Use online pH meter to detect the pH value in the production process of titanium dioxide
On-line detection of pH value in the industrial production process, especially in the production process of titanium dioxide, pollution of the pH electrode will affect the pH value detection. This article introduces you in detail the online pH detection of titanium dioxide production. The pH value detection of slurry materials, especially On-line detection in the process of industrial production, because the slurry is easy to adhere and pollute the pH electrode, resulting in inaccurate or even interruption of pH value detection, is a difficult point for automatic control in this type of chemical production. The following design and practical application, It well solves the difficult problem of online pH detection of slurry material in industrial production.
1. Rutile titanium dioxide is a kind of product in titanium dioxide (TiO2), which is widely used in paint, coating, plastic and other industries. In the production process of rutile titanium dioxide, surface treatment is a key production process. It is to change the physical properties of titanium dioxide by adding a certain amount of different metal salts and other hydroxide solutions to coat a layer of metal oxide on the surface of titanium dioxide particles. , chemical properties, to produce different specifications, varieties of rutile titanium dioxide. During the surface treatment process, the formation and thickness control of the metal oxide coating is closely related to the slurry temperature, concentration and pH value, among which the measurement and control of the pH value is the key to the entire process control. In the original production process, the outdated process operation mode of manual sampling measurement, analysis, and manual adjustment of the amount and rate of additive addition was adopted. In order to change this backward process operation mode, we have carried out DCS control transformation on the production process of surface treatment. Obviously, in the DCS control system, the acquisition of the important parameter of pH value, that is, the online detection of pH value, is the difficulty of the whole system.
the reason is:
(1) The change of pH value in the whole process is nonlinear, so the detection requires high accuracy and fast response.
(2) The main component of the slurry material at this time is TiO2 with an average particle size of 0.25 μm, so the slurry has poor fluidity and strong adhesion, and it is easy to adhere to the pH electrode and pollute the electrode. The detection accuracy is reduced, and even the determination and setting of the sampling point are blocked. The film damages the electrode of the pH meter.
(3) In industrial production, the process of surface treatment is carried out in a reactor of more than 30m3, accompanied by heating coils and stirring devices, so it is difficult to determine and set up sampling points. Therefore, the selection, configuration, installation and use of the pH measurement system have become the key points in the surface treatment DCS control system.
2. Based on the above analysis of the application of pH online measurement system in the surface treatment process of titanium dioxide, investigate the domestic titanium dioxide industry, there is no precedent for successful application, and then conduct market product research. The pH meters of well-known domestic and foreign manufacturers of pH meters, such as Chuanyi, Shangyi, Siemens, Omron, Endershaus (E+H), Mettler-Toledo, etc., and online Analyze and compare the performance and characteristics of the measurement system. Finally, the pH online measurement that can be cleaned online is composed of InPro4200pH composite electrode, pH2050e transmitter, InTrac777SLP/70/DN25N telescopic electrode sheath and EasycIean150 cleaning system produced by Mettler-Toledo. system. Its features and functions are:
(1) The use of polymer electrolyte electrodes can prolong the measurement life of the electrodes in corrosive chemical media. Open diaphragm prevents clogging. The electrode has a built-in temperature sensor for temperature measurement and automatic compensation. Electrode withstand voltage, explosion-proof;
(2) In addition to real-time display of pH and temperature values, the pH transmitter can output 4-20mA (0-20mA) analog signals and temperature signals through a variety of communication interfaces, which is convenient for connection with automatic control systems such as DCS, and has Sensor diagnosis and automatic cleaning function;
(3) The retractable electrode sheath is easy to install, and the electrode can be lifted for cleaning without interrupting the production process
(4) The automatic cleaning system can automatically clean the sensor at intervals to prolong the service life of the sensor and improve the measurement accuracy. The automatic cleaning system is pneumatic, and the air source pressure is 0.6mPa. In actual use, it can work normally at 0.4mPa. The cleaning system can also complete the cleaning of the electrode by pressing the manual cleaning button on the Easyclean150 at any time, making the cleaning operation more flexible and convenient. The system is complete, and the cleaning water and compressed air pipes all adopt socket-type interface, which is very convenient and reliable for installation. Before use, use a buffer solution with known pH value as a standard to perform a calibration, then insert the electrode into the telescopic sheath, connect the electrode cable, enter and exit compressed air and water pipes, and then turn on the power to work normally. The cleaning interval and cleaning time can be set arbitrarily according to the pollution of the measured medium to the electrode, so that the electrode can be cleaned regularly, and the output value of the pH value can be locked during cleaning to avoid interference to the DCS control system.
3. In the actual production process, the surface treatment process is carried out in a 30m3 reactor with a heating coil and a stirring device. During the process operation, the slurry is heated to about 70°C, and the additives are injected from the upper part of the reactor. After stirring until uniform, it is obvious that the sampling measurement on the upper surface of the material or the outlet at the bottom of the reactor is not representative, and cannot reflect the real pH value of the material in the kettle, which will bring great errors to the automatic control adjustment. Therefore, the location selection of sampling points must be considered. For the 30m3 large-volume reactor, the basic idea of "central sampling and external circulation detection" was determined in the design, and the material in the center of the reactor was extracted for pH measurement.
