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    My 3 stage cascade design - what you think??



    Hey all. I've been absorbing all the info I can from this forum and from the overclockers at xtremeSystems.org and created this PFD for a 3 stage cascade.

    We have a decent budget so I will use professionally built heat exchangers and have thermocouples and pressure transducers everywhere. We have LabView hardware for controls.

    The purpose of this thing is to provide 200-500 watts of cooling below -125 C for a new CO2 capturing technology we are developing. The full scale system on power plants won't use this cascade, but I need something to achieve these low temperatures for our laboratory tests. (I've looked at Polycold units but they didn't offer any guarantees that it could handle the loads I want.)

    Please review and provide any feedback you have. I still have a long way to go!

    (( NOTE: I removed this picture. There is an update in post #8 on this page. ))
    Last edited by SES Utah; 10-09-2011 at 04:13 AM.



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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by SES Utah View Post


    Please review and provide any feedback you have. I still have a long way to go!
    Attachment 7341
    Hi SES

    Got any jobs going there as it appears you have ALL the interesting projects all going on at once....No chance to get bored there mate !

    R's chillerman
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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by chillerman2006 View Post
    No chance to get bored there mate !
    You got that right!!

    I would certainly pay one of you experts to help design this! I would like to contract out a lot of the design and specification of equipment work to one of you guys if anyone is interested.

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    Re: My 3 stage cascade design - what you think??

    'Mad fridgie' is your man for this mate

    I have alot of interest but far from design level, have worked within R&D team but sadly lack too much knowledge to take a project alone

    If 'Mad' is too snowed under, the only other I know that would be able to take this on is 'Magoo'

    Will email them later if they do put in an appearance tonight
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    Re: My 3 stage cascade design - what you think??

    If you want repeatably, ease, time and dare I say cost, why not just use liquid nitrogen, total a wastage system.

    You not Canadian hiding in the US?

    MEA type system, absorb and strip, but specific for flue streams with high oxygen content?
    Last edited by mad fridgie; 10-09-2011 at 12:06 AM.

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    Re: My 3 stage cascade design - what you think??

    Hi Mad fridge,
    you beat me to the point about liquid nitrogen.
    Got dizzy trying to follow schematic, and thought all for 500 watts.

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    Re: My 3 stage cascade design - what you think??

    That is a good call, but liquid nitrogen is what we use now. It works fine for a few hundred watts but we go through 200 Liters per day (at $2 per liter) so the price quickly adds up. A lot of that is wasted money when transferring between dewars.

    The reason I want to go through all this complexity on such a small load is that we have a larger project right after this one that will also need a cascade. I'd much rather learn with a small system and then just scale it up once we've got it figured out.

    I'm not canadian, mad fridgie, but I'm an Oregonian - its close! We will be talking with the canadian government very soon, they are interested in capturing 60% of the CO2 from all their coal plants. We are competing with the MEA and absorption technologies and can capture CO2 with less cost and energy. Like I was saying earlier, the full scale coal plants (or natural gas, oil) that will use this process will have a must simpler refrigeration process because we will regeneratre (recuperate) the cooling from the CO2 and flue gas.

    What if we were to split up the work load and have one person per refrigerant loop? I'm sure that would be easier!

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    Re: My 3 stage cascade design - what you think??


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    Re: My 3 stage cascade design - what you think??

    Hi SES Utah.
    the second drg is getting better, but fundimentily flawed. Suggest you study the principles of 3 stage cascade systems.
    Plus brased plate HX are not the be all and end all of HX, they suffer from plate failures due to cyclic temp changes, SS has no memory and will fracture, as in craze cracking, alternative is double plate separation. But still susceptable to failure. I have killed a few in my time.
    magoo
    Last edited by Magoo; 12-09-2011 at 01:32 AM.

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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by SES Utah View Post
    You got that right!!

    I would certainly pay one of you experts to help design this! I would like to contract out a lot of the design and specification of equipment work to one of you guys if anyone is interested.


    Evening Magoo

    Could this be fitted into your busy schedule

    R's chillerman
    Last edited by chillerman2006; 12-09-2011 at 01:37 AM.
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    Re: My 3 stage cascade design - what you think??

    SES

    a drawing I had, might be of use

    R's chillerman
    Attached Images Attached Images
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    Re: My 3 stage cascade design - what you think??

    Hi CM
    principally correct, but difficult without screw compressors and side load sub cooling. Just follow the heat flow desired direction using cans or semihermetics on a PH chart. Use three charts to simplify things a bit.

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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by chillerman2006 View Post
    Evening Magoo

    Could this be fitted into your busy schedule

    R's chillerman
    Hi CM . short response would be yes, but difficult half a world away, plus I am not cheap dollars wise that is.

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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by Magoo View Post
    Hi CM . short response would be yes, but difficult half a world away, plus I am not cheap dollars wise that is.
    Hi SES

    If you really want to contract this work, all I can say is I had to connect my pc upto a 42 inch tv, to be able to have half a chance of following one of Magoo's projects, a huge low temp system on a scale I have not & will probaly not come across again

    Here's your chance mate, drop him a private message & see what you's can agree

    R's chillerman
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    Re: My 3 stage cascade design - what you think??

    Update 3 -
    Bench Scale Refrigeration Unit revC.png
    Is this what you were talking about Magoo? Removed all subcoolers and recuperators so that each stage high pressure side desuperheats and condenses in the same heat exchanger. I was under the impression that the compressors needed to operate at ambient temperatures but I think only the R14 loop may need a recuperator to lift the temperature of gas on the compressor suction.

    Thats a good drawing Chillerman, thanks. Do the compressors with 3 inlets represent 3 compressor stages, or do the 3 streams merge into a single compressor stage? If its multiple stages that may make things tricky.
    Attached Images Attached Images

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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by SES Utah View Post

    Thats a good drawing Chillerman, thanks. Do the compressors with 3 inlets represent 3 compressor stages, or do the 3 streams merge into a single compressor stage? If its multiple stages that may make things tricky.
    Hi SES

    I 'think' by looking at the drawing they are merging into one stream,

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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by Magoo View Post
    Hi CM
    principally correct, but difficult without screw compressors and side load sub cooling. Just follow the heat flow desired direction using cans or semihermetics on a PH chart. Use three charts to simplify things a bit.
    Thanks Magoo

    only just see this post (missed it) I will have a closer look and try that once I have had some zzz's today

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    Re: My 3 stage cascade design - what you think??

    Just had a closer look, why not go for a far simple air cycle system, "joule thompson".
    Size wise it looks just the same as the cryogenic tempering chamber I made (I down to 194C-196C)
    You just need a good quality 3 or 4 stage air dive compressor 200-400bar (higher the better), and a single R404a unit.
    Excellent for short runs (2 or 3 days), not ideal for long term use. (over the long term the pipes block with moisture or dry ice) I did not really have that much of a problem as charged with dry nitrogen.

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    Re: My 3 stage cascade design - what you think??

    [QUOTE=SES Utah;240244]Update 3 -
    Bench Scale Refrigeration Unit revC.png
    Is this what you were talking about Magoo? Removed all subcoolers and recuperators so that each stage high pressure side desuperheats and condenses in the same heat exchanger. I was under the impression that the compressors needed to operate at ambient temperatures but I think only the R14 loop may need a recuperator to lift the temperature of gas on the compressor suction.


    No, this a basic two stage common refrigerant, the side load is inter cooled from low stage discharge acting as an intercooler. possibe heat recovery, minor heat rcovery at high temps.
    Remember each system in cascade is an individual system with individual refrigerants operating at there particular optimim conditions. The devil is in the detail,

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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by mad fridgie View Post
    Just had a closer look, why not go for a far simple air cycle system, "joule thompson".
    Size wise it looks just the same as the cryogenic tempering chamber I made (I down to 194C-196C)
    You just need a good quality 3 or 4 stage air dive compressor 200-400bar (higher the better), and a single R404a unit.
    Excellent for short runs (2 or 3 days), not ideal for long term use. (over the long term the pipes block with moisture or dry ice) I did not really have that much of a problem as charged with dry nitrogen.
    Haven't looked at that process in awhile. Seems easy enough, its just a very high pressure compressor with a counter current heat exchanger to cool the high pressure gas prior to the expansion, right? Then a low temperature heat exchanger after the valve?

    Very high pressures are required due to the low cooling effect from joule thompson cooling of gas, correct?

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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by SES Utah View Post
    Haven't looked at that process in awhile. Seems easy enough, its just a very high pressure compressor with a counter current heat exchanger to cool the high pressure gas prior to the expansion, right? Then a low temperature heat exchanger after the valve?

    Very high pressures are required due to the low cooling effect from joule thompson cooling of gas, correct?
    On the contrary, the R14 is going to be evaporating and condensing at very low temperatures and therefore acceptable pressures.

    But then, what about when the system is off and rising to room temperature?

    The pressures will correspond to the temperatures, so long as there is both liquid and vapor in the R14 loop.

    As soon as all of the liquid becomes vapor, the temperature will continue to rise, but the pressure will not.

    That's what the expansion tank is for. It increases the internal volume to allow room for the vapor to expand into, thereby lowering the temperature point where all of the vapor is boiled off... so that the pressure stays within sane limits.

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    Re: My 3 stage cascade design - what you think??

    The simple PH Diagrams drawn by hand. The PH Data came from coolpack. (How awesome is coolpack?!)

    3 Stage Cascade PH Diagrams.jpg

    Can most rotary compressors handle a pressure ratio of 10 just fine? I'd like to be able to go up to 15...

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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by SES Utah View Post
    The simple PH Diagrams drawn by hand. The PH Data came from coolpack. (How awesome is coolpack?!)

    3 Stage Cascade PH Diagrams.jpg

    Can most rotary compressors handle a pressure ratio of 10 just fine? I'd like to be able to go up to 15...
    Hi SES

    I was looking at this earlier today & compression ratios the closer/smaller the better for efficiency

    obviously Magoo's the man for this but to me the R507 chart is huge, too much work being done, R170 superheat seems too much & little subcooling, R14 superheat too high and no subcooling......I would be looking at lowering superheat (more compressor cooling) & increasing subcooling, more latent heat exchange available - better efficiency

    when all three are put together this does not appear to be balanced very well

    or maybe I am looking at this all wrong & dont understand correctly ???

    Someone will jump on me here if I am wrong

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    Re: My 3 stage cascade design - what you think??

    I tried to show about 10 degrees of superheat for each stage prior to being compressed. As far as increasing the subcooling, I'm not sure I can get a whole lot of subcooling because I have the cascade boiling/condensing heat exchangers less than 8 degrees apart so subcooling is limited here.

    I don't want to have more than 3 stages, so I don't think I really have a choice but to have compression ratios of 10 or more in each stage. I like that I never have to get about 15 bar in condensers and lower than 1 bar in the evaporators as well.

    I should be able to balance the loads with the right flow rates.

    Gary, are you referring to R14 in the cascade or using it in the joule thompson cooling that mad fridgie described?

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    Re: My 3 stage cascade design - what you think??

    Hi SES

    Is there no way you can juggle your system to give you a minimum 8c subcooling & 5-7c superheat in each stage as you want more work to be done in the evaps & less by the compressors .....

    instead of de-superheaters I think the way forward here is flash coolers
    this way you will get more work out of the evaps & bring compressor work down by increasing mass in the suction side, increasing efficiency in both area's

    with industrial systems there is always (to my knowledge) good subcooling & superheat as low as possible without bringing liquid back to compressor

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    Re: My 3 stage cascade design - what you think??

    Is the subcooling requirement more for operational safety? I understand the superheat safety requirement and the efficiency gains by subcooling. Is 1 or 2 degrees subcooling too risky to operate with?

    There are only 3 ways I can subcool the R14. One is to add a subcooling heat exchanger that sends cold R14 vapor counter current to the saturated liquid. The other is to drop the pressure of the R170 evaporator. Or I could raise the pressure of the R14 condenser.

    The subcooler seems the safest and most convenient as it both superheats the R170 vapor and subcools the liquid at the same time. See the subcooler put back in on this drawing. It appears I can super heat the gas 20 degrees C to subcool the liquid 10 C (ie, heat capacity of vapor is about half that of the liquid).
    Bench Scale Refrigeration Unit revC R14 only.png

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    Re: My 3 stage cascade design - what you think??

    The joule thompson, yes basically as described, I added a refrigeration unit prior (high pressure side) to the counter flow heat exchanger (this just helps to get going).

    I totally built mine in a day (up and running), for just over US$10,000. (including heat exchangers from scratch)

    We have have saying NZ "every thing is made of number 8 bailing wire" In other words we use what is locally available, (you would have a greater selection of equipment and parts available and at better prices) Do not ask, it will make your eyes water!

    Just use Coolpack, (it has air as a refrigerant or nitrogen)

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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by SES Utah View Post
    Is the subcooling requirement more for operational safety? I understand the superheat safety requirement and the efficiency gains by subcooling. Is 1 or 2 degrees subcooling too risky to operate with?

    There are only 3 ways I can subcool the R14. One is to add a subcooling heat exchanger that sends cold R14 vapor counter current to the saturated liquid. The other is to drop the pressure of the R170 evaporator. Or I could raise the pressure of the R14 condenser.

    The subcooler seems the safest and most convenient as it both superheats the R170 vapor and subcools the liquid at the same time. See the subcooler put back in on this drawing. It appears I can super heat the gas 20 degrees C to subcool the liquid 10 C (ie, heat capacity of vapor is about half that of the liquid).
    Bench Scale Refrigeration Unit revC R14 only.png

    No there is no risk just poorer eficiency, Its just wasting available work
    If you look at, from 1kg of refrigerant can do x amount of work
    when you have good subcooling you have more mass/kg's per volume/area
    meaning you can transfer more heat into the evaporator / more work done
    thats why I also feel you need to keep the suction superheat low / more evap work done
    the use of flash coolers, increases subcooling & also increases the mass at compressor
    or look at it another way, with higher subcooling at each stage you can use refrigerants with pressures further apart in 3 stages, with low subcooling it may require different refrigerants with 4 stages...its about looking at your final temp and getting there as efficiently as possible in as less stages as possible

    I dont fully understand your final process (best kept to you & designer) so dont understand why you can not keep subcooling high and superheat low and compression ratio's close
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    Re: My 3 stage cascade design - what you think??

    Sub cooling is great, but not at the cost of increasing the condensing pressure. Because this is cascade, the saturated temp difference need to be as close as possible for efficiency.

    It is likely that you will need to superheat the compressor suction on second and third stage. This needs to be confirmed by the compressor and oil manufacture.

    This will then determine the discharge temperature (not saturated temp), it may or may not then be beneficial, to have additional cooling after the compressor, prior to the condensing heat exchanger. (Research then calcs need to be completed)

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    Re: My 3 stage cascade design - what you think??

    In troubleshooting cascades, I use interstage TD instead of subcooling. This is the difference between the higher stage SST and the lower stage SCT. This TD should be no more than 15F/8.5K.

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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by Gary View Post
    In troubleshooting cascades, I use interstage TD instead of subcooling. This is the difference between the higher stage SST and the lower stage SCT. This TD should be no more than 15F/8.5K.
    Argh ! Got Ya Gary

    you told me you dont do calcs, but there must be some in the above

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    Re: My 3 stage cascade design - what you think??

    Ya got me. I do subtraction.

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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by mad fridgie View Post
    Sub cooling is great, but not at the cost of increasing the condensing pressure. Because this is cascade, the saturated temp difference need to be as close as possible for efficiency.

    It is likely that you will need to superheat the compressor suction on second and third stage. This needs to be confirmed by the compressor and oil manufacture.

    This will then determine the discharge temperature (not saturated temp), it may or may not then be beneficial, to have additional cooling after the compressor, prior to the condensing heat exchanger. (Research then calcs need to be completed)
    Quote Originally Posted by Gary View Post
    In troubleshooting cascades, I use interstage TD instead of subcooling. This is the difference between the higher stage SST and the lower stage SCT. This TD should be no more than 15F/8.5K.
    There we go SES

    I said someone will set me straight if wrong
    Joys of f@@king up here, you dont break nothing - just learn

    Mad/Gary

    can we get some 'for instance's here so us less knowledgable can get to grips with this a bit easier ??? Please

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    Re: My 3 stage cascade design - what you think??

    Subcooling involves two factors: condensing temp and liquid temp. Higher condensing temp bad, lower liquid temp good.

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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by Gary View Post
    Subcooling involves two factors: condensing temp and liquid temp. Higher condensing temp bad, lower liquid temp good.
    Right Gents,

    From that & above can I gather,

    That the final stage needs to be worked out first ???

    Then from that you work out what your second stage evap temp needs to be for final stage condensing ???

    And the finaly you work out first stage evap temp to suit second stage condensor ???

    If correct its a case of final stage at best efficiency ...... then second stage refrigerant ect can be chosen then & only then ??? still looking for best efficiency and then repeat ???
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    Re: My 3 stage cascade design - what you think??

    Hmmm... start with the load? Yep... that makes sense.

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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by mad fridgie View Post
    If you want repeatably, ease, time and dare I say cost, why not just use liquid nitrogen, total a wastage system.

    You not Canadian hiding in the US?

    MEA type system, absorb and strip, but specific for flue streams with high oxygen content?
    just saw this post, MF thinks I 'm getting around all over the place

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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by Gary View Post
    Hmmm... start with the load? Yep... that makes sense.
    Do you ever give any info away ??? Or you just making sure I work for it, then I understand better ???

    I know its a sales pitch for your books...let me enough, so I know you have the answers but you want to see the colour of me money first

    R's chillerman
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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by MikeHolm View Post
    just saw this post, MF thinks I 'm getting around all over the place
    Commercial secrets, USA is the not the only country looking into resolving stack/flue gas CO2 removal

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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by chillerman2006 View Post
    Do you ever give any info away ??? Or you just making sure I work for it, then I understand better ???

    I know its a sales pitch for your books...let me enough, so I know you have the answers but you want to see the colour of me money first

    R's chillerman
    Nope... my books are about troubleshooting, not design... and in troubleshooting cascades you take the opposite approach, start with the highest stage and work your way down.

    In cascade design, you want a system that can handle the load... then you want a system that can handle the load plus heat of compression #1... then you want a system that can handle the load plus heat of compression #1 plus heat of compression #2... etc... so it makes sense to start with the load and work your way up the ladder.
    Last edited by Gary; 13-09-2011 at 12:50 AM.

  41. #41
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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by chillerman2006 View Post
    Do you ever give any info away ??? Or you just making sure I work for it, then I understand better ???

    I know its a sales pitch for your books...let me enough, so I know you have the answers but you want to see the colour of me money first

    R's chillerman
    When starting with any design you should all understand your application, this is basically load, how much cooling is required, at what temp is it required and what are the variants that apply to the load. (for heating basically in same)

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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by mad fridgie View Post
    Commercial secrets, USA is the not the only country looking into resolving stack/flue gas CO2 removal
    Argh ! from what I see now forgot info I had, Nz have already got the hat & wrote the book & sold to the masses

    R's chillerman
    If the World did not Suck, We would all fall off !

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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by Gary View Post
    Nope... my books are about troubleshooting, not design... and in troubleshooting cascades you take the opposite approach, start with the highest stage and work your way down.

    In cascade design, you want a system that can handle the load... then you want a system that can handle the load plus heat of compression #1... then you want a system that can handle the load plus heat of compression #1 plus heat of compression #2... etc... so it makes sense to start with the load and work your way up the ladder.
    Nice one Gary

    Thankyou, will have to put Florida higher up my list of places to visit & get the beers in sooner


    cheers mate
    Last edited by chillerman2006; 13-09-2011 at 12:55 AM.
    If the World did not Suck, We would all fall off !

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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by chillerman2006 View Post
    Nice one Gary

    Thankyou, will have to put Florida higher up my list of places to visit & get the beers in sooner


    cheers mate
    I'm allergic to the malt in beer... but I've been known to wine sometimes.

  45. #45
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    Re: My 3 stage cascade design - what you think??

    Quote Originally Posted by Gary View Post
    I'm allergic to the malt in beer... but I've been known to wine sometimes.
    Thats ok then.... hope they stock Guinness out there as I'm off beer too, especially since one of the Mike's hinted we were lager louts, what us Bwitish, cheeeeek !
    If the World did not Suck, We would all fall off !

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