PROCESS APPARATUS CONTROL SYSTEM FOR OPTIMIZING OBJECTIVE VARIABLE QUALITY

• US 3,828,171 A
• Filed: 08/14/1972
• Issued: 08/06/1974
• Est. Priority Date: 08/14/1972
• Status: Expired due to Term

• Current Assignee: Applied Automation, Inc. (Massman Automation Designs LLC)
• Original Assignee: Donald E. Griffin
• Inventors: Griffin, Donald E.
• Primary Examiner(s): Botz, Eugene G.
• Application Number:
  US05/280,535
• Time in Patent Office: 722 Days
• Field of Search: 235/151.12,150.1 208/164
• US Class Current: 700/273
• CPC Class Codes: C10G 11/187 Controlling or regulating
• CPC Class Codes: G05B 13/025 using a perturbation signal

Abstract

A procedure for on-line optimization of the operation of a petroleum catalytic cracking apparatus through control of six operational variables is disclosed using a linear model centered on the present operating condition of the apparatus. Minimum and/or maximum limits are placed on the controlled variables and certain other variables representing operational parameters of the apparatus and move limits are imposed on the controlled variables. The linear model is updated each time the optimization procedure is performed and the simplex technique is used to determine the values of the controlled variables required for optimization.

Claims

1. The method for controlling the operation of a petroleum catalytic cracking apparatus operated in conjunction with a petroleum fractionator, saId apparatus comprising a fluidized bed catalytic reactor and a fluidized bed catalyst regenerator and with said fractionator being operative on an input petroleum feed stream to produce a plurality of output product streams and having a set of controlled operational parameters which desirably will not violate certain limiting values and which may be altered to establish a desired operating condition of said apparatus and a set of constrained operational parameters which desirably will not violate certain limiting values, said method comprising the steps of:

sensing the rates of generation of said output streams, said constrained parameters, and said controlled parameters;

using a set of linear equations to express relationships between the rates of generation of said output streams, said objective variable quantity, said constrained parameters, and said controlled parameters;

determining the values of the rates of generation of said output streams, said objective variable quantity, said constrained parameters, and said controlled parameters corresponding to an operating condition of said apparatus;

evaluating the constants included in said linear equations by using the determined values of the rates of generation of said output streams, said objective variable quantity, said constrained parameters, and said controlled parameters, incrementing the values of said controlled parameters, and determining the corresponding alteration in the rates of generation of said output streams, said objective variable quantity, and said constrained parameters;

solving said linear equations with said evaluated constants to determine the values of said controlled parameters required to optimize said objective variable quantity; and

altering said controlled parameters toward said determined values.

2. The method of claim 1 further comprising using a set of linear inequalities to express said limits on said controlled operational parameters and said constrained operational parameters and said solving step comprises using said linear inequalities and said equations with said evaluated constants to determine the values of said controlled parameters required to optimize said objective variable quantity without violating said limits.

3. The method of claim 2 wherein the rate of change of certain ones of said controlled operational parameters desirably will not violate certain limiting values further comprising imposing move limits on the value of said operational parameters representing the maximum departure permitted from said determined value of said controlled parameters and including said move limits in said set of linear inequalities.

4. The method of claim 1 wherein said solving step uses a simplex linear programming technique.

5. Apparatus for controlling the operation of a petroleum catalytic cracking apparatus operated in conjunction with a petroleum fractionator to optimize an objective variable quantity associated with the operation of said cracking apparatus, said cracking apparatus comprising a fluidized bed catalytic reactor and a fluidized bed catalyst regenerator and with said fractionator being operative on an input petroleum feed stream to produce a plurality of output product streams and having a set of controlled operational parameters which may be altered to establish a desired operating condition of said cracking apparatus and a set of dependent operational parameters, said control apparatus comprising:

means for sensing the values of said controlled parameters, said dependent parameters, and the rates of generation of said output streams and generating a first plurality of signals related to the values of said controlled parameters, said dependent parameters, and the rates of generation of said output streams;

means for linearly combining according to a plurality of constants of combination said signals related to the values of said controlled parameters to form a second plurality of signals related to the values of said dependent Parameters and the rates of generation of said output streams;

means for evaluating said constants of combination making use of said first plurality of signals and including means for incrementing the signals representative of said controlled parameters and determining the corresponding alteration in said dependent parameters and the rates of generation of said output streams;

means for solving said linear combination with said evaluated constants and determining the values of said controlled parameters required to optimize said objective variable quantity; and

means for altering said controlled parameters toward the determined values of said controlled parameters required to optimize said objective variable quantity.

6. The apparatus of claim 5 wherein certain of said controlled operational parameters and said dependent parameters desirably will not violate certain limiting values and further comprising means for establishing limiting values on said certain ones of said controlled operational parameters and said dependent parameters and said solving means comprises means for solving said linear combination with said evaluated constants for the values of said controlled parameters restricted by said established limits on said certain ones of said controlled parameters and said dependent parameters for the values of said controlled parameters required to optimize said objective variable quantity.

7. The apparatus of claim 6 wherein the rate of change of specified ones of said certain controlled parameters desirably will not violate certain limiting rate values and further comprising means for including said limiting rate values into the limiting values established in said specified ones of said certain controlled parameters.

8. The apparatus of claim 7 wherein said evaluating means comprises:

second means for combining said first plurality of signals and said second plurality of signals;

means for incrementing the value of one of said first plurality of signals; and

means for iterating through said second combining means and determining the resultant changes in said dependent variables.

9. Apparatus for optimizing the operation of a fluidized bed petroleum catalytic cracking apparatus, said cracking apparatus comprising a fluidized bed catalytic reactor and a fluidized bed catalyst regenerator and operative to crack a petroleum feed stream into various fractions, operated in conjunction with a petroleum fractionator, said fractionator being operative to separate said cracked petroleum into a top product, a first intermediate relatively light product, a second intermediate relatively heavy product, and a bottom product with at least a portion of each of said second intermediate product and said bottom product being recycled to said catalytic cracking apparatus, said apparatus being operative to optimize the value of an objective variable quantity associated with the operation of said cracking apparatus and comprising:

first sensing means for generating first signals representative of first sensed parameters comprising the rate at which feed is introduced into said cracking apparatus, the temperature at which feed is introduced into said cracking apparatus, the level of the fluidized bed in said catalytic reactor, the temperature of the fluidized bed in said catalytic reactor, the rate at which said second intermediate product is recycled to said cracking apparatus, and the rate at which said bottom product is recycled to said cracking apparatus;

control means for maintaining said first sensed parameters at set point values;

second sensing means for generating second signals representative of second sensed parameters comprising the rate at which air is supplied to said catalyst regenerator, the temperature of the fluidized bed in said catalyst regenerator, the rate at which catalyst is supplied to said catalyst reactor, the rate at which stripping steam is supplied to said catalytic reactor, the specific gravity of said fRactionator bottom product, the composition of said top product, and the composition of said second intermediate product;

means for linearly combining said first signals in accord with a set of constants of combination to generate signals representative of said second sensed parameters;

means for determining said constants of combination comprising means for incrementing the value of said first sensed signals applied to said combining means and means for determining the resultant corresponding change in said signals representative of said second sensed parameters;

means for determining the values of said first sensed parameters required to optimize said objective variable; and

means for altering said control means set point values toward the determined values of said first sensed parameters required to optimize said objective variable.

10. The method of claim 3 wherein said evaluating step comprises the steps of:

using a set of yield and heat balance equations expressing relationships between various ones of said rates of generation of said output streams, said objective variable quantity, said constrained parameters, and said controlled parameters;

incrementing the values of one of said controlled parameters in said yield and heat balance equations; and

solving said yield and heat balance equations to determine the resultant changes in said rates of generation of said output streams, said objective variable quantity, and said constrained parameters.