Open Volumetric Air Receiver based Solar Convective Furnace System

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Date
30-06-2023
Researcher
Kumar, Vishwa Deepak
Supervisor
Chandra, Laltu
Mukhopadhyay, Sudipto
Journal Title
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Publisher
Indian Institute of Tehcnology, Jodhpur
Abstract
Electrical energy from fossil fuels or gas-fired systems is commonly used as a heat source for industrial process heating, such as the heat treatment of metals, which leads to harmful emissions. Freely available solar energy is a viable option for transitioning to a net zero carbon economy and reducing emissions. For instance, harnessed solar energy with a concentrated solar thermal (CST) system may be utilized, for example, in the melting, coating, and joining of metals. Recently, a novel, retrofitted solar convective furnace (SCF) system was developed for the heat treatment of Aluminum using hot air from a heliostat-based CST system. The developed SCF system comprises an open volumetric air receiver (OVAR), two pebble-bed sensible thermal energy storage (TES) systems, viz. primary and secondary, and the furnace itself. The OVAR produces hot air using the concentrated solar irradiance onto its aperture. The generated hot air is transported to the SCF directly or indirectly via the primary TES. The secondary TES is utilized for waste heat recovery from hot air at the furnace outlet. The feasibility assessment of the SCF system is performed using a two-step approach: (1) experiments are performed for each of the sub-systems and the integrated system, and (2) mathematical models are developed for scaling of OVAR, each of the sub-systems, and the integrated system analysis. The details are described as follows: Parametric experimental investigations are performed with primary TES for charging and discharging processes to evaluate its thermal evaluation. The experimental investigations for primary TES showed that the time-averaged charging and discharging efficiencies are 65-70% and 72-75%, respectively. Further analyses revealed the exergy efficiencies for charging and discharging are 45-50% and 58-60%, respectively. Experiments are performed to investigate heat transfer in the retrofitted solar convective furnace. These experiments include a provision for external heating for SCF. Experimental results of SCF, such as temperature profile and heating process, show the capability of heat treatment of metal-ingot via forced convection. For the numerical design, OVAR size (a key component of SCF) is selected based on a preliminary calculation for 0.58 MW capacity Aluminum furnace, with direct normal irradiance (DNI) of 220 W/m2 and a concentration ratio of 600. The modelling of unsteady heat transfer in OVAR is done by considering multiple zones of the receiver, viz. central, intermediate, and peripheral zones. The model was validated with experimental data and a two-zone model, which demonstrated the model's prediction capability within ±7%. A parametric investigation is carried out for the planned scale up OVAR design. An unsteady heat transfer model is developed for the TES. Analysis revealed that the deviation between the computed and experimental temperature is within ±15%. Also, a one-dimensional mathematical model is developed to analyze the unsteady heat transfer process for the retrofitted SCF. The calculations show a deviation of about ±15% from the experimental data. Finally, a mathematical model is developed for the installed lab-scale SCF system, including OVAR, connecting pipes with insulation, and TES. Findings demonstrate the potential of using the developed CST-based SCF system for the heat treatment of metal. However, the integrated model needs to be refined for better results and may be addressed in future.
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Citation
Kumar, Vishwa Deepak (2016). Open Volumetric Air Receiver based Solar Convective Furnace System (Doctor's thesis). Indian Institute of Tehcnology, Jodhpur
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