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The Biscuit Industry Carbon Footprint

The biscuit industry now uses gas as the fuel for baking in almost every country. Natural gas is widely available and economic. However, this gives our industry a large carbon footprint. It will attract pressure in many countries to reduce the use of gas, by using electricity or improving efficiency. The table below indicates some typical values for energy usage for baking.

Product type

Specific heat of dough

Energy for baking  kWh/kg  (excluding oven losses)

Energy for baking  kWh/kg   (including est. losses)

Short dough biscuits

1.67

0.212

0.404

Semi-sweet biscuits

1.86

0.236

0.454

Crackers

2.08

0.264

0.508

 

Consumption of gas for baking

Natural gas calorific value 10.6 kWh/m3
Density:  0.68 kg/m3    
Density at baking temperature 0.2 – 0.5 kg/m3

Heat value of burning natural gas (methane CH4):  50-55 MJ/kg  (13.9 – 15.2 kWh/kg )
www.world.nuclear.org

Average energy per kg of gas   14.5 kWh/kg

The calorific value, density, and energy for natural gas vary with the source, process, and delivery. The values above are from the references listed below.

Energy usage  kWh/kg natural gas consumption for baking one tonne of biscuits 
Short dough biscuits 0.404 kWh/kg  27.9 kg of gas 
Semi-sweet biscuits 0.454 kWh/kg 31.3 kg of gas 
Snack crackers  0.508 kWh/kg 35.0 kg of gas

Average kWh to bake 1T of biscuits 455 kWh

Average gas consumption per tonne of biscuits 31.4 kg  

Combustion process for natural gas

The combustion process is a reaction of rapid oxidisation started by the correct mixture of fuel, oxygen, and an ignition source. The chemical reaction for natural gas combustion is:

CH4 + 3O2  =  Heat + 2H2O + CO2 + O  

Air is composed of 20.9% of oxygen, 78% of nitrogen, and 1% of other gases. For most applications, every 1 m3 of oxygen, approximately 15 m3 of air is required to provide complete combustion of natural gas. To ensure complete combustion of the fuel, excess air is drawn in by the burners. The combustion efficiency will increase with increased excess air until the heat loss in the excess air is larger than the heat provided by more efficient combustion.

Typical excess air to achieve the best efficiency for combustion is:

5 - 10% for natural gas

The Carbon Footprint

The combustion of 1.0kg of natural gas produces 2.75kg of Co2 and 0.18 kWh of energy.

www.engineeringtoolbox.com

Engineering-toolbox-data

CO2 emissions: 86.3 kg per tonne of biscuits  

A bakery producing 50 tonnes per 8-hour shift and 20 shifts a week will produce 1000 tonnes of biscuits per week.

The CO2 emissions will be 86,300 T per week.


References:

https://www.engineeringtoolcox.com 

https://www.forestresearch.gov.uk

https://www.gov.uk

https://www.marquard-bahlis.com

www.nationalgrid.com

https://www.unitrove.com 

https://world.nuclear.org

Leading image: J.M. Image Factory/shutterstock.com

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