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Welcome

Welcome

(OP)
I find that there are a lot of "environmental" forums on the internet, but they mostly relate to Civil topics and not enough towards Air Pollution/Control/Air Permitting.

Air Permitting is a difficult topic to keep on top of with the speed with which US EPA changes rules. I hope that this can be a place people can ask questions and keep on top of some of the topics relating to air permitting including:
  • Clean Air Act
  • New Source Performance Standards (NSPS)
  • National Emisison Standards for Hazardous Air Pollutants (NESHAPS)
  • Title V/Part 70 Permitting
  • New Source Review
  • Prevention of Significant Deterioration
  • Nonattainment New Source Review
  • Air Dispersion Modeling
  • Health Risk Assessment
  • And all the other topics that come up related to air permitting...
I have 10 years of experience as an air permitting engineer so I am happy to answer questions, but I often have questions as well so I hope people will ask questions and share.

If you don't know know what some of the above topics are, don't worry, just ask. Perhaps you don't know when or if an air permit is needed, just ask. If the situation is very complex it may be nessesary to obtain ouside help; that is not the purpose of this group. The purpose of this group is to point people in the right direction.

Thanks!

Ryan Birkenholz (handle: birkato)

RE: Welcome

Hello,
Nice to see your post about air quality. I have a question that I hope you can answer.
I have a landfill gas project that is flaring the majority of the gas and using some for powering a 1Mw landfill gas engine. My problem is that my gas is high in H2S. some lines measuring < 1000 ppmv H2S also Si content is high.
The H2S will cause corrosion in my gas engine. Do you know of anything that is environmental, and economical in way of cleaning the H2S?
thank you for your inputs :)

RE: Welcome

(OP)
Hi Anouri. I work with permitting landfill gas (LFG) to energy facilities frequently. I know exactly what your concern is. There are several methods of removing H2S and siloxanes from landfill gas. The method chosen usually depends on how bad the gas is and how far down you need to go.

Siloxanes:
There are several companies that make siloxane removal systems. Essentially they are large canisters usually filled with a proprietary media, similar to activated carbon or some other sort of adsorbing media. The siloxanes are adsorbed onto the surface of the media. Eventually the media gets saturated. At that time, the canister is taken offline and the LFG is routed to another siloxane canister. Then the saturated media goes through a regeneration period where it is heated (usually by electric coils) and ambient air is forced through the system. This boils off the siloxanes from the media and results in an "offgas" containing the siloxane sand ambient air. In all the systems I have seen, the offgas is routed to an enclosed flare for destruction. These systems are capable of getting siloxanes down fairly low, but not to the undetectable level. Usually that is all that is necessary to protect the engines. However, if the engine will use a CatOx or SCR system to control pollutants, the siloxanes need to be at the "undetectable" level. There are some additional controls that can be installed after the siloxane removal canisters to get to the "undetectable" level.

As for this being "environmental" and "economical". I believe it is environmentally friendly. The system does require the use of an enclosed flare which could be thought of as "wasting" the LFG, but my personal opinion is that it is better in the long run because it saves the engines from being down. As far as economics go...these systems are not cheap so economics will depend on how desperate you are to remove the siloxanes and how profitable the project is.

I do not spec these systems out, but I do know that there are at least a couple manufacturers that make such a system; we have worked with systems made by Venture Engineering on a couple projects.

Hydrogen Sulfide:
There are probably a bunch of possible solutions to control H2S, but generally they boil down to two major categories, chemical and biological. Chemical systems remove H2S by bonding chemically thus removing it from the gas. These systems are fairly inexpensive to install and work great when the total H2S load is not high, but as H2S load increases, the operating costs can become a major issue. The chemical solution must be periodically removed and replaced. One example of such a system is produced by Sulfatreat

A biological system is the opposite. It is expensive to install, but given high H2S loads, the operating costs are much more attractive. Essentially, the gas goes through an alkaline scrubbing solution which bonds to the H2S and carries it away from the LFG. Then the saturated solution is fed to a biological reaction chamber where millions of sulfur eating bacteria are living and the bacteria essentially "eat" the H2S and turn it into elemental sulfur which precipitates out. The solid sulfur is remove and centrifuged to recover for use as fertilizer or whatever. One example of this type of system is produced by a company called THIOPAQ.

http://en.paques.nl/pageid=67/THIOPAQ%C2%AE.html

I believe there are also chemical systems that are similar to the biological system except that in place of the bacteria, they use some sort of catalyst bed to convert H2S into sulfur. I have never worked with such a system though.

All the sulfur removal technologies are environmentally friendly as they are all removing suflur that would have normally been transformed to SO2 and emitted to the air. In all cases, the sulfur is eventually recovered as elemental sulfur or used in another beneficial way. The economics depend on the project. These systems can be very expensive, but in many cases, there is no choice but to spend the money.

I hope that helps.

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