Optimizing Temp. Tappings on Distillation Columns - Ideas/Experience?

[rollingstein]

We have a distillation column with insufficient temperature tappings. In order to do a rough survey of the temperature profile externally an idea is to drill small (say 1 inch) holes in the insulation and take external temperature readings.

Would a IR temp. gun like this one be a good idea?

http://www.thermoworks.com/products/ir/irgun.html#AccessoriesTab

Any other ideas? Anyone try anything similar?

THe unit mentions an ~2% accuracy, is it really that good?

 

[AlephZero]

The basic question you need to answer is "what temperature are you actually measuring".

Clearly the outside temperature of the column, at a point where you removed some thermal insulation, may not be the same as the temperature of what you are distilling. If your column is made of something transparent to visible light, it might not be very obvious what is the source of the IR radiation you are measuring (i.e. is it transmitted through the material of the column, or emitted by the column itself?)

You didn't give any details of the column, and your link to the thermoworks site isn't working right now (my browser says "server not responding") so there are more questions here than answers...

 

[Nugatory]

http://www.thermoworks.com/products/ir/irgun.html#AccessoriesTab

Any other ideas? Anyone try anything similar?

The unit mentions an ~2% accuracy, is it really that good?

I'd expect that you will be able to make these cheapie IR guns work just fine in that application. They have several weaknesses, all of which you can correct for:
1) You can't trust the absolute temperature that they report; they're sensitive to the emissivity of the surface they're pointed at. So if you read 130 degrees on a shiny surface and a 150 degrees on a nearby black surface you can't be sure that the temperature difference is really 20 degrees. If both surfaces were black, you'd be fine.
2) The shinier the surface you're dealing with, the less accurate the IR gun is.
3) You can't compare readings taken between two different IR guns.

For your application, you might consider
- After you've made your 1" holes in the insulation, hit the bottom of each one with a spritz of flat black spray paint. That way, they'll be as similar as possible, with a minimum of weird reflective behaviors.
- Put one of your holes near one of your existing temperature tappings with a standard temperature gauge. That way you can check the IR gun reading against a new temperature so you'll know how to interpret the readings at the other locations.

There are much more sophisticated versons of these things with nice calibration capabilities, emissivity correction, and the like. You can't buy them for $49 though.

 

[rollingstein]

The basic question you need to answer is "what temperature are you actually measuring".


Clearly the outside temperature of the column, at a point where you removed some thermal insulation, may not be the same as the temperature of what you are distilling. If your column is made of something transparent to visible light, it might not be very obvious what is the source of the IR radiation you are measuring (i.e. is it transmitted through the material of the column, or emitted by the column itself?)

You didn't give any details of the column, and your link to the thermoworks site isn't working right now (my browser says "server not responding") so there are more questions here than answers...

Column is a SS vessel about 30 feet tall and ~4 feet dia. So, no not transperent. But there doesn't seem any feasible way to get internal temps. (unless you have any ideas)

Hence this is the closest I had. With some correction for the ΔT across the metal.

Temp. profile ranges from 60 C at top to 150 C at bottom.

 

[rollingstein]

I'd expect that you will be able to make these cheapie IR guns work just fine in that application. They have several weaknesses, all of which you can correct for:
1) You can't trust the absolute temperature that they report; they're sensitive to the emissivity of the surface they're pointed at. So if you read 130 degrees on a shiny surface and a 150 degrees on a nearby black surface you can't be sure that the temperature difference is really 20 degrees. If both surfaces were black, you'd be fine.
2) The shinier the surface you're dealing with, the less accurate the IR gun is.
3) You can't compare readings taken between two different IR guns.

For your application, you might consider
- After you've made your 1" holes in the insulation, hit the bottom of each one with a spritz of flat black spray paint. That way, they'll be as similar as possible, with a minimum of weird reflective behaviors.
- Put one of your holes near one of your existing temperature tappings with a standard temperature gauge. That way you can check the IR gun reading against a new temperature so you'll know how to interpret the readings at the other locations.

There are much more sophisticated versons of these things with nice calibration capabilities, emissivity correction, and the like. You can't buy them for $49 though.

Thanks for those very practical tips. The black paint is a neat trick. I will use that.

My budget isn't limited to $49 so if you have a better gun you'd recommend I'll be glad to have a shot.

 

[AlephZero]

Column is a SS vessel about 30 feet tall and ~4 feet dia. So, no not transperent. But there doesn't seem any feasible way to get internal temps. (unless you have any ideas)

Thermistors? Unless electrical connections would be a problem because of corrosive chemicals, etc.

 

[rollingstein]

Thermistors? Unless electrical connections would be a problem because of corrosive chemicals, etc.

Penetrating the shell is the problem. If you mean thermistors pressed against the metal from the outside, sure, that can work.

But then again, the gun will do pretty close to that, I suppose.