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luissandoval
22-10-2009, 12:52 AM
Dear Guys:

I have a problem I need to install a wet suction line and i'm not sure how can i do this? i attach a drawing please somobody can tell me if this drawing is Ok.

Luis Sandoval.

Pd: I'm sorry my english is no good.

US Iceman
22-10-2009, 01:25 AM
Do not have two separate rises in the suction line. On each evaporator pipe the risers (vertical suction lines) such that a single vertical riser is used for each evaporator. Trying to lift liquid in two steps will create temperature control problems (as in evaporators may not produce rated capacity).

The risers have to be sized correctly for pulling liquid refrigerant up.

Another methods is to put the recirc. pump vessel by the evaporators. Let the liquid run into the vessel from the wet returns, then pipe the dry suction line back to the compressors.

It is easier to lift gas, than to lift liquid. And... the penalties and negative issues are almost eliminated!

Magoo
22-10-2009, 04:23 AM
I go along with US Iceman, put the accumulator at first level, and dry suction off that to compressor, double list wet suctions is huge penalty on line losses.

luissandoval
22-10-2009, 04:30 PM
Very much thanks guys for your soon answers, but in this project
i can't install the accumulator or recirc. pump vessel near the evaporators and i can't avoid to elevate the wet suction line there is another method that i can use maybe some with the pipes????

josef
22-10-2009, 05:20 PM
I do not see the problem

sterl
22-10-2009, 06:30 PM
This a Spiral Freezer? Single enclosure, same load on both coils?

This is going to come down to how liquid distributes ( on the delivery side) and subsequently is entrained under low loads....

If its a single, "hard" operated production freezer its possible to do....as (2) coils in (2) boxes then US Iceman is correct, take individual risers to the uppermost level. Other than that: Tell us more about what these coils are intended to do. And how they are constructed, that is Header Arrangement and Air Flow direction...

coolcmt
22-10-2009, 06:41 PM
Hi Luis

If this is the only way you can do the piping i would have done it like this (and it will work):
One wet suction pipe from each evaporator going all the way up to the highest point of the dn 200 pipe (at 7,4 meters), entering on top of that pipe.
And if you dont want to drain the oil manually from the evaporators, install a hot gas return pipe the same way, going from the bottom of the evaporator with the hot gas return valve placed there

I hope this will help you....

luissandoval
22-10-2009, 08:51 PM
there are two blast freezer one coil for each blast frezer the coils have the same capacity i attach another drawing is this better?

US Iceman
23-10-2009, 03:50 AM
I have not verified the pipe diameters, but that's the general idea. Take the lift all at once, not twice. You might also put some P-traps at the bottom of the riser to create a liquid seal. Once the trap seals with liquid, the gas will blow all of the liquid up the riser if it is sized correctly.

The downside to using suction risers in wet suction lines is this. You want smaller pipes than you would normally use so that a high velocity is created to move the liquid refrigerant. Unfortunately, this increase in gas velocity must be paid for by operating at lower suction pressures, which can create a huge capacity penalty for the compressor at low suction pressures.

Another idea is: Can you run the suction around the building back to the recirc. vessel? Just take one lift on the risers, then allow the liquid and gas to return by gravity. Just a thought for you to consider.;)

coolcmt
23-10-2009, 10:50 AM
Hi Luis

Your last drawing will be the best way to do it.
I have tried the piping size in Dircalc, and i would use dn 125 from each evaporator instead of dn 150. You will get 0,915K pressure loss, and 12,5 m/s speed. With dn 150 this will be 0,84K and 8,5 m/s. Little more pressure loss with dn 125, but more speed, and you will save some money when you buy pipes and valves.( Maybe you have allready bought it?).

Anyway, this is how i would have made the piping.....

Good luck!

luissandoval
23-10-2009, 03:30 PM
So much thanks guys.

This forum is great i understood how i have make teh piping. You are cool.

thanks again.

Magoo
27-10-2009, 12:55 AM
Do not forget P traps top and bottom.

oonal
27-10-2009, 08:18 PM
Hi,
In my opinion you should use double riser for wet suction line, otherwise you have alot of of problem due to liquid accumulation at main vertical side. You can use ASHRAE reccomendation for double riser piping design.

Regards

Önder

jeremynh3
28-10-2009, 08:57 PM
I have not verified the pipe diameters, but that's the general idea. Take the lift all at once, not twice. You might also put some P-traps at the bottom of the riser to create a liquid seal. Once the trap seals with liquid, the gas will blow all of the liquid up the riser if it is sized correctly.

The downside to using suction risers in wet suction lines is this. You want smaller pipes than you would normally use so that a high velocity is created to move the liquid refrigerant. Unfortunately, this increase in gas velocity must be paid for by operating at lower suction pressures, which can create a huge capacity penalty for the compressor at low suction pressures.

Another idea is: Can you run the suction around the building back to the recirc. vessel? Just take one lift on the risers, then allow the liquid and gas to return by gravity. Just a thought for you to consider.;)

Good advice,

I would agree, the traps on outlets with the proper line sizing for lift. Load or no load, the risers will fill with liquid at some point. The penalty taken do to higher velocity's and pressure drop(With smaller returns) is negligible in comparison to the penalty taken with static liquid height on those risers! I've done it with twice that lift. On that installation I installed sight glasses , gauges, thermometers to measure theoretical vs actual. My finding was the riser needs to much smaller than you calculate.

US Iceman
29-10-2009, 01:00 AM
My finding was the riser needs to much smaller than you calculate.


Especially if the evaporator loads tend to be less than full capacity for extended durations. If the risers are too big, the riser will flood out and contribute the static liquid head penalty once more.

coolcmt
29-10-2009, 07:59 PM
Hi guys

i`ve had a interesting discussion with my colleagues(the designers) at our office about this.
A blast freezer in a pump circulated system runs pretty much at full load all the time, therefore we can not see the big advantage with double risers and the P traps at the bottom in this case. We do think that the vertical wet suction line always will have a mixture of gas and boiling liquid. And the velocity will bring the liquid up if the pipe is sized correct. We have build a lot of pump sirc system with blast freezers\freeze tunnels for herring and salmon with lifts of 6-8 meters, and this have never been a problem.

The ideal thing off course would be to have the blast freezer at the 2nd floor so that the wet suction could go downwards, but that doesnt happend to often.

We have measured 1-1,5K loss from the bottom of the freezer to the compressor at some of our blast freezer plants, at full load. This is off course a penalty for the compressor, but this could not have been better with double risers and P traps at the bottom of the freezer?
Or are we totally wrong?

I might have to get this with a teaspoon:), i am not a designer, i am just the guy who build, start up and serve these plants.... and has never thought about this before when building blast freezers..


Coolcmt

Ps. i would just like to say that i think this forum is great!
:)

US Iceman
29-10-2009, 08:07 PM
If the blast freezer operates at full load all the time then double risers are not required. They are only needed when an evaporator operates at less than full load conditions. The smaller riser in a dual riser arrangement handles the reduced load condition and when this is surpassed by the load returning to 100% the other larger riser becomes active. Then both risers handle the full load condition.

Vlada
31-10-2009, 11:56 PM
In my opinion refrigeration engineers in this kind of installations must be in full collaboration with food production specialist. Blast freezer is meant to work in full load and everything must be organized in that way. So piping too. If somebody want 50% of production than better solution is to have two smaller blast freezers. Starting one freezer and having good product is hell of a job from a food part of installation so why do it for just 50% of a load?

Nevertheless, wet suction is meanly consist of gas and static hight is much lower than for liquid one. It is very difficult to make somekind of calculation. But in my logic 8m hight would do no harm in evaporation temperature and overall production.