US3666931A

US3666931A - Control method and means for obtaining optimum yields of refined oil and extract oil from charge oil

Info

Publication number: US3666931A
Application number: US96193A
Authority: US
Inventors: Robert Alan Woodle
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1970-12-08
Filing date: 1970-12-08
Publication date: 1972-05-30
Anticipated expiration: 1989-05-30
Also published as: TR16797A; ES397538A1; AU3629271A; IT953151B; CA971122A; GB1336197A; FR2117898B1; DE2160881A1; NL7116759A; FR2117898A1; ZA717831B; BE776308A; BR7108100D0

Abstract

A system and method for controlling the solvent refining of a charge oil to obtain refined waxy oil of a specific quality which is subsequently dewaxed to provide refined oil. During a predetermined time period, the characteristics of the charge oil are sensed and corresponding signals provided. After the predetermined time period, characteristics of the charge oil, the refined waxy oil, extract oil and solvent are sensed and corresponding signals provided. Analog computers provide signals in accordance with equations, hereinafter disclosed, for controlling the charge oil flow rate and the temperature of the extract-mix in accordance with the condition signals and other signals corresponding to the current economic values of the charge oil, the refined oil and the extract oil.

Description

United States Patent Woodle 1451 May. 30, 1972 [54] CONTROL METHOD AND MEANS FOR 3,458,691 7/1969 Boyd, Jr ..23s/151.12 OBTAINING OPTIMUM YIELDS F 3,539,784 11/1970 Woodle ..23s/1s1.12

REFINED OIL AND EXTRACT OIL Primary Examiner-Eugene G. Botz FROM CHARGE OIL Attorney-Thomas 11. Whaley and Carl 0. Reis 72 Inventor: Robert Alan Woodle, Nederland, Tex. 1 [57] ABSTRACT 73 Assi nee: Texaco Inc. New York, NY. 1 g A system and method for controlling the solvent refining of a [22] Filed: Dec. 8, 1970 charge oil to obtain refined waxy oil of a specific quality which is subsequently dewaxed to provide refined oil. During a [2]] Appl 96193 predetermined timeperiod, the characteristics'of the charge oil are sensed and corresponding signals provided. After the 52 us. c1. ..23s/1s1.12, 208/DIG. 1, 208/311 predetermined time Period, characteristics of the charse'oil, [51] Clog 2 00 051, 15 02 the refined waxy oil, extract oil and solvent are sensed and [58] Field of Search ..235/151.12; 208/DIG. 1 corresponding Signals provided- Analog computers P d signals in accordance with equations, hereinafter disclosed, 56] References Cited for controlling the charge oil flow rate and the temperature of the extract-mix in accordance with the condition signals and UNITED STATES PATENTS other signals corresponding to the current economic values of the charge oil, the refined oil and the extract oil. 1 3,285,846 11/1966 King et a1. ..208/DIG. l UX 3,458,432 7/1969 Woodle et a1. ..208/DIG. l UX 14 Claims, Drawing Figures EB I 30 /El2 RE NEI RE FINING E TOWER f5 24 SOLVENT DEWAX'NG 37 fif f T 48 WAX RE R ER 2/4 1 STRIPPER CONTROLLER 4 4 C'B d ER E STRIPPER =5 |8 COOLING CHARGE 'V 8B OIL 5; WATER 5o EXTRACT OIL 1 48 E3 I Y 447 REQEJ A SER vd 1 17 1 no 3 i gg A FLOW 1r TARG. 30 1 X91 RECOR DER FRED. .E, COMPUTER 5'5 1 'YQ CONTROLLER l8 5] -COMPUTER c- 8 i 5 E E 0 ACT i "f Em En 5,, 32 (66 com ren V 's 9 1- q E PRED. 4I x 11 E 55 E1 coM PUTER sw. P 34 Q; E11* 100 E COMPUTER 460 21o Ev 185 -E E v 38 38 E COMPUTER Cd E24 W E \lae L. T MAX? L 1 L FRED L E44 COMPUTER 'f- E EC COMPUTE R Y V E9 64 v W MAX. P

' E: h I61 E COMPUTER Patented May 30, 1972 4 Sheets-Sheet l Patemited May 30, 1972 3,666,931

4 Sheets-Sheet 5 E FIG.5 E

EXPONENTIAL DIVIDER CRCUT MULTIPLIER [I06 V ('07 :Egg MULTIPLIER 4 E I 27 Q I I T u PRED. COMPUTER I u 7 EV 'f V0 C6 FIG. 6 l E E E S 52 EXPONENTIAL 3 T CIRCUT DIVIDER i MULTIPLIER l5| 122 23 I 1 I I DIVIDER EXPONENTIAL CIRCUIT 0 ACT. COMPUTER T I29 L J V e E4 S 34 MULTIPLIER MULTIPLIER DIVIDER l L k :38 m2 l :4? l ('46 I g l EXPONENTIAL CIRCUT MIVULTIPLIVEYR "Isl T I EXPONENTIAL CIRCUIT A ACT. I r

I l "fi l Patented May 30, 1972 3,666,931

4' Sheets-Sheet 4 60 V L Vn I E |67 TIE I'T5 't i 4 MULTI- MULTI- EXPON- I EXPON- PLIER PUER DIVIDER ENTIAL ENTIAL l I CIRCUIT I cIRcuI'r I76 I80 I I72 38 I I I l :lal DIVIDER l x MAX. P I :YMAXP I E EE L E I IE E L EE l -1 E I l E, 0, MAX. P COMPUTER 202 IEIZ l8 EXPON- I ..0IvI0ER ENTIAL 'g i'fg DIVIDER l CIRCUIT [I87 M90 l89 200 T I I MULTI- MULTIPLIER PUER f l 1 EXPON- l l |9| l94 EN'HAL I CIRCUIT I I l I I l l l VF s v1 E40 E38 u I ENPONENTIAL CIRCUIT r I I FEED I l BA K I I LOG AMP CIR IT a I E I I MULTIPLIER l l 205 OPERATIONAL AME:

CONTROL METHOD AND MEANS FOR OBTAINING OPTIMUM YIELDS OF REFINED OIL AND EXTRACT OIL FROM CHARGE OIL I BACKGROUND OF THE INVENTION 1. Field of the Invention The device of the present invention relates to control systems and, more particularly, to an automatic control system for use in an oil refinery.

2. Description of the Prior Art Heretofore, a control system for a solvent refining unit, such as disclosed in US. Pat. No. 3,458,432, is able to provide refined oil of a quality determined by the viscosity index (VI) of the refined oil. However, the VI of the refined oil, although important, is only one of several quality factors which need to be established before the refined oil can be converted to a commercially valuable product. For example, in inhibited heavy duty motor oil, other important quality factors are: sulfur content, susceptibility to reduction of pour point by pour depressant additives, and susceptibility to inhibition by engine cleanliness additives, and susceptibility to inhibition by engine cleanliness additives and corrosion and oxidation inhibitors. The means and method of the present invention utilizes the refractive index of the refined waxy oil as yet another characteristic to define the quality of the refined oil.

The means and method of the present invention further differs from US. Pat. No. 3,458,432 by using certain characteristics of the charge oil in controlling the flow rate of the charge oil and the temperature of the extract oil for a predetermined time period and thereafter using the refractive indices of the charge, oil and the refined waxy oil and the flow rates of the solvent, the refined waxy oil and the extract oil in controlling the flow rate of the charge oil and the temperature of the extract-mix.

The means and method of the present invention further distinguishes over the aforementioned US. patent in controlling the flow rate of the charge oil and the temperature of the extract-mix in accordance with the current economic values of the crude oil, the extract oil and the refined oil so as to provide optimum yields of the refined oil ant. the extract oil.

SUMMARY OF THE INVENTION A system for controlling the refining of charge oil to obtain optimum yields of refined oil and extract oil where in the refining operation the charge oil is treated with a solvent in a refining tower and a stream of raffinate and'a stream of extract-mix are withdrawn from saidv tower, strippers separate the solvent from the raffinate and from the extract-mix to provide refined waxy oil and the extract oil, respectively. The refined waxy oil is subsequently dewaxed to yield the refined oil. The control system includes sensing circuits which sense the characteristics of the charge oil, the refined waxy oil, the extract oil, and the solvent and provide corresponding condition signals. A signal source provides signals that correspond to the economic values of the charge oil, the extract oil, and the refined oil. Control circuits control some of the conditions of the refined waxy oil and the extract oil in accordance with the condition signals and the value signals from the sensing circuits and the signal source, respectively, to provide the optimum yields of the refined oil and the extract oil.

One object of the present invention is to control quantities of refined oil and extract oil and the temperature of the extract-mix during refining of crude oil so as to obtain optimum yields of the refined oil and the extract oil.

Another object of the present invention is to control the flow rate of charge oil and the temperature of extract-mix during the refining of the charge oil in accordance with predicted values, determined from sensed conditions of the charge oil, for a predetermined time period and after the predetermined time period in accordance with sensed conditions of a solvent, refined waxy oil and extract oil.

Another object of the present invention is to control the refining of charge oil in accordance with the economic values of the charge oil, extract oil and refined oil.

Another object of the present invention is to control the refining of charge oil to provide refined oil of a quality characterized by a predetermined viscosity index and a predetermined refractive index.

Another object of the present invention is to provide an automatic control system for use in the solvent refining of charge oil to provide optimum yields of extract oil and refined oil which considers the desired quality of the refined oil, the refining conditions, and the economic values of the charge oil, the extract oil and the refined oil.

The foregoing and other objects and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawings wherein one embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for illustration purposes only and are not to be construed as defining the limits of the invention. i

DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified block diagram of a system for refining charge oil using an automatic control system, constructed in accordance with the present invention, to obtain optimum quantities of refined oil and extract oil from the charge oil.

FIGS. 2 through 9 are detailed block diagrams of the H computer, A computer, the 5.0 computer, the a computer, the a computer, the a computer, the A computer, the X computer, the Y computer, and the T computer blocks shown in FIG. 1.

FIG. 10 is a block diagram of an exponential circuit of the type which may be used in the a,,,,,,, computer, the a computer, the a computer, the A computer, the X computer, the Y computer and the T computer shown in FIGS. 5 through 9.

, DESCRIPTION OF THE INVENTION Referring to FIG. 1, there is shown a control system for a conventional type furfural refining operation for providing an optimum yield of refined oil. The rate of flow of the charge oil is controlled so as to control the flow rates of refined waxy oil and extract oil. The temperature, which is also controlled, at which the refining of the charge oil takes place also affects the yield of the refined waxy oil and the extract oil. The rate of the charge oil entering a furfural refining tower 5 in a line 6 is sensed and controlled by conventional types sensing element 8, flow recorder controller 10 and valve 14. Sensing element 8 provides a signal to controller 10 corresponding to the flow rate of charge oil. Controller 10 operates valve 14 to control the rate of flow of the charge oil to tower 5 in accordance with the signal from sensing element 8 and a signal E,. Signal E, controls the set points of controller 10.

The charge oil is also sampled by a refractive index meter 17, a flash meter 18, a viscosity meter 19, a gravity meter 20 and the effluent from those meters may be applied to tower 5 or disposed of as slop. Refractive index meter 17, which may be of the type described by G. C. Eltenton in US Pat. No. 2,569,127, provides a signal E corresponding to the refractive index of the charge oil. Flash meter 18 provides a signal E corresponding to the Cleveland Open Cup Flash Point of the charge oil. A suitable meter for this purpose is the Precision Scientific Automatic Flash Tester recalibrated for the Cleveland Open Cup Flash Point. Viscosity meter 19 provides a Although not shown, for ease of explanation, the charge oil and a furfural refining solvent entering tower 5 through lines 6 and 24, respectively, have been heated to a predetermined temperature. Tower 5 contains packing 26 where the charge oil and solvent are contacted in counter current flow efiecting the extraction of low viscosity index constituents of the charge oil. Rafi'inate including the refined waxy oil and a small amount of dissolved solvent is withdrawn through line 30.

A temperature gradient is maintained in tower 5 by means of a cooling oil 32 having cooling water flowing through it. The temperature in tower 5 is sensed by conventional type sensing means 34 which provides a corresponding signal to a temperature recorder controller 37. Temperature recorder controller 37, which may be of a type wellknown in the art, operates a valve 38 in accordance with the signal from temperature sensing means 34 and a signal E Signal E controls the set points of temperature recorder controller 37. Valve 38 controls the rate of flow of the cooling water to control the temperature in tower 5. Temperature controller recorder 37 also provides asignal E which corresponds to the temperature T of the extract-mix.

Raffinate'in line 30 enters a stripper 40 which strips the solvent from the raffinate to yield the refined ,waxy oil. The solvent after treatment for the removal of water-in any suitable manner (e.g. Hydrocarbon Processing, Sept. 1966, Volume 45, Number 9, page 226) is returned to tower 5 by line 24 while the refined waxy oil is provided to dewaxing element 39 through a line 41. Element 40 removes the wax and provides refined oil for storage and blending with product lubricating oil. The refined waxy oil in line 41 is continuously sampled by a refractive index meter 17A, which providesa corresponding signal E and the effluent is either-returned to line 41 or disposed of as slop. Elements having a numerical designation with a suffix are identical in operation and connection to elements having the same numerical designation without a suffix.

Sensing means 8A and a conventional type flow recorder 44 measures the rate of flow of the refined waxy oil from stripper 40 and provides a correspondingsignal E,

Extract-mix comprising solvent and dissolved low viscosity index constituents of the charge oil is withdrawn from tower 5 through line 48 at a temperature controlled by cooling coil 32. The extract-mix in line 48 is passed to.a stripper 49 where the solvent is stripped from the extract oil which is discharged through a line 50. The recovered solvent is withdrawn through line 24 for return to tower 5 and r'e-use. Sensing means 88 and a flow recorder 44A senses the rate'of flow of extract oil in line 50 and provide a corresponding signal E Sensing means 8C and a flow recorder 44B'senses the flow rate of solvent in lirie 24 and provides a corresponding signal E When starting the refining of new charge oil, the characteristics of the extract oil and the refined waxy oil are initially unsettled due to the presence of old charge oil in the system. The control system of the present invention provides for this condition by controlling the quality of the refined waxy oil, using predictive values, for a predetermined time period of suitable duration to allow the characteristics of the refined waxy oil and the extract oil to stabilize. After the predetermined time period has elapsed, the control system of the 7 present invention senses the conditions of the refined waxy oil and the flow rates of the extract oil and the refined waxy oil to control the process.

It has been found that the quality of the refined waxy oil can be predicted to acertain extent by the following equations:

H= 870 Log Log (V,\.+ 0.6) 154 1, 94.9 0.149 H- 0.0826 Ala 0.0001 H2 2,

where H is the Bell and Sharpviscosity function of the charge oil at 210 Fahrenheit, V is the kinematic viscosity of the charge oil at 210 Fahrenheit, API is the API gravity-of the charge oil, A is the predicted characteristic constant for the charge oil, E0 is the predicted extract oil yield in percent by volume, R1, is the refractive index of the charge oil, F! is the flash point of the crude oil, V1 is the desired VI, a is the predicted characteristic constant for a desired quality of refined oil, S is the flow rate of the solvent in line 24 to tower 5, and constants C and C are constants having the following values:

Type of Charge Oil C, C,

Light Distillates 12.7 [.333 Heavy Distillates 25.4 1.668 Residual Oil l7.3 1.373

Signal E corresponding to the kinematic viscosity V term in Equation 1, is applied to an H computer 55 which also receives direct current voltages E E, and E, and which provides a signal E corresponding to H in accordance with Equation 1. Referring to FIG. 2, signal E, is summed with voltage E,,, which corresponds to the term 0.6 in Equation 1, by summing means 57. The resulting sum signal is amplified by conventional type

logarithmic amplifiers

58, 58A to provide a signal, corresponding to the log log of the sum signal from summing means 57, to a multiplier 60. Multiplier 60 multiplies the signal from logarithmic amplifier 58A with voltage E corresponding to the coefficient 870 in Equation 1, 'to provide a product signal. Summing means 61 sums the product signal from multiplier 60 with voltage E which corresponds to the term 154 in Equation 1, to provide signal E Signal E is applied to an A computer 64, as'shown in FIG. 1, along with signal E, from gravity meter 20 and direct current voltages E,,,, E E, and E,,. Computer 64 provides a signal E corresponding to 0.1.4,, of Equation 2. Referring to FIG. 3, a multiplier 66 in computer 64 multiplies signal E with voltage E which corresponds to the 0.149 coefficient in Equation 2, to provide a product signal to subtracting means 67. Subtracting means subtracts the product signal from multiplier 66 from voltage E,, which is related to the term 94.9 in Equation 2, to provide a corresponding signal. Signal E is effectively squared by a multiplier 70 and the resulting signal is multiplied with voltag E, which corresponds to the 0.0001 coefl'lcient in Equation 2, by a multiplier 71. Gravity signal E, is effectively squared by a multiplier 73 and the resulting signal is multiplied with voltage E,,, which corresponds to the coefficient 0.0826 in Equation 2, by a multiplier 74 to provide a corresponding product signal. The product signal from multiplier 74 is subtracted from the product signal from multiplier 71 by subtracting means 77 to provide a signal to summing means 78. Summing means 78 sums the signal from subtract- 7 ing means 67, 77 to provide signal E Referring again to FlG. 1, an 12.0 computer 70-receives signals E E from refractive index meter 17 and flash-meter 18, respectively, and direct current voltages E, through E,, and uses the signals and voltages to provide a signal E corresponding to the term BO in Equation 3. Referring to FIG. 4, signal E, from refractive index meter 17 is applied to subtracting means 80 which subtracts voltage E corresponding to the term 1.49 in Equation 3, from signal E The signal resulting from subtracting means 80 is multiplied with voltage E. by a multiplier 81 and the resulting product signal is ap-i plied to subtracting means 84. Signal E from flash meter 18 is multiplied with voltage E,, which corresponds to the coefficient 0.1 in Equation 3, by a multiplier 85 and the resulting product signal is applied to subtracting means 84. A multiplier 88 multiplies the output from subtracting means 84 with voltwith voltage 15,, which is a variable amplitude voltage that corresponds to the constant C in Equation 3, to provide a product signal to subtracting means 94. Subtracting means 94 subtracts the product signal from multiplier 90 from the sum signal from summing means 93 to provide signal E A signal E is provided by an a computer 100 in accordance with signals E E from flow recorder 44B and E.O.,,,,,, computer 70, respectively, direct current voltages E,, E,, E and E,,, asshown in FIG. 1, and Equation 4. All terms and coefficients referred to in the following description of computer 100 occur in Equation 4. Referring to FIG. 5, signal E received by computer l-and corresponding to the S term, is divided by voltage E,, which corresponds to the term 1,000, by a divider 101. The resulting signal is raised to the power of 0.35 by an exponential circuit 102, which may be of the type shown in FIG. 10, receiving voltage E, corresponding to the exponent 0.35. The output from circuit 102 is multiplied with voltage E corresponding to the coefficient 0.464, by a multiplier 106 to provide a product signal to another multiplier107. Signal E 21 from E.0.,,,.,, computer 70 is applied to a divider 108 where voltage E,,, which corresponds to the term 100, is divided by signal E Subtracting means 112 subtracts voltage 15,, which corresponds to the term 1, from the signal from divider 108 to provide a corresponding output. A multiplier 107 multiplies the product signal from multiplier 106 with the output from the subtracting means 112 to provide signal E Referring to FIG. 10, a typical exponential circuit receives a signal E corresponding to a value A and a direct current voltage V corresponding to a value B and provides a signal corresponding to A. The exponential circuit includes a conventional type logarithmic amplifier 205 which provides a signal corresponding to the logarithm of signal E. A multiplier 208 multiplies the signal from logarithmic amplifier 205 with the voltage to provide a product signal to a conventional type operational amplifier 210. Amplifier 210 has a feedback circuit 212, which may be of the type manufactured by Pace under part number PC-l2, causing amplifier 210 to provide the signal corresponding to A". All exponential circuits hereinafter referred to may be of the aforementioned type.

After the predetermined time period has elapsed, the quality of the refined oil is controlled by using monitored values obtained during the refining process in lieu of predicted values in accordance with the following equations:

0.935 (X (323 TI-1.0.)

where a is the actual characteristic constant for the desired quality of refined oil, Y, is the flow rate of refined waxy oil in line 41, X is the flow rate of extract oil in line 50m is the target characteristic constant foi' a desired quality of refined oil, ARI is the actual difference between the refractive index of the charge oil and the refractive index of the refined waxy oil, ARI is the target refractive index difference, S is the flow rate of the solvent in line 24 and T is the temperature of the extract-mix.

Referring to FIGS. 1 and 6', an a computer 116 computes a in accordance with signals E, E from

flow recorders

44 and 44A, respectively, a direct current voltage V,,, and equation to provide a corresponding signal E to an A computer 1 l8. Signal E from flow recorder 44A, corresponding to the X, term in Equation 5 and to the flow rate of the refined waxy oil in line 41, is raised by a power of 0.65 by an exponential circuit 122, which receives voltage V, corresponding to the exponent 0.65, and a resulting output is applied to a divider 123. Divider 123 divides signal E from recorder 44, corresponding to the Y term in Equation 5 and to the flow rate of the extract oil in line 50, by the resulting output from exponential circuit 122 to provide signal E corresponding to the term a in equation 5.

Computer 118 provides a signal E corresponding to A in accordance with signals E E and E from refractive index meters 17, 17A and A computer 116, respectively, direct current voltages V V,. and Equation 6. Subtracting means 127 subtracts signal E provided by refractive index meter 17 from signal E from refractive index meter 17 to provide a signal corresponding to the ARI term in Equation 6. A direct current voltage V,,, which corresponds to the term ARI is applied to a divider 128 which divides the signal from subtracting means 127 by voltage V,,, which corresponds to ARI in Equation 6, to provide a corresponding output. The output from divider 128 is effectively cubed by an exponential circuit 129, receiving voltage V, which corresponds to the exponent 3.0, to provide an output to a multiplier 130. Multiplier 130v multiplies the output from exponential circuit 129 with signal E from A computer 116 to provide signal Referring to FIGS. 1 and 7, an A computer 134 provides a signal E corresponding to the term 0.1.4,, in Equation 7 in accordance with signals E E E and E from temperature recorder controller 37,

flow recorders

44, 44A and 443, respectively, direct current voltages V,,, V,., V, and V,,, and Equation 7. Subtracting means 135 subtracts signal E corresponding to the temperature T of the extract-mix, from voltage V,,, which corresponds to the term 323 in Equation 7, to provide an output to a multiplier 137 where it is multiplied with voltage V, which corresponds to the term 0.935. Another multiplier 138 multiplies the output from multiplier 137 with signal E corresponding to the flow rate X, of the extract oil in line 50, to provide a product signal to a divider 142. Summing means sums signal E which corresponds to the flow rate Y of the refined waxy oil in line 41, with signal E to provide an output to exponential circuit 146 which receives voltage V, corresponding to the exponent 0.5 in equa tion 5. Exponential circuit 146 provides a corresponding signal to a multiplier 147. A divider 150 divides signal E which corresponds to the flow rate S of the solvent in line 24, by voltage V, which corresponds to the term 1,000 in Equation 7. An exponential circuit 151, which also receives voltage V,, raises the signal from divider 150 to the power of 0.5 and provides a corresponding signal. The signals from exponential circuits 146, and 151 are multiplied with each other by multiplier 147 to provide a product signal. Divider 142 divides the product signal from multiplier 138 with the product signal from multiplier 147 to provide signal E;,.,.

The quality of the refined oil is a constant for different sets of variable conditions. The flow rate of the charge oil and the temperature of the extract-mix leaving tower 5 may be simultaneously varied without changing the quality of the refined oil. The flow rate of the charge oil and the temperature of the extract-mix are controlled in accordance with the following equations to provide optimum refining of the charge oil.

where A is the predicted characteristic constant A for the charge stock during the predetermined time period and the actual characteristic constant A during the remainder of the refining process, X is the maximum profit flow rate of the extract oil in line 50, b is the value of the refined oil in dollars per barrel, e is the value of the charge oil in dollars per barrel, d is the value of extract oil in dollars per barrel, Y is the maximum profit flow rate of refined oil in line 41, 2 is the maximum profit flow rate of charge oil in line 23, and TLQMMP is the maximum profit temperature of the extract-mixfrom tower 5.

Referring to FIG. 1, the maximum profit flow rate of extract oil in line 50 is determined by an X computer 160 which provides a corresponding signal E to summing means 161. Summing means sums signal E with a signal E from a Y computer 162, which corresponds to the maximum profit flow rate of the refined waxy oil in line 41, to provide signal E corresponding to the maximum profit flow rate of the charge oil in line 23, to flow recorder controller 10. Switch 166 which may be of a type manufactured by Eagle Signal Co., Moline, Illinois, as model HPS Series, Cycl-I-ilex Reset Timer, passes signal E from A computer 100, as a signal E duringthe predetermined time to computer 160. Switch 66 then passes signal 5,, from A computer 118 as signal E thereafter to X computer 160. Computer 160 provides signal E in accordance-with the passed signal E from switch 166, direct current voltages V V V V, and V,,,, and Equation 8. All the terms referred to in the-following description of X computer 160 are contained in Equation 8.

Referring to FIG. 8, signal E from switch 166 is applied to a multiplier 167 where'it is multipliedwith voltage V corresponding to the term 0.65, to provide a product signal. Voltage V,, which corresponds to the term e, is subtracted from voltage V which corresponds to the term 17, by summing means 170 to provide a corresponding signal. A multiplier 171 multiplies the product signal from multiplier 167 with the signal from subtracting means 170 to provide-a product signal. Subtracting means 172 subtracts voltage V which corresponds to the term d, from voltage V to provide a signal to a .divider 175. Divider 175 divides the product signal from multiplier 171 by the signal from subtracting means 172. The resulting output from divider 175 is raised to the power l/0.35 by an exponential circuit 176 receiving voltage V,,,, which corresponds to the exponent l/0.35 to provide signal E fReferring to FIGS. 1 and 8,' Y computer 162 provides signal E in accordance with signals E E and Equation 9. Signal E which corresponds to the XM term in Equation '9, is. raised to the. power 065 by an exponential circuit 180 receiving a direct current voltage V,, which corresponds to'the exponent 0.65 in Equation 9. A divider 181 divides signal E which corresponds to the term A in Equation 9,'by the output from exponential circuit 181 to provide signal E Referring to FIG. 1, the maximum profit temperature T i, of the extract-mix leaving tower is computed by a T "up computer 185 which provides signal E to temperature recorder controller 37 to control the temperature of the extract-mix. Signal E is provided by computer 185 in accordance with signals E E E from flow recorder 44B, X computer 160 and Y computer 162, respectively, a signal E 'from a switch 186, and direct current voltages V,,, V V,, V,, V, and V, and equation 11. Switch 186 passes signal E relating to A from computer 64 as signal E during the predetermined time period and then passes signal E which corresponds to Am, from computer 134 thereafter as signal E a Referring to FIG. 9, signal E corresponding to the term S in Equation 1 l, is divided by voltage V, which corresponds to the term 1,000, by a divider 187 in Tgmmup computer 185. A signal corresponding to the resulting output from divider 187 raised to the 0.5 power is provided to a multiplier 189 by an exponential circuit 190 receiving voltage V corresponding to the exponent 0.5 in Equation 10. A multiplier 191 divides signal E from switch 186 by voltage V,, which corresponds to the coefficient 0.1 in Equation 11. The resulting output of multiplier 191 is multiplied with voltage V,,- which corresponds to the term 0.935, by a multiplier 194. Multiplier 189 multiplies the signal from circuit with the product signal from multiplier 194 to provide another product signal. Summing means 196 sums signals E and E corresponding to the X and Y terms, respectively, to provide a sum signal. An exponential circuit 197, receiving voltage V which corresponds to the exponent 0.5 in Equation 10, provides a signal relating to the sum signal from summing means 196 raised to the 0.5 power. A multiplier 200 multiplies the product signal from multiplier 189 with the signal from exponential circuit 197 to provide a product signal to a divider 201 where the product signal is divided by signal E,,,. Subtracting means 202 subtracts the output from divider 201 from voltage V,, corresponding to the term 323 in Equation ll to provide signal E I Although the device of the present invention hasbeen disclosed as using analog computers, a digital computer such as an 1800 Process Control Computer manufactured by IBM may be used.

Signals E E E E,, E E E E, and E from refractive index meter 17, flash meter 18, viscosity meter 19, gravity meter 20, temperature recorder controller 37, refractive index meter 17A,

flow recorders

44,44A and 448, respectively, are converted to digital signals by conventional type analog-todigital converters. The digital computer is programmed to provide control signals in accordance with Equations -l through 9. The control signals are then converted to analog signals E, and E by conventional type digital-to-analog converters. I

The device of the present invention as heretofore described controls quantities of refined oil and extract oil and the temperature of extract-mix during refining so as to obtain optimum yields of refined oil and extract oil during furfural refining of charge oil. The flow rate of the charge oil and the temperature of the extract-mix are automatically controlled during the. refining of the charge oil in accordance with predicted values, determined from sensed conditions of the charge oil, for a predetermined time period and in accordance with a sensed condition of the charge oil, solvent, refined waxy oil and the extract oil. The device of the present invention also controls the refining of the. charge oil in accordance with the economic values of the charge oil, the extract oil and the refined oil. The refined oil has a quality that is characterized by a predetermined viscosity index and a predetermined refractive index.

I Iclaim: I

l. A system for controlling the refining of charge oil to obtain optimum yields of refined oil and extract oil where the charge oil is treated with a solvent in a refining tower to yield raffinate and extract-mix, strippers separate the solvent from the rafiinate and from the extract-mix to provide refined waxy oil and the extract oil, respectively, the refined waxy oil is subsequently dewaxed to provide the refined oil and the solvent is fed back to the refining tower, comprising means for sensing characteristics of the charge oil, the refined waxy oil, the extract oil and the solvent and providing signals corresponding thereto; means for providing signals corresponding to the economic values of the charge oil, the refined oil and the extract oil, and means connected to the sensing means and to the value signal means for controlling some of the conditions of the refined waxy oil and the extract oil in accordance with the condition signals and the value signals to provide the optimum yields of the refined oil and the extract oil.

2. A system as described in claim 1 in which the sensed conditions are the refractive index of the charge oil, the flow rate and the refractive index of the refined waxy oil, the flow rate of the extract oil, the temperature of the extract-mix, and the flow rate of the solvent; and the controlled conditions are the flow rates of the refined waxy oil and the extract oil and the temperature of the extract mix.

3. A system as described in claim 2 in which the flow rates of the refined waxy oil and the extract oil are controlled by controlling the flow rate of the charge oil and the temperature of the extract-mix.

4. A system as described in claim 3 in which the control means includes first signal means for providing signals corresponding to a first actual characteristic 0. IA and a desired characteristic a of the refined oil in accordance with the following equations:

where X, is the flow rate of the extract oil, T is the temperature of the extract-mix, Y is the flow rate of the refined waxy oil, S is the flow rate of the solvent, a is a second actual characteristic of the refined waxy oil, ARI, is the difference between the refractive index of the charge oil and the refractive index of the refined waxy oil, and ARI is the desired difference between the refractive index of the charge oil and the refractive index of the refined oil.'

5. A system as described in claim 4 in which the control means includes control devices for controlling the flow rate of the charge oil and the temperature of the extract-mix,-and means connected to the first signal means and to the control devices for providing control signals to the control devices corresponding to the flow rate Z of the charge oil for maximum profit and the temperature 71 of the extract-mix for maximum profit, so that the control devices control the flow rate of the charge oil and the temperature of the extractmix in accordance with the signals from the first signal means and the following equations: 7

1/0135 MuIP 9 YMMP and

(0.935) (0.1A) (511000)"- (Ximp MaaP) T 11.0.11? 323 XMHP where a is 0 5,, X is the maximum profitable flow rate of the extract oil, Y is the maximum profitable flow rate of the refined waxy oil, S is the flow rate of the solvent, 0.1A is 0.1/1 b is the economic value of the refined oil, d is the economic value of the extract oil, and e is the economic value of the charge oil.

6, A system as described in claim 5 in which the sensing means includes a pair of refractive index meters, one refractive index meter sensing the refractive index of the refined waxy oil and providing a corresponding signal while the other refractive index meter senses the refractive index of the charge oil and provides a signal corresponding thereto, means connected to the refractive index meters for providing a signal corresponding to the difference between the refractive indices ARI, of the charge oil and the refined waxy oil, means for sensing the temperature T of the extract-mix and providing a corresponding signal, and means for sensing the flow rates X,,,,, Y, and S of the extract oil, the refined waxy oil and the solvent, respectively, and providing signals corresponding thereto.

7. A system as described in claim 6 in which the first signal means includes a first analog computer receiving direct current voltages corresponding to the numeric values 0.935, 323, 1,000 in the first mentioned equation and connected to the flow rate sensing means and providing the signal corresponding to 0.1.4,, in accordance with the first mentioned equation, the received direct current voltages and the signals corresponding to the flow rates X and Y of the refined waxy oil and the extract oil, respectively, a second analog computer connected to the flow rate sensing means and receiving a direct current voltage corresponding to the exponent 0.65 in the second mentioned equation and providing a signal corresponding to the tenn a in the second mentioned equation in accordance with the second mentioned equation, the signals from the flow rate sensing means corresponding to the flow rates X, and Y of the extract oil and-the refined waxy oil, respectively, and the received direct current voltage; and a third analog computer connected to the second analog computer and to the difference means and receiving direct current voltages corresponding to the ARI term and the exponent 3.0 in the third mentioned equation and providing the signal corresponding to a in accordance with the third mentioned equation, the signal corresponding to a from the second analog computer, the signal corresponding to ARI from the difference means, and the received direct current voltages.

8. A system as described in claim 7 in which control signal means includes a fourth analog computer connected to the third analog computer and receiving variable direct current voltages corresponding to the terms b, d and e and a fixed direct current voltage corresponding to the exponent l/0.35 0.35 and the 0.65 in the fourth mentioned equation and providing a signal corresponding to the maximum profit flow rate X of the extract oil in accordance with the fourth mentioned equation, the received direct current voltages and the signal from the third analog computer corresponding to the tenn a in the third mentioned equation and which also corresponds to the term a in the fourth and fifth mentioned equations; a fifth analog computer connected to the third and fourth analog computers and receiving a direct current volt-' age corresponding to the exponent 0.65 in the fifth mentioned equation and providing a signal corresponding to the maximum profit flow rate of refined waxy oil Y in accordance with the fifth mentioned equation, the signals from the third and fourth analog computers and the received direct voltage; summing means connected to the fourth and fifth analog computers for summing the signals from the fourth and the fifth analog computers to provide the control signal to the control devices corresponding to Z for controlling the flow rate of the charge oil; and a sixth analog computer connected to the first, fourth and fifth analog computers, to the flow rate signal means and receiving direct current voltages corresponding to the terms 323, 0.935, and 0,5, in the seventh mentioned equation and providing the control signal to the control devices corresponding to TBOMMP for controlling the temperature of the extract-mix in accordance with the signals from the first, fourth and fifth analog computers, the signal from the flow rate sensing means corresponding to the flow rate of the solvent, the received direct current voltages and the seventh mentioned equation.

9. A system of the kind described in claim 8 in which the sensing means further comprises means for sensing the flash point Fl of the crude oil, and providing a corresponding signal; means for sensing the API gravity of the charge oil and providing a signal corresponding thereto, and means for sensing the kinematic viscosity V,, and providing a corresponding signal; and the control means further includes second signal means, connected to the kinematic viscosity sensing means, to the API gravity sensing means, to the other refractive index meter, to the flash point sensing means and to the flow rate sensing means for providing signals corresponding to predicted first and second characteristics of the refined waxy oil in accordance with the signals from the kinematic viscosity sensing means, from the API gravity sensing means, from the other refractive index meter, from the flash point sensing means and from the flow rate sensing means and with the following equations:

H= 870 log log(V +O.6)+ 154, 01A 94.9.- 0.149 H 0.0826(API) 0,0001 1')"' l-j.(). 0.1281 [1,000 (RA -1.42) 0. l(F!)]-C,( 100 I VITI"U| where H is the Bell and Sharp viscosity function of the. charge oil at 210 F., V is the sensed kinematic viscosity of the charge oil at 210 F., APlis thesensed APlgravity of the charge oil, A is a predicted first characteristic of the refined waxy oil, E .0. is the yield of extract oil in per cent by volume of charge oil, C is a constant of the charge oil and equals 12.7 for light distillates, 25.4 for heavy distillates and 17.3 for residual oil, R1, 1 charge oil, F1 is the sensed flash point of the charge oil, C, is another constant of the charge oil and equals 1.333 for light distillates, 1.668 for heavy distillates and 1.373 for residual oil, W is the target viscosity index of the refined oil, a is asecond predicted characteristic of the refined waxy oil, and S is the sensed fiow rate of the solvent; and switching means connected to the first and second signal means and to the control signal means for passing the signals from the second signal means to the'control signal means-during a predetermined timeperiod while blocking the signals fromthe first signal means, and passing the signals from the first signal means to the control signal means while blocking the signals from the urn! l 0.215

second signal means afterthe predetennined time period, and

where the term a in the equations controlling the development of the control signals corresponds to during the predetermined time period and a thereafter and theterm 0.1A in the equations controlling the development of the control signals corresponds to 0.114,, during the predetermined time period and 01A,, thereafter.

10. -A system-as described in claim 9 in which the second signalmeans includes a seventh analog computer connected to the kinematic viscosity sensing means and receiving direct current voltages corresponding to the terms 870, 0.6 and 154 in the eighth mentioned equation and providing a signal corresponding to the Bell and Sharpe viscosity function]! in accordance with the signal from the kinematic viscosity sensing means, the received direct current voltages, and the eighth mentioned equation; an eighth analog computer connected to the seventh computer, to the API gravity sensing means and to the switching means and receiving direct current voltages corresponding to the terms 94.9, 0.149, 0.0826 and 0.0001 in the ninth mentioned equation for providing a signal to the switching means corresponding to 0. 1A,, in accordance with the signal, from the seventh computer, the signal from the APl gravity sensing means and the received direct current voltages; and a ninth computer connected to the flash point sensing means and to the other refractive index meter and receiving direct current voltages corresponding to the C 0.1281, 1,000, 1.42, 0.1, C 100 terms in the tenth mentioned equation and providing a signal corresponding to percent by volume E. 0. of extract oil obtained from the charge oil in accordance with signals from the flash point sensing means and the other refractive indexmeter, and the received direct current voltages; and a tenth comptiter connected to the flow rate sensing means, to the switching means and to the ninth computer and receiving direct current voltages corresponding to the terms 0.464, 1,000, 100 and l and the exponent 0.35 in the eleventh mentioned equation and providing the signal to the switching means corresponding to the second predicted characteristic a of the refined oil in accordance with the signal from the ninth analog computer, a' signal from the fiow rate sensing means corresponding to the flow rate S of the solvent and the received direct currentvoltages.

11. A method for controlling a refinery operation wherein charge oil is mixed with solvent in a refining tower to provide a stream of raffinate and a stream of extract-mix to strippers is the sensed refractive index of the which strip the solvent from the raffinate and the extract-mix to yield refined waxy oil and extract oil, the stripped solvent is returned to the refining tower and the refined waxy oil is subsequently dewaxed to provide refined oil; which comprises sensing conditions of the refined waxy oil, the extract oil and the solvent; providing signals corresponding to the sensed conditions; providing signals corresponding to the economic values of the charge oil, the refined oil and the extract oil; and controlling some of the conditions of the refined waxy oil, the extract oil and the extract-mix in accordance with the condition signals and the value signals.

12. A method as described in claim 11 in which the sensed conditions are the refractive index of the charge oil, the flow rate and the refractive index of the refined waxy oil, the fiow rate of the extract oil, the temperature of the extract-mix and the flow rate of the solvent; the controlled conditions are the flow rates'of the refined waxy oil and the extract oil; and the condition signals 0.1.4,, and a correspond to the sensed conditions in accordance with the following equations:

and

ARI Targ nd A R 11am) where 0.114 is one characteristic of the refined waxy oil, X is the flow rate of the extract oil, T is the temperature of the extract oil, Y is the flow rate of the refined waxy oil, S is the How rate of the solvent, a is the other characteristic of the refined waxy oil, ARI is the difference between the refra'c- 1 tive index of the charge oil and the refractive index of the refined waxy oil, and ARI is the target difference between the refractive index of the chargeoil and the'refractive index [a(0.65) (b il MaIP 9 I e-d YMQIP =m,

Z MaIP Ma1-P MruPn and ea/warp 323 XMGIP where X up is the maximum profit flow rate of the extract oil, a is a b is the economic value of the refined oil, d is the economic value of the extract oil, e is the economic value of the charge oil, m is the maximum profit flow rate of the refined waxy oil, TEDMMP is the maximum profit temperature of the extract oil, 0.1A is 0.114,, and S is the How rate of the solvent;

14. A methodas described in claim 13 in which other sensed conditions are the flash point, the API gravity and the kinematic viscosity of the charge oil, and the condition signals further are signals 0.114,, and a corresponding to the sensed conditions in accordance with the following equations:

01A 94.9 0.149 H- 0.0826 (API) 0.0001 H (EO' I),

12.7 when the charge oil is a light distillate, 25.4 when the charge oil is a heavy distillate and 17.3 when the charge oil is residual oil, R1, is the sensed refractive index of the charge oil, F1 is the sensed flash point of the charge oil, C is another constant of the charge oil and equals 1.333 when the charge oil is a light distillate, 1.668 when the charge oil is a heavy distillate and 1.373 for residual oil, V1 is the target viscosity index of the refined oil, a is another constant of the refined waxy oil, and S is the sensed flow rate of the solvent; the control signals Z and TLQMGM are provided in accordance with the 0.1.4,, and the a condition signals during a predetermined time period and with the 0.1.4,, and the a condition signals thereafter, the term a in the, fourth and fifth mentioned equations corresponds to the 0 term of the I lth mentioned equation during the predetermined time period and to the term o in the third mentioned equation thereafter; and the term 0.1.4 in the seventh mentioned equation corresponds to the term 0.114,, in the ninth mentioned equation during the predetermined time period and to the term 0.121,, in the first mentioned equation thereafter.

* I I l 39 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent: No. 3,666,931 Dated MAY 3 97 ROBERT A. WOODLE Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

T- c [100 v1 1-, c 1 lin 68 I 6 2 TARG a. o umn 3, es and 9, should d lOO- rea. C VI a gat Column 5, line 48, should act act read a --(X I )O 5 H act c (10 VI ARG at Column 11, line 6, should read 100- C VI Signed and sealed this 9th day of January 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents

Claims

1. A system for controlling the refining of charge oil to obtain optimum yields of refined oil and extract oil where the charge oil is treated with a solvent in a refining tower to yield raffinate and extract-mix, strippers separate the solvent from the raffinate and from the extract-mix to provide refined waxy oil and the extract oil, respectively, the refined waxy oil is subsequently dewaxed to provide the refined oil and the solvent is fed back to the refining tower, comprising means for sensing characteristics of the charge oil, the refined waxy oil, the extract oil and the solvent and providing signals corresponding thereto; means for providing signals corresponding to the economic values of the charge oil, the refined oil and the extract oil, and means connected to the sensing means and to the value signal means for controlling some of the conditions of the refined waxy oil and the extract oil in accordance with the condition signals and the value signals to provide the optimum yields of the refined oil and the extract oil.

4. A system as described in claim 3 in which the control means includes first signal means for providing signals corresponding to a first actual characteristic 0.1Aact and a desired characteristic aTarg of the refined oil in accordance with the following equations:

5. A system as described in claim 4 in which the control means includes control devices for controlling the flow rate of the charge oil and the temperature of the extract-mix, and means connected to the first signal means and to the control devices for providing control signals to the control devices corresponding to the flow rate ZMaxP of the charge oil for maximum profit and the temperature TE.O.MaxP of the extract-mix for maximum profit, so that the control devices control the flow rate of the charge oil and the temperature of the extract-mix in accordance with the signals from the first signal means and the following equations:

6. A system as described in claim 5 in which the sensing means includes a pair of refractive index meters, one refractive index meter sensing the refractive index of the refined waxy oil and providing a corresponding signal while the other refractive index meter senses the refractive index of the charge oil and provides a signal corresponding thereto, means connected to the refractive index meters for providing a signal corresponding to the difference between the refractive indices Delta RIact of the charge oil and the refined waxy oil, means for sensing the temperature TE.O. of the extract-mix and providing a corresponding signal, and means for sensing the flow rates Xact, Yact and S of the extract oil, the refined waxy oil and the solvent, respectively, and providing signals corresponding thereto.

7. A system as described in claim 6 in which the first signal means includes a first analog computer receiving direct current voltages corresponding to the numeric values 0.935, 323, 1,000 in the first mentioned equation and connected to the flow rate sensing means and providing the signal corresponding to 0.1Aact in accordance with the first mentioned equation, the received direct current voltages and the signals corresponding to the flow rates Xact and Yact of the refined waxy oil and the extract oil, respectively, a second analog computer connected to the flow rate sensing means and receiving a direct current voltage corresponding to the exponent 0.65 in the second mentioned equation and providing a signal corresponding to the term aact in the second mentioned equation in accordance with the second mentioned equation, the signals from the flow rate sensing means corresponding to the flow rates Xact and Yact of the extract oil and the refined waxy oil, respectively, and the received direct current voltage; and a third analog computer connected to the second analog computer and to the difference means and receiving direct current voltages corresponding to the Delta RITarg term and the exponent 3.0 in the third mentioned equation and providing the signal corresponding to aTarg in accordance with the third mentioned equation, the signal corresponding to aact from the second analog computer, the signal corresponding to Delta RIact from the difference means, and the received direct current voltages.

8. A system as described in claim 7 in which control signal means includes a fourth analog computer connected to the third analog computer and receiving variable direct current voltages corresponding to the terms b, d and e and a fixed direct current voltage corresponding to the exponent 1/0.35 0.35 and the 0.65 in the fourth mentioned equation and providing a signal corresponding to the maximum profit flow rate XMaxP of the extract oil in accordance with the fourth mentioned equation, the received direct current voltages and the signal from the third analog computer corresponding to the term aTarg in the third mentioned equation and which also corresponds to the term a in the fourth and fifth mentioned equations; a fifth analog computer connected to the third and fourth analog computers and receiving a direct current voltage corresponding to the exponent 0.65 in the fifth mentioned equation and providing a signal corresponding to the maximum profit flow rate of refined waxy oil YMaxP in accordance with the fifth mentioned equation, the signals from the third and fourth analog computers and the received direct voltage; summing means connected to the fourth and fifth analog computers for summing the signals from the fourth and the fifth analog computers to provide the control signal to the control devices corresponding to ZMaxP for controlling the flow rate of the charge oil; and a sixth analog computer connected to the first, fourth and fifth analog computers, to the flow rate signal means and receiving direct current voltages corresponding to the terms 323, 0.935, and 0.5, in the seventh mentioned equation and providing the control signal to the control devices corresponding to TE.O.MaxP for controlling the temperature of the extract-mix in accordance with the signals from the first, fourth and fifth analog computers, the signal from the flow rate sensing means corresponding to the flow rate of the solvent, the received direct current voltages and the seventh mentioned equation.

9. A system of the kind described in claim 8 in which the sensing means further comprises means for sensing the flash point Fl of the crude oil, and providing a corresponding signal; means for sensing the API gravity of the charge oil and providiNg a signal corresponding thereto, and means for sensing the kinematic viscosity Vk and providing a corresponding signal; and the control means further includes second signal means, connected to the kinematic viscosity sensing means, to the API gravity sensing means, to the other refractive index meter, to the flash point sensing means and to the flow rate sensing means for providing signals corresponding to predicted first and second characteristics of the refined waxy oil in accordance with the signals from the kinematic viscosity sensing means, from the API gravity sensing means, from the other refractive index meter, from the flash point sensing means and from the flow rate sensing means and with the following equations: H 870 log log (Vk + 0.6) + 154 , 0.1Apred 94.9 - 0.149 H - 0.0826(API)2 + 0.0001 H2 , E.O. C1 + 0.1281 ( 1,000 (RIwc-1.42) - 0.1(Fl))-C2(100 -VITarg), and where H is the Bell and Sharp viscosity function of the charge oil at 210* F., Vk is the sensed kinematic viscosity of the charge oil at 210* F., API is the sensed API gravity of the charge oil, Apred is a predicted first characteristic of the refined waxy oil, E.O. is the yield of extract oil in per cent by volume of charge oil, C1 is a constant of the charge oil and equals 12.7 for light distillates, 25.4 for heavy distillates and 17.3 for residual oil, RIwc is the sensed refractive index of the charge oil, Fl is the sensed flash point of the charge oil, C2 is another constant of the charge oil and equals 1.333 for light distillates, 1.668 for heavy distillates and 1.373 for residual oil, VITarg is the target viscosity index of the refined oil, apred is a second predicted characteristic of the refined waxy oil, and S is the sensed flow rate of the solvent; and switching means connected to the first and second signal means and to the control signal means for passing the signals from the second signal means to the control signal means during a predetermined time period while blocking the signals from the first signal means, and passing the signals from the first signal means to the control signal means while blocking the signals from the second signal means after the predetermined time period, and where the term a in the equations controlling the development of the control signals corresponds to apred during the predetermined time period and aTarg thereafter and the term 0.1A in the equations controlling the development of the control signals corresponds to 0.1Apred during the predetermined time period and 0.1Aact thereafter.

10. A system as described in claim 9 in which the second signal means includes a seventh analog computer connected to the kinematic viscosity sensing means and receiving direct current voltages corresponding to the terms 870, 0.6 and 154 in the eighth mentioned equation and providing a signal corresponding to the Bell and Sharpe viscosity function H in accordance with the signal from the kinematic viscosity sensing means, the received direct current voltages, and the eighth mentioned equation; an eighth analog computer connected to the seventh computer, to the API gravity sensing means and to the switching means and receiving direct current voltages corresponding to the terms 94.9, 0.149, 0.0826 and 0.0001 in the ninth mentioned equation for providing a signal to the switching means corresponding to 0.1Apred in accordance with the signal from the seventh computer, the signal from the API gravity sensing means anD the received direct current voltages; and a ninth computer connected to the flash point sensing means and to the other refractive index meter and receiving direct current voltages corresponding to the C1, 0.1281, 1,000, 1.42, 0.1, C2, 100 terms in the tenth mentioned equation and providing a signal corresponding to percent by volume E.O. of extract oil obtained from the charge oil in accordance with signals from the flash point sensing means and the other refractive index meter, and the received direct current voltages; and a tenth computer connected to the flow rate sensing means, to the switching means and to the ninth computer and receiving direct current voltages corresponding to the terms 0.464, 1,000, 100 and 1 and the exponent 0.35 in the eleventh mentioned equation and providing the signal to the switching means corresponding to the second predicted characteristic apred of the refined oil in accordance with the signal from the ninth analog computer, a signal from the flow rate sensing means corresponding to the flow rate S of the solvent and the received direct current voltages.

11. A method for controlling a refinery operation wherein charge oil is mixed with solvent in a refining tower to provide a stream of raffinate and a stream of extract-mix to strippers which strip the solvent from the raffinate and the extract-mix to yield refined waxy oil and extract oil, the stripped solvent is returned to the refining tower and the refined waxy oil is subsequently dewaxed to provide refined oil; which comprises sensing conditions of the refined waxy oil, the extract oil and the solvent; providing signals corresponding to the sensed conditions; providing signals corresponding to the economic values of the charge oil, the refined oil and the extract oil; and controlling some of the conditions of the refined waxy oil, the extract oil and the extract-mix in accordance with the condition signals and the value signals.

12. A method as described in claim 11 in which the sensed conditions are the refractive index of the charge oil, the flow rate and the refractive index of the refined waxy oil, the flow rate of the extract oil, the temperature of the extract-mix and the flow rate of the solvent; the controlled conditions are the flow rates of the refined waxy oil and the extract oil; and the condition signals 0.1Aact and aTarg correspond to the sensed conditions in accordance with the following equations:

13. A method as described in claim 12 in which the controlling step includes providing control signals ZMaxP and TE.O.MaxP corresponding to the maximum profit flow rate of the charge oil and to the maximum profit temperature of the extract-mix, respectively, in accordance with the 0.1Aact and the aTarg condition signals and the following equations:

14. A method as described in claim 13 in which other sensed conditions are the flash point, the API gravity and the kinematic viscosity of the charge oil, and the condition signals further are signals 0.1Apred and apred corresponding to the sensed conditions in accordance with the following equations: H 870 log log (Vk + 0.6) + 154, 0.1Apred 94.9 - 0.149 H - 0.0826 (API)2 + 0.0001 H2 , E.O. C1 + 0.1281( 1,000(RIwc-1.42) -0.1(Fl)) - C2(100- VITarg) , and where H is the Bell and Sharp viscosity function of the charge oil at 210* F., Vk is the sensed kinematic viscosity of the charge oil at 210* F., API is the sensed API gravity of the charge oil, 0.1Apred is a predicted characteristic of the refined waxy oil, E.O. is the yield of extract oil in percent by volume of the charge oil, C1 is a constant of the charge oil and equals 12.7 when the charge oil is a light distillate, 25.4 when the charge oil is a heavy distillate and 17.3 when the charge oil is residual oil, RIwc is the sensed refractive index of the charge oil, Fl is the sensed flash point of the charge oil, C2 is another constant of the charge oil and equals 1.333 when the charge oil is a light distillate, 1.668 when the charge oil is a heavy distillate and 1.373 for residual oil, VITarg is the target viscosity index of the refined oil, apred is another constant of the refined waxy oil, and S is the sensed flow rate of the solvent; the control signals ZMaxP and TE.O.MaxP are provided in accordance with the 0.1Apred and the apred condition signals during a predetermined time period and with the 0.1Aact and the aTarg condition signals thereafter, the term a in the fourth and fifth mentioned equations corresponds to the apred term of the 11th mentioned equation during the predetermined time period and to the term aTarg in the third mentioned equation thereafter; and the term 0.1A in the seventh mentioned equation corresponds to the term 0.1Apred in the ninth mentioned equation during the predetermined time period and to the term 0.1Aact in the first mentioned equation thereafter.