OPTIMIZATION OF THE CATALYTIC REFORMING PROCESS

The formulation and solution of the optimization problem requires the determination of the preliminary composition of the vector of input optimized values and the type of optimization criterion from, the justification and selection of which are presented below. The flow rate of the circulating gas at the inlet of the catalytic reforming unit is limited by the H2S/feedstock ratio (the H2S circulation rate), the value of which, according to the regulations, is 1650-1800 m3/m3. An increase in the H2S/feedstock ratio can manifest itself in two diametrically opposed directions. On the one hand, an increase in the partial pressure of hydrogen in the mixture inhibits dehydrogenation reactions (occurring with the release of H2), on the other hand, an increase in the amount of heated gas circulating through the reactor reduces the temperature drop in it. As a result, the average temperature of the catalyst and the rate of reactions increase. That is, there is some optimal value of this parameter inside or outside the permissible range depending on the value of other input variables. The reforming process occurs with heat absorption, therefore it is implemented in a cascade of 3 or 4 reactors with intermediate heating of the reaction mixture. The temperatures at the inlet of each of the reactors are in the range of 440-540 0С. The peculiarity of the transformations in the reactors ensures that the first reactor provides the greatest difference in input/outlet temperatures (30…60 ºС), and the last one has the smallest (7…15 ºС). To reduce the considered temperature gradient, in industrial catalytic reforming units, the smallest volume of catalyst is loaded into the first reactor, and the largest volume is loaded into the last one. For a catalytic reforming unit consisting of 3 reactors, the catalyst distribution can vary from 1:2:4 to 1:3:7. Based on the above, the following were selected as control actions for optimal control of the reforming unit: – temperatures of the reaction mixture at the inlet of each reactor of the unit;– flow rate of the HCG at the inlet of the catalytic reforming unit.The sensitivity of the process to the selected control actions was investigated using a mathematical model. The highest sensitivity of the process is provided by the temperatures of the gas-feedstock mixture at the inlets of the reactors, since the temperature indicator is included in explicitly in the reaction rate constants in the average heat capacity of the feedstock supplied to the catalytic reforming unit. Keywords: optimization, reforming process, catalytic cracking, coke, aromatic hydrocarbons, hydrogen-containing gas, raw material, octane numbers, catalyst.