Sewege Transfer Pump - Rotary Lobe Type 2

[hhmh2004]

In one of the jobs I have to specify a pump for domestic sewage transfer to waste water treatment plant. The Pump Flow is 290 USGPM and Required Head is 230 ft. The pump will take suction from an above ground Sewage Tank.

Here in Saudi Arabia, typically centrifugal non clog type impeller pumps are used for this service.

But due the required duty point specified above the centrifugal type of pump is not available in the market.

Second choice is to go for rotary lobe type of pump.

Is anybody familiar with use of rotary lobe pump in domestic sewege transfer?

Is it good in this service?

Does it require some kind of inlet protection i-e grinding or screening?

What is the maximum particle size it can pass?

Thanks and Regards

 

[DubMac]

Would agree, PC pump not a lift station solution, but this is transfer service drawing from above ground tank.
PC pumps get the nod many times as a result of being the only solution remaining; ergo, they get a lot of DOG services thrown at them.
I would first look at a dry-pit non-clog centrifugal here, but the head is too high for an economic solution with a centrifugal. Then in the PD pump family, I would consider a PC pump first over the other rotary type PD pumps: gear, lobe, etc.

They are very well suited to hard angular solids (which give trouble to gear/lobes) as the stator has the ability to conform to the solid's shape and "roll" them through the pump without much abrasion. Long stringy solids should be chopped by macerator/grinder; which needs to be a part of any PD pump package.

The PC pump, if sized properly, runs relatively slow and has a very high reliability. The gotchas with a PC are allowing it to run dry, which can tear up the stator in no time; and using the wrong rotor/stator materials. Natural rubber is the very best material we know of in terms of combating abrasion; it is not however very tolerant of hydrocarbons and other petroleum based oils. If they are present, go to a nitrile or Buna rubber.

If the rotor/stator is properly selected and kept wet, then the next thing to look at is the mechanism that translates the driver's concentric rotation into the elliptic motion of the rotor. This is sually acheived by some sort of geared universal joint. The very reputable vendors (Moyno, Netzsch, Mono(now NOV Mono?), all provide high quaility drive trains and these can make the PC the very lowest Total Life Cycle cost solutions in high solids service.

Would like to see a cost comparison among some of the several solutions we have talked about; remembering that this is tough duty on ANY type of pump. Its just a matter of finding the pump that will fail the least often.

 

[hhmh2004]

I am still waiting for Vendor Replies on issues raised in this thread and will update as soon as possible.

Actually the "Big" Oil and Gas Company in Saudi Arabia has very stringent guidelines for Centrifugal Pumps. It has to operate within 60% to 110% of BEP envelope, otherwise it is technically not acceptable. My first choice for this service was a centrifugal non-clog type pump but as explained above in this thread there is no pump in the market which falls in 60% to 110% BEP criteria.

So I have to go for a PD Pump and most common PD Pumps in market for sewage service are Rotary Lobe Type and PC Type. Thats why I asked in this thread whether somebody has an experience in using Rotary Lobe Pumps in Sewage Transfer.

Now based on all the discussion in this thread following can be conlcuded.

1. Rotary Lobe Type Pump can be used in this service.
2. It will have maintenance issues relating to fibers and solids in the sewage. But this pump will take suction from a Pre-aeration Tank which is above ground and will allow some solids settling time. Anyways, I will consider installing an inline grinder upstream of the pump to safeguard the pump.
3. Dry run protection will be required which can be offered by the pump Vendors.
4. Upgraded pump materials will be used with proven experience in Sewage Transfer.

Once again Thanks to everybody for their kind interest in this issue and providing me with their valuable knowledge.

Regards,

Haroon

 

[Artisi]

It is OK to have very strict guide-lines - but you have to live in the real world and sometimes these rules have to be bent / twisted / relaxed to suit what is available.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)