Air Receiver Research Articles

A solar air receiver with porous ceramic structures for process heat at above 1000 °C – Heat transfer analysis

Abstract Concentrated solar energy can be used as the source of heat at above 1000 °C for driving key energy-intensive industrial processes, such as cement manufacturing and metallurgical extraction, contributing to their decarbonization. The cornerstone technology is the solar receiver mounted on top of the solar tower, which absorbs the incident high-flux radiation and heats a heat transfer fluid. The proposed high-temperature solar receiver concept consists of a cavity containing a reticulated porous ceramic (RPC) structure for volumetric absorption of concentrated solar radiation entering through an open (windowless) aperture, which also serves for the access of ambient air used as the heat transfer fluid flowing across the RPC structure. A heat transfer analysis of the solar receiver is performed by means of two coupled models: a Monte Carlo (MC) ray-tracing model to solve the 3D radiative exchange and a computational fluid dynamics (CFD) model to solve the 2D convective and conductive heat transfer. Temperature distributions computed by the iteratively coupled models were compared with experimental data obtained by testing a lab-scale 5 kW receiver prototype with a silicon carbide RPC structure exposed to 3230 suns flux irradiation. The receiver model is applied to optimize its dimensions for maximum efficiency and to scale up for a 5 MW solar tower.

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Open volumetric air receivers in solar tower systems are attractive for electricity generation as well as for process heat in chemical and other industrial applications. From the experience of past development stages, a new receiver concept was created with a conical cavity, with hexagonal cross-section for the modularity and a two-stage air heating. Several simulations have been performed. A prototype receiver module with approx. 175 kW thermal output has been manufactured and will be tested in DLR’s Synlight. For different module sizes the cost estimation for industrial fabrication was calculated as well as the performance, ranging from 89% to 78% at 700°C hot air temperature.

A Cost-Effective Open Volumetric Air Receiver Design Based on Free Floating Stackable Absorber Modules

The CAPTure Open Volumetric Air Receiver (OVAR) design is based on ceramic stackable “free floating” absorber modules that form the receiver structure and avoid a complex metallic double membrane design. The novel receiver design has been validated at small-scale (15 kWth) at a solar simulator, as well as on the top of an experimental tower at 300 kWth, up to absorber module outlet temperatures above 900ºC. The novel OVAR concept is attractive for both the concentrated solar power (CSP) sector, as well as for high-temperature process heat supply. The thermal efficiency of the receiver concept is expected to be above 80% at outlet temperatures of 900ºC.

Design Evaluation of Air Receiver Tank for Gas Power Plant Using Finite Element Analysis

In order to improve the power capacity in Bali, an air receiver tank is required, which is a tank used to store compressed air produced by an air compressor. The design of this air receiver tank aims to analyze the performance of the existing air receiver tank and compare it with the proposed design in this research. The analysis includes the impact of various factors on the design of the air receiver tank regarding its performance. Several components were created during the fabrication process, including the shell, bottom head, top head, and several instruments of the required components with design pressures of 10, 12, and 1.6 MPa. The research process is mapped using three methods: manual calculations based on ASME Section VIII Division I standards, finite element analysis simulation using the SolidWorks application, and hydrostatic testing. The manual calculation results indicate a shell thickness of 7.57868 mm and head top and bottom thicknesses of 7.53 mm, which are capable of accommodating the maximum pressure with MAWP (Maximum Allowable Working Pressure) values of 1.38 MPa for both the shell and head. The design script support calculation yields a result of 0.3 mm. Based on the finite element analysis simulation using the SolidWorks application, the results show that the tank can withstand a load of up to 1.6 MPa, with material stresses at the head top being 90.0 MPa, head bottom at 0.1 MPa, and shell at 15.5 MPa, with a Min-Max value of 192.0 MPa. Hydrostatic testing with variations in time indicates that the tank can handle a pressure of up to 1.6 MPa, as shown by pressure gauge II-III and temperature gauge II and III, maintaining a stable reading of 1.6 MPa and 76°F.

Experimental Investigation on the Performance of Compressors for Small-Scale Compressed Air Energy Storage in Parallel Mode

The Compressed Air Energy Storage (CAES) system is a promising energy storage technology that has the advantages of low investment cost, high safety, long life, and is clean and non-polluting. The compressor/expander is the core equipment of the CAES system, and its performance has a decisive impact on the overall system efficiency and economic performance. Based on the pneumatic motor, this study proposes and designs a test bench of the CAES system that integrates compression and expansion functions. The off-design operation condition represented by the pressure change in the air tank has an important influence on the efficiency and economy of the CAES system. The effect of key parameters such as air tank pressure, torque, and mass flow rate on the output and efficiency of the compressor is investigated. When the CAES system is operating in energy storage mode, the compressor must continuously deliver gas to the gas storage. The working pressure of the compressor increases with the pressure in the air tank, so the compressor used for energy storage must operate continuously over a wide range of working conditions. The parallel operation mode of the compressor is proposed to improve the working condition range of the compressor torque and current, and improve the isotropic efficiency. When the air receiver pressure is 2.6 bar and the rotational speed is 2850 r/min, the power consumption of the compressor reaches the maximum value of approximately 1233.1 W. This new parallel mode could provide a CAES unit a systematic solution.

MATERIAL SELECTION OF PROPOSED AIR RECEIVER TANK APPLIED FOR ELECTRICAL GENERATOR

Air receiver tank in electrical generator used as pressured air vessel is mainly consisted of shell cylinder and head part. This work has searched for the more suitable material to be used for the shell and head of the proposed air receiver tank because the older material (SPV 355) has some limitations. This study has been conducted based on several parameters in standard references. The calculations have applied relevant technical formulas such as corrosion factor, thickness design, and Maximum Allowable Working Pressure (MAWP). There are three types of selected materials available that are expected to yield similar previous condition parameters addressing to operational pressure 10 bar and temperature 40oC, i.e., SA-36 (Type I), SA-516 Gr 70 (Type II), and SS-304 (Type III). The economic factor is also taken into consideration. Considering the economic cost and mechanical characteristics, finally the material of Type II is selected to be the most appropriate material to replace SPV 355 material for the proposed air receiver tank. In the upcoming, this study is useful for the knowledge of material design.

Review of Compressed Air Receiver Tanks for Improved Energy Efficiency of Various Pneumatic Systems

This review examines compressed air receiver tanks (CARTs) for the improved energy efficiency of various pneumatic systems such as compressed air systems (CAS), compressed air energy storage systems (CAESs), pneumatic propulsion systems (PPSs), pneumatic drive systems (PDSs), pneumatic servo drives (PSDs), pneumatic brake systems (PBSs), and compressed air vehicles (CAVs). The basic formulas and energy efficiency indicators used in a CART calculation and selection are included. New scientific research by the authors on measurements based on tank methods, numerical solutions in the process of charging and discharging, the valve-to-tank-to-valve system and pneumatic propulsion system was presented. The numerical model of the valve-tank-valve system takes into account CART polytropic charging and discharging processes, the mass flow balance equation, and the sound (choked) and subsonic mass flow rate in the inlet and outlet valves. Future research directions to improve the energy efficiency of a CART charging and discharge are highlighted. The effective density of energy storage in CART was compared to that of other renewable energy sources and other fuels. Economic and environmental issues were also considered by adopting various energy performance indicators. The discussion also focused on the design concept and computational model of the hybrid tricycle bike (HTB) pneumatic propulsion system.

Parabolic Air Collectors with an Evacuated Tube Containing Copper Tube and Spiral Strip, and a New Cavity Receiver: Experimental Performance Analysis

Sunray thermal energy is one of the most promising and quickly growing techniques globally. In parabolic trough air collectors (PTAC), receiver design and safety are of paramount importance because of their impact on the overall effectiveness of power plants. However, experimental studies of alternative receivers to improve heat transfer are still to be performed. In this study, a PTAC system was tested experimentally with an evacuated tube: open on one end, containing a copper tube and a spiral strip (case 1), and with a new cavity receiver consisting of several arranged tetragonal pyramidal elements (case 2). Afterward, the results were compared and showed a slightly superior exit air temperature and thermal efficiency performance for case 1. The overall results demonstrate a remarkable convergence of case 2 from case 1 in terms of temperature increase across PTAC, in which the maximum exit air temperature for case 1 is 58.2 °C, a 3.4% increase over case 2 at 0.0105 kg/s mass flow rate. Lastly, the results validate the potential and clarify the specific conclusions of these methods’ application in improving heat exchange in a PTAC.

An exhaustive search optimization of heat transfer and pressure drop in Kelvin’s open cell foams

Thanks to their high effective thermal conductivity, specific surface area, and tortuosity, open-cell foams are well-known for their capability to enhance heat transfer in applications such as heat exchangers and volumetric solar air receivers. In the very recent years, innovative manufacturing techniques, including 3D designing and printing, have been looked very helpful to find foam morphologies that allow to maximize heat transfer and minimize pressure drop. Optimal foam structures can be obtained by means of pore-scale simulations, employing an exhaustive search with a bearable computational effort. A multi-objective optimization of convective heat transfer and pressure drop in Kelvin’s foams with air is presented in this paper. A pore-scale numerical model, with a uniform heat flux at the solid/fluid interface, is used to predict the interfacial convective heat transfer coefficient, hc , and pressure drop, Δp, in the foam. The cell size, porosity, cell anisotropy stretching factor, as well as the inlet velocity and the direction of the air, are assumed as the design variables for the optimization model, while the interfacial convective heat transfer coefficient and pressure drop are chosen as the objective functions to be maximized and minimized, respectively. Pareto fronts ranging from h = 110 W/m2 K and Δp = 0.77 Pa to hc = 460 W/m2 K and Δp = 51 Pa are predicted, within which the optimum point for the chosen foam morphology, air velocity and direction can be selected, according to the chosen criterion.

Thermal and electrochemical performance analysis of an integrated solar SOEC reactor for hydrogen production

Hydrogen can be produced efficiently by combining solar energy and solid oxide electrolysis cell (SOEC). This paper proposes an integrated solar SOEC reactor, which integrates a volumetric air receiver with a tubular SOEC. The hot air from the air receiver can directly heat the tubular SOEC and thus avoid transport heat loss. Under the reference condition, the reactor's water conversion ratio and energy conversion efficiency are 74.13% and 25.58%, respectively. The simulation results indicate that solar irradiation significantly affects the reactor's thermal and electrochemical performance. When the peak incident flux density of solar irradiation decreases from 0.49 MW/m2 to 0.21 MW/m2, the water conversion ratio and energy conversion efficiency drop by 96.41% and 84.49%, respectively. Adjusting the air flow rate may help maintain the reactor temperature to avoid a reduction in the water conversion ratio and energy conversion efficiency.

Thermal stress durability and optical characteristics of a promising solar air receiver based black alumina ceramics

In solar thermal technology, solar receiver materials with high solar absorptivity and photocatalytic efficiency have recently become a mandatory requirement for promoting and maximizing the released thermal and electrical energy. This paper presents a detailed study of the optical performance and thermal stress durability of the promising solar receiver material, black Al2O3/CuO ceramics. Different Al2O3/CuO ceramics with different CuO content (10–40 wt%) were obtained by the pressureless sintering method. Optical properties such as solar absorbance and reflectance, band gap energy and photoluminescence are inclusively investigated. The thermal stress resistance of the obtained ceramic receivers is simulated using the finite element modeling (FEM) method at different temperatures. Results indicated that adding and increasing the content of CuO to Al2O3 has a significant role in transforming alumina from a non-solar light-absorbed material to a solar absorber material with high absorptivity in the Ultraviolet–Visible-Near Infrared (UV-VIS-NIR) spectrum. Composite with 40 wt% CuO has recorded the maximum absorbance of 75% in the visible light region. Moreover, Al2O3/CuO ceramics gave multiple graded band-gaps in the range of (1.6–5 eV). Composites with high wt% of CuO have the most increased photocatalytic activity and light emissivity efficiency. Thermal stress analysis of the different ceramics showed outstanding stress durability with uniform heat distribution. Hence, black Al2O3/CuO ceramics can be considered ideal solar absorber materials with high sustainability and durability at high temperatures.

Isobaric storage of compressed air: Introduction of a novel concept based on phase change materials and pressure equalizing modules

In industrial compressed air systems (CAS), compressed air receivers have a significant impact on the overall energy efficiency. Isobaric compressed air receivers have the potential to increase the amount of stored air significantly and, hence, the energy efficiency can be improved compared to the usage of conventional isochoric compressed air receivers. In this work, we propose a novel concept of an isobaric compressed air receiver based on pressure equalizing modules (PEQM). These PEQM are filled with a condensable gas – in this work called phase change material (PCMl/g) – and are placed inside the receiver. During the charging and discharging of a compressed air receiver equipped with PEQM, the PCMl/g condenses or evaporates, respectively. Due to the large volume change during the phase change of the PCMl/g air can be stored isobarically. However, a proper selection of suitable PCMl/g is crucial for efficient and safe use. Therefore, we introduce a three-step selection process based on an adapted digital-logic method. In this selection process, qualitative (e.g. flammability) and quantitative (e.g., heat of condensation) properties are considered. As a result, R-1234ze(E) is selected as PCMl/g which owns a vapor pressure of 800 kPa at a temperature of 314.7 K. First experiments with the novel PEQM filled with R-1234ze(E) have been conducted in a lab-scale test plant and the results are shown in this work. The storage capacity of the test plant has been increased by 37.9 %. Additionally, the phase change of the PCMl/g during charging and discharging has been observed. However, the phase change is not isobaric yet. Temperature changes during the phase change inside the PEQM hinder the isobaric storing of the working gas. Therefore, proper heat management inside the PEQM is necessary, for example, by using a second phase change material for heat storage.

IMPROVMENT OF ENVIRONMENTAL PERFORMANCE TWO-STROKE DIESEL DURING OPERATION

The development of world shipping is taking place in the context of ever-increasing requirements to reduce the concentrations of toxic components of gaseous combustion products of hydrocarbon fuels. Concentration limits for these substances are regulated in accordance with Appendix VI of the MARPOL 73/78 Convention. Among the controlled components of diesel exhaust gases, nitrogen oxides are the most dangerous for humans and environment. However, a decrease in the content of nitrogen oxides is inevitably associated with limitations on the maximum cycle temperature, that is, thermal efficiency, and hence with a deterioration in the fuel efficiency of the engine. At the moment, in order to reduce emissions of nitrogen oxides by large transport diesel engines, the most widely used is the recirculation of exhaust gases into the air receiver. A significant disadvantage of using this scheme is the need for cooling the exhaust gases and their additional purification, which leads to an increase in the weight and size characteristics of the system and to its rise in price. Therefore, to reduce its cost, it seems logical to combine exhaust gas recirculation with other ways to reduce nitrogen oxide emissions. For engines in operation, one of these methods is to change the angle of fuel injection. It can be assumed that the later the fuel is injected into the cylinder, the lower the temperature of the air charge will be and, accordingly, the lower the maximum combustion temperature, and hence the amount of nitrogen oxides. The calculation of nitrogen oxide emissions was simulated for the main engine MAN-B&W 7S50MC-C installed on the vessel "LILA SHANGHAI". Initially, the model created using the AVL-BOOST package was verified based on the available indexing results. After verification, the calculation of emissions of nitrogen oxides NOx was made with a variation in the angle of the start of fuel combustion at the nominal mode. The composition of the gases in the receiver was taken unchanged. As the fuel combustion start angle shifted further from the TDC, deterioration in fuel efficiency and a drop in cylinder power were observed, while reducing the mass of emitted nitrogen oxides NOx. However, it can be said that the environmental friendliness of an engine improves much faster than its fuel and power characteristics deteriorate. The above calculations show that for engines already in operation, changing the fuel injection angle makes it possible to reduce nitrogen oxide emissions. Therefore, this approach can be combined without much difficulty with other methods, thus reducing the cost of environmental improvement of the engine.

Experimental evaluation of wind induced pressure fluctuations in cavity shaped open volumetric air receivers

In this study wind induced surface pressure fluctuations during operation of an open volumetric cavity receiver were investigated in wind tunnel experiments. Due to the process design of the open volumetric receiver, surface pressure fluctuations impact the receiver mass flow which is crucial for cooling the highly irradiated receiver. For this study a model of a solar tower was constructed under the concept of similitude which allows wind tunnel experiments at Reynolds numbers up to 13.17 × 106. Transient pressure measurements were conducted under 17 different flow directions to evaluate the impact of separation induced pressure fluctuations. The experimental design further allows a rotation of the model to evaluate the impact of changes in wind direction on the surface pressure at the receiver. For cases under a constant wind direction, a critical angle range could be identified in head on wind with a horizontal inclination of 45.0 to 78.8° relative to the central receiver axis. The results further show that surface pressure fluctuations are more sensitive to changes in wind direction as the amplitudes with maximum 20Pa for a Reynolds number of 13.17 × 106 are about one order of magnitude higher compared to the cases with a constant flow direction. Furthermore, a frequency analysis shows the shielding effect of the cavity design for side-wind as no peaks in the pressure spectrum appear. For flow directions within the critical range of 45.0 to 78.8° a main vortex shedding frequency under constant Strouhal numbers of 0.25 to 0.50 can be observed.

Thermal Performance Improvement of Modified Hemispherical Cavity Receiver with Air Curtain

Heat losses from solar cavity receivers degrade the efficiency of solar parabolic dish collector system. Specifically, increased convection losses emulate a significant contribution in decreasing the performance of the modified solar cavity receiver and hence, reducing these convection losses has become a matter of great concern. The Air curtain plays a crucial role in minimizing the convection losses. This work proposes an air curtain-based modified cavity receiver wherein a plane nozzle is placed on the face of receiver to produce air curtain effect. Air curtain will prevent hot air from escaping the modified cavity receiver and increase the stagnation zone inside it to reduce natural convection on the surfaces. Numerical analyses are performed considering different air velocities and receiver orientations to evaluate the effect of air curtains on the convection losses. The impact of plane air nozzle parameters like outlet temperature, inclination, and outlet velocity of the nozzle on convection losses are shown and these parameters’ optimal value is evaluated. Our results state that the air curtain attached to the modified solar cavity receiver significantly improves performance by reducing the convection losses.

Numerical and experimental studies on a pressurized hybrid tubular and cavity solar air receiver using a Scheffler reflector

• Coupled optical and thermal model of a pressurized tubular and cavity solar air receiver. • Modelled the dynamic variation of concentrated solar radiation input to the receiver cavity surface. • Three-dimensional CFD analysis is performed on the hybrid receiver model. • Validation with on-sun experimental results using a Scheffler dish. • Natural convection and radiation heat loss estimation. In this study, a pressurized tubular and cavity solar air receiver is analyzed numerically, and the results are validated experimentally using a Scheffler fixed focus concentrator. Transient numerical analyses for periods similar to experimental testing duration allows realistic performance prediction of new receiver designs and help in understanding the dominant heat loss mechanisms, thus mitigating or reducing them. A coupled optical and thermal model is developed for analyzing the receiver with a novel method of capturing the spatial and temporal variation in the heat input to the receiver. The concentrated heat flux input to the receiver is defined as the product of two separate functions. The first function defines the incident radiation to the receiver as a spatially resolved flux profile on the cavity inside surface, obtained from the ray tracing algorithm. The second function captures the transience in heat input by curve-fitting the measured direct normal irradiation variation with time corresponding to the experimental testing period. Receiver heat loss modelling involves natural convection heat loss from the inside cavity surface estimated using an existing correlation, while radiation heat loss is estimated by prescribing the surface emissivity and computing the ambient view factor. A three-dimensional transient CFD analysis is performed on the hybrid receiver model under identical heating conditions as experiments to predict the flow heat transfer. The result from the numerical model is subsequently compared with on-sun experimental results obtained using a test rig equipped with a Scheffler dish for heat input and supply of compressed air as the heat transfer fluid through the receiver. The deviation between numerical and experimental results are less than 16 °C for air outlet temperature and less than 9% for the receiver thermal efficiency, thus proving the effectiveness of the coupled optical and thermal model. To account for the transient nature of the receiver heating during the on-sun experiments, the receiver thermal efficiency definition has been modified to include the thermal inertia of the receiver material. It is also observed that natural convection is the dominant heat loss mechanism for the present configuration and can significantly reduce the overall thermal efficiency of a receiver. The present numerical model incorporating an optical model of the solar field and as-measured variation of solar radiation input can be effectively used for optimizing the design of any generic concentrator-receiver system with high-pressure heat transfer fluid, with the objective of minimizing thermal losses.

Experiment and dynamic simulation of a solar tower collector system for power generation

Solar air Brayton cycle is a promising option to adjust the renewable power fluctuation due to its quick load regulation capacity. For the successful design and deployment of the solar air Brayton cycle system, the dynamic operation performance of solar collectors under real operating conditions are of great importance. In this study, experiments of a solar collector consisting of the heliostat field and the air receiver are carried out. Based on the experimental investigation of the operating characteristics for the solar collector, a dynamic model is further developed and well-validated to couple the heliostat field and air receiver. The dynamic performance of the air receiver is studied with various factors, including the DNI change and the receiver heat capacity. The results show that the receiver outlet temperature can reach up to 882 °C with a pressure loss of 7.10 kPa and a thermal power of 132 kW during the experiment. Two operation strategies of the air receiver are compared by carrying out the intraday simulation and the constant-outlet-temperature control strategy is more suitable for fast start-up. The method developed in this paper can serve as an efficient tool for the understanding, design and optimization of solar collectors.

Determining the Benefit of Air Receivers in South African Deep-Level Mines Using a Genetic Algorithm

Determining the Benefit of Air Receivers in South African Deep-Level Mines Using a Genetic Algorithm

Sistem Monitoring Instrument Air System Berbasis Internet Of Things di PT.Parna Raya

There is an operation process for facility & equipment support in the distribution process of the oil and gas company such as the Pressure Regulating System and Process Shutdown Valve. The supporting equipment uses pneumatic actuators as a driving force whose power source comes from air, as from the fact the compressor as an air producer is still manually used and the air pressure in the air receiver is not monitored from the control room. The purpose of this research is to develop the previous system by creating an integrated system that can be monitored remotely in real time by adding several electronic devices and utilizing Internet of Things technology. Based on the research that have been carried out, the pressure sensor has good accuracy with an average error of 0.06%, so it can be a reference in monitoring the pressure on the air receiver and a notification alarm will appear if the pressure on the air receiver reads 5.5 Bar as evidenced by testing 10 times the average pressure read on the blynk app of 5,460 Bar. Hardware and software function properly according to the design, air pressure at the air receiver and status of the compressor in stand-by or running state can be monitored through the blynk app, so that the gas distribution process does not stop again

A Multi-Zone Unsteady Heat Transfer Model for an Open Volumetric Air Receiver: A Step Towards Scale-Up and Design Optimization

A comprehensive, multi-zone, unsteady heat transfer model is developed for a straight absorber pore-based open volumetric air receiver. This includes heat exchange between the porous absorbers, absorbers and receiver casing, and absorbers and return air. The validation revealed its predictive capability within an uncertainty of ±7%. The model is used for the scale-up of receiver design with several intermediate absorber layers. The major recommendations for scale-up are a) multiple absorber layers is beneficial for mitigating thermal stress, b) higher flux concentration is required for non-volumetric heating, to achieve the desired air temperature, compared to volumetric heating, c) air return ratio should be 0.6, d) absorber porosity should be 0.6 for volumetric heating and higher for non-volumetric heating, e) absorber gap to length ratio should be 0.15 -0.25, f) the radiative heat loss is substantial for non-volumetric heating; therefore, the exposed surface area to ambient should be reduced, and g) absorber diameter to length ratio should be 1-2. The developed approach is generic and adaptable for the different open volumetric air receiver designs.