Does compressor efficiency account for intercooler energy costs?

[Sorade]

Hi all,

I am looking at a air compressor train design which looks like this:

I know how to work the compressor work needed for a two stage compressor, and hence how much work I can save using 2 instead of 1 stage.

The question I have is: How much energy does it require to operate an intercooler (in red on figure) ?

How do the savings in work compare to that. I was asked the question today while giving a talk and couldn't answer it. I am not an engineer.

Thank you for your help

 

[Chestermiller]

Well, assuming that water is used in the intercooler, you would have to evaluate the cost of pumping the water and re-cooling the water, and you would have to evaluate the cost of the intercooler itself, including its depreciation for tax purposes. So you are talking about an economic analysis. Presumably, since intercoolers are used in practice, their cost of operation plus purchase is warrented.

 

[Sorade]

Does anybody know if the efficiency listed for compressors include the energy losses due to the inter-coolers.

For example say a one stage system with no cooling consumes 500 kJ/kg.

and that one with two stages with an inter-cooler and an after cooler consumes 250 kJ/kg for compression + 100 kJ/kg for operating the coolers.

Even though consuming 350 is still more advantageous than 500 kJ/kg, it is not at good as 250 kJ/kg.