12 replies to this topic

[moein_omg]

Hi everybody,

 

I am encountering an engineering chalenge in the basic design stage of a project. it is about designing a cooling system for bitumen cooling and packing unit.

The normal practice is using oil as cooling medium and consequently cooling the oil with cooling water.

the intial tempratue of bitumen is 180 C which shall be cooled down to 80 C.

1- I am wondering whether we can use cooling water directly for this case as cooling agent. Is the high temprature a problem for this case?

2- if water cannot be used, what is the criteria for choosing the correct type of cooling oil?

 

thanks a lot in advance for your kind aznswers

[PingPong]

1. Problem is that when using cold cooling water directly to cool the bitumen, the skin temperature of the bitumen will be so low that it will solidify on the tube wall.

 

2. Therefor an intermediate fluid is used that is temperature controlled above the pour point of the bitumen.

I don't think there is a special requirement for the cooling oil, except that it should have a low pour point and a low viscosity.

You could even use water at high pressure (to avoid boiling) and temperature controlled above the pour point of the bitumen, instead of cooling oil.

[latexman]

Secondly, if flow of CW stops for some reason, and the CW temperature approaches 180 C of the bitumen, can the CW system handle the resulting high temperature and ~ 150 psig vapor pressure of the water?

Edited by latexman, 30 September 2015 - 09:08 AM.

[fallah]

1. Problem is that when using cold cooling water directly to cool the bitumen, the skin temperature of the bitumen will be so low that it will solidify on the tube wall.

 

 

Or it might the skin temperature of the water side will be so high causes precipitation of deposit....
 

[curious_cat]

Secondly, if flow of CW stops for some reason, and the CW temperature approaches 180 C of the bitumen, can the CW system handle the resulting high temperature and ~ 150 psig vapor pressure of the water?

 

 

Interesting point. Aren't there situations where CW is used to cool process fluids at high temperatures? Can safety instrumentation take care of the scenario you are describing? 

[PingPong]

Protecting the CW against high temperature, or against scaling, is not the reason to use an intermediate fluid for cooling.

 

The only reason is the pour point of the bitumen, as I tried to explain before.

 

If pour point is not an issue one could simply use an aircooler if one is concerned about the other things.

 

A tempered water system, using water (not oil) as an intermediate fluid, is sometimes used in a VDU or Visbreaker to cool residue rundown to storage.

[curious_cat]

 

1. Problem is that when using cold cooling water directly to cool the bitumen, the skin temperature of the bitumen will be so low that it will solidify on the tube wall.

 

 

Or it might the skin temperature of the water side will be so high causes precipitation of deposit....
 

 

 

@fallah

 

Based on your rich experience is there a certain temperature of process fluid above which you would allow using cooling water as a cooling medium because of these problems of deposits etc?

 

What's the highest temp. you've encountered in a HEX where CW was deemed an appropriate cooling fluid. 

[fallah]

 

Based on your rich experience is there a certain temperature of process fluid above which you would allow using cooling water as a cooling medium because of these problems of deposits etc?

 

What's the highest temp. you've encountered in a HEX where CW was deemed an appropriate cooling fluid. 

 

 

curious_cat,

 

To avoid accelerated fouling in CW side, outlet temperature of CW should be below 45 C, and relevant skin temperature shouldn't exceed 60 C...
 

[Zauberberg]

Why don't you use air cooling instead? Going from 180 to 80 degC can be achieved easily, and without facing any of the problems discussed above.

[moein_omg]

many thanks for your comments on such a hot debate.

to put it on nutshell, the main constraints are:

1- ordinary cooling water system cannot be used because of the pour point of bitument (in this case 60 C) and skin temprature limitation.

2- air cooler system cannot be used because of the pour point of bitument (in this case 60 C) and skin temprature limitation.

3- high pressure cooling water system at high temprature (>60 C) cannot be used as a result of water sedimentation which takes place at temprature hegher than 45 C.

 

does anybody know:

Is the rate of cooling of the bitumen another constrain? does it affect the bitumen quality?

can DM water be used at heigh temprature and pressure? is it an aconomocal solution comparing with the indirect cooling oil system?

[PingPong]

As I wrote before: A tempered water system, using water (not oil) as an intermediate fluid, is sometimes used in a VDU or Visbreaker to cool residue rundown to storage.

Demin water is then used as tempered water.

I have never seen an oil system in such service, but if you like you can design one..

Advantage of water (over oil) is higher specific heat, higher thermal conductivity, lower viscosity, not flammable.

 

If bitumen PP = 60 ^oC then the TW could be operated at 70 ^oC supply to bitumen exchanger, and 80 ^oC return (equal outlet as bitumen, so one shell).

 

In a cold climate the TWS system will require tracing if it is not always in operation, or glycol is added to the water.

The TW is usually cooled in an aircooler, but can also be cooled by CW.

An expansion vessel is installed at highest point in system, upstream of the circulation pump.

 

Cooling rate of bitumen does not matter.

[Bobby Strain]

PingPong got it right with his last statement. Use glycol/water with inhibitors just like in an automobile cooling system. Then use an air cooler to cool the closed system coolant. It is also possible to use an intermediate fluid that vaporizes and condenses within the proper temperature range.

 

Bobby

[moein_omg]

thanks alot indeed