Patent EA-000343-B1 (EA)
Title: Method for controlling chemical synthesis processes, synthesis of chemical products and device for controlling thereof
Inventor: DE SELLIERS JACQUES
IPC: B01J19/00
Filed: 1996-06-01
Abstract: 1. A method for controlling a process for synthesising at least one chemical in a plant including at least one reactor (R) that may be considered as a perfectly mixed reactor, wherein control variables (GC) enable the process to be controlled so that a number of variables known as controlled variables (GR) and related to the properties of the product and/or the operation of the process match corresponding set values (CGR), wherein said method comprises the steps of (a) inputting set values for the controlled variables (CGR); (b) using a prediction unit (OP) to calculate predictions of the controlled variables (PGR) on the basis of measurements of the process control variables (MGC); (c) using a control unit (OC) to calculate set values for the process control variables (CGC) on the basis o)f the set values (CGR) and predictions (PGR) of the controlled variables; d) transmitting set values for the process control variables (CGC) to process control actuators wherein the prediction unit (OP) is based on a mathematical process model known as a direct model (M), characterized in that the prediction unit (OP) designed in such a way that the mass MXR of at least one component (X) in the reactor (R) is predicted by means of the equation; MXR = LAG (FxRin - τX, τX), where FXRin where FxRin - is the mass flow rate of component X at the inlet of the reactor R; τX - is the dwell time of x in the reactor which is τX = MXR / (Σ Fxdis), where MxR - is the last calculated value of mass component X, present in reactor R; Σ Fxdis - summed flow rate of Fxdis, with which the component X is removed from the reactor R, in particular, in the result of the reaction and/or at the outlet of the reactor; the function y = LAG (u,τ) - is the solutionof the differential equation   calculated with the instantaneous value of u and τ, as well as with the last calculated value of y wherein the equation of the following type can be the solution of the above differential equation:   or  . 2. Method for controlling the process according to Claim 1, characterized in that set values, at least, one controllable variables (CGC) is corrected on the basis of the disagreement between the measured (MGR) and predicted values (PGR) of this controllable variable so as to make controlling effective even in case of an error in the prediction of this controllable variable (PGR). 3. Method for controlling the process according to Claim 1, characterized in that the model M is periodically adapted on the basis of the disagreement between the measured (MGR) and predicted values (PGR) of this controllable variables so as the model M provides the predicted values of the controllable variables (PGR) most close to the measured values of these variables (MGR). 4. Method for controlling the process according to Claim 3, characterized in that the result of measurement (MGR) of these controllable variables is considered only at possible adaptation of the model of the method and is not considered at the direct calculation of the set values of the controllable variables (CGC) of the method. 5. Method for controlling the process according to one of the preceding Claims, characterized in that when applying the process of polymerisation it comprises, at least, one of the additional steps: - calculation of the predetermined temperature value in the reactor depending on one or plurality of set parameters of the product properties and the transmission of this predetermined temperature value to one or several devices, permitting to change the temperature in the reactor, -calculation of the thermal balance of the reactor, in particular, on the basis of the temperature measurements, using this thermal balance to determine a quantity of polymer synthesized in a unit of time, and/or productivity of catalyst and/or concentration, at least one reagent in the reactor, - calculation of quantity of heat, produced at the polymerisation, using calculation of the quantity of one or plurality of reagents, indirect determination of the heat quantity to be added or evacuated to maintain the temperature of the reactor, using the obtained results to provide more precise regulation of the temperature to maintain the predetermined temperature value, in particular, at changing the process rate. 6. Method for controlling the process according to one of the preceding Claims, characterized in that the quantitative value of properties PxR component "x" in the reactor R as a perfectly mixed reactor, calculate on the basis of the ratio PxR = LAG (RxIN, MxR/FxIN), where "Px"-quantitative value of properties of component "x" responding substantially the law of linear mixing; Px1+2 = w1 x Px1 + w2 x Px2, wherein w1 and w2 - mass proportion of two fractions 1 and 2 with properties Px1 and Px2, which are mixed; Px1+2 -quantitative value of properties of component "x" at the outlet of the reactor, after mixing; PxIN - quantitative value of properties of component "x" at the inlet of the reactor R, MxR - mass of component "x" in the reactor R; FxIN - mass rate flow of component "x", introduced in the reactor R; function y = LAG (u,τ) is a solution of the differential equation   calculated with the instantaneous value of u and τ, as well as with the last calculated value of y wherein this differential equation can be solved in a digital form by an algebraic equation of one of the following types:   or   7. Method for controlling the process according to one of the preceding Claims, characterized in that comprises the following steps: - inputting set values related to one or plurality of properties of a product being synthesized in main algorithm, - inputting set value of the rate process in auxiliary algorithm, - calculating set values of the component concentration in the reactor using the main algorithm, depending, in particular on set values and measurements of the product properties, as well as on measurement and predicted concentrations of different components in the reactor, - transmitting set values of concentration, calculated using main algorithm as values to be introduced in auxiliary algorithm, - calculating set values of the component flow rate, introduced in the reactor using auxiliary algorithm, depending on set floe rate of the process, set values of concentration and measurements of the component floe rate, introduced in the reactor, and - transmitting set values of the flow rate calculated using auxiliary algorithm to one or a plurality devices to regulate the component flow rate, introducing in the reactor wherein main algorithm and/or auxiliary algorithm are used according to one of the preceding Claims. 8. Method for controlling the process according to Claim 7, characterized in that main algorithm is used, comprising the steps of: - predicting, based on use of the direct model of the method, at which properties of the product being synthesized are predicted depending on measured or predicted the components concentrations, - adapting, at which compare the predicted properties, obtained at the step of prediction, with values, measured on the product being synthesized and deduct from the result of comparison the parameters of adaptation, which are used as supplementary values of the inlet at the step of prediction of main algorithm, and - controlling, based on the inverse model of the method at which calculate set values of the concentration for auxiliary algorithm, depending on set values and predicted properties of the product, being synthesized, wherein said parameters of adaptation are also used as supplementary values of the inlet at the step of control 9. Method for controlling the process according to one of Claims 7 or 8, characterized in that auxiliary algorithm is used, comprising the steps of: - predicting, based on use of the direct model of the method, at which the concentrations for a plurality of components are predicted based on the material balance of the reactor; - adapting at which compare the predicted concentrations, determined by the direct model, with the measured concentrations, and deduct from the of comparison the parameters of adaptation, which are used as supplementary aqueous values at the step of prediction of auxiliary algorithm, and - controlling, based on the inverse model of the method at which calculate set values of the concentration depending on set flow rate calculated at the step of control of main algorithm, and from the predicted concentrations, calculated at the step of prediction of auxiliary algorithm, set values of flow rate, introducing in the reactor, wherein said parameters of adaptation are also used as supplementary values of the inlet at the step of control of auxiliary algorithm. 10. Method for controlling the process according to one of the preceding Claims characterized in that the regulation the synthesis process of ethylene polymerisation with obtaining polyethylene in, at least, one reactor. In which ethylene, hydrogen and/or comonomere, wherein the reaction of polymerisation is performed in the presence of a catalyst, and part of the content of the reactor is taken off permanently or periodically. 11. Method for controlling the process according to Claim 9 and 10, characterized in that at the step of adaptation of auxiliary algorithm the measured concentrations of ethylene, (Et) hydrogen (Hy) and/or comonomere (bt) are compared with the values, predicted at the step of prediction of auxiliary algorithm, thus determining, at least, one of the following parameters of adaptation a) specific activity of the catalyst respective to ethylene "AEt", measured in kg/hr of polyethylene per kg of catalyst and per kg/m<3> of ethylene, b) error in coefficient when measuring hydrogen "KfHy" flow, c) purity of comonomere feed "KfBt". 12. Method for controlling the process according to Claims 1-9, characterized in that the regulation of the process of continuous synthesis of propylene by the propylene polymerisa