**Bioethanol-Fuelled Solid Oxide Fuel Cell System for Electrical Power Generation**

Vorachatra Sukwattanajaroon1, Suttichai Assabumrungrat1, Sumittra Charojrochkul2, Navadol Laosiripojana3 and Worapon Kiatkittipong4 *1Chulalongkorn University, Faculty of Engineering, Department of Chemical Engineering 2National Metal and Materials Technology Center 3King Mongkut's University of Technology Thonburi 4Silpakorn University, Department of Chemical Engineering Thailand* 

### **1. Introduction**

190 Renewable Energy – Trends and Applications

Shiratori, Y.; Tran, Q.T.; Takahashi, Y. & Sasaki, K. (2011). Application of biofuels to solid

Staniforth, J. & Kendall, K. (1998). Biogas powering a small tubular solid oxide fuel cell.

Staniforth, J. & Kendall, K. (2000). Cannock landfill gas powering a small tubular solid oxide fuel cell - a case study. *Journal of Power Sources*, 86:401-403, ISSN 0378-7753. Steele, BCH & Heinzel A. (2001). Materials for Fuel-cell Technologies. *Nature*, 414:345–352,

Stöver, D.; Buchkremer, H.P. & Huijsmans, J.P.P. (2003) MEA/cell preparation methods:

Tran, Q.T.; Shiratori, Y. & Sasaki, K. (2011). Feasibility of palm-biodiesel fuel for internal

Van herle, J.; Membrez, Y. & Bucheli, O. (2004a). Biogas as a fuel source for SOFC co-

Van herle, J.; Maréchal, F.; Leuenberger, S.; Membrez, Y.; Bucheli, O. & Favrat, D. (2004b).

Xuan, J.; Leung, M.K.H.; Leung, D.Y.C. & Ni, M. (2009) A review of biomass-derived fuel

Yentekakis, I.V. (2006). Open- and closed-circuit study of an intermediate temperature SOFC

Yoon, S.; Kang, I. & Bae, J. (2008). Effects of ethylene on carbon formation in diesel autothermal reforming. *International Journal of Hydrogen Energy*, 33:4780-4788, ISSN 0360-3199. Yoon, S.; Kang, I. & Bae, J. (2009). Suppression of ethylene-induced carbon deposition in

Yoshida, S.; Kabata, T.; Nishiura, M.; Koga, S.; Tomida, K.; Miyamoto, K.; Teramoto, Y.;

Yuki, E.; Haga, K.; Shiratori, Y.; Ito, K. & Sasaki K. (2009). Co-poisoning effects by sulfur

Zhou, Z.F.; Gallo, C.; Pargue, M.B.; Schobert, H. & Lvov S.N. (2004). Direct oxidation of Jet

Zhou, Z.F.; Kumar, R.; Thakur, S.T.; Rudnick, L.R.; Schobert, H. & Lvov, S.N. (2007). Direct

Züttel, A. (2008). Material for the hydrogen world. in *Ceramic materials in energy system for* 

generators. *Journal of Power Sources*, 127:300–312, ISSN 0378-7753.

*Journal of Power Sources*, 131:127-141, ISSN 0378-7753.

*ECS Transactions*, 35(1):105-111, ISSN 1938-5862.

*Cells in Japan*, pp.104-107, Tokyo, Japan, December 2009.

Ceramics, ISBN 978-88-86538-50-3, pp.211-260, Italy, 2008.

Europe/USA, In: *Handbook of Fuel Cells-Fundamentals, Technology and Applications*, Vielstich, W.; Lamm, A. & Gasteiger, H. A. (Eds.), 1015-1031, John Wiley & Sons

reforming Solid Oxide Fuel Cells. *International Journal of Energy Research*

Process flow model of solid oxide fuel cell system supplied with sewage biogas.

processors for fuel cell systems. *Renewable and Sustainable Energy Reviews*, 13:1301-

directly fueled with simulated biogas mixtures. *Journal of Power Sources*, 160:422–

diesel autothermal reforming. *International Journal of Hydrogen Energy*, 34:1844–1851,

Matake, N.; Tsukuda, H.; Suemori, S.; Ando, Y. & Kobayashi, Y. (2011). Development of the SOFC-GT combined cycle system with tubular type cell stack.

impurities and hydrocarbons in SOFCs. *Proc. 18th Symposium on Solid Oxide Fuel* 

fuels and pennsylvania crude oil in a solid oxide fuel cell. *Journal of Power Sources*,

oxidation of waste vegetable oil in solid-oxide fuel cells. *Journal of Power Sources*,

*sustainable development*, Gauckler, L.J. Editor. Forum 2008 of the World Academy of

oxide fuel cell. *ECS Transactions*, 35(1):2641-2651, ISSN 2151-2051.

Fuel Cell Forum Proceedings Series, Switzerland, 2010.

*Journal of Power Sources*, 71(1-2):275-277, ISSN 0378-7753.

ISSN 0028-0836.

Ltd., ISBN 0-471-49926-9, England.

(submitted), ISSN 1099-114X.

1313, ISSN 1364-0321.

425, ISSN 0378-7753.

ISSN 0360-3199.

133:181–187, ISSN 0378-7753.

171:856-860, ISSN 0378-7753.

Cassidy, M.; Savaniu, C.; Smith, M. & Knowles, S. editors, pp.4-77-4-87, European

Tremendous consumption of energy to serve daily lives and economic activities has led to the critical problem of energy shortage since the current main energy sources rely on fossil fuels which are non-renewable. Therefore, efficient renewable energy sources need to be investigated and improved to replace or substitute the use of fossil fuels to alleviate environmental impacts while being sustainable. Biomass-derived fuels are recognized as promising alternatives among other renewable sources e.g. wind, solar, geothermal, hydropower, etc. This fuel can be produced from various available agricultural materials, hence there is no problem of feedstock supply. Instead, its use is beneficial for those countries having strong background in agriculture. In addition, this agro-based fuel can provide a CO2-closed cycle as the CO2 released from the fuel combustion can be redeemed with the CO2 required for biomass growth. Bioethanol plays an important role as a promising renewable energy among other biofuels due to its useful properties such as high hydrogen content, non-toxicity, safety, ease of storage and handling (Ni et al., 2007). An efficient energy conversion system is required to maximize bioethanol fuel utilization to obtain a full performance. Combustion heat engines which are widely used nowadays have a low conversion efficiency of power production due to losses during multiple energy conversion stages as well as a low value of chemical energy of bioethanol represented by LHV or HHV compared to those of fossil fuels (C6 hydrocarbons or above). Moreover, electrical energy efficiency produced from a combustion heat engine becomes even lower because of further losses from more energy conversion stages. Fuel cell technology is considered to be an interesting alternative for efficient energy conversion since it can directly convert chemical energy stored in the fuel into electrical energy via electrochemical reaction. Less energy is lost in the fuel cell operation and higher electrical efficiency can be obtained. However, the problems in using fuel cell technology such as short-life operating time, high manufacturing cost and impromptu infrastructure support are still issues to be tackled. The Solid Oxide Fuel Cell (SOFC), a type of fuel cells, is selected to be an electrical power generation unit fuelled by bioethanol because of its outstanding characteristics: ability to use low-cost catalyst, high temperature exhaust heat for cogeneration application, tolerance to some impurities e.g. CO and sulfur, internal reforming within the cell for reducing equipment cost, etc. For the SOFC system, bioethanol feed is heated up and reformed to hydrogen rich gas by the reformer before being introduced into the fuel cell at the anode side coupled with air feed at the cathode side for producing electricity. To achieve better performance from this process, it is necessary to consider every unit within the SOFC system. These units are investigated through their physical structure design and modification on the basis of worthwhile energy utilization in each unit and suitable energy allocation within the process to target an optimum energy management of the SOFC system. The objective of this chapter is to propose ideas and feasible approaches on how to improve the performance of bioethanol-fuelled SOFC systems by focusing on each essential unit modification in the process. Relevant useful approaches from other scientific literature reviews are included. The pros and cons in each proposed method are also discussed. Bioethanol pretreatment unit regarded as a significant unit compared to the other units for the process development is of particular focus in this chapter. The progressive work of our research on the efficiency improvement of the SOFC system with analytically appropriate selection of bioethanol pretreatment unit is presented. The simulation studies were conducted via experimental-verified SOFC model to predict the results under a frame of model assumptions. Performance assessment of the system in any scenario cases held the criteria of no external energy demand condition or *Q*net = 0 to compare and identify the optimal operating conditions among those of bioethanol pretreatment units. The simulation results could initially guide the right pathway for practical industrial applications.

## **2. Bioethanol**

Among various biomass-based fuel types such as bioethanol, biodiesel, bioglycerol, and biogas, bioethanol is considered a promising renewable energy compared to other biofuels. As shown in Table 1, the maximum amount of work from the fuel cell integrated with fuel processor system in comparison with five renewable fuels including *n*-octane represented as a gasoline characteristic are presented (Delsman et al., 2006). It was indicated that ethanol can offer the highest energy output (based on MJ/mol fuel) among the other renewable fuels (methanol, methane, ammonia, and hydrogen) except for *n*-octane. Furthermore, there are other outstanding advantages of bioethanol given by the following reasons. The production technologies of bioethanol are more mature and cheaper than those of biomethanol (Xuan et al., 2009). Biodiesel which is a popular alternative energy used in vehicle engines can be derived from ethanol (or purified bioethanol) reacted with vegetable oil via transesterification reaction. Biogas is a widely-used renewable power source because of many available feedstocks. It can be produced from several organic wastes by anaerobic biological fermentation. Consequently, it seems to be a promising renewable fuel but biogas mainly consists of methane and CO2. Both gases have serious negative environmental impacts especially from methane. Methane can remain in atmosphere for 9-15 years and retains heat radiation of 20 times higher than CO2 (U.S. Environmental Protection Agency). Furthermore, if the biogas is produced from non-agricultural wastes, e.g. cow and pig manure, it would bring this biogas production diverted from carbon-closed cycle. Hence, biogas should be produced and utilized in an effective way. Bioethanol production is mostly derived from biological fermentation using agro-based raw materials such as sucrose-

power generation unit fuelled by bioethanol because of its outstanding characteristics: ability to use low-cost catalyst, high temperature exhaust heat for cogeneration application, tolerance to some impurities e.g. CO and sulfur, internal reforming within the cell for reducing equipment cost, etc. For the SOFC system, bioethanol feed is heated up and reformed to hydrogen rich gas by the reformer before being introduced into the fuel cell at the anode side coupled with air feed at the cathode side for producing electricity. To achieve better performance from this process, it is necessary to consider every unit within the SOFC system. These units are investigated through their physical structure design and modification on the basis of worthwhile energy utilization in each unit and suitable energy allocation within the process to target an optimum energy management of the SOFC system. The objective of this chapter is to propose ideas and feasible approaches on how to improve the performance of bioethanol-fuelled SOFC systems by focusing on each essential unit modification in the process. Relevant useful approaches from other scientific literature reviews are included. The pros and cons in each proposed method are also discussed. Bioethanol pretreatment unit regarded as a significant unit compared to the other units for the process development is of particular focus in this chapter. The progressive work of our research on the efficiency improvement of the SOFC system with analytically appropriate selection of bioethanol pretreatment unit is presented. The simulation studies were conducted via experimental-verified SOFC model to predict the results under a frame of model assumptions. Performance assessment of the system in any scenario cases held the criteria of no external energy demand condition or *Q*net = 0 to compare and identify the optimal operating conditions among those of bioethanol pretreatment units. The simulation

results could initially guide the right pathway for practical industrial applications.

Among various biomass-based fuel types such as bioethanol, biodiesel, bioglycerol, and biogas, bioethanol is considered a promising renewable energy compared to other biofuels. As shown in Table 1, the maximum amount of work from the fuel cell integrated with fuel processor system in comparison with five renewable fuels including *n*-octane represented as a gasoline characteristic are presented (Delsman et al., 2006). It was indicated that ethanol can offer the highest energy output (based on MJ/mol fuel) among the other renewable fuels (methanol, methane, ammonia, and hydrogen) except for *n*-octane. Furthermore, there are other outstanding advantages of bioethanol given by the following reasons. The production technologies of bioethanol are more mature and cheaper than those of biomethanol (Xuan et al., 2009). Biodiesel which is a popular alternative energy used in vehicle engines can be derived from ethanol (or purified bioethanol) reacted with vegetable oil via transesterification reaction. Biogas is a widely-used renewable power source because of many available feedstocks. It can be produced from several organic wastes by anaerobic biological fermentation. Consequently, it seems to be a promising renewable fuel but biogas mainly consists of methane and CO2. Both gases have serious negative environmental impacts especially from methane. Methane can remain in atmosphere for 9-15 years and retains heat radiation of 20 times higher than CO2 (U.S. Environmental Protection Agency). Furthermore, if the biogas is produced from non-agricultural wastes, e.g. cow and pig manure, it would bring this biogas production diverted from carbon-closed cycle. Hence, biogas should be produced and utilized in an effective way. Bioethanol production is mostly derived from biological fermentation using agro-based raw materials such as sucrose-

**2. Bioethanol** 

containing crops, starchy materials, lignocellulosic biomass and agro-waste (Carlos & Oscar, 2007). In addition, the latest research reports that animal manure waste, waste paper, citrus peel waste, and municipal solid waste can be used as feedstock of bioethanol production by using saccharification and fermentation processes (Lal, 2008; Foyle et al., 2007; Wilkins et al., 2007).


Table 1. Maximum amount of work for the conversion of fuels to electricity calculated at 298 K and 1 bar (Source: Delsman et al., 2006)

However, bioethanol fermentation is a complicated process. The overall process is schematically shown in Figure 1. It requires many steps of biomass feed conditioning or pretreatment which can be mainly divided into four techniques as follows (Magnusson, 2006):


Thereafter, the pre-conditioned biomass is biologically transformed into ethanol. This procedure is a key step to be accounted for increasing bioethanol productivity. The basic concept of reactor design is applied with enzymatic fermentation technology. Starting from a simple batch reactor, this is close to organic culture system environment but a batch culture envisages the limitation of enlarging bioethanol production scale. Afterward, semi-batch reactors combining the benefits of batch and continuous reactors are employed. It can offer a long lifetime of cell culture, higher ethanol and cell concentration (Frison & Memmert, 2002). Finally, a continuous flow reactor is applied with cell recycle operation to serve more bioethanol productivity requirement. Influent stream containing substrate, nutrients and culture medium is fed to an agitated bioreactor. The product is removed from the fermenter but the residues (cells and nutrients) are collected and recycled to the vessel. In addition, the concept of process integration is introduced to the bioethanol production application such as Separate Hydrolysis and Fermentation (SHF), Simultaneous Saccharification and Fermentation (SSF) and Direct Microbial Conversion (DMC) (Balat, 2011). In the last step, the obtained dilute ethanol is then purified to gain a desired ethanol concentration. These difficult procedures need to be further developed to reduce the complexity and enable the process to compete with the cheaper oil-derived fuel production.

Many researchers attempt to develop such a biotechnical bioethanol production to be costeffective. Effective tools for the process evaluation such as thermo-economic, environmental indexes, process optimization and etc. are used to analyze the bioethanol production process as performance indicators to assist in the task of process design. Process integration is regarded as a significant approach since several production procedures are combined into a single unit. It can reduce production costs and provide a more intensive process. For example, the fermentation process integrated with membrane distillation (Gryta, 2001) involved the combination of tubular bioreactor and membrane distillation to synergistically enhance the yield of bioethanol without several units being required as for other common processes. A role of membrane distillation is to remove byproduct from the fermentation broth in bioreactor that can simultaneously forward glucose conversion to gain more ethanol. The objective of process integration is to have the energy requirement in procedures of bioethanol production to be less than the energy obtained from the bioethanol exploitation to utilize bioethanol effectively.

Fig. 1. Schematic diagram of bioethanol production process (Source: U.S. Department of Energy)

Bioethanol can be purified to anhydrous ethanol which is a useful chemical for various applications such as organic solvent, chemical reagent, reactant for biodiesel production, pharmaceutical formations, plastics, polishes and cosmetics industries (Kumar et al., 2010). However, in this chapter, the use of bioethanol is particularly focused on a role of renewable fuel. Application of bioethanol in term of fuel can be mainly divided by two directions:


For conventional direct combustion, it seems to be less complicated but the fuel is utilized in an ineffective way because thermal energy accumulated in bioethanol is obviously lower than fossil fuel as shown in Table 2.


Table 2. Properties of bioethanol in comparison with petrol (Source: Paul & Kemnitz, 2006)

Moreover, since water is the main constituent in bioethanol, the direct combustion of bioethanol is not possible. However, there is another effective way which is the conversion of bioethanol fuel into hydrogen rich gas. As presented in Table 3, the heating value of hydrogen is higher than that of ethanol (4.47 times). Therefore, the bioethanol reforming process for producing hydrogen is a promising pathway in term of upgrading fuel quality which can offer a higher performance for the SOFC system even in the combustion heat engine while the bioethanol fuel utilization can be conducted in an efficient way.


Table 3. Heating values of commonly-used fuels in comparison

Typically, there are three main reforming reactions for hydrogen production as described below:


194 Renewable Energy – Trends and Applications

Many researchers attempt to develop such a biotechnical bioethanol production to be costeffective. Effective tools for the process evaluation such as thermo-economic, environmental indexes, process optimization and etc. are used to analyze the bioethanol production process as performance indicators to assist in the task of process design. Process integration is regarded as a significant approach since several production procedures are combined into a single unit. It can reduce production costs and provide a more intensive process. For example, the fermentation process integrated with membrane distillation (Gryta, 2001) involved the combination of tubular bioreactor and membrane distillation to synergistically enhance the yield of bioethanol without several units being required as for other common processes. A role of membrane distillation is to remove byproduct from the fermentation broth in bioreactor that can simultaneously forward glucose conversion to gain more ethanol. The objective of process integration is to have the energy requirement in procedures of bioethanol production to be less than the energy obtained from the bioethanol

Fig. 1. Schematic diagram of bioethanol production process (Source: U.S. Department of

Bioethanol can be purified to anhydrous ethanol which is a useful chemical for various applications such as organic solvent, chemical reagent, reactant for biodiesel production, pharmaceutical formations, plastics, polishes and cosmetics industries (Kumar et al., 2010). However, in this chapter, the use of bioethanol is particularly focused on a role of renewable fuel. Application of bioethanol in term of fuel can be mainly divided by two

For conventional direct combustion, it seems to be less complicated but the fuel is utilized in an ineffective way because thermal energy accumulated in bioethanol is obviously lower

> **Caloric value (MJ/l)**

Petrol 0.76 42.7 32.45 92 1 Bioethanol 0.79 26.8 21.17 >100 0.65 Table 2. Properties of bioethanol in comparison with petrol (Source: Paul & Kemnitz, 2006)

**Octane-number (RON)** 

**Fuel-equivalence (l)** 

exploitation to utilize bioethanol effectively.


than fossil fuel as shown in Table 2.

**(kg/l)** 

**Fuel Density** 


**Caloric value at 200C (MJ/kg)** 

Energy)

directions:


Selection of an appropriate operation mode depends on the individual objective. Ethanol steam reforming (ESR) (Reaction (1)) is a suitable choice for the SOFC system because this reaction can produce hydrogen at high yield. Although ESR consumes a great amount of heat due to its high endothermicity, heat released from the fuel cell is enough to supply the heat demand for the reaction. For the ethanol partial oxidation (EPOX) (Reaction (2)), it is appropriate for the process required less complexity and integration design. Since EPOX requires the fuel to be partly combusted with air and releases thermal energy as an exothermic reaction, heat and steam supply are not required (Vourliotakis et al., 2009). Nonetheless, this reaction is less selective to hydrogen compared to the former reaction.

Autothermal reforming (ATR) is a combination of the previous two reactions in order to improve the hydrogen selectivity with minimum heat supply. The steam to carbon molar ratio and air to carbon molar ratio are significant parameters to adjust the system to operate close to thermal neutral condition from the exothermic partial oxidation and endothermic steam reforming. Generally, this reaction formula is defined as Reaction (3) with the standard exothermic heat ΔH298K = 50 kJ/mol (Deluga et al., 2004). There is a scientific literature (Liguras et al., 2003) reporting the stoichiometric ratio of H2O and O2 of 1.78 and 0.61, respectively per mol of ethanol can carry out thermal neutrality as shown in Reaction (4) but the yield of hydrogen becomes a little lower.

$$\rm C\_2H\_5OH + 3H\_2O \Rightarrow 2CO\_2 + 6H\_2 \tag{1}$$

$$\rm C\_2H\_5OH + 0.5O\_2 \Rightarrow 2CO + 3H\_2 \tag{2}$$

$$\rm C\_2H\_5OH + 2H\_2O + 0.5O\_2 \Rightarrow 2CO\_2 + 5H\_2 \tag{3}$$

$$\rm C\_2H\_5OH + 1.78HI\_2O + 0.61O\_2 \Rightarrow 2CO\_2 + 4.78H\_2 \tag{4}$$
