5 replies to this topic

[curious_cat]

We have a exothermic fed-batch process that needs to be run at 95 C for ~6 hours. Currently there is a SS316 Reactor (10 KL) with a jacket cooled by cooling water. 

 

I was wondering, would there be any point in cooling it by raising steam in the jacket (with a slight vacuum to enable boiling at below 100 C)? I'm not sure whether I've any use for said steam, but wouldn't the heat transfer coefficient of boiling water be better? Plus the advantage of essentially isothermal conditions and the large latent heat versus smaller specific heat. With the current setup maintaining isothermal conditions is a bit of a challenge. 

 

Wondering what people think? Is this a possibility or do you foresee problems? Has anyone used a setup like this? Would it need major modifications to the jacket? The mechanical calculations show it is rated for a full vacuum. It is often used for steam heating (140 psig) as well (in other batches). 

[mansari]

Steam system seldom operate on vacuum. In fact it is not practical to generate and transport steam under vacuum. In theory, your reaction requires a temperature of 95C and therefore you need to "raise" steam at around 85 C to maintain a reasonable approach. Which mean, you have to operate your jackets at a pressure of about 0.58 bar abs. (are the jackets designed for vacuum conditions?)

 

It is not the heat contents but the temperature which defines the quality of steam. If you remember, huge amount of steam energy is "dumped" into cooling water sink in surface condensers associated with steam turbines, why, because they operate under vacuum and temperature of steam is not high.

 

Cooling water is normally available at a temperature in the range of 15-30C (depending on ambinet conditions), therefore it offers an excellent approach for heat transfer. In the industry, we have to consider safety, doability and economics of any idea generated, before putting it into reality 

[markymaark]

Mansari is correct.  The heat transfer with steam is through a phase change.  With boiling water it would be through a drop in temperature.  A phase change is MUCH greater and faster of a heat transfer mechanism.

[Art Montemayor]

Mansari has hit on the most important part of this proposal: the mechanical design of the existing stainless steel reactor and jacket.  I seriously doubt you can justify applying a vacuum on your jacket without re-rating your reactor.  This could be expensive or impractical.  Besides, the cooling effect would still be relatively inefficient because of the fixed area and the inability to control the cooling rate accurately.

 

If the core topic of this thread is that you are having excessively long batch runs because you are depending on your jacket to control the exothermic reaction in your batch reactor, then you are doing it all wrong.  No practical or economic jacket design was ever devised to control a batch reactor.  It just isn't practical on an industrial basis.  I have stated this numerous times on this Forum and have proved it in the field.  The way to control a batch reaction accurately and efficiently is with agitators and an internal coil OR with an external circulated loop that is either cooled or heated (depending on exotherm or endothem) in an external exchanger.  Either way is the efficient way to do it in order to maximize quality batch yields in minimum time.

[curious_cat]

I agree that an external HEX or a coil would be the best options. One of the problems is that the reactor is glass lined so adding an internal coil would mean finding a glass lined coil or similar. Might be possible but don't know how expensive. 

 

Same with the HEX I think. The reaction medium has HCl and would need a fairly expensive MOC for the HEX. 

 

Hence the attractiveness of the jacket. But if my idea is a dud, it's a dud. 

[Art Montemayor]

Curious:

 

One thing is certain in the chemical processing business: if you can’t afford to make the investment in the proper equipment, you should sell and get into another business.

 

Just because the internal lining of your reactor is glass doesn’t mean you have to have a glass coated internal coil.  There are alloys that can probably be used – such as titanium and stainless steels.  Of course they will be relatively expensive, but then so was your glass lined reactor.

 

Don’t forget that by using a more efficient (and expensive) method of cooling the reaction, you will get more batches out of the reactor and with better quality product because of the better temperature control.  This means you will make more product in less time and probably pay back the investment you make in an expensive coil or heat exchanger.