Tunnel oven specialists: Innovation in improving the process efficiency

Efficiency at the end of the tunnel

In the industrial baking of any type of bread, and a multitude of other product ranges, tunnel ovens are the giants of large-volume, continuous baking, for which efficiency is a must.

+Innovation in improving the process efficiency of tunnel ovens is the result of a comprehensive investigation of every equipment part, product requirement and manufacturer needs. Savings can amount to values that are specific to every facility and its methods; however, every parameter optimization can translate into significant gains.

Energy efficiency: the THERMADOR

The efficiency of the THERMADOR oven by WP Bakerygroup is given by the length configuration of the heating gas zones, up to four, and their respective channels transferring the heat to the baking chamber. It requires lower heating gas temperatures for baking compared to its predecessors, which is made possible by increasing the mass-flow throughout the oven by 20-25%. This helps obtain a lower temperature difference between the entrance and the outlet of the radiators, independent of the length of the heating gas channels. It also enables a very good distribution of the temperature and of the heat transfer itself, with minimal energy loss released into the environment.

The lower temperature difference achieved is also combined with improved isolation: the entire oven is isolated manually with mineral wool. “Our specialists are able to insulate the THERMADOR ovens without compressing the mineral wool too much, to preserve heat in the oven. The goal is to keep the best isolation material in it: air,” explains Siegfried Lauer – head of overall project planning, WP Industrial Bakery Technology (WP IB). The isolation is done manually, so people can fill up spaces that are not normally easily accessible. “This is the traditional and, still, the best way to do this,” adds Ulrich Speck – head of oven design department at WP IB.

Airflow control

The traditional setup of the THERMADOR comprises a closed cyclotherm heating gas circulation system, heating products indirectly, by radiation. With convection systems gaining ground, other oven variants incorporate either active solutions, in which heat is transferred into the baking chamber, or with revolving air. In the latter version, an agitating unit revolves the air, with a Duo or a Quattro fan setup.

The calculation of the airflow is done based on the 3D design of the oven and a mathematical flow simulation software that determines the correct gaps for optimal airflow in the oven, over the full width of the oven. In the simulation, this program also includes temperature losses and differences in the baking chamber, based on real-life readings. WP Bakerygroup will select and input the data to obtain accurate simulations that take into consideration all relevant parameters.

In the length of a zone, which can be 4.5m, 6m, or 7.5m, the Duo unit has two fans, placed diagonally to achieve airflow and circulation internally in its baking chamber. “Air can also go through a channel system over the fan and return into the baking chamber, for a convection effect,” Lauer details. The Quatro system doubles the internal convection air capacity with four such fans, each placed in opposition to the others, 2-2.5m apart. Every fan is revolving air on half of the oven’s width, which is why for wider ovens, WP Bakerygroup recommends the Quattro setup. The result is an optimized temperature transfer to the product, which reduces baking time, as the Quattro System gives more turbulence in the oven. This is a particularly useful technology concept, given that the trend is for ovens to become even wider in the future. This air revolution in the baking chamber gives a better heat transfer as well.

“Duo and Quattro are particularly efficient when there is a lot of mass material (i.e., steel) involved in production, for example for toast bread, thanks to the very efficient heat transfer to the material supporting the dough,” Lauer

© WP Bakerygroup

highlights. The latest developments in these models are new air guides that improve air distribution and movement. “These helped achieve very good vertical convection in the THERMADOR,” Speck also says.

Case-by-case process efficiency

Each tunnel oven Sveba Dahlen makes is built specifically based on the type of products and process the bakery needs. “An advantage of this is that the oven goes into operation with the right capacity and adjusts the power outlet continuously,” Henrik Tillander, Industrial Sales manager tells us. This is achieved by optimizing the heat transfer in the oven chamber, by how Sveba Dahlen places the heating elements/power for the electrical oven, and by using several burners for the gas oven in each zone instead of a single burner for the entire oven.

One way to look at optimizing energy efficiency is to only supply the system with the amount of energy needed. By working with the right energy supply in production and insulation, Sveba Dahlen reduces the amount of waste heat to recycle. “We can also supply equipment to keep energy loss down as much as possible from the exhaust using a system for continuous under pressure/flow regulation,” Tillander explains.

By designing the oven according to the capacity requirement, the energy consumption is optimized from the start. Electric ovens can have elements working only when and where they are needed; Sveba Dahlen’s patented solution for the gas oven with several burners also only adds heat to the part of the oven when and where it is needed. To control the heat supply in exactly the right place in the oven room, there are different types of control equipment such as sensors. The electric ovens can use even more advanced technology to control each element in the oven, with sensors and software. The gas ovens use several small

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burners in each oven chamber to be able to fine-tune the heat supply. “Together with a very good insulation and regulated exhaust, the savings are optimal,” the specialist highlights.

Almost every Sveba Dahlen oven is tailor-made following specific customer requests. The oven is customized in terms of width and length. The company delivers ovens with a bandwidth of 4.2m and an oven length of 75m. In some cases, stainless-steel belts are needed; other customizations are needed when the production includes heavy loads, for example, which require a reinforced drive train. “The most common accessory that our customers choose is to supplement convection in the zones with turbo air,” Tillander notes. The advantage of ‘Turbo’ is increased efficiency in production, as it provides additional opportunities to fine-tune the heat distribution in the zone. This option increases the flexibility of production in a very cost-effective way, he adds. Steam is another popular request.

Efficiency level: 960

The 960 LTD Tunnel Oven manufactured by Bakery Thermal Solutions also incorporates several features increasing its energy efficiency. Some of the latest innovations include zonal heat control, product tracking, and exhaust control to optimize the heat into the oven as well as the extracted air based on product requirements and real-time production variables. “The 960 LTD tunnel ovens offer high-level controls to minimize fuel usage to only what is required to precisely and reliably produce desired products for their customers,” explains Charles Borders, mechanical engineer, Bakery Thermal Solutions.

To preserve heat, all exposed sides of the oven use high-R value insulations to keep as much heat as possible in the oven. Openings in the oven are minimized and exhaust is optimized for minimal required heat extraction, the specialist outlines. To preserve fuel and optimize baking, burners are regularly turned up or down based on product tracking, product requirements, and sensor feedback in the oven. The continuous control of the burners helps to save fuel and provide a consistent bake, even with production interruptions.

A variety of additional features are available to customize this oven as needed. It can be equipped with varying numbers of top burners, steam systems, variable coloraiders, oven bottom cleanout systems, belt and grid cleaning, redundant drives, automated dampers, upgraded burners, and advanced controls among other visual, sanitary, and safety features. “Features are recommended to customers based on the products going through the oven, control preferences, or safety standards in the bakery,” Borders adds.

Oven zones are used as multiple control points to optimize temperatures and air flows in a given section of the oven. Fuel use is minimized when the baking process closely matches the conditions required by each product throughout the process. +++