Tunnel ovens: The energy-efficient light at the end of the tunnel oven

The energyefficient light at the end of the tunnel oven

Under the current circumstances, it has never been more important to look into ways to increase efficiency in bakeries, starting with their centerpiece: the tunnel oven. Mindful technology innovation is here to provide benefits in efficiency and sustainability. Baking a vast range of high-quality products is only the start of what cutting-edge tunnel ovens can do.

+Oven preferences are different on each side of the ocean: while European bakeries favor product flexibility, high-capacity oven systems are preferred in the US. Electrically heated ovens are also more in demand in Europe. However, all markets and technology developers share one common priority for oven improvements: sustainability.

Hydrogen innovation: AMF

For AMF Bakery Systems, innovation in tunnel ovens means focusing on sustainability, primarily looking into energy efficiency and minimizing carbon footprint. As bakeries all over Europe are turning to electricity, AMF can turn its gas-fired Den Boer oven into an electric one, with several other solutions for modular electric baking. The newest development has already made a name for itself and earned awards for innovation in sustainability: the Multibake® VITA Tunnel Oven by AMF Den Boer is a directfired oven, with hydrogen-fueled burners. It comes in various configurations: it can have grids for pans, mesh belts for hearth products, and stone plates for pizza, flatbread and a large variation of bread products. The versatile Vesta oven is suitable for baking trays for almost any product baked in a tray or tin. Lex van Houten, Regional Marketing Manager at AMF explains: “AMF Vesta Vita Hydrogen-heated tunnel ovens can bake any product that is normally baked in a natural gas-heated oven. AMF is able to offer customized solutions for many baking processes, for sustainable futureproof bakeries with net-zero emissions.” Configurations are based on the type of products and the (current and anticipated) desired production rates. A stone- baked pizza will require significantly different conditions than a croissant, for example. Requested specifications will influence anything from steam and convection to impingement and moisture control. And the list continues. “That is why AMF teams and engineers all have a background in bakery and/or processing, so they know the right questions they need to ask and the advice they should provide to customers, to determine together the most advantageous configurations,” van Houten underlines. Given a ‘to-bake’ list of multiple products, this oven is designed for

flexibility based on the primary, most demanding product, and including elements identified after reviewing the whole product list in detail, to cover all bases. Based on this analysis, additional features can be added, such as extra top heat, bottom convection, infrared burners, or extra exhausts, to name some. Resulting configurations of the Multibake Vita Tunnel Oven can comprise loading systems, infeed modules with exhaust hoods, steam modules for creating crust and color, multiple convection modules, modules with higher density burners on the top or bottom of the baking chamber, discharge modules, and even cooling modules. Later upgrades, when needed, entail simply adding modules to address higher production volumes or/and additional product ranges.

Heavy-duty baking The AMF Vesta Tunnel Oven a is heavy-duty, high-capacity tunnel oven with lengths of up to 63 m, making it ideal for products requiring longer bake time or higher density. This oven has built-in grid hearths specifically for pans and trays. “It has a robust steam zone to condition products, and options for redundant drives, exhaust, and combustion blowers. It features the patented Guardian Chain Management System with predictive lubrication, and maintenance alarms,” van Houten details. The Guarding Chain Management System stores the length of the main grid chains at installation and keeps a log of the chain's length every time the oven starts and stops. It also incorporates independent pneumatic-hydraulic tensioning systems that use minimal pressure to tension the chain and allow the chain to cool without tensions. Low tension on the chains also facilitates the lubricant’s flow into the chain bushings. The Vesta Tunnel Oven comes with standard bottom burners and optional top burners and a complete Coloraider convection system, which consists of fans and tubes that collect heat from the top of the baking chamber. This heat circulates through a series of delivery tubes fitted across the baking chamber, above and below the product zone. “The main ducts are adjustable to direct the heat to the top or the bottom of the oven. In addition, the outlets of the tubes can be rotated to direct the airflow towards or away from the pans,” the specialist details. The number of Coloraider zones is relative to the length of the oven, each having its own fan and 25 to 30 tubes. “Its efficiency has been improved with better monitoring of the exhaust and the addition of AMF Sustainable Oven Service Technology,” van Houten highlights. Another efficiency feature is the Direct Spark Ignition (DSI). AMF uses custom build DSI for all its ovens. The Vesta Tunnel Oven, along with its sister the Vesta Tray Oven, are built to operate 24 hours per day for decades.

Baking smart and smart baking The AMF Sustainable Oven Service technology monitors all of the functions of the oven, tracking temperature, airflow, occupancy, gas consumption and fan vibration, and logging the data for analysis. “With this information, AMF makes solid recommendations that can improve combustion efficiency, even heat distribution, product color, and more,” he details. In the future, the AMF Mixer Guardian System will be able to provide information to the oven for automatic adjustments, based on mixing energy and dough temperature, AMF anticipates. For future developments, AMF is looking at alternative and sustainable heating sources that are the best match to the specific market: “Countries with plenty of electricity may choose all-electric ovens, or even hydrogen heated ovens, or both. Countries with limited electricity generation and distribution may choose natural gas, propane, hydrogen, or a blend of different fuels,” van Houten explains. What should be expected from AMF ovens going forward? He anticipates: “We will continue to develop more of our ovens modular that can reduce installation time and costs up to 80%. We will keep on developing turnkey systems that are scalable for the future.”

© AMF Oven innovation at Reading Bakery Systems

For Reading Bakery Systems (RBS), innovation in oven design currently revolves around sustainability initiatives and reducing carbon footprint. New ovens need to be more efficient, flexible in baking and easy to operate. Different goals can be achieved with similar means: “The European market needs efficiency and alternative energy solutions now, given the price of natural gas and the use of carbon credits. In America, large food companies are leading the push for sustainable oven technologies because the government lacks a clear and concise plan,” Joseph Zaleski, President, RBS, tells us. The company’s latest oven designs address all energyconsuming areas: “With the new, sustainable designs, we feature reclamation of exhaust heat, better insulation materials and lighter weight conveyor belts to help reduce wasted energy. We also offer alternative fuels and electric oven options,“ Zaleski explains. These features are not exclusive to the new ovens, either; existing equipment can also be upgraded to more sustainable options. A standard build uses a combination of radiation, conduction and convective heat to create the desired texture, taste and moisture profiles for all types of biscuits, crackers, or snacks. The first third of an RBS oven manages the humidity and the type of heat to help develop the flavor profiles of the product. The remaining two-thirds help set the product

shape and uses more convective heat to remove moisture. All these parameters are controlled via the user-friendly RBSConnect Controls Platform. Each product or recipe variation can be stored in the oven’s controls history for fast and easy start-up. “This level of automation and simplicity can eliminate a lot of the problems caused by high turnover and shortage of skilled operators,” Zaleski points out. RBSConnect downtime software can also improve efficiency by automatically reducing the fuel consumption of an oven. The software works by automatically setting the exhaust dampers to a minimum, lowering the belt speed to the slowest setting, and forcing all burners to the minimum firing rate or turning off burners once the cutting system on the production line stops. When additional dough is loaded in the hopper after a shutdown period, the extrusion or sheeting process can trigger the restoration of all production settings. The smart software provides trend information on parameters such as gas usage, temperature and final product moisture to ensure the line is always running optimally. Together with its ovens, RBS offers the SCORPION 2 Oven Profiling System, which allows bakeries to maximize operating efficiency by measuring the four key baking parameters – temperature, air velocity, heat flux, and humidity. “This allows you to benchmark your process for each product so you can optimize your baking process,” Zaleski highlights.

The future of the RBS baking oven Ovens are undeniably headed into a sustainable future; but, this requirement is only the beginning of the features they need to incorporate. Zaleski explains: “Ovens need to have simpler control systems as we move into the future. As the labor force moves around more freely in the job market, oven controls need to be more intuitive so that new operators can understand how to produce great-tasting products more consistently.” This is valid for all processes, as consistency starts with mixing and forming the dough. The SCORPION tools support baking consistency, as they can quickly identify and solve any issues in the process. Most RBS ovens currently operate with natural gas, propane, or butane. As countries move away from fossil fuels, ovens can too, and offer more sustainable processes in the future. “Electric heat is where we see oven technology moving into the future,” anticipates the company’s president. Products can be tested on a fully electric oven at the RBS Innovation Center in Pennsylvania. The company is also working on the development of an electric cracker oven to replace DGF ovens. This involves modifying the Emithermic Oven Zone that will enable this zone to impart the higher heat required by crackers without a lot of air currents which would dry the product before allowing flavor and texture development. The ovens’ road to carbon neutrality in 2050 starts today, given their lifespan that can be as long as 40 years. Zaleski shared how RBS envisions the future of oven technology: “RBS offers sustainable ovens that reduce energy, eliminate greenhouse gases and are easy to operate. We will continue to focus on improving our oven designs in each of these categories as we move forward.”

HEUFT tunnel ovens: all-rounders

Thermal oil oven specialist HEUFT offers the VULKAN oven in this category. Thermal oil is an excellent heat conductor, transporting 2,600 times more energy than air. Hot thermal oil runs inside the VULKAN’s radiators, which are positioned inside baking chambers. “The result is that, with our thermal oil technology, we need 45% less power to heat our ovens in comparison with traditional oven systems heated with hot air. On average, we can save 25% to 40% on energy consumption,” explains Simon Tabruyn, Export Manager, HEUFT.

© Heuft

Any heating method works just as well for thermal oil; either gas, fuel, or electricity will have the same results on the baking quality. Taking the ongoing energy crisis into account, HEUFT built a hybrid heat exchanger, to allow bakeries to switch between electricity and gas or fuel as an energy source. Other possible alternatives include liquid gas, biogas, wood pellets and hydrogen. “This means you can choose at any moment the type of energy you want to use: electricity during the day, when solar panels are producing electricity, and gas during the night, for example,” Tabruyn illustrates. The VULKAN can bake up to 12 tons of bread per hour, with a baking surface that can span 540 sqm. And it will require a small footprint to not only bake high volumes, but also diverse products. Tabruyn explains, “An advantage of our system is that we can easily work with different temperature zones. For example, we can build an oven with five or more decks for tray-baked products or tin breads and two additional decks with a stone belt, for artisan products. This makes it two-ovens-in-one which can be set to bake products coming from two different production lines. And all this on the same footprint!” Future expansions in production volumes/ variety are also considered in the design of the VULKAN oven; it can incorporate built-in additional decks, which can be easily enabled when needed. In this way, it is not necessary to stop the line to add decks. To best control temperature, top and bottom heating always work independently and different temperature zones can be chosen over the oven’s length. There are no temperature fluctuations: “A constant temperature is maintained thanks to the three-way valves that are continuously regulating the amount of hot oil going into the oven to preserve the requested temperature,” the specialist from HEUFT explains.

Optimized and mindful process The VULKAN tunnel oven is insulated with 700 mm of Rockwool, to preserve heat so that none radiates through. In addition, it is also equipped with a heat recovery system that uses flue gases for the burner and baking vapors from the oven to heat water up to 95°C. The hot water is then stored in tanks and can be used for various purposes, from feeding the crate washing machine, to heating the offices, or for cleaning. “Our Heat recovery management system controls the different heat recovery units and integrates it into the building requirements, custom-made. It is even possible to use it for air conditioning solutions,” HEUFT’s specialist details. The Energy Management System (EMM) is this oven’s smart energy-saving tool. It can measure precisely how much energy the oven needs during production. Using this data, the automated control system automatically shuts down one heat exchanger completely to be more efficient and to maximize energy savings. Moreover, all HEUFT ovens can be equipped with steam and turbulence systems, which help with process efficiency and product quality. To optimize efficiency, steam can also be generated with thermal oil heating, for example. Depending on the product, some convection (turbulence) can be added in certain oven zones. “This can be helpful if you’re looking for good volume and a crispy crust,” Tabruyn explains. Sustainability is also considered. Thermal oil technology contributes initially to considerable energy savings; if the oil is heated with an electric heat exchanger, there are no carbon emissions at all.

Big and bigger production rates with Koenig ovens

Koenig is also prioritizing sustainability, safety and sanitation for oven innovation that caters to product trends, as the company observes the American market is moving to Europe’s favorite, artisan bread. Trends the company is considering for the design of its tunnel ovens include stone conveyor ovens, bigger lines with bigger baking surfaces

to match, saving energy (heat recovery systems), and the ability to quickly swap between energy sources, from gas to electricity, or hydrogen. The increase in production rates means big lines, and therefore the oven has a bigger baking surface – the MDI STRATOS oven being a good solution to this kind of request,” Antonio Aiello, Technical Supervisor, Koenig, details. Custom solutions are the norm. Several unique features can be found in Koenig tunnel ovens: the MDI PHAROS is highly customizable, for example, with its independent zones and insertions of convection sections. It provides three different heat transfer principles: conduction (with wire mesh, stone plate, or metal plate conveyors), radiation, natural and forced convection. A cross-section heat exchange allows even baking throughout the oven and can fine-tune baking of the product rows placed laterally. The MDI STRATOS also includes the three heating methods and cross-section heat exchange. This oven is the choice for bakeries that can only assign a very small footprint for their oven, with a baking surface of up to 500 sqm. It features up to six decks, each with its own independent oven, which makes them suitable for baking various types of products simultaneously.

All under control Automation features help control all process parameters. The MDI STRATOS and the SDI PHAROS models manage baking times by adjusting the conveyor speed with a frequency converter, via the Automatic Control System. This system also manages temperatures, thanks to the proportional integral derivative (PID) burners and the baking chamber and fumes thermocouples. Humidity is provided by the steamer at the oven’s infeed zone, then air extraction along the oven is managed with fans. Turbulences (air convection) can be integrated into specific sections on customized ovens. Every zone has its own burner. The single-deck PHAROS is the recommended choice when the line needs a big proofer room, which can be placed just above the oven. SDI PHAROS and MDI STRATOS incorporate a system to finetune the flow distribution of fumes across the baking chamber’ heat exchanger: “This allows the heat transfer to be better adjusted to lateral product rows, preventing these rows from baking/drying incorrectly,” Aiello explains. For process accuracy and energy savings, each zone comes with its own power unit. For the MDI STRATOS, using several decks provides extra freedom in managing production rates, baking times and product distribution on the conveyor’s surface. The STRATOS can be upgraded by adding decks. Baking times and temperatures are managed the same way for the SDD EOS. Depending on its length and the requested power for specific products and production rates, a series of independent radiant burners are installed along the oven, over and underneath the conveyor. Depending on the types of products to be baked with Koenig’s tunnel ovens, a number of configurations can be custom-made, with different types of conveyors, different oven lengths and widths. More customizations can be made regarding the number and the length of zones, the burner capacities for each zone, the presence, location and number of turbulence sections, steaming, and the need to preheat conveyors.

Seamless production A constant product flow is the result of good line management. At the same time, process optimization translates into energy savings. Koenig ovens go on stand-by when they detect the product flow upstream has stopped, which reduces wasting flash heat at the beginning of the product flow. “This is greatly helped by a product tracking tool that can show product flow and related interruption-beginning instances along the line,” Aiello adds. To adjust and improve production, automatically logged data about line and oven settings/behavior can be analyzed, together with the resulting product. Going forward, Koenig anticipates an increase in the use of energy sources other than gas, oil, or electricity. Ovens will need to increasingly lower the consumption of whichever energy is used. Smart features will include computer vision at the end of the oven, for live feedback about the oven’s settings and quality measuring.

J4: the optimum baking curve

Czech Republic specialist J4 looks at the optimum baking curve for a wide variety of products when designing its tunnel ovens. To ensure it is consistently being reached, each step (and its dedicated zone) of the baking process is controlled. “For an example of a possible setup, an oven with a baking area of 4 x 22.5 m has five baking zones and one heating tower. For each zone, the temperature is automatically regulated, according to the recipe, with a pre-set ratio of bottom and upper heat,” J4 specialists explain. In addition, ‘STIR’ is incorporated in J4 ovens – a patented technology that changes radiant heat to infrared heat, helping the product to develop core temperature faster, and the final volume of the product, while contributing to the process efficiency by shortening baking times. STIR was developed by J4 in cooperation with German company IBT; thanks to a special coating applied to a part of the baking chamber, the heat resonance is changed so that it penetrates the product’s surface and reaches its core more easily. Optional oven accessories that are commonly used are the ‘Duotherm’ (a turbulence zone helping at the beginning of the baking process to heat pan straps and at the end, for fine-tuning the crust and color) and the exhaust fan, used for proper moisture management inside the oven. The system not only controls the current status of the oven, but also adjusts the process according to information received from the line, such as gaps between products, to always maintain the closest possible temperature to the one set in the recipe. Setting the best baking curve is the first step in production. The baker’s skill and experience play the main role in perfecting it, based on information about the product and the materials used, and by testing the oven’s parameters. The company shows how it can contribute with custom setups: “To get a perfect product, we offer solutions that include steam and moisture management, changes in the baking system itself, or combining heating methods (radiant/ convection/infrared – direct/indirect)m and oven control.” The amount of moisture is related to the volume of air exhausted from the baking chamber. In turn, the volume of air going out is related to the speed of the fan, J4 explains.

Looking at every product These settings vary for each type of product. For example, bread products need a high temperature at the point of contact with the oven belt and in the first zone, J4 specialists illustrate. Buns have a smoother temperature curve mid-way through baking. For their smoothness and shine, steam is released along the baking chamber. The cyclothermic oven with a shifted tower is mainly used for rye-wheat bread, where the high temperature in the first zone gives the best result. Rye products are steamed in the beginning; it is then best to bake them with very low moisture. “All these kinds of products and processes can be handled with just one oven,” J4 concludes. Looking at production volumes and product variety, J4 recommends considering tunnel ovens when making at least 150-200 kg of dough per hour, for bread-like products. One of the bigger challenges is in setting the optimum product order, especially when making goods with widely different requirements. “The oven needs a certain amount of time to heat up and there is some temperature inertia when cooling down. Skill and practice are needed to perfect this; but, we are here to help with production planning,” J4 says. How can they help? First of all, with know-how about the timing of temperature changes. J4 also provides this information as a part of the baker’s training during installation. “This is necessary because there are some oven features that save on the timings of these processes, which cannot be part of the oven preset included in the recipe,” the company explains. Based on discussions with clients, J4 can recommend the optimal sequence of products during a baking period. When choosing an oven, its size should be estimated to take into consideration future production growth. A bigger oven can be planned in advance, to use it at full capacity over time. Or, J4 can rebuild and extend an oven by prolonging the tunnel and inserting extra radiators. For the future, J4 is looking into alternatives to traditional fuels as well. “We have successfully developed cyclothermic ovens using wood pellets and developed a solution for switching between gas and electricity in the heating tower by touching the control panel.”

Flexibility for industrial volumes: MECATHERM

MECATHERM provides many choices to adapt tunnel ovens to specific needs, including certain cleaning options, different types of conveyors, energy sources, or settings to adjust baking parameters according to the product range. For the all-important product quality trend, MECATHERM developed the modular M-TA tunnel oven. This award winning oven offers multiple heat transfer modes, such as convection or radiant heat, or a combination of both, in each of its independent heating zones, to the required product

specifications. “It is a flexible oven choice for a line that excels at baking vastly different products, from crusty, pastry to patisserie products,” explains Marie Laisne, Product Marketing Manager at MECATHERM. “By providing just the right quantity of energy in a minimum baking time to reach the product quality criteria, this oven offers an optimal energy consumption solution,” she recommends. The kind of product influences the type of energy transfer that should be used for the best results. The baking phase is also considered for this choice, from development to stabilization and coloration. For industrial production, MECATHERM’s main focus is performance optimization. In this regard, the ease of access for the operators is key to enabling easier maintenance and cleaning operations. For instance, for baking products with the highest sanitation standards (e.g., protein-based products), the FDAN tunnel oven is fully accessible and can be easily cleaned with high-pressure water. MECATHERM is also making advances with innovative digital solutions to help with current market challenges: “The new M-CARE digital solution is an intuitive interface that enables industrial bakers to detect drifts in equipment, anticipate potential breakdowns, and support operators and maintenance teams to ease the first level of maintenance,” Laisne explains. Most of MECATHERM’s new ovens are ‘M-Care ready’. Through automatic settings, baking parameters can be precisely controlled via the HMI settings including baking times, temperatures, heat transfer modes and their intensity, as well as steam injection and extraction.

Sustainability and consistency Regarding the increasing concern for sustainable solutions, MECATHERM recommends using as much as possible convection as a heat transfer mode, which both shortens the baking time and reduces the fumes’ temperature (when using gas burners). In addition, “The oven temperature regulation should be monitored with precision to avoid unnecessary overheating,” she recommends. For instance, lowering the temperature of the fumes from 350°C to 150°C lowers energy loss through fumes by 40%. A new energy-saving feature of MECATHERM ovens manages the damper opening settings, to minimize the amount of fresh air that enters the oven during regular baking operations. “A digital solution assesses the exact quantity of extracted flow as well as the quantity that is effectively extracted. This data allows the baker to adjust the extraction settings close to the required balance point and optimize the energy consumption,” the French specialist adds. Additionally, MECATHERM is currently working on project development that will measure and precisely adjust the humidity rate inside the baking chamber, she reveals. To ensure process consistency between batches, recipes are pre-registered in the HMI. To finetune the process, MECATHERM runs numerous airflow simulations in the oven’s design phase. The company’s R&D team has developed its own simulation tool to help analyze the simulations, which is used for more than five years in every development process. Last but not least, all Mecatherm tunnel ovens are compatible with an electrical power supply without any changes in baking performance, while also reducing the ovens' CO2 emissions.

The next steps in oven tech A new solution is currently under development, to help provide adjustments for increased productivity: a data analysis tool for the information collected from a single piece of equipment, or an entire line. “Ultimately, it will provide a dashboard to monitor the equipment/line performance,” anticipates Laisne. Long-term developments at MECATHERM will aim to support industrial bakeries in their road to sustainability, with ovens with improved energy management and, consequently, lower CO2 emissions. Green baking is completed by baking precision: “A development area we are researching is, for instance, precise humidity management that plays a key role in the final product quality,” she shared. Sustainability is well on its way to being profitable, for the environment, for the baking process efficiency, and for the business, with plenty of interesting opportunities regarding tunnel ovens. +++