The applicable range of helium compressors is constrained by various technical parameters and operating conditions. Defining these boundary conditions is crucial for correct selection and ensuring reliable equipment operation. The following analysis is conducted from four dimensions: pressure range, flow characteristics, temperature conditions, and medium purity. In practical engineering applications, these parameters are often interrelated and influence each other, requiring systematic and comprehensive consideration to ensure the compressor operates under optimal conditions.
The pressure range is the primary parameter defining the applicability of a helium compressor. Based on the final discharge pressure, helium compressors can be classified into three grades: Low-pressure compressors (0.5-2.0MPa) are primarily used in helium liquefaction systems and cryogenic refrigerators; Medium-pressure compressors (2.0-15.0MPa) are suitable for scientific research experimental setups and semiconductor manufacturing; High-pressure compressors (15.0-35.0MPa) are mainly used in aerospace and specialized research fields. It is important to note that due to the low density of helium, achieving the same pressure grade requires 30-50% more compression stages compared to air compressors, making the structure of high-pressure helium compressors more complex. For example, when compressing helium to 30MPa, 4-6 compression stages are typically required, with the compression ratio per stage controlled between 2.5-3.5, and intercoolers are installed between stages to ensure the discharge temperature at each stage does not exceed 120°C. In ultra-high pressure applications, special consideration must be given to stress corrosion cracking and hydrogen embrittlement of materials, typically selecting high-strength stainless steel or nickel-based alloys.
Flow characteristics directly influence the compressor selection scheme. Small flow applications (<10 m³/min) typically employ piston compressors, which can achieve a volumetric efficiency of 85-92% and reach the required pressure through multi-stage compression. When selecting a piston compressor, particular attention must be paid to its pulsation characteristics. Sufficiently sized buffer tanks and pulsation dampeners must be configured to keep pressure fluctuations within ±1%. The medium flow range (10-100 m³/min) is suitable for screw compressors, whose continuous and stable output characteristics benefit the stability of downstream processes. The rotor profiles of screw compressors require specialized optimization to adapt to the low density of helium, often utilizing asymmetric profile designs to minimize leakage losses. Large flow applications (>100 m³/min) necessitate the use of centrifugal compressors. However, limited by the low molecular weight of helium, multi-shaft, multi-stage structures are often required, with rotational speeds frequently exceeding 20,000 rpm. In such cases, detailed rotodynamic analysis is essential to ensure the operating speed avoids all critical speeds, and active magnetic bearings or tilting pad bearings must be configured to ensure operational stability.
The operating temperature range is another key consideration factor. Standard industrial-grade helium compressors are suitable for ambient temperatures from -20°C to +40°C, requiring corresponding heating and cooling systems. In low-temperature environments, special attention must be paid to the low-temperature toughness of materials, typically selecting low-temperature steels like 16MnDR, which can have a minimum service temperature as low as -50°C. The lubrication system needs to be equipped with oil heating devices to ensure the lubricant temperature is not below 10°C during cold starts. In high-temperature environments, the high-temperature strength of materials and the thermal stability of sealing materials must be considered, usually requiring sealing materials to withstand long-term operation at 150°C. For the compression chamber interior, due to the high thermal conductivity of helium, the discharge temperature must be controlled below 120°C to prevent material performance degradation. Under high-temperature conditions, the effects of thermal expansion must also be specifically considered, reserving appropriate thermal expansion clearances in the structural design.
Medium purity requirements directly influence the compressor's structural design and material selection. For general industrial applications, where purity requirements are typically at the 99.995% (4.5N) level, oil-lubricated compressors coupled with high-efficiency filtration systems can be used. However, this requires configuring multi-stage precision filters, including coalescing filters, activated carbon filters, and membrane filters, to ensure oil content remains below 0.01 mg/m³. High-purity applications (>99.999%, 5N grade) must use oil-free compressors. All gas-wetted surfaces require electropolishing treatment, achieving a surface roughness of Ra < 0.4 μm. Piping systems should employ automatic orbital welding processes, and all connections should use double ferrule fittings to ensure system leak-tightness and cleanliness. For ultra-high purity applications (>99.9999%, 6N grade), special helium purification systems are additionally required, configuring palladium catalyst purifiers and molecular sieve adsorbers to ensure impurity levels are below 1 ppm. In such applications, online mass spectrometers are also necessary for real-time monitoring of gas purity.
The specificities of the operating environment also require key consideration. In laboratory environments, noise control is an important indicator, typically requiring noise levels to be below 75 dB(A). This is achieved through acoustic enclosure design and vibration isolation. Acoustic enclosures often use a double-layer steel plate structure with sound-absorbing material in between, lined with microporous acoustic panels. Compressors used in hazardous areas require ATEX or IECEx certification, utilizing explosion-proof motors and intrinsically safe control systems. The explosion-proof rating typically needs to reach Ex d IIC T4 level, and all electrical equipment must comply with corresponding explosion-proof requirements. For equipment installed in cleanrooms, corresponding cleanliness class requirements must be met, typically needing to achieve ISO Class 6 or higher. This necessitates compressor housings made of stainless steel with polished surfaces, and all interfaces designed to be sealed to prevent particle emission.
Beyond the main parameters mentioned above, some special operating conditions require particular attention. For instance, in offshore platform applications, compressors need corrosion resistance against salt spray, usually requiring a housing protection rating of at least IP56. In mobile applications, compressors need vibration and shock resistance, typically requiring passage of random vibration tests along 3-5 axes. For continuous operation applications, equipment reliability and maintainability must be considered, usually requiring an MTBF (Mean Time Between Failures) of over 8000 hours, and the ability for online replacement of key components.
During the actual selection process, a systematic approach is recommended. First, clarify the process requirements. Then, determine the compressor type and specification based on parameters like pressure, flow rate, and temperature. Finally, make detailed adjustments according to environmental conditions and special requirements. Simultaneously, the total lifecycle cost of the equipment should be considered, including initial investment, operating energy consumption, and maintenance costs, to ensure the selected compressor is optimal both technically and economically. Through such systematic analysis and selection, it can be ensured that helium compressors deliver optimal performance under various operating conditions, meeting the needs of different application fields.
