**2. Conclusions**

**Heating rate K/min**

228 Gasification for Low-grade Feedstock

ambience.

**(a) CO2**

CO<sup>2</sup>

3 mm

800 micron

 **ambience**

**(b) Steam and blended ambience** [36]

ambience

under argon, CO<sup>2</sup>

and steam ambience.

**900 μm 500 μm 60 μm**

 214.45 192. 179.88 151.83 138 129.24 161 143.54 134.24 202.69 179.41 167.94 189.28 168 157 197 181.27 175.58 195.52 175.77 171 210 190 184 194.8 181.31 175.5 212 189 184 171.75 156.8 153 207.8 193.27 187.3

**Table 6.** Comparison of the activation energy values (kJ/mol) of Indian coal-char gasified at 900, 950 and 1000°C in CO<sup>2</sup>

exhibits relatively lower values of activation energy as comparing with other two models. The changes in the activation energy over the char heating rate are almost consistent regardless of the particle sizes considered in the blended ambience. Moreover, a significant observation form this study is that the gasification activation energy of 3 mm char is higher when compared to 800 μm char particles. This is mainly caused due to the better reactivity potential of

100 132.5 132.51 131.63 132.9 132.93 132.33 500 115.71 115.63 115.26 130.85 130.66 130.32 800 128.21 128.47 128.19 138.34 138.35 137.37

K/min VM GM RPM VM GM RPM VM GM RPM

100 161.2 158.8 156.4 179.0 179.1 179.6 173.9 164.2 162.3 500 172.9 172.9 173.6 172.7 172.6 172.8 169.1 169.1 167.6 800 170.6 170.9 171.2 190.7 190.6 190.9 196.7 196.7 194.7

100 155.3 154.6 154.5 156.7 156.7 156.6 133.4 133.5 131.3 500 132.3 131.8 131.6 111.5 111.8 112.1 127.4 127.6 126.2 800 152.1 152.1 152.2 169.4 169.1 169.0 149.9 150.1 147.1

**VM** G**M RPM VM GM RPM**

**(steam — 0.7 & CO2**

 **— 0.1)**

**75 ml argon +50 ml CO2 (steam — 0.6 & CO2**

 **— 0.2)**

**Table 7.** Comparison of the activation energy values (kJ/mol) of 800 μm and 3 mm chars gasified at 850, 900 and 950°C

800 μm char owing to its higher specific surface area.

**Heating rate K/min 800 μm 3 mm**

**Heating rate 100 ml argon (steam — 0.8) 75 ml argon +25 ml CO2**

**VM GM RPM VM GM RPM VM GM RPM**

Pyrolysis and gasification studies of Indian and Turkish high ash coal samples have been carried out using coupled TGA-MS method. Coal samples were heated in the TGA apparatus in various gaseous mixture combinations at a temperature range of 25–1250°C under various heating rates. The mass loss data show that the devolatilisation is essentially influenced by the heating rate. Even at higher heating rates, particle sizes do not influence the pyrolysis process and the rate of volatilization is essentially constant. During thermal decomposition and devolatilization of coal, CO, CO<sup>2</sup> , H<sup>2</sup> and CH4 are the major gaseous products. The reaction of coal with steam starts around 800 °C. The complete carbon conversion takes place in the temperature range of 900– 950 °C. The syngas production rate is maximum in these temperature limits. In order to study char gasification, char particles are generated in argon ambience with various heating rates. Char gasification rates investigation in steam and CO<sup>2</sup> blended ambience shows that the pyrolysis heating rate (for char generation) has a considerable impact on the gasification reactivity of the char. Also smaller particles exhibit higher char-CO<sup>2</sup> and char-steam gasification rates. Increasing the temperature from 850 to 950°C leads to the reduction of the time required for 50% conversion by a ratio of more than fourfold. The chars generated under high heating rates present enhanced gasification rates which are mainly due to the alteration of the char pore structure and the accessibility of more active sites to initiate reactions with the gasification agent. The gasification rate of char-H<sup>2</sup> O is mainly dependent on H<sup>2</sup> O partial pressure, temperature and particle sizes. The maximum reaction rate is shifted to the higher conversion stage for chars produced with high heating rates. The introduction of CO<sup>2</sup> did not inhibit the steam-char gasification reactions and also did not compete for reactive sites. Steam and CO<sup>2</sup> react simultaneously on different active sites on the char surface. Kinetic parameters of the char particles were estimated using different kinetic models. The activation energy for steam gasification is 156–173 kJ/mol, whereas in the steam blended with CO<sup>2</sup> ambience they are between 162 and 196 kJ/mol for 3 mm Turkish coalchar particles. For the Indian coal, the reaction rate is chemically controlled in steam ambience at lower temperatures. The activation energy for steam gasification varies from 122 to 177 kJ mol−1 for different sized char particles. The activation energies estimated by the GM model for the three particles are in the range of 138–193 kJ mol−1. The RPM model predicted values in the range from 129 to 187 kJ mol−1 for CO<sup>2</sup> gasification. The activation energies for char gasification essentially depend on the char generation method (pyrolysis heating rate) and on the particle size.

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#### **Acknowledgements**

Financial support for this work is provided by the European Commission under Project OPTIMASH FP7-ENERGY, 2011-1 Project No. 283050.
