MOLTEN CARBONATE FUEL CELL (MCFC) FUELED BY ASH FREE

COAL (AFC)

Authors: Marcin Wołowicz, Lee Choong-Gon, Kim Yu-Jeong, Lee Sang-Woo, Kim Tae-

Kyun

("Rynek Energii"- 8/2015)

Key words: molten carbonate fuel cell, ash free coal (AFC), gasification

Summary. The paper presents behavior of molten carbonate fuel cell fueled by ash free coal (AFC) in compari-

son to hydrogen. The gasification process and production of ash free coal is described and literature review is

done. To check the composition of syngas after gasification, experiment with ash free coal in the laboratory

scale was performed. The gasification conditions were 850 0C and Nitrogen flow at level of 100 mL/min. Results

changing in 60 min for gas flow as well as for gas composition are presented. The experimental investigations

for coin type scale fuel cell testing (for ash free coal and hydrogen) and test bench scale fuel cell testing (for hy-

drogen) are described. Comparison between ash free coal and hydrogen as a fuel for molten carbonate fuel cell

is presented. Current-voltage curves for investigated cases are presented as well as results are discussed.

1. INTRODUCTION

Nowadays, power is produced in the same way as it was generated almost 100 years ago, i.e.

by utilization of heat cycles having their limitations (maximum efficiency on the level of

<50%). Limited natural resources and increasing electricity consumptions force to research

and develop more efficient devices. Fuel cells produce power as the consequence of electro-

chemical reactions, thus they are not bound by Carnot efficiency. This can results in very high

efficiency.

Fuel cells are considered as the most perspective sources of energy for future generations

[11]. Research and development associated with fuel cells are widely supported by national

and international organizations (European Union, USA Department of Energy, Republic of

Korea and others).

There are many types of fuel cells with various materials used as an electrolyte (Polymeric

Membrane, Phosphoric Acid, Molten Carbonates, Solid Oxides, and others). All of them have

advantages as well as disadvantages. Only very few (i.e. molten carbonate fuel cell) can ut i-

lize conventional fuels and provide the opportunity of producing additional energy for heating

purposes. Fuel cells can also be fed by biogas [3] and can work as combined heat and power

source for i.e. Distributed Generation [14]. Beside this advantages, molten carbonate fuel cells

can be considered as a very efficient way of separating CO2 from flue gases [5] which is com-

petitive to other methods [2, 6] that seek to reduce emissions from fossil fuel power plants [4].

Based on this statements, investigating molten carbonate fuel cells behavior seems to be justi-

fied. One of the ideas presented in this work is to use gasified ash free coal as a fuel for mol-

ten carbonate fuel cells.

2. GASIFICATION OF ASH FREE COAL

Coal is relatively abundant energy source compared with other fossil fuels. Regardless of its

abundance and long history of usage, inconvenience of its use reduces coal consumption at

present. Coal as a solid fuel has a big problem of remaining ash in its use. Ash free coal has

been attempted to overcome the problem. A trend of producing technologies of the ash free

coal is described widely in [9]. Possibilities and effect of hydrogen production via steam gasi-

fication of ash free coals is presented in [7]. In the same work also comparison of steam gasi-

fication reactivity of AFCs and raw coals is described. Also more about gasification of AFC

and using AFC as fuel for direct carbon fuel cell can be found in [10,12].

To check the composition of syngas after gasification, experiment with AFC in the laboratory

scale was performed. The gasification conditions were 850 0C and Nitrogen flow at level of

100 mL/min. Results changing in 60 min are presented in Table 1 for gas flow during gasifi-

cation process of ash free coal and in Table 2 for gas composition during gasification of ash

free coal. The data are in mL/min and percentage composition is also given.

Table 1. Gas flow during gasification process of ash free coal

Time, min Gas flow, mL/min

H2 N2 CO CH4 CO2

10 215,58 100 93,95 30,19 72,83

20 30,76 100 27,01 1,30 9,21

30 7,82 100 10,90 0,03 6,63

40 5,56 100 6,61 0 4,64

50 4,69 100 5,62 0 7,79

60 3,43 100 3,58 0 1,66

Gas flow during gasification of ash free coal is presented in Fig. 1 and percentage gas compo-

sition during gasification of ash free coal is presented also in Fig. 2.

Fig. 1. Gas flow during gasification of ash free coal in the first 60 min

Table 2. Gas composition during gasification process of ash free coal

Time, min Gas composition, %

H2 N2 CO CH4 CO2

10 42,06 19,51 18,33 5,89 14,21

20 18,28 59,42 16,05 0,77 5,47

30 6,24 79,76 8,69 0,02 5,29

40 4,76 85,61 5,66 0 3,97

50 3,97 84,68 4,76 0 6,6

60 3,16 92,02 3,29 0 1,53

Fig.2. Percentage gas composition during gasification of ash free coal

2. ASH FREE COAL AS FUEL FOR HIGH TEMPERATURE FUEL CELLS

The ash-free coal can be produced by solvent extraction. Figure 3 illustrates the coal produc-

tion process and the supply of pulverized coal along with the carrier gas to the anode. Recent-

ly, fuel cells in which ash-free coal was used as the fuel were reported by Dr. John Cooper,

who utilized ash-free coal as the fuel in a molten carbonate direct carbon fuel cell (DCFC).

Fig. 3. Ash-free coal production and supply of coal to the anode [8]

Direct Carbon Fuel Cells convert the chemical energy in carbon directly into electricity with-

out the need for gasification. It is the direct oxidation of fine (submicron) carbon particles in

an electrochemical cell at high temperatures (600 – 9000C). The Direct Carbon Fuel Cell was

first conceptualized in the 19th

century by William W. Jacques, who employed a cell consist-

ing of a steel pot filled with molten NaOH-KOH as the electrolyte in the temperature range

400-5000C. Molten carbonate electrolyte and solid-oxide-electrolyte fuel cells in which coal

was used directly as the fuel were reported by several researchers [8]. The efficiency for dif-

ferent fuels as a function of temperature is presented in Fig. 4. As presented, direct carbon

fuel cells can reach very high efficiency.

Fig. 4. The maximum or theoretical efficiency for different fuels

as a function of the operating temperature of the fuel cell [1]

3. EXPERIMENTAL COMPARISON BETWEEN AFC AND HYDROGEN

AS A FUEL FOR MCFC

To compare the behavior of molten carbonate fuel cell fueled by ash free coal and hydrogen,

adequate experiment was provided. A coin type molten carbonate fuel cell was investigated.

The diameter of electrodes was about 3 cm. The anode was porous Ni-Al alloy, and the cath-

ode was porous Ni. The matrix was made of LiAlO2. The elements of the fuel cell testing fa-

cility was alumina tube, steel manifolds and current collectors which is shown in Fig. 5. Fuel

cell being installed in the manifold is shown in Fig. 6. Before installation in the manifold, fuel

cells (cathode, anode and matrix) have to be cut to their size (3 cm diameter). The long alu-

mina tube at the upside of the cell was installed in the muffle furnace for the coal supply to

the anode as shown in Fig. 8.

Fig. 5. Components used for testing of coin type molten carbonate fuel cells fueled by ash free coal

All coin type experiments were provided in muffle furnace, which can be seen in Figure 3.

The operating temperature was 8500C. It has to be noticed, that providing experiments in the

muffle furnace takes less time, than making them in the test bench. The difference is of course

in the area of the cell (3 cm diameter in the case with furnace – so called “coin type” vs. 11 x

11 cm square shape in the test bench) and in heating system. In the furnace, fuel cell can be

heat up faster because of its size and of the heating process. In the test bench scale experi-

ments, heating is realized by two heaters (located below and above manifold).

It can causes thermal stresses, that is why the start-up of fuel cell takes longer than in furnace.

In example, the start-up for coin type fuel cell can be done in few hours, but the start up for

test bench scale fuel cell should take 2 days to reach the reference point.

Fig. 6. Fuel cell being installed in the manifold

For the experiments, as an electrolyte a mixture of 62 mol% Li2CO3 and 38 mol% K2CO3 was

used. The cathode gas was 70 % air and 30 % CO2. The normal H2 fuel for the anode was H2 -

125 mL/min, CO2 - 25 mL/min with ca. 5 % of H2O. The ash free coal was

a mixture of 3g coal and 3g of Li-K carbonates. More details of the molten carbonate fuel cell

operation with AFC as a fuel was described in a previous work [13].

Fig. 7. Test bench used for MCFC testing

The test bench experiments [15] were provided on square manifolds and in the test bench

made by HySyTech as presented in Fig. 7.

Fig. 8. Coin type molten carbonate fuel cell with alumina tube at the upside of the cell

used for experiment and installed in muffle furnace

Fig. 9. Experimental comparison between molten carbonate fuel cell fueled by AFC (3g of AFC and 3g of car-

bonates) and Hydrogen at 8500C and 6500C

On Fig. 9 the current-voltage curves for investigated cases (ash free coal and hydrogen at

8500C and 650

0C) are presented.

4. SUMMARY

The gasification process and production of ash free coal was performed and described. As

shown in Table 2. after 60 minutes of the process there is only about 3% of Hydrogen and

92% of Nitrogen.

Experimental comparison between ash free coal and hydrogen as a fuel for molten carbonate

fuel cell was provided. The ash free coal has much higher open circuit voltage (OCV) than

hydrogen in the same temperature. However, ash free coal has larger resistance than normal

hydrogen fuel. Increasing the load of the cell causes faster decreasing of voltage for ash free

coal in comparison to normal hydrogen fuel. Hydrogen in 6500C has lower open circuit volt-

age than ash free coal and hydrogen in 8500C.

ACKNOWLEDGEMENTS

This research was supported by Cooperation of Industrial R&D Programs through the Korea

Institute of Energy Technology Evaluation and Planning funded by the Ministry of Trade, In-

dustry and Energy (20143010031830).

For one of the authors (Marcin Wołowicz) work has been supported by the European Union in

the framework of European Social Fund through the “Didactic Development Program of the

Faculty of Power and Aeronautical Engineering of the Warsaw University of Technology”.

REFERENCES

[1] Badwall S., Giddey S.: The holy grail of carbon combustion – the direct carbon fuel cell

technology. Materials Forum Vol. 34 Edited by Jian Feng- Nie (2010) 181-185.

[2] Bartela L., Skorek-Osikowska A., Kotowicz J.: Integration of a supercritical coal-fired

heat and power plant with carbon capture installation and gas turbine. Rynek Energii

100 (3) (2012) 56–62.

[3] Budzianowski W.: Sustainable biogas energy in Poland: Prospects and challenges.

Renewable and Sustainable Energy Reviews 16 (1) (2012) 342–349.

[4] Bujalski W.: Optimization of electricity and heat generation in large chp plant equipped

with a heat accumulator. Rynek Energii 101 (4) (2012) 131–136.

[5] Discepoli G., Cinti G., Desideri U., Penchini D., Proietti S.: Carbon capture with molten

carbonate fuel cells: Experimental tests and fuel cell perfor-mance assessment.

International Journal of Green-house Gas Control 9 (2012) 372–384.

[6] Janusz-Szymanska K.: Economic efficiency of an IGCC system integrated with CCS

installation. Rynek Energii 102 (5) (2012) 24–30.

[7] Kim J., Choi H., Lim J., Rhim Y., Chun D., Kim S., Lee S., Yoo J.: Hydrogen production

via steam gasification of ash free coals. International Journal of Hydrogen Energy 38

(2013) 6014-6020.

[8] Kim J.-P., Choi H.-K., Chang Y.-J., Jeon C.-H.: Feasibility of using ash-free coal in a

solid-oxide-electrolyte direct carbon fuel cell. International Journal of Hydrogen Energy,

Volume 37, Issue 15, August 2012, Pages 11401-11408.

[9] Kim S.H., Lee C.G.: A Trend of Producing Technologies of the Ashless Hyper Coal as a

Clean Energy Source. Journal of Energy Engineering 21 (4) (2012) 325-338.

[10] Kong Y., Kim J., Chun D., Lee S., Rhim Y., Lim J., Choi H., Kim S., Yoo J.:

Comparative studies on steam gasification of ash-free coals and their orig-inal raw

coals. International Journal of Hydrogen Energy 39 (2014) 9212-9220.

[11] Kotowicz J., Skorek-Osikowska A., Bartela L.: Economic and environmental evaluation

of selected advanced power generation technologies. Journal of Power and Energy 225

(2011) 221–232.

[12] Lee C.G., Hur H., Song M.B.: Oxidation Behavior of Carbon in a Coin-Type Direct

Carbon Fuel Cell. Journal of Electrochemical Society 158(4) (2011) 410-415.

[13] Lee I., Jin S., Chun D., Choi H., Lee S., Lee K., Yoo J.: Ash-free coal as fuel for direct

carbon fuel cell. Chemistry 57 (7) (2014) 1010–1018.

[14] Milewski J., Wołowicz M., Badyda K., Misztal Z.: 36 kW Polymer exchange membrane

fuel cell as combined heat and power unit. ECS Transactions 42 (1) (2012) 75-87.

[15] Milewski J., Bujalski W., Wołowicz M., Futyma K., Kucowski J., Bernat R.:

Experimental investigation of CO2 separation from lignite flue gases by 100cm2

single

Molten Carbonate Fuel Cell. International Journal of Hydrogen Energy 39 (3) (2014)

1558-1563.

WĘGLANOWE OGNIWO PALIWOWE (MCFC) ZASILANE WĘGLEM

BEZPOPIOŁOWYM (AFC)

Słowa kluczowe: węglanowe ogniwa paliwowe, węgiel bezpopiołowy (AFC), gazyfikacja

Streszczenie. W artykule zaprezentowano charakterystyki węglanowego ogniwa paliwowego zasilanego wę-

glem bezpopiołowym (ang. Ash Free Coal – AFC) w porównaniu z paliwem wodorowym. Został opisany pro-

ces gazyfikacji oraz otrzymywania węgla bezpopiołowego. Przeprowadzono również studia literaturowe tego

tematu. W celu sprawdzenia składu gazu syntezowego powstałego w wyniku gazyfikacji, przeprowadzono eks-

peryment w skali laboratoryjnej z użyciem węgla bezpopiołowego. Gazyfikacja została przeprowadzona w tem-

peraturze 8500C oraz przy stałym wydatku azotu na poziomie 100 ml/min. Wynik zmiany wydatku gazu oraz

jego składu w przeciągu 60 minut został zaprezentowany graficznie. Opisano przeprowadzone doświadczenia w

skali “coin type” (wodór oraz węgiel bezpopiołowy) oraz w skali “test bench” (wodór). Zaprezentowano porów-

nanie pomiędzy węglem bezpopiołowym a wodorem jako paliwem do węglanowych ogniw paliwowych. Zostały

wygenerowane krzywe prądowo-napięciowe dla analizowanych przypadków wraz z podsumowaniem otrzyma-

nych wyników.

Marcin Wołowicz, doktor nauk technicznych, wykładowca na Wydziale Mechanicznym

Energetyki i Lotnictwa Politechniki Warszawskiej, autor i współautor ponad 20 publikacji z

zakresu energetyki konwencjonalnej, odnawialnej oraz ogniw paliwowych. E-mail: mar-

cin.wolowicz@itc.pw.edu.pl,

Lee Choong-Gon, profesor zwyczajny, wykładowca w Department of Chemical and Biologi-

cal Engineering, Hanbat National University, autor i współautor 34 publikacji cytowanych

290 razy, wieloletni pracownik Korea Electric Power Research Institute. E-mail: le-

ecg@hanbat.ac.kr

Kim Yu-Jeong, studentka studiów magisterskich w Hanbat National University. Tematyka jej

badań to przede wszystkim węglanowe ogniwa paliwowe oraz czyste technologie węglowe.

E-mail: soieu77@naver.com

Lee Sang-Woo, student studiów magisterskich w Hanbat National University. Tematyka jego

badań to przede wszystkim węglanowe ogniwa paliwowe oraz czyste technologie węglowe.

E-mail: ae301256@hanbat.ac.kr

Kim Tae-Kyun, student studiów magisterskich w Hanbat National University. Tematyka jego

badań to przede wszystkim węglanowe ogniwa paliwowe oraz czyste technologie węglowe.

E-mail: canonjgdl@naver.com