ZW series of liquefied petroleum gas recycle compressor is vertical, single acting, air-cooled, oil-free lubrication, reciprocating piston unit. This series compressor cylinder & packing components are oil-free to ensure the purity of its working medium. Crankshaft, connecting rod, crosshead components are pressure lubrication (splash lubrication) to ensure the reliability of lubrication. Excellent complement, satisfying performance, lightweight, small occupying area, more compressing ratio, smooth running, long service life of spare parts, simple operation, reliability, and easy maintenance. ZW series compressors have
both fixed or movable types; both normal atmosphere (0.1~1.5MPa) and high pressure (1.6~2.4MPa) to meet different requirements of customers
It is suitable for working in large, middle, and small LPG storage, conveying and distribution stations, bottle filling stations, gas filling stations, gas mixing stations, and tank vehicle loading and has the functions of vehicle loading, unloading, bottle filling, bottle emptying, conveying, residue removal and residual gas recycling and it can be also used in the processes of other petrol-industries.
The typical method of unloading LPG is to use a reciprocating compressor with a four-way valve. The compressor will draw vapor from the storage tank, where it will be compressed slightly, and injected into the railcar through a vapor line. This compressed gas will slightly reduce the pressure in the storage tank while raising the pressure in the railcar. This pressure difference will cause the liquid to be transferred from the railcar to the storage tank through a liquid line running from the top of the railcar to the bottom of the storage tank. Please see the diagram below for a schematic of this configuration:
The transfer process switches from liquid transfer to vapor recovery once all the liquid is transferred from the railcar to the storage tank. This is accomplished by rotating the four-way valve, causing the compressor to draw vapor from the railcar and insert it into the storage tank. This is opposite to what was done during liquid transfer. In addition, the liquid line is shut. The compressor will withdraw vapor from the top of the railcar, compress it slightly, and discharge the gas into the liquid section of the storage tank. The liquid already presents in the storage tank will condense these vapors back into the liquid. This causes the railcar pressure to gradually drop while increasing the storage tank pressure incrementally. This operation is stopped when the current pressure in the railcar is approximately 25-30% of the original railcar pressure. Going beyond this threshold is not economical due to the additional time and energy required when compared with the very small amount of product recovered at this stage.