Indirect radiant ovens (also known as “cyclotherm” ovens) are constructed in separate zones. Each zone is typically 10 – 20m long and it has a single burner, heat exchanger and circulation system for the hot gases from the burner.
Each zone has a burner firing into a burner tube. The hot burnt gases are drawn from the burner tube through ducts to rows of steel tubes, or ducts, at the top and bottom of the baking chamber. These radiant tubes, or ducts, run the whole length of the zone. The hot gases travel through the tubes or ducts which then radiate heat to the products from above and below. At the end of the zone, the hot gases are collected in a return duct through which they travel back to the circulating fan and from there to the burner tube to be re-circulated. It is essentially a closed, circulating system with a single burner, circulating fan and radiant tubes to heat the products from above and below.
A flue with natural convection is used to balance the pressure in the system resulting from the ingress of combustion air at the burner. The continuous re-circulation of the hot gases ensures a good efficiency. Fresh air is only drawn into the system at the burner for combustion and this is balanced by the natural extraction through the burner flue.
Since the products of combustion do not enter the baking chamber, the burner may use oil or gas. This system is commonly used where oil is the most economic fuel, for example in India.
This baking system bakes by infraredradiation with a high heat mass providing stable baking conditions. It is versatile, capable of baking all types of biscuit, cookies and some crackers. High rate crackers require a first zone of direct heating. The system is favoured by many bakers for producing a high quality of biscuit structure, texture and colour. It is an ideal system for achieving colour contrasts on rotary moulded and cracker products.
- Indirect radiant ovens provide a very stable, infrared radiant heat, preferred by many bakers.
- The “closed” circulation system retains and re-circulates the hot gases from the burner and contributes to good fuel efficiency
- Suitable for all types of products, except for the first zone(s) of ovens for baking high rate crackers (for example soda crackers) which required direct heating
- Suitable for all types of fuel including diesel oil
- Hot air and burnt gas may be recovered from the burner flues with the Heat Recovery System and used to heat the final zone of the oven, providing improved fuel efficiency.
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