C. Martinez CASTILLO, Endress+Hauser, Houston, Texas
As climate change continues to be a focus across industry, companies and governments around the world are looking for ways to viably reduce greenhouse gas (GHG) emissions. The transportation sector produces the most carbon dioxide (CO2) by segment, accounting for about 80% of GHG emissions globally. Furthermore, electric power generation is—ironically, given the obsession with electric vehicles—the second largest source of CO2 emissions. As a result, industry is exploring additional energy sources to meet net-zero targets for long-haul transportation infrastructure, including trucks, rail and ships.
Because it can be stored, transported and burned without GHG emissions, hydrogen (H2) is emerging as a potential frontrunner. Like other fuels, H2 must be transported from where it is made to where it is needed, which requires a distribution system for bulk quantities. However, there are challenges associated with transporting H2 conventionally via pipeline because of how it interacts with normal pipe materials, so another approach should be considered.
Additionally, transporting H2 must be efficient and cost-effective, a task that requires careful consideration and innovative solutions. This article will examine requirements for effective H2 transportation and accurate measurement in its challenging environments.
Cryogenic temperatures. Although bulk H2 can be stored as either a gas or liquid, liquefaction is vastly preferred when long-distance transportation is required due to its increased energy density in a liquid state and a 1:848 liquid-to-gas volume ratio. However, obtaining the extreme temperatures required for liquification consumes around 30% of H2’s energy content and presents significant measurement challenges.
Additionally, capacity concerns at a reasonable pressure makes another case for liquid storage. Storing H2 at 1 atmosphere as a liquid requires cryogenic temperatures below its boiling point of –252.9°C (–423.2°F), nearly 100°C (180°F) colder than temperatures needed to transport LNG. This is why, per the ideal gas law, H2—like other liquified gases—is stored in pressurized vessels. The phase diagram for H2 shows this pressure vs. temperature relationship and the limited combinations in which H2 can be commercially stored in a liquid state (FIG. 1).
Attaining temperatures this close to absolute zero is no trivial undertaking, so unsurprisingly, there are numerous energy consumption, process measurement and control factors that must be considered to achieve GHG targets. Most measurement technologies now available cannot operate below –40°C (–40°F) due to electronic limitations, let alone cryogenic temperatures. Therefore, without modifications, traditional instrumentation cannot be used to measure liquid H2 (LH2).
Since both temperature and material compatibility must be addressed when handling H2, the first measurement challenge to overcome is the environment. The LH2 operating temperature of –253°C (–423°F) is not only new, but it is also a major challenge for most suppliers because it introduces many unknown conditions which must be understood, evaluated and considered. It also mandates the highest safety requirements during transit due to minimal supporting infrastructure present at storage facilities.
H2 permeation is another challenge that affects metals used in H2 environments. All metals have a natural lattice structure. Under specific conditions, any H2 in the process can break down into 2 H+ ions. The H+ ion is small enough to move between the spaces in the lattice structure without displacing any of the metallic lattice structure itself. These minute amounts of H2 ion alter the integrity of the metal’s underlying lattice structure, leading to embrittlement—and hence reduced integrity—of the metal, including the high strength alloys typically used in pressure transmitter diaphragms.
The primary purpose of measurement and control is to maintain the process within its operating envelope. Temperature control, for instance, is vital to avoid unwanted boil-off, which results in vaporized product where the influence of vapor pressure can make inventory measurement challenging, and it poses safety risks. Accurate level measurement is also necessary to ensure safe operation of the tank and precise inventory. Reliable level gauges and independent alarm gauges for overfill are, therefore, also essential.
While most level-sensing technologies employ metal-based sensors in contact with the fluid being measured and electronics connected, servo gauges provide a method for measuring the exact liquid level while keeping the electronics outside the vessel and easily accessible. This measurement method meets relevant requirements according to the International Organization of Legal Metrology (OIML) R85 and the American Petroleum Institute (API) 3.1B because it is not influenced by vapor pressure or temperature, thus providing safe, reliable, and precise level and density measurement.
Servo level sensing technology. In addition to functioning under the severe conditions required for LH2 storage, servo tank measurements are ideally suited for high accuracy and custody transfer measurement applications. Servo level measurement relies on a small displacer that is accurately positioned in a liquid medium using a servo motor. The displacer is suspended on a measuring wire that is wound onto a finely grooved drum housing. When the displacer is lowered and touches the liquid, its weight is reduced by liquid buoyancy force. As a result, torque in the magnetic coupling changes: this is measured by a series of magnetic field sensors in the transmitter leveraging the Hall Effect to precisely track position.
Periodic verification is a best practice—especially in challenging applications and custody transfer—to maintain measurement integrity, in addition to complying with mandates and regulations. To uphold operational reliability, leading servo gauges support online testing without interrupting the process via remote-triggered verification. This empowers plant personnel to prove measurement accuracy from the safety of the ground, eliminating the need to climb tanks or remove instruments from service. When remote verification is initiated, the servo’s displacer travels the extremities of the tank to find the bottom and top references, identifying any deviation from the initial calibration points.
There are other fluids that lend themselves to liquid transportation under less extreme conditions than LH2, such as ammonia and methanol. Ammonia is almost 50% more energy intensive by volume than LH2, and it can be stored at just –33°C (–27°F), making it possible to measure with conventional instruments from a temperature standpoint. However, ammonia is corrosive and hazardous to health, as it easily forms acid ammonium hydroxide. Methanol is another alternative to LH2, but because it is a hydrocarbon, it emits CO2 when burned. Therefore, it does not meet net-zero requirements.
Case study: Bulk H2 transportation. Like many power sources, H2 supply and energy demand frequently span oceans, meaning ships capable of transporting super-chilled H2 are key to helping the world reduce carbon emissions. Shipbuilders are now producing specialized vessels for transporting LH2 over long distances, with live pilots running since 2022.
One of the first LH2 carriers included a cargo containment system comprising of a double-shielded and double-insulated tank with a capacity of 44,140 ft3 (1,250 m3), designed to transport cryogenic LH2 and cooled to a temperature of –253°C (–423°F) (FIG. 2).
For this pioneering LH2 carrier, the shipbuilder leveraged modern shipbuilding and safety-related technologies. The pressurized cryogenic cargo containment system made specifically for LH2 incorporated best practices from LNG and land-based LH2 projects, including servo level sensing technology. To protect the ship—which must maintain self-sufficiency in transit and safety around other vessels in port—it is critical that onboard sensing and control technologies support safety standards.
Because of successful deployment in numerous land transportation and storage implementations, the author’s company’s servo transmitters were selected for use in the H2 carrier’s storage tanks and at receiving terminals.
On the heels of the first vessel’s success, a second and larger bulk carrier production project is already underway to further reduce the cost of global H2 supply and progress this energy addition.
New horizons powered by terminal technology. H2 fuel is a novel power source, but as with every new venture, the journey to viability is laden with challenges, including in process measurement. However, industry is developing new solutions to overcome these challenges by working with instrumentation suppliers, as demonstrated by the novel LH2 carrier.
Tomorrow’s H2 power is attainable by innovative steps being taken today, with measurement technologies suitable in extremely low temperatures and harsh conditions. Paired with full compliance and support for global safety standards, these advances are propelling H2 as an energy source of the future. HP
Cesar Martinez Castillo is an electronic engineer with more than 15 yr of experience in the automation industry. He is passionate about automation, technology, digitalization and energy transition topics. In his current role at Endress+Hauser, Martinez Castillo serves as the Industry Manager for Natural Gas, LNG, Carbon Capture and Blue Hydrogen.