**4.1.3 IRSOFC operating on biodiesel fuels (BDFs)**

174 Renewable Energy – Trends and Applications

The SOFC testing system and automatic gas chromatograph were connected to the methane fermentation reactor placed in Tosu Kankyo Kaihatsu Ltd. as shown in Fig. 8 (Shiratori et al., 2010a). Garbage collected in Tosu-city of Saga prefecture was mixed with water resulting in waste slurry. After materials unsuitable for anaerobic fermentation were filtered out, cattle manure was added to the slurry followed by the treatment with acid and methane fermentation processes to produce biogas (mixture of CH4 and CO2) containing 790 ppm H2S. The raw biogas was passed through a desulfurizer packed with FeO pellets 20 cm3 in size. The typical composition of desulfurized biogas sampled from the fermentation reactor is listed in Table 4. The concentration of H2S was less than 0.5 ppm. The concentrations of the other fuel impurities, CH3SH, Cl2, HCl, NH3 and siloxane, were below the detection limits (2 ppb, 60 ppb, 0.4 ppm, 0.6 ppm and 10 ppb, respectively), indicating that this gas can be fed directly into a SOFC (Haga et al., 2008). In any case, 1 ppm level H2S contamination must be taken into account even after desulfurization treatment. The experimental setup for testing IRSOFC operating on biogas has been described elsewhere (Shiratori et al., 2010a). The pressure controlled real biogas (0.1 MPa) was directly distributed to the SOFC at 800 oC and the gas chromatograph with flow rates of 25 and 140 ml min-1, respectively, in order to evaluate the electrochemical performance with simultaneous monitoring of biogas composition. In this experiment, water vapor in the real biogas was removed by a cold trap thermostated at 0 oC.

Acid fermentation

5 m3 /day

Compressor

Weekday: 6 times / day Weekend: 4 times / day

0.5 m3 / day

Intermediate products

Reservoir

10 m3 28-30 oC pH 2.5-2.6

Water Cattle manure slurry

Waste slurry

Fig. 8. Connection of SOFC test system and gas chromatograph with the methane

Table 4. Typical composition of the actual desulfurixed biogas (Shiratori et al., 2010a).

fermentation reactor in Tosu-city, Japan (Shiratori et al., 2010a, 2010b).

4.5 m3 / day

Methane fermentation

> 144 m3 35-39.5 oC pH 7.4-7.5

Desulfurizer (FeO pellets)

Biogas

Dry air was supplied to the cathode side with a flow rate of 50 ml min-1

4 m3 / day

SOFC

Filtering

Gaschro

**Gaseous species Concentration**  CH4 62.6 vol % CO2 35.7 vol % H2O 1.62 vol % N2 0.09 vol % H2 99 vol ppm H2S < 0.5 ppm

**4.1.2 IRSOFC operating on biogas** 

Bio-wastes 0.5-1 t / day

Exhaust

Exhaust

Palm-, jatropha- and soybean-biodiesel fuels (BDFs) were produced from refined palm-, jatropha- and soybean-oils, respectively, at Bandung Institute of Technology, Indonesia (ITB). The main chemical components of the BDFs are listed in Table 5.


Table 5. Main components in the biodiesel fuels applied to SOFC (Shiratori et al., 2011).

Table 6 shows the concentrations of saturated and unsaturated components in the BDFs and their average structures. Palm-BDF consisted mainly of 46.8 % saturated fatty acid methyl esters (FAMEs) and 40.8 % mono-unsaturated FAMEs. Jatropha- and soybean-BDFs contained a higher amount of unsaturated FAMEs compared to palm-BDF. Jatropha-BDF consisted mainly of 40.9 % mono-unsaturated FAMEs and 37.6 % di-unsaturated FAME. Soybean-BDF consisted mainly of 24.8 % mono-unsaturated FAMEs and 54.0 % diunsaturated FAME. Soybean-BDF not only contained higher amount of di-unsaturated FAME compared to jatropha-BDF but also contained a rather high amount of triunsaturated FAME (5.75 % linolenic fatty acid methyl ester). All BDFs had almost the same physical properties similar to petro-diesel. The experimental setup for testing the IRSOFC running on BDFs has been described elsewhere (Shiratori et al., 2011; Tran et al., 2011). Dry air was supplied to the cathode side with the flow rare of 150 ml min-1. BDFs and H2O were supplied to the anode side with the flow rates of 6 and 21-22 l min-1, respectively. BDFs


were evaporated and mixed with H2O at 600 oC and then fed to the anode side together with nitrogen carrier gas with the flow rate of 50 ml min-1.

Table 6. Composition of saturated and unsaturated components in the tested BDFs (Shiratori et al., 2011).

The C-H-O diagram (see Fig. 9) clearly shows that unless a generous amount of oxidant is added, biogas (CH4/CO2 = 1.5) and BDF will form coke on the anode material during SOFC operation. We added air and water to gaseous biogas and liquid BDF, respectively, to avoid carbon deposition from the thermodynamic point of view.

Fig. 9. C-H-O ternary diagram showing the possibility of coking when the biofuels are fed directly to SOFC (Sasaki & Teraoka, 2003).
