Performance Improvement of a Solar-Powered Recompression Supercritical Carbon Dioxide Cycle by Introducing an Ammonia-Water Cooling-Power System

The wide utilization of solar energy is beneficial for the emission reduction of carbon dioxide. This paper proposes a novel power cycle system driven by solar energy, which consists of a recompression supercritical carbon dioxide cycle (RSCO2) and an ammonia-water cooling-power cycle (ACPC). The power system operates in a “self-production and self-sale” mode, which means that the refrigeration capacity produced by the ACPC is utilized to cool the main compressor inlet fluid of the RSCO2. The comprehensive energy and exergy analyses of the proposed novel system are presented. The effects of the six parameters on the system thermodynamic performance are evaluated, which are direct normal irradiation, the ammonia concentration of a basic solution, the pinch point temperature difference of an evaporator, the effectiveness of a recuperator, the pressure ratio of the RSCO2 and the molten salt outlet temperature. The results show that compared with the stand-alone RSCO2, the net power and energy efficiency of the proposed system are improved by 15.94 and 10.61%, respectively. In addition, the increasing ammonia concentration of the basic solution leads to the rise of the ACPC refrigeration output, and the inlet temperature of the main compressor can be declined to 32.97°C with the ammonia concentration of the basic solution of 0.88. Moreover, when the effectiveness of the recuperator in RSCO2 rises up to 0.98, the system energy and exergy efficiencies can reach their maximum value of 30.68 and 33.10%, respectively.

Research on Response Characteristics and Control Strategy of the Supercritical Carbon Dioxide Power Cycle

With the development of GEN-IV nuclear reactor technology, the supercritical carbon dioxide (SCO2) Brayton cycle has attracted wide attention for its simple structure and high efficiency. Correspondingly, a series of research has been carried out to study the characteristics of the cycle. The control flexibility of the power generation system has rarely been studied. This paper carried out a dynamic performance of the 20 MW-SCO2 recompression cycle based on the Simulink software. In the simulation, the response characteristics of the system main parameters under the disturbances of cooling water temperature, split ratio, main compressor inlet temperature and pressure were analyzed. The results show that the turbine inlet temperature is most affected by the disturbances, with a re-stabilization time of 2500–3000 s. According to the response characteristics of the system after being disturbed, this study proposed a stable operation control scheme. The scheme is coordinated with the main compressor inlet temperature and pressure control, recompressor outlet pressure control, turbine inlet temperature control and turbine load control. Finally, the control strategy is verified with the disturbance of reduced split ratio, and the results show that the control effect is good.

Mathematical modeling of electric consumption of the gas cooling process

In the article, the possibility of determining the consumption of electrical energy by gas air cooling devices. Special attention is paid to the processing of experimental results. There are some assumptions in the mathematical model that do not affect the final result. The factors influencing the consumption of electric energy by gas air coolers are given. It is stated that the ambient temperature and gas pressure significantly affect the consumption of electrical energy. Thus, based on experimental data, a model of electrical energy consumption by gas air cooling devices of main compressor stations has been obtained.

Thermodynamic performance analysis of supercritical carbon dioxide Brayton cycle

S-CO2 (supercritical carbon dioxide) is used as working fluid for power system cycle. This paper presents thermodynamic performance analysis results on S-CO2 Brayton cycle. Based on the assumptions of the relevant initial parameters, the mathematical models of compressor, turbine, recuperator and heater are constructed, and the thermal efficiency of regenerative Brayton cycle and recompression Brayton cycle are calculated and analyzed. The results reveal that the efficiency of the recompression cycle is higher than that of the simple regenerative cycle. The effects of inlet temperature, inlet pressure of the main compressor and inlet temperature, inlet pressure of the turbine on the thermodynamic performance of the recompression cycle are studied, and the influencing mechanism is explained. The results show that the cycle efficiency decreases with the increase of the inlet temperature of the main compressor; there exists an optimum inlet pressure in the main compressor to maximize the cycle efficiency; and the cycle efficiency of the system increases with the increase of the inlet temperature and pressure of the turbine. When the inlet temperature of the turbine exceeds 600 ?, the thermal efficiency of the cycle can reach more than 50%.

Development of operation strategy for recompression supercritical CO2 cycle with intercooled main compressor under off-design condition

The supercritical carbon dioxide (S-CO2) cycle is regarded as a potential option for the next generation power conversion system. Concentrated solar power (CSP) plant is one of the promising scenarios to adopt the S-CO2 cycle due to the appealing thermal efficiency and the ability to integrate thermal storage and dry cooling. Among various cycle configurations of S-CO2 cycle, the recompression S-CO2 cycle with intercooled main compressor is one of the optimal choices that can provide superior efficiency and a large enough temperature differential for thermal input, which together contribute to the minimization of the overall levelized cost of electricity (LCOE) of the whole CSP plant. The off-design performance and the associated control scheme have important effects on the CSP plant. This paper develops an off-design model for the recompression S-CO2 cycle with intercooled main compressor for the commercialized hundred-megawatt CSP plant. The effects of different off-design conditions on cycle performance are first evaluated. Different operating strategies regarding the control of cycle maximal pressure and preventing abnormal compressor conditions during off-design operation are then presented and compared. This work is expected to provide knowledge for the optimal control of recompression S-CO2 cycle with intercooled main compressor during the real operation of the CSP plant.

The Impeller Exit Flow Coefficient As a Performance Map Variable for Predicting Centrifugal Compressor Off-Design Operation Applied to a Supercritical CO2 Working Fluid

A multi-stage centrifugal compressor model is presented with emphasis on analyzing use of an exit flow coefficient vs. an inlet flow coefficient performance parameter to predict off-design conditions in the critical region of a supercritical carbon dioxide (CO2) power cycle. A description of the performance parameters is given along with their implementation in a design model (number of stages, basic sizing, etc.) and a dynamic model (for use in transient studies). A design case is shown for two compressors, a bypass compressor and a main compressor, as defined in a process simulation of a 10 megawatt (MW) supercritical CO2 recompression Brayton cycle. Simulation results are presented for a simple open cycle and closed cycle process with changes to the inlet temperature of the main compressor which operates near the CO2 critical point. Results showed some difference in results using the exit vs. inlet flow coefficient correction, however, it was not significant for the range of conditions examined. This paper also serves as a reference for future works, including a full process simulation of the 10 MW recompression Brayton cycle.

Semi-Closed Recuperated Cycle With Wet Compression

The semi-closed recuperated cycle (SCRC) has been suggested earlier by the author in several versions. The best of them used two compressors with one intercooling stage each. In this paper the intercooled main compressor has been replaced by a compressor with high fogging and no intercooling anymore. It is assumed that the system and the main compressor have its design points in the middle of the intended fogging water injection range. This turns out to allow another thermal efficiency gain by 2 to 3 percent points to clearly above 60% also combined with increased specific power related to the consumed combustion air and with no bottoming cycle. This paper demonstrates the technical feasibility based on Turbomachinery technologies, which have already proven commercial viability. The thermodynamic assumptions have been derived from existing gas turbine (GT) technology and are used within already confirmed operating ranges. With the same firing temperature also the thermal efficiency level of current Combined Cycles (GTCC) can be achieved. A special feature of the SCRC is the opportunity for inventory control of part load operation. This means that part load operation can be made by pressure reduction instead of temperature reduction as in open gas turbines. Thermal transients leading to hot part life consumption can therefore be avoided to a large extent and the combustor can operate at nearly constant temperature also at low part load with corresponding low emissions. Low part load operation achieves the same efficiency as base load. The result is more flexibility than in current GTCC technology associated with less complexity due to the needlessness of an extra bottoming cycle. Realizing this type of cycle aiming at its best efficiency potential however needs the development capability of a highly skilled gas turbine manufacturer. But it could also be developed for a lower efficiency range by using existing components with conservative data. The SCRC concept could also be aimed at combined heat and power applications or at naval propulsion by replacing CODOG’s. Due to its specific features the SCRC in general or with wet compression could be developed in the micro turbine power output size as well as up to above 1000MW single block size. Its inherent water condensation at elevated pressure makes an external source of make-up water obsolete.

Reynolds Number Effects in Axial Compressors

The influence of variations in flow Reynolds number on the performance of axial compressors has been studied (changes in Reynolds number being, for the most part, achieved by changes in the inlet total pressure at or near the design speed). The measured results, so achieved, have been correlated to show how the main compressor performance parameters vary with Reynolds number. Reference has been made to cascade data to assist in choosing the form of the correlation, which is essentially empirical. A good correlation of the measured performance changes on component tests has been obtained. The method described, therefore, appears to be satisfactory for predicting trends for project assessments and avoids considering the detailed flow changes that occur within the machine as the Reynolds number is varied.