ACERC
Abstracts - 1999 |
ACERC
Abstracts - 1999 |
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Research Area 3: Fine Particles |
Nazeer, W.A.; Jackson, R.E.;
Peart, J.A. and Tree, D.R.
Fuel, 78:689-699, 1999.
Gas composition and temperature profiles have been measured inside a 200 kW, entrained flow, pulverized coal, Controlled Profile Reactor (CPR) using reburning for NO reduction. NO, CO, NOx, O2, and samples were collected with a water-cooled and water-quenched stainless steel probe and analyzed on a dry basis with on-line gas analyzers and an ion-sensitive electrode (NH3) over a grid of 36 locations within the reactor. Temperature data were obtained with a suction pyrometer using a S-type shielded thermocouple. NO reduction with reburning was investigated over a range of residence times and reburning zone stoichiometric ratios to optimize for maximum NO reduction in the flue gases. A decrease in stoichiometric ratio of the reburning zone resulted in an increase in NO reduction up to a maximum of 70 % at a stoichiometric ratio of 0.78. Moving the tertiary air injector up and down axially varied the residence time in the reburning zone. Increasing residence time in the reburning zone was initially beneficial but became unimportant when residence time became longer than 700 ms. The location of the reburning zone was found to be optimal when reburning fuel was directed at the location of highest NO concentration (i.e., immediately following NO formation). In comparison to a baseline case without reburning, the rate of carbon burnout was found to be higher with 20 cm of primary fuel injection but proceeded more slowly through the reburning zone. At the end of the reactor, burnout was more complete in the baseline case. The species, temperature, and solid sample elemental concentrations appeared to be self-consistent and should provide accurate data for comparison with modeling results.
Nazeer, W.A.; Pickett, L.M.
and Tree, D.R.
Combustion Science and Technology, 143: 63, 1999.
A study of detailed species, velocity and temperature data of a pulverized coal flame is important to understanding the mechanisms that sustain the flame and lead to the formation of various pollutants such as NOx. The data can be particularly useful when compared to comprehensive combustion models that encapsulate the sub-models and processes of combustion. This data set contains in-situ axial and radial temperature, velocity and species concentrations for three swirl ratios of a pulverized coal flame located in a cylindrical, down-fired, 0.2 MWt reactor. Species measurements include CO, CO2, NO, and O2. Velocity measurements were obtained using Laser Doppler Anemometry (LDA) and are summarized here after the method and results were reported in detail in a companion paper. The data show the change in structure of the coal flame as swirl is increased. At zero swirl the flame was located along a centerline jet, but as swirl increased, a recirculation zone was created which carried the combustion products up along the centerline of the reactor. Effluent NO was found to correlate with the recirculation of products into the devolitilization zone and with the evidence of reduced mixing of fuel and secondary air at the primary tube outlet. Species measurements agreed with LDA results where concentrations of O2 were highest in the region of the secondary air jet. The species and temperature measurements are self-consistent suggesting the data is accurate and will be useful when compared to combustion models.
Pickett, L.M.; Jackson,
R.E. and Tree, D.R.
Combustion Science and Technology, 143:79, 1999.
A two-color Laser Doppler Anemometer (LDA) was used to obtain axial and tangential velocity information in a 0.2 MW pulverized coal flame. In addition to the reacting flow data, a study on the accuracy of using coal as a seed particle to measure gas phase velocity using LDA was performed. Non-reacting flow velocity measurements were also obtained near the fuel inlet and in the quarl region of a geometrically identical burner to assist in establishing modeling inlet conditions. Both the reacting and non-reacting velocity data were obtained at three or more swirl settings and various axial positions allowing a study of the affect of swirl on inlet turbulence and flame structure. The velocity results were compared with effluent NOx measurements. At the flow rates and accelerations experienced in this study, the coal particles were shown to be useful as seed particles for LDA gas phase velocity measurements. The coal-flame velocity indicated a centerline flame at 0 swirl transitioning to a radially directed flame with a central recirculation zone at swirl setting of 0.5 and 1.5. The transition of the flame structure to a central recirculation zone was also seen at the fuel inlet plane in the non-reacting flow studies and was found to correlate with a decrease in measured effluent NOx. Measured axial velocity profiles 5 mm below the fuel inlet showed negative axial velocities (in the opposite direction of the average flow velocity) were produced along the primary tube as swirl was increased from 0 to 1.5 with the transition occurring between 0.5 and 0.75 swirl. Transition in the flow near the fuel inlet correlated well with a drop in effluent NOx and with transitions in the recirculation zones measured further downstream. The strong interaction with burner velocity profiles and NOx suggest velocity is an important measured boundary condition for modeling. The velocity data shown here in combination with a companion paper showing temperature and species data should provide important information needed to develop better models of pulverized coal combustion.
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