IEEE TRANSACTIONS ON INDUSTRY AND GENERAL APPLICATIONS, VOL. IGA-6, NO. 5, SEPTEMBER/OCTOBER 1970 Kiln Interior Temperature Transducer PATRICK SULLIVAN, SENIOR MEMBER, IEEE Abstract-An important control variable for cement kiln process control is material temperature in the various processing zones. Temperature measurements in the calcining zone of the cement kiln utilizing thermocouples becomes impractical because of the corrosive action of the hot gases on the thermocouple protective sheath. The results of the development of a kiln interior temperature sensor which can be utilized in those sections of the kiln which are too hostile for thermocouple installation is described as are the air-purging system, pyrometer, port box, and sight-tube components of the sensor. Sensor-output charts are analyzed, and examples of data output from an on-line computer data-reduction program are discussed. Methods are discussed for determining the optimum sensor location along the rotary kiln. INTRODUCTION A PREREQUISITE of effective process control is the ability to supply the control system with accurate and timely information regarding key process variables. In gen- eral, as the control system increases in complexity and so- phistication, the requirement for feedback information from process variables to the control systems is also increased. Feed-forward control, for example, implies measurement of an additional variable time related to the desired control variables; multivariable control implies measurement of Paper 70 TOD 14-IGA, approved by the Cement Industry Com- mittee of the IEEE IGA Group for presentation at the 1970 IEEE Cement Industry Technical Conference, Indianapolis, Ind., May 12- 14. M-anuscript received June 1, 1970. The author is with the Allis-Chalmers Company, Milwaukee, Wis. 53201. additional variables which affect the desired control vari- ables; improved control response often dictates measure- ment of desired variables directly rather than indirectly or displaced in time. Instrumentation applied to the modern cement kiln must provide the control system with information on gas flows, fuel rates, gas pressures, gas and material tempera- tures, feed and product chemistry, material-flow rates, drive parameters, and numerous other process variables. The importance of one variable as compared to another could be debated at great length; suffice it to say that, in general, the control-system designer is never entirely satis- fied with either the amount or the quality of process in- formation attainable on line. Being basically a pyroprocess, the importance of temperature measurements for kiln con- trol is obvious. Dimensions of the modern cement kiln demand that temperature measurements along the length of the kiln, in addition to measurements at the feed and discharge end, be made in order to implement effective process control. Temperature measurements in the calcin- ing zone and even midkiln measurement utilizing thermo- couples becomes impractical because of the abrasive action of the hot material combined with the corrosive action of hot gases on the thermocouple protective sheath. The results of the development of a kiln interior tem- perature sensor which can be utilized in those sections of the kiln too hostile for thermocouple installation will be described. This sensor utilizes a radiation pyrometer which 503
Transcript
IEEE TRANSACTIONS ON INDUSTRY AND GENERAL APPLICATIONS, VOL. IGA-6, NO. 5, SEPTEMBER/OCTOBER 1970
Kiln Interior Temperature Transducer
PATRICK SULLIVAN, SENIOR MEMBER, IEEE
Abstract-An important control variable for cement kiln processcontrol is material temperature in the various processing zones.Temperature measurements in the calcining zone of the cement kilnutilizing thermocouples becomes impractical because of the corrosiveaction of the hot gases on the thermocouple protective sheath. Theresults of the development of a kiln interior temperature sensor whichcan be utilized in those sections of the kiln which are too hostile forthermocouple installation is described as are the air-purging system,pyrometer, port box, and sight-tube components of the sensor.Sensor-output charts are analyzed, and examples of data output froman on-line computer data-reduction program are discussed. Methodsare discussed for determining the optimum sensor location along therotary kiln.
INTRODUCTION
A PREREQUISITE of effective process control is theability to supply the control system with accurate and
timely information regarding key process variables. In gen-eral, as the control system increases in complexity and so-phistication, the requirement for feedback information fromprocess variables to the control systems is also increased.Feed-forward control, for example, implies measurement ofan additional variable time related to the desired controlvariables; multivariable control implies measurement of
Paper 70 TOD 14-IGA, approved by the Cement Industry Com-mittee of the IEEE IGA Group for presentation at the 1970 IEEECement Industry Technical Conference, Indianapolis, Ind., May 12-14. M-anuscript received June 1, 1970.The author is with the Allis-Chalmers Company, Milwaukee, Wis.
53201.
additional variables which affect the desired control vari-ables; improved control response often dictates measure-ment of desired variables directly rather than indirectly ordisplaced in time.
Instrumentation applied to the modern cement kilnmust provide the control system with information on gasflows, fuel rates, gas pressures, gas and material tempera-tures, feed and product chemistry, material-flow rates,drive parameters, and numerous other process variables.The importance of one variable as compared to anothercould be debated at great length; suffice it to say that, ingeneral, the control-system designer is never entirely satis-fied with either the amount or the quality of process in-formation attainable on line. Being basically a pyroprocess,the importance of temperature measurements for kiln con-trol is obvious. Dimensions of the modern cement kilndemand that temperature measurements along the lengthof the kiln, in addition to measurements at the feed anddischarge end, be made in order to implement effectiveprocess control. Temperature measurements in the calcin-ing zone and even midkiln measurement utilizing thermo-couples becomes impractical because of the abrasive actionof the hot material combined with the corrosive action ofhot gases on the thermocouple protective sheath.The results of the development of a kiln interior tem-
perature sensor which can be utilized in those sections ofthe kiln too hostile for thermocouple installation will bedescribed. This sensor utilizes a radiation pyrometer which
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IEEE TRANSACTIONS ON INDUSTRY AND GENERAL APPLICATIONS, SEPTEMBER/OCTOBER 1970
PYROMETER
KILN REFRACTORY
Fig. 1. Kiln interior temE
Fig. 2. Kiln interior temperature trarotary ki
Fig. 3. Blower ar
PORT BOX paO"US X
SIGHT TUBE X /
45
)erature transducer. /
\ ~~~~~/Fig. 4. Sighting angle of kiln interior temperature transducer.
I sights through a port in the kiln shell. A suitable air-purg-ing system is requaired to suspend the kiln burden materialand thus prevent plugging of the port during that segmentof the kiln rotation in which the port is underneath the kiln
gl v | ~~~load.
DESCRIPTION OF SENSOR
Fig. 1 schematically illustrates the major componentsof the kiln interior temperature transducers. These com-
l j|ponents are the sighting-tube assembly and port box,pyrometer, amplifier, and air-purging system. Electricalslip-ring conductors are required for signal and powertransmission. Figs. 2 and 3 show this equipment mounted ona rotary kiln. As illustrated in Fig. 2, the blower for theair-purge assembly and the signal amplifier are mounted on
a raised platform which is attached to the kiln shell.
SIGHTING-TUBE ASSEMBLY AND PORT Box
A swivel-type sighting tube has been developed for thensducer equipment mounted on kiln interior temperature transducer. This mounting ar-n. rangement permitted experimentation with the sighting
angle to determine the angle best suited for the sensor.Choice of the angle of the sighting tube is based on sev-
eral considerations. A major consideration is to set an anglewhich is least susceptible to probe plugging which is causedto a certain degree by a combination of material depth andprobe-scooping action. If the tube is aligned to sight alonga radius vector, the depth of material to be suspended isminimized. If the sighting angle lags the kiln rotation, thescooping action is decreased. There are also, from a dataviewpoint, certain advantages to adjusting the angle sothat either the pyrometer scans the top of the kiln loadimmediately prior to passing under the load or immediatelyafter passing under the load. One specific angle does notserve all of these considerations best. Repetitive tests in-dicate that a sighting angle that lags the radius vectorapproximately 45 degrees serves the majority of theseconsiderations best. This arrangement is shown in Fig. 4.The sighting tube has a 1-inch insideditameter and is 9
id pyrometer. inches long. These dimensions vary with pyrometer selec-
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SULLIVAN: KILN INTERIOR TEMPERATURE TRANSDUCER
Fig. 5. Port box sight tube removed.
Fig. 6. Port box, sight tube in place.
Fig. 7. Port box, view from inside of kiln.
tion since the target diameter needed to provide a suffi-cient amount of energy for the sensor will vary.The port box is approximately 12 inches long by 4 inches
wide. Depth is sufficient to match brick and shell thicknessof the kiln. Sight tube and port box are fabricated fromstainless steel to withstand the high ambient temperaturesand the corrosive atmosphere inside the kiln.
Fig. 5 illustrates the port box with the sighting tuberemoved. Fig. 6 illustrates the port box with the sightingtube in place. Fig. 7 illustrates the port box and sightingtube from inside the kiln.The pyrometer is attached to the sight tube by a quick-
disconnect twist assembly. The mounting flange is relievedto accept the pyrometer enclosure. This assures alignmentand prevents the pyrometer from viewing the sides of thesight tube.
PYROMETER AND SIGNAL AMPLIFIERThe pyrometer used to intercept the radiation energy
emitted by the kiln interior must operate in relativelyhigh-ambient air-temperature conditions. Both photon-sensitive and thermopile types of radiation pyrometerswere tested for the kiln interior temperature sensor project.The photon-sensitive pyrometer exhibited fast-responsecharacteristics which were desirable to sharply define thetransition from the refractory wall reading to the underloadreadings to the load surface temperature readings. Thephoton-sensitive pyrometer required a multirange elec-tronic controller to cover the 1200-2700-degree range en-countered. This controller when subjected to the highambient temperature on board the rotary kiln requiredexcessive maintenance and adjustment, and for this reason,a thermopile-type pyrometer was selected for this applica-tion.
Various lens material was tested for the pyrometerassembly. Pyrex provided too low an output for the desireddimensional constraints of the sight tube. Calcium fluoridecracked under thermal shock. A fused silica lens proveddurable and was used during data-collection runs.The pyrometer signal output must be conducted via slip
rings and shielded cable to the kiln-control panel. Theslip-ring impedance is variable and will introduce noise inthe sensor signal. Since the signal voltage generated by thethermopile pyrometer is low, an o n-board millivolt-to-current converter is used to amplify the pyrometer outputto a satisfactory level for transmission to the control room.This device, essentially a silicon transistor amplifier,contains no tubes, choppers, or extremely sensitive cir-cuitry and has proven sufficiently reliable for mountingon board the kiln. Because modular techniques are used inconstruction, maintenance as required can be performed"on the fly." A wire harness with a connector identical tothe fixed pyrometer connector is provided for simulatingthe pyrometer output with a portable precision-voltagesupply. A precision resistor in the converter output can beused for monitoring the converter output. These provisionspermit quick on-board calibration of the converter if re--quired.
506 IEEE TRANSACTIONS ON INDUSTRY AND GENERAL APPLICATIONS, SEPTEMBER/OCTOBER 1970
Fig. 8. Taking samples for blower sizing and kiln zone boundarydetermination.
AIR-PURGING ASSEMBLY
The air-purging system provides pressurized air forsuspending the load when the sight tube is under theload. In addition, the air provides cooling and cleansing forthe pyrometer lens and cooling for the sight tube. Consider-able testing was required to determine air volumes andpressures required to suspend the load in a suitable manner.Samples of material were taken at desired sensor locations,and tests were conducted to determine air requirements forsuspension and blow through for a sample depth of 1, 2,2'/2, and 3 feet (Fig. 8). Chemical analysis and temperaturereadings were taken to assist in identifying the actuallocation of the line of demarkation between various zones
in the kiln. Numerous blower-system configurations andblower types were tested for adequacy. A system deliveringapproximately 80 ft3/min at 2 lb-in2 was found to performadequately. Quick-disconnect mountings for the blowersallow installation and removal during kiln operation if re-
quired. The blower is mounted on an insulated stand-offplatform; and the interconnection between the blower andsight tube is made with flexible steel tubing.Power for the blower is brought on board the kiln via
another set of slip rings. These rings also supply the powerfor the pyrometer signal converter which was discussedearlier.The air stream from the blower is directed across the lens
of the pyrometer to cool and clean the lens and then flowsthrough the sight tube into the kiln interior.
SIGNAL ANALYSIS
A typical signal from the kiln interior temperaturetransducer is shown in Fig. 9. The maximum temperatureshown on the trace is the temperature of the interior refrac-tory wall. The load surface temperature is slightly lower
than the refractory-wall temperature. The valley is thereading taken of the suspended material when the sighttube is under the load. There was a very light load in thecalcining zone at the time this chart was taken, and cal-cining-zone temperatures were higher than usual. Fig. 10reflects a more likely sensor output with wall temperaturesranging up to about 2300°F and underload temperaturesaround 1500°F.The signal can be trend recorded, as shown in Fig. 11.
Information presented in this manner enables determina-tion of trends in calcining-zone refractory-wall tempera-ture, and if abnormal variations are detected, appropriatecompensation of fuel or speed can be made. A sample andhold amplifier can be used if a trend of wall temperature orload surface temperature alone is desired.
Considerable information regarding kiln conditions canbe gleaned from the sensor output signal. A computerprogram has been written which reduces the signal to thethree respective kiln interior temperatures and also cal-culates the load volume present at the point in the kilnwhere the sensor is located by using knowledge of the chordlength of the load surface. Conditions such as cold loadflushing or light load can be detected prior to their appear-ance in the burning zone, and proper control action can beimplemented by kiln speed or fuel control. The angle ofrepose of the load is also detected and can be logged. Ahigher angle of repose, for a given burden volume, occursas temperature increases.Table I is a sample of computer output generated from
an on-line data-reduction program written for the sensor.This output was taken concurrent with the analog dataillustrated in Fig. 9. The load angle is an indication of theamount of material present. Zeros in this column indicatethat the angle was below an arbitrary minimum value atthe time this data was logged.
A critical determination that must be made in applyingthe kiln interior temperature transducer is the physicallocation of the sensor on the kiln. For best operation, the
sensor should be located approximately 15 feet upstreamfrom the beginning of the burning-zone coating. It is possi-ble to locate the sensor closer to the burning zone and byincreasing air pressure keep the sight tube unplugged.However, channeling and spiraling occur in the load mate-rial which is in a plastic state and this prevents a consistentaccurate determination of the interior refractory-wall tem-perature.A typical sensor location for a 400-foot kiln is 75 to 100
feet from the discharge end. Sample analysis, kiln shelltemperature profile analysis, and inspection of the coatingon the kiln interior provide the information needed toproperly locate the sensor.
CONCLUSION
Effective control of the rotary kiln is dependent on in-formation sensed at many points in the process. The kilninterior temperature transducer provides, in a reliablemanner, continuous information regarding material load-ing and temperature prior to the entry of this materialinto the burning zone. Integration of this additional processinformation into existing kiln instrumentation and con-trol schemes will make possible more effective control ofthe cement-making process.
Patrick Sullivan (M'57-SM'69) was born in East St. Louis, Ill., on November 17, 1932. Hereceived the B.S. degree in electrical engineering from St. Louis University, St. Louis, Mo.,in 1954 and the M.S. degree in electrical engineering from the University of Wisconsin,Madison, in 1968.
In 1954 he joined the Allis-Chalmers Company, Milwaukee, Wis., where he has held avariety of engineering and managerial positions. As an Analytical and Senior Process SystemsEngineer, he was concerned with the analysis, computer simulation, and design of industrialand special electrical-drive systems. He supervised the development of automatic crusher-control systems, grinding mill controls, and centralized and digital computer-control systems.In his current assignment as Manager of Process Systems, he is concerned with all aspects ofdigital systems, variable-speed drives, power rectifiers, and electrical packages for the ProcessElectrical Systems Department.Mr. Sullivan is a Registered Professional Engineer in the State of Wisconsin.
