Sandia National Laboratories (SNL) has recently purchased a supercritical carbon dioxide (sCO2) turbocompressor that operates at 118,000 rpm, 750 °C turbine inlet temperature, and 42.9 MPa compressor discharge pressure, and is sized to pressurize the flow for a 1 MWe closed Brayton cycle. The turbocompressor is a line replaceable unit designed by Peregrine Turbine Technologies (PTT) located in Wiscasset, Maine, as part of their closed Brayton electric power genset rated at 1 MWe. Both this machine and a 6MW variant are intended for commercial applications burning a variety of aircombustible fuels including biomass materials.
Sandia purchased this turbocompressor as the first phase of a program to construct a 1 MWe commercially viable sCO2 recompression closed Brayton-cycle system. During this phase, the development platform resident at the SNL Brayton Lab was reconfigured to support testing of the PTT turbocompressor to moderate, or idle, conditions. The testing infrastructure at the Brayton Lab limited maximum pressure to 13.8 MPa. This pressure limitation consequently limited turbocompressor operations to a speed of 52,000 rpm and a turbine inlet temperature of 150 °C. While these conditions are far removed from the machine design point, they are sufficient to demonstrate a range of important features. Numerous testing objectives were identified and researched, most notably: the development of a reliable cycle bootstrapping process for a motorless turbocompressor; the demonstration of consistent start, steady state, and shutdown performance and operations; performance demonstration of the numerous internal seals and bearings designs that are new to this environment; demonstration of controllability via turbine back pressuring and turbine inlet temperature; and turbomachinery performance map validation.
This paper presents the design and development of the testing platform, the PTT turbocompressor and progress achieved on each of the objectives.