The emission of waste gas varies with the production industry and working conditions, and its composition and concentration are also different. Therefore, the selection of its treatment technology depends on the nature, concentration, purification requirements, economy and other factors of the organic pollutants in various industries. The conventional treatment methods for VOCs organic waste gas include absorption, adsorption, combustion and biological methods. For the organic waste gas with large air volume (≥ 20000m3 / h), low concentration (≥ 1000mg / m3) and stable emission, the most mature and thorough treatment technology abroad is: pretreatment + activated carbon adsorption purification combined with catalytic combustion desorption regeneration process.
Working principle: firstly, the paint mist particles in the original waste gas are removed by the wet + dry integrated pretreatment equipment, and then the organic waste gas is absorbed and purified by the adsorbent (active carbon or molecular sieve, etc.) to reach the emission standard. At the same time, in the adsorption process, there will be unit concentration (the total concentration will be about 15 times) to reduce the total amount of organic waste gas treated by catalytic combustion. When desorption, the catalyst is used The high temperature gas produced by chemical combustion is used for desorption and regeneration of adsorbent, and the high concentration gas is thoroughly oxidized and decomposed by catalytic combustion technology and discharged up to the standard. The essence of this process is to transform the organic waste gas with large air volume and low concentration into the organic waste gas with small air volume and high concentration for final purification.
Notes on Application of adsorption concentration + catalytic combustion technology
1. Select honeycomb adsorbent and catalyst
2. Prevent catalyst poisoning
3. Dedusting and dehydration pretreatment are very important
Purification technology of organic waste gas with small air volume and high concentration
This kind of waste gas mainly comes from the pollutants discharged in the production process of coating, printing, home appliances, wire and motor manufacturing, insulation materials, paint production and other industries. The emission of waste gas varies with the production industry and working conditions, and its composition and concentration are also different. Therefore, the selection of its treatment technology depends on the nature, concentration, purification requirements, economy and other factors of the organic pollutants in various industries. The conventional treatment methods for VOCs organic waste gas include absorption, adsorption, combustion, biological methods, etc. for the organic waste gas with small air volume (< 20000m3 / h), high concentration (2000-8000mg / m3) and stable emission, the most mature and thorough treatment technologies are direct combustion (RTO) and catalytic combustion (RCO).
Working principle: after the system works normally, the flue gas with a temperature of about 70 ℃ enters the catalytic purification device via flame arrester, exchanges heat with the high-temperature exhaust gas in the plate heat exchanger, and the preheated exhaust gas enters the heating chamber (equipped with an electric heating tube) to further raise the temperature to about 250 ℃, and the exhaust gas reaching the ignition temperature continues to enter the catalytic bed. In the case of precious metal Pt and Pd Catalysts Under the action, the organic solvent is completely oxidized and decomposed into H2O and CO2, and a large amount of reaction heat is released, which can maintain the ignition temperature required for catalytic combustion and achieve heat balance. The high-temperature exhaust gas can reach more than 300 ℃, and the heat exchange between the high-temperature exhaust gas and the imported low-temperature exhaust gas is carried out through the plate heat exchanger, part of the heat can be recovered, and the preheating energy consumption is reduced. The high-temperature tail gas recovered part of the heat can also be used for heat exchange through other heat exchange devices, and finally the tail gas can be discharged through the exhaust funnel under the action of the suction force of the induced draft fan. After the system reaches heat balance, the electric heating device will be shut down automatically. After that, the heat energy generated when the organic solvent in the reliable exhaust gas of the catalytic combustion system burns will continue the catalytic combustion until the end without additional energy.
Notes on Application of catalytic combustion technology
1. Select honeycomb catalyst
The catalyst is granular and honeycomb. The granular catalyst has a large pressure drop, and the friction between the catalyst and the support will cause the wear loss of the active component, so it is not recommended to use it. Honeycomb catalyst is an ideal catalyst with high specific surface, low pressure drop, high mechanical strength, wear resistance and heat shock resistance.
2. Prevent catalyst poisoning
Catalyst poisoning refers to the phenomenon that catalyst activity declines or loses due to the action of some substances. It can be divided into temporary poisoning and permanent poisoning. If the temperature of catalyst bed is too low, or the concentration of combustibles in the waste gas is too high, or the power is cut off suddenly, the coke on the catalyst surface will cause temporary poisoning. When the catalyst bed is turned on again, the preheating temperature before the catalyst bed can be raised to about 500 ℃ and fresh air can be used for 1-2 hours, then the catalyst activity can be recovered or partially recovered. However, some chemicals (such as organic or inorganic substances such as s and Pb) have a strong destructive effect on the catalyst, which will lead to the permanent deactivation of the catalyst and can not be recovered, so special attention should be paid.
3. Set fresh air valve
Fresh air valve shall be set before catalytic purification unit. When the temperature of catalytic bed is higher than a certain set value, open the valve to supplement cold air and control the temperature of catalytic bed within a certain range, which can extend the service life of equipment and catalyst.