Tandem Compressors

[Sawsan311]

Dears,

I need to know about tandem compressors and how they are different from back to back compressors, do tandem compressors mean compression stages located within the same casing and having a common seal gas system with a a balance line between the two stages?

thanks

 

[quadtracker]

I am only familiar with one Tandem centrifugal compressor package which included 3 separate centrifugal compressor casings driven by one Gas Turbine. The first low pressure stage (LP) compressor was directly driven from the gas turbine. The second intermediate pressure stage (IP) was driven by a high speed gearbox driven from the output shaft from the (LP) compressor. The third high pressure stage (HP)compressor was directly driven by the output shaft from the (IP) compressor. Compressed Gas flowed from the (LP) compressor discharge through an outside gas cooler then back into the (IP) compressor suction. From the discharge of the (IP) compressor the gas flowed through a gas cooler and into the (HP) compressor suction. From the (HP) compressor discharge the gas flowed through the gas cooler through the gas dehydration process then down the sales line. Each compressor casing had its own seal gas system and there was no outer balance line.

 

[rotw]

A matter of definition.
Tandem can mean several casings organized in serie (process compression sequence) on same shaft / train line.
You can also have two sections in serie on a single casing not necessarily arranged in back to back. But this is called inline arrangement. In back to back compressors, it can occur that the pressure differential is relatively high between outlets of each section. Some licensors for example do not want that, they would ask for inline arrangement.

Life is not about waiting for the storm to pass. It's about learning dance in the rain.

 

[Sawsan311]

Thanks all, So tandem compressors can involve compression stages within a single casing and can also be with separate casing??, however in both cases it is one shaft driver and same seal system??

We decide to have a combined settle out between the compression stages as long as they have a a balance line for their common seal system within the same casing. Yet, if separate casings adapted but driven with the same shaft , then also combined settle put to be considered due to the leakage across the shaft's balance piston/drum?

Appreciate your views.

 

[rotw]

Yet, if separate casings adapted but driven with the same shaft , then also combined settle put to be considered due to the leakage across the shaft's balance piston/drum?

can you clarify?

Life is not about waiting for the storm to pass. It's about learning dance in the rain.

 

[Sawsan311]

Hi Mr.Rotw,

I came across the fact that balance drums/piston as well as division walls in back to back compressors have a balance line from compressor discharge side at the shaft end back to the low pressure suction side. Is the settle out pressure for stages driven by the same shaft also driven by this balance drum? Or that the combined settle out pressure is only driven by having the various stages within the same casing.

I have experienced designs with two compressor stages/sections driven by the same shaft but fitted in separate casing with separate seal gas system but still with a combined settle out instructed by vendor.

Also I would like to ask about the difference between seal balance and gas balance within the same compressor section.

Regards,

 

[rotw]

sorry for late.

I came across the fact that balance drums/piston as well as division walls in back to back compressors have a balance line from compressor discharge side at the shaft end back to the low pressure suction side. Is the settle out pressure for stages driven by the same shaft also driven by this balance drum? Or that the combined settle out pressure is only driven by having the various stages within the same casing.

For interstate balance piston, the balance flow goes from discharge 2nd stage to discharge first stage. The line is not external (does not run 'around' the casing). At stop, both leakages (shaft end and interstate drums) will contribute to establish an equalized pressure in the two casing compartments.

I have experienced designs with two compressor stages/sections driven by the same shaft but fitted in separate casing with separate seal gas system but still with a combined settle out instructed by vendor.

Like explained in another thread I guess, the casing's pressures can equalize via process too (not tight shut off valve, check valves, etc.).

Also I would like to ask about the difference between seal balance and gas balance within the same compressor section.

Not sure about what you mean. Try check 1st response, possibly there is some element of answer. Otherwise please re-clarify or give more context.