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Active Contributor

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Heat Exchanger for Toluene not Performing

03/12/2016 12:12 PM

Hi everybody,

I am currently in Bayer and is commissioning a liquid ring vacuum package containing a liquid ring vacuum pump, heat exchanger, separator/tank, intruments and gauges.

The machine was designed to create vacuum using toluene as fluid. the liquid ring vacuum pump is supposed to be running at 80 millibars absolute.

The heat exchanger, 4 pass on tube side, 53 tubes of SS304 having dia of 9.53 mm, and single pass on shell side has the following inputs

Brine input on shell side - minus 15 degree celsius, flow of 8.5 m3/hour

Brine out on shell side - minus 13 deg celsius,flow of 8.5 m3/hour

Toluene on tube side - 30 degree celsius, flow of 1 m3/hour

the heat exchanger was designed for 20 degree delta T on tube side and 2 degree delta T on shell side. it should cool the toluene to minus 7 degrees later as a final temperature.

The pump discharge is adding heat of 7 degree in its output measure through a infrared temp. gun.

The first fill of toluene contains some water and which is collected by leaving the toluene standstill for some time and then taking out some water from drain.

The machine running philosophy is , the pump is initially half filled,heat exchanger is completely filled, and tank is half filled with toluene which will be recirculated by pressure difference.

Results:-

As soon as the machine is started, the the pump starts creating vacuum, toluene is recirculated to tank and to heat exchanger which comes to pump again at 1m3/hour. Brine parameters are mentioned as above,

The toluene going to the pump, initially looses heat to the brine and goes down to 21 degree celsius and then it starts rising. In half hour the temperature of toluene rises to 38 degree celsius when i stop the machine because the vacuum level in the pumo decreases.

The real question is why does heat exchanger first reduces the temperature and the increases rapidly. Does it happen because the heat exchanger was designed for only toluene and now it has traces of water as well as toluene present in it.

What will happen to heat transfer when the toluene and water were present in the system.

Manish Kesari

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#1

Re: Heat exchanger for Toluene not performing

03/12/2016 6:44 PM

How long did you let it run, are the readings static? Improving? getting worse? Maybe it just needs to run for a while to sort itself out...

http://www.dekkervacuum.com/static4/operation.asp

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#4
In reply to #1

Re: Heat exchanger for Toluene not performing

03/12/2016 11:05 PM

I let it run twice for half an hour.

The situation improved in the first ten minutes and then it started getting worse with time. we are not able to understand why it is reducing first and then increasing.

Sometimes it reduces to -1 degree celsius from 31 degree celsius and sometimes to 21 degree celsius from 29 degree celsius. the trend of heat increase or decrease is not similar.

the only heat input is pump discharge. By the way its Nash Pump.

Can water or any other additive in the toluene might make it behave differently in the heat exchanger.

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#2

Re: Heat exchanger for Toluene not performing

03/12/2016 10:25 PM

If the toluene is undergoing evaporation, its temperature does not change as it absorbs heat. (I haven't looked anything up to see if this pertains to your situation.)

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#3

Re: Heat exchanger for Toluene not performing

03/12/2016 10:47 PM

Is it "water" or "brine" that you find traces of in the toluene? Sounds like you have a leak in the heat exchanger between your fluids.

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#5
In reply to #3

Re: Heat exchanger for Toluene not performing

03/12/2016 11:08 PM

hi.. no there is no leak in the heat exchanger. The process of toluene collection in the plant involves distillation and water is separated from it. water was present from the start.

The amount of miscibility of water in toluene is as less as 0.05 percent.

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#6
In reply to #5

Re: Heat exchanger for Toluene not performing

03/12/2016 11:40 PM

So the water is present as part of the process? Is your separator operating properly?

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#7
In reply to #6

Re: Heat exchanger for Toluene not performing

03/13/2016 1:37 AM

The separator is designed as a collection tank of the vacuum pump where the heated liquid will go and it will again come back to the pump through the heat exchanger.

The height of the process is that , the heat exchanger first cools and then heat up the toluene.

Sometimes it cools upto -1 degree and some times to 21 drgree before taking its trend to heat up again.

What is bringing down the heat exchanging capacity of the heat exchanger. This is my question.

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#8
In reply to #7

Re: Heat exchanger for Toluene not performing

03/13/2016 10:58 AM

Just offhand I would say check the toluene quantity, it sounds like it is low level...

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#9

Re: Heat Exchanger for Toluene not Performing

03/14/2016 2:45 AM

I am a chemical engineer with 20 yrs experience. There are several points in your narrative that I have questions about, that a diagram would most likely lend to a quantum leap of understanding on my part.

Please upload a diagram of your setup and I'll see what I can come up with.

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#10

Re: Heat Exchanger for Toluene not Performing

03/15/2016 9:20 PM

Trace water in the toluene is of no consequence to the the problem at hand. At 80 millibar water will flash off solution and dissipate on the feed tank overhead space.

Problem gotta be on the coolant loop.

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#11

Re: Heat Exchanger for Toluene not Performing

03/18/2016 8:26 PM

I have to agree with Mikerho that a diagram would be helpful in attempting to analyze the situation.

Excuse my confusion, but based on your description:

"...pump is initially half filled,heat exchanger is completely filled, and tank is half filled with toluene which will be recirculated by pressure difference."

and

"...pump starts creating vacuum, toluene is recirculated to tank and to heat exchanger which comes to pump again..."

it appears that you are describing a closed system that does nothing but circulate and cool toluene, and I highly doubt that a company would waste engineering talent on this.

The diagram showing any other equipment connected to the loop you describe may provide that "quantum leap" noted by Mikerho. Please also indicate any joints or connections, as they may be contributing to the lack of performance.

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