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Show Co-firing Pulverized Coal with Pinion Pine/Juniper Wood in Raw, Torrefied and Pyrolyzed Forms Eric Eddings1,3, Andrew Vance1, Ryan Okerlund1, Dallas Hanks2, Ralph Coates3, Scott Bell4 1Dept. of Chemical Engineering, University of Utah, Salt Lake City, Utah 2Center for Agronomic and Woody Biofuels, Utah State University, Logan, Utah 3Amaron Energy, Salt Lake City, Utah 4U.S. Forest Service, Ogden, Utah Introduction The U.S. Forest Service hires contractors each year to clear vast quantities of pinion pine and juniper (P-J) as part of their mandated woodland management program to break up fuel loads, and to control and maintain habitats and watersheds. Much of this material is chained, chipped and left on site. The Institute for Clean and Secure Energy at the University of Utah has teamed with agronomists from Utah State University, a local company Amaron Energy, and representatives from the U.S. Forest Service and the Bureau of Land Management to identify potential uses for this woody biomass waste. One approach that is being considered is use of the P-J material as a co-firing fuel in a coal-fired power plant. One significant drawback of the use of woody biomass as a co-firing fuel is the low energy density of the wood relative to coal, which makes collection and shipping of the fuel less viable. The use of a distributed system of pyrolysis or torrefaction units would allow for densification of the biomass prior to shipping. Amaron Energy, in conjunction with the University of Utah, has developed a field-deployable unit capable of operating in either a pyrolysis or torrefaction mode for processing the P-J material. A program has been funded by the U.S. Forest Service to perform pilot-scale co-firing studies at the University of Utah in their L1500 test facility, to examine the emissions, deposition behavior and ash characteristics, when co-firing pulverized coal with the pinion-juniper material in each of three forms: 1) raw, untreated material; 2) torrefied material, and 3) biochar from the pyrolysis of the P-J material. The various forms of the P-J material will be produced by Amaron Energy in a 1/2 ton/day prototype facility prior to the testing at the University of Utah. Preliminary meetings have been held with representatives from PacifiCorp, who have have identified the Carbon Power Plant near Price, Utah to be used as the test location for a full-scale demonstration, if the pilot-scale testing provides sufficient confidence that the co-firing will not create significant operational problems. Experimental Conditions The pilot-scale trials were carried out at the University of Utah in the Spring and Summer of 2012. The main testing campaign was held in the Spring, with a few data points were repeated and two additional conditions were explored in the Summer at the tail end of another biomass co-firing campaign. The experimental matrix included baseline coal operation with a Utah bituminous coal (Sufco mine), and co-firing of the P-J fuel in raw, torrefied and pyrolyzed (biochar) forms at 5 and 10% (on a thermal input basis). Additional data were taken at at 20% co-firing level for torrefied wood and biochar in the brief Summer campaign. The firing conditions were selected to be similar to those used at the Carbon plant, and consisted of staged operation with a burner stoichiometric ratio of approximately 0.9-0.95, with an overall excess O2 level of 3% (dry basis). Summary of Results While a detailed overview of results will be provided in the podium presentation, a summary will be provided here. Operationally, the raw wood was much more difficult to feed than the torrefied wood or the biochar, particularly at the 10% level. The biochar was by far the easiest to handle and feed. It properties were also quite similar to the Utah coal, in terms of its heating value and ultimate analysis. Ash compositions were significantly different, however. There was limited impact on gaseous emissions. The NOx levels were essentially the same with and without the co-fired biomass. The biomass fed in a manner that completely mixed the two fuels prior to entering the coal pipe, to simulate the co-mingling that would take place if both fuels were mixed prior to a pulverizer. There could be some NOx benefits if the biomass were fed separately and introduced to the burner in such a way as to produce a highly fuel-rich zone for NOx reduction, as has been demonstrated in past biomass co-firing trials; however, this process was not replicated in this study. Sulfur emissions decreased in proportion to the overall reduction in sufur with coal replacement. CO emissions were consistently low, except when there were feeding problems with the raw wood at 10% co-firing that resulted in surges of biomass that momentarily changed the furnace stoichiometry. Unburned carbon samples were taken of the flyash, and no loss-on-ignition (LOI) problems were observed during the co-firing, with the exception of upset conditions to the feeding problems with the raw wood at high rates, as mentioned previously. Deposition probe were used to simulate fouling of water-wall tubes in the boiler, and ash samples were taken from the deposition probes, the entrained flyash at the furnace exit, and of the baghouse ash. These ash samples were analyzed for elemental composition and for ash melting temperatures, to determine if co-firing of this material would result in increased tendencies for sticky or slagging ash deposits. A comparison of all ash samples indicated very little variation in ash fusion data for all of the conditions tests. The slight variations where within the limit of accuracy for the tests methods used. In summary, we did not observe any significant detrimental effects to operation with the biomass as a co-firing fuel, particularly with the biomass in torrefied or biochar forms. The only challenge came with attempts at high feeding rates with the unheated or raw wood, and some of these challenges may be attributed to our smaller scale. However, if the fuel is to be co-fed into a pulverizer there is potential for problems in grinding the biomass sufficiently in the raw and possibly even torrefied forms (depending on the severity of torrefaction), due to the physical nature of the biomass. It is anticipated that the biochar would behave in a satisfactory manor in a pulverizer, although grinding tests are recommended to confirm this. Overall the biochar is a very good candidate for co-firing due to its many favorable attributes; however, the economics of producing the biochar must be a primary consideration, including potential sale or use of the pyrolysis oil and gas by-products created in the production of biochar, in addition to the benefits of local energy densification of the biomass prior to shipping to the point-of-use. |
