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View Full Version : Closed econimizer piping vs efficiency/proper function?







Tycho
09-09-2016, 05:26 PM
I recently visited a site where a competitor is installing a new NH3 freezing plant, it's going to be a beautiful plant, and I could see that a considerable amount of time had gone into planning the component placement and the pipe work and I can say that this is a system the plant owner is going to be very happy with.

I didn't take any pictures since the place was crawling with electricians and I didn't want any "oooh, your competitor was here, taking pictures of everything" when the supervisor came by.

As I was leaving, I met the supervisor and we ended up talking about the system for 30 minutes :)

I mentioned to him that I noticed something with the economizer vessel and how it was connected to the rest of the system and how it was different from how I would have connected it.

He said that this way was how they always connected it, and I didn't want to push the issue since we are competitors and that the place was crawling with electricians and to be honest, I wasn't sure if it would really matter for the efficiency of the economizer.


This is how it was connected:

14316

This is how I would have connected it:

14317

Theoretical plant data (taken from thin air :))

Condenser pressure: 20 - 25 C (70 - 77F)
Economizer pressure: -20 - -25C (-4 - - 7F)
Liquid sep. pressure: -38 C (-37F)

Temperature of liquid leaving the economizer: -20 C (-4F) (it's very efficient :))


Arguments:

-My way:

Counterflow, warm liquid from the condenser enter the coil at the top of the liquid level in the vessel and gets cooled down as it travels downwards, which I think makes for a more stable level and less surging in the vessel.

My way injects "warm" liquid from the receiver to the economizer, all the diagrams I have seen does it this way, would this decrease the efficiency of the economizer by injecting 20C liquid and causing an effect more like an LRI?


Their way:

Same way flow, warm liquid enters the bottom of the coil where the liquid outside the coil will be marginally colder than the liquid outside the coil at the top. In my mind this will cause a lot of boiling in the liquid and as the liquid inside the coil is traveling upwards it will be followed by gas bubbles in the liquid outside the coil, and this in my mind will mean less and less contact between the coil and the liquid outside that is supposed to sub-cool the liquid inside.

Their way injects sub-cooled liquid into the economizer, again, in my mind, maybe this counteracts the excess boiling.


Conclusion?

Is either way better than the other?

Would a combination of both ways make for a more efficient econimizer?

My way with counterflow and their way with injecting sub-cooled liquid?


What do you guys think?

mbc
09-09-2016, 07:56 PM
hi
1- sorry about my poor English.

As you know the name of this system is flash ECO.

both system is right

mostly all manufacturing Co. has 2 ed drawing

in first one you have a little extra load one ECO flash system ( by cooling amount of NH3 you use for charge flash tank) but you have a little more efficiency to cooling liquid is going to flash tank .


I used both system, both of them works

mbc
09-09-2016, 08:16 PM
hi again

from flash tank to compressor as you know you need STV- PM3 - STV

RANGER1
09-09-2016, 10:18 PM
Tycho,
We would do it your way, as for efficiencies who knows, surely not noticeable.
Unusual to subcool liquid that makes up level in economiser, except makeup valve might be a bit smaller
& save $1, then lose $100 to have to insulate it.
Maybe bypass line another expense we would not do, no real reason unless coil in economiser springs a leak (which does happen occasionally, once every 20 years, which our 20 years was up this year).

Tycho
09-09-2016, 10:55 PM
hi
1- sorry about my poor English.

As you know the name of this system is flash ECO.

both system is right

mostly all manufacturing Co. has 2 ed drawing

in first one you have a little extra load one ECO flash system ( by cooling amount of NH3 you use for charge flash tank) but you have a little more efficiency to cooling liquid is going to flash tank .


I used both system, both of them works

Hello mbc!

Thank you for your reply!

as a service technician, I saw myself that the two different ways may end up being just as efficiant.... But is there a right way to do it?

Tycho
09-09-2016, 11:03 PM
Tycho,
We would do it your way, as for efficiencies who knows, surely not noticeable.
Unusual to subcool liquid that makes up level in economiser, except makeup valve might be a bit smaller
& save $1, then lose $100 to have to insulate it.
Maybe bypass line another expense we would not do, no real reason unless coil in economiser springs a leak (which does happen occasionally, once every 20 years, which our 20 years was up this year).

I agree Ranger1! leak in the eco coil happens once every 20-200 years max. but what I have experienced is that instead of using a float valve, a danfoss level indicator is used instead, and they tend to fail and flood the economizer because they can't keep up with the boiling of the liquid, or the electronics fail...

Seriously, what if wrong with using a good old fashion float valve?


I was just wondering if flow-flow or counter flow would make any difference :D

RANGER1
09-09-2016, 11:38 PM
I agree Ranger1! leak in the eco coil happens once every 20-200 years max. but what I have experienced is that instead of using a float valve, a danfoss level indicator is used instead, and they tend to fail and flood the economizer because they can't keep up with the boiling of the liquid, or the electronics fail...

Seriously, what if wrong with using a good old fashion float valve?


I was just wondering if flow-flow or counter flow would make any difference :D

We would ALWAYS install a high level float switch as a back up on any vessel.
Previously used TEVA valve for liquid makeup, now not sure if we use TEVA or EVRA/ICM, depends how big system is.
TEVA cheap as no need for probes etc, just have to buy them in individual components these days.

cricri
11-09-2016, 07:55 PM
Hi Tycho,
Only one question about your drawings, HP liquid is coming from a condenser or a receiver?
If it is from condenser, both solutions are wrong....

mbc
12-09-2016, 12:21 PM
hi.
Dear cricri

it should comes from receiver ( liquid) NH3

Also I think float valve with Hi level it better than 2 level
in Float valve , you have stable pressure in ECO.

Tycho
19-09-2016, 05:53 PM
The liquid is coming from receiver, not condenser as I wrote :)

I was just making a quick sketch, which is also why there is no hi level float switch in the drawing :)


I have had bad experience using float valves, especially on ships where there is a lot of movement in the liquid and that has caused the float valve to open and allow liquid into the economizer to the point where it triggers high level switch.

We use a solenoid before the float valve to stop the feed on high level, but the high level also closes the feed to the compressor, so for the on board engineer to bleed down the economizer tank takes a lot of time because they have a thousand things going on :)

mbc
19-09-2016, 06:39 PM
Hi Tycho
they should have some thing to control the level in flash tank

you right in ship there is a lot of movement and solenoid before the float valve is a good idea

also I always use solenoid before the float valve and it run when system is working
it protect you system if you have a little bit leak in float valve

Also you can use the hi level to cut of low level power and it cut of solenoid before the float valve
so if some thing happens in low level hi cover it