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Energy & Fuels 1999, 13, 914-921
Fuel Oil Quality of Biomass Pyrolysis OilssState of the Art for the End Users Anja Oasmaa† and Stefan Czernik*,‡ VTT Energy, P.O. Box 1601, Espoo, Finland, and NREL, 1617 Cole Boulevard, Golden, Colorado 80401 Received December 22, 1998. Revised Manuscript Received March 18, 1999
Biomass pyrolysis oils have potential to be used as a fuel oil substitute. Combustion tests have shown that the oils burn efficiently in standard or slightly modified boilers and engines with rates similar to those for commercial fuels. However, these tests also identified several challenges in bio-oils applications resulting from their properties. The oils have heating values of only 4050% of that for hydrocarbon fuels. They have a high water content that is detrimental for ignition. Organic acids in the oils are corrosive to common construction materials. Solids (char) can block injectors or erode turbine blades. Over time, reactivity of some components in the oils leads to formation of larger molecules that results in high viscosity and in slower combustion. This paper discusses physical and chemical characteristics of bio-oils relevant to fuel applications as well as some low-cost methods for improvement of these properties. It also provides bio-oil specifications proposed by some industrial users and recommendations for storage and handling.
Introduction Since the oil crisis in the mid 1970s considerable effort has been directed toward development of processes for producing liquid fuels from biomass. One of the most efficient methods for such conversion is fast pyrolysis. Fast pyrolysis is a thermal decomposition process that requires a high heat transfer rate to the biomass particles and a short vapor residence time in the reaction zone. Several reactor configurations have been shown to ensure this condition and to achieve yields of liquid product as high as 70-80% based on the starting biomass weight. They include bubbling fluid beds,1,2 transport reactors,3,4 and cyclonic reactors.5,6 In the 1990s several fast pyrolysis technologies have reached near-commercial status. Two circulating fluidized bed plants have been operated by Red Arrow Products Co., * Corresponding author. † VTT Energy. ‡ NREL. (1) Scott, D. S.; Piskorz, J.; Radlein, D. Liquid products from the Continuous Flash Pyrolysis of Biomass. Ind. Eng. Chem. Process Des. Dev. 1985, 24, 581-586. (2) Piskorz, J.; Scott, D. S.; Radlein, D. Composition of Oils Obtained by Fast Pyrolysis of Different Woods. In Pyrolysis Oils from Biomass: Producing, Analyzing, and Upgrading; Soltes, E. J, Milne, T. A., Eds.; ACS Symposium Series 376, ACS: Washington, D. C. 1988; pp 167178. (3) Graham, R. G.; Freel, B. A.; Bergougnou, M. A. The Production of Pyrolysis Liquids, Gas, and Char from Wood and Cellulose by Fast Pyrolysis. In Research in Thermochemical Biomass Conversion; Bridgwater, A. V., Kuester, J. L., Eds.; Elsevier Applied Science: London 1988; pp 629-641. (4) Kovac, R. J.; Gorton, C. W.; O’Neil, D. J. Entrained Flow Pyrolysis of Biomass. In Proceedings of Thermochemical Conversion Program Annual Meeting; SERI/CP-231-2355; Solar Energy Research Institute: Golden, CO, 1988; pp 5-20. (5) Diebold, J.; Scahill, J. Production of Primary Pyrolysis Oils in a Vortex reactor. In Pyrolysis Oils from Biomass: Producing, Analyzing, and Upgrading; Soltes, E. J, Milne, T. A., Eds.; ACS Symposium Series 376, ACS, Washington, D. C. 1988; pp 31-40. (6) Czernik, S.; Scahill, J.; Diebold, J. The Production of Liquid Fuel by Fast Pyrolysis of Biomass. J. Sol. Energy. Eng. 1995, 117, 2-6.
Inc., in Wisconsin, with a nominal capacity of 50 t/day. Another installation using the same technology has been constructed in Umbria, Italy, by ENEL (the Italian Electricity Company) with the designed capacity of 15 t/day. A bubbling fluidized bed pilot process has been demonstrated by Union Fenosa, a Spanish Electricity Company, in Galicia, Spain, at 3 t/day. In any case the yields and properties of the generated liquid product, bio-oil, depend on the feedstock, process type and conditions, and the product collection train efficiency. Biomass pyrolysis liquid product, bio-oil, has the potential to be used as a fuel oil substitute. Combustion tests performed using different scale burners7-12 and internal combustion engines13-18 have demonstrated (7) Van de Kamp, W. L.; Smart, J. P. 6th European Conference on Biomass for Industry and Energy, 1991. (8) Salvi, G.; Salvi, G., Jr. Pyrolytic Products Utilization Assessment Study, Commission of European Communities, Contract No. EN3B0191-1(CH), 1991. (9) Wornat, M. J.; Porter, B. J.; Yang, N. Y. C. Single droplet Combustion of Biomass Pyrolysis Oils. Energy Fuels 1994, 8, 11311142. (10) Hallgren, B. Test Report of Metlab Miljo¨ AB. Skelleftehamn: Metlab Miljo¨ AB, 1996; 17 pp. (Reg. No. ALL-1668, 1996 02 08-09.) (11) Shaddix, C. R.; Huey, S. P. Combustion Characteristics of Fast Pyrolysis Oils Derived from Hybrid Poplar. In Developments in Thermochemical Biomass Conversion; Bridgwater, A. V., Boocock, D. G. B., Eds.; Blackie Academic & Professional: London, 1997; pp 465480. (12) Gust, S. Combustion Experiences of Flash Pyrolysis Fuel in Intermediate Size Boilers. In Developments in Thermochemical Biomass Conversion; Bridgwater, A. V., Boocock, D. G. B., Eds.; Blackie Academic & Professional: London, 1997; pp 481-488. (13) Solantausta, Y.; Nylund, N.-O.; Gust, S. Use of Pyrolysis Oil in a Test Diesel Engine to Study the Feasibility of a Diesel Power Plant Concept. Biomass Bioenergy 1994, 7, 297-306. (14) Gros, S. Pyrolysis liquid as diesel fuel. Wa¨rtsila¨ Diesel International. In Seminar on power production from biomass II, 27.-28.3, Espoo, Finland, 1995. (15) Sipila¨, K.; Oasmaa, A.; Arpiainen, V.; Westerholm, M.; Solantausta, Y.; Ahnger, A.; Gros, S.; Nyro¨nen, T.; Gust, S. Pyrolysis oils for power plants and boilers. In Proceedings of the 9th European Bioenergy Conference; Copenhagen, 24-27 June, 1996.
10.1021/ef980272b CCC: $18.00 © 1999 American Chemical Society Published on Web 04/24/1999
Fuel Oil Quality of Biomass Pyrolysis Oils
that the oils could be burnt efficiently in standard or slightly modified equipment. These tests also identified several challenges in bio-oils applications resulting from their properties. However, the most important obstacle for commercial applications is the variability of properties and the lack of standard quality specifications for these oils required by the end users.19,20 This paper advances the discussion on bio-oils fuel quality aspects, mostly focusing on the physical and chemical properties that can create major problems for combustion applications. It also considers certain aspects (storage, environmental issues, proposed specifications) important for commercial uses of the oils. Properties of Biomass Pyrolysis Oils Bio-oils, also known under the names of pyrolysis oils or pyrolysis liquids, are usually dark-brown organic liquids. The physical properties of the oils as well as methods for their measurements are described in several publications.21-25 These properties result from the chemical composition of the oils, which is significantly different from that of petroleum-derived fuels. Chemical Composition. Bio-oils are comprised of different size molecules derived from depolymerization and fragmentation reactions of three key biomass building blocks: cellulose, hemicellulose, and lignin. Therefore, the elemental composition of bio-oil resembles that of biomass. In contrast to petroleum fuels, bio-oils contain a large amount of oxygen, usually 45-50 wt. %. This oxygen is present in most of the more than 200 compounds that have been identified26 in the oils. The distribution of these compounds mostly depends on the (16) Suppes, G.; Bryan, M.; Regehr, E. V.; Rui, Y. Ignition Delay Time Analysis of Pyrolysis Oil. In Proceedings of the Third Biomass Conference of the Americas; Overend, R. P., Chornet, E., Eds.; Elsevier Science Limited: 1997; p 869. (17) Andrews, R. G.; Fuleki, D.; Zukowski, S.; Patnaik, P. C. Results of Industrial Gas Turbine Tests Using a Biomass Derived Fuel. In Proceedings of the Third Biomass Conference of the Americas; Overend, R. P., Chornet, E., Eds.; Elsevier Science Limited: 1997; pp 425-436. (18) Shihadeh, A. L. Rural Electrification from Local Resources: Biomass Pyrolysis Oil Combustion in a Direct Injection Diesel Engine. Ph.D. Thesis, Massachussetts Institute of Technology, 1998. (19) Rick, F.; Vix, U. Product Standards for Pyrolysis Products for Use as Fuel in Industrial Firing Plants. In Biomass Pyrolysis Liquids Upgrading and Utilisation; Bridgwater, A. V.; Grassi, G., Eds.; Elsevier Applied Science: London, 1991; pp 177-218. (20) Diebold, J. P.; Milne, T. A.; Czernik, S.; Oasmaa, A.; Bridgwater, A. V.; Cuevas, A.; Gust, S.; Huffman, D.; Piskorz, J. Proposed Specifications for Various Grades of Pyrolysis Oils. In Developments in Thermochemical Biomass Conversion; Bridgwater, A. V., Boocock, D. G. B., Eds.; Blackie Academic & Professional: London, 1997; pp 433-447. (21) Elliott, D. C. Analysis and Comparison of Biomass Pyrolysis/ Gasification Condesates-Final Report, PNL-5943, Contract DE-AC0676RLO 1830, 1986. (22) Peacocke, G. V. C.; Russel, P. A.; Jenkins, J. D.; Bridgwater, A. V.; Physical Properties of Flash Pyrolysis Liquids. Biomass Bioenergy 1994, 7, 169-178. (23) Fagerna¨s, L. Chemical and Physical Characterisation of Biomass-Based Pyrolysis Oils. Literature Review. Espoo 1995, Technical Research Centre of Finland. (24) Meier, D.; Oasmaa, A.; Peacocke, G. V. C. Properties of Fast Pyrolysis Liquids: Status of Test Methods. Characterization of Fast Pyrolysis Liquids. In Developments in Thermochemical Biomass Conversion; Bridgwater, A. V., Boocock, D. G. B., Eds.; Blackie Academic & Professional: London, 1997; pp 391-408. (25) Oasmaa, A.; Leppa¨ma¨ki, E.; Koponen, P.; Levander, J.; Tapola, E. Physical Characterisation of Biomass-Based Pyrolysis Liquids. Application of Standard fuel oil Analyses. Espoo 1997, Technical Research Centre of Finland. (26) Soltes, E. J.; Elder, T. J. Pyrolysis. In Organic Chemicals from Biomass; Goldstein, I. S., Ed.; CRC Press: Boca Raton, FL., 1981; p 63.
Energy & Fuels, Vol. 13, No. 4, 1999 915 Table 1. Pyrolysis Liquid Properties pyrolysis liquids from different feedstocks property solids (wt %) pH water (wt %) density (kg/m3) viscosity, cSt (50 °C) LHV (MJ/kg) Ash (wt %) CCR (wt %) C (wt %) H (wt %) N (wt %) S (wt %) O (wt %) Na + K (ppm) Ca (ppm) Mg (ppm) Flash point (°C) Pour point (°C)
birch pine poplar
various
0.06 2.5 18.9 1.25 28
0.03 2.4 17.0 1.24 28
0.045 2.8 18.9 1.20 13.5
0.01-1 2.0-3.7 15-30 1.1-1.3 13-80
16.5 0.004 20 44.0 6.9
