Process Heat Applications Research Articles

Performance enhancement of Scheffler concentrator receiver using Conical type Secondary Reflector (CSR) fitted with toughened glass cover

Fixed focus type Scheffler Concentrators and convex receivers are popularly employed for several medium temperature process heat applications. The excessive convection heat loss from the receiver surface and the improper distribution of solar flux at the receiver are few key issues commonly observed for the Scheffler concentrators. The excessive heat lost is attributed to the convection losses at the receiver convex surface due to the wind. Moreover, experimental studies carried out on the receiver of 16 m2 Scheffler concentrator revealed that about 15–20 % of the total radiations received at the receiver are lost due to the focusing and tracking errors of the Scheffler reflector. In order to minimize the heat losses from the receiver convex surface, a Conical type Secondary Reflector (CSR) made up of highly polished mirror finished stainless steel material, in the form of frustum of a cone, and covered with toughened glass was designed and developed. The semi-cone angle of 36° has been estimated for the CSR based on the ray trace diagram analysis. The CSR, fixed over the periphery of the convex type receiver refocuses the lost solar radiations over the receiver surface and enhances the heat flux received at the receiver, while improving the overall efficiency of the concentrator. The toughened glass cover over the CSR, shields the receiver from the wind and thus reduces the overall convection losses due to wind. Experimental analysis carried with the installation of CSR revealed that the convective heat transfer coefficient has been reduced by 10–12 % on average while the overall system efficiency has been increased by at least 3–5 %. The increased heat flux received at the receiver has not only reduced the convection losses but also reduced the initial idle or lag time for the system by almost 15 min based on the solar insolation for the day.

A dual-mode novel Parabolic Trough Collector for process heating applications in small scale industries—Thermo-hydraulic and performance investigation

Only a few industries worldwide use solar heat for industrial processes, despite the fact that it is a proven and cleaner solution. More over, Small-scale industries need hot water and low-enthalpy steam, but such systems receive scant attention due to the active nature of Parabolic Trough Collectors as well as the use of less efficient flat plate technology in this temperature range. This delineate the opportunity for research focus in efficient passive technologies especially in low temperature range. In this regard a novel dual mode Parabolic Trough Collector based on an Open Natural Circulation Loop (PTC-ONCL) is proposed here. Focus of this work is to assess the proposed system’s suitability for process heating applications requiring hot water/low enthalpy steam, especially in rural areas. Experiments are conducted on an in-house prototype. A novel methodology for correlating actual solar data to the input heat load for the in-house test facility is developed. Five representative solar days are considered for individual tests. Startup, transient, and efficiency parameters are evaluated. Productivity, industrial viability, and environmental impact are also accessed. Throughout the test, the loop maintained a stable flow, where the start-up oscillations, thermal oscillations and type-I instabilities are observed. The system operates at an unprecedented efficiency of 72 ± 4% in hot water mode and 70 ± 5% in Steam generation over a 7 h period. The economic analysis shows an ambitious Levelized Cost of Heat of 2.8 cents/kWh, with a payback period of 3.21 years. Moreover environmental study shows its huge potential in reducing the CO 2 emissions. A dimensionless index is proposed to represent the solar day and is correlated to predict the average water temperature and steam generated with RMSE values of 0.98 °C and 0.125 kg respectively. The solar day index comprehends the total irradiation, wind velocity and the ambient temperature. The proposed PTC-ONCL system is capable of producing an annual average of 8.67 kgday −1 and/or 150 L of hot water at an average temperature of 89.07 °C. The results, and the system’s low cost and near-maintenance-free nature demonstrates its capability in the desired application, both technologically and economically. • A passive Parabolic Trough Collector based on an Open Natural Circulation Loop for process heat at low temperature. • New methodology correlates actual solar data to input for an in-house test facility. • Generates 8.67 kg of steam/ hot water at 89 °C on a yearly average with 65% efficiency. • Levelized Cost of Heat of 2.8 cent/kWh & 3.2 years of payback period found promising. • Dimensionless solar day index includes combines irradiation and ambient condition.

Prospects and Challenges of Solar Thermal for Process Heating: A Comprehensive Review

To mitigate the consequences of climate change, there is an increasing need to minimize the usage of fossil fuels, especially in the industrial sector because the majority of the industrial sector primarily rely on fossil fuels to meet their needs for heat energy, and a practical strategy to reduce reliance on fossil fuels is to use energy from the sun. Due to their environmental advantages, energy security, and viability as a potential substitute for fossil fuels, solar thermal collectors are acknowledged as promising technology to harness solar thermal energy fir process heating applications. This review is a thorough compendium and evaluation of contemporary literature on solar thermal collectors and their applications in industry. Apart from applications, this review paper also assesses the challenges and limitations currently hindering the global acceptance of this technology in the industrial sector.

Analytical characterization of improvised design of parabolic trough solar collector

The analytical characterization of a mini-parabolic trough collector (mini-PTC) designed for industrial process heating applications that require hot water in the range of 75 to 90 °C is presented in this work. The analysis is carried out for Pune, Maharashtra, India from October to May. The average slope FRUl and average intercept FR(τα) are evaluated. The paper also presents the performance analysis of mini-PTC. The maximum optical efficiency (ɳ) is found out to be 61.9 % while the average value of a slope is 0.8282 W/m2-K. The analytical results indicate that mini-PTC offers a prospect for Industrial Process heat applications requiring temperatures up to 90 °C.

Numerical Investigations of Molten Salt Pump Journal Bearings Under Hydrodynamic Lubrication Conditions for FHRs

Fluoride salt-cooled, High-temperature Reactors (FHRs), featuring particle fuel, graphite moderator, and molten fluoride salt coolant, are used for electricity generation and process heat applications. The primary loop of an FHR is a closed loop that operates slightly above the atmospheric pressure with the fluoride salt temperature over 600°C. Reliable high-temperature molten salt pumps are critical to the successful deployment of FHRs. To stabilize rotating shafts and reduce the associated friction coefficients, well-designed bearings are required for molten salt pumps. Therefore, it is necessary to investigate the detailed hydrodynamic performance of bearings under high-temperature molten salt conditions. In this study, a computational fluid dynamics software package, i.e., STAR-CCM+, was used to predict the performance of fluoride salt–lubricated bearings. The numerical models were verified and validated respectively based on an analytical solution derived from the Reynolds equation and experimental data published in the literature. Good agreement was observed between the simulation results and the analytical solution and experimental data with a maximum relative discrepancy of less than 5%. The validated numerical model was then employed to predict the pressure distributions, applied static loads, and power losses of high-temperature fluoride salt–lubricated bearings with various Sommerfeld numbers. In addition, a parametric analysis was performed to investigate the influence of the axial and helical grooves of bearings on applied static load and power loss. It is found that under the same salt lubrication conditions, the bearings with helical grooves and axial grooves respectively yield 20% off and 14% off power loss compared with the bearing without grooves.

Nuclear process heat application options: Highlights from the European GEMINI+ project

The European Nuclear Cogeneration Industrial Initiative (https://www.nc2i.eu) has run the GEMINI+ project (https://www.gemini-initiative.com/geminiplus/) from September 2017 through February 2021 with the objective of supporting the industrial demonstration of a cogeneration High Temperature Gas-cooled Reactor (HTGR) power plant. This should help de-risk further projects and accelerate deployment. Recently, the Polish government has reconfirmed its interest, in particular to reduce the country’s carbon footprint and its dependence on natural gas imports both for heating purposes and as a feedstock for chemical products.The GEMINI+ project has performed several studies about how to use process heat from an HTGR for a variety of industrial purposes. These are of interest for most industrialized countries, and they often enable the integration of nuclear energy in Hybrid Energy Systems with variable renewables:•Nitrogen fertilizers and chemical products.•Hydrocarbon or ammonia synthesis.•Dry reforming of methane with CO2 to produce syngas as a feedstock for numerous chemicals.•Hydrogen production for integration of nuclear energy in Hybrid Energy Systems.This paper provides an overview of these studies and concludes with an impact analysis by evaluating the market and CO2 savings potential of these technologies.

Parametric study of evacuated tube collector solar air heater with inserted baffles on thermal network for low-temperature applications

The great challenge in the evacuated tube solar air heater for the industrial application is choosing the optimum thermal networks to get target temperature for the desired air flow rate. In this work, theoretical analysis is done to investigate the influence of the significant design parameters such as evacuated tube length, diameter and number of tubes in a collector on the thermal performance and to design a thermal network model for achieving the desired temperature at specified flow rate of air for industrial process heat applications. Further, establishing an empirical correlation to simplify the thermal network design process. Based on the results of design parametric study, optimal parameters identified for a collector system are 20 numbers of evacuated tubes having dimensions of 1.8 m length, 58 and 47 mm outer and inner diameters. It is noticed that a considerable drop in temperature rise attained in each collector while increasing the number of collectors in series network. The enviro-economic analysis reveals that the overall useful energy gain per annum can be achieved around 8252 kWh which will reduce 17.16 tonne of carbon dioxide emission through the utilization of a thermal network comprising six modules working at 500 kg/h mass flow rate of air. The correlation relates the attainable effective thermal with the non-dimensional operating parameters such as mass flow number, temperature ratio, and number of collectors. The correlation can be used to design a solar evacuated tube thermal network and the proposed solar evacuated tube thermal network can be effectively employed for fulfilling the industrial process heating applications require hot air between 80 and 120 °C.

Design aspects of a fixed focus type Scheffler concentrator and its receiver for its utilization in thermal processing units

Fixed focus type Scheffler concentrators introduced by Wolfgang Scheffler are popularly used for different low to medium industrial process heat applications. These Scheffler concentrators are available in the standard sizes of 8 m2 and 16 m2. The present paper provides a detailed stepwise procedure for the design of a standing type 16 m2 Scheffler concentrator and its fixed focus receiver, intended to be utilized in a solar thermal processing unit for essential oil distillation at our institute. The dome type receivers of boiler steel grade material, SS-304, are selected for the present application. The diameter of the receiver is estimated based on the analysis of the image formed at the receiver of the Scheffler concentrator. The crossbar equations, seasonal parabola calculations and aperture area calculations for the Scheffler concentrator have also been presented in the paper. The geometrical concentration ratio for the Scheffler reflector dish and receiver system are also evaluated for any given day of the year. The design procedure presented in the paper can be used for designing any suitable size Scheffler concentrator and its receiver as per the energy requirement of the application.

A technical note on integrating thermal energy systems into solar photovoltaic panels toward a circular economy

Solar energy can sustain the global energy demand if utilized effectively through practical solar systems. Solar photovoltaic (PV) installations are increasing fast globally, and the nexus is the end-of-life (EOL) management of solar panels and other components. This perspective discusses integrating solar collectors into PV panels. Simultaneous electricity and heat production using PV help achieve our energy needs. The PV cooling improves their electrical productivity and life. Integrating solar air/water heating systems into solar PV finds space-heating, drying, hot water, process heating, and solar desalination applications. Thus, integrating thermal units with new PV panels during manufacturing, retrofitting the deployed panels, and converting EOL panels can undoubtedly minimize carbon footprints. Such sustainable PV measures can help all solar community stakeholders and lead to effective resource utilization and a circular economy.

Energy Efficiency and Energy Saving Potential Analysis of Biomass Boiler at the PT Greenfields Indonesia Milk Processing Plant

Boilers are essential utility equipment in a milk processing plant because they produce steam primarily used in process heating applications, including pasteurization, cooking, and evaporation. Energy use in boilers is the most effective energy use in milk processing plants. Therefore it is crucial to keep the boiler efficiency. This study aims to evaluate the efficiency and energy-saving opportunities of the biomass boiler in the milk processing plant of PT Greenfield Indonesia, which is located in Malang, East Java, Indonesia. The fuel used in the boiler is candlenut shell, which is widely available in the area. Boiler efficiency was evaluated by direct and indirect methods referring to ASME PTC 4-1. In the direct method, the energy gained by working fluid is compared with the energy content of the fuel. In contrast, various losses are compared to the energy input in the indirect method. The data used in this study were obtained from operation logbook data and field measurement data. Our result shows that the biomass boiler efficiency is 82.24% using the direct method and 79,64% using the indirect method. Flue gas is the most significant energy loss in the biomass boiler. Energy savings can be obtained by installing an air preheater, setting excess air, and adding insulation on some boiler walls.

Nuclear Heat Utilization For Natural Gas Steam Reforming To Produce Hydrogen

The assessment of nuclear heat utilization for natural gas steam reforming to produce hydrogen has been carried out. Most of hydrogen production in the world, is produced by steam reforming of natural gas. This process is an endothermic reaction at high temperature that needs a huge amount of heat energy to proceed the reaction. Conventionally, the heat energy needed is supplied by direct burning of fossil fuel. If the huge amount of those heat energy can be substituted by nuclear process heat, some advantages can be obtained such as, reducing combustion of fossil fuels that give implication of significant decreasing of CO2 emission to the environment. On application of nuclear process heat to steam reforming of natural gas, there are some inferior conditions related to the limitation of temperature and pressure provided by nuclear reactor which directly gives impact on lower thermal efficiency (~50%) compared to the fossil-fuelled plant (80-85%). Some modification design and operation of reformer can improve the lack condition, and capable to increase the thermal efficiency of nuclear heated natural gas steam reformer become about 78%.

Geopolymer Concrete Performance Study for High-Temperature Thermal Energy Storage (TES) Applications

Solar energy is an energy intermittent source that faces a substantial challenge for its power dispatchability. Hence, concentrating solar power (CSP) plants and solar process heat (SPH) applications employ thermal energy storage (TES) technologies as a link between power generation and optimal load distribution. Ordinary Portland cement (OPC)-based materials are widely used in sensible TES, but their use is limited to operation temperatures below 400 to 500 °C because of thermal degradation processes. This work proposes a geopolymer (GEO)-based concrete as a suitable alternative to OPC concrete for TES that withstands high running temperatures, higher than 500 °C. To this end, thermophysical properties of a geopolymer-based concrete sample were initially measured experimentally; later, energy storage capacity and thermal behavior of the GEO sample were modeled numerically. In fact, different thermal scenarios were modeled, revealing that GEO-based concrete can be a sound choice due to its thermal energy storage capacity, high thermal diffusivity and capability to work at high temperature regimes.

Experimental and numerical investigation of turbulent heat transfer enhancement of an intermediate heat exchanger using corrugated tubes

The intermediate heat exchanger (IHX) in a very-high-temperature gas-cooled reactor (VHTR) can realize a variety of process heat applications including hydrogen production, which is beneficial to the green and sustainable development of global energy. In the present study, three corrugated tubes are adopted to enhance the heat transfer capabilities of the IHX. The flow and heat transfer characteristics of these tubes are comprehensively investigated and compared using experiments and three-dimensional numerical simulations. Air and helium are the working fluid of the experiment and numerical simulation, respectively, with Reynolds number (Re) ranging from 10,000 to 20,000 and Prandtl numbers of 0.70 and 0.66. An innovative corrugation parameter acquisition method is proposed by combing high-precision computed tomography imaging and computer vision techniques. Thermal-hydraulic experiments are conducted and the k-kl-ω transition model is applied and validates well with the experimental data obtained for Nusselt number (Nu) and friction factor (f). By analyzing the flow field, heat flux field and the synergy angle distribution, it is found that corrugation disrupts the boundary layer development, strengthens the turbulent mixing, reduces the temperature gradient in the boundary layer and improves the synergy between the velocity field and the heat flux field, thus enhancing the heat transfer. The effects of corrugation parameters on the thermal-hydraulic performance of the three tubes are also discussed. The transversely corrugated tube with dimensionless height e/d = 0.03, dimensionless pitch p/d = 0.6, and Re = 20,000 produces the maximum Nu obtained, which is about 60% larger than that of a smooth tube. The helically corrugated tube with e/d = 0.03, p/d = 0.6, and Re = 12,000 has the best comprehensive performance, with a performance evaluation criterion of about 1.09. Finally, empirical correlations with geometric parameters (e/d and p/d) and Re are proposed for Nu and f for all three corrugated tubes.

Performance Evaluation of Solar Air Collector in Sensible Heat Storage by Forced Convection with Cherry Powder

In practice different kinds of solar air heaters are available for domestic heating and industrial air heating purposes, space heating, process heating and agricultural applications. Advantage of this system is to use of renewable energy source that is free in cost and an eco-friendly, economical and simple device. There are so many researcher who focuses to improve the efficiency and to maintain the continuous heat supply of the double pass solar air heater using sensible storage material. The heat transfer and friction characteristics due to the sensible storage material of solar air heaters have been reviewed in this research. A double pass solar air heater was fabricated and integrated with thermal storage system and powdered cherry pits are used as a thermal storage medium. The performance of this heater was studied for different configurations. The solar heater integrated with thermal storage delivered comparatively high temperature. The efficiency of the air heater integrated with thermal storage was also higher than the air heater without thermal storage system. The study concluded that the presence of the thermal storage medium at the absorber plate is the best configuration.

Comparison of RC-model and FEM-model for a PCM-plate storage including free convection

Latent heat storage is one option to increase the efficiency and reduce CO2-emissions of process heat applications in the temperature range between 100 °C and 250 °C. In the present study a latent heat storage system based on flown through heat exchanger plates according to the FracTherm®-design is examined. The sugar alcohol d-mannitol is used as PCM. A simplified capacity resistor (RC) simulation model is developed. In contrast to common RC-models, this model can simulate free convection of the storage material in liquid phase during charging. Additionally, a detailed physical simulation model based on the Finite-Element-Method is developed and validated with measured data. A verification of the new RC-model and the FEM-model is carried out. The mean deviation of the outlet fluid temperature between both models is 0.62 K. The mean deviation of the PCM-temperature is 0.85 K. Due to the 20 to 30 times shorter simulation time, the RC-model is well suited for dimensioning and optimizing plate type heat exchangers for latent heat storages.

Stability analysis of the thermocline thermal energy storage system during high flow rates for solar process heating applications

The thermal energy storage system is a pivotal system for solar thermal plants for improving reliability. The stability in the thermocline is more significant to clarify and improve the performance of thermal energy storage tank which legitimately shows the quality of the thermocline. In this stability analysis investigation, the modern engineering energy storage material concrete was used as a filler material for high-temperature thermal energy storage applications as a result of the intrinsic properties. A comprehensive laminar and k-ε turbulent flow energy transport model accounts for the heat transfer fluid and filler material with adiabatic and non-adiabatic conditions using LTNE (Local Thermal Non-Equilibrium model). The axial, radial, and diagonal temperature differences were identified which was used to calculate the stability of the thermocline. A thermal energy storage tank size of 1 m height and 0.250 m diameter with a 0.030 m size of filler material packed with an average porosity of 0.3 for the storage capacity of 150 kWh/m3 is used for solar process heating applications considered for the present study. The thermocline stabilities are performed with Reynolds numbers, Re varied from 1 to 3000. It is found that the Re = 1 provides better stability in the axial and radial direction as well as diagonal than other Reynolds number. It is observed that Re = 1 provides superior discharging efficiency for nearly 5.84 hrs which is highly suitable for solar process heating applications and the discharging efficiency consistently drops, when Re increases from 1 to 3000. The wall condition of the tank and velocity of the heat transfer fluid is highly disturbing the thermocline in the radial direction and it creates a ‘spike’ profile in the axial direction. Based on the newly introduced stability scale, the effective length of packing and timing to achieve stability is identified for H/D = 4. From that result, the top and bottom layer of the thermocline tank porosity is also found which is used to decide the porosity of the packed bed distributors. The identified porosity for the top and bottom distributors in the ɛ = 0.3 thermal energy storage tank is less than 0.3 is more suitable for provide the uniform flow in the tank.

Control of Concentrated Solar Direct Steam Generation Collectors for Process Heat Applications

Abstract Solar direct steam generation (DSG) systems are well suited for process steam applications and are able to provide steam at the pressure required by common industrial processes. Nevertheless, reliable control has always been a challenge for solar DSG system hindering its wider adoption. In this paper, a control strategy for solar DSG systems is presented. The control strategy is based on proportional-integral-derivative (PID) control theory combined with model-based feedforward control. Experimental data demonstrate that the control strategy provides good performance in terms of stability and setpoint tracking. The error in setpoint tracking for the load pressure controller is shown to be as low as ±0.005 MPa under real life conditions. The said strategy is currently implemented in two commercially operating plants providing solar steam for industrial processes.

Determination of lattice physics properties and uncertainties in a solid fuel molten salt cooled assembly using OpenMC

The desire for reducing our carbon footprint is driving significant interest in advanced nuclear reactors to produce energy. One promising technology is the Fluoride Salt-Cooled High-Temperature Reactor (FHR) which provides both electricity and high temperatures for use in process heat applications. The reactor technology considered in this work is a Generation IV design that uses TRISO particles uniformly embedded in fuel stripes within the fuel plates and liquid salt as coolant. The fuel design and conditions are the same as those used in a recent OECD/NEA FHR Benchmark. This paper reports the multiplication factor, fission reaction rate, and neutron spectrum for different cases from that benchmark study. A unique contribution of this work is the assessment of nuclear data uncertainty impact on the Figures of Merit used in the FHR benchmark. The OpenMC Monte Carlo code and perturbed nuclear data files from the TENDL-2017 library were utilized in these analyses. This work is part of the ongoing international efforts to explore and identify the applicability of current methods and codes for FHR simulations and molten salt reactors in general.

Solar Field Output Temperature Optimization Using a MILP Algorithm and a 0D Model in the Case of a Hybrid Concentrated Solar Thermal Power Plant for SHIP Applications

Using solar power for industrial process heat is an increasing trend to fight against climate change thanks to renewable heat. Process heat demand and solar flux can both present intermittency issues in industrial systems, therefore solar systems with storage introduce a degree of freedom on which optimization, on a mathematical basis, can be performed. As the efficiency of solar thermal receivers varies as a function of temperature and solar flux, it seems natural to consider an optimization on the operating temperature of the solar field. In this paper, a Mixed Integer Linear Programming (MILP) algorithm is developed to optimize the operating temperature in a system consisting of a concentrated solar thermal field with storage, hybridized with a boiler. The MILP algorithm optimizes the control trajectory on a time horizon of 48 h in order to minimize boiler use. Objective function corresponds to the boiler use, for completion of the heat from the solar field, whereas the linear constraints are a simplified representation of the system. The solar field mass flow rate is the optimization variable which is directly linked to the outlet temperature of the solar field. The control trajectory consists of the solar field mass flow rate and outlet temperature, along with the auxiliary mass flow rate going directly to the boiler. The control trajectory is then injected in a 0D model of the plant which performs more detailed calculations. For the purpose of the study, a Linear Fresnel system is investigated, with generic heat demand curves and constant temperature demand. The value of the developed algorithm is compared with two other control approaches: one operating at the nominal solar field output temperature, and the other one operating at the actual demand mass flow rate. Finally, a case study and a sensitivity analysis are presented. The MILP’s control shows to be more performant, up to a relative increase of the annual solar fraction of 4% at 350 °C process temperature. Novelty of this work resides in the MILP optimization of temperature levels presenting high non-linearities, applied to a solar thermal system with storage for process heat applications.

Integrating paraffin phase change material in the storage tank of a solar water heater to maintain a consistent hot water output temperature

The temperature of the hot water withdrawn for a solar water heater varies throughout a day. However, for process heat applications, constant temperature water can be required from a solar water heater. This is usually achieved by providing additional auxiliary heat input. Disadvantageously, such extra water heating incurs additional cost and, if met from fossil fuels, produces greenhouse gas emissions. An alternative approach of using a phase change material to moderate variations in the outlet temperature of hot water from the store is examined in this paper using an experimentally-validated CFD model of a solar water heater with a phase change material thermal energy storage in the hot water tank. The CFD model was solved by COMSOL Multiphysics. For a particular solar water heating system, incorporating an encapsulated paraffin wax phase change material has been shown to able to deliver up to 1200 L of hot water at a temperature of 60 °C ± 2 °C for more than 8 h.