2 replies to this topic

Hello, my company is curerently designing a new molecular sieve carbon scrubber for the controlled atmosphere fruit storage industry. We are experiencing some problems during both the adsorption phase as well as the regeneration phase. Below I will list all of our conditions in as much detail as possible. Any assistance is greatly appreciated.

Tower Design: Twin towers, each tower has two sieve beds, 24" x 24" equalling 300 lbs of media per tower. Each bed is heated from above with a 14kw electric heater with a maximum temperature of 840 deg F. Heater elements are within 1" of the sieve beds, both top and bottom. Towers are made of 24" carbon steel pipe with no internal insulation.

Molecular Sieve: 13x

Incoming Air (scrub air): is approximately 32 deg F, low humidity (less than 5%), low oxygen (less than 5%), and has approximately 2 - 2.5% CO2 being brought to the beds via a process blower at ambient pressure and 340 CFM @ atmospheric pressure.

Regeneration Air: is from atmosphere, approximately 50-80 deg F (depending on time of year), and brought to the beds via regeneration blower at 240 CFM @ atmospheric pressure.

We are trying to attain a 1.5 hour cycle time. The problems we are experiencing during the scrubbing cycle is almost immediate CO2 break-through at exhaust (which is being sent back to the fruit storage room). During tests we have injected approximately 2% CO2 mixed with N2 to produce the most accurate conditions. (Low oxygen atmosphere at approximately 32 deg F.) We are seeing CO2 break-through almost immediately, then a steady climb in CO2 to almost 7% in the first 20-25 minutes of the cycle, then a sharp drop back to 2% where it stays for the duration of the cycle. Is the air flow moving too fast for the sieve to completely adsorb the incoming CO2? Sieve temperature at this phase is below 80 deg F. Could this be the result of an incomplete regeneration cycle?

During the regeneration cycle we are having issues with cooling the beds back down to 70 deg F in the proper amount of time to obtain full regeneration. The manufacturer of our sieve states that the regeneration temperature should be approximately 350 deg F. Is this accurate? I have seen documentation on other forums that suggest temperatures upwards of 700 deg F. Our tower design isn't insulated at the time and is in the process of being modified, as we know our heaters are working needlessly in heating the .25" wall thickness of the tower, and I know the this is also hindering our ability to cool the sieve back down for the scrub cycle.

Any help is much appreciated and if I've left any information out that would be required please let me know immediately.

[Zauberberg]

The problem sounds very interesting. Could you post a sketch in MS Excel, showing required and actual parameters (compositions, flows, pressures, temperatures, time) of all streams?

We've just finished very extensive troubleshooting of Mol Sieve (3A) dehydration unit in the Gas/LNG plant, and there might be some similarities in our cases.

Best regards,

The problem sounds very interesting. Could you post a sketch in MS Excel, showing required and actual parameters (compositions, flows, pressures, temperatures, time) of all streams?

We've just finished very extensive troubleshooting of Mol Sieve (3A) dehydration unit in the Gas/LNG plant, and there might be some similarities in our cases.

Best regards,

I will post a schematic of our tower design using a PDF format, as I already have one completed. The rest of the information I can list via excel. I have not gotten information on pressure drops from the inlet to the exhaust on either the scrub or regen cycles at this time. If this information is pertinent to the solution in your opinion let me know and I can try to obtain it.

Thanks for the reply.