2 replies to this topic

[ProcEngr]

Hi guys,

I am currently working on sizing a 'buffer' tank for our fuel gas system. Currently, pressure spikes are experienced in the fuel gas system whenever one of the consumers - one turbine trips or is started-up. The buffer tanks should dampen the pressure spikes. I am also considering other options to this problem but this is one of the options.

I simulated the fuel gas system using pipe segments and using the isometric drawings, I inputted pipe sizes, elbows, etc into the pipe segments. I simulated the controls using the PIDs. I used the separator as to simulate the buffer tank. Filters were simulated as valves. I adjusted the tuning parameters of the pressure controllers to get a similar pressure spikes as what is observed at the plant instead of using the actual tuning parameters. I initially calculated the size of the of the buffer tanks using a sizing calculation for air receivers and used the calculated volume as the volume of the separators in the simulation. I examined several cases such as turbine trips and start-ups using the model by opening and closing valves, i.e., directly inputting 0 opening to the valves to simulate a trip and opening the valve for start-ups.

This is my first time to use dynamic simulation in HYSYS. Can anybody tell me if I am doing this the right way? Thanks!

Best regards,

ProcEngr

[Zauberberg]

You should be on the right track. To have a representative picture of dynamic behavior of the system, you will need to feed the model with accurate data with regards to:

- Total system volume;
- Accurate representation of all lines and fittings;
- Accurate pressure-flow characteristics of control valves;
- Exact parameters of the PID (and any other) controllers involved.

I remember similar study done for the Fuel gas system in my previous company, with the same purpose - evaluating different scenarios when one or multiple sources or consumers of Fuel gas are put online or tripped. The study has shown the need to modify (replace) several control valves in order to improve and stabilize system performance. You should be having a great time when doing this kind of work.

[M-Engineer]

Hello,

I am also working on solving an existing operational problem where pressure spikes are experienced in the fuel gas system whenever one of Gas engines trips or is started-up. These pressure spikes lead to tripping a high-high or low-low pressure switches.

Exactly the same as ProcEngr did, i simulated the fuel gas system using pipe segments and using the isometric drawings, control valves Cv's & characteristics from the datasheets and the volume of the existing buffer vessel from the datasheets.

However, the Hysys model doesn't reflect the pressure spikes experienced at the site, and the only method to get a similar behavior as that experienced in the site is to De-tune the parameters of the controller.

But i can't understand why the Hysys model didn't reflect the actual behavior when using the tuning parameters that is being currently used in the site ?, taking into consideration that tuning the parameters of the controller in the site couldn't solve the problem and it seems that an additional buffer volume is required to dampen the effect of starting or tripping one of the gas engines.

Can anybody give me an explanation for the discrepancy in behavior between Hysys model and the real case ???,

Thanks in advance for your kind help,

M-Engineer (M_Refaat@enppi.com)