(84aw) Optimizing Reformer Performance for Integrated Blue Hydrogen-Methanol Production: A Multi-Objective Optimization and Techno-Economic Study | AIChE

(84aw) Optimizing Reformer Performance for Integrated Blue Hydrogen-Methanol Production: A Multi-Objective Optimization and Techno-Economic Study

Introduction

Utilizing CO2 as a potential feedstock for producing value-added chemicals is an essential field of research both from environmental and economic perspectives. In this regard, methanol is one of the chemicals that can be produced from CO2. It has been extensively studied throughout the literature owing to its high demand and wide range of applications. However, producing methanol from CO2 requires vast quantities of hydrogen (1 mole of CO2 requires 3 moles of H2 to make 1 mole of methanol). Several articles in the literature have studied the techno-economic feasibility of conversion of CO2 to methanol [1,2]; however, most of them considered the source of hydrogen as “green”, i.e., hydrogen produced through the hydrolysis of water using renewable electricity. But producing green hydrogen is a technology that is still in a developmental phase. Additionally, if hydrogen is purchased from an external source, ways of storing and transporting it efficiently must be taken care of, further complicating the process. To overcome these challenges, a process scheme is presented in this work where the hydrogen is produced “in-house” without the need to purchase/store/transport it.

Integrated Blue Hydrogen-Methanol Synthesis (IBHM)

This process flowsheet contains a methane reformer followed by a methanol reactor. The methane reformer produces syngas from methane, which feeds into the methanol reactor. The hydrogen produced is categorized as blue hydrogen because the CO2 emissions associated with its production are utilized within the unit. The syngas is mixed with the process CO2 and sent to the final reactor, where methanol is produced. Although this process has more process equipment than direct methanol synthesis, it eliminates the need to purchase, transport and store external hydrogen.

Reformer Technologies

The IBHM flowsheet has a methane reformer that provides syngas for methanol synthesis. H2O, CO2, and O2 can all be used as oxidants for methane reforming, either individually or in combination, each with its pros and cons. Steam reforming produces syngas of an H2/CO ratio too high for methanol synthesis. CO2 is a flue gas that can be ‘utilized’ for methane reforming (two greenhouse gases react to produce a useful chemical here); however, it has issues such as low-quality syngas and coking on the catalyst surface. Achieving the optimal amount of CO2 for the reformer and the methanol reactor can be done through optimization. Using oxygen for methane reforming is an exothermic process. It needs to be conducted in a controlled environment, which otherwise would lead to the complete combustion of methane (and some associated safety issues). A combination of two or three of these is being extensively studied in the literature to overcome the shortcomings of these three oxidants individually [3].

Workplan and Expected Outcomes

This work aims to provide a detailed techno-economic and environmental analysis for the optimized IBHM flowsheet. To do so, reformer optimization is necessary as there are several levers, such as the feed flow rates of CH4, H2O, CO2, and O2 and the reaction operating conditions to control the overall outcomes of the process. In this case, two important objectives are chosen for the optimization of the IBHM flowsheet

  1. Maximize CO2 utilization while decreasing coking on the catalyst
  2. Maximize methanol yield while reducing energy requirement

Since this formulates a multi-objective optimization (MOO) problem, there won’t be a single solution but rather a collection of ‘optimal’ solutions from which the best set of solutions (i.e., feed ratios and reactor operating conditions) would be chosen for the techno-economic and environmental impact analysis.

Overall, this work will enable one to understand different reforming processes and their impact on the overall methanol yield. The objectives include several factors of practical relevance, such as coking. This work aims to assist the user in identifying the most appropriate reformer configuration for enhancing methanol throughput while maximizing CO2 utilization, thereby contributing towards a greener and cleaner future.

References

[1] M. Nizami, N. Slamet, W.W. Purwanto, Solar PV based power-to-methanol via direct CO2 hydrogenation and H2O electrolysis: Techno-economic and environmental assessment, Journal of CO2 Utilization. (2022). https://doi.org/10.1016/j.jcou.2022.102253.

[2] G. Lombardelli, S. Consonni, A. Conversano, M. Mureddu, A. Pettinau, M. Gatti, Process Design and Techno-Economic Assessment of biogenic CO2 Hydrogenation-to-Methanol with innovative catalyst, Journal of Physics: Conference Series. 2385 (2022). https://doi.org/10.1088/1742-6596/2385/1/012038.

[3] P. Balasubramanian, I. Bajaj, M.M.F. Hasan, Simulation and optimization of reforming reactors for carbon dioxide utilization using both rigorous and reduced models, Journal of CO2 Utilization. 23 (2018) 80–104. https://doi.org/10.1016/j.jcou.2017.10.014.