Means and method for controlling a solvent refining unit for maximum yield

Claim 2

A control system for a solvent refining unit which treats charge oil with a solvent in a refining tower to yield raffinate and extract-mix, strippers separate the solvent from the raffinate and from the extract-mix to provide refined waxy oil and extract oil, respectively, the solvent is returned to the tower and the refined waxy oil is subsequently dewaxed to provide refined oil, comprising means for controlling the operation of the refining unit, first means connected to the control means for providing control signals to the control means to operate the refining unit for a predetermined time period at a predetermined solvent dosage-temperature combination so as to provide refined oil of a desired quality, means for measuring at least one condition of the extract oil and one condition of the refined waxy oil anD providing signals corresponding thereto, means for measuring at least one property of the charge oil and providing a corresponding signal, signal means for providing signals corresponding to limitations of operating parameters of the refining unit and the refining operation, means connected to the condition measuring means, to the property measuring means and to the limitation signal means for determining which operating parameter is limiting and providing signals corresponding thereto, and second means connected to the determining means and to the control means for providing control signals to the control means after the predetermined time period in accordance with the signals from the determination means to control the operation of the refining unit so that the refining unit operates at a maximum capability while maintaining the quality of the refined oil.

Claim 3

A system of the kind described in claim 1 in which the solvent is N-methyl-2-pyrrolidone and the solvent flows at a maximum possible rate SOLLIM.

Claim 4

A system as described in claim 2 in which the first control signal means includes means for providing direct current control signals corresponding to a selected charge oil flow rate COSEL and to a selected refining temperature TSEL, and switching means connecting the COSEL, TSEL signal means to the control devices for momentarily applying the COSEL and the TSEL signals to the control devices to control the refining unit so that the refining unit operates with the selected charge oil flow rate and refining temperature until other control signals are applied to the control devices.

Claim 5

A system as described in claim 3 in which the signal means provides signals corresponding to the maximum possible flow rates EOLIM and ROLIM of the extract oil and the refined waxy oil, respectively.

Claim 6

A system as described in claim 4 in which the measured property of the charge oil is the viscosity, and the measured conditions of the extract oil and the refined waxy oil are the extract oil flow rate EOM and the refined waxy oil flow rate ROM; and the determining means includes means connected to the property measuring means for providing a signal corresponding to a correlation constant n in accordance with the viscosity signal from the property measuring means, means connected to the condition measuring means and to the n constant signal means for providing a signal corresponding to an a constant in accordance with the EOM and ROM signals from the condition signal means and the n constant signal from the n factor signal means, means connected to the limitation signal means for providing a signal corresponding to an aLIM constant in accordance with the EOLIM and ROLIM signals from the limitation signal means, and a comparator connected to the a constant signal means and to the aLIM constant signal means for comparing the a constant signal to the aLIM constant signal to determine whether the refined waxy oil flow rate is the limiting operating parameter, the extract oil flow rate is the limiting operating parameter, or the refining unit is balanced.

Claim 7

A system as described in claim 5 in which the n constant signal means includes memory means in various values of n have been stored, and selection means connected to the memory means and to the viscosity measuring means for selecting the proper n value from the memory means in accordance with the viscosity signal from viscosity measuring means; the a constant signal means is an a constant analog computer providing the a constant signal in accordance with the following first equation: a ROM/(EOM)n; and the aLIM constant signal means is an aLIM constant analog computeR providing the aLIM constant signal in accordance with the following second equation: aLIM ROLIM/(EOLIM)n.

Claim 8

A system as described in claim 6 in which the comparator provides a signal having one amplitude when the a constant signal is equal to or greater than the aLIM constant signal and another amplitude when the a constant signal is less than the aLIM constant signal; and the determining means includes a b constant analog computer receiving direct current voltages and being connected to the condition measuring means and to the first control means for providing a signal corresponding to the b constant in accordance with the EOM and ROM signals from the condition measuring means, the SSEL and TSEL signals from the COSEL, TSEL signal means, the direct current voltages and the following third equation: where m is a constant having a value within the range of 0.75 to 0.80; and the second control signal means includes means connected to the a constant computer, to the b constant computer and to the n constant signal means and receiving direct current voltages for providing signals corresponding to the charge oil flow rate COE and to the refining temperature TE for the condition where the extract oil flow rate is at its maximum possible rate EOLIM; means connected to the a and b constant computers and to the n constant signal means for providing signals corresponding to the charge oil flow rate COR and to the refining temperature TR for the condition where the refined waxy oil flow rate is at its maximum possible rate ROLIM; switching means connected to the COE, TE signal means, to the COR, TR signal means and to the comparator and controlled by the signal from the comparator to pass the COR and TR signals from the COR, TR signal means when the signal from the comparator is of the one amplitude and to pass the COE and the TE signals from the COE, TE signal means when the signal from the comparator is of the other amplitude; subtracting means receiving direct current voltages, corresponding to the miscible temperature TMISC of the charge oil and the N-methyl-2-pyrrolidone and to a temperature T1 occurring within the range of 10* to 20* F. for subtracting the T1 voltage from the TMISC voltage to provide a signal corresponding to the maximum permissable refining temperature TMAX; means connected to the a and b constant computers, to the n constant signal means and to the subtracting means and receiving direct current voltages for providing a signal corresponding to the charge oil flow rate COT for the condition where the refining temperature is at its maximum permissable level TMAX; a second comparator connected to the first switching means and to the subtracting means for comparing the TMAX signal with the TE or TR signal passed by the first switching means and providing a signal of one amplitude when the TR or TE signal is less than the TMAX signal and of another amplitude when the TR or TE signal is equal to or greater than the TMAX signal, and second switching means connected to the subtracting means, to the first switching means, to the COT signal means, to the control devices and to the second comparator for blocking the signals from the first switching means, from the subtracting means and from the COT signal means during the predetermined time period and for pAssing the COE, TE or the COR, TR signals from the first switching to the control devices as the control signals after the predetermined time period in response to the signal from the second comparator being of the one amplitude and for passing the COT signal from the COT signal means and the TMAX signal from the subtracting means to the control devices as the control signals after the predetermined time period in response to the signal from the second comparator being of the other amplitude.

Claim 9

A system as described in claim 7 in which the COE, TE signal means is an analog computer providing the COE and the TE signals in accordance with the following fourth through seventh equations:

Claim 12

A method as described in claim 9 in which the solvent is N-methyl-2-pyrrolidone.

Claim 13

A method as described in claim 10 in which the measured property of the charge oil is the viscosity, the limitation signals correspond to the maximum possible flow rates EOLIM and ROLIM of the extract oil and the refined waxy oil, respectively, and to the maximum permissable refining temperature TMAX, the measured conditions of the extract oil and the refined waxy oil are their flow rates EOM and ROM, respectively, and the charge oil flow rate and the refining temperature are controlled in accordance with the determination.

Claim 14

A method as described in claim 11 in which the determining step includes providing an n constant signal in accordance with the measured viscosity signal, providing an a constant signal in accordance with the measured extract oil flow rate EOM signal, the measured refined waxy oil flow rate ROM signal, the n constant signal and the following equation: a ROm/(EOM)n, providing an aLIM constant signal in accordance with the maximum possible extract oil and refined waxy oil flow rates EOLIM and ROLIM signals, respectively, the n factor signal and the following equation: aLIM ROLIM/(EOLIM)n, providing an m constant signal, having a value within the range of 0.75 to 0.80, and providing a b constant signal in accordance with the selected dosage SSEL signal, the selected refining temperature TSEL signal, the measured extract oil and refined waxy oil flow rates EOM and ROM signals, direct current voltages corresponding to a value of 1 and to an exponent m, respectively, and the following equation:

Claim 15

A method as described in claim 12 in which the determining step includes comparing the a constant and the aLIM constant signals, providing a comparison signal having one amplitude when the a constant signal is less than the aLIM constant signal and another amplitude when the a constant signal is equal to or greater than the aLIM constant signal, providing control signals COE and TE corresponding to a flow rate for the charge oil and a refining temperature, respectively, when the comparison signal is of the one amplitude, providing control signals COR and TR when the comparison signal is of the other amplitude, determining the miscible temperature of the charge oil and the solvent, providing a signal corresponding to a maximum refining temperature TMAX which is substantially less than the miscible temperature, comparing the TR or TE signal, whichever is provided, with the TMAX signal, providing a second comparison signal having one amplitude when the TR or TE signal is less than the TMAX signal and another amplitude when the TR or TE signal is equal or greater than the TMAX signal, providing a COT signal, corresponding to a flow rate for the charge oil, and the TMAX signal as control signals after the predetermined time period when the second comparison signal is of the other amplitude, and providing the COR, TR signals or the COE, TE signals as control signals after the predetermined time period when the second comparison signal is of the one amplitude.

Claim 16

A method as described in claim 13 in which the COR and TR signals are provided in accordance with the n constant signal, the ROLIM signal, the SOLLIM signal, the a constant signal, direct current voltages corresponding to values of 1, 100, and m and the following equations: