Abstract : Since blowers are key equipment in fertilizer production, and the outlet gas pressure system is a crucial component, this paper introduces the use of microcomputer technology and frequency converters to stabilize the outlet gas pressure of Roots blowers. This replaces the original method of regulating the auxiliary line, which is significant for saving energy, reducing product costs, improving control quality, and extending the service life of motors and blowers. The main key technology lies in preventing backflow of outlet gas from the variable frequency blower to the variable frequency blower when the variable frequency and fixed frequency blowers are operating in parallel, preventing surge and smooth switching of the variable frequency blower. Keywords : Automatic control; Frequency converter; PLC; Roots blower. In fertilizer production, the blower delivers semi-water gas to the desulfurization and conversion section. First, H₂S in the semi-water gas needs to be removed. Then, CO in the semi-water gas is converted to H₂ and CO using steam under the action of a catalyst. In the carbonization section, the conversion gas is combined with gaseous ammonia (NH₃) from the synthesis process to produce concentrated ammonia water and ammonium bicarbonate, as shown in Figure 1. Therefore, the quality of semi-water gas delivery plays a crucial role in fertilizer production. The stability of the delivered gas pressure directly affects the overall operation of the production process. Roots blowers are key equipment in fertilizer production, and their outlet gas constant pressure system is a vital component of the process. Traditional control methods (manual or automatic) involve changing the flow rate of the bypass gas to ensure pressure stability, as shown in Figure 2. Due to the continuous and complex nature of fertilizer production, influenced by numerous factors, the capacity of the Roots blower must have sufficient margin, which comes at the cost of increased power consumption. Furthermore, the motor and blower operate continuously at full load, reducing equipment lifespan. To save energy, reduce product costs, improve control quality, and extend the lifespan of motors, blowers, and other related equipment, a more ideal and effective control scheme has been designed: using constant pressure variable frequency speed control at the outlet of the Roots blower, which is crucial for fertilizer production capacity and product quality, as shown in Figure 3. [b][align=center]For details, please click: Constant Pressure Control of Fans in Fertilizer Production[/align][/b]