Process/Project Optimization

 

S. WALSPURGER, Technip Energies, Zoetermeer, Netherlands and S. GEBERT, Clariant Catalysts, Munich, Germany

Of all gases used in the chemical, refining and petrochemical industries, H₂ and synthesis gas (a mixture of H₂ and CO, otherwise known as syngas) are by far the most in demand. Syngas has a diverse range of applications, including the synthesis of methanol, oxo alcohols and synthetic fuels; approximately half of all H₂ produced worldwide is used to make ammonia, which is then turned into fertilizers or other chemicals. The demand for H₂ continues to grow. This upturn is driven by increased demand for biofuels and stricter requirements for fuel upgrading through hydrotreatment and hydrocracking. Additionally, an extremely strong demand for decarbonized H₂ (so-called green or blue H₂) is forecasted for the coming years in energy-intensive sectors such as steelmaking and transportation, as well as the energy industry itself.

Presently, however, most H₂ and syngas production worldwide relies on the process of steam reforming, which emits significant amounts of carbon dioxide (CO₂). Despite gradual improvements in energy efficiency and productivity at scale, more improvements are needed. Fortunately, technologies in this area continue to develop. This article is primarily concerned with one such technology^a, a combination of a concentric tubular insert and a tailor-made catalyst for steam reformer tubes that aims to increase the steam reforming process’s productivity while lowering CO₂ emissions. 

Conventional steam reforming. H₂, ammonia and syngas are commonly produced on a commercial scale through steam reforming of natural gas and/or higher hydrocarbons. The process, which relies on catalysts, occurs at high reactor outlet temperatures (750°C–950°C, depending on the desired H₂, CO and conversion yields) and moderate pressures (20 bar–40 bar). Because the reaction is endothermic, steam reforming requires a substantial amount of heat. This is usually obtained by burning makeup fuel (additional natural gas) and waste gas in a furnace in which tubes filled with catalysts are located. The reaction medium is heated by burners arranged around numerous reactor tubes. In a conventional top-fired steam reformer (FIG. 1A), steam and feed gas supplied through the inlet are converted into syngas. This consumes approximately half the energy released by the burners.

FIG. 1. Conventional reformer tubes (A); U-shaped reformer with internal riser for counter-current heat exchange (B); and conventional reformer connected in parallel to heat exchanger recuperative reformer (C). Source: Technip Energies and Clariant Catalysts.

Not all of the heat is absorbed by the feed gas during the reaction. A convection section is therefore installed next to the reformer to recover residual heat, which can then be used for any of several purposes, including heating process gas, preheating combustion air, producing steam, powering machinery such as pumps or compressors, and transferring to nearby units.

Despite its many advantages, steam reformers are the largest single-point emitters of CO₂ in large refineries and petrochemical plants. Producing 1 t of H₂ releases 9 t–12 t of CO₂, depending on feedstock quality and reformer design. In ammonia production, CO₂ is released before the ammonia synthesis loop and from the steam reformer stack, resulting in between 1.8 t and 2.2 t of CO₂ emitted per 1 t of ammonia (excluding CO₂ captured and used for urea production). It is no surprise that producers and technology providers have been searching for ways to minimize carbon emissions and improve plant profitability.

Recuperative reforming. One way to improve this process is through recuperative reforming, a technology that has been in use since the 2000s. Recuperative reforming reuses heat from the process gas emitted by the reformer to drive the reforming reaction itself. In the U-shaped reformer reactor pictured in FIG. 1B, for example, heat is recovered directly within the reformer tubes; the highest temperature occurs at the bottom of the catalyst bed, while syngas emitted from the top outlet is partly cooled through counter-current heat exchange. 

This design belongs to the first generation of recuperative reforming reactors. A newer alternative for heat recovery is the use of an external heat exchanger recuperative reformer (FIG. 1C) located parallel to a conventional steam reformer. The syngas exiting the steam reformer is channeled to the bottom of the recuperative reformer and used as a heat source to convert further feed gas and steam, which is supplied from the top. Parallel arrangements of this kind are increasingly used in ammonia and methanol plants to raise production capacity and in refineries to enhance production of clean fuels; they have also gained popularity with conventional plants attempting to minimize carbon footprint and energy usage. 

New steam methane reformer (SMR) insert technology. A newly developed SMR insert technology^a (FIG. 2) designed for existing and new reformer tubes enables an increased process efficiency at relatively low investment costs. This innovative drop-in technology consists of a concentric tubular structure and a tailor-made structured catalyst, jointly developed by the authors’ companies. As for conventional SMRs, inlet and outlet sections are at opposing ends of the furnace and its installation does not require additional plot space. This new insert technology results in an efficient heat recovery, allowing a more intense SMR process, higher throughput, and a significantly lower pressure drop vs. conventional catalyst and tube layouts.

FIG. 2. Concentric tubular structure of new technology showing internal flow recirculation. Source: Technip Energies.

Lower costs and emissions. The increased heat recovery of this proprietary technology^a presents major advantages for H₂ and syngas producers. It significantly reduces external heat flux demand through firing, producing a corresponding drop in operating costs and CO₂ emissions at equal yield; alternately, producers can choose to increase plant throughput and capacity by up to 20% while maintaining previous costs and process conditions (TABLE 1). Less intense firing also reduces mechanical stress on the reformer tube material and outlet system: as a result, critical components of these systems are better protected from damage and require less frequent maintenance and replacement than would otherwise be the case.

TABLE 1. Characteristic performance advantages of the new technology vs. conventional steam reforming

Low-pressure drop, high-performance catalysts. The benefits of the new drop-in heat recovery technology are not only due to the unique geometry of the tubular inserts, but also to the newly developed catalyst. Consisting of a coated, low-pressure drop, structured substrate, these catalysts are designed for maximum activity, stability, heat transfer and a catalyst bed with severely limited volume. Additionally, mechanical strength is optimized for loading in the annular space between the insert’s outer concentric layer and the surrounding reformer tube. Compared to traditional ceramic pellet catalysts in random-packed bed configurations, these features allow significantly higher gas throughput in the catalyst tube within the desired pressure drop range. The new catalyst’s high surface-to-volume ratio and geometric advantages also significantly increase its activity and heat transfer capacity over conventional designs. 

Successful industrial application. These SMR inserts and their component catalysts have been operating at an H₂ plant since January 2019 and thus far have produced excellent results. The operator of the plant, Akkim Kimya Sanayi ve Ticaret A.S. (Ak-Kim), is one Turkey’s leading chemicals manufacturers. For its H₂ peroxide production facility, Ak-Kim relies primarily on H₂ produced from the chloralkali process; additional H₂ is supplied by a small syngas plant (FIG. 3). This syngas plant had been in operation for 20 yr at the time it was upgraded with the new insert technology. The insert tubes were delivered preloaded with the catalyst and installed onsite in one day. The plant was put into operation 1 wk later, achieving a smooth startup and demonstrating almost immediate performance improvements with considerably lower steam export and fuel consumption. Within 3 wk of installation, the plant had attained stable operation at up to 100% of its design capacity.

FIG. 3. Ak-Kim syngas plant in Turkey. Source: Ak-Kim.

Since then, performance tests at Ak-Kim have shown results significantly superior to those of the conventional catalyst technology previously used by the plant (TABLE 2). According to these tests, ~16% of the total heat absorbed by the process is recuperated, demonstrating improved energy efficiency, and the plant benefits from fuel savings of ~ 38% ( ~400 tpy of natural gas makeup) at an equal production rate and separation performance. Radiant efficiency is also ~21% higher, resulting in a 57% lower export steam flowrate. Most notably, since the upgrade the plant’s CO₂ emissions have decreased by ~ 20% (excluding CO₂e of the CO product).

TABLE 2. Comparative performance of AK-Kim reformer before and after tubular inserts were installed

Further assessments have verified the pressure drop advantage of the new catalyst: pressure was measured at < 1 bar, far lower than its predecessor, and catalyst performance was nearly at equilibrium conversion with a temperature of 853°C while the process gas temperature was 855°C. Ak-Kim appears satisfied with the results and plans to expand H₂ production once other plant issues (PSA, membrane and front end) have been resolved. 

In the immediate future, this new technology will be used in an upcoming H₂ plant located in Cartagena, Spain, as well as helping upgrade an existing H₂ plant elsewhere in Europe. Both projects are scheduled to come online in 2022.

NOTES

^a EARTH® technology created by Clariant and Technip Energies

STÉPHANE WALSPURGER holds a PhD in catalysis from the University of Strasbourg, France. In 2006 and 2007, he contributed to research projects on the methanol economy at the University of Southern California; and from 2008 to 2013 he contributed to the development and scale-up of novel CO₂ capture and utilization technologies as an R&D Project Engineer at the Energy Research Centre of the Netherlands (currently TNO). Since then, Dr. Walspurger has worked to extend Technip Energies’ technology portfolio in the field of decarbonized H₂ and syngas, low-carbon ethylene and biofuels/biochemicals production. Dr. Walspurger now manages the product development and new technologies departments of Technip Energies’ operation center in Zoetermeer, the Netherlands. 

STEFAN GEBERT holds a PhD in chemistry from the University of Heidelberg, Germany. He started his career in the catalyst business with Süd-Chemie AG in 2003 and now has more than 18 yr experience in the field of syngas catalysts for H₂, ammonia and methanol production. Having held various roles in sales, technical service and product management, he is now responsible for Clariant’s catalyst portfolio for standard syngas applications, as well as its transition to the needs of sustainable H₂ and ammonia production.