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    how do i calculate actual mass flow through a compressor without flowmeters?



    greetings,
    I am attempting to calculate actual mass flow through our ammonia compressors to determine a KW/ton efficiency rating that is not just based on design flow. I want to use these calculations to determine a part load sharing strategy that will reduce electrical consumption while continuing to supply the plant with appropriate refrigeration tonnage.

    Is there a way to do this that does not require a flow meter at the suction of each compressor?



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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Scubasteve,
    The best way that I know is using compressor selection software, which only a few would have access to.
    It's theoretical to a certain degree, depends on compressor manufacturer.
    Assuming it's a Frick or Mycom let us know.
    Can you give example & model etc of Machine/s in question as well as running conditions.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    yeah i have already calculated the theoretical values, the problem is i dont really know for sure wether higher KWH usage is due to wear, or due to more actual mass flow resulting in higher joules of work.

    here is what i have so far.
    https://drive.google.com/open?id=0B9...VdJWGZvODNiNmc

    you will have to download it, as the file is too large to view on google drive, its an excel file.
    Last edited by scubasteve4sq; 22-10-2016 at 04:25 AM.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    there are 9 machines,
    4- 1,000 ton recips (Clark)
    1- 1,300 ton recip (Clark)
    1- 500 ton twin screw (Frick)
    2- 750 ton twin screws (Dunham-Bush)
    1- 1500 ton twin screw (Frick)

    average main house suction pressure is 36-38 PSI

    one 750 machine dedicated to 45 PSI system
    one 500 machine dedicated to 25 PSI system
    remaining compressors are all 37PSI system

    Discharge PSI average 150-180 PSI depending on season.
    we run a wet bulb float on discharge pressure controlled by VFD evaporative condenser fans

    big swing loads, this is a large brewery, we get hit with 800 ton load swings.

    all the data is in the excel file linked in the post above, everything i have on each compressor and a month of trend data for each.
    Last edited by scubasteve4sq; 22-10-2016 at 07:47 AM. Reason: spelling

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Scubasteve,
    Sometimes hard to check performance of equipment with varying loads.
    Basic checks on compressors to make sure they are at full load & recips check with amps for each step.
    Screws can have performance issues with wear over time, like rotor tips, slide valve wear, discharge end clearances.
    Probably not telling you anything new.
    - Can you advise what type of oil cooling you have on screw compressors?
    - Do you have any VSD on any of the screws?
    - The Clark recips unload 7 do you run them normally?
    - The Dunham Bush compressors, how old are they?
    - Do you have any kind of auto air purger?
    Are condensers working at 100%, fans, sprays etc
    - are the machines overhauled on a regular basis, as Frick No8 is a big machine to have down.

    I would have thought one screw on a VSD for fine trim & select a Clark to load & unload, as recips efficient throughout steps of unloading.
    Calibrate all pressure/temperature transducers.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    liquid injection cooling for the screws, water cooling for the recips

    i have recommended a VSD for the big screw, but it is costly, so no progress there yet.

    the clark recips only unload in increments of 25%, but yes we run them every day

    the dunham bush screws are 1980 machines

    we have an auto purger and I track and record the level of air and non-condensibles in the system daily, i try to keep it under 3-5PSI

    the condensers are at 100% we have excellent water treatment, we clean the diffusers every 6 months per unit. check fan belts. every day we test PH and conductivity to ensure no leaks.

    the machines have an overhaul schedule, but we have a corporate spare for Frick #8 so we install the spare and send ours off for rebuild, it then becomes the spare, for the next plant.

    i would really like a VSD on frick #8 thats the most efficient solution i think.

    i know its splitting hairs at this point, but our load is so large than small improvements make large differences in the monthly power bill.

    when i see #1 clark using more kwh than #2 clark, i just cant assume that it is more inefficient based on theoretical values, maybe its just moving more gas? that's my dilemma.
    Last edited by scubasteve4sq; 22-10-2016 at 06:52 PM.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by scubasteve4sq View Post
    liquid injection cooling for the screws, water cooling for the recips

    i have recommended a VSD for the big screw, but it is costly, so no progress there yet.

    the clark recips only unload in increments of 25%, but yes we run them every day

    the dunham bush screws are 1980 machines

    we have an auto purger and I track and record the level of air and non-condensibles in the system daily, i try to keep it under 3-5PSI

    the condensers are at 100% we have excellent water treatment, we clean the diffusers every 6 months per unit. check fan belts. every day we test PH and conductivity to ensure no leaks.

    the machines have an overhaul schedule, but we have a corporate spare for Frick #8 so we install the spare and send ours off for rebuild, it then becomes the spare, for the next plant.

    i would really like a VSD on frick #8 thats the most efficient solution i think.

    i know its splitting hairs at this point, but our load is so large than small improvements make large differences in the monthly power bill.

    when i see #1 clark using more kwh than #2 clark, i just cant assume that it is more inefficient based on theoretical values, maybe its just moving more gas? that's my dilemma.
    Steve,
    Thanks for giving insight into your plant.
    My opinion would be the following if you want to save power, not rocket science, but basics
    in the industry.

    - change from liquid injection to water or thermosyphon oil cooling.
    If tips worn on any of the compressors it gets worse efficiency wise.
    Liquid injection costs power & screw efficiency, but obviously cheaper.
    USA seem driven this way,why I'm not sure.

    - Dunham Bush, do they have old profile or latest profile rotors.
    If old style rotors, or even age, I would consider new screws.
    In the ones I work on, with no real wear you can see clearances, you use a ruler, not a micrometer.
    They are machines 36 years old, need to update.

    - Frick No8 may not be the most economical to convert to VSD.
    I would suggest put it on a good size screw with ample capacity & turn down.
    Frick can go down to 800rpm up 3550rpm on larger models.
    No8's drive very big & motor may require modifications, maybe it has whitemetal bearings , but drive price probably not viable.
    Wish list buy latest screw with it on & ensure it's water cooled as well.
    Use a dedicated cooling tower with VSD on fan/s, pipe up either a spare cooling tower or connect to a large condenser for redundancy.

    - Clark compressors cannot say, but if regularly inspected top end, valves etc.
    Check discharge pressure on each machine with accurate gauge or transducer, also check amps with tong tester & compare.
    Could machine with higher amps if mechanically OK have a restriction in suction or discharge line?


    How is the brewery set up, chilled water & brine, or NH3 direct cooling on fermentors?
    In Australia
    updated brewery have PHE in plant room to reduce NH3 charge.
    Also use CO2 for air conditioning as save power, small compressor, very efficient.
    Imagine you would also have serious CO2 recovery to save money as well?
    Thanks for rep points, please check paper on link regarding liquid injection Frick screw.

    http://turbolab.tamu.edu/proc/turbop...8/Vol28015.pdf
    Last edited by RANGER1; 22-10-2016 at 11:30 PM.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Actually, I think that energy savings in industrial refrigeration is a science. You can't measure real life capacity without measuring flow.
    Rule of thumb. Keep capacity of screw compressors as maximum as possible and run reciprocated compressors as trimming ones. Efficiency of reciprocated compressor doesn't suffer as much as efficiency of screw compressor when it unloads.
    Reduce minimum allowable condensing pressure as low as possible(winter operation). Keep optimum wet bulb approach for summer operation of the condensers.
    I'm just curious. How did you determine that you have 3-5 psig of air in the system?

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Hi scuba.
    use the enthalpy change method between sst temp of suction versus the SDT of liquid to establish circulated flow rate.
    Roy J Dossat / principals of refrigeration , vapor compression cycle chapter.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by RANGER1 View Post
    Steve,
    Thanks for giving insight into your plant.
    My opinion would be the following if you want to save power, not rocket science, but basics
    in the industry.

    - change from liquid injection to water or thermosyphon oil cooling.
    If tips worn on any of the compressors it gets worse efficiency wise.
    Liquid injection costs power & screw efficiency, but obviously cheaper.
    USA seem driven this way,why I'm not sure.
    I've been pushing this for a while now, but they want to save money without spending money. as for why alot of the USA is liquid injection, its because it is a lower initial installation cost. we actually already have capped stubs on our HPR for thermosyphon cooling.

    Quote Originally Posted by RANGER1 View Post
    - Dunham Bush, do they have old profile or latest profile rotors.
    If old style rotors, or even age, I would consider new screws.
    In the ones I work on, with no real wear you can see clearances, you use a ruler, not a micrometer.
    They are machines 36 years old, need to update.
    I'm not sure on that, they have been rebuilt several times, and they have had the Vi ports machined out to 2.4 due to operating pressure design changes.

    Quote Originally Posted by RANGER1 View Post
    - Frick No8 may not be the most economical to convert to VSD.
    I would suggest put it on a good size screw with ample capacity & turn down.
    Frick can go down to 800rpm up 3550rpm on larger models.
    No8's drive very big & motor may require modifications, maybe it has whitemetal bearings , but drive price probably not viable.
    Wish list buy latest screw with it on & ensure it's water cooled as well.
    Use a dedicated cooling tower with VSD on fan/s, pipe up either a spare cooling tower or connect to a large condenser for redundancy.
    yeah again its the money thing

    Quote Originally Posted by RANGER1 View Post
    - Clark compressors cannot say, but if regularly inspected top end, valves etc.
    Check discharge pressure on each machine with accurate gauge or transducer, also check amps with tong tester & compare.
    Could machine with higher amps if mechanically OK have a restriction in suction or discharge line?
    we have regularly calibrated senors for all of that with redundancy on most.
    i dont think we have any restrictions, i would see that in the discharge pressure, when the ammonia discharge desuperheater water heater is lined up improperly and flow is restricted we get a D/P alarm due to the increased discharge pressure.


    Quote Originally Posted by RANGER1 View Post
    How is the brewery set up, chilled water & brine, or NH3 direct cooling on fermentors?
    In Australia
    we use alot of glycol brine, as well as direct cooling, ~170K Lbs of ammonia on site

    Quote Originally Posted by RANGER1 View Post
    updated brewery have PHE in plant room to reduce NH3 charge.
    Also use CO2 for air conditioning as save power, small compressor, very efficient.
    Imagine you would also have serious CO2 recovery to save money as well?
    huge Co2 liquefaction cascade system although it is physically isolated from the main ammonia system due to the risk of Co2 and ammonia reaction in the event of a leak.

    Quote Originally Posted by RANGER1 View Post
    Thanks for rep points, please check paper on link regarding liquid injection Frick screw.

    http://turbolab.tamu.edu/proc/turbop...8/Vol28015.pdf
    Last edited by scubasteve4sq; 23-10-2016 at 05:41 AM. Reason: spelling

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by Segei View Post
    Actually, I think that energy savings in industrial refrigeration is a science. You can't measure real life capacity without measuring flow.
    Rule of thumb. Keep capacity of screw compressors as maximum as possible and run reciprocated compressors as trimming ones. Efficiency of reciprocated compressor doesn't suffer as much as efficiency of screw compressor when it unloads.
    Reduce minimum allowable condensing pressure as low as possible(winter operation). Keep optimum wet bulb approach for summer operation of the condensers.
    I'm just curious. How did you determine that you have 3-5 psig of air in the system?
    that's my assessment as well, without flow meters i think we are pissing in the wind.

    as for non condensibles, i just take the temperature of the ammonia exiting the condensers, a vlookup table in excel checks that temp against an ammonia saturation table and derives the corresponding pressure, then that is subtracted from actual head pressure and the difference is air and non condensibles in the towers. Dalton's law of partial pressure.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by Magoo View Post
    Hi scuba.
    use the enthalpy change method between sst temp of suction versus the SDT of liquid to establish circulated flow rate.
    Roy J Dossat / principals of refrigeration , vapor compression cycle chapter.
    that might work for a small hvac compressor, but were not dealing with adiabatic compression here, a lot of the heat is removed by liquid injection cooling and water cooling systems.
    Last edited by scubasteve4sq; 23-10-2016 at 05:59 AM.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Steve,
    It would be normal for most companies to not spend money & with some management hard to turn around.
    We see it all the time, change of manager etc over time it might change.
    Can only do basics as Segei suggests.
    You can only get numbers together like you are trying to do to prove inefficiencies.
    Liquid injection could be one, finding out about Dunham Bush could be another.
    There was a rotor change about then from symmetrical to asymmetrical & approx 10% or more efficient.
    Instead of overhaul get new, not rebuilt. if available.
    Ask for report of rebuild & ask a few more questions.
    Rebuild company are not going to say throw away, as then they have no job.
    We had an instance of installing VSD on 2513 DB, overhauled, all looked very good.
    Could not get it to pump until 35Hz 40% slide valve, discharge pressure only then began to rise in package to plant discharge pressure.
    With thermosyphon change the biggest machine first, then progressive, again to see results difficult as usually at the same time production increased, or a new extra piece of equipment installed.
    Same with old motors, newer more efficient, so if maintenance on it, upgrade to new.
    Not many drive 1980 cars.
    Last edited by RANGER1; 23-10-2016 at 09:32 PM.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by RANGER1 View Post
    Steve,
    It would be normal for most companies to not spend money & with some management hard to turn around.
    We see it all the time, change of manager etc over time it might change.
    Can only do basics as Segei suggests.
    You can only get numbers together like you are trying to do to prove inefficiencies.
    Liquid injection could be one, finding out about Dunham Bush could be another.
    There was a rotor change about then from symmetrical to asymmetrical & approx 10% or more efficient.
    Instead of overhaul get new, not rebuilt. if available.
    Ask for report of rebuild & ask a few more questions.
    Rebuild company are not going to say throw away, as then they have no job.
    We had an instance of installing VSD on 2513 DB, overhauled, all looked very good.
    Could not get it to pump until 35Hz 40% slide valve, discharge pressure only then began to rise in package to plant discharge pressure.
    With thermosyphon change the biggest machine first, then progressive, again to see results difficult as usually at the same time production increased, or a new extra piece of equipment installed.
    Same with old motors, newer more efficient, so if maintenance on it, upgrade to new.
    Not many drive 1980 cars.
    that's good advice, i'll look into the DB's history and i'll keep pushing for the thermosyphon oil cooling.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Scubasteve:
    My curiosity has the best of me.
    I learned on 2 Cylinder VSA Ammonia Compressors.
    The biggest I have personally worked on was a 14 X 10 inch X 4 Cyl Kohlenberger.
    I have never heard of Clark.
    The part about 4 cylinders, every other revolution I am not too clear on.
    Perhaps you could give us a little history on the machines and their Manufacture, as well as explain the every other revolution part.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    You've done it right if liquid not subcooled. Most likely is not.
    Since 2005 I educate people how to save energy in industrial refrigeration. Have written 100+ newsletters and you can read them on website www.skenergy.ca (articles). Optimization of the refrigeration plant operation is the most cost effective way to save energy.
    Let's review VFD for one screw compressor. Compressor VFD save energy. How much? VFD recover losses related to part load operation. These losses depends of slide valve position and compression ration. Compression ratio of your compressors is 3-4. This is very low. It means that VFD will recover some losses but not a lot. VFD itself use 3-3.5% of energy. It means that at 100% load compressor with VFD will use 103% of energy. At capacity 85% efficiencies of compressors with and without VFD will be equal. At 70% load compressor with VFD will be 3% more efficient than compressor without VFD. It means that if compressor operate between 70% and 100% average efficiency of compressors with and without VFD will be equal.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    I'm using regularly an ultra sonic flow meter to check the capacity of compressors or whole plant. Electrical energy consumption is logged by an energy meter.
    With a liquid flow meter it's easy on brine, ammonia from receiver or HFC (impossible on liquid before a float valve). A liquid flow meter is not so expensive......
    But for gas it's an other story. Gas datas available only for ammonia, mesurement only on discharge side, nearly impossible on boosters, discharge pressure too low.
    It cost twice more than for liquid...! it takes about half an hour to set on site.

    You can see then, in real field conditions, good things and awful others.
    Worn rotors, re used after overhaul, cost finaly a lot for exemple!
    Compressors on VFD at low speed and low slide valve capacity running at zéro flow.....
    you have then an other view on energy savings

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Hi, Cricri.
    I visited many plants in North America, but I didn't see any flow meters. Can you give us more information about these meters? Manufacturer... Are they portable or stationary?

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Hi Segei
    it's a portable 2 ways ultrasonic flow meter. you can use it on liquid with the appropriate set of sensors.
    a set of temp probes can be used to calculate the capacity for usual brines, capacity displayed and logged as the other parameters.

    you can switch it to gas mesurement with an other set of sensors. a set will cover X to Y diameter and A to B wall thickness
    http://www.flexim.com/en/devices/por...es/fluxus-g601
    the difficult is that you need a straigth pipe to get a stable flow, you apply then an accoustic tape of about 800mm o the pipe. the flow is displayed in m3/h....you have then some calculations to do, like at school!

    DSCN1133.jpg

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Thanks. However, you can't measure flow in insulated pipe. Even pipe from high pressure receiver sometimes has mixture of vapor and liquid.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by NH3LVR View Post
    Scubasteve:
    My curiosity has the best of me.
    I learned on 2 Cylinder VSA Ammonia Compressors.
    The biggest I have personally worked on was a 14 X 10 inch X 4 Cyl Kohlenberger.
    I have never heard of Clark.
    The part about 4 cylinders, every other revolution I am not too clear on.
    Perhaps you could give us a little history on the machines and their Manufacture, as well as explain the every other revolution part.
    Was hoping someone would reply to this. I really am interested.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Last edited by RANGER1; 02-11-2016 at 09:51 PM.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Had no idea reciprocating machines were built this big.
    Very interesting stuff applied to an NH3 system.
    Appreciate it Ranger.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    hey sorry i was away, i'll post up something on the clarks shortly, they are very big machines, and they make them a lot bigger than the ones we have, our biggest is 1300 tons. double acting cylinders, basically one revolution is 4 compression strokes.
    Last edited by scubasteve4sq; 04-11-2016 at 09:44 PM.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    they are dresser rand Clarks, this is the closest thing i could find to what we have, i will take pictures and post model numbers tomorrow


    https://youtu.be/Z3S86RCcMIY



    Last edited by scubasteve4sq; 04-11-2016 at 10:41 PM.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by Segei View Post
    You've done it right if liquid not subcooled. Most likely is not.
    Since 2005 I educate people how to save energy in industrial refrigeration. Have written 100+ newsletters and you can read them on website www.skenergy.ca (articles). Optimization of the refrigeration plant operation is the most cost effective way to save energy.
    Let's review VFD for one screw compressor. Compressor VFD save energy. How much? VFD recover losses related to part load operation. These losses depends of slide valve position and compression ration. Compression ratio of your compressors is 3-4. This is very low. It means that VFD will recover some losses but not a lot. VFD itself use 3-3.5% of energy. It means that at 100% load compressor with VFD will use 103% of energy. At capacity 85% efficiencies of compressors with and without VFD will be equal. At 70% load compressor with VFD will be 3% more efficient than compressor without VFD. It means that if compressor operate between 70% and 100% average efficiency of compressors with and without VFD will be equal.

    i agree with everything you have said here, but keep in mind, i can run all the recip compressors at 100% base load(most efficient) and trim with a screw compressor at 100% slide valve. its more beneficial that just one compressor.

    thanks for the links to your articles, i am enjoying reading them, overall i feel we are in pretty good shape, as we do most of the things you suggest.
    Last edited by scubasteve4sq; 04-11-2016 at 10:04 PM.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by cricri View Post
    Hi Segei
    it's a portable 2 ways ultrasonic flow meter. you can use it on liquid with the appropriate set of sensors.
    a set of temp probes can be used to calculate the capacity for usual brines, capacity displayed and logged as the other parameters.

    you can switch it to gas mesurement with an other set of sensors. a set will cover X to Y diameter and A to B wall thickness
    http://www.flexim.com/en/devices/por...es/fluxus-g601
    the difficult is that you need a straigth pipe to get a stable flow, you apply then an accoustic tape of about 800mm o the pipe. the flow is displayed in m3/h....you have then some calculations to do, like at school!

    DSCN1133.jpg
    this looks perfect, how much does a meter like this cost?

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Steve,
    Try hire company, Australia would be Tech Rentals, probably same or similar in your neck of the woods.
    You mention your plant uses liquid injection cooling for compressors, can you tell us what control temperature you have?
    You mention about wire drawing in valves, have you ha ammonia checked for water?

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by RANGER1 View Post
    Steve,
    Try hire company, Australia would be Tech Rentals, probably same or similar in your neck of the woods.
    You mention your plant uses liquid injection cooling for compressors, can you tell us what control temperature you have?
    You mention about wire drawing in valves, have you ha ammonia checked for water?
    control temp for liquid injection cooling is 136F-140F

    we have a still, that all vessel oil drains are piped directly to, it has a steam coil that cooks off ammonia back to the suction line, any water or oil that remains is then removed from the system. last time a purity check was done, we had 99.95%

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    I scubasteve,
    Mine cost around 20 k€. Including two sets of sensors for liquid and one for gas.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    I gave you that example to show that most likely little or no benefits of VFDs for your screw compressors.
    To save energy in industrial refrigeration, people should know optimum set points and should know how to achieve these set points. I don't know where is your plant located in USA but most likely optimum condensing pressure for winter operation is below 100 psig. You have 150 psig. It means a lot of room for improvement. Actually, lowering condensing pressure very often gives people majority(over 50%) of the energy savings.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    we are located in florida, minimum pressure is 125 PSIG before we cannot push liquid to the load units.
    coldest it gets here is 20F maybe once or twice a year.

    here is a pic of the clarks as requested by NH3Lvr


    Last edited by scubasteve4sq; 05-11-2016 at 04:28 PM.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Even if you are located in Florida, your optimum condensing pressure is below 100 psig. Definitely, to achieve this optimum you should overcome several barriers but every barrier has a solution.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by Segei View Post
    Even if you are located in Florida, your optimum condensing pressure is below 100 psig. Definitely, to achieve this optimum you should overcome several barriers but every barrier has a solution.
    Segei,
    Don't want to hijack thread, if so someone can change, but we are talking about power savings.
    What advice can you give for condensing pressure in summer for a large industrial ammonia plant.
    In Australia we would normally design for 35 Deg C condensing, design engineers keep saying that, am I brainwashed to a certain degree!
    If you have the money & real estate, would it be worth designing for anything less than that?
    I realize in winter you can benefit with lower condensing with the equipment you have already for summer.
    Last edited by RANGER1; 05-11-2016 at 10:12 PM.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by Segei View Post
    Even if you are located in Florida, your optimum condensing pressure is below 100 psig. Definitely, to achieve this optimum you should overcome several barriers but every barrier has a solution.
    That is just unrealistic for a plant of this size, age, and location. We run a wet bulb head pressure in the warm months, and in the cold months we run at 125 psi. If we go below 125 we cannot feed liquid to the plant, remember we have thousands of feet of piping to get to load units, and those load units operate at 38-45 psi suction, there is a limit to what you can achieve with so small a pressure differential, and line loss on the way to the unit. you are probably used to two stage plants that run a much higher psid between suction and head pressure.
    Last edited by scubasteve4sq; 05-11-2016 at 11:51 PM.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by RANGER1 View Post
    Segei,
    Don't want to hijack thread, if so someone can change, but we are talking about power savings.
    What advice can you give for condensing pressure in summer for a large industrial ammonia plant.
    In Australia we would normally design for 35 Deg C condensing, design engineers keep saying that, am I brainwashed to a certain degree!
    If you have the money & real estate, would it be worth designing for anything less than that?
    I realize in winter you can benefit with lower condensing with the equipment you have already for summer.
    Ranger1.
    It depends of design wet bulb temperature. Here in Toronto area design wet bulb temperature is 75F. As far as I know it will be 80F+ for Florida. To choose right design temperature we should add optimum wet bulb approach. Typically, this is 10 - 15F. Design for 95F(35C) is not bad for Florida but for Toronto condensers designed for 95F (approach 20F) are undersized. At optimum wet bulb approach total energy use of compressors + condensers are minimal.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by scubasteve4sq View Post
    That is just unrealistic for a plant of this size, age, and location. We run a wet bulb head pressure in the warm months, and in the cold months we run at 125 psi. If we go below 125 we cannot feed liquid to the plant, remember we have thousands of feet of piping to get to load units, and those load units operate at 38-45 psi suction, there is a limit to what you can achieve with so small a pressure differential, and line loss on the way to the unit. you are probably used to two stage plants that run a much higher psid between suction and head pressure.
    Steve,
    It is common misconception in our industry that we need 80+psig pressure difference to supply liquid to cooling units at far end of the plant. However, you supply liquid from high pressure receiver and it has saturated liquid. It means that any insignificant pressure drop in the liquid line create vapor and a lot of vapor. Cooling unit metering device recieve mixture of liquid and vapor. This vapor will choke metering device and unit will get less liquid than required. Typically, 30-40 psig pressure difference is enough to supply liquid but this liquid should be free of vapor.
    However, this is just one barrier to run plant at lower condensing pressure. I don't know your plant but I see at least 2-3 additional barriers that should be overcome. It is not easy but it can be done.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    [QUOTE=scubasteve4sq;315956]we are located in florida, minimum pressure is 125 PSIG before we cannot push liquid to the load units.
    coldest it gets here is 20F maybe once or twice a year.

    here is a pic of the clarks as requested by NH3Lvr


    [/QUOT

    Steve, serious equipment that I have never seen in industrial ammonia.
    Although I'm not really sure it looks expensive but simple design, low speed, last forever.
    Can't imagine it would like any liquid at all, different design than smaller multi cylinder recips.
    Do they require much maintenance, or annual valve checks/ replacement?

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by Segei View Post
    Ranger1.
    It depends of design wet bulb temperature. Here in Toronto area design wet bulb temperature is 75F. As far as I know it will be 80F+ for Florida. To choose right design temperature we should add optimum wet bulb approach. Typically, this is 10 - 15F. Design for 95F(35C) is not bad for Florida but for Toronto condensers designed for 95F (approach 20F) are undersized. At optimum wet bulb approach total energy use of compressors + condensers are minimal.
    Thanks for reply

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by Segei View Post
    Steve,
    It is common misconception in our industry that we need 80+psig pressure difference to supply liquid to cooling units at far end of the plant. However, you supply liquid from high pressure receiver and it has saturated liquid. It means that any insignificant pressure drop in the liquid line create vapor and a lot of vapor. Cooling unit metering device recieve mixture of liquid and vapor. This vapor will choke metering device and unit will get less liquid than required. Typically, 30-40 psig pressure difference is enough to supply liquid but this liquid should be free of vapor.
    However, this is just one barrier to run plant at lower condensing pressure. I don't know your plant but I see at least 2-3 additional barriers that should be overcome. It is not easy but it can be done.

    Yes I understand what you are saying, but our liquid lines are run through a 45 degree beer cellar, so the liquid is not flashing due to pressure drop in the line. One of the problems we have is that the engineer who designed the plant did not install any metering devices on the load units as he believed they were not nessecary. So we do not have a restriction, but we do destroy solenoid valves very quickly from flash gas. The reason I say we can't supply liquid at below 125 psi is because I have tried it. Our 45 psig units starve out every time.
    Last edited by scubasteve4sq; 06-11-2016 at 11:01 PM.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    [QUOTE=RANGER1;315973]
    Quote Originally Posted by scubasteve4sq View Post
    we are located in florida, minimum pressure is 125 PSIG before we cannot push liquid to the load units.
    coldest it gets here is 20F maybe once or twice a year.

    here is a pic of the clarks as requested by NH3Lvr


    [/QUOT

    Steve, serious equipment that I have never seen in industrial ammonia.
    Although I'm not really sure it looks expensive but simple design, low speed, last forever.
    Can't imagine it would like any liquid at all, different design than smaller multi cylinder recips.
    Do they require much maintenance, or annual valve checks/ replacement?
    They do last forever, but they require constant maintenance, they allow ammonia leakage into the distance piece, which really adds up in a year's time. They also use a significant amount of oil. If I had a choice I would replace with screw compressors.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by scubasteve4sq View Post
    Yes I understand what you are saying, but our liquid lines are run through a 45 degree beer cellar, so the liquid is not flashing due to pressure drop in the line. One of the problems we have is that the engineer who designed the plant did not install any metering devices on the load units as he believed they were not nessecary. So we do not have a restriction, but we do destroy solenoid valves very quickly from flash gas. The reason I say we can't supply liquid at below 125 psi is because I have tried it. Our 45 psig units starve out every time.
    Steve
    I think that your liquid don't cool enough to prevent flashing in the pipe. Outside heat transfer is very low. I suggest you to talk to solenoid manufacturer. They better know capacities of their solenoids. Most likely they will confirm that you have flashing in the pipe.
    Than you need a energy efficiency adviser. Person who will review design and operation of your plant. Based on this review he will give you advice how to save energy. As I mention this is only one barrier to reduce condensing pressure. Others barriers should be reviewed as well.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    scubasteve:

    Sorry it took so long to reply. I was out of town as well.
    Great pictures! Never knew such compressors could be used on NH3.

    You certainly do have some issues. Coming right out of the solenoid valves with no restriction moves the expansion, and wire drawing, to the valve. With having to keep the head pressure up I would guess you are undersized on the pipe sizing, as you are already aware.

    One possibility might be to install a pump to boost the liquid line pressure. I have little experience in this area and do not know if anything is available in the size you would require.

    I also expect that in your business downtime to make the changes would be hard to come by.

    Lowering head pressure to save energy can be a tricky thing unless every aspect is looked at. Our local power company sent people out to the plants in my area and told them to lower the head pressure to save money. All of a sudden the evaporators would not defrost and the oil separators were undersized and every one was unhappy.

    That is not to say that it cannot save a lot of energy. I made a small modification to a 770 horsepower installation in Alaska. We got the purger working correctly and dropped the head 30 psi.
    The savings in power we were not so concerned with. We picked up enough capacity however that it made a big difference in our capabilities.

    Again-thanks for the information and pictures.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by NH3LVR View Post
    scubasteve:

    Sorry it took so long to reply. I was out of town as well.
    Great pictures! Never knew such compressors could be used on NH3.

    You certainly do have some issues. Coming right out of the solenoid valves with no restriction moves the expansion, and wire drawing, to the valve. With having to keep the head pressure up I would guess you are undersized on the pipe sizing, as you are already aware.

    One possibility might be to install a pump to boost the liquid line pressure. I have little experience in this area and do not know if anything is available in the size you would require.

    I also expect that in your business downtime to make the changes would be hard to come by.

    Lowering head pressure to save energy can be a tricky thing unless every aspect is looked at. Our local power company sent people out to the plants in my area and told them to lower the head pressure to save money. All of a sudden the evaporators would not defrost and the oil separators were undersized and every one was unhappy.

    That is not to say that it cannot save a lot of energy. I made a small modification to a 770 horsepower installation in Alaska. We got the purger working correctly and dropped the head 30 psi.
    The savings in power we were not so concerned with. We picked up enough capacity however that it made a big difference in our capabilities.

    Again-thanks for the information and pictures.
    NH3LVR
    I think that energy savings should be done by the experts not by people from local hydro company. Yes, initial steps of optimization can be done by site engineers but at later stage of this process you need someone who has in depth knowledge of the energy savings in industrial refrigeration.
    Steve mentioned about wet bulb control of condensing pressure during summer operation. This is right approach but this control should be set up properly. I saw many plants where engineers have no clue how this control works and why do they need it. Actually, this control is not complicated but nobody explain them how it works and how to check proper operation of this control.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Segei,
    Would you agree about removing liquid injection for thermosyphon, also old technology screw compressor to be at least investigated
    Apparently USA does not mind how many thousands of lbs of ammonia!
    Most breweries would use chilled water & brine/ glycol to circulate, instead of piped ammonia, the ones I know anyway!

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by RANGER1 View Post
    Segei,
    Would you agree about removing liquid injection for thermosyphon, also old technology screw compressor to be at least investigated
    Apparently USA does not mind how many thousands of lbs of ammonia!
    Most breweries would use chilled water & brine/ glycol to circulate, instead of piped ammonia, the ones I know anyway!
    RANGER1
    Definitely, I prefer thermosyphon. It saves energy(not a lot of savings but it is better than liquid injection). No damage compressors. Thermosyphon is not a barrier to reduce condensing pressure(and save energy). However, it costs money. Many companies in US will not invest in something unless they get 2 years payback. Definitely, you will not get 2 years payback for this plant.

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Hi Ranger
    I do not know of any formal test done that proofs liquid injection damages a screw compressor VS thermosyphon? We have screws running on thermosyphon for 12 years straight, services and inspection done as per manufacturer and only 1 thrust bearing change. as you said the cost to convert a liquid injection compressor to thermosyphon will non pay back in 5 years even so is it worth changing? (Compressor hours at 120,000 hrs)
    THE BEST WAY OF LEARNING IS TO DO IT YOURSELF!!!

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    Re: how do i calculate actual mass flow through a compressor without flowmeters?

    Quote Originally Posted by Lodiev View Post
    Hi Ranger
    I do not know of any formal test done that proofs liquid injection damages a screw compressor VS thermosyphon? We have screws running on thermosyphon for 12 years straight, services and inspection done as per manufacturer and only 1 thrust bearing change. as you said the cost to convert a liquid injection compressor to thermosyphon will non pay back in 5 years even so is it worth changing? (Compressor hours at 120,000 hrs)
    Lodiev,
    Liquid injection you lose a small amount of capacity & use small amount of power, so over time it costs you.
    Also the older the screw, if it has ant wear on rotor tips etc, it would compound effects on efficiency.

    Everything has it's place,thermosyphon is good, as no maintenance.

    http://turbolab.tamu.edu/proc/turbop...8/Vol28015.pdf

    see page 153
    Last edited by RANGER1; 20-11-2016 at 09:04 PM.

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