Portland General Electric (PGE) potentially plans to replace the coal with torrefied Arundo donax for their Boardman coal-fired power plant by 2020. Since there is only a limited amount of experience with this high yield energy crop, PGE would like to characterize raw and torrefied Arundo before a test burn and therefore avoid possible ash related operational problems such as slagging, deposit formation and corrosion. This report describes the results from characterization of ground and cross-sectioned samples of Arundo with a high-resolution scanning electron microscopy and energy dispersive spectroscopy, and also includes analytical results from a short water-leaching test for concentrations of Ca, Mg, K, Na, S, and Cl in the non-leached and leached Arundo and leachates. SEM-EDS analysis of torrefied Arundo revealed that condensation of volatile components during torrefaction can result in their undesirable re-deposition on the outside surfaces in the form of amorphous or crystallized clusters with a size from a few µm’s to as large as 100 µm. A short exposure of Arundo to water resulted in an efficient removal of volatile species from the raw and torrefied Arundo, e.g., ~ 98 wt% of total K and Cl, and ~75 wt% of total S were removed from raw Arundo, and more than 90 wt% of total K and Cl, and 70 wt% of S from torrefied Arundo, suggesting that water-leaching of Arundo before combustion can be an effective pre-treatment method because high concentrations of Cl increase emissions of HCl, and in combination with K can form large amounts of KCl deposits on boiler surfaces and in combination with H2O or SO3 cause corrosion.
Revised: November 9, 2012 |
Published: August 1, 2012