Letter to the Editors on the feasibilit y of thermo c hemical and bacterial h ydrogen pro duction metho ds for n uclear systems

Derek A. Sutherland

Dep artment of Nucle ar Scienc e and Engine ering, M assachusetts Institute of T e chnolo gy, 77 Massachusetts A venue, Cambridge, MA 02139, USA.

5 Octob er 2011

Abstract

Multiple h ydrogen pro duction metho ds w ere in v estigated for implemen tation in a n uclear system that gener­ ates e lectricit y , h y drogen, and biofuels. The Br-Ca-F e (UT-3) and the Sulfur-Io dine (SI) h ydrogen pro duction cycles are t w o app ealing thermo c hemical metho ds for commercially pro ducing h ydrogen using heat from a high temp erature n uclear reactor. Bacterial h ydrogen pro duction metho ds w ere also in v estigated for their commercial feasibilit y . The UT-3 pro cess w as found to b e the most fa v orable for our purp oses out of the three h y d r ogen pro d uction metho ds in v estigated, and w as c hosen o v erall as the desired h ydrogen pro duction pro cess for this pro ject.

1. In tro duction

The o v erall design problem b eing addressed with this study is the dev elopmen t of a n uclear reactor system whic h can pro duce at least 100 mega w at ts of electrical energy (MW e), h ydrogen, and syn thetic biofuels. The main motiv ation b eh ind this design problem is the concern o v er climate c hange f rom h uman generated greenhouse emissions, and also the des ire to reduce dep endence on foreign sources of fossil fuels to ensure domestic energy securit y . Nuclear p o w er pro vides an greenhouse emission-free source of base-load electricit y whic h eliminates a p ortion of our greenhouse emissions from coal-fire p o w er plan ts. Ho w ev er, oil, the fuel relie d on most hea vily for transp ortation to da y , is a subs ta n tial greenhous e emission source, and m uc h of the oil consumed domestically is imp orted from v arious foreign sources. T o ensure domestic energy securit y and lo w er greenhouse emissions, biofuels and h ydrogen ha v e b een pres en ted as domestic, green alternativ es to con v en tional oil pro du cts. The pro duction of h ydrogen and biofuels is largely an energy in tensiv e pro cess, and th us requires an greenhouse emiss ion free source of energy to pro duce carb on neutral pro ducts. Th us, n uclear heat can b e used to pro duce h ydrogen and biofuels domestically and with zero net greenhouse emis sions.

2. Bac kground

The ob jectiv e for our sub-group w as to dev elop a h ydrogen pro duc tio n plan t for use in the design pro ject. The prelim inar y design decision w as to determine what the purp ose of the h ydrogen pro duction plan t w ould b e, either for mass pro ducing h ydro gen for sale in a future h ydrogen econom y , or pro viding enough h ydrogen for mass pro duction of biofuels at the nearb y plan t. The ultimate decis ion for th e latter purp ose for the h ydrogen plan t w as made due to the uncertain t y of a future h ydrogen econom y , resulting from distribu­ tion infrastructure issues that could render suc h an infrastructure economically and tec hnically in viable [2]. Biofuels are already b eing used in small quan tities in gas o li ne and diesel engines to da y , and c an b e used in greater concen tration with mo difications to curren t in ternal com bustion engine des igns [5]. F r om these economical and tec hnical conside r ations , the c hoice w as made to pro duce h ydrogen solely for mass biofuel pro duction, 0.1 kg p er second at 4 b a r pressure. The main c hallenges for the group w ere to determine the h ydrogen pro duction metho ds that could yield the q u a n tit y of h ydrogen the biofuel group requested, and to address the material concerns from c hemical, temp erature, and pressure requiremen ts, and emissions from eac h particular h ydrogen pro duction pro cess of in terest.

Pr eprint submitte d to Elsevier

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Octob er 5, 2011

3. Results

The main design considerations use d to c ompare h ydrogen pro duction metho ds w ere: the maxim um of temp eratures required for eac h pro cess, the commerci a l viabilit y of eac h approac h, and material consider­ ations that could jeopardize the reliabilit y and longevit y of the plan t. F our ma jor h ydrogen pro du ction metho ds w ere in v estigated: w ater electrolysis, high-temp erature steam electrolysis , thermo c hemical w ater splitting, and bac terial h ydrogen pro duction. Other h ydrogen pro duction me tho ds using natural gases w ere quic kly rejected due to the requiremen t for greenhouse gas emissions fo r the pro duction of h ydr ogen , whic h compromises an o v erall design goal of a greenhouse emission-free n uclear system. Material concerns dominate the high temp erature steam elec tr olysis and thermo c hemical w ater splittin g due to relativ ely high temp er­ atures (500-900 C) and corr os iv e reactan ts and pro ducts, whereas the concern o v er commercial viabilit y dominates the w ater electrolysis and bacterial h ydrogen pro duction metho ds.

My con tribution to the h ydrogen pro duc tio n researc h pro cess w as in v estigating the Sulfur-Io dine (SI), Br-Ca-F e (UT-3), and bacterial h ydrogen pro duc t i o n pro cesses in detail to determine their feasibilit y for our purp oses. Dark fermen tation h ydrogen pro duction w as determined to b e the m o s t commercial viable bacterial metho d; ho w ev er, the rather large v olume required for our desired h ydrogen pro duction rate coupled with the risk of system failure from biological con tamination led to the rejection of this metho d for our purp oses [3]. After in v estigating the t w o thermo c hemical pro cesses men tioned, the UT-3 pro cess w as fa v ored o v er SI since it o ccurs at a lo w er temp erature, and has m inor material concerns relativ e to the SI pro cess [6]. The UT-3 reaction pro ceeds as follo ws at the v arious desired temp eratures [4],

C aB r 2 + H 2 O → C aO + 2 H B r (760 C )

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C aO + B r 2 → C aB r 2 + 2 O 2 (571 C )

F e 3 O 4 + 8 H B r → 3 F eB r 2 + 4 H 2 O + B r 2 (220 C )

3 F eB r 2 + 4 H 2 O → F e 3 O 4 + 6 H B r + H 2 (560 C )

The UT-3 pro ce ss has b een w ell demonstrated, and h a s b een cited as b oth an economically and tec hnically viable approa c h for commercial h ydrogen pro duction [1]. The UT-3 pro cess can also b e scaled sp ecifically for our h ydrogen pro duction needs, 0.1 kg p er second at 4 b a r pressure. With thes e m ultiple adv an tages in fa v or of the UT-3 pro cess, and with the fa v orabilit y of UT-3 o v er pro cesses researc hed b y the other mem b ers of the gr oup, UT-3 w as c hosen as the pro cess for our h ydrogen pro duction plan t.

4. Conclusion

After in v es tiga ti ng the SI, UT-3, and bacterial h ydrogen pro duction pro cesses, the UT-3 pro ce ss w as determined to b e the most viable of the three for our purp oses. Manageable material concerns and the pro v en commercial scalabilit y of the UT-3 pro cess w ere the ma j or adv an tages that led to th is resu lt. In comparing UT-3 to other metho ds of h ydro ge n pro duction in v estigated b y other mem b ers of the group, it w as determined that UT-3 is the most fa v orable of all the pro ce sses, a n d w as c hosen as the pro ce ss for the h ydrogen pro duction plan t. Next, the flo w rates of reactan ts and heat req u ired in m ultiple v ariations of UT-3 plan t designs m ust b e determined for our desired h ydr ogen output of 0.1 kg p er second at 4 bar press ure. A storage system for h ydrog e n m ust a l so b e dev elop ed to ensure some biofuel pro duction capabilities ev en during h ydrogen plan t main tenance p erio ds. Finally , material c o n cerns should b e addressed more r igorously to ensure the reliabilit y and o v erall longevit y of the h ydrogen plan t in accordance with the exp ected lifetimes of the biofuel fuel pro duction plan t and the n uclear reactor itself.

5. References

[1] A. A o c hi, T. T adok oro, K. Y oshida, H. Kamey ama, M. Nobue, and T. Y amaguc hi. Economical and tec hnical ev aluation of ut-3 thermo c hem ical h ydrogen pro duction pro cess for an industrial scale plan t. Int. J. Hydr o gen Ener gy , 14(7):421–429, 1989.

[2] Ulf Bossel. Do es a h ydrogen econom y mak e sens e? Pr o c e e dings of the IEEE , 94(10), 2006.

[3] P atric k C. Hallen b ec k and John R. Benemann. Biological h ydrogen pro duction; fundamen tals and limiting pro cesses. International Journal of Hydr o gen Ener gy , 27:1185–1193, 2002.

[4] H. Kamey ama and K. Y oshida. Br-ca-fe w ater decomp osition cycles for h ydrogen pro duction. Pr o c. 2nd WHEC. , pages 829 –850, 1978.

[5] Matthew C. Rob erts. E85 a n d fuel efficiency: An empirical analysis of 2007 epa test data. Ener gy Policy , 36:1233–1235, 2008.

[6] X. Vitart, A. Le Duigou, and P . Carles. H y drogen pro duc t i o n using the sulfur-io dine cycle coupled to a vh tr: An o v erview. Ener gy Conversion and Management , 47:2740–2747, 2006.

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22.033 / 22.33 Nuclear Systems Design Project

Fall 2011

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