Plate Heat exchanger as a economiser on NH3 systems

[Rajkumar]

Do any one have experience using brazed plate heat exchanger as a economizer on a NH3 system?

Thanks.

[Josip]

Hi, Rajkumar

Do any one have experience using brazed plate heat exchanger as a economizer on a NH3 system?

Thanks.

Welded type like http://www.vahterus.com/en/front-page

is working fine, proofed ..... why to take a chance with brazed one .... lower price.... maybe, but what about safety?

Best regards, Josip

[michaelm]

Do any one have experience using brazed plate heat exchanger as a economizer on a NH3 system?

Thanks.

B”H
Rajkumar,
Be aware that majority of PHE are brazed with big cooper % content in brazing material.

[RANGER1]

It all depends on what ammonia comes in contact with.
Supplier should be able to advise on this area of compatability.

Otherwise PHE is OK to use for economizer if controlled correctly.
Best to have modulating level control valve on the subcooled liquid you produce from it , so its a more constant load on compressor economizer port.

[Rajkumar]

Ranzer, I think you got my point. I am having trouble with Dx type Brazed Economiser (Alfa Laval Alfa Nova) System. Compressor is working at (-)42 deg C. I have Bit low load approx (60%) but i am driving the compressor at full load using the VFD. I am not getting the proper return on compressor economiser port. The Economiser liquid feed assembly is having a TX Valve.

Do any one know what i should do to get the constant load.

[Josip]

Hi, gentlemen

It all depends on what ammonia comes in contact with.
Supplier should be able to advise on this area of compatability.

Otherwise PHE is OK to use for economizer if controlled correctly.
Best to have modulating level control valve on the subcooled liquid you produce from it , so its a more constant load on compressor economizer port.

It is OK to use some brazed PHE because there are some brazing material resisting to ammonia.... maybe this one too, why not .... somebody gave info to Alfa Laval about refrigerants with order ...

Ranzer, I think you got my point. I am having trouble with Dx type Brazed Economiser (Alfa Laval Alfa Nova) System. Compressor is working at (-)42 deg C. I have Bit low load approx (60%) but i am driving the compressor at full load using the VFD. I am not getting the proper return on compressor economiser port. The Economiser liquid feed assembly is having a TX Valve.

Do any one know what i should do to get the constant load.

Not sure, but seems your TX is giving too high suction superheat and there is not enough capacity... for ammonia SS can be low, sometimes, as 0K using PHE....

But I think that TX is not the good one (maybe I'm wrong) there must be a special type of injection valve electronically operated via electronic temperature probes mounted on suction pipe running to compressor's ECO port I think that's the same as per RANGER1 suggestion ... many years ago in Turkey, York Italy installed the similar system on PHE without surge drum, similar to your economizer ... working very nice ..

Best regards, Josip

[Segei]

Ranzer, I think you got my point. I am having trouble with Dx type Brazed Economiser (Alfa Laval Alfa Nova) System. Compressor is working at (-)42 deg C. I have Bit low load approx (60%) but i am driving the compressor at full load using the VFD. I am not getting the proper return on compressor economiser port. The Economiser liquid feed assembly is having a TX Valve.

Do any one know what i should do to get the constant load.

It is not clear for me. Why do you run compressor at 100% when load is 60%? What do you mean by not getting proper return on compressor economizer port?

[charlie n]

To be sure, we need to know all details of the compressor and economizer. I've used the Alfa Nova without any problems but a flash economizer or even a flooded arrangement of the Alfa Nova would be better.
Anyway, DX can work. Is the expansion valve sized correctly. Is it mechanical or electronic? Is the liquid distribution tube in place inside the PHE inlet connection? Have you drained oil from the bottom of the evaporator circuit inlet connection?

[Rajkumar]

We are using the mechanical expansion valve. Earlier there was no distribution tube, now we had place the distribution tube with dia 4mm hole on each chaanel but still facing the same problem.

[RANGER1]

To me you need a very constant load for TX valve to settle down with reasonable superheat.

As I suggested the liquid line which is the heat load for the PHE ideally should be as constant
flow as possible .
This is best achieved with a modulating on the vessel or whatever you are delivering high pressure subcooled liquid too.
An EEV may be able to control more accurately with a quicker response time.

Ley s know more about your plant & how it works.

[charlie n]

Ranger1 has a good point. If the liquid flow to the low side is through a float and solenoid valve arrangement, the DX economizer will never work. liquid flow must be almost constant for this to work.

[Magoo]

I am not a fan of economizers with welded type with TXV. I have killed a few on ***** plants. The thermal expansion and contraction effects over a period of time creates stress fractures and leaks, if crack occurr internally you end up sending HP liquid the econo port of screw, so then went to double plate welded PHE.
Generally prefer flooded with surge drum header and add evap press reg and flow stop check valve on suction.
For ammonia I prefer the stacked / re-stackable type with surge header, level controller float and pulse fill valve. The ultimate would be a closed flash shell and coil economizer.