5 replies to this topic

[keby9]

Dear all,

 

How do I simulate 2-stage reciprocating compressor (contains first and second stage cylinders in single compressor) with the same specified RPM. The first stage compressor allows me to specify the RPM and it auto generates the mass flow rate intake. However when the outlet of  1st stage compressor connects to 2nd stage , it's unable to specify the RPM (overspecified Molar flow for 2nd stage feed stream).

 

http://www.filedropper.com/casestudy

The link above contains the simulation file

 

Thank you

Attached Files

•  1.JPG   89.97KB   24 downloads

[Bobby Strain]

Have you tried anything to resolve the issue? Engineers are supposed to solve problems. This one should be simple for you.

 

Bobby

[keby9]

@BobbyStrain, I tried to disconnect the connection between 1st and 2nd stage, separately simulate the stages at the same RPM. Both mmscfd arent the same for 1st and 2nd stages. Maybe I keyed in the wrong compressor design specs. Any advice on this matter?

[Bobby Strain]

You can add a controller and vary clearance, for example, and adjust it until the rpm matches.

Bobby

[Lucian Gomoescu]

Hello,

First of all, i have to mention that the capacity (more specifically, the mass flow rate)
delivered by a reciprocating compressor cylinder depends on the following parameters and
conditions:
- cylinder volume and piston action type;
- cylinder volumetric efficiency (depends on suction valve, cylinder geometry and Variable Volume

Pocket);
- speed;
- gas mass density (inlet gas T, P and MW)

In the attached snapshot is the HYSYS PFD for the following situation:
Two cylinders with double acting pistons have the same geometry, clearance etc specified at
Settings in Design tab after Reciprocating Compressor radio button is checked.

An ADJ block (ADJ1) is used to set the 2nd stage speed equal to the 1st stage speed (condition
which has to be fulfilled because pistons share the same shaft with no gearbox in between) by
adjusting the interstage pressure. Naturally, for a steady state there is an unique pressure
which satisfy the equality: mass_flow_out_stage1 = mass_flow_in_stage2.

The same flowsheet configuration can be applied for cylinders with different geometry and clearances.

To summarize the main variables type:
- speed is dependent;
- interstage pressure is dependent;
- inlet T, P and outlet P are independent.

@ Bobby:

Also this is a solution, but for a different scenario (clearance adjusted, interstage pressure
specified by user - which is not natural).

 Two Stage Recip Compressor.PNG   114.5KB   51 downloads

[Yogesh_Bhintade]

You must link two compressors in the Design Tab, this allows to run both stages with same rpm.

 

Thanks

Yogesh