Polystyrene, abbreviated as PS, is a homopolymer of styrene, which is mainly used in packaging, construction, medicine, electronics, automotive, home appliances, instrumentation and other industries. Generally speaking, PS refers to amorphous polystyrene, and the most common ones are general purpose polystyrene (GPPS), impact grade polystyrene (IPS), high impact grade polystyrene (HIPS), and evaporable polystyrene (EPS). Polystyrene resins are generally produced using four processes, including propriety polymerization, solution polymerization, emulsion polymerization, and suspension polymerization. The body polymerization method is the simplest, the most economical, high yield, the least amount of three wastes, the lowest impurity content of the product, the best transparency. The world's production of GPPS and HIPS are used in continuous propriety polymerization method. This article introduces the polystyrene production unit is the use of continuous ontology polymerization process for the production of polystyrene, its main sections are divided into: raw materials post, pre-polymerization post, polymerization post, de-volatile post, vacuum post, utility components.

2、Measurement of the size of the feeding system and preparation

Among them, there are 12 string-level split-range control circuits, 1 string-level and ratio adjustment system with multiple parameters, 16 single circuits, and the system's linkage, alarm, and metering and totalization of materials are mainly realized by switching DIO logic control.

This system has one field control station and two operator stations (one of which is also an engineer station).

2) Operator station, engineer station for each other for hot redundancy, the computer are selected P4/1.8G/256M/40G, monitor for the Samsung 21-inch color flat screen.

3) Configuration of a black and white laser printer, can play A4 paper, for reports, alarm records printing.

4) The main controller of on-site control station, chassis power supply and communication network are 1:1 redundant configuration.

3、Automatic batching control program

According to the process of polystyrene production, the quality of the products of metering and feeding system is mainly determined by the temperature of polymerization reaction and whether the polymerization reaction is complete or not, and whether there are monomers and other residues in the polymerization reactants. In this project, in the pre-polymerization post and polymerization post, we adopt the serial step-by-step temperature control program for the temperature in the polymerization kettle, in the pre-polymerization post, the main circuit is the temperature in the polymerization kettle, and the sub-circuit is the pressure (vacuum) control program of the polymerization kettle to carry out the automatic control; in the polymerization post, the main circuit is the temperature in the polymerization kettle, and the sub-circuit is the temperature control program of the heat transfer oil to carry on the automatic control and adjustment.

According to the needs of the production process, the temperature inside the polymerization kettle is a very important control index. This production process, due to the chemical reaction of the reactants, the temperature will produce drastic changes in the temperature if the control is not good, will seriously affect product quality. It needs to be strictly controlled. At the beginning of production, the reaction kettle charging production at the same time the temperature of the reaction kettle is also appropriate automatic adjustment and control, the method is to adjust the polymerization kettle within the flow of hot and cold oil to regulate. At this time for the exothermic reaction. When the temperature rises to a certain point, stop heating the oil; when the reactants react to a certain temperature, in a very short period of time, the temperature will produce very drastic changes, it must be quickly controlled. The method is to the pressure in the polymerization kettle using vacuum method to the unpolymerized monomer quickly pumped away from the method of temperature control, so that the temperature to meet the requirements.

Weighing and feeding system according to the process requirements of polystyrene production, polymerization reactor level and into the kettle of the three kinds of materials composed of multi-parameter series, ratio adjustment, according to the application of the scene, the dosage system fully meets the production requirements.

4、Control effect and significance

The application of this project in polystyrene production line batching machine. The application effect shows that the whole polystyrene production polymerization process runs smoothly and achieves the expected control target. Specifically manifested in the following aspects: the temperature, pressure and flow rate set values of each unit equipment are automatically adjusted, and the joint control of the system meets the requirements of the process, which reduces the labor intensity of the operators; the degree of smooth operation is improved, which lays the foundation for ensuring the "safe, stable, long, full and excellent" production of the device; and the quality of the product of the polystyrene is improved substantially. The quality of polystyrene products has been greatly improved.