The Heat Recovery System (HRS) uses the waste heat from the burner flues. This may be used to heat one or two final zones of the oven. These zones would not require burners, giving a saving in capital and running costs.
All gas burners draw in a large amount of air for combustion. 1.0m3 of gas requires 3.0m3 of oxygen, (approximately 15m3 of air) for complete combustion. This air is exhausted through the extraction system of a direct gas fired oven and through the natural draught burner flue of an indirect oven. The hot air and burnt gas in the burner flues of an Indirect Radiant oven are at a high temperature, typically up to 200oC in the first zones and this hot air can be recovered and used for baking in a Heat Recovery System.
A proportion of the hot gases in the burner flues are diverted to an HRS collection pipe which runs along the top of the oven. Hot gases are collected from each zone with a burner. The hot gases are drawn along the collection pipe by a fan and blown into radiant ducts in the final oven zone.
The HRS zone is constructed with radiant ducts above and below the oven band. The hot gases recovered from the burner flues are fed by the fan to the ducts. The fan is located on top of the oven at the end of the collection pipe.
Oven efficiency with Heat Recovery System
Independent tests were carried out on 3 ovens in the same factory producing identical rotary moulded biscuits with the same baking time. The tests measured the oven efficiency by calculating the energy usage (gas) in kWh (kilowatt hours) to produce one kilo of baked biscuit.
The Baker Pacific Indirect Radiant oven was 18% more efficient than the DGF/cyclotherm oven and 6% more efficient than the DGF/convection oven. The savings in gas consumption per 8 hour shift (23 tonnes of biscuits) are approximately 212 m3 of gas compared to the DGF/cyclo and 62 m3 compared to the DGF/convection ovens.