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  1. #1
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    Arrow Carbon Dioxide Refrigeration



    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
    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



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    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

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    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?

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

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    Thanks Andy. I have a better picture of the system and some of the challenges it presents. Pressure washer pumps, eh? Fascinating.

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    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
    Attached Images Attached Images

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    Hi,
    I see the enthalpy lines don't extend low enough on the above attachment, sorry about that
    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
    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

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    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

    Iīm a sales man and what you say itīs true!!!!but it is the way it works. In two weeks iīm having a meeting where i am supossed to be an expert in CO2 world. But I donīt. 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

    Bye

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    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

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    I know this thread's been hanging round for a while, but Andy, how did you overcome the defrost problem (high CO2 pressures)?

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    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.

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    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!).
    --------------
    Manuel Camacho
    Dartford, England

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    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

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    Hi Andy,

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

    I really donīt 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

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    I am attaching a cycle for drawing on it, if you want, or anybody else

    Hasta la vista amigos
    Attached Images Attached Images

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    Smile Re: Carbon Dioxide Refrigeration

    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.

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    Re: Carbon Dioxide Refrigeration

    Quote Originally Posted by Lancer
    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?

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    Re: Carbon Dioxide Refrigeration

    Hi Lance;

    Youīre 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

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    Re: Carbon Dioxide Refrigeration

    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 , Chiller’s 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, that’s 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 it’s to big”, well you know it’s 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.

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    Re: Carbon Dioxide Refrigeration

    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

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    Lightbulb Re: Carbon Dioxide Refrigeration

    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 don’t 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

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    Re: Carbon Dioxide Refrigeration

    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

  23. #23
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    Re: Carbon Dioxide Refrigeration

    hi
    i need help finding co2 refrigerant properties (mollier charts or p-h diagrams).
    pls help!!

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    Re: Carbon Dioxide Refrigeration

    Quote Originally Posted by murduc74 View Post
    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

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    Re: Carbon Dioxide Refrigeration

    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.

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    Re: Carbon Dioxide Refrigeration

    Quote Originally Posted by Andy P View Post
    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

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    Re: Carbon Dioxide Refrigeration

    Quote Originally Posted by guapo
    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.

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    Re: Carbon Dioxide Refrigeration

    Hi, Guapo

    Quote Originally Posted by guapo View Post
    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/file...sors_06.03.pdf

    Best regards, Josip

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    Re: Carbon Dioxide Refrigeration

    Quote Originally Posted by 750 Valve View Post
    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

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    Re: Carbon Dioxide Refrigeration

    Quote Originally Posted by bruceboldy View Post
    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
    If you can't fix it leave it that no one else will:rolleyes:

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    Re: Carbon Dioxide Refrigeration

    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,

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    Re: Carbon Dioxide Refrigeration

    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

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    Re: Carbon Dioxide Refrigeration

    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.

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    Re: Carbon Dioxide Refrigeration

    CO2 for phase change is limited to about -67F (-55C) if I remembered the triple point correctly.

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    Re: Carbon Dioxide Refrigeration

    Hi, Samarjit Sen

    Quote Originally Posted by Samarjit Sen View Post
    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?



    Quote Originally Posted by sabroe.com
    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 8–12 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 80–400 kW at -50°C or 140–650 kW at -40°C.
    Please follow this link:

    http://www.sabroe.com/fileadmin/file...CAFP_06.03.pdf
    http://docnav.grasso-global.com/DocN..._gbr_10-04.pdf

    Best regards, Josip

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    Re: Carbon Dioxide Refrigeration

    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,

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    Re: Carbon Dioxide Refrigeration

    Hi,

    Quote Originally Posted by Samarjit Sen View Post
    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

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  38. #38
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    Re: Carbon Dioxide Refrigeration

    Quote Originally Posted by Josip View Post
    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

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    Re: Carbon Dioxide Refrigeration

    Quote Originally Posted by Andy P View Post
    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
    If you can't fix it leave it that no one else will:rolleyes:

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    Re: Carbon Dioxide Refrigeration

    Quote Originally Posted by Andy View Post
    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

    cheers
    Andy P

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    Re: Carbon Dioxide Refrigeration

    Quote Originally Posted by Andy P View Post
    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

    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
    If you can't fix it leave it that no one else will:rolleyes:

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    Re: Carbon Dioxide Refrigeration

    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/20...article02.html

    I am sure that you will find it useful.

    With best wishes,

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    Re: Carbon Dioxide Refrigeration

    Please only post the information in one thread.

    Thank you.

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    Re: Carbon Dioxide Refrigeration

    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,

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    Re: Carbon Dioxide Refrigeration

    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

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    Re: Carbon Dioxide Refrigeration

    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.

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    Re: Carbon Dioxide Refrigeration

    Dear nh3wizard,

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

    Thank you,

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    Re: Carbon Dioxide Refrigeration

    Hi, Andy P

    Quote Originally Posted by Andy P View Post
    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

    It's impossible to make anything foolproof because fools are so ingenious...

    Don't ever underestimate the power of stupid people when they are in large groups.

    Please, don't teach me how to be stupid....
    No job is as important as to jeopardize the safety of you or those that you work with.

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    Re: Carbon Dioxide Refrigeration

    Hi, all

    Quote Originally Posted by Samarjit Sen View Post
    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/20...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

    It's impossible to make anything foolproof because fools are so ingenious...

    Don't ever underestimate the power of stupid people when they are in large groups.

    Please, don't teach me how to be stupid....
    No job is as important as to jeopardize the safety of you or those that you work with.

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    Re: Carbon Dioxide Refrigeration

    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.

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