3 replies to this topic

[ankur2061]

Dear All,

After looking around all over, I am still confused over the various configurations for reciprocating machines such as:

Single-Stage single-acting

Single-stage double-acting

Two-stage single-acting

Single-Stage Triple-acting

I would like to undertstand these configurations in terms of pictorial representation or an animated video / film showing these various configurations. Can somebody provide such a pictorial representation and / or an animated video / film regarding the reciprocating machine configuration.

Thanks and Regards,
Ankur.

[Zauberberg]

Ankur,

Try browsing the "You Tube" website. I was surprised myself to see what kind of technical information is available there.

See:


Some of the clips are taken from http://www.changent.ispeedway.com/

[Art Montemayor]

Ankur:

It is my opinion that the understandings and explanations surrounding the configurations of all possible reciprocating compressors has been – and remains – in much unneeded and wasteful confusion. I have always considered this a tragic and totally preventable situation that hinders and taxes all engineers, especially young graduates.

I have been working on putting together a detailed and simple Excel Workbook that serves to explain and describe the workings of all reciprocating compressors in order to clear the air and make engineers – especially young Chemical Engineers – aware of the uses and applications of these machines. Unfortunately, with the advent of passing years I have been separated from the operations arena and cast into the consulting/consulting sector. This change in priorities has left me with little room and time to concentrate and finish what I have wanted to communicate and pass on.

It is indeed a pity that this very important subject is scarcely mentioned in the university ChE courses and much less understood by the leading ChE instructors of such courses. Mechanical engineers stand a better chance of being exposed to this knowledge, but they are currently being directed towards centrifugal machines instead. No matter what others may think or theorize, positive displacement machines – especially reciprocating compressors – are here to stay. There is no other invention or device that can handle or attack the problem of elevating gases to pressures in excess of 100 to 200 bargs (especially gases such as Hydrogen) with a maximum of thermodynamic efficiency and simple, direct process controls. There are many gas compression applications where centrifugals simply cannot be applied. And due to many centrifugal shortcomings, this will persist into the future, in my opinion. The reciprocating machine continues to play the part of the “threshold” into gas thermodynamics by offering a simple, direct, and straight-forward understanding of gas compression and its measurement. It’s drawbacks and trade-offs, unfortunately, fall outside of the Chemical Engineering realm in the academic circles and consequently we are left to their exposure once we are in the competitive industrial arena. There is a gap of very important mechanical information that is lacking in Chemical Engineering training, and this area is a significant part of it.

Before attempting to explain the features that you describe, I would emphasize that the mechanical design features of a reciprocating compressor – and their practical importance – should first be well-understood in order to proceed forward with a complete understanding of the various configuration features. For example, allow me to ask what is a “Single-Stage Triple-acting” reciprocating compressor? I ask, not because I never have heard of such a device but because it goes entirely against the basic definition of a compression cylinder’s action. (could it be that you are merely introducing levity to draw our attention?). The basic definition of cylinder action is: A specific piston operating in a specific cylinder can compress gas in either of its TWO faces (defined as the HEAD end and the CRANK end). There can be no third face of a reciprocating piston – as determined by inherent design and definition. Consequently there can be no “Triple” action.

Reciprocating compressor simulation and You Tube videos are great materials for engineers to study and visually get acquainted with. However, they are far too terse and overly simplified in their explanations – without allowing the audience to ponder, inquire, ask relevant questions, and inquire as to advantages and disadvantages. I have yet to see or experience a thorough and instructive video on reciprocating compressors that would allow a chemical engineer the ability to walk out afterwards feeling secure that the workings, design, configuration, and applications have been thoroughly understood and digested. This is what is presently lacking and gives the compressor manufacturers the upper hand in selling what they want to sell – and not specifically what the user NEEDS OR REQUIRES. This is not to put blame on the manufacturers; the responsibility of understanding what is needed and required is in the hands of the user. If the user (or his representative – such as we engineers) does not make it a point to become dominant in understanding and applying these machines, no one else will. Unfortunately, the typical You Tube videos don’t go into the real important details that affect operation, control, safety, and ultimate control. They are overly-simplified and don’t focus on the real important features or explanations that lead to the practical need for different configurations and their advantages/disadvantages.

I have offered explanations and illustrations of some reciprocating compressor configurations in our Forums from time-to-time, as the opportunity has presented itself. Witness, for example: http://www.cheresour...pacity-control/

Here you will find a typical balance-opposed, double-acting reciprocating compressor illustrated. A similar, single-acting version is a simple modification of the same configuration.

The quantity of stages that a reciprocating compressor has is determined in large part by the over-all compression ratio it has to comply with. The quantity of compression stages plays a large part in determining the model, configuration, and size of the over-all machine. Many mechanical engineering important details immediately become priorities to resolve – such as balance, pulsation control, crank-end and cylinder lubrication, power transmission, etc., etc.. Regardless of his/her background, a Chemical Engineer MUST thoroughly understand and dominate the lubrication design and requirements of a reciprocating compressor if he is to specify, operate it, or supervise its operation. The success of his operation depends on his/her ability to understand and apply proper lubrication to all the key and critical components. And to do that, he/she must know and understand what components are the important ones and why.

This, in my humble opinion, is a never-ending subject and is liable to continue for some time. It nevertheless is one of my favorite subjects because it forms part of many interesting and successful encounters in the first half of my engineering career. I have many memories and fond recollections of problems, situations, applications, modifications, and people. I would gladly share my experiences with whosoever has need of such matter and perhaps I will go back to trying to finish the Workbook that I started some time back.

[mrdear23]

Hiii Mr Ankur:

This is my first reply on this site. I don't have the Pictorial Representations but I can surely help in making the pictures in mind.

Stage: One cylinder cannot act as more than one stage, However More than one cylinder can act as one stage. The easiest way to find the no. of stages is to locate no. of Suction volume bottles since both are same in no. Also, between two stages there must be an intercooler, since the prime objective of staging is to reduce the discharge temperature and thsu making the machine more efficient.

It means that Compressor may have 4 cylinders but only three stages.
No. of stages = No. of Suction Volume Bottles = No. of discharge volume bottles = (No of Interstage coolers-1)

Single acting: When piston produces Compression on only one side of a cylinder.

Double acting: When Piston produces Compression on both sides of a cylinder.

Triple acting: I may be incorrect but i find No logic in triple acting cylinder, means it is impossible as piston can have maximum two sides to compress on. Please recheck.

Single stage Single acting: Logically: Any No of Cylinders (each single acting) with any type of configuration, however generally such configurations are single cylinder on one side of crank shaft.

Single stage Double acting: Logically Any No. of cylinders with different configurations, However generally such configuartions are two cylinder balanced opposed, both cylinders double acting.

I mean to say that the configuration is not decided on only Stages and single or double acting. It is decided on the Flow rates, Head ,,,, balancing of forces ,,,, Discherge temeratures etc,.....
Hope it clarifies...

mrdear23