Control of a Supercritical CO2 Recompression Brayton Cycle Demonstration Loop

Abstract

The U.S. Department of Energy is currently focused on the development of nextgeneration nuclear power reactors, with an eye towards improved efficiency and reduced capital cost. To this end, reactors using a closed-Brayton power conversion cycle have been proposed as an attractive alternative to steam turbines. The supercritical-C02 recompression cycle has been identified as a leading candidate for this application since it can achieve high efficiency at relatively low operating temperatures with extremely compact turbomachinery. Sandia National Laboratories has been a leader in hardware and component development for the supercritical-C02 cycle. With contractor BarberNichols Inc., Sandia has constructed a megawatt-class S-CO2 cycle test-loop to investigate the key areas of technological uncertainty for this power cycle and to confirm model estimates of advantageous thermodynamic performance. Until recently, much of the work has centered on the simple S-CO2 cycle-a recuperated Brayton loop with a single turbine and compressor. However, work has recently progressed to a recompression cycle with split-shaft turbo-alternator-compressors, unlocking the potential for much greater efficiency power conversion, but introducing greater complexity in control operations. The following sections use testing experience to frame control actions made by test loop operators in bringing the recompression cycle from cold startup conditions through transition to power generation on both turbines, to the desired test conditions, and finally to a safe shutdown. During this process, considerations regarding the turbocompressor thrust state, CO2 thermodynamic state at the compressor inlet, compressor surge and stall, turbine ulc ratio, and numerous other factors must be taken into account. The development of these procedures on the Sandia test facility has greatly reduced the risk to industry in commercial development of the S-CO2 power cycle.

A trade-off between maxima in efficiency and specific work output of super- and trans-critical CO2 Brayton cycles

“…The interest in CO 2 based cycles arises as a part of our effort to explore them for possible power generation using CSP [1,19]. There have been some studies suggesting the use of supercritical CO 2 for nuclear power generation also [19][20][21][22][23][24][25].…”

“…The objective of this paper is to further explore the above two path function coordinate system to understand the intricate link between the performance indicators and cycle operating parameters for the specific case of CO 2 Brayton cycle power plants. This study is motivated by recent developments in concentrated solar power using CO 2 based Brayton cycles [1,2,[18][19][20][21][22][23][24][25]. Recently, Mohagheghi et al [26] used Pareto-based multi objective optimization for optimizing the process parameters of transcritical regenerative CO 2 Brayton cycle.…”

Development of the turbomachinery for the supercritical carbon dioxide power cycle

“…An immersion type of electric heater was used to make a high-temperature supercritical CO 2 , and two printed circuit heat exchangers (PCHEs) were manufactured as a recuperator. In recent publication [6,7], experimental results obtained in 2012 showed that net power of 15 kWe was generated at 10,500 kPa/477°C/50,000 rpm operating conditions. Bechtel Marine Propulsion Corporation (BMPC) including Knolls Atomic Power Laboratory and Bettis Atomic Power Laboratory also designed and built a 100-kWe supercritical CO 2 Brayton cycle integrated systems test experimental apparatus for evaluating the applicability of a supercritical CO 2 power generation system in a nuclear propulsion shipboard [8][9][10][11].…”

“…Sandia National Lab (SNL) has been implementing and improving a supercritical CO 2 power generation test loop since 2005 [4][5][6][7]. In collaboration with Barber-Nichols, SNL has developed technologies for the key components of supercritical CO 2 power generation systems and conducted compressor tests Turbomachinery for the supercritical carbon dioxide power cycle J.…”

Supercritical CO2 Brayton power cycles for DEMO (demonstration power plant) fusion reactor based on dual coolant lithium lead blanket

“…SNL studied the Brayton power cycle using different ideal gases, far from their critical point in 2006 [30]. This analysis entailed to the S-CO 2 power cycle, constructing a compressor loop and a complete cycle in unrecuperated layout [31], a recuperated layout [32] and finally a re-compression layout [33]. Future plans include the construction of the Nuclear Energy System Laboratory/Brayton Lab, with a 10 MWe power plant for SFR in 2020 [34].…”