*From Biomass to Biobased Products*

**Table 4.** *Experimental*

 *results.* *Application of the Six Sigma DMAIC Methodology to the Gasification Process DOI: http://dx.doi.org/10.5772/intechopen.111850*

**Figure 6.** *Temperature profile over time.*

temperatures (>1000°C). **Figure 6** depicts the temperature profiles over time (see also Bubbling Fluidized Bed Reactor P&ID).

The temperature profiles for the different experiments showed similar behavior. Yet, the experiments performed with pine chips had higher temperature fluctuations than those performed with pine pellets. Pine chip particle size is heterogeneous. At the same time, wood pellets have a more homogeneous particle size, which can justify the temperature fluctuations.

#### *4.3.3 Gas composition*

Adding RDF to the fuel mixes significantly reduced the CO content in the produced gas for comparable ER. The phenomenon may be related to the methanation reactions described below.

$$\text{C}2\text{CO} + 2\text{H}\_2 \rightarrow \text{CH}\_4 + \text{CO}\_2\tag{5}$$

$$\text{CO} + \text{\text{\textdegree}}\_2\text{O} \rightarrow \text{CH}\_4 + H\_2\text{O} \tag{6}$$

However, there is a discrepancy between experiment PC90 - RDF10: ER022 and experiment PC80 - RDF20: ER022. Both experiments were performed at ER = 0.22, having 10 and 20% of RDF, respectively. Therefore, a lower CO concentration in the mixture of 20% RDF was expected (See **Table 4**).

On the other hand, If ER increases, then CO decreases even more. However, there is a discrepancy between experiments PC80 - RDF20: ER031 and PC50 - RDF50: ER032, which were run at 20% of RDF and ER = 0.31 for the first one and 50% of RDF and ER=0.31 for the second one. The results show that the CO concentration was 12.6 and 13.6%, respectively. These discrepancies may be related to a wrong ER since a higher ER means more nitrogen. Never less. In these examples, the nitrogen concentration is lower in blends with higher RDF.

Generally, **Figure 7** illustrates the effect of the RDF weight % in the fuel mixture on the composition of the produced gas. The gasification of pine chips with 0.23 ER produced the highest CO concentration (18.6 vol%, experiment reference PC100: ER0.23), whereas RDF with 0.23 ER produced the lowest CO concentration (6.9 vol%, experiment reference RDF100: ER0.23). Increasing the amount of RDF in the

**Figure 7.** *Influence of the RDF weight percentage on the gas composition (H2, CO, and CO2).*

feedstock combination from 10 to 20%, 20 to 50%, and 50 to 100% resulted in CO reductions of 6.3, 1.5, and 42.0%, respectively. In contrast, increasing the RDF weight percentage from 0 to 10% in the fuel combination resulted in an average CO increase of 5.5%.

The effect of adding RDF on CH4 and C2H4 results in a higher composition as wt%. of RDF increases. For the gasification of RDF with ER 0.27 (experiment reference RDF100: ER 0.27), the maximum CH4 and C2H4 concentrations were 5.6 and 5%, respectively. On the one hand, this may be rationalized by the thermal breaking of polymers in RDF pellets, which yields light hydrocarbons. On the other hand, the increased quantity of ashes rich in alkali and alkali earth metals (e.g., calcium, sodium, magnesium, potassium) found in RDF pellets compared to biomass (**Table 2**) may stimulate a catalytic effect that also results in the synthesis of light hydrocarbons. However, **Figure 8** shows a higher amount of CH4 for blends of pine chips with no RDF, which can be an error derivate from a wrong ER measured or wrong feedstock measure derivate from the particle size and shape since this problem is seen to be reduced with pine pellets.

#### *4.3.4 LHV, Ygas, CGE, and CCE*

As shown in **Table 2**, although RDF contains a considerable amount of ash, it also contains more carbon and hydrogen than pine chips and pellets. Therefore, mixtures with more RDF will need more air in a given ER than those with less RDF in the same ER. For example, if it is assumed that carbon of 100 g of samples of RDF, pine chips, and pine pellets will burn completely (ER = 1), then 18.84% more oxygen will be required for RDF than for pine chips. At the same time, 13.68% more oxygen will be needed for RDF than for pine pellets (see **Table 5**). This situation indicates that blends with more RDF will deliver higher Ygas values than those with less RDF.

*Application of the Six Sigma DMAIC Methodology to the Gasification Process DOI: http://dx.doi.org/10.5772/intechopen.111850*

**Figure 8.** *Influence of the RDF weight percentage on the gas composition (CH4, C2H4, C2H6, and C3H8).*


**Table 5.**

*Required oxygen for complete combustion of 100 g of sample of each feedstock.*

This analysis indicates that blends with more RDF will deliver higher Ygas values than those with less RDF. However, **Figure 9** is not entirely aligned with this analysis, which may indicate a potential error in the ER or the fed feedstock amount.

On the other hand, the LHV of the generated gas improved with increasing ER (from 5.8 to 6.4 MJ/Nm<sup>3</sup> ), mainly due to an increase in CH4 and C2H4. This behavior is not expected in operations involving biomass gasification. It may be due to the higher ER promoting the thermal breaking of the organic molecules in the plastic fractions of RDF. Thus, this effect increases in blends with higher RDF amounts. However, this effect is unclear, so it may be an error in ER or the fed feedstock.

**Figure 10** depicts the influence of RDF wt.% on CGE and CCE. Adding RDF to the fuel mixture has no appreciable effect on the CGE. However, there is a slight tendency for CGE to grow when the RDF weight % rises. The RDF gasification with an ER of 0.27 yielded the highest CGE value (53.5%). (Experiment reference RDF100: ER0.27). The lowest CGE value (32.6%) was reported for the gasification of pine pellets with an ER of 0.30. (Experiment reference PP100: ER0.30).

Gas Composition: Higher RDF wt.% increases CH4 and C2H4 and reduces CO concentration. This effect might be due to the thermal cracking of the plastic polymers in the RDF pellets and the catalytic effect promoted by the ashes (alkali and alkali earth metals). In contrast, no significant trends were observed for the variation of H2.

**Figure 9.** *Influence of the RDF weight percentage on the LHV and Ygas.*

**Figure 10.** *Influence of the RDF weight percentage on the CGE and CCE.*


In conclusion, the following tendencies are noticed, and numbers outside the trend may sometimes suggest a measurement mistake, causing variance in the process.
