Jiangfeng Wang

Thermodynamic Comparison and Optimization of Supercritical CO2 Brayton Cycles with a Bottoming Transcritical CO2 Cycle

AbstractThis study investigated the feasibility of a combined cycle comprising a topping SCO2 cycle and a bottoming TCO2 cycle (SCO2-TCO2 cycle). A simple SCO2 cycle and a recompression SCO2 cycle were considered as the topping configurations. Thermodynamic analyses and comparison were performed to evaluate the effects of key thermodynamic parameters on the behavior of combined SCO2-TCO2 cycles. In addition, a parameter optimization was achieved by means of a genetic algorithm to reach the maximum overall thermal efficiency. The results show that the thermal efficiency of the simple SCO2-TCO2 cycle increased with an increase in SCO2 turbine expansion ratio and compressor inlet temperature. However, for the recompression SCO2-TCO2 cycle the thermal efficiency increased and then decreased as the SCO2 turbine expansion ratio increased. Both the modified SCO2 cycles with a bottoming TCO2 cycle had higher performance, with thermal efficiency increase of 10.12 and 19.34% for combined recompression and simple co...

Experimental Evaluation of the Regenerative and Basic Organic Rankine Cycles for Low-Grade Heat Source Utilization

AbstractThe present paper conducts the experimental evaluation of the performance of a regenerative organic Rankine cycle (ORC) system working with refrigerant R123 and generating 10-kW-level power. The ORC system consists of an axial-flow single-stage turbine, a regenerator, an evaporator, a condenser, and a pump. The regenerative ORC and the basic ORC system efficiency are evaluated under the same conditions. The degree of superheat of the turbine inlet vapor is controlled by the evaporating temperature. The cooling water flow rate is controlled by adjusting the opening of the valve. The experiment results show that the thermal efficiency of the regenerative ORC is higher than that of the basic ORC by about 25%. The thermal efficiency of basic ORC with saturated vapor at turbine inlet is higher than that with superheated vapor by 3.2%, and the thermal efficiency of the regenerative ORC with saturated vapor at turbine inlet is higher than that with superheated vapor by 4.36%. The enthalpy drop across the...

Thermo-Economic Analysis of a Recompression Supercritical CO2 Cycle Combined With a Transcritical CO2 Cycle

The transcritical CO2 cycle (TCO2 cycle) exhibits good performance in low-grade waste heat recovery area. In this study, a TCO2 cycle was employed as a bottoming cycle to recover the waste heat in the topping recompression supercritical CO2 Brayton cycle (SCO2 cycle). A detailed system analysis was performed of a recompression SCO2 cycle combined with a TCO2 cycle to improve the efficiency of energy conversion. Thermodynamic analysis, calculation of heat exchangers’ area and economic analysis were considered. The SCO2 turbine expansion ratio, TCO2 turbine inlet pressure, high temperature recuperator (HTR) effectiveness and condensation temperature were studied to investigate their effect on the system performance. For the basic analysis, SCO2 turbine inlet temperature was conservatively selected to be 550 °C and the compressor outlet pressure set at 20 MPa. For these operating conditions the proposed combined SCO2-TCO2 cycle yielded about 46% thermal efficiency at a SCO2 turbine expansion ratio of 2.7 and TCO2 turbine inlet pressure of 10 MPa. Similarly, the capital cost per net power output of the combined cycle was found as 6.6 k

Theoretical analysis of a reverse osmosis desalination system driven by solar-powered organic Rankine cycle and wind energy

/kW, which was ∼ 6% more expensive than that of the recompression SCO2 cycle without the bottoming cycle under the same operating condition. An optimum TCO2 turbine inlet pressure and an optimum SCO2 turbine expansion ratio existed where the system thermal efficiency reached the maximum value. Furthermore, the system thermal efficiency was very sensitive to the changes in the condensation temperature and the HTR effectiveness. The HTR effectiveness also had a strong effect on the ratio of heat exchangers’ cost to the plant capital cost. Additionally, increasing SCO2 turbine inlet temperature would significantly improve the cycle overall thermal efficiency and decrease the plant capital cost per net power output.Copyright

Experimental Study and Numerical Simulation of a Regenerative ORC Utilizing Low-Grade Heat Source

AbstractThe utilization of renewable energy for desalination can solve the problems of energy crisis and fresh water shortage. In this study, a reverse osmosis (RO) desalination system driven by solar-powered organic Rankine cycle (ORC) and wind energy is proposed, which is different from the current desalination system driven by single energy source. In order to ensure the continuous production, energy storage units are employed. A mathematical model is established to simulate the overall system which mainly consists of a solar collector subsystem, an ORC subsystem, a wind power subsystem and a RO desalination subsystem. The sensitive analysis of some key parameters, namely turbine inlet pressure, condenser temperature of ORC, feed water pressure and the water salinity, is conducted to determine the relationship between parameters and fresh water output. The result shows daily fresh water output increases with the increase in the turbine inlet pressure under the given conditions. The condenser temperatur...

Modeling and control system design of a marine electric power generating system

AbstractIn this paper, the performance of the regenerative organic rankine cycle (ORC) working with R123 is experimentally analyzed at different heat source temperatures of approximately 85, 95, 110, and 130°C. The higher heat source temperature leads to higher turbine inlet temperature, turbine inlet pressure, and turbine rotation speed. The regenerator and the increment of turbine inlet temperature can both increase the efficiency of the system. The experimental data of ORC are compared with that of the conventional Rankine cycle (CRC), which employs water as the working fluid. The results indicate that the thermal efficiency and the turbine isentropic efficiency of the ORC are higher than that of the CRC by approximately 5.9 and 24%, respectively. A numerical model is built by interconnecting different submodels: a turbine model, a volumetric pump model, and the heat exchanger models. The numerical results show a good agreement with the experimental data in terms of system efficiency. The model is fina...

Off-design performance analysis of a transcritical CO2 Rankine cycle with LNG as cold source

Steam turbine generators are generally adopted as the main generators in steam ships. A nonlinear mathematical model for marine electrical power generating system consisting of two steam turbine driving generators is developed in this paper. Primary frequency control and load frequency control systems are both designed to regulate the system frequency and electrical power. Adaptive proportional (P) controller is developed to enhance the primary frequency control performance. Proportional integral (PI) controller is employed for load frequency control. Step experiment of main steam pressure is simulated to study the system transient behavior. Load dump tests are conducted to investigate the control performance. For load frequency control, the influences of power and frequency weight and delay time between primary frequency control and load frequency control are studied, and recommendations are provided for parameter selection.

Theoretical Study of a Building Cooling Heating Power (BCHP) System Driven by Solar Energy Based on Organic Working Fluid

ABSTRACT The transcritical CO2 Rankine cycle with liquefied natural gas (LNG) as cold source is a promising power system to utilize mid- and low-temperature heat source. Most previous works focused on thermodynamic and thermoeconomic analysis or optimization for the system. In this article, an off-design performance analysis for the system is conducted. An off-design mathematical model for the system is established to examine the variation of system performance with the variations of heat source mass flow rate and temperature. A modified sliding pressure regulation control strategy, which regulates turbine inlet pressure to keep the temperature difference between heat source temperature and turbine inlet temperature constant, is applied to control the system when off-design conditions happen. The results show that when the mass flow rate or the temperature of heat source is less or lower than that of design condition, both the net power output of system and the system exergy efficiency decrease, whereas when they are more or higher than the values of design condition, the net power output of system increases but the system exergy efficiency still decreases. In addition, both CO2 turbine and NG turbine could almost keep the designed efficiency values under the applied control strategy.

Parametric Analysis of a New CCHP System Utilizing Liquefied Natural Gas (LNG)

Recently, BCHP systems as a kind of distributed energy resource present a great potential in improving energy efficiency and meeting multiple energy demands. Compared with traditional CCHP systems driven by fossil fuel, on-site renewable energy systems have more advantages in reducing carbon emissions. This paper proposes a new Building Cooling Heating Power system driven by solar energy with flat-plate solar collectors and R245fa as the working fluid. A thermal storage system is integrated into the system to store the collected solar energy and to supply heat when solar radiation is insufficient. By establishing the mathematical models of the proposed system we are able to conduct the numerical simulation of the system working in three typical operation modes around a whole year, namely the Combined Heating Power (CHP) mode in winter, the Combined Cooling Power (CCP) mode in summer, and the power production mode in spring or autumn. Results indicate that the system is able to operate continuously over a day, offering uninterrupted heating, cooling and power to building applications.Copyright

Performance Analysis and Comparison Study of Transcritical Power Cycles Using CO2-Based Mixtures as Working Fluids

Liquefied natural gas (LNG) contains considerable cold energy because a significant amount of energy is consumed to produce low-temperature LNG. So, finding a good way to utilize the LNG effectively, particularly its cold energy, is an important issue to solve the problem of energy crisis. In the present study, a new CCHP system utilizing liquid natural gas is proposed to provide cooling, heat and electricity output simultaneously to meet user’s different energy requirements. This CCHP system consists of a gas/steam combined cycle and an ejector refrigeration cycle. For cold energy utilization, LNG is firstly considered as a heat sink to condense the steam turbine exhaust in Rankine cycle, then cools down the suction air of compressor in Brayton cycle, and finally enters the combustion chamber after preheated by HRSG exhaust. The steam turbine has two streams of extraction steam. One is used to drive an ejector refrigeration cycle to produce the cooling effect, and the other is used to provide the heat. To evaluate the system performance, the exergy efficiency is selected as an evaluation criterion to eliminate the difference of energy quality. A thermodynamic simulation of the new CCHP system utilizing LNG is achieved using a simulation program. A parametric analysis is conducted to examine the effects of several key thermodynamic parameters on the performance of the proposed CCHP system. The results indicate that as gas turbine inlet temperature, pressure ratio of compressor and steam turbine inlet pressure increase, the exergy efficiency increases. In addition, as steam turbine back pressure, extraction mass rate ratio for heat, extraction mass rate ratio and extraction pressure for refrigeration increase, the exergy efficiency decreases.Copyright