Demonstration of Supercritical CO2 Closed Regenerative Brayton Cycle in a Bench Scale Experiment

Abstract

Power generation with a supercritical CO2 closed regenerative Brayton cycle has been successfully demonstrated using a bench scale test facility. A set of a centrifugal compressor and a radial inflow turbine of finger top size is driven by a synchronous motor/generator controlled using a high-speed inverter. A 110 W power generating operation is achieved under the operational condition of rotational speed of 1.15kHz, CO2 flow rate of 1.1 kg/s, and respective thermodynamic states (7.5 MPa, 304.6 K) at compressor and (10.6 MPa, 533 K) at turbine inlet. Compressor work reduction owing to real gas effect is experimentally examined. Compressor to turbine work ratio in supercritical liquid like state is measured to be 28% relative to the case of ideal gas. Major loss of power output is identified as rotor windage. It is found the isentropic efficiency depends little on compressibility coefficient. Off design performance of gas turbine working in supercritical state is well predicted by a Meanline program. The CFD analysis on compressor internal flow indicates that the presence of backward flow around the tip region might create a locally depressurized region leading eventually to the onset of flow instability.

Design consideration of supercritical CO2 power cycle integral experiment loop

“…compressor geometry, careful consideration is required when designing the SeCO 2 compressor. From the previous research works, it has been consistently shown that the compressor efficiency was significantly affected by the windage loss and the system operation was influenced by the thrust load balancing [17,20,21]. Therefore, the development of SCIEL requires step-bystep construction approach while examining the component (especially turbomachinery) performance carefully at each stage.…”

“…First of all, it was determined from the first design phase, the recompressing (split-flow) process is not planned to be demonstrated in SCIEL due to the limit in infrastructure capacity. In the previous studies, the recompressing process is discarded due to the small power size [7,17]. However, the recompressing layout will be considered for the long-term goal to further resolve turbomachinery design, operation and control issues in the sophisticated cycle layout.…”

“…The experimental facility design and operating data were reported in Ref. [17]. The power output was limited due to the windage losses in the rotor.…”

“…The final design is simple recuperated cycle with two recuperators connected in series. In the early design status, the recompressing layout with an adoption of reciprocating type recompressing compressor was considered but it was discarded from the final design [7,17]. The test scale was determined with the consideration of turbomachinery rotating speed feasibility from a manufacturing perspective.…”

Preliminary Design and Model Assessment of a Supercritical CO2 Compressor

“…But neither of them did a 3D calculation for their design results. There are also many other universities and research institutes that have carried out relevant research on the design strategy of SCO 2 compressors [7][8][9][10][11][12] and some research institutes have carried out experiments [13][14][15]. More recently, Rinaldi (2014) and colleagues utilized an in-house fluid dynamic solver and simulated the test compressor of Sandia National Laboratories (SNL) based on the steady state method [16].…”