US3778603A - Means and method for achieving an optimum operating condition for an alkylation unit - Google Patents

Abstract

A system controls the temperature at which olefins are contacted with an isoparaffin in the presence of acid in an alkylation unit, and the flow rate of acid entering or leaving the alkylation unit. The system senses conditions of a hydrocarbon product, which results when the acid is removed from a hydrocarbon-acid mixture after the contacting process, the contact temperature, a condition relating to the contact acid and the olefin composition. The system includes a source providing signals corresponding to the economic values related to the octane rating of alkylate, which is produced from the hydrocarbon product, to the acid consumption and to the cost of controlling the contact temperature. The system uses the signals corresponding to the sensed conditions and the economic value signals to develop control signals for apparatus that control the contact temperature and the acid flow rate.

Description

United States Patent 11 1 1111 3,778,603

Sweeney, Jr. Dec. 11, 1973 MEANS AND METHOD FOR ACHIEVING Primary ExaminerEugene G. Botz AN OPTIMUM OPERATING CONDITION Art0rneyThomas Whaley et 3].

FOR AN ALKYLATION UNIT [75] Inventor: Donald E. Sweeney, Jr., Beaumont,

' Tex.

[57] ABSTRACT A system controls the temperature at which olefins are contacted with an isoparaffin in the presence of acid [73] Asmgnee: Texaco Inc-r New York in an alkylation unit, and the flow rate of acid entering [22] Filed; May 26, 1972 or leaving the alkylation unit. The system senses conditions of a hydrocarbon product, which results when [21] Appl- NOJ 257,408 the acid is removed from a hydrocarbon-acid mixture after the contacting process, the contact temperature,

5 Cl 235/15L12, 203/133 ZQS/DIG. 1 a condition relating to the contact acid and the olefin 260/68359 235/1501 composition. The system includes a source providing 5 Int G0 15/46, 606g 7/58, G051) 13/02 signals corresponding to the economic values related [58] Field of Search 235/151.12, 150.1 to the Octane rating of alkylate, which is Produced from the hydrocarbon product, to the acid consumption and to the cost of controlling the contact temperature. The system uses the signals corresponding to the sensed conditions and the economic value signals [56] References Cited UNITED STATES PATENTS to develop control signals for apparatus that control 3,002,818 10/1961 Berger 235/15112 the Contact temparature and the and flow rate 12 Claims, 6 Drawing Figures ALKYLATE SIGNAL M EA NS 37 CHROM- COOLANT ATOGRAPHY MEANS 34 SETTLER CONTROL 12 COM P7L{TER NTACTOR 4 304 NTRO FRESH ACID FRC 300 DlSCHARGE ATOGR PH ACID EANS 36 SOURCE OF D.C. V0 LTAGES PATENTED HEB I l i973 EEEEEOQ i 9 MEANS AND METHOD FOR ACHIEVING AN OPTIMUM OPERATING CONDITION FOR AN ALKYLATION UNIT BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to control systems in general and, more particularly, to a control system for controlling an alkylation unit to achieve an optimum condition.

2. Description of the Prior Art Heretofore control systems such as disclosed in U.S. applications Ser. Nos. 169,385 and 169,443, now U.S. Pat. No. 3,729,629, both of which are assigned to Texaco lnc., assignee of the present invention, controlled an alkylation unit to achieve a more rapid response in controlling the acid strength to changes in the composition of the olefin and isoparaffin stream or in the process itself. Neither of the disclosed systems dealt with the problem of achieving an optimum control system for an alkylation unit. Nor is it obvious from the information disclosed in those applications how one would go about achieving an optimum operating condition for an alkylation unit.

Another control system disclosed in US. application Ser. No. 118,374, now US. Pat. No. 3,720,730, Inc., assignee of the present invention, concerns the problem of reducing the stabilizing time required for an alkylation unit where there are several acid settlers being used simultaneously. The last mentioned application does not concern itself with achieving an optimum condition for an alkylation unit.

SUMMARY OF THE INVENTION A system controls an alkylation unit in such a manner so as to achieve an optimum operating condition for the alkylation unit. The alkylation unit includes a contactor wherein an olefin-isoparaffin mixture is contacted with acid at a temperature controlled by a utility. The contactor provides an acid-hydrocarbon mixture to a settler which separates the acid from ahydrocarbon product. The hydrocarbon product includes alkylate. -A portion of the separated acid is discharged from the alkylation unit while the remaining separated acid is fed back to the contactor. Fresh acid is added to the feedback acid to replace the discharged acid. The contacting temperature, the operating rate of the utility, a condition related to the strength of the contact acid and a condition of the alkylate are sensed by sensing circuits which provide corresponding signals. A signal source provides signals corresponding to economic values related to the octane rating of the alkylate, to the acid consumption by the alkylation unit and to the utility. A control network provides control signals in accordance with the signals from the sensing circuits and from the signal source. At least one control signal is used to control the contacting temperature while another control signal is used to control either the acid entering the alkylation unit or the acid being discharged from the alkylation unit.

The objects and advantages of the invention will appear hereinafter from 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 includes a simplified block diagram of a con- I DESCRIPTION OF THE INVENTION Referring to FIG. I, there is shown a portion of an alkylation unit in which an olefin is reacted with isoparaffin at a predetermined temperature and in the presence of a catalyst, such as sulfuric acid and which is hereinafter referred to as the reaction acid, to form a higher molecular weight isoparaffin. For purpose of explanation, the acid in the following description shall be sulfuric acid. The, olefin may be butylenes, propylene or a mixture of butylenes and propylene, while the isoparaffin may be isobutane. The control system shown in FIG. 1 controls the reaction temperature and the flow rate of discharge acid leaving the alkylation unit to achieve an optimum operating condition. The flow rate of fresh acid entering the alkylation unit may be controlled instead of the discharge acid. I

The oletins and isoparaffin enter a contactor 4 by wayof a line 6, where the olefins and isoparaftin are contacted with the reaction acid entering by way of a line 7. Contactor 4 provides an acid-hydrocarbon mix by way of a line 8 to an acid settler 12. The reaction temperature is controlled by coolant passing through a coil 13 inside contactor 4. Settler 12 separates the hydrocarbon product from the reaction acid. The hydrocarbon product, which includes alkylate, is removed through a line 14 for further processing while the reaction acid is removed by way of a line 16. Acid settler 12 may be the only acid settler in the unit or it may be the last acid settler of a group of acid settlers. Fresh acid enters line 16 by way of a line 17 as needed to maintain a desired reaction acid strength. A pump 20 pumps the reaction acid from line 16 into line 7. A portion of the reaction acid in line 7 is discharged by way of a line 21. The discharge acid may be provided to another alkylation unit or disposed of.

In order that an optimum operating condition, such as the contactor temperature, be determined, it is necessary that a differential earnings E be determined in accordance with the following equation:

where A Q is the differential octane rating of the alkylate product resulting from a change in the contactors temperature, W is the incremental worth of a unit change in octane rating, A A is the differential acid consumption resulting from a change in the contactors temperature, W is the cost of acid, A U, through A U, are differential utilities requirements for utilities 1 through n resulting from a change in the contactors temperature, W through W are the cost of utilities 1 through n. For purpose of illustration, one utility will be hereinafter described and that utility concerns the 3 coolant passing through coil 13. Therefore, equation 1 may be written as:

The terms W W and W are predetermined economic values for the octane rating, the acid and the utility, while A Q, A A and A U are determined as follows:

3- A Q GC GB where G is a calculated quantity based on sensed conditions such as the sensed contactor temperature T; and the ratio P of propylene to olefins in line 6, while 6 is the same type of quantity calculated at a contactor temperature other than the sensed temperature and for the existing propylene to olefin ratio. The quantities G and G may be calculated from the following equations 4 through 6 by substituting G or C for G G or 6 t/ 1.)] GU where T may be the sensed temperature T, or a calculated temperature T,, T, is a first reference temperature which, by way of example, may be 45F and T, is a higher reference temperature which for purposes of i1- lustration may be 55F. The selection of which equation to use in calculating G and 6, depends on the ratio of the propylene to olefins in line 6. When the actual ratio R, is below a predetermined ratio P equation 4 is used. When the ratio P, is above another predetermined ratio P equation 5 is used. When the ratio P, is greater than P but less than F equation 6 is used. By way of example, P may be 0.35 while P may be 0.60. The following Table I shows values for a, through a, and b, through b,, which have been determined for an existing alkylation unit.

TABLE I a, 2.l7592 b, 4.7 a, -14.668939 b, -s.sss239 a, 37.63l287 b, 0.0 a. -29.92o927 b -9.4274o9 0.0 b, 0.0

The differential acid consumption A A is determined from equation 7.

7. A A =Ag 1 where A 'is the existing acid consumption, F, is a quantity calculated at the existing contactor temperature and the existing propylene ratio, while F is a similar quantity calculated at any other contactor temperature and the existing propylene ratio. The existing acid consumption A, is obtained from the following equation 8:

RUB/RX where R is a sensed discharge acid flow rate, R is the alkylate rate and a is a constant to convert the discharge acid rate from barrels per hour to tons per hour and by way of example may be 0.3213.

The calculated acid consumption A for a current calculation step is:

9. A6 Ag A Equation 9 may be rewritten as:

10 AC A5 '1' (5 1 which simplifies to 11. AC=AB (FE/Fe) Using equation 8, which is applicable for A by substituting R for R the calculated discharge acid flow rate R may be solved to yield equation 12.

nc m; a/ e) The alkylate product rate R is obtained from equation 13.

13. R VKRC where V is the volume fraction of alkylate product in the crude alkylate stream, R is the crude alkylate flow rate. The quantities F B and F are obtained from equations 14, 15 and 16 by substituting the sensed temperature T, for T when the quantity F, is desired and the calculate temperature T when the quantity F is desired.

14. F 1.0 c [(TT1)/100] C2[(T T1)/1O0]2 3[( l)/ 4[( 1)/ 5[( 1)/ 15. F =1.0 d [(TT,)/100] .d [(T-T;)/100] :r[( z)/100l 4[( z)/100] s[( :)/l00] FL-U [(PU PB)/(PU PL)] 1. [(PBPL)/' u 1.)] u 1 Equation 14 is used when the ratio P is less than the reference ratio P equation 15 is used when the ratio P, is greater than the reference ratio P and equation 16 is used when the ratio P is equal to or greater than the ratio P but less than or equal to ratio P Table 1] relates specific values for the terms c, through c, and d through d, in equations 14 and 15 for a particular alkylation unit.

TABLE 11 TERM VALUE TERM VALUE c -2.901263 4, 7.7l9104 0, 1.3076425 d, 29.247134 0, 0.0 d; 0.0

0 0.0 4 -2l1.32222 c, 0.0 d. 0.0

culated temperature T, is substituted for T when the quantity H is desired.

The following table contains specific values for the co-efficients e through c in equation 18 as determined for a particular alkylation unit.

TABLE 111 e, 6.005l3l 2-, 0.0011537 e 0.0 e, 0.26122 e. 0.0 e 0.0 e, -0.002753 e, 5.82 e 1.5 e 0.0 e 0.l538 e 0.0 e. 2.1067 c 0.0 e 0.0 e. 0.0

The calculated utility rate R which in this case is the coolant flow rate, is determined from equation 19.

uc RUB U )(RK) where R is the sensed utility rate which happens, in this case, to be the sensed coolant flow rate.

The control system as hereinafter described calculates the differential earnings for selected temperatures and when the differential earnings decreased or an operating parameter exceeds a constraint limit, the controls system returns to the next previous selected temperature and changes the contactor 4 temperature and the discharge acid flow rate accordingly to obtain an optimum operating condition. The selected temperatures are determined in accordance with the following equation 20.

l TB l( j)/ l( TM) where J is any positive integer, j is a selected integer from zero to J and A T is the maximum allowable change in the contactor temperature.

Referring to FIGS. 1 and 2, programmer 27 receives a voltage V, from a source 28 of direct current voltages. An operator initiates the optimizing control by closing switch 26 to apply voltage V to clock means 34. Switch 26 may be an on-off toggle switch. Clock means 34 provides pulses IE at a repetition rate which corresponds to a periodic initiation of an operation sequence. Pulse E resets chromatograph means 36 and 37.

Chromatograph means 36 samples the olefin and isoparaffin stream in line 6 and provides a pulse signal E to programmer 27 and a continuous signal E to P signal means 41. The peaks of signal 13, correspond to the concentrations of the constituents of the olefins and isoparaffin stream in line 6.

Reset pulse E, is also applied to control pulse circuit 43 to reset a counter 44. With counter 44 at a zero count, a logic decoder 45 provides a high level direct current voltage to an AND gate 48 which also receives signals E, from chromatograph means 36. The pulses pass through the enabled AND gate 48 and are counted by counter 44. Logic, decoder 45 decodes the count in counter 44 to provide a plurality of outputs to a plurality of one shot multivibrators 52. Each multivibrator of multivibrators 52 is triggered by a different output from logic decoder 45 and provides a control pulse coinciding with a different peak of signal 13,. Multivibrators 52 provide control pulses B, through E which is shown as being on one line. Pulse E triggers another one shot multivibrator 53 which provides a time delay pulse whose width is of sufficient duration to allow calculations to be made by P signal means 41. The delay pulse from multivibrator 53 triggers another multivibrator 54 which provides control pulse E Programmer 27 provides control pulses E through E,; to P signal means 41.

Signal means 41 provides a signal E corresponding to the ratio P, of propylene in line 6 to the oletins in line 6. Signal means 41 is similar to the olefin signal means disclosed and described in a U.S. application Ser. No. 228,826 filed on Feb. 24, 1972. The aforementioned application is assigned to Texaco Inc., assignee of the present invention. In the aforementioned application, signal E corresponds to signal E in the present application while control pulses E, through E have the same function as described in the aforementioned application. Signal means 41 also receives scaling voltages V, through V from source 28, which corresponds to the scaling voltages V through V in the aforementioned application. The output from the olefin signal means represents a ratio having a range from 0 to 100, P signal means 41 is modified, so that E, corresponds to a range of O to l, in a manner which is obvious to one skilled in the art.

Chromatograph means 37 samples the hydrocarbon product stream in line 14 and provides a pulse signal E to a programmer 27 and a signal E, to alkylate signal means 56 receiving direct current voltages V through V from source 28 and control pulses E through E from programmer 27. The peaks of signal E correspond to the concentrations of different constituents of the stream in line 14. Each pulse in pulse signal E coincides with a different peak of signal E-,. Alkylate signal means 56 is controlled by pulse signals E through E to provide a signal E corresponding to the concentration of alkylate in the stream in line 14. Alkylate signal means 56 is similar to the signal means desribed in U.S. application Ser. No. 169,443 filed Aug. 5, 1971 and assigned to Texaco the present invention, except that signal 13, corresponds to a normalized concentration constituent with six or more carbon atoms. Alkylate-signal means 56 samples and holds the peaks of signal E corresponding to the concentrations of propane, isobutane, n-butane, pentanes, and all compound with six or more carbon atoms. Alkylate signal means 56 normalizes the determined concentration of compounds with six or more carbon atoms by summing all of the sampled peaks of signal E and dividing into the sampled peak of signal 1 pounds of six or more carbon atoms, to provide signal E5.

Pulse signal E is applied to a control pulse circuit 43A, which is similar in operation to control pulse circuit 43, which provides control pulses B, through E Pulse E is also applied to a delay one shot multivibrator 60 which provides a delay pulse of sufficient duration to allow alkylate signal means 56 to make the necessary calculations. The pulse from multivibrator 60 triggers another one shot multivibrator 61 which provides control pulse Ep.

Pulse Ep triggers yet another one shot multivibrator 62 to provide control pulse E A T, computer provides a signal E corresponding to a calculated temperature T, in accordance with signals 13, E and E direct current voltages V, through V pulse 1'1 and equation 20.

Referring now to FIG. 3, pulse E resets a counter in T, computer 70. Counter 75 is a conventional updown counter. Signal E from a control computer 71 enables an AND gate 76 to pass timing pulses from clock means 78 to counter 75. Counter 75 counts the timing pulses passed by AND gate 76. The count in counter 75 is decoded by a logic decoder 82 which provides a plurality of outputs corresponding to the count in counter 75. By way of example, one output from logic decoder 82 will be at a high level for a particular count in counter 75 and at a low level when that count is not in counter 75. Thus when counter 75 reaches a first predetermined count, an output from count 75 is applied to an electronic switch 83 goes to a high level rendering switch 83 conductive to passed voltage V;,. When the output from counter 75 is at a low level, switch 83 is rendered non-conductive to block voltage V,,. Voltage V, corresponds to a value of 0.0 for the term j in equation 20. Similarly switches 83A, 83B and 83C receive direct current voltages V V and V,

lnc., assignee of corresponding to the concentration of the com-.

7 corresponding to values 1.0, 2.0 and 3.0, respectively; for the term j in equation 20.

It should be noted that if there are more values desired for the term j, more switches need to be connected to logic decoder 82. It can be readily seen that in effect counter 75 and logic decoder 82 control switches 83 through 83C so that the different voltages may be used in equation 20 for different values ofj to determine the T, temperature. A voltage passed by a switch 83, 83A, 838 or 83C is applied to a multiplier 84 receiving voltage V to provide a signal, corresponding to the term 2j, to a divider 85 which also receives voltage V which corresponds to the term J in this instance. Divider 85 provides a signal corresponding to 2j/J. Subtracting means 87 subtracts voltage V, from the output from divider 85 to provide a signal to a mu]- tiplier 92 corresponding to the term [(2j/J) l] in equation 20. Multiplier 92 multiplies the signal from subtracting means 87 with voltage V, corresponding to a maximum allowable temperature change (A T The output from multiplier 92 is summed with signal E by summing means 93 to provide signal E Signal E corresponds to the temperature T of the acid hydrocarbon mixture leaving contactor 4 by a sensor 91 in line 8. V

The outputs from logic decoder 82 are inverted by plurality of inverters 94 through 94C and are applied to corresponding time delay one shot multivibrators 94 through 95C, respectively. When an output from decoder 82 goes to a high level in response to a particular count in counter 75, an inverter 94, 94A, 948 or 94C inverts the output to a low level thereby triggering a corresponding multivibrator 95, 95A, 95B or 95C, respectively. A pulse from the triggered one shot multivibrator 95, 95A, 95B or 95C passes through an OR gate 96 and the trailing edge of the passed pulse triggers another one shot multivibrator 99 causing it to provide a sampling pulse E The pulse width of the pulses provided by multivibrators 95 through 95C are of such a duration as to allow the various computers to make the calculations based on the new T, temperature before sampling and holding is performed.

In operation, signal E is at a high level unless a certain predetermined condition exists. For example, if the earnings decrease or the constraint on an operating parameter is exceeded at the new calculated operating condition, then E goes to a low level. However, since the new calculated operating condition is an undesirable condition, E remains at a high level for a period of time before changing to a low level to allow one more timing pulse from clock means 78 to pass through AND gate 76. Counting direction signal E changes immediately from a high level to a low level so that the last pulse passed by AND gate 76 causes the count in counter 75 to be reduced by one. The net result is that the control system is returned to its next previous calculation step which is the most desirable operating condition.

The T temperature signal E from sensor 91 is also applied to a G computer 100, to an F computer 100A and to a H, computer 101 while T, temperature signal E from T, computer 70 is applied to a computer 1008, to an F computer 100C and to an H computer 101A. Computers 100A, 100B and 100C are similar to computer 100 except that computer 100A differs from computer 100 in receiving different direct current voltages so it can solve equations l4, l and 16, while computer solves equations 4, 5 and 6. Computers 100B, 100C differ from computer 100 and 100A, respectively, in that they use the T,- temperature instead of the sensed temperature T,, in their calculations. Therefore, it is necessary only to explain the operation of computer 100.

Referring to FIG. 4, there is shown the G computer 100 which includes-computing circuit 105. Circuit 105 receives signal E and direct current voltages V through V,,, which correspond to the lower reference temperature T,, the constant of 100 and the coefficients a, through a respectively, in equation 4. Computing circuit 105 includes subtracting means 106 which subtracts voltage V, from signal E to provide a signal to a divider 107 receiving voltage V,. Divider 107 provides a signal corresponding to the term [(T,,-T1)/100]. The signal from divider 107 is effectively squared by a multiplier 110 to provide a signal corresponding to the [(T,,T )/l00] which is applied to series connected multipliers 111 through 113. Multipliers 111, 112 and 113 provide outputs corresponding to the quantities [(T -T1)/l00] [(T,r,T,)/l00] and T T )/10O] respectively. A plurality of multipliers through 124 multiply the outputs from divider 107 and multipliers 110 through 113, respectively, with voltages V through V respectively. The outputs from multipliers 120 through 124 are summed by summing means 126 to provide a signal E corresponding to the term 6,, in equation 4.

Another computer circuit 105A receives signal E and direct current voltages V, and V through V Voltages V through V correspond to the coefficients b, through 17;, in equation 5. Computer circuit 105A operates in a similar manner as computer circuit 105, except that voltages V and V through V replace voltages V and V through V respectively, to provide a signal E which corresponds to the term G in equation 5 for the condition that the propylene ratio is greater than the second predetermined reference ratio which by way of example may be 0.60.

Subtracting means 130, 131 and 132, dividers 135 and 136, multipliers 137 and 138 and summing means 139 cooperate to provide a signal E corresponding to the term G in equation 6 for a propylene ratio that lies within the upper and lower propylene reference ratios in accordance with equation 6, signals E E and E and direct current voltage V and V from source 28. Voltages V and V correspond to the predetermined upper and lower propylene reference ratios, respectively. Subtracting means 130 subtracts signal E, from voltage V to provide a signal corresponding to the term (P -P in equation 6, while subtracting means 131 subtracts voltage V from signal E to provide a signal corresponding to the term (P -P Subtracting means 132 subtracts voltage V from voltage V to provide a signal corresponding to the term (P -P in equation 6. Divider 135 divides the signal from subtracting means 130 with the signal from subtracting means 132 to provide a signal, corresponding to the term [(P P )/(P -P which is multiplied with signal E by multiplier 137. The output from multiplier 137 corresponds to the term G,,[(P -P,)/- (P -P0] in equation 6. Similarly, divider 136 divides the signal from subtracting means 131 with the signal from subtracting means 132 to provide a signal which is multiplied with signal E by multiplier 138. Multiplier 138 provides a signal corresponding to the term 9 6,, [(P,,P )/(P P to summing means 139. Summing means 139 sums the signals from multipliers 137, 138 to provide signal E The proper G signal is selected by comparing signal E with voltages V V The comparison is then used to control switching means to pass the selected 6,, signal. The comparison is made by comparators 145 and 145A, while the switching means include inverters 146 and 146A, an AND gate 150 and electronic switches 153, 151 and 152. Comparators 145, 145A compare signal E with voltages V and V respectively. When the propylene ratio signal E is more positive than voltages V and V comparators 145 and 145A provide a low level and a high level output, respectively, to inverters 146, 146A, respectively. The outputs from comparators 145, 145A are also provided to AND gate 150. The high output from comparator 145A is inverted to a low level by inverter 146A which disables electronic switch 151 so that switch 151 blocks signal E Since the output from comparator 145 is at a low level it is inverted to a high level by inverter 146 to render electronic switch 152, conductive so that switch 152 passes E as the G signal E The low output from comparator 145 disables AND gate 150 so that AND gate 150 provides a low output to render electronic switch 153 non-conductive thereby blocking signal E For the condition when the propylene ratio is within the upper and lower limits, comparators 145, 145A provide high level outputs which cause AND gate 150 to enable switch 153. When enabled switch 153 passes signal E as signal E Inverters 146, 146A invert the high level outputs from comparators 145 and 145A, respectively, to low level voltages which render switches 152 and 151 non-conductive, respectively. Switches 151, 152 block signals E and E respectively.

For the condition when the propylene ratio is less than the lower limit, comparators 145, 145A provide a high level and low level output, respectively. The high level output from comparator 145 is inverted by inverter 146 to render switch 152 non-conductive to block signal E The low level output from comparator 145A disables AND gate 150 causing it to render electronic switch 153 non-conductive thereby blocking signal E The low level output from comparator 145A is inverted to a high level by inverter 146A which renders electronic switch 151 conductive to pass signal E as signal E Voltages V V V V and V are provided by source 28 to computers 100A, 1008 and 100C, while voltages V to V and V to V are also applied to computer 1008, and voltages V through V V through V are applied to computers 100A and 100C. In this regard, voltages V through V correspond to the coefficients through 0 in equation 14, voltages V through V correspond to the coefficients d, through d in equation 15, while voltage V corresponds to the term 1.0 in equations 14 and 15. It should be noted that the term 1.0 in equations 14 and 15 is not present in equations 4 and 5. Computers 100A and 100C have computing circuits similar to computing circuit 105, which sum voltage V with the signals from the multipliers as is done by summing means 126 with the outputs from multipliers 120 through 124 in computing circuit 105.

Referring to FIG. 5, signal E is provided to multipliers 160 through 165. Multiplier 160 in 11,, computer 101 effectively squares signal E to provide a signal corresponding to the term T in equation 18 to multipliers 165 through 169. It should be noted that since l-l computer 101 uses signal E the Tin equation 18, for 5 purpose of evaluation, may be replaced by T Multipliers 161 through 164 multiply signal E with direct current voltages V through V from source 28, which correspond to the coefficients e e e and e in equation 18, to provide outputs representative of the terms e T 2 T e T and 2 T respectively. Multipliers 166 through 169 multiply the output from multiplier 160 with direct current voltages V through V from source 28 which correspond to the coefficients e e e and e in equation 18 to provide outputs representative of the terms e T e T e T and e, T respectively.

Multiplier 165 multiplies the output from multiplier 160 with signal E to provide an output corresponding to the term T in equation 18. Multipliers 170 through 173 multiply the output from multiplier 165 with direct current voltages V through V from source 28 which correspond to the coefficients e e e and e respectively, in equation 18 to provide outputs representative of the terms e T e T e T and e T Summing means 177 sums the outputs of multipliers 161, 166 and 170 with a direct current voltage V from source 28 which corresponds to the coefficient e, to provide a signal corresponding to the term (e, e T e T e T A multiplier 178 effectively squares signal E to provide a signal corresponding to the term P while another multiplier 179 multiplies the signal from multiplier 178 with signal E to provide a signal corresponding to the term P Summing means 180 sums the outputs from multipliers 162, 167 and 171 with a direct current voltage V from source 28 corresponding to the coefficient e The signal from summing means 180 is multiplied with signal E, by a multiplier 185 to provide a signal corresponding to the term (e +e T +e T +e T )P in equation 18. Summing means 181 sums the outputs from multipliers 163, 168 and 172 with a direct current voltage V from source 28 corresponding to the coefficient e A multiplier 186 multiplies the signal from summing means 181 with the output from multiplier 178 to provide a signal corresponding to the term (e9+e oTB+ e T +e T )P in equation 18. Summing means 182 sums the outputs from multipliers 164, 169 and 173 with a direct current voltage V from source 28 corresponding to the coefficient e A multiplier 187 multiplies the signal from summing means 182 with the output from multiplier 179 to provide a signal which corresponds to the term (e, +e, T +e T +e T )P in equation 18. Summing means 188 sums the output from summing means 177 and multipliers 185, 186 and 187 to provide signal E corresponding to H H computer 101A operates in a similar manner as H computer 101 except that computer 101A uses the T, signal E instead of the T signal E Referring to FIG. 1, subtracting means 200 subtracts signal E provided by G computer 100 from signal E provided by G computer 1008 to provide a signal E corresponding to the A Q term of equations 2 and 3. The signal from subtracting means 200 is applied to control computer 71.

A divider 201 divides signal E from F computer 100A by signal E from F computer 100C. Subtracting means 202 subtracts direct current voltage V from source 28 from the output from divider 201 to provide a signal corresponding to the term [(F /F l] in equation 7. A multiplier 207 multiplies the output from subtracting means 202 with a signal E which corresponds to the acid consumption A to provide a signal E corresponding to the term A A in equations 2 and 7, to control computer 71.

Signal B is developed in the following manner. A multiplier 208 multiplies the alkylate concentration signal E, from alkylate signal means 56 with a hydrocarbon flow rate signal E from a sensor 206 in line 14, to provide a signal corresponding to the term R in accordance with equation l3. A flow rate sensor 236 senses the flow rate of the discharge acid in line 21 and provides a signal E corresponding to the sensed discharge acid flow rate R,,,,. Signal E is divided into the signal from multiplier 208 by a divider 209 to provide a signal to another multiplier 210. Multiplier 210 multiplies a signal provided by divider 209 with a direct voltage V which corresponds to the constant a in equation 8, from source 28 to provide signal E Subtracting means 215 subtracts signal E provided by H computer 101 from signal E provided by H computer 101A. Subtracting means 215 provides an output E corresponding to AU in equations 2 and 17, to control computer 71.

Referring to FIGS. 1 and 6, control computer 71 controls the operation of the alkylation unit by determining four conditions: whether or not the trial temperature T, exceeds predetermined temperature limits T and T whether or not the calculated utility rate R exceeds predetermined utility rate limits R and R whether or not the calculated discharge acid flow rate R exceeds predetermined discharge acid flow rate limits R and R and whether or not the calculated earnings for the current calculation step is greater than the earnings for the next previous calculation step. Control computer 71 controls the alkylation unit in accordance with Signals 11 14 22, 25 25 29 30 33 and 34 and direct current voltages V through V from source 28.

Signal E corresponding to the temperature T,, is applied to comparators 220, 221 receiving the upper temperature limit T voltage V and the lower temperature limit T voltage V respectively. Comparators 220, 221 provide a low level and a high level direct current output, respectively, when signal E is more positive than voltages V V high level outputs when signal E is more positive than voltage V but not more positive than voltage V and a high level and a low level output, respectively, when signal E is not more positive than voltages V V An AND gate 224 provides a high level direct current output when comparators 220, 221 provide high level outputs and a low level output when either comparators 220 and 221, or both comparators, provide a low level output. Thus, AND gate 224 provides a high level output when the calculated temperature T, does not exceed the predetermined limits and a low level output when T, does exceed a predetermined limit.

Signal E corresponding to the term (A U in equations 2, l7 and 19 provided by subtracting means 215 is multiplied with the alkylate rate R output from multiplier 208 by a multiplier 228. The output provided by multiplier 228 corresponds to the term (A U (R in equation 19. Summing means 229 sums a signal E corresponding to the coolant flow rate, provided by a sensor 230, with the output from multiplier 228 to provide a signal E corresponding to the term R in equation 19.

Comparators 220A and 221A and an AND gate 224A cooperate in a manner similar to the cooperation of comparators 220, 221 and AND gate 224 to make the determination as to whether or not the rate of the utility exceeds predetermined limits. Comparators 220A, 221A compare signal E with direct current voltages V and V from source 28 corresponding to the predetermined upper and lower limits, respectively, for the utility rate R and R respectively. AND gate 224A provides a high level output when the utility rate R does not exceed the predetermined limits and a low level output when R exceeds a predetermined limit.

The calculated discharge acid flow rate is computed in accordance with equation 12. A multiplier 235 multiplies a signal E corresponding to the discharge acid flow rate provided by a sensor 236 in line 21, with signal E from divider 201 to provide a signal E corresponding to the calculated discharge acid flow rate R in equation 12 for the current cal-culation step.

Comparators 2208 and 221B cooperate with AND gate 2248, in a manner similar to comparators 220, 221 and AND gate 224, to determine whether the calculated discharge acid flow rate R is within predetermined limits. Comparators 2208 and 221B compare signal E with direct current voltages V and V corresponding to a predetermined upper flow rate limit R and to a predetermined lower flow rate limit R respectively, for the discharge acid in line 21. AND gate 224B is controlled by comparators 2208 and 2218 to provide a high level output when the calculated discharge acid flow rate R does not exceed predetermined limits defined by voltages V V and a low level output when R does exceed a predetermined limit.

Multipliers 240, 241 and 242 and subtracting means 246 and 247 compute the earnings in accordance with equation 2, signals E E and E and direct current voltages V V and V from source 28. Multipliers 240, 241 and 2 42 multiply signals E E and E respectively, with voltages V V and V respectively. Voltages V V and V correspond to the terms W W and W respectively. Multipliers 240, 241 and 242 provide outputs corresponding to the terms (AQ) (W (AA) (W and (AU) (W respectively, in equation 2. Subtracting means 246 subtracts the output provided by multiplier 241 from the output provided by the multiplier 240 to provide an output to subtracting means 247. Subtracting means 247 subtracts the output provided by multiplier 242 from the output provided by subtracting means 246 to provide an output to an earnings comparison network 253.

Earnings comparison network 253 compares the earnings for the current calculation step with the earnings for the next previous calculation step and includes sample and hold circuits 254, 255, a one-shot multivibrator 256 and a comparator 257. The output from subtracting means 247 is applied to sample and hold circuit 254 while sampling pulse E from T, computer are applied to multivibrator 256 and to sample and hold circuit 255. One shot multivibrator 256 provides a pulse output to sample and hold circuit 254 in response to the trailing edge of a pulse E The sequence of sampling and holding is such that sample and hold circuit 255 holds the output from sample and hold circuit 254. The output provided by sample and hold circuit 255 corresponds to the earnings for the next previous calculation step while the output from sample and hold circuit 254 corresponds to the earnings for the current calculation step. Comparator 257 compares the outputs from sample and hold circuits 254 and 255 and provides a high level direct current output when the output from sample and hold circuit 254 is more positive than the output from sample and hold circuit 255 and a low level output when the output from sample and hold circuit 254 is not more positive than the output from sample and hold circuit 255. Thus comparator 257 provides a high level output when the current calculated earnings are greater than the earnings for the next previous calculation step, and provides a low level output when the current earnings are equal to or less than the next previous earnings. An AND gate 260 provides directional signal E at a high level when AND gates 224, 224A, 2243 and comparator 257 provide high level outputs and a low level output when one or more of the outputs from AND gates 224, 224A and 224B and comparator 257 is at a low level.

Signal E from AND gate 260 is applied to an OR gate 261 and to a one-shot multivibrator 262. As each calculation satisfies all of the aforementioned conditions, signal E from AND gate 260 remains at a high level and passes through OR gate 261 to become signal E During the course of a calculation if one of the limits is exceeded or the earnings does not increase, signal E from AND gate 260 goes to a low level and triggers one-shot multivibrator 262. It would be expected that signal E would go to a low level when signal E did. However, if this was to occur, the control operation would remain in an undesirable state so that it is necessary to go back one calculation step. This is provided for by the pulse output from one-shot multivibrator 262 which passes through OR gate 261 to become signal E so that signal E remains at a high level for duration of the pulse from multivibrator 262 while signal E is at a low level. The duration of the pulse from one-shot multivibrator 262 is such that it enables one more pulse E from clock means 78 to pass through AND gate 76. The low level signal E from AND gate 260 causes the counter to count down the last pulse passed by AND gate 76 resulting in all of the computers being returned to their next previous calculation step.

When the desired operating condition has been determined, control computer 70 implements the required changes. The pulse from multivibrator 262 which returns the control system to the next previous calculation step, triggers a one-shot multivibrator 268 causing it to provide a time delay pulse. The time delay is to allow time for all of the calculations of the next previous calculation step to be made. The trailing edge of the pulse from multivibrator 268 triggers another one shot multivibrator 269 causing it to provide an enter" pulse E to set point signal means 270, 270A. Set point signal means 270 also receives signals E E and provides a directional signal E and a pulse signal E. to a temperature recorder controller 271. Signals E E position the set point ofcontroller 271 so as to control the temperature of contactor 4. Subtracting means 273 in signal means 270 subtracts signal E from signal E to provide an output corresponding to the change in the contactor temperature required to achieve the desired operating condition. A comparator 277 compares the output from subtracting means 273 with a ground reference 278 to provide directional signal E When the selected temperature, which is now temperature T is less than the sensed temperature T the output from subtracting means 273 is negative and hence is less positive than ground 278 causing comparator 277 to provide a low level direct current output as directional signal E When the sensed temperature T is less than the selected temperature T,-, the output from subtracting means 273 is positive causing comparator 277 to provide a high level output as signal E A conventional type analog-to digital converter 276 converts the output from subtracting means 273 to digital signals which are applied to a count down counter 280. The entry of digital signals into counter 280 is controlled by enter pulse E from multivibrator 269 and presets counter 280 to the desired change in temperature.

The trailing edge of the enter pulse E from multivibrator 269 triggers a multivibrator 286 which provides an enabling pulse to an AND gate 287. AND gate 287 is connected to counter 280 in such a manner that counter 280 provides a low level direct current signal to AND gate 287 when the count in counter 280 is zero and a high level direct current signal when the count in counter 280 is not zero. Clock means 290 provides timing pulses to AND gate 287. As a result of a count in counter 280 not being zero and the enabling pulse from multivibrator 286, and timing pulses from clock means 290 pass through AND gate 287 to be counted down by counter 280 from the entered count. The timing pulses passed by AND gate 287 are also provided as pulse signal E to temperature recorder controller 271. Each pulse in pulse signal E changes the position of the set point in temperature recorder controller 271 by a predetermined amount and in a direction in accordance with signal E The set point changing process continues until a count of zero is reached by counter 280, at which time counter 280 output to AND gate 287 goes to a low level thereby disabling AND gate 287. When disabled, AND gate 287 blocks the timing pulses from clock means 290. It is obvious that the duration of the enabling pulse from multivibrator 286 must be such to allow the largest anticipated count in counter 280 to be counted down to zero.

Temperature recorder controller 271 receives signal E from the temperature sensor 91 in line 8 and provides a signal to a valve 295 which controls the flow rate of the coolant flowing through coil 13. Temperature recorder controller 271 controls valve 295 in accordance with signal E and the position of its set point so that the temperature of the acid-hydrocarbon mixture leaving contactor 4 will assume the desired temperature as represented by the position of temperature recorder controller 271 set point.

Set point signal means 270A is similar in construction and operation to set point signal means 270 except that the sensed discharge acid flow rate signal E replaces signal E and the calculated discharge acid flow rate signal E replaces signal E Set point signal means 270A provides a directional signal E and a pulse signal E instead ofdirectional signal E and pulse signal E respectively, to a flow recorder controller 300 which also receives signal E Flow recorder controller 300 provides a signal to a valve 301 in line 21 which controls the flow rate of the discharge acid. Set point signal means 270A is activated by enter pulse E from one-shot multivibrator 269 to provide signals E E In response to signals E and E the set point of flow recorder controller 300 changes accordingly and provides a signal to valve 301 which corresponds to the difference between the sensed signal E and the position of set point causing valve 301 to increase or decrease the discharge acid flow rate in accordance with the position of the set point of flow recorder controller 300 so that the discharge acid flow rate is the desired discharge acid flow rate.

Since the acid strength changes when the contact temperature is changed, the discharge acid flow rate is changed to maintain the strength of the acid entering contactor 4. In this regard, when the discharge acid flow rate is increased, the acid level in settler 12 would decrease. A level sensor 303 provides a signal to a level controller 304. Level controller 304 provides a signal which corresponds to the difference between the sensed level and a predetermined level, to a valve 308 in line 17 in accordance with the signal from sensor 303 and the position of levelcontroller 304 set point. The signal from level controller 304 causes valve 308 to increase the fresh acid flow rate so as to increase the acid level in settler 12. The increase in the fresh acid flow rate increases the strength of the acid entering contactor 4. Similarly, a decrease in the discharge acid flow rate will result in a decreased acid strength.

The system of the present invention as heretofore described controls an alkylation unit to achieve an optimum operating condition for the alkylation unit. The discharge acid, the contactors temperature and the alkylate product are monitored to determine values using equations heretofore described so that earnings may be determined. The control system uses a set of trial contactor temperatures and calculates the effect of a change in contactors temperature on the earnings. The control system of the present invention as heretofore described controls an alkylation unit to achieve the optimum operating condition without exceeding a constraint value of an operating parameter.

What is claimed is:

l. A system for controlling an alkylation unit to achieve an optimum operating condition and said alkylation unit includes a contactor wherein an olefinisoparaffin mixture is contacted with acid at a temperature controlled by utility means in accordance with a control signal and the contactor provides an acidhydrocarbon mixture to a settler which separates the acid to provide a hydrocarbon product which include alkylate and acid, a portion of the separated acid is discharged while a portion of the separated acid is fed back to the contactor along with fresh acid entering the alkylation unit that is added to the feedback to replace the discharge acid, comprising means for sensing the contact temperature T and providing a signal corresponding thereto, means for sensing a utility rate and providing a signal corresponding thereto, means for sensing a condition related to the contact acid and providing a corresponding signal, means for sensing conditions of the hydrocarbon product and providing signals representative thereof, means for sensing the olefin and providing a signal representative thereof, means for providing signals corresponding to economic values W W and W related to the octane rating of the alkylate, to the acid consumption and to the utility, respectively, means for controlling the acid entering or leaving the alkylation unit in'accordance with a control signal and means connected to all of the other means for providing the control signals to the acid control means and to the utility means in accordance with the signals from the sensing means and from the signal means so as to achieve a desired operating condition for the alkylation unit.

2. A system as described in claim 1 in which the utility means includes means for passing a coolant through the contactor so as to control the contact temperature.

3. A system as described in claim 2 in which the control signal means determines the effect that a change in the contact temperature would have on the earnings of the alkylation unit.

4. A system as described in claim 3 in which the control signal means includes first means connected to the temperature sensing means, to the olefin sensing means and to the hydrocarbon product sensing means for calculating values of factors G F and H from the signals from the temperature sensing means, from the olefin sensing means and from the hydrocarbon product sensing means, means connected to the temperature sensing means for providing a signal, corresponding to a trial temperature T in accordance with the sensed contact temperature T signal and the following equation:

1. T, T [(2j/J l A T where T is the sensed contacting temperature, J is any positive integer and j is iterativeely changed in value between 0 and J; in response to a command signal, second means connected to the trial temperature signal means, to the hydrocarbon product sensing means and to the olefin sensing means for calculating values of factors G F and H in accordance with a trial temperature signal from the trial temperature signal means and the signals from the hydrocarbon product sensing means and from the olefin sensing means and providing signals corresponding thereto; means connected to the acid sensing means, to the hydrocarbon product sensing means and to the first and second calculating means for determining changes A Q, A A and A U in the octane rating, the acid consumption and the utility rate, respectively, means connected to the change determining means and to the economic value signal means for determining the earnings for the alkylation unit for a current trial temperature and providing an earnings signal corresponding thereto for earnings control means connected to the earnings signal means and to the trial temperature signal means for providing a command signal to the trial temperature means causing the trial temperature means to iteratively change the trial temperature until the command signal is representative of a decrease in earnings and then to control the trial temperature signal means to the next previous trial temperature, and means connected to the earnings control means, to the utility means, to the acid control means, means for providing the control signals to the utility means and to the acid control means in response to the command signal from the earnings control means being representative of a decrease in earnings.

5. A system as described in claim 4 in which the olefin sensing means includes means for sensing concentrations of the different olefins and providing signals corresponding thereto, means connected to the olefin concentration sensing means for providing a signal corresponding to the ratio P of propylene to olefins; and the first and second calculating means includes G signal means connected to the temperaturesensing means and to the trial temperature signal means, respectively, and receiving direct current voltages corresponding to reference temperatures T and T and predetermined coefficients a through a and b through b for providing signals corresponding to the quantities G and G in accordance with the following equations:-

GL a1 a2 a 1/100l 4 l( 1)/ 1)/ u 1 2)/100] 2 l( 2)/ l 3 [(T-TQ/IOOP, and b, [(TT )/100] b (TT2)/lO0] 161! [(PU PB)/(PU PL)] 1. [(PB PL)/(PUPL)] U so that a signal G or G is provided in accordance with each equation by each G signal means using sensed temperature T and the trial temperature T, for the term T to provide the G signal, first switching means'receiving direct current voltages corresponding to reference ratios P and P and connected to the P ratio signal means and to each G signal means for selecting the proper signal G or G in accordance with the ratio P signal and the P and P reference voltages so that the signals corresponding to the term G L are provided as the G and G signals to the change determining means when the ratio P is more negative than the lower reference ratio P signal, and signals corresponding to the term G,, are provided as the G and G signals to the change determining means when the ratio signal P is more positive than the upper reference ratio P voltages, the signals corresponding to the term G are provided as the G and G signals to the determining means when the sensed ratio P signal is not more negative than the lower reference ratio P voltage nor more positive than the upper reference ratio P voltage; F signal means connected to the temperature sensing means and to the trial temperature signal means and receiving the direct current voltages corresponding to reference temperatures T and T a term of 1.0 and predetermined coefficients c through 0 and 11 through (i for providing signals corresponding to quantities F and F in accordance with the following equations:

F 1.0 c [(T--T )/lOO] 0 [(TT )/l0O] 3[( l)/ F 1.0 d [(T-T )/l00] d [(T-T 100] d ,[(T--T )/l00-rr 4]( 2)/ 5[( 2)/ L-ll y n)/( u U] FL B PL)/(P U] u second switching means receiving the direct current voltages corresponding to the reference ratios P and P and connected to the P ratio signal means and to each F signal means for selecting the proper signal F or F in accordance with the P signal and the P and P reference voltages sov that signals corresponding to the term F L are provided as the F and F signals to the change determining means when the ratio P is more negative than the P reference voltage, signals corresponding to the term F are provided as the F and F signals to the change determining means when ratio P signal is more positive than reference ratio P voltage, and signals corresponding to the term F are provided as the F and F signals to the change determining means when the ratio P signal is not more negative for the term T to provide the G signal,

than the reference ratio P voltage; and means connected to the temperature sensing means, to the trial temperature signal means and to the ratio P signal means and receiving direct current voltages corresponding to the coefficients e through e for providing signals corresponding to the quantities H and H in accordance with the following equation:

l3 l4 15 l6 H where the sensed temperature T is used for T to provide the signal H and the trial temperature T, is used for T to provide the signal corresponding to the calculated quantity H 6. A system as described in claim 4 in which the hydrocarbon product sensing means includes means for sensing the flow rate R of the hydrocarbon product and providing a signal corresponding thereto, means for sensing the alkylate content V of the hydrocarbon product and providing a corresponding signal, and means connected to the hydrocarbon product flow rate sensing means and to the alkylate content sensing means for providing a signal corresponding to the alkylate flow rate R in accordance with the following equation:

RK VKRC and the acid sensing means includes means for sensing the flow rate R of discharge acid and providing a signal corresponding thereto.

7 A system as described in claim 6 in which the change determining means includes means connected to the earnings signal means and to the first switching means for subtracting the G signal from the G signal to provide a signal to the earnings signal means, corresponding to the change in octane rate A Q, means connected to the alkylate flow rate signal means and to the discharge acid flow rate sensing means and receiving a direct current voltage corresponding to a predetermined conversion factor a for providing a signal corresponding to the acid consumption A B by the alkylation unit inv accordance with the following equation:

AB os/ x means receiving a direct current voltage corresponding to a term 1 in the next following equation and connected to the second switching means to the earnings signal means and to the acid consumption signal means for providing a signal corresponding to the differential acid consumption A A to the earnings signal means in accordance with the following equation:

A AB[(FB/FC)"1] and means connected to the H and H signal means and to the earnings signal means for subtracting the H signal from the H signal to provide a signal to the earnings signal means corresponding to the change A U in the utility rate.

8. A system as described in claim 7 in which the earnings signal means provides the earnings signal in accordance with the A Q,AA,AU,W W and W signals and the following equation:

Q)( a) AXWA) U v) where E is the earnings; and the earnings control means includes means connected to the earnings signal means for sampling and holding the earnings signal to provide a pair of signals, one signal corresponding to the earnings for a current trial temperature while the other signal corresponds to the earnings for a next previous trial temperature, comparing means connected to the sample and hold means and to the trial temperature signal means and responsive to the signals from the sample and hold means for providing a high level direct current signal as the command. signal to the trial temperature signal means when the earnings for the current trial temperature is not less than the earnings for the next previous trial temperature and providing a low level direct current signal as the command signal to the trial temperature signal means when the earnings for the current trial temperature is less than the earnings for the next previous trial signal, and temperature control signal means connected to the first comparing means, to the trial temperature means and to the utility means for providing the signal corresponding to the next previous trial temperature as the temperature control signal in response to the command signal from the comparing means changing from a high level to a low level.

9. A system as described in claim 8 in which the earnings control means further comprises means connected to the AU signal means, to the discharge acid flow rate sensing means and to the alkylate flow rate signal means for providing a signal corresponding to a utility rate R in accordance with the A U signal, the R signal and the R K signal and the following equation:

u os X K), and means connected to the acid consumption A signal means, to the A A signal means and to the alkylate flow rate R signal means and receiving the direct current voltage corresponding to the conversion factor a for providing a signal corresponding to a calculated discharge acid flow rate R DC in accordance with the A A, A and R K signals, thedirect current voltage and the following equation:

(AB A x/ and the comparing means is also connected to the R signal means andreceiving direct current reference voltages corresponding to predetermined limits for the trial temperature T for the utility rate R and for the calculated discharge acid flow rate R and provides the high level signal to the temperature control signal means when the earnings for the current trial temperature is not less than the earnings for the next previous trial temperature, the trial temperature T, does not exceed a predetermined limit, the utility rate R does not the earnings for the next previous trial temperature, the

trial temperature T,- exceeds a predetermined limit, the utility rate R exceeds a predetermined limit, or the calculated discharge acid flow rate exceeds a predetermined limit.

10. A method for controlling an alkylation unit to achieve an optimum operating condition and said alkylation unit includes a contactor wherein an olefinisoparaffin mixture is contacted with acid at a temperature controlled by utility means and the contactor provides an acid-hydrocarbon mixture to a settler which separates the acid from the acid-hydrocarbon mixture to provide a hydrocarbon product, which includes alkylate and acid, a portion of the separated acid is discharged while a portion of the separated acid is fed back to the contactor along with fresh acid entering the alkylation unit that is added to feedback acid to replace the discharge acid, which comprises the following steps: sensing the contact temperature T sensing a utility rate, sensing a condition related to the contact acid, sensing conditions to the hydrocarbon product, sensing conditions of the olefin, determining economic values related to the octane rating of the alkylate, to acid consumption and to the utility and controlling the acid entering the alkylation unit and the contact temperature in accordance with the sensed contact temperature, the sensed utility rate, the sensed condition related to the contact acid, the sensed condition of the hydrocarbon product and the sensed olefin conditions and the determined economic values, so as to achieve an optimum operating condition for the alkylation unit.

11. A method as described in claim 10 in which the contact temperature is controlled by passing a coolant through the contactor.

12. A method as described in claim 11 in which the controlling step includes determining the effect that a change in the contact temperature would have on the earnings of the alkylation unit.

Claims (11)

1. 2. A system as described in claim 1 in which the utility means includes means for passing a coolant through the contactor so as to control the contact temperature.
2. 3. A system as described in claim 2 in which the control signal means determines the effect that a change in the contact temperature would have on the earnings of the alkylation unit.
3. 4. A system as described in claim 3 in which the control signal means includes first means connected to the temperature sensing means, to the olefin sensing means and to the hydrocarbon product sensing means for calculating values of factors GB, FB and HB from the signals from the temperature sensing means, from the olefin sensing means and from the hydrocarbon product sensing means, means connected to the temperature sensing means for providing a signal, corresponding to a trial temperature Tj, in accordance with the sensed contact temperature TB signal and the following equation:
4. 5. A system as described in claim 4 in which the olefin sensing means includes means for sensing concentrations of the different olefins and providing signals corresponding thereto, means connected to the olefin concentration sensing means for providing a signal corresponding to the ratio PB of propylene to olefins; and the first and second calculating means includes G signal means connected to the temperature sensing means and to the trial temperature signal means, respectively, and receiving direct current voltages corresponding to reference temperatures T1 and T2 and predetermined coefficients a1 through a5 and b1 through b5 for providing signals corresponding to the quantities GB and GC in accordance with the following equations: GL a1 ((T-T1/100) + a2 ((T-T1/100)2 + a3 ((T-T1/100)3 + a4 ((T-T1)/100)4 + a5 ((T-T1)/100)5 GU b1 ((T-T2)/100) + b2 ((T-T2)/100)2 + b3 ((T-T2)/100)3, and + b4 ((T-T2)/100)4 + b5(T-T2)/100)5 GL U ((PU-PB)/(PU-PL))GL + ((PB-PL)/(PU-PL)) GU so that a signal GB or GC is provided in accordance with each equation by each G signal means using sensed temperature TB for the term T to provide the GB signal and the trial temperature Tj for the term T to provide the GC signal, first switching means receiving direct current voltages corresponding to reference ratios PU and PL and connected to the PB ratio signal means and to each G signal means for selecting the proper signal GB or GC in accordance with the ratio PB signal and the PU and PL reference voltages so that the signals corresponding to the term GL are provided as the GB and GC signals to the change determining means when the ratio PB is more negative than the lower reference ratio PL signal, and signals corresponding to the term GU are provided as the GB and GC signals to the change determining means when the ratio signal PB is more positive than the upper reference ratio PU voltages, the signals corresponding to the term GU L are provided as the GB and GC signals to the determining means when the sensed ratio PB signal is not more negative than the lower reference ratio PL voltage nor more positive than the upper reference ratio PU voltage; F signal means connected to the temperature sensing means and to the trial temperature signal means and receiving the direct current voltages corresponding to reference temperatures T1 and T2, a term of 1.0 and predetermined coefficients c1 through c5 and d1 through d5 for providing signals corresponding to quantities FB and FC in accordance with the following equations: FL 1.0 + c1((T-T1)/100) + c2 ((T-T1)/100)2 + c3((T-T1)/100)3 + c4((T-T1)/100) + c5((T-T1/100)5 FU 1.0 + d1((T-T2)/100) + d2((T-T2)/100)2 + d3((T-T2)/100 pi 3 + d4)(T-T2)/100) + d5((T-T2)/100)5 FL U ((PU - PB)/(PU - PL)) FL + ((PB - PL)/(P - PL)) FU second switching means receiving the direct current voltages corresponding to the reference ratios PU and PL and connected to the PB ratio signal means and to each F signal means for selecting the proper signal FB or FC in accordance with the PB signal and the PU and PL reference voltages so that signals corresponding to the term FL are provided as the FB and FC signals to the change determining means when the ratio PB is more negative than the PU reference voltage, signals corresponding to the term FU are provided as the FB and FC signals to the change determining means when ratio PB signal is more positive than reference ratio PU voltage, and signals corresponding to the term FU L are provided as the FB and FC signals to the change determining means when the ratio PB signal is not more negative than the reference ratio PU voltage; and means connected to the temperature sensing means, to the trial temperature signal means and to the ratio PB signal means and receiving direct current voltages corresponding to the coefficients e1 through e16 for providing signals corresponding to the quantities HB and HC in accordance with the following equation: H e1 + e2 T + e3 T2 + e4 T3 + (e5+e6T+e7T2+e8T3)PB + (e9+e10T+e11T2+e12T3)PB2 + (e13+e14T+e15T2+e16T3)PB3 where the sensed temperature TB is used for T to provide the signal HB and the trial temperature Tj is used for T to provide the signal corresponding to the calculated quantity HC.
5. 6. A system as described in claim 4 in which the hydrocarbon product sensing means includes means for sensing the flow rate RC of the hydrocarbon product and providing a signal corresponding thereto, means for sensing the alkylate content VK of the hydrocarbon product and providing a corresponding signal, and means connected to the hydrocarbon product flow rate sensing means and to the alkylate content sensing means for providing a signal corresponding to the alkylate flow rate RK in accordance with the following equation: RK VKRC and the acid sensing means includes means for sensing the flow rate RDB of discharge acid and providing a signal corresponding thereto.
6. 7. A system as described in claim 6 in which the change determining means includes means connected to the earnings signal means and to the first switching means for subtracting the GB signal from the GC signal to provide a signal to the earnings signal means, corresponding to the change in octane rate Delta Q, means cOnnected to the alkylate flow rate signal means and to the discharge acid flow rate sensing means and receiving a direct current voltage corresponding to a predetermined conversion factor Alpha for providing a signal corresponding to the acid consumption AB by the alkylation unit in accordance with the following equation: AB Alpha RDB/RK means receiving a direct current voltage corresponding to a term 1 in the next following equation and connected to the second switching means to the earnings signal means and to the acid consumption signal means for providing a signal corresponding to the differential acid consumption Delta A to the earnings signal means in accordance with the following equation: Delta A AB((FB/FC) - 1) and means connected to the HB and HC signal means and to the earnings signal means for subtracting the HB signal from the HC signal to provide a signal to the earnings signal means corresponding to the change Delta U in the utility rate.
7. 8. A system as described in claim 7 in which the earnings signal means provides the earnings signal in accordance with the Delta Q, Delta A, Delta U,WQ, WA and WU signals and the following equation: E ( Delta Q)(WQ) - ( Delta A)(WA) - ( Delta U )(WU ) where E is the earnings; and the earnings control means includes means connected to the earnings signal means for sampling and holding the earnings signal to provide a pair of signals, one signal corresponding to the earnings for a current trial temperature while the other signal corresponds to the earnings for a next previous trial temperature, comparing means connected to the sample and hold means and to the trial temperature signal means and responsive to the signals from the sample and hold means for providing a high level direct current signal as the command signal to the trial temperature signal means when the earnings for the current trial temperature is not less than the earnings for the next previous trial temperature and providing a low level direct current signal as the command signal to the trial temperature signal means when the earnings for the current trial temperature is less than the earnings for the next previous trial signal, and temperature control signal means connected to the first comparing means, to the trial temperature means and to the utility means for providing the signal corresponding to the next previous trial temperature as the temperature control signal in response to the command signal from the comparing means changing from a high level to a low level.
8. 9. A system as described in claim 8 in which the earnings control means further comprises means connected to the Delta U signal means, to the discharge acid flow rate sensing means and to the alkylate flow rate signal means for providing a signal corresponding to a utility rate RU in accordance with the Delta U signal, the RDB signal and the RK signal and the following equation: RU RDB + ( Delta U)(RK), and means connected to the acid consumption AB signal means, to the Delta A signal means and to the alkylate flow rate RK signal means and receiving the direct current voltage corresponding to the conversion factor Alpha for providing a signal corresponding to a calculated discharge acid flow rate RDC in accordance with the Delta A, AB and RK signals, the direct current voltage and the following equation: RDC (AB + Delta A)RK/ Alpha , and the comparing means is also connected to the RU signal means and receiving direct current reference voltages corresponding to prEdetermined limits for the trial temperature Tj, for the utility rate RU and for the calculated discharge acid flow rate RDC and provides the high level signal to the temperature control signal means when the earnings for the current trial temperature is not less than the earnings for the next previous trial temperature, the trial temperature Tj does not exceed a predetermined limit, the utility rate RU does not exceed a predetermined limit, and the calculated discharge acid flow rate RDC does not exceed a predetermined limit, and providing the low level signal when the earnings for the current trial temperature is less than the earnings for the next previous trial temperature, the trial temperature Tj exceeds a predetermined limit, the utility rate RU exceeds a predetermined limit, or the calculated discharge acid flow rate exceeds a predetermined limit.
9. 10. A method for controlling an alkylation unit to achieve an optimum operating condition and said alkylation unit includes a contactor wherein an olefinisoparaffin mixture is contacted with acid at a temperature controlled by utility means and the contactor provides an acid-hydrocarbon mixture to a settler which separates the acid from the acid-hydrocarbon mixture to provide a hydrocarbon product, which includes alkylate and acid, a portion of the separated acid is discharged while a portion of the separated acid is fed back to the contactor along with fresh acid entering the alkylation unit that is added to feedback acid to replace the discharge acid, which comprises the following steps: sensing the contact temperature TB, sensing a utility rate, sensing a condition related to the contact acid, sensing conditions to the hydrocarbon product, sensing conditions of the olefin, determining economic values related to the octane rating of the alkylate, to acid consumption and to the utility and controlling the acid entering the alkylation unit and the contact temperature in accordance with the sensed contact temperature, the sensed utility rate, the sensed condition related to the contact acid, the sensed condition of the hydrocarbon product and the sensed olefin conditions and the determined economic values, so as to achieve an optimum operating condition for the alkylation unit.
10. 11. A method as described in claim 10 in which the contact temperature is controlled by passing a coolant through the contactor.
11. 12. A method as described in claim 11 in which the controlling step includes determining the effect that a change in the contact temperature would have on the earnings of the alkylation unit.

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