Thank you for your responses.
The final system that will be installed will incorporate all standard safety measures, including temperature readings, CO monitoring, SIS bypass/nitrogen cooling/flushing, and oxygen monitor/vent header alarm, in accordance with best practices. I was more curious about the specific mechanism, but based on the above information, I assume that it is due to the unknown or complex chemistry that can occur in the bed of typical chemical facilities, in addition to the usual presence of ketones, aldehydes, and sulphates. Therefore, the standard protection setup approach that is recommended.
Thank you again,
Andrew.
1/ AC is planned to adsorb toluene, but are you sure that toluene will stay stable all the time? Is toluene (or impurities) able to condense and form tar, for example during steaming? Note that toluene derivatives have low self ignition temperature and are able to self warming up in contact with air.
The solvents in the system are relatively inert VOC, but complex unknown chemistry couldn't be ruled out.
2/ Are you sure that air is not able to get in contact with AC? Is inbreathing possible caused by liquid level drop or VOC condensation inside of vent system? How is such controlled and ensured?
The system is operated with a positive pressure and has absence of flammable atmosphere via less than MOC as it's basis of safety - nitrogen purge flow with oxygen analyser.
3/ Imagine - a worker opens filter for AC replacement and tar caught fire. What a worker shall do? How the whole system will work while personnel fight with burning AC?
Workers are not to open the AC as per supplier instructions (acute exposure risk) and the modular unit is removed as one item. The system will have a nitrogen cooling purge system if high temperature, CO or high oxygen is detected.
4/ AC adsorbs organics layer by layer. Inlet layer the first and outlet layer the last. This means this hot spots and tar will be concentrated at front layer and this front layer is critical for adiabatic heating calculation. Other layers will not take part in adsorbtion&heating, those will provide only final polishing.
Is the above suggesting that the adsorption on the carbon surface shouldn't consider the specific heat of carbon as it's localised on the surface? I'm not sure how activated carbon can do that with it's large surface area being the mechanism?
5/ If a thin front layer got tar then all AC bed becomes inoperable.
Does that safety risk or is this more of an operational issue - backpressure etc?
6/ What is planned period of operation of this bed between replacement/regeneration? Who has calculated this time and how and by what criteria/tests?
The beds are replaced based on breakthrough. Time is estimated based on carbon loading for toluene and as mentioned above, the bed is replaced as a modular unit and chemical break-in is done externally by the supplier.
Edited by AndyChemEng, 21 August 2023 - 06:43 AM.