Burning Hydrogen: Pollution Or Clean Energy?

Hydrogen is the most abundant element in the universe and can be used as a fuel. However, burning hydrogen is a highly debated topic, with some arguing that it causes pollution and others claiming it to be a clean fuel. Hydrogen burns at a much higher temperature than methane gas, and the combustion of hydrogen may result in higher NOx emissions, which are hazardous air pollutants. On the other hand, hydrogen does not produce carbon dioxide emissions when burned and can be used in fuel cells to generate electricity without harmful emissions.

Burning hydrogen produces nitrogen oxide, a dangerous air pollutant

Burning hydrogen does not produce carbon dioxide (CO2) emissions, which is good news for the climate. However, hydrogen combustion produces other air emissions, such as nitrogen oxide (NOx), a dangerous air pollutant. Nitrogen oxide is a family of poisonous, highly reactive gases that form when fuel is burned at high temperatures. Hydrogen burns at a much higher temperature than the methane gas conventionally used in furnaces and stoves, and NOx emissions are directly correlated with combustion temperature. NOx emissions are hazardous because they trigger breathing and lung problems in people, especially in children, who have smaller airways, developing lungs, and faster breathing rates than adults.

The production of hydrogen itself can also be heavily polluting. The most common way to produce hydrogen is through steam-methane reformation (SMR), which involves burning fossil fuels that emit harmful pollutants like particulate matter and nitrogen oxides. Hydrogen is also highly flammable and prone to leaking, and when leaked into the atmosphere, it can have a greenhouse gas effect five times more potent than CO2.

Despite these concerns, hydrogen has been touted as a clean fuel of the future, with the ability to power automobiles and home appliances without producing greenhouse-enhancing carbon dioxide emissions. However, it is important to note that hydrogen combustion in appliances designed for fossil gas risks polluting the indoor air with NOx and posing safety hazards due to embrittled pipes and gas line leaks.

To address the issue of NOx emissions, mitigation strategies and emerging technologies are being developed to prevent or reduce these pollutants when hydrogen is used for combustion. For example, flue gas treatment approaches can convert harmful emissions into less harmful compounds, similar to the processes used in catalytic converters for gasoline and diesel-powered vehicles. Additionally, hydrogen can be used in fuel cells to generate electricity without any harmful emissions, emitting only pure water vapor.

Hydrogen combustion can be used for industrial heating and energy storage

Despite the challenges, hydrogen has potential as an energy storage medium due to its versatility. It can be easily produced by electrolysis of water, integrating with electricity generation. The resulting hydrogen can then be burned in thermal power plants to generate electricity or used as fuel for piston engines, gas turbines, or hydrogen fuel cells. Hydrogen has a high energy density, making it an efficient energy storage option.

However, the storage of hydrogen presents challenges due to its light weight and low volume-energy density. It must be stored in a concentrated state, typically in high-pressure tanks or as a liquid at cryogenic temperatures. For power generation, storage in steel or composite tanks is commonly favoured. Hydrogen can also be stored in underground caverns for large-scale energy storage or in steel containers for smaller-scale applications.

The combustion of hydrogen for industrial heating has been a subject of debate. While it does not produce carbon dioxide (CO2) emissions, it can lead to high levels of nitrogen oxide (NOx) emissions, which are harmful pollutants. The burner design plays a significant role in influencing NOx emissions, and the increase in flame temperature with higher hydrogen concentrations can exacerbate this issue.

In conclusion, hydrogen combustion has potential for industrial heating and energy storage, but it is essential to address the challenges associated with hydrogen production, storage, and emissions to ensure its sustainable and safe utilization.

Hydrogen is highly flammable and prone to leaking, which can cause explosions

Hydrogen is a highly flammable gas that can cause fires and explosions if not handled properly. It has a wide explosive/ignition mix range with air, and only a small amount is required for ignition. This means that when ignited in an enclosed space, a hydrogen leak will likely lead to an explosion.

Hydrogen is also prone to leaking. It is a very light gas that rises quickly and collects under roofs and overhangs, forming an explosion hazard. It can also enter pipes and follow them to their destinations. Hydrogen pipes should be well-labeled and located above other pipes to prevent this. Even with proper design, hydrogen leaks can support combustion at very low flow rates, as low as 4 micrograms per second.

The storage and use of hydrogen pose unique challenges due to its ease of leaking, low-energy ignition, wide range of combustible fuel-air mixtures, buoyancy, and ability to embrittle metals. Liquid hydrogen poses additional challenges due to its increased density and the extremely low temperatures needed to keep it in liquid form. It is difficult to maintain such low temperatures, and hydrogen will gradually leak away at a rate of 1% per day. The main danger with cryogenic hydrogen is what is known as BLEVE (boiling liquid expanding vapor explosion).

Hydrogen sensors or katharometers can be used to rapidly detect hydrogen leaks, and hydrogen fueling has been found to be as safe as, or safer than, compressed natural gas (CNG) fueling. However, it is hard to tell if there is a hydrogen leak because it has no odor. By the time a worker smells an odorant, hydrogen concentrations might have already exceeded its lower flammability limit.

Hydrogen can be used in fuel cells to generate electricity without harmful emissions

Burning hydrogen does not produce carbon dioxide (CO2) emissions, which is good news for the climate. However, hydrogen combustion produces other air emissions, such as nitrogen oxide (NOx), which is a family of poisonous, highly reactive gases. This is a problem that is slowly emerging in public conversation.

Despite this, hydrogen can still be used in fuel cells to generate electricity without harmful emissions. Hydrogen fuel cells generate electricity through a chemical reaction between hydrogen and oxygen. Hydrogen fuel cells and batteries are both electrochemical cells that have two electrodes in contact with a material that can conduct ions, called an electrolyte. One electrode is the anode, and the other is the cathode. In a hydrogen fuel cell, electrons are released from the hydrogen that is supplied to the anode, whereas in a battery, the electrons are released from the material in the anode itself.

The hydrogen ions (protons) produced from the hydrogen at the anode travel through the electrolyte in the fuel cell to the cathode. Oxygen supplied to the cathode reacts with these hydrogen ions and electrons arriving via the external circuit to produce water and heat, both of which are removed from the fuel cell. This is an example of a reduction reaction. In a PEM fuel cell, bipolar plates are positioned at either side of the cell to help distribute gases and serve as current collectors. The electrolyte is contained in a membrane between the anode and cathode, which are all sandwiched between the bipolar plates. The membrane allows only protons to pass through and is called a proton exchange membrane, or PEM.

Fuel cells have been used in NASA spacecraft since the Gemini program in the 1960s and even today they provide electricity and drinking water for astronauts on Space Shuttle flights. Hydrogen fuel cells produce electricity by combining hydrogen and oxygen atoms. The hydrogen reacts with oxygen across an electrochemical cell, similar to a battery, to produce electricity, water, and small amounts of heat. Hydrogen fuel cells are an efficient power source for trucks, construction equipment, buses, and industrial or marine applications, as they benefit from a high energy-to-weight ratio. Unlike batteries, which add weight and require longer recharge times, fuel cells can power heavy loads over longer distances and be refueled quickly.

Hydrogen can be produced from water, making it almost inexhaustible. Hydrogen combustion is clean, with water being the only byproduct, compared to the CO2 and other harmful emissions from gasoline or diesel. Hydrogen fuel cells are seen as one of the key enablers of fossil-free transportation systems, supporting the transition to net-zero greenhouse gas emissions.

Hydrogen production is heavily polluting, especially when derived from methane gas

Hydrogen is the most abundant element in the universe. However, it is not naturally occurring on Earth in its pure form due to its tendency to attach to other molecules. Hydrogen can be used as a fuel because it releases energy when combined with oxygen.

The most common way to produce hydrogen is through the steam-methane reformation (SMR) process, which involves separating hydrogen from methane gas using extremely high heat and pressure. This process is heavily polluting as the heat required comes from burning fossil fuels, which emit harmful pollutants like particulate matter and nitrogen oxides. These gases create smog and can damage lungs, posing a major threat to human health and the climate.

The production of hydrogen through the SMR process emits 6.6-9.3 tonnes of carbon dioxide for every tonne of hydrogen produced. This carbon dioxide is a greenhouse gas that contributes to climate change. Additionally, the burning of hydrogen, especially in home appliances, can produce dangerous levels of nitrogen oxide (NOx), a family of poisonous and highly reactive gases that are a threat to human health, particularly for children with their smaller, developing airways.

The fossil fuel industry has a vested interest in promoting hydrogen as a fuel source as it creates a new demand for their products and allows them to continue polluting. Hydrogen is often portrayed as a "carbon-free" fuel, but this is misleading as most hydrogen is derived from fossil fuels, with only 1% generated renewably. Increasing hydrogen production will likely lead to increased production of fossil-fuel-derived hydrogen, perpetuating health inequities and negatively impacting vulnerable communities.

While hydrogen has been touted as the clean fuel of the future, it is evident that hydrogen production, especially when derived from methane gas, is heavily polluting. The process of extracting hydrogen from methane gas emits significant amounts of carbon dioxide and contributes to air pollution, posing risks to both the environment and human health.

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