(521f) Techno-Economic Assessment of Dry Reforming of Methane Process

The reaction of methane and carbon-dioxide to produce syngas (mixture of CO and H₂) is called Dry Reforming of Methane (DRM). DRM has received considerable interest in academia and industry due to CO₂ being one of the reactant feed. Most of the work done in DRM research involves novel catalysts to reduce the coking problem and thermodynamic studies to estimate product composition at different operating conditions. Very few studies have addressed the issue of understanding the CO₂ balance of the whole process and one recent study has used an optimization-based approach to study CO₂ fixation rates for different syngas ratios. If the motivation for DRM is to reduce the carbon footprint of producing syngas, then it is crucial to track CO₂ flows in and out of the system. As DRM has not been tried on an industrial scale yet, quantifying the environmental benefits and plant economics of the process is necessary in the path of commercialization.

In this work, our focus is on understanding the maximum potential of the DRM reaction to reduce CO₂ emissions of a process. Unlike previous studies which mainly considered reformer duty as the energy penalty, in our work, all major sources of emissions in each process pathway have been accounted. LINGO software has been used for equilibrium calculations and optimization. For sake of brevity, we have presented the analysis in two parts. In the first study, DRM is studied with other available reforming technologies in parallel. In the second study, we have investigated the potential of producing syngas of high H₂/CO ratio from a stand-alone DRM unit operating at low temperatures (500-700 °C).

From the reaction stoichiometry of DRM, it can be inferred that normally at industrial reforming conditions (800-1200 °C), DRM alone will produce a syngas of H₂/CO ratio of 1 and below. Hence, to produce syngas of higher syngas ratios, we need another existing syngas production technology (Partial Oxidation – POx or Steam Methane Reforming – SMR) in parallel to make up the desired syngas ratio. These 3 processes (DRM, POx and SMR) are in parallel and the optimization model selects the optimum choices to minimize carbon emissions of the overall unit while producing syngas of the desired ratio. The results indicate that DRM has the potential of having a net CO₂ fixation (net reduction in CO₂ across the process boundary) only for low syngas ratio of below 1. At syngas ratio of 2 and above, the optimization model does not select DRM. This work signifies the importance of understanding the CO₂ balance of the DRM process before proposing it as an emissions reduction strategy. The operating costs of producing syngas in the optimized syngas production networks are also presented.

In the second part of the study, we have only looked at a stand-alone DRM unit to study different scenarios and its potential in producing syngas of high H₂/CO ratio. To avoid the carbon formation regime of 600-750 °C, industrial reformers are operated at very high operating temperatures. However, most of the catalysis studies of DRM seem to focus on the 500-700 °C range, and the reason is to reduce the reformer duty which will help enhance the CO₂ fixation rates. These studies entirely ignore that coke is removed as CO₂ and this negatively impacts the CO₂ balance. Hence, it is essential to quantify the carbon emissions before claiming that DRM has lesser carbon footprint. We have analyzed the performance of different DRM catalysts and compared the CO₂ balance for different ways of catalyst regeneration. These results have been compared with the industry benchmarks of SMR and POx. The results show that coke management plays a major role in deciding the CO₂ balance of DRM process. If the coke formed can be removed physically (which is still an experimental challenge), then DRM alone can produce syngas of high H₂/CO ratio as it produces the additional H₂ by methane decomposition. And such a unit will have significantly lower carbon footprint than existing technologies (SMR, POx). However, if coke is removed by burning in air, it will result in CO₂, which will negatively affect the CO₂ balance. The results presented in this section will provide directions to researchers in the DRM area to realign focus to those operating conditions where we have better CO₂ fixation rates. The operating costs of such a novel unit have been estimated and compared with industry standards of SMR and POx.

This study will help understand the impact of DRM unit on carbon emissions and the operating costs of a syngas generation unit. The results can then be compared with other CO₂ reduction strategies in the plant to prioritize projects aiming towards a low-carbon emissions future.