Efect of Temperature on the Flow Profile of the Bio-oil Produced from the Fast Pyrolysis of Sisal Residue

Abstract

The objective of this study was to evaluate the flow of a film of bio-oil in a cylindrical tube similar to the tube of a heat exchanger found in a fast pyrolysis unit of sisal residue in a fluidized bed. The velocity profile of bio-oil was determined from the momentum balance and the equation that describes the rheological behavior of the fluid. The rheological behavior of bio-oil was determined at 60, 70, 80, 90, and 110 °C, and eight models to describe the rheological behavior were evaluated. The Sisko, Herschel–Bulkley, Mizrahi−Berk and Robertson−Stiff models all performed similarly, and they adequately represented the rheological behavior of bio-oil with a pour point of 55 °C derived from sisal residue. The variation of the thickness of the bio-oil film on the walls of a cylindrical tube and the velocity profile in the film as a function of temperature were determined empirically using the four best rheological models. Only the equation of flow employing the rheological model of Sisko showed results consistent with the behavior of the fluid.

Bio-Oil Viscosity of Sisal Residue: Process and Temperature Influence

“…Fast pyrolysis of eucalyptus was carried out in the same pilot plant, under similar operating conditions as the sisal residue tests (N 2 F = 11 N m 3 /h; BioF = 1083 g/h and temp = 500 °C), and the results showed that the viscosity values of the eucalyptus bio-oil are about 10 times smaller than those coming from the sisal residue (Appendix A, Supporting Information), being close to those found by other authors. Figure shows that the viscosity of sisal residue bio-oil decreases with increasing shear rate, which confirms the yield-pseudoplastic rheological behavior of this fluid, as reported in the work of Pereira and Pires . It has also been observed that viscosity is influenced by temperature, and, as discussed above, the values obtained are comparable to those of other bio-oils at temperatures above 70 °C.…”

“…Some tests were carried out to produce 4 additional bio-oil samples under different operating conditions. The results (Appendix A, Supporting Information) showed that the water contents of the bio-oil samples are influenced by the operational conditions of production, although the variation between the samples is small and the water content is close to the value reported by Pereira and Pires (biomass = 6.11 wt %; bio-oil = 5.18 wt %). This fact reinforces that smaller flow rates of drag gas were responsible for the production of a bio-oil with lower viscosity due to the increase in the residence time of the molecules in the reactor, causing the reduction of their size.…”

“…According to Pereira and Pires, the bio-oil produced from sisal residue had an incredibly waxy and viscous appearance at room temperature, which was very different from the reports in the literature regarding the bio-oil produced from other biomass sources. While some authors have reported that bio-oil behaves as a Newtonian fluid above 46 °C and as a Bingham plastic below this temperature, sisal residue bio-oil simply does not flow at temperatures lower than 55 °C.…”

“…After being cooled to room temperature, the short sisal fibers were removed from the biomass, leaving dried slices. The general properties of sisal residue, as well as those of the bio-oil produced, were reported by Pereira and Pires . The sisal residue used in the reaction was not submitted to any diameter adjustment and used the same granulometric distribution from the sisal leaf defibration process.…”

“…The bio-oils commonly found in the literature have viscosity values ranging from 100 to 400 mPa•s at 40 °C. 4 However, the work of Pereira and Pires 7 showed that the biooil of sisal residue had very high viscosities, with values reaching 2000 mPa•s. These authors reported that bio-oil from sisal residue caused incrustations on the inner walls of the pilot plant heat exchangers, making it difficult to recover.…”