Recuperative reforming for reducing carbon footprint

DECARBONISATION

Recuperative reforming for reducing carbon footprint

Previously, recuperative reforming has been mostly applied for capacity increase revamps, but nowadays it is a key enabler for efficient low carbon hydrogen and syngas production. Jan-Jaap Riegman of Technip Energies, Francesco Baratto of Casale and Stefan Gebert of Clariant discuss the benefits of recuperative reforming for reducing the carbon footprint of existing assets.

With global warming coming closer to 1.5°C above pre-industrial levels, countries and industries are setting more and more ambitious pledges and targets for their CO2 emission reduction. As hydrogen is a carbon-free molecule it is an important energy carrier as well as a building block (either as hydrogen or syngas) for the production of other chemicals, for example ammonia.

Among commercially available hydrogen and syngas production technologies, steam reforming (SMR) and/or autothermal reforming (ATR) of natural gas are usually the most cost-effective means to ensure profitable hydrogen, syngas and ammonia production on an industrial scale. Traditionally about 60-70% of the CO2 emissions from such plants comes from the reforming reaction and, together with the firing in a heater, represents a significant emission source of CO2 . Therefore, there is a large drive to reduce the carbon footprint of this industry.

Partly, this can be achieved with so-called green hydrogen (hydrogen produced from water electrolysis). On the other hand, blue H2 /syngas technology (production of H2 /syngas via a reforming route with the addition of carbon capture and subsequent storage or utilisation (CCUS)) is already available and affordable at a large scale and will therefore play a significant role in the energy transition. A blue syngas/H2 concept can effectively be applied in grassroot as well as revamp applications.

The excess high-grade energy available in both SMR and ATR reforming schemes is applied to generate steam, which is only partially utilised internally and widely exported or used for steam-driven machinery. Over the last two decades reforming technology licensors have shifted the efficiency and heat integration paradigm and deployed advanced technologies capable of re-utilising the heat contained in the hot process gas exiting the reformer as a heat source to drive the reforming reaction itself. Such technologies are commonly called “recuperative reforming” and lower the energy input required for the reforming process and thus play a crucial role in effectively producing blue syngas and hydrogen.

Fig. 1: (a) U-shaped reformer tubes having an internal riser allowing for internal counter current heat exchange; (b) heat-exchanger reformer connected in parallel to the conventional reformer.

Fig. 2: (a) Schematic representation of TPR; (b) Schematic representation of EARTH®

Recuperative reforming

While in past years recuperative reforming was mostly applied for capacity increase revamps, nowadays it is a key enabler for efficient low carbon hydrogen and syngas production. By utilising the high-grade heat from the reformer effluent for heating the reforming reaction instead of generating steam, the load in the primary and or secondary reformer and thus the overall energy input is reduced. This results in lower energy consumption as well as a lower carbon footprint.

Two main concepts for recuperative reforming can be differentiated and are depicted schematically in Fig. 1 in combination with a steam reformer.

Fig. 1a shows a recuperative reforming technology, whereby a tube is inserted in a U-shaped reformer reactor, creating an annular counterflow arrangement to enable high-grade heat recovery within the tube itself. In this layout, the highest temperature is obtained at the end of the catalyst bed located at the U end of the tube, while the syngas exiting at the (top) outlet of the tube is partially cooled by counter-current heat transfer, thereby significantly reducing the firing demand and thus increasing the furnace efficiency. The downside of this concept is that it can only be applied for grassroot applications. Technip Energies (T.EN) developed its EARTH® technology as a similar concept with three passes entering at the top and exiting at the bottom. EARTH® is schematically depicted in Fig. 2b and its first commercial application has been in operation since January 2019.

Fig. 1b shows an alternative design whereby the heat recuperation is carried out in a separate, external heat exchanger recuperative tubular reactor, placed in parallel to the fired steam reformer. In this configuration, syngas exiting the fired reformer is routed to the parallel reactor as the heat source, while additional fresh feed + steam is converted on the tube side (cold side) of the reactor against the provision of this heat. Fig. 2b, schematically depicts the T.EN Parallel Reformer (TPR), which can be applied in parallel to either the steam reformer and/or autothermal reformer and is well referenced.

For EARTH® technology, Clariant and T.EN combined their collective expertise to drastically improve the efficiency and throughput per catalyst tube in the reformer. It is patented by T.EN and contains two concentric heat exchanger tubes with a highly active structured catalyst co-developed with Clariant. The combination of both allows for simultaneously improving the catalyst activity and additional heat recovery.

As the inlet is at the top and the outlet at the bottom it can be applied in both grassroot and revamp applications. The tailor-made proprietary catalyst structure is extremely robust and promotes low pressure drop, optimised heat transfer properties and highest activity. The highly active and mechanically stable catalyst coating on a metal structure has been developed based on Clariant’s extensive and long-lasting experience with structured catalysts for fuel cell applications.

The first application has been online since January 2019 in a syngas production unit and has been in continuous operation for more than four years at the design capacity. The catalyst performance remains close to the equilibrium to date and potentially opens pathways to significantly longer catalyst lifetimes. EARTH® reduced the total hydrocarbon consumption by 10% resulting in CO2 emission savings of 20%. In 2022, EARTH® was installed as a revamp in a large-scale reformer in Europe to accommodate a capacity increase of more than 20%, while simultaneously having 5% lower CO2 emissions per hydrogen produced. The EARTH® inserts were delivered at the site preloaded with catalyst. The complete EARTH® assembly was inserted into the catalyst tube as a drop-in solution. This minimised the site work and eliminated most of the catalyst handling at site. The installation was successfully completed within the shutdown period and showed that the EARTH® installation can be completed within a similar timeframe as conventional catalyst loading. The catalyst structures are very stable and ensure that the catalyst pressure drop is the same in every tube eliminating the need for correcting and reloading. The plant was successfully started-up and has been in stable operation since.

Next to the EARTH® catalyst, Clariant also offers the very active, stable and robust ReforMax® -series catalysts for TPR and ATR. There are numerous references of these high-performance catalysts on the market.

Recuperative concepts for blue hydrogen

As traditional hydrogen production is a significant source of CO2 emissions formed during the production as well as in combustion, CO2 curtailment and carbon capture are widely considered for hydrogen production. This is valid for both grassroot applications as well as for revamping existing assets. Grassroot blue hydrogen plants are typically designed to achieve hydrogen production with a carbon capture rate of 95% or higher. For revamping of existing assets, the target can be lower or staged. In low-carbon fuel production there is an interest in minimising the carbon emission associated with the conversion of natural gas (NG) to the final product. In particular, in the blue hydrogen market there is an interest in reaching a carbon intensity of around 0.1 kg of CO2 per kg of hydrogen. This value includes the direct emissions from the plant (scope 1), the emission related to the utilities required by the plant i.e. electricity (scope 2) and the emission associated with the final use of the product (scope 3).

Both TPR and EARTH® technology typically reduce the carbon footprint of the syngas production plant intrinsically by up to 10%. When combined with CCUS and possibly further synergistic design changes it allows for up to 99% reduction of the carbon footprint. At the same time the excess steam production can be reduced to zero. Fig. 3 indicates the typical levelised CO2 footprint as well as levelised export steam flowrate for a typical hydrogen plant. The figure is based on an SMR-based plant, but the trend is also valid for ATR-based hydrogen plants.

An ATR-based blue hydrogen plant fed with pure oxygen can be combined with a parallel heat exchanger reformer (TPR) in series/parallel to ATR. The use of TPR as well as the heating of feed gas with the ATR effluent allows the furnace duty and steam production to be greatly reduced, with relevant improvements to the unit efficiency and capex savings, for example, in parallel to an ATR as part of Casale’s technology portfolio, which has proven references since 2002.

In specific applications both recuperative technologies (in-tube and external heat exchanger reformer) can be applied together and combine and exceed the benefits of both technologies applied separately. This is particularly beneficial in case of a combination of a primary and secondary reformer, where EARTH® is applied to the primary reformer and the outlet reformer effluent is fed to the secondary reformer, and where the TPR is installed in parallel to the primary plus secondary reformer. As the concept amplifies the positive effects of both separate technologies a combined intrinsic CO2 emission reduction of up to 30% is achievable. As a large part of the high-level duty available from the secondary reformer is utilised for the reforming reaction instead of steam production, the total steam production is reduced. The emissions can be further reduced by synergistic design changes.

Fig. 3: Levelised CO2 footprint and export steam flow for a typical hydrogen plant

Recuperative concepts for low carbon ammonia revamp

To achieve significant decarbonisation by revamping ammonia plants, careful evaluation of necessary modifications for each plant section is crucial. Though there is no single most important section for an ammonia plant, the reforming section is often a main focus in decarbonisation for simple reasons:

it is the main source of CO2 emissions to the atmosphere;
the performance of this section also impacts the performance of other sections;
the hydrogen required by the ammonia synthesis is generated here.

In the process scheme of a single recuperative concept, the reforming section is revamped by adding a TPR. The pre-heated mixed feed consisting of natural gas and process steam flows in parallel to the primary reformer radiant box and secondary reformer (about 70-85% of the gas) and to the TPR (about 15-30% of the gas).

The main advantages provided by the TPR are:

adds up to 30% additional hydrogen in capacity revamps of existing plants without additional firing demand or major modifications to the existing reformer;
minimises export steam;
lowers CO2 footprint per unit of hydrogen up to 15% compared to a standalone steam reformer of equal capacity.

In addition to the TPR in parallel to the primary and secondary reformer, EARTH® can also be applied in the primary reformer in a so-called double recuperative concept (Fig. 4). The concept allows for an additional significant reduction of carbon footprint per syngas produced and for effective low carbon ammonia production.

In this process scheme, EARTH® is applied directly in the primary reformer as the inlet gas is from the top and the outlet remains at the bottom of the firebox. The heat recovery allows intensification of the primary reformer while maintaining an equal or lower inlet temperature of the secondary reformer and can be optimised to have the minimum overall impact in the syngas generation section.

The TPR is installed in parallel to the primary and secondary reformer and produces additional syngas with the available high-grade heat from the secondary reformer. The syngas to the downstream ammonia synthesis loop is not impacted and direct decarbonisation of the syngas production section thus results in a carbon footprint reduction of the ammonia production unit.

Fig. 4: Simplified flow diagram for the double recuperative concept with the TPR in parallel to the primary and secondary reformer as well as EARTH® in the primary reformer. Alternatively, the TPR can be applied in parallel to the primary and secondary reformer without EARTH® in the primary reformer

The combination of these two recuperative concepts as described can reduce CO2 emissions from the syngas generation section by up to 30%, while maintaining the same methane slip and nitrogen to hydrogen ratio to the synthesis loop. The combination boosts the positive effects of the separate recuperative technologies while eliminating most of the drawbacks. As the high-grade heat is utilised for the reforming reaction, this reduces the overall steam production, and the steam balance of the ammonia plant needs to cope with this reduced steam production. Casale technologies and combined process schemes for energy saving perfectly fit this scenario, increasing plant efficiency by reducing steam demand. Finally, onsite electrification efforts to apply electric motors to drive compressors instead of steam turbines is also a possibility.

Table 1 compares a typical ammonia production unit comprising a primary reformer, an air blown secondary reformer, with a similar scheme with the addition of a TPR and the double recuperative flow scheme as indicated above. The addition of a TPR allows for a slightly lower hydrocarbon consumption and results in up to 15% reduction of the CO2 emissions. At the same time, steam production is reduced by up to 25%.

The double recuperative concept enables a step change in further reduction of the hydrocarbon input by up to 10%. This also relates to a CO2 emission reduction of up to 30% without impacting the downstream synthesis loop. On the downside, the steam production is reduced by up to 40% and therefore would typically be combined with electrification efforts for the downstream compressors.

“Recuperative reforming technologies are essential to decarbonise hydrogen and syngas generation of existing assets as it enables an intrinsic reduction of CO2 emissions.

Conclusion

Recuperative reforming technologies are essential to decarbonise hydrogen and syngas generation of existing assets as it enables an intrinsic reduction of CO2 emissions. It also enables more effective application of carbon capture and utilisation, for both SMR and ATR based plants and allows up to more than 99% carbon capture rate.

Technip Energies recuperative technologies are commercially proven. Its TPR technology is applied in parallel to SMR and/or ATR. EARTH® technology (with a structured catalyst jointly designed with Clariant) is applied inside the SMR catalyst tubes. Both TPR and EARTH® technology can be applied separately and result in a CO2 emission reduction of typically up to 10-15%. In the case of a hybrid reforming scheme with a primary and secondary reformer both EARTH® and TPR technology can be applied together in a double recuperative reforming concept. This combines the benefits of both recuperative technologies and enables a CO2 footprint reduction of up to 30% and is especially attractive for decarbonising existing ammonia assets.

Both EARTH® and TPR can be effectively applied together with Casale’s technologies and experience and Clariant’s catalyst technologies to revamp both ammonia and methanol production units. This allows the plant’s energy consumption and CO2 footprint to be reduced, while coping with reduced steam generation in the syngas generation section.