Green and Blue Hydrogen and their Impact on Environment

Hydrogen is one of the most abundant and highly flammable gas on earth’s surface. Many researches and developments are progressing on the integration of hydrogen technologies, most specifically green and blue hydrogen and their impact on environment and contribution towards greenhouse gas emissions.

Hydrogen is the third most abundant chemical element on Earth, after oxygen and silicon but it is not independently available in its pure form, and thus it cannot be considered an energy source rather it is an energy carrier produced from other sources.

Although some types of hydrogen emit harmful pollutants but to face the huge challenges of a transition towards a zero-carbon energy system, methods of hydrogen combustion have brought innovative developments by introducing green and blue hydrogen technologies. These clean or low-carbon hydrogen types offer promising opportunities to fight climate change.

What is Hydrogen Energy and where is this used?

Hydrogen is not very abundant in Earth's atmosphere independently but rather very abundant in chemical compounds such as water (H₂O) and hydrocarbons. The existing small amount of hydrogen in the atmosphere is primarily due to processes like the breakdown of methane or water vapors, as well as from human activities like hydrogen fuel use.

Hydrogen is a highly flammable gas that burns with a pale blue, almost invisible flame and during the combustion process, it reacts with oxygen, producing intense heat and water vapor (H₂O) as the main byproduct.

Traditional hydrogen production methods, such as coal gasification and steam methane significantly contribute to air pollution due to their reliance on fossil fuels and lack of carbon capture. While blue hydrogen offers a reduction in greenhouse gas emission and turquoise and green hydrogen, produced via methane pyrolysis and water electrolysis, respectively, present cleaner alternatives with zero GHG emissions.

Hydrogen is primarily used in production of electricity, production of ammonia (NH₃), a key component in fertilizers, as a fuel in running automotive, ships and rockets, involved in various chemical processes in pharmaceutical manufacturing, in the production of semiconductors and in the purification of metals, act as a reducing agent to replace carbon in steel manufacturing process and in food sector to hydrogenate vegetable oils to produce solid fats like margarine.

Impacts of Hydrogen Combustion to the Environment

Although Hydrogen production itself does not generate greenhouse gas emissions, but hydrogen combustion, like any other combustion reaction that heats air to high temperatures, creates harmful pollutants called nitrogen oxides.

However, when combusted with air in specialized internal combustion engines, hydrogen produces low or negligible emissions introducing the concept of low-carbon green and blue hydrogen.

Different Types of Hydrogen

Hydrogen production technologies are referred in different colors for identification and scientific reference. The main colors that are being considered are the following:

Grey (or brown/black) hydrogen is produced by fossil fuels (mostly natural gas and coal) causing the emission of carbon dioxide and other pollutants.

Blue hydrogen is produced through the combination of grey hydrogen and carbon capture storage (CCS) avoiding most of the GHG emissions.

Turquoise hydrogen is produced by the pyrolysis of a fossil fuel, where the by-product is solid carbon.

Green hydrogen is produced by electrolyzers supplied by renewable electricity (and in some cases through biomethane reforming or solid biomass gasification.

Yellow (or purple) hydrogen is produced by electrolyzers supplied by electricity from nuclear power plants.

This color-based classification is established on a number of parameters due to a significant variability of carbon intensity in production of each of these types. Therefore, green, blue, turquoise and yellow hydrogen are mostly referred as a group of “clean hydrogen”, “low-carbon hydrogen” or “renewable hydrogen”. While In particular cases, hydrogen may be even carbon-negative, using involvement of bioenergy and carbon capture storage CCS together.

An Overview of Global Hydrogen Energy Demand

Currently, Hydrogen contributes to only 1% of the total energy demand worldwide. Global hydrogen demand reached more than 97 million tons (Mt) in 2023 and is estimated at almost 100 Mt in 2024.

However, it is expected to increase over time, with projections ranging from 3% to 14% by 2050. Although this still would equal only one-tenth of the recommended needs of the Net Zero targets of International Energy Agency (IEA) to achieve net zero emissions by 2050.

Fukushima Hydrogen Energy Research Field, Fukushima, Japan is currently the largest hydrogen production facility using renewable energy. Equipped with a 10,000 kW class hydrogen production facility, the plant is producing hydrogen by utilizing electricity generated from solar panels. Enough hydrogen fuel can be produced at the facility every day to supply monthly power for about 150 households.

However, NEOM Green Hydrogen Project, the world's largest utility scale, commercially-based hydrogen facility located in NEOM, Saudi Arabia, powered completely by renewable energy is expected to be operational in 2026. It will produce 600 tons per day of clean hydrogen, up to 1.2 million tons per year of green ammonia, 4 Giga Watt integrated onshore wind and solar energy and projected to mitigate the impact of 5 million metric tons of carbon emissions per year.

The world's largest green hydrogen facility is located in Xinjiang, China and was developed by state oil company Sinopec. It had an initial output of 10,000 tons a year which eventually was integrated up to 20,000 tons a year.

In United States, the major hydrogen-producing states are California, Louisiana, and Texas and almost all the hydrogen produced in the United States is used for refining petroleum, treating metals, producing fertilizer, and processing foods.

Hydrogen demand is prioritized in refining and industrial applications, where it has been used for many years but it can play a key role in the clean energy transition, most specifically in consumption in heavy industry. Currently, its long-distance transport and energy storage costs remain a primary hurdle in its growth globally.

On the other hand, demand for low-emissions hydrogen grew almost 10% in 2023, which is still very low. Diversified incentive schemes, market development tools and involvement of government actions globally can boost demand in future.

What is Green Hydrogen?

The green hydrogen is referred to as the combination of power generation from renewable sources and water electrolysis. By supplying electricity and pure water to an electrolyzer, output flows of hydrogen and oxygen are produced.

Sustainability of Blue Hydrogen and Climate Change

Blue hydrogen is based on the idea that the current processes used to produce hydrogen from fossil fuels could be coupled to carbon capture storage CCS technologies to minimize most of their greenhouse gas (GHG) emissions.

Although there are no standard definitions of the CO2 capture rate required to shift the definition from grey to blue hydrogen, different scientific studies account a range of 60%-70% and sometimes 95% carbon capture, depending on the technology and the stages in which CO2 capture is applied in different processes.

Existing plants of grey hydrogen in some cases, can have the advantage to build their current industrial experience to blue hydrogen by adding CCS systems. In addition, the operation of a CCS system may decrease the energy efficiency of a steam methane reforming SMR process by 5%–14%.

On the other hand, while water consumption is often associated to the electrolysis process, blue hydrogen production consume a significant amount of water ranging from water consumption per kg of H2 and as high as 24 L for SMR and 38 L for coal gasification.

But overall, the most significant advantage of blue hydrogen over grey hydrogen is its ability to significantly reduce CO₂ emissions.

Implications of Hydrogen Consumption in Different Sectors

Transportation sector

Hydrogen-run vehicles, in comparison with electric vehicles have specific advantages of almost zero emissions, especially in the longer range and shorter refueling duration but higher prices of hydrogen are currently hindering their market development, and additionally due to consequence of their lower efficiency than electric vehicles when considering the entire supply chain.

In comparison, an electric car can convert about three quarters of electricity towards useful energy, the same figure for hydrogen car is as low as one third. Battery electric cars incur losses for power transmission and storage, while hydrogen cars need additional components, including electrolyzers, hydrogen compression and storage, and on-board fuel cells making them more costly in the current scenario.

Industrial Sector

Hydrogen is currently used in refineries to reduce sulphur content in oil products to meet environmental standards, and in some cases to upgrade low-quality heavy oil.

Hydrogen is also used a feedstock for ammonia and methanol production. Ammonia production is primarily used for fertilizers, while methanol is used for a range of applications, including high-value chemicals for plastics or its blend with fuels to increase their performance.

The steel sector also relies on hydrogen in the production via the direct reduction of iron (DRI) systems. This technique is currently used in less than 10% of global primary steel production, its share may increase in the future, due to the need to decarbonizing all sectors.

Future uses of hydrogen in industry could also extend to other industries connected to generate high-temperature heat, where direct electrification is not an option.

In industrial sector, around one third of the current demand is covered by hydrogen obtained as by-product of other refinery processes, while the remainder is locally produced via SMR or supplied by commercial producers.

Buildings Sector

Some projects are considering potential hydrogen use in the different applications to buildings’ heating systems when compared to other low-carbon technologies.

Power Generation Sector

Hydrogen is also considered in power generation sector but while the efficiency of conventional electricity generation itself is usually high, considering the dependence of entire power generation process including an additional hydrogen production and storage costs, the energy losses can be as high as 70%. But, to reach a fully decarbonized energy system, hydrogen may be among the few available solutions.

Conclusion

There is currently significant momentum towards the development of future hydrogen production strategies across the world. We have highlighted only main aspects related to the implementation of an energy system based on hydrogen technologies.

Building basis of a future hydrogen economy, we will require to tackle multiple aspects. The current focus should be on transition of the current energy system towards low-carbon alternatives. Thus, hydrogen is a key component of a broader picture, and it is important that future strategies for its implementation are well integrated with other solutions. In this perspective, green and blue hydrogen streams should be addressed to support a low-carbon energy system.