Energy Efficiency Limits for a Recuperative Bayonet Sulfuric Acid Decomposition Reactor for Sulfur Cycle Thermochemical Hydrogen Production

Abstract

A recuperative bayonet reactor design for the high-temperature sulfuric acid decomposition step in sulfur-based thermochemical hydrogen cycles was evaluated using pinch analysis in conjunction with statistical methods. The objective was to establish the minimum energy requirement. Taking hydrogen production via alkaline electrolysis with nuclear power as the benchmark, the acid decomposition step can consume no more than 450 kJ/mol SO 2 for sulfur cycles to be competitive. The lowest value of the minimum heating target, 320.9 kJ/mol SO 2 , was found at the highest pressure (90 bar) and peak process temperature (900°C) considered, and at a feed concentration of 42.5 mol% H 2 SO 4 . This should be low enough for a practical watersplitting process, even including the additional energy required to concentrate the acid feed.Lower temperatures consistently gave higher minimum heating targets. The lowest peak process temperature that could meet the 450-kJ/mol SO 2 benchmark was 750°C. If the decomposition reactor were to be heated indirectly by an advanced gas-cooled reactor heat source (50°C temperature difference between primary and secondary coolants, 25°C minimum temperature difference between the secondary coolant and the process), then sulfur cycles using this concept could be competitive with alkaline electrolysis provided the primary heat source temperature is at least 825°C. The bayonet design will not be practical if the (primary heat source) reactor outlet temperature is below 825°C.

Review of Anodic Catalysts for SO2 Depolarized Electrolysis for “Green Hydrogen” Production

“…Now the catalyst technology used in PEMFC systems has been copied, and the electrodes are based on a catalyst supported by carbon-based materials deposited on gas diffusion layers. The sulphuric acid decomposition has been widely investigated in different studies, such as the one from Sandia National Laboratories [11], and most efforts have been devoted to the optimization of the SO 2 depolarized electrolysis (the electrochemical stage) to increase the global efficiency of the cycle [16]. Challenges for this process are the reduction of the overpotentials in the electrolysis step in order to improve the overall efficiency of the process-the development of high corrosion resistance materials due to the use of acid solutions.…”

“…The results showed that the best catalyst was 60 wt % Pt-Cr/XC72R, which was better than the catalyst containing only platinum. In this work [11], the influence of the atomic ratio was also studied. The ratio 1:2 (Pt:Cr) resulted in equal or even better electrolysis performance than that of 60 wt % Pt/C.…”

“…In this work [11], the influence of the atomic ratio was also studied. The ratio 1:2 (Pt:Cr) resulted in equal or even better electrolysis performance than that of 60 wt % Pt/C.…”

“…There are different routes to produce hydrogen with low or zero CO 2 emissions, including promising processes based on water splitting (in which new catalysts are being developed)photoelectrochemical water splitting [4][5][6], thermochemical cycles [3,7,8] or hybrid thermochemical cycles [9,10] are some examples. Hybrid thermochemical cycles using a high temperature thermal source have been proposed as one of the most promising technologies for massive hydrogen production [11]; moreover, they have been included as one of the candidates for "Green hydrogen" production, as it can be seen in Figure 1. Proposed and selected (highlighted in green) "Green Hydrogen" production pathways in the European Union (EU) (adapted from [1]).…”

Numerical study of heat transfer and sulfuric acid decomposition in the process of hydrogen production

“…Kim et al proposed a thermodynamic design of a laboratory scale sulfuric acid decomposer for nuclear hydrogen production. Gorensek and Edwards combined a pinch analysis and statistical methods to calculate the minimum energy requirement of a bayonet‐type sulfuric acid decomposer, which consumed less than 450 kJ/(mol of SO 2 ) for sulfur cycles through alkaline electrolysis. Noguchi et al used a direct‐contact heat exchanger to recover heat and separate the undecomposed sulfuric acid in the sulfuric acid decomposition section with experimental results being in good agreement with an empirical correlation.…”