Ind. Eng. Chem. Res. 2009, 48, 2179–2187
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Sewage Sludge Pyrolysis in a Fluidized Bed, 2: Influence of Operating Conditions on Some Physicochemical Properties of the Liquid Product I. Fonts,*,† A. Juan,† G. Gea,‡ M. B. Murillo,‡ and J. Arauzo‡ Arago´n Institute for Engineering Research (I3A) and Chemical and EnVironmental Engineering Department, Thermochemical Processes Group (GPT), UniVersity of Zaragoza, 50018 Zaragoza, Spain
Sewage sludge was pyrolyzed at different operating conditions with the aim of producing pyrolysis liquid. In this work, the influence of some operating conditions was studied in relation to some liquid properties such as homogeneity (phase separation), solids content, water content, and high heating value. The operating variables studied were bed temperature (450-650 °C), inlet nitrogen rate (0.057-0.090 m s-1), and solid feed rate per volumetric unit (0.169-0.338 kg s-1 m-3). Phase separation appeared in the samples obtained at almost all operating conditions studied, and it was different depending on the operating temperature and the sample of sewage sludge. The experimental methodology for analyzing the quantitative properties of the pyrolysis liquid under study was based on experimental design techniques. These liquid properties were influenced in different ways by the three studied operating conditions, but above all by the temperature, the inlet nitrogen rate, and also the sample of sewage sludge. Based on the experimental data, empirical models were built to describe the influence of the operating conditions on the liquid properties. Additionally, using these empirical models, operating conditions (within the intervals under study) that allow a high liquid yield and a liquid product with desirable values of the studied properties to be obtained were predicted theoretically. Introduction 1–3
Biomass pyrolysis liquids are currently of significant interest because of their possibilities as biofuels for combustion systems such as engines, boilers, and turbines. The possibility of their being used in this type of equipment depends above all on the improvement of some of their properties including homogeneity (phase separation), water content, solids content, viscosity, density, flash point, pour point, pH, stability, and heating value. Recommended values of these properties for each application are available in the literature.4–6 Several authors have studied the values of these properties for pyrolysis liquids obtained from various raw materials.7–9 Ways of improving some of these properties by means of secondary treatments have also been described in the literature.10,11 However, there is little information about how operating conditions affect the characteristics of the liquids obtained from sewage sludge pyrolysis.12–15 The objectives of the present work, therefore, were to study experimentally the effects of some operating conditions of sewage sludge pyrolysis in a fluidized bed on the quality of the liquid product. The quality of pyrolysis liquids is determined by several physical and chemical properties.4–6 In this work, some of these properties were studied, namely, phase separation, solid and water contents of the liquid product, and higher heating values of the organic phase and liquid product. These properties are important if the liquid is intended for use in energy applications for several reasons. Phase separation is one of the main problems of pyrolysis liquids in view of their application and commercialization. A low solids content is required because the solids can contain metals with catalytic activity that cause the liquid to become unstable during storage.16,17 Moreover, the solids are capable of causing mechanical problems in * To whom correspondence should be addressed. Tel.: +34976762897. E-mail:
[email protected]. † Chemical and Environmental Engineering Department, Thermochemical Processes Group (GPT). ‡ Arago´n Institute for Engineering Research (I3A).
some applications, for example, in turbines and engines, because of their erosion power.18 Moderate water contents ( 1.6 s, uN2
