*3.2.3 Effect of fountain confinement on biomass gasification*

Runs have been carried out with a S/B ratio of 2 and at a temperature of 850°C with different spouting regimes and gas flow patterns developed in conical spouted beds, such as (i) standard spouting regime without fountain confiner, (ii) standard spouting regime with fountain confiner, and (iii) enhanced fountain regime with fountain confiner. **Table 5** compares the gas yield, tar content, carbon conversion efficiency, char yield, and H2 production results obtained for the three configurations mentioned.

As observed in **Table 5**, the incorporation of the fountain confiner leads to a decrease in tar content in the syngas from 49.2 g Nm<sup>−</sup><sup>3</sup> without fountain confiner to 34.6 g Nm<sup>−</sup><sup>3</sup> when this device is inserted. The volatiles in the conventional spouted bed gasifier leave quickly from the reaction zone through the outlet located in the gasifier upper section. Thus, the short residence time of the volatiles limits the contact of tars and other gaseous products with the catalyst, which hinders cracking and reforming reactions and therefore lowers conversion efficiency. On the contrary, the fountain confiner prevents the premature leaving of the gases at an initial stage in the biomass gasification and causes a downward gas flow inside the confiner, which favors the contact between the volatile stream and the catalyst. Furthermore, the confined fountain and the use of draft tubes lead to a highly stable hydrodynamic regime, which allows operating with finer materials (lower particle sizes of olivine) and higher fountain heights [24].

In order to analyze the influence on the gasification performance by changing the gas-catalyst contact in the reactor, especially in the fountain region, runs with the fountain confiner were performed under similar residence times (same reactor geometry and gas flow rate) as in conventional conical spouted beds. As observed in **Table 5**, the promotion of steam reforming of tars and gaseous hydrocarbons using the confinement system improved the gas yield and H2 production from 1.1 to 1.2 m3 kg<sup>−</sup><sup>1</sup> and from 3.5 to 4.6 wt%, respectively. In the same line, the carbon conversion efficiency also increased when the confinement system was used, given that a value of 83.6% was obtained instead of 81.5% without this system. It should be remarked that these values are slightly higher than those reported by other authors in fluidized bed reactors under similar conditions [51, 52].


**87**

increases to 43.2%.

**Figure 6.**

**4. Conclusions**

*Development of the Conical Spouted Bed Technology for Biomass and Waste Plastic Gasification*

**Table 5** also shows that the results are greatly improved under fountainenhanced regime by decreasing olivine particle size and increasing the fountain

improvement is associated with the better gas-catalyst contact and heat transfer rates in the fountain region due to the higher fountain height. Furthermore, the smaller particle size of olivine increased the catalyst surface area available for cracking and reforming reactions [14]. Moreover, gas composition with and without confiner (under conventional and fountain-enhanced regime) is shown in **Figure 6**. As observed in **Figure 6**, H2 concentration increases from 36 to 42% with and without the fountain confiner, whereas that of CO decreases. The effect on CO2 is not so remarkable, but its concentration is slightly higher when the fountain confiner is introduced. Furthermore, the concentration of methane and the other gaseous hydrocarbons decreased due to the higher extent of steam reforming reactions involving methane (Eq. (2)) and tar (Eq. (1)), as well as of water-gas shift (Eq. (6)) reactions when the fountain confiner was used. This improvement is related to the increase in the gas residence time and the better contact of the gas with the catalyst attained when the fountain confiner is used. It is noteworthy that effect of the fountain-enhanced regime on the gas composition is rather limited. The most significant change is that regarding H2 concentration, whose value

The conical spouted bed reactor is an interesting technology for the continuous steam gasification of biomass and waste plastics due to the high heat transfer rates for a highly endothermic process (as is gasification) as well as to the absence of defluidization problems. An increase in gasification temperature improves process efficiency in terms of conversion to gases, with the maximum carbon conversion being of 70 and 91.1% at 900°C for biomass and HDPE, respectively. Furthermore, steam/feed ratio has a positive effect on the composition of the gas by increasing the H2 concentration from 32 to 61% in the HDPE gasification and from 28 to 42% in that of biomass when steam/feed ratio is increased from 0 to 2. In fact, higher steam concentrations in the reaction environment enhance both tar cracking and char

under con-

under enhanced fountain regime. This

height. In fact, the tar content in the gas is reduced from 34.6 g Nm<sup>−</sup><sup>3</sup>

*Influence of the confinement system and spouting regime on gas composition.*

ventional spouting regime up to 20.6 g Nm<sup>−</sup><sup>3</sup>

*DOI: http://dx.doi.org/10.5772/intechopen.86761*

#### **Table 5.**

*Influence of the confinement system and spouting regime on the reaction indices.*

*Development of the Conical Spouted Bed Technology for Biomass and Waste Plastic Gasification DOI: http://dx.doi.org/10.5772/intechopen.86761*

**Figure 6.** *Influence of the confinement system and spouting regime on gas composition.*

**Table 5** also shows that the results are greatly improved under fountainenhanced regime by decreasing olivine particle size and increasing the fountain height. In fact, the tar content in the gas is reduced from 34.6 g Nm<sup>−</sup><sup>3</sup> under conventional spouting regime up to 20.6 g Nm<sup>−</sup><sup>3</sup> under enhanced fountain regime. This improvement is associated with the better gas-catalyst contact and heat transfer rates in the fountain region due to the higher fountain height. Furthermore, the smaller particle size of olivine increased the catalyst surface area available for cracking and reforming reactions [14]. Moreover, gas composition with and without confiner (under conventional and fountain-enhanced regime) is shown in **Figure 6**.

As observed in **Figure 6**, H2 concentration increases from 36 to 42% with and without the fountain confiner, whereas that of CO decreases. The effect on CO2 is not so remarkable, but its concentration is slightly higher when the fountain confiner is introduced. Furthermore, the concentration of methane and the other gaseous hydrocarbons decreased due to the higher extent of steam reforming reactions involving methane (Eq. (2)) and tar (Eq. (1)), as well as of water-gas shift (Eq. (6)) reactions when the fountain confiner was used. This improvement is related to the increase in the gas residence time and the better contact of the gas with the catalyst attained when the fountain confiner is used. It is noteworthy that effect of the fountain-enhanced regime on the gas composition is rather limited. The most significant change is that regarding H2 concentration, whose value increases to 43.2%.

## **4. Conclusions**

The conical spouted bed reactor is an interesting technology for the continuous steam gasification of biomass and waste plastics due to the high heat transfer rates for a highly endothermic process (as is gasification) as well as to the absence of defluidization problems. An increase in gasification temperature improves process efficiency in terms of conversion to gases, with the maximum carbon conversion being of 70 and 91.1% at 900°C for biomass and HDPE, respectively. Furthermore, steam/feed ratio has a positive effect on the composition of the gas by increasing the H2 concentration from 32 to 61% in the HDPE gasification and from 28 to 42% in that of biomass when steam/feed ratio is increased from 0 to 2. In fact, higher steam concentrations in the reaction environment enhance both tar cracking and char

*Sustainable Alternative Syngas Fuel*

of this catalyst.

tions mentioned.

34.6 g Nm<sup>−</sup><sup>3</sup>

1.2 m3

kg<sup>−</sup><sup>1</sup>

Tar content (g Nm<sup>−</sup><sup>3</sup>

Char yield (g Nm<sup>−</sup><sup>3</sup>

kg<sup>−</sup><sup>1</sup>

Gas yield (m3

reduction in that of CO due to the promotion of the water-gas shift reaction (Eq. (6)). In addition, the higher concentration of H2 by the presence of this type of catalyst is also related to the enhancement of tar cracking and reforming reactions (Eq. (1)). Moreover, γ-alumina also seems to promote methane and light hydrocarbon reforming (Eq. (3)), which can be deduced from their lower concentration in the presence

Runs have been carried out with a S/B ratio of 2 and at a temperature of 850°C with different spouting regimes and gas flow patterns developed in conical spouted beds, such as (i) standard spouting regime without fountain confiner, (ii) standard spouting regime with fountain confiner, and (iii) enhanced fountain regime with fountain confiner. **Table 5** compares the gas yield, tar content, carbon conversion efficiency, char yield, and H2 production results obtained for the three configura-

As observed in **Table 5**, the incorporation of the fountain confiner leads to a

bed gasifier leave quickly from the reaction zone through the outlet located in the gasifier upper section. Thus, the short residence time of the volatiles limits the contact of tars and other gaseous products with the catalyst, which hinders cracking and reforming reactions and therefore lowers conversion efficiency. On the contrary, the fountain confiner prevents the premature leaving of the gases at an initial stage in the biomass gasification and causes a downward gas flow inside the confiner, which favors the contact between the volatile stream and the catalyst. Furthermore, the confined fountain and the use of draft tubes lead to a highly stable hydrodynamic regime, which allows operating with finer materials (lower

In order to analyze the influence on the gasification performance by changing the gas-catalyst contact in the reactor, especially in the fountain region, runs with the fountain confiner were performed under similar residence times (same reactor geometry and gas flow rate) as in conventional conical spouted beds. As observed in **Table 5**, the promotion of steam reforming of tars and gaseous hydrocarbons using the confinement system improved the gas yield and H2 production from 1.1 to

version efficiency also increased when the confinement system was used, given that a value of 83.6% was obtained instead of 81.5% without this system. It should be remarked that these values are slightly higher than those reported by other authors

and from 3.5 to 4.6 wt%, respectively. In the same line, the carbon con-

**With confiner (standard spouting)**

) 49.2 34.6 20.6

) 1.1 1.2 1.3

) 6.5 6.2 6.0

Carbon conversion (%) 81.5 83.6 86.1

H2 production (wt%) 3.5 4.6 5.0

when this device is inserted. The volatiles in the conventional spouted

without fountain confiner to

**With confiner (enhanced fountain)**

*3.2.3 Effect of fountain confinement on biomass gasification*

decrease in tar content in the syngas from 49.2 g Nm<sup>−</sup><sup>3</sup>

particle sizes of olivine) and higher fountain heights [24].

in fluidized bed reactors under similar conditions [51, 52].

**Without confiner**

*Influence of the confinement system and spouting regime on the reaction indices.*

**86**

**Table 5.**

gasification and so increase carbon conversion efficiency. Nevertheless, the concentration of the tars attained is still high for its direct application. The use of primary catalysts, such as olivine and γ-alumina, has shown an excellent performance for tar elimination as their content is being reduced by up to 30.1 and 22.4 g Nm<sup>−</sup><sup>3</sup> with olivine and γ-alumina, respectively.

The incorporation of a fountain confiner in the CSBR allows modifying bed hydrodynamics, i.e., increase the residence time of the volatiles and improve their contact with the catalyst in order to promote gasification performance and favor tar cracking. Hence, H2 productions and carbon conversion efficiencies increase when the fountain confiner is introduced from 3.5 to 4.6 wt% and from 81.5 to 83.6%, respectively. Moreover, the H2 concentration increases from 36 to 42%, whereas that of CO decreases from 34 to 29% with and without the fountain confiner. This device allows operating under enhanced fountain regime by reducing olivine particle size, which leads to a better contact between olivine and the gases, and therefore tar content is further reduced, and the carbon conversion efficiency increases up to 86.1%.
