Has hydrogen’s time finally come?
Hydrogen could offer a greener future for us all, but harnessing its full potential requires a degree of technical understanding
The most abundant element in the universe, hydrogen, offers our best chance yet to combat global climate change. That’s because when it is produced using renewable energy sources such as wind or solar, hydrogen combustion emits no carbon dioxide, giving it potentially a central role to play in next-generation, clean energy networks.
There’s growing urgency to harness its potential. From the forest fires igniting the American West and droughts in Australia, to increasingly devastating Caribbean hurricanes and the melting of the Antarctic ice shield, the tens of billions of tons of carbon dioxide we are emitting globally per year is taking its toll.
Public support for reducing the impact of climate change has never been higher, even where there is no legislation in place or restrictions imposed. That sentiment is reflected in increasingly stringent regulations such as the European Community’s commitment to reduce carbon dioxide emissions by around 40% in 2030 and achieve carbon neutrality by 2050. However, to successfully meet these targets, hydrogen and other alternative energy sources must transition from trials into the mainstream. There is consensus between the scientific and economic communities that hydrogen can move us to a carbon-neutral future without sacrificing the flexibility, safety, efficiency and performance required to serve residential and industrial energy consumers.
Let’s take a closer look at some of the key issues, considerations and challenges to making hydrogen ubiquitous within everyday applications and industrial processes.
Hydrogen versus natural gas
It’s worth beginning with some basics about hydrogen and in particular, how it compares with natural gas. On a volume basis, the heating value of hydrogen is about one-third that of natural gas and when combusted, it produces pure, plain water vapor. But unlike oil and gas, hydrogen is not a fuel in itself; it’s a way of storing and transporting energy, which is particularly important for renewable energy.
Consisting of one proton and one electron, hydrogen is colorless, odorless, tasteless, non-toxic and non-poisonous. It is eight times lighter than natural gas and burns eight times faster, which leads to shorter flame lengths. Unlike natural gas and many other carbon fuels, hydrogen heats up when reducing pressures. The spark energy required to ignite it is 15 times lower than natural gas.
Hydrogen has a wide flammability range compared to natural gas. Whereas natural gas is flammable between four and 16 vol% gas in a gas and air mixture, hydrogen is flammable between four and 77 vol% hydrogen in an equivalent mixture.
Hydrogen holds significant promise for the transmission of clean energy, but given its flammability, it must be handled and processed very differently than other fuels.
Tackling industrial emissions
Hydrogen offers the greatest transformative impact in the industrial sector because approximately two-thirds of the world’s non-agriculture related carbon dioxide emissions are generated by the combustion of fossil fuels in transportation and power generation plants. A further 25% is emitted by thermal appliances across a variety of applications in the manufacturing industry and commercial heating. Most of these thermal appliances are natural gas-fired (nearly 90%) and only a small part is oil-fired.
Hydrogen has the potential to reduce or even eliminate carbon emissions in these applications. For example, by simply switching the fuel of a 25 million Btu/h low heating value (LHV) (about 7.5 MW) burner running in a continuous process 24 hours per day from natural gas to hydrogen, a massive 33 metric tons of carbon dioxide emissions could be saved per day.
Driven by government legislation and public opinion, energy companies are gradually migrating from fossil fuel-fired power plants to renewable forms of energy such as wind and solar power. However, the unpredictable fluctuations of these renewable energy sources cause growing concern about how to match energy generation with energy demand in the long term. But here, green hydrogen offers significant value as an energy buffer or carrier.
It’s not yet feasible for industries to move directly to hydrogen, so they are taking their first steps by mixing hydrogen with natural gas in much the same way that ethanol is mixed with gasoline in some sectors. Combined, the two fuels produce less carbon dioxide, with the level dictated by the amount of hydrogen added. For example, if a blend of 20% hydrogen and 80% natural gas was continuously fired at 10 million Btu/h LHV (about 3,200 kW), there would be a reduction of about one metric ton per day of carbon dioxide, which would be equivalent to nearly 350 fewer tons of carbon dioxide per year (see Figure 1).
Initially, energy companies are planning to mix 10% to 20% of hydrogen into existing natural gas distribution networks to lower the emissions of a wide range of industrial, commercial and residential heating applications. However, the real industry shift to hydrogen will occur between 2030 and 2035 when it is expected to be ready for high-temperature steel and metal applications, with lower temperature applications following thereafter. Where will we net out? For its part, to meet long-term obligations under the United Nations’ COP21 Paris Climate Agreement, the European Union expects hydrogen to comprise about a quarter of its energy mix by 2050. In the meantime, we can expect to see a number of pilot projects in both high and low-temperature industrial applications.
Overcoming barriers to adoption
To date, the mainstream application of hydrogen has been held back by a variety of factors, including a lack of infrastructure, limited production capabilities, high costs and unique properties that make the element tricky to handle. However, the balance is now tipping toward a hydrogen-propelled future.
A fundamental challenge has been how to safely transport and store hydrogen. Whereas suitable infrastructure was limited in the past, new transmission networks and storage facilities are being built to accommodate hydrogen (see Figure 2). Energy companies are realizing their natural gas grids can be adapted to accommodate hydrogen at acceptable cost. For example, Europe has a vast gas grid that could be converted relatively quickly and there are separate initiatives underway to create 100% hydrogen-powered energy grids.
Meanwhile, the cost of hydrogen is falling and is expected to continue to do so over the next decade. In fact, this year, the Hydrogen Council reported that hydrogen will be competitive across 22 industry applications with other low-carbon alternatives and even some conventional energy sources by 2030.
A further challenge to hydrogen has been the lack of machinery and components from which to harness it for the manufacturing of goods, specifically, via thermal appliances in which heat is required. However, companies such as Honeywell Thermal Solutions are rapidly expanding their solution portfolios to encompass hydrogen-ready burners, valves, combustion controls and other specialty equipment.
A final challenge worth noting is that NOX emissions produced with hydrogen combustion are greater than with natural gas due to faster flame speeds and the higher flame temperatures and faster flame speeds associated with hydrogen. Typically, NOX increases steadily as the amount of hydrogen increases in the blend with natural gas up to about 60% hydrogen. The impact on NOX can become quite dramatic for blends with more than 60% hydrogen, depending on burner design. Regulations on NOX emissions are growing stricter and more widespread as well. The convergence of carbon and NOX emission regulations will likely necessitate the development of new combustion technologies when higher concentrations of hydrogen achieve broader adoption.
Handling with extraordinary care
In addition to the technical and cost barriers of hydrogen production, the manner by which it should be handled and processed is different from other fuels. Because of its special properties, a wide range of precautions must be taken to harness it safely.
First, hydrogen combustion systems must be designed differently to their natural gas counterparts because of the high flammability of the fuel. They must undergo extensive risk assessments at proposal and execution phases to meet hydrogen application safety requirements and comply with local safety codes and standards. In addition, hydrogen’s wide flammability range, high flame speed and low ignition temperature require proper electrical design and wiring principles to be followed, with special attention paid to purging, ratio-control, temperature protection and burner management functions.
Furthermore, knowing a burner can fire safely and reliably on hydrogen is one thing; knowing its effect on an application is another. When firing a burner on hydrogen, the combustion characteristics are different compared to the same burner firing on natural gas. The differences in flammability, speed of the combustion reaction, flame luminosity, flame length and changes in flue gas composition impact how products are heated and how combustion chambers or ovens should be constructed to accommodate them.
It is important to test-fire burners on hydrogen and make sure critical parts such as mixing plates or mixing cones and gas nozzle material and ports are such that hydrogen combustion remains stable and safe without overheating or even destroying parts of the equipment.
After decades of speculation and theory about the role hydrogen could play in clean energy networks, we’re finally edging closer to reality. Given acute climate change pressures, diminishing barriers to adoption and better industry understanding of how to handle hydrogen safely and harness its full potential, it’s increasingly looking like hydrogen will indeed contribute to a greener future for us all.