Multivariate analysis for ascertaining the influence of biomass composition and fast pyrolysis conditions on product distribution in conical spouted bed reactors

This study evaluates the influence of biomass composition and fast pyrolysis conditions in conical spouted bed reactors (CSBR) for the identification of relevant correlations involving parameters of pyrolysis process, biomasses composition and products (biochar, bio-oil and gas) yields, applying Pearson's correlation followed by Principal Component Analysis (PCA). In total, 40 experiments were carried out in a CSBR with eight different plant biomasses: Pinus sawdust (Pin); poplar wood (Po); eucalyptus trunk residues (Euc); orange peel residue (Ow); acacia (Ac); gorse (Car); rice husk (Rh) and forest species mixture (Mix). The highest bio-oil yield (OY) obtained were associated with clusters of experiments using Mix, Ac, Car, Euc, and Pin biomasses. OY was negatively correlated with the following variables: fixed carbon content (FC vs OY: - 0,41; p-value: 0.0082); mass flow rate of biomass (Mfr vs OY: - 0.42; p-value: 0.0073); and volume flow rate of inert gas (N2fr vs OY: 0.41; p-value: 0.0082). The highest biochar yields (CY) were associated with experiments in which Rh and Ow biomasses were used. CY was positively correlated with the contents of fixed carbon (FC vs CY: 0.49; p-value: 0.0014) and ash (CZ vs CY: 0.55; p-value: 0.0003), but negatively correlated with moisture content (M vs CY: 0.75; p-value: 0.0000). The highest values of gas yield (SY) were associated with the experiments using Pin and Po biomasses. SY was positively correlated with the process variables mass flow rate (Mfr vs SY: 0.54; p-value: 0.0003); nitrogen gas flow rate (N2fr vs SY: 0.54; p-value: 0.0003); and temperature (T vs SY: 0.44; p-value: 0.0049) but negatively correlated with ash content (CZ vs SY: - 0.40; p-value: 0.0102). From linear combinations among different pairs of correlated variables (PCA analysis), 68.8 % of the variance of the original dataset was explained by the first three principal components (PC1: 34.5 %; PC2: 20.8 % and PC3: 13.5 %). The variables with significant contribution to PC1 in descending order were: M, CY, N2fr, Mfr, CZ and SY. In the case of PC2, the descending order is OY, FC, SY, VM, N2fr, Mfr; and for PC3: T, SY and CY. The groups G1 (23 experimental runs with Pin) and G3 (4 experimental runs with Rh) favored OY yield. G4 (3 experimental runs with Ow) favored biochar yield (CY), and groups G2 (4 experimental runs, with Mix, Ac, Car and Euc) and G5 (6 experimental runs with Po) accounted for higher gas yield (SY).