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Title: EFFECT OF ELECTROLYZER CONFIGURATION AND PERFORMANCE ON HYBRID SULFUR PROCESS NET THERMAL EFFICIENCY

Abstract

Hybrid Sulfur cycle is gaining popularity as a possible means for massive production of hydrogen from nuclear energy. Several different ways of carrying out the SO{sub 2}-depolarized electrolysis step are being pursued by a number of researchers. These alternatives are evaluated with complete flowsheet simulations and on a common design basis using Aspen Plus{trademark}. Sensitivity analyses are performed to assess the performance potential of each configuration, and the flowsheets are optimized for energy recovery. Net thermal efficiencies are calculated for the best set of operating conditions for each flowsheet and the results compared. This will help focus attention on the most promising electrolysis alternatives. The sensitivity analyses should also help identify those features that offer the greatest potential for improvement.

Authors:
Publication Date:
Research Org.:
SRS
Sponsoring Org.:
USDOE
OSTI Identifier:
901320
Report Number(s):
WSRC-STI-2007-00136
TRN: US0702575
DOE Contract Number:
DE-AC09-96SR18500
Resource Type:
Conference
Resource Relation:
Conference: 2007 International Congress on Advances in Nuclear Power Plants
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; 21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS; 29 ENERGY PLANNING, POLICY AND ECONOMY; CONFIGURATION; DESIGN; ELECTROLYSIS; ENERGY RECOVERY; FLOWSHEETS; HYDROGEN; NUCLEAR ENERGY; NUCLEAR POWER PLANTS; PERFORMANCE; PRODUCTION; SENSITIVITY; SULFUR; SULFUR CYCLE; THERMAL EFFICIENCY

Citation Formats

Gorensek, M. EFFECT OF ELECTROLYZER CONFIGURATION AND PERFORMANCE ON HYBRID SULFUR PROCESS NET THERMAL EFFICIENCY. United States: N. p., 2007. Web.
Gorensek, M. EFFECT OF ELECTROLYZER CONFIGURATION AND PERFORMANCE ON HYBRID SULFUR PROCESS NET THERMAL EFFICIENCY. United States.
Gorensek, M. Fri . "EFFECT OF ELECTROLYZER CONFIGURATION AND PERFORMANCE ON HYBRID SULFUR PROCESS NET THERMAL EFFICIENCY". United States. doi:. https://www.osti.gov/servlets/purl/901320.
@article{osti_901320,
title = {EFFECT OF ELECTROLYZER CONFIGURATION AND PERFORMANCE ON HYBRID SULFUR PROCESS NET THERMAL EFFICIENCY},
author = {Gorensek, M},
abstractNote = {Hybrid Sulfur cycle is gaining popularity as a possible means for massive production of hydrogen from nuclear energy. Several different ways of carrying out the SO{sub 2}-depolarized electrolysis step are being pursued by a number of researchers. These alternatives are evaluated with complete flowsheet simulations and on a common design basis using Aspen Plus{trademark}. Sensitivity analyses are performed to assess the performance potential of each configuration, and the flowsheets are optimized for energy recovery. Net thermal efficiencies are calculated for the best set of operating conditions for each flowsheet and the results compared. This will help focus attention on the most promising electrolysis alternatives. The sensitivity analyses should also help identify those features that offer the greatest potential for improvement.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Mar 16 00:00:00 EDT 2007},
month = {Fri Mar 16 00:00:00 EDT 2007}
}

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  • The Hybrid Sulfur (HyS) cycle (Fig. 1) is one of the simplest, all-fluids thermochemical cycles that has been devised for splitting water with a high-temperature nuclear or solar heat source. It was originally patented by Brecher and Wu in 1975 and extensively developed by Westinghouse in the late 1970s and early 1980s. As its name suggests, the only element used besides hydrogen and oxygen is sulfur, which is cycled between the +4 and +6 oxidation states. HyS comprises two steps. One is the thermochemical (>800 C) decomposition of sulfuric acid (H{sub 2}SO{sub 4}) to sulfur dioxide (SO{sub 2}), oxygen (O{submore » 2}), and water. H{sub 2}SO{sub 4} = SO{sub 2} + 1/2 O{sub 2} + H{sub 2}O. The other is the SO{sub 2}-depolarized electrolysis of water to H{sub 2}SO{sub 4} and hydrogen (H{sub 2}), SO{sub 2} + 2 H{sub 2}O = H{sub 2}SO{sub 4} + H{sub 2}, E{sup o} = -0.156 V, explaining the 'hybrid' designation. These two steps taken together split water into H{sub 2} and O{sub 2} using heat and electricity. Researchers at the Savannah River National Laboratory (SRNL) and at the University of South Carolina (USC) have successfully demonstrated the use of proton exchange membrane (PEM) electrolyzers (Fig. 2) for the SO{sub 2}-depolarized electrolysis (sulfur oxidation) step, while Sandia National Laboratories (SNL) successfully demonstrated the high-temperature sulfuric acid decomposition (sulfur reduction) step using a bayonet-type reactor (Fig. 3). This latter work was performed as part of the Sulfur-Iodine (SI) cycle Integrated Laboratory Scale demonstration at General Atomics (GA). The combination of these two operations results in a simple process that will be more efficient and cost-effective for the massive production of hydrogen than alkaline electrolysis. Recent developments suggest that the use of PEMs other than Nafion will allow sulfuric acid to be produced at higher concentrations (>60 wt%), offering the possibility of net thermal efficiencies around 50% (HHV basis). The effect of operation at higher anolyte concentrations on the flowsheet, and on the net thermal efficiency for a nuclear-heated HyS process, is examined and quantified.« less
  • Advantages and disadvantages of various coal-gasification processes are discussed, and their thermal efficiencies are calculated. Discussion on the effect of the amount of methane formed in the gasifier on the overall thermal efficiency of the process and on the cost of production of high Btu gas is included. Economics of various coal-gasification processes are also examined. Suitability of the gasification process for production of either pipeline gas or electricity via combustion of low Btu gas is also discussed. The results show that the process producing a gas of higher heating value in the gasifier requires high pressure operation and wouldmore » provide high thermal efficiency for the production of pipeline gas. On the other hand, the process producing gas of lower heating value in the gasifier can be carried out under low pressure and is more suitable for production of low Btu gas necessary for generation of electricity.« less
  • A detailed consideration of the energy flows entering the energy balance on a building space and the effect of random measurement errors on the determination of fenestration performance is presented. Estimates of the error magnitudes are made for a passive test cell and it is shown that a more accurate test facility is necessary for reliable measurements on fenestration systems with thermal resistance in the range 2 to 10 times that of single glazing or shading coefficient less than 0.7. A test facility of this type, the MoWiTT, which has been built at Lawrence Berkeley Laboratory, is described. The effectmore » of random errors in the MoWiTT is discussed and computer calculations of its performance are presented. The discussion shows that, for any measurement facility, random errors are most serious for nighttime measurements, while systematic errors are most important for daytime measurements. It is concluded that, for the MoWiTT, errors from both sources are expected to be small.« less
  • The Hybrid Sulfur (HyS) process is one of the leading thermochemical cycles being studied as part of the DOE Nuclear Hydrogen Initiative (NHI). SRNL is conducting analyses and research and development for the Department of Energy on the HyS process. A conceptual design report and development plan for the HyS process was issued on April 1, 2005 [Buckner, et. al., 2005] , and a report on atmospheric testing of a sulfur dioxide depolarized electrolyzer (SDE), a major component of the HyS process, was issued on August 1, 2005 [Steimke, 2005]. The purpose of this report is to document work relatedmore » to the design and experimental test plan for a pressurized SDE. Pressurized operation of the SDE is a key requirement for development of an efficient and cost-effective HyS process. The HyS process, a hybrid thermochemical cycle proposed and investigated in the 1970s and early 1980s by Westinghouse Electric Corporation, is a high priority candidate for NHI due to the potential for high efficiency and its relatively high level of technical maturity. It was demonstrated in laboratory experiments by Westinghouse in 1978. Process improvements and component advancements that build on that work are being pursued. One of the objectives of the current work is to develop the SDE in order to permit the demonstration of a closed-loop laboratory model of the HyS process. The heart of the HyS process for generating hydrogen is a bank of electrolyzers incorporating sulfur dioxide depolarized anodes. SRNL planned, designed, built and operated a facility for testing single cell electrolyzers at ambient temperature and near atmospheric pressure during the spring and summer of 2005. The major contribution of the SRNL work was the establishment of the proof-of-concept for utilizing the proton-exchange-membrane (PEM) cell design for the SDE operation. Since PEM cells are being extensively developed for automotive fuel cell use, they offer significant potential for cost-effective application for the HyS Process. This report discusses the modifications necessary to the existing SRNL sulfur dioxide depolarized electrolyzer test facility to allow testing at up to 80 C and 90 psig. Because of the need for significant additional equipment and the ability to infer performance results to higher pressures, it recommends delaying further modifications to support testing at up to 300 psig (the commercial goal) until other, higher priority technical issues are addressed. These issues include membrane material selection, component designs, catalyst type and loading, etc. The factors and rationale that should be considered in developing and executing a detailed test matrix for pressurized operation are also discussed. In addition, an electrolyzer assembly design has been developed to allow the testing of different Membrane Electrode Assemblies (MEA's) as part of the planned FY06 HyS Development Program to complete selection of component design specifications for the HyS electrolyzer. MEA's are used in PEM cells to allow intimate contact and minimal resistance between the electrodes and the electrolyte layer. The pressurized electrolyzer assembly presented in this report will facilitate rapid change-out and testing of various MEA designs as part of the electrolyzer development effort.« less