Selection of a Heat-Recovery Turbine Unit for a Self-Contained Power Supply of Compressor Stations in Gas Mains

Two design options for a heat-recovery turbine unit (HRTU), which generates electricity for self-contained power supply of gas mains' compressor stations (GMCSs) using the heat of exhaust gases from gas-turbine engines (GTEs) driving gas-pumping units (GPUs), are examined. The working fluid of the recovery circuit is octafluorocyclobutane (c-C4F8, engineering name is RC318) in one of the two HRTUs and the exhaust gases of GPU GTE in the other HRTU. The HRTU operating on RC318 has a three-circuit cycle, including three turbines, three recuperative heat exchangers, three RC318 heaters, and one common condenser. An alternative design of HRTU is a vacuum-type GTU consisting of an overexpansion gas turbine, whose inlet is connected with the exhaust of GPU GTE, exhaust gas coolers, a cooled gas compressor, and an induced-draft fan. The excess power of this HRTU above the current power demand at the GMCS is used to create a vacuum at the exhaust of the gas turbine of the GPU GTE. The results are presented of the comparative balance calculations of parameters and characteristics of both HRTUs as applied to a 16-MW Ural GPU GTE. They were performed using the updated initial data and the software library RefProp (in the CoolProp high-level interface) for the calculation of thermodynamic parameters of working fluids. It has been demonstrated that a more compact and easier to implement gas-type HRTU (with an overexpansion gas turbine), although having a lower power than the RC318-type HRTU, can still fully cover the demand of the GMCS for high-quality power and also to solve the problem of substituting imported gas piston and diesel generators at the GMCS within the shortest possible time and with the lowest capital and operating expenditures.