Liquid Overfeed Systems

[US Iceman]

I recently investigated a large liquid overfeed system (ammonia). The system was using multiple refrigerant pumps piped in parallel.

Each refrigerant pump was installed with a separate suction line and suction service valve dropping down from the vessel. The pump discharge pipes were installed into a common main pipe for the liquid supply to the evaporators.

What has your experience been with systems like this?

[ecclesk]

I look after some systems in which the pumps are installed in this way, one vessel with two pumps, common discharge,

i only usually run one pump and keep one as stand by, i do have cavitation problems on occasion with one system and have tried everything we could think of but i think it's a design issue, also found that one of the two pumps on this plant in question seems to deliver a more stable pressure and doesnt cavitate as much as the other, even after changing the pump & motor for a spare one we still have the same issues?

i believe it may be to do with the way the vessel is designed/piped. the suction lines of the pumps are at different ends of the vessel as to are the wet return and the compressor suction, the pump situated under the wet return end of the vessel is the one we have problems with.

I'm also aware of another site within our company that has the same set up but with three pumps, it was designed to have two pumps running and one stand by but they have never been able to run two pumps due to cavitation problems.

[Tycho]

with non returnvalves on the discharge it works like a charm.

Also, if three pipes are connected to a circular vessel, you need a vortex stopper inside the vessel so you dont get cavitation.

What kinda pump is it?

on our systems you have to manualy start and stop the pumps. On systems with two or more pumps we have diff.pressostats to start the pumps in sequence.


but on the majority of the systems we use our KS-E5 ( kvaerner pump), and usually one is enough to supply 8-12 vertical platefrezers with a stable pressure of 2 bar.

[Renato RR]

Try to contact pump suplier to find out what he recomends and how he advice to install the pumps.

R enato

[SteveDixey]

I recently investigated a large liquid overfeed system (ammonia). The system was using multiple refrigerant pumps piped in parallel.

Each refrigerant pump was installed with a separate suction line and suction service valve dropping down from the vessel. The pump discharge pipes were installed into a common main pipe for the liquid supply to the evaporators.

What has your experience been with systems like this?

Key thing is getting the suction piping right and keeping the wet suction return away from the section of the vessel feeding the pumps.

Most now recognise pumps need 3" or even 4" suction lines and take as direct a route as possible. If the evaps have no load, and so reduced liquid feeding in, pumps can start to cavitate in low pressure \ off-load conditions. If the design is wrong, you can suffer no end of problems and it is costly to fix.

Quite common on large industrial plants, and have come across up to 3 pumps feeding in, but most use 2 with one as stand-by.

Steve

Steve

[US Iceman]

Hi guys,

I wanted to see what sort of problems the rest of you have seen or had.

i only usually run one pump and keep one as stand by

This is what I would recommend. One pump for 100% of the requirements with one standby pump for redundancy. Either of these pumps are sized for the design flow rate and head.

...the pump situated under the wet return end of the vessel is the one we have problems with

As you probably suspect the splashing of the liquid into the vessel is creating problems for that specific pump. When the entering liquid disturbs the liquid around the pump suction connection some gas bubbles are probably being entrained in the liquid.

If liquid has bubbles in it the density of the liquid is decreased slightly. This reduces the static head on the pump suction. Any decrease in static head is a decrease in net positive suction head for the pump.

A pump curve will provide the minimum Net Positive Suction Head Required (NPSHR) that is needed at some flow condition. If the Net Positive Suction Head Available (NPSHA) is less than the requirement of the pump (NPSHR), the pump will cavitate.

One of the trouble areas is solving for the correct NPSHA and making sure the pump operating point does not change.

...it was designed to have two pumps running and one stand by but they have never been able to run two pumps due to cavitation problems

If these are centrifugal pumps they are probably fighting each other during operation. One pump is more than likely pumping more liquid than the other pump. The pump that has a higher volume flow is probably the one cavitating.

Check the motor amps to see if they are the same or different. Also compare the running amps to the motor nameplate full load amps.

[US Iceman]

What kinda pump is it?

Hi Tycho, they are Cornell refrigerant pumps (open drive, not the hermetic ones) See the link below for additional information.

http://www.cornellpump.com/industria...eticHansen.pdf

...you need a vortex stopper inside the vessel so you don't get cavitation

These certainly help, but they don't prevent all of the cavitation issues. Without a vortex eliminator (stopper) you will have all sorts of problems if the operating conditions are close to the minimum pump requirements.

The vortex eliminators do provide a very much needed operational requirement.

[US Iceman]

Most now recognise pumps need 3" or even 4" suction lines and take as direct a route as possible.

I agree. I think the suction lines should be full size (same as the pump suction connection). The pump isolation valve on the suction side should be either a full size angle valve, or a high performance butterfly valve (Much less friction loss than an angle valve).

I also believe it is important to have about 6-10 pipe diameters down stream of the angle valve to allow the liquid to straighten out before it enters the pump suction.

If the evaps have no load, and so reduced liquid feeding in, pumps can start to cavitate in low pressure \ off-load conditions. If the design is wrong, you can suffer no end of problems and it is costly to fix.

Yes sir. The minimum flow situation can be just as bad as the full load condition. Worse if you are using hermetic pumps that are not set up properly.

This system had four pumps in parallel. All pumps were running at 3550 RPM also!

[Tycho]

Now that is the oddest looking pump I've ever seen

Here's how we do it


Also note the gas trap on the suction line.

The pump we use is the same one as in the drawing, One of the engineers that worked with us before have one running a water fountain in his garden

Hi Tycho, they are Cornell refrigerant pumps (open drive, not the hermetic ones) See the link below for additional information.

http://www.cornellpump.com/industria...eticHansen.pdf



These certainly help, but they don't prevent all of the cavitation issues. Without a vortex eliminator (stopper) you will have all sorts of problems if the operating conditions are close to the minimum pump requirements.

The vortex eliminators do provide a very much needed operational requirement.

[US Iceman]

Beauty is in the eye of the person looking.

The pump link I posted shows the pumps that are similar to most of those used here in the US.

Some people build their packages very similar to what you show Tycho. Others will use two independent pump suction lines instead of the one large drop leg with the pump suctions connected to it.

Why does the piping for the gas trap in the pump suction line only project a short distance into the vessel?

Do you actually run the liquid level this low in the vessel?

[Tycho]

I'd say that our pump looks like a Rolls Royce, next to a Yugo if it was placed side by side with the one you showed

It's only projecting (poking ) a short way into the vessel, so that if the customer choose to run with a minimum liquid level it wont work as an injector (speed of liquid passing the gas trap sucking gas into the pump).


"drop leg" is that what you call the the thing sticking out from under the tank? here in Norway we call it "udder" like the ones you have on cows

No, we dont run with that low liquid level, it's usually a few inches higher
seriously, the number on the drawing is the minimum liquid head needed for the pump to maintain it's pressure.

the good thing about having the drop leg is that with this kind of pump you can maintain a liquid head with a minimum of Kg's of refrigerant instead of having to keep a ton of extra refrigerant in the seperator, you can do it with a 100kg instead.

On our Spray chillers, all of the charge is in the drop leg of the chiller, nothing up in the shell.

we used to be world-wide when we were a part of Kvaerner, but now we are somewhat limited to Norway, Denmark, Sweden, UK, Scottland, Iceland and Faroe Islands.

(Btw, if any of you UK engineers are situated close to Peterhead, and know your way around RSW, we might be interested in a service partner over there... If I get my way, you will be taken to Norway for education on our plants )

do you mean that they use two separate suction lines on each side of the vessel, instead of the central drop leg?


we use the drop leg on all our pump systems, no exceptions.


We used to have a department in Seattle 5 years or so back... are you saying they failed in converting the U.S to our ways?

We now co-operate with Highland refrigeration (I seem to remember they are in Seattle also)

[US Iceman]

I'd say that our pump looks like a Rolls Royce, next to a Yugo if it was placed side by side with the one you showed

No need to get nasty.

the good thing about having the drop leg is that with this kind of pump you can maintain a liquid head with a minimum of Kg's of refrigerant instead of having to keep a ton of extra refrigerant in the seperator, you can do it with a 100kg instead.

Absolutely right and no argument from me.

do you mean that the use two separate suction lines on each side of the vessel, instead of the central drop leg?

Some do, some people do not. Everyone has a personal preference. For the separate lines they connect into the bottom of the vessel. I'll try to find some pictures to show you.

are you saying they failed in converting the U.S to our ways?

You know how it is... some people are slower than others.

There has not been much research on these vessels since Prof. Lorentzen wrote some articles back in the 60's and 70's. I am still trying to find some copies of these.

Do you know anyone who may have some English copies of his work?

[Chopper]

Tycho, what is the name of the company you work for? I work for the largest and best refrigeration company in the world and am based in Peterhead, Scotland. I persume you are looking for someone to do service work on the pelagic vessels based across here with their RSW plants.

Kind Regards

Chopper

[Tycho]

Neener neener, your pump sucks neener neener

personal preference? we dont go that way when it comes to the construction of the plant, Kvaerner had some pretty good engineers (the office kind, and the working kind) and they came up with some pretty good solutions back in the days, so we have stuck with them and we have some pretty sturdy plants, not saying they are the best, but they are way up there *floats away on a white sky*

Oh, we'll whip you into submission soon enough
*Whip crack*

(if you need a place to host the pictures, let me know)

We do struggle with (working)engineers having different minds abround the regulating, alarm and warning settings on our PLC load control system


I'll talk to a guy who knows a guy who is a friend with someone who has heard of a guy that has a friend who knows someone who once heard of someone who had seen some of Lorentzen's work in English somewhere

Kidding, I'll shoot a mail to the Lorentzen foundation and hear if they have anything, or know about any of his work in English

No need to get nasty.



Absolutely right and no argument from me.



Some do, some people do not. Everyone has a personal preference. For the separate lines they connect into the bottom of the vessel. I'll try to find some pictures to show you.



You know how it is... some people are slower than others.

There has not been much research on these vessels since Prof. Lorentzen wrote some articles back in the 60's and 70's. I am still trying to find some copies of these.

Do you know anyone who may have some English copies of his work?

[Tycho]

Tycho, what is the name of the company you work for? I work for the largest and best refrigeration company in the world and am based in Peterhead, Scotland. I persume you are looking for someone to do service work on the pelagic vessels based across here with their RSW plants.

Kind Regards

Chopper

You mean you work for the largest company... yes?

I work for MMC Kulde (translates to MMC Refrigeration), we are the continuation of Kvarener Kulde, or Kvaerner Fish Process Technology (KFPT), our sister company MMC Tendos (translates to MMC Tendos ) delivers vacuumpumps and vacuum systems for unloading fish from pelagic vessels.

we have an engineer heading over there on monday or tuesday to do some service on a vessel.

Seen this one before:
http://www.pbase.com/kimmo98/image/49607781

************Edit**************
Called him, he's going to Fraserbourgh, Fraserburoh or something like that (sorry, but the rough ending is hard on us lesser ones )

He didnt know yet if it was monday or tuesday, but I can hook you up if you want...

[Chopper]

I know it very well, It normally fishes out of Fraserburgh.
Did it not burst the cooler? I thought it was an optimar install.
Do you have many systems across here?
Coincidently its York i work for and we have a just recently opened a new branch in the area.

Regards

Chopper

[Tycho]

I know it very well, It normally fishes out of Fraserburgh.
Did it not burst the cooler? I thought it was an optimar install.
Do you have many systems across here?
Coincidently its York i work for and we have a just recently opened a new branch in the area.

Regards

Chopper

First of all, the cooler did not burst.. very important

What happened was that the company that produce the coolers for us didnt roll (extrude? you know, when you put the pipe in the cooler and use a special tool to widen the pipe so it is "widened" to fit the hole in the endplate) all the pipes on the cooler, my guess is the cooler was made on a monday or a friday

They use a Loctite compound on the pipes before they roll them, but seeing as they didnt roll all the pipes, the loctite hardened and kept it tight for a while, but with the water on one side and ammonia on the other side it wore off and the cooler started leaking. Nothing wrong with the cooler apart from that.

Yes, it was an Optimar install, we used to be called "Optimar Kulde" we seem to be changing name so often, so when anyone asks anyone of us engineers out on site about the name we usually give a reply along the lines of "Yeah, we got to be known out in the market, so we decided to change names... You know, so people wouldnt recognice us"


We have a few over there, but as you work for York... a certain place will freeze solid before our higher up's will allow you to know anything about our systems :/' as we are competing with York in our area,

By the way, did you know that the branch in our district (Aalesund) doest work overtime? dig that, I clocked in 600 hours of overtime last year and all of their 6 engineers clocked in maybe 100 together

[Tycho]

I'll just throw in one that show's our work site

MMC Kulde is situated in the building infront of the wheelhouse, while Optimar, the company that makes factory processing equipment is in the larger buildings to the right.

http://www.pbase.com/kimmo98/image/49607769


(you can click the link called "ships" in the top left to get to a gallery showing some of the ships we service)

[Chopper]

For years all the vessels were kitted out with teknotherm chillers but the norm appears to either York or Optimar these days. Service on these systems is very minimal at the moment due to cut backs on fishing quotas and the chillers only clocking up 2'000 running hours per year! Alot of plant but not a good turn around o service work.
My previous employer used to be Teknotherms prefered contractor for warranty and service work on their installations. Wasnt too impressed!
If you are looking for a contractor to carry out such work across here i can give you a list of reputable contractors and there contact numbers if it would be of intrest.
Beautiful place Norway, was across working last summer up in Kristinsund on a dive support vessel. Scotland has some cracking veiws but Norways got some breath taking veiws, especially of the women. Beers too expensive though!!!

[Tycho]

Teknotherm seems to be a swear word among 95% off fishingboats around here, I find it odd, as I know the people working there and they are competent people, but as soon as I enter a vessel that has had teknotherm onboard I'll be going "whoooah, it cant be that bad... NOOOooo, they didnt... really, they did that? no way... you were there yourself? and they said that?" I dont know what the deal is, but around here teknotherm is pretty much the devil...

good for us, but bad for them, it's kinda sad tho, as the people working for them are good guys and they know what they are doing.

But teknotherm, in my eyes, are stuck in the last century with their equipment... it's obsolete, end of story.

As R.J Mitchell said "It is not good enough to follow conventional methods of design. It is essential to invent and involve new methods and new ideas."

The service on our plants would be limited to the occasional solenoid calling it a day, but every now and again a relay in the controlcabinet going tits up and it would be nice to have someone over there be able to drop by and take a look at it.

If you have numbers and contact adresses for local companies that you feel are competent, it would be great if you could shoot them over, as the only ones we work with in GB is KER refrigeration in Ireland (and it seems like we only work with them, so they can get discounts on our spare parts )

Beautiful country my arse

This is me driving home from work last week... I'll agree with the beer price tho... costs an arm and a leg to get drunk in Norway and you'll have to sign you firstborne over to the government.. and I''m not kidding

For years all the vessels were kitted out with teknotherm chillers but the norm appears to either York or Optimar these days. Service on these systems is very minimal at the moment due to cut backs on fishing quotas and the chillers only clocking up 2'000 running hours per year! Alot of plant but not a good turn around o service work.
My previous employer used to be Teknotherms prefered contractor for warranty and service work on their installations. Wasnt too impressed!
If you are looking for a contractor to carry out such work across here i can give you a list of reputable contractors and there contact numbers if it would be of intrest.
Beautiful place Norway, was across working last summer up in Kristinsund on a dive support vessel. Scotland has some cracking veiws but Norways got some breath taking veiws, especially of the women. Beers too expensive though!!!

[US Iceman]

...not saying they are the best, but they are way up there

I do agree with you the plants should be designed and built to last for a long time without problems. This is always my goal to "do it right the first time". It is not much harder to design it right and does not cost much extra to do it right. What I like to see is a system that you can start up without much trouble and walk away from knowing it will work properly.

Oh, we'll whip you into submission soon enough

Sure you will. I have been know to change my mind if presented with facts.

Control logic and safety and alarm points are always a fun discussion topic. Everyone has an idea for the best way. Myself, I like two layers of controls (at least). One layer is a fail-safe when all else goes balls up. The second layer is the upper-most layer for all of the automatic controls, PLC, computers, etc.

An example would be a mechanical float switch for a high level shutdown, while a capacitance probe can be used for normal operations and safeties. If one fails, the other is sure to catch it.

I do appreciate you inquiring about the Lorentzen papers. He wrote about some of the most interesting topics and was always based on solid evidence. Unfortunately, I suspect most of it has been forgotten by most.

Oh, by the way... The picture you took is very cloudy and out of focus.

And what is this talk about beautiful women??? You didn't answer that one.

[US Iceman]

Tycho,

Do have any information you can share about the spray chillers? I think these are very interesting, but this is one item I have limited experience with.

I understand the principles and the benefits but have not been able to find any technical information related to design aspects.

Thanks,
US Iceman

[Andy]

Tycho,

Do have any information you can share about the spray chillers? I think these are very interesting, but this is one item I have limited experience with.

I understand the principles and the benefits but have not been able to find any technical information related to design aspects.

Thanks,
US Iceman

Try this sitehttp://www.th-witt.com/

In their news section.

Also their way of piping the pumps is the way to go. 6" drop leg turning thru 90 deg and then reducing uinto the pump, minimum drop leg lenght is about 1m I think.

Kind Regards. Andy

[US Iceman]

Thanks Andy. I reviewed the website, but it appeared they only listed a picture of a chiller without much additional information.

[SteveDixey]

If you click on this line in the downloads section,

"installation manual GP" it is a pdf file, and look at pages 23 and 24.

Steve

[aawood1]

Hi US Iceman, I have a 500 ton per hour surge drum that has 3 Douglas 4A pumps freeding a Freezer that needs 400 tons of Ammonia per hour in the 7 evaporators. The pump main is 6" about 230 ft. in lenght with a working pressure of .5 Bar,with a wet return of
10" the same lenght that feeds back in at each end of the surge drum. It was about 2 days untill we got it right on each coil, but now works well at -38oC on the coils and -42oC off the surge drun to the compressors.
( Got called to a Ashworth Inc. freezer today it had Frigoscandia on the door but the plate inside said Ashworth Inc. USA, Mini gryo belt freezer as the belt had stoped. found it had come over the top of the drum. Not bad it was made in 1972. The freezers we get now are the Frigoscandia Gryocompact units self-stacking belt, We had the first one in the UK 3 years of over time untill it was right and lots of nights out with the Frigo boss men.( Good old days)
all the best Arthur.

[US Iceman]

"installation manual GP" it is a pdf file, and look at pages 23 and 24.

This is for the pump installation manual. I did look at this but i did not see anything about spray chiller requirements.

I would assume the pump suction design is similar for both liquid overfeed or spray chillers. The inside of the spray chiller is what I'm interested in.

Thanks Steve.

[US Iceman]

...It was about 2 days until we got it right on each coil...

Was this time for the adjustment of the hand expansion valves on the coils?

It does not really surprise me that it took this long. These adjustments can really eat up time.

What type of methods did you use for the hand expansion valve adjustments?

[aawood1]

Yes it was time taken to adjust the hand expansion valves. When the freezer was moved we had 18 probe pockets welded in to the coil infeed and return pipe work and the liquid line header and wet return header, all feeding back to one digital thermometer. Then with some good luck it all started to get a good balance over the coils. Down side was the main contractor did not work out the right Ammonia charge for the new pipe work, Had to charge 5 Tons of Ammonia into the old and new system, 4 Tons more that they worked out. I have adjusted the liquid feed pressure down on the RS A4A pressure regulators on each pump to .5 Bar from 1 Bar.

[US Iceman]

I have adjusted the liquid feed pressure down on the RS A4A pressure regulators on each pump to .5 Bar from 1 Bar.

Where are these regulators installed? Are they at the end of liquid line and connected into the wet suction lines?

If I am following your description then these regulators are for the minimum flow pressure control?

The four extra Tons of ammonia is a fairly big mistake. Any ideas on how they were this far off of the system charge?

[aawood1]

Hi Iceman, The RS valves are fitted next to the pumps before the right angle non-return/ stop valves where the 3 pumps connect into the liquid line. As for the Ammonia charge they said it was the fact that the main system was low to start with. But if you take 50 ft of 10" pipe that makes up the wet return header on the freezer and the coils that have about 1/4 a ton of Ammonia in each one with the 25 ft. up lift onto the roof. (They did not have to put the cost of charging into the cost of moveing the freezer it made the bill look good. The job was put out with us doing all the pump outs and venting of the pipe work and the pressure testing/ recharging of the plant.) What would say.
Arthur.

[US Iceman]

Here are some pictures from one system.

One picture is of the low-pressure receiver and pump looking down the engine room.

The other picture shows a single pump installed before insulation was applied.

I apologize for the small pictures, but the file size was too large to post directly. They were printed into a PDF to get the file size down to the limit allowed by the RE site.

[US Iceman]

Hi Arthur,

The RS valves are fitted next to the pumps before the right angle non-return/ stop valves where the 3 pumps connect into the liquid line.

OK, I think I see how they are installed. These are the bypass valves that maintain a constant head on the pumps. If all of the solenoid valves are closed and the pumps are still running, the pressure is bypassed back into the vessel or wet suction line. Is that right?

As for the Ammonia charge they said it was the fact that the main system was low to start with.

That is a lot of ammonia to be short of. When the system was operating it must have been right at the lowest minimum level to still run.

They did not have to put the cost of charging into the cost of moving the freezer it made the bill look good. The job was put out with us doing all the pump outs and venting of the pipe work and the pressure testing/ recharging of the plant. What would say.

Sounds like a way to make the first cost look better.

I think it is a good idea for the facility people to do the pump outs and venting since they probably know more about the system though.

[aawood1]

Hi Iceman, Yes the pressure valves return into the surge drum at just over the liquid high level control about 1/3 up at one end. The Freezer was made by Hardy Lucas of the USA and is about 30Ft wide 50 Ft long and 30Ft high with a 6Ft 6ins wide belt.
Arthur

[US Iceman]

On the overfeed systems you guys work on do you install the pressure control valves at the pump discharge or at the end of the liquid line (as shown in the attached drawing)?

For those of you who have done it both ways, any complaints or suggestions with either method?

I am interested in learning more about the installations you work on and the problems you frequently encounter.

Thanks,
US Iceman

[Tycho]

Tycho,

Do have any information you can share about the spray chillers? I think these are very interesting, but this is one item I have limited experience with.

I understand the principles and the benefits but have not been able to find any technical information related to design aspects.

Thanks,
US Iceman

We dont have much information about the Chillers ourselves, as it's not our product.

The design is very simple, looks alomst like a normal chiller, tho on the inside only the lower half has tubes, in the top half there are two pipes with nozzles, side by side running the length of the chiller. The two top pipes are fed by the ref.pump.

No charge in the shell, all the charge is in the dropleg.


------------------

And on the girls, I'm not sure... the wintergear makes it kinda hard to determin

[US Iceman]

Thanks for the information Tycho. The arrangement you describe sounds very similar to the water spray headers used on evaporative condensers.

Do you know the spacing on the spray nozzles, nozzle type, and flow rate through the nozzles?

I think the idea of using the large drop leg for the pump makes a lot sense. The volume of liquid required for the chiller is fairly small and the piping circuit is really short. The amount of refrigerant in suspension could be contained within the drop leg very easily.

I'm getting a pretty good picture of these now. Thanks again.

And on the girls, I'm not sure... the wintergear makes it kinda hard to determine

OK you got me with that comment. Almost fell out of the chair.

[Tycho]

Thanks for the information Tycho. The arrangement you describe sounds very similar to the water spray headers used on evaporative condensers.

Do you know the spacing on the spray nozzles, nozzle type, and flow rate through the nozzles?

I think the idea of using the large drop leg for the pump makes a lot sense. The volume of liquid required for the chiller is fairly small and the piping circuit is really short. The amount of refrigerant in suspension could be contained within the drop leg very easily.

I'm getting a pretty good picture of these now. Thanks again.



OK you got me with that comment. Almost fell out of the chair.

I (My company, as far as I know) Have no information when it comes to the design features of the chillers, as I said, it's not our product we are only informed when it comes to the waterflow, cooling effect and so such.
we do all the calculation on the piping and compressor/condencer capacity needed and ship it all off to SES in Holland and they build the units for us.
By the time we touch it, it's all placed on a skid allready welded to the hull or placed on vib.dampers.

I was looking through my papers just now, but couldnt find the flow chart... from the top of my head I'm gonna say ummmm... cant remember... was gonna say 653 cubic yards an hour... but that just sounds wrong in my head

When are you 'muricans gonna submit and start using the metric system anyways?
It all goes in 10's... how hard can it be
5280 feet to a mile? I mean c'mon...
wouldnt 10 Km to a metric mile be better?


Oh and the ladies are starting to dress down in anticipation of summer... I'm still wearing my winter jacket while at work... but dang... some of those girls HAS to be freezing with their bellies uncovered like that... makes me wanna jump out of my car, run over and drape my jacket around them and go "here... come home with me"

[Tycho]

On the overfeed systems you guys work on do you install the pressure control valves at the pump discharge or at the end of the liquid line (as shown in the attached drawing)?

For those of you who have done it both ways, any complaints or suggestions with either method?

I am interested in learning more about the installations you work on and the problems you frequently encounter.

Thanks,
US Iceman

Our systems is just like the one in your drawing, except we have a 5 bar overflow valve connected to a 3/8" line between the pump and the non return valve. other than that we have nothing.

to paint a flow diagram:
Pump - ofv - flashgas trap (or whatever you call it) - nrv - main liquid tine - reg.valve - freezer/evaporator.

Not many problems on our installations... we also have 0.2" nozzles on each plate on our freezers. the reg valves we use to ensure a stable pump pressure to the last consumer on the liquid line.


Must say your piping looks very clean, and I envy you for gettion to work on land installations when we work on ships, the only line we refuse to yield on is the return line and every time we have shipbuilders tearing their hair out while we stand there saying "Thats the way it is"

[US Iceman]

When are you 'muricans gonna submit and start using the metric system anyways?

Sorry about that. We are kind of used to it by now.

I will say talking to people on this forum has forced me to remember things I had forgotten.

...some of those girls HAS to be freezing with their bellies uncovered like that

Perhaps you should try that also. Maybe the girls will ask you to come home with them.

the reg valves are there to ensure a stable pump pressure to the last consumer on the liquid line.

I think this makes a lot of sense, but I've only seen this a couple of times here. I intend to use this on the next system for the reason you said.

I can well imagine the issues you have to deal with on marine systems. A lot more issues to deal with than just level and stationary.

[bruceboldy]

having built recirculator packages for many years i have found that the majority of the problems have been not following the pump company guidelines.

Pumping volatiole liquid like ammonia or ***** is easy if you have enough npsh and keep the pd down with proper inlet sizing i think Iceman was all correct in his observations

I mostly saw npsh problems causing the most difficulties.
I also like the seperate suction lines in lieu of the common drop leg.

Sometimes i have found engineers overthinking the problems.

i never tried it but i want to put in some of the witt pumps simply hanging from the vessel. with the suction straight into the pump inlet. with a valve of course.

Have seen a few sketches of this but never seen it in practice.
Would really save us on installing cost. Anyone do it ?? and what problems or success have you had.

David in texas

[US Iceman]

Hi David,

I mostly saw npsh problems causing the most difficulties.

I agree. These are normally the result of too much inlet loss, insufficient static head, or the pump is not setup properly allowing it to run out on the pump curve.

i never tried it but i want to put in some of the Witt pumps simply hanging from the vessel. with the suction straight into the pump inlet. with a valve of course.

I have a friend who told me was thinking of this for some Cornell pumps. He was planning on using high-performance butterfly valves for the suction valve instead of an angle valve.

If the suction valve was a globe style in the vertical suction line, I think you would loose more than you can gain because of the inherent extra length of the globe valve.

Using a high-performance butterfly valve would of course drastically reduce the equivalent pressure loss.

I should check in with him and see what the results were. Thanks for reminding me of that.

[Nico]

I installed Witt pumps type HRP 3232. They hang directly under the separator (with only a ball valve in between if you want). Works superb, easy to install, insulate and to service. As we always use one stand-by pump, the piping as shown in the attached file is standard. It clearly shows the advantages of the pump directly fit to the separator. However, only one capacity available at Witt(for now that is). Find info in the WITT HRP manual at th-witt.com.

As for the pipe inserted into the dome; as to my understanding that was invented to prevent falling oil from the separator to enter the pump, but being collected at the bottom of the dome.

We always use leg's as drawn in the attached file. Very little (never) problems with oil in the pumps.

Also standard is the use of a pressure regulator near the pump. That, with a good(!) discharge head of the pump makes it easy to set the regulating valves, and the system will be very stable. No need to go to the end of the wet return line.

[Nico]

****, forgot the drawing.
This will be better I think.

[US Iceman]

Very nice drawings Nico. Thank you for sharing these.

[Tycho]

****, forgot the drawing.
This will be better I think.

If I'm correct, the pumps are shown on the left side of the drawing, and you have the suction pipe taken out on the bottom of the drop leg... am I correct?

On ***** R-22 this will work fine, as the oil will gather in a "layer" around the top of the liquid head...

but on ammonia, you will have no way of draining the oil before it enters the pump and is flushed out into the system along with the liquid ammonia.

As I have shown previously in this thread.. (I know might sound like a "know it all" in showing this again... but I know it works)

(added some english text in the picture)

Notice that there is a ring around the drop leg preventing oil from draining down into the dropleg, there is a seperate dropleg for draining of oil... and as a precaution, there is an oil drain valve on the dropleg just in case


Just have to say that I'm not a big fan of having any important pipes going out of the bottom of a dropleg like that, cause any "contamination" in the plant that finds it's way to the liquid tank will go straight into the pumps.

[AMARNATH JHA]

Generally in the large overfeed system has liquid feed pumps which supply liquid refrigerant to the evaporators.
I think your system must have multiple evaporators. I have read that your system has separate lines connected to pumps. This is not advisable.There must be a common header between vessel & pumps.I have handled very large overfeed ammonia system.If any querry pls write to me.
Thanks
AMARNATH JHA

[US Iceman]

I have read that your system has separate lines connected to pumps. This is not advisable.There must be a common header between vessel & pumps.

Can you explain your comments please?

Thanks.

[Nico]

Both left and right side of the drawing are of a separator with pumps. One with horizontal and one with vertical shaft. The top is a detail of the oil dome with ammonia down pipe to the pump(s) in the middle. The system is for Ammonia indeed! As oil is more heavy than Ammonia, it will fall down to the bottom of the separator, and than sort of fall off the edge into the oil dome. Ammonia is collected just 10mm higher than the bottom of the separator. That's why the vortex breaker is so important.

[Nico]

This detail will be more clear I guess.