Abstract:
A furfural refining unit treats light sour charge oil with a furfural solvent in a refining tower to yield raffinate and extract mix. The furfural is recovered from the raffinate and from the extract mix and returned to the refining tower. A system controlling the refining unit includes a gravity analyzer, a flash point temperature analyzer and viscosity analyzers; all analyzing the light sour charge oil and providing corresponding signals, sensors sense the flow rates of the charge oil and the furfural flowing into the refining tower and the temperature of the extract mix and provide corresponding signals. One of the flow rates of its light sour charge oil and the furfural flow rates is controlled in accordance with the signals from all the analyzers and all the sensors, while the other flow rate of the light sour charge oil and the furfural flow rates is constant.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation as to all subject matter common to U.S. application Ser. No. 851,994 filed Nov. 16, 1977, and now abandoned by Avilino Sequeira, Jr., John D. Begnaud, and Frank L. Barger, and assigned to Texaco Inc., assignee of the present invention, and a continuation-in-part for additional subject matter. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to control systems and methods in general and, more particularly, to control systems and methods for oil refining units. 
     SUMMARY OF THE INVENTION 
     A furfural refining unit treats light sour charge oil with a furfural solvent in a refining tower to yield raffinate and extract mix. The furfural is recovered from the raffinate and from the extract mix and returned to the refining tower. A system controlling the refining unit includes a gravity analyzer, a flash point temperature analyzer and viscosity analyzers. The analyzers analyze the light sour charge oil and provide corresponding signals. Sensors sense the flow rates of the charge oil and the furfural flowing into the refining tower and the temperature of the extract-mix and provide corresponding signals. The flow rate of the light sour charge oil or the furfural is controlled in accordance with the signals provided by all the sensors and the analyzers while the other flow rate of the light sour charge oil or the furfural is constant. 
     The 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. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a furfural refining unit in partial schematic form and a control system, constructed in accordance with the present invention, in simple block diagram form. 
     FIG. 2 is a detailed block diagram of the control means shown in FIG. 1. 
     FIGS. 3 through 12 are detailed block diagrams of the H computer, the K signal means, the H signal means, the KV computer, the VI signal means, the SUS computer, the SUS 210  computer, the VI DWC .sbsb.O computer, the VI DWC .sbsb.P computer and the J computer, respectively, shown in FIG. 2. 
    
    
     DESCRIPTION OF THE INVENTION 
     An extractor 1 in a furfural refining unit is receiving sour light charge oil by way of a line 4 and furfural solvent by way of a line 7 and providing raffinate to recovery by way of a line 10, and an extract mix to recovery by way of a line 14. 
     Light sour charge oil is a charge oil having a sulfur content greater than a predetermined sulfur content and having a kinematic viscosity, corrected to a predetermined temperature, equal to or less than a predetermined kinematic viscosity. Preferably, the predetermined sulfur content is 1.0%, the predetermined temperature is 210° F., and the predetermined kinematic viscosity is 7.0. The temperature in extractor 1 is controlled by cooling water passing through a line 16. A gravity analyzer 20, flash point analyzer 22 and viscosity analyzers 23 and 24, sample the charge oil in line 4 and provide signals API, FL, KV 210  and KV 150  respectively, corresponding to the API gravity, the flash point, the kinematic viscosity at 210° F., and the kinematic viscosity at 150° F. respectively. 
     A flow transmitter 30 in line 4 provide a signal CHG corresponding to the flow rate of the charge oil in line 4. Another flow transmitter 33 in line 7 provides a signal SOLV corresponding to the furfural flow rate. A temperature sensor 38, sensing the temperature of the extract mix leaving extractor 1, provides a signal T corresponding to the sensed temperature. All signals hereinbefore mentioned are provided to control means 40. 
     Control means 40 provides signal C to a flow recorder controller 43. Recorder controller 43 receives signals CHG and C and provides a signal to a valve 48 to control the flow rate of the charge oil in line 4 in accordance with signals CHG and C so that the charge oil assumes a desired flow rate. Signal T is also provided to temperature controller 50. Temperature controller 50 provides a signal to a valve 51 to control the amount of cooling water entering extractor 1 and hence the temperature of the extract-mix in accordance with its set point position and signal T. 
     The following equations are used in practicing the present invention for light sour charge oil: 
     
         H.sub.210 =1n1n(KV.sub.210 +C.sub.1)                       (1) 
    
     where H 210  is a viscosity H value for 210° F., KV 210  is the kinematic viscosity of the charge oil at 210° F. and C 1  is a constant having a preferred value of 0.6. 
     
         H.sub.150 =1n1n(KV.sub.150 +C.sub.1)                       (2) 
    
     where H 150  is a viscosity H value for 150° F., and KV 150  is the kinematic viscosity of the charge oil at 150° F. 
     
         k.sub.150 =[c.sub.2 -1n(T.sub.150 +C.sub.3)]/C.sub.4       (3) 
    
     where K 150  is a constant needed for estimation of the kinematic viscosity at 100° F., T 150  is 150, and C 2  through C 4  are constants having preferred values of 6.5073, 460 and 0.17937, respectively. 
     
         H.sub.100 =H.sub.210 +(H.sub.150 -H.sub.210)/K.sub.150     (4) 
    
     where H 100  is a viscosity H value for 100° F. 
     
         kv.sub.100 =exp[exp(H.sub.100)]-C.sub.1                    (5) 
    
     where KV 100  is the kinematic viscosity of the charge oil at 100° F. 
     
         sus=c.sub.5 (kv.sub.210)+[c.sub.6 +c.sub.7 (kv.sub.210)]/[c.sub.8 +c.sub.9 (kv.sub.210)+c.sub.10 (kv.sub.210).sup.2 +c.sub.11 (kv.sub.210).sup.3 ](c.sub.12)                                               (6) 
    
     where SUS is the viscosity in Saybolt Universal Seconds and C 5  through C 12  are constants having preferred values of 4.6324, 1.0, 0.03264, 3930.2, 262.7, 23.97, 1.646 and 10 -5 , respectively. 
     
         SUS.sub.210 =[C.sub.13 +C.sub.14 (C.sub.15 -C.sub.16)]SUS  (7) 
    
     where SUS 210  is the viscosity in Saybolt Universal Seconds at 210° F. and C 13  through C 16  are constants having preferred values of 1.0, 0.000061, 210 and 100, respectively. 
     
         VI.sub.DWC.sbsb.O =C.sub.17 -C.sub.18 (FL)+C.sub.19 (VI)+C.sub.20 (KV.sub.210)(API)                                         (8) 
    
     where VI DWC .sbsb.O, FL, VI, and API are the viscosity index of the dewaxed product at zero pour point, the flash point temperature of the charge oil, the viscosity index of the charge oil and the API gravity of the charge oil, respectively, and C 12  through C 20  are constants having preferred values of 27.35, 0.1159, 0.69819 and 0.21112, respectively. 
     
         VI.sub.DWC.sbsb.P =VI.sub.DWC.sbsb.O +(Pour)[C.sub.21 -C.sub.22 1nSUS.sub.210 +C.sub.23 (1nSUS.sub.210).sup.2 ]           (9) 
    
     where VI DWC .sbsb.P and Pour are the viscosity index of the dewaxed product at a predetermined temperature and the Pour Point of the dewaxed product, respectively, and C 21  through C 23  are constants having preferred values of 2.856, 1.18 and 0.126, respectively. 
     
         ΔVI=VI.sub.RO -V.sub.DWC.sbsb.O =VI.sub.RP -VI.sub.DWC.sbsb.P (10) 
    
     where VI RO  and VI RP  are the VI of the refined oil at 0° F., and the predetermined temperature, respectively. 
     
         J={{-C.sub.39 +{(C.sub.39).sup.2 -4(C.sub.40)(T)(-C.sub.41 +C.sub.42 √T-ΔVI]}.sup.1/2 }/2[C.sub.40 T]}.sup.2      (11) 
    
     where J is the furfural dosage and C 39  through C 42  are constants having preferred values of 3.0093, 0.00023815, 54.88 and 5.3621, respectively. 
     
         C=(SOLV)(100)/J                                            (12) 
    
     where C is the new charge oil flow rate. 
     Referring now to FIG. 2, signal KV 210  is provided to an H computer 50 in control means 40, while signal KV 150  is applied to an H computer 50A. It should be noted that elements having a number and a letter suffix are similar in construction and operation as to those elements having the same numeric designation without a suffix. All elements in FIG. 2, except elements whose operation is obvious, will be disclosed in detail hereinafter. Computers 50 and 50A provide signals E 1  and E 2  corresponding to H 210  and H 150 , respectively, in equations 1 and 2, respectively, to H signal means 53. K signal means 55 provides a signal E 3  corresponding to the term K 150  in equation 3 to H signal means 53. H signal means 53 provides a signal E 4  corresponding to the term H 100  in equation 4 to a KV computer 60 which provides a signal E 5  corresponding to the term KV 100  in accordance with signal E 4  and equation 5 as hereinafter explained. 
     Signals E 5  and KV 210  are applied to VI signal means 63 which provides a signal E 6  corresponding to the viscosity index. 
     An SUS computer 65 receives signal KV 210  and provides a signal E 7  corresponding to the term SUS in accordance with the received signals and equation 6 as hereinafter explained. 
     An SUS 210 computer 68 receives signal E 7  and applies signal E 8  corresponding to the term SUS 210  in accordance with the received signal and equation 7 as hereinafter explained. 
     A VI DWC .sbsb.O computer 70 receives signal KV 210 , API, FL, and E 6  and provides a signal E 9  corresponding to the term VI DWC .sbsb.O in accordance with the received signals and equation 8 as hereinafter explained. 
     A VI DWC .sbsb.P computer 72 receives signal E 8  and E 9  and provides a signal E 10  corresponding to the term VI DWC .sbsb.P in accordance with the received signals and equation 9. Subtracting means 76 performs the function of equation 10 by subtracting signal E 10  from a direct current voltage V 9 , corresponding to the term VI RP , to provide a signal E 11  corresponding to the term ΔVI in equation 10. 
     A J computer 80 receives signals T, E 11  and provide a signal E 13  corresponding to the term J in accordance with the received signals and equation 11 as hereinafter explained to a divider 81. 
     Signal SOLV is provided to a multiplier 83 where it is multiplied by a direct current voltage V 2  corresponding to a value of 100 to provide a signal corresponding to the term (SOLV)(100) in equation 12. The product signal is applied to divider 81 where it is divided by signal E 13  to provide signal C corresponding to the desired new charge oil flow rate. 
     It would be obvious to one skilled in the art that if the charge oil flow rate was maintained constant and the furfural flow rate varied, equation 13 would be rewritten as 
     
         SO=(J)(CHG)/100                                            (13) 
    
     where SO is the new furfural flow rate. Control means 40 would be modified accordingly. 
     Referring now to FIG. 3, H computer 50 includes summing means 112 receiving signal KV 210  and summing it with a direct current voltage C 1  to provide a signal corresponding to the term [KV 210  +C 1  ] shown in equation 1. The signal from summing means 112 is applied to a natural logarithm function generator 113 which provides a signal corresponding to the natural log of the sum signal which is then applied to another natural log function generator 113A which in turn provides signal E 10 . 
     Referring now to FIG. 4, K signal means 55 includes summing means 114 summing direct current voltage T 150  and C 3  to provide a signal corresponding to the term [T 150  +C 3  ] which is provided to a natural log function generator 113B which in turn provides a signal corresponding to the natural log of the sum signal from summing means 114. Subtracting means 115 subtracts the signal provided by function generator 113B from a direct current voltage C 2  to provide a signal corresponding to the numerator of equation 3. A divider 116 divides the signal from subtracting means 115 with a direct current voltage C 4  to provide signal E 3 . 
     Referring now to FIG. 5, H signal means 53 includes subtracting means 117 which subtracts signal E 1  from signal E 2  to provide a signal corresponding to the term H 150  -H 210 , in equation 4, to a divider 118. Divider 118 divides the signal from subtracting means 117 by signal E 3 . Divider 114 provides a signal which is summed with signal E 1  by summing means 119 to provide signal E 4  corresponding to H 100 . 
     Referring now to FIG. 6, a direct current voltage V 3  is applied to a logarithmic amplifier 120 in KV computer 60. Direct current voltage V 3  corresponds to the mathematical constant e. The output from amplifier 120 is applied to a multiplier 122 where it is multiplied with signal E 4 . The product signal from multiplier 122 is applied to an antilog circuit 125 which provides a signal corresponding to the term exp (H 100 ) in equation 5. The signal from circuit 125 is multiplied with the output from logarithmic amplifier 120 by a multiplier 127 which provides a signal to antilog circuit 125A. Circuit 125A is provided to subtracting means 128 which subtracts a direct current voltage C 1  from the signal provided by circuit 125A to provide signal E 5 . 
     Referring now to FIG. 7, VI signal means 63 is essentially memory means which is addressed by signals E 5 , corresponding to KV 100 , and signal KV 210 . In this regard, a comparator 130 and comparator 130A represent a plurality of comparators which receive signal E 5  and compare signal E 5  to reference voltages, represented by voltages R 1  and R 2 , so as to decode signal E 5 . Similarly, comparators 130B and 130C represent a plurality of comparators receiving signal KV 210  which compare signal KV 210  with reference voltages RA and RB so as to decode signal KV 210 . The outputs from comparators 130 and 130B are applied to an AND gate 133 whose output controls a switch 135. Thus, should comparators 130 and 130B provide a high output, AND gate 133 is enabled and causes switch 135 to be rendered conductive to pass a direct current voltage V A  corresponding to a predetermined value, as signal E 6  which corresponds to VI C . Similarly, the outputs of comparators 130 and 130C control an AND gate 133A which in turn controls a switch 135A to pass or to block a direct current voltage V B . Similarly, another AND gate 133B is controlled by the outputs from comparators 130A and 130B to control a switch 135B so as to pass or block a direct current voltage V C . Again, an AND gate 133C is controlled by the outputs from comparators 130A and 130C to control a switch 135C to pass or to block a direct current voltage V D . The outputs of switches 135 through 135C are tied together so as to provide a common output. 
     Referring now to FIG. 8, the SUS computer 65 includes multipliers 136, 137 and 138 multiplying signal KV 210  with direct current voltages C 9 , C 7  and C 5 , respectively, to provide signals corresponding to the terms C 9  (KV 210 ), C 7  (KV 210 ) and cC 5  (KV 210 ), respectively in equation 6. A multiplier 139 effectively squares signal KV 210  to provide a signal to multipliers 140, 141. Multiplier 140 multiplies the signal from multiplier 139 with a direct current voltage C 10  to provide a signal corresponding to the term C 10  (KV 210 ) 2  in equation 6. Multiplier 141 multiplies the signal from multiplier 139 with signal KV 210  to provide a signal corresponding to (KV 210 ) 3 . A multiplier 142 multiplies the signal from multiplier 141 with a direct current voltage C 11  to provide a signal corresponding to the term C 11  (KV 210 ) 3  in equation 6. Summing means 143 sums the signals from multipliers 136, 140 and 142 with a direct current voltage C 8   to provide a signal to a multiplier 144 where it is multiplied with a direct current voltage C 12 . The signal from multiplier 137 is summed with a direct current voltage C 6  by summing means 145 to provide a signal corresponding to the term [C 6  +C 7  (KV 210  ]. A divider 146 divide the signal provided by summing means 145 with the signal provided by multiplier 144 to provide a signal which is summed with the signal from multiplier 138 by summing means 147 to provide signal E 7 . 
     Referring now to FIG. 9, SUS 210  computer 68 includes subtracting means 148 which subtracts a direct current voltage C 16  from another direct current voltage C 16  from another direct current voltage C 15  to provide a signal corresponding to the term (C 15  -C 16 ) in equation 7. The signal from subtracting means 148 is multiplied with a direct current voltage C 14  by a multiplier 149 to provide a product signal which is summed with another direct current voltage C 13  by summing means 150. Summing means 150 provides a signal corresponding to the term [C 13  +C 14  (C 15  -C 16  ] in equation 7. The signal from summing means 150 is multiplied with signal E 7  by a multiplier 152 to provide signal E 8 . 
     Referring now to FIG. 10, there is shown VI DWC .sbsb.O computer 70 having a multiplier 156 multiplying signals KV 210  and API to provide a signal corresponding to the term (KV 210 )(API) in equation 8. Another multiplier 157 multiplies the signal from multiplier 156 with direct current voltage C 20  to provide a signal corresponding to the term C 20  (KV 210 )(API). A multiplier 160 multiplies signal E 6  with direct current voltage C 19  to provide a signal corresponding to the term C 19  (VI). Summing means 162 sums the signals from multiplier 157 and 160 with a direct current voltage C 17  to provide a sum signal. Multiplier 164 multiplies signal FL with direct current voltage C 18  to provide a signal corresponding to the term C 18  (FL) in equation 8. Subtracting means 165 subtracts the signals provided by multiplier 164 from the signal provided by summing means 162 to provide signal E 9 . 
     VI DWC .sbsb.P computer 72 shown in FIG. 11, includes a natural logarithm function generator 168 receiving signal E 8  and providing a signal corresponding to the term 1nSUS 210  to multipliers 170, 171 and 172. Multiplier 170 multiplies the signal from function generator 168 with a direct current voltage E 22  to provide a signal corresponding to the term C 22  1nSUS 210  in equation 9. Multiplier 171 effectively squares the signal from function generator 168 to provide a signal that is multiplied with the direct current voltage C 23  by a multiplier 175. Multiplier 175 provides a signal corresponding to the term C 23  (1nSUS 210 ) in equation 9. Subtracting means 176 subtracts the signals provided to multiplier 175 from the signal provided by multiplier 175. Summing means 177 sums the signal from outstanding means 176 with a direct current voltage C 21 . A multiplier 178 multiplies the sum signals from summing means 177 to direct current voltage POUR to provide a signal which is summed with signal E 9  by summing means 180 which provides signal E 10 . 
     Referring now to FIG. 12 J computer 80 includes a square root circuit 182 receiving signal T and providing a signal to a multiplier 184 where it is multiplied with a direct current C 42 . Signal E 11  is summed with a direct current voltage C 41  by summing means 187 to provide a sum signal to subtracting means 188. Subtracting means 188 subtracts the signal provided by summing means 187 from the signal provided by multiplier 184. A multiplier 190 multiplies signal T with a direct current voltage C 40  to provide a signal to multiplier 192, 193 which multiplies the signal with direct current voltages V 4  and V 23 , corresponding to values of 4 and 2, respectively. Multiplier 192 provides a signal, corresponding to the term 4(C 40 )(T) in equation 12, to a multiplier 196 where it is multiplied with the signal from subtracting means 188. 
     A multiplier 200 effectively squares a direct current voltage C 39  to provide a signal corresponding to the term (C 39 ) 2  in equation 12. Subtracting means 202 subtracts the signal provided by multiplier 196 from the signal provided by multiplier 200 to provide a signal to a square root circuit 205. Subtracting means 207 subtracts voltage C 39  from the signal provided by square root circuit 205 to provide a signal to a divider 210. Divider 210 divides the signal from subtracting means 265 with the signal from multiplier 257 to provide a signal that is effectively served by a multiplier 212 to provide signal E 13 . 
     The present invention as hereinbefore described controls a furfural refining unit receiving light sour charge oil to achieve a desired charge oil flow rate for a constant furfural flow rate. It is also within the scope of the present invention, as hereinbefore described, to control the furfural flow rate while the light sour charge oil flow is maintained at a constant rate. Under such an arrangement, multiplier 83 is connected to computer 80 and to flow transmitter 30 and multiplies signals J and CHG to provide a product signal to divider 81. Divider 81 divides the product signal with voltage V 2  to provide signal SO to a flow recorder-controller which would be associated with the controlling of the furfural in line 7.