3 replies to this topic

[drdave]

In oil coolers for Industrial machineries,It is often observed that it does not give reasonable maintenace period resulting unplanned shutdown or running with overheat bearing temperatures. Will you please explain on the following:
1) How much fouling factor is universally recommended for oil on shell side?
2) What are the estimation methods of thermal conductivity,viscosity & specific heat for oil (like Iso VG 46 )?
3) What is the shellside effective chemical cleaning of oil cooler?
4) Howmuch leakage rate is permissible through multi-baffled shell of oil cooler?
Thanks & kind regards

Continuing......

Hello All!
Motor driven auxiliary oil pump & gearbox shaft mounted main oil pump are provided for lubricating oil system of turbine driven centrifugal process pump. Oil pumps are in operation for lubrication of bearings & gearbox.
Two oil coolers are provided as sketched below:
It can be seen that the second oil cooler is contributing additional pressure drop without effective cooling.
Queries:
[1] Is it better to propose installation of one cooler with improved heat transfer area if pump-house space permits to accommodate? During rating of given heat exchanger, there is found almost no excess area to impart reasonable maintenance period.
[2] To save on cost, May we consider any other configuration of existing oil coolers? (e.g. both streams in parallel or otherwise)
[3] For process simulation (e.g. Aspen+), What chemical component is to be considered for oil in general?Thanks.

D.R.Dave

[drdave]

I have revived old query as shown above with new inputs in blue letters & a sketch to get technical comments .

D.R.Dave

[Art Montemayor]

D.R.Dave:

You are stating that industrial water-cooled oil coolers are expected to foul on the oil side as if it were a fact. It isn't. In truth, I have never applied a fouling factor to the oil side of my hydraulic oil coolers whether the oil were meant for lubrication of critical machinery or used as the hydraulic medium in presses or actuators. Let's get one thing straight: if your oil side is fouling while the oil is meant to lubricate critical machinery downstream, something is deadly wrong about your oil handling system. The oil should be 100% pure, filtered and clean. Now, the water side is another totally different issue. The fouling factor to be used on your water side is all in your hands. You are the only one controlling the quality of CWS (cooling water supply) and you should have the most accurate idea as to its condition.

If you are fouling in the oil side, you have dirty oil or are creating dirty oil within your system. You have a major problem that will result in gross maintenance problems in your machinery dependent for lubrication on this oil. I would find out how the oil is getting fouled and stop it immediately. Your oil system must be maintained 100% clean; if you can't maintain it this way, something is wrong and it should be corrected immediately.

There are no estimation methods for the oil's properties. One simply calls up or uses the plant's oil supplier or vendor for this information. The lube oil probably comes from a major refiner-producer (like Shell, Exxon, etc.) and they will gladly give you all this information in great detail.

As I stated, your oil system MUST BE MAINTAINED CLEAN. Since it is a clean system, there is no fouling and, therefore, no reason to open the oil side and to clean it. All oil coolers that I have employed have been totally sealed on the oil side. In fact, if you check major hydraulic or oil powered machinery, you will see that their oil coolers are sealed on the oil side and can't be opened by conventional means. This proves, or is in line with, my logic and assertions.

The baffle leakage on the shell side should be the same as is given to most all other applications and depends on the shop's quality of fabrication and the design employed. Unless you are designing the cooler - which I doubt - you have little concern with this clearance as long as the cooler's duty is warranted by the designer/fabricator that I assume you will purchase the unit from.

Whether you use one, two, or more coolers is all up to you. I would use one unit designed for the process temperatures specified. Normally, the outlet oil temperature will be in the order of 100 - 130 oF, depending on the gearbox specifications and the oil's viscosity required. So this is a moot issue that really isn't very important unless you want to spend more money using more coolers - which I don't think is the case here.

I don't understand your mention of an Aspen simulation. For what? I wouldn't simulate the performance of an oil cooler on Aspen; it isn't required for making the unit work correctly and I fail to see what results a simulator could reveal to me that I couldn't find out first-hand. Also, I've never heard of anyone using such an expensive simulator package to simulate the performance of a cooler. Either the design works according to the furnished specifications - or it doesn't. That's why an outside, expert, recognized designer and fabricator is selected for the oil cooler. If you do your job of selecting a competent designer/fabricator, you won't have any problems. That's the way that projects are put together all over the world.

One important note: you haven't even mentioned the quality of the CWS you are presently using and whether it is clean or fouling. I would certainly be more wary of the CWS before I suspected any contamination of the lubricating oil system. You also haven't said anything about the history of this fouling: is it recent or has it always behaved that way? Who specified it and who designed it? Was fouling of the oil anticipated? If it was, how then could they justify using it for lubricating a gear box and subjecting it to contamination and subsequent damage?

I'll await you reply to these concerns.

Art Montemayor

[drdave]

Art,
Thanks for your valuable comments.Let me elaborate further:
There is one oil cooler on 25 years old turbine driven centrifugal recycle solution pump of Urea plant where very corrosive carbamate solution is being handled.
Performance of single oil cooler was not ok resulting insufficient cooling from 65 deg_C to 55 deg_C in stead of 45 deg_C.It was basic cause of bearing/gear box mechanical failures frequently.
Original oil cooler is of US make(American standards)namely Ferex-135.It is true to consider zero fouling for lubricating oils but original datasheet shows fouling factor value of 0.001 hr.ft2-deg_F/Btu.It made me suspicious about fouling parameters accepted in normal engineering practice probably with respect to Urea technology.Of course, There seems no chances of oil contamination due to process infiltration.There continued a long struggle between mechanical maintenance & production groups.Later on, The other oil cooler got fabricated and put in series with lubricating oil and in parallel with water as shown in a sketch. History of oil coolers remained hot and came into our hands to evaluate technically as there is heavy pressure drop on oil side .Hence,it requires two pumps in line.Our first attack was CW side fouling check.It found not alarming.CW chemistry is also normal without affecting many more heat exchangers of the same plant.Rating of oil cooler in single run has shown that oil side reynold No.=250,shell side velocity is 1 meter/second LMTD correction factor(Ft)=0.85 and almost no excess area in hand.Hence,less turbulence due to baffle leakage came into mind.So,I tried to confirm from the forum.
Now, We have process simulator for our separation processes evaluation where heat exchangers are also available to get rated. But, Process simulator does not know lubricating oil component forwhich I requested Forum to say equivalent component to run simulation as a second check.Normally, We rate heat exchangers through our own PC program based on Kern's procedure.
I hope, I have covered all your concerns on my original queries.
Thanks again.
D.R.Dave