University of South Carolina Scholar Commons Theses and Dissertations 2018 Dynamic Simulation of a Solar Powered Hybrid sulfur Process for Hydrogen Production Satwick Boddu University of South Carolina Follow this and additional works at: https://scholarcommons.sc.edu/etd Part of the Chemical Engineering Commons Recommended Citation Boddu, S.(2018). Dynamic Simulation of a Solar Powered Hybrid sulfur Process for Hydrogen Production. (Master's thesis). Retrieved from https://scholarcommons.sc.edu/etd/4820 This Open Access Thesis is brought to you by Scholar Commons. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. Dynamic Simulation of a Solar Powered Hybrid sulfur Process for Hydrogen Production by Satwick Boddu Bachelor of Technology, Indian Institute of Technology - Guwahati, 2014 Submitted in Partial Fulfillment of the Requirements For the Degree of Master of Science in Chemical Engineering College of Engineering and Computing University of South Carolina 2018 Accepted by: Edward P. Gatzke, Director of Thesis Stanford G. Thomas, Reader John W. Weidner, Reader Cheryl L. Addy, Vice Provost and Dean of the Graduate School Abstract The Hybrid Sulfur process is a thermo-electrochemical cycle used to produce hydrogen from water. The process requires a high temperature energy source for H 2SO 4 decomposition with temperature reaching 800°C. This step is followed by SO 2 - depolarized water electrolysis. Using solar energy as the high temperature energy source allows for efficient environmentally friendly production of hydrogen. This method is an alternative to traditional photovoltaic electrolysis for hydrogen production. Making the process economically competitive is a major challenge. Operating the process with changes in the availability of solar energy also increases process complexity. The dependence of the process on solar energy requires analysis of the electrolysis and decomposition sections separately. The Hybrid Sulphur process was modelled in ASPEN Plus for a target production rate of 500 gram moles of H 2 per second. The process simulation includes H2SO 4 decomposition and O 2 separation of the SO 2/O 2 product from the H 2SO 4 decomposition. Given the transient nature of solar energy utilized for the decomposition reaction, analysis of the dynamics of the separation section is of primary importance. A dynamic simulation was developed with control schemes to stabilize the process. This simulation was analyzed for step changes in feed flowrate corresponding to the target hydrogen production rate of 500 gram moles per second. With the proposed controller ii configuration, the separation process exhibits time constants ranging from approximately 40 min for a step change in the overall production rate from 100% to 50%. The settling time for the same production rate change is approximately 60 min. The separation system can accommodate the system operating a 0% capacity by maintaining column flow with dilution water. At zero feed the process is functional but it just the recycles the water from the electrolyzer section through the system making it entirely redundant and uneconomical. To avoid shutdown of the separation section at low production rates, this work proposes to include holdup storage tanks for the product streams from the decomposition section. This will allow the distillation columns to run continuously, but the separation system must accommodate variable feed rates. Dynamic variation in the separation section caused by changes in the solar-powered decomposition reactor may thus be mitigated by use of gas and liquid holdup tanks. The results of these simulation prove vital in analysis of the viability of the future for large scale hydrogen production through high temperature Hybrid Sulphur process. iii Table of Contents Abstract ................................................................................................................................ii List of Figures ....................................................................................................................... v List of Tables ....................................................................................................................... vi Chapter 1. Introduction ...................................................................................................... 1 Chapter 2. Chemistry of Hydrogen Production .................................................................. 4 2.1 Hybrid Sulphur Cycle ................................................................................................. 4 2.2 The Bayonet Decomposition Reactor ....................................................................... 7 Chapter 3. Simulation ....................................................................................................... 10 3.1 Steady state simulation ........................................................................................... 10 3.2. Dynamic simulation ................................................................................................ 15 Chapter 4. Results ............................................................................................................. 19 4.1 Steady state results ................................................................................................. 19 4.2 Energy ...................................................................................................................... 19 4.3 Dynamic simulation ................................................................................................. 20 4.4. Analysis of the Dynamic response ......................................................................... 32 4.5. Limitations of the Simulation ................................................................................. 34 Chapter 5. Conclusion ...................................................................................................... 36 Chapter 6. Future Work .................................................................................................... 37 References ........................................................................................................................ 38 Appendix A: Aspen plus results ........................................................................................ 40 iv List of Figures Figure 2. 1. Schematic diagram of an SO 2 – depolarized electrolyzer ................................ 6 Figure 2. 2. Schematic diagram of Bayonet Decomposition Reactor ................................. 9 Figure 3. 1. Schematic diagram of Hybrid Sulphur process (high temperature section) . 12 Figure 3. 2. Hybrid Sulphur process dynamic Simulation ................................................. 13 Figure 3. 3. Gas Separation section .................................................................................. 14 Figure 3. 4. Control schemes in the Aspen Dynamics simulation ..................................... 17 Figure 3. 5. Control schemes in the Aspen Dynamics simulation ..................................... 18 Figure 4. 1. Temperature profile of the decomposition reactor (step change: +25%) .... 21 Figure 4. 2. Sump Liquid level profile in the O 2 distillation column (step change: +25%) 22 Figure 4. 3. Pressure profile of the O 2 distillation column (step change: +25%).. ............ 23 Figure 4. 4. Liquid level profile of the SO 2 distillation column (step change: +25%). ....... 24 Figure 4. 5. Pressure profile of the SO 2 distillation column (step change: +25%). ........... 25 Figure 4. 6. Temperature profile of the decomposition reactor (step change: -50%) ..... 26 Figure 4. 7. Sump Liquid level profile in the O 2 distillation column (step change: -50%). 27 Figure 4. 8. Pressure profile of the O 2 Distillation column (step change: -50%). ............. 28 Figure 4. 9. Sump Liquid level of the SO 2 distillation column (step change: -50%). ......... 29 Figure 4. 10. Pressure profile of SO 2 distillation column (step change: -50%). ................ 30 Figure 4. 11. Final product stream at zero feed flow rate ................................................ 31 v List of Tables Table 4. 1. Utilities for the steady state SO 2 production rate of 1161 Kmol/hr ............... 19 Table 4. 2. Tank sizes for liquid and gas storages for excess decomposition products ... 33 Table 4. 3. Results of control loop response for vital blocks ............................................ 34 Table A. 1 Components specified in Aspen Plus ............................................................... 40 Table A. 2 Global reactions ............................................................................................... 40 Table A. 3 High Temperature reactions ............................................................................ 41 Table A. 4 Decomposition output stream ......................................................................... 42 Table A. 5 Aspen results for the Output stream ............................................................... 44 Table A. 6 Results of Energy analysis on Aspen Plus ........................................................ 45 Table A. 7 The Gaseous stream entering the gas separation section .............................. 46 Table A. 8 The liquid stream entering the separation section ......................................... 48 Table A. 9 Outlet stream after oxygen separation ..........................................................