Flash pyrolysis of forestry residues from the Portuguese Central Inland Region within the framework of the BioREFINA-Ter project
Graphical abstract
Highlights
► Biomass wastes of Portuguese Central Region can be used as bio-refinery feedstock. ► Spouted bed reactor is suitable for handling irregular texture biomass wastes. ► High bio-oil yields (75–80 wt.%) are obtained for the three residues. ► Bio-oil contains interesting compounds and is adequate for catalytic upgrading. ► The biomass materials could be jointly valorized avoiding separation costs.
Introduction
The alternative routes to obtain fuels and raw materials from biomass have been grouped into the broad concept of bio-refinery, which has been defined as “a facility that integrates biomass conversion processes and equipment to produce fuels, power, and chemicals from biomass” (NREL, 2009). Fig. 1 shows the scheme of the design of a lignocellulosic biomass-based bio-refinery, where several chemical and thermochemical routes, such as gasification, pyrolysis, hydrolysis and anaerobic digestion have been considered. The technological development and industrial application of these processes should be carried out through their incorporation into existing or future refinery processes, with the development of specific valorization routes for biomass (Huber and Corma, 2007).
Biomass flash pyrolysis technology is versatile, simple and requires little capital investment, whereby its deployment on a moderate scale in the regions where the raw material is available can be decoupled from the further upgrading of bio-oil in large scale bio-refineries (Anex et al., 2010, Balat et al., 2009, Bridgwater, 2012). Flash pyrolysis technology is currently at a major development stage and it has been extended worldwide by several firms: Ensyn Technologies, Dinamotive, Agri-Therm, KIT, BTG and Wellman Engineering (Bridgwater, 2012, Butler et al., 2011).
Biomass flash pyrolysis leads to a bio-oil yield of around 60–75 wt.%, which consists of a very complex mixture of oxygenated compounds whose composition depends on the nature of the biomass used, as well as on the operating conditions (Mohan et al., 2006). The fuel properties of bio-oil differ greatly from those of petroleum-derived fuels because of its high content of water (20–30 wt.%) and oxygen (45–50 wt.%), which leads to a low heating value and high corrosiveness (Oasmaa and Czernik, 1999). Furthermore, stored bio-oil undergoes an aging process that results in an increase in viscosity and water content, whereas volatility decreases (Hilten and Das, 2010).
In order to ensure the feasibility of bio-oil upgrading, accounts need to be taken of the diversification, adapting the applications accordingly. Bio-oil can be directly used as a source of either chemicals or fuel (Czernik and Bridgwater, 2004); however, the drawbacks related to the instability and corrosiveness of the bio-oil require treatments prior to its use as fuel or raw material in refinery units. These treatments include physical and thermal processes or catalytic transformation for reducing the oxygen content of the bio-oil (Huber et al., 2006, Bridgwater, 2012). Furthermore, bio-oil is an essential raw material in a bio-refinery, as shown in Fig. 1. Bio-oil can therefore be converted into hydrocarbons in catalytic cracking units, using zeolites as catalysts (Gayubo et al., 2010), and subjected to steam reforming for hydrogen or syngas production (Wu et al., 2008).
A wide range of reactor configurations has been used to perform biomass flash pyrolysis, with the more outstanding ones being bubbling fluidized bed reactors (Heo et al., 2010, Jung et al., 2012), circulating and transported fluidized bed reactors (Lappas et al., 2008, Oasmaa et al., 2010), ablative reactors (Faix et al., 2010), rotating cones (Venderbosch and Prins, 2010), auger reactors (Brown and Brown, 2012), vacuum reactors (Yang et al., 2001) and conical spouted bed reactors (Amutio et al., 2011, Amutio et al., 2012a, Amutio et al., 2012b).
The conical spouted bed reactor (CSBR), which is an alternative to fluidized beds, performs well for biomass flash pyrolysis with continuous solid feeding. In addition, the bio-oil yields obtained with this reactor are high in a wide range of temperatures, from 71 wt.% at 400 °C to 75 wt.% at 500 °C for pinewood pyrolysis (Amutio et al., 2012a). The vigorous cyclic movement contributes to high heat and mass transfer rates between phases (Makibar et al., 2011) and the great versatility of the gas flow rate allows operating with short gas residence times (Olazar et al., 1993). Several improvements have been carried out in previous studies for scaling up the process, which are additional advantages to the CSBR’s simplicity and low commissioning cost. Thus, vacuum operation reduces the gas flow rate to be heated to the reaction temperature and simplifies bio-oil condensation, reducing the associated costs (Amutio et al., 2011). Additionally, the process can be carried out autothermally by feeding a small amount of oxygen into the reaction environment, which does not compromise bio-oil quality (Amutio et al., 2012b). Furthermore, the excellent performance of the conical spouted bed reactor has been confirmed in the scaling-up of the biomass pyrolysis process, with the development of a 25 kg h−1 pilot plant (Makibar et al., 2011).
Section snippets
The BioREFINA-Ter project
Raw materials originating from bushes, uncultivated land, and forestry and agricultural wastes are the major sources for the production of renewable and sustainable liquid fuels in Portugal, constituting a strategic option for reducing the energy dependence of the transport sector. Portugal has a very significant area of woods and uncultivated land (22%) and forest of pure and mixed strands of Pinus pinaster and Eucalyptus globulus (21%). Agriculture takes up an area of 33%, composed mainly of
Raw materials
Three types of biomass residues have been pyrolyzed in this study: a mixture of two broom species made up of 50% Cytisus multiflorus and 50% Spartium junceum (Bio1), Acacia dealbata (Bio2) and Pterospartum tridentatum known as carqueisa (Bio3). The main feature of these forestry wastes is their heterogeneous nature, given they are shrubby flowering plants made up of wood, bark and leaves. The biomass materials have been milled into a particle size in the 1–2 mm range in order to facilitate their
Results and discussion
The valorization feasibility of these biomass waste materials by flash pyrolysis has been studied in terms of product yields and properties.
Conclusions
The Portuguese Central Inland Region contains readily available biomass resources that can be used as bio-refinery feedstock, thus improving the local economy and contributing to the technological development of renewable energy sources. The flash pyrolysis of forestry wastes in a CSBR is a suitable process for the valorization of biomass materials of irregular texture in continuous mode. This process gives way to high bio-oil yields with a suitable composition for extracting individual
Acknowledgements
This work was carried out with the financial support of the University of the Basque Country (UFI 11/39), Permanent Forest Fund – Portugal (Project IFADAP/INGA 2110090013466), the Local Authority of Oliveira do Hospital (Portugal) and of the Basque Government (Project GIC07/24-IT-220-07). Maider Amutio thanks the University of the Basque Country UPV/EHU for her post-graduate Grant (UPV/EHU 2011) and Jon Alvarez the Basque Government for his research training Grant (BFI2010-206).
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