(514h) Technoeconomic Study of Advanced H2 Production Technologies: Membrane-Supported H2O Splitting, Thermochemical Redox H2O Splitting and Fuel-Assisted H2O Electrolysis

Authors: 
Wu, X. Y., MIT
Ghoniem, A. F., Massachusetts Institute of Technology
In this presentation, we discuss three advanced hydrogen production technologies, (i.e., membrane-supported water splitting, thermochemical redox (chemical looping) water splitting and fuel-assisted water electrolysis) and compare them with the conventional steam methane reforming (SMR) process for high purity hydrogen (>99.95% purity) production. Membrane-supported water splitting utilizes a mixed ionic-electronic conductive (MIEC) membrane, (e.g., La0.9Ca0.1O3-δ and BaFe0.9Zr0.1O3-δ) to separate the water splitting products (i.e., O2 and H2), so that thermodynamic equilibrium of water splitting is shifted and higher hydrogen production rates have been achieved in the literature [1] [2]. Thermochemical redox water splitting uses an oxygen carrier (OC, e.g., CeO2 [3]) to transfer the oxygen species. In the OC oxidation reaction, water is converted into lattice oxygen and hydrogen gas, while in the OC reduction reaction, the lattice oxygen is released or consumed. For the fuel-assisted water electrolysis process, hydrocarbons, (e.g., CH4) is added on the anode side of the electrolysis cell to drive the water splitting process. Less electricity will be consumed compared with the conventional electrolysis cell and higher first law efficiency can be achieved [4].

First, we compare the thermodynamic efficiency of these technologies with renewable heat source at 282oC (540oF) based on the system-scaled thermodynamic models. The membrane and redox systems have similar first law efficiency compared with the SMR system, all reaching around 88%. Yet the electrolysis system has lower efficiency of ~83%, and electricity consumption accounts for around 31% of the total energy consumed. Secondly, the renewable heat accounts for 28.2%, 36.4% and 34.7% of the total energy consumption for membrane, redox and electrolysis systems, respectively. But the conventional SMR system could hardly utilize the renewable heat source as the overall system is exothermic. In addition, we compared the energy costs (i.e., fuel and electricity costs) of these systems (the cost for the renewable heat source is neglected). Results show that both membrane and redox systems have lower energy costs than the SMR system, decreasing the costs by 9% and 14%, respectively. However, electrolysis has 24% higher energy costs than the SMR system, due to the high price of the electricity (using averaged US electricity costs as the base case). We also investigate the CO2 emissions and found that all the advanced systems emit less CO2 than the conventional SMR system. The redox system has the largest CO2 emission abatement potential with 12% emission decrease compared with the SMR system. The membrane and electrolysis systems also decrease CO2 emissions by 7% and 5%, respectively. Furthermore, the total as-spent cost for these three advanced systems for a small-scaled hydrogen plant of 100 kmol H2/h will be estimated to compare their costs of high purity hydrogen production.

Reference

[1] Wu, X.-Y., Ghoniem, A. F., and Uddi, M., 2016, "Enhancing co-production of H2 and syngas via water splitting and POM on surface-modified oxygen permeable membranes," AlChE J., 62(12), pp. 4427-4435.

[2] Dimitrakopoulos, G., Schucker, R. C., Derrickson, K., Johnson, J. R., Kopeć, K. K., Shao, L., Alahmadi, F., and Ghoniem, A. F., 2017, "Hydrogen and Ethylene Production through Water-Splitting and Ethane Dehydrogenation Using BaFe0.9Zr0.1O3-δ Mixed-Conductors," ECS Trans., 80(9), pp. 181-190.

[3] Zhao, Z. L., Uddi, M., Tsvetkov, N., Yildiz, B., and Ghoniem, A. F., 2016, "Redox Kinetics Study of Fuel Reduced Ceria for Chemical-Looping Water Splitting," Journal of Physical Chemistry C, 120(30), pp. 16271-16289.

[4] Luo, Y., Shi, Y., Li, W., Ni, M., and Cai, N., 2014, "Elementary reaction modeling and experimental characterization of solid oxide fuel-assisted steam electrolysis cells," Int. J. Hydrogen Energy, 39(20), pp. 10359-10373.