Special Focus: Pathways for Sustainable Hydrogen
K. FINNAN, Yokogawa, Hartford, Connecticut
The hydrogen (H2) industry is at an inflection point. As the world focuses on sustainability goals including the achievement of net-zero emissions by the year 2050, H2 has emerged as an extremely attractive energy source. In the combustion process with pure oxygen (O2), the only byproduct is water vapor.
However, H2 deployment presents commercial and technical problems. Although H2 is the most abundant element in the universe, it is present on earth almost exclusively in chemical compounds such as hydrocarbons and water. Separating it from other elements is energy-intensive and, in most cases, produces greenhouse gases (GHGs), such as carbon dioxide (CO2) and harmful byproducts such as nitrogen oxide (NOx). According to the U.S. Department of Energy (DOE), 95% of the H2 produced in the U.S. is by steam methane reforming (SMR) in refineries and industrial plants.
The produced H2—in practically all cases as dual-atom H2 molecules—emerges at a high cost compared to fossil fuels. Currently, it is cheaper to charge an electric car than to refill a vehicle with H2. The cost of H2 for use in a fuel cell electric vehicle (FCEV) is three times higher per mile than a gasoline hybrid and two times higher than a conventional gasoline vehicle. In addition, the cost of H2 produced using fossil fuel processes is about one-fourth to one-third the cost of H2 produced using renewable energy.
Therefore, for more than 60 yr, H2 production has been largely limited to the energy and chemical industries. Outside of those industries, very little infrastructure exists.
The promise of H2. However, today there are initiatives in many countries to develop nationwide H2 ecosystems, which would include infrastructure for production, transportation, storage and consumption. Due to its clean burning nature, H2 is considered essential to achieving net-zero emissions.
The Regional Clean Hydrogen Hubs (H2Hubs) program in the U.S. includes up to $7 B to establish up to ten regional clean H2 hubs across America. As part of a larger $8-B H2 hub program funded through the Bipartisan Infrastructure Law. According to the DOE, the H2Hubs will be central drivers in helping communities across the country benefit from clean energy investments, good-paying jobs and improved energy security.
The DOE went on to state that clean H2 hubs will create networks of H2 producers, consumers and local connective infrastructure to accelerate the use of H2 as a clean energy carrier that can deliver or store tremendous amounts of energy.
What is a H2 hub? In the simplest sense, a H2 hub is a local cluster of H2 production, storage and demand. The DOE defines a H2 hub as a network of clean H2 producers, potential clean H2 consumers and connective infrastructure located in close proximity.
Colors of H2. To achieve net-zero emissions, the clean aspect of H2 must include its consumption and production. Recently, the concept of assigning colors to describe how the H2 is produced has become popular. The ultimate clean form is green H2. This is the only variety that is produced in a sustainable manner. Production processes such as electrolysis use carbon-zero power sources such as solar photovoltaic and wind.
Traditional methods using coal gasification produce the highest emissions. The black H2 production process uses bituminous coal, while brown H2 production uses lignite coal—both methods produce carbon monoxide (CO) and CO2.
Today, the majority of H2 produced is gray. Most often, methane (CH4) is the key feedstock, but some gray H2 production processes use ethane, propane or naphtha. According to the DOE, production using SMR is an important technological pathway for near-term H2 production. However, emissions are only modestly below those resulting from black or brown H2 production.
Blue H2 is distinguished from gray H2 because its production processes use carbon capture and storage (CCS) for the produced GHGs. Although blue H2 is sometimes referred to as carbon neutral, all the CO2 byproduct is not captured. However, a blue H2 process can result in up to a 95% reduction in CO2 emissions.
While black, brown, gray, blue and green are the fundamental colors of H2, there are many others. Pink H2, sometimes referred to as red or purple H2, is generated through electrolysis powered by nuclear energy. Definitions of yellow H2 vary—according to some sources, it is made through electrolysis using solar power, but others claim the energy could come from the broader electrical grid.
Turquoise H2 is produced by CH4 pyrolysis, which also produces solid carbon. Although turquoise H2 is largely viewed as promising since the production cost is potentially lower than electrolysis, handling of the solid carbon presents problems. Finally, white H2 is the relatively small amount that is naturally occurring in underground deposits. At this point, there appear to be no plans to attempt to exploit white H2 (FIGS 1 and 2).
Bridging the infrastructure chasm. Although the technology to produce green H2 exists, efforts continue to bridge the chasm—between today’s deployment and that required in 2050—with existing fuels and infrastructure, particularly around natural gas.
In the long term, natural gas pipeline infrastructure is expected to play a role in H2 transport. Natural gas pipelines repurposed for H2 are forecast to make up one-fourth of all H2 pipelines in 2050. However, in the near term, there are problems transporting H2 in existing pipelines. In fact, this is one reason for the local clustering nature of H2 hubs.
Unlike natural gas, H2 can be detrimental to pipeline integrity due to embrittlement, in which H2 molecules permeate the steel pipeline material. Embrittlement accelerates crack growth and reduces the lifetime of the pipeline. In the future, H2 pipelines must comply with new material standards and operating practices. In an example of the latter, pressure swings such as from cyclical line packing and unloading must be more limited than those in natural gas operations.
Meanwhile, an alternative is for a pipeline to transport a mixture of natural gas and H2. A lower H2 content reduces the risks of embrittlement. Concurrently, equipment on the consuming side must adapt to a new fuel mixture. Gas turbine operations can burn 20% H2 and 80% natural gas blends, enabling significant reductions in CO2 emissions.
In another scenario as a step toward net-zero emissions, ammonia (NH4) is used as a carrier to transport H2. NH4 is produced using nitrogen sourced from the air and H2, 70% of which is produced through SMR of natural gas. Since this process produces carbon emissions, CCS technologies are required.
On the receiving side, the NH4 is cracked to deliver the H2. NH4, itself, can also be used as a fuel in power plants and shipping. NH4 combustion is carbon-free but it does produce NOx emissions. While the infrastructure for NH4 storage and transport already exists on a large scale and international shipping is well-established, a substantial expansion of the shipping infrastructure would be necessary to accommodate the transportation of NH4 as a H2 carrier.
UNLOCKING THE H2 ECOSYSTEM
A H2 hub is typically considered the center of the H2 ecosystem. The entirety of the ecosystem extends well beyond the hub in at least two directions: backward to power plants and the electrical grid that supply energy to it and conversely, to consumer applications. A single enterprise could conceivably operate across the entire ecosystem.
At a minimum, a H2 hub consists of H2 production and storage but often extends to power plants that produce electricity using the H2 or other renewable sources, fueling stations for H2-powered vehicles or H2 fuel cell electric vehicles (FCEVs) and transportation via local pipelines to large users such as airports, buildings and fleet depots. Other electrical grid facilities such as battery energy storage might also be within the H2 hub.
H2 production. Although it would be ideal for the hub to use electrolysis to produce green H2 with power supplied by renewable sources, many proposals call for natural gas-fired SMR. Carbon capture technology would result in blue H2, resulting in considerably lower emissions than gray H2.
In addition, H2 derived from NH4 crackers, which separate H2 from nitrogen, are under evaluation. To minimize emissions, the NH4 would ideally be green NH4, which is produced by combining nitrogen with H2 derived from renewable energy sources.
There are also incentives in Europe and the U.S. to exploit organic waste, which would otherwise be destined for landfills, using a non-combustion steam/CO2 reforming process. Since the supply of organic waste is limited compared to other fuels, this process often supplements others to ultimately provide H2 production with very low emissions.
H2 storage. H2 hub proposals typically include storage containers, which can provide power to the local area for a matter of hours or days. The H2 could be a supplement to intermittent, renewable energy sources or used for peak shaving. H2 can also be stored underground in geologic features such as rock or salt caverns and provide energy that would last for months. According to 1898 & Co., holding H2 in existing underground storage is cheaper than batteries and the life of an underground storage facility is decades longer than most batteries.
Power plants. Natural gas-powered turbines can be modified to run on mixtures of natural gas and green H2. Plants could also be repurposed with turbines that are fired with 100% H2. For example, several manufacturers are creating H2 power generation to replace diesel generators for onsite or backup power needs. The power plants provide electricity to the local area and can supplement intermittent, renewable energy sources.
H2 fueling stations. Consumers can refuel their H2-powered vehicles at fueling stations similar to traditional gas stations. A fueling station could be within the H2 hub enterprise or it could be an independent operation which purchases H2 from the hub enterprise. The H2 could be used by FCEVs or vehicles with H2 internal combustion engines (H2-ICEs).
While the H2-ICE uses technology which stands out for the absence of any harmful emissions, it has proven less beneficial for light road transport compared to electric power from renewable sources. The main use for H2 is in a fuel cell in which an electrochemical process combines H2 and oxygen to generate electrical energy that, in turn, powers an efficient electric motor. In an electric engine, 80% of the energy drives the powertrain while only 20% is dispersed as heat. In a gasoline-powered engine, by comparison, 20%–25% of the energy drives the powertrain while 75%–80% is dispersed as heat.
H2 for buildings. Although the feasibility of small-scale H2 combustion applications such as in appliances remains questionable, H2, as described earlier, can be blended into existing gas networks. Currently, instead of supplying larger volumes of H2 to buildings in the local area, it is more economical for a H2 hub to operate a power plant which supplies them with clean electricity.
H2 mobility applications. Unlike small vehicles such as automobiles, very heavy-duty transport and trains could benefit from H2 combustion. In these cases, H2 offers the advantages of more compact propulsion systems, rapid refueling and long travel ranges. Fueling stations can be located along roadways and at main stations along railroad lines. Additionally, H2 FCEVs are well suited to heavy-duty vehicles, such as buses, tractor trailers and forklifts, in which electric batteries would be very large, heavy and require extremely long charging times.
Aviation. A H2 hub can provide H2 to local airports for use as an aviation fuel. According to National Grid, as the airline industry explores options for zero-carbon flights, H2-based renewable liquid fuels could be a good option for long-range flights, while batteries are being piloted for short-range flights. Important in the context of flight, H2 has a high energy content by weight—three times more than jet fuel and a hundred times more than lithium-ion batteries (FIG. 3).
Takeaway. Although its potential in the net-zero world makes it extremely attractive, H2 presents economic and technological challenges. It is significantly more expensive than fossil fuels and traditional processes that separate it from other elements.
However, government programs such as the Bipartisan Infrastructure Law and H2Hubs in the U.S. are focused on establishing infrastructure for production, storage and transportation, reducing the cost of H2 to a range that makes it commercially feasible. By 2050, H2 production will be powered by renewable sources (solar and wind) and other sources which do produce emissions but are used in conjunction with carbon capture technologies.
In response to global government initiatives, business enterprises are proposing H2 hubs, which are local clusters of production, storage and demand. Given technical issues such as embrittlement, long-distance H2 pipelines will develop more slowly. Meanwhile, enterprises could extend beyond H2 hubs to include consumer applications such as mobility-as-a-service and power generation using various renewable and traditional assets.
A follow-up article will describe how to manage the H2 ecosystem using contemporary, real-time digital technologies.H2T
About the author
KEVIN FINNAN is a Market Intelligence and Strategy Advisor at Yokogawa. He was previously an independent consultant, Vice President of Marketing for CSE-Semaphore and Director of Marketing at Bristol Babcock. Finnan has more than 30 yr of experience in various vertical markets and has launched more than 40 products in automation and measurement technologies.