Dynamic simulation of steam generation system in solar tower power plant

Concentrated solar power (CSP) plant with thermal energy storage can be operated as a peak load regulation plant. The steam generation system (SGS) is the central hub between the heat transfer fluid and the working fluid, of which the dynamic characteristics need to be further investigated. The SGS of Solar Two power tower plant was selected as the object. The mathematical model with lumped parameter method was developed and verified to analyze its dynamic characteristics. Five simulation tests were carried out under the disturbances that the solar tower power plant may encounter under various solar irradiations and output electrical loads. Both dynamic and static characteristics of SGS were analyzed with the response curves of the system state parameters. The dynamic response and time constants of the working fluids out of SGS was obtained when the step disturbances are imposed. It was indicated that the disturbances imposed to both working fluids lead to heat load reassignment to the preheater, evaporator and superheater. The proposed step-by-step disturbance method could reduce the fluid temperature and pressure fluctuations by 1.5 °C and 0.03 MPa, respectively. The results could be references for control strategies as well as the safe operation of and SGS.Peer reviewe

Study on thermal-hydraulic characteristics of novel channels for printed circuit heat exchanger using supercritical CO2

© 2023 The American Society of Mechanical Engineers. All rights reserved. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1115/1.4062998Two new types of PCHE channels are proposed based on the typical airfoil fin PCHE channel proposed in literatures (standard channel) to further improve the thermal-hydraulic performances of airfoil fin PCHE channel. The small shuttle fins and oval fins are employed between the adjacent two airfoil fins of two novel channels, respectively. Using supercritical CO2 as the working fluid, the thermal-hydraulic performances and enhancement mechanisms of the novel channels are numerically investigated. The results show that the channel with shuttle fins has the best comprehensive performance. The Nusselt number of the channel with shuttle fins is 6.7–26% larger, and the f factor is 8.3–18.6% larger than that of the standard channel under the selected conditions, which leads to a 3–19.1% increase in the PEC (comprehensive performance evaluation criteria). The Nusselt number of the channel with oval fins is 9–27.3% larger, and the f factor is 26.6–43.4% larger than that of the standard channel, which leads to a 1–15.3% increase in the PEC. The applications of small fins between the adjacent two fins can effectively reduce the low-velocity region area and enhance the local disturbance, thereby effectively improving the thermal-hydraulic performance. The enhancement mechanism of the novel fin PCHE channel structure can be well explained by the principle of field synergy. It can be found that the synergies of the temperature gradient field and the velocity field in two novel channels are significantly improved.Peer reviewe

Numerical Simulation of Plate Evaporators in Multi-effect Distillation Seawater Desalination

AbstractOwning to the high heat transfer coefficient and relatively small heat transfer areas, plate evaporator is now becoming more dominant in the desalination market. However, literatures on plate evaporator performance for seawater desalination are rather limited. Physical and mathematics model for plate evaporator with corrugated plate was developed for computational fluid dynamics (CFD) simulation. Two-phase flow and heat transfer characteristics in the channel of plate evaporator were analyzed in detail. The effects of different geometric parameters of corrugated plate inclination angle on seawater evaporating performance were revealed and discussed. In order to verify the simulation results, the experimental correlation for flow performance characteristics of plate evaporator was employed to compare with that of CFD results. The results may benefit the design of plate evaporators for multi effect distillation seawater desalination

Photocatalytic reduction of CO2 by CO co-feed combined with photocatalytic water splitting in a novel twin reactor

As a promising way to control greenhouse gas emission and alleviate global energy shortage, photocatalytic reduction of carbon dioxide attracts more attentions in recent years since it can produce fuels efficiently with the combination of H2 through water splitting. In this work, a computational model which characterizes the photocatalytic reduction of carbon dioxide by CO co-feed in a novel twin reactor is developed with three subsidiaries of chemical reaction kinetics, gas–liquid mass transfer, and transient sun light intensity distribution. Thanks to previous experimental work as the reliable verification for the numerical simulation, the variations of the CH3OH concentration with the CO/CO2 ratio of gas mixture, pressure and temperature are obtained and analyzed. The results show that the carbon in CO can form CH3OH directly, however the excessive CO will react with HCOOCH3 to form CH3CHO, which results in a reduced CH3OH concentration. Besides, the CH3OH concentration subsequently increases as the temperature and pressure increase, and the CH3OH product and reaction rate vary widely with time due to the changing sun light intensity during the day

Enhanced photocatalytic reduction of carbon dioxide in optical fiber monolith reactor with transparent glass balls

Photocatalytic reduction of carbon dioxide to produce methanol is a promising approach to restrain greenhouse gases emissions and mitigate energy shortage, which attracts extensive concerns in recent years. The optical fiber monolith reactor with solid glass balls for photocatalytic carbon dioxide reduction is proposed in this work to increase the product concentration, and the glass balls are transparent and coated with photocatalysts evenly to absorb light. The photocatalytic reduction of carbon dioxide in optical fiber monolith reactor is numerically investigated, by which the effects of glass ball number, location, circle and layer on the production are analyzed. The results show that in the single-circle and single-layer model, the outlet methanol concentration increases with increasing the ball number. The closer to the fiber and reactor inlet the balls keep, the higher the methanol production is. As the circle and layer numbers increase, the methanol concentration also increases. The outlet methanol average concentration of the optical fiber monolith reactor with 3-circle and 5-layer balls gets 11.43% higher than the case without glass balls

Novel design of central dual-receiver for solar power tower

A novel dual-receiver with a surrounding solar field was proposed to improve the efficiency of a solar power tower (SPT). The new design combined an external and a cavity receiver, corresponding to the boiling and superheating sections respectively, and provided a simple yet controllable heat flux distribution on both sections. A case study of a 11 MW solar power plant was conducted. It was demonstrated that the present dual-receiver could produce superheated steam of 515 °C and 10.7 MPa at an impressive solar heat absorbing efficiency of 86.55%. By considering various heat losses, the surface heat flux, the surface temperature and the heat transfer fluid distribution were obtained for the dual-receiver. A comparison with a two-external cylindrical receiver showed that the present design could improve the global thermal efficiency by 3.2%. Off-design performance of the dual-receiver indicated that the plant performance was affected significantly by the incident solar fluxes at different times of a day. The influence of heat transfer tube size suggested that an optimized tube diameter for the superheating section of the present dual-receiver should be used

Off-design performance of concentrated solar heat and coal double-source boiler power generation with thermocline energy storage

Integration of solar thermal energy into a coal-fired power station is a promising technology for many coal-dependent countries. This work investigated the off-design performance of such a dual heat source boiler power generation from a system-level modelling approach. As an example study, heat from a solar power tower (SPT) was integrated into a 660 MW supercritical coal-fired power unit, and two integration schemes were considered. A system level analytical model was established that coupled the transient process of heliostat field with one-tank thermocline thermal energy storage. The off-design performance of such a hybrid system in one typical year was analyzed accordingly. The results revealed the importance of the seasonal variation of direct normal insolation (DNI), thermal energy storage scheme and integration methodology. Both the quality of sunshine and the amount of sun flux could influence the solar power efficiency; while an increase in the storage volume could decrease the discharging efficiency. Under the maximum capacity of DNI, increasing the storage capacity by 1 h could improve the efficiency by 0.5–0.8%. For either integration scheme, the coal consumption could be economized at least 9 × 103 ton per year. The maximum of solar efficiency for Scheme I, where solar energy was used to heat the superheat steam, could reach 20.42%, which also came with a penalty of reduced efficiency of thermal receiver. Under the minimum storage capacity, the solar efficiency for Scheme I was changed from 16.7% to 19.6%, while for Scheme II the change was from 14.7% to 17.3%