Nickel and sulfur speciation of residual oil fly ashes from two electric utility steam-generating units.
Representative duplicate fly ash samples were obtained from the stacks of 400- and 385-MW utility boilers (Unit A and Unit B, respectively) using a modified U.S. Environmental Protection Agency (EPA) Method 17 sampling train assembly as they burned 0.9 and 0.3 wt % S residual (No. 6 fuel) oils, respectively, during routine power plant operations. Residual oil fly ash (ROFA) samples were analyzed for Ni concentrations and speciation using inductively coupled plasma-atomic emission spectroscopy, X-ray absorption fine structure (XAFS) spectroscopy, and X-ray diffraction (XRD). ROFA deionized H2O extraction residues were also analyzed for Ni speciation using XAFS and XRD. Total Ni concentrations in the ROFAs were similar, ranging from 1.3-1.5 wt%; however, stack gas Ni concentrations in the Unit A were 0.990 microg/Nm3 compared with 0.620 microg/Nm3 for Unit B because of the greater residual oil feed rates employed at Unit A to attain higher 400-MW load conditions with a lower heating value oil. Ni speciation analysis results indicated that ROFAs from Unit A contain approximately 3 wt % NiSO4 x xH2O (where x is assumed to be 6 for calculation purposes) and appoximately 4.5 wt% of a Ni-containing spinel compound, similar in composition to (Mg,Ni)(Al,Fe)2O4. ROFAs from Unit B contain on average 2 wt% NiSO4 x 6 H20 and 1.1 wt% NiO. XAFS and XRD analyses did not detect any nickel sulfide compounds, including carcinogenic nickel subsulfide (Ni3S2) (XAFS detection limit is 5% of the total Ni concentration). In addition, XAFS measurements indicated that inorganic sulfate and organic thiophene species accounted for > 97% of the total S in the ROFAs. Unit A ROFAs contained much lower thiophene proportions because cyclone-separated ROFA reinjection is employed on this unit to collect and reburn the larger carbonaceous particles.
Galbreath
Kevin C
KC
Energy & Environmental Research Center, University of North Dakota, Grand Forks, ND 58202-9018, USA. kgalbreath@undeerc.org
Schulz
Richard L
RL
Toman
Donald L
DL
Nyberg
Carolyn M
CM
Huggins
Frank E
FE
Huffman
Gerald P
GP
Zillioux
Edward J
EJ
D000397:Air Pollution / Q000517:prevention & control; D002244:Carbon; D060729:Coal Ash; D004560:Electricity; D004784:Environmental Monitoring; D006801:Humans; D019570:Inhalation Exposure; D007509:Irritants / Q000032:analysis*; D009369:Neoplasms / Q000209:etiology; D009532:Nickel / Q000032:analysis* / Q000737:chemistry*; D052638:Particulate Matter; D018570:Risk Assessment; D013455:Sulfur / Q000737:chemistry*
D060729:Coal Ash; D007509:Irritants; D052638:Particulate Matter; C029938:nickel sulfate; D013455:Sulfur; D002244:Carbon; D009532:Nickel; C028007:nickel monoxide