Heatrix performance 1

[Rob247]

Good Morning guys,

I'm wondering if you can help, As stated in my previous posts i'm trying to gain a little more process and mechanical knowledge whilst working in the hyrdrocarbon processing industry and I'v come across a problem that's got me confused.

We have a heat ex-changer that's over efficient, this creates a problem down stream as the temperature of the process gas coming out is to cold and is creating a knock effect further down stream. The process team have suggested that we drop the operating pressure of the cooling medium system thus increasing the temperature on the outlet of the heatrix. The mechanical issues are getting ironed in terms of valve replacements but this is there interim solution.

My issue is perhaps " simple" to you boffins but am I understanding that by dropping the pressure through the ex changer, i m actually decreasing the flow rate thus less heat transfer or is it connect to the boiling properties of the Cooling medium system when under pressure thus less heat transfer when pressure decreased.

I'm aware that this question is relatively simple in relation to the rest of questions on this site but I would really appreciate some advice or even a gentle push in the right direction.

Cheers

 

[Artisi]

Not really my area of expertise, however I would think reduced flow this will reduce the rate of cooling. I would initially throttle discharge flow to prove the theory with a view to reducing the pump impeller diameter once proved.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

Rob 247, you should know by now that providing a much info as possible will get you better responses. What is your cooling medium?, I can only assume it's some sort of gas as a reduction of pressure would lead to reduction of mass flow and reduced cooling.

Some more info would be useful.

However I can't see why you don't just throttle the cooling medium flow. This is a common control loop controlling flow based on downstream temperature.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Rob247]

LittleInch,

Sincere apologies, I'm just getting my head around how best to work my questions.

Here are the facts, My cooling medium is 80 % demineralised water / 20% Teg mixture working in a system generally running at 5.8 barg. It normally runs through a heatrix and cools our discharge gas from a temperature of 170 degrees down to 45 degrees. Our Process team decided to drop the pressure down to 5.1 barg to see what affect it had on the cooling and it did actually work but they were then concerned with "flash boiling " of the cooling medium so we had to reinstate the original SP of the controller..

So they got the desired affect but No one ( out here ) can explain why this happened, and i have googled till i'm blue in the face.

Thanks

 

[LittleInch]

Without seeing the flow loop it's difficult to say what is going on, but assuming your water/teg system is running around a loop it's affecting the flow rate somehow. Are there any flow controls on the water loop? I assume your set pressure is a separate thing keeping the system at an elevated pressure whilst another pump actually pumps the water/teg mixture round your cooling circuit?

It could be that the water did flash and create a pressure disturbance. A control valve downstream of the hx or a variable speed circulating pump will give you the controllability apparently missing.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[25362]

One way to reduce the cooling load is to by-pass the cooler on temperature control.