Select Fossil Fuels – A Closer Look
Last week we ranked some more popularly used fossil fuels in terms of:
1.????? Specific Energy (Energy per unit of Mass of Fuel – Terajoules per Gigagrams)
2.????? Emissions Intensity by Energy basis (Mass of CO2 emissions per unit of Energy – kg of CO2 per Terajoule)
3.????? Emissions Intensity by Mass basis (Mass of CO2 emissions per unit Mass of Fuel – kg of CO2 per Ton of Fuel)
Overall Ranking of fossil fuels:
From last week , we see that:
So, we want to rank all these fuels based on the above. We scaled them and scored them across each parameter. Then we added the scores. Figure 1 below ranks the fuels from highest scores to lowest scores.
This week we will look at the most preferred fossil fuels. We will list out its origins, use cases and what are its supposed substitutes.
The “Most Preferred” fossil fuels:
Gas Works Gas: Coal Based
Specific Energy = 38.7 TJ/Gg
Emissions Intensity by Energy basis = 44.4 tons of CO2e/TJ
Emissions Intensity by Mass basis = 1.72 tons of CO2e/ton
What is it: "Gas Works Gas," also known as coal gas or town gas, was produced by heating coal to create a mix of hydrogen, carbon monoxide, methane, and other compounds. It was widely used in the 19th and early 20th centuries for lighting, heating, and cooking before natural gas became common.
Where is/was it used: Gas Works Gas was utilized in urban areas globally, lighting streets and homes while providing fuel for heating and cooking.
Annual Production: Historical production levels varied, but today, coal gas production has drastically declined due to environmental concerns. Current annual production is minimal compared to the past.
Substitutes: Natural gas, electricity, and renewable energy sources like solar and wind power have largely replaced Gas Works Gas due to being cleaner and more sustainable options.
The decline in Gas Works Gas production is due to environmental and health concerns, alongside advancements in cleaner energy technologies. The usage has declined in developed countries. It is fairly widely prevalent in industrial processes in developing countries that don’t have easy access to natural gas.
Coke Oven Gas: Coal Based
Specific Energy = 38.7 TJ/Gg
Emissions Intensity by Energy basis = 44.4 tons of CO2e/TJ
Emissions Intensity by Mass basis = 1.72 tons of CO2e/ton
What is it: "Coke Oven Gas" is a byproduct of heating coal in ovens to make coke used in steel production. It contains hydrogen, methane, carbon monoxide, and other gases. It is a highly rated as a valuable by-product of coal?carbonization ?to produce coke in the steel industry. Typically, a single ton of coke generates approximately 360?m3?COG (Rauf Razzaq, Chunshan Li, 2013)[1].
Where is/was it used: It's used in steel plants for fuel or chemical production and heating. It also is used as a feedstock in the production of ammonia, methanol and others.
Annual Production: Annual production figures vary but are significant due to steel manufacturing demands.
Substitutes: Substitutes include natural gas, renewable energy, and technologies that capture and use industrial waste gases for energy.
Sludge Gas: Biomass based
Specific Energy = 50.7 TJ/Gg
Emissions Intensity by Energy basis = 54.6 tons of CO2e/TJ
Emissions Intensity by Mass basis = 2.75 tons of CO2e/ton
What is it: Sludge gas, also known as digester gas or biogas, is a byproduct of the anaerobic digestion of organic matter, typically sewage sludge or wastewater solids. It is a combustible gas composed primarily of methane (CH4) and carbon dioxide (CO2), with trace amounts of other gases such as hydrogen sulfide (H2S) and ammonia (NH3). The methane content of sludge gas typically ranges from 50% to 70%, making it a valuable source of energy. Between Europe, USA and China, they manufacture about 22 million tons of Sewage sludge (Nwabunwanne, et al., 2023)[2].
Where is/was it used: Energy generation: used to fuel internal combustion engines to generate electricity or heat, or it can be upgraded to biomethane, a high-purity methane that can be used as a substitute for natural gas. Helps in manufacturing of Compressed Natural Gas, Hydrogen and Ammonia.
Annual: This varies widely across the world depending on the method and the efficiency of production processes involved.
Substitutes: Biogas sourced from organic waste and conventional natural gas.
Sludge Gas comes from waste sewage sludge. Therefore, it is renewable. And it can be used for waste management.
Other Biogas: Biomass based
Specific Energy = 50.7 TJ/Gg
Emissions Intensity by Energy basis = 54.6 tons of CO2e/TJ
Emissions Intensity by Mass basis = 2.75 tons of CO2e/ton
What is it: In the GHG (Greenhouse Gas) Protocols, "Other Biogas" is produced from the anaerobic fermentation of animal slurries and of wastes in abattoirs, breweries and other agro-food industries[3], typically generated from organic materials apart from sewage sludge. Other Biogas mainly consists of methane (CH4) and carbon dioxide (CO2), along with small amounts of other gases like hydrogen sulfide (H2S).
Where is it used: It is used primarily for energy production, similar to sludge gas, where it can be used for electricity generation, heating, or as a fuel for vehicles. Additionally, it can be purified to produce biomethane, which can be injected into natural gas pipelines or used as a transportation fuel.
Annual Production: This varies widely across the world depending on the method and the efficiency of production processes involved.
Substitutes: Natural Gas is good substitute for Other Biogas. If used for electricity production, Solar, Wind and other renewable sources are preferred substitutes.
Given the environmental concerns, Other Biogas may still be preferred over Natural Gas, because of its renewable sources and in managing waste.
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Landfill Gas: Biomass based
Specific Energy = 50.7 TJ/Gg
Emissions Intensity by Energy basis = 54.6 tons of CO2e/TJ
Emissions Intensity by Mass basis = 2.75 tons of CO2e/ton
What is it: Landfill gas, formed by the digestion of landfilled wastes. As organic waste decomposes anaerobically (without oxygen) in landfills, it generates Landfill Gas. Methane, a potent greenhouse gas, is the primary component, making up around 50%-60% of the gas mixture, while carbon dioxide constitutes about 40%-50%.
Where is it used: Methane from Landfill Gas can be collected, treated, and used to generate electricity or heat. Additionally, it can serve as a fuel for vehicles after suitable purification. If the Gas is not captured and used, it is typically flared. Flaring is the controlled burning of Landfill Gas to prevent it from escaping into the atmosphere.
Annual Production: Difficult to quantify. The annual production of Landfill Gas varies widely based on factors such as the size of the landfill, the type of waste disposed of, the age of the landfill, and the efficiency of gas collection systems. Estimates suggest that significant quantities of Landfill Gas are generated globally due to the substantial amount of organic waste disposed of in landfills.
Substitutes: Natural Gas is an immediate substitute given the efficiency of extracting and using Landfill Gas can be more polluting than Natural Gas. However, Landfill Gas, its capture and usage helps in better waste management and possibly reclaim land that was previously dumping grounds.
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Natural Gas (NG): Gas based
Specific Energy = 48 TJ/Gg
Emissions Intensity by Energy basis = 56.1 tons of CO2e/TJ
Emissions Intensity by Mass basis = 2.69 tons of CO2e/ton
What is it: Naturally occurring underground deposits of gases consisting of 50 to 90 percent methane (CH4) and small amounts of heavier gaseous hydrocarbon compounds such as propane (C3H4) and butane (C4H10). Natural gas does not include the following gaseous fuels: landfill gas, digester gas, refinery gas, sour gas, blast furnace gas, coal-derived gas, producer gas, or coke oven gas[4].
Where is it used: NG is used widely in electricity generation, heat production and in other industrial processes. It is the most preferred fossil fuel for such purposes as compared to Coal and Oil. The earlier Gas Works Gas and Coke Oven Gas are more used in specific industrial processes rather than large scale energy production.
Annual Production: As on 2022, the world produced about 4.08 trillion cubic feet of Natural Gas[5]. The global reserves of this fossil fuel is about 6,923 trillion cubic feet as of 2017[6]. At current rates of consumption the world will run out of Natural Gas in about 50 years.
Substitutes: Biogas in all its forms is an immediate and renewable alternative to Natural Gas. When used for electricity production, it can be readily and economically be substituted by Solar and Wind.
Refinery Gas: Oil based
Specific Energy = 49.5 TJ/Gg
Emissions Intensity by Energy basis = 57.6 tons of CO2e/TJ
Emissions Intensity by Mass basis = 2.85 tons of CO2e/ton
What is it: Refinery gas includes a mixture of non-condensable gases mainly consisting of hydrogen, methane, ethane and olefins obtained during distillation of crude oil or treatment of oil products (e.g. cracking) in refineries. This also includes gases which are returned from the petrochemical industry[7].
Where is it used: Refinery Gas is used within the refinery itself, for internal processes, such as providing heat and energy for refining operations. Additionally, some components of Refinery Gas, especially propane and butane, might be extracted and used for various industrial and commercial purposes, such as heating, cooking, or as feedstock for the production of chemicals.
Annual Production: It is unclear how much is produced. The global refining capacity, however, is about 102.7 million barrels/day in 2022. It may increase to 105.2 million barrels/day by 2030. India is expected to increase from 5.2 million barrels/day in 2022 to 7.5 million barrels/day in 2030[8].
Substitutes: Refinery Gas is a very specialised fuel, used in a very specific industry for a very specific purpose. There are no substitutes for this.
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Ethane: Oil based
Specific Energy = 46.4 TJ/Gg
Emissions Intensity by Energy basis = 61.6 tons of CO2e/TJ
Emissions Intensity by Mass basis = 2.85 tons of CO2e/ton
What is it: Ethane is a colorless, flammable gas with a chemical formula of C2H6. It is the second-smallest alkane, a hydrocarbon composed only of carbon and hydrogen atoms. Ethane is a major component of natural gas, constituting about 30% of its volume. It is also produced as a byproduct of petroleum refining and petrochemical processes.
Ethane is primarily produced from natural gas using a process called cryogenic fractionation. In this process, natural gas is cooled to extremely low temperatures, causing its components to separate based on their boiling points. Ethane condenses at a higher temperature than methane, the primary component of natural gas, allowing for its separation.
Petroleum refining and petrochemical processes also produce ethane as a byproduct. In petroleum refining, ethane is produced during cracking, a process that breaks down larger hydrocarbon molecules into smaller ones. In petrochemical processes, ethane is produced as a byproduct of ethylene production.
Where is it used: Ethane is largely used in the production of Ethylene and as a versatile feedstock for many industrial processes and applications. Ethylene is the most widely used organic compound in the world. Ethylene is used in the manufacturing of various plastics, such as polyethylene (PE), polyvinyl chloride (PVC), and polyethylene terephthalate (PET).
Ethane can also be used as a fuel in gas turbines and internal combustion engines. It is a cleaner-burning fuel than natural gas, reducing emissions of nitrogen oxides (NOx) and sulfur dioxide (SO2).
Annual Production: Theoretically 1 ton of ethane can produce 1 ton of ethylene. The global production of ethylene is 223.86 million tons per year[9].
Substitutes: Ethylene industry is expected to increase by 5% annually. Therefore, Ethane is similarly expected to grow. The objective therefore is to find alternative, biomass/renewable feedstock for ethane. Or to find renewable alternatives to ethylene. Sugarcane and Sorghum are seen as sources of bioethylene[10]. But this has its implications on water conservation. We may try to solve CO2 emissions by exacerbating a water crisis.
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[3] https://ghgprotocol.org/sites/default/files/2023-02/Stationary_Combustion_Guidance_final_1_0.pdf
[4] https://ghgprotocol.org/sites/default/files/2023-02/Stationary_Combustion_Guidance_final_1_0.pdf
[7] GHG Protocol, Ibid.