decarbonisation solution for both new and existing plants. These advanced DRM technologies permit coke-free reforming operations at a much lower S/C ratio than the conventional SMR process, resulting in significant savings on Opex. Also, several start-up companies, including Raven SR, HyCO1, and Syzygy Plasmonics, are in the proof-of-concept and pilot stages of developing syngas plants based on the DRM technology pathway. Raven SR is offering a non- catalytic steam-CO 2 methane reforming process, while Syzygy Plasmonics is offering its Rigel photoreactor cell and catalyst, which are integral to its GHG gas e-Reforming Modular Reactor that enables light-driven catalytic steam-CO 2 methane reforming reactions. 14 A few plasma- assisted DRM technologies have been under research for a considerable time.15 However, these techniques have not advanced beyond TRL 3/4, so they will not be discussed further here. Plasma pyrolysis of methane integrated with Boudouard/heterogeneous water gas steps This innovative technology pathway, offered by a start-up company, Caphenia, uses biogas (50- 95% CH 4 ), waste CO 2 , water, and renewable power to produce syngas (H 2 and CO) via plasma pyrolysis of methane in a single 3-in-1 Plasma-Boudouard Reactor (PBR) without any green H 2.16 It is noteworthy that, as opposed to other emerging low-CI syngas pathways based on catalytic or electrochemical processes, this is a non-catalytic once-through process in a single reactor (see Figure 2 ). This unique process scheme integrates the following three well-known chemical reactions in a single 3-in-1 PBR to produce syngas – something that has never been conceptualised before: Methane pyrolysis : The process begins in the upper chamber, in the so-called Plasma Zone, with the thermal process of plasma pyrolysis of methane. Here, CH 4 is introduced and heated to 2,000ºC, at which point it transforms into the fourth state of matter: the plasma state. The heating takes place via plasma torch using renewable electricity. During plasma pyrolysis, each CH 4 molecule splits into one carbon atom (C) and two molecules of H 2 . This process has already been successfully employed in several demo and commercial-scale units worldwide.
Biogas
Plasma technology
Methane pyrolysis
CO
Boudouard
hetWG
H O
Syngas
Figure 2 Plasma-Boudouard Reactor
Additionally, DRM can produce syngas with lower hydrogen-to-carbon monoxide (H 2 -to-CO) ratios than SMR. Therefore, a lot of research on dry reforming has been conducted and continues today, not only because of the aspects of CO 2 utilisation but also because access to CO-rich syngas obtained from dry reforming is facilitated. Easier access to CO-rich syngas offers potential for certain downstream processes. Besides utilising CO 2 , DRM also provides better thermodynamic equilibrium, resulting in lower net CO₂ to be removed. This, in turn, shrinks the CO₂ removal equipment footprint, with lower regeneration and recompression energy required, leading to Opex and Capex benefits. However, metal sintering and carbon laydown on the catalyst surface remain a monumental impediment towards wider industrialisation and commercialisation of the DRM pathway. Linde, Topsoe, and GTI Energy are three leading process licensors that offer plants based on DRM technology. Linde’s proprietary Dryref technology is an advanced DRM process based on BASF’s Synspire catalyst.11 Topsoe’s eREACT technology12 and GTI Energy’s Cool GTL technology offer an electrified compact reactor for the production of green syngas using renewable energy, water, and CO 2 . On the other hand, Topsoe’s ReShift technology13 mitigates the challenges of carbon laydown caused by the addition of CO 2 to the feed of conventional SMR at a much lower steam-to-carbon (S/C) ratio by introducing preheated CO 2 downstream of the SMR. This is converted over a nickel-based ReShift catalyst in an adiabatic converter to produce CO-rich syngas. This technology can be applied as a
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