In order to reduce the amount of carbon dioxide (CO_2)greenhouse gases released into the atmosphere, significantwork has been made in sequestration of CO_2 from power plantsand other major producers of greenhouse gas emissions. Thecompression of the captured CO_2 stream requires significantpower, which impacts plant availability, capital expenditures,and operational cost. Preliminary analysis has estimated that theCO_2 compression process alone reduces the plant efficiency by8-12 percent for a typical power plant. The goal of the presentresearch is to reduce this penalty through development of novelcompression and pumping processes. The research supports theU.S. Department of Energy (DOE) National EnergyTechnology Laboratory (NETL) objectives of reducing theenergy requirements for carbon capture and sequestration inelectrical power production. However, the technologypresented here is applicable to other gases includinghydrocarbons as well as smaller scale carbon capture projectsincluding CO_2 separation from natural gas. The primaryobjective of this study is to boost the pressure of CO_2 from nearatmospheric to pipeline pressures with the minimal amount ofenergy required. Previous thermodynamic analysis identifiedoptimum processes for pressure rise in both liquid and gaseousstates. Isothermal compression is well known to reduce thepower requirements by minimizing the temperature of the gasentering downstream stages. Intercooling is typicallyaccomplished using external gas coolers and integrally gearedcompressors. Integrally geared compressors do not offer thesame robustness and reliability as in-line centrifugal compressors. The current research develops an internallycooled compressor diaphragm to remove heat internal to thecompressor. Results documenting the design process will bepresented including 3-dimensional (3D) conjugate heat transfercomputational fluid dynamics (CFD) studies. Experimentaldemonstration of the design was performed using a centrifugalcompressor closed loop test facility at the authors’ company. Arange of operating conditions was tested to evaluate the effecton heat transfer. At elevated pressures, CO_2 assumes a liquidstate at moderate temperatures. This liquefaction can beachieved through commercially available refrigerationschemes. However, liquid CO_2 turbopumps of the size andpressure needed for a typical power plant were not readilyavailable. This paper describes the test stand design andconstruction as well as the qualification testing of a 150 barcryogenic turbopump. A range of suction pressures were testedand net positive suction head (NPSH) studies were performed.
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