Treatment method and treatment device for VOCs-containing waste gas

Abstract

The invention relates to a treatment method and a treatment device for VOCs-containing waste gas, the VOCs-containing waste gas is heated and then enters a catalytic oxidation reactor, the reactor takes a fluidized bed as a main body and is filled with a particle catalytic oxidation catalyst, and the waste gas and the particle catalyst are subjected to a fluidized oxidation reaction; a cylindrical fixed bed is radially arranged in the fluidized bed and filled with a regular catalytic oxidation catalyst, and the lower end of the fixed bed penetrates through the bottom of the reactor and is gathered at an exhaust pipe; a gas-solid separator is arranged at the upper part of the fluidized bed, fluidized and oxidized waste gas passes through the gas-solid separator, catalyst particles carried by the waste gas are intercepted, separated gas enters from the top of the fixed bed and is continuously oxidized, and high-temperature purified gas is exhausted through an exhaust pipe. According to the method and the device, the reaction temperature of catalytic oxidation is effectively homogenized, high-temperature hot spots of a catalyst bed layer and influences on the service life of the catalyst are avoided, and meanwhile deep treatment of waste gas and effective utilization of heat are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste gas treatment, and specifically relates to a treatment method and a treatment device for waste gas containing VOCs. Background Art

[0002] Volatile organic compounds (VOCs) are characteristic pollutants in oil refining and petrochemical enterprises. During the production process, VOCs mainly come from process exhaust, leakage of equipment and pipeline components, storage and transportation of volatile organic liquids, and atmospheric pollutant emissions from wastewater collection, treatment and storage facilities. They can be divided into organized emission sources and unorganized emission sources, and usually unorganized emissions account for a larger proportion.

[0003] The treatment technologies for VOCs-containing waste gas are roughly divided into recovery method, destruction method and direct utilization method. The recovery method is to use absorbent absorption, adsorbent adsorption or condensation method to recover most of the organic components in the waste gas, but the total hydrocarbon content of organic waste gas treated by such methods is still high and cannot be directly discharged in compliance with the standards. Therefore, it is also necessary to use the destruction method to treat it, that is, to use catalytic oxidation, high-temperature oxidation and other methods for deep treatment.

[0004] Among them, the fixed bed catalytic oxidation is to fill the catalyst in the fixed bed reactor, and the organic waste gas passes through the catalyst bed for catalytic oxidation reaction, releasing a large amount of heat to increase the reaction temperature step by step. Often, the temperature at the end of the catalyst bed has reached the maximum temperature allowed by the catalyst. The catalyst reacts at this temperature for a long time, resulting in a shortened catalyst life. Moreover, with the increasingly stringent environmental protection requirements, in order to meet emission requirements, the reaction temperature of the catalytic oxidation method will be increased, increasing the risk of catalyst deactivation due to temperature rise, thereby further shortening the catalyst life. At the same time, the existing VOCs catalytic oxidation reaction process is that the high-temperature exhaust gas discharged from the catalytic oxidation reactor is exchanged with the normal-temperature VOCs exhaust gas entering through a heat exchanger. Due to the increase in the exhaust gas temperature at the outlet of the catalytic oxidation reactor, the requirements for the heat exchanger are further increased. Under the condition of being made of ordinary stainless steel, the existing heat exchangers such as heat pipe type, shell and tube type, plate type heat exchanger, etc. have relatively low heat exchange efficiency. Due to the increase in heat exchange, to achieve the expected heat exchange effect, the heat exchange area needs to be further increased, which increases the investment in the heat exchanger.

[0005] CN207025073U discloses an energy-saving and highly adaptable catalytic oxidation waste gas treatment device, including a heat exchanger, a heater, a catalytic oxidation reactor, an air cooler, a reflux air system, and a heat exchanger bypass system. The reflux air system includes a reflux air device and a control component, wherein the heat exchanger cold flow outlet is connected to the heater inlet, the heater outlet is connected to the catalytic oxidation reactor inlet, and the catalytic oxidation reactor outlet is divided into two paths, one is connected to the heat exchanger hot flow inlet, and the other is connected to the reflux air device inlet; the heat exchanger hot flow outlet is connected to the air cooler inlet, and the air cooler outlet is divided into two paths, one is connected to the exhaust pipe, and the other is connected to the reflux air device inlet, and the reflux air device outlet is connected to the heater waste gas inlet; the heat exchanger bypass system connects the heat exchanger hot flow inlet and outlet. This patent can efficiently and energy-savingly treat intermittently discharged waste gas with large fluctuations in organic matter concentration, and realize safe and stable operation of the waste gas treatment device. However, this method adopts fixed bed treatment. With the increasingly stringent environmental protection requirements, the reaction temperature needs to be further increased to meet the emission requirements. There is a risk of catalyst deactivation due to temperature rise, which will shorten the service life of the catalyst.

[0006] CN110296424A discloses an anti-scaling fluidized bed thermal storage oxidation device and a thermal oxidation method for VOCs gas, wherein the anti-scaling fluidized bed thermal storage oxidation device comprises a scrubber 1, a burner 2, a fluidized thermal storage bed 11, a cyclone separator 6 and an exhaust gas treatment device 7; the outlet of the scrubber 1 and the outlet of the burner 2 are respectively connected to the inlet of the fluidized thermal storage bed 11; the outlet of the fluidized thermal storage bed 11 is connected to the inlet of the cyclone separator 6; the outlet of the cyclone separator 6 is connected to the inlet of the exhaust gas treatment device 7; and a spherical thermal storage body layer 8 is provided inside the fluidized thermal storage bed 11. The invention provides a spherical thermal storage body layer inside the fluidized thermal storage bed, and when hot air passes through, the thermal storage body flows to generate friction, and the scale is removed and enters the cyclone separator with the wind, thereby effectively solving the problem of thermal storage body scaling and blockage, and greatly reducing the operation and maintenance costs. However, the temperature of the oxidation combustion reaction is preferably 600-1200°C, and more preferably 800°C. The reaction temperature is relatively high and the operating cost is relatively high. Summary of the invention

[0007] In view of the shortcomings of the prior art, the present invention provides a method and device for treating waste gas containing VOCs. The method and device of the present invention effectively homogenize the reaction temperature of catalytic oxidation, avoid high temperature hot spots in the catalyst bed and the impact on the life of the catalyst, and realize the deep treatment of waste gas and the effective use of heat.

[0008] The present invention provides a method for treating waste gas containing VOCs, comprising the following contents:

[0009] After the temperature of VOCs-containing waste gas is raised, it enters the catalytic oxidation reactor. The reactor is mainly composed of a fluidized bed and is loaded with granular catalytic oxidation catalyst. The waste gas and the catalyst particles undergo fluidized oxidation reaction. Several tubular fixed beds are radially arranged in the fluidized bed and are loaded with regular catalytic oxidation catalyst. The lower end of the tubular fixed bed penetrates the bottom of the reactor and is collected in an exhaust pipe. Several gas-solid separators are arranged on the upper part of the fluidized bed. After fluidized oxidation, the waste gas passes through the gas-solid separator, and the catalyst particles carried are intercepted. After separation, the gas enters from the top of the fixed bed and continues to oxidize, and the high-temperature purified gas is discharged through the exhaust pipe.

[0010] In the present invention, the temperature of the VOCs-containing waste gas is generally 100-500°C, preferably 250-400°C, when the temperature is raised to the starting temperature required for the catalytic oxidation reaction. A heat exchanger or / and a heater are used for heating. Preferably, the high-temperature purified gas discharged from the fixed bed is used as the heat source of the heat exchanger. If the temperature after heat exchange cannot reach the starting temperature required for the catalytic oxidation reaction, the heater is used for heating. In principle, the heater is only used when the device is started. When the entire reaction system reaches thermal balance, the heater can no longer be started. The heat exchanger can be any one of a heat pipe type, a shell and tube type, a plate heat exchanger, etc., preferably a plate heat exchanger. The heater can be any one of an electric heater, a gas heater, a fuel heater, etc., preferably an electric heater.

[0011] In the present invention, the catalytic oxidation reactor can be in various reactor forms such as column type and tower type, and the reactor diameter should be selected so that the flow rate in the fluidized bed is 0.2-2 m / s, preferably 0.8-1.4 m / s. An air inlet is provided at the bottom of the reactor, and the VOCs-containing waste gas is heated to the starting temperature and then transported to the fluidized bed through the air inlet, and the particle catalyst is fluidized by adjusting the pressure.

[0012] In the present invention, the particle catalytic oxidation catalyst loaded in the fluidized bed is a conventional catalyst, and the particle diameter is 0.6-10 mm, preferably 0.8-3.0 mm; the amount of catalyst is such that the reaction volume space velocity is 500-50000h -1 The particle catalytic oxidation catalyst is preferably a catalyst with particle-shaped alumina or molecular sieve as a carrier and loaded with precious metal Pt and / or Pd, and the loading amount of the precious metal is 0.01%-0.15%.

[0013] In the present invention, at least one cylindrical fixed bed is radially arranged in the fluidized bed, preferably 1-20. The cross-sectional area ratio of the fluidized bed to the fixed bed is 3-10:1, and it is best to be symmetrically distributed on the cross section of the fluidized bed. The cross section of the fixed bed can be in a variety of shapes, such as any one of circular, elliptical, rectangular, triangular, etc. Further, the outer surface of the preferred fixed bed is in the form of fins or threads, and the wall material can be any one of stainless steel, ceramic, etc.

[0014] In the present invention, the structured catalytic oxidation catalyst loaded in the fixed bed is a monolithic or random type, such as a monolithic honeycomb ceramic or other random type catalyst, and the amount of catalyst is such that the reaction volume space velocity is 500-50000h -1 The structured catalytic oxidation catalyst preferably uses a honeycomb carrier catalyst loaded with precious metals Pt and / or Pd, and the loading amount of the precious metals Pt and / or Pd is 0.01%-0.15% based on the mass of the honeycomb carrier.

[0015] In the present invention, the reaction temperature of fluidized oxidation is maintained at 300-550° C., preferably 400-500° C., by regulating the heater and the exhaust gas concentration entering the fluidized bed. The gas separated by the gas-solid separator directly enters the fixed bed, and the outlet temperature of the fixed bed is 1-100° C. higher than the inlet temperature, preferably not higher than 650° C.

[0016] In the present invention, the lower end of each fixed bed penetrates the bottom of the reactor and is collected in an exhaust pipe. The high-temperature purified gas after deep oxidation in the fixed bed is discharged through the exhaust pipe and transported to the heat exchanger for heat exchange with the VOCs waste gas to be treated. After the heat exchange, the purified gas is discharged out of the device. The temperature of the discharged purified gas is generally 90-300°C, preferably 120-180°C.

[0017] In the present invention, the gas-solid separator is arranged on the upper part of the fluidized bed, and the outlet is connected to the inlet of the fixed bed, which is used to intercept the catalyst particles carried in the exhaust gas discharged from the fluidized bed, and the gas enters the fixed bed after separation. The gas-solid separator is mainly composed of a filter component, which can be any structure of various forms such as hole type, cylinder type, bag type, etc. The material can be selected from any one of glass fiber, metal sintered mesh, ceramic membrane, etc. The filter hole diameter is larger than the diameter of the particulate catalytic oxidation catalyst, generally 5-100μm. The total cross-sectional area of ​​the gas-solid separator is 1-4 times the total cross-sectional area of ​​the fixed bed, and the number is generally 8-20, preferably symmetrically distributed. A back-purge component is correspondingly arranged on the upper part of each gas-solid separator, and the purge medium can be at least one of air, N2 and other gases.

[0018] In the present invention, the total hydrocarbon concentration in the VOCs-containing waste gas is generally 2000-12000 mg / m 3 , preferably 4000-8000mg / m 3 When the total hydrocarbon concentration is high, pretreatment or introduction of diluent gas is required to reduce the concentration to a specified value. The diluent gas can be any one of air, nitrogen, inert gas, etc.

[0019] The present invention also provides a treatment device for the above-mentioned VOCs-containing waste gas treatment method, which includes a heat exchanger, a heater and a catalytic oxidation reactor in sequence according to the flow direction of the waste gas, and the heat exchanger and / or the heater are used to heat the VOCs-containing waste gas to the starting temperature required for the catalytic oxidation reaction; the catalytic oxidation reactor is mainly composed of a fluidized bed, which is loaded with a granular catalytic oxidation catalyst and is used for fluidized oxidation reaction of the waste gas and the catalyst particles; a plurality of cylindrical fixed beds are radially arranged in the fluidized bed, which are loaded with a regular catalytic oxidation catalyst, and the reaction heat of the fluidized oxidation is transferred to the catalyst in the bed through the wall of the fixed bed; a plurality of gas-solid separators are arranged on the upper part of the fluidized bed, and the waste gas after fluidized oxidation passes through the gas-solid separator, and the catalyst particles carried are intercepted, and the gas enters the fixed bed for further oxidation, and the high-temperature purified gas is discharged through the exhaust pipe at the bottom of the fixed bed.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The catalytic oxidation reactor of the present invention is mainly a fluidized bed and is provided with a plurality of cylindrical fixed beds. After fluidized oxidation, the exhaust gas enters the fixed bed for oxidation, so that the two are connected in series in time and heat transfer is achieved in space, thereby effectively homogenizing the reaction temperature of the entire catalytic oxidation, avoiding the occurrence of high-temperature hot spots of the catalyst and overheating at the end of the fixed bed, ensuring the reaction activity and service life of the catalyst, and realizing deep oxidation of the exhaust gas and effective utilization of heat.

[0022] (2) A fluidized bed-fixed bed two-stage catalytic oxidation reaction module is designed in one reactor. Through heat transfer and temperature control, the temperature difference between the inlet and outlet of the fixed bed is reduced to less than 100°C, thereby reducing the exhaust temperature of the fixed bed and further reducing the heat exchange area and investment cost of the heat exchanger.

[0023] (3) By setting a gas-solid separator between the upper part of the fluidized bed and the inlet of the fixed bed, the quality and concentration of the exhaust gas flow can be regulated, so that the temperature and solid content of the exhaust gas flow are beneficial to the regulation of the fixed bed, thereby achieving deep oxidation of the exhaust gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a process flow diagram of the method and device of the present invention;

[0025] Among them: 1-heat exchanger, 2-heater, 3-catalytic oxidation reactor, 4-gas-solid separator, 5-fixed bed, 6-exhaust pipe, 7-backflush assembly, 8-particulate catalytic oxidation catalyst, 9-regular catalytic oxidation catalyst; 101-waste gas containing VOCs, 102-backflush gas, 103-high-temperature purified gas, 104-emission purified gas.

[0026] Figure 2 It is a top view of the distribution of the fixed bed and the gas-solid separator in the present invention. DETAILED DESCRIPTION

[0027] The technical solution of the present invention and its effects are further illustrated by the following examples. The examples are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following examples.

[0028] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, can all be purchased from biochemical reagent stores.

[0029] The VOCs-containing waste gas treatment device of the present invention is as follows Figure 1 As shown, according to the exhaust gas flow direction, a heat exchanger 1, a heater 2 and a catalytic oxidation reactor 3 are included in sequence. The heat exchanger 1 or / and the heater 2 are used to heat the VOCs-containing exhaust gas 101 to be treated to the starting temperature required for the catalytic oxidation reaction and then enter the catalytic oxidation reactor 3. The catalytic oxidation reactor 3 is mainly composed of a fluidized bed, which is filled with a granular catalytic oxidation catalyst 8, and the exhaust gas and the catalyst particles undergo a fluidized oxidation reaction; a plurality of cylindrical fixed beds 5 are radially arranged in the fluidized bed, and a regular catalytic oxidation catalyst 9 is filled in the fixed bed, and the reaction heat of the fluidized oxidation is transferred to the catalyst 9 in the bed through the fixed bed wall; the lower end of each fixed bed penetrates the bottom of the reactor and converges into an exhaust pipe 6; a plurality of gas-solid separators 4 are arranged on the upper part of the fluidized bed, and the outlet of the gas-solid separator is connected to the inlet of the fixed bed. After fluidized oxidation, the exhaust gas passes through the gas-solid separator 4, and the catalyst particles carried are intercepted. After separation, the gas enters the fixed bed for further oxidation, and the high-temperature purified gas is discharged through the exhaust pipe 6. A backflush component 7 is correspondingly arranged on the upper part of each gas-solid separator 4, and the purge medium can be air, N2 and other gases.

[0030] In the embodiment of the present invention, the particle catalytic oxidation catalyst is a granular alumina carrier, loaded with precious metals Pt and Pd, the loading amount is 0.04% respectively, and the particle diameter is 0.8-3.0mm. The amount of catalyst used is to make the reaction volume space velocity between 500-50000h -1 .

[0031] In the embodiment of the present invention, the fixed bed is filled with a honeycomb ceramic catalyst loaded with precious metals Pt and Pd, and a cordierite honeycomb carrier is used. The loading amount of precious metals Pt and Pd is 0.04% respectively based on the mass of the honeycomb carrier. The amount of catalyst used is to make the volume space velocity between 500-50000h -1 . A loading grid for fixing the catalyst is arranged at the upper and lower ends of the fixed bed.

[0032] Example 1

[0033] Use attached Figure 1The VOCs-containing waste gas treatment device shown in the figure has a cylindrical catalytic oxidation reactor with a diameter of 2.8m. Five symmetrically distributed cylindrical fixed beds are arranged in the fluidized bed. The material is stainless steel, and the cross-sectional area ratio of the fluidized bed to the fixed bed is 5:1. Twelve symmetrically distributed gas-solid separators are arranged on the upper part of the fluidized bed. The gas-solid separator adopts a circular hole structure, and the material is a metal sintered mesh. The filter hole diameter is 50μm, and its cross-sectional size is the same as that of the fixed bed. It is used to intercept the particulate catalyst carried in the waste gas discharged from the fluidized bed. After separation, the gas enters the fixed bed for further oxidation. A backflush component is arranged on the upper part of each gas-solid separator, and the purge medium is N2.

[0034] The concentration of non-methane total hydrocarbons in the VOCs waste gas to be treated is 5000 mg / m 3 about.

[0035] The VOCs-containing waste gas is heated to 300°C after passing through a heat exchanger or / and a heater. The heat exchanger uses the high-temperature purified gas discharged from the fixed bed for heat exchange. When the temperature after heat exchange cannot reach the required starting reaction temperature, it is heated by the heater. When the entire reaction system reaches heat balance, the heater is no longer started. The heat exchanger uses a plate heat exchanger and the heater uses an electric heater.

[0036] The exhaust gas is transported to the fluidized bed through the air inlet at the bottom of the fluidized bed. The fluidized bed is filled with granular catalytic oxidation catalyst with a particle diameter of about 0.8 mm. The amount of catalyst used is to make the reaction volume space velocity at 10,000 h -1 , and adjust the pressure to achieve fluidization of the particle catalyst. The reaction temperature of the fluidized catalytic oxidation is maintained at 400°C by adjusting the exhaust gas concentration. The fixed bed inlet temperature is kept consistent with the gas-solid separator outlet temperature, and the amount of catalyst used in the fixed bed is such that the reaction volume space velocity is 5000h -1 The temperature of the high-temperature purified gas discharged from the fixed bed is 500°C, and it is discharged after heat exchange with the room-temperature VOCs waste gas entering the catalytic oxidation reactor in the heat exchanger, and the exhaust gas temperature is 170°C.

[0037] After 1000 hours of operation, the concentration of non-methane total hydrocarbons in the discharged purified gas is always lower than 100 mg / m 3 During long-term operation, no catalyst hot spots or fixed bed reaction overheating occurred, and the catalyst service life was 131% of the original design life. Moreover, due to the full utilization of heat, energy consumption can be saved by more than 24%.

[0038] Example 2

[0039] Use attached Figure 1The VOCs-containing waste gas treatment device shown in the figure has a cylindrical catalytic oxidation reactor with a diameter of 2.8m. Five symmetrically distributed cylindrical fixed beds are arranged in the fluidized bed. The material is stainless steel, and the cross-sectional area ratio of the fluidized bed to the fixed bed is 5:1. Twelve symmetrically distributed gas-solid separators are arranged on the upper part of the fluidized bed. The gas-solid separator adopts a circular hole structure, and the material is a metal sintered mesh. The filter hole diameter is 50μm, and its cross-sectional size is the same as that of the fixed bed. The gas-solid separator is used to intercept the catalyst particles carried in the waste gas discharged from the fluidized bed. After separation, the gas enters the fixed bed for further oxidation. A backflush assembly is arranged on the upper part of each gas-solid separator, and the purge medium is N2.

[0040] The concentration of non-methane total hydrocarbons in the VOCs waste gas to be treated is 8000mg / m 3 about.

[0041] The VOCs-containing waste gas is heated to 350°C after passing through a heat exchanger or / and a heater. The heat exchanger uses the high-temperature purified gas discharged from the fixed bed for heat exchange. When the temperature after heat exchange cannot reach the required starting temperature of the reactor, it is heated by the heater. When the entire reaction system reaches heat balance, the heater is no longer started. The heat exchanger uses a plate heat exchanger and the heater uses an electric heater.

[0042] The exhaust gas is transported to the fluidized bed through the air inlet at the bottom of the fluidized bed. The fluidized bed is filled with granular catalytic oxidation catalyst with a particle diameter of 2 mm. The amount of catalyst used is to make the reaction space velocity at 20,000 h -1 , and adjust the pressure to fluidize the particle catalyst. The reaction temperature of fluidized catalytic oxidation is maintained at 500°C by controlling the exhaust gas concentration entering the fluidized bed. The fixed bed inlet temperature is kept consistent with the gas-solid separator outlet temperature. The amount of catalyst used in the fixed bed is to ensure that the reaction volume space velocity is 10,000 h -1 The temperature of the high-temperature purified gas discharged from the fixed bed is 650°C. It is discharged after heat exchange with the room-temperature VOCs waste gas entering the catalytic oxidation reactor in the heat exchanger. The exhaust gas temperature is 220°C.

[0043] After 1000 hours of operation, the concentration of non-methane total hydrocarbons in the discharged purified gas is always lower than 100 mg / m 3 , avoiding the occurrence of high-temperature hot spots of the catalyst and overheating of the fixed bed reaction, the service life of the catalyst is 118% of the original design life. And because the heat is fully utilized, it can save more than 29% of energy consumption.

[0044] Example 3

[0045] Use attached Figure 1The VOCs-containing waste gas treatment device shown has a cylindrical catalytic oxidation reactor with a diameter of 2.8m. Five symmetrically distributed cylindrical fixed beds are set in the fluidized bed. The material is stainless steel, and the cross-sectional area ratio of the fluidized bed to the fixed bed is 5:1. Twelve symmetrically distributed gas-solid separators are set on the upper part of the fluidized bed. The gas-solid separator adopts a circular hole structure, the material is a metal sintered mesh, the filter hole diameter is 50μm, and its cross-sectional size is the same as that of the fixed bed. The gas-solid separator is used to intercept the catalyst particles carried in the oxidized waste gas discharged from the fluidized bed. After separation, the gas enters the fixed bed for further oxidation. A backflush component is set on the upper part of each gas-solid separator, and the purge medium is N2.

[0046] The concentration of non-methane total hydrocarbons in the VOCs waste gas to be treated is 3000 mg / m 3 about.

[0047] The VOCs waste gas is heated to 280°C after passing through the heat exchanger and heater. The heat exchanger uses the high-temperature purified gas discharged from the fixed bed for heat exchange. When the temperature after heat exchange cannot reach the required starting reaction temperature, it is heated by the heater. When the entire reaction system reaches heat balance, the heater is no longer started. The heat exchanger uses a plate heat exchanger and the heater uses an electric heater.

[0048] The waste gas is transported to the fluidized bed through the waste gas inlet at the bottom of the fluidized bed. The fluidized bed is filled with granular catalytic oxidation catalyst with a particle diameter of 1.0 mm. The amount of catalyst used in the fluidized bed is such that the reaction space velocity is 30,000 h -1 , and adjust the pressure to fluidize the particle catalyst. The reaction temperature of the fluidized catalytic oxidation is maintained at 400°C by controlling the exhaust gas concentration entering the fluidized bed. The fixed bed inlet temperature is kept consistent with the gas-solid separator outlet temperature, and the amount of catalyst used in the fixed bed is such that the reaction space velocity is 30,000 h -1 The temperature of the discharged high-temperature purified gas is 480°C. It is discharged after heat exchange with the room-temperature VOCs waste gas entering the catalytic oxidation reactor in the heat exchanger. The exhaust gas temperature is 110°C.

[0049] After 1000 hours of operation, the concentration of non-methane total hydrocarbons in the discharged purified gas is always lower than 100 mg / m 3 , avoiding the occurrence of high-temperature hot spots of the catalyst and overheating of the fixed bed reaction, the service life of the catalyst is 139% of the original design life. And because the heat is fully utilized, it can save more than 16% of energy consumption.

[0050] Example 4

[0051] The difference from Example 1 is that the gas-solid separator is changed to a cartridge filter, the cartridge height is 1 / 4 of the fixed bed height, the material is a metal sintered mesh, the filter pore diameter is 50 μm, and the total cross-sectional area is twice the total cross-sectional area of ​​the fixed bed.

[0052] After 1000 hours of operation, the concentration of non-methane total hydrocarbons in the discharged purified gas is always lower than 100 mg / m 3 , avoiding the occurrence of high-temperature hot spots of the catalyst and over-temperature of the fixed bed reaction. Compared with Example 1, due to the increase in the filtration area, the increase in bed pressure drop is avoided, which helps to further homogenize the reaction temperature, and the service life of the catalyst is 142% of the original design life.

[0053] Example 5

[0054] The difference from Example 1 is that the cylindrical fixed bed adopts a tubular structure, the outer surface of the fixed bed adopts fins, and the material is ceramic. After 1000 hours of operation, the concentration of non-methane total hydrocarbons in the discharged purified gas is always lower than 100 mg / m 3 , avoiding the occurrence of high-temperature hot spots of the catalyst and overheating of the fixed bed reaction. Compared with Example 1, the heat transfer between the fluidized bed and the fixed bed is more sufficient, the service life of the catalyst is 136% of the original design life, and energy consumption can be saved by more than 33%.

[0055] Comparative Example 1

[0056] The same as Example 1, except that a fixed bed of the same size as the fluidized bed is used instead of the fluidized bed, and the regular catalyst is loaded. To meet the treatment requirements, the reactor inlet temperature needs to be increased to above 500°C, and the outlet temperature is at 600-650°C for a long time. After running for 500 hours, hot spots exceeding 650°C are generated at some locations of the fixed bed catalyst, and the service life of the catalyst is 78% of the original design life.

[0057] Comparative Example 2

[0058] The same as Example 1, except that only a fluidized bed is used, and no fixed bed is set therein. After 1000 hours of operation, the concentration of non-methane total hydrocarbons in the purified gas increased to 300 mg / m 3 In the above, the exhaust gas is not deeply treated; the fluidized reaction of the catalyst causes a certain amount of loss, and the heat is not effectively utilized.

[0059] Comparative Example 3

[0060] The same as Example 1, except that the fluidized bed and the fixed bed are connected in series, the fixed bed is a bed layer, and the exhaust gas after fluidized oxidation enters the fixed bed. After 1000 hours of operation, the concentration of non-methane total hydrocarbons in the discharged purified gas increased to 200 mg / m 3 As mentioned above, the exhaust gas was not deeply treated and the heat was not effectively utilized, especially hot spots exceeding 650°C were generated in some locations of the fixed bed layer, and the service life of the catalyst was 78.5% of the original design life.

Claims

1. A method for treating waste gas containing VOCs, characterized in that It includes the following contents: after the VOCs-containing waste gas is heated, it enters the catalytic oxidation reactor. The reactor is mainly composed of a fluidized bed and is loaded with granular catalytic oxidation catalyst. The waste gas and the catalyst particles undergo fluidized oxidation reaction. A number of cylindrical fixed beds are radially arranged in the fluidized bed and are loaded with regular catalytic oxidation catalyst. The lower end of the fixed bed penetrates the bottom of the reactor and is collected in an exhaust pipe. A number of gas-solid separators are arranged on the upper part of the fluidized bed. After fluidized oxidation, the waste gas passes through the gas-solid separator, and the catalyst particles carried are intercepted. After separation, the gas enters from the top of the fixed bed and continues to oxidize, and the high-temperature purified gas is discharged through the exhaust pipe.

2. The method according to claim 1, characterized in that: The starting temperature required for heating the VOCs-containing waste gas to catalytic oxidation is 100-500°C, preferably 250-400°C.

3. The method according to claim 1 or 2, characterized in that: The temperature is increased by using a heat exchanger and / or a heater. Preferably, the high-temperature purified gas discharged from the fixed bed is used for heat exchange in a heat exchanger. If the temperature cannot reach the starting temperature after heat exchange, it is heated by a heater. In principle, the heater is used when the device is started. When the entire reaction system reaches thermal balance, the heater is no longer started.

4. The method according to claim 3, characterized in that: The heat exchanger is any one of a heat pipe type, a shell and tube type, and a plate type heat exchanger, preferably a plate type heat exchanger; the heater is any one of an electric heater, a gas heater, and a fuel heater, preferably an electric heater.

5. The method according to claim 1, characterized in that: The catalytic oxidation reactor is column-type or tower-type, and the diameter of the reactor is selected so that the flow rate in the fluidized bed is 0.2-2 m / s, preferably 0.8-1.4 m / s.

6. The method according to claim 1 or 5, characterized in that: An air inlet is provided at the bottom of the reactor. The VOCs-containing waste gas is heated and transported to the fluidized bed through the air inlet. The particle catalyst is fluidized by adjusting the pressure.

7. The method according to claim 1, characterized in that: The diameter of the particle catalytic oxidation catalyst in the fluidized bed is 0.6-10 mm, preferably 0.8-3.0 mm; the amount of catalyst used is such that the reaction volume space velocity is 500-50000h -1 .

8. The method according to claim 1 or 7, characterized in that: The granular catalytic oxidation catalyst uses granular alumina or molecular sieve as a carrier and loads precious metals Pt and / or Pd, with the precious metal loading being 0.01%-0.15%.

9. The method according to claim 1, characterized in that: At least one cylindrical fixed bed is radially arranged in the fluidized bed, preferably 1 to 20 cylindrical fixed beds.

10. The method according to claim 1 or 9, characterized in that: The cross-sectional area ratio of the fluidized bed to the fixed bed is 3-10:1, and the fixed bed is preferably symmetrically distributed on the cross section of the fluidized bed.

11. The method according to claim 1 or 9, characterized in that: The cross-sectional shape of the cylindrical fixed bed is at least one of circular, elliptical, rectangular and triangular. Preferably, the outer surface of the fixed bed is in the form of fins or threads, and the material is stainless steel or ceramic.

12. The method according to claim 1 or 9, characterized in that: The structured catalytic oxidation catalyst loaded in the fixed bed is a monolithic or random type, preferably a monolithic honeycomb ceramic catalyst; the amount of catalyst used is such that the reaction volume space velocity is 500-50000h -1 .

13. The method according to claim 1 or 9, characterized in that: The catalytic oxidation catalyst loaded in the fixed bed is a honeycomb carrier catalyst loaded with precious metals Pt and / or Pd. The loading amount of the precious metals Pt and / or Pd is 0.01%-0.15% based on the mass of the honeycomb carrier.

14. The method according to claim 1, characterized in that: The fluidized oxidation reaction temperature is maintained at 300-550°C, preferably 400-500°C, by adjusting the heater and the exhaust gas concentration.

15. The method according to claim 1, characterized in that: The gas separated by the gas-solid separator directly enters the fixed bed, and the fixed bed outlet temperature is 1-100°C higher than the fixed bed inlet temperature, preferably not higher than 650°C.

16. The method according to claim 1, characterized in that: The high-temperature purified gas after deep oxidation in the fixed bed is discharged through the exhaust pipe and transported to the heat exchanger for heat exchange with the waste gas to be treated. After heat exchange, the purified gas is discharged out of the device. The discharged purified gas temperature is 90-300°C, preferably 120-180°C.

17. The method according to claim 1, characterized in that: The gas-solid separator is arranged on the upper part of the fluidized bed, and the outlet is connected to the inlet of the fixed bed, which is used to intercept the catalyst particles carried in the exhaust gas discharged from the fluidized bed. The gas enters the fixed bed after separation; the gas-solid separator is any one of the hole type, cylinder type and bag type filter components, and the material is any one of glass fiber, metal sintered mesh and ceramic membrane. The filter hole diameter is larger than the particle catalyst diameter, preferably 5-100μm.

18. The method according to claim 1 or 17, characterized in that: The total cross-sectional area of ​​the gas-solid separators is 1-4 times the total cross-sectional area of ​​the fixed beds, and the number of the gas-solid separators is 8-20, preferably symmetrically distributed.

19. The method according to claim 1 or 17, characterized in that: A back-purge assembly is correspondingly arranged on the upper part of each gas-solid separator, and the purge medium is at least one of air and N2.

20. The method according to claim 1, characterized in that: The total hydrocarbon concentration in VOCs exhaust gas is 2000-12000mg / m 3 , preferably 4000-8000mg / m 3 When the total hydrocarbon concentration is high, pretreatment or introduction of dilution gas is required to reduce the concentration to a specified value. The dilution gas is any one of air, nitrogen, and inert gas.

21. A treatment device for the VOCs-containing waste gas treatment method according to any one of claims 1 to 20, characterized in that: According to the flow direction of exhaust gas, it includes a heat exchanger, a heater and a catalytic oxidation reactor in sequence. The heat exchanger and / or the heater are used to heat the exhaust gas containing VOCs to the starting temperature required for the catalytic oxidation reaction. The catalytic oxidation reactor is mainly composed of a fluidized bed, which is loaded with catalytic oxidation granular catalysts, and the exhaust gas and the catalyst particles undergo fluidized oxidation reaction. A number of cylindrical fixed beds are radially arranged in the fluidized bed, which are loaded with regular catalytic oxidation catalysts, and the reaction heat of fluidized oxidation is transferred to the catalyst in the bed through the fixed bed wall. The lower end of each fixed bed penetrates the bottom of the reactor and is collected in an exhaust pipe. A number of gas-solid separators are arranged on the upper part of the fluidized bed, and the outlet is connected to the inlet of the fixed bed. The fluidized oxidation stream flows through the gas-solid separator, and the carried catalyst particles are intercepted. The separated gas enters the fixed bed for further oxidation, and the high-temperature purified gas is discharged through the exhaust pipe.

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