The BOG (boil-off gas) recovery process has strict requirements on the performance, reliability, and adaptability of the compressor to ensure that BOG can be efficiently and stably recovered and processed. The following is a detailed introduction:
Performance requirements
1. Compression ratio: During the BOG recovery process, different subsequent treatment processes have different pressure requirements for BOG. For example, if BOG is used for recondensation storage after recovery, it is usually necessary to compress BOG to a higher pressure, which requires the compressor to have a higher compression ratio. Generally speaking, for such application scenarios, reciprocating compressors can provide a higher compression ratio and can meet the needs of compressing BOG to a higher pressure.
2. Flow rate: The amount of BOG generated varies depending on factors such as storage scale and environmental conditions. In large-scale LNG storage facilities, the amount of BOG generated is large, which requires the compressor to have a large enough flow rate to ensure that the generated BOG can be processed in time. Centrifugal compressors and screw compressors have advantages in handling large BOG flows. They can operate continuously at higher speeds to achieve larger gas flows.
3. Efficiency: The efficiency of the compressor directly affects the energy consumption and operating costs of the BOG recovery process. An efficient compressor can compress BOG to the required pressure while consuming less energy. For example, some new screw compressors and centrifugal compressors have greatly improved the efficiency of the compressor and reduced energy consumption by adopting advanced design concepts, optimized impeller and screw structures, and efficient sealing technology. When selecting a compressor, its efficiency performance under different working conditions should be comprehensively considered to ensure efficient and energy-saving operation throughout the BOG recovery process.
Reliability requirements
1. Continuous operation capability: BOG is generated continuously. In order to ensure that BOG can be recovered and processed in a timely manner and avoid safety hazards or affect the normal operation of storage facilities due to BOG accumulation, the compressor needs to have the ability to operate continuously and stably for a long time. This requires that the durability and reliability of key components should be fully considered during the design and manufacturing process of the compressor, and high-quality materials and advanced manufacturing processes should be used to ensure that the compressor can maintain stable performance during long-term continuous operation. For example, the centrifugal compressors used in some large LNG receiving stations have greatly improved the continuous operation capability and reliability of the compressors by adopting high-precision impeller processing technology, advanced bearing and sealing technology, and perfect lubrication and cooling systems, etc., which can meet the needs of long-term continuous and stable operation under complex working conditions of large LNG receiving stations.
2. Low failure rate: During the BOG recovery process, once the compressor fails, it will not only cause the BOG recovery process to be interrupted and affect the normal operation of the storage facilities, but may also cause safety accidents, resulting in serious casualties and property losses. Therefore, the compressor needs to have the characteristics of low failure rate to ensure reliable operation throughout the BOG recovery process. In order to achieve a low failure rate, compressor manufacturers usually take a series of measures in product design, manufacturing, quality control and after-sales service. In the product design stage, the operating reliability of the compressor under various working conditions will be fully considered, and advanced design concepts and calculation methods will be adopted to optimize the design of the key components of the compressor to ensure that it has good mechanical properties and stability during operation. In the manufacturing stage, in strict accordance with the requirements of the quality control system, high-quality raw materials and advanced manufacturing processes will be used to finely process and assemble the various components of the compressor to ensure that the quality of each component meets the design requirements. In terms of quality control, a complete quality inspection system will be established to conduct strict quality inspections on all links of the compressor manufacturing process, including raw material inspection, component processing size and precision inspection, assembly quality inspection, and whole machine performance test, etc., to ensure that only compressors that pass all quality inspections can enter the market for sale. In terms of after-sales service, a professional after-sales service team will be established to provide users with timely, efficient and high-quality after-sales service. The after-sales service team will regularly visit and maintain the compressors used by users, promptly discover and solve problems that arise during the operation of the compressors, and ensure that the compressors are always in good operating condition. At the same time, the after-sales service team will also provide users with technical consulting and training services to help users better understand and use compressors, improve users' operating skills and maintenance levels, thereby further reducing the failure rate of the compressors and ensuring that they can operate reliably during the BOG recovery process.
Adaptability requirements
1. Gas composition adaptability: The composition of BOG is not fixed, and it will be affected by many factors such as the source of LNG, production process, and storage conditions. For example, the content ratio of hydrocarbon gases such as methane, ethane, and propane in LNG from different origins may be different, and it may also contain a small amount of impurity gases such as nitrogen, carbon dioxide, and hydrogen sulfide. Changes in these components will affect the performance and reliability of the compressor. Therefore, the compressor needs to have good adaptability to gas composition and be able to maintain stable operating performance and high reliability when the BOG composition changes. In order to achieve this goal, compressor manufacturers usually fully consider the impact of BOG composition changes during the product design stage, adopt advanced design concepts and calculation methods, and optimize the design of key components of the compressor to ensure that they have good mechanical properties and stability under different gas composition conditions. For example, for BOG that may contain corrosive gases such as hydrogen sulfide, in the design and material selection process of the compressor, materials with good corrosion resistance, such as stainless steel, alloy steel, etc., will be selected to manufacture parts that come into contact with BOG, such as impellers, volutes, screws, etc., to prevent these parts from being damaged by corrosive gases such as hydrogen sulfide during operation, thereby ensuring that the compressor can operate reliably in a BOG environment containing corrosive gases. At the same time, during the operation of the compressor, the BOG composition can be monitored in real time, and the operating parameters of the compressor, such as speed, inlet and outlet pressure, temperature, etc., can be adjusted in time according to the monitoring results to optimize the operating performance of the compressor so that it can better adapt to the changes in BOG composition.
2. Adaptability to working conditions: The operating conditions of the BOG recovery system will change due to many factors, such as changes in ambient temperature and pressure, fluctuations in the LNG liquid level in the storage facility, and instability in the amount of BOG produced. These changes in working conditions will challenge the operating performance and reliability of the compressor. Therefore, the compressor needs to have good adaptability to working conditions, be able to operate stably under different working conditions, and maintain high performance and efficiency. In order to meet this requirement, the compressor is usually equipped with some advanced control technologies and adjustment devices to achieve precise control and adjustment of the compressor operating parameters so that it can adapt to changes in different working conditions. For example, some centrifugal compressors and screw compressors are equipped with adjustable inlet guide vanes (IGV) or slide valve adjustment devices. By adjusting the opening of the IGV or the position of the slide valve, the intake volume and compression ratio of the compressor can be changed, so that the compressor can automatically adjust the operating parameters according to different working conditions, maintain a stable operating state and high performance efficiency. At the same time, some compressors are also equipped with advanced intelligent control systems, which can monitor the operating parameters of the compressor in real time, such as inlet and outlet pressure, temperature, flow, speed, etc., as well as the operating status of key components of the compressor, such as vibration, temperature, wear, etc. Through real-time analysis and processing of these monitoring data, the intelligent control system can promptly detect abnormal conditions that occur during the operation of the compressor, and automatically adjust the operating parameters of the compressor according to the preset control strategy, or send an alarm signal to remind the operator to take corresponding measures to ensure that the compressor can operate safely, stably and efficiently under different working conditions.
Safety and environmental protection requirements
1. Explosion-proof performance: BOG is mainly composed of combustible gases such as methane, which are flammable and explosive. During the BOG recovery process, once the compressor fails or is improperly operated, BOG may leak and form a combustible mixture with air. When encountering a fire source (such as static electricity, open flames, sparks generated by electrical equipment, etc.), it is very easy to cause combustion or even explosion accidents, posing a serious threat to the safety of life and property. Therefore, the compressor used for BOG recovery must have good explosion-proof performance to ensure safe and reliable operation throughout the recovery process. In order to achieve this goal, compressor manufacturers usually strictly follow relevant explosion-proof standards and specifications during product design and manufacturing, such as China's GB 3836 series standards and the IEC 60079 series standards of the International Electrotechnical Commission (IEC), and take a series of effective explosion-proof measures. For example, in the structural design of the compressor, a flameproof structure is adopted to place electrical components that may generate sparks, arcs or dangerous high temperatures (such as motors, junction boxes, control switches, etc.) in a flameproof enclosure with sufficient strength. The design and manufacture of the flameproof enclosure must meet the requirements of relevant explosion-proof standards to ensure that when an explosion occurs inside the enclosure, the flame and pressure generated by the explosion will not spread to the outside of the enclosure through the gap of the enclosure, thereby avoiding igniting the combustible mixture outside the enclosure and causing an explosion accident. At the same time, during the manufacturing process of the compressor, the processing size, precision and assembly quality of the flameproof enclosure will be strictly controlled and tested to ensure that the performance of the flameproof enclosure meets the requirements of relevant explosion-proof standards. In addition, in order to further improve the explosion-proof performance of the compressor, a series of measures will be taken in the design of the electrical system of the compressor, such as selecting electrical equipment and components with explosion-proof performance, reasonably arranging and protecting electrical circuits, and adopting intrinsically safe circuit design, etc., to ensure that during the operation of the compressor, the electrical system will not generate sparks, arcs or dangerous high temperatures sufficient to ignite the combustible mixture, thereby effectively preventing the occurrence of explosion accidents.
2. Low leakage rate: BOG contains greenhouse gases such as methane, which leak into the atmosphere will have a negative impact on the environment and aggravate the greenhouse effect. In addition, BOG leakage may also lead to the formation of combustible mixed gas, increase the risk of fire and explosion, and pose a threat to the safety of life and property. Therefore, in the BOG recovery process, the compressor is required to have a low leakage rate to reduce the harm caused by BOG leakage to the environment and safety. In order to achieve a low leakage rate, compressor manufacturers usually take a series of effective sealing measures in the product design and manufacturing process, select high-performance sealing materials and advanced sealing structures to ensure that the compressor can effectively prevent BOG leakage during operation. For example, in the shaft seal of the compressor, mechanical seals or packing seals are usually used for sealing. Mechanical seals are a commonly used and efficient sealing method. They are mainly composed of static rings, dynamic rings, elastic elements (such as springs, bellows, etc.) and auxiliary seals (such as O-rings, rubber pads, etc.). During the operation of the compressor, the dynamic ring rotates with the shaft, and the static ring is fixed on the compressor housing. A small gap is formed between the dynamic ring and the static ring. Through the elastic force of the elastic element, the dynamic ring and the static ring are tightly fitted together, thereby effectively preventing BOG from leaking from the shaft seal. At the same time, the role of the auxiliary seal is to further improve the sealing effect and prevent BOG from leaking from the gap between the static ring and the housing and between the dynamic ring and the shaft. In addition, in order to ensure the performance and reliability of the mechanical seal, the material selection, structural design, installation and commissioning of the mechanical seal will be strictly controlled and tested during the design and manufacturing process of the compressor. For example, in terms of material selection, materials with good wear resistance, corrosion resistance and high temperature resistance, such as silicon carbide, cemented carbide, polytetrafluoroethylene, etc., will be selected according to the properties of BOG and the operating conditions of the compressor to manufacture the dynamic ring, static ring and auxiliary seals of the mechanical seal, so as to ensure that these components can maintain good performance during long-term operation and effectively prevent BOG leakage. In terms of structural design, the structure of the mechanical seal will be optimized according to the shaft diameter, speed, pressure, temperature and other parameters of the compressor, to ensure that the mechanical seal can effectively balance the axial force and radial force during operation, reduce the wear between the dynamic ring and the static ring, and improve the sealing effect and reliability. In terms of installation and commissioning, the mechanical seal will be installed and commissioned in strict accordance with the installation instructions of the mechanical seal and the requirements of relevant standards and specifications. During the installation process, it is ensured that the various components of the mechanical seal are installed correctly and firmly, the gap between the dynamic ring and the static ring is uniform, and the compression of the elastic element meets the design requirements. During the commissioning process, the operation of the mechanical seal will be closely observed to check whether the mechanical seal has leakage, abnormal vibration or heating. If problems are found, they will be adjusted and handled in time to ensure that the mechanical seal can work reliably during the operation of the compressor and effectively prevent BOG leakage. In addition to the shaft seal, corresponding sealing measures will be adopted in other connection parts of the compressor, such as the connection parts between the inlet and outlet pipes and the compressor, and the connection parts between the compressor shell and the end cover, so as to ensure that these parts will not leak BOG during the operation of the compressor. At the same time, during the manufacturing and assembly process of the compressor, the processing dimensions, precision and assembly quality of these connection parts will be strictly controlled and tested to ensure that the sealing performance of the connection parts meets the requirements of relevant standards and specifications. In addition, in order to timely discover and deal with BOG leakage problems that may occur during the operation of the compressor, corresponding leakage detection and alarm devices will be set in the system design of the compressor. These devices usually use advanced sensor technology, such as gas concentration sensors, pressure sensors, flow sensors, etc., which can monitor the leakage of BOG in the compressor system in real time. When the BOG leakage concentration is detected to exceed the set alarm threshold, the leakage detection and alarm device will immediately send out an audible and visual alarm signal to remind the operator to take appropriate measures in time, such as finding the leakage point, repairing the sealing device, stopping the compressor operation, etc., to prevent the BOG leakage from further expanding and reduce the harm to the environment and safety.
