Introduction In May 1996, a factory expanded its No. 2 rotary kiln clinker production line to 700t/d. A Φ15m×30m mixing chamber was chosen for the raw material homogenization silo. The initial design for its air filling control was to use an air distributor. During construction, through actual investigation, a comparison was made between the PLC + solenoid valve control and the air distributor scheme: 1) The air distributor's air filling time is fixed and cannot be changed according to specific operating conditions, making it difficult to guarantee the homogenization effect. In contrast, with solenoid valve control, the solenoid valve's action time can be arbitrarily adjusted by the PLC program, and various control modes can be implemented according to different situations, achieving the best raw material homogenization effect. 2) The total price of 3 air distributors was 125,000 yuan, while the price of 20 solenoid valves and a PLC was only 74,000 yuan. Therefore, in May 1997, the factory decided to adopt the PLC + solenoid valve control scheme, and the factory itself undertook all the design modifications, installation, and commissioning. The raw material homogenization control system was put into operation in December 1997 and has been running normally for over a year, with good homogenization effect. 1. Homogenization Principle of the Mixing Chamber Silo The mixing chamber homogenization silo mainly includes: a storage silo, a mixing chamber, a top distributor, an internal aeration system, and a side unloading device. The internal aeration system includes: an annular unloading aeration trough, a mixing aeration trough for the mixing chamber, and a tunnel conveying aeration trough. Raw material is fed into the top distributor and uniformly distributed in a fluidized state into the conveying chute, entering the storage silo through the chute's discharge port to form a material layer. The bottom annular aeration trough is divided into four zones, supplied with air by one Roots blower. Each zone includes three aeration units. The circulating aeration of individual aeration units is controlled by solenoid valves, cutting the material layer into sections and unloading it into the mixing chamber. The mixing chamber aeration trough is also divided into four zones, supplied with air by two Roots blowers. Controlled by solenoid valves, the raw materials in the aeration and mixing chamber are alternately aerated and mixed in a "one zone strong, three zones weak" manner to form a fluidized material layer of a certain height, which is then discharged from the unloading port in the tunnel area. 2 PLC Control Electrical Design 2.1 Hardware Design To meet the requirements of PLC control and connection with the S7400PCS system and equipment control, S1 automatic/manual/local switching and S2 central control/local control switching are set. When S1 is in the automatic position, S2 can select the central control computer start/stop operation or the local control PLC control cabinet start/stop operation. When S1 is in the manual position, the equipment can be started and stopped by the buttons on the PLC control cabinet. When S1 is in the local position, the equipment can be started and stopped by the buttons on the local control box. A Mitsubishi PLC: FX2-32MR extended FX-16EYR is selected to control 4 Roots blowers and 20 solenoid valves. 2.2 Software Design The program design adopts ladder diagram language. Based on the control principle, the program design consists of four parts: 1) Outer loop sequential control section; 2) Inner loop "one strong, three weak" control section; 3) Roots blower motor control section; 4) Mode switching and alarm detection section. To adapt to changes in production conditions, the time in the outer and inner loops of the program can be adjusted at any time and has a memory function. The homogenization cycle is 55 minutes. 3. PLC System Installation and Debugging After the electrical design is completed, the control system can be installed and debugged. Install the PLC in the control cabinet, connect the power supply and input/output control lines, and input the control program for debugging. First, use simulation debugging, that is, cut off the output power, simulate various input signals and test all output signals to see if the functions of each part of the program meet the requirements of the control process, in order to examine the integrity and reliability of the PLC control program. Then, turn on the PLC output power and perform no-load linkage test, and finally perform load linkage test. 4. Usage Effect 1) After the PLC control system is put into operation, the CaCO3 index of the raw material leaving the warehouse is all qualified, the homogenization coefficient can reach 5.4, and the system is running well. 2) The time parameters of each inflation unit can be adjusted at any time according to process requirements and have a memory function, unaffected by power outages or other factors, and parameter modification is convenient. Different combinations of inflation sequences for each zone's inflation units can achieve various homogenization methods. The unloading speed of the annular zone can also be controlled to ensure thorough mixing of the raw material in the mixing chamber, maintaining a certain fluidized material layer height, guaranteeing homogenization effects, and meeting process requirements. 3) Software-based control simplifies control equipment, saves equipment investment, increases equipment reliability, reduces maintenance workload, and lowers maintenance costs. The system is flexible in switching, simple and convenient to operate, and easy for operators to master.