Cattle biomass (CB) has been proposed as a renewable, supplementary fuel for co-firing and
reburning. Reburning coal with CB has the potential to reduce NOx and Hg emissions from coal
fired systems. The present research focuses on three areas of combustion: 1) Biomass reburning
experiments are conducted to determine the optimum operating conditions for the NOx reduction
using blends of coal and CB as reburn fuels. 2) Since CB contains higher ash contents compared
to coals, the fouling behavior is also investigated under the transient and short-time operation. 3)
Finally CB contains higher Cl compared to coals, which oxidizes Hg to HgCl2. To understand
the Hg oxidation behavior, a fundamental study of Hg oxidation in coal combustion is conducted
using a plug flow reactor (PFR).
The main parameters investigated are types of the reburn fuel, reburn equivalence ratios
(ERRBZ), O2 concentrations in the reburn gas, injection angles of the reburn fuel, cross-sectional
geometries of the reburn nozzles, symmetric and asymmetric reburn injections, reburn heat
inputs, baseline NOx concentrations, and presence and absence of the heat exchangers (HEX).
The results of reburning show that CB is a very effective fuel in NOx reduction, and the extent of
NOx reduction is strongly dependent to the ERRBZ. The optimum conditions of the boiler
operation for biomass reburning are as follows: ERRBZ = 1.1, 45° upward circular reburn nozzles, 12.5% O2 in the reburn gas, symmetric injection, and presence of HEXs. To make an effective
reburn process, the baseline NOx concentrations must be higher than 230 g/GJ (0.5 lb/mmBTU)
and the reburn heat input higher than 20%.
The results of ash fouling show the presence of ash in the hotter region of the furnace seems
to promote heat radiation thus augmenting the heat transfer to the HEX. The growth of the layer
of ash depositions over longer periods typically lowers overall heat transfer coefficients.
The addition of HCl to Hg containing gases in the PFR significantly increases Hg oxidations.
The addition of NO inhibited the overall reaction and shifted the reaction temperature higher
while the addition of O2 promoted Hg oxidations and lowered the reaction temperature. For
heterogeneous cases, the use of the VWT catalyst promotes the reduction of Hg0 and shifted the
reaction temperatures lower than those for homogeneous cases.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-3009 |
| Date | 15 May 2009 |
| Creators | Oh, Hyuk Jin |
| Contributors | Annamalai, Kalyan, Caton, Jerald |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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