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Andy
28-12-2002, 11:25 PM
Hi,:)
just thought you all might be interested in an old type of refrigeration which has become popular again due to enviromental restraints.
Link is as follows:
Nestles Case Study (http://www.star-ref.co.uk/Tnestle%20case%20study.htm)
Sorry about advertising for Star, but it's an interesting topic none the less.

Now where's Marc when you want a good debate.

Regards. Andy:D

PobodysNerfect
09-01-2003, 09:09 PM
Hi Andy,
Interesting consept. However, it would have been nice to have more details such as a schematic drawing with the actual pressures - both for the CO2 & NH3.
Saludos

Dan
11-01-2003, 05:57 AM
Andy, this looks like good stuff. But the blather makes it hard to understand. No, let me say it differently. The blather makes me gag and I cannot read it for more than 30 seconds.

Could you explain what we have here in a more technical and practical manner?

Andy
11-01-2003, 01:06 PM
Hi, Dan:)
Well if you want to complicate a thing ask aa sales man to explain it:rolleyes:
Me I 'am too thick to be in sales and not near fat enough to pilot a desk yet.
Anyway here goes. The plant is basically two different plants, a coventional NH3 system at the high stage evaporating at -18 deg C and condensing at 35 deg C, not much in the way differing from the normal. Where things get interesting is on the low temp side, a pumped co2 system is fitted evaporating at -45 deg and condensing at -18 deg C, to all intense purposes this system again is very similar to a pumped NH3 system except for the pressures used and the design allowances to enable operation at these pressure, things like Stainless Steel pipework to withstand the pressures, thick vessel walls and heavier bodied control and shut off valves. The liquid pumps for the co2 are a bit special too being CAT powerwasher pumps (or a modified version of) these pumps work in the pressure range of 35 to 40 bar gauge, as you can see they have to be a little bit special!
Plant operation.
Heat is removed at -45 deg C and rejected to the cascade condenser where it is condensed by the cooling effect of the NH3 evaporation taking place in the same vessel, heat exchange is indirect, with the cascade vessel being basically an coil in shell heat exchanger (the only special bit of this is the way it is constructed so that in the event of a leak the two refrigerant cannot conbine into crystals within the system).
Co2 has a number of issues to be overcome as follows:-
[list=1]
1/high pressures in the low temperature side which must be controlled and not allowed to rise even when the plant is off cycled.
dryness, CO2 is a very dry gas which doesnot lubricated compressors in the conventional manner.
defrost, it is not usually feasible to bring the CO2 pressure above 40 barg to defrost the low temp evaporator (40 bar is only 5 deg C)
recaction, CO2 will react with NH3 to form a crystilite structure that is corrosive to plant components.
[/list=1]

All of these factors have to be overcome before a CO2 plant can be utilized, some are easily overcome such as the pressure limitation, by good plant contol, others like the defrost require different thinking to normal industry practice.
I have a system flow diagram I will try and post when I get it transfered to the correct format, in the meantime I hope this helps.
Regards. Andy:)

Dan
11-01-2003, 06:41 PM
Thanks Andy. I have a better picture of the system and some of the challenges it presents.:) Pressure washer pumps, eh? Fascinating.

Andy
12-01-2003, 09:33 PM
Hi,
please find attached a Pressure Enthalpy diagram (simple system) for co2, no pressure drops included as at present I have no idea how many degrees of drop will occur in the various areas.
Regards. Andy

Andy
12-01-2003, 09:41 PM
Hi,
I see the enthalpy lines don't extend low enough on the above attachment, sorry about that:o
As for the system diagram I have attached a link to the Grasso site, they have report on co2 which can be downloaded.Grasso Index (http://www.grasso-global.com/english/nbsp/index.html)
If you follow the link to site then go to News and in there you will find the article on Co2.
Happy reading . Regards, Andy:)

Friobernal
17-06-2003, 06:39 PM
Hi Andy;

It has been a long time since i post for the last time, but this time i have to reply about your comment:

Well if you want to complicate a thing ask aa sales man to explain it

Im a sales man and what you say its true!!!!but it is the way it works. In two weeks im having a meeting where i am supossed to be an expert in CO2 world. But I dont. So i have to study like in university. So i would like people to ask all you can imagine to prepare my meeting, and perhaps in a future i will be an expert in CO2 world:D

Bye

Andy
17-06-2003, 06:55 PM
Hi Friobernal,
nice to hear from you.
Danfoss have a very good paper on R744 that can be found at http://danfoss.com
Regards. Andy

750 Valve
16-11-2003, 01:18 PM
I know this thread's been hanging round for a while, but Andy, how did you overcome the defrost problem (high CO2 pressures)?

Andy
16-11-2003, 03:09 PM
Hi 750 valve:)
the higher hot gas pressures are obtained not by a compressor (manufacturers won't supply compressors to us at these pressures) but by a vapour generator. This is basically a liquid pump, a vessel and two heat exchangers and is a patented idea.
We take liquid from the main R744 liquid line and boost it with high pressure liquid pumps, then we add heat to this liquid until it becomes a saturated vapour at 10 deg C. We then add further heat to the vapour until it is superheated by about another 10K.
This vapour is then supplied to a valve station, with three control valves (Suction liquid and Hot gas) and defrosting is carried out much the same as in pump circ R717 systems.
Hope this helps, Regards. Andy.:)

mcamacho
25-11-2003, 11:59 PM
I attended Mr. Pearson's presentation on IIR2003, regarding another warehouse using CO2 as refrigerant. There Star used the oil coolers of screw compressors to heat the CO2 required for defrost (nice idea!).

Andy
26-11-2003, 01:37 PM
Hi Mcamacho:)
Nice to see you have heard of Star Refrigeration:)
We also us discharge gas from the NH3/High stage to heat the liquid into vapour for defrosting on some jobs.
Kind Regards. Andy:)

Friobernal
28-11-2003, 08:33 PM
Hi Andy,

Its been a long time... i keep on studying

I really dont see what you explain about hot gas defrost CO2, is it possible, you attach a scheme or a drawing,

where are the heat exchangers?

About PHE (and sorry for the advertaising), have you heard about AlfaNova (Brazed plate heat exchager 100% SS), What do you think?

Bye

Friobernal
28-11-2003, 08:58 PM
I am attaching a cycle for drawing on it, if you want, or anybody else

Hasta la vista amigos

Lancer
04-08-2005, 04:47 PM
Hey guy's
We are just piping up a NH3/CO2 cascaded system where I am
currently working. To overcome the defrost problem/critical temperature of the CO2, the CO2 liquid is cooled with an ancillery coil built into the CO2 receiver (little 404a unit no bigger than a fridge compressor runs this) If the ancillery fails the CO2 is vented to atmosphere at a design pressure.

Hope to have every thing going in about 6 weeks, interesting stuff, I think this system will be the first cascaded CO2/NH3 commission in Australia (maybe).

Andy, the major cost difference we found was the CO2/NH3 shell and tube heat exchanger, which was about 4 time the cost of an flooded NH3 system for about 500kW. But because the CO2 pressures are so high, the piping to and from the evaporator are small incomparrison to an NH3 system so this
negates some of this cost.


Lance.

frank
04-08-2005, 07:44 PM
Hey guy's
We are just piping up a NH3/CO2 cascaded system where I am
currently working. To overcome the defrost problem/critical temperature of the CO2, the CO2 liquid is cooled with an ancillery coil built into the CO2 receiver (little 404a unit no bigger than a fridge compressor runs this) If the ancillery fails the CO2 is vented to atmosphere at a design pressure.

Hope to have every thing going in about 6 weeks, interesting stuff, I think this system will be the first cascaded CO2/NH3 commission in Australia (maybe).

Andy, the major cost difference we found was the CO2/NH3 shell and tube heat exchanger, which was about 4 time the cost of an flooded NH3 system for about 500kW. But because the CO2 pressures are so high, the piping to and from the evaporator are small incomparrison to an NH3 system so this
negates some of this cost.


Lance.

Sounds like an interesting install. Any chance of some pictures?

Friobernal
04-08-2005, 08:02 PM
Hi Lance;

Youre talking about a S&t heat exchanger. I know about shell and plate heat exchangers used in cascade systems

http://www.vahterus.com/refrig_case5.htm

Fyi

Regards

Lancer
05-08-2005, 12:30 PM
Frank, I'll take my digital in next week and grab a few snaps, it has been an excellent project and great experience. The system has a HT and LT unit, the HT (-13 degC) is the side load for AHU's , Chillers with the LT (-50 degC) driving the CO2 condenser for a 23 tier Spiral Freezer.

Frioberral, our unit is a little smaller (about 800kW) and the nozzles for the NH3 are top over bottom, thats about the only difference.

I couldn't believe my luck when I stumbled upon this forum, I googled for some info about speed control on screw compressors and up popped this thread. Please forgive my limited grip of the refrigeration realm, electrics are my poison and I have been trying to track down some informed opinion upon screw compressor control and this seems a great place to ask.

I am curious about the consequences of using speed control rather than slide control, or a combination of both on a large screw. I have read that even under no load, a screw will still use 75% of full load duty. The screw in question is a Stal (S57 I think, may need to check this) with a 260 kW motor; 416 amps FLC @ 415V, 2 poles, 2950 RPM.

Previously the unit had been set up for R22 and controlled by an AB SLC 5/03 PLC. When called the PLC toggled the open slide solenoid, 5 sec on, 15sec off, until the demand was meet, or the motor current reached FLC limit, at which the slide was closed in the same manner until it reached a lower limit resetting the sequence. The slide has no linear position feedback just discrete limits for fully open and closed.

In the present situation, the variability of the load may be an issue due to the screws limited turn down ratio. Yes I can hear you say then its to big, well you know its the old story, the equipment was brought at a fire sale for the right price with no thought given to lifecycle cost.

I was thinking of using a Variable Speed Drive to match the compressor speed with the load, obviously for a motor this size the drive would be costly, hence my hesitation, has anyone had similar experiences that they care to relate. Is this a viable option and what limitations should be considered? Will reducing the speed dramatically affect compressor performance or mechanical integrity?

Any comment appreciated

Lance.

US Iceman
05-08-2005, 02:05 PM
Lancer,

Variable speed control for screw compressors is a viable option.
I'll try to address this as a typical situation for a generic application. Without all of the compressor performance data (full load & part load) it is a little difficult to discuss specific numbers.

Part load performance (power/capacity) on twin screws is non-linear. Another item to clearly distinguish between is, slide valve position and part load capacity expressed as percent part load capacity. These are also non-linear. The exact data is dependent on the actual operating conditions for a specific compressor size (rotor diameter, speed, and rotor length).

When a twin-screw is completely unloaded (the slide valve is at 0% slide valve position) most of them will still be pumping about 10-20% of their full capacity CFM. Full capacity equals 100% slide valve position.

Following based on constant speed (are you 50 or 60 Hertz?).
At 0% slide valve position, the compressor would have about 10% of the full-load capacity, but may be using about 40% of the full-load power.

At 25% capacity (not slide valve position), the part-load power would be about 45% of the full-load power.

At 50% capacity the part-load power would be about 60%.

At 75% capacity, the part-load power would be about 80%.

And of course, at 100% capacity, the full load-power would be 100%.

Using a variable frequency drive (VFD), the ratio between percent capacity and percent power starts to become linear, if the slide valve is at 100% (fully loaded).

Using the suction pressure controller to modulate the speed with the slide valve fully closed you get a roughly linear performance down to about 50% speed. Strange things can begin to happen below this speed (the slide valve is still at 100%).

Below 50% speed, the slide valve position can be modulated but the performance ratio (power/capacity) begins to fall off.

Speed control for a motor this size may be expensive, but it should have a decent return on investment if the compressor would be operated at reduced loads for long periods of time.

From a mechanical integrity viewpoint, the life of the compressor should be increased. Lower speed somewhat equates to longer life.

Another item to watch out for is the oil pump. Is the oil pump driven from the rotors, or by a separate oil pump with it's own motor? If the oil pump is driven off of the rotors, you may loose oil pressure for injection and lubrication at reduced speeds.

If the oil pump is for pre-lube only, and the main oil pressure is supplied by differential pressure (discharge pressure minus suciton pressure), this may not be a factor.

In either case, you need to check with the manufacturer to make sure they find the application acceptable. Someone may find themselves in the unfortunate position of trying to explain why the compressor failed!!

One other thing to consider: Can the discharge pressure be reduced at different times of the year? Reducing the discharge pressure will provide a significant reduction in power input. A lot of this depends on how the system was designed.

This discussion can take on a life of it's own. This is a complex subject that should not be taken as a license to apply VFD's.

The use of VFD's for screw compressors is starting to be done here in the US, but I would recommend that someone check with the compressor manufacturer. This way you should be able to get specific answers to your questions.

Hope this helps.

Best Regards,
US Iceman

Lancer
07-08-2005, 01:47 PM
US Iceman,

Hi and thanks for your valued advice,


Part load performance ...................................
.....................................................
...................... the slide valve position can be modulated
but the performance ratio (power/capacity) begins to fall off.


I have put VSD's on large centrifugal fans to take advantage of power saving relating to "affinity fan law" but did not think the same benefits applied to twin-screw compressors. I am encouraged to see from your comments that by varying the speed I will have a far greater range of control over the power consumed as opposed to just using the slide alone.


Another item to watch out for is the oil pump. ..............................................................
...........................................
.......in the unfortunate position of trying to explain why the compressor failed!!


Yes, the oil pump is a sperate pump with its own motor; the oil return from the discharge receiver is delivered through a pressure regulator to an distributor block which feeds the screw oil journals. I dont believe Stal still operate within Australia, but we have just had the screw end reconditioned by a reputable firm who should know the do's and don'ts with this unit, so I will run it past them.


One other thing to consider: Can the discharge pressure be reduced at different times of the year? Reducing the discharge pressure will provide a significant reduction in power input. A lot of this depends on how the system was designed.


I am sorry, you have lost me here (dumb electrician), all I know about the discharge is that it is piped through a superheater to a water cooled Grasso plate heat exchanger (NH3 condenser) as to how to vary the discharge pressure I am at a loss.

Thanks a lot for your help,

Lance

US Iceman
07-08-2005, 06:39 PM
Dear Lance,

I hope the information is useful.

Positive displacement machines (pumps or compressors) do not follow the affinity laws as centrifugal pumps or fans do. The power savings are based on the capability of the compressor, based on tip speed of the rotors and how the slide valve responds to changing the effective length of the rotors.

Think of unloading a screw compressor as changing the length of the stroke of a reciprocating compressor. The shorter stroke would decrease the dispacement. When the slide valve unloads the rotors, the effective length of the rotor used for gas compression is shortened.

When all of this is taken into consideration with variable speed operation, the part load performance starts to become linear. At least down to about 50% speed with the slide valve fully loaded.

To get the exact data, you would need the manufacturers performance program. The various data points need to be ran for the suction and discharge pressure. Then vary the speed. Once the data is plotted as a percentage of full load capability, the curve starts to make sense.

The oil pressure is a major issue. If you have a full-time oil pump driven externally by a separate motor this becomes less of an issue.

It sounds like you are using some heat recovery devices off of the compressor discharge. Depending on the application, hot water generation will be reduced during part-load operation of the screw. Your operators may not want to decrease the discharge pressure if they think it affects the water heating.

On the other side of the discussion though, reducing the discharge pressure will reduce the motor amp draw, which also saves energy. You, or they may have to find a good balance between operation and heat recovery methods.

If your system uses water-cooled condensers, the water supply will determine how low the discharge pressure could potentially be reduced. If you have evaporative condensers, any lower wet bulb temperature will allow the discharge pressure to reduce. Assuming all fans and pumps are operating at full speed.

If you have VFD's on the condenser fans, it may be better to run the fans at full speed and reduce the compressor power input. The best course of action is whatever uses the least amount of energy.

If I can be of help, let me know.

Best of luck down under,
US Iceman

murduc74
27-08-2006, 12:54 PM
hi
i need help finding co2 refrigerant properties (mollier charts or p-h diagrams).
pls help!!

Andy P
27-08-2006, 10:33 PM
hi
i need help finding co2 refrigerant properties (mollier charts or p-h diagrams).
pls help!!

You will find them in the ASHRAE handbook (along with loads of others - or if you prefer an electronic version check out "CoolPack" from the Technical University of Denmark. Google should take you straight to it

Cheers
Andy P

guapo
28-08-2006, 12:37 PM
Hi every body,

Is it Possible to compressor to Install a VFD and fixed the slide valve to full load? The loading of the compressor is just base on the RPM.

frank
28-08-2006, 03:10 PM
You will find them in the ASHRAE handbook (along with loads of others - or if you prefer an electronic version check out "CoolPack" from the Technical University of Denmark. Google should take you straight to it

Cheers
Andy P
There is also a direct download from the RE Database on the top of each page

US Iceman
28-08-2006, 03:23 PM
Is it Possible to compressor to Install a VFD and fixed the slide valve to full load? The loading of the compressor is just base on the RPM.


That is the preferred method. When the load is reduced to about one-half (half speed capacity), the compressor performance begins to reduce very quickly.

Josip
11-09-2006, 08:12 PM
Hi, Guapo :)


Hi every body,

Is it Possible to compressor to Install a VFD and fixed the slide valve to full load? The loading of the compressor is just base on the RPM.

Please visit this page:
http://www.sabroe.com/fileadmin/filer/pdf/Rotatune_variable-speed_screw_compressors_06.03.pdf

Best regards, Josip :)

bruceboldy
11-09-2006, 11:54 PM
I know this thread's been hanging round for a while, but Andy, how did you overcome the defrost problem (high CO2 pressures)?

I am intersted and have a few potential projects in low temp cascade co2
I am also very interested in what has proven best practice in defrost of the low temp co2 coil..

bruceboldy

Andy
14-09-2006, 10:52 PM
I am intersted and have a few potential projects in low temp cascade co2
I am also very interested in what has proven best practice in defrost of the low temp co2 coil..

bruceboldy


Hi Bruce:)

AndyP's company use a hot gas generator. Liquid is taken off the R744 condenser, fed to a pump which raises it's pressure to about 10 deg c saturation. The liquid is then boiled oil using waste compressor heat and the subsequent hot gas is used for defrosting the evaporators.

Hope this helps. Kind Regards Andy:)

Samarjit Sen
19-09-2006, 06:23 PM
Dear Andy,

I was browsing through the forums web, when I came across this thread. I am not much aquainted with CO2/NH3 refrigeration and am keen to know more about it.

In one of your posts you had referred the schematic drawing of the system. Unfortunately it appears that site has been removed. Will it be possible to to give some link where I can get the schematic drawing of the system.

Thank you and with best wishes,

TXiceman
20-09-2006, 03:02 AM
It is simply a cascade system with ammonia on the high temp system and CO2 in the low temp system. The ammonia evaporator acts as the CO2 condenser for the low temp system.

Ken

Samarjit Sen
20-09-2006, 06:09 AM
What is the lowest temperature one can achieve with CO2. Are their any literatures on these systems. What I understand that onle CO2 can be used as a refrigerant for a single stage compressor. Could you please provide me with some information on this.

US Iceman
20-09-2006, 10:07 PM
CO2 for phase change is limited to about -67F (-55C) if I remembered the triple point correctly.

Josip
21-09-2006, 09:13 PM
Hi, Samarjit Sen :)


What is the lowest temperature one can achieve with CO2. Are their any literatures on these systems. What I understand that onle CO2 can be used as a refrigerant for a single stage compressor. Could you please provide me with some information on this.

Can you explain this, please?




The Sabroe CO2/Ammonia Freeze Package (CAFP) concept combines the advantages of CO2 on the low-temperature side and ammonia on the high-temperature side.

A CO2 compressor has a capacity 812 times greater than a similar ammonia unit, making the low-temperature compressor much smaller, and the whole unit significantly more compact.

CO2/Ammonia Freeze Package (CAFP) equipment is available with capacities of 80400 kW at -50C or 140650 kW at -40C.
Please follow this link:

http://www.sabroe.com/fileadmin/filer/pdf/CO2_Ammonia_Freeze_Package_CAFP_06.03.pdf
http://docnav.grasso-global.com/DocNav_Eng/Sources_e/DBo_e/ca0536_Bro_Cascade__gbr_10-04.pdf

Best regards, Josip :)

Samarjit Sen
22-09-2006, 06:18 PM
Thank you Josip,

You see I have worked on ***** and R 404A refrigerant till now. With ammonia we have installed units for Potato Cold Storages. Now with alternative refrigerants coming in and the latest being CO2, I would like to know more about it. As far as I was made to understand that CO2 are used only for single stage compressors, but now I understand that with NH3 it could used for two stage so as to lower the temperature further. You have clarified lot of things and I have learnt a lot from you all.

With best wishes,

Josip
22-09-2006, 08:59 PM
Hi,


As far as I was made to understand that CO2 are used only for single stage compressors, but now I understand that with NH3 it could used for two stage so as to lower the temperature further.


It is still a single stage compressor (for each system NH3 and for CO2) but it is two stage plant. With CO2 is not possible to use, for example: one single compressor having two stages as we can use for *****s or for ammonia.

We can obtain those temperatures also with ammonia but it is not economical at all. I have here in my country one system with 3 stage ammonia sistem (built before 20+ years) -60/-35/-10/+35 but they stop to use -60 compressors. You spend so much energy for very small work.

Best regards, Josip:)

Andy P
22-09-2006, 10:47 PM
With CO2 is not possible to use, for example: one single compressor having two stages as we can use for *****s or for ammonia.
Hi Josip,

Why not - it's just a compressor? The CO2 compressors developed by J&E Hall in the 1880s which dominated the marine market for about 30 years were two stage. "The first CO2 machine made by J&E Hall was a two-stage compressor in which the first stage of compression was effected in the orthodox way by the action of a piston in a horizontal cylinder, and the second stage completed in a vertical cylinder containing a column of glycerine....A machine of this type was installed on 16 August 1889 in a frozen meat store in Smithfield and set to work. At 2am the pipe conveying the gas from the first to the second stage compressor burst because of a mechanical fault. 'The pipe was literally blown to ribbons' said Everard Hesketh [company chairman and designer of the compressor] 'and had it not been for the sides of the water tank surrounding the compressor...my head which was only a yard away would have been the target for some of the pieces.'"

Fortunately compressors have improved since then!!

Cheers
Andy P

PS Quotation is from "Halls of Dartford 1785-1985" by Harry Miller

Andy
22-09-2006, 11:47 PM
Hi Josip,

Why not - it's just a compressor? The CO2 compressors developed by J&E Hall in the 1880s which dominated the marine market for about 30 years were two stage. "The first CO2 machine made by J&E Hall was a two-stage compressor in which the first stage of compression was effected in the orthodox way by the action of a piston in a horizontal cylinder, and the second stage completed in a vertical cylinder containing a column of glycerine....A machine of this type was installed on 16 August 1889 in a frozen meat store in Smithfield and set to work. At 2am the pipe conveying the gas from the first to the second stage compressor burst because of a mechanical fault. 'The pipe was literally blown to ribbons' said Everard Hesketh [company chairman and designer of the compressor] 'and had it not been for the sides of the water tank surrounding the compressor...my head which was only a yard away would have been the target for some of the pieces.'"

Fortunately compressors have improved since then!!

Cheers
Andy P

PS Quotation is from "Halls of Dartford 1785-1985" by Harry Miller

Hi AndyP:)

Have you tried, or to that matter has anyone built a compressor with an expander on it for transcritical operation ??

Kind Regards Andy:)

Andy P
24-09-2006, 01:23 PM
Have you tried, or to that matter has anyone built a compressor with an expander on it for transcritical operation ??

The expander developed at Dresden University compresses at one end by expanding the gascooler outlet at the other. This device would sit "on top of" a lower stage compressor driven by a motor because the power recovered from full expansion is only enough to drive a portion of the compression path, due to losses in the expander and the second stage compressor. Its a neat device, and can give useful heat recovery too.

I've never tried it - they are a bit small for our stuff:D

cheers
Andy P

Andy
24-09-2006, 03:37 PM
The expander developed at Dresden University compresses at one end by expanding the gascooler outlet at the other. This device would sit "on top of" a lower stage compressor driven by a motor because the power recovered from full expansion is only enough to drive a portion of the compression path, due to losses in the expander and the second stage compressor. Its a neat device, and can give useful heat recovery too.

I've never tried it - they are a bit small for our stuff:D

cheers
Andy P

Neat principle:) uses waste energy to improve system effeciency.

Heat recovery with a transcritical system would be the way to go, kind of like CHP, but instead combined refrieration and heating. Most applicable to supermarkets:)

Kind Regards Andy:)

Samarjit Sen
01-10-2006, 12:40 PM
I was trying to locate some literatures and informations on NH3/CO2 cascading, when I cam accross an article the link to which I am providing.

http://www.hvacindia.com/journals/2002oct/article02.html

I am sure that you will find it useful.

With best wishes,

US Iceman
01-10-2006, 06:31 PM
Please only post the information in one thread.

Thank you.

Samarjit Sen
02-10-2006, 03:57 AM
Dear US Iceman,

I was not aware of this. I thought that others may read it also. Anyway I am sorry for my mistake.

With best wishes,

US Iceman
02-10-2006, 03:18 PM
We try to maintain an unwritten rule for single posts only to prevent accumulation of multiple posts in different areas.

I do thank you for posting the link to the article, it was useful and I think worthwhile for others to review.

Best Regards,
US Iceman

nh3wizard
02-10-2006, 09:09 PM
I have some basic flow charts for CO2/Nh3 applications, but due to them being larger than this site will accept I can not post them, if you are interested let me know and Ill email them to you.:D

Samarjit Sen
03-10-2006, 11:11 AM
Dear nh3wizard,

Could you please mail the flow charts for CO2/NH3 applications to me at samarjitsen@rediffmail.com .

Thank you,

Josip
03-10-2006, 08:18 PM
Hi, Andy P :)


Hi Josip,

Why not - it's just a compressor? The CO2 compressors developed by J&E Hall in the 1880s which dominated the marine market for about 30 years were two stage. "The first CO2 machine made by J&E Hall was a two-stage compressor in which the first stage of compression was effected in the orthodox way by the action of a piston in a horizontal cylinder, and the second stage completed in a vertical cylinder containing a column of glycerine....A machine of this type was installed on 16 August 1889 in a frozen meat store in Smithfield and set to work. At 2am the pipe conveying the gas from the first to the second stage compressor burst because of a mechanical fault. 'The pipe was literally blown to ribbons' said Everard Hesketh [company chairman and designer of the compressor] 'and had it not been for the sides of the water tank surrounding the compressor...my head which was only a yard away would have been the target for some of the pieces.'"

Fortunately compressors have improved since then!!

Cheers
Andy P

PS Quotation is from "Halls of Dartford 1785-1985" by Harry Miller

I think answer to your question is in your quotation. It is not impossible but then you are coming into high pressure area - what is dangerous, then big power consumption and so on...but as Andy said, why not to try;)


Best regards, Josip :)

Josip
03-10-2006, 09:46 PM
Hi, all :)


I was trying to locate some literatures and informations on NH3/CO2 cascading, when I cam accross an article the link to which I am providing.

http://www.hvacindia.com/journals/2002oct/article02.html

I am sure that you will find it useful.

With best wishes,

Reading this journal and some other I came to one question: Why a lot of (but not all) smart people writing similar journals about CO2/NH3 cascade systems presume to have NH3 condensing temp at +40C, why not at +35C

Is there maybe some explanation for that which I do not know or maybe.........

Best regards, Josip :)

US Iceman
03-10-2006, 11:14 PM
Hi Josip,

A good question you ask.

My guess is these people have done a lot of air conditioning work with water-cooled condensers. 40C (105F) is the normal design temperature for condensing with water-cooled condensers.

I have also seen something similar to this. Designing systems that use evaporative condensers based on 48.8C (120F) condensing, or higher.:D

Samarjit Sen
05-10-2006, 05:55 PM
Since I am not much aware of the CO2/NH3 system and I am yet to come accross one which has been and in operation in our country, I would like to ask a (maybe a stupid) question. But as I have said earlier, that I have no experience in these systems as I have been handling mostly halocarbons.

My question is that could the CO2 in the lower stage be used as a DX system with suitable TEV and Air Cooling Unit for maintaining the desired temperature in the rooms or we have to chill the brine solution and circulate the same through Coils?

From the Forum it appears that a lot of work in this field are being done in Europe and USA.

With best wishes.

US Iceman
06-10-2006, 01:13 AM
My question is that could the CO2 in the lower stage be used as a DX system with suitable TEV and Air Cooling Unit for maintaining the desired temperature in the rooms or we have to chill the brine solution and circulate the same through Coils?


Hi, you need to be careful with the application of CO2 due to it's inherently higher pressures. I can't think of reason why you could not use CO2 for DX, flooded, or liquid overfeed. It's just another refrigerant.

However, like any other refrigerant you can only apply it within the guidelines of safety and equipment limitations.

If you tried to use CO2 at normal refrigeration or AC conditions of say, -30C to +4.4C you would expect to see very high pressures. These higher pressures have to be contained by the components and piping.

On the other hand, if you were to use CO2 as we normally use common refrigerants you would find very low temperatures until you get to the triple point of CO2, which is about -67F (-55C).

Using air or liquid depends on the cooling process. In either case, air or liquid/brine are secondary refrigerants. The primary refrigerant would be CO2.

Samarjit Sen
06-10-2006, 03:03 AM
Thank you US Iceman. We propose to use CO2 in the lower stage and NH3 in the higher stage. The CO2 temperatures required are to be -45 Deg. C Te and -5 Deg. C Tc. There shall be three rooms. One to be maintained at - 40 Deg. C, and the other two at - 30 Deg. C. I would prefer to use a DX system as I am more aquainted with this . If you advice flooded we can also go for it.

Further you and Andy has been repeatedly emphasising on the maintaing the safety norms and controlling the pressure and temperatures. Could you please elaborate on this point, and as to how does one control the temperature of CO2 at the initial stage of commissioning and also at the idle stage.

With best wishes and thanks a lot for the guidance.

US Iceman
06-10-2006, 02:37 PM
as to how does one control the temperature of CO2 at the initial stage of commissioning and also at the idle stage


When the CO2 system is shut down (but still containing CO2) you have two options that I know of.

1) You can use a smaller, separate refrigeration to coil the main CO2 vessel. This is verysimilar to the CO2 storage tanks commonly found. A small heat exchanger is installed in the CO2 tank. As this little refrigeration system operates it keeps the CO2 pressure down by condensing the CO2 vapor in this vessel.

2) You can use what we call fade-out vessels (sometimes called an expansion tank). In this example you have to provide sufficient additional volume in the CO2 system. When the system is idle, the liquid CO2 will evaporate. This causes th epressure to increase. By adding sufficient volume to the CO2 system you can limit the pressure rise so that it stays within acceptable limits (of the pressure vessels and safety relief valves).

For start up or initial commisioning you have to have the high stage system in operation first. This is the same on a two-stage compression system. You have to pull the temperature down before starting the low stage.

Samarjit Sen
06-10-2006, 05:22 PM
Dear US Iceman,

Thank you for advice. What now I understand that as in a R 404A/R 23 cascade system we provide an expansion tank the same process has to be adopted.

I have been enquiring in our country, and it appears that there are no CO2/NH3 Cascade plants installed as yet. Now what I would like to know that cost wise if you compare with a two stage reciprocating compressor using R 404A, what would be the position. The running cost will be lower but one must have an expert technician who has handled such plant available, which unfortunately there are none. It is the capital cost that matters. Will it be worth while to install CO2/NH3 cascade system of 130 Kw capacity in our country considering the points that I have stated above.

With best wishes,

Josip
06-10-2006, 11:10 PM
Hi, Samarjit Sen :)


Dear US Iceman,

Thank you for advice. What now I understand that as in a R 404A/R 23 cascade system we provide an expansion tank the same process has to be adopted.

I have been enquiring in our country, and it appears that there are no CO2/NH3 Cascade plants installed as yet. Now what I would like to know that cost wise if you compare with a two stage reciprocating compressor using R 404A, what would be the position. The running cost will be lower but one must have an expert technician who has handled such plant available, which unfortunately there are none. It is the capital cost that matters. Will it be worth while to install CO2/NH3 cascade system of 130 Kw capacity in our country considering the points that I have stated above.

With best wishes,

In your case I will go to your proposal (R404a) or to use 2 stage ammonia.

Down to -40C ammonia is the best one for sure even as 2 stage system, for capacity less then 750 kW!


Why CO2?
Advantages:

1. CO2 is a natural gas. Compared to the other new refrigerants it has a friendly global environmental character. The ozone deletion potential (ODP) is zero and the global warming potential (GWP) is one.
2. CO2 is a class 1 refrigerant (non toxic, non flammable)
3. CO2 has a very large volumetric refrigeration capacity (it means small compressors, small pipe dimensions)
4. CO2 has very good heat transfer characteristics.
5. It is not foreseen that law in the future will limit CO2.
Disadvantages:

1. Large operation pressures inside the evaporator and the condenser, for defrosting a pressure of 40 bar is required (condensing temperature of CO2 +5 C at this pressure)
2. Pressure limitation is required when the plant stops.
3. Reaction of CO2 and NH3 generates solid particles.
4. CO2 could be a local danger due to its absence of smell and higher density than air.
5. Limitation of evaporation temperature of 54 C caused by the triple point at 56,6 C.

CO2 has been investigated as a refrigerant in non-critical refrigeration processes for a long time especially for mobile car air conditioning plants.
Due to the thermodynamic characteristic and huge volumetric refrigeration capacity of CO2 a cascade plant has small compressor and small pipe diameters at the low temperature side. One has to accept that the use of CO2 with evaporation temperatures below the triple point is not yet possible. Therefore the application field of a CO2-cascade refrigeration plant is limited within an evaporation temperature range of 40 C and 54 C.
Above 40 C evaporation temperature the use of CO2 is not so interesting since efficiency becomes less when compared to a two-stage ammonia plant.


The CO2/NH3-cascade refrigeration plant offers reduced refrigerant charges, higher efficiency and a contribution for environment protection by the use of natural substances without ozone depletion potential and possibly without direct greenhouse potential. The ammonia charge being reduced to a minimum is located only in the machine room.
Based on our own investigations with two different refrigeration systems with refrigeration capacities of 750 kW and 1500 kW and an evaporation temperature range of between 40C and 54C, it is clear that the cascade refrigeration plant is more efficient than a two stage refrigeration plant with ammonia in this evaporation temperature range. Therefore the application focuses on freeze drying of coffee, freezing of fish and meat, low temperature storage and quick-freezing processes.

You mentioned 3 rooms (one at -40C, and 2 at -30C) and all is 130kW.


Best regards, Josip :)

US Iceman
07-10-2006, 01:16 AM
I'm going to agree with Josip and suggest the R-404a or two-stage ammonia system. Yes, there are some trade-offs between efficiencies and installed costs.

However, if the system is more complicated than the service people have experience with an efficienct cascade system does the owner no good. It's also probably much safer to provide a system close the experience level of the service technicians.

Josip, where did you find that web page?

Thanks my friend.

Samarjit Sen
07-10-2006, 02:44 AM
Dear Josip,

Thank you for the clear picture put up by you . The total refrigeration load of the system for all the three rooms is 130 kw.

Regarding the comparison of cost of the two system, it is still not clear. Could you please let me know as to the cost of whish system would be cheaper.

With best wishes,

Josip
08-10-2006, 10:04 AM
Hi, US Iceman :)


Hi Josip,

A good question you ask.

My guess is these people have done a lot of air conditioning work with water-cooled condensers. 40C (105F) is the normal design temperature for condensing with water-cooled condensers.

I have also seen something similar to this. Designing systems that use evaporative condensers based on 48.8C (120F) condensing, or higher.:D

I can agree for ***** plants, but for ammonia!?

Check this standard:

http://www.ari.org/NR/rdonlyres/193A407C-10E0-4D6F-8E5F-40EA39C6C718/0/51093.pdf

maybe is too old, or...

Best regards, Josip :)

Josip
08-10-2006, 10:35 AM
Hi, Samarjit Sen :)


Dear Josip,

Thank you for the clear picture put up by you . The total refrigeration load of the system for all the three rooms is 130 kw.

Regarding the comparison of cost of the two system, it is still not clear. Could you please let me know as to the cost of whish system would be cheaper.

With best wishes,

It is not clear for me either, but coming into new field with so many safety units, electronic devices, and so on; for me is clear: CO2/NH3 must be more expensive then the good old way: double stage R404a or ammonia.

From my previous post you can see they made comparison with two plants 750kW and 1500kW, what is about 6 to 12 times bigger then your plant i.e. under 750kW it is maybe too expensive, even to start to think about;) .

You can ask for an budget offer from Sabroe (http://www.sabroe.com/Information/CO2/index.html), or Gea-Grasso (http://www.grasso-global.com/Applications.14.0.html) or ask Andy for some help.

Maybe I am not right;) , but other guys will come with some better info...

Best regards, Josip :)

US Iceman
08-10-2006, 06:26 PM
Hi, US Iceman :)



I can agree for ***** plants, but for ammonia!?

Check this standard:

http://www.ari.org/NR/rdonlyres/193A407C-10E0-4D6F-8E5F-40EA39C6C718/0/51093.pdf

maybe is too old, or...

Best regards, Josip :)


The evaporative condenser project I saw was used on ***** systems for condensing temperatures about 48.8C (120F). From what I was able to learn Carrier tried this back in the 1950's & 60's. Unfortunately the condensers were never maintained and in a short time the condenser was converted into a solid block of concrete.:D Needless to say the condensers did not work well when that happened.

The 40C condensing for the NH3/CO2 system may have been due to higher supply water temperatures for some reason.

Or then again, someone may have tried to save money on the water cooling system with regard to the impact to the refrigeration system power use.

US Iceman
08-10-2006, 06:32 PM
Hi Josip,

I just looked at the ARI standard you posted. This standard applies to the actual process used for rating the compressor performance and the tolerance for capacity & power deviation from published to test data.

It is not an actual design document for ammonia refrigeration systems.

You might see some ammonia systems using air-cooled condensers on some facilities such as atmospheric ammonia storage. In those examples, the condensing temperature are quite higher than 35C.

Josip
08-10-2006, 08:56 PM
Hi, US Iceman :)


Hi Josip,

I just looked at the ARI standard you posted. This standard applies to the actual process used for rating the compressor performance and the tolerance for capacity & power deviation from published to test data.

It is not an actual design document for ammonia refrigeration systems.

You might see some ammonia systems using air-cooled condensers on some facilities such as atmospheric ammonia storage. In those examples, the condensing temperature are quite higher than 35C.

Agree 100%, it is not actual design document, what I was trying to said, it is possible to start design with CT at 35C, 13.5Bar i.e. lower energy consumption. If we have too hot water or too high temp with high humidty (some part of the year, in some part of the world) we will have, for short time higher CT.

With design of EC to work with CT at 35C, there should be more capacity in hard weather condition, then if design is for CT at 40C.

In another hand I was working with ammonia air condensers (CT=50C, 20Bar) in Saudi Arabia (still in use because there is not water available) but it is very hard for compressors and you need a lot of money for el.power ;).

To design a low energy consumption plant for sure is not to start with high condensing temp/press.

Of course there were and there are some facilities with condensing temp higher of 35C, due to process request but that is another story.

Best regards, Josip :)

US Iceman
08-10-2006, 09:12 PM
Hi Josip,

I agree 100% with what you mentioned.

I would like to know the reasoning behind th euse of 40C CT on ammonia for the NH3/CO2 system you posted earlier.

I normally use 35C CT as the starting point in the design, but also include greater allowances for higher entering wet bulb temperatures.

Most of the weather data I've seen for the US is of course based on the ASHRAE data. Then we have to select the percentage factors for the actual design conditions.

I prefer to use the accumulated weather data that shows the actual values. As you know, the weather is always hotter or more humid for some period of the year than what the weather data suggests.

For HVAC purposes this data is probably OK. However, for process requirements I would rather have the equipment sized to run in the extreme cases.

If we save money on the installation and equipment costs, this is a small portion of what the "real costs" are for production cooling.

The way I look at this is... It might be cheaper to use the "design conditions", but if the refrigeration system has to run at partial capacity due to high discharge pressures, who looses?

I can certainly understand the logic in using AC condensers in Saudia Arabia at first glance. But, is the quantity of water that might be needed for the evaporative condensers really that limited?

What do they do for all of those large HVAC chillers? Are they AC also?

Josip
08-10-2006, 10:02 PM
Hi, US Iceman :)


Hi Josip,

I agree 100% with what you mentioned.

I would like to know the reasoning behind th euse of 40C CT on ammonia for the NH3/CO2 system you posted earlier.

I normally use 35C CT as the starting point in the design, but also include greater allowances for higher entering wet bulb temperatures.

Most of the weather data I've seen for the US is of course based on the ASHRAE data. Then we have to select the percentage factors for the actual design conditions.

I prefer to use the accumulated weather data that shows the actual values. As you know, the weather is always hotter or more humid for some period of the year than what the weather data suggests.

For HVAC purposes this data is probably OK. However, for process requirements I would rather have the equipment sized to run in the extreme cases.

If we save money on the installation and equipment costs, this is a small portion of what the "real costs" are for production cooling.

The way I look at this is... It might be cheaper to use the "design conditions", but if the refrigeration system has to run at partial capacity due to high discharge pressures, who looses?

I can certainly understand the logic in using AC condensers in Saudia Arabia at first glance. But, is the quantity of water that might be needed for the evaporative condensers really that limited?

What do they do for all of those large HVAC chillers? Are they AC also?

It seems we are coming back to another question again:
-first cost or running cost;)

Agree with you to use design conditions for HVAC units but for refrigeration we have to use extreme conditions and try to design refrigeration plant to work with max COP even with partial load in extreme conditions.

All AC in SA are quite old and nowdays they start to change them with EC for ammonia plants.

HVAC chillers still today are with AC, because EC is more expensive. ***** is another story because we cannot beat them with the prices but you know that very well.

They approach with; we have green *****, not harmful, extra effective:eek: :mad: almost good as clear air you need for breathing and all that story to make a profit (and they are good in that). Another problem is a lack of knowledge about ammonia

Best regards, Josip :)

US Iceman
08-10-2006, 11:47 PM
Hi Josip,

Here is some information you can use with your next discussion of R-22 with the HVAC people.

This information comes from the Material Safety Data Sheets (MSDS) for R-22. I found this for another discussion taking place with some other gentlemen.

Flash Point: Will not burn
Auto-decomposition: 632 C (1170 F)

Other burning materials may cause "*****" 22 to burn weakly. Chlorodifluoromethane is not flammable at ambient temperatures and atmospheric pressure. However, chlorodifluoromethane has been shown in tests to be combustible at pressures as low as 60 psig at ambient temperature when mixed with air at concentrations of 65 volume % air. Experimental data have also been reported which indicate combustibility of "*****" 22 in the presence of certain concentrations of chlorine.

This does not even include the comments about disrupting the heart rate, potenital oxygen deprivation, or other fun things that can happen.

Samarjit Sen
09-10-2006, 06:44 AM
Dear Freinds,

Although I have hardly done any projects with NH3 and none involving CO2, but after seeing the datas that you all have provided and the details taught to me, I am really facinated with this refrigerant. You people have been a tremendous help to me and I wish some of my coleagues in our country could take advantage and learn a lot of things from this thread. I am now very keen to execute some contracts in CO2/NH3, and would request you all to please provide me some more technical details on the same.

Regarding the Condensing temperature of 40 Deg. C, we use it at places where the ambient are very high which are generally in the part of Northern side of our country. There are a number of projects where Condensing is taken as 35 deg. C. The ambient conditions in our country vary very much.

With all the best,

Samarjit

US Iceman
09-10-2006, 04:38 PM
One of the items I tend to use for designing systems is an upper limit for condensing temperature on ammonia systems of 33.8C (93F).

35C (95F) is the normal "design" temperature commonly used, but I seem to remember some factors that can be minimized by a slightly lower condensing temperature when evaporative condenser are used.

It has to do with water quality and the chemical treatment of the recirculated water. It has nothing to do with Legionella bacteria, only scale formation.

I'll have to do a little research to refresh my memory. I will add these comments later.

Josip
09-10-2006, 09:48 PM
Hi, US Iceman :)


One of the items I tend to use for designing systems is an upper limit for condensing temperature on ammonia systems of 33.8C (93F).

35C (95F) is the normal "design" temperature commonly used, but I seem to remember some factors that can be minimized by a slightly lower condensing temperature when evaporative condenser are used.

It has to do with water quality and the chemical treatment of the recirculated water. It has nothing to do with Legionella bacteria, only scale formation.

I'll have to do a little research to refresh my memory. I will add these comments later.

You are right, I remember the past time when we design EC with desuperheater section (above water eliminator) where the inlet gas temperature were reduced to prevent extraction of calcium carbonate from cooling water. In that time water was treated only with NaCl to be soft, no other chemicals were added.

Best regards, Josip :)

US Iceman
09-10-2006, 11:18 PM
You are right, I remember the past time when we design EC with desuperheater section (above water eliminator) where the inlet gas temperature were reduced to prevent extraction of calcium carbonate from cooling water. In that time water was treated only with NaCl to be soft, no other chemicals were added.


This is the same thing. Desuperheaters are very seldom used anymore on recip. plants, but they should be. They do make a difference on scale formation on the top row of tubes.

The desuperheaters do accumulate some very small amounts of scale. But since they are in a humid air, rather than complete liquid water this makes a big difference.

I think it is a combination of discharge temperature in the tubes and the actual water temperature. Where both are high, the scale formation is much worse.

This makes another good example of why we should keep condensing temperatures/discharge pressures lower.:D

cygbob
19-10-2006, 06:16 AM
hi,everyone
i am a new engineer, and now working on designing co2 liquifier, could someone help me especially on calculating the co2 condensation heat transfer coefficients in-tube? and more information on the shell and tube exchanger design? thanks a lot!
best regards

mickandlee
19-10-2006, 09:02 PM
Another plus for desuperheaters is that in winter the airflow leaving the condenser is slightly heated away from the saturation curve so that when mixed with the lower temperature ambient air it is kept clear of fogging conditions. Hence reducing the annoying (to some) plume of steam.

mick

ART KUHN
12-11-2006, 09:39 PM
hi i'm new at this forum but i was sent to a co2/r410a system becase of high pressure alarm in the r410a system.After 3,5 hours of checking i got a bit frustated and opened a liquid service valve for 2 seconds and all i saw was snow:mad: .Reason was a leaking heat exchanger(co2 condensor/r410a evaperator).Now when you try to recover 2500 kg r410a when it's mixed with co2 you will find enorm pressure in the tank All in all all the oil changed cleaned the inst. with n2 new ***** and co2(4000kg) and 60 hours later with 3 engineers inst. was up and running.
Just to point out one of the riscs

Andy
12-11-2006, 09:53 PM
hi i'm new at this forum but i was sent to a co2/r410a system becase of high pressure alarm in the r410a system.After 3,5 hours of checking i got a bit frustated and opened a liquid service valve for 2 seconds and all i saw was snow:mad: .Reason was a leaking heat exchanger(co2 condensor/r410a evaperator).Now when you try to recover 2500 kg r410a when it's mixed with co2 you will find enorm pressure in the tank All in all all the oil changed cleaned the inst. with n2 new ***** and co2(4000kg) and 60 hours later with 3 engineers inst. was up and running.
Just to point out one of the riscs

Hi Art:)

good job it was R404a not an ammonia job;) now that would be fun:D

Kind Regards Andy:)

sagittarius
17-11-2006, 04:54 AM
hi,all.
Long long long time no see!
I am missing in the nh3/co2.

sagittarius

sunilkvb2005
22-06-2007, 11:29 AM
HAI, iam refrigeration engineer in uae .please send me a
drawing digrem in co2 and ammonia pumping
"xxxxxxxxxxxxxxx".

Kawaljeet Singh
12-08-2007, 01:24 PM
Hi fellows
I am interested for Co2 / NH4 Cacade Refrigeration cycle. If any body have a case study with system details for any existing refrigeration plant please let me know.

Samarjit Sen
12-08-2007, 06:30 PM
Hi Kawaljeet Singh,

It is very difficult much information on CO2/NH3 at present. However for your information a portal has been opened in Germany very recently. You may visit the same at www.co2refrigeration.com (http://www.co2refrigeration.com) . Further Danfoss and Bock have done and are still working on this application. Just for your information the cascade system is just like anyothe cascade system. Here the NH3 is used in the High Stage and CO2 is used in Low Stage. CO2 has the pressure of building up a very high pressure at a higher temperature and as such to control the pressure is important. If you study this thread from the begining you will get a lot of reply to your questions.

Buckiesr
23-09-2007, 11:04 PM
I would be interested in the drawings for the cascade system. Please send them to me. I do not know how to email you directly. Can you find me?

Buckiesr
23-09-2007, 11:09 PM
Our plant manager is terrified of NH3, he says it all has to go. he wants all co2. I surmise that in the long run, more deaths will be attributed to co2 deaths than ammonia. (due to sensory properties.)
So he asked me, can we put smell in it like they do natural gas? I don't have a clue if it can be or is done or if anyone ever tried. I suggested maybe we should try color, then when you see purple haze you vacate.
WM

US Iceman
23-09-2007, 11:15 PM
Hi Buckiesr,

Welcome to the RE forums.

The manager is using some of the most convoluted logic I have heard yet.:o

Get rid of the smelly refrigerant, spend several million dollars, use a different refrigerant and then make that refrigerant stink???

That has got to be one of the strangest arguments I have ever seen.:D

Buckiesr
23-09-2007, 11:50 PM
Once people get ideas in their head they are closed to reason. I think that co2 will indeed be regulated jsut as much as other refrigerants because the real issue is about money, not so much environment. I usually, "it is because someone's brother-in-law needs a job!" (i.e. it is really about money.)
When

Buckiesr
23-09-2007, 11:56 PM
When the industry lowers the use of the other highly regulated refrigerants, then they will go after the others. co2 is a big issue in emmisions and might be in other industries except for the fact that production of biofuels are producing the greatest ammounts of co2, and they are funded by the biggest money holders who also have the most connected lobiest. Laws will be stimed until the lobiests stand down. Not to soon I suppose that would mean. But before long they will go after co2 also.
WM

Buckiesr
24-09-2007, 12:06 AM
Iceman, you are in the US, the plant manager has discounted my observation that nearly all of the knowledge with co2 has been acquired in Europe. He says we now know this is not true and that there is substantual project development in the US. He says they are building tons of new facilities in the US using only co2 systems. Much safer, much cheaper, much more effecient. I know he is being fed a lot of stuff from a company that wants to contract the new quick freezer facility we would like to add to our existing ammonia refrigerated plant. I can't seem to even get anyone to think about how we could design the new freezer in such a way that it would help the existing system and solve some of the existing complications. When we met on this issue the other day the IRR numbers were mostly in the red. the one option that was not in the red was pretty low. how many total co2 plants do you know of in the US currently? I keep telling him it is to stinkin cold for what we need. I just consult, I am not the decision maker. but I will inherit whatever we install.
WM

BigJon3475
24-09-2007, 12:27 AM
Iceman, you are in the US, the plant manager has discounted my observation that nearly all of the knowledge with co2 has been acquired in Europe. He says we now know this is not true and that there is substantual project development in the US. He says they are building tons of new facilities in the US using only co2 systems. Much safer, much cheaper, much more effecient. I know he is being fed a lot of stuff from a company that wants to contract the new quick freezer facility we would like to add to our existing ammonia refrigerated plant. I can't seem to even get anyone to think about how we could design the new freezer in such a way that it would help the existing system and solve some of the existing complications. When we met on this issue the other day the IRR numbers were mostly in the red. the one option that was not in the red was pretty low. how many total co2 plants do you know of in the US currently? I keep telling him it is to stinkin cold for what we need. I just consult, I am not the decision maker. but I will inherit whatever we install.
WM

Check out this one companies idea on the "future"

http://www.gartner-refrig.com/whatsnew/index.asp

US Iceman
24-09-2007, 01:16 AM
Buckiesr,

All of the reasons you are stating from your manager are the typical marketing BS used by everyone who wants to sell against ammonia.

Refrigeration systems are as safe as they are designed, maintained, and operated. The refrigerant is only a small portion of the selection process.

Efficiency is one of those over-used words that people throw out when they want to get someones attention.

My guess is there is not more than several dozen large CO2 systems installed right now. There are some benefits to using this, but I think the best selling point is the use of CO2 reduces the total ammonia charge.

People tend to think this is a good thing if it allows them to get out of a PSM or RMP program. Those are the same people who would not fix or maintain a refrigeration system until it blew up too.



I can't seem to even get anyone to think about how we could design the new freezer in such a way that it would help the existing system and solve some of the existing complications.


I understand. No one wants to touch the "old" system. They always want to install a new separate system so they do not inherit any of the problems which might creep up with the additional equipment being installed. I think this is just an excuse to not think!

Is IRR who I think it is?:rolleyes:

Buckiesr
24-09-2007, 01:49 AM
IRR = Internal Rate of Return This is one method for calculating the return on an investment. Not the most accurate way in my opinion. It is really easy to make mistakes and arrive at a false return. There can be multiple IRRs for the same input. The ROI (return on investment) is normally used and is how long will it take for the savings on the project to pay for the investment, including taxes, depreciation cost for the firm to borrow the investment money. By comparing what the end result ends up compared to what they are paying their investors, and/ or what they calculate they could make by investing in some other opportunity. (this is called Opportunity Cost). I bet you already knew all of that I wanted to see if I can remember it still.
WM

US Iceman
24-09-2007, 04:52 AM
Sorry, I didn't mean to turn that into a memory test. You did OK though.;)

It would be interesting to see the actual power input differences between the NH3 and CO2 systems. It can't be too much if the economic costs were in the red.

Plank!
24-09-2007, 08:23 PM
good job it was R404a not an ammonia job;) now that would be fun:D

Ah, the delightful Ammonia Carbamate :eek:

Don't we have detectors for that?

Josip
24-09-2007, 11:03 PM
Hi, Buckiesr :)

Welcome to RE


Our plant manager is terrified of NH3, he says it all has to go. he wants all co2. I surmise that in the long run, more deaths will be attributed to co2 deaths than ammonia. (due to sensory properties.)
So he asked me, can we put smell in it like they do natural gas? I don't have a clue if it can be or is done or if anyone ever tried. I suggested maybe we should try color, then when you see purple haze you vacate.
WM

I am so sorry about you having that type of person for manager;), your life must be very complicated... I must ask is he/she younger or older of you?

.....agree with you about accidents with CO2...for me is normal if lot of people use something (electricity, gas, cars...etc) there should be more accidents relating to that -whatever is...

I assume that you have an old ammonia plant with many problems due to bad design, maintenance, installation, etc (maybe I am wrong), but that is not and must not be a reason to not use ammonia especially in industrial area....

Coming back to CO2....


...co2 is a big issue in emmisions and might be in other industries except for the fact that production of biofuels are producing the greatest ammounts of co2, and they are funded by the biggest money holders who also have the most connected lobiest....

I've been told the biggest emission of CO2 is when raise rice...but who have the power to stop production of main food for almost 60%+ of Earth population..


..He says they are building tons of new facilities in the US using only co2 systems. Much safer, much cheaper, much more effecient. I know he is being fed a lot of stuff from a company that wants to contract the new quick freezer facility we would like to add to our existing ammonia refrigerated plant. I can't seem to even get anyone to think about how we could design the new freezer in such a way that it would help the existing system and solve some of the existing complications....

Using only CO2 in primary circuit is possible and then R404 or NH3 in secondary, but to use CO2 only :confused: without cascade I cannot see to much common sense,


All of the reasons you are stating from your manager are the typical marketing BS used by everyone who wants to sell against ammonia.
Refrigeration systems are as safe as they are designed, maintained, and operated. The refrigerant is only a small portion of the selection process.
Efficiency is one of those over-used words that people throw out when they want to get someones attention.
My guess is there is not more than several dozen large CO2 systems installed right now. There are some benefits to using this, but I think the best selling point is the use of CO2 reduces the total ammonia charge.
People tend to think this is a good thing if it allows them to get out of a PSM or RMP program. Those are the same people who would not fix or maintain a refrigeration system until it blew up too.

...US Iceman, sorry, English is not my mother tongue and I found on www. ...marketing BS=marketing bull**** is that right, I believe it is;) from complete sentence and I agree with you...furthermore please can you post some link or send me something about those CO2 plants...thanks.


IRR = Internal Rate of Return This is one method for calculating the return on an investment. Not the most accurate way in my opinion. It is really easy to make mistakes and arrive at a false return. There can be multiple IRRs for the same input. The ROI (return on investment) is normally used and is how long will it take for the savings on the project to pay for the investment, including taxes, depreciation cost for the firm to borrow the investment money. By comparing what the end result ends up compared to what they are paying their investors, and/ or what they calculate they could make by investing in some other opportunity. (this is called Opportunity Cost). I bet you already knew all of that I wanted to see if I can remember it still.
WM

...profit....bigger profit...the biggest profit whatever it cost. No, I am not against to calculate IRR, ROI, etc...to see what we'll get for money we invest...,

but to install one "safe, cheap, efficient" plant using too much energy to run it, we must burn more fossil fuel and produce much more CO2 and release it in atmosphere, is that logical:confused: - safe, cheap or efficient???

Best regards, Josip :)

US Iceman
25-09-2007, 12:02 AM
...marketing BS=marketing bull**** is that right...


Yes sir you are correct.:D

The few adverts I have seen for CO2 systems have not provided very much raw data. I'm sure you realize any numbers provided may be suspect, because someone is trying to sell something.;)

Buckiesr
25-09-2007, 12:44 PM
I am so sorry about you having that type of person for manager;), your life must be very complicated... I must ask is he/she younger or older of you?

.....agree with you about accidents with CO2...for me is normal if lot of people use something (electricity, gas, cars...etc) there should be more accidents relating to that -whatever is...

RE: Josip. I assume that you have an old ammonia plant with many problems due to bad design, maintenance, installation, etc (maybe I am wrong), but that is not and must not be a reason to not use ammonia especially in industrial area....

My system is nearing 50 years old. But We have retrofitted many things to keep it up. I keep fining ways to gain effeciencies. To answer your question. The manager is near my age. I think older but not positive. He has read about bad things with ammonia. He is inherently fearful of it that is all. Ignorance can cause great anxiety in people of great responsability. We have had several deaths in the industry in the US this past several years. His fears are partly due to this. sales people like to play on fear if they detect it. They lead him along but now they are promoting a seald ***** or ammonia system for the new freezer and not co2. The other day one of my co-managers made a comment in a business meeting concerning the Engine Room here. he said that he has seldom ever walked through an engin room for an ammonia system and not been able to detect the slightest smell of ammonia but our is the exception. "that has to testify to our Engineer" I liked that comment. I try to keep the Engin Room as nice as I can, even at 50+ years old.
WM

Buckiesr
25-09-2007, 01:09 PM
Jesip

Yes sir you are correct.:D

The few adverts I have seen for CO2 systems have not provided very much raw data. I'm sure you realize any numbers provided may be suspect, because someone is trying to sell something.;)

If you can know what the costs will be innitionally, and future costs, as well as the returns, then you can do an IRR. However when your guessing, it is tough. You sell your idea to the investor by showing what the return on his investment will be. it is like saying: If you give me this ammount of money to invest in my project, I will give you a return on that investment of ??% which will get all of your investment back in you hands in this much time, and then you will make all profit after that for the life of the project. Projects have a set ammount of time to depreciate completly out. companies set that time. ours is set for 7 years. My projects need to pay back the investment in 5 years or less to look good. calculating the IRR is the method of showing them how much this project is worth to them. If I set up the figures and add future costs to the project I can show more than one IRR. If you only used money you already have there is no IRR. Every time there is a sign change (putting in money-a cost- that is a minus, when you get money back- that is a plus. if you put in more money, that is what a sign change is; going from taking out to putting in.) I buy a flashlight for 5.00; -5.00, I save .50 on each candle I don't have to buy because I am using the flashlight for light. But after 10 candles worth of light, the batteries run down. Now I have to buy new batteries at 3.00. so -5.00 buy flashlight, +.50X10saved not buying candles, -3.00 new batteries. that is a sign change. Every time you have to add investment money to keep it going the IRR for the project would change. My point was that I can actually arrive at the number I want to show by playing with the numbers. I was saying this is why it is not the best method for calculating the return on an investment. I recomend that the ROI be used to demonstrate the value, present and furture, of a project.
I hope that helps you understand what I was saying.
WM

Buckiesr
30-09-2007, 04:12 AM
I'm sorry if I messed up sight. No posts since my last?
WM

crashbang
14-10-2007, 10:44 AM
Incressed the co2 pressure to 40 barg and use the glycol oil cooling system via heat exchanger to incress the temp to get around 20 to 30 deg C and we defrost the coolers.

Javier+
05-11-2007, 07:42 PM
I want to design a small co2 cooling system and I don t know how to start, I need to select all the equipement.
Can some help me !

JFK
11-11-2007, 06:52 PM
what is the application? evap temp? capacity in kw?

NoNickName
05-03-2008, 03:20 PM
Hi Bruce:)

AndyP's company use a hot gas generator. Liquid is taken off the R744 condenser, fed to a pump which raises it's pressure to about 10 deg c saturation. The liquid is then boiled oil using waste compressor heat and the subsequent hot gas is used for defrosting the evaporators.

Hope this helps. Kind Regards Andy:)

Let me revamp and resurrect this thread.
I don't understand the principle of operation of this defrost.
In a R717/R744 cascade system, in order to defros CO2 evaporator, NH3 is taken off the condenser and then what?

mauricio Fort
27-05-2008, 11:22 PM
Andy, I have some questions, because a customer said in USA existing plant for precool with CO2 or N2 the fruit that enter to the IQF. You have some experience with that??.

Fillinchen
06-06-2008, 10:26 AM
Sorry to interrupt your technical discussion, but this is absolutely worth to be mentioned here: Have you seen the major announcement by the Coca-Cola CEO, that Coke will use 100,000 CO2 beverage coolers by 2010? He said, CO2 is safe, reliable, and more efficient than HFC. I am not allowed to post direct URLs yet but the story is quite good: r744.com/article.view.php?Id=666&latest=1

Sounds like a real commitment this time... Let's see if others get moving soon.

Plank!
02-08-2008, 08:06 AM
Let me revamp and resurrect this thread.
I don't understand the principle of operation of this defrost.
In a R717/R744 cascade system, in order to defros CO2 evaporator, NH3 is taken off the condenser and then what?
You've missed a small detail in Andy's post - no mention was made about using NH3 (R717)

liquid R744 (CO2) is taken from the condenser - actually its from the HP reciever - then boosted in pressure and fed into the defrost hot gas generator, where heat from the high stage oil coolers is used to superheat the liquid into hot gas suitable for defrost.

Star have this system patented so perhaps if you need more info contact them or Andy P.

jepoy_02
12-08-2008, 03:33 AM
hi guys, newbie here in the forum!

right now, i need to design a CO2-NH3 cascade system. i already have some major components selected already (compressor, aircooler, condenser), but i have no idea on how to select the pipe size, vessel and valves for the co2 side. is there any table / guide i can use?

hope you could me out on this one. thanks!!