Means and method for controlling the strength of acid in an alkylation unit

Claim 2

A control system as described in claim 1 further comprising programming means connected to the determining means and to the control signal means for starting and stopping the operation of the control system and for periodically recycling the operation of the control system.

Claim 3

A control system as described in claim 3 in which the acid strength determining means includes acid strength analyzing means controlled by the programming means for periodically sampling the acid and titrating the sample acid with a caustic entering the analyzing means and providing signals corresponding to the elapsed time Delta T required for titration, and to the density DA of the acid; and means for providing a signal corresponding to the flow rate FC of the caustic entering the analyzing means and providing a signal corresponding thereto.

Claim 4

A control system as described in claim 4 in which the acid strength determining means also provides a signal corresponding to the average acid strength ASn for the current cycle of operation as the acid strength signal in accordance with the following equations: AS ( Delta T)(Fc(Nc)(MEQA)/(VOLS)(DA) ASn ASn 1 + C5(ASn-ASn 1) where AS is the instantaneous acid strength, Nc is the normality of the caustic, MEQA is the milliequivalent weight of the acid, and VOLS is the volume of the acid sample, ASn 1 is the acid strength for the previous cycle, ASn is the instantaneous acid strength during the current cycle, and C5 is a constant having the following value: 0.75.

Claim 5

A control system as described in claim 5 in which the composition signal means includes chromatograph means sampling the olefin and providing a signal corresponding to constituents of the charge olefin, as the composition signal, and the sensed condition of the olefin is the sensed flow rate of the olefin.

Claim 6

A control system as described in claim 6 in which the control signal means includes means for providing a signal corresponding to the instantaneous acid consumption A due to the acid consuming constituents of the olefin, and meanS connected to the constituents signal means for providing a signal corresponding to an anticipated required acid strength Un for the current cycle of operation in accordance with the following equations: A K R(C1 Q1 + C2 Q2 + C3 Q3 + C4 Q4), and Un P3/Ao (P1 An + P2 An 1) where K is a constant corresponding to volume of hydrocarbon product obtained from a unit volume of olefin, R is the flow rate of the olefin, C1, C2, C3 and C4 are pounds of acid per gallon of product produced for corresponding constituents of the olefin, Q1, Q2, Q3 and Q4 are ratios of the acid consuming constituents to the whole olefin, Ao is the acid consumption a short time after the start of operation of the control method, An is the acid consumption during the current cycle, An 1 is the acid consumption during the previous cycle, and P1, P2 and P3 are constants pertaining to the dynamic characteristics of the control system.

Claim 7

A control system as described in claim 7 in which the control means includes a valve through which the discharge acid flows and the acid strength is controlled by controlling the flow rate of the discharge acid, a sensor sensing the flow rate of the discharge acid and providing a signal corresponding thereto, and the control signal means includes a flow controller, having a set point whose position corresponds to a flow rate, connected to the discharge acid flow rate sensor and providing the control signal to the valve in accordance with a difference between the flow rate determined by the position of the flow controller''s set point and the flow rate signal from the discharge acid flow rate sensor, and means connected to the flow controller, to the anticipated required acid strength signal means, to the reference signal means and to the average acid strength signal means for providing a direction signal and a pulse train, each pulse in the pulse train changing the position of the set point in the flow controller by a predetermined amount in a direction determined by the direction signal, in accordance with the following equation: SPn SPn 1 +G4(G1Fn 1 + GFn 2 + G3 Fn Fn) + SPn 1(Un), where SPn is the number of pulses in the pulse train during the current cycle, SPn 1 is the number of pulses in the pulse train for the previous cycle, Fn is a difference between the desired acid strength, and the average acid strength for the current cycle, Fn is the absolute value of Fn, Fn 1 is a difference between the desired acid strength and the average acid strength for the previous cycle, and G1, G2 and G3 are dynamic constants of the control system.

Claim 8

A method as described in claim 2 in which the steps are repeated periodically.

Claim 9

A method as described in claim 9 in which the acid strength determining step includes sampling the acid in the processing unit, titrating the sample acid with a steady flow of a caustic, and the acid strength signal step includes providing a signal corresponding to the titration time Delta T of the sample acid, a signal corresponding to the flow rate Fc of the caustic, and a signal corresponding to the density DA of the acid sample, and providing the acid strength signal, which corresponds to an average acid strength AS for the current cycle, in accordance with the Delta T, FC and DA signals and following equations: AS ( Delta T)(FC)(NC)(MEQA)/(DA)(VOLS) and ASn ASn 1 + C5(ASn - ASn 1) where AS is the instantaneous acid strength, Nc is the normality of the caustic, MEQA is the milliequivalent weight of the acid, VOLS is the volume of the acid sample, ASn 1 is the average acid strength for the next previous cycle, ASn is an instantaneous acid strength occurring during the current cycle, and C5 is a constant having the following value: 0.75.

Claim 10

A method as described in claim 10 in which the olefin quantity and composition step includes sensing the quantities of acid consuming constituents of the olefin entering the processing unit during each cycle, and providing signals corresponding to the quantities of acid consuming constituents of the olefin.

Claim 11

A method as described in claim 11 in the control signal step includes providing a signal corresponding to an anticipated required acid strength Un for the current cycle in accordance with the acid consuming constituents signal and the following equation: A KR(C1Q1 + C2Q2 + C3Q3 + C4Q4) and Un P3/Ao (P1An + P2An 1) where A is the instantaneous acid consumption due to the acid consuming constituents of the olefin, K is a constant corresponding to volume of bycarbon product obtained from a unit volume of olefin, R is the flow rate of the olefin, C1, C2, C3 and C4 are pounds of acid per gallon of product produced for corresponding constituents of the olefin, Q1, Q2, Q3 and Q4 are ratios of the acid consuming constituents to the whole olefin, Ao is the acid consumption a short time after the start of operation of the control method, An is the acid consumption during the current cycle, An 1 is the acid consumption during the previous cycle, and P1, P2 and P3 are relating to the dynamic constants of the control method.

Claim 12

A method as described in claim 12 in which the acid strength is controlled by controlling the flow rate of the discharge acid with a value responsive to the control signal, and the control signal is provided by a flow controller having set points in accordance with a difference between a signal corresponding to the flow rate of the discharge acid and the position of set points corresponding to a flow rate of the discharge acid, and the control signal step includes providing a reference signal corresponding to a desired acid strength, providing a direction signal and a pulse train to the flow controller, each pulse in the pulse train changes the position of the set points a predetermined amount in a direction controlled by the direction signal, in accordance with the average acid strength signal, the reference signal and the anticipated required acid strength signal and the following equation: SPn SPn 1 + G4(G1Fn + G2Fn 1 + G3 Fn Fn) + SPn 1 (Un) where SPn corresponds to the number of pulses in the pulse train for the current cycle, SPn 1 corresponds to the number of pulses in the pulse train for the next previous cycle, Fn corresponds to the difference between the reference signal and the average acid strength signal for the current cycle, Fn is the absolute value of Fn, Fn 1 is the difference between the reference signal and the average acid strength signal for the next previous cycle.