5 replies to this topic

[medelamine]

How can I estimate the efficiency of conversion between chemical energy (combustion) and mechanical energy (compression) ? Let's say that I want to compress natural gas from 30bars to 80bars, (5MMSCM), how much natural gas do I need to burn ?

 

Can I simulate that case in hysys,

Thnaks in advance,

 

[Bobby Strain]

All you need to do is simulate the compressor in HYSYS. Then go to a gas turbine supplier, like GE, and match the power with a turbine selection. You should find the heat rate for the gas turbine at the manufacturer's website.

 

Bobby

[medelamine]

thnx bobby, that's helpful,

I was wondering however if we can simulate the gas turbines in HYSYS as an expander ? well, I still need to have an accurate efficiency from the manufacturer, but basically, is it a feasible approach ? 

Thanks again sir !

[Bobby Strain]

Yes, you can do that. But you need to provide the hot gas flow and conditions to the expander. Along with the inlet and outlet conditions and efficiency. So, you will still need the manufacturers turbine information. And, if you are really good, you can use automation to couple the simulator with Excel to do the work.

 

Bobby

[medelamine]

Okay, thank you Bobby,

well I will use the sheet function within hysys to set the efficiency formula, thnx for the hint !

med amine,

[Saml]

Don't forget to include the air compressor section of the turbine.

 

Basically you need to simulate:

- An adiabatic compressor for air. Typically from 15 to 25 bar.

- A reactor for the combustion. You have to regulate the excess air not to exceed 

- An adiabatic expansion of the combustion gases.

The net work from adding the expansion to the compressor is what you get at the turbine shaft to use in your natural gas compressor.

 

Both compressor and expansion are highly efficient in modern turbines (think 85%+ isentropic)

 

The thing you need to vary is the excess air to obtain a reasonable combustion temperature.1200°C is typical. 1500 °C is achievable in some cooled blades, special coating turbines.

 

Overal efficiency is 35%+ against lower heating value.