6 replies to this topic

[MrSimple12345678]

Hello everyone, I had just tried HYSYS to model a system. I was simply clicking the values. And I find it a little too easy to model the compressor that I find it is incorrectly. I would like to ask what is a proper way to model the screw type compressor.

 

1. I already predefined the output temperature and pressure for the inlet stream and outlet stream for compressor however it does not give the power rating range that I was expecting. It was way lesser in the sense that 5.5MW of power was expected but it return results of around 50kw 

 

2. As characteristics curves are difficult to obtain over the internet (which I believe to protect their products), is there any other approachable ways other than to use affinity laws? 

 

3. Is there any good websites to model the affinity laws clearly? What is the difference between getting the characteristics curve into the modelling and not? 

 

Thank you very much for reading the post and I welcome any type of inputs! Have a great day!

 

Best Wishes

[serra]

a simple solution could be to contact a manufacturer and get detailed data sheets and may be help,

with std. models you should be able to simulate oil free compressors while for  oil injected machines

you may need specific models to account for liquid phase,

I have used the polytropic model with phase equilibria  available in Prode, see

"http://www.eng-tips....cfm?qid=338808"

there are many books discussing the topic, see for example

Screw Compressors, Mathematical Modelling and Performance Calculation

[MrSimple12345678]

Hello Serra thank you for your inputs I had just finished reading the Affinity Law in its simplest form. I managed to find a set of characteristic curve and applied the procedure. But its not quite the flow rate which is Q1 that I needed apply this to obtain Q2

 

Q1 = 2000 m3/hr

Q2 = 1800 m3/hr

 

Affinity Law

Q1/Q2 = N1/N2

where N = RPM

 

Hence N1/N2 = 0.9

 

On the other hand H1/H2 = N1/N2

 

Thus H2 = H1/ (N1/N2) , where H1 = 5000

H2 = 5555.555556m 

 

Is this procedure valid for a polytrophic process?

 

Best Regards

Edited by MrSimple12345678, 22 March 2016 - 03:39 AM.

[serra]

screws are positive displacement compressors, for a general introduction see

 

"http://sageenergy.ca...sion-Intro.pdf"

 

as suggested you may start from some manufacturer's data , see Atlas, Ingersoll, Curtis etc.

[Pilesar]

What question do you need answered by simulation? Can you not just use a flash unit and set the outlet temperature and pressure that you already know? The flash unit will calculate the enthalpy change and you can assume an efficiency to calculate the compressor work. Your flow rate and pressure change are small so I would not expect anywhere near 5.5 MW power. Confirm your input data.

[MrSimple12345678]

@serra: Thank you Serra for your inputs, I have tried searching the net for characteristic curves for compressors, centrifugal types as substitutes but its not was not a fruitful search but I appreciate it!! 

 

@Pilesar: Hello there, however I am not sure what you meant by flash unit. I did try inputting the stream temperature for inlet and outlet of the compressor in HYSYS steady state and it did some calculation. Is that what you trying to mean ?

[serra]

as said, screws are positive displacement compressors,

see petrowiki for differences with centrifugal (dynamic) compressors,

"http://petrowiki.org/Compressors"

note that isentropic efficiency = isentropic compression work / actual work
and initial and final values for H, S can be estimated from tables , charts (mollier) or calculated with a simulator,

but before to run a software you may wish to learn the basis.