Selecting the right valves for blue hydrogen production

Natural gas is desulfurized and preheated, then mixed with high-pressure steam and further heated together with a catalyst in a fuel gas-fired reformer. The heat and the catalyst separate the methane (CH4) and water vapor (H2O), producing a synthesis gas (syngas) consisting of hydrogen, carbon dioxide (CO2), and carbon monoxide (CO). In the CO shift reactor, the remaining CO and water (H2O) are converted into CO2 and hydrogen (H2).  

The purified synthesis gas mixture then enters the amine absorber, where circulating amine liquid absorbs the CO2. The hydrogen leaves the absorber to be further purified in a pressure swing adsorption (PSA) process. Meanwhile, the CO₂-containing amine is heated and depressurized in the amine regenerator to separate the CO₂ from the liquid. The CO₂ is then released and removed. The low-CO₂ amine is cooled and returned to the amine absorber to process further synthesis gas.  

In the production of gray hydrogen using the SMR process, the carbon dioxide generated is not stored but simply released into the atmosphere together with the amine carbon dioxide produced in the amine process. In a blue hydrogen plant, a carbon dioxide recovery plant is also installed to store the CO2. Although these process steps incur additional capital and operating costs, they enable an existing SMR plant to be operated with a much lower carbon footprint (blue hydrogen).  

The main advantages of SMR plants over ATR plants are their current global prevalence and the high level of experience with this process. The additional costs of installing a carbon dioxide capture plant in an SMR block are lower than those of building a new plant. The disadvantage of an SMR process is that it is difficult to completely capture carbon dioxide. The relatively concentrated and clean CO(2) that leaves the amine unit can be easily captured, but the less concentrated and impure CO2 that is produced and associated with the flue gas in the amine scrubbing and PSA processes is not as easy to capture and recover. 

Converting SMR systems to blue hydrogen production is relatively straightforward. The CO2 from the amine unit is further purified, pressurized, and liquefied for transfer to a carbon capture and storage (CCS) facility. If the flue gas is directed to the amine unit, as shown in the image, additional processing steps may be required to purify the gas. Most SMR plants that are converted to blue hydrogen production focus on the carbon dioxide produced in the amine scrubbing process, while the flue gas is vented because its recovery is much more difficult and expensive. 

Production of blue hydrogen with ATR 

ATR is a newer process that is becoming increasingly important in the field of blue hydrogen development. It uses many of the same steps as the SMR process but is more fuel-efficient and produces a single concentrated CO2 stream instead of two, as is the case with SMR. 

The natural gas is desulfurized and preheated, then mixed with high-pressure steam (not shown) and further heated by a catalyst. This gas is then burned with pure oxygen to produce a very hot synthesis gas. The difference between ATR and SMR is that the initial ATR steps require very little fuel, if any. Most of the energy is generated from the oxygen injection step. This reduces energy requirements and produces a single, pure, and concentrated CO2 stream that is easy to capture.  

Following the autothermal reformer, as shown in the image, the SMR and ATR processes are essentially identical. The water gas shift reaction converts the remaining CO and water into CO2 and hydrogen, and the amine scrubbing absorbs the CO2 from the gas stream before the hydrogen is further purified by the PSA process.  

The main advantage of ATR plants is that they are more efficient than SMR plants in producing blue hydrogen. The ATR process also produces fewer greenhouse gases (flue gas) than SMR. The disadvantage of ATR is that it requires an oxygen source or an air separation plant. In addition, there are far fewer ATR plants, so the technology is less mature and is only now being introduced into production.  

However, ATR is a promising and likely preferred technology for future blue hydrogen production plants, as it was developed specifically for this purpose. There are several ATR plants worldwide that are in various stages of planning and early construction. 

Fittings, regulators, and pressure relief valves in blue hydrogen production 

Regardless of whether SMR or ATR technology is used, the blue hydrogen process poses several challenges for automated valves, controllers, and relief valves that help control and protect the process. The presence of hydrogen in hot syngas streams near the reformers and in the final product poses significant challenges for control equipment. Hydrogen embrittlement (HIC) can compromise the mechanical integrity and performance of valves, which can lead to increased emissions and inefficiencies. High pressures and temperatures are also common. Ultimately, the various gas components also require a range of housing materials that are suitable for each application.  

Manual and automatic shut-off valves must contain the right materials, have an API 607-certified fire safety rating, and may require SIL 3 certification for shutdown applications. 

The selected ball valves should have durable seat systems for low-temperature applications and the right materials for high-temperature applications. They must also have the required API and SIL certifications, offer low-emission preloaded packings and a variety of body shapes, and be able to prove themselves in high-pressure and hydrogen applications.  

Depending on the specific conditions and nominal sizes, double eccentric C-ball valves (2XC) or triple eccentric, metal-sealed butterfly valves (TOV) can also serve as alternatives. Both valves are suitable for a wide range of temperatures, pressures, and media and are inherently fire-safe. These valves are discussed in more detail below.  

The wide range of material requirements can pose a problem when selecting a regulator due to the limited choices available. Some models can be specified in stainless steel, Monel, Hastelloy, or nickel-aluminum bronze to enable control over a wide pressure range of 0.34-10.34 bar. 

These processes often require high-capacity pressure relief valves, which typically need to close tightly to prevent product loss. In addition, pressure relief valves can operate close to their set point specifications, making it even more difficult to achieve and maintain a permanently tight seal. Pilot-operated relief valves with improved tightness are well suited for these applications. These types of pilot-operated relief valves have a very high capacity. These models allow operation within 2% of the set point with very low leakage. 

Selection of control valves for CO2 capture 

Regardless of whether the SMR or ATR process is used, the process steps after the synthesis gas has been produced are similar for both plant concepts. In both processes, it is crucial that the valve that regulates the mass flow of the recovered amine is selected in accordance with the requirements and regulates and operates reliably within these parameters. 

To efficiently wash CO2 from the synthesis gas, the amine control valve must ensure a constant flow of amine to the upper part of the absorber despite high pressure drops and cavitation conditions. The best valve for this application is a stainless-steel valve (316SS, Alloy 6) with anti-cavitation internals and improved packing.

PSA butterfly valves  

The valves used in the PSA process are exposed to very demanding operating conditions. These butterfly valves are constantly opened and closed and must be leak-free and low-emission despite high pressures or vacuums, high temperatures, and erosive powdered filter media, while also meeting ZERO leakage requirements.  

Compared to other automated valves, the triple eccentric valve design offers less weight, better operability, lower fugitive emissions (EN 15848), and longer valve life for this difficult application. 

The triple eccentric process valve selected for this application should use a valve seat reinforced with Stellite™ 21 to achieve greater resistance to abrasion, erosion, and corrosion. This feature, combined with a solid metal sealing ring, reinforced internal parts, and a spring-loaded gland design (LLP), makes this valve type the preferred choice for this application, as the design does not leak despite very difficult operating conditions. 

Another option for PSA shut-off valves is a double eccentric C-ball valve. Its torque-sealing design enables a leak-free seal that functions independently of the applied pressure. 

This special eccentricity moves the C-ball design away from the seat during opening and closing to minimize wear. The combination of a metal seat, mechanical sealing independent of process pressure, low wear, and a low-emission design works excellently even under these difficult conditions. 

Remote-controlled pipeline actuators 

Some automatic valves are installed in locations where instrument air is not available. In such cases, electric actuators or actuators driven by the pressure in the pipeline are required. For applications with low or moderate torque requirements, modern electric actuators or control drives can be used. These also have an optional spring assembly which, in the event of a fault, moves the unit to the safe position using spring force.  

For pipeline applications that require high torque or involve multiple valves, emission-free hydraulic actuator systems can be used. These units use the pressure in the pipeline to operate the hydraulics of the actuator components. The circuit with the pipeline itself is closed, so there are no emissions.

Hydrogen processing plants have been in operation for decades, but not yet on the scale that will be required in the future. Leading automation providers have extensive experience in the design and operation of these plants, and much of their expertise is applicable to the new processes described in this article, namely carbon capture, transport, and storage, which are necessary for the conversion of gray to blue hydrogen.  

When designing the systems, operators should consult a provider who has extensive experience in handling hydrogen and is able to apply this expertise on a large scale worldwide.