.

(6) Liquid storage tank

The spray liquid of the venturi quench absorber and the cyclone plate spray demister converges into the liquid reservoir A, and the spray liquid of the packing tower and the wet electrostatic demister converges into the liquid reservoir B, as shown in Figure 2. After sedimentation, clarification, and sewage discharge, the liquid reservoir A and the liquid reservoir B are pressurized by the circulation pump A and the circulation pump B, and then sprayed into the venturi quench absorber, the cyclone plate spray demister and the packing tower through the nozzle again to realize the recycling of the spray water. The design of the liquid reservoir and the circulation pump increases the circulation rate of the spray water in the tower, improves the heat transfer and mass transfer and capture efficiency, and realizes the recycling of the system and energy and water saving.

The overflow baffle 711, oil discharge port 712 and liquid level meter 713 are arranged inside the liquid storage tank A and the liquid storage tank B, as shown in Figure 2. The oil collected by the tail gas washing floats on the liquid surface of the liquid storage tank A and the liquid storage tank B, and accumulates and thickens continuously, affecting the normal operation of the equipment.

When the oil in the liquid storage tank accumulates to a certain height, the indicator light of the liquid level meter 713 lights up, and the oil discharge port 712 is automatically opened to discharge the oil in the liquid storage tank. In view of the characteristics of the oil, the present invention specially designs an overflow baffle in the liquid storage tank, the purpose of which is to ensure that all floating oil above the overflow baffle can flow to the side of the oil discharge port when the oil discharge port is opened (if the overflow baffle is not provided, the floating oil cannot be completely discharged, and most of the discharged oil is water).

The moisture content of the exhaust gas at the outlet of the swirl plate spray demister has reached the saturated state at 70℃. In the packed tower, when the exhaust gas is cooled from 70℃ to 50~60℃, a large amount of water vapor in the exhaust gas will condense and flow into the liquid storage tank B. The condensed water can be pumped to the liquid storage tank A to achieve the cascade reuse of water.

(7) Cooling water heat exchanger

The moisture content of the outlet tail gas of the cyclone plate spray demister has reached a saturated state of 70℃. In the packed tower, when the tail gas is cooled from 70℃ to 50~60℃, the water vapor in the tail gas also releases a large amount of latent heat of vaporization during the condensation process. This heat is transferred to the circulating water, which will cause the circulating water temperature to continue to rise. In order to ensure that the outlet tail gas temperature of the packed tower is below 50~60℃, which is conducive to the deep removal of ammonia and oil mist, the device is also equipped with a cooling water heat exchanger, which continuously cools the circulating water of the liquid storage tank B to remove the system heat to ensure that the packed tower works within the temperature range required by the process.

The cooling water heat exchanger is designed as a tubular heat exchanger, the working medium inside the tube is 25℃-32℃ industrial cooling water, and the working medium outside the tube is circulating water that needs to be cooled. The cooling water heat exchanger continuously removes the system heat to ensure that the temperature of the tail gas drops below 50~60℃, ensuring the deep removal of ammonia and oil mist in the packed tower.

As shown in FIG3 , the method for purifying tail gas using the denitration catalyst of the above-mentioned purification device is as follows:

The high-temperature tail gas discharged from the resistance furnace or tunnel kiln is 550~650℃. When the tail gas from the high-temperature oil removal process of the mesh belt is discharged, the shut-off valve of the high-temperature oil removal tail gas pipeline is opened, and the shut-off valve of the roasting tail gas pipeline is closed. The tail gas is first cooled to 200~400℃ by cooling water, and then enters the catalytic oxidation reactor to degrade most of the oil mist. Then, the tail gas is pre-treated by the Venturi quench absorber to remove most of the oil mist and reduce the tail gas to below 70℃; the tail gas from the Venturi quench absorber passes through the cyclone plate spray demister to spray, absorb and separate the oil mist; then it enters the packed tower for further deep ammonia and oil removal, and the tail gas temperature is further reduced to 50-60℃; finally, it passes through the wet electrostatic demister for deep demisting, and the clean tail gas is discharged into the atmosphere through the chimney through the induced draft fan;

When the exhaust is from the catalyst roasting process, close the shut-off valve of the high-temperature de-oiling exhaust pipeline, open the shut-off valve of the roasting exhaust pipeline, and the exhaust gas is cooled to 200-400°C by cooling water before directly entering the Venturi quench absorber, and then enters the cyclone plate spray demister, packed tower, and wet electrostatic demister for purification.

The spray water of the venturi quench absorber and the cyclone plate spray demister converges into the liquid storage tank A, and the spray water of the packing tower and the wet electrostatic demister converges into the liquid storage tank B; after sedimentation, clarification and sewage discharge, the liquid storage tanks A and B are pressurized by the circulating pumps A and B; among them, the circulating pump A is pressurized and sprayed into the venturi quench absorber and the cyclone plate spray demister again through the nozzle, and the circulating pump B is pressurized and enters the packing tower to realize the recycling of the spray water;

In the packed tower, when the tail gas is cooled from 70℃ to 50~60℃, a large amount of water vapor in the tail gas will condense and flow into the liquid storage tank B. The condensed water is pumped to the liquid storage tank A to achieve the cascade reuse of water.

The cooling water heat exchanger removes system heat by continuously cooling the circulating water in the liquid storage tank B to ensure that the packed tower operates within the temperature range required by the process.

The embodiments described above are merely descriptions of preferred implementation modes of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims (10)

1. The utility model provides a purifier of denitration catalyst production tail gas which characterized in that: the catalytic oxidation device comprises a catalytic oxidation reactor (2), wherein an inlet of the catalytic oxidation reactor (2) is connected with a high-temperature oil removal tail gas pipeline of a resistance furnace or a tunnel kiln (1), an outlet of the catalytic oxidation reactor (2) is connected with a top inlet of a Venturi quenching absorber (3), an outlet of the Venturi quenching absorber (3) is connected with a tail gas inlet (41) of a cyclone plate spray mist eliminator (4), and a liquid storage tank A (71) is arranged below the Venturi quenching absorber (3) and the cyclone plate spray mist eliminator (4); the roasting tail gas pipeline of the resistance furnace or tunnel kiln (1) is connected with the top inlet of the Venturi quenching absorber (3);

The tail gas outlet (48) of the cyclone plate spray mist eliminator (4) is connected with the inlet of the filler tower (5), the outlet of the filler tower (5) is connected with the inlet of the wet electrostatic mist eliminator (6), and the outlet of the wet electrostatic mist eliminator (6) is connected with the induced draft fan (10); a liquid storage tank B (72) is arranged below the packing tower (5) and the wet electrostatic demister (6);

the high-temperature oil removal tail gas pipeline, the roasting tail gas pipeline, the top inlet of the Venturi quenching absorber (3), the upper inlet of the cyclone plate spray demister (4), the side inlet of the packing tower (5) and the side inlet of the wet electrostatic demister (6) are all connected with the process water pipeline and are used for cooling tail gas, supplementing water and flushing equipment; the liquid storage tank A (71) is connected with the circulating pump A (91), and the outlet of the circulating pump A (91) is respectively connected with the annular nozzle (34), the throat nozzle (35) and the inlet of the first layer of swirl plate spraying device (43) of the swirl plate spraying demister (4) of the Venturi quenching absorber (3); the liquid storage tank B (72) is connected with the circulating pump B (92), an outlet of the circulating pump B (92) is connected with the cooling water heat exchanger (8), an outlet of the cooling water heat exchanger (8) is connected with the packed tower spraying device (52), and a heat exchange inlet and a heat exchange outlet of the cooling water heat exchanger (8) are connected with a process water pipeline.

2. The purification device for exhaust gas produced by a denitration catalyst according to claim 1, characterized in that: and the high-temperature oil removal tail gas pipeline and the roasting tail gas pipeline are both provided with cut-off valves (11).

3. The purification device for exhaust gas produced by a denitration catalyst according to claim 1, characterized in that: the venturi quenching absorber (3) is vertically arranged, a reducing pipe (31), a throat (32) and a diverging pipe (33) are sequentially arranged from top to bottom, an annular nozzle (34) is arranged at the top of the reducing pipe (31), and throat nozzles (35) are uniformly distributed at the lower part of the reducing pipe (31) close to the throat.

4. A purification device for exhaust gas produced by a denitration catalyst according to claim 3, wherein: the annular nozzle (34) comprises a water inlet (341), the water inlet (341) is connected with a water distribution ring pipe (342), a plurality of water spray holes (343) are uniformly distributed on the wall surface of the water distribution ring pipe (342), a flow guide ring pipe (345) is arranged in the water distribution ring pipe (342), the flow guide ring pipe (345) is an integral structure formed by a semicircular ring and an inclined plate, the cross section of the flow guide ring pipe is in a q shape, the semicircular ring is positioned in the water distribution ring pipe (342), the lower part of the inclined plate obliquely extends out along an annular gap (344) at the lower part of the water distribution ring pipe (342), and a connecting flange (346) is arranged at the outer side of the annular nozzle (34).

5. A purification device for exhaust gas produced by a denitration catalyst according to claim 3, wherein: the distance between the throat nozzle (35) and the throat (32) is 100-200mm; the number of the throat nozzles (35) is multiple, the nozzles are uniformly distributed along the circumferential direction, the nozzles are of a single-fluid hollow cone structure, and the atomization angle is 90-150 degrees; the speed of the throat opening (32) is 35-60 m/s; the length of the laryngeal opening is 1-3 times of the diameter of the laryngeal opening.

6. The purification device for exhaust gas produced by a denitration catalyst according to claim 1, characterized in that: the cyclone plate spray demister (4) is of a multi-pipe design and is internally provided with a plurality of cyclones, and each cyclone consists of three layers of cyclone plates and a connected cylinder;

The three layers of cyclone plates are respectively a first layer of cyclone plate (42) positioned at the bottom, a second layer of cyclone plate (44) positioned at the middle and upper parts and a third layer of cyclone plate (46) positioned at the top, and a first layer of cyclone plate spraying device (43) is arranged above the first layer of cyclone plate (42); the top of the cyclone plate spray demister (4) is provided with a flushing device (47).

7. The purification device for exhaust gas produced by a denitration catalyst according to claim 6, wherein: the cyclone plate comprises a cyclone plate blind plate (442) positioned in the center, and a plurality of cyclone plate blades (441) which are spirally arranged are arranged on the outer side of the cyclone plate blind plate (442);

The cyclone plate is divided into an inward plate and an outward plate, the inward plate has inward centripetal separation speed after the airflow passes through the blades, and the track line of the inward plate is longer; the outward plate has outward separation speed after the airflow passes through the blades, and the liquid drops are thrown outward to the wall surface, so that the track line of the outward plate is shorter, the time for the liquid drops to reach the wall surface is shorter, and the separation of gas and liquid is facilitated;

The first layer of swirl plates (42) are inward plates, and the second layer of swirl plates (44) and the third layer of swirl plates (46) are outward plates;

The swirl plate adopts an elevation angle of 22-30 degrees, and a radial angle is less than 55 degrees; the number of the blades is 8-18; the diameter Dm of the blind plate (442) of the cyclone plate and the diameter Dx of the blade (441) of the cyclone plate meet that Dm is more than or equal to 0.35Dx.

8. The purification device for exhaust gas produced by a denitration catalyst according to claim 1, characterized in that: the flushing water pressure of the packing tower (5) is 0.15-0.2 mpa, and the flushing coverage is 100% -300%; the wet electrostatic mist eliminator (6) adopts a honeycomb type.

9. The purification device for exhaust gas produced by a denitration catalyst according to claim 1, characterized in that: and overflow baffles, oil stain discharge ports and liquid level meters are arranged in the liquid storage tank A (71) and the liquid storage tank B (72).

10. A method for purifying exhaust gas produced by using the denitration catalyst of the purification apparatus as claimed in any one of claims 1 to 9, characterized by: when the high-temperature tail gas discharged from the resistance furnace or the tunnel kiln is 550-650 ℃, when the high-temperature tail gas in the mesh belt high-temperature oil removal process is discharged, a cut-off valve of a high-temperature oil removal tail gas pipeline is opened, a cut-off valve of a roasting tail gas pipeline is closed, the tail gas is cooled to 200-400 ℃ through cooling water, enters a catalytic oxidation reactor to degrade most of oil mist, and is pretreated through a Venturi quenching absorber to remove most of oil mist, and the tail gas is cooled to below 70 ℃; tail gas from the Venturi quenching absorber passes through a cyclone plate spray demister to spray, absorb and separate oil mist for demisting; then the mixture enters a packing tower to further deeply remove ammonia and oil, and the temperature of the tail gas is further reduced to 50-60 ℃; finally, deep defogging is carried out by a wet electrostatic defogger, and clean tail gas is discharged into the atmosphere from a chimney through a draught fan;

When the tail gas of the catalyst roasting process is discharged, closing a cut-off valve of a high-temperature oil removal tail gas pipeline, opening the cut-off valve of the roasting tail gas pipeline, cooling the tail gas to 200-400 ℃ through cooling water, directly entering a Venturi quenching absorber, and then sequentially entering a cyclone plate spray demister, a filler tower and a wet electrostatic demister for purification treatment;

The spray water of the Venturi quenching absorber and the cyclone plate spray mist eliminator is converged into a liquid storage tank A, and the spray water of the packing tower and the wet electrostatic mist eliminator is converged into a liquid storage tank B; after sedimentation, clarification and pollution discharge, the liquid storage tank A and the liquid storage tank B are pressurized by the circulating pump A and the circulating pump B; the circulating pump A is pressurized and then sprayed into the Venturi quenching absorber and the cyclone plate spray demister through the nozzle, and the circulating pump B is pressurized and then enters the packing tower to realize the cyclic utilization of spray water;

in the packing tower, when the tail gas is cooled from 70 ℃ to 50-60 ℃, a large amount of vapor in the tail gas is condensed and converged into a liquid storage tank B, and the condensed water is pumped into the liquid storage tank A to realize the cascade recycling of water;

the cooling water heat exchanger takes out the system heat through continuously cooling the circulating water of the liquid storage tank B so as to ensure that the packed tower works within the temperature range required by the process.