Second, the catalytic combustion method
Catalytic combustion is actually a complete catalytic oxidation, that is, under the action of the catalyst, the harmful combustible gas in the exhaust gas is completely oxidized to CO2 and H2O. As most organic compounds are combustible, catalytic combustion is one of the effective methods to purify organic waste gas.
At present, the catalytic combustion method has been applied to the coating production in the steel drum industry to purify the organic waste gas because the drying exhaust gas discharged in the coating production process has a high temperature and is favorable to the combustion reaction and the heat recovery, and has an effective economy Therefore, this method is the most widely used in China's barrel making enterprises.
There are three types of catalysts for catalytic combustion: noble metal catalysts (palladium, platinum), transition metal oxide catalysts, and rare earth metal oxide catalysts.
China first for the combustion of organic waste gas catalyst is Pb-Al2O3, ceramic honeycomb catalyst. This catalyst free space, its low wear rate, bed resistance, more suitable for the governance of steel drum exhaust gas. However, due to its large free space, the reaction gas is often not as effective as the particulate catalyst in contact with the catalyst surface and therefore has lower activity than the granular catalyst of the same active component. At the same time, its mechanical strength is poor, easy to hot and cold broken, heat stability is not good. In order to overcome the weak point of contact with the poor, China has developed a microporous flat catalyst, the application effect is very good.
Different forms of catalytic combustion can be used for different situations of exhaust gas emissions, but the composition of the process has the following common features regardless of the process type used:
(1) The gas entering the catalytic combustion unit must be pre-treated to remove the dust, droplets and harmful components to avoid clogging of the catalyst bed and catalyst poisoning;
(2) the temperature of the gas entering the catalytic bed must reach the light-off temperature of the catalyst used;
(3) The catalytic combustion reaction emits a large amount of heat of reaction, and the quantity of this component must be recovered.
Catalytic combustion process is divided into two types and combination of two:
(1) In the sub-process, the preheater, heat exchanger and reactor are all distributed as independent equipment with the corresponding pipelines connected, which is generally applied to the coating production line with larger gas volume;
(2) The combined process of preheating, heat exchange and reaction part of the combination of the installation of the same equipment (ie, catalytic combustion furnace), the process is compact, generally used in the processing gas volume coating production line.
Exhaust gas treated with catalytic combustion typically contains organic pollutants at concentrations below 0.2%. Economical and reasonable conversion rate of industrial installations is generally considered 85% to 90%.
Fig. 3 is a schematic diagram of a typical device (KIC) for treating exhaust gas from a barrel paint painting production line by a catalytic combustion method. After collecting the exhaust gas, the device is drawn into the KIC environmental protection equipment. The equipment is firstly indirectly warmed up → combustion heating (primary purification) → catalytic reaction (secondary purification) → indirect warming up → then into the waste heat utilization equipment or emptying.
Figure 3 Shanghai Overseas Chinese KIC catalytic green furnace process flow chart
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