A staged catalytic combustion process for high-concentration organic waste gas

Abstract

The present invention provides a purification process for high-concentration organic waste gas, which belongs to the technical field of waste gas treatment. The specific method is to collect high-concentration waste gas containing toluene, n-hexane, methyl tert-butyl ether, and ethyl acetate. Under the action of the induced draft fan, the high-concentration organic waste gas passes through the primary heat exchanger, the electric heating area, the first-stage catalytic combustion chamber, the secondary heat exchanger, the second-stage catalytic combustion chamber, and finally passes through the exhaust pipe to meet the emission standards. The present invention utilizes the low ignition temperature of the precious metal catalyst to first catalytically oxidize and decompose part of the high-concentration organic waste gas, then uses the secondary heat exchanger to remove the excess heat of the oxidation reaction, and finally passes through a large amount of common metal catalysts in the second-stage catalytic combustion chamber to completely oxidize and decompose the waste gas.

Description

Technical Field

[0001] The invention relates to a high-concentration organic waste gas purification process, in particular to a high-concentration organic waste gas staged catalytic combustion process. Background Art

[0002] With the development of modern industry, organic solvents, as an important type of raw material, are widely used in chemical, pharmaceutical, preservative, leather, textile, coating, electronics and pesticide industries. These organic solvents are mainly hydrocarbons. Due to their volatility, a large amount of VOCS waste gas will be generated during the production and use process.

[0003] In view of the serious environmental pollution caused by volatile organic pollutants (VOCS), their treatment has become a hot topic in environmental research at home and abroad. At present, the more mature organic waste gas treatment processes mainly include: condensation method, adsorption method, organic solvent absorption method, biological method, photocatalytic oxidation method, UV photolysis method, direct combustion method and catalytic combustion method.

[0004] In order to deal with high concentration of volatile organic pollutants (VOCs), the combustion method is often used in industry, and the combustion method is divided into direct combustion, catalytic combustion and thermal storage combustion. Because catalytic combustion can completely oxidize and decompose the exhaust gas between 250 and 500°C, which can greatly reduce the operating cost, catalytic combustion is becoming more and more common in the field of industrial exhaust gas treatment.

[0005] At present, the intake concentration of conventional catalytic combustion devices needs to be controlled between 2 and 3 g / m3. If the concentration is too low, a large amount of heat needs to be added. If the concentration is too high, it exceeds the normal operating temperature range of the catalytic combustion device and the equipment is at risk of being burned out. However, the exhaust gas concentration generated in the actual production process often exceeds 3 g / m3, and even reaches more than 10 g / m3. Therefore, the application of catalytic combustion in the field of high-concentration exhaust gas treatment is limited. Summary of the invention

[0006] The present invention mainly solves the problems that the traditional catalytic combustion device is inefficient in treating high-concentration organic waste gas and is prone to overheating of the furnace body. At the same time, the investment cost of treating high-concentration organic waste gas by the heat storage combustion method is too high. It provides a new process for the treatment of high-concentration organic waste gas that is technically feasible, economically reasonable, and reliable in meeting standards.

[0007] To achieve the above object, the technical solution provided by the present invention includes the following five steps:

[0008] In the step 1, high-concentration organic waste gas enters the catalytic combustion device through the collection pipe. The waste gas first flows in from the cold side of the first-stage heat exchanger and flows out from the hot side of the first-stage heat exchanger; the high-temperature flue gas in the second-stage catalytic combustion chamber flows in from the hot side of the first-stage heat exchanger and flows out from the cold side of the first-stage heat exchanger. In this process, the temperature of the waste gas increases, achieving the purpose of energy saving; at the same time, the temperature of the high-temperature flue gas decreases, meeting the requirements of the emission standards.

[0009] Step 2: The preheated exhaust gas then enters the electric heating zone. When the thermal resistor in the electric heating zone detects that the exhaust gas temperature is lower than 180°C, the interlocking electric heating zone starts, and the electrical energy is converted into thermal energy through the finned tube electric heater, and then transferred to the exhaust gas to raise its temperature to above 180°C; when the exhaust gas temperature is higher than 180°C, the electric heating zone stops.

[0010] The third step: the exhaust gas passing through the electric heating zone continues to enter the first stage catalytic combustion chamber, and by reducing the loading amount of the precious metal catalyst, part of the exhaust gas is oxidized and decomposed. On the one hand, it can avoid the risk of overheating of the first stage catalytic combustion chamber caused by complete oxidation and decomposition of the exhaust gas; on the other hand, since the price of the precious metal catalyst is relatively high, reducing its loading amount can also achieve the purpose of saving investment costs.

[0011] The above-mentioned precious metal catalyst is characterized in that: the precious metal catalyst uses bimetallic platinum and palladium as active components, uses cordierite honeycomb ceramics as a carrier, and is a high-activity precious metal catalyst prepared by adding multiple rare earth metals.

[0012] The properties of the above-mentioned precious metal catalyst are: low ignition temperature, high activity, long service life and strong adaptability.

[0013] Step 4: Since the high temperature flue gas in the first stage catalytic combustion chamber needs to be cooled down due to its high temperature, a secondary heat exchanger is set to cool down the high temperature flue gas. The high temperature flue gas in the first stage catalytic combustion chamber flows in from the hot side of the secondary heat exchanger and flows out from the cold side of the secondary heat exchanger; the circulating cooling water flows in from the cold side of the secondary heat exchanger and flows out from the hot side of the secondary heat exchanger. The flue gas temperature is controlled between 250 and 300°C by controlling the flow rate of the circulating cooling water.

[0014] The step five: the high-temperature flue gas after cooling continues to enter the second-stage catalytic combustion chamber, and by increasing the loading amount of the common metal catalyst, the exhaust gas is completely oxidized and decomposed to meet the requirements of meeting emission standards.

[0015] The above common metal catalyst is characterized in that: the common metal catalyst is a high-activity common metal catalyst prepared by using bimetallic manganese and copper as active components, cordierite honeycomb ceramics as a carrier, and adding multiple rare earth metals.

[0016] The above-mentioned common metal catalysts have the following properties: low price, high activity, long service life and strong adaptability.

[0017] Compared with the existing technology, the advantages of this technology are:

[0018] (1) It can be applied to various waste gas working conditions, especially suitable for treating high-concentration organic waste gas with a waste gas concentration of more than 10g / m3.

[0019] (2) The precious metal catalyst loaded in the first catalytic combustion zone is less, which can significantly reduce the cost of the catalyst.

[0020] (3) The second-stage catalytic combustion zone is loaded with more common catalysts, which can improve the oxidation and decomposition efficiency of organic waste gas.

[0021] (4) The first stage catalytic combustion chamber is equipped with a precious metal catalyst. Since it can catalytically oxidize and decompose organic waste gas at a relatively low temperature of 180°C, the high-temperature flue gas discharged from the second stage combustion chamber can be used to preheat the high-concentration organic waste gas to a temperature above 180°C.

[0022] (5) The second-stage catalytic combustion chamber is equipped with an ordinary metal catalyst. Since its ignition temperature is relatively high, usually around 250°C, the second-stage catalytic combustion can be directly carried out using the flue gas temperature at the outlet of the first-stage catalytic combustion chamber.

[0023] (6) Since the flue gas temperature at the outlet of the first combustion chamber is generally above 400°C, a large amount of hot water can be generated through the secondary heat exchanger for use in plant production.

[0024] (7) In summary, the high-concentration organic waste gas catalytic combustion process provided by the present invention has incomparable advantages such as high safety performance, low investment cost, low operating cost, high removal efficiency, and strong adaptability compared to the traditional catalytic combustion process. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural schematic diagram of a high-concentration organic waste gas staged catalytic combustion process device of the present invention, wherein 1-catalytic combustion device body, 2-primary heat exchanger, 3-electric heating zone, 4-first stage catalytic combustion chamber, 5-secondary heat exchanger, 6-second stage catalytic combustion chamber.

[0026] Figure 2 The present invention discloses a gas flow diagram of a high-concentration organic waste gas staged catalytic combustion process device. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention are described clearly and completely below. The implementation cases described are only some embodiments of the present invention, not all embodiments, and the present invention is not limited by the embodiments.

[0028] The present invention provides a high-concentration organic waste gas purification process, such as Figure 1 As shown, the specific steps of the method are as follows:

[0029] (1) High-concentration organic waste gas enters the catalytic combustion device through the waste gas collection pipe under the action of the induced draft fan. It first passes through the first-stage heat exchanger and the high-temperature flue gas at the outlet of the second-stage catalytic combustion chamber for heat exchange, and the waste gas temperature increases.

[0030] (2) The preheated exhaust gas passes through the electric heating zone. When the thermocouple detects that the exhaust gas temperature is lower than 180°C, the electric heating starts to heat the exhaust gas to raise its temperature to above 180°C. When the exhaust gas temperature is higher than 180°C, the electric heating stops.

[0031] (3) The exhaust gas then enters the first stage catalytic combustion chamber, where the low ignition temperature of the precious metal catalyst is used to oxidize and decompose the exhaust gas into CO2 and H2O. By reducing the loading amount, part of the exhaust gas is oxidized and decomposed, thus avoiding overheating in the first stage catalytic combustion zone.

[0032] (4) Then the high-temperature flue gas from the first stage of catalytic combustion passes through the secondary heat exchanger and exchanges heat with the cooling circulating water. The exhaust gas temperature is reduced to avoid overheating of the second stage catalytic combustion chamber. At the same time, the temperature of the cooling circulating water is increased, generating a large amount of hot water for use in the plant.

[0033] (5) Finally, the exhaust gas passes through the second-stage catalytic combustion chamber. Since ordinary metal catalysts are cheap, by increasing their loading amount, the exhaust gas is completely oxidized and decomposed to ensure that the exhaust gas meets the emission standards.

[0034] (6) Specifically, the working process of the above-mentioned high-concentration organic waste gas staged catalytic combustion device is as follows: Figure 2 As shown, the exhaust gas flow specific steps are as follows:

[0035] (7) Figure 2 As shown, the exhaust gas passes through the primary heat exchanger 2, one end of its cold source channel is the exhaust gas inlet 11, which is connected to the air inlet 13, and the other end is the exhaust gas outlet 14, which is connected to the electric heating zone inlet 15; one end of its heat source channel is the high-temperature flue gas inlet 17, which is connected to the second-stage catalytic combustion zone outlet 18; the other end is the high-temperature flue gas outlet 19, which is connected to the exhaust port 20.

[0036] (8) The electric heating zone inlet 15 is connected to the electric heating zone outlet 21; the electric heating zone outlet 21 is connected to the first stage catalytic combustion zone inlet 22.

[0037] (9) The first stage catalytic combustion zone inlet 22 is connected to the first stage catalytic combustion zone outlet 23; the high-temperature flue gas at the first stage catalytic combustion zone outlet 23 passes through the secondary heat exchanger 5. One end of its heat source channel is the high-temperature flue gas inlet 25, which is connected to the first stage catalytic combustion zone outlet 23, and the other end is the high-temperature flue gas outlet 26, which is connected to the second stage catalytic combustion zone inlet 27; one end of its cold source channel is the tap water inlet 29, and the other end is the tap water outlet 30.

[0038] (10) The second stage catalytic combustion zone inlet 27 is connected to the second stage combustion zone outlet 18; the second stage combustion zone outlet 18 is connected to the first stage heat exchanger heat source channel inlet 17. In this way, a complete exhaust gas catalytic oxidation decomposition process is formed.

[0039] (11) Depending on the type, concentration and air volume of high-concentration organic waste gas, the selected fin plate heat exchanger heat exchange area, electric heating power, catalyst space velocity, cooling circulation water volume, residence time and equipment size will vary greatly.

[0040] (12) It should be pointed out that ordinary technicians in the field of waste gas treatment can make several improvements and adjustments without departing from the technical principles of the present invention, and these improvements and adjustments are also considered to be within the scope of protection of the present invention.

[0041] Example 1

[0042] A pharmaceutical company emits high-concentration organic waste gas with a temperature of 30°C and an air volume of 2000Nm3 / h. The main components are as follows: toluene 3000ppm, n-hexane 1200ppm, methyl tert-butyl ether 180ppm, ethyl acetate 460ppm, methanol 580ppm, and ethanol 840ppm.

[0043] The high-concentration organic waste gas is introduced into the catalytic combustion device through the waste gas collection pipe, wherein the heat exchange area of ​​the first-stage heat exchanger is 60m2. After the waste gas passes through the first-stage heat exchanger, the temperature rises from 30°C to above 180°C; then the waste gas enters the electric heating zone, where 60 finned tube electric heating tubes with a single power of 1kW are arranged. When the waste gas temperature is lower than 180°C, the electric heating is started to heat the waste gas to raise its temperature to above 180°C; then the waste gas enters a catalytic combustion chamber, the loading amount of the precious metal catalyst is 0.08m3, the catalyst air velocity is controlled at 25000-h, the cross-sectional wind speed is controlled at 0.8-1.2m / s, the organic waste gas is decomposed, and the temperature of the catalytic combustion chamber is raised to 480°C. After sampling and testing, the waste gas concentration at the outlet of the first-stage catalytic combustion chamber is as follows: toluene 632ppm, n-hexane 481ppm, methyl tert-butyl ether 92ppm , ethyl acetate 248ppm, methanol 306ppm, ethanol 458ppm, calculated organic matter removal rate is about 55%; the high temperature flue gas in the first stage catalytic combustion chamber passes through the secondary heat exchanger, where the heat exchange area of ​​the secondary heat exchanger is 20m2, and the circulating cooling water is used for cooling, the flue gas temperature is reduced from 480℃ to 250℃, and then enters the second stage catalytic combustion chamber, the loading amount of the common metal catalyst is 0.25m3, the catalyst air velocity is controlled at 8000-h, the cross-sectional wind speed is controlled at 0.8~1.2m / s, the organic waste gas is decomposed, the temperature of the catalytic combustion chamber is increased to 500℃, and the exhaust gas concentration at the outlet of the first stage catalytic combustion chamber is as follows after sampling and detection: toluene 13ppm, n-hexane 10ppm, methyl tert-butyl ether 2ppm, ethyl acetate 5ppm, methanol 6ppm, ethanol 10ppm, calculated organic matter removal rate is above 98%. Through the two-stage catalytic combustion process, the total removal rate of organic matter reaches above 99.1%.

[0044] Comparative Example 1

[0045] A pharmaceutical company emits high-concentration organic waste gas with a temperature of 30°C and an air volume of 2000Nm3 / h. The main components are as follows: toluene 3000ppm, n-hexane 1200ppm, methyl tert-butyl ether 180ppm, ethyl acetate 460ppm, methanol 580ppm, and ethanol 840ppm.

[0046] The high-concentration organic waste gas is introduced into the catalytic combustion device through the waste gas collection pipeline, wherein the heat exchange area of ​​the first-stage heat exchanger is 60m2. After the waste gas passes through the first-stage heat exchanger, the temperature rises from 30°C to above 180°C; then the waste gas enters the electric heating area, where 60 finned tube electric heating tubes with a single power of 1kW are arranged. When the waste gas temperature is lower than 180°C, the electric heating starts to heat the waste gas to raise its temperature to above 180°C; then the waste gas enters the catalytic combustion chamber, and the loading amount of the precious metal catalyst is 0.08m 3. The loading amount of ordinary metal catalyst is 0.25m3. Keeping the total loading amount of catalyst unchanged, the temperature of catalytic combustion chamber reaches above 550℃. At this time, the thermal bypass is opened to discharge the excess heat in the system to maintain the normal operation of the system. The exhaust gas concentration at the outlet of catalytic combustion chamber is tested by sampling as follows: toluene 840ppm, n-hexane 609ppm, methyl tert-butyl ether 126ppm, ethyl acetate 322ppm, methanol 406ppm, ethanol 588ppm. The calculated organic matter removal rate is about 70%.

[0047] In summary, the present invention discloses a staged catalytic combustion process for high-concentration organic waste gas. Through two-stage catalytic combustion, a small amount of precious metal catalyst is loaded in the first catalytic combustion zone, and the characteristic of low ignition temperature of precious metal catalyst is utilized to achieve the purpose of saving electric energy; the second catalytic combustion zone is loaded with ordinary metal catalyst, and the loading amount of ordinary catalyst is increased to achieve the purpose of efficient oxidation and decomposition of waste gas. At the same time, a heat exchanger is added between the first catalytic combustion zone and the second catalytic combustion zone to take away the excess heat released by the oxidation and decomposition of the waste gas in the first catalytic combustion zone, and generate a large amount of hot water for use in the factory area. On the one hand, it can solve the risk of excessive heat in the complete oxidation and decomposition of high-concentration organic waste gas, and on the other hand, it can improve the efficiency of waste gas oxidation and decomposition. Therefore, the process is highly innovative.

Claims

1. A high-concentration organic waste gas staged catalytic combustion process, comprising the following steps:

1. High-concentration organic waste gas first passes through the primary heat exchanger and the high-temperature flue gas after the secondary catalytic combustion for heat exchange, and the waste gas temperature rises to above 180°C; 2. The preheated exhaust gas enters the electric heating zone. When the exhaust gas temperature is lower than 180°C, the electric heating starts to raise its temperature to above 180°C. When the exhaust gas temperature is higher than 180°C, the electric heating stops.

3. The exhaust gas passing through the electric heating zone continues to enter the first catalytic combustion chamber. The catalyst used in the first catalytic combustion chamber is a precious metal catalyst. Taking advantage of the low ignition temperature of the precious metal catalyst, by reducing its loading amount, the exhaust gas is partially oxidized and decomposed, and the temperature rises to 400~500℃. The loading amount of the precious metal catalyst is 0.08m 3 ; 4. After the first stage of catalytic combustion, the high-temperature flue gas passes through the secondary heat exchanger and exchanges heat with cooling water, and the temperature is reduced to 250~300℃; 5. After cooling, the flue gas enters the second stage catalytic combustion chamber. The catalyst used in the second stage catalytic combustion chamber is a common metal catalyst. Taking advantage of the low price of the common metal catalyst, the exhaust gas is completely oxidized and decomposed by increasing its loading amount. The loading amount of the common metal catalyst is 0.25m 3 ; The high-concentration organic waste gas is an organic waste gas containing toluene, n-hexane, methyl tert-butyl ether, ethyl acetate, methanol and ethanol.

2. A high-concentration organic waste gas staged catalytic combustion process according to claim 1, characterized in that: The heat exchanger in step one is a fin plate heat exchanger made of SUS304. The heat source of the heat exchange in step one is the high-temperature flue gas at the outlet of the second-stage catalytic combustion chamber, and the cold source of the heat exchange in step one is the high-concentration organic waste gas.

3. A high-concentration organic waste gas staged catalytic combustion process according to claim 1, characterized in that: The electric heating zone in step 2 is characterized in that the electric heating device is a fin-tube electric heater made of 316L and is evenly arranged in a matrix.

4. The high-concentration organic waste gas staged catalytic combustion process according to claim 1, characterized in that: The secondary heat exchanger in step 4 is a finned plate heat exchanger made of SUS304. The heat source of the heat exchange in step 4 is the high-temperature flue gas at the outlet of a catalytic combustion chamber, and the cold source of the heat exchange in step 4 is cooling water.

5. The high-concentration organic waste gas staged catalytic combustion process according to claim 1, characterized in that: The noble metal catalyst is a high-activity noble metal catalyst prepared by using bimetallic platinum and palladium as active components, cordierite honeycomb ceramics as a carrier, and adding a variety of rare earth metals.

6. The high-concentration organic waste gas staged catalytic combustion process according to claim 1, characterized in that: The common metal catalyst is a high-activity common metal catalyst prepared by using bimetallic manganese and copper as active components, cordierite honeycomb ceramics as a carrier, and adding a variety of rare earth metals.

7. The high-concentration organic waste gas staged catalytic combustion process according to claim 1, characterized in that: The concentration of the high-concentration organic waste gas is 10g / m 3 above.

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