Multi-dimensional comparative analysis of systematic energy saving of centrifugal compressors

Multi-dimensional comparative analysis of systematic energy saving of centrifugal compressors

With the continuous development of my country's industry, enterprises themselves not only face fierce competition in the market, but also put forward strict requirements on their own production and operation costs. "Throttling" means "open source". As a general air compression equipment, centrifugal air compressors (hereinafter referred to as centrifuges) are more and more favored by users due to their oil-free compressed air and high operating efficiency.

However, most users only have a conceptual understanding of "the centrifuge is very energy-efficient", knowing that the centrifuge is more energy-efficient than other compression forms such as oil-free screw compressors, but there is no systematic consideration of this issue from the product itself to actual use. .

　　 This article will briefly explain the impact of these four factors on "whether the centrifuge is energy-saving" from four perspectives: the comparison of commonly used compression forms, the differences of centrifuges of various brands on the market, the design of the centrifuge air compressor station, and the daily maintenance.

　　 1. Comparison of different compression formats

　　The oil-free compressed air market mainly includes screw compressors and centrifuges. The approximate air volume ranges are shown in Table 1.

Multi-dimensional comparative analysis of systematic energy saving of centrifugal compressors

　　 It can be seen from Table 1 that the oil-free screw compressor mainly meets the demand for small air volume. At present, the competition of various brands in the oil-free screw market is mainly concentrated in 75kW～315kW.

　　 The minimum centrifuge can be 25m3/min. So, when the required air volume is 50～70m3/min, is it more appropriate to choose multiple oil-free screws or a centrifuge.

Multi-dimensional comparative analysis of systematic energy saving of centrifugal compressors

　　1) Analysis from the perspective of air compression principle

　　 Regardless of the design of the screw rotor profile and internal pressure ratio of each brand, the screw rotor clearance is a key factor affecting efficiency. The higher the ratio of rotor diameter to clearance, the higher the compression efficiency. Similarly, the larger the diameter of the centrifuge impeller and the ratio of the gap between the impeller and the volute, the higher the compression efficiency.

　　2) Comparison of the efficiency of the two compression methods

　　 Taking a gas demand of 68m3/min and 8barg as an example, the power consumption of the centrifuge and screw machine scheme is compared, see Table 2.

Multi-dimensional comparative analysis of systematic energy saving of centrifugal compressors

　　It can be seen from Table 2:

When a.68m3/min is required, the centrifuge efficiency is higher than the screw machine.

　　B. According to the effect of the compression gap on the efficiency, it can be judged: the larger the screw diameter, the higher the efficiency; the smaller the centrifuge gas volume and the smaller the impeller diameter, the larger the gap ratio, and the efficiency is gradually decreasing.

　　C. It can also be seen from Table 3 that the centrifuge and screw machine basically maintain the same level of change under different working conditions.

　　3) Comprehensive efficiency comparison between theory and practice

　　A simple comparison of machine efficiency cannot reflect the results of actual use. From the perspective of actual use, 80% of users' actual gas consumption fluctuates. See Table 4 for a schematic diagram of typical user gas demand fluctuations. However, the safety adjustment range of the centrifuge is only 70% to 100%. When the air consumption exceeds the adjustment range, a large amount of venting will occur. Venting is a waste of energy, so the overall efficiency of this centrifuge is not high.

If the user fully understands their own gas consumption fluctuations, the combination of multiple screw machines, especially the N+1, that is, N fixed-frequency screw + 1 variable-frequency machine, the variable-frequency screw adjusts the gas volume in real time The overall efficiency is higher than the centrifuge.

　　 Therefore, the centrifuge does not save energy in the bottom section. It cannot be purely from the equipment point of view, but the fluctuation of actual gas consumption must be fully considered. If you want to use a 50-70m3/min centrifuge, you need to ensure that the gas consumption fluctuates within the fluctuation range of 15-21m3/min, that is, try to ensure that the centrifuge is not empty. If the user predicts that his gas consumption fluctuates more than 21m3/min, the screw compressor solution will be more energy-efficient.

　　 2. Different configurations of centrifuge

　　 The centrifuge market is mainly occupied by several major international brands, such as Atlas Copco of Sweden, IHI-Sullair of Japan, Ingersoll Rand of the United States and so on. According to the author's understanding, each brand basically only produces the centrifuge impeller part with core technology, and other parts adopt the global supplier procurement model. Therefore, the quality of the parts also has an important influence on the efficiency of the whole machine.

　　1) The high-voltage motor driving the centrifuge head

　　The efficiency of the motor has a great influence on the overall efficiency of the centrifuge. With motors with different efficiencies, the input power calculation difference of the whole machine is shown in Table 3.

Multi-dimensional comparative analysis of systematic energy saving of centrifugal compressors

　　 It can be seen from Table 5 that the high-efficiency motor can effectively ensure the lowest input power of the whole machine during long-term use of the centrifuge, thereby improving the operating efficiency of the whole machine.

　　 GB 30254-2013 "High-voltage three-phase cage asynchronous motor energy efficiency limit value and energy efficiency grade" promulgated by the National Standards Committee has made a detailed division of each motor grade. Among them, motors with level 2 energy efficiency or higher are defined as energy-saving motors. It is believed that with the continuous improvement and promotion of this standard, motors will serve as an important criterion for determining whether the centrifuge is energy-saving.

　　2) Transmission mechanism—coupling and gear box

　　The centrifuge impeller is driven by gears. Therefore, the transmission efficiency of the coupling, the transmission efficiency of the high and low speed gear system, the form of the bearing and other factors will further affect the efficiency of the centrifuge. However, the design parameters of these parts are regarded as confidential data of various manufacturers and are not disclosed to the public. Therefore, only simple judgments can be made from the actual use process.

　　A. Coupling: From the perspective of long-term operation, dry laminated couplings have higher transmission efficiency than gear couplings, and gear couplings have a faster transmission efficiency.

　　B. Gear speed increasing system: If the transmission efficiency drops, the machine will have high noise and vibration, the vibration value of the impeller will increase in a short time, and the transmission efficiency will decrease.

　　C. Bearing: Multi-piece sliding bearing is adopted, which can effectively protect the stable oil film of the high-speed shaft driving the impeller, and will not cause wear to the bearing bush when starting and stopping.

Multi-dimensional comparative analysis of systematic energy saving of centrifugal compressors

　　3) Cooling system

　　 The impeller of each stage of the centrifuge needs to be cooled after compression, and then enter the next stage for compression.

　　A. Cooling: The design of the cooler should fully consider the influence of the intake air temperature and cooling water temperature in different seasons on the cooling effect.

　　B. Pressure drop: When the gas passes through the cooler, the gas pressure drop should be minimized.

　　C. Precipitation of condensed water: The more condensed water is deposited during the cooling process, the greater the proportion of the work done by the next-stage impeller to the gas, the higher the gas compression efficiency.

　　D. Drain the condensed water: quickly drain the condensed water out of the cooler without generating compressed air leakage.

The cooling effect of the cooler has a great influence on the efficiency of the whole machine, and it also tests the technical strength of each centrifuge manufacturer.

Multi-dimensional comparative analysis of systematic energy saving of centrifugal compressors

　　4) Other factors affecting the efficiency of the centrifuge

　　A. The form of the intake control valve: the multi-disc intake guide vane valve can pre-rotate the gas during adjustment, reduce the rectification of the first-stage impeller, and reduce the pressure ratio of the first-stage impeller, thereby improving the efficiency of the centrifuge.

　　B. Interstage piping: A compact design of the interstage piping system can effectively reduce the pressure loss in the compression process.

　　C. Adjustment range: A wider adjustment range means less risk of venting, and it is also an important indicator for testing whether a centrifuge has energy saving capabilities.

　　D. Internal surface coating: The exhaust temperature of each stage of the centrifuge is 90～110℃, and a good internal temperature-resistant coating is also a guarantee for long-term efficient operation.

Multi-dimensional comparative analysis of systematic energy saving of centrifugal compressors

　　 Three, air compressor station design stage

　　 The system design of the centrifugal air compressor station is still in a relatively extensive stage, mainly reflected in:

　　1) Gas production and demand do not match

　　The air volume of an air compressor station will be counted during the design stage, multiplied by the coefficient of simultaneous use, and other data, which has left enough margin. However, in actual purchase, the maximum and most unfavorable conditions must be met, plus the centrifuge selection factor. Therefore, from the actual results, the actual gas consumption is mostly less than the gas output of the purchased compressors. In addition to the actual gas consumption fluctuations and the differences in the adjustment capabilities of the centrifuges of various brands, the centrifuges are vented in stages.

Multi-dimensional comparative analysis of systematic energy saving of centrifugal compressors

　　2) The exhaust pressure does not match the gas pressure

Many centrifuge air compressor stations have only 1 to 2 pressure pipe networks to select centrifuges based on the highest pressure point, but in fact, the highest pressure point requires a small proportion of air volume, or there are more low-pressure air At this point, the downstream pressure reducing valve needs to be used to reduce the pressure. According to authoritative data, the total operating energy consumption can be reduced by 8% every time the centrifuge reduces the exhaust pressure by 1 barg.

　　3) The impact of pressure mismatch on the machine

　　 The efficiency of the centrifuge is highest only when it is running at the design point. For example, for a machine with a designed exhaust pressure of 8barg, and the actual exhaust pressure is 5.5barg, the actual operating power consumption of 6.5barg should be referred to.

Multi-dimensional comparative analysis of systematic energy saving of centrifugal compressors

　　 　　4) Inadequate air compressor station management

　　The user thinks that as long as it is a stable gas supply to ensure production, everything else can be released first, and the above-mentioned problems or energy saving points will be ignored. Then, the energy consumption of actual operation will be much higher than the ideal state, and this ideal state could have been calculated through more detailed calculations in the early stage, simulation of actual gas consumption fluctuations, more detailed gas volume, pressure division, and more accurate selection. Type match to achieve.

　　 Fourth, the impact of daily maintenance on efficiency

　　 Daily maintenance also plays an extremely important role in whether the centrifuge can run efficiently. In addition to the conventional three filters and one oil of mechanical equipment, and the replacement of valve body seals, the centrifuge also needs to pay attention to the following points:

　　1) Dust particles in the air

　　After the gas is filtered by the intake filter, there will still be fine dust entering, and after a long time it will be deposited on the impeller, diffuser, and cooler fins, which will affect the air intake and the efficiency of the whole machine.

　　2) Gas characteristics during compression

During the compression process, the gas is in a state of supersaturation, high temperature and high humidity. The liquid water in the compressed air will combine with the acid gas in the air, which will corrode the gas inner wall, impeller, diffuser, etc., affect the intake air volume and reduce efficiency. .

　　3) The quality of cooling water

　　The difference in carbonate hardness and total suspended particulate matter concentration in the cooling water causes fouling and scaling on the water side of the cooler, which affects the heat exchange efficiency and thus the operating efficiency of the entire machine.

　　【Conclusion】

Centrifuge is currently the most efficient type of air compressor on the market. In actual use, if you want to truly achieve "make the most of the material and enjoy the effect", it is not only necessary for centrifuge manufacturers to continue to develop more efficient products; at the same time, more An accurate selection plan is closer to the actual gas demand, and it is especially important to achieve "how much gas is used to produce as much gas, and how high pressure is used to produce high pressure". In addition, strengthening the maintenance of the centrifuge is also a reliable guarantee for the long-term stable and efficient operation of the centrifuge.

According to authoritative statistics, the power consumption of compressed air accounts for 10% of the entire industrial power consumption. As the centrifuge becomes more and more widely used, it is believed that more and more users will not only know that "the centrifuge is very energy-efficient", but also From the perspective of system design, operation and maintenance to achieve the goal of energy saving, improve the competitiveness of the enterprise itself, and make its own contribution to reduce carbon emissions and maintain a green earth!