Kiln waste gas treatment method based on SCR denitration

Abstract

The invention discloses a kiln waste gas treatment method based on SCR denitration, and belongs to the technical field of industrial waste gas treatment. The treatment method comprises the following steps: heating kiln flue gas through a preheater, and introducing the heated kiln flue gas into a dust remover; raising the temperature of the flue gas at the outlet of the dust remover to 200-240 DEG C, and introducing the flue gas into a denitration system; carrying out medium-temperature denitration reaction in a denitration system, cooling, and carrying out desulfurization treatment in a desulfurization system; wherein the medium-temperature denitration reaction comprises the steps that a reducing agent is sprayed into the flue gas on the upstream of the catalyst, SCR denitration is carried out through the catalyst, the catalyst is obtained by loading a V2O5-WO3-MoO3 composite system through a three-level pore channel carrier, and the reducing agent is ammonia water. By means of the treatment method, the denitration efficiency can be remarkably improved, and the smoke dust discharge amount can be reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of industrial waste gas treatment, and particularly relates to a kiln waste gas treatment method based on SCR denitration. BACKGROUND

[0002] Kilns are key equipment for high-temperature heating and firing of materials in industrial production, and are widely used in cement, glass, ceramics, metallurgy and other industries. During the operation of the kiln, a large amount of flue gas is generated due to fuel combustion and chemical reactions of the materials. These flue gases contain sulfur dioxide (SO2), nitrogen oxides (NOx), particulate matter (PM), heavy metals and other harmful substances, and if they are directly discharged into the atmosphere without treatment, they will cause serious pollution to the environment.

[0003] The kiln flue gas treatment process usually includes the following steps: 1. Reduce the flue gas temperature by heat exchanger or spray tower, etc.; 2. Remove particulate matter in the flue gas using an electric precipitator or a bag-type precipitator; 3. Remove SO2 by wet desulfurization (such as limestone / gypsum method) or dry desulfurization (such as calcium injection method); 4. Remove NOx by selective catalytic reduction (SCR) or non-selective catalytic reduction (SNCR) technology. Among them, the selective catalytic reduction method refers to the use of reducing agents (such as NH3, liquid ammonia, urea) to "selectively" react with NOx in the flue gas under the action of a catalyst to generate non-toxic and non-polluting N2 and H2O. x

[0004] The existing kiln flue gas treatment process based on SCR denitration has the following problems: (1) The SO2 concentration of the flue gas inlet of the denitration system is high, the denitration reaction temperature is about 190°C, and the ammonium bisulfate produced by the reaction condenses on the surface of the catalyst, which seriously affects the denitration efficiency, and the flue gas after treatment cannot meet the environmental emission standard.

[0005] (2) The operating temperature of the dust collector system and the denitration system is not higher than 200°C, which is in a low-temperature state, and a large amount of organic matter and oil in the flue gas is easy to condense out, which can easily block the filter bag and the surface of the catalyst, affecting the dust removal and denitration efficiency. At the same time, after the organic matter condenses out, it is a flammable substance, and the equipment and flue are prone to fire.

[0006] Therefore, how to effectively avoid the blockage of the catalyst surface by ammonium bisulfate, organic matter and oil is a problem to be solved. SUMMARY

[0007] The purpose of the present application is to provide a kiln waste gas treatment method based on SCR denitration, which can reduce the adhesion of ammonium bisulfate, organic matter and oil to the catalyst, thereby improving the SCR denitration efficiency. ​

[0008] To achieve the above object, the application provides a kiln waste gas treatment method based on SCR denitration, comprising the following steps: The kiln flue gas is treated by preheater to increase the temperature, and then is introduced into the dust collector; The outlet flue gas temperature of the dust collector is increased to 200℃-240℃, and then is introduced into the denitration system; The medium-temperature denitration reaction is carried out in the denitration system, and then the flue gas is treated by cooling and desulfurization in the desulfurization system; wherein, The medium-temperature denitration reaction comprises: spraying a reducing agent into the flue gas upstream of the catalyst, and using the catalyst for SCR denitration; the catalyst is obtained by loading V2O5-WO3-MoO3 composite system on a three-stage pore carrier; and the reducing agent is ammonia water.

[0009] Further, the filter bag of the dust collector is a nano-fiber structure, and a V2O5 / TiO2 surface catalyst coating is embedded on the filter bag.

[0010] Further, the denitration system comprises a combustion chamber and a reactor connected in sequence; the upstream flue of the combustion chamber is connected with the dust collector; and the flue gas temperature in the downstream flue of the combustion chamber is 280℃-320℃. The reducing agent is sprayed into the downstream flue of the combustion chamber, and the catalyst is fixed inside the reactor.

[0011] Further, the inlet of the reactor is provided with a mechanical vibration device and a hot gas blowing device; the mechanical vibration device is used for vibrating to remove the ash on the surface of the catalyst; and the hot gas blowing device is used for heating air and spraying the air to the surface of the catalyst to decompose the residual ammonium bisulfate.

[0012] Further, the catalyst is prepared by the following method: The Al2O3-SiO2 composite oxide is introduced into 5wt%-8wt% ZrO2 to form a solid solution; The pore size distribution of the solid solution is regulated by a pore-forming agent to prepare a carrier with large pores, mesopores and micropores; V2O5, WO3 and MoO3 are loaded in the carrier by impregnation method, and the carrier is calcined at 525℃-550℃ to obtain a carrier loaded with active ingredients; A 5μm-10μm thick SiO2-TiO2 composite sol is coated on the surface of the carrier loaded with active ingredients, and the modified carrier is obtained by calcining at 450℃-500℃; The modified carrier is subjected to plasma treatment in an NH3 / H2 mixed atmosphere, and then is activated in saturated steam at 280℃-320℃ for 1h-3h to obtain the catalyst.

[0013] Further, the Al2O3 content in the Al2O3-SiO2 composite oxide is 60wt%-70wt%, and the large pore, medium pore and micropore diameters are 50nm-100nm, 20nm-50nm and <2nm respectively; the pore-forming agent accounts for 10%-15% of the mass of the solid solution.

[0014] Further, in the carrier loaded with the active ingredient, the loadings of V2O5, WO3 and MoO3 are 6wt%-8wt%, 10wt%-12wt% and 3wt%-5wt% respectively. The power of the plasma treatment is 100W-150W, and the time is 15min-20min.

[0015] Further, the temperature after the temperature rising treatment is 280°C-320°C, the flue gas temperature after the medium-temperature denitration reaction is 305°C-315°C, and the temperature of the medium-temperature denitration reaction is 250°C-450°C.

[0016] Further, the temperature lowering treatment comprises: after the flue gas after the medium-temperature denitration treatment is cooled to 170°C-180°C by the motor air cooler, the flue gas enters the desulfurization system for desulfurization treatment.

[0017] Further, a heat pipe type waste heat recovery device connected with the inlet of the preheater is arranged at the rear end of the motor air cooler. A secondary air heat exchanger is arranged at the intersection of the flue gas pipeline at the tail of the combustion chamber and the combustion air inlet pipeline.

[0018] In summary, the present application has the following advantages: The present application provides a kiln flue gas treatment method based on SCR denitration, which firstly controls the flue gas temperature in each stage to ensure that ammonium bisulfate is in a gaseous or molten state under a high-temperature environment and is not easy to condense; the preheater temperature rising treatment can maintain the organic matter and oil in the flue gas in a gaseous state, thereby reducing condensation. At the same time, WO3 and MoO3 are used to improve the thermal stability of the catalyst and broaden the active temperature window to the medium-temperature interval; the three-stage pore structure increases the flue gas flow path, reduces the deposition probability and accelerates the reaction rate of NOx and NH3, thereby inhibiting the side reaction of SO2 and NH3. Based on this, the present application solves the problems of low denitration efficiency, equipment blockage and safety risk caused by low-temperature condensation in the existing kiln flue gas treatment, and realizes the multiple effects of efficient removal of pollutants, long-period stable operation of the system and energy saving. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A flowchart of the kiln flue gas treatment method based on SCR denitration provided by the present application is provided.

[0020] Figure 2 A production flowchart of the catalyst provided by the present application is provided.

[0021] Figure 3 A structural diagram of a device for a kiln waste gas treatment method based on SCR denitration is provided.

[0022] 1 - preheater; 2 - dust collector; 3 - combustion chamber; 4 - reactor; 5 - motor air cooler; 6 - heat pipe type waste heat recovery device; 7 - desulfurization system; 8 - chimney. DETAILED DESCRIPTION

[0023] The principles and characteristics of the present application are described below in conjunction with examples, which are used to explain the present application and are not intended to limit the scope of the present application. If no specific conditions are noted in the examples, conventional conditions or manufacturer recommended conditions are used. If no manufacturer of reagents or instruments is noted, conventional products available on the market are used.

[0024] The SO2 concentration of the flue gas inlet of the denitration system of the traditional kiln waste gas treatment is high, and the reaction temperature of denitration is about 190℃, so the ammonia and SOx sprayed in the denitration system are easy to produce ammonium bisulfate in the reactor, which condenses on the surface of the catalyst, seriously reduces the SCR denitration efficiency, and leads to the inability to stably guarantee the NOx emission concentration. Secondly, ammonium bisulfate also reduces the activity and service life of the catalyst, greatly increasing the denitration cost. At the same time, the operating temperature of the dust collector and the reactor of the traditional denitration system is lower than 200℃, which will cause the condensation of organic matter and oil in the flue gas, thereby blocking the filter bag and the surface of the catalyst, affecting the dust removal and denitration efficiency. Moreover, after the condensation of organic matter, it is a flammable substance, and the equipment and flue are prone to fire, which not only seriously reduces the operating efficiency and increases the cost, but also gradually expands the safety hidden trouble.

[0025] In view of the defects of the prior art, the present application provides a kiln waste gas treatment method based on SCR denitration, as shown in Figure 1 The method comprises the following steps: S1, the kiln flue gas is treated by preheater 1 and then introduced into dust collector 2.

[0026] In the specific embodiment, the temperature after the temperature treatment is 280℃-320℃, which is higher than the condensation point of most organic matter and oil, and lower than the temperature at which the catalyst may sinter, providing suitable temperature conditions for loading the catalyst on the dust collector 2, and also helping to crack or convert part of the organic matter.

[0027] As an optional embodiment of the present application, the filter bag of the dust collector 2 is a nanofiber structure, and a V2O5 / TiO2 surface catalyst coating with a thickness of 5-10 μm is embedded on the filter bag. Preferably, the mass of V2O5 accounts for 3-8% of the mass of the surface coating of the filter bag, and the mass of TiO2 accounts for 92-97% of the mass of the surface coating of the filter bag, forming a stable composite system with V2O5 and improving the acid corrosion resistance of the catalyst. Preferably, the fiber diameter of the filter bag is 50-200 nm, the thickness of the filter bag is 50-100 μm, and the filter bag can be a polyacrylonitrile (PAN) nanofiber. The embedding method can be a conventional coating method, a spinning blending method, a chemical vapor deposition method, etc.

[0028] In the above scheme, the nanofiber structure filter bag has higher filtration precision, larger specific surface area and better interception / diffusion efficiency, and can more effectively capture fine particulate matter. The catalyst embedded on the filter bag enables the dust collector 2 to not only have a physical filtration function, but also have a preliminary catalytic oxidation or reduction function, so that the NOx catalytic reduction reaction occurs simultaneously during the dust removal process. When the flue gas temperature is above 220℃, preliminary denitrification can be achieved by using the filter material surface catalyst, reducing the subsequent medium-temperature denitrification load.

[0029] S2, the outlet flue gas temperature of the dust collector 2 is increased to 200-240℃, and the denitrification system is connected.

[0030] In the specific implementation, the dust collector 2 is modified into a high-temperature dust collector to adapt to the increase of the flue gas temperature, and the flue gas entering the denitrification system is heated, so that the high-temperature dust collector makes the outlet flue gas reach about 220℃, so as to ensure the heating effect of the combustion chamber 3 of the denitrification system and the denitrification effect.

[0031] As an optional embodiment of the present application, the denitrification system comprises a combustion chamber 3 and a reactor 4 connected in sequence, the upstream flue of the combustion chamber 3 is connected with the dust collector 2, and the flue gas temperature in the downstream flue of the combustion chamber 3 is 280-320℃; wherein, the reducing agent is sprayed into the downstream flue of the combustion chamber 3, and the catalyst is fixed inside the reactor 4.

[0032] In the above scheme, the design of the combustion chamber 3 ensures that the flue gas temperature entering the reactor 4 is stably in the medium-temperature range (280-320℃) of the high-efficiency work of the SCR catalyst, provides the best reaction window for the V2O5-WO3-MoO3 catalyst, and improves the NOx conversion efficiency. The reducing agent is sprayed downstream of the combustion chamber 3 and before the entrance of the reactor 4, which can ensure that the reducing agent has enough time to mix uniformly with the flue gas before entering the catalyst bed, avoid the local concentration being too high to cause ammonia escape or too low to cause insufficient denitrification efficiency, and optimize the reaction kinetic conditions.

[0033] As an optional embodiment of the present application, the inlet of the reactor 4 is provided with a mechanical vibration device for vibrating to remove the catalyst surface ash and a hot gas blowing device for decomposing the residual ammonium bisulfate by heating air and spraying it to the catalyst surface.

[0034] In the above scheme, the mechanical vibration can effectively loosen and remove the accumulated particulate matter on the catalyst surface and bed, prevent excessive pressure drop, and maintain smooth flue gas passage. The hot gas blowing device uses high-temperature air (which may carry a small amount of water vapor) to directly act on the catalyst surface, which can effectively decompose or blow off the condensed ammonium bisulfate, prolonging the effective operation period of the catalyst.

[0035] Specifically, the mechanical vibration device adopts a cast steel hammer head (weight 2 kg~3 kg), which is fixed on the top beam of the reactor 4 through a spring connecting rod (diameter 10 mm spring steel), and is arranged every 500 mm along the top of the catalyst layer, a total of 3~4 groups. A 50mm~80mm stroke electric push rod (500N~800N thrust) is selected, which is connected with the hammer through a connecting rod, and the push rod motor power is 0.75kW, which can drive the hammer to knock the outer wall of the reactor 4 at a frequency of 2~3 times per second.

[0036] Specifically, the hot gas blowing device includes 1) an electric heating air box made of stainless steel (size 800mm×600mm×400mm), with built-in finned electric heating pipes (total power 10kW~15kW), matched with a centrifugal fan (air volume 300m 3 / h~500m 3 / h), and the outlet temperature can be adjusted to 250℃~300℃.

[0037] 2) a strip-shaped blowing pipe made of Φ32mm stainless steel pipe, arranged along the width direction of the reactor 4, with Φ8mm long strip-shaped holes (hole length 50mm, spacing 100mm) at the bottom, installed at 800mm above the catalyst layer, and the blowing direction is opposite to the flue gas flow direction.

[0038] 3) a support structure, the hammer holder is welded with ∠50×5 angle steel, fixed on the top flange of the reactor 4; the hot air box is installed on the column beside the reactor 4 through expansion bolts, and the blowing pipe is fixed on the inner wall of the reactor 4 through a U-shaped clamp.

[0039] The principle of the mechanical vibration device and the hot gas blowing device of the present application includes: (1) The electric push rod drives the hammer to periodically knock the outer wall of the reactor 4, and the vibration is transmitted to the catalyst surface through the shell, so that the condensed ammonium bisulfate particles fall off due to mechanical force, which is suitable for removing loose surface ash.

[0040] (2) When the vibration is finished, the electric heating air box is started, and hot air at about 280℃ is sprayed to the surface of the catalyst through the strip-shaped hole to decompose the residual ammonium bisulfate (decomposition temperature 230℃) by using heat, and at the same time, the temperature of the surface of the catalyst is raised to above 250℃ to reduce the possibility of subsequent dust accumulation.

[0041] The optimization can be achieved by setting the time relay to automatically start the dust removal program every 4h; the electric push rod is operated at a frequency of 2 times / s for 1min to mechanically vibrate the surface of the catalyst; after the vibration is stopped, the hot air system is started and continues to blow for 5min, the hot air temperature is maintained at 280±10℃; after completion, it is automatically stopped and waits for the next cycle.

[0042] S3, a medium-temperature denitration reaction is carried out in the denitration system, and then the flue gas is cooled and enters the desulfurization system 7 for desulfurization treatment.

[0043] The medium-temperature denitration reaction includes: spraying a reducing agent into the flue gas upstream of the catalyst, using the catalyst for SCR denitration, the catalyst is obtained by loading V2O5-WO3-MoO3 composite system through a three-stage pore carrier, and the reducing agent is ammonia water. The flue gas temperature after the medium-temperature denitration reaction is 305℃-315℃.

[0044] As an optional embodiment of the present application, since the temperature after denitration is about 310℃, the temperature is too high when directly entering the desulfurization system 7, so cooling treatment is needed. The cooling treatment includes: using the motor air cooler 5 to cool the flue gas after medium-temperature denitration treatment to 170℃-180℃, and then entering the desulfurization system 7 for desulfurization treatment.

[0045] In the above scheme, the motor air cooler 5 cools the flue gas to 170℃-180℃, which is generally considered to be the appropriate inlet temperature range of wet desulfurization, which is conducive to the desulfurization reaction, and at the same time, avoids problems such as too high temperature causing water evaporation in the absorption tower too fast or too low temperature causing slurry freezing, corrosion intensification, etc.

[0046] As an optional embodiment of the present application, a heat pipe type waste heat recovery device 6 connected with the inlet of the preheater is arranged at the rear end of the motor air cooler 5; a secondary air heat exchanger is arranged at the intersection of the flue gas pipeline at the tail of the combustion chamber 3 and the combustion air inlet pipeline.

[0047] The secondary air heat exchanger can adopt a tubular heat exchanger structure. The main body of the heat exchanger consists of hundreds of finned tubes (25mm~50mm in diameter, fins made of stainless steel). The exhaust gas flows inside the tubes, while the combustion air flows laterally across the fins outside the tubes, achieving heat transfer through the metal tube walls. The principle is as follows: The exhaust gas from combustion chamber 3, at approximately 320℃, carries a large amount of sensible heat into the heat exchanger tube bundle. The gas velocity inside the tubes is controlled at 8m / s~12m / s, enhancing heat transfer efficiency through turbulent flow. At ambient temperature (20℃~30℃), the combustion air enters from the outer shell side of the heat exchanger, flowing laterally through the tube bundle along the fin gaps. The air velocity is controlled at 5m / s~8m / s. The finned structure expands the heat transfer area by 3~5 times, ensuring full contact between the air and the tube walls.

[0048] In the above scheme, a heat pipe type waste heat recovery device 6 is added to the rear end of the motor air cooler 5 to transfer the heat of the denitrified flue gas at 310℃ to the cold air at the preheater inlet, raising the cold air temperature from room temperature to 150℃ and reducing the energy consumption of the preheater. At the same time, a secondary air heat exchanger is installed at the tail end of the combustion chamber 3 to use the waste heat of the exhaust gas to heat the combustion air, thereby improving the combustion efficiency.

[0049] As an optional implementation of this application, such as Figure 3 As shown, the processing method of this application uses the following structure: 1) Preheater 1 is used to heat and treat the nitrogen- and sulfur-containing flue gas emitted from the kiln.

[0050] 2) The dust collector 2, which is connected to the outlet of the preheater 1, is used to heat the flue gas entering the denitrification system and to remove a large amount of dust particles contained in the kiln flue gas. The structure is not modified and it is a conventional setting.

[0051] 3) The combustion chamber 3, which is connected to the outlet of the dust collector 2, is used to supplement the combustion and heat up the flue gas after dust removal, and control the flue gas temperature at 280℃~320℃.

[0052] 4) In reactor 4, which is connected to the outlet of combustion chamber 3, nitrogen oxides in flue gas undergo selective catalytic reduction reaction with injected reducing agent under the action of catalyst to generate harmless nitrogen and water.

[0053] 5) The motor air cooler 5, which is connected to the outlet of reactor 4, is used to reduce the flue gas temperature from the suitable temperature of SCR to the suitable temperature of desulfurization system 7 (170℃~180℃) after SCR denitrification and before desulfurization.

[0054] 6) The heat pipe type waste heat recovery device 6 installed at the tail of the motor air cooler 5 is used to preheat the combustion air, making the maximum use of the waste heat of the flue gas after denitrification and improving the overall energy efficiency.

[0055] 7) Desulfurization system 7 connected with the outlet of the heat pipe waste heat recovery device 6, used for removing sulfur dioxide in the flue gas. Generally, an alkaline absorbent (such as limestone slurry, lime slurry, ammonia water, etc.) is used to react with SO2 in the flue gas, so as to transfer SO2 from the gas phase to the liquid phase or solid phase, thereby effectively reducing the concentration of SO2 in the flue gas and making it meet the environmental protection emission standard.

[0056] 8) Chimney 8 connected with the outlet of the desulfurization system 7, used for discharging the kiln tail flue gas which has been subjected to desulfurization and denitrification treatment.

[0057] As an optional embodiment of the present application, as shown in Figure 2 The catalyst is prepared by the following method: S101, introducing 5%-8% ZrO2 into Al2O3-SiO2 composite oxide to form a solid solution.

[0058] S102, adjusting the pore size distribution of the solid solution by a pore forming agent to prepare a carrier with large-mesopore-micropore multi-level channels.

[0059] S103, loading V2O5, WO3 and MoO3 in the carrier by an impregnation method, and calcining at 525-550°C for 1-3h to obtain a carrier loaded with active components.

[0060] S104, coating a 5-10μm thick SiO2-TiO2 composite sol on the surface of the carrier loaded with active components, and calcining at 450-500°C for 1-2h to prepare a modified carrier.

[0061] S105, placing the modified carrier in an NH3 / H2 mixed atmosphere for plasma treatment, and then activating in saturated steam at 280-320°C for 1-3h to obtain a catalyst.

[0062] In the present application, 50% V2O5-WO3-MoO3 active components are first loaded in the large pores and inside of the carrier by an impregnation method, and a "core catalytic layer" is formed after calcination. Then, a SiO2-TiO2 composite coating is coated on the surface of the carrier by a sol-gel method, and a "anti-pollution functional layer" is formed after calcination, so as to realize the gradient structure of "internal catalysis-external anti-pollution". The prepared catalyst is subjected to plasma treatment, -NH2 functional groups are introduced on the surface, NH3 selective adsorption is enhanced, and the probability of generating ammonium bisulfate by reacting with SO2 is reduced. The catalyst is activated in saturated steam at 300°C for 2h, hydroxylation of the surface of the active components is promoted, more catalytically active sites (V-OH) are formed, and the denitration reaction activation energy is improved. In particular, the multi-level channel design can improve the diffusion rate of organic molecules, and the large pore channel can accommodate oil droplets with a particle size >50nm to pass through directly, avoiding aggregation and blockage in the mesopore and micropore.

[0063] In the specific embodiment, the Al2O3 content in the Al2O3-SiO2 composite oxide is 60% to 70%, the macropore, mesopore and micropore diameters are 50 nm to 100 nm, 20 nm to 50 nm and < 2 nm respectively; and the pore-forming agent (preferably polyvinyl alcohol PEG-4000) accounts for 10% to 15% of the mass of the solid solution. The pore-forming agent is used to control the pore size distribution of the solid solution, forming a three-level pore channel system of macropore-mesopore-micropore. The macropore serves as the main passage for flue gas, which can quickly transport gas; the mesopore and micropore increase the specific surface area, providing more active sites for the reaction, shortening the diffusion path of the reactants and the catalyst, and significantly improving the mass transfer efficiency in the denitration reaction, especially suitable for treating high-concentration flue gas. The multi-level pore channel structure makes the catalyst have a more complex pore network, which can effectively disperse and accommodate particulate matter, ammonium bisulfate and organic matter and other impurities in the flue gas, reducing their accumulation and blockage on the surface of the catalyst. Even if part of the pore channels are blocked, other pore channels can still maintain the reaction, ensuring the long-term stable operation of the catalyst under complex flue gas conditions. In this scheme, controlling the ratio of Al2O3 to SiO2 can balance the specific surface area, mechanical strength, thermal stability and surface acidity of the carrier, making it more suitable as a carrier for SCR catalysts.

[0064] Preferably, the number of macropores accounts for 30%, the number of mesopores accounts for 45%, and the number of micropores accounts for 25%.

[0065] In the specific embodiment, the mass ratio of SiO2 to TiO2 in the SiO2-TiO2 composite sol is 3:1. After calcination, a hydrophobic interface is formed, and the hydrophobicity of the SiO2-TiO2 coating on the surface makes the contact angle of the ammonium bisulfate droplets > 110°, which is difficult to spread into a film and exists only in the form of isolated particles, which falls off with the flue gas flow, inhibiting the spreading and condensation of ammonium bisulfate droplets. Moreover, the activity temperature window of the modified carrier is lowered to 280°C to 350°C, which is higher than the condensation temperature of ammonium bisulfate (190°C to 230°C), which inhibits its formation from a thermodynamic point of view. After the formation of the modified layer on the surface of the carrier, it can effectively block the erosion of SO2 and H2O in the flue gas to the active component, reduce the deposition of sulfates on the surface of the catalyst, improve the sulfur and water resistance of the catalyst, and prolong the service life.

[0066] In the embodiment, the loadings of V2O5, WO3 and MoO3 in the carrier loaded with the active ingredient are 6wt%-8wt%, 10wt%-12wt% and 3wt%-5wt% respectively. WO3 and MoO3 form a solid solution, which can expand the monolayer dispersity of V2O5 and increase the number of active sites per unit area. The introduced MoO3 helps to improve the activity and sulfur resistance of the catalyst under certain conditions. V2O5, as the main active component, has high catalytic capacity for the reduction reaction of NOx under medium temperature conditions; WO3 and MoO3, as the cocatalyst, can improve the thermal stability, sulfur resistance and activity temperature window of the catalyst. The composite system formed by the three can enhance the adsorption and activation capacity of the reducing agent (ammonia water) through synergistic effect, improve the reaction rate of NOx and the reducing agent, and thus improve the denitration efficiency. At the same time, the addition of WO3 and MoO3 can inhibit the sintering and deactivation of V2O5 at high temperature, and at the same time make the catalyst maintain good catalytic activity in the medium temperature range, thus meeting the temperature requirements of the medium temperature denitration reaction in the application and avoiding the problem of ammonium bisulfate condensation at low temperature.

[0067] In the embodiment, the power of the plasma treatment is 100W-150W, and the time is 15min-20min. The plasma treatment in the NH3 / H2 mixed atmosphere can introduce more active groups (such as amino, hydroxyl, etc.) on the surface of the catalyst, increase the surface adsorption sites; the saturated steam activation treatment further optimizes the surface pore structure and acid site distribution, enhances the adsorption capacity of NH3 and the catalytic reduction activity of NOx, and makes the catalyst exert the best performance under medium temperature conditions.

[0068] In summary, the treatment method of the application has at least the following advantages: 1. Temperature gradient synergy: from preheating (280℃-320℃) → dust collector 2 outlet (200℃-240℃) → SCR reaction (280℃-320℃, after reaction 305℃-315℃) → cooling (170℃-180℃), the accurately designed temperature curve is the key to solving the problem of the application. High-temperature preheating and SCR reaction ensure the efficient work of the catalyst and the inhibition of organic matter, and the cooling after SCR ensures the appropriate temperature for subsequent desulfurization. The flue gas of the kiln is heated to 280℃-320℃ by the preheater, the flue gas temperature at the outlet of the dust collector 2 is controlled at 200℃-240℃, and the flue gas temperature downstream of the combustion chamber 3 in the denitration system is maintained at 280℃-320℃, so that the flue gas temperature is higher than the dew point temperature of ammonium bisulfate (about 147℃), effectively preventing its condensation on the surface of the catalyst, and solving the problem of reduced denitration efficiency caused by ammonium bisulfate condensation in the prior art. Under high-temperature conditions, the organic matter and oil in the flue gas are in a gaseous or liquid state and are not easy to condense on the filter bag and the catalyst surface, reducing the risk of filter bag blockage and catalyst deactivation, and reducing the possibility of fire in the equipment and flue.

[0069] 2. Synergy between the dust collector 2 and the denitration system: The dust collector 2 not only removes particulate matters, but also plays a pretreatment role due to the nanofiber filter bag and the loaded V2O5 / TiO2 catalyst. The increase of the outlet temperature of the dust collector 2 (200℃~240℃) not only avoids the condensation and plugging of organic matters in the dust collector 2 itself, but also provides a relatively stable inlet temperature basis for the subsequent SCR. At the same time, the combustion chamber 3 in the denitration system further heats to the optimal SCR temperature.

[0070] 3. Synergy between the catalyst design and the process flow: The excellent performance of the catalyst (multi-level pores, specific active components, surface modification) is the basis for solving the plugging of ammonium bisulfate and organic matters. The optimized process flow provides the best external conditions for the catalyst to exert its high performance, and makes up for the possible deficiencies of the catalyst (such as dealing with partial plugging by online ash removal).

[0071] 4. The whole treatment process not only focuses on the removal of pollutants (material flow), but also highly focuses on the generation and consumption of energy (energy flow). Through waste heat recovery and secondary air heat exchange, the recycling of energy within the system is realized, the overall energy consumption is reduced, and the synergy of material flow and energy flow optimization is embodied.

[0072] The above technical solutions of the present application will be described in detail below in combination with specific embodiments.

[0073] Embodiment 1 The embodiment provides a preparation method of a catalyst in a kiln exhaust gas treatment method based on SCR denitration, comprising the following steps: (1) Al2O3-SiO2 composite oxide (Al2O3 content is 60wt%) is used to introduce 5% ZrO2 to form a solid solution.

[0074] (2) The pore size distribution of the solid solution (the mass ratio of the pore-forming agent to the solid solution is 1:10) is regulated by polyvinyl alcohol to prepare a carrier with multi-level pores of large pores, mesopores and micropores. Among them, the number of large pores (50nm~100nm) accounts for 30%, the number of mesopores (20nm~50nm) accounts for 45%, and the number of micropores (<2nm) accounts for 25%.

[0075] (3) V2O5, WO3 and MoO3 are mixed uniformly by a coprecipitation method to obtain a mixture, and then the mixture is loaded in the carrier by an impregnation method, and the carrier loaded with active components is obtained after being calcined at 550℃ for 3h. Among them, the loading amount of V2O5, WO3 and MoO3 in the carrier is 8%, 12% and 5% respectively.

[0076] (4) The surface of the carrier loaded with the active ingredient is coated with 5 μm thick SiO2-TiO2 (mass ratio of SiO2 to TiO2 is 3:1) composite sol, and the modified carrier is prepared by calcining at 500°C for 1 h.

[0077] (5) The modified carrier is placed in an NH3 / H2 (10:1) mixed gas atmosphere for plasma treatment (150 W, 20 min), and then activated in saturated steam at 300°C for 2 h to obtain the carrier.

[0078] Example 2 The embodiment provides a preparation method of a catalyst in a kiln waste gas treatment method based on SCR denitration, and the method comprises the following steps: (1) An Al2O3-SiO2 composite oxide (Al2O3 content is 60 wt%) is used to introduce 6% ZrO2 to form a solid solution.

[0079] (2) A carrier with large pore-mesopore-micropore multi-level pores is prepared by adjusting the pore size distribution of the solid solution (mass ratio of pore forming agent to solid solution is 1:10). The number of large pores (50 nm-100 nm) accounts for 30%, the number of mesopores (20 nm-50 nm) accounts for 45%, and the number of micropores (<2 nm) accounts for 25%.

[0080] (3) V2O5, WO3 and MoO3 are uniformly mixed by a coprecipitation method to obtain a mixture, and the mixture is loaded in the carrier by an impregnation method, and a carrier loaded with active ingredients is obtained by calcining at 530°C for 3 h. The loadings of V2O5, WO3 and MoO3 in the carrier are 7%, 10% and 3% respectively.

[0081] (4) The surface of the carrier loaded with the active ingredient is coated with 5 μm thick SiO2-TiO2 (mass ratio of SiO2 to TiO2 is 3:1) composite sol, and the modified carrier is prepared by calcining at 480°C for 1 h.

[0082] (5) The modified carrier is placed in an NH3 / H2 (10:1) mixed gas atmosphere for plasma treatment (120 W, 20 min), and then activated in saturated steam at 280°C for 3 h to obtain the carrier.

[0083] Example 3 The embodiment provides a preparation method of a catalyst in a kiln waste gas treatment method based on SCR denitration, and the method comprises the following steps: (1) An Al2O3-SiO2 composite oxide (Al2O3 content is 60 wt%) is used to introduce 8% ZrO2 to form a solid solution.

[0084] (2) The pore size distribution of the solid solution (mass ratio of pore-forming agent to solid solution is 1:10) is regulated by the pore-forming agent, and a carrier with large-mesopore-micropore multi-level channels is prepared. Among them, the number of large pores (50nm-100nm) accounts for 30%, the number of mesopores (20nm-50nm) accounts for 45%, and the number of micropores (<2nm) accounts for 25%.

[0085] (3) The V2O5, WO3 and MoO3 are mixed uniformly by the coprecipitation method to obtain a mixture, and then the mixture is loaded into the carrier by the impregnation method. After being calcined at 550°C for 3h, a carrier loaded with active ingredients is obtained. Among them, the loading amounts of V2O5, WO3 and MoO3 in the carrier are 8%, 10% and 3% respectively.

[0086] (4) A 5μm thick SiO2-TiO2 (mass ratio of SiO2 to TiO2 is 3:1) composite sol is coated on the surface of the carrier loaded with active ingredients, and then the carrier is calcined at 500°C for 1h to obtain a modified carrier.

[0087] (5) The modified carrier is placed in an NH3 / H2 (10:1) mixed gas atmosphere for plasma treatment (150W, 15min), and then activated in saturated steam at 320°C for 1h to obtain a carrier.

[0088] Example 4 The present embodiment provides a device for treating kiln exhaust gas, as shown in Figure 3 The device comprises, in sequence, a preheater 1, a dust collector 2, a combustion chamber 3, a reactor 4, a motor air cooler 5, a heat pipe type waste heat recovery device 6, a desulfurization system 7 and a chimney 8.

[0089] The filter bag of the dust collector 2 is of nanofiber structure, and a 5μm thick V2O5 / TiO2 surface catalyst coating is coated on the filter bag by coating method. The mass of V2O5 accounts for 8% of the mass of the filter bag surface coating, and the mass of TiO2 accounts for 92% of the mass of the filter bag surface coating. The fiber diameter of the filter bag is 100nm, the thickness of the filter bag is 50μm, and the filter bag is polyacrylonitrile nanofiber.

[0090] The reducing agent is sprayed into the downstream flue of the combustion chamber 3, and the catalyst is fixed in the reactor 4. The reducing agent is ammonia water.

[0091] The inlet of the reactor 4 is provided with a mechanical vibration device and a hot gas purging device. The mechanical vibration device adopts a cast steel hammer head (weight 2 kg), which is fixed on the top beam of the reactor 4 through a spring connecting rod (diameter 10 mm spring steel), and is arranged every 500 mm above the catalyst layer, a total of 3 groups. An electric push rod (thrust 500 N) with a stroke of 50 mm is selected, which is connected with the hammer through a connecting rod, and the push rod motor power is 0.75 kW, which can drive the hammer to knock the outer wall of the reactor 4 at a frequency of 3 times per second. The hot gas purging device includes 1) an electric heating air box made of stainless steel (size 800 mm x 600 mm x 400 mm), which is provided with finned electric heating pipes (total power 10 kW) and a supporting centrifugal fan (air volume 300 m 3 / h), and the outlet temperature can be adjusted to 250℃~300℃.

[0092] 2) A strip-shaped purging pipe made of Φ32 mm stainless steel pipe is arranged along the width direction of the reactor 4, and a Φ8 mm long strip-shaped hole (hole length 50 mm, interval 100 mm) is opened at the bottom of the pipe, which is installed at 800 mm above the catalyst layer, and the purging direction is opposite to the flue gas flow direction.

[0093] 3) A support structure, the vibration hammer support is welded with ∠50x5 angle steel and fixed on the top flange of the reactor 4; the hot air box is installed on the column beside the reactor 4 through expansion bolts, and the purging pipe is fixed on the inner wall of the reactor 4 through a U-shaped clamp. The time relay is set to automatically start the dust removal program every 4 h; the electric push rod operates at a frequency of 2 times per second for 1 min to mechanically vibrate the surface of the catalyst; after the vibration stops, the hot air system starts and continues to blow for 5 min, and the hot air temperature is maintained at 280±10℃; after completion, it is automatically stopped and waits for the next cycle.

[0094] The intersection of the exhaust gas pipeline at the tail of the combustion chamber 3 and the combustion air inlet pipeline is provided with a secondary air heat exchanger.

[0095] Example 5 The present embodiment provides a kiln waste gas treatment method based on SCR denitration, which uses the catalyst prepared in examples 1-3 and the device of example 4, including the following steps: (1) The kiln flue gas is heated to 300℃ by the preheater and then enters the dust collector 2 to remove particulate matter dust in the flue gas.

[0096] (2) The outlet flue gas temperature of the dust collector 2 is increased to 220℃, and then enters the combustion chamber 3 to mix with combustion air and perform supplementary combustion to increase the temperature.

[0097] (3) After passing through the combustion chamber 3, the flue gas temperature is controlled at about 300°C, and then mixed with ammonia gas (the volume ratio of ammonia gas to nitrogen oxides is 1:1) to enter the reactor 4 for medium-temperature denitration treatment. The ammonia gas is obtained by atomizing ammonia water sprayed by an ammonia water spraying gun under the action of compressed air.

[0098] (4) After denitration, the flue gas temperature is 310°C, and then cooled by the motor air cooler 5 to about 175°C, and then discharged into the desulfurization system 7 by the denitration exhaust fan. The wet desulfurization desulfurizer used in the desulfurization system 7 is 10wt% ammonia water.

[0099] (5) After desulfurization, the NOx emission concentration and the dust emission amount of the flue gas in the chimney 8 are detected, and discharged after reaching the standard.

[0100] Taking the catalyst prepared in Example 1 as an example, it is used in the treatment method of Example 5 to perform denitration and desulfurization treatment on the kiln tail flue gas, and the results are shown in Table 1. Among them, before the transformation, that is, after the treatment by the traditional kiln waste gas treatment process.

[0101] Table 1

[0102] Although the specific embodiments of the present application are described in detail, it should not be understood as limiting the scope of protection of the present application. Various modifications and variations made by those skilled in the art within the scope described in the claims are still within the scope of protection of the present application.

Claims

1. A method for treating kiln exhaust gas based on SCR denitrification, characterized in that, Includes the following steps: The kiln flue gas is preheated in a preheater and then introduced into a dust collector. Increase the outlet flue gas temperature of the dust collector to 200℃~240℃ and introduce it into the denitrification system; The nitrogen oxides undergo a medium-temperature denitrification reaction in the denitrification system, and after cooling, they enter the desulfurization system for desulfurization treatment; among which, The intermediate-temperature denitrification reaction includes: injecting a reducing agent into the flue gas upstream of the catalyst, and using the catalyst for SCR denitrification. The catalyst is obtained by loading a V2O5-WO3-MoO3 composite system through a three-stage porous support, and the reducing agent is ammonia water.

2. The method according to claim 1, characterized in that, The filter bag of the dust collector has a nanofiber structure, and a V2O5 / TiO2 surface catalyst is embedded on the filter bag.

3. The method according to claim 1, characterized in that, The denitrification system includes a combustion chamber and a reactor connected in sequence. The upstream flue of the combustion chamber is connected to the dust collector, and the flue gas temperature in the downstream flue of the combustion chamber is 280℃~320℃. The reducing agent is injected into the downstream flue of the combustion chamber, and the catalyst is fixed inside the reactor.

4. The method according to claim 3, characterized in that, The reactor inlet is equipped with a mechanical vibration device and a hot gas purging device. The mechanical vibration device is used to vibrate and remove dust from the surface of the catalyst, and the hot gas purging device decomposes residual ammonium bisulfate by heating air and spraying it onto the surface of the catalyst.

5. The method according to claim 1, characterized in that, The catalyst was prepared by the following method: Al2O3-SiO2 composite oxide is introduced into 5wt%~8wt% ZrO2 to form a solid solution; By controlling the pore size distribution of the solid solution with a pore-forming agent, a carrier with a multi-level pore structure of macropores, mesopores, and micropores is prepared. V2O5, WO3 and MoO3 were loaded into the support by impregnation and then calcined at 525℃~550℃ to obtain the support loaded with active ingredients. A 5μm~10μm thick SiO2-TiO2 composite sol was coated on the surface of the carrier loaded with the active ingredient, and then calcined at 450℃~500℃ to obtain the modified carrier. The modified support was subjected to plasma treatment in an NH3 / H2 mixed atmosphere, and then activated in saturated steam at 280℃~320℃ for 1h~3h to obtain the product.

6. The method according to claim 5, characterized in that, The Al2O3-SiO2 composite oxide contains 60wt%~70wt% Al2O3, and the macropore, mesopore and micropore diameters are 50nm~100nm, 20nm~50nm and <2nm, respectively; the pore-forming agent accounts for 10%~15% of the mass of the solid solution.

7. The method according to claim 5, characterized in that, In the carrier loaded with the active ingredients, the loading amounts of V2O5, WO3, and MoO3 are 6wt%~8wt%, 10wt%~12wt%, and 3wt%~5wt%, respectively. The plasma treatment power is 100W~150W, and the time is 15min~20min.

8. The method according to claim 1, characterized in that, The temperature after the heating treatment is 280℃~320℃, and the flue gas temperature after the medium-temperature denitrification reaction is 305℃~315℃.

9. The method according to claim 1, characterized in that, The cooling process includes: using a motor-cooled air cooler to cool the flue gas after medium-temperature denitrification to 170℃~180℃ before it enters the desulfurization system for desulfurization.

10. The method according to claim 9, characterized in that, The rear end of the motor air cooler is equipped with a heat pipe type waste heat recovery device connected to the inlet of the preheater. A secondary air heat exchanger is installed at the intersection of the exhaust pipe at the rear of the combustion chamber and the combustion air inlet pipe.

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