Why can't get -40C for the Sprial??? Ammonia overfeed

[JERRYCOOL]

Hi,
-42C Suction pressure

The pump pressure is 2.5BarG and the rating flow rate is 6m3/hr. (Teikoku 40P40-NB) Current is about 6A.

We pull down the Spiral without any product in. The -35C will be got within 40 minutes with -42C saturated suction pressure.

The problem is that we can't get the temperature lower with that setting. When we set the pressure lower to 350mmHG, the room temperature can reach -38C.

We tried throttling the HEV more. the temperature will increase.

We measure the pressure drop from lower pressure receiver to compressor. it is about 0.

The wet suction line is about 7m higher than the Spriral. Will this be the problem?

Or anybody has any good idea? Please let me know!!!!

Thanks!!
:confused:

[JERRYCOOL]

The capacity is 180KW per Spiral freezer. Attached is the skech of the piping.
10846

[HVACRsaurus]

Hi Jerry,

For -40°C air temperature wouldn't something more like -50°C refrigerant be required?

[Magoo]

The 7 metre lift from spiral coils with be increasing pressure drop and creating temp loses at coil, increase over feed rate to compensate for loses, possibly reduce the minimum flow bypass rate at pump discharge which will increase pump discharge pressure marginally.
Generally you will get a 2 degree ' C split between coil temp and air temp in spiral. So minus 40' C air is -42' C coil condition, and roughly -40Kpa at compressor or -44' C SST

[JERRYCOOL]

Thanks Magoo,
I will try to get the pump performance curve to see if i can get the actual pump flow rate. We did use 2 pumps for one Spiral, but the superheat can't be lower and air temperature is the same.

The suction temperature is about 17C higher that evaporating tempeauture.

10847
:o

[Magoo]

Hi JERRYCOOL.
the suction vapour temp entering the compressor is a good indication of system performance, I would expect nominal 10 > 12 ' C higher than SST at compressor .
Crank open the HEV and monitor the reaction with min flow by pass closed, the pump discharge should drop and motor amps increase a little bit with higher flow rate hopefully. Then crack open the bypass and keep pump motor amps within range.
It is difficult to calculate the effect of vertical riser from coils with a over feed system as the gas/liquid mix leaving coil is boiling agitated so the actual net head loss is a mixed volume of liquid and vapour . Generally a large pump is applied and HEV to maintain required effect at max design conditions.
I see on the drgs that there seems to a probable flow orifice feeding each coil section, now they are a black art to calculate and get right. They are usually a disc with a specific hole size between two flanges.

cheers magoo

[RANGER1]

Jerrycool,
Also a good idea to drain oil out of evaporator before doing anything , adjustments etc.
Obviously lowering suction pressure as everyone has suggested with use of accurate instrument.
YUo can also put accurate gauge on oil drain or low point on evaporator to see what pressure really is, which effects refrigerant boiling point.

Also if suspect liquid pump pressure, close standby pump discharge valves to eliminate any possible back feed from pumped liquid line.
Pump suction filters could also be checked if installed (never installed in most Australian systems).

[Magoo]

I agree with Ranger1
check and drain oil in evaps as at -40 it goes like honey consistency and slows flow rates etc., basically warm coil up to ambient to get it drain, with system shut down, will get smelly and will bark and spit at you, so be cautious, masks and gloves etc..
What brand of spiral is this installation?

[JERRYCOOL]

The Spiral is http://www.ntsquare.com/product.asp?sort=2.
We use more Frigo's before with very good performance.

We will see if we can drain some oil from the spiral and close discharge valves of other liquid pumps. The pumps inlet strainer has already been removed.

[JERRYCOOL]

We checked the oil. No oil!
And we closed the discharge valves of other pumps. Nothing changed.

[JERRYCOOL]

The pump is 6.25 m3/hr @40m head. The flow rate may be too high. The liquid supply pipe is 1 1/4" . The pipe is suitable for the refrigeration capacity(180KW) but is too small for the liquid flow rate. Will this be the problem?

:rolleyes:

[Segei]

The issue is static pressure of overfed evaporators. Column of liquid in suction raiser increase pressure(and temperature) at lower part of the coil. This is the reason of higher temperature. I would suggest to adjust HEVs at full load. At full load, in suction raiser will be mixture of liquid and vapor. This mixture have less density than liquid and static penalty will be less as well.
I assume that refrigerant is NH3.

[RANGER1]

Jerrycool,
Have you lowered suction pressure set point yet to at least - 46 deg C ?

[JERRYCOOL]

Jerrycool,
Have you lowered suction pressure set point yet to at least - 46 deg C ?

Hi Raner1,Yes. With lowered pressure to 400mmhg, the empty room temperature can be -40C. It is not right.

[JERRYCOOL]

The issue is static pressure of overfed evaporators. Column of liquid in suction raiser increase pressure(and temperature) at lower part of the coil. This is the reason of higher temperature. I would suggest to adjust HEVs at full load. At full load, in suction raiser will be mixture of liquid and vapor. This mixture have less density than liquid and static penalty will be less as well.
I assume that refrigerant is NH3.

Hello Segei,
Do you mean the static head of the suction line will affect the evaporating temperature even in overfeed the system? is there any good way to resolve it?

[RANGER1]

Usually a double riser carefully engineered can assist with this problem.
Similar design in ***** plants for oil return, but used in ammonia for varying loads in plant.
May even need another "p" or "s" trap halfway up riser.
Also see Magoo's post adjusting regulating valve for correct TD across air cooler.
This helps by getting coil to perform as well as eliminates "brining".

[RANGER1]

Hi Raner1,Yes. With lowered pressure to 400mmhg, the empty room temperature can be -40C. It is not right.

What do you not like about this lower suction pressure 40mmhg?

[Segei]

Hello Segei,
Do you mean the static head of the suction line will affect the evaporating temperature even in overfeed the system? is there any good way to resolve it?
Yes. It is not easy to solve this issue. Some plant have liquid separator and pump to pump liquid up. Double riser reduce the static penalties, but not eliminate them. Double riser, usually, used for the blast freezers to accommodate changes in refrigeration loads.

[JERRYCOOL]

[QUOTE=RANGER1;287733]Usually a double riser carefully engineered can assist with this problem.
Similar design in ***** plants for oil return, but used in ammonia for varying loads in plant.
May even need another "p" or "s" trap halfway up riser.
Also see Magoo's post adjusting regulating valve for correct TD across air cooler.
This helps by getting coil to perform as well as eliminates "brining".[/QUOT

We are going to add traps to the vertical suction line and hopefully can solve the problem.

[JERRYCOOL]

What do you not like about this lower suction pressure 40mmhg?

Normally we can put the room temperature to -40C with 280mmHG. The lowered suction pressure means poor performance of the system.

[RANGER1]

[QUOTE=RANGER1;287733]Usually a double riser carefully engineered can assist with this problem.
Similar design in ***** plants for oil return, but used in ammonia for varying loads in plant.
May even need another "p" or "s" trap halfway up riser.
Also see Magoo's post adjusting regulating valve for correct TD across air cooler.
This helps by getting coil to perform as well as eliminates "brining".[/QUOT

We are going to add traps to the vertical suction line and hopefully can solve the problem.

Top & bottom of suction riser?

[RANGER1]

Jerrycool,
Going back to basics have you checked for coil frosting from any infiltration etc.

[JERRYCOOL]

[QUOTE=RANGER1;287774][QUOTE=JERRYCOOL;287764]

Top & bottom of suction riser?[/QUO

The outlet of the Spiral is vertical. We will add some more elbows for the U trap.

[JERRYCOOL]

Jerrycool,
Going back to basics have you checked for coil frosting from any infiltration etc.


The frost is not heavy. It is just a little.

[mad fridgie]

Firstly need to get the pressure measurement understood.
when you say 240mmhg, you actually mean 510mmhg, as the lower the pressure the the lower mmhg.
So at if your pressure is at SST of -42, then I see it being very difficult to achieve temps of -40C, Air off possible.
But if you are sensing in return after after energy has been absorbed, then the air temp will be higher "as it should"
First questions is it freezing the product, at the required rate.
If so I would say the position of the probe may be different, calibration of the probe and/or pressure measuring devices may also be different. (from other set ups)

[JERRYCOOL]

10897
We add u trap to the suction vertical line and run the system today. Nothing better.
But we found there was water inside the suction pipe. see attached picture. Will this be the reason or not?

The ammonia pump has 6.25m3/hr flow rate and the liquid line is DN32(since the required refrigeration capacity is 180KW). Will this cause the problem?

[RANGER1]

Yes water can be a problem, you need to test it yourself or send to a lab.
you can buy special test tubes with fine graduations to test, someone on RE may be able to post procedure.
Riser has to be correct size as well as have a trap on top of riser, or at least slope away so liquid that goes up stays up

[Josip]

Hi, JERRYCOOL :)


The capacity is 180KW per Spiral freezer. Attached is the skech of the piping.
10846

for me feeding line is not correct ... each evaporator should have separate feeding line and hand regulating valve ....

another question ... do you have straight 7 meters vertical pipe above evaporators or you have some horizontal pipe sections until you reach suction header ...

in ammonia systems and we do not use suction risers (maybe sometimes in special cases this is not that one), because we do not need to collect oil and return back to suction separator ... there are drain valves on evaporators to remove that oil from the system ... then with your SSH of 17K there is no way to have a liquid in that pipe ...


Thanks Magoo,
I will try to get the pump performance curve to see if i can get the actual pump flow rate. We did use 2 pumps for one Spiral, but the superheat can't be lower and air temperature is the same.

The suction temperature is about 17C higher that evaporating tempeauture.

10847
:o

When you run 2 pumps what was discharge pressure in liquid line/s to evaporators?

Suction superheat is definitely tooo high ... can be 2-4K .... your evaporators are starving ....



Hi JERRYCOOL.
the suction vapour temp entering the compressor is a good indication of system performance, I would expect nominal 10 > 12 ' C higher than SST at compressor .
Crank open the HEV and monitor the reaction with min flow by pass closed, the pump discharge should drop and motor amps increase a little bit with higher flow rate hopefully. Then crack open the bypass and keep pump motor amps within range.
It is difficult to calculate the effect of vertical riser from coils with a over feed system as the gas/liquid mix leaving coil is boiling agitated so the actual net head loss is a mixed volume of liquid and vapour . Generally a large pump is applied and HEV to maintain required effect at max design conditions.
I see on the drgs that there seems to a probable flow orifice feeding each coil section, now they are a black art to calculate and get right. They are usually a disc with a specific hole size between two flanges.

cheers magoo

Seems someone made some mistake with flow orifice ... there is no need to use hand expansion-regulating valve and orifice (I would remove orifice if installed and use only hand regulating valve) ... btw. what size is your regulating valve?


The frost is not heavy. It is just a little.

Little frost means there is no liquid in that pipe ... your evaporator is dry ...



We checked the oil. No oil!
And we closed the discharge valves of other pumps. Nothing changed.

So when you drain your evaporators no oil came out ...





10897
We add u trap to the suction vertical line and run the system today. Nothing better.
But we found there was water inside the suction pipe. see attached picture. Will this be the reason or not?

The ammonia pump has 6.25m3/hr flow rate and the liquid line is DN32(since the required refrigeration capacity is 180KW). Will this cause the problem?

It is not clear is there some water at the bottom of the pipe or his wet area only !?! .... I think this is not a water ... just condensation, because your pipes were very cold and when you opened them humidity within air just condensate on the cold pipe giving you impression there is some water .... btw. did you evacuate complete system with vacuum pump ... there you can see if you have or not any water within system ...

but before vacuuming you can get the evaporators to environment temperature (to melt ice if any inside evaporators) and then with pressurized air drain all through drain valves ... but you know that ...


Best regards, Josip :)

[JERRYCOOL]

Hi Josip,

To me the feeding line can distribute the liquid ammonia equally to 2 pipings. It should be ok I think. I will try to prove it.

T10913

See attached picture. We add one U trap in the middle of the suction riser. We want to remove the static head and return the oil back to the low pressure receiver.

Since the suction temperature is measured closed to the compressor. So we are not sure if it is really the suction temperature. Maybe it is affected by compressor.

The evaporator can't be drained since there was no drain port at the bottom of the evaporator. But I think the oil will back with the ammonia easily since it is overfeed system.

We got out some ammonia to a bottle and we found water after the ammonia evaporated.

[JERRYCOOL]

Is anybody know the reason that the oil became like milk!!?10914
Will water cause that or any other reasons?!

[RANGER1]

JERRYCOOL, I guess this oil is from the compressor, can you expand!

Also how & where did you take ammonia sample from, as it can effect results.
Best place is low side recirculator vessel at basically atmospheric pressure to avoid flashing of liquid to vapor.
We take 3 beakers of 100ml let them stand to boil off naturally, then take the average of the remaining water.

Water will definitely upset performance.
Water could come from initial installation, left in vessels etc from factory pressure testing, wrong type of ammonia.
Water in compressor would have to be from flood back, leaking oil cooler if water cooled (unlikely), water sucked in when venting compressor into water, liquid injection if no oil cooler.

Also could get sucked in from air purger if your unlucky.

In your case you need to set up as still if you have as much water as you think, also change all compressor oil ASAP draining oil separator, oil cooler, possibly run for a number of hours, monitor then change again.

Another possibility is dump ammonia charge, drain from all low points in system, very expensive to dump charge (In Australia anyway).
Install drain point on evaporator lowest point if possible.

Was there any lead up to this contamination, looks like a disaster of a plant!

[Josip]

Hi, JERRYCOOL :)

I was asking you some questions in my previous post, but unfortunately no answer ...


Hi Josip,

To me the feeding line can distribute the liquid ammonia equally to 2 pipings. It should be ok I think. I will try to prove it.

T10913

See attached picture. We add one U trap in the middle of the suction riser. We want to remove the static head and return the oil back to the low pressure receiver.

In this way distribution of liquid is not equal, believe me ...

one example ... at my home each radiator of central heating system has a stop valve at the inlet end and a regulating&trim valve on the outlet end to balance the whole system otherwise when we get water circulation through few radiators others will never be in function ... i.e. no water flow through them ... without regulating valves there is no way to force the water to pass through those radiators ...

If I am in your position I'll remove U-trap. Straight vertical pipe with top connection to suction header.



Since the suction temperature is measured closed to the compressor. So we are not sure if it is really the suction temperature. Maybe it is affected by compressor.

Suction temperature must be measured at compressor inlet also suction pressure must be measured at the same point ... that is the only way to calculate suction superheat .... we need to take in consideration all loses within suction pipe from evaporator til compressor ... it is not affected by compressor after few minutes of compressor run ...


The evaporator can't be drained since there was no drain port at the bottom of the evaporator. But I think the oil will back with the ammonia easily since it is overfeed system.

We got out some ammonia to a bottle and we found water after the ammonia evaporated.

If you remove U-trap it is a good possibility to install draining valves on evaporators to drain water or oil from coils - it will be a proof what you have inside of coils ... vacuuming of water will last too long .... what about leak test and vacuuming how you performed that?


Is anybody know the reason that the oil became like milk!!?10914
Will water cause that or any other reasons?!
Where from you took out that ammonia? How much of oil came out?

I am not sure how you perform your test with ammonia and water ... if you drain ammonia in the same container like on your photo that can be condensed humidity from the air mixed with oil within refrigerant ... the best is to take sample from the bottom of receiver into vacuumed steel bottle then slowly release ammonia into air till atmospheric pressure ... close the valve and leave the bottle to come to environment temperature and then drain the bottle into the glass bowl

As far as I know one reason can be present of water in the system, the second one is mixing of mineral and synthetic oils and the third one can be a vacuum leak on system ... running the system below -33*C system is below atmospheric pressure and air with humidity is sucked in ... for that reason it is recommended to install air purgers on such systems ...

it is easy to tight the overpressure, but to make a system tight to vacuum is another story ....

And the most important thing is ... You can do with your system whatever you want to prove something ... whatever ... what is partially OK ... but, learning on own mistakes can be very difficult and expensive too ...

I am not trying to prove I'm smart guy or I'm right, even less to argue with you, just want to help .... because, I've been there ... listening advices and learning of some other smart people and now trying to handover that knowledge ...


Best regards, Josip :)

[Segei]

Hi Josip,

To me the feeding line can distribute the liquid ammonia equally to 2 pipings. It should be ok I think. I will try to prove it.

T10913

See attached picture. We add one U trap in the middle of the suction riser. We want to remove the static head and return the oil back to the low pressure receiver.

Since the suction temperature is measured closed to the compressor. So we are not sure if it is really the suction temperature. Maybe it is affected by compressor.

The evaporator can't be drained since there was no drain port at the bottom of the evaporator. But I think the oil will back with the ammonia easily since it is overfeed system.

We got out some ammonia to a bottle and we found water after the ammonia evaporated.
I think this trap is useless. Look at ASHRAE Handbook(2006) Fig.48, p.3.25. It shows double riser.

[JERRYCOOL]

Hello Ranger1,

JERRYCOOL, I guess this oil is from the compressor, can you expand!

Yes, the oil is from oil separator.


Also how & where did you take ammonia sample from, as it can effect results.
Best place is low side recirculator vessel at basically atmospheric pressure to avoid flashing of liquid to vapor.

Yes, we take it from low side recirculator vessel.





Water will definitely upset performance.
Water could come from initial installation, left in vessels etc from factory pressure testing, wrong type of ammonia.
Water in compressor would have to be from flood back, leaking oil cooler if water cooled (unlikely), water sucked in when venting compressor into water, liquid injection if no oil cooler.

We got ammonia flood back. So this is the reason we got water in oil.




In your case you need to set up as still if you have as much water as you think, also change all compressor oil ASAP draining oil separator, oil cooler, possibly run for a number of hours, monitor then change again.

We have already change the oil of the compressor package. Not all, just the package with milk type oil.


Another possibility is dump ammonia charge, drain from all low points in system, very expensive to dump charge (In Australia anyway).

We have not make the decision to replace all the ammonia charge. As you say, this will cost a lot of money. And, do you how to deal with the ammonia drained from the system?

[Magoo]

Hi Jerrycool.
OK back to basics, anhydrous ammonia will contain a degree of moisture, despite what ever the manufacturer states.
Next what compressor set and set up do you have on the spiral ? Mainly the pull down timing for spiral ready for production. Rapid compressor loading will create oil carry over, and oil will be problem in system add water contamination, equals major problem. Generally slow and easy is the recommended operation. Minimum 45 minutes pull down without product loading. Remember the enclosure goes from + 25 ' C or higher after defrost and cleaning to -40' C daily not your regular cold store situation. Slow and easy is preferred. Do not hit system with max refrigeration effect.
Does the compressor set/system have an auto purger, and what are the cycle rates.

[JERRYCOOL]

Hi Josip,
Thanks for your reply.

When we run 2 pumps, the discharge pressure will increase to about 3 barg,

Now there is no product iniside the spiral, the superheat may be lower when the load is high per my experience. But i don't know if the superheat will be good enough for us at that time.

[JERRYCOOL]

Yes, we have Hansen's autopurger.