Supercritical Carbon Dioxide Power Cycle Research Articles

Design of a partial discharge shrouded impeller for the centrifugal compressor of supercritical carbon dioxide power cycles

In this paper, the concept of partial discharge shrouded impeller is proposed to enhance the performance of supercritical carbon dioxide (S-CO2) centrifugal compressor under low flow rates, thereby increasing the overall efficiency of the S-CO2 Brayton cycle. The influence mechanism of the partial discharge shrouded impeller on the flow behavior inside the impeller domain has been revealed by computational fluid dynamics (CFD) simulation. The results indicate a notable enhancement in the pressure ratio and isentropic efficiency of the S-CO2 centrifugal compressor utilizing the best partial discharge shrouded impeller, showcasing improvements of 0.9% and 10.2% respectively under designed flow rate condition, while the stability parameter (SP) surpasses 0 at lower flow rates when compared to conventional impeller. With the partial discharge shrouded impeller, the flow separation on the blade pressure surface tends to occur nearer the impeller outlet, restricting the wake secondary flow shedding off to the diffuser, thus the flow loss being weakened. Meanwhile, with the optimized compressor by employing the best partial discharge shrouded impeller, the efficiency of S-CO2 Brayton cycle has been increased by 5% relative to that with full discharge shrouded impeller.

Oxygen Storage Incorporated Into Net Power and the Allam–Fetvedt Oxy-Fuel sCO2 Power Cycle—Techno-Economic Analysis

Abstract With the planned future reliance on variable renewable energy, the ability to store energy for prolonged time periods will be required to reduce the disruption of market fluctuations. This paper presents a method to analyze a hybrid liquid-oxygen (LOx) storage/direct-fired supercritical carbon dioxide (sCO2) power cycle and optimize the economic performance over a diverse range of scenarios. The system utilizes a modified version of the NET Power process to produce energy when energy demand exceeds the supply while displacing much of the cost of the air separation unit (ASU) energy requirements through cryogenic storage of oxygen. The model uses marginal cost of energy data to determine the optimal times to charge and discharge the system over a given scenario. The model then applies ramp rates and other time-dependent factors to generate an economic model for the system without storage considerations. The size of the storage system is then applied to create a realistic model of the plant operation. From the real plant operation model, the amount of energy charged and discharged, the capital expenditures (CAPEX) of each system, energy costs and revenue and other parameters can be calculated. The economic parameters are then combined to calculate the net present value (NPV) of the system for the given scenario. The model was then run through the SMPSO genetic algorithm in Python for a variety of geographic regions and large-scale scenarios (high solar penetration) to maximize the NPV based on multiple parameters for each subsystem. The LOx storage requirements will also be discussed.

A comprehensive multi-variable approach for evaluating the feasibility of integration a novel heat recovery model into a gas turbine power plant, producing electricity, heat, and methanol

Considering the importance of efficient thermal integration for a gas turbine cycle using its energetic flue gas, the current paper proposes an eco-friendly and efficient process integrated into a gas turbine cycle. The newly designed polygeneration structure produces power, hot water, and methanol. The components of this system include a heat provider unit, a direct carbon dioxide hydrogenation unit for the production of methanol, an ammonia Rankine cycle, a proton exchange membrane electrolyzer, a supercritical carbon dioxide power cycle, and two organic Rankine cycles. The feasibility of the proposed model is evaluated using a comprehensive multi-variable assessment from energy, exergy, economic, and environmental approaches. This system exhibits a power production capacity of 17197.23 kW and a methanol generation rate of 0.7573 kg/s. Also, the total irreversibility is equal to 68161.18 kW. Besides, the total energy and exergy efficiencies are found as 68.73% and 32.03%, respectively. This model's carbon dioxide emission is 18667.36 kgCO2/h, and its carbon footprint equals 0.2196 kgCO2/kWh. Furthermore, the economic analysis reveals that the project has an annual total cost of 194,602,338 and a net present value of 686,221,616. Besides, the computed total unit costs for products and energy are 0.3385 $/kWh and 89.81 $/GJ, respectively.

Dynamic Modeling and Control of Supercritical Carbon Dioxide Power Cycle for Gas Turbine Waste Heat Recovery

The gas turbine is a crucial piece of equipment in the energy and power industry. The exhaust gas has a sufficiently high temperature to be recovered for energy cascade use. The supercritical carbon dioxide (S-CO2) Brayton cycle is an advanced power system that offers benefits in terms of efficiency, volume, and flexibility. It may be utilized for waste heat recovery (WHR) in gas turbines. This study involved the design of a 5 MW S-CO2 recompression cycle specifically for the purpose of operational control. The dynamic models for the printed circuit heat exchangers, compressors, and turbines were developed. The stability and dynamic behavior of the components were validated. The suggested control strategies entail utilizing the cooling water controller to maintain the compressor inlet temperature above the critical temperature of CO2 (304.13 K). Additionally, the circulating mass flow rate is regulated to modify the output power, while the exhaust gas flow rate is controlled to ensure that the turbine inlet temperature remains within safe limits. The simulations compare the performance of PI controllers tuned using the SIMC rule and ADRC controllers tuned using the bandwidth method. The findings demonstrated that both controllers are capable of adjusting operating conditions and effectively suppressing fluctuations in the exhaust gas. The ADRC controllers exhibit a superior control performance, resulting in a 55% reduction in settling time under the load-tracking scenario.

Assessment of a sustainable multigeneration system integrating supercritical CO2 Brayton cycle and LNG regasification: Thermodynamic and exergoeconomic evaluation

This study proposes a cost-effective multigeneration system that integrates a supercritical carbon dioxide (sCO2) power cycle with a liquefied natural gas (LNG) regasification process. The system aims to deliver electricity, cooling, heating, and hydrogen simultaneously. Utilizing the temperature difference between the sCO2 cycle and the LNG thermal sink, an ammonia-water-based absorption refrigeration cycle (ARC) recovers waste heat from the sCO2 power cycle, producing cooling. The elevated ammonia concentration at the ARC's condenser outlet is leveraged by a heat pump system for heating production. Concurrently, cold energy from LNG is used to recover latent heat from the condenser and heat rejected from the sCO2 power cycle, providing inputs for additional electrical power through an NG turbine. The system incorporates a PEM electrolyzer (PEME) for hydrogen production. A comprehensive examination, including energy, exergy, and exergoeconomic analyses, evaluates system performance. A sensitivity analysis illustrates the impacts of key parameters. In the baseline scenario, the system achieves energy and exergy efficiencies of 62.79% and 54.89%, with a low product unit cost of 11.35 ($/GJ). The system demonstrates substantial net power output (259.184 MW), cooling capacity (88.938 MW), heating capacity (2.839 MW), and hydrogen production (391.68 kg/h). This robust performance, coupled with cost-effectiveness, positions the proposed system as a versatile and impactful solution for sustainable and environmentally friendly energy applications.

Research on recompression supercritical CO2 power cycle system considering performance and stability of main compressor

The supercritical carbon dioxide (sCO2) power cycle has good prospects for use in many energy applications. Ensuring the stable operation of the power cycle is an important issue. The inlet condition of the main compressor in the sCO2 recompression cycle is close to the critical point of CO2 and the physical properties of CO2 change drastically near the critical point, so the study of inlet parameter change behavior of the main compressor is of great significance to the stable operation of the equipment and the system. This paper investigates the performance of an sCO2 recompression power cycle system under off-design conditions with different cooling and heating conditions. Unlike previous studies, this paper uses more accurate compressor and heat exchanger models to simulate the system for off-designed performance. A 1-D optimization prediction model of the compressor and a density-based segmented heat exchanger model are introduced to predict the performance changes of the system. The operating conditions, performance, and stability of the compressor under different cooling and heating conditions were compared. The results show that variations in different cooling and heating conditions change the inlet temperature of the compressor, causing the sCO2 compressor to deviate from optimal operation. As the inlet temperature increases, the power consumption of the compressor increases. At an inlet temperature of 305 K, the power is 1.93 MW (main compressor, MC) and 2.17 MW (recompressor, RC). When the inlet temperature increases to 310 K, the power increases by more than 10 %. The largest change in system efficiency is 3.76 % for a change in cooling conditions, and the largest change in compressor speed is 14.23 % (MC) and 7.79 % (RC) for a change in heating conditions, respectively. The operating condition of the main compressor moves far away from the surge line when its inlet temperature increases, which means the operation of the main compressor is more stable in this situation. The results of this paper contribute to the stable operation of the sCO2 recompression cycle.

Design and techno economic optimization of an additively manufactured compact heat exchanger for high temperature and high pressure applications

Additive manufacturing (AM) has tremendous potential to produce high-power-density heat exchangers. However, manufacturing AM-heat exchangers at a competitive cost impedes their commercial adoption. In this paper, a novel design of an AM counter flow pin–fin compact recuperator, and its manufacturing costs when using laser powder bed fusion method, are presented. The compact recuperator, which can operate at a high temperature of 800 °C, a high fluid pressure (250 bar) on the cold side and withstand a differential pressure of 170 bars across the fluid streams, as seen in supercritical carbon dioxide power cycles, is designed for a lifetime of 40,000 h. Numerical models to predict the thermo-fluidic performance, and a simplified mechanical model based on plate theory to predict the mechanical stresses, of the recuperator are presented. The recuperator's thermal performance and compactness are studied, and its manufacturability is evaluated via a multi-objective techno-economic optimization. The optimization process considers thermo-fluidic, structural, and manufacturing constraints. The recuperator was fabricated using Haynes 282, and the printability of the design features using a laser-powder-bed-fusion machine is demonstrated. The choice of employing two different AM machines, with different build plate dimensions, number of lasers, and design constraints, on the recuperator's cost/unit, cost/UA, and cost/kW-th o are examined. It is observed that the cost/UA and cost/kW-th decrease exponentially from 13,839 USD-K/kW to 1,994 USD-K/kW and from 80 USD/kW-th to 18 USD/kW-th, respectively, with the size and thermal rating of the recuperator. The exponential decrease in cost/UA and cost/kW-th with increase in power rating opens the possibility of manufacturing large-scale additively manufactured recuperators at a competitive cost. The recuperator, including headers, can achieve a maximum volumetric heat density of 200 MW/m3. The optimization framework can be used to obtain optimal pin-array heat exchanger dimensions for other applications and materials using laser powder bed fusion method.

Numerical research on performance of new structure centrifugal compressor for supercritical CO2 power systems

The supercritical carbon dioxide (sCO2) power cycle system is a potential thermoelectric conversion system with the advantages of high efficiency and compactness, which can be used in the fields of solar thermal power, nuclear power, and other thermal power systems. The compressor is one of the important machines in sCO2 power systems. To improve the performance and reduce the condensation risk of sCO2 centrifugal compressors, a new structure sCO2 centrifugal compressor is proposed in this paper, which has a partial-cover impeller and self-circulation-channel casing (PISC). The internal flow of the compressor with the new structure is analyzed by the CFD method. The flow and condensation in sCO2 centrifugal compressors with the PISC structure and that with the semi-open impeller and traditional casing (SITC) are compared. The results show that the PISC sCO2 compressor has an inhibiting effect on the condensation at the compressor inlet location, reducing the condensation volume to approximately 82% of that of the original structure under design conditions. The total pressure ratio and isentropic efficiency of compressors are simulated, and the result shows that the minimum stable mass flow rate is reduced by about 13% by introducing the new PISC structure into the sCO2 centrifugal compressor, and the maximum isentropic efficiency is increased from 83.5% to 84.4% compared to that of the SITC compressor. A new design idea for the impeller and sCO2 compressor structure is provided in this paper. The research results can be applied to sCO2 compressors and improve the performance and stability of sCO2 power cycle systems.

Performance Analysis of High-Efficiency Supercritical CO2 Power Cycles Using Recompression

Abstract System simulation, parametric analysis, and exergy analysis were performed to identify the advantages and drawbacks of recompression in the direct-fired supercritical carbon dioxide (sCO2) power cycle. In a parametric investigation, the recompression ratio, turbine inlet temperature (TIT), and pressure ratio were changed, and the obtained values for the efficiency of the power cycle were compared. The TIT was varied between 600 °C and 1600 °C, revealing that recompression is highly effective for lower TIT values but is less effected at higher TIT values. For TITs above 1400 °C, the recompression cycle obtains almost no increase in efficiency. Different optimal recompression ratios were obtained for the different pressure ratios between the high- and low-pressure sides. Exergy analysis reveals that exergy destruction occurs primarily in the oxy-fuel combustor due to a chemical reaction and mixing of the high recirculation fluid. Higher TIT decreases the exergy destruction of the oxy-fuel combustor, but increases the exergy destruction in the lower temperature recuperator, and is not always favorable for obtaining efficiency improvements.

Comparing the partial cooling and recompression cycles for a 50 MWe sCO2 CSP plant using detailed recuperator models

Supercritical carbon dioxide (sCO2) power cycles are attractive for renewable energy technologies as they exhibit high thermal efficiencies, compact components, and reduced cycle complexity and levelized cost of energy (LCOE) relative to traditional steam power cycles. Consequently, numerous studies have investigated different layouts and operating parameters in search of an optimal cycle configuration. Two cycle layouts provide promising results, namely the partial cooling with reheating (PCRH) cycle, and the recompression with intercooling and reheating (RCICRH) cycle. Both cycles utilise recuperators with high heat transfer rates and literature suggests that the cost for the recuperators may account for a significant portion of the total plant capital expenditure. When modelling the recuperator, most cycle comparative studies employ simplified recuperator models where heat exchanger effectiveness or conductance is utilised to approximate heat transfer. These models do not consider the effect of recuperator size and geometry on heat transfer and pressure drop in detail. In this work, for a concentrated solar power (CSP) application, the performance and component size requirements of the cycles are evaluated parametrically for different cycle mass flow split ratios, pressure ratios, and ratio of pressure ratios across the compressors using detailed discretised one-dimensional (1D) recuperator models. Furthermore, the geometry of these models are optimised (by volume) for straight and zigzag channel printed circuit heat exchangers (PCHEs), widely accepted as the most suitable for this application. Finally, a high-level cost comparison is conducted. The results show that if appropriate pressure drop assumptions are made, a simplified model approach yields valid cycle level results when compared with the results obtained using detailed models which consider practical recuperator geometry. However, the pressures and temperatures within the recuperator may not be predicted to a sufficient level of accuracy. In addition to providing clarity regarding the interplay between key cycle process parameters and cycle performance, straight channel PCHEs provide better thermofluid performance than zigzag channel PCHEs. Furthermore, the RCICRH cycle requires larger turbomachinery and a marginally higher capital outlay for the power cycle, but offers superior thermal efficiencies and requires smaller heat exchangers. For sCO2-CSP applications employing dry cooling, this suggests that the RCICRH cycle requires a smaller solar field and cooling system, and may therefore offer increased revenue in adverse weather conditions where direct normal irradiance (DNI) is low and/or ambient temperatures are high. However, the PCRH cycle requires a smaller solar receiver system, a smaller thermal energy storage (TES) system, and smaller turbomachinery, the cost savings of which may outweigh the benefits of the RCICRH cycle.

Optimizing Supercritical Carbon Dioxide Cycles Performance With Respect to Split Ratio and Intermediate Pressure

Abstract Supercritical carbon dioxide power cycles are getting more attention every day due to their high efficiencies. This study has examined determination of split ratio and intermediate pressure for maximum efficiency in various supercritical carbon dioxide recompression cycle configurations. Five cycle variants have been analyzed: reheating, partial cooling, partial cooling with reheating, intercooling, and intercooling with reheating. Partial derivatives of efficiency with respect to split ratio and intermediate pressure have been determined and set equal to zero to find optimum split ratio and intermediate pressure. This process has isolated the system's response to these two key parameters while keeping other cycle variables constant. Across all configurations, following parameters have been fixed: inlet temperatures of 550 °C and 32 °C for turbine and compressor components, an energy source temperature of 600 °C, an ambient temperature of 27 °C, and pressure limits of 75 bar and 200 bar. Optimization results show that recompression–reheating cycle achieves the highest efficiency of 39.62% at an optimum intermediate pressure of 139.43 bar and a split ratio of 71.1%. Recompression–partial cooling cycle exhibits the lowest maximum efficiency at 37.35%, with an optimum intermediate pressure of 85.87 bar and a split ratio of 62.6%. Recompression–partial cooling with reheating cycle reaches a maximum efficiency of 37.98% at an optimum intermediate pressure of 123.94 bar and a split ratio of 67.2%, while the intercooling cycle and intercooling with reheating cycle attain 39.57% at an optimum intermediate pressure of 80.03 bar and a split ratio of 66.4% and 39.59% at an optimum intermediate pressure of 116.1 bar and a split ratio of 69.2%, respectively. Additionally, exergy destruction has been calculated for all components of the system and it is related to thermal efficiency of the cycle.

A novel supercritical carbon dioxide combined cycle fueled by biomass: Thermodynamic assessment

As a carbon-neutral type of renewable energy, biomass is beneficial for reducing carbon emissions in the electricity sector. A biomass gasification process integrated with a combined cycle is proposed here. Wood is chosen as the fuel and air as the gasifying agent. A supercritical carbon dioxide (SCO2) power cycle with recompression is selected for the recovery of waste heat from the combustion chamber. The net power output is considered to be 1 MW for the combined cycle in the investigation of component ratings and biomass feed rate. For a comprehensive thermodynamic analysis of this combined cycle, we examine three key parameters: gas turbine inlet temperature (1200–1400 K), topping cycle pressure ratio (5-10) and CO2 turbine inlet temperature (600–700 K). The maximum energy efficiency is achieved for the system at a specific pressure ratio and CO2 turbine inlet temperature. The energy efficiency rises with gas turbine inlet temperature, which reduces biomass consumption (at a fixed net power output). The CO2 emission rate to the environment is examined for various parameters; it is observed to decrease as biomass consumption decreases and to take on a value of 0.254 kg/s at an optimized state.

Optimizing power, cooling, and hydrogen generation: A thermodynamic and exergoeconomic study of an advanced sCO2 trigeneration system

This paper presents an innovative trigeneration system designed for efficient power, cooling, and hydrogen production. It combines a supercritical carbon dioxide (sCO2) power cycle with a Kalina cycle (KC) and an ammonia-water-based absorption refrigeration cycle (ARC), all integrated with a PEM electrolyzer (PEME) unit. The system optimally utilizes waste heat from the sCO2 power cycle to enhance power generation through the KC and provide cooling via the ARC. Additionally, it leverages the PEME system and KC-generated power for eco-friendly hydrogen production. Mathematical models, thermodynamic, and exergoeconomic analyses were performed, including parametric studies, optimization, and comparative analyses. The results indicate that the reactor experiences the highest exergy destruction rate, while components in the bottoming cycles exhibit lower exergy destruction. From an exergoeconomic perspective, the reactor and sCO2 turbine are ranked as the first and second most significant components. Under the optimal conditions, the system achieved a 9.76 % increase in exergy efficiency and a 6.63 % reduction in total product unit cost. The system also provides substantial net power output, cooling capacity, and hydrogen production rates of 261.74 MW, 123.95 MW, and 176.328 kg/h, respectively. These findings highlight the system's significant thermodynamic and economic advantages, making it a promising choice for diverse user needs.

SCO2 power cycle/reverse osmosis distillation system for water-electricity cogeneration in nuclear powered ships and submarines

As global concerns about climate change and environmental impacts continue to grow, there is a strong demand for cleaner, greener, and more efficient propulsion solutions in the maritime industry. By leveraging nuclear energy, which offers low carbon emissions and high efficiency, naval vessels can significantly reduce their environmental footprints and contribute to global efforts to combat climate change. Additionally, the ability to produce electricity and freshwater simultaneously addresses the critical need for self-sufficiency during long missions, particularly in remote or resource-constrained areas where access to freshwater may be limited. This study explores a novel approach to address water and energy supply challenges in naval applications through a nuclear-driven supercritical carbon dioxide (sCO2) power cycle–Reverse Osmosis (RO) cogeneration system. The aim is to assess the feasibility and benefits of this system for meeting water and electricity demands in maritime operations and enhancing the sustainability, efficiency, and self-sufficiency of naval vessels with nuclear energy and advanced technologies. A parametric study has been performed to understand the effects of important parameters such as the maximum and minimum cycle temperature and pressure, seawater inlet conditions, pressure vessel design, and membrane properties on the system performance. Moreover, an optimization study has been performed to determine the best possible combination of these parameters to achieve the highest system efficiency. For the determined optimal set of parameter values, it is possible to have an sCO2 power cycle with a cycle efficiency of 40.5 %, an electrical power output of 121.6 MW and an RO system with an efficiency of 29.4 %, a recovery ratio of 29.3 %, a specific fuel consumption (SEC) of 2.29 kW·h/m3, and a freshwater production rate of 1531.6 m3/d by utilizing 145.9 kW electrical power. The positive outcomes of this study indicate that the system has the potential to be a viable and effective solution for addressing water and energy supply challenges in naval operations.

Process splitting analysis and thermodynamic optimization of the Allam cycle with turbine cooling and recompression modification

Allam cycle is an advanced semi-closed supercritical carbon dioxide (sCO2) power cycle that utilizes hydrocarbon fuels with nearly zero carbon emission. Different from other closed power cycles, in the Allam cycle, the oxy-fuel combustion products are directly mixed with the working fluid and the turbine blade cooling is necessary for the high cycle temperature above 1000 °C; moreover, the heat integration might be applied to the Allam cycle to improve the thermodynamic performance, making the Allam cycle complex and hard to conduct the process and parameter optimization. To deepen the understanding on the performance of the Allam cycle with turbine cooling and recompression modification, a novel splitting analytical method is developed that the Allam cycle is split into the closed cycle and open process, and the closed cycle is further split into the simple host cycle and two equivalent power cycles. Using the constructed splitting analytical models, the influences of the turbine cooling and the recompression modification on the net efficiency are clearly evaluated by the split cycles, and the highest efficiency of the Allam cycle is optimized to be 49.92 % (higher heating value) as the coolant temperature and recompression mass flow rate are 320 °C and 439.5 kg/s, respectively.

Investigation on the effect of the cooler design on the performance of onboard supercritical carbon dioxide power cycle for hypersonic vehicles

The scramjet cooling and power generation are the key demands for the hypersonic vehicle. To satisfy the cooling and electricity generation requirements of hypersonic vehicles, the onboard supercritical carbon dioxide (sCO2) power cycle is adopted in this paper. Moreover, the cooler design has a significant effect on the feasibility and overall performance of onboard sCO2 power cycle, but there is no research considering the effect of the cooler design. Accordingly, the effects of the cooler design on the overall performance of onboard sCO2 power cycles applied in hypersonic vehicles are comprehensively investigated based on the thermodynamic models. The results indicated that the optimum cooler designs are suggested to adopt a small channel diameter and a relatively large channel number for minimizing the cooler mass and fuel consumption for cooling sCO2 and maximizing the system thermal efficiency. Moreover, the cold channel diameter is designed to be smaller than the hot channel diameter. The cold channel number is required to be larger than the hot channel number. The total flow area of cold channel is smaller than that of hot channel. The geometric parameters of cooler hot channel could be designed based on the Re ranging from 15,000 to 34,000.

Rational design process for gas turbine exhaust to supercritical CO2 waste heat recovery heat exchanger using topology optimization

Advances in additive manufacturing (AM) technologies and topology optimization methodologies are enabling sophisticated novel designs for heat exchanger performance. These tools have been demonstrated for development of high-performance heat sinks considering local or component-level performance factors (e.g., heat transfer per volume). To leverage such capabilities in larger-scale energy systems, structured design methodologies are needed that consider system-level factors, such as production cost, cycle-level efficiency, and operational constraints. This study seeks to develop and assess a rational approach for designing thermo-economically optimal heat exchangers for such applications. The methodology is illustrated through development of the Primary Heat Exchanger (PHX) for a supercritical carbon dioxide (sCO2) power cycle recovering exhaust heat from a 6 MW-scale natural gas turbine. The proposed approach begins with a detailed thermodynamic cycle model, which is then extended to account for techno-economics. Next, an optimal PHX heat transfer capacity target is identified, and a high-level geometry is selected based on operating characteristics. This geometry is then divided into repeating 2D prismatic unit cells, for which topology optimization is applied to identify high-performance heat transfer geometries. A key aspect of this process is that the unit cell geometries are optimized using the total PHX mass as the objective function, which represents a surrogate for production cost. This leads to distinct designs compared with approaches that optimize local heat transfer and flow resistance factors. A second topology-optimized design is developed using a representative local thermal-fluid performance objective function and is found to require 1.6× the mass of the design generated with the system-level techno-economic objective for the same unit cell size. Conventional-type PHX designs with simple longitudinally finned tubes are developed for comparison, and are found to require total masses 1.5× or greater than the design obtained with the proposed process. Integrating this approach with detailed additive manufacturing costing models and experimentally validated fabrication constraints can yield a streamlined workflow for HX design for future energy systems.

Improvement design and performance assessment of two supercritical carbon dioxide power cycles for waste heat recovery

Waste heat recovery (WHR) from thermal engines and industrial processes is significantly beneficial to cutting fossil fuel consumptions and carbon dioxide emissions. Recompression supercritical carbon dioxide (sCO2) power cycles have many advantages of high efficiency, compact design and environmentally friendly property, and they are regarded as the competitive and promising energy conversion technology for WHR. However, a large space is still left for recompression sCO2 power cycle to improve its capability with regard to waste heat extraction and power output. The novelty of this work is the development of two novel sCO2 power cycles based on the recompression sCO2 cycle aimed at thoroughly and efficiently reusing the waste heat. Thermodynamic and exergoeconomic models are established to perform the quantitative parametric analyses, multi-objective optimizations, exergy and exergoeconomic analyses on the proposed systems. The results indicate that the second proposed system is preferred, since it can significantly improve the net power output by 43.81% and 12.32% while reducing the total product unit cost by 7.24% and 10.39%, compared with the traditional recompression sCO2 cycle and the improved sCO2 cycle, respectively. Although the first proposed system has a better performance in waste heat extraction and net power output, it requires a higher cost.

Experimental study on the heat transfer characteristics of supercritical carbon dioxide in spiral tube with high pitch to spiral diameter ratio

Spiral tubes are compact and extremely heat-transfer-efficient that are suited for supercritical carbon dioxide (S-CO2) power cycles. Some existing experiments of S-CO2 heating in tubes are mainly conducted in spiral tubes with low ratio of pitch to spiral diameter (p/C<0.5) and straight tubes. In this study, experimental studies are conducted in a high p/C spiral tube with pitch (p) and spiral diameter (C) of 60 mm and 77 mm, diameter (d) and length (L) of 4.57 mm and 1000 mm, and compared with the straight tube of the same size. The results show that the spiral tube can alleviate heat transfer deterioration, with the maximum wall temperature dropping by 47 °C and the average heat transfer coefficient increasing by about 2.6 times from 1437 W·m−2·K − 1 to 3729 W·m−2·K−1 as compared to the straight tube. The wall temperature near the inlet of the spiral tube rises obviously at high q/G. The heat transfer coefficient and uniformity decrease with mass flux decreasing or heat flux increasing, and is little affected by pressure and inlet temperature. The buoyancy effect is analyzed using 1190 and 1260 experimental data points from spiral and straight tubes. The effect of buoyancy on heat transfer in the spiral tube is weakened as compared with the straight tube. A heat transfer correlation is proposed utilizing the experimental data.

Off-design and control performance analysis of a novel supercritical carbon dioxide power cycle for waste heat recovery

A novel supercritical carbon dioxide power cycle (sCO2) for waste heat recovery (WHR) is developed. This novel cycle has high efficiency, and it could make a more complete utilization of the waste heat. Besides, the flexible and independent controls of recompression compressor and main compressor can be made to obtain the better off-design performance. The off-design and control performance of this system is quantitatively investigated in this paper. The results indicate that the optimal net power output increases as mass flow rate or temperature of flue gas increases, whereas it decreases with increasing ambient temperature. The first and second highest exergy destruction shares always belong to the cooler and LTWHE under various external conditions. The adjustment of two compressor outlet pressures should be a priority under various mass flow rates or temperatures of flue gas, while the adjustment of cycle minimum pressure should be given a high-priority rating in response to variation of ambient temperature. Moreover, the control performance of recompression compressor is more sensitive to the variation of flue gas mass flow rate, while the control performance of main compressor is more sensitive to the variation of flue gas temperature and ambient temperature.