Fuel oil quality properties of wood-based pyrolysis liquids

The main objective of the study was to create data for the standardization of pyrolysis liquid as a fuel for heat and power production. This study included testing of standard fuel oil analyses, development of new methods, research on critical fuel oil properties of pyrolysis liquids, and proposing fuel oil specifications. In order to promote the acceptance of a new fuel into markets to replace light or heavy fuel oil, the methodology should be as similar as possible. Standard fuel oil analyses of ASTM, DIN, and EN were tested with various pyrolysis liquids and modifications to methods were done when needed. The main changes concerned sampling and sample pretreatment. Due to the specific properties of pyrolysis liquids, like instability, water-solubility, unmiscibility with mineral oils, and high solids content, new test methods were developed. These included an accelerated aging test, by which the viscosity increase of the liquid during storage can be predicted. The instability of pyrolysis liquids is a determining factor when considering the handling, transport, storage, and use of pyrolysis liquids. In order to understand and control this property the changes in chemical composition of pyrolysis liquids were followed over typical storage time (six months). Because only a small part of pyrolysis liquids can be characterized using conventional methods like GC/MSD, a chemical characterization scheme based on solvent extractions was developed. Through this scheme, the changes in various chemical fractions of the liquid were obtained. In addition, changes in physical properties were observed. In aging the high-molecular-mass (HMM) water-insoluble fraction, especially the HMM lignin, increased. Aldehydes and ketones reacted gradually. The amount of sugar constituents decreased most during the first months, after which it more or less levelled out. Water was formed in condensation reactions. The increase in HMM substance increased the M̅w of the liquid and caused the increase in viscosity and pour point. The decrease in aldehydes and ketones increased the flash point. The addition of alcohols homogenized the liquid and decreased its viscosity by dilution. Alcohols decreased the aging rate for a few months, after which the changes followed the same pattern as that of the reference liquid. Based on feedback from pyrolysis liquid end-users, preliminary fuel oil specifications were proposed. Another approach was suggested in an EU project. The properties that could be directly affected were specified. These properties were water, solids, homogeneity, stability, and flash point. However, final fuel oil specifications can be assessed when more data are obtained regarding critical properties from long-duration field tests in boilers and engines. The standardization of pyrolysis liquid as a heating fuel will be initiated in 2003 in CEN.