US3591783A
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US
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Automatic control of fluid catalytic cracking units
Assignee: ExxonMobil Technology and Engineering Co
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Filing: 1969-02-24
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Granted: 1971-07-06
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Expires: 1989-02-24
Abstract
Abstract A fluidized catalytic cracking unit is controlled for carbon balance and maximization of a secondary control function by using a general purpose digital computer, which is responsive to various temperatures and pressures, as the controlling means for variables such as the settings on the regenerator flue gas control valve and the regenerated catalyst circulation control valve. The process of the present invention involves obtaining a plurality of signals representing control variables, comparing these with the desired values for the control variables, and carrying out in a general purpose computer the calculation of a carbon adjustment factor according to the algorithm: WHERE EACH OF THE VARIABLES HAS THE DEFINITION SET FORTH IN THE SPECIFICATION. When Delta SVn is positive, indicating a correction for carbonburning conditions, the desired control action is obtained by a logic sequence which determines whether either of the controlled variables is under constraint and if not, takes the control step most consistent with optimization of the secondary variable. If one or both of the controlled variables are under constraint, the logic sequence indicates the correct control step to be taken or, if no control step can be taken, indicates that none can be taken. When Delta SVn is negative, indicating a correction for carbonbuilding conditions, the logic sequence likewise allows the choice of the optimum control step to be taken or, if none can be taken, indicates this fact. After the logic sequence based upon the algorithm has been completed, a signal is obtained to move the correct control valve (that is, make the required adjustment in the controlled variable), the signal being corrected to reflect the difference in control function (depending upon which valve is to be moved) and for the position of the valve immediately prior to movement to the new position. By carrying out the control function of the present invention, carbon balance can be well controlled in a catalytic cracking unit while the secondary control variable (such as regenerator air velocity) can be controlled or maximized.
Inventors
- 👤 Robert E Zumwalt
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 05:12
CPC Classifications
C; C10; C10G; C10G11/00; C10G11/14; C10G11/18; C10G11/187; Y; Y10; Y10T; Y10T436/00; Y10T436/12
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
692 words
A method for controlling carbon balance in a fluid catalytic cracking unit while concurrently maximizing a secondary control variable which comprises A. supplying to a digital computer a plurality of signals representing control variables: a first signal representing a temperature differential between two locations in the unit, chosen to provide an indication of carbon balance in the unit, a second signal representing the pressure drop across the regenerated catalyst slide valve, a third signal representing the regenerator pressure, and a fourth signal representing a secondary control variable; B. supplying said digital computer with values representing predetermined limits for the variables represented by said second and third signals, with the predetermined target value of the temperature differential represented by said first signal, and with the predetermined target value for said secondary control variable; C. when the regenerator is not being supplied with torch oil carrying out in said digital computer the following sequence of steps, repeatedly at predetermined sample periods not greater than 30 minutes, 1. determining the carbon adjustment factor, Delta SVn, according to the algorithm: where Delta SVn is the indicated correction in slide valve position for the nth sampling expressed in percent based upon slide valve travel, from fully closed to fully open being 100 percent; Kr is the reset control constant; Ks is a control constant greater than zero; delta Tn is the deviation at the nth sampling; Kp is the proportional control constant; Delta Tn is the temperature difference represented by said first signal at the nth sampling; Delta Tn 1 is the temperature difference represented by said first signal at the nth-1 sampling; and Delta t is the sample period between samplings; 2. when Delta SVn is positive, indicating a correction for carbon-burning conditions, determining the desirable control action by the logic sequence: a. if the pressure drop across the regenerated catalyst slide valve is above the predetermined minimum limit therefor and the secondary control variable is below its target value, obtain a signal to reposition the regenerated catalyst slide valve; b. if the pressure drop across the regenerated catalyst slide valve is above the minimum limit therefor and the secondary control variable is at or above its target value and the regenerator pressure is at or above the predetermined maximum limit therefor, obtain a signal to reposition the regenerated catalyst slide valve; c. if the pressure drop across the regenerated catalyst slide valve is above the minimum limit therefor and the secondary control variable is at or above its target value and the regenerator pressure is below the predetermined maximum light therefor, obtain a signal to reposition the flue gas slide valve; d. if the pressure drop across the regenerated catalyst slide valve is at or below the minimum limit therefor, and if the regenerator pressure is at or above the predetermined maximum limit therefor, take no control action, but if the regenerator pressure is below the predetermined maximum limit therefor, obtain a signal to reposition the flue gas slide valve; 3. when Delta SVn is negative, indicating a correction for carbon-building conditions determining the desirable control action by the logic sequence: a. if the secondary control variable is at or above its target value, obtain a signal to reposition the regenerated catalyst slide valve; b. if the secondary control variable is below its target value and the pressure drop across the regenerated catalyst slide valve is at or below the predetermined minimum value therefor, obtain a signal to reposition the regenerated catalyst slide valve; c. if the secondary control variable is below its target value and the pressure drop across the regenerated catalyst slide valve is above the predetermined minimum limit therefor, and the regenerator pressure is at or below the predetermined minimum limit therefor, obtain a signal to reposition the regenerated catalyst slide valve; d. if the secondary control variable is below its target value and the pressure drop across the regenerated catalyst slide valve is above the predetermined minimum limit therefor, and the regenerator pressure is above the predetermined minimum therefor, obtain a signal to reposition the flue gas slide valve; 4. and repositioning the valve for which a repositioning signal is obtained.
Claim 2
Independent Claim
692 words
A method for controlling carbon balance in a fluid catalytic cracking unit while concurrently maximizing a secondary control variable which comprises A. supplying to a digital computer a plurality of signals representing control variables: a first signal representing a temperature differential between two locations in the unit, chosen to provide an indication of carbon balance in the unit, a second signal representing the pressure drop across the regenerated catalyst slide valve, a third signal representing the regenerator pressure, and a fourth signal representing a secondary control variable; B. supplying said digital computer with values representing predetermined limits for the variables represented by said second and third signals, with the predetermined target value of the temperature differential represented by said first signal, and with the predetermined target value for said secondary control variable; C. when the regenerator is not being supplied with torch oil carrying out in said digital computer the following sequence of steps, repeatedly at predetermined sample periods not greater than 30 minutes, 1. determining the carbon adjustment factor, Delta SVn, according to the algorithm: where Delta SVn is the indicated correction in slide valve position for the nth sampling expressed in percent based upon slide valve travel, from fully closed to fully open being 100 percent; Kr is the reset control constant; Ks is a control constant greater than zero; delta Tn is the deviation at the nth sampling; Kp is the proportional control constant; Delta Tn is the temperature difference represented by said first signal at the nth sampling; Delta Tn 1 is the temperature difference represented by said first signal at the nth-1 sampling; and Delta t is the sample period between samplings; 2. when Delta SVn is positive, indicating a correction for carbon-burning conditions, determining the desirable control action by the logic sequence: a. if the pressure drop across the regenerated catalyst slide valve is above the predetermined minimum limit therefor and the secondary control variable is below its target value, obtain a signal to reposition the regenerated catalyst slide valve; b. if the pressure drop across the regenerated catalyst slide valve is above the minimum limit therefor and the secondary control variable is at or above its target value and the regenerator pressure is at or above the predetermined maximum limit therefor, obtain a signal to reposition the regenerated catalyst slide valve; c. if the pressure drop across the regenerated catalyst slide valve is above the minimum limit therefor and the secondary control variable is at or above its target value and the regenerator pressure is below the predetermined maximum light therefor, obtain a signal to reposition the flue gas slide valve; d. if the pressure drop across the regenerated catalyst slide valve is at or below the minimum limit therefor, and if the regenerator pressure is at or above the predetermined maximum limit therefor, take no control action, but if the regenerator pressure is below the predetermined maximum limit therefor, obtain a signal to reposition the flue gas slide valve; 3. when Delta SVn is negative, indicating a correction for carbon-building conditions determining the desirable control action by the logic sequence: a. if the secondary control variable is at or above its target value, obtain a signal to reposition the regenerated catalyst slide valve; b. if the secondary control variable is below its target value and the pressure drop across the regenerated catalyst slide valve is at or below the predetermined minimum value therefor, obtain a signal to reposition the regenerated catalyst slide valve; c. if the secondary control variable is below its target value and the pressure drop across the regenerated catalyst slide valve is above the predetermined minimum limit therefor, and the regenerator pressure is at or below the predetermined minimum limit therefor, obtain a signal to reposition the regenerated catalyst slide valve; d. if the secondary control variable is below its target value and the pressure drop across the regenerated catalyst slide valve is above the predetermined minimum limit therefor, and the regenerator pressure is above the predetermined minimum therefor, obtain a signal to reposition the flue gas slide valve; 4. and repositioning the valve for which a repositioning signal is obtained.
Claim 3
Dependent Claim
219 words
when Delta SVn is positive, indicating a correction for carbon-burning conditions, determining the desirable control action by the logic sequence: a. if the pressure drop across the regenerated catalyst slide valve is above the predetermined minimum limit therefor and the secondary control variable is below its target value, obtain a signal to reposition the regenerated catalyst slide valve; b. if the pressure drop across the regenerated catalyst slide valve is above the minimum limit therefor and the secondary control variable is at or above its target value and the regenerator pressure is at or above the predetermined maximum limit therefor, obtain a signal to reposition the regenerated catalyst slide valve; c. if the pressure drop across the regenerated catalyst slide valve is above the minimum limit therefor and the secondary control variable is at or above its target value and the regenerator pressure is below the predetermined maximum light therefor, obtain a signal to reposition the flue gas slide valve; d. if the pressure drop across the regenerated catalyst slide valve is at or below the minimum limit therefor, and if the regenerator pressure is at or above the predetermined maximum limit therefor, take no control action, but if the regenerator pressure is below the predetermined maximum limit therefor, obtain a signal to reposition the flue gas slide valve;
Claim 4
Dependent Claim
219 words
when Delta SVn is positive, indicating a correction for carbon-burning conditions, determining the desirable control action by the logic sequence: a. if the pressure drop across the regenerated catalyst slide valve is above the predetermined minimum limit therefor and the secondary control variable is below its target value, obtain a signal to reposition the regenerated catalyst slide valve; b. if the pressure drop across the regenerated catalyst slide valve is above the minimum limit therefor and the secondary control variable is at or above its target value and the regenerator pressure is at or above the predetermined maximum limit therefor, obtain a signal to reposition the regenerated catalyst slide valve; c. if the pressure drop across the regenerated catalyst slide valve is above the minimum limit therefor and the secondary control variable is at or above its target value and the regenerator pressure is below the predetermined maximum light therefor, obtain a signal to reposition the flue gas slide valve; d. if the pressure drop across the regenerated catalyst slide valve is at or below the minimum limit therefor, and if the regenerator pressure is at or above the predetermined maximum limit therefor, take no control action, but if the regenerator pressure is below the predetermined maximum limit therefor, obtain a signal to reposition the flue gas slide valve;
Claim 5
Dependent Claim
227 words
A method as in claim 1 further comprising the steps: a. if the selected valve is the regenerated catalyst slide valve, correcting said signal by the equation: Delta RCSVn Krc Delta SVn where Delta RCSVn is the corrected amount of movement to be made in the regenerated catalyst slide valve, no greater than Delta RCSVmax Krc is the regenerated catalyst slide valve correction factor, Delta SVn is the carbon adjustment factor, and Delta RCSVmax is from 1 to 2 percent of slide valve travel, to obtain a repositioning signal proportional to the desired amount and direction by which the regenerated catalyst slide valve is to be repositioned; b. if the selected valve is the flue gas slide valve, correcting said signal by the equation: Delta FGSVn -Kfg Delta SVn where Delta FGSVn is the corrected amount of movement to be made in the flue gas slide valve, no greater than Delta FGSVmax, Kfg is the flue gas slide valve correction factor, and Delta FGSVmax is from 1 to 2 percent of slide valve travel, to obtain a repositioning signal proportional to the desired amount and direction by which the flue gas slide valve is to be repositioned; and c. repositioning the selected valve in response to the respective repositioning signal, opening said valve when the signal is positive and closing said valve when the signal is negative.
Claim 6
Dependent Claim
182 words
when Delta SVn is negative, indicating a correction for carbon-building conditions determining the desirable control action by the logic sequence: a. if the secondary control variable is at or above its target value, obtain a signal to reposition the regenerated catalyst slide valve; b. if the secondary control variable is below its target value and the pressure drop across the regenerated catalyst slide valve is at or below the predetermined minimum value therefor, obtain a signal to reposition the regenerated catalyst slide valve; c. if the secondary control variable is below its target value and the pressure drop across the regenerated catalyst slide valve is above the predetermined minimum limit therefor, and the regenerator pressure is at or below the predetermined minimum limit therefor, obtain a signal to reposition the regenerated catalyst slide valve; d. if the secondary control variable is below its target value and the pressure drop across the regenerated catalyst slide valve is above the predetermined minimum limit therefor, and the regenerator pressure is above the predetermined minimum therefor, obtain a signal to reposition the flue gas slide valve;
Claim 7
Dependent Claim
182 words
when Delta SVn is negative, indicating a correction for carbon-building conditions determining the desirable control action by the logic sequence: a. if the secondary control variable is at or above its target value, obtain a signal to reposition the regenerated catalyst slide valve; b. if the secondary control variable is below its target value and the pressure drop across the regenerated catalyst slide valve is at or below the predetermined minimum value therefor, obtain a signal to reposition the regenerated catalyst slide valve; c. if the secondary control variable is below its target value and the pressure drop across the regenerated catalyst slide valve is above the predetermined minimum limit therefor, and the regenerator pressure is at or below the predetermined minimum limit therefor, obtain a signal to reposition the regenerated catalyst slide valve; d. if the secondary control variable is below its target value and the pressure drop across the regenerated catalyst slide valve is above the predetermined minimum limit therefor, and the regenerator pressure is above the predetermined minimum therefor, obtain a signal to reposition the flue gas slide valve;
Claim 8
Dependent Claim
15 words
A method in accordance with claim 1 wherein the secondary variable is regenerator air velocity.
Claim 9
Dependent Claim
11 words
and repositioning the valve for which a repositioning signal is obtained.
Claim 10
Dependent Claim
11 words
and repositioning the valve for which a repositioning signal is obtained.
Claim 11
Dependent Claim
14 words
A method in acCordance with claim 1 wherein the secondary variable is reactor temperature.
Claim 12
Dependent Claim
15 words
A method in accordance with claim 1 wherein the sample period is about 2 minutes.
Claim 13
Dependent Claim
41 words
A method in accordance with claim 1 wherein the secondary variable is regenerator air velocity, the regenerator air velocity is below its predetermined target value, and the sampling period if about 2 minutes, whereby air rate to the regenerator is maximized.
Claim 14
Dependent Claim
30 words
A method in accordance with claim 1 wherein, when torch oil is introduced into the regenerator, Kr is increased by a factor of two to four times and Kp 0.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1974-07-05 | 1975-01-04 | 1975-07-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-07-05 | 1979-01-04 | 1979-07-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-07-05 | 1983-01-04 | 1983-07-06 | $7700.00 | Window Closed / Lapsed |