Method and apparatus for cement kiln control

Claim 2

A control for a rotary cement kiln as recited in claim 2 additionally comprising steering function generating means in response to the feedback signal for combination with the burning zone temperature deviation, the torque error signal and the feedback signal in said total process error determining means, means responsive to said fuel error derivation means and said steering function generating means for generating a base fuel level variable in response to long term process changes for combination with the fuel error to obtain a fuel level, said heat input means being responsive to the fuel level for controlling the heating in response to short term process disturbances. 4 In a rotary cement kiln control system including drive means for normally rotating the kiln at a constant speed, heating means for causing a material transformation in the kiln at a burning zone, first sensing means responsive to the torque developed by the drive means to rotate the kiln for supplying a corresponding output, second sensing means responsive to material temperature in the burning zone for providing a corresponding output and control means comprising: a. means responsive to said second sensing means and a predetermined burning zone temperature for indicating the burning zone temperature deviation, b. means responsivE to said first sensing means for indicating a torque error, c. means for generating process feedback and means responsive thereto for generating a steering function, d. means for combining the burning zone temperature deviation, torque error, feedback and steering function to obtain a total process error, e. means responsive to a first range of total process errors for deriving therefrom a fuel-related error and to total process errors beyond the first range for deriving therefrom a speed-related error, f. means responsive to an initial fuel level and said steering function for generating a base fuel variable in accordance with long term process changes for addition to the fuel-related error and a fuel-related error feedback, said heating means being responsive to the combined base fuel and fuel-related error, and g. means responsive to the speed-related error for generating a speed-related error feedback, said feedback means storing previous fuel and speed feedback for combining selected ones representing expected variations in the output of said first and second sensing means due to previous control actions to generate the feedback and said steering function means being responsive to the feedback to cause the heating means and drive means to be controlled in response to short term disturbances.

Claim 3

A rotary cement kiln control system as recited in claim 4 additionally comprising means responsive to said second sensing means for generating a representation of kiln thermal stability, said burning zone temperature deviation indicating means and said torque error indicating means being responsive to said thermal stability indicating means to vary the relative contributions of burning zone temperature deviation and torque error to the total process error in accordance with kiln thermal stability.

Claim 4

A rotary cement kiln control system as recited in claim 4 additionally comprising means responsive to said first sensing means and said torque error generating means for generating a rate amp forcing function to be added to the speed-related error in response to predetermined rates of change of torque whereby such variations in torque measurement alter kiln speed.

Claim 5

A rotary cement kiln control system as recited in claim 4 including means responsive to the speed-related error for generating a speed change signal, first means responsive thereto for obtaining a speed signal from the speed change signal and a predetermined base speed signal and second means responsive to the speed change and base speed signals for modifying the fuel-related error whereby decreases in the speed cause decreases in the fuel-related error.

Claim 6

A rotary cement kiln control system as recited in claim 7 comprising means responsive to said burning zone temperature for indicating kiln thermal stability in response to said burning zone temperature deviation means, means responsive to the speed-related error for generating a speed change signal and means responsive to said thermal stability indicating means and a burning zone temperature error generated by said burning zone temperature deviation means for generating a high temperature speed forcing signal when the burning zone temperature error exceeds a predetermined error range.

Claim 7

A rotary cement kiln control system as recited in claim 4 wherein said burning zone temperature deviation means includes means responsive to said second sensing means for determining a burning zone error additionally comprising means responsive to burning zone temperatures in a range above the predetermined burning zone temperature for decreasing the heat input to the kiln by a factor which is variable in accordance with burning zone temperature error.

Claim 8

A rotary cement kiln control system as recited in claim 4 wherein said burning zone temperature deviation means generates a burning zone temperature error in response to said second sensing means, said control system additionally comprising means responsive to the burning zone temperature error fOr generating a low temperature speed forcing function when said burning zone temperatures exceed a range lower than the predetermined burning zone temperature and adding the low temperature forcing function to the speed-related error.

Claim 9

A rotary cement kiln control system as recited in claim 4 adapted for controlling a wet kiln having chain means for contacting wet feed entering the kiln and driving moisture therefrom, said control system additionally comprising means for measuring gas flow through the kiln, gas temperatures at the ends of the chain means and the rates at which feed and dust enter the kiln and means responsive to said measuring means and coupled to said feedback means for indicating the effect on torque measured by said first sensing means by conditions in the chain means for immediately and directly altering the feedback signal to nullify such variations in said first sensing means output.

Claim 11

A control method for a rotary cement kiln as recited in claim 12 including the additional step of determining the thermal stability of the kiln from said burning zone temperature measurement, and said burning zone temperature deviation and torque error determinations being responsive to said thermal stability determination to vary the relative contributions thereof to the total process error in accordance with the thermal stability of the kiln.

Claim 12

A control method for a rotary cement kiln as recited in claim 12 including the additional step of controlling the drive means to reduce kiln speed in response to predetermined rates of change of torque as obtained from said torque measurement.

Claim 13

A control method for a rotary cement kiln as recited in claim 12 wherein said drive means control determines a speed change from said speed error apportionment and combines said speed change with a base speed and, in response to the base speed and said speed change determination modifies said heating means control in response to said fuel error apportionment whereby decreases in said combination of speed change and base speed cause said heat input control to decrease heat input to the kiln.

Claim 14

A control method for rotary cement kiln as recited in claim 15 wherein said drive means control responds to a burning zone temperature error determination in response to said burning zone temperature measurement and kiln thermal stability as determined from said burning zone temperature measurement by decreasing kiln speed in response to burning zone temperature errors indicating burning zone temperatures exceeding a range above a predetermined burning zone temperature.

Claim 15

A method for a rotary cement kiln as recited in claim 12 wherein said burning zone temperature deviation includes the step of determining a burning zone temperature error in response to said burning zone temperature measurement, said control method additionally causing said control of heat input to respond to burning zone temperature error for errors above predetermined values.

Claim 16

A control method for a rotary cement kiln as recited in claim 12 wherein said drive means control responds to burning zone temperature errors generated in response to said burning zone temperature measurement which represent burning zone temperatures below a predetermined burning zone temperature to decrease kiln speed.

Claim 17

A control method for a rotary cement kiln as recited in claim 12 having chain means for contacting wet feed entering the kiln and driving moisture therefrom including the additional steps of measuring gas flow through the kiln, gas temperatures at the ends of the chain means and material and dust feed rates and responding to said measurements by indicating the effect on said torque measurement which is related to conditions in the chain means and immediately and directly altering the feedback signal to nullify variations in the said torque measurement caused by variations of conditions in the chain means.