Cooling Reactor Contents Using an Air Sparge
Cooling Reactor Contents Using an Air Sparge
(OP)
Does anyone have experience of cooling reactor contents using an air sparge?
We have just taken over a process in which a 30m3 glass fiber reactor (vented to atmosphere) contains 25m3 of an aqueous solution which requires cooling from 110 deg c to 70 deg C.
We do not want to use a graphite type heat exchanger (cost) and I would like to know if anyone has experience of using an air sparge as a means of cooling.
Thanks
Saffer
We have just taken over a process in which a 30m3 glass fiber reactor (vented to atmosphere) contains 25m3 of an aqueous solution which requires cooling from 110 deg c to 70 deg C.
We do not want to use a graphite type heat exchanger (cost) and I would like to know if anyone has experience of using an air sparge as a means of cooling.
Thanks
Saffer





RE: Cooling Reactor Contents Using an Air Sparge
RE: Cooling Reactor Contents Using an Air Sparge
Happy to supply more details if you think the concept is feasible.
Regards Saffer
RE: Cooling Reactor Contents Using an Air Sparge
You could calculate it out simply just based on heat capacity of the two fluids assuming perfect heat transfer.
25m3 aqueous solution is a lot to cool down. If your tank is vacuum rated you would have better luck with autorefrigeration than the air sparge. I would either pump it around to a heat exchanger or have submerged coils in the mix tank.
Regards
Stonecold
RE: Cooling Reactor Contents Using an Air Sparge
Evaporation will remove quite a bit of heat and fairly quickly- especially at the beginning. How much heat and how quickly you'll get down to 70 C depends on how fast and how effectively you add and remove the air (i.e. the kla), and what else is in your "aqueous solution" (i.e. the partial pressure of water above that solution versus temperature)- and of course, the pressure.
What's the source of your air? If you're feeding it from a blower or compressor directly, it won't be cold, and that will matter a great deal at the end of your cooling cycle.
In future, more information helps us give you better advice.
RE: Cooling Reactor Contents Using an Air Sparge
RE: Cooling Reactor Contents Using an Air Sparge
We have just taken over the plant which manufactures ferric sulphate solution (very unsuccessfully) from iron oxide water and 98% sulphuric acid using the said GRP reactor under atmospheric pressure.
There is no cooling capability on the reactor (dont ask why I dont know either?) so after a 24 hour period when the reaction is complete the reactor contents are at about 110 deg C. The GRP reactor then takes 3 days to cool to 70 deg C the temperature at which it can be filtered (filter limitations).
You are right there is a scrubber (not effective) with a 3.5 kw blower drawing off vapours from the reactor to atmosphere.The nasties you refer to would be ferric sulphate droplets.
Because of the plant history I am required to to spend "too much" on rectifing the problems hence my idea of using an air sparge to cool powered by a blower or compressor fitted with an air cooler.
I would appreciate some guide lines in sizing the compressor/blower to cool the reactor contents in say 12 hours.
The reactor vent is 4 inch as is the reactor outlet where I propose to inject the air.
Regards and Thanks
Saffer
RE: Cooling Reactor Contents Using an Air Sparge
If you were making ferrous sulphate, you'd be out of luck obviously!
Assuming you don't have a simulator handy, I'd suggest you set up a very crude model- assume that the bubbling tank is, say, 80% of a theoretical stage (i.e. you get the exiting air up to about 80% saturation of water vapour at the temperature of the liquor at any point in time). That's a total guess- you can get more accurate guesses from a simulator or more detailed calcs- or you can just set the % approach to a theoretical stage as another variable.
Set up a finite difference table in Excel, with a time period of about a minute or so. You know the mass and heat capacity of the material in the tank. Set an air mass flow, and see how much heat you remove with a minute's worth of air, how much the temperature drops, how much water you lose, and what the new vapour pressure of water is at that temperature. If you think the sensible heat capacity of the air itself will help, you can add that in too, but it's probably negligible. By difference, set up the conditions for the next minute, and the next...
Once you come up with an air mass flow that's necessary to do what you want, you can dig through Perry's or McCabe, Smith & Harriot or Treybal or the like to find out if that's a reasonable amount of air to bubble through that much water- what gas hold up you should expect, whether or not that will overflow your tank, and whether or not the cost of the blower will bankrupt you or the air will overwhelm the scrubber etc. Of course, if your solution foams, you're screwed.
Best of luck- others here might want to suggest better models, or you might come up with one yourself.
RE: Cooling Reactor Contents Using an Air Sparge
Your are basically air cooling your reactor now, but very inefficiently. Just blowing air through the head space will greatly improve your efficiency.
RE: Cooling Reactor Contents Using an Air Sparge
Your cup of coffee can cool effectively by blowing across it only because it's not very deep. Your cup of coffee is 25,000 litres and probably more than 30 tonnes. But if you have a mixer, the mixer will ensure that the surface is rapidly replaced with hot liquid, so bubbling through the liquid isn't required. A fan could work quite well- it will achieve a much lower approach to a theoretical stage, but would allow you to move a MUCH larger mass of air per minute. That said, your 4" inlet and outlet are a problem. You'll still need quite a blower to get enough air through there to do the trick.
RE: Cooling Reactor Contents Using an Air Sparge
To elaborate on my straw analogy, compare using a straw to blow air at the surface of the coffee cup to blowing through the straw to the bottom of the coffee cup. You have to throttle way back on airflow because air velocity cannot be higher than the velocity of rising bubbles or you blow the coffee out of the cup.
A blower on a 4" nozzle will give at least an order of magnitude increase in cooling versus a covered tank. You do want the air to impinge onto the surface and not merely sweep the head space for maximum heat transfer.
RE: Cooling Reactor Contents Using an Air Sparge
RE: Cooling Reactor Contents Using an Air Sparge
Moltenmetal,Compositepro and StoneCold thanks for your help.Will remember "site etiquette" re fishing in future.
Both the air sparge and air blow over the surface (the tank is stirred)worked and will provide a cost effective solution to our problem.
Will post details when the GRP reactor is assembled after repairs and in operation.
Many Thanks and Regards
Saffer