(698d) Dual-Stage Vacuum Pressure Swing Adsorption for Green Hydrogen Recovery from Natural Gas Grids | AIChE

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(698d) Dual-Stage Vacuum Pressure Swing Adsorption for Green Hydrogen Recovery from Natural Gas Grids

Authors 

Zafanelli, L. - Presenter, Polytechnic Institute of Bragança
Aly, E.
Henrique, A., Faculty of Engineering University of Porto
Rodrigues, A. E., LSRE - Laboratory of Separation and Reaction Engineering - Associate Laboratory LSRE/LCM
Silva, J. A. C., ESTiG-IPB
A shift to renewable sources of energy is crucial to the mitigation of climate change. Fossil fuels, such as petroleum, natural gas, and coal, are the main contributors to the economy’s growth, however, their use is also the main contributor to global warming. According to the IPCC report, in 2019, the combined energy supply, industry, and transport sectors represented 73% of the total net anthropogenic emissions, which means approximately 42.7 GtCO2 was released into the atmosphere by these sectors [1]. Green Hydrogen (GH), produced from the electrolysis of water, has the potential to play a significant role in reducing CO2 emissions from fossil fuel systems. Additionally, GH can serve as an intersectoral bridge by storing and utilizing intermittent renewable energy sources (such as wind and solar) for later use in the energy supply, industry, and transport sectors [2]. Following the production of GH, it can be injected into existing natural gas grids (NGG) for cost-effective transportation, thus eliminating the need for extensive infrastructure investments [3]. However, when GH is blended into the NGG, it is necessary to recover and purify it to a high purity level to facilitate applications such as fuel cells (H2 > 99.97%). One challenge associated with separating and purifying GH blended in NGG is the low H2 feed concentration (<20%), which is significantly lower than that required for traditional H2 adsorption purification processes, for example, H2 produced from steam methane reforming (>70%).

In this work, we develop a conceptual dual-stage vacuum pressure swing adsorption (VPSA) process to separate and purify H2 blended into the natural gas grids with low H2 feed concentration (<20%). Figure 1A shows the dual-stage VPSA coupled in the NGG diagram. Stage 1 consists of a VPSA filled with a carbon molecular sieve (CMS-3K-172), which adsorbs preferentially H2 and blocks CH4 from entering its pores. In this way, CH4 is produced in the feed step while H2 is enriched in the blowdown vacuum depressurization step. In our previous work [4], we showed that the VPSA filled with CMS-3K-172 can enrich the H2 molar fraction from about 20% to 60 – 70%, with a recovery higher than 90%. This is highlighted by the green circle in Figure 1C which shows the trade-off between H2 purity and recovery for stage 1. In this way, to feed stage 2, two H2 concentrations were considered, namely 55% and 65%. Stage 2 consists of a conventional VPSA filled with binder-free zeolite 13X (13XBFK) that has a greater affinity towards CH4 than H2, as shown in our previous work [5]. Oppositely to stage 1, in stage 2, H2 is produced in the feed step while CH4 is recovered in the blowdown vacuum depressurization step.

Each stage has its independent cycle configuration, that is, they have a different sequence of elementary steps through which the column undergoes, as seen in Figure 1B. Stage 1 VPSA consists of 5 steps, namely (1) pressurization with feed, (2) feed, (3) H2 purge, and (4) countercurrent vacuum blowdown. Stage 2 consists of a VPSA with 11 steps including 3 pressure-equalization steps, namely (1) feed, (2) depressurization-equalization 1, (3) depressurization-equalization 2, (4) depressurization-equalization 3, (5) countercurrent vacuum blowdown, (6) re-pressurization 1, (7) idle 1, (8) re-pressurization 2, (9) idle 2, (10) re-pressurization 3, and (11) re-pressurization with product. Stage 1 was optimized previously [4], therefore, only stage 2 is optimized in the present work. Stage 2 performance, i.e., H2 purity and recovery, was evaluated by changing the process variables such as feed step time, blowdown vacuum pressure (Pv), and H2 feed molar fraction. The trade-off between H2 purity-recover for stage 2 can be seen in Figure 1D. From a feed of 55% H2, stage 2 allows obtaining an H2 purity higher than 98% with a recovery up to 80% as highlighted by the green circle in Figure 1D. The CH4 purity in both stages is higher than 88%.

In this work, we reported a conceptual dual-stage VPSA to separate and purify GH from NGG. Stage 1 is a VPSA with a CMS-3K-172 that kinetically separates CH4 from H2, intending to pre-concentrate H2 from a value in the feed of 20% to a value around 60%, and stage 2 is a conventional VPSA using benchmark zeolite 13X from thereof 60% to a final H2 purity higher than 98%. With this strategy, it was possible to enrich GH mixed in NGG from 20 to c.a. 99% with a high recovery rate (>80%). In conclusion, the developed dual-stage VPSA process can provide a technically viable way to recover and purify H2 blended into the natural gas grids. We are currently working on an economical evaluation of the dual-stage VPSA process.

Figure 1. A) Diagram of dual-stage VPSA coupled in the natural gas grids (NGG); B) Stage VPSA cycle configurations (steps are defined in the main text); C) Trade-off between H2 (20% in the feed) purity and recovery for stage 1; and D) Trade-off between H2 (55-65% in the feed) purity and recovery for stage 2.

Acknowledgments

The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) for financial support: (1) under project PTDC/EQU-EPQ/0467/2020 (DOI: 10.54499/PTDC/EQU-EPQ/0467/2020), (2) through the national funds FCT/MCTES (PIDDAC) to CIMO (UIDB/00690/2020 and UIDP/00690/2020), and SusTEC (LA/P/0007/2020), (3) by the national funds through FCT/MCTES (PIDDAC): LSRE-LCM, UIDB/50020/2020 (DOI: 10.54499/UIDB/50020/2020) and UIDP/50020/2020 (DOI: 10.54499/UIDP/50020/2020); and ALiCE, LA/P/0045/2020 (DOI: 10.54499/LA/P/0045/2020). Additionally, we thank national funding by FCT, Foundation for Science and Technology, through the individual research grant SFRH/BD/7925/2020 of Lucas F. A. S. Zafanelli. Moreover, the authors are grateful to Osaka Co. for kindly providing the CMS-3K-172 and Chemiewerk Bad Koestritz GmbH (Germany) for kindly providing the binder-free zeolite 13X studied in this work.

References

[1] - IPCC, 2022: Summary for Policymakers [P.R. Shukla, J. Skea, A. Reisinger, R. Slade, R. Fradera, M. Pathak, A. Al Khourdajie, M. Belkacemi, R. van Diemen, A. Hasija, G. Lisboa, S. Luz, J. Malley, D. McCollum, S. Some, P. Vyas, (eds.)]. In: Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [P.R. Shukla, J. Skea, R. Slade, A. Al Khourdajie, R. van Diemen, D. McCollum, M. Pathak, S. Some, P. Vyas, R. Fradera, M. Belkacemi, A. Hasija, G. Lisboa, S. Luz, J. Malley, (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA. doi: 10.1017/9781009157926.001.

[2] - Dehdari, L.; Burgers, I.; Xiao, P.; Li, K. G.; Singh, R.; Webley, P. A. Purification of hydrogen from natural gas/hydrogen pipeline mixtures. Sep Purif Technol 2022, 282, 120094. DOI: 10.1016/j.seppur.2021.120094.

[3] - Liemberger, W.; Gross, M.; Miltner, M.; Prazak-Reisinger, H.; Harasek, M. Extraction of Green Hydrogen at Fuel Cell Quality from Mixtures with Natural Gas. Chem Engineer Trans 2016, 52, 427-432. DOI: 10.3303/Cet1652072.

[4] - Zafanelli, L. F. A. S.; Aly, E.; Henrique, A.; Rodrigues, A. E.; Mouchaham, G.; Silva, J. A. C. Green Hydrogen Recovery from Natural Gas Grids by Vacuum Pressure Swing Adsorption. Ind Eng Chem Res 2024, XXXX, XXX, XXX-XXX. DOI: https://doi.org/10.1021/acs.iecr.3c04532.

[5] - Zafanelli, L. F. A. S.; Aly, E.; Rodrigues, A. E.; Silva, J. A. C. A novel cryogenic fixed-bed adsorption apparatus for studying green hydrogen recovery from natural gas grids. Sep Purif Technol 2023, 307, 122824. DOI: 10.1016/j.seppur.2022.122824.

Topics 

Adsorption
Hydrogen Production & Storage
Process Design & Development

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