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II. Characteristics of centrifugal compressors: Reciprocating compressors are suitable for applications where the pressure is relatively high and the amount of gas to be compressed is small, whereas centrifugal compressors are generally used in processes where the pressure is lower and the volume of gas to be transported is larger. As chemical production becomes more large-scale, and catalysts become more active at lower temperatures and pressures, the pressure in production systems tends to decrease. Additionally, the increasing scale of production makes centrifugal compressors an even more appropriate choice. Compared to the latter, centrifugal compressors have the following advantages: 1. They have a large gas handling capacity, are small in size, light in weight, and require little space. There is no need for a backup unit. By using a cheaper steam drive instead of an electric motor, the equipment investment, space requirements, construction costs, as well as the costs associated with operators and maintenance can all be **reduced**. 2. It has fewer vulnerable parts, operates smoothly, can run for over a year, is easy to maintain, and thus has low operating costs. 3. Even gas supply, stable operation, easy adjustment, and suitable for automated control. 4. No lubricating oil needs to be injected into the cylinder, so the compressed gas is not contaminated by oil. Therefore, it is the preferred choice for centrifugal compressors in systems where catalyst contamination is a concern. Disadvantages: 1. Due to the losses associated with high-speed airflow, the efficiency of centrifugal compressors is 5-20% lower than that of reciprocating compressors. 2. They are only suitable for applications with large flow rates; otherwise, their mechanical efficiency decreases. A daily methanol production of less than 660 tons (600 tons of ammonia) is not suitable for use. If the load is insufficient, more gas needs to be returned to prevent surging; as a result, little savings in power consumption are achieved, heat recovery is reduced, and there is an imbalance in energy balance. 3. Due to the high operating speed, reaching tens of thousands of revolutions per minute, in addition to the quality of mechanical installation, it is particularly important during normal operation that the compressed gas does not contain dust, liquid droplets, or corrosive substances. 4. The operating conditions change with the gas temperature, pressure, and composition; special attention must be paid during startup/shutdown and in case of accidents to prevent surging and other fluctuations. Due to the lack of a backup unit, any accident can cause the entire system to stop operating. This requires operators to have a thorough understanding of its characteristics, ensuring a successful start-up each time and enabling safe operation under high loads over long periods, in order to maximize its effectiveness.