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| | | | | | | | | | | | | | | | | | | | | In contrast to many other compressor types, reciprocating compressors offer a large variety of capacity control systems. The correct type of capacity control is determined by many parameters. Not all types of capacity controls can be used with a given compressor model, a specific pressure range and gas composition. The engineer who has to specify a process compressor, should clearly describe the required turndown requirements and ask the compressor manufacturer to recommend the best applicable type of capacity control. The compressors in the Taiwanese Terminal are equipped with valve unloaders 100/75/50/0 %. For two stage compression without gas industrial coolers and reliquefaction of the compressed gas, this is the favorite solution (Fig. 11). The described compressor in the Middle East, however, as an alternative to valve unloaders, is equipped with a bypass over the first stage. This system is very common for three stage compression in industrial gas applications. With an intercooler between second and third stage the discharge temperature of the third stage is well under control. By using the superheating effect of the bypassed gas on the suction temperature of the first stage, the mass flow can be continuously turned down to 50 %. This system has demonstrated: • Simple reliable low cost solution, as standardized components can be used • Continuous and flexible capacity control with a good partial load efficiency (Fig. 12) | | | | | | 8 Plant design In addition to being a compressor designer and maker, Burckhardt Compression also engineers, procures and provides commissioning of whole systems. The use of their systems is demonstrated in every nut and bolt from suction to discharge side of the compression unit, comprising pulsation equipment, industrial filters, lube oil systems, motor driver, gas and water piping, pulsation studies, mechanical- and thermal stress analysis of the gas pipings, as well as complete control systems (Fig. 13). | | | | | | | | | | Fig. 13: One of two Labys® in the design stage and as installed on site at the BBG Bilbao LNG receiving terminal in Spain | | | | | | | | | | Conclusion • Physical contact with cold gas and consequences for material properties • Absence of humidity (low dew point) with a strong bearing on tribology in non-lubricated areas The application of labyrinth seals in reciprocating compressors is a logical answer to these problems. Labys® have demonstrated this in industrial operation successfully down to boil-off temperature of natural gas at minus 160 °C. Such machines can be built with zero leakage to the environment, combining reliability with low maintenance. | | | | | | | | | | | | | | | | | | | | | | | | 7 | | | | | | | | | | | | | | | | | | | | |
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