SU1019024A1 - Method for controlling process in diaphragm electrolytic cell - Google Patents

Description

The invention relates to methods for controlling the process of electrolysis in (Production of chlorine and caustic in diaphragm electrolyzers with low-wearing anodes and can be used in the chemical industry. A method is known for controlling and regulating the electrolysis process by measuring the alkali concentration and stabilizing the hydrogen temperature and the ratio of ampere load to water consumption, while the current output of the electrolysis process is determined by the ratio of water consumption, alkali concentration and ampere load. The known method is the increased energy consumption for carrying out the process. The closest to the invention to the technical essence and the achieved result is the method of controlling the process of diaphragm electrolysis of chlorine and caustic production in electrolyzers with low-wear anodes by changing the brine in the electrolyzer 2. The disadvantage of the known control method is the relatively low productivity of the electrolyzer and high energy consumption for the process due to the fact that it is not optimal ologicheskih parameters. The purpose of the invention is to increase the performance of electrolyzers and reduce energy consumption. The goal is achieved by the method of controlling the diaphragm electrolysis process of chlorine and caustic production in electrolyzers with low-wearing anodes by: changing the brine feed to the electrolyzer, additionally measuring the oxygen concentration in chlorine gas at the electrolyzer outlet and the pressure drop across its diaphragm and depending on the products of differential pressure per first derivative of oxygen concentration by differential pressure regulate the flow of brine into the electrolyzer. FIG. 1 shows an approximate dependence of the current output (curve A), (oxygen concentrations in chlorine gas (curve B), and sodium sodium chloride concentration 5 | y | q5 o (curve B) on the flow rate of saline Q} in figure 2) This method is carried out as follows. When the brine flow to the electrolyzer is reduced to a certain minimum QO value, the total unit costs for the production of products (chlorine, caustic, hydrogen) are reduced by changing the salt recycle (with reverse brine) and determination of alkali concentration in the electrolytic alkali practically without any change in the quality of the products obtained. With a further decrease in the brine flow rate, a sharp decrease in the current output of all products (approximately equally) was observed with contamination of the gap products by substances of side processes occurring in the electrolyzer along with the main processes. As a result, the unit cost of electricity also increases, while the concentration of sodium chlorate contaminating alkali increases in the electric alkali. This is due to the mass migration of hydroxyl ions (OH) from the cathode space to the anode one, as a result of a decrease in the rate of the countercurrent of the anolyte in cadillaries of the diaphragm. The technical and economic analysis of the process shows that it is most advantageous to maintain the electrolysis mode on the verge of mass penetration of hydroxyl ions into the anode space or at the very beginning of this process when the concentration of sodium chlorate in the electro-alkali is below acceptable. In the process of electrolysis in a diaphragm electrolyzer with low-wearing anodes, there is a proportional relationship between the rate of penetration of hydroxyl ions into the anode space and the oxygen concentration in chlorine gas, i.e. the beginning of the mass migration of hydroxyl ions with a decrease in the flow of brine into the electrolyzer can be detected by a sharp increase in oxygen concentration in chlorine, az; ah. Since the oxygen concentration in chlorine gas depends on many factors (air flow, composition and temperature of the brine, diaphragm quality, electrolysis, etc., to eliminate the influence of these factors on the accuracy of the electrolyzer output in the most favorable mode of operation and on maintaining it mode, the control signal does not use the absolute value of the oxygen concentration in chlorine gas, but the value of the first derivative of the oxygen concentration in chlorine gas in terms of the brine consumption in the electrolyzer and the control task is reduced to stabilization and this value is within the specified limits, .k, .e, where S is the oxygen concentration in chlorine gas; G is the brine flow rate in the electrolysis Kjjux is the set value of the first pro, is derived; 6 is the allowable limit of variation from the set value In production, another parameter is used to control electrolysis — the pressure drop across the cell diaphragm. Since the pressure drop is related to the flow rate of the brine ratio / ..P, where P is the current value of the pressure drop f and the diaphragm .; C - coefficient of flowability di. fragments, then ".substituted (2) in (1 J, we get || p |. k ,, o -Hi OR without a big practical error. 8, (4) .A Jp G .. O: k- - A - iGA G Cr - nominal consumption of sawdust. Implementation, control in terms of the iA expression is simpler than using the expression (1 |, since the need to install an additional instrument for measuring the flow is eliminated, while anolyte is mandatory. According to the safety conditions of the technique. The flags K d and E are determined once by an experimental or calculated path and are set equal (equal / for all electrolyzers. At constant values of the electrolysis current, the brine composition and temperature, the only disturbing factor is the change in the quality of the diaphragm. Because it changes slowly, control over the expressions (.1) and (k L) produce periodically. In this case, in a relatively short time, the consumption sign that corresponds to the specified mode is found. The rest of the time this value stabilizes. The brine flow stabilization circuit operates continuously and ensures the stabilization of the set value of the pressure difference on the diaphragm of the electrolyzer. The signal from the differential sensor 1 is applied as a variable to the regulator input 2, which, in accordance with the command signal, generates a controlling effect on the regulator 3, which changes the flow brine in the electrolyzer. The correction circuit consists of an oxygen concentration sensor 5 in chlorine gas, a computing device 6 and a setting unit of the adder 7. Into the computing device 6 analog signals are sent from the oxygen concentration sensor 5 and from the pressure differential sensor t and a predetermined value of the computing device is entered 6 sub-entry of a discrete initiating signal through channel 8. The output of computing device 6 is fed to the input of setpoint-adder 7, the output signal of which is inputted as Task to controller 2, Contour corrector The section operates periodically when the initiating signal arrives through channel 8. The process mode of the parameter Parameter Pressure drop {or level in the electrolyzer) is stabilized by the stabilization circuit. When the correction mode is necessary, the initiation signal is supplied to the computing device 6. In this case, the computing device 6 outputs to the setter-adder 7 an increment of the set pressure differential across the diaphragm aP (por g 5 10 10 mm water column), which is summed up with the previous value of the set differential pressure and fed to the regulator 2 as a New task, After some time (the time when the electrolyzer A goes to the mode around tO-1 $ min), the value of K is determined by the expression (k), while .REi jdfprf lR is allowed. The sign of the next increment generated is determined by the ratio; "A- u where. - set error. At K C Ke db, the setting of the LB is given, at K K501D + f, an h-other is issued. The issuance of increments of ± LR and verification of the relations (5) and (6) is repeated until the condition (6) is fulfilled, after which the correction circuit stops its operation, the setting unit adder 7 remembers the last specified value of the differential 1 24 until the next crust; regimes Practically, correction is carried out every 3-5 days of the operation of the electrolyzer. The use of this Control Method will allow to maintain the specified electrolysis mode with high accuracy, which will significantly reduce the expenditure ratio for energy consumption (approximately by 10-15 for heating steam for evaporation of the electric kettle and by 13% for electricity, increase the performance of electrolyzers by 1-21 and improve the quality alkali produced.

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Claims (1)

METHOD FOR CONTROLLING THE PROCESS OF DIAGRAPHIC ELECTROLYSIS of chlorine and caustic production in electrolyzers with low-wear anodes by changing the brine supply to the electrolyzer, and so that, in order to increase the productivity of electrolyzers and reduce energy consumption, oxygen concentration is additionally measured chlorine gas at the outlet of the electrolyzer and * the pressure drop across its diaphragm and, depending on the product of the pressure differential by the first derivative of the oxygen concentration, the flow brine in the electrolyzer. > Ί019024 ϊ