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faryuki
30-03-2007, 09:20 AM
Hi everybody,

i need your help. i have a refrigration system for soft dring, recently the system is use one compressor and shell and tube as evaporator for cooling the glycol. Now i have a problem whith fluctuation glycol outlet temperature from evaporator. The system is use a hotgas bypass injection for evaporator to prevent the glycol freezing. So i need your experience, how to maintain the glycol temp not fluctuation

thank you before

lana
30-03-2007, 09:39 AM
Hi Faryuki,

Why would the glycol freez?:confused:
Maybe the hot gas by-pass system is for capacity control.
If the temp is flactuating then the hot gas system is malfunctioning.
Also check the suction pressure. Is it fluctuating a lot? If so, maybe the TEV has a problem.
Keep us posted.
Cheers:)

NoNickName
30-03-2007, 10:28 AM
I assume propylene glycol is used for human beverage production. 30% PG does not freeze until -14°C. When that happens, only ice crystals are formed, like miniscule hail grains.
I don't see the point of the whole system.

Toolman
31-03-2007, 03:43 AM
I assume propylene glycol is used for human beverage production. 30% PG does not freeze until -14°C. When that happens, only ice crystals are formed, like miniscule hail grains.
I don't see the point of the whole system.

Remove current Glycol and add a new batch ( is there any specs on the required quantity ) sounds like theres too much water in the mix this will make ity freeze quick smart .
:D

Toolman
31-03-2007, 03:55 AM
NoNickName is correct

Peter_1
31-03-2007, 08:06 AM
Is the glycol flow constant, is suction pressure/temperature constant, do you hear the hot ghass bypass making noise (sissing)

faryuki
12-04-2007, 02:45 AM
thank you for your kind advice, i will consider and try.

many thanks..

TXiceman
13-04-2007, 02:55 AM
As hinted above, first check your glycol flow. You can use a manometer across the chiller to see if you flow is constant. If you have users which are opening and closing feed valves, it is quiet likely that the flow will vary and the leaving temp will follow.

What kind of feed controls do you have on the evaporator. Also what kind of hotgas valve is used and where is the sensing port conected.

You do need to check your glycol concentration to see if you are well away from the "freeze" point.

Put a good pressure gauge on the refrigerant side of the evaporator and see what is happening to the pressure.

Ken

Vernon
15-04-2007, 03:05 PM
Faryuki

1) First all what temperature Glycol do you need?
2) What is your average suction pressure of your separation vessel?
3) At what pressure does your hot gas start injecting into your liquid in the separation vessel?
4) What is the specific gravity of your Glycol water mixture?

Vernon

faryuki
17-04-2007, 03:16 AM
) First all what temperature Glycol do you need? 0.5 degC
2) What is your average suction pressure of your separation vessel? 2.5 kgf/cm2
3) At what pressure does your hot gas start injecting into your liquid in the separation vessel? hotgas is control by glycol outlet temp. if glycol temp reach -3 degC hotgas on.
4) What is the specific gravity of your Glycol water mixture? glycol is measure by percentage not by specivic gravity, the percentage is 30%.

faryuki
17-04-2007, 03:21 AM
Hi Faryuki,

Why would the glycol freez?:confused:
Maybe the hot gas by-pass system is for capacity control.
If the temp is flactuating then the hot gas system is malfunctioning.
Also check the suction pressure. Is it fluctuating a lot? If so, maybe the TEV has a problem.
Keep us posted.
Cheers:)

Dear Iana,

Hotgas bypass is for maintain the glycol temp. is 0.5 degC also to prevent freezing of glycol.
The expansion is use float valve also to control the level ammonia at the evaporator.

many thanks

lana
17-04-2007, 03:39 PM
I am not familiar with float valves so I can not say anything. I hope ammonia guys will give you some good advise.
Cheers:)

US Iceman
17-04-2007, 04:18 PM
The expansion is use Float Valve (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=177) also to Control (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=144) the level ammonia at the evaporator.


Sounds like a low side float valve to control the liquid level in the evaporator/surge drum.

Lana, this float valve is the same as a float mechanism for toilets. As the water level in the tank decreases, the float valve opens up to allow more liquid to flow in. They just maintain a liquid level in whatever space the float exists in.

TXiceman
18-04-2007, 03:59 AM
) First all what temperature Glycol do you need? 0.5 degC
2) What is your average suction pressure of your separation vessel? 2.5 kgf/cm2
3) At what pressure does your hot gas start injecting into your liquid in the separation vessel? hotgas is control by glycol outlet temp. if glycol temp reach -3 degC hotgas on.
4) What is the specific gravity of your Glycol water mixture? glycol is measure by percentage not by specivic gravity, the percentage is 30%.



Specific gravity is an indication of the concentration. When you indicate "by percentage" you have to specify if it is by weight or volume...there is a difference.

In order to properly check the concentration, you have to get a specific gravity reading at a temperature. You look in a chart of table for the gravity and temperature and you get a concentration and a freeze point.

There is still not enough info to begin trouble shooting.
I am beginning to think you are seeing a situation where your hot-gas control and liquid fed valves are fight each other.

What type and brand of hot-gas control and liquid feed control are you using?

Ken

Vernon
21-04-2007, 03:44 PM
Faryuki

My five cents worth I hope this will be of assistance to you, this will work if your system is sized correctly for your required load and if your glycol mix is correct. Beverage cooling requirements are normally very erratic when coupled to a bottling line, the load is very direct. When the bottling line starts your refrigeration requirements peaks and as quickly drops to nothing when the bottling line stops. There are many people with years of knowledge in this forum and I am sure they will agree or correct me to ensure you get the best help possible.

1) You know you require a glycol temperature of 0.5 °C.
2) Your compressor capacity control is set to maintain a suction pressure of 2.5 bar absolute. (2.5 kgf/cm2)
3) Your plant has a single compressor and is connected to one shell and tube cooler and the liquid level in your separation vessel is controlled by a level control controlling your liquid line solenoid.
4) In order to maintain the above glycol temperature I would suggest you adjust your back pressure regulator on your wet suction line between your separation vessel and compressor regulating the ammonia pressure in you separation vessel at 3.8 bar absolute allowing your ammonia to reach a minimum temperature of -3 °C. This doubles as a safety keeping your ammonia pressure from dropping to low causing your glycol to freeze..
5) On your hot gas line you should have a hand expansion valve (Hand regulator valve)
6) Installing a pressure control (Danfoss RT 1 A auto reset) onto your separation vessel to replace your thermostat you are currently using to use to open and close your hot gas injection with when the Glycol temperature reaches -3 °C.
7) This pressure switch can be set to activate your hot gas injection line at 4.3 bar absolute with a differential setting of 0.2 bar, and by adjusting your hand expansion valve on this line you can adjust the hot gas to gently inject into the liquid ammonia allowing the ammonia pressure to stay at a reasonable constant pressure also allowing you to maintain a constant glycol temperature.
8) Depending on how efficient your glycol cooler is this should give you a glycol temperature of around 0 to 1 °C, should you require the glycol to be colder set the pressure switch setting (Proposed setting 4.3 bar) down in increments of 0.1 bar and if you require warmer set the pressure switch up in increments of 0.1 bar.
9) To smooth out the effect of starting and stopping of your bottling line on your refrigeration system which effects your glycol temperature, I would also recommend you fit a hot and cold well buffer tank that holds additional glycol. By doing this you have additional cooled glycol in storage allowing your refrigeration system to react to temperature changes in your glycol quicker and maintain your required temperature.
10) Mixing glycol with water by percentage volume can be done accurately when the glycol is added to the system for the first time, as you loose glycol and water, water is added to maintain the correct glycol level in the system. One can very quickly loose track of what was added when, and this is why it is better to measure the specific gravity of your glycol mixture,
11) I have charts for the measurement of specific gravity for various different types of glycol, should you indicate what glycol you are using I will email a chart to you. You will have to obtain a hydrometer to measure the specific gravity. As correctly indicated by Ken the charts are setup to measure your specific gravity of your glycol mix at a fixed temperature which will be clearly indicated on the chart.

Regards

Vernon