Activated carbon bed

[laliyo]

Hello,

Does anyone has experience with activated carbon bed installation?

we are doing some investigation of carbon bed and my question is , can it be installed outdoors where ambient temperatures can go as low as -40 deg C ?

thanks

 

[bimr]

It depends on the application as well as the duration of the project.

 

[moltenmetal]

There's nothing magical about activated carbon which will prevent water from freezing, whether that water be vapor in a gas stream or liquid water going through the beds.

At -40 ambient, water freezes quickly enough that "project duration" doesn't really enter into it.

What exactly is your question?

 

[bimr]

"project duration" certainly does enter into it. The project may be a temporary installation, operate 2 hours once per month, or operate 24/7. This project could be in MN and see this climate for 1-2 months a year or in the artic. The post does not include much information.

Why would one discard options before you know the scope of the project?

 

[cheute79]

I have specified, installed, and operated carbon adsorption systems in several facilities, including outdoors in Minnesota, where the need was for 24/7 operation for years. Ambient temp is considered, but typically the solvent-laden air (SLA) is heated, and the ducting and the adsorbers are usually insulated. They are insulated to minimize condensing of water and of the solvent to be removed prior to getting to the carbon, and sometimes to prevent contact with hot surfaces. The adsorbers I have used are usually larger (2.5 to 4 m in dia, by 3 to 10 m in length), and are desorbed on-site, "automatically", using steam or hot inert gas, or very dry gas. In all cases, the system is insulated to save energy, since during desorption, they carbon is usually heated to something in excess of 100°C. Therefore, the only "real" issue with low ambient temperatures is during extended shutdowns in the middle of winter, and then there can a problem (in rare years) in Tucson or LA or Orlando.

If using small "disposable" canisters (they often are a 55-gallon drum filled with carbon, and the supplier recharges them with carbon they regenerate on their site), put an insulating blanket on it and an heating belt under the insulation. I've done that in many places.

 

[moltenmetal]

cheute79, that was my point. The OP didn't specify liquid or gas-phase service, the size of the installation or its permanence- only that it was going outdoors. The adsorption isotherms actually improve with lower temperatures, but that's not the major concern in this case.

Outdoor applications of carbon in low ambient temperatures need heat tracing and insulating for freeze protection at minimum. Sometimes a heated shed is cheaper than that, sometimes not. If the carbon must be changed frequently (ie. when it is not being re-activated on site), you have to ask yourself whether or not you want that even attempted outdoors at -20 much less at -40. And no project duration will be short enough to permit you to install such a system outdoors in -40 without heat trace and insulation in my opinion, unless the stream is scrupulously free of condensibles (and "solidifyables", if that's a word!).

 

[bimr]

Carbon based odor scrubber are installed in northern climates like Wisconsin. Temperaturs there may reach close to the -40 C or F some nights.

Emergency scrubbers for chlorine leaks are also supplied.

It all depends on the application.

 

[laliyo]

thanks everyone for their reply.

The app is for gas phase (mostly air with around 100-300 ppm of VOCs) ,24/7 operation.

Other thing is , the air is totally saturated with water vapor .
Based on preliminary sizing, looks like 2 m in diameter and 3-4 m in height(for 12-14 weeks of service).

We are also looking at some other options for the problem , rightnow.

thanks all for replying.

 

[bimr]

Carbon adsorption is not generally considered to be economical at that low of a concentration. You should consider changing the production process. You may be able to use alternative materials.

 

[cheute79]

The adsorption isotherms for VOCs all assume humidity levels well below saturated. Since most solvent-laden air applications are for a drying operation of some sort, the temperature is somewhat elevated (35-40°C, minimum). The amount of water in saturated air at higher temps is so high that carbon has significantly reduced affinity for any organic solvent. Not only is carbon adsorption not economical at the low concentrations (per bimr), but it is markedly less economical at very high humidities. CA will not work well enough to even be considered.

I suggest that you just condense the humidity, and you will probably also reduce the VOC loading or the air by more than 50% (depending on the species), which might get you low enough to emit. The resulting wastewater can be sent to a POTW for BOD removal. The BOD surcharges will be cheap compared to any other method of control.

 

[gregp10596]

A lttle help please, any idea for rule of thumb calcs for H2S removal from air stream at STP. Approx 66 ppm H2S at 12,000 cfm.

 

[bimr]

What is the application? You may able to remove this with a dry scrubber containing a permanganate oxidizer. Purafil may be able to help you:

http://www.purafil.com/index.aspx

 

[gregp10596]

Thanks for your suggestion I would be interested in looking at your product, any idea how long your media would last before break through given my intial conditions. 66 ppm at 12000 cfm. also cost ?