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Learning Process From Cleaning Plate Heat Exchanger

In my previous post "Some Updates", I mentioned about Process Plant - Heat Recovery View. The plate heat exchanger that has been thoroughly cleaned via "cleaning in place" (CIP) could not produced the desired output temperature (but we got the flow rate). I blamed the RTD for the output temperature not correct. Although the RTD has been serviced, it still shows the same reading.

Today, we realized what was wrong with the plate heat exchanger (or cleaning program). We only conducted (CIP) for one side only (cold oil 1) i.e. the side which we assumed dirty, contained scale and fouling. The other side (hot oil 2) which we thought was clean (free from scale and fouling) was not cleaned with hot caustic (main ingredient for CIP). We found out from the newly installed vortex flow meter that the 'hot oil 2' side flow rate is low i.e. about only 54m3/hr. The 'cold oil 1' flow rate can reached up to 105 m3/hr. This shows that the 'hot oil 2' side in the plate heat exchanger is partially blocked with probably scale and fouling. The heat transfer is therefore not efficient and effective. The 'cold oil 1' temperature should reached 240oC from 105oC. However, it only managed to reached 210oC which is not sufficient for the process.

Now that we know the problem, we are doing CIP for the 'hot oil 2' side. After 6 hours of CIP, the flow rate has became 76m3/hr which shows some sign of improvement. We'll circulate the hot caustic until the flow rate reaches at least 90m3/hr. I'm glad that we learned and experienced this. At least our understanding and comprehension, tricks and technique of handling the plate heat exchanger improved. Thanks to one of my supervisor who informed us about the slow flow rate of 'hot oil 2' which as a result could not heat up the 'cold oil 1'.

I hope this post provide some valuable infos for you. If you're confused or do not understand what I'm discussing here, feel free to ask.

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posted by zaki yamani @ 11:05 PM,

4 Comments:

At Wednesday, August 13, 2008, Blogger Olga said...

Dear Zaki Yamani,

I'm a process engineer and your article is very useful and interesting. Could you say (if it possible) how long time did this plate heatexchanger work good without cleaning?
And was the concentration of caustic solution high?

 
At Thursday, August 14, 2008, Blogger alzack said...

Thanks for your kind words Olga.

how long time did this plate heatexchanger work good without cleaning?

That depends on how you use the PHE and the types and quality of fluid that passes the PHE. From my experiences, the PHE can operate effectively up to 1.5 years without cleaning, but that is because the feed oil is clean and other combining parameters are good. There are also cases where we have to clean the heat exchanger after 4-5 months... There's no straight answer to this. It depends on a lot of factors.

The caustic concentration was 3-5%. This also depends on how severe the scale build up is inside the plates. You can have lower concentration if the scale is lesser.

I hope I answered your question.

 
At Sunday, August 17, 2008, Blogger baley said...

how heavy and fooling is that oil?

Does it really worth the trouble to use a plate exchanger respect to a shell and tube for such fluids? After all a shell and tube is much easier to clean.

 
At Sunday, August 17, 2008, Blogger alzack said...

Baley,

it depends on your process and application. What is the type of flow? what is the pressure and temperature? You have to use a shell and tube heat exchanger if you have a high pressure and high temperature. A shell and tube heat exchanger is more expensive. A plate heat exchanger is cheaper and can be used for lower temperature and lower pressure. The main constraint of the plate heat exchanger is because of the gasket used cannot cope with temperature higher then 200oC. so, it's a matter of the effect of process parameters and not the easiness to clean the heat exchanger. A shell and tube heat exchanger 2 pass (or U tube) is also sometimes very difficult to clear especially at the U bend. You need a special equipment with high pressure of jet water to clear the scale, fouling. In worse cases, you need to introduce a small drill combined with the high jet water, preferably up to 20,000 psi to ensure you eliminate the stubborn scale.

 

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The Author

zyz

I’m Zaki. I used to be a project, process and chemical engineer. Few years ago I successfully became a Chartered Engineer (IChemE) and Professional Engineer (BEM). I'm now employed as a chemical engineering educator/researcher/consultant. Hope you like reading my blog. I welcome any feedback from you. My email: zaki.yz[alias]gmail.com. TQ!


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