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sagittarius
29-03-2006, 09:15 AM
Dear all,during designing the system of R290 I met some questions.
One important is the float level switch.When I select a fit switch.Many providers, such as Danfoss,Hansen,Parker etc.,cant provide the suit switch.The main reason is the density of propane under this condition is too low.about 0.54KG/L.Who can tell me the right provider?
Thanks a lot!
sagittarius

NoNickName
29-03-2006, 10:03 AM
The reason is not that one: switches for R290 and all other HC refrigerant have to be explosion proof, and the mentioned providers do not have the appropriate switch and do not take the responsibility.

US Iceman
29-03-2006, 05:41 PM
sagittarius,

Try Magnetrol. They can provide explosion proof switches on the mechanical floats. I have used these before on propane refrigeration systems. Just make sure the electrical connections, conduit, and other is appropriate for potentially explosive atmospheres.

Try this link for additional information:

http://www.magnetrol.com/us/html/view_pdf.asp?pdf=mii\238

The fluid density affects the actuation level of the switches.

sagittarius
30-03-2006, 02:15 AM
Thanks NoNickName and US Iceman.Yep,explosion proof is first mensioned thing.At the beginning of the case,Hansen replied there was suit type switch for me.He said the HLLC was right.but I looked it up in his handbook,only inert gas surround the switch for inhibiting corrosion,NoNickName is right,it is not explosion proof.other reason is that switch only for minimum density 0.6kg/l as same as Parker.Danfoss is to 0.4kg/l,but no explosion proof.
Thank US Iceman again.I try to connect them.
sagittarius

sagittarius
30-03-2006, 09:05 AM
How about Fisher?It is said very expensive?
I call the representative of magnetrol,they said the level difference of the normal Serials 75 float level switch couldn't be to 50mm. I use Danfoss's AKS38 in the ammonia system ago,the difference is set to 50mm.I don't know whether the same value is correct for propane.Standard magnetrol switch level difference is about 17mm. Is it enough?I think it is enough myself.On the condition the feed solenoid valve will act frequently.is it right?
tks.
sagittarius

sagittarius
30-03-2006, 09:30 AM
Another case is that the running condition is -35*C/14bar,must the material of switch chamber is 316 or 304?

US Iceman
30-03-2006, 02:34 PM
On the condition the feed solenoid valve will act frequently.is it right?

The frequency of the solenoid valve opening is only one aspect of this. The time to re-fill the vessel (to maintain a liquid level) depends on the hand expansion valve setting.

If the solenoid valve is cycling often then the hand expansion valve is too far open. The hand expansion valve needs to be adjusted so that the solenoid valve is open more than it is closed.

This provides a smoother suction pressure for control.

One other item you may wish to review is the Level-Trol and control valve from Fisher. These are expensive, but work very well. These are all pneumatic except for the AFR air-set solenoid. The AFR is the air filter/regulator for the control air to the device.

http://www.documentation.emersonprocess.com/groups/public/documents/instruction_manuals/d103219x012.pdf

EDIT: (this is the control valve that is used with the Level-Trol unit)

http://www.documentation.emersonprocess.com/groups/public/documents/product_fliers/d102414x412.pdf

I think Magnetrol also has a similar item.

Yes these are expensive, but worth the money for process cooling requirements in strict atmospheres.

US Iceman
30-03-2006, 02:39 PM
Another case is that the running condition is -35*C/14bar,must the material of switch chamber is 316 or 304?

This is something you must decide on, or, this could be required by customer specification.

If you are using the ASME B31.3 piping code (for process piping) the temperature limits are listed I believe.

Stainless steel is one way to deal with low temperatures. Another is impact tested material.

sagittarius
31-03-2006, 02:18 AM
Thank you,US Iceman.Your advice is very helpful to me.
Magnetrol have replied me and selected the float level switch.Scheme I:J75-2B20-HM3 - Sealed Cage External Float Level Switch,the level difference is set to 17mm;Scheme II: B74-2B30-HM3 - Sealed Cage External Displacer Level Switch,the LD is set to 67mm.I think the last one maybe right for me. To adjust the hand expansion valve will be in a wide range.Then the suction pressure is smoother.Is right?

US Iceman
31-03-2006, 02:51 AM
Hi,


To adjust the hand expansion valve will be in a wide range. Then the suction pressure is smoother

The hand expansion valve needs to be adjusted so that the liquid feed solenoid is feeding almost continuously during full load operation. The Fisher Level-Trol does just this. It controls the liquid level on a steady basis. By doing so the pressure in the vessel is relatively consistent.

If you use a float switch and hand expansion valve, the hand expansion valve needs to be adjusted to provide a similar response (steady flow).

If the solenoid valve is opening too frequently(with the hand expansion valve set too far open), the level changes in the vessel are increased too fast. By closing down the hand expansion valve during the liquid make-up cycle (solenoid on), the solenoid will stay open longer.

Refrigeration systems operate much better when the control response is slower.

On any of the propane systems I worked on we always used the Fisher control valves and Level-Trol. Always.

If the loads fluctuate a large amount you might also consider a two-stage liquid make-up control scheme. One level is the first to energize. If this valve cannot maintain a constant liquid level, a second solenoid valve is energized to feed additional liquid into the vessel.

This is also much better than one large valve.

One thing to be aware of. If the suction pressure changes rapidly, the boiling in the vessel is also rapid. This potentially violent boiling can cause the liquid level to rise in the float switch chambers or the displace cages.

I would recommend you use a hand expansion valve in the top equalizing line of the float switch. By adjusting this valve you can control how fast the vapor is vented on the float chamber. This keeps the float from creating nuisance trips.

sagittarius
31-03-2006, 09:58 AM
If the loads fluctuate a large amount you might also consider a two-stage liquid make-up control scheme. One level is the first to energize. If this valve cannot maintain a constant liquid level, a second solenoid valve is energized to feed additional liquid into the vessel.

Yep,I have select two-stage feed line.But the other line is fixed a hand valve.
Thank you very much, US Iceman.:)

US Iceman
31-03-2006, 03:43 PM
Yep,I have select two-stage feed line.But the other line is fixed a hand valve.

Both liquid lines feeding into the vessel should have a hand expansion valve to provide the pressure reduction necassary and metering.

The hand expansion valves should be installed after the solenoid valves.

sagittarius
03-04-2006, 01:36 AM
Yes,Both the feed lines have the hand expansion valve,only one line has the solenoid valve .I think the line no solenoid valve be used the standby ,Only using it when the normal feeding line runs out or something wrong.
I am a new designer to the propane system.I have many questions to the system. Maybe along the system running there are always questions. Thank you ,US Iceman and RE forum.
What about the lube?

US Iceman
03-04-2006, 02:02 AM
...only one line has the solenoid valve

OK, it seems the other hand expansion valve is provided as a bypass, if something happens to the main line with the solenoid.

The oil must be carefully selected for hydrocarbon refrigeration systems. The amount of oil dilution can be severe depending on the operating conditions.

Do the vessels and heat exchangers have oil recovery lines on them to return oil to the compressors? This is common problem with R-290 and R-1270 systems.

sagittarius
04-04-2006, 06:24 AM
Yes,the hand expansion valve to do that.I know that the oil recovery line have been set to the vessels of the system.The other thing confuses me-the sort of oil.I know the MO and alkyl benzene oil dissolves into the R290 deeply, on the contrary the PAG dissolves slightly.Whether the all sorts of oil be suit to the r290 or HCs?Now I selected the PAG for the propane system.

US Iceman
04-04-2006, 01:50 PM
The PAG oil should be OK. If you check the solubility curves of the oil you can determine the percent of dilution at the operating pressures and temperatures.

The amount of dilution at these conditions is the final impact on the oil viscosity, which is the main concern.

The diluted point for the viscosity should be checked so that the ultimate viscosity (at the dilution condition) is sufficient for the compressors.

NoNickName
04-04-2006, 07:40 PM
Mineral oil is also ok. SUNISO 3GS is fine, provided at least 25°K of useful superheat is granted.

US Iceman
04-04-2006, 08:09 PM
Are the compressors reciprocating or twin screws?

NoNickName
04-04-2006, 10:39 PM
Are the compressors reciprocating or twin screws?

If the question is asked to me, I was thinking about reciprocating.

sagittarius
05-04-2006, 03:25 AM
Thank you all for replying,US Iceman and NoNickName.
I think the mineral oil maybe used to air-conditioner condition,high evaporative temperature. and the PAG oil maybe suit to low temperature.Is right?
I describe the propane I designed working condition:
twin screws compressor
gravity cycling
condense temp.38*C
evaporate temp.-30*C
capacity 160kW
condensor and evaporator are all shell-tube exchanger
I don't know what will meet to me while running.I am nervous now about the system.

sagittarius

US Iceman
05-04-2006, 04:07 AM
sagittarius,

Can you provide a simple flow diagram of the system? That would help me to understand exactly what the system is.

Since you are running twin screws on this system, whose compressor are you using?

I have seen some propane systems where the oil cooling load is small enough that the discharge temperature can be too low. This results in oil foaming and carryover, if the discharge gas temperature is too low. Not enough discharge superheat to prevent oil dilution in the oil separator.

If your evaporator is a flooded shell & tube, the suction gas will be almost saturated. This can contribute to low oil cooling loads.

What type of oil cooling are you using on this compressor?

Is the screw compressor using an economiser cycle to pre-cool the liquid propane before feeding it into the evaporator?

Also, who designed the oil separator? Did the compressor manufacturer supply this, or did you build it?


Are the compressors reciprocating or twin screws?


If the question is asked to me, I was thinking about reciprocating.

Both are suitable if everything is designed properly.

sagittarius
09-04-2006, 04:38 AM
I have received the Email,Mike.After the CR2006 (China Refrigeration)in Shanghai,I'll be back.And continue discussing the problem.
The simple answer: domestic twin-screw compressor;shell and tube oil cooler,secondary agent is water.using an economiser.The details will be described in Email after 13th of April,maybe.

US Iceman
09-04-2006, 09:30 PM
When you have the opportunity, send whatever information you can and we will discuss it.

sagittarius
20-04-2006, 04:58 AM
Thank you Mike.I am back now. After the CR2006,I went to Guangzhou for a bid, LPG project.The project is to compress the LPG,using screw compressor.The main component of LPG is propane.

sagittarius
21-04-2006, 11:05 AM
I can't paste the picture on this web page,how to do?

sagittarius
27-04-2006, 01:51 AM
I want to discuss this tread deeply,but I can't paste the pid due to the limit of my web condition.How to do?

Andy
27-04-2006, 08:54 PM
Sagittarius:)

export the file out of CAD to bitmap, then use microsoft paint to cut down the pixel size.

Should work, or PM Peter he posts lots of web photos he is alway willing to help others:)

Kind Regards. Andy:)

sagittarius
30-04-2006, 04:49 AM
Thank you, Andy.On the now condition of "quick reply",using the above botton, "insert image",it will display dialogue box"Please enter the URL of your image",http://......Till this display, I can't understand how link to my image.I should ask PM Peter.I need grasp function.
I have emailed to Us Iceman,thank you again,US Iceman.The line you asked connect air seperator and oil reservor and seperator is used to lead the flash vapor to suction line.

sagittarius
26-05-2006, 06:51 AM
A new question about the refrigerant,what is the requirements of R290?concertration?purity?

US Iceman
26-05-2006, 02:35 PM
I will look for some information on the purity, etc.

One thing to consider is the transport of the propane. It is possible to get propane with some other gases in it. This may be caused by the transport vessel.

In some propane systems you can get refrigerant that has etylene and ethane in it. These other gases can separate and act as non-condensable gas in the system.

NoNickName
26-05-2006, 03:18 PM
R290 can be bought in vessels with 99.7 or 99.8% purity.
Impurities are other HC, besides it is complete dehydrated. In Italy it is sold by Rivoira and others.

sagittarius
27-05-2006, 05:22 AM
THank you all.I know the purity at least. Are there some criteria or standards,or requirements for the refrigerants? esp. HCs,R744? I am a beginner in the HCs.
I have the criteria of R22 in hand.It is difficult to find others.

US Iceman
27-05-2006, 06:50 PM
Here is a link to food grade CO2.

http://www.wittemann.com/techdocs/food_grade_co2.pdf

Still looking for the refrigerant grade specifications.

sagittarius
29-05-2006, 05:57 AM
Thank you US Iceman.I know a little about the grade Co2 ,because I have designed the grade Co2 compress unit for beverage.But I don't know if the grade Co2 is suit for refrigerant?
Anyway what about you have used for Propane system?

US Iceman
29-05-2006, 11:04 PM
Anyway what about you have used for Propane system?

When I worked for a manufacturer we just stated the need for refrigerant grade propane. I know that's not much help, but it is what I remember we did.

In some of the systems they simply used propane from the process. This gas sometimes had other gases mixed in that would separate out in the condenser and flash tanks sometimes, so they had to be purged.

I can't believe I'm having such a difficult time finding the specifications for refrigerant grade propane.

sagittarius
30-05-2006, 01:05 AM
Ok,I know that my customer just running propane system use the propane from the process.They decided it. I think that is my duty to advise customer to use what grade propane.So I put forward this question.

sagittarius
31-05-2006, 04:27 AM
I learn the Hydrocarbon purity level required 98%~99.5% as stated from the document of OORG (ozone operation resource group).