The internal high-pressure system of the explosion-proof electric heater can provide alarm signals such as operation, high temperature, fault, and shutdown to the DCS system, and can also accept operation commands such as automatic and shutdown issued by DCS. In addition, a reliable and safe monitoring device has been added to the explosion-proof electric heater system, but the price of the explosion-proof electric heater is relatively high.
For the control system of the outlet water temperature of the duct electric heater, we can analyze it by taking the water outlet temperature as the controlled parameter and the fuel flow as the manipulated variable. At the same time, this system also belongs to the temperature control system, which has the characteristics of large lag, long pure delay time, large disturbance amplitude, frequent and drastic load changes. For production processes with complex dynamic characteristics, multiple disturbances or large disturbance amplitudes, and high control quality requirements, simple control systems cannot achieve good performance and cannot meet the process control accuracy requirements. The cascade control system belongs to a complex control system, used for controlled processes with large capacity lag, long pure delay time, large disturbance amplitude, and frequent and drastic load changes. Therefore, a cascade control system can be considered in this case.
If external interference occurs in the explosion-proof electric heater, causing damage to the steady-state operating condition, the cascade control system will start control immediately. Depending on the location of the disturbance application point, this system realizes the function of controlling the temperature inside the explosion-proof electric heater and the function of controlling the outlet water temperature of the explosion-proof electric heater. Selection of controlled variables and manipulated variables: The main controlled variable is the outlet water temperature, the secondary controlled variable is the temperature inside the heater, the main manipulated variable is the opening of the fuel valve, and the secondary manipulated variable is the opening of the water supply valve. The temperature sensor for the explosion-proof electric heater uses a platinum resistance Pt1000. Because the physical and chemical properties of platinum thermal resistance are very stable in high temperature and oxidizing media, it can be used as an industrial temperature measurement element, and this element has good linearity. At 0-100 degrees Celsius, the upper limit nonlinear error is less than 0.5 degrees Celsius.
