Abstract: This article introduces the characteristics of variable frequency speed regulation and the process control methods in urea synthesis, the working principle of the frequency converter in the urea synthesis tower, and how to achieve the constant pressure energy-saving principle of the pump, and achieve practical benefits. Keywords: frequency converter; urea synthesis; energy saving. Variable frequency speed regulation is a method that changes the power frequency from 0 to 50 Hz by changing the conduction state, causing the motor speed to increase from the initial value to the maximum value. Its speed regulation principle conforms to the asynchronous motor speed formula n=60f/p. Changing the power supply frequency f can change the motor speed, thereby realizing AC speed regulation of the asynchronous motor. Due to the high efficiency of the frequency converter, the absence of additional slip loss due to speed regulation, the wide speed range, high precision, good stability, strong logic operation capability, and self-diagnosis and fault recording, the frequency converter is gradually occupying a dominant position in the field of speed regulation. This article uses a frequency converter to control the circulation of the solution in urea synthesis production, which is suitable for the process and has energy-saving effects. 1. Process Control Principle In the urea synthesis tower, ammonia and carbon dioxide react to produce urea and water, with a single-stage synthesis rate of only about 68%. Unreacted ammonia and carbon dioxide are separated and recycled for urea synthesis. Returning to the synthesis tower to participate in the reaction improves the utilization rate of the raw material gas; this method is called the aqueous solution full-cycle method. Figure 1 shows the flow chart of urea synthesis using the aqueous solution full-cycle method. The synthesis gas from the urea synthesis tower enters a decomposition tower, where unreacted NH3 and CO are separated to form an ammonium carbamate solution. After concentration, this is called primary ammonium carbamate solution (PM2.5), which flows out from the first-stage absorption tower. A pump driven by a variable frequency motor pumps the PM2.5 solution back into the urea synthesis tower. Part of the ammonium carbamate solution in the first-stage absorption tower enters the second-stage absorption tower via the second-stage decomposition tower. The PM2.5 solution flowing out from the second-stage absorption tower is recycled back to the first-stage absorption tower by a PM2.5 pump driven by a variable frequency motor, and then pumped back into the urea synthesis tower by the PM2.5 pump again. Through these two circuits, NH3 and CO are recycled, improving the overall conversion rate of the raw material gas reaction. The key technology in this process is that the frequency of the inverter changes according to the changes in the liquid levels in the first and second stage absorption towers, maintaining the NH3, CO, and H2O components in the primary and secondary urea solutions within the required concentration range. Its control principle is: [b][align=center]For details, please click: Application of Frequency Converters in Urea Synthesis Process Control[/align][/b]