2 replies to this topic

[Mr.Z]

Hello,

I'm new to this site (used it as a student but never posted). Now that I am an engineer in the field I have real life situations I had not considered in my studies.

I'm in charge of replacing several jacketed mixing tanks that are past their salvage life. Currently in use are the spiral conventional jackets. The transfer media is typical water (not steam). The water is kept constant at approximately 90 degree celsius. The volume of the tank is by measured dimensions at approximately 400 gallons and 10% headspace taken into account. The product being heated is similar in properties to that of a natural honey/water mixture (not as thick as pure honey).



I'm unsure as to the pros and cons for convential jackets versus half pipe or dimpled jackets.

The process requires two mixing tanks of the 400 gallon size.

since I am replacing the tanks I could also implement a new design such as installing 4 tanks of less size to allow for more surface area.

I'm just looking to better understand is the most cost efficient jacket at these with these conditions.

Thanks!

Mr.Z

[Art Montemayor]

Mr.Z:

Now that you are out in the field, it behooves you to start thinking as a practical person rather than an academically interested individual. The main point that I try to show you here is that no matter what size, shape, type, or cost of tank you decide to build and install, you will ultimately wind up accepting the type of jacket that you most like, want, need, or can justify. You will design the tank based on process requirements and economic guidelines. But you will ACCEPT the size of jacket that fits the tank – not in reverse order of importance.

Therefore, it should be an established practical fact that you can’t make the tank bigger (or smaller) because you require a bigger (or smaller jacket). This type of practical horse sense quickly brings you to the fact that only the TYPE of jacket is what is left to your discretion. Now lets look at the jacket type of options:

• Conventional cylindrical annulus;
• Spiral coils, welded on;
• Dimpled jacket;
• Prefabricated, welded, or wrapped panels.

Before going into the above, you must have a concrete and solid reason for using any jacket. Is the cooling/heating speed of the tank contents CRITICAL? Is the accurate control of the cooling/heating to be done CRITICAL? OR, like most jackets, is it a situation where you are free to take as much cooling/heating as the tank surface allows and be done with it? If the latter is true (as is often the real life case), then the selection of an acceptable jacket is straight-forward. If any of the first two reasons applies, then you should NOT BE APPLYING A JACKET; you should be using an external cooling/heating recirculation system with a pump and exchanger.

Normally, when applying jackets, two things are of prime importance: the cost and the integrity.

Prefabricated, welded, or wrapped panels are always the most economical to install, followed by the Conventional cylindrical annulus. A spiral coil – while very “sexy” and sophisticated - is very demanding in fabrication cost, labor, and tank stress/warpage problems arising from the excessive welding heat generated. Dimple jackets are simply not justifiable in today’s age and applications – UNLESS you have a very pure cooling/heating medium and a LOT of cash.

I don’t go into more details because we don’t know your scope of work and more basic data. But I think you should have the idea from the above about how to go about selecting and designing your application.

I hope this experience helps you out.

[Mr.Z]

Art Montemayor,

Thank you for your reply. It is not critical that the product meets a certain temperature, only that it is maintained at a temperature relative to about 67 deg C. The jackets are merely to maintain and preheat the the product before it enters the HX downstream. So, as I understand it, the more practical consideration would be the tank itself and the jackets secondary, considering they are not critical to having the product reach a certain temperature.

I look forward to contributing to this forum in the future, as I gain more experience!

Best regards,
Mr.Z