EFCF 2025: Low-Temp. Fuel Cells, Elec olyse s & H2 P ocessing 1 – 4 July 2025, Luce ne Swi ze land
h ps://doi.o g/10.5281/zenodo.17244117 A0717 Page 1/6
A0717
Flow analysis and geome y op imiza ion o an
in eg a ed ammonia decomposi ion-combus ion eac o
h ough CFD Modeling
Soomin Lee (1), Jihyeon Son (1), Sangho Lee (2), Sanghun Lee* (1)
(1) Depa men o Clima e and Ene gy Sys em Enginee ing, Ewha Womans Uni e si y;
(2) Depa men o Mobili y Powe Resea ch, Eco-F iendly Ene gy Con e sion Resea ch
Di ision, KIMM Ins i u e o Ca bon Neu al Ene gy Machine y;
*Con ac co esponding au ho s: www.EFCF.com/Con ac Reques
Abs ac
Ammonia, one o he hyd ogen compounds, has gained a en ion as a hyd ogen ca ie due
o i s ease o lique ac ion, high s o age capaci y, and en i onmen al iendliness. Ammonia
can also be u ilized as a di ec uel in some uel cells. Howe e , i is necessa y o conside
a sys em wi h an ammonia e o me (c acke ) because he pe o mance o he uel cell is
signi ican ly imp o ed when he ammonia is p e ea ed (c acked) a he han di ec ly injec ed.
In o de o imp o e he e iciency o he ammonia e o me , his s udy analyzes a sys em in
which he o -gas om he uel cell is eused in he combus o and he hea gene a ed
h ough combus ion is u ilized o e o ming. The in e nal low and combus ion eac ions a e
simula ed by modeling he in eg a ed ammonia e o me and combus o using
Compu a ional Fluid Dynamics. Based on his, he op imal ope a ing condi ions and eac o
geome y a e de i ed o imp o e ammonia e o ming e iciency, achie e a uni o m in e nal
empe a u e, and educe NOx emissions. The e o me sys em de eloped h ough he
esul s o his s udy is expec ed o p o ide insigh s o ammonia-based uel cell sys em
design and ope a ion s a egies.
EFCF 2025: Low-Temp. Fuel Cells, Elec olyse s & H2 P ocessing 1 – 4 July 2025, Luce ne Swi ze land
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In oduc ion
As he demand o an ene gy ansi ion owa d low-ca bon ene gy sou ces inc eases,
ammonia is gaining a en ion as an e icien hyd ogen ca ie . Ammonia, a hyd ogen-
con aining compound, has long been widely used a ound he wo ld, pa icula ly in he
e ilize indus y. A well-es ablished global in as uc u e o ammonia p oduc ion, s o age,
and anspo a ion u he highligh s i s ad an ages o a low-ca bon ene gy socie y.
Ammonia can se e no only as a hyd ogen ca ie bu also as a di ec uel o powe
gene a ion h ough solid oxide uel cells (SOFCs). SOFCs ope a e a high empe a u es and
o e uel lexibili y, making i possible o u ilize a ious uels such as hyd ogen, na u al gas,
ammonia, and biogas. Howe e , a 1 kW SOFC s ack demons a ion conduc ed a Kyo o
Uni e si y con i med pe o mance di e ences be ween di ec ammonia injec ion and
injec ion a e p e- e o ming [1]. Imp o ed uel cell pe o mance was obse ed when
ammonia was decomposed p io o injec ion, and supplying p e-c acked ammonia also
helped mi iga e deg ada ion eac ions a he anode [2].
The e o e, o achie e s able and e icien uel cell ope a ion, i is necessa y o p e- ea
ammonia be o e injec ion. The Ko ea Ins i u e o Machine y and Ma e ials (KIMM) has
de eloped an ammonia p e- ea men sys em ha in eg a es an ammonia decomposi ion
eac o wi h a combus o [3]. This sys em is designed o euse he o -gas om he uel cell
o combus ion, and he hea gene a ed du ing combus ion is hen u ilized o d i e he
e o ming eac ion. A schema ic o he sys em is shown in Figu e 1.
This s udy aims o op imize he sys em o imp o e e o ming e iciency, achie e empe a u e
uni o mi y, and educe NOx emissions in he de eloped ammonia p e- ea men uni . Since
he ab ica ion o a physical p o o ype equi es signi ican cos s and ma e ials, his s udy
adop s compu a ional luid dynamics (CFD) simula ions o op imize he geome y o he
ammonia p e- ea men sys em. CFD is a powe ul ool ha nume ically sol es luid mo ion
equa ions o simula e low, empe a u e, and p essu e ields in a i ual en i onmen . I is
widely used ac oss indus ies such as au omo i e, ene gy, and chemical enginee ing o
e alua e sys em pe o mance and educe de elopmen ime h ough simula ion.
In his s udy, e o ming e iciency is de ined as he op imiza ion a ge , and key a iables
include he numbe and olume o ca alys laye s, ope a ing empe a u e, and he di ec ion
o ammonia injec ion. P io o analyzing he ull-scale p e- ea men uni , a simpli ied base
model using a 3/4’’ s ainless s eel (STS) ube was analyzed. Based on alida ion wi h
expe imen al da a, he s udy will be ex ended o he ac ual eac o geome y.
Figu e 1. The con igu a ion o he ammonia p e- ea men sys em
EFCF 2025: Low-Temp. Fuel Cells, Elec olyse s & H2 P ocessing 1 – 4 July 2025, Luce ne Swi ze land
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1. Modeling Se up
Be o e conduc ing CFD modeling o he ammonia p e- ea men uni , a base model was i s
de eloped and analyzed. The o e all and elemen a y eac ions o ammonia decomposi ion
a e shown below [4]. In he base model, he decomposi ion was modeled based on he
o e all eac ion.
𝑶𝒗𝒆𝒓𝒂𝒍𝒍 𝒓𝒆𝒂𝒄𝒕𝒊𝒐𝒏
2𝑁𝐻3→𝑁2+3𝐻2
𝑬𝒍𝒆𝒎𝒆𝒏𝒕𝒂𝒓𝒚 𝒓𝒆𝒂𝒄𝒕𝒊𝒐𝒏𝒔
(𝑅1) 𝑁𝐻3+ ∗ ↔𝑁𝐻3
∗
(𝑅2) 𝑁𝐻3
∗+ ∗ ↔𝑁𝐻2∗+𝐻∗
(𝑅3) 𝑁𝐻2
∗+ ∗ ↔𝑁𝐻∗+𝐻∗
(𝑅4) 𝑁𝐻∗+ ∗ ↔𝑁∗+𝐻∗
(𝑅5) 2𝑁∗↔𝑁2+2∗
(𝑅6) 2𝐻∗↔𝐻2+2∗
∗:𝑉𝑎𝑐𝑎𝑛𝑡 𝑠𝑖𝑡𝑒
Fo he kine ics o he ammonia decomposi ion eac ion, he A henius cons an and
ac i a ion ene gy we e ob ained using he buil -in Pa ame e S udy unc ion in COMSOL
Mul iphysics. The calcula ed alues we e applied o he chemical eac ion a e equa ions
(Eq. 1 and 2). The ammonia decomposi ion eac ion was conduc ed in a plug low- ype
eac o a 973.15 K.
𝑟=𝑘𝑓∏ 𝑐𝑖−𝑣𝑖
𝑖 ∈ 𝑟𝑒𝑎𝑐𝑡 −𝑘𝑟∏ 𝑐𝑖𝑣𝑖
𝑖 ∈ 𝑝𝑟𝑜𝑑 (𝑒𝑞.1)
𝑘=𝐴( 𝑇
𝑇𝑟𝑒𝑓)𝑛𝑒𝑥𝑝(−𝐸𝑎
𝑅𝑇) , 𝑇𝑟𝑒𝑓 =1𝐾 (𝑒𝑞.2)
The geome y o he ammonia base model was simpli ied, as shown in Figu e 2. The eac o
and ca alys se ings, assump ions, and bounda y condi ions we e de ined as p esen ed in
Tables 1–4. These alues we e se o ma ch he expe imen al condi ions p o ided by he
Ko ea Ins i u e o Machine y and Ma e ials (KIMM). The o e all eac ion conside ed
mul icomponen species anspo . As o bounda y condi ions, a GHSV o 2000/h and a low
a e o 167 mL/min we e applied, and he wall was se o a no-slip condi ion.
Table 1. Reac o pa ame e s used in he CFD simula ion o he base model
Reac o
3/4‘’ STS ube
Ou side
diame e
27.2 mm (KS S anda d)
Wall hickness
2.1 mm (KS S anda d)
Reac o heigh
81.6 mm
Ca alys laye
heigh
10.10 mm
Table 2. Ca alys pa ame e s used in he CFD simula ion o he base model
Ca alys
Ru/Al2O3 (Ru 2.00 w .%, 24.5 g/L)
Pelle size
Φ1.4mm~3.0mm
EFCF 2025: Low-Temp. Fuel Cells, Elec olyse s & H2 P ocessing 1 – 4 July 2025, Luce ne Swi ze land
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Ca alys olume
5 mL
Po osi y
0.7 [5]
Table 3. Assump ions and bounda y condi ions in he CFD simula ion o he base model
Assump ions
Bounda y condi ions
- S eady-s a e
- Plug low ype eac ion
- T anspo o concen a ed species
in po ous ca alys s
- Ou e walls: adiaba ic
- GHSV = 2000/h
- CNH3 = C0, CN2 = 0, CH2 = 0
- NH3 low a e = 167 mL/min
- T eac = 973.15 K
- No slip a wall
Figu e 2. Geome y o he base model o he ammonia decomposi ion eac o
Fo luid low in po ous media, he B inkman equa ion (Eq. 3) was used as he go e ning
equa ion. This equa ion was employed o accoun o mass and momen um conse a ion,
as well as po ous media esis ance and luid iscosi y e ec s. The B inkman equa ion is
commonly used in complex po ous low p oblems.
Nex , o species conse a ion, he Maxwell–S e an equa ion (Eq. 4) was applied. Unlike
Fick’s law—which is ypically used o ideal gases o single componen sys ems and does
no conside mul icomponen in e ac ions o p essu e g adien s— he Maxwell–S e an
equa ion p o ides a mo e de ailed mul icomponen di usion model ha inco po a es species
in e ac ions, p essu e g adien s, and con ec i e e ec s.
0=𝛻[−𝑝𝐼+1
𝜖𝑝{𝜇(𝛻𝑢+(𝛻𝑢)⊤) −2
3𝜇(𝛻∙𝑢)𝐼}]−(𝜇
𝜅+𝛽𝜌|𝑢|+𝑄𝑚
𝜖𝑝
2)𝑢 (𝑒𝑞.3)
𝛻∙−[𝜌𝜔𝑖∑𝐷
𝑖𝑘
𝑘𝜔𝑘
𝑀𝑘𝑀𝑛+1
𝑝𝐴{(𝜔𝑘
𝑀𝑘𝑀𝑛−𝑤𝑘)𝛻𝑝𝐴}+𝐷𝑖⊤𝛻𝑇
𝑇]+𝜌(𝑢∙𝛻)𝜔𝑖=𝑅𝑖 (𝑒𝑞.4)
EFCF 2025: Low-Temp. Fuel Cells, Elec olyse s & H2 P ocessing 1 – 4 July 2025, Luce ne Swi ze land
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2. Resul s
The esul s o he PFR eac ion modeled using a 0D app oach a e shown in Figu e 3. The
igu e p esen s he mola low a es o each species wi h espec o he eac o olume.
Ini ially, he eac ion p oceeds igo ously, esul ing in a apid dec ease in ammonia and an
inc ease in hyd ogen and ni ogen. A ound a eac o olume o 0.8 mL, he eac ion eaches
equilib ium, as obse ed in he plo .
Figu e 3. Mola low a e o ammonia decomposi ion in PFR
A e con i ming ha he ammonia decomposi ion eac ion was p ope ly ep esen ed in he
0D componen , modeling o he designed 3D base model was conduc ed. Ammonia is
injec ed om he op (inle ), esul ing in a high ammonia concen a ion nea he op egion.
As he eac ion occu s a he ca alys zone, he ammonia concen a ion dec eases along he
eac o leng h.
In he case o hyd ogen and ni ogen, since hey a e no p esen a he inle , hei
concen a ions a e ini ially ze o. Howe e , as he eac ion p og esses owa d he lowe pa
o he eac o due o he mal e ec s, hyd ogen and ni ogen a e apidly gene a ed in he
ca alys zone, leading o inc eased mola concen a ions. The mola concen a ion o
hyd ogen eaches app oxima ely h ee imes ha o ammonia, indica ing ha he 0D
chemical eac ion model has been success ully inco po a ed in o he 3D simula ion.
Figu e 4. CFD modelling esul s o ammonia decomposi ion in he base eac o
EFCF 2025: Low-Temp. Fuel Cells, Elec olyse s & H2 P ocessing 1 – 4 July 2025, Luce ne Swi ze land
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3. Conclusion
In his s udy, CFD modeling o a base model was conduc ed as a p elimina y s ep o
simula ing he ammonia p e- ea men uni . The modeling was pe o med by applying he
chemical eac ion a e equa ion, he B inkman equa ion, and he Maxwell–S e an equa ion.
As a esul , i was con i med ha he ammonia decomposi ion eac ion was app op ia ely
ep esen ed in he simula ion.
The eliabili y o he modeling esul s will be alida ed h ough compa ison wi h expe imen al
da a in u u e wo k. A e alida ion, he geome y will be u he e ined o pe o m CFD
modeling o he ully de eloped p e- ea men sys em.
Re e ences
[1] Kishimo o, M., e al, De elopmen o 1 kW‐class ammonia‐ ueled solid oxide uel cell
s ack, Fuel Cells 20.1, 2020
[2] Wan, Zhijian, e al, Ammonia as an e ec i e hyd ogen ca ie and a clean uel o solid
oxide uel cells, Ene gy Con e sion and Managemen 228, 2021
[3] Lee, Sangho, e al, De elopmen o an ammonia decomposi ion eac o , a e bu ne
and pos -decomposi ion eac o o 1 kW solid oxide uel cells using ammonia, Ene gy
Con e sion and Managemen 314, 2024
[4] P asad, V., e al, Assessmen o o e all a e exp essions and mul iscale, mic okine ic
model uniqueness ia expe imen al da a injec ion: Ammonia decomposi ion on Ru/γ-
Al2O3 o hyd ogen p oduc ion, Indus ial & enginee ing chemis y esea ch 48.11,
2009
[5] Wu, Gaowei, e al, Con inuous low ae obic oxida ion o benzyl alcohol on Ru/Al2O3
ca alys in a la memb ane mic ochannel eac o : An expe imen al and modelling s udy,
Chemical Enginee ing Science 201, 2019
Keywo ds: EFCF2025, H2, LowTemp. Fuel Cells & Elec olyse s, Ammonia p e- ea men ,
Compu a ional Fluid Dynamics, Modeling & Simula ion, Op imiza ion
Rema k: This wo k is licensed unde C ea i e Commons A ibu ion 4.0 In e na ional
