Degassing of high points in in sludge lines

[MartinLe]

In a current project we will have high points in sludge pipelines from the anaerobic digester to the sludge HX. There's the question on how to get residual gas from these high points. There's space where we can safely vent this gas, the question is how to get the gas from the pipeline

How much gas will we actually have? What's a good way to estimate this amount?

One idea for degassing involves a (created for this purpose) piping dead end above a high point, the idea is that once in a qhile someone from the plant staff whacks the part with a wrench, if it sounds empty it's isolated from the main piping with a knife valve and filled with water to get rid of the gas.

Another idea is to use one of these Mankenberg devices:

https://www.mankenberg.com/en/bleeding-and-venting-valves/eb-184

- we have not yet heard back from mankenberg if they handle sewage sludge.

There's countless other options, I'm sure. Which is the best will depend on how much gas there will actually be, and I don't have a good idea on how to estimate this - so this would be my first question

 

[QualityTime]

Slope everything upward from the digester to the heat exchanger and back to the digester. That way there is no gas trapped in the piping

 

[MartinLe]

The joy of building within existing plants and around existing pipework ... so much existing pipework!
Sadly we are very constrained in our routing and can't avoid high points.

Mankenber advise against their devices, there's a concern that the thick sludge will hinder the ball from moving.

 

[bimr]

Yes, Garr Jones also recommends against the use of air release valves in sludge piping as well for the same reason.

 

[Pfdubz]

Digested sludge is such yucky stuff that an automatic method to do anything is almost impossible. I like your idea of a "dead end", but I don't follow your explanation. I would put a size on size tee at the high point and a blind flange on the third leg of the tee. Tap the blind flange with a relatively large diameter connection for release of the gas (at least 2") and double valve it. Place a cross connection to a non-potable water supply between the two valves so that the gas relief line can be backflushed to clean it each time it is used.

 

[MartinLe]

My idea is essentially (from bottom to top) tee - gate valve - short length of pipe DN200 with two 2" ball valves (near top and bottom). Use water to vent the gas without entraining air into the system.

 

[Pfdubz]

I think I understand.
The volume of sludge in the piping between the low points on either side of a high point should be equal to the volume of sludge that can generate gas that needs to be vented. This could be substantial and require a large commitment form O&M staff to maintain. Ergo, Air Release valve. It will still be a major headache, but I think it would be the lesser of two evils.

 

[QualityTime]

look closer at moving equipment and piping around to get the sloping and do it right the first time. no one is going to thank you when the half ass solution does not work. wasted time and money

 

[QualityTime]

The last thing you want is explosive digested gas being released into a room via an air release valve or a manual bleed valve

 

[MartinLe]

The points where we attach the sludge lines are below ground level, the only possible routing is to go above ground level and then down again. Upside: Venting would be outside.

 

[QualityTime]

I do not know the layout of your plant but trying to make a square peg fit into a round hole sometimes makes people think about really weird solutions. You get twisted in a knot. And then when it does not work all the logic you used to convince yourself back then about why it would work all of a sudden does not make sense anymore.

Use the KISS principle. You will be able to sleep at night without worrying about whether your "solution" will work as it gets constructed. Let the client know about the really safe alternatives. The really safe alternatives will cost more money but we know it will work. Why are you taking the risk and putting your neck on the line?

In an ideal world this is what it would look like:
[ul]
[li]Look at locating the sludge withdrawal pumps at the lowest level of the digester complex (i.e. basement).[/li]
[li]Have the heat exchanger located on the first floor[/li]
[li]Pipe the sludge withdrawal pump discharge to the bottom mounted heat exchanger inlet on the first floor.[/li]
[li]Pipe the heat exchanger top mounted heated sludge discharge to the digester.[/li]
[/ul]
The continuous sloping of the piping upward will naturally move the gas bubbles back to the digester. There will be no need for manual or automatic air bleed valves. Besides, are these automatic air bleed valves rated for digester gas service? I doubt there is such a thing.

Even if the piping is horizontal, the flow direction of the pumped sludge will move the gas bubbles along as long as there are no high points in the piping

BTW, is this project in the Niagara Region?