Oct-2024

Innovative PSA process solutions

For over 20 years, UNICAT has been a key player in the hydrogen value chain, offering comprehensive capabilities and technologies.

Kathy Picioccio, James Esteban and Matt Thompson
Unicat Catalyst Technologies

Article Summary

From supplying catalysts and adsorbents to providing innovative solutions and technical expertise, UNICAT meets unique customer requirements while reducing costs. Our commitment to innovation drives growth and global expansion. As an ISO-9000 certified provider, UNICAT offers full R&D, engineering, design, build, and service capabilities. Our advancements in adsorbent technology and control systems have led to higher efficiencies and increased hydrogen production, while our dedication to excellence and collaboration aligns with our mission to help customers achieve their goals.

Pressure swing adsorption (PSA) is a gas separation technology that uses adsorbent materials to capture specific gases under pressure. It operates as a batch process, with multiple vessels cycling through each process step in sequence. Multiple vessels can simultaneously produce hydrogen and off-gas, reducing fluctuations for downstream users.

The process involves alternating between high-pressure adsorption, where target gases are trapped, and low-pressure desorption, where these gases are released. The separation is driven by the ratio of feed pressure to off-gas pressure. Thus, small changes in feed pressure have minimal impact on performance, whereas similar changes in off-gas pressure can significantly affect purity and efficiency.

Since their commercialization in the 1960s, PSA units have been essential in purifying feed streams to produce high-purity hydrogen. High-purity hydrogen is a critical resource that allows for the efficient production of conventional fuels and renewables. While this technology can handle various feed streams, it is predominantly used in steam methane reforming (SMR) and refinery off-gas (ROG) applications.

PSA units have become the industry standard for providing high-purity hydrogen to the refining and petrochemical sectors. Commercial PSA units vary in size, producing between less than 1 MMSCFD and over 200 MMSCFD of hydrogen. Purified hydrogen typically exceeds 99.9% purity, with carbon oxides (CO and CO2) present only in parts per million by volume (ppmv). Controlling these impurities is crucial, as they can poison downstream processes.

PSA process flow diagram
As shown in Figure 1, feed gas enters the system at high pressure (optimally 300-400 psig). This feed is a hydrogen-containing stream with additional impurities. During the adsorption step, these impurities are selectively removed by the appropriate layer of adsorbents, allowing high-purity hydrogen to exit the unit as the product. The pressure drop across the system is less than 10 psi.

The adsorbents are regenerated in place during the cycle at low pressure, releasing impurities and unrecovered hydrogen to off-gas. In SMR applications, the off-gas is sent to low-pressure burners. For ROG streams, the off-gas is typically compressed to fuel header pressure. A low suction pressure allows the unit to maximize hydrogen recovery.

Expanding scope of supply
UNICAT Catalyst Technologies, a portfolio company of White Deer Energy, acquired Magma Group, a UK-based leader in ceramics and catalyst manufacturing in 2021. This acquisition brought several benefits to UNICAT, including an expanded product range and enhanced technical services. UNICAT’s approach is to understand customer problems and process limitations to innovate comprehensive solutions to facilitate increasing customer profitability and sustainability. This acquisition strengthened UNICAT’s global manufacturing presence whilst expanding expertise in design, manufacturing, and installing engineering process equipment and control systems for various industries, including oil & gas, pharmaceuticals, and renewables. This allows UNICAT to better offer vertically integrated processes and innovative catalyst solutions to customer problems which leads to improved efficiency. This strategic move has positioned UNICAT to improve their service to customers.

UNICAT is focusing on customer lead internal technological product and process innovation, and fostering partnership collaborations, to expand our ability to increase customer process efficiencies further. This evolution has enabled a transition from basic adsorbent reloads, troubleshooting, and control system upgrades to offering comprehensive design and fabrication services with innovative and optimized catalysts. UNICAT recently advanced further and can supply complete PSA systems!

Case study: Reduced capacity (technical expertise)
Operating consistently at or above design conditions is crucial for maximizing the production of both traditional and renewable fuels. Monitoring plant efficiencies is crucial to this process. While adsorbents in PSA units are designed for continuous regeneration and typically require infrequent replacements, unexpected upsets can still cause damage. Detecting performance impacts early is vital to prevent irreversible damage and the need for replacement.

For example, a large PSA unit designed to process 50 MMSCFD of syngas from SMR and produce 33.5 MMSCFD of high-purity H₂ (88% recovery) experienced a 20% capacity loss and a 4% drop in hydrogen recovery, reducing production by almost 8 MMSCFD. Efforts to increase rates resulted in off-spec product with excessive levels of CO.

UNICAT’s technical experts identified that the capacity loss was primarily due to inadequate plant procedures. Although these were corrected after several years of operation, the damage was irreversible. Operations have since stabilized, but had this issue been identified earlier, the damage could have been significantly reduced or even reversed. Table 1 shows operating data confirming the reduced recovery and capacity.

Case study: Troubleshooting (technology solutions)
Control systems have advanced significantly over the years, paralleling improvements in computer technology. From early systems controlled by relays and timers to sophisticated systems using programmable logic controllers (PLCs) and distributed control systems (DCS), maintaining proper control over PSA steps is crucial to ensure adsorbents remain intact and do not degrade into dust.

UNICAT’s latest control system upgrade utilized the existing equipment, minimizing capital expenditure (CapEx) and installation time while introducing new logic for enhanced controls. The benefits include smoother product flow, which improves downstream hydrogen compression. Better control of the off-gas significantly reduces fluctuations, enhancing stability for SMR burners and increasing H2 production.

The ability to optimize the unit across a wide range of capacities will greatly enhance hydrogen recovery and production. Stable adsorbent life is also achieved through independent control of process valves and automated learning to mitigate the impact of drifting instrumentation.

In addition, rapid trends in PSA vessel pressures make it easy to identify differences between the vessels. In this case, a control valve is leaking across its seat, causing a high-pressure to low-pressure leak (see the red circled areas on Figure 2). This results in gas exiting the system through the off-gas, increasing pressure and negatively impacting operations. Additionally, off-gas fluctuations can cause issues in the upstream SMR.