Investigation of a Radial Turbine Design for a Utility-Scale Supercritical CO₂ Power Cycle

• Main Authors: Tala El Samad, Joao Amaral Teixeira, John Oakey
• Format: Article
• Language: English
• Published: MDPI AG 2020-06-01
• Series: Applied Sciences
• Subjects: supercritical carbon dioxide; radial turbine; utility-scale; turbomachinery design; NET Power
• Online Access: https://www.mdpi.com/2076-3417/10/12/4168

This paper presents the design procedure and analysis of a radial turbine design for a mid-scale supercritical CO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula> power cycle. Firstly, thermodynamic analysis of a mid-range utility-scale cycle, similar to that proposed by NET Power, is established while lowering the turbine inlet temperature to 900 <inline-formula> <math display="inline"> <semantics> <msup> <mrow></mrow> <mo>∘</mo> </msup> </semantics> </math> </inline-formula>C in order to remove cooling complexities within the radial turbine passages. The cycle conditions are then considered for the design of a 100 MW<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mrow> <mi>t</mi> <mi>h</mi> </mrow> </msub> </semantics> </math> </inline-formula> power scale turbine by using lower and higher fidelity methods. A 510 mm diameter radial turbine, running at 21,409 rpm, capable of operating within a 5% range of the required cycle conditions, is designed and presented. Results from computational fluid dynamics simulations indicate the loss mechanisms responsible for the low-end value of the turbine total-to-total efficiency which is 69.87%. Those include shock losses at stator outlet, incidence losses at rotor inlet, and various mixing zones within the passage. Mechanical stress calculations show that the current blade design flow path of the rotor experiences tolerable stress values, however a more detailed re-visitation of disc design is necessitated to ensure an adequate safety margin for given materials. A discussion of the enabling technologies needed for the adoption of a mid-size radial turbine is given based on current advancements in seals, bearings, and materials for supercritical CO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula> cycles.