Zeolite molecular sieves are mainly used in VOC control in the form of disc runners, drum runners, and fixed bed molecular sieves.
One disc runner
The structure of the disc zeolite runner is divided into three parts: adsorption zone, regeneration zone, and cooling zone. Generally, the partition ratio is 10:1:1.
1) Adsorption area:
On the windward side of the exhaust gas, the wind speed is generally controlled at 2-4Nm/s, the purification efficiency is generally 90-97%, and the purified gas enters the chimney.
2) Cooling area:
Generally, process gas is used for cooling. On the one hand, it reduces the temperature of the zeolite in the cooling zone, making it adsorbable. On the other hand, it also successfully realizes heat energy recovery.
3) Desorption zone:
The heat-recovered gas is heated to a temperature of about 200°C and then enters the desorption zone for cooling. The air volume for desorption regeneration is generally 10-20 times that of the incoming air. When performing high-temperature regeneration, the maximum temperature can reach about 300°C, so it is necessary to select a high-temperature regeneration type runner during design.
4) Common materials that zeolite runner is not suitable for processing
Olefins, organosilanes, and macromolecular substances with boiling points exceeding 260°C that are prone to polymerization on the molecular sieve runner may cause permanent damage to the runner. Divided by material components that cannot be processed, substances that are not allowed to enter the runner, and substances that are restricted from entering the runner.
The destruction of the base material and zeolite crystal structure is irreversible. The destruction of the base material and zeolite crystal structure caused by the polymer causing blockage of the air channels is irreversible. The blockage of the air channels caused by the polymer is reversible. The blockage of the stone air passage caused by the residue of high boiling point substances is reversible, and a specific offline activation process can restore 80-90% of the original performance.
5) Problems and shortcomings of zeolite runner technology
Problems with wheel technology
The runner cannot handle all gases. For some exhaust gases that are difficult to treat, such as easily polymerized olefins, alkyne components (easy to polymerize and block during desorption), styrene, polymethyl acrylate, polymethyl acrylate, etc. of UV paint in the coating industry, zeolite is powerless.
The runner's ability to concentrate waste gas is related to its adsorption capacity.
It is generally said that "the runner can concentrate the exhaust gas 20 to 40 times" is just a conceptual issue. If the exhaust gas concentration is already very low, it is possible to concentrate it not only 40 times but also 50 to 60 times. If the exhaust gas concentration is high, such as 1000mg/m3, then the concentration ratio of 10 times may not be achieved.
Any adsorption device has adsorption cycle problems.
In other words, any adsorption device has the problem of breaking point. If the adsorption operation is switched when it is about to reach the breaking point when the operation is unstable, it will easily exceed the standard. However, if there is still a long time before the breaking point If the time is switched in advance, the standard will not be exceeded. Therefore, the adsorption time set by the general runner will be much shorter than the time to reach the breaking point, so it is easy to achieve emission standards.
The wind speed of exhaust gas passing through the bed is determined by its residence time. For exhaust gas with a dilute concentration, a larger wind speed can be used. When designers design the runner wind speed, they must make a selection based on the concentration of the gas. Since the exhaust gas concentration treated by the rotor is generally low, a larger wind speed can be used. However, the wind speed of the runner cannot be increased arbitrarily, and resistance issues must also be considered. Therefore, the maximum thickness of the adsorption layer of the runner will not exceed 500mm.
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