3 replies to this topic

[Dmitry]

Hello dear all,

I am currently work with Refrigeration propane loop in Hysys. I've made a simulation (PFD 1), with next input data:
Condenser outlet temperature (streem 2)= 55 ° C
Condenser outlet Vapours fr (streem 2)=0
Chiller In pressure (streem 8) = 0.12 MPag
Chiller In Molar flow (streem 8) = 125 kgmole/h
Chiller Out Vapours fr (streem 6) = 1
Pressure dpor across Cooller, chiller = 0

After it Hysys has calculated Chiller Duty = -293. kw. I can use it to calculate temperature of gas after chiller.

As I know Economizer can increase Chiller Duty, so I put economizer it in my PFD 2

I put valve, which reduced pressure in economizer from to 0.6 MPag. I used recycle operation to send vapours streem from economizer to compressor In. But as you see I've got problem with simulation. Please see attached files. I miss something? Why I've got it problem? Is any procedure for installing economizer? I can send mu simulation if it required by email.

Regards and many thanks for help.
Dmitry

Attached Files

•  Refr loop_1.jpg   97.5KB   158 downloads
•  Refr Loop_2.jpg   76.52KB   134 downloads

[Bobby Strain]

Dmitry,
Maybe you left a specification for one of the streams that causes conflict. I always place the convergence operation at the compressor discharge. You just have to carefully check your fixed parameters.

Bobby

[Padmakar Katre]

Hi,
I have doubts over the flow-sheet as a valve followed by a separator is used as economizer. From the flow-sheet it indicates that there is two stage of expansion, BUT actual expansion is in J-T valves placed upstream of the users. I will recommend you to to understand the flow sheet of refrigeration package. The economizer is used to sub-cool the refrigerant before it goes J-T valve where it expands with some generated vapors. In order to keep lesser vaporization in downstream of J-T valve, economizer is used for sub-cooling. The same is achieved with withdrawing/splitting the condenser outlet stream in two streams, one stream with less flow is expanded to a pressure equals the economizer (exchanger) pressure drop + line drop + the compressor suction pressure and subsequently exchanging the colder energy/heat in economizer with the another higher refrigerant flow stream and sub-cools it before sending to J-T valves placed upstream of various users. Hope you understand. Correct the Hysys model accordingly, if there is any issue please let us know.

Edited by Padmakar S Katre, 20 July 2012 - 01:18 AM.

[Fletch]

Hi Dmitry,
I quickly built up your simulation, i saw your error in the process, but i have it working.

Like what others had recommended, i suggest moving the recycle downstream of your mixer, to Stream 10-2.
Both lines essentially need a recycle now and having it on one spot works best... this should really help fix the issue.
Also, put in a valve to reduce the pressure of your economiser vapour stream to your suction pressure... move your pressure specification to downstream of your mixer, and equalise all (means that the pressure is specified only in one place) ... or actually the economiser stream should really be routed back to a second stage suction as it is at an intermediate pressure.

For propane loops, i find it best to specify the chiller duty, this will then calculate the flow.
This is because you typically have the process cooling duty in your model, and means you can just let the propane circuit calculate what it needs to calculate.
Means all that is specified, is condensing pressure (suction presure in your single stage case), discharge pressure, condensor and chiller vapour fractions.
Your cases was a bit different as you had a specific flow, but if you wanted to keep in this "duty specified mode" an adjust would work (changing duty until flow rate is met).

This should fix your simulation issue, but reflect on what Padmakar has provided above.

Edited by Fletch, 09 August 2012 - 01:37 AM.