Optimal adjustment cooling water Turbocompressor

[cryotechnic]

In order to optimize our cooling water system we are investigating the adjustments of cooling water of our turbocompressor gascoolers.
The way we adjust the cooling water till now is: Set the total cooling water flow to a point around the value given by the manufacturer. Balans the cooling water over the different intercoolers by adjusting the butterfly valves. When gasoutlet temperatures from the coolers becomes to high (normal temp aroun 25 dgrC) We adjust a little more with the butterfly valves.

What happens by using this system is that we create a lot of pressuredrop over the valves since many valves are half closed and many times we use more cooling water then instructed by the manufacturer.

Gas temperatures are fine, so from that point of few it all works.

My question is: What is the most efficient way of adjusting the cooling water flow? So that we have an optimal gascooling (and most efficient operation of our turbo compressors) and a minimum of pressure drop in our cooling water system, and an optimum total waterflow so that also our cooling water pumps run at the lowest power needed.

Cryotechnic

"Math is the ruler of your potential succes...."

 

[zdas04]

The cooling water flow rates recommended by the manufacturer have got a lot of CYA built in. What you are really looking for is to maintain an optimum outlet temp for each of the cooled streams. There are a couple of things that people do to achieve this.

First, you can actuate your butterfly valves and automatically throttle them to keep the outlet temperature of that stream at your target value. Standard butterfly valves are a poor choice for this, but I'm assuming that you're using the new generation of nearly linear throttling butterfly valves.

Second, you can put a VFD on the cooling water pumps to keep header pressure constant as the actuated valves open and close. For a dynamic pump, power consumption is the cube of pump speed so cutting speed in half will reduce power by a factor of 8.

You would have to have a VERY large power bill to pay for these two changes, but it sounds like you have power concerns and it may make sense.

David

 

[cryotechnic]

Thanks for your answer David. Your right, we want to maintain an optimum outlet temperature for the cooled streams, in that way the compressor runs the most efficient.

We don't really have a power concern. I mean, not in a way that we we're scared by a suddenly high power bill. Our power bill is allways high, (it's a air separation plant....) But in these days every kW that is saved is allways good.

It's al running well, it's more a matter of searching for the final kiloWatts.

Cryotechnic

"Math is the ruler of your potential succes...."

 

[dcasto]

In an air plant the only coolers that have large impact on your overall efiecency are the ones that discharge into the cold box. Interstage coolers only have minor impact. I'd get my large coolers at maximum flow and closest temperature approach the tweek the interstages from there.