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.
Image 1: Baker Pacific Heat Recovery 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.
Image 2: Heat Recovery Zone
The final zone of the oven has radiant ducts above and below the oven band. These ducts are divided along their length into 3 sections (control side, centre and non-control side). The flow of hot air into each section is controlled by a damper. These dampers may be adjusted to ensure the optimum heat balance top to bottom and across the width of the oven.
The following data is from a multi-national biscuit manufacturer comparing several ovens baking short dough biscuits
|Product||Oven type||Oven size||kWh/kg of biscuits|
|Rotary moulded||Indirect Radiant with Heat Recovery Zone||1.2 x 100m||0.404|
|Rotary moulded||DGF/Convection||1.2 x 60m||0.430|
|Rotary moulded||DGF/Convection||1.5 x 100m||0.441|
|Rotary moulded||Cyclotherm||1.2 x 100m||0.475|
|Rotary moulded||DGF/Convection||1.2 x 60m||0.492|
Baker Pacific are now able to offer a complete Technology Transfer for the design of the Heat Recovery Zone with manufacturing drawings from S.Eldridge Design Ltd.
The Technology Transfer includes:
Leading image: rudall30/Shutterstock.com