Tunnel Baking Oven

Overview

A tunnel baking oven bakes a continuous stream of product by carrying it on a moving band through a long, insulated tunnel split into heat zones. Unlike a batch oven, where one load goes in and comes out, a tunnel oven never stops: dough enters one end, travels the length of the tunnel while it bakes, and leaves the other end finished. Bake time is set by how fast the band moves, and the bake profile, the temperature the product sees minute by minute, is set by the temperatures of the zones it passes through. This combination of a long band and independent zones is what lets a tunnel oven bake high volumes of bread, rolls, biscuits, crackers, or pizza to a consistent result.

The oven is built from a few major systems. The Insulated Tunnel is the insulated chamber, the Band Conveyor carries the product through it, the Heating Zones zones supply the heat, the Air Circulation fans spread it evenly, the Steam System system wets bread at the entrance, the Exhaust and Heat Recovery removes moisture and reclaims heat, and the Control System holds the whole profile.

The tunnel and zones

The Insulated Tunnel is a long welded Tunnel Shell packed with Mineral-Wool Insulation so it holds heat in and stays cool on the outside. Its key feature is that it is divided by Zone Baffle baffles into several zones, each able to hold a different temperature. This lets the oven shape a bake profile: a hot first zone to set the crust and drive oven spring, a steady middle to bake through, and a final zone tuned for color. Inspection Door doors and View Window windows let crews service and watch the bake without stopping the line.

The band conveyor

The Band Conveyor is the moving floor of the oven. A Baking Band of steel wire mesh or solid steel runs the length of the tunnel, pulled by a Drive Drum at the discharge end and returning over a Tail Drum at the feed end. Because a band many metres long expands a great deal when heated, a Band Tensioner keeps it taut and Band Tracker rollers keep it running straight. The Band Drive Motor is variable-speed, and its speed is the single control that sets bake time: slower band means longer in the oven, faster band means a shorter bake.

Heating the zones

Heat usually comes from gas. The Heating Zones section places a Gas Burner on each zone, fed through a Gas Train with a Gas Regulator and Safety Shutoff Valve valves required by burner codes. In a direct oven the flame products pass through the baking chamber; in an indirect oven a Heat Exchanger keeps combustion gases separate and heats clean air, and Radiant Tube tubes above and below the band radiate onto the product. Each burner modulates its Gas Modulating Valve to hold the temperature read by a Zone Thermocouple, and a Flame Sensing Rod proves the flame so gas cannot flow without one.

Convection and steam

Even baking needs moving air, not just hot walls. The Air Circulation system runs high-temperature Circulation Fan fans, driven by Fan Motor motors mounted outside the heat, that push hot air through Air Ducting ducts and out Air Nozzle nozzles onto the product. Convection speeds and evens the bake, which matters most for biscuits and crackers. For bread, the Steam System system injects steam through Steam Nozzle nozzles at the entrance: a wet dough surface stays soft longer, so the loaf springs more in the oven and bakes to a glossy, crackled crust.

Exhaust and heat recovery

Baking releases a great deal of moisture, and combustion produces flue gas, both of which must leave the oven. The Exhaust and Heat Recovery system pulls them out with Exhaust Fan fans balanced by Exhaust Damper dampers along the tunnel, venting through a Exhaust Stack. Because that exhaust is hot, a Heat Economizer reclaims some of its heat to preheat incoming air or process water, which cuts the oven's large energy bill.

Control, construction, and use

The Control System ties everything together. A PLC Controller holds the bake profile by commanding each zone's Burner Controller, setting the band speed and fan speeds through Drive (VFD) drives, and timing the steam. An Operator Panel (HMI) panel shows zone temperatures and lets the operator load a recipe. The oven is carried on a long Steel Frame with cladding, a Service Walkway for service, and Door Interlock interlocks on the doors. Tunnel ovens anchor high-volume bakeries and biscuit plants, baking a continuous stream to a fixed profile so every product that leaves the tunnel matches the one before it.