WHEC 16 / June 2006 Lyon France. Development program of a key component of the Iodine Sulfur thermochemical cycle : the SO 3 decomposer

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1 Development program of a key component of the Iodine Sulfur thermochemical cycle : the SO 3 decomposer G. RODRIGUEZ a, J.C. ROBIN b, P. BILLOT c, A. BERJON d, L. CACHON e, P. CARLES f, J. LEYBROS g, F LE NAOUR h, F. PRA i, A. TERLAIN j, P. TOCHON k. a : CEA Cadarache, DEN/CAD/DTN/STPA, Bât 208, St Paul lez Durance, France, gilles.rodriguez@cea.fr b : CEA Cadarache, DEN/CAD/DTN/STPA, Bât 208, St Paul lez Durance, France, jean-charles.robin@cea.fr c : CEA Saclay, DEN/SAC/DDIN, Bât 121,, Gif-sur-Yvette, France, philippe.billot@cea.fr d : CEA Cadarache, DEN/CAD/DTN/STPA, Bât 208, St Paul lez Durance, France, alain.berjon@cea.fr e : CEA Cadarache, DEN/CAD/DTN/STPA, Bât 208, St Paul lez Durance, France, lionel.cachon@cea.fr f : CEA Saclay, DEN/SAC/DPC/DIR, Bât 450N, Gif-sur-Yvette France, philippe.carles@cea.fr g : CEA Marcoule, DEN/VRH/DTEC, Site de Marcoule - BP 171, Bagnols-sur-Cèze, France, jean.leybros@cea.fr h : CEA Grenoble, DRT/LITEN, 17, rue des Martyrs, Grenoble, France, France, francois.le-naour@cea.fr i : CEA Grenoble, DRT/GRETh, 17, rue des Martyrs, Grenoble, France, franck.pra@cea.fr j : CEA Saclay, DEN/SAC/DPC/SCCME, Bât 458, Gif-sur-Yvette France, anne.terlain@cea.fr k : CEA Grenoble, DRT/GRETh, 17, rue des Martyrs, Grenoble, France, patrice.tochon@cea.fr ABSTRACT: The Iodine/Sulfur cycle is considered to be one of the most promising thermochemical cycle for massive hydrogen production. One of the key operation of this process is the sulfuric acid decomposition that requires high temperature (over 800 C). Thus, if the coupling of this thermochemical cycle with high temperature heat delivery (from solar or nuclear source) is envisaged, it is mainly to provide energy during this chemical step. The development of components allowing this chemical step is of main importance and requires today a technological involvement. Indeed, mainly parameters remains uncertain for this key component : - material selection enable to resist to high temperature corrosion and allowing good heat transfer, - selection of the best heat exchanger design to perform this chemical reaction with best efficiency, - selection of best catalyst, - evaluation of mock up design to validate several technological improvements and operating conditions. Therefore CEA has decided to initiate this year the development program for this key component : SO 3 decomposer producing SO 2 and O 2. This paper aims to present this development methodology. KEYWORDS : I/S thermochemical cycle, SO 3 decomposer, nuclear heat coupling. 1 Massive production of hydrogen : process developed at CEA For massive production of hydrogen, CEA s strategy [1] is guided by criteria of sustainable development. Therefore the CEA choice is to favor the processes : - free of greenhouse emissions, - economically competitive : high efficiency processes using high temperature plus the tentative use of low cost technologies, - allowing to meet the needs for transport : design of processes for centralized massive production, - ensuring the energy independency. In that way, CEA is evaluating several production processes that can be divided into three directions : - the thermochemical cycles with a preference for the Iodine Sulfur cycle but keeping interest to sulfur hybrid process or other thermochemical processes, - the High Temperature Electrolysis (HTE), - the production from Biomass with high temperature processes. In parallel of these process development, generic R&D items have been identified that can cover several field of hydrogen production : new material development, membranes and specific components. Moreover CEA has launched an integrated program to choose by 2008/2009 the most promising way to produce massively hydrogen using the heat produced by a Helium cooled Very High Temperature nuclear Reactor [2] [3]. Therefore the CEA roadmap for massive hydrogen production with nuclear heat will allow before 2010 to select the best process with regard to the above criteria to start the design a pilot plant or demonstration facility (see Fig.1). 1/8

2 Figure 1 : The hydrogen production development CEA roadmap (extracted from [1]) 2 The development of the iodine/sulfur process The iodine/sulfur process appears to be the most promising thermochemical cycle for massive hydrogen production in terms of technical feasibility, suitability with heat provided by high temperature Helium reactor, economical competitiveness, absence of CO 2 gas emission [4] [5]. The iodine/sulfur process is based on a combination of three chemical reactions leading to water splitting ; all other chemical products are recycled. This process requires high temperature for one section of the set of chemical reactions : the sulfuric acid decomposition, which justify its coupling with nuclear heat (see Fig. 2) O 2 H 2 SO 4 = H 2 O + SO 2 + 1/2O 2 Principle of the Iodine-Sulphur thermochemical process H 2 SO 4 decomposition (endothermic) Section II Temperature ( C) H 2 SO 4 H 2 O SO 2 HI decomposition HI DISTILLATION H 2 2 HI = H 2 + I 2 Section III 200 x I 2 + SO H 2 O = H 2 SO 4 +2 HI x HI x x I 2 H 2 O H 2 O 0 Bunsen reaction (exothermic) Section I Figure 2 : Principle of the Iodine/sulfur process and range of temperature requirements On this process, CEA has chosen to develop a scientific approach based on : - data acquisition and modeling [6], - small facility development in collaboration with US Department Of Energy [7] (CEA has the responsibility of the development of the Bunsen section), - a preliminary design of a hydrogen production plant coupled to a VHTR, including energy distribution and safety issues [2] [8], 2/8

3 - efficiency and cost analysis based on the previous data [9], - evaluation and comparison in terms of cost and thermal efficiency of the iodine/sulfur process with the hybrid sulfur cycle. This study is done under a European joined program : HYTECH [10], - and the anticipated development of some sensitive components and technology in connection with this process : o membranes separation for HI decomposition, o specific program development for the sulfuric acid decomposition at high temperature using nuclear heat source. Indeed, the development of sulfuric acid decomposition component is deemed to be one of the key factor of the iodine/sulfur process. This component is making the major coupling between the chemical process and the nuclear heat source, it requires the highest temperature range, and will necessitate challenging material performances due to chemical species involved (H 2 SO 4 and derived products such as SO 3 and SO 2 ; high temperature requirement (over 800 C) and high pressure for the heat transportation (Helium at a range of pressure between 50 and 80 bars). The following chapters will present the HYPRO project : demonstration at pilot scale of the feasibility of the I/S process coupled to Helium heat source, and will particularly focus on the development program of the SO 3 decomposition reactor (CERSO 3 component). 3 Development program of the HYPRO project 3.1 The schedule and development objectives of the HYPRO project Objectives of the HYPRO project (HYdrogen PROduction project) are set as follow : - To demonstrate the feasibility of producing hydrogen at pilot scale with I/S process, coupled with high temperature Helium heat source as a representative simulation of coupling a hydrogen production pilot plant with a nuclear reactor. - HYPRO project is situated on the pathway between some laboratory scale development of the I/S process done jointly with US/DOE, and larger industrial pilot coupled with GENIV Very High Temperature Reactors (VHTR). The objective is to perform this demonstration at pilot scale on the Helium loop facility (HELITE) [11], that will be built at CEA/Cadarache research center, able to deliver up to 1 MWth (Fig. 3). Time schedule for HYPRO is foreseen at around 2012 (Fig. 4). Figure 3 : 3D drawing of the HELITE loop - Technological choices selected for the HYPRO project have to be easily extrapolated to a larger scale (i.e. industrial application) including from the viewpoint of capital costs. - In a first step, this feasibility study will be specifically oriented towards the sulfuric acid decomposition because this section remains critical to achieve a coupling between a nuclear reactor providing heat at high temperature range and a thermochemical process. Development of a high temperature heat exchanger reactor for trioxide sulfur decomposition (CERSO 3 ) is therefore on the critical path of the HYPRO project. 3/8

4 Maximum production capacity H2 (Nm3/h) GEN IV project 600 MWth workshop on ANTARES HYPRO Project 10 1 CEA/DOE common lab loop 0, Estimated delivery time Figure 4 : The route to the industrial production of hydrogen with nuclear energy 3.2 The methodology to define best options for CERSO 3 To define best options for CERSO 3, four domains are considered : - process performances requirement for the component and the catalytic kinetic associated to the chemical decomposition reaction, - identification of candidate materials for heat exchanger components (compatibility with respect to temperature range, high pressure level and corrosive materials), - selection of most suitable design for heat exchanger/reactor according to several criteria as efficiency, inspection feasibility, ageing and lifetime performances, safety requirements, etc - integration of a final concept as an industrial prototype (fabrication development). In parallel of this selection criteria, the comparison with the international development of the same design component or equivalent study is investigated to evaluate the different choices and their respective motivations. Finally a cross comparison between the selection based on the above criteria and the existing development worldwide will be made to see if the investigated ways proposed are complementary to international developments or can be optimized in symbiosis through international collaborations Process parameters Sulfuric acid dissociation is the result of two strongly endothermic chemical reaction : H 2 SO 4 = H 2 O + SO 3 H 298 = + 97,54 kj.m -1 (1) SO 3 = SO 2 + 1/2 O 2 H 298 = + 98,92 kj.m -1 (2) The dissociation rate of sulfuric acid to sulfur trioxide is strongly temperature dependant : 50% around 620 K, and over 95% above 800 to 850 K (527 to 577 C). Recent studies [13] have shown that the chemical decomposition of sulfur trioxide is achievable without catalyst at a temperature range over 1300 K (1000 C). Without catalyst the reaction can not occur below 1123 K (850 C). With the use of catalysts (such as Ag-Pd or Fe 2 O 3 ) it has been experimentally demonstrated that the decomposition starts at about 773 K and is almost complete at T = 1100 K. At this temperature range, the kinetic of reaction has not been exactly determined and is indeed extrapolated from other operating conditions. According to this consideration, optimal operating conditions have been settled with a conversion rate around 0.8, in a counter current heat exchanger/reactor. Helium from the reactor (or loop) provides the heat source (inlet = 900 C, P = 50 bars). The process fluid inlet temperature is 750 C and P = 4.3 bars. Nevertheless some developments remains to be done in that technical area : - What are the optimal parameters according to accurate kinetic data, - What are the most efficient catalysts in terms of reaction enhancing, lifetime, catalyst cost, possibility of poisoning, possibility of regeneration, etc - What is the acceptable set of operating parameters, in accordance with some other constraints such as design criteria of the components, best operating conditions target, corrosion limits, lifetime, etc. 4/8

5 3.2.2 Selection of material Material selection for component, including qualification and application, is one of the technical barrier of this project. Some material candidates have been selected based on laboratory scale study [14], see Table 1. But beyond this first selection, the final materials selection will necessitate a larger qualification program before being retained. Principal unit operation Fluids Approximate fluid temperature (K) Material candidates for components Sulfuric acid concentration H 2SO 4 (55 to 65 wt %) 370 to 425 Hastelloy B-2 or C-276, impervious graphite, glass or brick-lined steel Sulfuric acid concentration H 2SO 4 (65 to 75 wt %) 425 to 455 Hastelloy B-2 or C-276, impervious graphite, glass or brick-lined steel Sulfuric acid concentration H 2SO 4 (75 to 98 wt %) 455 to 700 Brick-lined steel, cast iron- 14 wt % Si, SiC, Si3N4 Vapor formation and dehydratation H 2SO 4 + H 2O + SO to 873 Brick-lined steel, cast iron 14 wt % Si, silicide coatings on steel, Hastelloy C Vapor decomposition SO 3 + H 2O + O 2 + SO to 1144 Incoloy 800H with aluminide coating, SiC Gaskets H 2SO 4 + H 2O + SO 3 O 2 + SO to 1144 Depending on temperature range : Gold, Graphite, Teflon, Viton Table 1 : Compatibility material extracted from [14] The following qualification program will be necessary, in agreement with the methodology currently developed for the Intermediate Heat exchanger (IHX) development in the frame of GENIV/VHTR program : - Tensile tests (from room temperature up to 900 C). - Creep tests (at high temperature). - Fatigue and creep-fatigue interaction tests. - Ageing effect on mechanical properties. - Corrosion tests in contact with the chemical product respecting temperature range, pressure, duration. - Thermal expansion evaluation. - Material behavior with respect to radioactive product (tritium diffusion limitation). One additional constraint, for an industrial application, is also the cost of the base material Component design Heat exchanger/reactor design selection will be based upon several parameters : - High efficiency of the heat transfer associated to the minimization of the surface area, - Ability to realize a good contact of the chemical products with the catalyst. - Ability to inspect and repair the component. Ability to replace the catalyst. - Selection of an innovative solution (i.e. compact heat exchanger), or a more classic design (tube and shell), or orientation toward compromise in term of innovative development. Today, US/DOE has decided to focus on a compact ceramic (SiC base) IHX design [17]. In the frame of the ANTARES program [12], CEA has orientated its research studies on two kinds of innovative concepts for the HTR/IHX : Printed Circuit Heat Exchanger (PCHE) technology, and Plate Fin Heat Exchanger (PFHE). These options have to be evaluated for the SO 3, for example by comparison with other technical options proposed today by JAEA [18], [19] : shell and SiC plate heat exchanger/reactor. It must be noted also that, in the frame of a CEA study, the design calculation of a tube and shell Heat Exchanger/reactor which can be connected with the HELITE Helium loop providing 1 MWth has been done. This design calculation has shown that a heat exchanger tube and shell design calculated according to the TEMA standard specifications [20], could comply with the reaction conditions and heat transfer demand (Fig. 5). 5/8

6 3.2.4 Fabrication development For this part, screening of the materials remains the initial step, with the associated selection. Then samples will be fabricated and tested to perform brazing, welding tests, to define creep damage, rupture behavior, ageing, identify potential oxidation and sulfuration, etc In parallel and depending on the type of design pre-selected, small-scale module tests could be built. Test series to cover will be the following : performance (heat transfer efficiency and pressure drop), flow distribution, pressure and thermal cycling, vibration, structural integrity (leak tightness), thermal expansion, correct start-up and shutdown of the component. The benches must provide heat source and be able to comply with the safety requirements linked with the products used (sulfuric acid, SO 3, SO 2 ) in terms of safety requirements. In that frame the international collaboration and the share of high temperature facilities (from solar source or simulated nuclear source) is an issue. The fabrication of the final mock-up (the CERSO 3 component) is the final stage, devoted to be coupled with the CEA/HELITE loop (Fig. 5). At this scale, main objectives will be as follow : - provide a demonstration at a large scale of the feasibility of the coupling of the I/S process to a Helium heat source, - realize endurance testing, - realize transient test such as fast shutdown in case of loss of the heat source and/or reactor scram, - appreciate the handling and operating constraints on preindustrial prototype, - appreciate the construction technological difficulties and barriers of such as prototype, - evaluate the potential adaptability of the I/S process to the fluctuation of the heat source (small fluctuations, daily fluctuation, or yearly strategy of the reactor operation), - in parallel, the capital cost of the mock up will allow to provide better accuracy on the cost evaluation of a I/S workshop (50 to 60 MWth) connected to a HTR [21]. CERSO 3 component focusing on design of SO 3 decomposition reactor LT Cooler 950 C < 850 C Electric Heater 500 C 50 C 450 C Recuperator HT Test Section 150 C 100 C Circulator Filter 900 C I/S Process 850 C H 2 SO 4 decomposition HT Cooler HELITE : ~ 1 MW Figure 5 : The coupling of CERSO 3 component coupled to HELITE loop 3.3 The CERSO 3 specifications To proceed a this CERSO 3 development, a working team composed of CEA specialist in their respective field (engineering, process, heat exchanger design, corrosion, fabrication development and innovative material qualification) have been settled. Objectives are to define the CERSO 3 specifications, the R&D program development and to achieve the CERSO 3 realization and implementation on the HELITE loop. At the present stage, the SO 3 decomposition heat exchanger/reactor performance specifications have been defined. They are summarized in Table 2. 6/8

7 Input Specifications required Admitted fluctuations Inlet reactive gas H 2SO 4 (gas) 0.80% wt ± 20% rel SO 3 (gas) 68.3% wt ± 10% rel SO 2 (gas) 0.06% wt ± 100% rel H 2O (gas) 30.9% wt ± 10% rel Temperature 750 C ± 50 C Pressure 4.25 bars 4 to 7 bars Flow rate 0.14 kg/s 0.1 to 0.2 kg/s Heat source inlet Composition He He / N 2 Temperature 900 C ± 50 C Pressure 50 bars ± 5 bars Performance SO 3 Conversion yield 85% 50% - 100% abs Table 2 : Specifications of the CERSO 3 component Upon these specifications, the next coming step will be an evaluation grid to determine the technical ways selected and the associated R&D development in coherence with the international program and the CEA programs on IHX development for the VHTR (material investigation and qualification). By anticipation of this evaluation study; a qualification program of a SiC/SiC compact heat exchanger (small scale module) has started this year at CEA/GRENOBLE. This mock-up will be first tested in 2006 on a High temperature air loop called CLAIRE, located at CEA/Grenoble [23]. 4 The SUSHYPRO platform It must be noted that CEA in collaboration with CIEMAT (Spain), ENEA (Italy) and DLR (Germany) intend to develop a European platform to test and develop high temperature hydrogen production processes. This program is called SUSHYPRO : SUStainable HYdrogen PROduction. This European platform initiative proposes a synergy between solar source and nuclear high temperature source for a common goal : the massive production of hydrogen by high temperature processes (thermochemical, steam electrolysis, or hybrid). This European platform is planned from The HYPRO project and particularly the development of the CERSO 3 component aims to be included in this European program context. References Figure 6 : The SUSHYPRO logo [1] : F. LE NAOUR, P. ANZIEU, An overview of the CEA road-map for hydrogen production, Third Information Exchange Meeting on the Nuclear Production of Hydrogen, Japan Atomic Energy Research Institute, Ibaraki-ken, Japan, 5-7 October [2] : P. ANZIEU, P. AUJOLLET, D. BARBIER, A. BASSI, F. BERTRAND, A. LE DUIGOU, J. LEYBROS, G. RODRIGUEZ, Coupling a Hydrogen production process to a nuclear reactor, NEA, Third Information Exchange Meeting on the Nuclear Production of Hydrogen, Japan Atomic Energy Research Institute, Ibaraki-ken, Japan, 5-7 October [3] : X. VITARD, P. CARLES, A. LE DUIGOU, Thermochemical production of hydrogen using nuclear heat: a survey of technical and economical issues, Proceeding of GLOBAL 2005, Tsukuba, Japan, Oct 9-13, [4] : R. E. UHRIG, Producing hydrogen using nuclear energy, Proceedings International Hydrogen Energy Congress and Exhibition IHEC, 2005, Istanbul (Turkey), July, [5] : B.C.R. EWAN, R.W.K. Allen, A figure of merit assessment of the routes to hydrogen, International Journal of Hydrogen Energy 30 (2005), [6] : : S. GOLDSTEIN, J.M. BORGARD, X. VITARD, Upper bound and best estimate of the efficiency of the iodine sulfur cycle, International Journal of Hydrogen Energy, vol. 30 (2005), pp [7] : P. PICKARD et al., Sulfur-iodine thermochemical cycle, DOE Hydrogen Program, 2005 Annual progress report, Chap IV.G.2, [8] : : A. BASSI et al, Massive H2 production with nuclear heating, safety approach for coupling A VHTR with an Iodine Sulfur process cycle, ICHS, Pisa, September 8-10, [9] : F. WERKOFF, S. AVRIL, C. MANSILLA, J. SIGURVINSSON, Processes of hydrogen production, coupled with nuclear reactors : economic perspectives, ENC 2005, paper n 227, Versailles (France), December 11-14, [10] : A. LE DUIGOU et al., HYTECH : a search for a long term massive hydrogen production route, Proceedings International hydrogen Energy Congress and Exhibition, IHEC 2005, Istanbul, Turkey, July, /8

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