Nitration of polynuclear aromatic hydrocarbons in coal combustors and exhaust streams: Final report, September 1, 1991--September 30, 1994 Page: 4 of 32
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1. SUMMARY OF RESEARCH APPROACH
Nitro-polynuclear aromatic hydrocarbons (nitro-PAH) are the predominant muta-
gens on respirable particles from coal-fired boilers. Since nitro-PAH are not primary
products of coal devolatilization, their formation must involve secondary chemistry at
elevated temperatures. However, it is not known where in the combustion or exhaust
processes they form, which reaction species are involved, or how concentrations are
influenced by- operating conditions. The objectives of this three-year project were to (1)
identify the conditions which promote the nitration of PAH during primary combustion,
returning, hot gas cleanup, and particulate removal; and (2) investigate the potential
relationship between NOx abatement and PAH nitration.
Meeting the objectives of this program involved two broad tasks: (1) Preparing the
polynuclear aromatic hydrocarbons (PAH) under closely monitored pulverized fuel (p. f.)
firing conditions; and, (2) analyzing the PAH samples to monitor extents of nitration,
ring number distribution, etc. While both activities were essential to this project, they
involved completely separate scientific procedures and equipment. So in this, as in all
previous reports, our findings are segregated according to their relation to either sample
preparation or sample analysis. In actuality, Dr. Niksa and Prof. Hildemann each had a
student working on these respective parts of this project.
A novel coal flow reactor burning actual coal products that operates over the domains
of heating rates, temperatures, fuel-equivalence ratios, and residence times in utility boilers
was used to generate the coal tar samples. The distribution of products obtained from
primary, secondary, and oxidative pyrolysis of two coal types, Pittsburgh No. 8 and Dietz,
were analyzed, with emphasis on the nitrogen-containing species generated.
The coal tar samples collected from the coal flow reactor were fractionated based on
their size and polarity using gravity flow column chromatography. After examining how
the sample fractionation depended on the coal type and pyrolysis conditions, the relatively
nonpolar fraction was further analyzed via high performance liquid chromatography, to
characterize the ring number distribution of the polycyclic aromatic compounds (PAC)
present. Finally, gas chromatographic techniques were utilized to measure the amount of
nitrogen-containing PAC present, and to investigate how much of these nitrogen-containing
species consist of nitro-PAH.1
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Yu, L.; Cho, S.; Hildemann, L. & Niksa, S. Nitration of polynuclear aromatic hydrocarbons in coal combustors and exhaust streams: Final report, September 1, 1991--September 30, 1994, report, February 1, 1995; Stanford, California. (https://digital.library.unt.edu/ark:/67531/metadc697120/m1/4/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.