View Full Version : Help, needed susction and discharge pipes sizes

Josip

11-09-2008, 03:36 PM

Hi, all :)

... have a problem ... do not have a right documentation (have some, but to be honest, cannot follow it:confused:), and urgently need compressor's suction and discharge pipe nominal size (flange size) ... hope someone can help... suggest...

All are Grasso units...

SP1-TB-2B

Q=1598 kW

±0°/+40°C

N=408kW;n=3550RPM

60Hz;3x440V

SP1-VB-2B

Q=1373 kW

-9°/+40°C

N=450kW;n=3550RPM

60Hz;3x440V

SP1 MB-2B

Q=534 kW

-8°/+40°C

N=200kW;n=3550RPM

60Hz;3x440V

SP1 NB-2B

Q=907 kW

±0°/+40°C

N=250kW;n=3550RPM

60Hz;3x440V

or your "rule of thumb" suggestion;), or real one ... we made our calculation but......

... I'll come back later with explanation of this case...

thanks for help ....

Best regards, Josip :)

Hello Josip:)

SP1 2B TB 10" and 6"

SP1 VB 2B Same as above

SP1 MB 2B 6" and 3"

SP1 NB 2B 8" and 5"

Sizes using Dircal.

Kind Regards Andy D

Peter_1

12-09-2008, 06:48 AM

Assuming NH3 Andy?

Right Josip?

Peter_1

12-09-2008, 06:55 AM

Assuming NH3 Andy?

Right Josip?

I got for NH3, suction and discharge 8 m/s, 5 K SC and 5K SH

1. DN 300 (261) and DN200 (167)

2. DN 300 (286) and DN 65 (59)

3. DN 200 (175) and DN 100 (98)

4. DN 200 (196) and DN 125 (126)

Josip

12-09-2008, 11:18 AM

Hi, Andy and Peter_1 :)

....yes, ammonia ... I like that odour

thanks for answers.... we also used for calculation DirCalc, CoolPack and some old Stal programs and came to the same/similar results....

Something what I forgot to ask in my starting post...

....regarding refrigerant velocities within pipes .... for ammonia... applicable for other refrigerants too, but with different values for SH/SC .... we use those values ... of course you can always play with ;) ....

1. Discharge pipe 15 m/s ... ? max

2. Suction wet pipe 12 m/s .... ? max

3. Suction dry pipe 12 m/s ..... ? max

... not less than 8m/s for *****s... oil return

4. Liquid line/s o,3 -1m/s .... ? max

... "rule of thumb" is not the best, but ok if used as a "milestone"....

.... which values you use/recommend - kind of best practice quide .... where is the limit with high velocities ....

.... asking this because our client wants to use "capillary" tubes to reduce investment (turnkey contract)- of course, our client is not the owner and will not pay running cost later on .....

what do you think about.... for the moment we are calculating pipe sizes only for the first two compressors.... our client wants to use

SP1 2B TB Q=1598 kW 6" and 4"

SP1 VB 2B Q=1373 kW 5" and 3"

we are :confused: ....awaiting your comments....

.... developing this discussion during weekend maybe we can learn something here ...

Best regards, Josip :)

Assuming NH3 Andy?

Right Josip?

I got for NH3, suction and discharge 8 m/s, 5 K SC and 5K SH

1. DN 300 (261) and DN200 (167)

2. DN 300 (286) and DN 65 (59)

3. DN 200 (175) and DN 100 (98)

4. DN 200 (196) and DN 125 (126)

Hi Peter:)

yes I'm assuming Ammonia.

Kind Regards Andy

Hi, Andy and Peter_1 :)

....yes, ammonia ... I like that odour

thanks for answers.... we also used for calculation DirCalc, CoolPack and some old Stal programs and came to the same/similar results....

Something what I forgot to ask in my starting post...

....regarding refrigerant velocities within pipes .... for ammonia... applicable for other refrigerants too, but with different values for SH/SC .... we use those values ... of course you can always play with ;) ....

1. Discharge pipe 15 m/s ... ? max

2. Suction wet pipe 12 m/s .... ? max

3. Suction dry pipe 12 m/s ..... ? max

... not less than 8m/s for *****s... oil return

4. Liquid line/s o,3 -1m/s .... ? max

... "rule of thumb" is not the best, but ok if used as a "milestone"....

.... which values you use/recommend - kind of best practice quide .... where is the limit with high velocities ....

.... asking this because our client wants to use "capillary" tubes to reduce investment (turnkey contract)- of course, our client is not the owner and will not pay running cost later on .....

what do you think about.... for the moment we are calculating pipe sizes only for the first two compressors.... our client wants to use

SP1 2B TB Q=1598 kW 6" and 4"

SP1 VB 2B Q=1373 kW 5" and 3"

we are :confused: ....awaiting your comments....

.... developing this discussion during weekend maybe we can learn something here ...

Best regards, Josip :)

Hello Josip,

I suppose the velocity can be quite high, provided that the whole system penalty is below the design.

Say 2k for suctio and maybe 1k for discharge.

Still the sizes you quote sound very small, what are the velocities in the lines?

Kind Regards Andy :)

Josip

14-09-2008, 11:52 PM

Hi, Andy :)

Hello Josip,

I suppose the velocity can be quite high, provided that the whole system penalty is below the design.

Say 2k for suctio and maybe 1k for discharge.

Still the sizes you quote sound very small, what are the velocities in the lines?

Kind Regards Andy :)

Thanks for answer ...

...... yes sometimes we can use higher velocity or bigger pressure drop like on suction/discharge valve, but what about pipe/s before and after .... how high we can go? ....

SP1-TB-2B

Q=1598 kW

±0°/+40°C

6"= 20+ m/s

4"= 17 m/s

SP1-VB-2B

Q=1373 kW

-9°/+40°C

5"= 35+ m/s

3"= 24+ m/s

.... roughly .... with 5K (SH=SC)

... first proposal is ok, and that one was not a problem, but for second one .....

... anyhow you can see how far we are from, proposed 10" suction and 6" discharge ... this I will call "walking on the edge"

.... or maybe to use "optimal" pipes 8"/5" for the first compressor and 6"/4" for the second one...

... really waiting for some other members to contribute to this discussion and give some valuable comments, if ;) ... seems like forbidden area for discussion

... of course I realize this is completely industrial area and only a couple of RE members are in touch with plants of this size ....

Best regards, Josip :)

US Iceman

15-09-2008, 12:19 AM

I do not use velocity for my calculations. I prefer to use a maximum pressure loss of 2 psi (0.14 bar) for the entire equivalent length of pipe (which includes the valves & pipe fittings).

If the pressure loss is higher than the design values used when the equipment is selected, then the equipment performance will suffer. At high evaporating temperatures this has less of an effect than lower temperatures will have.

The one area where I might suggest the use of velocity is for liquid lines (< 350 feet/minute or ~ 1.8 m/sec.). This helps to limit the liquid velocity for potential issues related to liquid hammer when valves close.

Hope that helps...;)

Hi, Andy :)

Thanks for answer ...

...... yes sometimes we can use higher velocity or bigger pressure drop like on suction/discharge valve, but what about pipe/s before and after .... how high we can go? ....

SP1-TB-2B

Q=1598 kW

±0°/+40°C

6"= 20+ m/s

4"= 17 m/s

SP1-VB-2B

Q=1373 kW

-9°/+40°C

5"= 35+ m/s

3"= 24+ m/s

.... roughly .... with 5K (SH=SC)

... first proposal is ok, and that one was not a problem, but for second one .....

... anyhow you can see how far we are from, proposed 10" suction and 6" discharge ... this I will call "walking on the edge"

.... or maybe to use "optimal" pipes 8"/5" for the first compressor and 6"/4" for the second one...

... really waiting for some other members to contribute to this discussion and give some valuable comments, if ;) ... seems like forbidden area for discussion

... of course I realize this is completely industrial area and only a couple of RE members are in touch with plants of this size ....

Best regards, Josip :)

Hello Josip:)

I would be ok with the first set of pipes, but the second is way out. I would sugest that if you started the plant up with a 35m/s velocity in the suction you would hear the pressure drop:eek:

I would say an minimum of 8" (15.7m/s) and 5" (12.2m/s) for the 1371kw.

Probably best not to exceed 18m/s on the suction and say 14m/s on the discharge.

Large kit alright, I can only think of one or two plants in this size I have worked on either on the tools or the design side.

Kind Regards Andy

Josip

15-09-2008, 08:59 PM

Hi, US Iceman :)

I do not use velocity for my calculations. I prefer to use a maximum pressure loss of 2 psi (0.14 bar) for the entire equivalent length of pipe (which includes the valves & pipe fittings).

If the pressure loss is higher than the design values used when the equipment is selected, then the equipment performance will suffer. At high evaporating temperatures this has less of an effect than lower temperatures will have.

The one area where I might suggest the use of velocity is for liquid lines (< 350 feet/minute or ~ 1.8 m/sec.). This helps to limit the liquid velocity for potential issues related to liquid hammer when valves close.

Hope that helps...;)

.... of course, as always ;) .... thanks...

Best regards, Josip :)

Sinke

30-11-2008, 04:04 PM

...Hi Josipe...

...I have a few questions about compressors who made in our ex country...

....thanks...

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