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gwapa
11-04-2008, 03:46 AM
Dear Friends
Im working in a two stage ammonia system
It will have a low temperature separator tank,a hight temperature separator tank and an intercooler flash tank.

We are thinking to install an ammonia transfer unit in each vessel in order to evoid that the ammonia level could raise to dangerus point and stop the compressors.

The ammanio will be transfer to the HP receiver

I appreciat your thought
Best regards
Gwapa

Oregon Jim
11-04-2008, 04:33 AM
I had this high level problem last year, and of course we had no way of lowering the level designed into the system. A power failure caused a rapid pressure swing, the intercooler (flash cooler really) level went high, and the second stage machines shut down just as liquid NH3 was beginning to carry over into the second stage compressors. Compressor oil temperatures dropped like rocks in a well and the oil became as thick as honey. It was a mess...

I ended up pressurizing the flash cooler with hot gas via our oil drain system to move the excess NH3 into a low pressure receiver and we were back to production in a couple of hours (after the oil had warmed back up in our compressors).

We looked into installing an ammonia pump into the flash cooler, but there always seems to be an issue with money.... Rather than beating my head against the wall fighting management over money issues I chose to simply plumb a new hot gas line and a valve directly from my second stage compressor discharge header into the flash cooler.

There is a terrible problem with this quick-fix, and that is that the refrigeration system must be down to it. I cannot pressurize the flash cooler without isolating it first. Installing a pump would be a much better plan because you could use the pump to help control your level before the level becomes a critical issue. My system only allows you to take corrective action after the problem occurs.

I think you should be congratulated for having the foresight to see and plan for the problem before it occurs, but I would suggest that you look into a way to move your NH3 into a low pressure receiver rather than the high pressure receiver. It would be more energy efficient.

RANGER1
11-04-2008, 08:11 AM
Hi gwapa ,this can be as simple or as complicated as you like.Depending on your circumstances and money situation.It is easier to transfer liquid from vessel to vessel using pressure differance ie intercooler/high temp accumulator to low temp accumulator with a hose off oil drain point or pipe it up permanently.Or use a tap off point on liquid pump discharge and run hose or pipe to whichever vessel .This may allow you to transfer from low pressure vessel to intercooler/high temp accumulator etc.
As far as transfering to high pressure liquid reciever from any vessel it is possible but a seperate vessel with possitive displacement pump would be required,as well as valves and controls. This new vessel would be a drain off whichever vessel you want to lower level in which also requires a vent line back into top of vessel.Pressure equalization to reciever pressure would have to take place for transfer pump to work reliably(or if all your accumulators are above high pressure reciever you could gravity drain it without any pump at all).
If it is made to be automatic it can be achieved but if you have a problem eg leaking liquid make up solonoid valve it can mask a problem and it will still end up out of control.
If plant is designed well with good controls and adequate vessel sizing it should hardly have to be used.If you had enough connections to achieve the transfers from vessel to vessel it could be run in 1/2" stainless steel hydraulic tube (put a relief valve somewhere in line to prevent liquid lock).
Some plants have a dual duty evaporator which you could also use by swapping liquid and suction lines.Good luck

gwapa
11-04-2008, 06:26 PM
Thanks Jim / Ranger1

I agree with your thought " If plant is designed well with good controls and adequate vessel sizing it should hardly have to be used"

But as you also pointed out if a solenoid valve or an expation valve leaks your level will raise and you will have a "Plant Shutdown" untill you be able to low the level again.

I also agree to pump the liquid to a vessel at lower pressure but finally the vessel with the lowest pressure should have a ammonia transfer sistem to where???
Apprecite again your advise
regards
Gwapa

Josip
11-04-2008, 07:07 PM
Thanks Jim / Ranger1

I agree with your thought " If plant is designed well with good controls and adequate vessel sizing it should hardly have to be used"

But as you also pointed out if a solenoid valve or an expation valve leaks your level will raise and you will have a "Plant Shutdown" untill you be able to low the level again.

:confused::confused: why....you can set up your controls to stop the plant before flooding, with additional pneumatic NC valves on feeding lines acting with an early alarm .... and then you have a time to act;) ... very simple...


I also agree to pump the liquid to a vessel at lower pressure but finally the vessel with the lowest pressure should have a ammonia transfer sistem to where???

...with high pressure piston pump back to HP receiver or to another empty separator... very simple.... all by manual operation (do not forget to install bypass lines with bypass valves on liquid lines:eek:)

.... anyhow, me personally, will try to make a good and simple design.... must run without problems;)

Best regards, Josip :)

RANGER1
12-04-2008, 12:32 AM
gwapa,two ways come to mind to transfer from low side vessel.
Instal anew transfer vessel of say 300 litre capacity close by .Instal drain line from bottom of low side vessel into transfer vessel as well as a vent line off
top of transfer vessel back into top of low side vessel.
Drain excess ammonia from low side vessel into transfer vessel then valve off and pressurize with discharge pressure (until transfer vessel is empty).
Off bottom of transfer vessel ammonia is transferred to high pressure liquid line downstream of a stop valve which is closed.
Transfer vessel is acting like main liquid reciever until empty ,so excess ammonia is recirculated lowering low pressure vessel level
Alternatively a pump on bottom of transfer vessel (while pressurized with discharge pressure until empty) could transfer directly to high pressure liquid reciever.
Of course it can be automated,using low pressure non return valve into drain line of transfer vessel as well as low pressure drop solonoid in transfer vessel vent line.
Solonoids can be installed in high pressure liquid line and a non return valve in transfer line from transfer vessel to high pressure liquid line
Float switches can be installed on upper /lower levels of transfer vessel

Josip
12-04-2008, 01:00 AM
Hi, RANGER1 :)


gwapa,two ways come to mind to transfer from low side vessel.
Instal anew transfer vessel of say 300 litre capacity close by .Instal drain line from bottom of low side vessel into transfer vessel as well as a vent line off
top of transfer vessel back into top of low side vessel.
Drain excess ammonia from low side vessel into transfer vessel then valve off and pressurize with discharge pressure (until transfer vessel is empty).
Off bottom of transfer vessel ammonia is transferred to high pressure liquid line downstream of a stop valve which is closed.
Transfer vessel is acting like main liquid reciever until empty ,so excess ammonia is recirculated lowering low pressure vessel level
Alternatively a pump on bottom of transfer vessel (while pressurized with discharge pressure until empty) could transfer directly to high pressure liquid reciever.
Of course it can be automated,using low pressure non return valve into drain line of transfer vessel as well as low pressure drop solonoid in transfer vessel vent line.
Solonoids can be installed in high pressure liquid line and a non return valve in transfer line from transfer vessel to high pressure liquid line
Float switches can be installed on upper /lower levels of transfer vessel

...... :confused::confused:, please can you make a hand scheme/sketch of above said.... we are engineers here and much better is to use kind of drawing;)

Best regards, Josip :)

US Iceman
12-04-2008, 02:08 AM
...try to make a good and simple design


This is what I like also. IF you have to have a transfer system then I would follow the KISS principle (Keep it simple stupid - sorry, but that is the explanation of the word).:o

A single transfer pump could be piped between the three vessels and returned to the main drain line from the condenser (returning back to the receiver). If a vessel floods out, then at this point you should be doing the transfer manually until the vessel level is OK.

Of course, another way is to not use a transfer pump and design the system for any operational problem. Very seldom will a vessel flood out unless someone or something crazy happens (which should not occur anyway).

RANGER1
12-04-2008, 07:25 AM
US Iceman can you please advise what type of pump that can transfer ammonia from 0kpa to discharge pressure,say 1250kpa . I realize it is nice to keep it simple and reliable but unless you can still buy an old type piston type pump i didnt think there was much available ?
I wouldnt say it is a common system in Australia, but they are out there.Some older systems with TX valves on ammonia and lots of surge drums which carry over liquid back to a common suction trap have utilized this system mainly because a transfer pump capable and/or reliable is not available.
As far as a sketch unfortunantly my printer is in for repairs.
Looking forward to reply ,thanks RANGER1

US Iceman
12-04-2008, 04:52 PM
Hi RANGER1,

Most of the transfer pumps used here in the US are gear type pumps. This is a very common type of pump.

As you have indicated, the flooding problem (or constant liquid return) is more prevalent on older systems using TXV's. The valve pin carriers and orifices are worn out and should be replaced. Another problem is with undersized vessels that have been out grown with expansions of capacity that were not part of the original design.

These are the two common reasons I see a lot of the time.

Oregon Jim
12-04-2008, 05:29 PM
I'd like to add a little from an operator's point of view.

There is really not much to consider here. If you want the ability to transfer NH3 back into your high pressure receiver you need an expensive pump that can move a lot of NH3 at high pressure in a short time. It costs too much, and it should be unnecessary.

The only real answer is to allow yourself enough room in your low pressure receivers, or to keep an ammonia storage / shipping vessel on-site for such emergencies. It is a simple task to use your ammonia pumps to fill a temporary storage vessel, and with far less money than a pump would cost you can add piping to pressurize your flash cooler as I did, so getting you high level down should be nothing more than a minor inconvenience.

Save yourself a lot of money and complication. As the smart fellows above said, keep it simple...

gwapa
13-04-2008, 01:53 AM
The gear pumps that I know are not hermetic pumps. It has a seal and all the time are leaking ammonia.

The LP separator and the HP separator have pumps to pump to the evaporators. Also there are some process machines which are ammonia flooded and are feeding from the HP receiver with subcooled ammonia. The suction come back to the LP separators

I was thinking to hook up a line from the discharges of the pumps to the intercooler (just in case) and Install in the intercooler a Ammonia Transfer Unit (ATU)as mentioned RANGER1. In case of high level alarm in the LP or HP separators I can open manualy a valve located in the line and transfer the ammonia to the intercooler. The ATU will then transfer the excess ammonia from the intercooler to the receiver. After the alarm shut down I will close the valve and start to look valves leaking.

What do you think??
Best regards
Gwapa

RANGER1
14-04-2008, 12:58 AM
Gwapa, i dont think you should transfer to HP reciever unless you use a gear pump as US Iceman suggested.Because ATU would be same pressure so it wont transfer.I think you have to pipe it into HP liquid line with valve upstream of ATU entry point closed so ATU is temporarily acting as liquid reciever liquid supply to plant.
Oregon Jim also has a good idea with a spare vessel to dump any excess NH3 into it if you have enough room to have it near your plant room.
I agree with your comment on transfer pump seal leaking,usually when you want it most.
I dont know if anyone can recommend brand/type of pump to use(preferably sealess like a mag drive or simmilar.

US Iceman
14-04-2008, 01:42 AM
You can purchase a mag-drive gear pump here in the US. I have to believe some others manufacture these also.

One option is to use a smaller vessel mounted about the high pressure receiver. Vent this vessel to the pressure of the vessel being drained or transferred from. Then pump the liquid up to the vessel mounted above the receiver. The only head loss is the piping and elevation change (both very small).

When you have transferred enough liquid to fill this vessel (mounted above the receiver). Stop the pump, equalize this vessel to the receiver pressure, and then let the liquid gravity drain down into the receiver.

It's a little messy, but the stress on the pump is greatly minimized.;)

Various configurations of this have been around for many years!

gwapa
15-04-2008, 12:46 AM
Dear Friends
Attached you can see an sketch where I draw the lines for a emergency situation of hight level in the acumulators (separators,Knock down Tank) .

See also the ATU located in the intercooler. In can also be located in the -10C separators

All the pumps are standad hermetic pumps due to the fact that the Head (H) is easy handel in each case.

What do you advise?
Regards
Gwapa

fassi
16-04-2008, 05:38 AM
To move NH3 from the intermediate accumulation tank over into the high pressure receiver can be done by means of applying the discharge pressure form the compressors to the intermediate tank when it is full , (it is presumed that this tank is equipped with necessary solenoid/check valves, level switches and controller).

The needed pressure difference is obtained by installing a fix delta P control valve after the point of taking out the discharge pressure to the intermediate tank and before the condenser. This valve creates a delta P which can push the NH3 over into the receiver. The valve can be a Danfoss PM3 or ICS equipped with a EVM and CVPP HP, the last mentioned is equipped with both internal and external pressure connection. Remember to install pressure gauge up and down stream

RANGER1
16-04-2008, 09:19 AM
Fassi,where would you generate hot gas from if intercooler is isolated and hot gas is applied to it?

fassi
18-04-2008, 09:03 PM
To the right of the inter cooler of the "gwapa" pdf sketch there is shown an accumulation tank which is supposed to accumulate the surplus liquid comming from the inter cooler.

When this accumulation tank is full the content is pushed over into the HP receiver by means of the hot gas pressure from the compressor discharge system by means of the pressure difference made by the Danfoss PM/ICs valve.

RANGER1
19-04-2008, 01:42 AM
Sorry fassi,your idea sounds fair enough ,i think the system gwapa has shown us will work .The system could be running or off depending on severity of flood back or high level.
The system proposed is not cheap but only gwapa can make the decision because he lives with the high level problems on a regular basis by the sound of it.

gwapa
22-04-2008, 04:33 AM
Ranger1
Thanks for your words.I would like to ask you
Why do you think the system proposed is not cheap?
Do you think it would be made cheaper?
Thanks again
Gwapa

RANGER1
22-04-2008, 11:32 AM
gwapa, the only way to make it a bit cheaper is to eliminate non seal pump as they can be expensive on their own.Otherwise if you are happy with the design go for it .
Lost production might pay for it in a few hours depending what your plant is producing and how many people have down time.

rcouture
22-04-2008, 04:54 PM
Phillips Transfer vessels work very well I operate 2 transfer vessels one on the house suction vertical receiver Int. Press and one on an horizontal receiver booster package Low Press. Why do you want to put one on your flash cooler or tank? Are you over feeding it? :rolleyes:

gwapa
22-04-2008, 10:16 PM
rcouture
I have pointed out the the transfer system is a safety system just in case we could have a leak in a valve.It allows the operator to low the ammonia level faster . It is like a fire extiguisher. It is better have have when you need it.

Now back to the begining: Which is the best way to do it? Which is the cheaper one?
In the system I posted I am using the recirculation pump to pump manually to the intecooler or to the HP separator
What do you think? What do you advise?

Regards
Gwapa

Josip
26-04-2008, 09:25 PM
Hi, gwapa :)


rcouture
I have pointed out the the transfer system is a safety system just in case we could have a leak in a valve.It allows the operator to low the ammonia level faster . It is like a fire extiguisher. It is better have have when you need it.

Now back to the begining: Which is the best way to do it? Which is the cheaper one?
In the system I posted I am using the recirculation pump to pump manually to the intecooler or to the HP separator
What do you think? What do you advise?

Regards
Gwapa

... seems you decide to do it (seeing your scheme I can suppose why;))

... it will be better if you show heights of each vessel in your sketch ... maybe you can drain liquid by gravity;)

... so let's make it easy ... you can transfer surplus ammonia to any of your vessels, but you need to install common liquid pipes to each vessel with stop valves and also common gas pipes in the same manner like liquid pipes.... then you equalize pressures in your empty vessel and in overfill vessel and use your pumps like circulating pumps (like in heating system) to transfer ammonia ....

... about price is not easy to speak ... you must accept one of suggestion/solution and try to calculate time and material to install it....

.... maybe I am wrong, but I will think about that to change one by one vertical separator with horizontal one of a right size:cool: and without intercooler and ATU ...

Best regards, Josip :)

gwapa
28-04-2008, 04:09 AM
hi Josip
All the vessels will be at the same bottom level. They will be vertical shape

sodielectric
01-05-2008, 08:16 PM
Teikoku makes a hermetic pump that can pump up to 200 psid (~1,300kpa).