Feed rate control in a cement kiln incorporating dust return

Claim 1

A method for controlling the feed rate of raw material to a rotary cement kiln in relationship to the speed of rotation of the kiln to maintain a substantially constant effective depth of the feed in the kiln while feeding to the kiln the available recirculating dust under varying kiln rotation speeds comprising the steps of producing a first signal representative of the mass flow rate of the dust being returned to the kiln. producing a second signal representative of the average of said mass flow rate of the dust, producing in response to the difference between said first and second signals a third signal representative of the deviation of the mass flow rate of the dust from said average, producing a fourth signal representative of the deviation of the speed of rotation of the kiln from a predetermined set point value, producing a fifth signal representative of the desired change in the rate of feed of the raw material to the kiln to compensate for the rate of dust return and deviations of the kiln speed, said fifth signal being produced by multiplying the third signal by a first constant representative of the equivalent contribution of dust to the effective depth in terms of the raw feed equivalent to the dust and adding a quantity which is the product of the ratio of the fourth signal to the kiln speed set point multiplied by a quantity determined from the difference between the second signal times a second constant and the third signal times a third constant, said second and third constants being approximately equal to said first constant, and modifying said raw material feed rate in accordance with said fifth signal to thereby maintain a substantially constant effective depth of feed in the kiln.

Claim 2

A method for controlling the feed rate of raw material to a rotary cement kiln in relationship to the speed of rotation of the kiln to maintain a substantially constant effective depth of the feed in the kiln while feeding to the kiln the available recirculating dust under varying kiln rotation speeds comprising the steps of producing a first signal representative of the mass flow rate of the dust being returned to the kiln. producing a second signal representative of the average of said mass flow rate of the dust, producing in response to the difference between said first and second signals a third signal representative of the deviation of the mass flow rate of the dust from said average, producing a fourth signal representative of the deviation of the speed of rotation of the kiln from a predetermined set point value, producing a fifth signal representative of the desired change in the rate of feed of the raw material to the kiln to compensate for the rate of dust return and deviations of the kiln speed, said fifth signal being produced by multiplying the third signal by a first constant representative of the equivalent contribution of dust to the effective depth in terms of the raw feed equivalent to the dust and adding a quantity which is the product of the ratio of the fourth signal to the kiln speed set point multiplied by a quantity determined from the difference between the second signal times a second constant and the third signal times a third constant, said second and third constants being approximately equal to said first constant, and modifying said raw material feed rate in accordance with said fifth signal to thereby maintain a substantially constant effective depth of feed in the kiln.

Claim 3

A method for controlling the feed rate of raw material to a rotary cement kiln so as to maintain the relationship between the raw material feed rate and the speed of rotation of the kiln at a value such that there is maintained a substantially constant effective depth of feed in the kiln during periods when the available recirculated dust is being fed to the kiln and the kiln is subject to variations in its speed of rotation comprising the steps of producing a first signal representative of the mass flow rate of the dust being returned to the kiln, filtering said first signal by a high-frequency filter, producing a second signal representative of the average of said mass flow rate of the dust being recirculated, producing in response to the difference between said filtered first signal and said second signal a third signal representative of the deviation of the mass flow rate of the dust from said average, said second signal being produced by integrating said third signal so that said second signal becomes effectively representative of a running average of said mass flow rate of dust, producing a fourth signal representative of the deviation of the speed of rotation of the kiln from a predetermined set point value, producing a fifth signal representative of said kiln speed set point value, producing a sixth signal in response to the division of the fourth signal by said fifth signal, producing a seventh signal in response to the sum of said third signal and said second signal as modified by constants representative of the equivalent contribution to the effective depth of said recirculating dust in terms of raw feed material, producing an eighth signal in response to the product of said sixth and seventh signals, producing a ninth signal representative of the desired change in the rate of feed of the raw material to the kiln in response to the sum of said eighth signal and said third signal as modified in accordance with the equivalent contribution to the effective depth Made by the dust in terms of raw material, and modifying the rate of feed of said raw material in accordance with changes in said ninth signal to maintain substantially constant the effective depth of feed in the kiln.

Claim 4

A method for controlling the feed rate of raw material to a rotary cement kiln so as to maintain the relationship between the raw material feed rate and the speed of rotation of the kiln at a value such that there is maintained a substantially constant effective depth of feed in the kiln during periods when the available recirculated dust is being fed to the kiln and the kiln is subject to variations in its speed of rotation comprising the steps of producing a first signal representative of the mass flow rate of the dust being returned to the kiln, filtering said first signal by a high-frequency filter, producing a second signal representative of the average of said mass flow rate of the dust being recirculated, producing in response to the difference between said filtered first signal and said second signal a third signal representative of the deviation of the mass flow rate of the dust from said average, said second signal being produced by integrating said third signal so that said second signal becomes effectively representative of a running average of said mass flow rate of dust, producing a fourth signal representative of the deviation of the speed of rotation of the kiln from a predetermined set point value, producing a fifth signal representative of said kiln speed set point value, producing a sixth signal in response to the division of the fourth signal by said fifth signal, producing a seventh signal in response to the sum of said third signal and said second signal as modified by constants representative of the equivalent contribution to the effective depth of said recirculating dust in terms of raw feed material, producing an eighth signal in response to the product of said sixth and seventh signals, producing a ninth signal representative of the desired change in the rate of feed of the raw material to the kiln in response to the sum of said eighth signal and said third signal as modified in accordance with the equivalent contribution to the effective depth Made by the dust in terms of raw material, and modifying the rate of feed of said raw material in accordance with changes in said ninth signal to maintain substantially constant the effective depth of feed in the kiln.

Claim 6

A method for controlling the feed rate of raw material to a rotary cement kiln in a relationship to the speed of rotation of the kiln to maintain a substantially constant effective depth of the feed in the kiln while feeding to the kiln the available recirculating dust under varying kiln rotation speeds comprising the steps of measuring the mass flow rate of the dust, measuring the speed of rotation of the kiln, and modifying the feed rate of the raw material in accordance with the equivalent contribution in terms of raw feed made by the recirculated dust to the effective depth and in accordance with the deviation of the kiln speed from a particular desired value, including the steps of a. producing a first signal representative of the equivalent contribution due to the change in the return dust in terms of change in the raw feed, b. producing a second signal representative of the change in the raw feed rate necessary to accommodate the effect of a change in kiln speed from its desired value on the effective depth of feed in the kiln, c. producing a third signal in accordance with the sum of said first and second signals, and d. modifying the raw feed rate in response to said third signal.

Claim 7

A method for controlling the feed rate of raw material to a rotary cement kiln in a relationship to the speed of rotation of the kiln to maintain a substantially constant effective depth of the feed in the kiln while feeding to the kiln the available recirculating dust under varying kiln rotation speeds comprising the steps of measuring the mass flow rate of the dust, measuring the speed of rotation of the kiln, and modifying the feed rate of the raw material in accordance with the equivalent contribution in terms of raw feed made by the recirculated dust to the effective depth and in accordance with the deviation of the kiln speed from a particular desired value, including the steps of a. producing a first signal representative of the equivalent contribution due to the change in the return dust in terms of change in the raw feed, b. producing a second signal representative of the change in the raw feed rate necessary to accommodate the effect of a change in kiln speed from its desired value on the effective depth of feed in the kiln, c. producing a third signal in accordance with the sum of said first and second signals, and d. modifying the raw feed rate in response to said third signal.

Claim 8

A method for controlling the feed rate of raw material to a rotary cement kiln in a relationship to the speed of rotation of the kiln to maintain a substantially constant effective depth of the feed in the kiln while feeding to the kiln the available recirculating dust under varying kiln rotation speeds comprising the steps of measuring the mass flow rate of the dust, measuring the speed of rotation of the kiln, and modifying the feed rate of the raw material in accordance with the equivalent contribution in terms of raw feed made by the recirculated dust to the effective depth and in accordance with the deviation of the kiln speed from a particular desired value, including the steps of a. producing a first signal representative of the equivalent contribution due to the change in the return dust in terms of change in the raw feed, b. producing a second signal representative of the change in the raw feed rate necessary to accommodate the effect of a change in kiln speed from its desired value on the effective depth of feed in the kiln, c. producing a third signal in accordance with the sum of said first and second signals, and d. modifying the ratio of the raw feed rate to the kiln speed in response to said third signal.

Claim 9

A method for controlling the feed rate of raw material to a rotary cement kiln in a relationship to the speed of rotation of the kiln to maintain a substantially constant effective depth of the feed in the kiln while feeding to the kiln the available recirculating dust under varying kiln rotation speeds comprising the steps of measuring the mass flow rate of the dust, measuring the speed of rotation of the kiln, and modifying the feed rate of the raw material in accordance with the equivalent contribution in terms of raw feed made by the recirculated dust to the effective depth and in accordance with the deviation of the kiln speed from a particular desired value, including the steps of a. producing a first signal representative of the equivalent contribution due to the change in the return dust in terms of change in the raw feed, b. producing a second signal representative of the change in the raw feed rate necessary to accommodate the effect of a change in kiln speed from its desired value on the effective depth of feed in the kiln, c. producing a third signal in accordance with the sum of said first and second signals, and d. modifying the ratio of the raw feed rate to the kiln speed in response to said third signal.