dear syaChAh,

The Atlas Copco ZT 37 AC is a two stage oil free screw compressor.

To reach 7.5 bar(o) it is necessary to use a 2-stage configuration in order to keep the compression temperatures within limits.

The intermediate cooling controls the intermediate pressure between the first stage and the second stage compressor.

The first stage compressor volume and the second stage compressor volume are tuned to each other by design at a chosen intermediate pressure and intermediate temperature.

The internal leakage of the second stage can increase by time due to the wearing of the screw gap. The second stage will compress less air then the first stage and the intermediate pressure rises and becomes hotter.

If the cooling is not functioning properly (too hot cooling medium, dirty cooler) then the intermediate temperature rises as well as the intermediate pressure.

The first thing to do now is to measure the intermediate pressure and temperature and compare those measurements with the data sheets.

And call in an Atlas Copco service expert.

best regards

Teus ■

Dear SYachah ,

You did not mention that you have checked the intermediate pressure.

If the intermediate pressure rises above the specification pressure and the cooling is functioning properly, then the screws could be worn too much, causing internal leakage and heating up.

When screws are worn out, there is only one remedy (other than running at a lower load for a while):

Consult Atlas Copco and eventually replace the rotors

best regards

Teus ■

I have always found Atlas Copco aloof & uncoordinated at the top end of their machinery range. Customers & potential customers, & myself when I worked there, get shunted between Belgium & Sweden as if they were adjacent stations on an urban metro. The whole operation runs like a multi-lingual call centre.

After you've got the A-C prices for a rotor set you'd better buy an extra spare (don't forget to store it on end) just in case A-C drop out of the heavy side marketplace in the interim. You're working on 4 year increments; don't forget.

You might also like to compare the replacement rotor price against the excellent Japanese (Mycom) & Scottish (Howden) alternatives for complete new units. ■

Dear SYachah ,

"german technology"

Is that Aerzen technology ?

best regards

teus ■

Dear syachah,

Another manufacturer in Germany is GHH Rand.

A screw compressor consists of 2 rotor screws, paired together with the gas intake at one end and the outlet at the other end.

Before the formed gas chamber is released to the outlet, the chamber is reduced in size against the end shield of the screw housing, thereby internally compressing the gas.

The rotors are not touching each other, thereby leaving a gap that causes the internal leakage.

An oil free screw compressor compresses the gas in this way. The compression is abiabatic + isochoric.

An oil injected compressor uses the injected oil for 2 purposes:

1)

The oil seals the rotor clearances, thereby improving the volumetric efficiency considerably.

High compression temperatures limit the compression ratio of one stage.

2)

Cooling the compressed air

The compression is the isothermal + isochoric. (Causing energy savings)

The oil is removed from the gas stream, cooled and re-injected again

Due to the isothermal compression, higher pressure ratios in one stage are possible.

It is your process that requires oil free compressed gas (medical or food applications) or whether it can accept a trace of oil in the gas flow.

If the process can accept some oil than the oil injected screw compressor is preferred.

BR

Teus ■

Kind attention Teus Tuinenburg

If not forgot ihd lot of conversation regarding compressor with yoy

well this time i comeup with some new queries related to densephase conveying system

One of my client has problem with conveying of ash ie our design was to convey 80tph ash to the silo instead which he is able to convey 30tph 60% less than design

As per our design structure he must use air 14m3/min @3bar which he is able to maintain , but since he is not able to convey the same as per their requirement that makes them unhappy with system

Actually why iam emphasizing on this matter ie, in densephase flow rate of material is 3m/s

.In their system conveying time is 120sec and length of conveying is probably not more than 100Mtr Now since flow rate is 3m/s they must have the distance of conveying 3x120=360mtr which is not there

Kindly forgive me if iam wrong but i want to keep my self on the same track ie wat would be the effect on the system if situation comes out to be like this

Thanx in anticipation

regards

rahul ■

Dear Rahul,

As you will understand, it is very difficult (impossible) to analyze a built system and its design without the relevant data available.

From the decision to build a system until the realization, many steps are taken and each step can be the source of a not expected performance.

First thing to do is to check and measure if possible, whether all the field parameters match with the design parameters.

Conclusion: more info needed.

best regards

Teus

PS: As this thread is about 2-stage screw compressors it would be better to create a new thread with your question about the pneumatic ash conveying installation. ■

Dear teus

As per your mail u hve asked for various parameters whether is matching or not, sir lets forget about their parameters as they are new to this system and perhabs may not be able to match all our input design paparemeter

But my worry is

In their system conveying time is 120sec and length of conveying is probably not more than 100Mtr . Now since velocity of conveying is 3m/s , they must have the distance of conveying 3x120=360mtr which is not there

wat would be the effect on the system if situation comes out to be like this ie if distance of conveying is much lesser rather it require more as per our design.

regards

rahul ■

Dear Rahul,

If a built system does not perform as expected, there can be a variety of reasons.

Are the conveyed material conveying properties the same as the material conveying properties that are used in the design?

Is the installation built as designed (Or was it designed as built?)

If the capacity of the built installation is too low, then the installation should become bigger.

Compressor size and pipe diameter are linked by the suspension velocity of the material and/or the chosen velocities and pressures.

Again: without relevant data it is not possible to make statements.

best regards

teus

PS: As this thread is about 2-stage screw compressors it is better to create a new thread with your question about the pneumatic ash conveying installation ■

To add to what valuable information my dear freind Teus has given to you:

You shold strongly consider and hastily change the cooling radiators in your air compressor system in due haste as the radiators may be and most likely are plugged from oil sludge;

if not you risk the definet possibility of an exploding air compressor system due to internal blockage in the coolers. ■

Dear Syachah, Hello Leon,

A blocked intermediate cooler at the pressure side can cause indeed a considerable pressure rise at the inlet of the cooler and thereby a temperature rize.

Also the pressure drop over the cooler increases.

That is why I asked for pressure readings in my previous replies.

But, being a little bit experienced with AC compressors, I am almost certain that the ELRKTRIKON control display would monitor that as an alarm. And it should be also possible to read the required information from that display (Although it might need some complicated scrolling).

How the cooler could be contaminated inside with clean and oil free air and inlet filters is another issue .

have a nice day ■

Dear syachah

If you visit the website of Atlas Copco :

href="http://www.atlascopco.com" target="blank">www.atlascopco.com

then you will find all the basic information about your oil free compressor.

The 2 compressors are designed in series ( 2-stage compression)

happy new year

teus

Attachments

atlascopcozt (JPG)

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Dear,

Please note that by two stage compression it is meant that the compressor is doing the required compression in two stages i.e if te discharge pressure is z = x + y. Then first stage willl do x and second stage will do y. while as Sir Teus had alrady told their is some intermediate compression because of the the cooling process.

Regards

Sachin Kr. Arora ■

Hello,

interesting, the ZT is actually a hook and claw type compressor - not a helical screw. The overall flow and pressure situation does not change much. Since the ZT appears to be completely air cooled (discharge air and lube oil), it would seem that the trouble is related to either larger than normal air end clearances, or the interstage air cooler is still somehow plugged. The previous repliers provided you with excellent advice by recommending to review all the air pressures and temperaturs. Did you have any luck with calling AC's local service guys? Going back to the manufacturer usually provides you with the shortest route to finding root cause of a problem.

By the way, Aerzen has a oil free rotary screw solution above 60KW - but not anything to substiture this one.

Mehrer Kompressoren Germany also make oil free packages package. I believe they use GHH air ends. I did not see a rep in the Maylasia region though. ■

Hi Syachah,

GMBH in Germany stands for something like Corporation. GHH stands for GuteHoffnungsHuette and they are part of the Ingersoll Rand brand.

They are global company and can be found under http://www.ghh-rand.com/IS/category....aspx-en-18343

As far as your intention to buy an oil flooded screw compressor is concerned, I am concerned that someone would sell you this technology as "oil free". In the compressor marketing world this has sometimes been used incorectly as normal single stage oil flooded screw compressors will still carry over around 5 ppm of oil in form of an Aerosol. This is very difficult to remove even with the best of after treatment, which also usually increases your daily operation cost - which is really where you spend the majority of your money in the service life of any compressor.

If you can tolerate some oil in your air stream your world opened up to many, many compressor manufacturers. I can recommend Boge compressors www.boge.com This company makes pretty cool machines in oil free and oil flooded designs as well.

I hope this helped a little. ■

Dear syachah,

GHH Rand is a manufacturer (use the internet)

GMBH is German and means “Gemeinschaft Mit Beschraenkter Haftung“ and is an enterprise form with limited responsibilities. (Ltd).

If your compressed air is used in food- or medical processes, be careful that you have sufficient prove from the supplier that his system is approved, guaranteed or even licensed.

Nobody wants an oily pill.

Take care

teus ■

Dear Mr. Syachah,

I want to clarify what is oil free air

If the hydro carbon content in the air is less than or equivalent to 0.01 mg/m3 it is Class 1 of ISO 8573 - 1.

Even if you are using a non lube compressor, the compressor is sucking air which are having hyderocarbons in the air. It is pressurising the same air and the concentration of the hydrocarbons increases. The out let of the air is not oil free even you use a non lube compressor. Filtration system has to be used for a non lube machine

However you have completed 4 years and the air end has to be replaced. for the cost of the air end replacement you can plan for a lubricated machine with good filtration system. You can save energy and lesser maint. cost when compared to non lube.

COmpressor - Reciever - Dryer -MF- ACF you can get an air quality of 0.001 mg/m3 hydrocarbon content in the air (Which is almost zero).

If you have any quiries pls. mail me on pneumaticsolutions@gmail.com

Warm Regards

Varun ■

Dear syachch,

we market Kaeser air compressors in india. Kaeser is 90 yers old german company. Kaeser is user friendly and energy efficient.

If you are interested we will send you the contact details in your area.

warm regards

Varun

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