Hydrogen: Clean Energy, Zero Air Pollutants

Hydrogen is a clean fuel that, when burned, produces no carbon dioxide (CO2) emissions, which is good news for the climate. However, hydrogen combustion produces other air emissions, such as nitrogen oxides (NOx). NOx formation occurs when air, which contains nitrogen and oxygen, is exposed to very high temperatures (above 1,500°C). Hydrogen combustion in turbines and industrial heating applications can produce NOx, which include nitric oxide (NO) and nitrogen dioxide (NO2), both hazardous air pollutants. While hydrogen has the potential to reduce pollution and provide clean energy, it is important to address the production of NOx through mitigation strategies and technologies to reduce its release into the atmosphere.

Hydrogen burned in fuel cells produces no harmful emissions

Hydrogen is an energy carrier and can be used in fuel cells to generate electricity without any harmful emissions. When burned in a fuel cell, hydrogen produces only pure water vapour and warm air. This is because fuel cells operate via an electrochemical reaction instead of combustion, so even high-temperature fuel cells do not create any harmful direct emissions.

The use of hydrogen in fuel cells can provide a zero-emissions option for certain applications, such as in heavy trucks, trains, and ships, thereby improving local air quality. Hydrogen fuel cells can also be used in vehicles, with NASA using them to power the Apollo and Space Shuttle missions. Hydrogen can be stored in super-cooled (cryogenic) tanks for transportation applications in fuel cell vehicles.

However, it is important to note that the production of hydrogen can result in carbon dioxide emissions. Hydrogen is often produced by burning fossil fuels such as coal, oil, and natural gas, which releases carbon dioxide into the atmosphere. Additionally, while hydrogen burned in fuel cells produces no harmful emissions, hydrogen burned through combustion can produce nitrogen oxide (NOx) emissions, which are hazardous air pollutants.

To address the issue of NOx emissions, several mitigation strategies and technologies exist, such as flue gas treatment approaches, to reduce or prevent these emissions when hydrogen is used for combustion. Furthermore, hydrogen has a larger stable combustion temperature range, allowing for a higher ratio of air to fuel, which dilutes the hydrogen and results in lower-temperature combustion, thereby reducing NOx emissions.

Hydrogen combustion produces nitrogen oxides

While hydrogen combustion does not produce carbon dioxide (CO2) emissions, it can produce nitrogen oxides (NOx). NOx formation occurs when air, which contains nitrogen and oxygen, is exposed to very high temperatures (above 1,500°C). Any type of high-temperature combustion, including that of hydrogen, can produce NOx, which include nitric oxide (NO) and nitrogen dioxide (NO2), both hazardous air pollutants.

Because hydrogen burns at higher temperatures than natural gas, combustion of pure hydrogen may result in comparably higher NOx emissions. However, this can be mitigated by the fact that hydrogen has a larger stable combustion temperature range, meaning a higher ratio of air to fuel can be used. This additional air effectively dilutes the hydrogen, which cools off the flame and results in lower-temperature combustion, thereby reducing the amount of NOx emissions produced.

Research has shown that hydrogen combustion via turbines can achieve comparable performance and NOx emissions to those of today's turbines running on natural gas. Additionally, multiple mitigation strategies exist to prevent or reduce NOx emissions when hydrogen is used for combustion. For example, flue gas treatment approaches can convert harmful emissions into less harmful compounds, using processes similar to those in catalytic converters in gasoline and diesel-powered vehicles.

It is important to note that the standard method for calculating NOx emissions may not be accurate when applied to hydrogen, and that we may be overestimating NOx emissions from hydrogen combustion. The unique characteristics of H2 flames, such as higher flame speeds and sensitivity to flame stretch and thermal-diffusive instability, also need to be considered when evaluating NOx emissions.

Hydrogen is a clean, low-carbon fuel

Hydrogen can be used in fuel cells to generate electricity without any harmful emissions, emitting only water vapour and oxygen-depleted air. This is because fuel cells operate via an electrochemical reaction instead of combustion, even at high temperatures of up to 1,000°C. By shifting from fossil fuels and internal combustion engines to hydrogen fuel cells, we can improve local air quality and reduce greenhouse gas emissions.

However, it is important to note that the combustion of hydrogen can produce nitrogen oxides (NOx), which are hazardous air pollutants. This occurs when air, which contains nitrogen and oxygen, is exposed to very high temperatures (above 1,500°C). Hydrogen burns at higher temperatures than natural gas, so combustion may result in higher NOx emissions. Nevertheless, hydrogen has a larger stable combustion temperature range, allowing for a higher ratio of air to fuel, which dilutes the hydrogen and lowers the combustion temperature, thereby reducing NOx emissions.

The production of hydrogen is a key consideration when discussing its environmental impact. Hydrogen can be produced from a variety of domestic resources, including natural gas, nuclear power, biomass, and renewable power like solar and wind. While hydrogen fuel cells produce no carbon dioxide emissions, the process of producing hydrogen can. For instance, producing hydrogen from methane releases carbon dioxide into the atmosphere, although it is about half as much as burning fossil fuels.

In conclusion, hydrogen is a promising clean, low-carbon fuel with the potential to replace fossil fuels in the transportation and energy sectors. While hydrogen combustion can produce nitrogen oxide pollutants, there are strategies to mitigate these emissions. Additionally, the production of hydrogen is an area of concern, as it currently involves the burning of fossil fuels in some cases. However, with further research and development, hydrogen has the potential to play a significant role in a cleaner, more sustainable future.

Hydrogen combustion can be used to reduce reliance on fossil fuels

One of the main advantages of hydrogen combustion is that it does not produce carbon dioxide (CO2) emissions when burned. This is a significant advantage over fossil fuels, which release large amounts of CO2 into the atmosphere and contribute to global warming. By replacing fossil fuels with hydrogen, we can reduce our carbon emissions and work towards a more sustainable future.

Additionally, hydrogen can be used in fuel cells to generate electricity without any harmful emissions, emitting only water vapour. Fuel cells operate through an electrochemical reaction, which means that even at high temperatures, they do not create any harmful direct emissions. This makes hydrogen an attractive option for heavy trucks, trains, ships, and other applications where reducing local air pollution is a priority.

However, it is important to note that hydrogen combustion is not entirely emissions-free. When hydrogen is burned, it can produce high levels of nitrogen oxide (NOx), which is a hazardous air pollutant. The formation of NOx occurs during high-temperature combustion, and hydrogen burns at higher temperatures than natural gas, leading to potentially higher NOx emissions. Nevertheless, there are strategies to mitigate NOx emissions, such as flue gas treatment approaches that convert harmful emissions into less harmful compounds.

Another challenge with hydrogen is its low energy content by volume, which makes storage difficult. Hydrogen requires high pressures, low temperatures, or chemical processes to be stored compactly, which can be a limitation for vehicles with limited size and weight capacity for fuel storage. Additionally, the cost of hydrogen fuel cells needs to decrease substantially for it to be competitive in the marketplace.

While hydrogen combustion has the potential to reduce our reliance on fossil fuels, it should be noted that the production of hydrogen can also be energy-intensive and may involve the use of fossil fuels. For example, the process of producing hydrogen from water requires electricity, and if this electricity is generated from fossil fuels, it could negate some of the environmental benefits of using hydrogen as a fuel.

In conclusion, hydrogen combustion can be a valuable tool in our efforts to reduce reliance on fossil fuels and combat climate change. However, it is not a perfect solution and should be considered as part of a broader strategy that includes electrification, direct renewable energy deployment, and behavioural changes.

Hydrogen is not a source of energy, but a way of storing and transporting it

Hydrogen is a clean fuel that, when consumed in a fuel cell, produces only water and oxygen-depleted air as exhaust products. It can be produced from a variety of resources, including natural gas, nuclear power, biomass, and renewable power like solar and wind. Hydrogen can be used to power vehicles, generate electricity, power industry, and heat homes and businesses. It is an energy carrier that can be used to store, move, and deliver energy produced from other sources.

However, hydrogen is not a source of energy in itself. It is a way of storing and transporting energy. The process of producing hydrogen can result in the release of carbon dioxide into the atmosphere, particularly when fossil fuels like coal, oil, and natural gas are burned to produce hydrogen. While hydrogen combustion does not produce carbon dioxide emissions, it can lead to the emission of nitrogen oxides (NOx), which are hazardous air pollutants.

The use of hydrogen in fuel cells is considered a zero-emissions option as it does not produce harmful direct emissions. Fuel cells operate via an electrochemical reaction instead of combustion, even at high temperatures. This makes hydrogen a promising alternative transportation fuel for vehicles with no emissions of air pollutants. Hydrogen can be stored in portable tanks and transported through gas pipelines, making it a viable option for road, air, and shipping transportation.

While hydrogen has the potential to reduce carbon emissions and facilitate decarbonization, it is important to recognize that its production and combustion can have environmental impacts. The combustion of hydrogen can result in NOx emissions, which are harmful pollutants. However, mitigation strategies exist to prevent or reduce these emissions, such as flue gas treatment approaches that convert harmful emissions into less harmful compounds. Additionally, hydrogen's larger stable combustion temperature range allows for a higher ratio of air to fuel, diluting the hydrogen and resulting in lower-temperature combustion, thereby reducing NOx emissions.

In conclusion, hydrogen is a valuable energy carrier and storage solution but is not a source of energy itself. Its use can help reduce pollution and improve air quality, particularly when used in fuel cells, but the production and combustion of hydrogen must be carefully managed to minimize any negative environmental consequences.

Frequently asked questions