ARTICLE pubs.acs.org/EF
Bioslurry as a Fuel. 4. Preparation of Bioslurry Fuels from Biochar and the Bio-oil-Rich Fractions after Bio-oil/Biodiesel Extraction Hanisom Abdullah and Hongwei Wu* Curtin Centre for Advanced Energy Science and Engineering, Department of Chemical Engineering, Curtin University of Technology, GPO Box U1987, Perth, Western Australia 6845, Australia ABSTRACT: In this study, bio-oil is extracted using biodiesel to produce two fractions: a biodiesel-rich fraction (also referred as biodiesel/bio-oil blend) and a bio-oil-rich fraction. The results show that the compounds (mainly phenolic) extracted from bio-oil into the biodiesel-rich fraction reduce the surface tension of the biodiesel/bio-oil blends. The bio-oil-rich fraction is mixed with ground biochar to produce a bioslurry fuel. It is found that the bioslurry fuels with 10 and 20% biochar loading prepared from the biooil-rich fraction of biodiesel extraction at a biodiesel/bio-oil blend ratio of 0.67 have similar fuel properties (e.g., density, surface tension, volumetric energy density, and stability) in comparison to those prepared using the original whole bio-oil. The slurry fuels exhibit non-Newtonian with pseudo-plastic characteristics and good pumpability, desirable for fuel handling. The viscoelastic behavior of the slurry fuels also shows dominantly fluid-like behavior in the linear viscoelastic region, therefore favorable for atomization in practical applications. This study proposes a new bio-oil use strategy via co-production of a biodiesel/bio-oil blend and a bioslurry fuel. It is known that the biodiesel/bio-oil blend can be used as a liquid transport fuel, using a proportion of bio-oil compounds (relatively high value and small volume). The bioslurry fuel is prepared by mixing the low-quality bio-oil-rich fractions (relatively low value and large volume) with ground biochar, suitable for stationary applications, such as combustion and gasification.
1. INTRODUCTION Mallee biomass in Australia is a second-generation bioenergy feedstock because it is a byproduct of dryland salinity management of premium agriculture land and enhances (rather than competes with) food production.1,2 Mallee biomass production is of large scale and economic and has small carbon and energy footprints.1,35 Pyrolysis is an attractive technology to produce high-energy-density fuels, such as biochar and/or bio-oil, from biomass, such as mallee, addressing the key problems of high transport costs and technical difficulties hindering the use of biomass as a direct fuel because of its bulky nature, high moisture content, and poor grindability.614 It has been demonstrated that biochar has good fuel properties, high volumetric energy density (after grinding), and excellent grindability.12,13 An attractive approach is to mix fine biochar (after grinding if necessary) into bio-oil to produce a bioslurry fuel. Commercial developers have attempted such a concept, e.g., Dynomotive (“BioOil Plus”15) in Canada and Karlsruhe (“Bioliq”16) in Germany. Recently, Wu et al.5,17,18 have carried out a series of systematic studies dedicated to the production, environmental performance, characterization, and use of bioslurry fuels from mallee biomass in Western Australia (WA). Part 1 of the series of papers has illustrated the economic viability of a bioslurry-based bioenergy supply chain in the context of mallee biomass in WA (10.1021/ef1008105).17 Particularly, a bioslurry-based supply chain makes it economically feasible to substantially increase the uptake of bioenergy proportion in coal-based power stations. Part 2 reports the life-cycle energy and carbon balance for bioslurry fuels in WA (10.1021/ef100957a).5 It is demonstrated that mallee-based bioslurry fuels have small energy and carbon footprints, which are less than 4 and 3% of the total energy and carbon embedded in the delivered bioslurry fuels, respectively. r 2011 American Chemical Society
Part 3 further illustrates the favorable fuel and rheological properties of bioslurry fuels, produced from bio-oil and biochar that are products of mallee biomass fast pyrolysis, for combustion and gasification applications (10.1021/ef1008117).18 However, thus far, the preparations of such bioslurry fuels use the whole bio-oil produced from the fast pyrolysis of biomass, such as mallee. Such an approach may not be the best option for bio-oil use. It is known that bio-oil contains a wide range of components, of which some are suitable for value-added applications.8,9 For example, significant research and development have been carried out to develop various technologies for bio-oil upgrading and refining for the production of liquid transport fuels, including direct biodiesel extraction,19 esterification,20,21 catalytic upgrading,22,23 hydrotreating,24,25 and emulsification with diesel26,27 or biodiesel,28,29 with the aid of a surfactant. Particularly, it is worthwhile to note that Garcia et al.19 developed a method that uses biodiesel to extract some of the best fuel fractions of bio-oil, resulting in a biodiesel/bio-oil fuel blend that is proven to be a good transport fuel. Monolignols, furans, sugars, extractive-derived compounds, and a small fraction of oligomers were the main bio-oil compounds extracted in biodiesel. The addition of these bio-oil fractions to biodiesel did not seem to greatly influence the calorific value of the resulting biodiesel/bio-oil blend. A subsequent investigation was also carried out to apply the same method for extracting bio-oil produced from mallee biomass fast pyrolysis, leading to similar conclusions.30 Therefore, instead of using the whole bio-oil for preparing bioslurry fuels, it is plausible to use biodiesel for bio-oil extraction first that enables a better use of bio-oil. The best (high-quality) Received: November 13, 2010 Revised: December 20, 2010 Published: February 03, 2011 1759
dx.doi.org/10.1021/ef101535e | Energy Fuels 2011, 25, 1759–1771
Energy & Fuels
ARTICLE
Table 1. Fuel Properties and Heating Valuesa proximate analysis (% ar) fuel
ultimate analysis (% daf) fixed carbon
C
H
N
S
heating value Ob
LHVc (GJ/ton)
water content
ash
volatile matter
bio-oil
33.7
0.09
ndd
nd
42.3
7.3
0.06
0.02
50.3
17.3
BOR 0.25
33.7
0.04
nd
nd
41.4
7.6
0.07
0.02
50.9
16.9
BOR 0.67
34.1
0.03
nd
nd
43.3
8.1
0.11
0.01
48.5
17.1
BOR 1.50
35.0
0.04
nd
nd
40.2
7.8
0.11
0.01
51.9
16.4
BOR 4.00
38.7
0.06
nd
nd
37.9
7.8
0.14
0.01
54.2
15.4
biodiesel
0.3
