Comparison of a Solvent-Free Tar Quantification Method to the International Energy Agency’s Tar Measurement Protocol Ming Xu, Robert C. Brown,* Glenn Norton, and Jerod Smeenk Center for Sustainable Environmental Technologies, Iowa State University, Ames, Iowa 50011 Received June 12, 2005. Revised Manuscript Received September 23, 2005 This paper presents a new method for measuring tar concentration in biomass-derived producer gas streams. This solvent-free method is much simpler than the evaporative method of the International Energy Agency (IEA) tar protocol. In tests on producer gas from a fluidized bed biomass gasifier this so-called dry condenser method yielded tar measurements with precision better than 5% and accuracy averaging to within 10% of the IEA tar protocol. Comparisons of water vapor concentrations in producer gas as determined by the two methodologies showed poor agreement, which appears to be due to the low precision of both techniques for this measurement, possibly the result of dissolved hydrocarbons in the recovered aqueous phases. Introduction Producer gas generated by biomass gasification in- evitably contains condensable hydrocarbons known as tar. 1 If not removed, tar can cause operational problems in equipment located downstream of the gasifier. Ac- curate measurement of this contaminant is important in monitoring gasifier performance. 2 A large variety of sampling and analysis methods have been developed to determine the concentration of tar in biomass-derived producer gas, 3-6 which makes the comparison of data among researchers and manu- facturers difficult. Most tar measurements are based on cold trapping in impinger trains with various organic solvents followed by laboratory analysis. 1 In an effort to improve accuracy and repeatability of tar measure- ments, the Working Group of the Biomass Gasification Task of the International Energy Agency (IEA) Bio- energy Agreement 7 developed a protocol for sampling and analysis of particulates and tar from biomass gasifiers, which is commonly referred to as the IEA tar protocol. This protocol, originally designed to use dichlo- romethane (DCM) as a tar solvent, has recently been revised to recommend the use of less volatile and toxic 2-propanol. 8 However, the work reported here employs the original protocol because of the ease in separating water from the DCM/tar solution and its continuing usefulness to researchers. Regardless of the solvent used, the IEA tar protocol has several prominent shortcomings. Handling of or- ganic solvents requires special skills and extra attention to prevent toxic exposure and environmental contami- nation. In the case of DCM, operators must wear gloves, masks, or properly fitted organic vapor respirators, and unprotected personnel must be kept away from the sampling and analysis areas. In addition, the IEA tar protocol requires considerable time for equipment setup, sampling, analysis, and cleanup. As a result, it is difficult to obtain more than one data point every few hours, and in many cases it is inconvenient to obtain more than one data point per day. Finally, the procedure requires extreme operator skill, which results in sig- nificant variation in results among less skilled opera- tors. We have developed a solvent-free tar quantification method as an alternative to the IEA tar protocol that is suitable for routine field applications and yields results comparable to the evaporative method of the IEA tar protocol. This dry condenser method, as it is called, condenses organic compounds at 105 °C (referred to as “heavy tar”) in a disposable tube and a fiberglass mat. By operating above the boiling point of water, the heavy tar is not contaminated with moisture. A simple gravi- metric analysis of the tube and fiberglass mat allows the mass of heavy tar to be determined. No solvents are employed for collection or analysis, and the tube and fiberglass mat can be disposed of upon completion of the analysis. This methodology was hypothesized to yield results comparable to the evaporative method of the IEA tar protocol, which recovers “heavy tar” from DCM-tar solutions by evaporation at 105 °C. This * To whom correspondence should be addressed. Phone: 515-294- 7934. Fax: 515-294-3091. E-mail: rcbrown@iastate.edu. (1) Milne, T. A.; Abatzoglou, N.; Evans, R. J. Biomass Gasifier ‘Tars’: Their Nature, Formation, and Conversion; NREL/TP-570-25357, 1998. (2) Lopamudra, D.; Ptasinski, K. J.; Janssen, F. J. Biomass Bio- energy 2003, 24, 125-140. (3) Hasler, Ph.; Nussbaumer, Th. Guideline for Sampling and Analysis of Tars and Particulates from Biomass Gasifiers; Swiss Federal Office of Energy: Berne, 1998. (4) Moersch, O.; Spliethoff, H.; Hein, K R. G. A New System for Tar Sampling and Analysis. In Biomass Gasification and Pyrolysis; CPL Press: Newbury, U.K., 1997. (5) Moersch, O.; Spliethoff, H.; Hein, K. R. G. Biomass Bioenergy 2000, 18, 79-86. (6) Hasler, Ph.; Nussbaumer, Th. Biomass Bioenergy 2000, 18, 61- 66. (7) Simell, P.; Stahlberg, P.; Kurkela, E.; Albrecht, J.; Deutsch, S.; Sjostrom, K. Biomass Bioenergy 2000, 18, 19-38. (8) Neeft, J. P. A.; Knoef, H. A. M.; Zielke, U.; Sjostrom, K. Guideline for Sampling and Analysis of Tar and Particles in Biomass Producer Gases, Version 3.1; Energy Project EEN5-1999-00507. 2509 Energy & Fuels 2005, 19, 2509-2513 10.1021/ef0501703 CCC: $30.25 © 2005 American Chemical Society Published on Web 10/29/2005