I'm working on blast furnace oven, I need to check if it's full with materials in levels one , two and three as shown :-

Representation of a furnace oven

The main problems:

It's very hot as you see in the picture (200°C to 900°C), thus I need to protect my sensors from this heat and also I need them not to be affected with the emissions.

Can I use IR sensors, camera or ultra sonic to solve this problem?

Update 1:-

The oven is used to melt down lime stones. I'm afraid that the heat could damage the sensors or that dropped stones may hit them.

  • \$\begingroup\$ What about what type of material you need to detect? That would help in choosing the sensor. Ultrasonic probably works but I think it would cost more than you are willing to pay. Maybe the material is conductive and some metallic probes can work... I don't know, try to add as much details as you can/want. \$\endgroup\$ – Vladimir Cravero Aug 7 '14 at 13:11
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    \$\begingroup\$ How big is this furance? The cart at the top of the image makes it look very large. \$\endgroup\$ – Matt Young Aug 7 '14 at 13:15
  • \$\begingroup\$ @VladimirCravero It used to melt down lime stone , which for sure may hit the sensor while dropping from the hole , I'm afraid that ultrasonic may get effected by the heat \$\endgroup\$ – xsari3x Aug 7 '14 at 13:15
  • \$\begingroup\$ what Matt said, and I'd like to know also in what status is limestone in zones 1, 2 and 3. Is it already liquid? \$\endgroup\$ – Vladimir Cravero Aug 7 '14 at 13:17
  • \$\begingroup\$ It's 10 meters long , Lime stones status in all zones is solid , it just get some oxides off from it \$\endgroup\$ – xsari3x Aug 7 '14 at 13:20

A radar sensor might work for you. This is a commercial 10GHz sensor.


Since the temperature at the top is not too bad for many dielectrics, you could design and construct a radome with purge air that would keep the worst of the fumes away from the sensor.

  • \$\begingroup\$ Can I have a link for this module ? \$\endgroup\$ – xsari3x Aug 7 '14 at 13:47
  • \$\begingroup\$ In the image description. \$\endgroup\$ – Spehro Pefhany Aug 7 '14 at 13:49
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    \$\begingroup\$ That seems to be how its been done before: instrumentation.co.za/news.aspx?pklnewsid=34490 \$\endgroup\$ – Scott Seidman Aug 7 '14 at 14:15
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    \$\begingroup\$ $4k is surely a very small part of the cost of a blast furnace? \$\endgroup\$ – pjc50 Aug 7 '14 at 15:36
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    \$\begingroup\$ I'm a boiler engineer, and radar level sensors are used in steam drums all the time, admittedly only up to about 300C. Purge air is used to cool certain types of sensor in the flue gas path, so I concur with that as well. I see the OP is a student, so this may be an academic question. The way this is solved in industry is to talk to your instrument supplier, for example Emerson, or the company in @ScottSeidman's link. \$\endgroup\$ – Level River St Aug 7 '14 at 20:36

This isn't so much an answer, but suggestions on how to approach the problem.

I'd throw a VERY wide net at this problem. Start brainstorming around it, but first we need to really understand the issue.

Specifically, what is the problem you're trying to solve? Put it in a different language. I know you said "I need to check if its full with materials in levels one,...", but that's not the problem you're actually trying to solve. It's more like a stab at some solution to the REAL problem. A useful exercise that some six sigma folks like to use is "Five Why's". Why do you need to to this? Is the goal to keep some process going without intervention? Is the idea that if you run out of material, your whole structure starts to melt? Keep asking "Why" for all the answers you develop, and by the time you're five why's deep, you'll have a much better understanding of the issues.

Now, some particulars. Are levels loaded separately, and do materials get used up differently in different levels? Are the materials fuel, or stuff to be melted?

Is this a new problem, or is it something process engineers deal with as their bread and butter? How do people with similar problems approach this. Blast furnaces have been around a long time -- why all of a sudden have you come upon an unsolved issue? What's different about your situation that all these folks haven't encountered before? This type of research is necessary, and not optional.

Why have you focused on temperature? Does temp go down or up when you run out of stuff in different levels?

Now, with a better understanding of the problem you're trying to solve, brainstorming can be useful. Gather interested parties, and have at it. At this point, you're generating solutions --- ALL solutions, NOT good solutions! Get creative. Later is the time for picking which solutions are good. Don't try to develop the ideas too much at this time.

A few brainstorming ideas to get you started:

  • Is there any way to get the info you need from monitoring process exhaust? Can you add something to the limestone that vaporizes and you can assay it on the way out?
  • Is there any info to be gained by weighing the stucture?
  • Can you measure the skin temps of the structure, and use some thermal modeling techniques to map that back to the inside>
  • ...
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    \$\begingroup\$ +1 for "this must be a solved problem" \$\endgroup\$ – pjc50 Aug 7 '14 at 15:38

An optical pyrometer measures the surface temperature of an "object" and, the "object" in your application is the rising (or falling) surface inside the blast furnace. Given your diagram, it makes sense to assume that the lower the surface is, the hotter the surface is.

Therefore, use a non-contacting industrial pyrometer mounted at the top of the furnace to measure the surface temperature of the molten substance and from this temperature determine the height of the surface.

They use optical pyrometers in jet engines to "look for" hot spots on engine turbine blades so the idea is ruggedized already.

enter image description here

The ruggedized probe is to the left of the screen. Maybe it would work?

Optical pyro system


Another way is to use the electrical conductivity of the molten metal to reduce the inductance of a coil built into the side of the furnace at the requisite points. Basically it's a metal detector and should be able to pin-point the molten-metal surface to a couple of inches. The slag that sits on top of the molten metal probably won't be detectable - slight downfall.

Another idea might be to measure the temperature of the gases coming off the molten fluid. If I remember correctly, these gases are mainly carbon monoxide and dioxide in about equal quantities (for steel production) - maybe the higher the surface is, the lower the temperature is.

Also, maybe the ratio of CO to CO\$_2\$ might give an indication of fluid height?

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    \$\begingroup\$ That screen would melt in a second ;) \$\endgroup\$ – Scott Seidman Aug 7 '14 at 13:47
  • \$\begingroup\$ It's very nice idea to use CO & CO2 approach \$\endgroup\$ – xsari3x Aug 7 '14 at 13:53
  • \$\begingroup\$ Yeah, I'm running right toward process exhaust, too. I don't know enough about the process to know if that's the right direction, but it would get my research time. \$\endgroup\$ – Scott Seidman Aug 7 '14 at 13:55
  • \$\begingroup\$ @ScottSeidman yeah the screen would need protection LOL. British steel operate gas mass spectrometers at their Scunthorpe plant in order to optimize the steel yield so it's not an unheard-of technology to apply i.e. sampling the exhaust gasses is a do-able thing. \$\endgroup\$ – Andy aka Aug 7 '14 at 14:29

As I already said, just buy a furance glass like this and put it in the wall of the furance and detect the levels that you want. that's just $60 and also it's guaranteed up to 2300°F (1260c).

have a good time!

figure 1


In my opinion the dust is not very important but to avoid of it you can make several branch upper than the level of the limestone and and do your job! look like this:


there are several approach that you can do it simple than above approach.


in the melted part you can use my trick and for none-melted part you can put in the wall diagonal.

  • \$\begingroup\$ The limestone dust will soon sick to the inside of the glass. \$\endgroup\$ – Ian Ringrose Aug 7 '14 at 14:21
  • \$\begingroup\$ @IanRingrose Trust me. I edited it. \$\endgroup\$ – Roh Aug 7 '14 at 14:31

I'd drill holes into the side of the furnace, and solve this problem mechanically by trying to insert a rod. That way you could even pull samples from the different heights.

But I guess this is a not-problem. A furnace should, the way furnaces work, always be filled to the top, shouldn't it?

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    \$\begingroup\$ Saying 'the furnace ... should always be filled to the top' simply begs the question 'how to check that the furnace is full' \$\endgroup\$ – Pete Kirkham Aug 7 '14 at 18:24
  • \$\begingroup\$ btw I'm checking is it's full so i don't overload it with more stones \$\endgroup\$ – xsari3x Aug 8 '14 at 12:32

Can you make the lower loading cone sufficiently heat-resistant for it to be briefly lowered on to the top of the charge? If so, then just measure the chain length until it goes slack, as when taking marine soundings by swinging the lead.


I might be naive but I'd do this one of the two ways:

a) Use ultrasound or similar measurment vertically, to determine level of liquid. This will/might be fuzzy while adding cold stuff from above.

b) Use a (possibly IR) camera from the top. If the slope of the inner wall is steep enough, you should be able to derive a simple formula to determine liquid level, given fixed camera position [Edit: from the image pixels of course]. That is by detecting the visual/thermal edge between the wall and the contents. Given a one full recording of the furnace's operation, you will determine the relation and the error (between distance from fixed point-pixel directly underneath camera and the edge of liquid).

Cheapest IMHO.


Going by the difference in the weight of the furnace compared to empty should give you a decent idea on how full it is. It may not be as precise as other options, but you probably won't have to worry about heat.

This obviously isn't very practical if the furnace is already constructed, but might be a useful alternative to more complex sensing methods if it can be designed into the initial construction of the furnace itself.

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    \$\begingroup\$ And how do you propose weighing a 10m tall brick structure? \$\endgroup\$ – Matt Young Aug 7 '14 at 20:36
  • \$\begingroup\$ The same way you weigh anything, with a scale. \$\endgroup\$ – Mike Aug 7 '14 at 21:20

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