Temperature measuring device for rotary kilns

A temperature measurement device for rotary kilns comprises a stripping sleeve rigidly mounted in a bore or the shell of a rotary kiln and has one end portion extending into the rotary kiln. A ceramic ring is mounted at the one end portion of the sleeve and a protective tube is slidably mounted in the stripping sleeve and through the opening in the ceramic ring. A thermocouple is disposed in the protective tube at one end portion thereof that corresponds to the one end portion of the stripping sleeve. The protective tube is lifted to retract its one end portion until the end thereof is disposed in the ceramic ring thereby scraping off any crust thereon and the tube is then lowered to such an extent that the one end portion thereof protrudes from the ceramic ring so that temperature measurement can be effected.

BACKGROUND OF THE INVENTION 
This invention relates to a temperature-measuring device for rotary kilns, 
comprising a stripping sleeve, which is rigidly mounted in a bore in the 
shell of the rotary kiln and protrudes to some extent into the rotary 
kiln, and a thermocouple, which is disposed in a protective tube, which is 
movably disposed in the stripping sleeve and secured to a lifting and 
lowering device, which is mounted on the outside of the shell. 
In processes carried out in a rotary kiln, e.g., in the direct reduction of 
iron oxides below the melting and softening point of the charge by means 
of solid and gaseous reducing agents, the temperature must be exactly 
controlled throughout the length of the rotary kiln. The temperature is 
usually measured by means of thermocouples, which are disposed in 
protective tubes, which are spaced along the rotary kiln and extend 
through the wall and revolve with the kiln. Because the charge tends to 
cake on the protective tubes or to soil the same in the kiln, the 
resulting deposits must be removed from time to time because an error 
would otherwise be introduced into the result of the measurement. 
A known temperature-measuring device for rotary kilns disclosed in German 
application P 21 32 687 comprises a thermocouple disposed in a protective 
tube, which is surrounded by a sleeve, except for its lower-most portion. 
The protective tube and the sleeve are secured outside the shell of the 
rotary kiln to a holder, which bears on a spring element, which is secured 
laterally of the protective tube. A roller is disposed above the spring 
element and during a rotation of the rotary kiln enters a cam track, which 
causes the roller to force the protective tube and sleeve into the 
interior of the furnace. As the roller leaves the cam track, the spring 
element returns the protective tube and the sleeve. The parts are 
depressed when they reach that range of the rotary kiln which contains the 
charge and are returned as they leave that charge-containing range. 
Whereas crusts can be knocked off the kiln wall by this device as it is 
forced into the kiln, it is not possible to remove crusts or dirt from the 
protective tube. Besides the fact that the protective tube and the sleeve 
are laterally secured and guided may easily result in canting. 
For measuring temperature in the kiln atmosphere of kilns for making cement 
it is known from German application P 12 66 538 to arrange the 
thermocouple and the protective tube in a stripping sleeve, which is 
disposed in a guide sleeve. Outside the kiln, the stripping sleeve is 
secured to a bellcrank lever and the latter is secured to a crank drive. 
When it is desired to remove dust from the protective tube, the stripping 
sleeve is pushed into the kiln beyond the end of the protective tube and 
is then pulled out. As the stripping sleeve is pulled out, dust is removed 
also from the stripping sleeve as a result of its cooperation with the 
guide sleeve. The crank drive may be replaced by an eccentric mechanism or 
similar drive means, which directly strikes against a projection of the 
stripping sleeve, which is resiliently mounted. Whereas this arrangement 
can be used to remove dust which has been deposited from the kiln 
atmosphere, difficulties are involved in the use of the arrangement with 
rotary kilns. As the device moves through the charge, crusts are formed on 
the protective tube and when the stripping sleeve is pushed inwardly these 
crusts can easily be seized between the stripping sleeve and protective 
tube and may then cause destruction. Particularly the edge of the 
stripping sleeve tends to be damaged quickly and to burn off and there is 
also a danger of canting. 
From "Neues aus der Technik", Vogel-Verlag, Wurzburg, No. 3, June 1, 1973, 
page 1, it is known to provide a thermocouple in a protective tube, to 
arrange the latter in a fixed sleeve, to secure the protective tube 
outside the rotary kiln to a toggle joint, which is loaded by a 
compression spring, and to control the toggle joint by a cam disc during 
the rotation of the rotary kiln. In this arrangement, the protective tube 
is pulled into the sleeve and cleaned and as it leaves the cam disc is 
pushed out on the sleeve by the spring pressure. In that case too, crusts 
formed on the protective tube can easily be seized between the sleeve and 
the protective tube as the latter is pulled into the sleeve so that damage 
results and specifically the edge of the sleeve is damaged and burns off. 
There is also a danger of canting in this arrangement. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to avoid the disadvantages of the 
known temperature-measuring devices and particularly to provide for rotary 
kilns a temperature-measuring device which enables coarse crusts to be 
knocked off and small impurities to be removed. It is another object of 
the invention that the device has a long life and is quickly replaceable. 
Those and other objects are accomplished according to the invention wherein 
a ceramic ring is disposed in the stripping sleeve at its lower end, the 
lower end of the protective tube is mounted in the opening of the ceramic 
ring, the upper end of the protective tube is secured to a rod, which is 
coaxially guided in the lifting and lowering device with respect to the 
opening of the ceramic ring, the rod is first lowered toward the shell by 
the lifting and lowering device when it is desired to clean the protective 
tube and is then lifted so that the protective tube is retracted until its 
lower end is disposed in the ceramic ring, and the rod is lowered for a 
measurement of temperature to such an extent that part of the protective 
tube protrudes from the ceramic ring. The ceramic ring serves to guide the 
protective tube in the stripping sleeve and also as a stripper during the 
upward movement of the protective tube. Coarse crusts are knocked off as 
the protective tube is lowered at the beginning of the cleaning operation, 
and crusts and dirt which have been desposited directly on the ceramic 
ring and the protective tube are knocked off at the same time so that they 
cannot cause destruction or seizing during the subsequent lifting 
movement. Small crusts and impurities still adhering to the protective 
sleeve will be stripped off during the lifting movement. The cleaned 
protective tube is then extended to its position for measurement. The 
protective tube is cleaned when it is disposed in the free kiln atmosphere 
rather than in the charge. To facilitate a replacement of the ceramic 
ring, the stripping sleeve is arranged so that it can easily be pulled out 
of the kiln. Because the rod is coaxially guided as it is moved toward the 
opening of the ceramic ring, any canting of the protective tube during the 
cleaning operation is avoided. The protective tube can be pushed into the 
kiln when it has been separated from the rod. 
In a preferred embodiment, the rod is vertically guided between two rollers 
with this arrangement an exact vertical guidance of the protective tube is 
ensured in a simple manner. 
According to another preferred feature, a holder consisting of a clamp is 
secured to the lower end of the rod and serves to secure the upper end of 
the protective tube. With this arrangement, the protective tube can be 
secured to the rod and can quickly be released therefrom. This frictional 
clamp fastener has also the advantage that the protective tube will 
separate from its fixing means during the upward movement when the exposed 
portion of the protective tube in the kiln has become bent. As a result, 
damage to other parts will be avoided. 
According to still another preferred feature, the lifting and lowering 
device comprises and eccentric mechanism, which is driven by a gearmotor, 
and the initial and final positions of the eccentric sheave are adjustable 
by a camwheel and by a brake, which is incorporated in the gearmotor. The 
eccentric mechanism engages the rod vertically over the same and enables 
in a simple manner a movement without canting. 
According to a further preferred feature, the lifting and lowering device 
is pivoted on a lateral axis of rotation on a frame with this arrangement 
and the lifting and lowering device can quickly be tilted aside to render 
the other parts freely accessible.

DETAILED DESCRIPTION OF THE INVENTION 
A bore extending through a kiln shell 6 and a kiln lining 14 is provided 
with a sleeve 15 for the protection of the kiln lining 14. A stripping 
sleeve 1 is pushed into the protective sleeve 15 and carries a plate 16, 
which engages a bracket 17 and is fixed by screws. The plate 16 is 
provided with handles 18 to facilitate removal and insertion. A ceramic 
ring 2 is disposed in the stripping sleeve 1 at its lower end. The lower 
portion of a protective tube 3 has been inserted through the opening of 
the ceramic ring. The upper end of the protective tube 3 is secured in a 
holder 8, which consists of a clamp comprising a screw 19, which can be 
tightened to clamp the upper end of the protective tube 3 in position. The 
holder 8 is secured to a rod 4, which is coaxially guided in a lifting and 
lowering device 5 between two rollers 7 with respect to the opening of the 
ceramic ring 2. The lifting and lowering device 5 is carried by a frame 
12, which is fixed with screws to the bracket 17. The lifting and lowering 
device 5 may be swung toward the side about a lateral pivot 13 when a 
quickly tightenable screw 20 has been released. A thermocouple 21 is 
disposed in the protective tube 3 and connected to leads 22, which extend 
out of the upper portion of the protective tube 3. The eccentric mechanism 
in the lifting and lowering device 5 is operated by a gearmotor 9. The 
initial and final positions of an eccentric sheave 10 are adjusted by a 
camwheel 11. In this way, the desired lowering movement, lifting movement, 
and measuring position of the protective tube are adjusted. The 
arrangement is held in position for measurement by a brake, which is 
incorporated in the gearmotor 9. When the gearmotor 9 is started, an 
eccentrically mounted connecting rod 23 moves the rod 4, to which it is 
connected by a pivot 24. 
In accordance with FIG. 3, a cam 25 secured to the kiln shell 6 is arranged 
to actuate a limit switch 26 once during each revolution of the kiln. The 
limit switch 26 is secured to a walkway 27. In response to each actuation, 
the limit switch 26 delivers a pulse to a presettable counter 28. When the 
preset number of pulses has been counted, an auxiliary motor 29 moves a 
coulisse 30 toward the rotary kiln to such a position that a limit switch 
31 mounted on the rotary kiln is actuated and the gearmotor 9 is started. 
The coulisse 30 is so long that the limit switch 31 remains actuated until 
a limit switch 32 has been disengaged by the camwheel 11, which is mounted 
on a camshaft 33, and the circuit has thus been closed. The protective 
tube is now moved through a full cleaning cycle, until the camwheel 11 
actuates the limit switch 32 once more to interrupt the circuit. 
In the foregoing specification and in the claims, various statements of 
position and direction, such as "upper" and "lower", "upwardly" and 
"downwardly", "lifting" and "lowering", are applicable to the 
temperature-measuring device when it is at the top of the rotary kiln. 
The advantages of the invention reside mainly in that the protective tube 
can be virtually completely cleaned from coarse crusts and small 
impurities and damage is substantially prevented as well as a canting of 
the protective tube during the cleaning operation and a rapid replacement 
is enabled. 
It will be appreciated that the instand specification and claims are set 
for the by way of illustration and not limitation, and that various 
modifications and changes may be made without departing from the spirit 
and scope of the present invention.