System and method for improving model product property estimates
First Claim
1. A computer-based method for processing stream composition and/or product property estimates generated from dynamic process models, said stream composition and/or product property estimates used to control a physical process, comprising the steps of:
- (1) measuring, in a process comprising one or more units and two or more streams, pressure, temperature, and flow of said streams to produce raw process variable signals;
(2) comparing said current raw process variable signals with previously predicted process variable signals to determine error measures;
(3) using said error measures to adjust the dynamic process models to reduce future estimates of said error measures;
(4) predicting future process variable signals and future stream composition and/or product property signals from the dynamic process models;
(5) using said predicted future stream composition and/or product property values to directly or indirectly change the state of a control element(s) of said process; and
(6) operating said process using said control element(s) to produce a product.
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Abstract
The present invention is a system and method for improving stream composition and/or product property estimates from process models, which better reflect the true conditions of the process. One or more process simulation models are run on a computer in parallel with the actual process to provide estimates of stream composition and/or product properties to be used to control the process. Adjustments are made to the models to maintain them in alignment with continuously measured key process variables that are closely related to stream composition and/or product properties where such a relationship exists. This greatly improves the ability of the model to track the actual process. Additional adjustments are made to both the models and to the model estimates based on differences between measured and calculated stream composition/product properties. The combination of model calibration adjustments and direct correction of model estimates greatly improves the accuracy of the stream composition/product property estimates. Adjustments are made to model input variables and model parameters through use of controllers acting on the difference between measured and calculated properties. Differences obtained using relative error or the logarithm of the ratio of the measured and calculated values produce improved adjustments of component concentrations at low concentrations. Artificial measurements of stream composition and/or product properties can be synthesized by combining model composition estimates and flows at two or more locations in the process with an analytical measurement to produce and artificial analytical value at a second location in the process.
100 Citations
33 Claims
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1. A computer-based method for processing stream composition and/or product property estimates generated from dynamic process models, said stream composition and/or product property estimates used to control a physical process, comprising the steps of:
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(1) measuring, in a process comprising one or more units and two or more streams, pressure, temperature, and flow of said streams to produce raw process variable signals; (2) comparing said current raw process variable signals with previously predicted process variable signals to determine error measures; (3) using said error measures to adjust the dynamic process models to reduce future estimates of said error measures; (4) predicting future process variable signals and future stream composition and/or product property signals from the dynamic process models; (5) using said predicted future stream composition and/or product property values to directly or indirectly change the state of a control element(s) of said process; and (6) operating said process using said control element(s) to produce a product. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 18)
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16. A computer-based system for processing dynamic model generated stream composition and/or product property estimates, comprising:
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(a) two or more sensors for producing raw pressure and temperature signals from two or more streams in a process comprising one or more units and two or more streams; (b) one or more computer-based process dynamic models connected to receive limit checked pressure, temperature, and level signals, reconciled flows, feed composition signals, and model alignment factors, to produce predicted pressure and temperature signals and predicted stream composition and/or product property signals; (c) a process variable comparison module connected to use said raw pressure and temperature signals and said predicted pressure and temperature signals to determine an error between said raw signals and said predicted signals; (d) a statistical filter module connected to take said error and determine a new moving average error from the statistical history of said error; (e) an alignment module connected to take said new moving average error and produce one or more model alignment factors and connected to adjust said one or more computer-based process dynamic models based on said one or more model alignment factors; (f) a stream composition and/or product property controllers, connected to directly or indirectly use said predicted stream composition and/or product property signals as input, for producing a controller output signal in accordance with said input and a control objective; and (g) an actuator connected to change one or more states of said process in accordance with said controller output signal.
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17. A computer-based system for processing model generated stream composition and/or product property estimates, comprising:
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two or more sensors for producing raw stream composition and/or product property signals from two or more streams in a process comprising one or more units and two or more streams; one or more computer-based process models connected to receive reconciled flows and pressure, temperature, and level signals, said raw stream composition and/or product property signals, and model calibration factors, and produce predicted stream composition and/or product property signals; a product property transform module connected to use said reconciled flows, said raw stream composition and/or product property signals, and said predicted stream composition and/or product property signals to produce artificial stream composition and/or product property signals for streams lacking raw stream composition and/or product property signals; a product property comparison module connected to use said raw stream composition and/or product property signals, said artificial stream composition and/or product property signals, and said predicted stream composition and/or product property signals to determine an error between said raw signals and said predicted signals; a statistical filter module connected to take the said error and determine a new moving average error from the statistical history of said error; a calibration module connected to take the said new moving average error and produce model calibration factors for adjusting said process models; and a product property corrector module connected to take said new moving average error and said predicted stream composition and/or product property signals and apply said new moving average error to said predicted stream composition and/or product property signals to produce a corrected stream composition and/or product property signal. - View Dependent Claims (19)
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20. A computer-based method for processing dynamic model generated stream composition and/or product property estimates, comprising the steps of:
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(1) measuring, in a process comprising one or more units and two or more streams, stream composition and/or product property signals of said streams to produce raw stream composition and/or product property signals; (2) comparing said raw stream composition and/or product property signals with previously predicted stream composition and/or product property signals to determine an error measure; (3) using said error measure to adjust dynamic process models to reduce future estimates of said error measure; (4) predicting, using said dynamic process models, future process stream composition and/or product property signals for one or more of said streams; (5) using said predicted future stream composition and/or product property values to directly or indirectly change the state of a control element(s) of said process; and (6) operating said process using said control element(s) to produce a product. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33)
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Specification