16 replies to this topic

[yassgh]

Dear All,

 

Can I use the depressuring utility from HYSYS steady model to study the depressurization of multistage reciprocating compressor?

I NEED YOUR HEPL PLEASE.

 

Best Regards;

 

 

[fallah]

 

Can I use the depressuring utility from HYSYS steady model to study the depressurization of multistage reciprocating compressor?

I NEED YOUR HEPL PLEASE.

 

 

yassgh,

 

If there is a recycle valve around the compressors stages which opens after every shutdown, and the suction of 1st stage and the discharge of last stage can be subject to a settle out pressure a while after shutdown; then the isolated volume including the 1st suction drum might be same as the model based on which depressuring can be studied by using HYSYS utilities in an dynamic/unsteady simulation...
 

[yassgh]

thank you Fallah,

 

in our case, we have a BDV installed on the downstream of fourth stage and it will be opened after every SD. then the compressor will not reach the settle out pressure.

 

I look to calculate the peak flow of derpressurization. 

 

Best regards;

[fallah]

 

in our case, we have a BDV installed on the downstream of fourth stage and it will be opened after every SD. then the compressor will not reach the settle out pressure.

 

I look to calculate the peak flow of derpressurization. 

 

 

yassgh,

 

The pressurized discharge side, without settling the pressure out, can be depressurized through the BDV after every SD as well; this type of depressuring is normally performed in reciprocating compressors in which the relevant driver hasn't be specified to handle compressor restart while the discharge side is pressurized i.e. need to more power to overcome the starting torque...

[yassgh]

Fallah,

 

the RECYCLE VALVE will be opened after the depressurization of the pressurized discharge side or simultaneously? 

 

we have us pressure:

 

* first stage: suction 3.45 barg... discharge 8.9 barg

* second stage: suction 8.7 barg... discharge 26.4 barg

* third stage: suction 25.7 barg... discharge 60.24 barg

* fourth stage: suction 59.7 barg... discharge 143.4 barg

 can you explain more the process of depressurization, please.

 

Best Regards;

[fallah]

 

the RECYCLE VALVE will be opened after the depressurization of the pressurized discharge side or simultaneously? 

 

we have us pressure:

 

* first stage: suction 3.45 barg... discharge 8.9 barg

* second stage: suction 8.7 barg... discharge 26.4 barg

* third stage: suction 25.7 barg... discharge 60.24 barg

* fourth stage: suction 59.7 barg... discharge 143.4 barg

 can you explain more the process of depressurization, please.

 

 

yassgh,

 

To find the right answer you should refer to the relevant operating manual...

[serra]

why do you wish to use a depressuring utility for that  purpose ?

If you know (as you should) the different volumes (of each section) and initial operating conditions you can solve the problem in many ways,

for example I solve these problems with Excel....

[yassgh]

thank you serra,

 

i have the volume of each suction and the initial conditions.

 

do you have a Excel sheet for guidance please?

 

Best Regards,

[serra]

you may create yourself the Excel page for your application,
from volume and density calculate the mass of fluid on each section,
then you can model blowdown in n steps (in Excel I normally adopt 10 steps),
at each step re calculate mass (from mass balance) and conditions on each section,
since it's gas phase you shouldn't find particular problems...

(probably not more difficult than doing the same with a different software....)

[yassgh]

Serra,

 

I will be limited in the pressurized section to calculate the peak flow ? 

 

BR,

[Art Montemayor]

All:

 

I add my comments because this topic has been brought up before and the answer still continues to be: There is NO "settle-out" pressure attained or de-pressurizing calculation, or special procedure required on a reciprocating compressor.  A reciprocating compressor is mechanically different from a centrifugal compressor (where there is a settle-out pressure) and all that is required is a thorough blow-down, usually in the direction of the last compression stage.

 

The cylinders on a multi-stage compressor all have different MAWPs and these have to be respected.  Reciprocating compressors are all normally shut down by unloading the machine first (the same requirement as for startup) and this usually involves the necessary blow-down.  As Fallah states, the related Operating Manual should always be read, studied, and followed as to the correct startup and shut down procedures.

 

I believe that the Original Poster, like many engineers today, does not realize or know how a reciprocating compressor works or the difference between it and a centrifugal compressor.  That piece of knowledge has to be acquired first and foremost before running to apply a simulation program - which unfortunately is the case today with students and recent graduates. 

[serra]

yassgh,

you have different sections... with directional valves...

it shouldn't be difficult to calculate the total volume of fluid to discharge...

I don't think a dynamic/unsteady simulation is required for that...

[Bobby Strain]

Seems like many brought an answer to a question that was not posed. But us engineers like to solve problems, and maybe don't carefully assess the task in our eagerness to help. I think the question asked is still unanswered, and maybe even lost in the conversation. Maybe yassgh will pose his query more directly and to the point. Then someone can give him a correct answer. Maybe. But he gained a lot of good information and advice, well worth the effort.

 

Bobby

[walidd_23]

Hi,

 

I used to use Depressuring utilty in  Aspen Hysys to determine the peak flow for simple vessel, but if your system is complicated and you want to include pipes volume.. ect  Dynamic simulation will give more accurate resultes, which you can use spreadsheet to launch the blowdown senario.

 

The attached picture is a sample of BD senario from Aspen Hysys Dynamic including pipe voulum.

 

Walid.

 

Regards

Attached Files

•  pic.png   75.48KB   7 downloads

[rahulk_19]

We are facing a typical problem in H2 rich gas compressor of our CCR unit.The motor amps increase from 430 to 490 in night and became normal latter on.We checked following things and found no abnormalities. Parameters checked were vibrations ,liquid carry over , exciter voltage and current ,,motor voltage ,suction pressure, discharge pressure but no significant variation was observed.Has any one faced similar problem.It is a Thomassen compressor with 3 stages.

[Bobby Strain]

You have the answer with the information you have. Model the compressor with the proper parameters and this will reveal what the power is with varying conditions.

 

Bobby

[rahulk_19]

Thanks for the reply Bobby ,have you experienced similar case for reciprocating compressor. What are the probable troubleshooting measures?

 

regards

Rahul Kamble