deposits in a thermal oil system (mobiltherm)

[pbrod]

Dear All,

We have a deposit problem in our thermal oil system (150m³) It is a two temperature system with a heat exchanger heating the oil to 170°C and a cold loop with a temperature of 70°C. Heating is with a steam shell and tube exchanger, cooling is done in a 200m² air cooler.

Since long there was no filter system on the circuit and deposits were noticed in the tubes of the air cooler. The deposit is very sticky and looks a bit like tar (contains a lot of iron).

We now put one 3M 744/743/742 (5-2-1µm) on a bypass oil stream that we tap from the pressure site of our pumps. The contamination of the oil is about 1g/l. After several 5µm filters the concentration dropped till 0,5g/l but after two weeks without filtration it increased again to about 1g/l.

Anyone has tips to:
- increase the deposit removal in the air cooler (additive,...)? We do not want to open them because of pollution concerns.
- alternative for the expensive filter carteridges (because if we do the calculation we need a lot of filters)?
- regenerative filters?
- other interesting tips?

Best regards,
pieter

 

[Compositepro]

Do you have a nitrogen blanket on your oils system, and is it working properly? Oxidation is the primary reason for oil degradation. You must keep oxygen and water out if you don't want these problems.

As for filtering, you do not want plugged filters to stop the flow. So use a depth filter in a side stream. This filters only a part of the flow, but will eventually remove all particles. Depth filters can capture far more material than surface filters before plugging. Again, they will also not capture every particle on every pass.

Once oil starts to degrade the process accelerates rapidly. Many oils become acidic. Filters will not remove the acids. Mobil has books on how to design and operate hot oil systems. Call them.