Patent GB-1330342-A (GB)
Title: Method and apparatus for cement kiln control
IPC: F27B7/42
Filed: 1970-09-23
Abstract: 1330342 Automatic control of rotary cement kilns GENERAL ELECTRIC CO 23 Sept 1970 [26 Sept 1969] 45327/70 Heading G3R The cement kiln control system described in Specification 1245276 is improved by varying the heat input to the kiln in response to a combined error signal comprised of the deviation of the burning zone temperature from a predetermined value and the deviation of the drive motor torque from a predetermined value, the arrangement being such that for error signals in a range below a predetermined value the fuel signal set point is adjusted to produce the control action whilst the speed of the drive motor remains at a constant pre-set value, and for error signals above the predetermined value the fuel signal remains at a maximum value and the speed is varied. In this way, the fuel and speed are controlled to deal with small disturbances and large disturbances respectively. The basic improvement is modified to provide the following additional control features:- (1) variation of the predetermined value of torque in accordance with changes in the burning zone temperature. (2) use of a thermal stability gain factor, derived from the burning zone temperature, to allow the torque error or the temperature error to become the primary control variable according to whether the kiln process condition is unstable or stable. (3) reduction of the fuel signal when the speed is altered (decrease of fuel with decrease of speed). (4) use of the feedback signal from the process model to generate a steering function signal which acts on as initial fuel signal to provide a base fuel signal varying in accordance with changes caused by previous control actions. (5) use of the feed and temperature signal to vary the fuel set point signal. (6) use of a signal dependent on the rate of change of torque to vary the kiln speed. (7) reduction of speed and fuel signal set point when the burning zone temperature exceeds a first predetermined high value. (8) production of a signal to reduce the fuel set point signal when a second predetermined high value of burning zone temperature is exceeded. (9) reduction of the kiln speed when the burning zone temperature falls below a predetermined low temperature. (10) production of a signal for application to the process model dependent on the rate of feed of material into the kiln, the rate of feed of dust into the kiln and the temperatures at the feed end and the end of the chain section of the kiln, and on signals set by the operator representing per cent moisture in the feed and the input temperature of the feed. As shown in Figure 1, additional sensers are provided as follows: - (1) Optical pyrometer 165 to measure the burning zone temperature. (2) Senser 161 to measure the motor speed. (3) Senser 159 to measure the rate of dust flow. (4) Senser 53 to measure the chain end temperature. An additional controller 175 varies the speed of the drive motor 20 in response to the output of the main controller 51 shown in detail in Fig.2, in which members 120, 122, 84 and 121 provide the combined error signal which is passed to members 127, 140 providing the fuel and speed error signals respectively. The above mentioned additional control features are provided as follows: - Feature (1) by members 123, 125 " (2) " " 122, 123 " (3) " " 130, 145 " (4) " " 152, 150, 151 " (5) " " 90, 168 " (6) " " 169, 141 " (7) " " 170, 171, 143 " (8) " " 173, 131 " (9) " " 170, 174, 141 " (10)" " 180, 181, 182, 183 The parameter-signal reference relationship is as follows: - AMP SP  represents the desired value of torque. TBZ SP  represents the desired burning zone temperature. FET SP  represents the desired feed end temperature. KSPD base represents the desired normal constant speed of motor 20. Suffix SCAN represents the desired sensed parameter. Suffix 'n' or 'SP' represents the desired control signal. FEED represents the desired rate of material input. TIG represents the desired chain end temperature. DR represents the desired dust flow-rate. OXY represents the desired rate of oxygen flow. FUEL represents the desired rate of fuel supply. Logic circuits 101, 89, 105 etc. monitor senser operation to exclude signals outside a pre-set range.