Startup and Operation of a Supercritical Carbon Dioxide Brayton Cycle

Clementoni, Eric M.; Cox, Timothy L.; Sprague, Christopher P.

doi:10.1115/1.4026539

Cited by 70 publications

(15 citation statements)

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“…This increased heat generation in sCO 2 seals requires attention toward thermal management of the seal, which will be discussed in Sec. 4.…”

Section: Face Seal For Utility-scale Turbinesmentioning

confidence: 99%

“…Additional benefits include reduced water consumption, reduced power block size (smaller turbomachinery and condenser due to the higher working fluid density), and better thermodynamic integration with postcombustion CO 2 capture and compression equipment as shown by LeMoullec [1]. Due to these potential benefits, sCO 2 power cycles and associated turbomachinery components have been the focus of recent research efforts [2][3][4][5][6]. Turbomachinery components like seals [7,8] and gas bearings [9,10] have a direct impact on the power cycle efficiencies and are critical for enabling sCO 2 power cycles.…”

Section: Introductionmentioning

confidence: 99%

“…Turbomachinery development for large-scale sCO 2 recompression cycles is still in its infancy. The majority of the recent work in this field has been for small-scale turbines [2,4,6] that are typically rated for 0.3-10 MW power. Such small turbines either do not need end seals (in cases where the turbine is coupled with a hermetically sealed generator cavity with internal gas-foil bearings) or need small-sized end seals (typically hydrodynamic face seals 4-6 in.…”

Section: Introductionmentioning

confidence: 99%

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Low-Leakage Shaft-End Seals for Utility-Scale Supercritical CO2 Turboexpanders

Bidkar

Sevincer

Wang

et al. 2016

Journal of Engineering for Gas Turbines and Power

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Supercritical carbon dioxide (sCO2) power cycles could be a more efficient alternative to steam Rankine cycles for power generation from coal. Using existing labyrinth seal technology, shaft-end-seal leakage can result in a 0.55–0.65% points efficiency loss for a nominally 500 MWe sCO2 power cycle plant. Low-leakage hydrodynamic face seals are capable of reducing this leakage loss and are considered a key enabling component technology for achieving 50–52% thermodynamic cycle efficiencies with indirect coal-fired sCO2 power cycles. In this paper, a hydrodynamic face seal concept is presented for utility-scale sCO2 turbines. A 3D computational fluid dynamics (CFD) model with real gas CO2 properties is developed for studying the thin-film physics. These CFD results are also compared with the predictions of a Reynolds-equation-based solver. The 3D CFD model results show large viscous shear and the associated windage heating challenge in sCO2 face seals. Following the CFD model, an axisymmetric finite-element analysis (FEA) model is developed for parametric optimization of the face seal cross section with the goal of minimizing the coning of the stationary ring. A preliminary thermal analysis of the seal is also presented. The fluid, structural, and thermal results show that large-diameter (about 24 in.) face seals with small coning (of the order of 0.0005 in.) are possible. The fluid, structural, and thermal results are used to highlight the design challenges in developing face seals for utility-scale sCO2 turbines.

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“…This increased heat generation in sCO 2 seals requires attention toward thermal management of the seal, which will be discussed in Sec. 4.…”

Section: Face Seal For Utility-scale Turbinesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Low-Leakage Shaft-End Seals for Utility-Scale Supercritical CO2 Turboexpanders

Bidkar

Sevincer

Wang

et al. 2016

Journal of Engineering for Gas Turbines and Power

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“…A full description of system startup and operation is provided in [5]; for easy reference, the primary steps are repeated here. The IST is started by first warming the system and adjusting system CO 2 mass to achieve the desired temperatures and pressures to achieve supercritical conditions throughout the entire main Brayton loop and promote forward flow through the turbines during startup.…”

Section: System Operational Overviewmentioning

confidence: 99%

Steady-State Power Operation of a Supercritical Carbon Dioxide Brayton Cycle

Clementoni

Cox

2014

Volume 3B: Oil and Gas Applications; Organic Rankine Cycle Power Systems; Supercritical CO2 Power Cycles; Wind Energy

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Bechtel Marine Propulsion Corporation (BMPC) is testing a supercritical carbon dioxide (S-CO2) Brayton system at the Bettis Atomic Power Laboratory. The Integrated System Test (IST) is a two shaft recuperated closed Brayton cycle with a variable speed turbine driven compressor and a constant speed turbine driven generator using S-CO2 as the working fluid designed to output 100 kWe. The main focus of the IST is to demonstrate operational, control and performance characteristics of an S-CO2 Brayton power cycle over a wide range of conditions. IST operation has reached the point where the system can be operated with the turbine-compressor thermal-hydraulically balanced so that the net output of the system is equal to the turbine-generator output. In this operating mode, power level is changed by using the compressor recirculation valve which changes the fraction of compressor flow that goes to the turbines. Steady-state operation with the turbine-compressor thermal hydraulically balanced at near zero net system power is presented.

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“…A further consideration for decoupling of machinery is the split in cycle mass flow on the compressor side of the recompression cycle. A brief inspection of experimental loops summarised in [2] shows that multiple shaft layouts have been considered, with system start-up and control being a key concern [33,34,35].…”

Section: Current Investigations For Supercritical Co 2 Power Cyclesmentioning

confidence: 99%

On the design of small to medium scale radial inflow turbines for supercritical CO2 power cycles

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In rural Australia, concentrating solar power at sub 10 MWe scale is a candidate technology to displace current fossil fuel based technologies [1]. For concentrating solar power to be competitive for this application, coupling with an advanced power cycle is essential. A candidate is the supercritical CO 2 Brayton cycle, which is suitable for higher turbine inlet temperature operation, and has the potential to exceed the efficiency of the steam Rankine cycle. Furthermore, due to lower volumetric flow variation over the cycle, simpler turbomachinery may be used, which enables the cycle to be downscaled while maintaining turbomachinery and cycle efficiency. Of the constituent components in the cycle, turbine efficiency has the greatest impact on cycle efficiency [2]. Radial turbomachinery is a key technology for energy conversion in the supercritical CO 2 Brayton cycle at small scales (i.e. below 30 MW shaft power). While the design of efficient turbines for the supercritical CO 2 Brayton cycle is critical to realising efficient concentrating solar power plants, only a limited number of prototypes have been tested, and none at representative inlet conditions. Radial inflow supercritical CO 2 turbines are characterised by small dimensional scale and high shaft speeds. Prototype turbine designs are characterised by low expansion ratio and medium specific speed to accommodate mechanical restrictions on shaft speed. Medium specific speed designs are selected for prototypes designs due to their implied optimal efficiency. Demonstration test facilities have utilised multiple stages, or lower expansion ratio cycles in order to accommodate designs of this specific speed without exceeding mechanical limits. Increasing inlet conditions to representative cycle conditions for concentrating solar power applications will require higher shaft speeds, or additional stages if specific speed of the stage is to be maintained. Alternatively, the use of single stage low specific speed designs may pose a feasible alternative, however these designs are generally disregarded owing to the implied efficiency penalties shown on gas turbine derived architecture selection charts. Better understanding of loss characteristics of low specific speed supercritical CO 2 turbomachinery is required in order to make an assessment on the feasibility of single stage expansions. Further to sizing of the stator and rotor, stage design also includes components upstream and downstream of the rotor. The broadest challenge for supercritical CO 2 turbomachinery is designing components within a system for high pressure, high density, high temperature, and high shaft speed operation. These constraints may have significant impact on the geometry of these hot gas path features. Details of these features are not clearly detailed in published prototype designs. Considering the knowledge gap for supercritical CO 2 turbines, one key aim of this thesis is to quantify the performance of low specific speed radial inflow turbines using numerical methods. A further aim is t...

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Startup and Operation of a Supercritical Carbon Dioxide Brayton Cycle

Cited by 70 publications

References 1 publication

Low-Leakage Shaft-End Seals for Utility-Scale Supercritical CO2 Turboexpanders

Low-Leakage Shaft-End Seals for Utility-Scale Supercritical CO2 Turboexpanders

Steady-State Power Operation of a Supercritical Carbon Dioxide Brayton Cycle

On the design of small to medium scale radial inflow turbines for supercritical CO2 power cycles

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