Hydrogen Production by Thermochemical Water-splitting is Process Utilizing Heat From High...

7/31/2019 Hydrogen Production by Thermochemical Water-splitting is Process Utilizing Heat From High Temperature Reactor

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WHEC 16 / 13-16 June 2006 Lyon France

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Hydrogen production by thermochemical water-splitting IS processutilizing heat from high-temperature reactor HTTR

Nariaki SAKABA a,b , Seiji KASAHARA b, Hirofumi OHASHI a , Hiroyuki SATO a , Shinji KUBO b, Atsuhiko TERADA b, Tetsuo NISHIHARA b, Kaoru ONUKI b, Kazuhiko KUNITOMI a

a HTGR Cogeneration Design and Assessment Group, Nuclear Science and Engineering Directorate(Japan Atomic Energy Agency (JAEA), Oarai, Higashiibaraki, Ibaraki, 311-1393, Japan,

[email protected])bIS Process Technology Group, Nuclear Science and Engineering Directorate, JAEA

ABSTRACT:

High-temperature reactors (HTRs) are particularly attractive due to their wide industrial application fromelectricity generation to hydrogen production. The Japan Atomic Energy Agencys (JAEAs) HTTR, which is

the first HTR in Japan, attained its maximum reactor-outlet coolant temperature and successfully delivered 950C coolant helium outside its reactor vessel. A hydrogen production system based on thethermochemical water-splitting iodine sulphur (IS) process is planned to be connected to the HTTR in thenear future. This will establish the hydrogen production technology with an HTR, including the systemintegration technology for connection of hydrogen production system to HTRs. It will probably be the worldsfirst demonstration of hydrogen production directly using heat supplied from an HTR. The HTTR-IS systemdesign was launched from a conceptual design in 2005. This paper shows the summary of the HTTR, planfor developing the IS process in JAEA, thermal efficiency evaluation for the HTTR-IS system, etc. Theverification of the hydrogen production by the HTTR-IS system by using heat from a nuclear reactor is greatly expected to contribute to the commercialization of nuclear hydrogen in coming hydrogen society.

KEYWORDS : Nuclear hydrogen, IS process, VHTR, HTR, HTTR.

1. Introduction

High Temperature Reactors (HTRs) are particularly attractive due to those inherent safety, economic viability,high efficiency, very high burnup, and wide industrial application (from electricity generation to hydrogenproduction). They are expected to play a dominant role in the future hydrogen society. The Japan AtomicEnergy Agencys (JAEAs) High Temperature Engineering Test Reactor (HTTR), which is the first HTGR inJapan, attained its maximum reactor-outlet coolant temperature and successfully delivered 950C coolanthelium outside its reactor vessel [1]. The rector-outlet coolant temperature of 950C makes it possible toextend HTR use beyond the field of electric power. Also, highly effective power generation with a high-temperature gas turbine becomes possible, as does hydrogen production from water.This paper describes the summary of the HTTR, R&D on the thermochemical water-splitting iodine sulphur (IS) process as well as a preliminary project plan and conceptual design of the HTTR-IS system.

2. Summary of the HTTR-IS system

2.1 Summary of the HTTR

As the HTTR is the first HTR in Japan and a test reactor, it has following purposes:

Establishment of basic HTGR technologies, Demonstration of HTGR safety operations and inherent safety characteristics, Demonstration of nuclear process heat utilization, Irradiation of HTGR fuels and materials in an HTGR core condition, and, Provision of testing equipment for basic advanced studies.

In order to demonstrate the nuclear process heat utilization, the intermediate heat exchanger (IHX) isequipped in the cooling system to supply high-temperature helium gas to a process heat application system


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being coupled to the HTTR in the future. The detailed HTTR design was already reported [2] and the maincooling system is described in this chapter.

As shown in Fig. 1 , the cooling system of the HTTR consists of a main cooling system operating at normaloperations; and an auxiliary cooling system and a vessel cooling system, the engineered safety features,operating after a reactor scram to remove residual heat from the core. The main cooling system, whichconsists of a primary cooling system, a secondary helium cooling system, and a pressurised water coolingsystem, removes heat generated in the core and dissipates it to the atmosphere by a pressurised water air cooler. The primary cooling system consists of an IHX, a primary pressurised water cooler (PPWC), aprimary concentric hot-gas-duct, etc. Primary coolant of helium gas from the reactor at 950C maximumflows inside the inner-pipe of the primary concentric hot-gas-duct to the IHX and PPWC. The primary heliumis cooled to about 400C by the IHX and PPWC and returns to the reactor flowing through the annulusbetween the inner- and outer-pipes of the primary concentric hot-gas-duct. The HTTR has two operationmodes. One is the single-loaded operation mode using only the PPWC for the primary heat exchange.

Almost all the basic performance of the HTTR system has been confirmed by the single-loaded operationmode. The other is the parallel-loaded operation mode using the PPWC and IHX. In a single-loadedoperation mode the PPWC removes 30MW of heat and in a parallel-loaded operation mode the PPWC andIHX remove 20MW and 10MW, respectively. It is planned to utilize the secondary helium gas of the IHX for the thermochemical water-splitting IS process and the secondary pressurised water cooler (SPWC) will bereplaced to the main components, e.g. SO 3 decomposer, HI decomposer, of the IS process.

Reactor containment vessel

Vessel cooling system

AHX AGC

Auxiliary water

air cooler

Auxiliary water

pump Auxiliary cooling system Main cooling system

PGC

IHX

PPWC

SPWC

SGC

PGC Reactor

IHX : Intermediate heat exchanger PPWC : Primary pressurized

water cooler PGC : Primary gas circulator SPWC : Secondary pressurized

water cooler SGC : Secondary gas circulator

AHX : Auxiliary heat exchanger AGC : Auxiliary gas circulator

Pressurized water pump

Pressurized water air cooler

( 3)


Vessel cooling system

AHX AGC

Auxiliary water

air cooler

Auxiliary water

pump Auxiliary cooling system Main cooling system

PGC

IHX

PPWC

SPWC

SGC

PGC Reactor

IHX : Intermediate heat exchanger PPWC : Primary pressurized

water cooler PGC : Primary gas circulator SPWC : Secondary pressurized

water cooler SGC : Secondary gas circulator

AHX : Auxiliary heat exchanger AGC : Auxiliary gas circulator

Pressurized water pump

Pressurized water air cooler

( 3)

Fig. 1 Schematic diagram of the reactor cooling systems of the HTTR

2.2 R&D on the IS Process

Thermochemical water-splitting is the method of obtaining hydrogen from water that consists of severalreactions. The concept was first proposed in 1960s with the thermodynamic study [3], and since then,various processes have been proposed. The IS process [4] is one of the processes that have beenresearched intensively. The IS process consists of the following chemical reactions:

I2 + SO 2 + 2H 2O 2HI + H 2SO 4 (the Bunsen reaction) (1)H2SO 4 H2O + SO 2 + 0.5O 2 (2)2HI H2 + I2 (3)

The thermodynamically optimum temperature for decomposition of ideal gas of SO 3 made by vaporization of H2SO 4, which is the highest temperature reaction, is 779 C [5]. The optimum temperature in actual processcondition is considered to be near of that. Therefore the IS process is a candidate process of utilization of the HTGR heat.

Table 1 shows the overview of the R&D on the IS process in JAEA. The R&D started in the middle of 1980s.The main goal of the lab stage study was to show feasibility of the continuous hydrogen production. Theinitial stage was completed by the demonstration of the continuous and stochiometric hydrogen production of 1 NL/h for 48 hours [6].


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Table 1 Overview of the R&D on the IS process in JAEALab stage Bench stage

Pilot stage(Tentative)

HTTR-IS stage(Tentative)

Durationmiddle of

1980s ~ 1997 1998 ~ 2005 2006 ~ 2010 2009 ~ 2014

Hydrogen production rate[Nm 3 /h]

0.001 0.05 30 1000

Heat supply Electric Electric Helium heated electrically Helium heated by HTTR

Material of apparatus Glass GlassIndustrial materials

Industrial materials

Process pressure Atmospheric Atmospheric High pressure High pressure

In the bench-scale study, the second stage, the following research fields were investigated:

To control the process for long-time stable hydrogen production, To process HI decomposition procedure using membrane technologies, and, To screen corrosion resistant materials for the construction of the process.

In achieving long-term stable hydrogen production, automated reaction control methods of the Bunsenreaction and devices were proposed. A bench-scale test apparatus was constructed for the verification of the methods and devices. Fig. 2 shows the simplified flowsheet of the test apparatus [7]. The IS processwas split into three procedures; Bunsen reaction procedure (Bunsen PROC), H 2SO 4 decompositionprocedure (H 2SO 4 PROC) and HI decomposition procedure (HI PROC). H 2SO 4 solution and HIx solution(solution of HI, I 2 and H 2O) obtained in the Bunsen reactor are separated. Each of the solution isconcentrated, vaporised and decomposed in H 2SO 4 PROC and HI PROC, respectively. H 2 and O 2 areobtained as products and other compounds return into the Bunsen reactor. The control methods anddevices were tested in the demonstration experiment with the hydrogen production rate of 31 NL/h for 175hours [2] [7]. The results verified the effectiveness of the devised control method for long-term stableoperation.Efficient separation of HI from the HIx solution and enhancement of the HI conversion ratio are effective toimprove thermal efficiency. As for the former requirement, HIx solution was successfully concentrated toover the pseudo-azeotropic composition by the beaker size experiment of electro-electrodialysis (EED) [8].The result shows highly concentrated HI can be obtained in the following distillation by application of the cell.

As for the latter, a hydrogen permselective membrane reactor (HPMR) achieved to improve the HI one-passconversion ratio to over equilibrium ratio by extracting hydrogen from reaction field [9].Corrosion resistant materials are necessary because corrosive compounds are used at high temperatures inthe IS process. Selection of the materials by corrosion tests has been carried out [10]. Prototypes of heatexchanging blocks for the H 2SO 4 vaporiser [11] and SO 3 decomposer [12] were fabricated by using SiCceramics, which show corrosion resistance in liquid phase environments. Structural integrity of these blockswas confirmed by thermal stress analysis as well as leakage tests of the block for H 2SO 4 vaporiser under horizontal loading were performed [11].

H2SO 4concentrator Liquid-liquid

separator

H20.5O 2 H2O

SO 3 decomposer (SO 3 SO2 +

0.5O 2)

H2SO 4vaporizer H2SO 4

SO 3 + H 2O)

HIxsolution

H2SO 4solution

HI distillationcolumn

HI decomposer (2HI H2 + I 2)

Bunsen reactor (I2 + SO 2 + 2H 2O 2HI + H 2SO4)

H2SO 4 purifier HIx

purifier

H2SO 4 cooler,separator

HI recoverycolumn

H2SO4 PROC Bunsen PROC HI PROC

Refluxdrum

H2SO 4concentrator Liquid-liquid

separator

H20.5O 2 H2O

SO 3 decomposer (SO 3 SO2 +

0.5O 2)

H2SO 4vaporizer H2SO 4

SO 3 + H 2O)

HIxsolution

H2SO 4solution

HI distillationcolumn

HI decomposer (2HI H2 + I 2)

Bunsen reactor (I2 + SO 2 + 2H 2O 2HI + H 2SO4)

H2SO 4 purifier HIx

purifier

H2SO 4 cooler,separator

HI recoverycolumn

H2SO4 PROC Bunsen PROC HI PROC

Refluxdrum

Fig. 2 Simplified flowsheet of the bench-scale test apparatus [7]


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The pilot stage is to follow the bench stage. Objectives of the pilot stage study are described as follows [10]:

Construction of a pilot test plant made of industrial materials and completion of hydrogen productiontest utilizing electrically-heated helium gas as the process heat supplier,

Development of analytical code system for the HTTR-IS system safety case review, Component tests to assist the hydrogen production test and to improve the process performance for

the commercial plant, and, Design study of the HTTR-IS system.

Heat from electrically heated helium is supplied to components such as SO 3 decomposer, H 2SO 4 vaporiser and HI decomposer. Verification of developed control procedure, obtaining operation data useful for verification of analytical codes, verification of integrity of apparatuses for corrosive environments, andfeasibility of newly added apparatuses are expected through the hydrogen production tests.Computational codes were selected and an analytical code system was constructed based on the CAD/CAE[13]. This analytical code system is to be developed in the pilot stage for the design of the HTTR-IS system.The code will be utilized in the evaluations of the total process, materials, mechanical strength, thermalhydraulics, and safety case analysis.

Component test apparatuses were constructed and experiments utilizing them have been carried out in order to improve the process performances. For instance, H 2SO 4 thermal-hydraulic test loops and a catalyst testapparatus for SO 3 decomposition were fabricated with corrosion resistant materials [14] . Data of, for example, performance and integrity of components, visualisation of boiling H 2SO 4, and performance of catalysts for SO 3 decomposition is expected. Important data for scaling-up and for the improvement of HIconcentration efficiency are expected to be taken by larger scale EED cells [13]. Corrosion rates of somestructural materials were evaluated in Bunsen reaction environment as a part of the component test [15] .Design study of the HTTR-IS system where the HTTR and the IS process will be connected by the IHX arecarried out during the pilot stage period.

In the HTTR-IS stage, the integration of the HTTR and IS process will be conducted. The preliminaryconceptual design of the HTTR-IS system has launched in 2005 in order to complete its design by the 2010.

3. Conceptual design of the HTTR-IS system

A hydrogen production system based on the IS process is planned to be connected to the actual high-temperature reactor HTTR in the near future. This will establish the hydrogen production technology with anHTR including the system integration technology for connection of hydrogen production system to HTRs. Itwill probably be the worlds first demonstration of hydrogen production directly using heat supplied from anuclear system. The HTTR-IS system aims to:

Establish procedures on safety design and evaluation, Establish the technology on key high-temperature components, such as high-temperature valves,

high-temperature bellows, Establish the control technology for both of the IS process and reactor, Add to experience of construction, operation, and maintenance, and,

Show the roadmap towards the commercialisation of nuclear hydrogen production systems by the ISprocess including cost evaluation of the produced hydrogen by the VHTR (Very High TemperatureReactor) which is one of the Generation IV reactor candidates.

The requirements of users, such as efficiency, amount and cost of produced hydrogen, safety scenario of theconnection between a nuclear reactor and chemical plant, should be satisfied or should be shown its way tocommercial reactors by the HTTR-IS system development. Since the secondary helium of the HTTR will beutilized in this system, the possibility of utilization of a non-nuclear class IS system as a chemical plant isinvestigated. Hydrogen explosion, tritium transfer, etc. will be evaluated in order to separate IS process fromnuclear facilities by high-temperature valves.

Development of the HTTR-IS system started from a conceptual design. Available structure of the systemand its heat mass balance is evaluated initially. Basic design will be performed from design of apparatuses,

kinetic analysis, and design of instrumentation and control systems in 2007. Safety case studies, detaileddesign, cost evaluation, and risk evaluation will be carried out in 2008. The safety analysis codes will bevalidated by using the component tests data and IS pilot plant operation data. The know-how of the pilotplant tests will be applied to the HTTR-IS system design. In 2009, safety assessment will be started. The


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assessment will possibly need about two years, while some studies for the higher efficiency of the HTTR-ISsystem continues. The design of the HTTR-IS system will be completed until 2010. Separation technologyof hydrogen will also be expected to be applied. The development schedule of the HTTR-IS system isshown in Table 2 .

Table 2 Development schedule of the HTTR-IS system

2005

Conceptual Design

Cost Evaluation

System Flow EvaluationDetermination of Number of

Main Component Heat Mass Balance

Plot Planning Apparatus

Design

Abnormal Event Study (HAZOP) (IS process)

Abnormal Event Study (Reactor)

Code Validationby Indivisual

Component TestsFailure Rate

Data CollectionRepresentative

Abnormal Event

2006 2007 2008 2009

DesignStage

Detailed Design, Cost Evaluation, Rationalization DesignFablication Design

Determination of Flowsheet

Detail

Fablication DesignCode Development (Coupling

with Reactor & IS process)

Detailed Apparatus DesignSeismic Design

Component Design Rationalization Design

Safety AnalysisSafety Case Review by

Government

Basic Design

Code Validation by Pilot Plant Test

Design of Instrumentation &Control System

Prior to the abnormal event study, the number of main apparatuses in the IS process should be decided.The most severe event will be selected as a representative event in the HTTR-IS system. Then the eventwill be compared with the abnormal transient of the HTTR secondary system which was already evaluated

during the HTTR design stage [2]. The IS process is designed conceptually using results of the componenttests performed from 2005 and the concept of the GTHTR-300H [16] which is the Japanese future HTRdesigned by JAEA. In order to achieve higher efficiency in the HTTR-IS system, for instance, concentrationof hydrogen iodide will be studied.

The verification of the hydrogen production by the HTTR-IS system by using heat from a nuclear reactor isgreatly expected to contribute to the commercialisation of nuclear hydrogen in coming hydrogen society.Fig. 3 shows the schematic diagram of a candidate HTTR-IS system [17] . Heat produced by the HTTR coreis transferred to the secondary helium gas at the IHX. The secondary helium flows through the inner-pipe of the concentric hot-gas-duct and a high-temperature valve, and supplies heat to the components of the ISprocess such as SO 3 decomposer, H 2SO 4 vaporiser and HI decomposer. Finally, after cooled by the steamgenerator and a helium cooler, the secondary helium is pressurised by the helium gas circulator. Secondaryhelium returns to the IHX through the outer-pipe of the concentric hot-gas-duct.

Secondaryhelium gascirculator

IHX


(inside) (o utside)

Helium gascooler

(Legend)F F

M

M

M

M

F

Steamgenerator Secondary helium

purificationsystem

MM

MM

SO 3decomposer

H2SO 4vaporizer

HIdecomposer

MMFF

Secondary helium purification

system

Cooling water

Cooling water

Cooling water

By-pass diverter valveDiverter valve

8.81G

905T

4.01P

8.81G

905T

4.01P

8.81G

128T

4.04P

8.81G

128T

4.04P

Flow rate [t/h]G

Temperature [ OC]T

Pressure [MPa (gauge)]P

Flow rate [t/h]G

Temperature [ OC]T

Pressure [MPa (gauge)]P

15G

105T4.05P

15G

105T4.05P

15G

95T

3.90P

15G

95T

3.90P

8.81G

104T

4.05P

8.81G

104T

4.05P

8.81G

875T

3.99P

8.81G

875T

3.99P 8.81G

475T

3.94P

8.81G

475T

3.94P

8.81G

275T

3.92P

8.81G

275T

3.92P

8.81G

88T

3.91P

8.81G

88T

3.91P

Cooling water

Fig. 3 Schematic diagram of a candidate HTTR-IS system [17]


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Chemical impurity in the secondary helium will be removed by the secondary helium purification system. Inorder to construct the IS process by utilizing the non-nuclear standard, tritium permeation is one of the mostimportant key parameters. The secondary helium purification system will be re-designed and will bereplaced by using the newly developed chemistry control method [18]. The secondary pressure should becontrolled to be higher than that of the primary in order to avoid the graphite-core oxidation as does in theHTTR. The pressure is kept below 1.1 times of the maximum design pressure by releasing gas from relief valves in a case of abnormal pressure increase. The process pressure of the IS process will be kept lower than that of secondary helium in order to avoid corrosions of the secondary pipes and equipment by enteringthe process gas or liquid, e.g. H2SO 4 to the secondary system. During the loss of heat transfer fromsecondary helium to the IS process components, the steam generator and the helium cooler remove all of the secondary heat of 10MWt. At the same time, the by-pass diverter valve will open and the IS processcomponents will be isolated by closing the diverter valves which will be installed at the entrance and exit of the IS process. In the commercial high-temperature gas-cooled reactors, the gas-turbine will be able to playits role of the steam generator adapting at the HTTR-IS system.

The conceptual layout of the HTTR-IS system is shown in Fig. 4 . Concerning the hydrogen explosion [19] which will be an assumed accident event in the hydrogen production system, the position of the HI sectionwhich includes hydrogen in its system should be set appropriate distance from the reactor facility. In addition,considering the effect of missile phenomenon, any equipment should not locate between the reactor and HIdecomposer. From the viewpoint of the diffusion prevention such as the noxious fumes, the equipmentutilized in some of the H 2SO 4 section and some of the HI section is stored in buildings. The results of conceptual layout design shows that it is possible that the IS process can construct compactly within30m103m. On the other hand, since our final target of IS produced hydrogen cost is 15JPY (about 0.1euroor 0.125USD)/m 3, it is necessary for economic evaluation to reduce the IS process area in the commercial ISprocess (VHTR-IS system, e.g. GTHTR300-IS system). Some R&D is in progress for reducing the quantityor number of apparatus, for instance, grouping and packaging of some of main equipment, designing all-in-one type heat exchanger, passive safety function to prevent entering liquid H 2SO 4 to some vapour section,etc. Detailed layout design will be determined based on both of the apparatus design and safety design in2006.

HI section

Secondary helium loop

HTTR

IS processcontrol room

Bunsen reaction section

Concentric hot gas duct

H 2 SO 4 section

SO 3 decomposer H 2 SO 4 vaporizer

Steam generator

30m

HI decomposer

HI section

Secondary helium loop

HTTR

IS processcontrol room

Bunsen reaction section

Concentric hot gas duct Concentric

hot gas duct H 2 SO 4 section

SO 3 decomposer SO 3 decomposer H 2 SO 4 vaporizer H 2 SO 4 vaporizer

Steam generator

30m

HI decomposer

Fig.4 Conceptual layout of the HTTR-IS system


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Dynamic simulation code is necessary not only for the process simulation of the HTTR-IS system but also itssafety case analysis. Since there was no needs of the coupling dynamic simulation code for a nuclear system and a chemical plant in the past, we are developing a code for the HTTR-IS system which cananalyse plant dynamics and thermal hydraulics, and transient simulations for both of the HTTR and the ISprocess. The analytical code Conan-GTHTR based on RELAP5/MOD3 was successfully developed byJAEA and applied to heat transfer calculations of the HTTR for its verification [20]. For the steam generator an analytical code was successfully developed based on the RELAP5/MOD2 and MOD3 and it was verifiedby mock-up test facility of the steam reformer hydrogen production system [21] . For the IS process dynamicsimulation code development is now underway within the IS pilot plant project. The IS process dynamicsimulation code and Conan-GTHTR code will be coupled in the FY2006. The coupling code will be verifiedby IS process apparatus test results and pilot plant tests, and it will be utilized for the safety case studies astransients simulation for reactor start-up and shut-down, reactor emergency shut-down, abnormal transientstriggered by some IS process apparatus breakdown e.g. pump trip, etc., accident simulation by rupture of secondary helium system, etc. The results will be utilized for the safety case review for the government. Thecurrent accident simulation of the HTTR [2], the most severe accident of the secondary helium coolingsystem is rupture of the concentric hot-gas-duct. Even after replacing the secondary helium cooling systemto the IS process, the most severe accident is assumed to be rupture of concentric hot-gas-duct besideshydrogen explosion [19]. The detailed analysis will be performed from the FY2007 to FY2009.

Since attaining the higher thermal efficiency is not a purpose of the bench stage, the thermal efficiency of hydrogen production by the bench-scale IS process is calculated as 6.4 % by using components used in thebench-scale apparatus [2]. In the HTTR-IS system, higher thermal efficiency of about 40 % is expected tocontribute to the commercialisation of water-splitting nuclear hydrogen production systems.

Table 3 Main properties of the IS process used in efficiency calculation

The process using components inthe bench-scale apparatus [2]

The processusing

components inthe bench-

scaleapparatus [2]

HTTR-IS plant (using using a

HPMR for separation of

H 2 in HI decomposer)

Procedure Apparatus Operation parameter Unit Bunsen PROC Bunsen reactor H 2 SO 4 concentration in light phase mol% 20 19.4

HI concentration in heavy phase mol% 10 10.7 I 2 concentration in heavy phase mol% 40 33.2 H 2 SO 4 purifier HI, I 2 removal ratio mol% 100 100

HIx purifier H 2 SO 4 removal ratio mol% 100 100

H 2 SO 4 PROC Direct contact heat exchanger

H 2 SO 4 recovery ratio mol% - 100

H 2 SO 4 vaporizer H 2 SO 4 concentration at the inlet of the H 2 SO 4 decomposer

mol% 63 69.8

H 2 SO 4 decomposition ratio mol% 100 28.2 SO 3 decomposer SO 3 decomposition ratio * mol% 83 58.6 Heat exchanger minimum temperature difference ** K - 5.6

HI PROC EED cell apparent transport number of

proton of the CEM *** mol/mol-e- - 0.8

apparent electroosmosiscoefficient of the CEM *** mol/mol-e

- - 0.4

voltage V - 0.2 concentration of HI at cell exit mol% - 19.0

RO membrane H 2 O selectivity - - infiniteconcentration of HI at exit mol% - 20.4

HI, I 2 recovery column HI, I 2 recovery ratio mol% - 100 HI distillation column pressure in the column MPa 0.1 1.20 HI decomposer HI one-pass conversion ratio mol% 20 80 Heat exchanger minimum temperature difference **** K - 7

* SO 3 decomposition ratio = [outlet SO 2 ]/([inlet H 2 SO 4 ] + [inlet SO 3 ]) 100 ** liquid phase / gas phase*** CEM: Cation exchange membrane**** liquid phase / liquid phase

Fig. 5(a) illustrates a tentative schematic flowsheet of the HTTR-IS system. There are several differencesfrom bench-scale test apparatus. A three stage multiple-effect vaporiser is used as H 2SO 4 concentrator. Adirect contact heat exchanger at upper stream of the H 2SO 4 vaporiser is adapted in order to recover unreacted H 2SO 4 in the SO 3 decomposer and exchange heat efficiently. An EED cell and a reverse osmosis(RO) membrane are added in order to increase the HI concentration of the HIx solution to over pseudo-azeotropic one. When the concentrated HIx solution is fed to the HI distillation column, HI-rich vapour is


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0

1000

2000

3000

4000

5000

6000

0 200 400 600 800 1000Temperature [ ]

H e a

t s u p p l y

[ k W ]

Process flow

Secondary Helium

H2SO 4vaporizer

HIdistillation

column

Co recovery column

SO 3 decomposer

0

1000

2000

3000

4000

5000

6000

0 200 400 600 800 1000Temperature [ ]

H e a

t s u p p l y

[ k W ]

Process flow

Secondary Helium

H2SO 4vaporizer

HIdistillation

column

Co recovery column

SO 3 decomposer

Fig. 6(a) Q-T diagram of HTTR-IS plant (absorption of

I2 by Co in the HI decomposer)

0

1000

2000

3000

4000

5000

6000

7000

8000

0 200 400 600 800 1000Temperature [ ]

H e a

t s u p p l y

[ k W ]

Process flow

Secondary Helium

HIdecomposer

H2SO 4vaporizer

HIdistillationcolumn

SO 3 decomposer

0

1000

2000

3000

4000

5000

6000

7000

8000

0 200 400 600 800 1000Temperature [ ]

H e a

t s u p p l y

[ k W ]

Process flow

Secondary Helium

HIdecomposer

H2SO 4vaporizer

HIdistillationcolumn

SO 3 decomposer

Fig. 6(b) Q-T diagram of HTTR-IS plant (utilizing aHPMR for separation of H 2 in the HI decomposer)

Table 4 Heat demands and thermal efficiency

Unit

The processusing

components inthe bench-scale

apparatus [2]

HTTR-IS plant (using a HPMR

for separation of H 2 in HI

decomposer)

GTHTR300C-IS plant (using Coabsorption of I 2

for separation of H 2 in HI

decomposer)

Heat demand kJ/mol-H 2 4447.4 514.0 511.0

Heat for electricity kJ/mol-H 2 0.0 * 141.9 143.1

Total kJ/mol-H 2 4447.4 655.8 654.0

Thermal efficiency ( ) % 6.4 43.6 43.7

* Not including the electricity for pump and utilities

JAEAs design of the commercial reactor and its IS system, GTHTR300-IS process plant, is almost same asthat of the HTTR-IS system using I 2 absorption by Co in HI decomposition reactor [16]. Hydrogen productionrate is calculated as about 26,000 Nm 3/h by the application of the GTHTR300C.

4. Concluding remarks

Japan Atomic Energy Agency (JAEA) launched a preliminary design of the hydrogen production system byusing heat from the Japans first high-temperature gas-cooled reactor HTTR from 2005. Thethermochemical water-splitting iodine sulphur (IS) process is the progressive candidate for the hydrogenproduction system. The conceptual design of the HTTR-IS system and its thermal efficiency for thehydrogen production are evaluated in this paper.

Since the secondary helium of the HTTR will be utilized in this hydrogen production system, the possibility of utilization of a non-nuclear class IS process as a chemical plant is investigated and available structure of theHTTR-IS system with its approved heat mass balance is proposed. Hydrogen explosion, tritium transfer, etc.should be evaluated in order to separate IS process from nuclear facilities by high-temperature valves.The results of flowsheet evaluation show that the hydrogen production rate of about 1,100 Nm 3/h and itsthermal efficiency of 44 % can be achieved by the optimized HTTR-IS system. The design of the HTTR-ISsystem will finally be determined considering economy and efficiency.

It is expected that the HTTR-IS system will be a world first water-splitting hydrogen production demonstrationby using the direct heat from a high-temperature gas-cooled reactor and the verification of the hydrogenproduction by nuclear system is greatly expected to produce massive quantity of hydrogen in cominghydrogen society.


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References

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[2] Topical issue of Japans HTTR. Nucl Eng Des 2004;233(1-3).

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[5] Nomura M, Kasahara S, Onuki K. Evaluation of thermal efficiency to produce hydrogen through the ISprocess by thermodynamics. JAERI-Research 2002;2002-039 [in Japanese].

[6] Nakajima H, Sakurai M, Ikenoya K, Hwang G-J, Onuki K, Shimizu S. A study on a closed-cyclehydrogen production by thermochemical water-splitting IS process, Proc. 7th Int Conf Nucl Eng, Tokyo,Japan, April 19-23 1999;ICONE-7104.

[7] Kubo S, Nakajima H, Shimizu S, Onuki K, Hino R. A bench scale hydrogen production test by thethermochemical water-splitting iodine-sulfur process, Proc. GLOBAL 2005, Tsukuba, Japan, October 9-13 2005, Paper 474.

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[13] Terada A, Kubo S, Okuda H, Kasahara S, Tanaka N, Oota H, Kanagawa A, Onuki K, Hino R,Development program of hydrogen production by thermo-chemical water splitting process, Proc. 13thInt Conf Nucl Eng, Beijing, China, May 16-20, 2005; ICONE13-50183.

[14] Terada A, Imai Y, Noguchi H, Ota H, Kanagawa A, Ishikura S, Kubo S, Iwatsuki J, Onuki K, Hino R.Experimental and analytical results on H 2SO 4 and SO 3 decomposers for IS Process pilot plant. Proc.3rd Information Exchange Meeting on the Nuclear Production of Hydrogen including the 2nd HTTRWorkshop on Hydrogen Production Technologies, Oarai, Japan; 2005; 18.

[15] Kubo S, Futakawa M, Tanaka N, Iwatsuki J, Yamaguchi A, Tsukada R, Onuki K. Corrosion rateevaluations of structural materials for a iodine-sulfur thermochemical water-splitting cycle, Proc.ICAPP06, Reno, USA, June 4-8, 2006; paper 6170.

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[17] Sakaba N, Homma H, Takahashi T, Kasahara S, Ohashi H, Nishihara T, Onuki K, Kunitomi K.Hydrogen production with high-temperature gas-cooled reactors (11) Conceptual design study of theHTTR-IS system. Proc. 2006 annual meeting of AESJ, N49, Oarai, Japan; 2006 [in Japanese].


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