Designing of plants with wave expander-compressor (WEC) demands the special approach owing to operating conditions inherent in him and feature of realizable processes. Base circuit and principles of plants construction with use of WEC are considered. The calculated parameters and circuits of plants for processing of oil gas are resulted at various initial pressure, receptions of liquefied natural gas, and also extraction of metane from hydrocarbonic gases with its lowered contents (mine gas, biogas). The plant circuit for additional extraction of propane from natural gas on gas-distributing stations is submitted.