Refrigerant and system choices on Fishing vessels.

[Neptune Refrig]

Many a sleepless night trying to come to a successful decision on which way to go. I maintain and service a large section of the Northern Prawn Fishery in Australia. The vessels here are purpose made 'machines'. Space is limited. The staff (1 x 'engineer') operating the equipment, is at best... adequate. These vessels use a total of approx. 120 - 150Kw refrigeration capacity with 2 stage Grasso's or Bitzer's or Bitzer Screws. and in ali. plate snaps, brines and FDC's. 5 ton of 25C prawn is frozen to -18C in 9-13 hours.
Thse boats have a more complex problem, than terrafirma installations, to solve with the impending end of R22 and the unjustified increase in price of the next prefered gas R507.
The GWP friendlier choices are not suitible in these vessels. Namely 1/ CO2 requiring low ambient water temp for condensing (20c - 30C in Oz), and it's off cycle pressure problems, + leakage concequenses . (I do acknowledge cascade systems for this condensing reason...but a complex system is not and option bearing in mind the operating staff whilst at sea) 2/ Ammonia requiring a close plant room, having oil migration problems and still having to use open drive compressors etc. 3/HC's. Love the refrigeration qualities. But on board these vessels, actastrophe looms. Furthermore it requires a sealed plantroom, unique safety components and the surety of future prohibitive legistlations. (I am aware of the quidelines in Europe and Britan re. charge maximums and Ignition points already).
Now, I am really only airing my thoughts, but this fishing industry and many other similar areas involving fishing vessels, is not able to economically and feasibly adapt to the change to natural gas's. I am at present advising (as are many) to increase the emphasis on early and pre-emptive leak detection and repair. I am pushing towards upgrading and using every leak minimising procedure possible.
However, for the next 2 seasons or so they will continue with R22. Hopefully the bureaucrats, that used their wisdom to impose refrigerant changes will acknowledge that 'one cap does not fit all' and that this fishing industry needs to be recognised as unsuitible for using natural gas's presently availible.

[mad fridgie]

You can look at air as a refrigerant.
Contact your local Mycom agent.

[hookster]

I like your thinking mad! natural refrigerants are the way to go and the future.
With the latest developments in R718 (water vapour) and liquid air storage systems.

The problem with your suggestion is back to the limitations for the application. There is with every selection pro's and cons and a decision is always needed to weigh up all the factors to give the best selection.

The limitations with air refrigeration is the mass flow of air for every ton of refrigerating capacity required. This then requires large compressors and a bulky plant and is not applicable for Marine applications where space for non cargo (earning capability) is at a premium. Power requirement is large for equivalent accepted refrigeration systems and maintenance costs are high with the air systems.

The marine industry used to be a leader in ammonia as a refrigerant for selection and actually the Cunard Liner QM2 was originally proposed to be a natural refrigeration system. If the plant is well designed, I would always advocate that this is the best refrigerant for Marine applications. What is required is more understanding by non refrigeration decision makers on the reality of this refrigeration.

The explosive nature of ammonia which is much vaunted is a red herring and it has a very tight flammable range 16 - 25%, it is not self propagating and the energy release is low. The self warning nature of ammonia and the lighter than air aspects make this a safe refrigerant which is easily detectable for leakage via electronic or other means and is easily dispersed with ventilation.

It is cheap to replace refrigerant, construction is in cheaper materials, it is more efficient and has a GWP of 0

[mad fridgie]

Ah, water! have not kept up with play in developments, last time I heard, multi stage axial, required approx 1% increase in efficiency per stage to make it viable. But of cause water is not right for this application.

Re air cycle systems " Branton or Claude"(not to be confused with liquefaction), if we look at the aircraft industry, these are relatively small in size for the duty produced. Effectively like a turbo charger. Not the best efficiency.

I designed on of these many moons ago for a tuna boat -65C (never went a head, the bloody boat sank in a storm) I believe Mycom have perfected such a system for commercial use.

There does seem to be some fear of ammonia.

With a lot of waste energy available close by, there is no reason why other heat driven systems could not be used.

Maybe even look at going backwards, have small limited charge system (of what ever type) and have secondary refrigerant loop calcium chloride, or some of the other specialist low temp working fluids.

[Neptune Refrig]

Thanks for the comments Mad and Hookster.
A delay in repsonding but I have been rather busy of late.
If there were to be new vessels constructed, allowance could be made for there required extra space that open up more options, such as air. However with the present aging fleet of vessels in operation, space is (once again) limited for system redesign. The boats need around an extra 15m2 of space for design versatility.
The installation of sealed plant rooms required for ammonia and HC's pose a large logistical hurdle if they are to allow for serviceability and safety of the staff, along with maintaining the vessels integrity.
Plant rooms would still be required for any fluid circulation system such as calcium chloride or glycol.
I am an advocate of ammonia. However I don't wish to be taking steps backwards with the evolution of compressors & other R717 technical issues.
Until there is the availibility of presently comparable semi hermetics, I am hesitant to advise my clients of this path of application.

Agreed. Natural refrigerants are a good way to go. However from a ground level prawn fishing operation perspective and looking objectively at the problem, I cannot get completely on board until there these alternatives have the advantageous characteristics that R22 has.
I can almost hear many saying 'there is no choice', but this is where the cliche` "Between a rock and a hard place" applies.
I hope relevant governing bodies read these forums. There is some extremely valueable information and opinions from people on the refrigeration front line....and not of the nature found in environmental department reports and technical manuals.
Perhaps the Aust. government will subsidise the constuction of new vessels for these companies. There has to be some economic feasibility to make this GWP reduction path work. There can't be industries that become collateral damage in it's wake.

[mad fridgie]

Ok, think about the application and the solution.
You basically want to use your present set up, you need to have on eye on the environmental issues and refrigerant cost. Changes that occur, have to be minmal changes to the mindset (skils) of the on board guys.

So think out of the box, but keeping the above in mind.

Lets look at R134a, lowest GWP of this type of refrigerant, so lower cost (carbon tax), is compatible with just about all your present components (oil change required and maybe some seals/gaskets) these are fairly minimal and could be completed before any change actaully took place.

We know look at performance, you present plant set up would not work, but if we introduce a "Booster" (we add another stage of compression), it would then be easy to bring the system back into spec. This Booster need not take up a lot of space.

We then come down to a precieved technical problem, R134a low pressure side would be lower than atmosperic pressure "the system would be running in a vacuum" You would have to ensure that the system is leak free, which is not a bad thing. (even these issues can be over come, with a non condensable purger and driers as required.)

A low cost retrofit option.

Some design work would be required, more than just replacement of the refrigerant, which would be the preferred option

[Neptune Refrig]

Thanks for the reply.
I haven't detailed the present systems adequately.
Except for some Bitzer screws, they are all already 2 stage machines (2 x 4210 Grasso's, or 2 x Mycoms, or 2 x Gramms and 4 x Bitzers recips).
Only a few have capacity control beyond turning one compressor off.
Whilst still using R22, (250kg per system), they operate in vacuums for about half of the operating time. This is due to the high capacities which are still applied to the evaporators, even when loads are reduced or when the latent heat removal stage has finished. The TD is beyond the norm.
But the result is extremely rapid freezing.

[mad fridgie]

are you running 50 or 60 Hz

[Neptune Refrig]

All the vessels are 50 Hz

[mad fridgie]

Introduction of a VSD will give you a least another 20% extra displacement (60Hz equ), more is possible but you would need to check with the manufactures.

Something to think about.

[Neptune Refrig]

Thanks Mr Mad Fridgie,
Many of the vessels already have Variable Speed Drives. I intend to fit the same to new installations (hopefully Bitzer semi-hermetics).
Presently the VSD's are in place to improve starting and hence reduce loading on the auxilliary alternator, and to allow capacity control via adjusting suction pressures. These also have the pulley to pulley ratio being one to one and 1500 rev's is maximum allowed for the Grasso compressors used. (4 pole motors).

[hookster]

Hi Neptune
I would assume flooded evaporators but i would stand to be corrected. This would limit the use of R134a and then you will be down the R507 route.

[Neptune Refrig]

Hello Hookster,

actually all but a few of the evaportaors are DX (electronic TXV). (the flooded few are for circulated water chilling assisting in prechilling the prawns and increasing quality).
The extra refrigerant required to have the 2 or 3 snaps (each around 14 Ton) and the FDC (around 6 Ton) would mean even larger receivers...and now they are holding at least 240kg's.
However I have come to the R507 probable decision. R134a will create even more sever vacuums. R507 has higher pressures at both ends. However I will consider 134a to cover all avenues.

Like many, my emphasis is insisting to these companies on the implementation of severe and extreme leak detection and maintenance programs, combined with thorough documentation and individual responsibility.
Maybe changing the past culture of accepting some leakage, will solve a large part of the problem. Hard to convince them as it means more paperwork for them!!

Gotta be a fridgy and a politician these days!

A lot of these engineers within this fishing industry are there for only 1 or 2 seasons. All that concerns them is that if refrigerant gas comes out, they can put some back in, and that the boat operates adequately for the season. Then the engineer disappears.

[mad fridgie]

So I guess form what has been said you would need spend around $75K on R507.

So keeping an open mind, you say you have a 2 stage system (low and high stage comps?), what about going cascade (not a major change if comps separate ), R507, low stage R134a high stage. Without knowing the details, would this reduce the R507 charge by a reason amount.

[Neptune Refrig]

More around the $36000 amount per system. Buying in bulk (1000kg) the price is more reasonable.
The present 2 stage systems are mainly Grassos 4210 (6 cylinder- 4 LS 2HS), Bitzers S6G-30.2F (6 cyl. 4 LS 2HS) and then Gramms and Mycoms (all stages in one compressor).
Replacement systems with 507 will be along the Bitzer 2 stage recip line or Bitzer screw line.
I am not keen on complicating the system with a cascade (remember simplicity is the motto for the staff who operate the systems.), just to save a bit of inital gas charge cost.(the only advantage I like here is the ability to choose single stage operation (with correct design), such as during water chilling.

[mad fridgie]

Well that puts a nail in that coffin.
Its looking like R507 is the way to go.
Is there any way to reduce the charge? PHE cond, and a vertical receiver for example.
as well as improved leak prevention and detection.

[Neptune Refrig]

We will definitely make every effort to reduce the charge where possible, however only within lmits as the 4 evaporators on the one system can get greedy for gas so it has to have adequate charge. Vertical receiver will help.
Plate Heat Exchangers...I have only had exposure to these with liquid subcoolers. I thought salt water posed a problem with small particles with PHE ?
I'll post again when a path is set. If not before.

[mad fridgie]

We will definitely make every effort to reduce the charge where possible, however only within lmits as the 4 evaporators on the one system can get greedy for gas so it has to have adequate charge. Vertical receiver will help.
Plate Heat Exchangers...I have only had exposure to these with liquid subcoolers. I thought salt water posed a problem with small particles with PHE ?
I'll post again when a path is set. If not before.

I think you already have good handle on the situation, we look forward to how you go on. (pics always help)
Re; the PHE, no real issues, just have to pick the right one!!!. You often see them as oil coolers on the engine or part of the desalination plant if you have one.

[Goober]

Quite the interesting thread this...

[hookster]

I thought salt water posed a problem with small particles with PHE ? .

Go wide stream plate heat with titanium plates

[curt]

I like your thinking mad! natural refrigerants are the way to go and the future.
With the latest developments in R718 (water vapour) and liquid air storage systems.

The problem with your suggestion is back to the limitations for the application. There is with every selection pro's and cons and a decision is always needed to weigh up all the factors to give the best selection.

The limitations with air refrigeration is the mass flow of air for every ton of refrigerating capacity required. This then requires large compressors and a bulky plant and is not applicable for Marine applications where space for non cargo (earning capability) is at a premium. Power requirement is large for equivalent accepted refrigeration systems and maintenance costs are high with the air systems.

The marine industry used to be a leader in ammonia as a refrigerant for selection and actually the Cunard Liner QM2 was originally proposed to be a natural refrigeration system. If the plant is well designed, I would always advocate that this is the best refrigerant for Marine applications. What is required is more understanding by non refrigeration decision makers on the reality of this refrigeration.

The explosive nature of ammonia which is much vaunted is a red herring and it has a very tight flammable range 16 - 25%, it is not self propagating and the energy release is low. The self warning nature of ammonia and the lighter than air aspects make this a safe refrigerant which is easily detectable for leakage via electronic or other means and is easily dispersed with ventilation.

It is cheap to replace refrigerant, construction is in cheaper materials, it is more efficient and has a GWP of 0

I know this is a bit late but isn't mo99 a better choice its basically a drop in replacement for r22

[chiefbecker]

I am in a similar situation. We are running a flooded system that holds around 6k-7k pounds of R-22. We have four 200 Hp Grasso screw compressors and use horizontal plate freezers to freeze up to 120 MT of fish products per 24 hour period. I hear pro's and con's to using the R-507. Dupont recommends using R-438A in this system. The concern is a seperation problem with the refrigerant.

Has anyone used any of these replacement gasses in tehse larger flooded systems?

[FreezerGeezer]

Just wondering why R407c appears to be out of the question?

Also - I remember being told about total loss refrigeration systems used in trucks. Refrigerant was Nitrogen. So, question: could the refrigeration plant be replaced with Nitrogen tanks large enough to provide the refrigerating effect required? Or, assuming Nitrogen can provide the RE but you can't store enough aboard - how large is the plant required to extract Nitrogen from air, and how energy efficient is it compared to vapour compression refrigeration?