Container ships, oil tankers, cruisers-now most sea-going ships with an engine power of at least 20,000 kW are equipped with a three-stage air-cooled starter air compressor. Powerful technology can reduce heat and save a lot of costs. Sauer Compressors has long discovered the potential of three-stage air-cooled compressors for the shipping industry, and has been a pioneer in the development of these compressors for nearly 50 years. When Railship I was first put into service on the Travemünde (Germany)-Hanko (Finland) route in 1975, it was the largest rail ferry in the world. The length of about 180m was quite remarkable at the time, but next to today's ULVC (Ultra Large Container Vessels), it is almost like a toy ship. The ferry is equipped with Sauer's three-stage air-cooled compressor, which is the first time in the current era. Nearly five years have passed since then, during which time Sauer Compressor delivered more than 30,000 such starter air compressors. Despite many developments, the basic working principle of the technology has not changed much. “Today, approximately 80% of large container ships are equipped with three-stage air-cooled compressors, which makes it an industry standard,” said Stephan Behrens, global director of commercial shipping business development for Sauer Compressors. However, it will take some time for the three-stage air-cooled start air compressor to be fully completed. Many shipping companies and shipyards insist on using the previously common 2-stage water-cooled compressor instead of switching to the generally advantageous air-cooled compressor.

Sauer 3-stage air-cooled compressor KOBE, JP

Large ships, large engines, and large filling capacity are used to start the ship engine. The compressor fills the air receiver with 30 bar of compressed air. The capacity of the air receiver is determined by the size of the engine. According to the requirements of classification societies, the amount of compressed air must be sufficient for a certain number of engine starts. The increase in international trade since the 1950s led to larger ships and engines, and therefore a higher demand for compressed air. The 2-stage water-cooled compressor is the most common solution for starting larger and larger diesel engines. Due to its relatively low filling capacity, 2-stage air-cooled compressors usually used in small ships are not a viable alternative.

But Sauer Compressors is also eager to use air-cooled compressors in large ships and engines. In the early 1970s, the company proposed the idea of ​​using three-stage air-cooled compressors as the established solution from the industrial sector to commercial shipping. However, despite their successful application on Railship I and several other ships, three-stage air-cooled compressors cannot become the industry standard. “The construction of large cargo ships was transferred to Asia, and the local shipyard just took over the established design standards,” explains Stephan Behrens. It was not until the millennium that multi-stage air-cooled compressors were finally included in the list of standard manufacturers in Asian shipyards. Sauer Compressors was able to convince ship owners and builders not only through reference materials but also through specific demonstrations. To this end, a three-stage air-cooled compressor was installed in the TEU container and displayed on a global scale. "Decision makers can experience the benefits of this technology first-hand, such as how the compressor works reliably at high ambient temperatures, with low vibration, and there is no condensation in the crank drive because the compressor is always adjusted according to the temperature. Ambient temperature" , Stephan Behrens described this field work.

Three-stage compression can reduce the temperature. The three-stage air-cooled compressor is larger and therefore has a higher filling capacity than the two-stage air-cooled compressor. The total heat to be dissipated is divided into three levels instead of two, and the heat dissipation surface area is increased, while the amount of heat generation remains the same. Air is better than water

For many reasons, three-stage air-cooled compressors are better than water-cooled ones. By dividing the total compression ratio by three, the compression temperature of the cylinders and valves of the three-stage air-cooled compressor is 30% lower than that of the two-stage water-cooled compressor, and is likely to reach 250°C. Due to these relatively low temperatures, standard mineral oils will not undergo thermal cracking. As a result, the valve maintenance interval is increased to 4,000 hours, compared to 2,000 hours for water-cooled compressors. Instead of expensive synthetic oils, traditional SAE-30 mineral oils (such as those used in 2-stroke marine diesel engines to cycle lubrication of crank transmissions) can be used to lubricate the compressor. Therefore, no expensive synthetic oil is required. With continuous operation, the long-term maintenance cost of air-cooled compressors is 30% lower than that of water-cooled compressors.

The rapid amortization of air-cooled compressors uses indoor air cooling to start the air compressor to make the cooling water circuit obsolete. "This can save up to $7,500 in installation costs," said Stephan Behrens. In addition, it avoids leakage and troublesome condensate in the crank transmission when traversing different climate zones. Other benefits are reduced space requirements in the machine room, higher reliability, and minimum operating workload for self-regulating air cooling. There is no need to modify the fan output of the engine room ventilation, because the waste heat of the compressor is negligible compared to the heat of the ship's engine. Due to the very high power of the new generation of 3-stage air-cooled compressors, the number of compressors required to reach the refilling capacity required by large ships has been reduced compared to a few years ago. “A 24,000 TEU ship usually only needs three to four start-up air compressors, one of which is only used as a backup”, explains Stephan Behrens.

SAUER Levante-the new compressor with a capacity of up to 460 m³/h Sauer Compressors is a technology leader in the field of three-stage air-cooled compressors and covers the entire market demand range with two series. The models of the new SAUER Levante series are particularly powerful. "By launching our Levante series, we have responded to the continuous development of large ships and are the only manufacturer in the world that has recently launched a newly developed product," said Stephan Behrens. The compressor has been specially developed for commercial transportation and is available in three different types with a capacity between 275 and 460 m³/h and a final pressure of up to 30 bar.g. Due to its compact and space-saving design, the compressor fits any engine compartment. A unique selling point of the design is the use of block coolers in all three stages. By installing the newly developed SAUER CubeCooler between the engine and the compressor, the airflow is optimized and moving parts are shielded. Before going public, Levante compressors have been tested for more than 20,000 hours on Sauer compressor test stands and ships operated by cooperative shipping companies.

SAUER Passat-the classic three-stage air-cooled compressor SAUER Passat three-stage air-cooled compressor is one of the best-selling products of Sauer compressors. With their unique reliability, efficiency and simple operation, these compressors have proven to be responsible "main force". There are five different types of SAUER Passat compressors to choose from, with capacities ranging from 63 to 175 m³/h and final pressures up to 30 bar.g.

Box: Sauer Compressor is a medium-sized German group company with 14 international subsidiaries. The company has more than 135 years of history and more than 85 years of experience in compressed air and gas technology. At present, the focus is on the development, manufacture and sale of oil-lubricated and oil-free medium and high pressure compressors for commercial shipping, industry, petroleum industry and national defense. The four product lines SAUER, HAUG, GIRODIN and EK focus on specific application areas. The SAUER series includes oil-lubricated high-pressure compressors suitable for various applications, while HAUG stands for oil-free and hermetically sealed compressors. The GIRODIN and EK series provide special compressors for the naval market. Modern reciprocating compressors used to compress air and various gases can reach pressures from 20 to 500 bar.g. In addition to standard products, it also provides customized solutions for each type of application for individual customers, original equipment manufacturers and global active companies. With a worldwide network of representatives and partners, Sauer is always close to customers. By supplementing the compressor series with high-quality accessories, engineering services, assembly and service concepts, Sauer provides complete system solutions up to a complete turnkey installation. Source: Sauer Compressor