Mineralogy and geochemistry of feed coals and their combustion residues from the Cayirhan power plant, Ankara, Turkey

A total of 48 samples, feed (run-of-mine) coals and their combustion residu es (Ay ash and bottom ash) were systematically collected twice a week over a 4 week period (June 1998) from two boiler units (I and II) of the Cayirha n power plant (630 MW) that burns zeolite-bearing coals of late Miocene age . The feed coals are high in moisture (22.8% as-received) content and ash ( 44.9%) yield and total S content (5.1%), and low in calorific value (2995 k cal/kg). The mineralogy of the feed coals contains unusually high contents of the zeolites (clinoptilolite/heulandite and analcime), which are distrib uted within the organic matter of coal. Other minerals determined are gypsu m, quartz, feldspar, pyrite, dolomite, calcite, cristobalite and clays. Com mon minerals in the crystalline phase of the combustion residues are anhydr ite, feldspar, quartz, hematite, lime and Ca-Mg silicate. Minor and trace a mounts of magnetite, cristobalite, maghemite, gehlenite, calcite and clinop tilolite/heulandite are also present in the combustion residues. Trace elem ent contents of the feed coals, except for W, fall within the estimated ran ge of values for most world coals; however, the mean values of Mn, Ta, Th, U and Zr are near maximum values of most world coals. Elements such as As, Bi, Ge, Mo, Pb, Tl, W and Zn are enriched more in the Hy ash compared to th e bottom ash. (C) 2001 Elsevier Science Ltd. All rights reserved.