Measurement and analysis of shell temperature distribution

Crank of the geometrical axis of the shell may be decomposed for the permanent and temporary component. Permanent component comes from the various kinds of mechanical irregularities remaining from the shell’s manufacturing and assembly stage. Temporary component – comes from the uneven distribution of temperature on the circumference of the drum, but in case of long time acting of high temperature on the shell of the drum it may also become a permanent deformation.
Permanent component may be corrected during the repair of the object, i.e. by the straightening or replacement of shell sections. Temporary component is changeable and depends on the process conditions taking place inside the object (in case of rotary kilns – mainly on the thickness of buildups, but also depending on the state and thickness of lining).
To accurately evaluate technical state of the shell and to plan properly the scope of its repair, essential is therefore the ability to separate those two components. During the repair and/or modernization we should focus on the first of them i.e. on the determination and elimination of the permanent part of crank and deformation. Minimization of temporary component is in hands of the team determining the process conditions, where the base is the ability to maintain even temperature on the circumference of the drum in each of its sections.
Previously used methods of shell state evaluation did not give the possibility to distinguish those two components of the crank of geometrical axis. Having separate data in the form of map of distribution of total eccentricity (including hidden component of the crank - /1/) and the map of temperature distribution on the shell (for example obtained from the thermal scanner of the object - /2/), one did not know how to quantify which portion of the measured crank comes from the interference visible on the thermal map (“hot” and “cold” spots) and which one is a permanent deformation, mechanical – independent from the changeable conditions of the process taking place inside the object.
The only thing that could offer so far an experienced diagnostician was to conclude if there are on the shell any areas of uneven temperature distribution /2/ and if they may influence obtained results of eccentricity /1/. Such evaluation was basing on the visual recognition of such places on the map of temperature distribution /2/. If such places existed, there was a reasonable suspicious, that the measured distribution of eccentricity vector /1/ is only temporary and after changing (equalizing) of temperatures, the real shape of the shell’s geometrical axis might be more or less different from the measured one. Routine conclusion was to recommend new measurement (verification) in conditions with equal temperatures on the particular circumferences of shell sections of the drum.
In the year of 2015 engineers of ZMP have implemented a novel device, which in a synchronic way is measuring both the radial run-out and the temperature distribution of the shell obtaining additionally to the maps of eccentricity distribution /1/ and local deformation also the map of distribution of real temperature of shell /3/.
This map /3/ after further mathematical treatment, depending on capturing in each measurement section the values diverging from the median /4/ this states clearer picture of thermal state of shell and in parallel states input data for further analysis.
On this map /4/ it is easier to see places with higher or lower temperature. This map is not „contaminated” with absolute values, which has no influence on the shape of shell geometrical axis, but only causes thermal expansion along kiln axis.
In the next step, knowing the geometry of the shell and using specially prepared algorithms (which are intellectual property of ZMP) from this map we can calculate distribution of eccentricity vector resulting from these temperature deviations. Map which has been obtained as result states the thermal component of the distribution of total eccentricity /5/.
For the presented example /5/ it is clearly seen, that the „cold spot” visible on the map of distribution of temperature differences /4/ results in crank of shell’s geometrical axis, i.e. in maximal deflection of its outline on the angle of circumference partitioning opposite to the place of location of „cold spot”.
This component is a temporary one and for sure it will vanish as soon as its cause will be removed i.e. will disappear when the temperature on the circumference of particular shell sections will equalize.
Having at disposal two maps: one – obtained basing on the results of measurements of radial run-out of the shell and measurements of cyclical deflections of support rollers’ shafts, this is the total eccentricity map /1/, second – obtained from the results of measurements and analysis of influence of temperature distribution of shell on its geometrical axis – being a thermal component of the first map /5/, it may be done a superposition of obtained values providing in result a map of distribution of eccentricity vector after separation of thermal component /6c/ ((c) = (a) - (b)).
This map states so called permanent component of crank of geometrical shell axis of analyzed drum (after separation of thermal factors).
From the analysis of maps (/6a/, /6b/ and /6c/) clearly can be seen, that the current (obtained during measurement – /6a/) crank of analyzed drum is the result of both the permanent bent of shell axis /6c/, and as well the thermal bent /6b/, which in this case amplifies (increases) values of total (permanent) eccentricity ((a) = (b) + (c)).
A similar analysis can be made for the local deformations i.e. from the map of distribution of shell temperature differences presented on /4/, calculate local deformations which are derivatives of this distribution /7/.
Presented analysis of influence of shell’s temperature distribution on the distribution of eccentricity vector and local deformations can be done also without the measurement of temperature, but based on the properly prepared (formatted) data obtained from the drum’s operator for example from the temperature scanner which is installed on the object.