A high efficiency, single-stage pipeline centrifugal gas compressor, originally designed with a wedge-type vaned diffuser, was retrofitted with a vaneless diffuser along with two low solidity diffuser configurations in order to improve the operating flow range. The low solidity diffuser configurations included a flat-plate design and an airfoil-type design. The vaneless and flat-plate low solidity diffusers were derived from the existing wedge-type vaned diffuser, while the airfoil-type low solidity diffuser was designed specifically to match the existing impeller, but within the design envelope available for retrofit purposes. Computational fluid dynamics (CFD) was used to establish impeller discharge conditions, analyze candidate diffusers, and provide some guidance as to the expected operating range improvement. Both factory and field testing were conducted to verify the performance of the diffuser configurations. Test results indicated that the airfoiltype low solidity diffuser had the best overall efficiency and operating flow range combination, with one percent and 22 percent improvements, respectively, when compared to the wedge-type vaned diffuser.
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