Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Gas seperator / scrubber.

Gas seperator / scrubber.

Gas seperator / scrubber.

We have a prototype high temp incinerator, the exhaust gas which is urged along, at low pressure, by a vac pump which is way down stream in the cool area.  When the gas leaves the incinerator it is at approx 600 deg C. but as it cools down there is a tar like substance that settles out  and completely gums up the pipework etc.   We are trying a simple home made wet cascade scrubber, but I'm sure this is not the best technique,  would have thought the best place to deal with the problem is where the gas is quite hot. I think we are trying to re-invent the wheel,  is there a "off the shelf" solution.  Any ideas  PLEASE  ? .

RE: Gas seperator / scrubber.

elvey, Due to the residuals condensing out in the exhaust duct, you're undoubtedly burning something else than just standard hydrocarbon fuels. BTW, what are you guts doing with scrubber fluid on your homemade scrubber? I take it this gas stream that's being incinerated is proprietary.

There a many manufactures of scrubbers, here is a potential list of suppliers:

Anderson 200, Tri-Mer, Clean Gas systems, Advance Air Technology, GPI Corp., CECo Group, Koch-Glitsch Inc., Wheelabrator.

Hope this helps.


RE: Gas seperator / scrubber.

Saxon. Many thanks for your reply.
Unfortunately I am not a chemical engr. so I am struggling with some of the probs. Our incineration process is dealing with semi dried sewage. The scrubber water is returned to drainage system ( which just cant be right ). Regret I dont know the make up of the exhaust gas, we havent yet had it analysed.
The scrubber mnfrs you quote, I dont recognise the companies, are they US or European?

RE: Gas seperator / scrubber.

elvey, As for the manufacturers these are all US Companies. They're listed in the Thomas register, this is short list which was extracted from the Chemical Engineering Buyers Guide. Check with any of them. They will be able to tell what you need and types of analysis they will need in order to design equipment. If they can't help, they will know someone who can.  

As for the straight incineration of sewage sludge, this stuff has all sorts of organics in it. Now I understand why you're getting "tar" condensation on the exhaust gas ducts.
Contact the above reps. they will be able to help you out.

Good Luck!


RE: Gas seperator / scrubber.

To incinerate sewage is to burn all waste and this includes products that need high retention times or higher temperatures. I would suggest you have a sample of the condensed discharge analyzed.



RE: Gas seperator / scrubber.

The condensates are a mixture of 'tars' and the best way to get rid of tars, as Gordonba suggests, is to first know what is contained (at least the major fractions). The answer lies not in the scrubbing, but in the elimination of tars. Higher temperatures and a control on the residence time is the direction I would look at for reducing tar formation or eliminating it almost completely. That is what we do in 'gasification' processes. As for solvents for the tar, try anisole....better still, look up google / tarweb. But I believe incineration may not be the only solution to your problem. Have you measured the particulate emissions yet? - that could be another problem area for you.

RE: Gas seperator / scrubber.

Gordonba - you posted something on the 'waste to power' thread......but nothing appeared on the screen. Could you post it again, please? Thanks.

RE: Gas seperator / scrubber.

hi, could anyone suggest how to treat biocides ( 2-methyl-4-isothiazolin-3-one is of a particular interest) before they hit bioplant? expected influent concentration is 0.5-1 ppm. i heard something about sodium bisulfite but cannot understand the mechanism. appreciate very much any input.

RE: Gas seperator / scrubber.

I'm sure you must be burning some type of plastic waste to great a tar like product.  This tar like by product is actually a petroleum product.  Why not send your gas through and afterburner system to burn of the tar by product & then on through a high temperature ceramic filter element baghouse.

RE: Gas seperator / scrubber.

I'm sure you must be burning some type of plastic waste to great a tar like product.  This tar like by product is actually a petroleum product.  Why not send your gas through and afterburner system to burn of the tar by product & then on through a high temperature ceramic filter element baghouse.

RE: Gas seperator / scrubber.

We have seen this problem before on odour problems with maltings roasters. The tar is caused by a visible fume that cools down.

The existing thermal incinerator fails to get rid of the smell & lets the fume through.

The tar is a problem as it will clog up scrubber, BioFilter & regernative thernal oxidiser beds quickly if not removed.

We suggest that either mist eliminators (low capital, high operating cost) or fluid bed scrubbers (high capital, low operating cost) could be solutions.

Hope this helps.

RE: Gas seperator / scrubber.


You stated that you are incinerating semi-dried sewage.

First, what is the moisture content of the sewage?

Second, what fuel are you supplementing the incinerator with?

Third, was the sewage sludge limed up?

It is highly likely that you are gasing off the volatile solids and the volatile solids are not burning to completion.  Thus, you are left with a tar-like substance that is a combination of sulfates, particulate matter and unburned sewage.  Sort of similar to black liquor in pulp & paper mills.

Your problem can be solved by first predrying the sewage until moisture content is below 5%.  Or reduce the feedrate of the sewage sludge.

Keep this in mind - any biomass with a high moisture content requires a much large boiler then bone dry biomass.  The moisture must be flashed off prior to ignition of the biomass.

You can reach me at the following email:  toddforet@usa.net

RE: Gas seperator / scrubber.

Hi elvey
I agree with oxilume . Probably you are evaporating some stuff and condensing it again.

You should use a wet scrubber of the ventury jet type , but u will have to treat the water after it.


RE: Gas seperator / scrubber.

I agree with mmo. Venturi scrubber should be the better option. You may however need to replace your vacuum pump to one which is capable of higher water gauge. If the law governing the air discharge is strict, The venturi should be followed by a wet packed bed air scrubber.

You need to treat the discharge from wet scrubbers.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close