Process exhaust gas treatment
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I would like to ask everyone: our factory’s original design for treating process exhaust gases involved the use of liquid nitrogen cryogenic treatment in combination with an RTO. The environmental impact assessment raised concerns regarding excessive nitrogen oxide emissions, and from an energy-saving perspective as well, this approach is not the best option. Could the method of cryogenic treatment (to remove most VOCs) combined with activated carbon adsorption be used? Since the exhaust gas may contain hydrogen, could the activated carbon react with carbon?
Activated carbon has a certain hydrogen storage capacity, but the amount available under normal pressure is limited. What is the level of VOCs in the waste? Whether RTOs or activated carbon adsorption methods are used, it is necessary to take into account energy consumption and the comprehensive use of resources in order to reduce treatment costs.
This post was last edited by zhaolijun on 2015-6-7 at 14:54; the use of liquid nitrogen for condensation means that the concentration of VOCs in the exhaust gases is certainly high. The key is the VOC concentration and air volume after condensation. The concern over excessive nitrogen oxide emissions is mainly due to nitrogen-containing organic compounds in the exhaust gases, which produce nitrogen oxides upon combustion. An alkaline water scrubber can be added after the RTO. If the condensation treatment is efficient and the concentration of the exhaust gas produced is low, or if the volume of air flow isn’t very high, then using activated carbon results in lower costs.
Is the liquid nitrogen you use produced by a KDN nitrogen generator?
I’ve always bought ready-made liquid nitrogen; I don’t make it myself
How dare one use activated carbon for adsorption when there is hydrogen present? It is recommended to consider other treatment methods, as the concentration and volume of VOC emissions have not been provided. However, given that deep cooling + RTO is being considered, both the emission concentration and volume are likely to be high; otherwise, it wouldn’t be worthwhile to use this approach. But such a method requires a lot of energy, right? Actually, if you just want a simple modification, you can add a spray tower after the RTO. If a thorough renovation is carried out, the energy-intensive cryogenic process can be eliminated, and instead the absorption+desorption method can be used; if emissions need to meet regulatory standards, the exhaust gas can then be sent to an RTO ；
Only a small amount of hydrogen is produced as a result of the reaction, and that amount is also relatively low. What are the main concerns regarding the use of activated carbon? Explosive? Since both the process purge gas and the protective gas N2 end up in the exhaust gases, the issue with using RTOs or TOs is that it may lead to an increase in NOx emissions after treatment, which is also a concern raised in environmental impact assessments.
For chemical plants, RTOs are not recommended; it’s necessary to check what’s present in the exhaust gases. If the concentrations are high, why not use activated carbon? Activated carbon can indeed be used for adsorption and purification. Consider using hydrogen as a replacement – it’s quite safe and can also bring economic benefits.
The disposal cost of spent activated carbon is high. First, measure the exhaust volume, concentration, and composition of VOCs. Activated carbon fiber adsorption followed by separation yields good subsequent treatment results.
Currently, imported RTO technologies are capable of achieving zero NOx emissions, but the cost of such imported equipment is still significantly higher than that of domestic alternatives. In terms of energy conservation, RTO systems can generally achieve self-sufficiency in energy by recovering energy from the processed waste stream!
In my opinion, the adsorption process does not meet the requirements