Industrial tunnel ovens are among the most energy-intensive equipment in large-scale bakeries and a significant contributor to greenhouse gas emissions. This review synthesises experimental, computational, and industrial evidence on tunnel-oven performance and decarbonisation options, focusing on gas-fired, electric, and emerging heating technologies relevant to continuous baking. Studies were assessed with respect to thermal performance and product-quality outcomes. To enable consistent comparison across studies, thermal performance is interpreted using defined system boundaries. Supplied heat is taken as burner fuel input on a lower heating value basis for gas and hydrogen systems, or electrical power delivered to heating elements for electric systems. Useful heat absorbed by the product includes sensible heating of the dough and latent heat associated with moisture evaporation. Under these boundaries, reported product heat utilisation varies widely and can fall to around 16% in high-temperature direct-fired tunnel operation, indicating substantial losses through exhaust gases and heat transfer to the oven structure and surroundings. Electrification through resistance heating improves controllability and avoids combustion losses, although reduced radiative heat transfer can affect crust development. Hybrid concepts combining resistance heating with infrared or convection show potential to maintain surface quality while reducing energy use. Advanced electrothermal approaches, including induction, microwave, and ohmic heating, remain constrained by scale-up and control challenges and lack full-scale validation. Hydrogen combustion represents a possible longer-term pathway, but direct evidence for hydrogen-fired tunnel ovens in baking remains absent. Overall feasibility depends on grid carbon intensity, energy prices, and retrofit constraints.

This research investigates a novel tube heater designed for the seamless integration of an innovative solar thermal system into the powder-based coating process to heat steel tube at a temperature of 240 degrees C. It incorporates a comprehensive numerical model developed and assessed using ANSYS FLUENT, concentrating on seven critical parameters that significantly influence the tube heater's performance and size. These parameters include tube heater length, jets' length, funnel height, Z/Djet, Y/Djet and X/Djet ratios, as well as jet diameter. The findings underline the critical role of tube heater length in enhancing heat transfer and maximising thermal efficiency, while reducing jet length and funnel height demonstrated negligible effects on thermal performance, promoting material economy. A lower Z/Djet ratio enhanced heat transfer uniformity, improving thermal performance, while optimal X/Djet and Y/Djet ratios were identified as 4, maintaining a balance between heat transfer rate and energy consumption. A smaller jet diameter proved beneficial since the potential core was not achieved, increasing heat transfer to the steel tubes. The experimental model, conducted to validate the novel tube heater's performance, remarkably aligns with the numerical model, showing an R-squared value of 0.992. These results affirm the numerical setup's accuracy and reliability in capturing the tube heater's thermal behaviour. It is concluded that the novel tube heater stands as a highly efficient solution for the seamless integration of solar thermal systems into the powder-based coating process of steel tubes, promising significant emissions reduction.

The dairy industry uses a number of energy intensive thermal processes like cooling, heating and cleaning that require thermal and electrical energy. Those processes use temperatures between 4 degrees C and 200 degrees C that could be potentially powered using solar thermal energy but one of the main challenges is the complexity of selection and integration of the components used for the solar system such as solar collectors, solar heating and cooling equipment. The heating processes with the temperature requirements between 300 degrees C and 400 degrees C are mainly powdered using solar parabolic trough collectors and linear Fresnel reflectors while cooling processes with solar absorption chillers. The excesses of energy of above 200 degrees C could be stored in a thermal energy storage system. This study critically evaluates the thermal demands of the dairy processes, review their existing solar thermal applications and recommends a concept design for solar thermal energy integration based on the available data. The concept design includes connection of the solar collectors and thermal energy storage to the thermal energy supply line through the absorption chiller and steam drum. The benefits comprise flexibility of the heat transfer fluid selection, independency of solar energy production to conventional production and no further modification of the conventional production system or additional capacity to support the future upgrades are required.

The application of the Solar Thermal Energy (STEn) systems to the dairy processes have shown a great potential for reducing fossil fuels use and greenhouse gas (GHG) emissions.There are thirty-three STEn systems currently operating in the dairy industries worldwide providing temperatures from 140 o C to 200 o C that are mainly used for the heating purposes in the processes like pasteurization, preheating, and cleaning.The challenges of those systems include various operational issues such as shad and unoptimized equipment that affect the performance of the collector, tracking and control systems and other apparatus that could be overcome by a preliminary analysis of the dairy plant's thermal load and use of integrated STEn systems.This study relates to a case study of the dairy industry, analyses the current thermal and cooling demands for production of skimmed milk, yogurt and cream, recommends two new scenarios for the integration and simulation of the STEn systems and evaluates the potential the process optimization.The Specific Energy Consumption (SEC) for each product and operational capacity requirement for the current and simulated processes are calculated and the most technically efficient solution considered.

This paper investigates the use of solar thermal energy systems in SPIRE (sustainable process industry through resource and energy efficiency) and non-SPIRE industries and evaluates the use a novel solar Fresnel collector for generating temperatures of up to 400 °C. The investigation showed that solar thermal energy systems were mostly integrated into the non-SPIRE industries like food and beverages, paper and pulp and the textile industries with temperature requirements of up to 150 °C while few of them were used in the SPIRE industries like the non-metallic minerals, chemicals, basic metals and water industries with temperature requirements of up to 1500 °C. The limitation of those solar energy systems was seen in their application in higher irradiance regions due to the limited operation temperature of certain types of solar collectors, which particularly affected the SPIRE industry sector. To increase their use in high and low irradiance regions, a novel solar thermal system developed by the EU-ASTEP project that could achieve a temperature of up to 400 °C was introduced. The calculations of the theoretical and technical potential application of the ASTEP system in EU industrial processes showed an increase of 43%, of which 802.6 TWh totalled the theoretical potential and 96.3 TWh the technical potential. This resulted in a reduction of greenhouse gas (GHG) emissions by 24 thousand kt CO2 equivalent, which could help industries to achieve their 2050 targets for net-zero GHG emissions.

This paper evaluates the performance of a solar-powered tube heater that uses air impingement jets to heat steel tubes in the powder-based coating process.To evaluate the thermal performance of the tube heater, two numerical models, ANSYS FLUENT Dynamic Mesh (FDM) and ANSYS FLUENT Transient Thermal (FTT), were developed and their accuracy and computational efficiency were compared.The FDM model analyzed the heat transfer in the tube heater by simulating a moving steel tube with a steady heat source while the FTT model by simulating a steady steel tube with a moving heat source.Results showed the FDM model to be computationally more time and cost-efficient, requiring 4 processors and 4 days to run compared to the FTT model which required 40 processors and 31 days.On the other hand, the FDM model showed a more detailed temperature contour of the tube with higher temperatures on the edges due to air crossflow.However, this did not have any significant effect on the final average temperature of the tube which was found to reach 76 o C by both models, consequently reducing the required load of the induction heater by 22% and the Greenhouse gas (GHG) emissions of the induction heater by 2.15 gCO2e/m.