high discharge pressure problem in ammonia phe condenser

[ghanghas85]

Dear all i have installed an new ammonia refrigeration system with priority vessel and de superheater. Now i m facing a problem that my pressure going to 16 bar and compressor get trip on high discharge pressure.i have also installed an temp transmitter in main discharge header but its temp goes upto 46 deg c.I have installed 2 Phe desuperheater and below the desuperheater 4 nos. phe condenser in parallel .I have taken condensers inlet tappings from bottom of de superheater outlet header. I have made an common condensate liquid header from condenser to Priority vessel. The height difference between condenser outlet bottom and condensate header top is 50 mm and condensate header bottom to liquid level in priority vessel is 1.2 mtr. I have given an vent line from priority vessel to desuperheater main inlet header. kindly give your valuable advise to resolve the high discharge pressure problem.

[sterl]

The priority vessel is equalized to the inlet of the desuperheater means that all of the fluid pressure drop from inlet of DSH to outlet of condensers needs to be overcome by a column of liquid...If the height of that column is insufficient liquid will continue to accumulate in the condensers and not free drain out....Solution is to raise all or lower priority vessel (which may not be possible if priority vessel is feed point for oil coolers on compressors). Find out what the real pressure difference across your heat PHE's on the high side is.

How many machines do you have? and is the priority vessel feeding all the oil coolers or?

[ghanghas85]

Dear sir thanks for your reply.I have given an bypass line between condenser to priority vessel and priority vessel to reciever. The hight difference between condenser outlet to reciever is 4 mtr. But the problem is same nothing has been change.I have 1 grasso screw compressor and 1 no. vilter reciprocating compressor. I have started with reciprocating compressor but discharge pressure rise very rapidly and trip.

[Josip]

Hi, ghanghas85

Dear all i have installed an new ammonia refrigeration system with priority vessel and de superheater. Now i m facing a problem that my pressure going to 16 bar and compressor get trip on high discharge pressure.i have also installed an temp transmitter in main discharge header but its temp goes upto 46 deg c.I have installed 2 Phe desuperheater and below the desuperheater 4 nos. phe condenser in parallel .I have taken condensers inlet tappings from bottom of de superheater outlet header. I have made an common condensate liquid header from condenser to Priority vessel. The height difference between condenser outlet bottom and condensate header top is 50 mm and condensate header bottom to liquid level in priority vessel is 1.2 mtr. I have given an vent line from priority vessel to desuperheater main inlet header. kindly give your valuable advise to resolve the high discharge pressure problem.

Sorry, but have to ask ... did you perform system vacuuming before ammonia charging?

If, yes then probably you have a piping problem, but I can be wrong. Another and the best way, to be able to give you some better help; can you make isometric drawing/scheme of your condensers, desuperheaters and vessels with measures of course ... we are engineers not lawyers and drawing is a must .... unfortunately, sometimes we face language barrier, too

Best regards, Josip

[Magoo]

A wild guess, that system has non-condensable/ air in it.

[ghanghas85]

I just attach the line diagram of my refrigeration system. Kindly check and suggests yours valuable advices.

[Josip]

Hi, Magoo

A wild guess, that system has non-condensable/ air in it.

Why .... see this...

http://www.refrigeration-engineer.co...ack-to-basics.

I have one question more, wild too.... but happen to some guys

Best regards, Josip

[Josip]

Hi, ghanghas85

Dear sir thanks for your reply.I have given an bypass line between condenser to priority vessel and priority vessel to reciever. The hight difference between condenser outlet to reciever is 4 mtr. But the problem is same nothing has been change.I have 1 grasso screw compressor and 1 no. vilter reciprocating compressor. I have started with reciprocating compressor but discharge pressure rise very rapidly and trip.

Sorry, I miss this sentence earlier ... please, check your NRV on discharge pipe ... sounds like installed in wrong direction ... check the arrow direction on plate ....

What about vacuuming of your system?

Best regards, Josip

[ghanghas85]

Dear sir, i HAVE CHECK THE NRVS AND DONE THE VACCUM BEFORE FIRST CHARGE OF AMMONIA. bUT PROBLEM IS SAME. pLS SUGGEST

[research]

It looks like the drop legs from the PHE condensers is only 65 mm??
ASHRAE suggests a minimum drop leg from parallel condensers of 5 ft. approx 1.5 meters. before connecting to a common condensate line. ( 2006 ASHRAE HAndbook Refrigeration pg3.17)
A one psi refrigerant pressure difference between two condenser require a 48" head of liquid to accommodate the pressure drop. On a plate heat exchanger, 48" will fill the condenser with liquid.

Measure the subcooling leaving the condensers. if there is a substantial difference. then you could be filling some condensers, and then your will be short of condenser surface.

[Magoo]

Hi Josip.
you are cool dude, thanks for reminder. The terminolygy in original post confused me

[ghanghas85]

Thanks for reply sir if i closed 3 condensers ammonia in & out valves . Now i have taken only 1 condenser in use and i have taken all the condensate liquid to HPR by open the bypass valve. Now net distance between condenser out bottom to hpr top is 4 mtr. Does we need now 1.5MTR net distance from condenser out to common condensate header if i have taken only one condenser in use.Pls reply

[Josip]

Hi, ghanghas85

Thanks for reply sir if i closed 3 condensers ammonia in & out valves . Now i have taken only 1 condenser in use and i have taken all the condensate liquid to HPR by open the bypass valve. Now net distance between condenser out bottom to hpr top is 4 mtr. Does we need now 1.5MTR net distance from condenser out to common condensate header if i have taken only one condenser in use.Pls reply

000 Doc1.pdf

000 Doc2.pdf


it is not so simple .... please see attached drawings...

important is connection and height to primary receiver and ventilation pipes to header before desuperheaters or condensers .... depending on execution...

for HPR is missing equalizing line ....


Best regards, Josip

[ghanghas85]

thanks sir i observe 1 thing when i open my equalising line then my discharge pressure goes high and equalising line so hot and its size is 50 mm.How i can resolve this problem

[RANGER1]

Nothing to do with the problem, but there must be some serious water pumps on this system sucking lots of power?

[Magoo]

Hi Ranger 1
please clarify statement

[Josip]

Hi, RANGER1

Nothing to do with the problem, but there must be some serious water pumps on this system sucking lots of power?

Wild guess, also, but it is OK, all of us forgot about cooling water for condensers....


N.B. for ghanghas85

all bypass valves must be closed for normal run .... only open main lines and ventilation lines from priority vessel and HPR ....

btw .... what and how is connected to priority vessel - scheme, please if possible


Best regards, Josip

[ghanghas85]

Dear sir when i open my vent and hpr equalising line to condenser then my discharge pressure goes to 16.5 bar and both the priority vessel and High pressure reciever become very hot. My vent line size is 100 mm and equalising line size is 50 mm.For connection kindly check my attached diagram.Kindly give yous valuable suggestion.

[Peter_1]

Josip, from which book did you get these copies? :-)

[Josip]

Hi, Peter_1

Josip, from which book did you get these copies? :-)

From an old Gram manual, some from Stal some from Sabroe and ASHRAE, but installed and proved ....


Best regards, Josip

[Josip]

Hi, ghanghas85

Dear sir when i open my vent and hpr equalising line to condenser then my discharge pressure goes to 16.5 bar and both the priority vessel and High pressure reciever become very hot. My vent line size is 100 mm and equalising line size is 50 mm.For connection kindly check my attached diagram.Kindly give yous valuable suggestion.

in this post no attached diagram ... do you mean about attached diagram in previous post?

For normal run equalizing lines/valves must be closed only must be open drain/liquid and vent lines to and from all vessels...

one more question ... do you have any liquid in priority vessel during normal run or all liquid is drained into HPR? ... according to your diagram there is no liquid at all


what about cooling water for condensers and desuperheaters ... can you see the difference between your and mine diagram for piping?

Best regards, Josip

[ghanghas85]

Level in priority vessel is around half of vessel.I have given the vent line condenser inlet header after de super heater.i have tapping my vent line to header on top not given inside the header. Does this connection affect the vent because when i open my vent line my discharge pressure goes upto 16.5 bar. Kindly suggest something
Regds

Jitender Ghanghas

[Josip]

Level in priority vessel is around half of vessel.I have given the vent line condenser inlet header after de super heater.i have tapping my vent line to header on top not given inside the header. Does this connection affect the vent because when i open my vent line my discharge pressure goes upto 16.5 bar. Kindly suggest something
Regds

Jitender Ghanghas

I'm a little bit ...let's start from beginning ...
Bypass valves for DS must be closed for normal run. Vent line from priority vessel to header before condensers must be open, equalizing line from HPR to condenser's header too, but there is a big problem because you have installed double siphons ...one on outlet from condensers and another one is siphon before priority vessel and probably that is the biggest problem in piping ...

It looks like the drop legs from the PHE condensers is only 65 mm??
ASHRAE suggests a minimum drop leg from parallel condensers of 5 ft. approx 1.5 meters. before connecting to a common condensate line. ( 2006 ASHRAE HAndbook Refrigeration pg3.17)
A one psi refrigerant pressure difference between two condenser require a 48" head of liquid to accommodate the pressure drop. On a plate heat exchanger, 48" will fill the condenser with liquid.

Measure the subcooling leaving the condensers. if there is a substantial difference. then you could be filling some condensers, and then your will be short of condenser surface.

this above is a good observation ... in my installations I'm always trying to follow that suggestion ...

..... in my attached diagram and pdf files you can see how I'll make connections for vent line from priority vessel and equalizing line from HPRs - it is possible to check pipe sizes one more time .... bypass lines for DS are not needed .... seems that liquid header after condensers is too high with siphons instead of straight lines tapping from above and using only one siphon at priority vessel .. this header must be bellow priority vessel to avoid siphons after condensers ...


sorry, English is not my mother tongue and maybe you cannot follow what I mean ... it is not easy for me to explain what I'll do to make plant running ... unfortunately some piping must be changed ... hope some other valuable members will come with some comments which can help you maybe better then me.


Best regards, Josip

[ghanghas85]

I'm a little bit ...let's start from beginning ...
Bypass valves for DS must be closed for normal run. Vent line from priority vessel to header before condensers must be open, equalizing line from HPR to condenser's header too, but there is a big problem because you have installed double siphons ...one on outlet from condensers and another one is siphon before priority vessel and probably that is the biggest problem in piping ...



this above is a good observation ... in my installations I'm always trying to follow that suggestion ...

..... in my attached diagram and pdf files you can see how I'll make connections for vent line from priority vessel and equalizing line from HPRs - it is possible to check pipe sizes one more time .... bypass lines for DS are not needed .... seems that liquid header after condensers is too high with siphons instead of straight lines tapping from above and using only one siphon at priority vessel .. this header must be bellow priority vessel to avoid siphons after condensers ...


sorry, English is not my mother tongue and maybe you cannot follow what I mean ... it is not easy for me to explain what I'll do to make plant running ... unfortunately some piping must be changed ... hope some other valuable members will come with some comments which can help you maybe better then me.


Best regards, Josip

Dear sir,

I have made modification in my piping in condenser area. As per your attached diagram i have down my priority vessel . Now net distance from level in priority vessel to condenser bottom is 1.7 mtr. But still problem is same. I have put pressure transmitter across condenser inlet and outlet. I observe that the .1 bar pressure difference between inlet and outlet. Pressure between priority vessel and condenser inlet is never equalised nad found .03 bar difference. When i am open my vent and equalising line my discharge pressure rising very rapidly.Give your valuable suggestion regards this problem.

Regds,

Jitender ghanghas

[Josip]

Hi, ghanghas85

Dear sir,

I have made modification in my piping in condenser area. As per your attached diagram i have down my priority vessel . Now net distance from level in priority vessel to condenser bottom is 1.7 mtr. But still problem is same. I have put pressure transmitter across condenser inlet and outlet. I observe that the .1 bar pressure difference between inlet and outlet. Pressure between priority vessel and condenser inlet is never equalised nad found .03 bar difference. When i am open my vent and equalising line my discharge pressure rising very rapidly.Give your valuable suggestion regards this problem.

Regds,

Jitender ghanghas

Kindly ask you to make a kind of disposition scheme with new piping, together with measures- distances etc...

Best regards, Josip

[ghanghas85]

hi, ghanghas85



kindly ask you to make a kind of disposition scheme with new piping, together with measures- distances etc...

Best regards, josip

sir pls find the diagram

[Josip]

Hi, dear ghanghas85

sir pls find the diagram

Sorry, this is not the same as in my drawing ... please check again ....


Best regards, Josip

[Segei]

It looks like your condensers are flooded. What are the condenser water temperatures(in and out)? What is temperature of the liquid ammonia that come from condenser? What is the condensing pressure?

[ghanghas85]

dear sir condenser water inlet and outlet temp. are 26 and 28 approx and my liquid outlet temp is around 28 deg c

[ghanghas85]

Hi, dear ghanghas85



Sorry, this is not the same as in my drawing ... please check again ....


Best regards, Josip

Dear josip sir i just made individual u- trap on condenser out let line and vent line and equalising line connected to the condenser inlet header not on the desuperheater header because i am not running my de superheater.Does this affect and how pls reply.


Regds,

Jitender ghanghas

[Segei]

dear sir condenser water inlet and outlet temp. are 26 and 28 approx and my liquid outlet temp is around 28 deg c

Condensers are flooded. Assume that condensing pressure is 12 bars(180 psig). This is 35 degC. Liquid ammonia should have temp. 35C. If it is lower than that it means cond. is flooded. Probably, this is the reason of high cond. pressure. What is the distance between bottom of the condensers and condensate header?
ASHRAE suggests minimum drop leg 1.5 m. This is for evaporative condensers. I think that PHE condensers have greater pressure drop and this drop leg should be increased. Why do you need priority vessel?

[ghanghas85]

Sir net distance between condenser outlet bottom to condensate header is 2 mtr. How i can resolve this problem.

[Josip]

Hi, ghanghas85

Dear josip sir i just made individual u- trap on condenser out let line and vent line and equalising line connected to the condenser inlet header not on the desuperheater header because i am not running my de superheater.Does this affect and how pls reply.


Regds,

Jitender ghanghas

Of course your condensers are flooded ... if not, you will not have a high discharge pressure ... here we are trying to release liquid to the place where it belongs ... into priority vessel and HPRs and we have to follow some basic rules of gas flow through the pipes ...

Seems none is reading this thread/posts and do not following data and suggestion/s...

sorry, Ghanghas85, maybe I sounds rude,

but (if you visit doctor who prescribed some medicine to you and you do not use that medicine how you can be better , and then you return to doctor saying "sorry doctor I'm still feeling very bad" ..... if you ask for help an do not follow suggestion/s (use medicine) what we can do ...

I made a drawing (my post #13) of your plant in the way how I did piping before and will make piping in the future, simply because it is working ... sorry I do not know the better way .... it is up to you if you want to follow that or not ...


Regarding individual U/traps at the outlet of condensers they are not needed because you have a common liquid trap in the liquid header and priority vessel ... check, please ....

In my opinion, the biggest problem are connection points/tapping of equalizing line from HPRs and vent line from priority vessel ... those pipes must be connected to discharge header from compressors before desuperheaters (you use them or not i.e. open desuperheaters by-pass line between discharge header and header before condensers)

I sent you drawings regarding tapping/connections of equalizing and venting line into discharge header .... it is not my invention, some other smart people suggest that way - I'm just following -

Regarding net distance between condensers outlet and liquid header is not important - important is net distance between condenser outlet and liquid level within priority vessel, because your liquid header is flooded and liquid level in each outlet condenser pipe is the same as in your priority vessel .... later I will make a drawing to explain you this

Best regards, Josip

[RANGER1]

ghanghas85,
I'm assuming priority vessel is for thermosyphon oil coolers, is this correct?

I cannot see piping of priority vessel on your scan which may have important information.

Can you show detail of priority vessel along with piping connections & sizes etc.

[RANGER1]

thanks sir i observe 1 thing when i open my equalising line then my discharge pressure goes high and equalising line so hot and its size is 50 mm.How i can resolve this problem

ghanghas85 , can you describe where this 50mm line is a bit better!

[RANGER1]

ghangas85,
We are also assuming you have a lot of cooling water going through all PHE condensers even with 1 Vilter running.

Can you advise?

[ghanghas85]

Dear Josip

I have a few queries please for understanding :

a) If the system runs with the despuerheater by passed, then the condensor header is the discharge header.

b) If the gas is taken through the desuperheater there would be pressure drop in the desuperheater which would be atleast 0.06 bar, This would mean that the pressure at the outlet of condensor will be lesser than as is being operated now as there would be a drop across the condensor also. This could mean the requirement of a taller liquid leg.

Your views on this please


Rgds

Rs

[Josip]

Hi, ghanghas85

Dear Josip

I have a few queries please for understanding :

a) If the system runs with the despuerheater by passed, then the condensor header is the discharge header.

NO, your discharge header is always pipe coming from compressor/s either delivery hot gas to desuperheater/s or directly to condenser/s (if desuperheater/s are bypassed) ....

b) If the gas is taken through the desuperheater there would be pressure drop in the desuperheater which would be atleast 0.06 bar, This would mean that the pressure at the outlet of condensor will be lesser than as is being operated now as there would be a drop across the condensor also. This could mean the requirement of a taller liquid leg.

Your views on this please


Rgds

Rs

Of course, using desuperheater we would increase pressure drop for some amount,but from desuperheater must come out gas (remove only sensible heat within desuperheater - even some evaporative condensers have desuperheater section (above water nozzles and water drops eliminators - cooling that section-desuperheater only with air but for some other purpose then to gain some energy) .... I will use flow through the desuperheaters even if you have not connection to second cooling medium, why not?



sorry, this part I cannot follow:

pressure at the outlet of condensor will be lesser than as is being operated now as there would be a drop across the condensor also. This could mean the requirement of a taller liquid leg

Drawing new RE 01.JPG

what do you mean with requirement of a taller leg - which one leg do you mean? make a drawing and mark "taller leg" , please.

Liquid trap within liquid header is enough to be 150-300 mm for ammonia no need bigger at all.

Best regards, Josip

[mbc]

I think you should look again what equalizing pipe is doing.
It is balancing pressure between inlet of condenser and receiver, And mainly use when the weather is changing in winter and summer and we want to have enough heat in discharge line for defrosting rooms by keeping liquid in condenser ( reducing heat area in condenser) So this line should not be open fully and we use spindle type stop valve ( regulator valve) and size of pipe 1/2 is enough.
And the reason why receiver getting hot is a your valve is open and you should adjust that , So close the valve in equalizing pipe and open it very gentle(spindle stop valve)

And it is not important you have de supper heater or not . Connections are after compressor inlet of condenser or de super heater

[RANGER1]

Josip,
The latest sketch with thermosyphon oil cooler hooked up looks suspect to me.
If ghanghas85 has it piped like your sketch it may not be current problem ,but it will be the next one if screw is started.

The oil cooler "vent line" should be piped to return into top of priority vessel.

In its current form either thermosyphon would not work very well, or liquid would be
returning back into main discharge line before desuperheater PHE possibly flooding condensor with liquid.

[Segei]

Actually priority vessel is thermosiphon receiver. I agree with Ranger 1. Return line from oil cooler should go to the top of priority vessel not discharge line. This is fundamentally wrong. It is difficult to help people if they give partial information. OP never mentioned that priority vessel use for thermosiphon oil cooling.

[Josip]

Dear RANGER1 and Segei

Josip,
The latest sketch with thermosyphon oil cooler hooked up looks suspect to me.
If ghanghas85 has it piped like your sketch it may not be current problem ,but it will be the next one if screw is started.

The oil cooler "vent line" should be piped to return into top of priority vessel.

In its current form either thermosyphon would not work very well, or liquid would be
returning back into main discharge line before desuperheater PHE possibly flooding condensor with liquid.

Actually priority vessel is thermosiphon receiver. I agree with Ranger 1. Return line from oil cooler should go to the top of priority vessel not discharge line. This is fundamentally wrong. It is difficult to help people if they give partial information. OP never mentioned that priority vessel use for thermosiphon oil cooling.

I'm not sure if OP is using priority vessel to feed thermo siphon oil coolers, it was only my assumption and suggestion how to make piping ...


Please, check this attachment ....
Attachment 6594

SABROE OIL COOLERS.jpg

... if we are in the year 1995. when I did not know too much about thermosiphon oil coolers .... and installation&piping of such oil coolers were something new for me I will accept your suggestion, but ... I made one installation as per your suggestion (also shown in attached file as primary arrangement) and then we faced some problems with oil cooling (5 Mycom units assembled by Technofrigo-Bologna) ... then I start to search and find some other solution ....

.... unfortunately I cannot find a document showing installation and piping in the same way I suggest to ghanghas85, but from this one is visible that is possible ...

There is no way to flood condenser with return liquid from oil cooler/s ... why ... liquid can be at the same level like we have in priority vessel not more, but there in return line we have no liquid because oil coolers are working on latent heat, thus we can have some drops of liquid there due to partial evaporation of liquid refrigerant within oil cooler with speed of gas around 2 - 5 m/s (return line must be designed in this way).

For that reason piping of oil cooler is very important .... liquid inlet from the bottom and vent line on the top of oil cooler/s all the way to condenser's inlet header with inclination i.e. climbing pipes (without horizontal pipe either in liquid or vent pipe).

Further, my attachment from some previous post (07.04.2011) showing tapping of return lines (equalizing&vent pipes) into discharge header, pretty close to desuperheater/condenser inlet are acting similar like venturi pipe thus reducing height H1 for about 0,5 - 1,5 m.

One more thing... if we connect all return lines back to priority vessel via pipe B then pipe D must be dimensioned for pressure equalizing and for flow of gas load from oil coolers with speed of 2-5 m/s ... if we make connection as per my suggestion line D is only for equalizing purpose.

Of course there is some more mathematics to design thermosiphon oil cooler/s piping.

I want to say both of you are right regarding piping of return lines from oil cooler/s, but since year 1996. all my designs and installations of thermo siphon oil coolers I did like in my suggestion and all plants are working without any problem, even if it is looking "fundamentally wrong".


We have to blame some designers from Gram, Stal and from Sabroe why they invent and suggest something wrong, but still working very well.


With all my respect to you I do not see the reason to change that.


Best regards, Josip

[RANGER1]

Thanks Josip , you learn something new every day.
I remember seeing it in Sabroe manual but dismissed it as had never seen it in practice.

I guess our engineers & like yourself use what works.

We still have not heard fron ghanghas on his piping arrangement ie priority vessel/thermosyphon!

Josip have you used this method on PHE condensers?

The reason I requested priority vessel details as it was the part of system I could not see.

In some applications I have seen thermosyphon oil cooler return & balance line used in same connection on thermosyphon reciever, with liquid migrating in main discharge line.
I thought if this was the case PHE could be flooded with liquid reducing its performance due to inlet restricted.

[Segei]

Dear RANGER1 and Segei






I'm not sure if OP is using priority vessel to feed thermo siphon oil coolers, it was only my assumption and suggestion how to make piping ...


Please, check this attachment ....
Attachment 6594

SABROE OIL COOLERS.jpg

... if we are in the year 1995. when I did not know too much about thermosiphon oil coolers .... and installation&piping of such oil coolers were something new for me I will accept your suggestion, but ... I made one installation as per your suggestion (also shown in attached file as primary arrangement) and then we faced some problems with oil cooling (5 Mycom units assembled by Technofrigo-Bologna) ... then I start to search and find some other solution ....

.... unfortunately I cannot find a document showing installation and piping in the same way I suggest to ghanghas85, but from this one is visible that is possible ...

There is no way to flood condenser with return liquid from oil cooler/s ... why ... liquid can be at the same level like we have in priority vessel not more, but there in return line we have no liquid because oil coolers are working on latent heat, thus we can have some drops of liquid there due to partial evaporation of liquid refrigerant within oil cooler with speed of gas around 2 - 5 m/s (return line must be designed in this way).

For that reason piping of oil cooler is very important .... liquid inlet from the bottom and vent line on the top of oil cooler/s all the way to condenser's inlet header with inclination i.e. climbing pipes (without horizontal pipe either in liquid or vent pipe).

Further, my attachment from some previous post (07.04.2011) showing tapping of return lines (equalizing&vent pipes) into discharge header, pretty close to desuperheater/condenser inlet are acting similar like venturi pipe thus reducing height H1 for about 0,5 - 1,5 m.

One more thing... if we connect all return lines back to priority vessel via pipe B then pipe D must be dimensioned for pressure equalizing and for flow of gas load from oil coolers with speed of 2-5 m/s ... if we make connection as per my suggestion line D is only for equalizing purpose.

Of course there is some more mathematics to design thermosiphon oil cooler/s piping.

I want to say both of you are right regarding piping of return lines from oil cooler/s, but since year 1996. all my designs and installations of thermo siphon oil coolers I did like in my suggestion and all plants are working without any problem, even if it is looking "fundamentally wrong".


We have to blame some designers from Gram, Stal and from Sabroe why they invent and suggest something wrong, but still working very well.


With all my respect to you I do not see the reason to change that.


Best regards, Josip

11111111111

[Segei]

I double checked W.Stoecker book, IIAR Piping Handbook, ASHRAE Handbook 2006, Frick manual and I didn't find any suggestion that return line can be connected to the discharge line. However everybody suggest that liquid goes to the oil cooler, part of this liquid will evaporate and mixture of the liquid and vapor will go back to thermosiphon receiver. Movement in this circuit will happen because liquid in supply line are more dense that liquid and vapor in return line. This is the reason we call it thermosyphon. This is overfeed system has typical rate 1:3.
One remark from W.Stoker book p.387. '"Separation of liquid and vapor indeed also takes place in thermosyphon receiver, but requirements are not stringent. Some liquid mist could pass through the vent line to the condenser inlet without an adverse effect, but it should be emphasized that return of the liquid and vapor from the oil cooler should not be delivered to the consener inlet, because such a large fraction of liquid would degrade the condenser performance".

[Josip]

Hi, RANGER1

Thanks Josip , you learn something new every day.
I remember seeing it in Sabroe manual but dismissed it as had never seen it in practice.

I guess our engineers & like yourself use what works.

We still have not heard fron ghanghas on his piping arrangement ie priority vessel/thermosyphon!

Josip have you used this method on PHE condensers?

The reason I requested priority vessel details as it was the part of system I could not see.

In some applications I have seen thermosyphon oil cooler return & balance line used in same connection on thermosyphon reciever, with liquid migrating in main discharge line.
I thought if this was the case PHE could be flooded with liquid reducing its performance due to inlet restricted.

I'm repeating once again, the way of piping (return line connected to priority vessel) as you suggested is OK, but believe me this one is too.

No, I did not use this system with PHE condensers, because I was working mostly in desert area where is not possible to keep cooling water for condenser/s clean and PHE condensers are not "familiar" with dirty water. Some of my colleagues did.

I think there is some positive thing regarding PHE condensers - flow within PHE is vertical, thus gravity helps to drain liquid faster, in EC we have pipes with some slope which is almost horizontal thus liquid is not drain fast.

I believe, ghanghas85 will revert with drawing/s regarding utility of priority vessel and further piping to oil cooler or some other HE. The best will be to scan complete scheme of his plant and upload it, then we can see all, but.... let's wait for a while.


please check this link ... http://postharvest.tfrec.wsu.edu/pages/PC97P Figure 2 ... interesting ....


Best regards, Josip

[ghanghas85]

Dear Jossip /Ranger 1

Enclosed is the schematic of the plant

We have added some plates in the PHE condensor to reduce the pressure drop.Subsquently the system is operating with a pressure of 14.5 bar with two condensor in operation. The vent valve is now partially open (2-3 rounds). If the valve is fully opened then the pressure rises to 16 bar.

The system is running with the equalising valve on the receiver closed. IF we open this valve then there is a rise in pressure.

The other problem which we note is that in case we close the receiver outlet valve (feeding to the system), the pressure goes up again very fast. The equalising valve is closed in this case. We though that the system should equalise through the liquid line from the thermosyphon to the receiver. This is an issue as there is a possibility that the liquid line solenoid valves will all be in a closed position during operation and we would have a high pressure.

The receiver is less than ¼ full and is of 2000 Ltrs each. We are running two receivers in parallel


Request your suggestion pls .

Jossip, In the previous mail we had mentioned about additional leg in case we connect the vent line from the thermosyphon receiver to the discharge line. The leg is shown in the sketch and is the vertical distance from the outlet of condensor and the liquid level in the thermosyphon vessel

The thinking of ours was as follows:

Assuming that the discharge pressure is 14.5 bar. When we take the gas through the desuperheater the pressure at the outlet of the desuperheater would be 14.45 bar (assuming a drop of 0.05 bar). This gas flows through the condensor and has a outlet pressure of 14.4 bar.

The pressure in the thermosyphon vessel would be 14.5 bar as it is connected to the discharge header. Hence the liquid column has to offset the pressure difference between the outlet of condensor 14.4 bar and thermosyphon vessel which is 14.5 bar.

When we connect the vent line to the inlet header of the condensor, the liquid column has to offset a pressure drop across the condensor only.

Look forward to your advise.


Rgds

Ghanghas

[Josip]

Hi, ghanghas85

Dear Jossip /Ranger 1

Enclosed is the schematic of the plant

We have added some plates in the PHE condensor to reduce the pressure drop.Subsquently the system is operating with a pressure of 14.5 bar with two condensor in operation. The vent valve is now partially open (2-3 rounds). If the valve is fully opened then the pressure rises to 16 bar.

The system is running with the equalising valve on the receiver closed. IF we open this valve then there is a rise in pressure.

Something new i.e. new important data from your attached drawing (compressor working points -10*C/+40*C), but at evaporating pressure of -10*C and condensing temperature of +40*C= 15,6 bar
(quite high, is there some particular reason for that?)
It will be better (in my opinion) to have condensing pressure 30/32*C max 35*C, but maybe you have some good reason to spend so much electrical energy.

Why do you not run with all condensers in the same time and check what you have then?

One more thing actually question, do you have pump recirculation or DX evaporators?

The other problem which we note is that in case we close the receiver outlet valve (feeding to the system), the pressure goes up again very fast. The equalising valve is closed in this case. We though that the system should equalise through the liquid line from the thermosyphon to the receiver. This is an issue as there is a possibility that the liquid line solenoid valves will all be in a closed position during operation and we would have a high pressure.

The receiver is less than ¼ full and is of 2000 Ltrs each. We are running two receivers in parallel

What to say... valve/s on equalizing line/s from receiver to discharge header must be open, but that line must be connected as per attached JPG file red lines ....

By-pass valves on desuperheater/s must be closed - marked with short red line too.

Do you have a liquid equalizing pipe beneath receivers to equalize level within receivers ... marked red also

Do you have all receivers installed or that will be in the future?

Request your suggestion pls .

Jossip, In the previous mail we had mentioned about additional leg in case we connect the vent line from the thermosyphon receiver to the discharge line. The leg is shown in the sketch and is the vertical distance from the outlet of condensor and the liquid level in the thermosyphon vessel

Vent line from priority vessel must be connected as per attached JPG file even if your desuperheaters are not working now (assume them like a piece of inlet header to condensers .... marked as red line ... valve B must be fully open to vent gases from priority vessel and return gases from oil cooler...

The most important is to move your eccentric reducer from horizontal condenser outlet (marked next to condenser 1) line on the vertical line ... marked with circle ... instead of reducer put an 90* elbow with the same size of vertical pipe (L=500-600mm) down to liquid header

Angle valve you must put in vertical part of pipe after reducer ... you can cut an elbow of 90* into two of 45* to make a straight valve...

The thinking of ours was as follows:

Assuming that the discharge pressure is 14.5 bar. When we take the gas through the desuperheater the pressure at the outlet of the desuperheater would be 14.45 bar (assuming a drop of 0.05 bar). This gas flows through the condensor and has a outlet pressure of 14.4 bar.

The pressure in the thermosyphon vessel would be 14.5 bar as it is connected to the discharge header. Hence the liquid column has to offset the pressure difference between the outlet of condensor 14.4 bar and thermosyphon vessel which is 14.5 bar.

When we connect the vent line to the inlet header of the condensor, the liquid column has to offset a pressure drop across the condensor only.

Look forward to your advise.

Rgds

Ghanghas

If you connect your vent line to discharge header as per attached JPG file, your present connection for me is in a wrong place. We have to assure easy draining of condenser/s and liquid seal what you have now ... about 700mm must be enough.

Replay SCHEMATIC DIAGRAM.jpg

Hope this will help a little.

Best regards, Josip

[D.D.KORANNE]

Just basics to verify :

@ Load on the condenser : Evaporator load + motor heat equivalent + losses ,if any
also check , heat rejected to water , water flow
CONDENSER LOAD BTU/HR
USGPM = ----------------------------
500 x Water outlet temp - water inlet temp ( in deg F )

@ verify the dischare line ( pipe) sizing ........ ??????

[Segei]

Dear Jossip /Ranger 1

Enclosed is the schematic of the plant

We have added some plates in the PHE condensor to reduce the pressure drop.Subsquently the system is operating with a pressure of 14.5 bar with two condensor in operation. The vent valve is now partially open (2-3 rounds). If the valve is fully opened then the pressure rises to 16 bar.

The system is running with the equalising valve on the receiver closed. IF we open this valve then there is a rise in pressure.

The other problem which we note is that in case we close the receiver outlet valve (feeding to the system), the pressure goes up again very fast. The equalising valve is closed in this case. We though that the system should equalise through the liquid line from the thermosyphon to the receiver. This is an issue as there is a possibility that the liquid line solenoid valves will all be in a closed position during operation and we would have a high pressure.

The receiver is less than ¼ full and is of 2000 Ltrs each. We are running two receivers in parallel


Request your suggestion pls .

Jossip, In the previous mail we had mentioned about additional leg in case we connect the vent line from the thermosyphon receiver to the discharge line. The leg is shown in the sketch and is the vertical distance from the outlet of condensor and the liquid level in the thermosyphon vessel

The thinking of ours was as follows:

Assuming that the discharge pressure is 14.5 bar. When we take the gas through the desuperheater the pressure at the outlet of the desuperheater would be 14.45 bar (assuming a drop of 0.05 bar). This gas flows through the condensor and has a outlet pressure of 14.4 bar.

The pressure in the thermosyphon vessel would be 14.5 bar as it is connected to the discharge header. Hence the liquid column has to offset the pressure difference between the outlet of condensor 14.4 bar and thermosyphon vessel which is 14.5 bar.

When we connect the vent line to the inlet header of the condensor, the liquid column has to offset a pressure drop across the condensor only.

Look forward to your advise.


Rgds

Ghanghas

I agree that equalizing line from thermosyphon receiver should be connected between desuperheators and condensers. I would increase the size of this line. Vent line from high pressure receivers should be connected to thermosyphon receiver. However, these are secondary issues.
Major issue is that drop leg is too small compare to pressure drop. Solutions are:
1. Reduce pressure drop by adding or/and operating more condensers in parallel.
2. Increase drop leg.
a. Move condensers up. Probably isn't possible.
b. Move thermosyphon down. Probably is very expensive.
c. Remove condenser liquid line traps and hook up them to the bottom of the high pressure receiver. The same way it was hooked up to the thermosyphon receiver now. Use liquid pump to move liquid from high pressure receiver to the thermosyphon receiver. Probably, this is the best solution in this situation.
Sizing the lines check IIAR, ASHRAE, Frick, IRC(industrial refrigeration consortium).