CO removal from atmosferic emissions

[guerky]

I have a gas stream ranging from 10 to 40 ppm of Carbon Monoxide that must be reduced to 0,08 ppm for emission (flow rates: 1.000 Nm²/h). This stream also have 10 to 40 ppm of dimethyl ether, toluene and dimethylamine.

Most of the processes for CO elimination that I checked involves thermo-oxidation or catalytic oxidation, both very expensive for my low rates and concentrations.

The literature shows some promising data on Biofilters for CO removal (

http://www.sciencedirect.com/science/article/pii/S0045653508012587).

We are developing a pilot unit to test this technology under our operational conditions.
The plant produces Fungicides; there are two water scrubbers before the biofilter bed, even so there is some skepticism about the viability to use biofilters as well as its efficiency, especially for CO removal, so i dont intend to wait a few months for the results to start analysing alternatives (even the expensive ones).

What are the most cost effective technologies available?
I apreciate any tips and the State of Art of industrial CO removal.

 

[georgeverghese]

Is your flowrate 1.000Nm3/hr or 1000Nm3/hr ? What are the feedstream concentrations for each of these components listed and what else is there ? Stream temp ?

Check if a thermal oxidiser will get you down to the concentrations required. CO oxidation to CO2 would be faster at higher temp but you'd get lower conversion rates at higher temps based on Le Chatelier rule, given this is an exothermic reaction. If the inerts concentration is high, you may need fuel gas enrichment to get up to the required reaction temp. Presume you also require near complete destruction of DME, TOL and dimethyl amine? I'd avoid catalytic oxidation if possible given the risk of catalyst poisoning. You also need to tell the TO vendor what the max flow turndown ratio should be.

With a TO, there may also be the additional requirement to meet NOx limits on flue gas, with these limits depending on where this TO is to be located.

 

[moltenmetal]

If your concentrations are very low, heating the air to temperatures necessary to burn that CO completely to CO2 is going to be very costly. Your stream has very little fuel content so your fuel costs would be high even if you had excellent heat recovery on the effluent. Catalytic combustion might be a better option- lower temperatures- but you'll still have to heat the air quite a bit even with heat recovery.

A chemisorption method specific to CO might be possible but might be very expensive too. You'd need something separate to take out the rest of your contaminants.

I have zero confidence in a biofilter for removing CO, irrespective of what might work in the lab.

 

[guerky]

Thanks for the answers, this already gave me some usefull insights, especially about the TOs.

Still have some questions:
1)What would cause the catalyst poisoning in this stream?
2 Typically, what are the concentrations and flows handled by catalytic oxidizers?
3)There is not such a thing like a regenerable catalyst bed or a oxidizer agent that could be used in scrubbind solution?
4)Typically, what is the average fuel concentrations and flowrates handled by TOs, just to make a rough cost estimative?
5)The specific chemisorption method, could you direct me to a vendor of this technology?
6)There aren't molecular sieves designed for CO adsortion?
7)moltenmetal, have you seen a biofilter designed for CO removal working poorly or is this an assumption? The bed can be inoculated with MOs with affinity to the CO so, theoretically, it dont seems impossible with the right hydraulic conditions.

Aditional information:
Flowrate: 1.000 Nm³/h
Stream temp: 35°C in the summer (after the scrubbers)
Estimated CO concentration: 20 ppm
Estimated DME concentration: 20 ppm too
Estimated Toluene concentration: 40 ppm
Dimethylamine can be neglected (removed in acid scrubbing)
DME and Toluene can be held in activated carbon bed (already installed).
CO treatment would be installed after the scrubbing system, so moisture is to be expected (however, a condensation system would not be hard to design and install).



In God we trust. All the others must bring data.

 

[georgeverghese]

Would be better to get answers to these questions from a TO vendor.

If you have only 1Nm3/hr to be handled, can you not just vent this stream to atm via an elevated stack, with stack elevation such that dispersion by air gets you to ground level concencentrations which are permitted by the local environmental authorities? Od do these people also impose absolute limits on the quantity / flowrate of each of these components in the emissions stream at the exhaust stack?

If not, and with only such a small quantity of these chemicals which are easily combusted ( CO, DME and TOL), would also look to installing a dedicated waste gas burner in the radiant section of an existing furnace if you have one. A dedicated TO may be a little over the top for these easily combusted chemicals.

 

[georgeverghese]

Have my doubts if you will find an industrial burner that can handle just 1.0Nm3/hr of this waste gas, whether this be in a TO or a dedicated waste gas burner in a furnace.

 

[moltenmetal]

1 Nm3/hr? Wow- run the flow as the air supply to a Bunsen burner and forget about it!

 

[guerky]

OBS.: 1.000 Nm³/h = 1000 Nm³/h
Sorry for the confusion. In my country we use commas for decimals and dots between thousands.

In God we trust. All the others must bring data.

 

[georgeverghese]

At 1000Nm3/hr, that would be a significant amount of fuel gas to bring this mix up to reaction temp. You still havent said what the rest of this stream is ( air??).

You should check what the local environmental emissions limits are for these components. What are they for each? In some cases, state and federal limits may not be the same.

 

[guerky]

Yes, the inert % of the stream is air.
The State laws limit the total mass of polutants that can be emitted. I can't just change flow rates or discharge those gases higher (just curious: these kind of allowance still exists in developed countries?)

Cars use small catalyst vessels for CO treatment. They are expensive, but pretty durable. There aren't industrial equivalents?
OBS.: My flowrates can be manipulated down to about 400 Nm3/h by dividing them in two streams if it would help the final gas treatment.

Edit: Reanalysing the whole gas abatement system, i'm sure i can, with some cheap and simple line modifications, separate all the CO, DME and Toluene in a single 400-500 Nm³/h stream, doubling its concentrations.
This change anything?
OBS.2: I will contact vendors anyway for the final solution. But i wish to have a better understanding of the available technologies and its limitations before.

 

[georgeverghese]

Minute amounts of particulates and other metals / sulfides etc in vapor phase may de activate catalyst activity.
You would need to get a detailed analysis of this stream composition for both steady and unsteady state operations if you want to consider catalyst aided combustion. Some kind of particulates filtration and solvent (water or other solvent) scrubbing will help to increase effective catalyst run time.
Yes, reducing stream rate by half will certainly help to reduce operating cost in terms of the amount of fuel gas required to bring this stream up to the required combustion - reaction temp.

 

[mbt22]

Cars use small catalyst vessels for CO treatment. They are expensive, but pretty durable. There aren't industrial equivalents?

There are, almost identical, but they need to be hot to operate so you need to heat up your stream for the oxidation to take place. Typical CO limits for exhaust are 0.3-0.5 %vol in the UK, so far above the levels you're interested in.

Developed countries can certainly allow dispersion without abatement. Best available technology (or best available technology not entailing excessive cost), so if you can't reduce further you have to decide whether to build the process or not. Say you really want to go from 40 ppm to 80 ppb via oxidation, so heat the stream up by burning nat gas. The furnace could easily emit more CO than the emission you're trying to mitigate, so why do it? You're emitting roughly roughly 1 te/hr exhaust at 40 ppm CO, so 40 g/hr CO. Euro 6 emission limits for a petrol car are 0.5 g/km, so it is the same order if magnitude as a single car at motorway speeds.

Incidentally, reliably measuring 80 ppb in a vent stream is non-trivial, how are you planning on monitoring to demonstrate compliance? Is this a requirement, or have you back-calculated it from a total flow?

Matt

 

[georgeverghese]

Pre concentrating / separating the organics on to a regenerable carbon bed adsorber may help to reduce TO operating costs.

 

[Rocco8]

Google the COPure Process.

 

[guerky]

I've installed a pilot unit biofilter on our fungicides plant.

In a few weeks i must have some results to share.