IHEA Sustainability Glossary of Terms

Sustainability Terms & Definitions

Carbon Footprint: The total amount of greenhouse gases generated by an activity, site, entity, person, or process used to assess and measure its environmental impact.
Carbon Neutral: A process, activity or location that yields no net carbon emissions to the environment. This may be achieved by emissions controls, decarbonization, electrification, renewable energy sources, and the purchase or attainment of carbon credits.
Clean Fuel: A term referring to energy sources that contain little or no carbon content, no particulate matter emissions, or are derived from renewable sources.

Decarbonization: An initiative to reduce carbon emissions as greenhouse gases to reduce climate change and global warming. Decarbonization generally refers to reduction of new emissions and carbon capture of existing greenhouse gases.

Electrification

Reducing the emission of greenhouse gases or carbon emissions by converting fossil fuel usage to electric power supplied by sustainable sources.

Electrolysis

Electrolysis is the process of using electricity to split water into hydrogen and oxygen using an electrolyzer.

Emissions Levels

The measure of fuel combustion constituents that are considered pollutants. The most common emissions measured and controlled are nitrous oxide (NO), nitrogen dioxide (NO2), carbon monoxide (CO), carbon dioxide (CO₂), sulfur dioxide (SO2), and particulate matter less than 10 microns (PM10). Pollutant emissions are typically reported by a mass basis or a concentration basis with reporting standards differing in various countries or regions.

Energy Efficiency

The numerical expression of useful net energy converted to work or power divided by the gross energy input.

Combustion Efficiency: An expression of the percentage of gross fuel heat input at ideal stoichiometry that is liberated in a heating process for heat transfer. A measurement of how effectively the heat content of a fuel is transferred into usable heat. The stack/flue gas temperature and flue gas oxygen concentrations are primary indicators of combustion efficiency.
Thermal Efficiency: The percentage of the gross heat input that is transferred into a product or process. Also defined as the percentage of heat input that becomes useful work. It is the measure of output energy divided by the input energy in a system.to a process that is transferred to a product of process. Thermal efficiency may be reduced by stack gas losses, heat storage, radiation losses, leakage, and dynamic control errors.
Process Efficiency: The percentage of total energy input to a process that is converted to a product or useful work. Process efficiency includes all inputs of energy including mechanical, electrical, thermal, or fuel.

Energy Intensity

A measure of the total energy used to produce a product or conduct an activity. The measure allows various products or activities to be compared for energy per unit output.

EPA Scope 1 Emissions

Direct greenhouse gas emissions that are from company-owned and controlled resources of an organization. These are emissions released into the atmosphere as a direct result of a company's activities.

Stationary Combustion: This category includes emissions that come from the combustion of fossil fuels. Think of sources that include boilers that heat buildings or other industrial applications (e.g. gas-fired combined heat and power (CHP) plants).
Mobile Combustion: This category includes greenhouse gas emissions from the burning of fuel of all vehicles that are owned or leased by an organization.
Fugitive Emissions: Fugitive emissions are unintentional releases/leaks of greenhouse gases, such as refrigerant gases or gases from air-conditioning units.
Process Emissions: This final emissions category is process emissions. These are the emissions that are released during industrial processes and on-site manufacturing. Think of the CO₂ emissions that are produced during cement manufacturing or the processing or manufacturing of chemicals.

EPA Scope 2 Emissions: (Indirect Emissions – Owned)

Indirect greenhouse gas emissions associated with the purchase of electricity, steam, heat, or cooling by an organization. Although scope 2 emissions physically occur at the facility where they are generated, they are accounted for in an organization's Green House Gas (GHG) inventory because they are a result of the organization’s energy use.

EPA Scope 3 Emissions (Indirect Emissions – Not Owned)

These emissions are the result of activities from assets not owned or controlled by the reporting organization, but that the organization indirectly impacts in its value chain. Scope 3 emissions include all sources not within an organization’s scope 1 and 2 boundary. The scope 3 emissions for one organization are the scope 1 and 2 emissions of another organization. Scope 3 emissions, also referred to as value chain emissions, often represent the majority of an organization’s total GHG emissions. This can be things like raw materials, raw material processing, raw material transportation, supply chain energy, capital equipment, product distribution, product use, product disposal, etc.

Flame Speed: The measured rate at which a flame front propagates through a combusting fuel and air or fuel and oxidant mixture. Flame speed is affected by fuel composition, fuel to oxidant ratio, relative temperature, diluting inerts, and fuel to oxidant mixture dynamics.

Greenhouse Gases: Any gaseous element or compound that contributes to climate change by absorbing infrared radiation from the sun, thereby acting as an insulating blanket to the planet.

Hydrogen

A chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element that may be used as a carbon free fuel when in the form of diatomic hydrogen (H₂). It is colorless, odorless, tasteless, and highly combustible. Hydrogen is the most abundant element in the universe.

Hydrogen Color Classifications

Blue Hydrogen: Produced through same technique as Gray Hydrogen but all CO₂ is captured and sequestered.
Black or Brown Hydrogen: Produced through gasification of coal with resultant CO₂ emissions and other pollutants.
Green Hydrogen: Produced through the electrolysis (the separation of hydrogen and oxygen molecules by applying electrical energy to water). This process is powered by renewable electricity such as wind and solar to be truly carbon free so zero CO₂ emissions are produced.
Gray Hydrogen: The most prevalent form of hydrogen that is produced from natural gas through a process called steam-methane reforming which combines natural gas and water (as steam) and produces of hydrogen gas (H₂) and large volumes of CO₂.
Purple Hydrogen: Produced using nuclear power and heat through combined chemo thermal electrolysis splitting of water.
Pink Hydrogen: Produced through the electrolysis of water by using the electricity produced from a nuclear power plant.
Red Hydrogen: Produced through high temperature catalytic splitting of water using nuclear power as the energy source.
Turquoise Hydrogen: Similar to blue hydrogen but produced through the thermal splitting of methane (methane pyrolysis) that produces hydrogen and solid carbon and the carbon removed, stored and used, eliminating CO₂ emissions.
White Hydrogen: Naturally occurring hydrogen. Gaseous diatomic hydrogen in the air is accepted to be 0.6 parts per million making it a trace constituent in air.

Post Treatment/Sequestration: Any process or technology that removes greenhouse gases from emissions to be repurposed or stored to reduce the impacts of climate change.
Pyrolysis: Hydrogen which is produced from the decomposition of methane (also called pyrolysis).

Renewable Energy Certificate (RECs): a market-based instrument expressing renewable energy generation for environmental concern that may be bought, sold, or traded in pursuit of carbon footprint reduction.

Stoichiometric: The chemically balanced proportion of fuel and oxidant the results in theoretical perfect combustion or oxidation yielding no excess fuel or oxidant once reacted.
Sustainability: A term broadly used to refer to the maintenance and protection of natural resources by balancing the usage and replenishment of the resource.

Transmission Losses: The amount of electricity that is lost to resistance as it travels down distribution lines from the point of generation to the point of use. Generally, grid transmission losses are estimated to be between 2% to 5%.

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