Which is better: centrifugal compressors or oil-free screw compressors? Reposted

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Which is better, centrifugal compressors or oil-free screw compressors? Whatever a customer buys, whether for domestic use or industrial equipment, there are three key factors that determine their decision to make a purchase: price, quality, and service. So, we say here that centrifugal compressors are better than oil-free screw compressors – but what exactly are their advantages? Let’s explore this starting with the above three elements. I. Price: The price we are referring to here is a broad concept; in reality, it refers to the cost. Here, setting aside the initial purchase cost for now, let’s compare centrifuges and oil-free screw compressors in terms of operating costs and maintenance costs: Operating costs: The operating cost of centrifuges is more than 10% lower than that of oil-free screw compressors. Why 10%? Let’s analyze it. Firstly, all oil-free screw compressors available on the market today use two-stage compression with one stage of cooling, whereas centrifugal compressors employ three-stage compression with two stages of cooling. What does having this extra level mean? It means 6% less compression work can be saved. An oil-free screw compressor has 7 gears, 14–18 bearings, and 4 sets of meshing. A centrifugal compressor has 3 gears, 6 bearings, and 2 meshings. Based on mechanical experience, for each additional set of meshings, mechanical losses increase by about 2%; therefore, the centrifuge can save around 4% in terms of mechanical losses. 6% + 4% = 10%! Careful readers will notice that there is also a “above” in the text we just read. Where does this above all come from? That is, what we just mentioned – that \"for each additional set of meshings, mechanical losses increase by about 2%\" – is based on certain assumptions: the same gear machining precision and the same bearings. The gear machining precision of centrifuges is generally at the AGMA12 level, whereas that of oil-free screw compressors available on the market is usually at the AGMA7 level! As for bearings, centrifugal compressors use sliding bearings, while screw compressors use rolling bearings. This is how the term “above” came about! We did a rough calculation: for a compressor with the same air intake volume of 100 m3/min and exhaust pressure of 7 kgf/cm2, the centrifugal compressor saves over 300,000 yuan in operating costs compared to an oil-free screw compressor! (Calculated based on 8,000 hours of operation per year and 0.7 yuan per kilowatt-hour.) ) Maintenance costs: The annual maintenance costs for centrifuges and oil-free screw compressors are similar; the annual expense is roughly 2–3% of the initial purchase cost. But there is one thing – the design life of the screw compressor’s head is approximately 4 to 5 years (with 8,000 hours of operation per year). What does this mean? It means that a new compressor head must be replaced after five years of operation! From what we’ve learned from the market, the cost of replacing a single head on an oil-free screw compressor is 50–60% of the total price of the compressor; in other words, this amounts to 10–12% per year! In other words, the actual annual maintenance cost for oil-free screw compressors is 13–16%. So, does the centrifuge have the problems mentioned above? The design life of the main components of the centrifuge is over 20 years (8,000 hours of operation per year)! Users of centrifuges don’t have such concerns at all. II. Quality Quality also encompasses two aspects: one is manufacturing quality, which we will not discuss here for now ； The other aspect is the performance quality of the machine itself; we will mainly discuss the differences between centrifuges and oil-free screw compressors from this perspective. When it comes to performance, there are various aspects involved, and the energy consumption mentioned earlier is also part of that. We would like to use the table below for comparison: Noise (A: Centrifugal compressor; B: Oil-free screw compressor). A: Approximately 85–90 decibels; the main source of noise is the main motor, so a sound insulation cover is not necessary, which makes maintenance, inspection, and heat dissipation easier. B: Up to 100 decibels; the main source of noise comes from the air compressor, so a soundproof enclosure is necessary. Maintenance and inspections are difficult, and heat accumulation inside the enclosure can more easily lead to motor burnout. Cleanliness of compressed air: Grade 2 filtration is used, resulting in a final filtration level of over 2 microns; this corresponds to nearly 100% purity. The filtration level at over 0.4 microns is also as high as 90%. B: With a final filtration rating of 10 microns, systems that require clean air need to be equipped with an additional rear filter. Exhaust pressure fluctuations: A: The compression method with constant pressure and variable volume allows for a fairly stable system pressure, with pressure fluctuations remaining within 1–3% (even without an air reservoir). B: With the compression method of constant volume and variable pressure, pressure fluctuations range from 5–10% or more; therefore, an air reservoir is necessary to reduce these fluctuations. Reliability A: Long design life and high reliability. Limited load control ensures the motor is free from overload concerns. B: There is no load limit control, so the motor is prone to overload in winter. The most important point is that the reliability of backup machines is relatively higher compared to centrifuges. Primarily, dust in the intake air can damage the Teflon coating on the surface of the screw rotor, while condensation water in the spare unit’s head can cause the screw to rust. If a standby unit is started without taking certain measures, it may lead to problems such as motor burnout, coupling damage, and screw damage. III. Services Services can also be discussed from the following aspects: 1. The manufacturer’s service capabilities. 2. The serviceability of the machine itself. A centrifuge is a machine featuring high rotational speed, high precision, and high reliability; maintenance personnel must receive specialized training to be competent in carrying out repairs and routine inspections on site. But for customers, the amount of work required for routine daily maintenance is very small. It can be said that we, as the manufacturer, have taken care of all the difficult and troublesome aspects, so the customers don’t need to worry about anything! Put more plainly: centrifuges are easy to maintain. Oil-free screw compressors are different; in particular, their compressors are considered trade secrets, and no one is allowed or authorized to repair or perform maintenance on them. Any issue with the compressor part must be sent abroad for repair or replacement, which is both costly and time-consuming. The cost also lies in this aspect – how can the loss in benefits incurred for the customer due to the air compressor not operating be calculated? IV. Others: “Centrifuges have advantages such as stability, durability, energy efficiency, and easy maintenance; however, the initial cost of machines with a capacity of less than 500 HP is relatively high.” ”“Oil-free screw compressors remain relatively stable when operated over long periods; they are easier to maintain than reciprocating compressors, and their low cost is their main advantage. However, its nose cone has a short lifespan, the replacement cost is high, and the reliability of spare units is low. ” The above statements represent the market’s main feedback regarding centrifuges and oil-free screw compressors. Therefore, from an overall market perspective, increasingly smaller centrifugal compressors will be the mainstream for oil-free air compressors in the future. The oil-free screw compressor, as a revolutionary model that replaced reciprocating compressors in the market for small oil-free air compressors in the past, has gradually declined due to inherent flaws and the harsh demands of the market. The major screw compressor manufacturers around the world ceased research and development 15 years ago and no longer compete in this market. Reposted from: http://www.66kyj.cn/News/20082211097883.shtml