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Selection principles for screw compressors. As an essential piece of equipment in modern industrial production, screw compressors are widely used in industries such as chemicals, petroleum, metallurgy, and machinery manufacturing, thanks to their advantages of compact structure, stable operation, and high energy efficiency. The correct selection not only ensures the efficient and stable operation of the equipment, but also reduces energy consumption and maintenance costs, as well as enhancing production safety. By integrating technical standards and engineering practices, this article systematically explains the selection principles for screw compressors, providing a scientific reference for users. I. Basic Principles: Aligning Requirements with Performance. The first step in selection is to clarify the process requirements; key parameters include the gas medium, exhaust pressure, exhaust volume, and operating environment temperature. The physical properties of different media (such as specific heat capacity and compressibility coefficient) have a direct impact on compressor design. Especially for flammable, explosive, toxic, and harmful gases, safety must be given top priority. In accordance with international standards such as API 619, the unit design must meet lifetime requirements of 20 years of continuous operation and 3 years of uninterrupted operation to ensure long-term reliability. Furthermore, there should be no negative deviation in flow rate and head, while the shaft power tolerance should be maintained within the range of +4% to 0, in order to avoid either excessive or insufficient performance. II. Structure and Materials: Meeting the Special Requirements of Operating Conditions 1. In situations with high inlet and exhaust pressure differences: When the compression ratio is high, the rotor should be manufactured using a solid forging process to enhance its fatigue resistance and prevent failure due to stress concentration. The radial split structure is suitable for low molecular weight and high exhaust pressure conditions, enhancing the sealing of the housing and reducing the risk of leaks. 2. Wet oil-free design: Large wet oil-free compressors feature an inlet at the top and an outlet at the bottom, which prevents fluid accumulation in the pipes from causing corrosion to the equipment and thus extends the maintenance interval. 3. Bearing and sealing system: The selection of bearings follows the API 619 standards; rolling bearings must meet the required design life, while sliding bearings employ a tilting-pad design to accommodate bidirectional axial thrust. The shaft seal design must be customized based on the site conditions to ensure zero leakage of process gases and prevent any infiltration of the sealing medium, while also adapting to start-up/shutdown operations and various special operating conditions. III. Power Matching and Transmission Optimization 1. The selection of drive equipment is crucial. When driven by an electric motor or turbine, the nameplate rating should be at least 110% of the compressor’s rated shaft power, with a power margin provided to handle sudden loads. 2. The gearbox must comply with the API 613 standard, and its rated power has also been increased by 10% to ensure reliable transmission. 3. The coupling complies with API 671 standards, reducing vibration transmission and extending the equipment’s lifespan. 4. Critical speed and torsional analysis must be conducted to ensure that the operating speed is well away from the resonance frequency, thereby preventing mechanical damage. 5. Rotating components, such as male and female rotors, couplings, gears, etc., should all be dynamically balanced separately. IV. Energy Efficiency and Environmental Protection: Sustainability Considerations 1. Energy efficiency optimization: Prioritize the use of high-efficiency motors and variable frequency drive systems to reduce energy consumption. Multiple unit combinations are arranged based on fluctuations in gas demand, and an intelligent control system is used to achieve dynamic adjustment of the load, thereby reducing idle losses. 2. Noise and vibration control: Silencers, soundproof enclosures, or vibration-isolating bases are used to keep noise levels below 85 dB, in compliance with occupational health standards. 3. Environmental compliance: The lubricating oil system meets API 614 requirements, reducing the risk of oil contamination. The exhaust gases must comply with local environmental regulations; where necessary, post-treatment devices such as oil removal purifiers and dryers should be installed to reduce pollutant levels. V. Auxiliary Systems and Maintenance Convenience 1. Lubrication and Cooling Systems: The oil circuit design must ensure adequate lubrication of all components, with a clear schedule for replacing the oil filters. A forced cooling system is used under high-temperature operating conditions to maintain stable oil temperature. 2. Monitoring and maintenance: Install an intelligent monitoring system to detect parameters such as pressure, temperature, and vibration in real time, thereby providing early warnings of potential failures. Universal design of spare parts reduces spare part costs and shortens downtime for repairs. 3. Installation and space adaptation: The equipment dimensions are matched to the plant layout, with maintenance passages and spaces reserved to facilitate disassembly and routine inspections. VI. Special Design for Special Operating Conditions 1. Corrosive media: Use corrosion-resistant materials (such as duplex stainless steel and Hastelloy), with enhanced protection for seals and coatings. 2. High-temperature and high-pressure environment: The compressor unit is equipped with a cooling structure, as well as high-temperature bearings and lubricants, to ensure stability under extreme operating conditions. 3. Treatment of trace impurities: High-efficiency filters are installed at the air inlet, and the heat exchangers are regularly backwashed or chemically cleaned to prevent scaling and blockages from affecting performance. VII. Brand and After-sales Service: Long-term support system. Choose qualified brand suppliers whose products have passed certifications such as ISO and API. A comprehensive after-sales service network provides regular inspections, emergency repairs, and technical upgrade support to ensure the full-life-cycle management of the equipment. The contract specifies the spare parts supply timeline and technical training provisions, thereby reducing operational risks for users. VIII. Economic evaluation: Life cycle cost – When making a selection, it is necessary to balance the initial investment with long-term costs. Although high-performance models have a higher purchase price, their lower energy consumption and maintenance costs result in a more favorable total cost of ownership (TCO). Through technical-economic analysis, indicators such as energy consumption, maintenance costs, and downtime losses for different options are quantified, in order to select the option with the best overall benefits. Conclusion: The selection of screw compressors is a systems engineering task that requires comprehensive evaluation from multiple aspects such as process requirements, equipment performance, safety and environmental protection, and cost-effectiveness. Only by adhering to standardized design, adapting to specific operating conditions, and enhancing energy efficiency and maintenance considerations can a perfect match be achieved between the equipment and the production environment. In the future, with the advancement of intelligent technologies, compressors will evolve toward predictive maintenance and remote monitoring. Users can further leverage digital tools to improve equipment management efficiency, thereby supporting the sustainable development of industrial production.