Re: Water Treatment Works Core Blow
Quite a nice problem. Fifteen percent solids is definitely wet and would pump well except that there isn't enough to keep the line filled. Pigging the line is out because of the number of bends. Check your ABS pipe rating is good for 10 bar.
It will all get there eventually but not within the daily blast of 20 seconds.
When cleaning bitumen lines after tanker delivery there is always some runback at lesser elevations than your 7 m. Then we are talking about blasting the 4" line from a 30m^3 x 2 bar source. I would guess that your 150mm pipe is a bit big for the job. Smaller pipe will also carry a higher rating and might just allow for larger bend radii. ■
Re: Water Treatment Works Core Blow
Thanks for the reply.
Due to the 'open' nature of the filter cloth, reverse pumping the residual sludge is out of the question as this may have the tendency to dislodge the filter cake around the periphery of the core. I suppose that a core of at least 175m + the core length would be required but this brings problems with suction over that distance! Besides, this makes the contract a different beast than that which is now sold as part of the package and this then brings a multitude of other problems.
As previously stated, historically we have used short runs and at the same time using ABS pipework good for 15 bar ambient. Being a water treatment works and this being a batch process there is not too much concern regarding runback of any significance. Blockages are of a greater problem but these can be dealt with using rodding points that will have to be capped swept tees going with the flow. I get the point with the larger ABS elbows although on the short system we can get away with tight corners and no rodding points.
Going for a 4" pipeline would be more cost effective but this will reduce the available area to push the core slug compared to the 6". Then again, would there be a tendancy over that distance for the slug to break down and not carry using the 6"?
The client will look to our company for the feasibility of this design and I am looking to satisfy myself what we have on hand is within the distance required. ■
Re: Water Treatment Works Core Blow
Hi Andrew,
This is one intersting issue. I will ask around our contacts and let you know if we have anyone on hand who has seen or done something like this before. WWTP type engineering contract usually will not let you experiment with anything. I understand your problem correctly, you are to deliver an engineered and proven solution, correct?
What I have worked on quite a few times are system conversions that used to use 8-10Bar plant air and / or plant air reservoir tanks for pneumatic conveying applications. The pickle with receivers is that for the distance and any potential plugs can exhaust your air supply before the material is conveyed to its final destination. A constant low pressure air source ~2-3BarG can eliminate that issue. Then of course the capital cost goes up for such a machine that I guess would only operate once a day. Finding someone who has done this before is key - or you have to get gutsy.
Regards, ■
Re: Water Treatment Works Core Blow
The calculation on this forum by Mr Agarwal is for Dilute Phase, I assume that what I have is Dense Phase. Could someone point to the either the parts of the equations that can be omitted or where and what I need to also include?
Gas Velocityft/sVg
Gas Densitylbs/ft3g
Solids mass velocitylbs/ft2W
Particle velocityft/sVp
Fanning friction factorf
Equiv length pipelineftL
Pipe inside diameterftD
Gravitational Acceleration32.2ft/s2g
Constant32.174ft-lbs/lbs s 2gc
Friction multiplierfor solids conveyedk
Solids to gas mass flow ratiolb/lbR
Elevation changeftZ
It appears that I have to take some assumptions in particular the Friction multiplier or as RalfWeiser rightly states, "Get gutsy" Being 85% water I think the slug would have a low friction co-efficient but also be quite turbulent. Being non homogenous and a rare process may be the reason why I have turned in a puzzler?
I have started a spreadsheet to get myself going and am continuing to work on it now. If anyone wishes to jump in with ideas I would appreciate it.
Attachments
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Re: Water Treatment Works Core Blow
Dear Andrew,
Assume that the wet sludge slug leaves a layer of sludge along the pipe wall while passing.
Also assume that the slug’s volume is spread over the whole length of 175 m.
Then there would be a layer of 0.57 mm in the pipe over the whole length.
This seams not really unrealistic to me.
The conclusion must then be that at the end of the 175 m pipe line some wet air with a few drops is exiting.
Purging with a blower as Ralf suggested will dry the internals of the pipe, leaving behind a cake of solids.
Until the pipe is blocked.
This system cannot be treated as a dense- or dilute pneumatic conveying system and
certainly not be calculated with a program that is specially made for a stationary working pneumatic conveying system.
The system, which you describe is transient from the beginning to the end.
May be the long pipe should be purged (flushed) with water.
Or may be a pipe capsule system?
Success
Teus ■
Teus
Re: Water Treatment Works Core Blow
Teus
I believe you have hit the proverbial nail on the head. The slug will quickly break down and smear the pipeline. Thanks for a different perspective on the issue; sometimes another point of view can be invaluable.
We have to go back to the client and tell him his requirement cannot be fulfilled on paper at least!
The flushed water option would not be available, as I believe that due to the remote location of the water treatment works power usage is at its limit so installing an additional pump is out. Mmmm! I wonder if an existing diverted on-site pump could be used? I need to have a think about that one.
Also, louispanjang's suggestion put together from what you say may have some merit in reducing the pipe diameter to try and maintain the plug as best as is possible. Add to this I think over a day the lining on the pipe would not dry sufficiently enough so that the subsequent blasts would dislodge the remnants? Clutching at straws here or back to the client for a variation order maybe?
Please excuse my ignorance but could you explain a pipe capsule system? Is this something that is automated or manual? Will it be able to handle the slug size? Teus, I have searched the web and this sytem is not possible. The core blow is part of an automated process and it looks like a pipe capsule system would require a complex loading/unloading regime which again would be I believe be quite costly. ■
Re: Water Treatment Works Core Blow
Andrew,
Have a look at
http://www.pneutrans.net/
Notice that I used a question mark, when suggesting such a system
All for now
Teus ■
Teus
Re: Water Treatment Works Core Blow
I thought I had already covered the inadequacy of an 8.5m slug to fill a 175 m long pipeline. You cannot consider the process as pneumatic conveying, a 15% pulp will, as Teus said, smear a wet film along the pipe walls and this will dry out under the influences of external weathering and subsequent internal airflow.
Before the malicious accretion can block the pipe it will be scoured by the subsequent blasts and, as previously stated, will eventually reach the target vessel.
If your process develops blocked pipes you will have to resort to rodding the lines dry since you say flushing water would not be available. Pigging is not viable either because of the soft pipe material.
If you mananged to hurl the plug down the line and around the numerous bends how would you hold the pipes in place?
Not being aware of the downstream process I would agree with you that, so far, this is a complete non starter.i.e. if you pump it; can the receiver take the volume; and won't you have a resurgent dewatering issue?? ■
Re: Water Treatment Works Core Blow
Another expensive way of conveying this sludge like material would be a piston pump made by Schwing. I attaended a start up of such a pump at a power plant where they had to convey paper pulp.
6 to one, half a dozen to another: The bottom line would be that a pretty substantial invenstment would have to be made. 175m worth of conveying this small amount of material is probably better transported in a hopper.
Good luck and have a great day. ■
Re: Water Treatment Works Core Blow
louispanjang
I was merely trying to get my head around to nature and configuration of the core slug after leaving the filter press. In mind was a rolling elongated mass as I figured that it would be similar to the shorter run system. Incidentally these are in general 30-40 metre runs.
I had issues with a previous client where they were responsible for the core blow piping external to the building but failed to secure the section near the receiving sludge tank. The ABS pipework didn't break due to the heavy kick when the slug (shouldn't call it that!) came down the line but it certainly jumped around. Better still, the client asked us to fix it in their snagging list until it was pointed out that it was up to them as they installed that section!!
RalfWeiser
It's down to expense again. You know what it's like once a contract is signed. Being a subcontractor we have to apply to the main contractor to sign off on any variation order. They in turn go to the water company to do the same. Where commercial issues have to be considered so do the time constraints.
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After the very useful posts here, what we are now looking at is reducing down the pipe size, swept bends, plenty of rodding points and perhaps just give the basic figures for the period of blow and volume of air shifted to the client. Bonus is that another main contractor has just asked the same question on another water job! Looks like the same water company is passing it down.
Thank you all for your contributions.
Andrew T. Finney ■
Water Treatment Works Core Blow
I work for a company that supplies filter presses to several WTW and Sewage Treatment Works and need guidance on an issue that has been raised by our client.
Upon completion of the filtration cycle a 'wet' solution, containing about 15% solids remains in the core of the filter press. A core blow valve is opened and at the opposite end of the slug of sludge a 2" air valve is opened to deliver 4 bar air pressure for about 20 seconds to clear the core and the line. Historically the receiving tank for this slug is in close proximity to the filter press and fine-tuning carried out on commissioning. There was never and need to provide proving calculations.
However, our client now wants to convey the plug to a tank 175m away and asked for confirmation that our system is able to do this! I'm looking for some ideas on whether this is feasible, as we have no data in relation to friction characteristics of the sludge.
Vertical rise = 7m
150 NB ABS pipework.
Estimated number of 90 deg bends = 10
2 cu/m air receiver.
Max air pressure = 10 bar
2" air feed from air receiver to core of 150mm diameter
Vent to atmosphere inside a sludge tank
Estimated slug length = 8.5m
Solids within the sludge generally made up of apart from water: peat, grit and small stones up to 3mm. This is not a production type conveyor and the core blow will take place only once a day allowing the compressor to catch up.
Can someone help me out here? ■