Gas has been and continues to be the predominant fuel for biscuit baking ovens world-wide. The combustion of natural gas is a major source of greenhouse gases which are causing climate change. This is a major concern and makes it essential that we seek ways to reduce the carbon footprint of the biscuit baking industry.
The combustion process is a reaction of rapid oxidisation started by the correct mixture of fuel, oxygen and an ignition source. In order for complete combustion of natural gas, excess air is supplied to the burners.
The chemical reaction for natural gas combustion with 20% excess air is:
CH4 + 1.20 x 2(O2 + 3.76 N2) -> CO2 + 2 H2O + 0.5 O2 + 9.4 N2
CH4 = natural gas
O2 = oxygen
N2 = nitrogen
2H2O = water vapour
CO2 = Carbon Dioxide
Reference: Engineering Toolbox
Air is composed of 20.9% of oxygen, 78% of nitrogen and 1% of other gases. For most applications, every 1 m3 of natural gas, approximately 10 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.
When fuel and oxygen in the air are in perfect balance and the fuel is burned completely, the combustion is said to be stoichiometric. Typical excess air to achieve the best efficiency for combustion is 10-20%.
Carbon dioxide is a product of the combustion and the content in the flue gas is an important indication of the combustion efficiency. The content of carbon dioxide after combustion with excess air is approximately 10.5% for natural gas and approximately 13% for light fuel oils.
Figure 1. Combustion efficiency and excess air/ engineeringtoolbox.com
Carbon Dioxide emission from burning methane, natural gas, is given below:
Specific carbon content: kgc / kg fuel 0.75
Specific energy content: kWh / kg fuel 15.4
Specific CO2 emission kgco2 / kg fuel 2.75
(amount of fuel basis)
Specific CO2 emission kgco2 / kWh 0.18
(amount of energy basis)
Reference: Engineering Toolbox: Combustion of fuels – carbon dioxide emissions
Greenhouse gases in the atmosphere absorb heat energy from the sun and emit it, keeping the earth’s surface and lower atmosphere warm. Greenhouse gases include carbon dioxide, water vapour, methane and nitrous oxide. The biggest contributor to the warming of the climate is carbon dioxide, CO2. Since pre-industrial times the atmospheric concentration of CO2 has increased by over 40% and methane by over 150%. More than half of this increase has occurred since 1970.
The biscuit industry now uses gas as the fuel for baking in almost every country. Natural gas is now 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 from renewable sources and improving efficiency.
Efficiency can be improved by:
The table below indicates some typical values for energy usage for baking.
|Product type||Energy for baking kWh/kg (excluding oven losses)||
Energy for baking kWh/kg(including est. losses
|Short dough biscuits||0.2121||0.404|
Note: 1 From actual installation
Note: 2 From calculations
Density: 0.68 kg/m3
Density at baking temperature: 0.4 kg/m3
Heat value of burning natural gas (methane):
42 - 55 MJ/kg (11.6 – 15.3 kWh/kg )
Average energy per kg of gas: 13.45 kWh/kg
The calorific value, density and energy for natural gas vary with the source, process and delivery. The values above are from the sources listed under references.
|Energy usage||kWh/kg||Natural gas consumption for baking one tonne of biscuits|
|Short dough biscuits||0.404 kWh/kg||30.0kg of gas|
|Semi-sweet biscuits||0.477 kWh/kg||35.5kg of gas|
|Crackers||0. 646 kWh/kg||48.0kg of gas|
Average power requirement 509 kWh per tonne of product range
Average gas consumption per tonne 37.8 kg
The combustion of 1.0kg of natural gas produces 2.75kg of CO2 and 0.18 kWh of energy. <www.engineeringtoolbox.com>
The average production of CO2 for one tonne of product range (short dough / semi-sweet, cracker) is: 37.8 x 2.75 = 104 kg
CO2 emissions: 104 kg per tonne of product range
A bakery with 3 production lines producing a total of 50 tonnes per 8 hour shift and 20 shifts a week will produce approximately 1000 tonnes of biscuits per week.
The CO2 emissions will be approximately 104,000 T per week and over 5,200,000 T per year.
Biscuit production and CO2 emissions in several countries:
In these countries the total population of 3749 million produce 980,000 T of CO2 emissions each year from biscuit production. Per capita emissions: 0.261 kg/year.
The total global CO2 emissions: 37.12 billion T. The world population is 8.0 billion. Per capita CO2 emissions: 4.64 T.
The current energy source for biscuit baking world-wide is gas. The option in some countries is fuel oil. However oil has a higher CO2 emission rate than gas, 3.15 kgco2/kg fuel compared to 2.75 kgco2/kgfuel for gas.
Electricity has substantial advantages for baking, but currently is expensive and the main generation systems involve substantial CO2 emissions. Fossil fuels have been the cheapest source of power for generating electricity. However, burning fossil fuels for generating electricity and heat is the largest source of greenhouse gases, causing 30% of global emissions.
The concern over climate change and the urgent need to reduce carbon emissions has led to development of renewable energy sources, solar, hydropower, wind and biomass. In addition nuclear power is an important source for the generation of electricity. The methods of the generation of electricity have changed during the last 10 years and now energy from some renewables is less costly than energy from new fossil fuel sources.
Energy Consumption by source: total percentages
Renewables made up 26.2% of global electricity generation in 2018. It is expected to rise to 45% by 2040. Over half of all utility scale renewable capacity additions in 2019 achieved lower costs than the cheapest equivalent new coal plant.
<www.c2es.org> < www.energypost.eu>
The price of generation from onshore wind and solar PV-generated power have both fallen below USD 0.05 / kWh. Fossil fuel powered generation usually costs between USD 0.05/kWh and 0.18/kWh.
These developments will continue based on concerns over climate change and the need to reduce carbon emissions. This will affect the options for energy for biscuit baking.
Renewable energy became the biggest source of electricity in the European Union in 2020 reaching 38% of the total electricity generated. For several individual countries it is now the main source of electricity, including United Kingdom, Germany and Spain. In United Kingdom 54% of electricity came from low carbon sources. In 2020 renewable energy sources accounted for 12% of the total energy consumption and 20% of electricity generation in the USA.
Japan’s government has pledged to increase renewable sources, solar and wind, for electricity generation from 10% in 2018 to 22-24% by 2030.
The Renewable Energy Master Plan (REMP) for Nigeria seeks to increase the supply of renewable electricity from 13% of total electricity generation in 2015 to 23% in 2025 and 36% by 2030. Renewable electricity would then account for 10% of Nigerian total energy consumption by 2025. REMP targets higher electrification rates, from 42% in 2005 to 60% in 2015 and 75% by 2025.
In a number of countries in Asia Pacific, Latin America and Africa energy from biomass contributes a significant source of energy with low carbon dioxide emissions. The most common biomass materials used for energy are plants, such as corn and soy and wood. The energy from these materials can be burned to create heat or converted into electricity. Some coal fired power stations are now being converted to burn biomass.
Increase in energy from renewables 2019 - 2025 - From International Energy Agency. <www.iea.org>
Renewables will become the largest source of energy by 2025, surpassing coal.
It is predicted that electricity will in the future be a preferred energy for many industries, based on competitive costs with current gas supplies and the need to reduce reliance on fossil fuels. In addition electricity is a clean and easily controlled energy source. Electric baking ovens have the following features:
PT Mayora Indah bakery in Indonesia with solar panels
Modern biscuit bakeries have long flat roofed production areas. The image above is an example of modern bakery design. New bakeries now often have production areas of around 150m x 30m, 4,500m2. This area could be used for solar panels.
Solar energy for a new bakery
A bakery roof of 4,500m2 could support 2300 solar panels of 400W capacity for each panel. The panel size is 1.7m x 1.1m.
Energy = solar panel watts x average hours of sunlight per year x 0.75
0.75 typical efficiency factor. Hours based on mid Europe: 2000 hours of sunlight per year
400 W x 2000 hrs x 0.75 = 600,000W per year per panel
600 kWh/panel x 2300 panels = 1,380,000kWh per year
Power requirement for a production line:
Average power requirement for operating a complete production line is 250kw. (This excludes the energy for baking, which is normally from gas).
The 2300 solar panels would power the production line for 5,520 hours (690 shifts)
Please can you advise which type of energy source is good for the wafer baking oven. As I know most of the time Gas is the best solution but it's really expensive in here.
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