Ronald Whiddon

Catalytic oxidation of NO by O2 over CeO2–MnOx: SO2 poisoning mechanism

The catalytic oxidation of NO by O2 was performed over a series of CeO2–MnOx catalysts with different molar ratios of Mn/Ce, which were prepared by the sol–gel method. The highest NO conversion efficiency reached 96% over the catalyst with a 0.4 Mn doping value at 238 °C. The possible reaction pathways of the catalytic oxidation process were proposed according to several characterization measurements. NO was adsorbed on the catalyst surface to form nitrates and then decomposed into NO2. However, the catalyst was completely deactivated under an atmosphere of SO2. NO conversion efficiency dramatically declined from 92% to 22% within only 400 min. Comparing the BET, TPR, TPD, XRD, XPS, FTIR, and TGA results of fresh and poisoned catalysts, the catalyst deactivation could be mainly attributed to manganese sulfate formation on the catalyst surface, which could only slightly decompose. The active sites for NO adsorption were occupied. Finally, the oxidation of NO to NO2 was terminated due to lack of nitrates, which are intermediates for NO oxidation.

Vapor phase tri-methyl-indium seeding system suitable for high temperature spectroscopy and thermometry

Tri-methyl-indium (TMI) is used as an indium transport molecule to introduce indium atoms to reactive hot gas flows/combustion environments for spectroscopic diagnostics. A seeding system was constructed to allow the addition of an inert TMI laden carrier gas into an air/fuel mixture burning consequently on a burner. The amount of the seeded TMI in the carrier gas can be readily varied by controlling the vapor pressure through the temperature of the container. The seeding process was calibrated using the fluorescent emission intensity from the indium 6(2)S1/2 → 5(2)P1/2 and 6(2)S1/2 → 5(2)P3/2 transitions as a function of the calculated TMI seeding concentration over a range of 2-45 ppm. The response was found to be linear over the range 3-22.5 ppm; at concentrations above 25 ppm there is a loss of linearity attributable to self-absorption or loss of saturation of TMI vapor pressure in the carrier gas flow. When TMI was introduced into a post-combustion environment via an inert carrier gas, molecular transition from InH and InOH radicals were observed in the flame emission spectrum. Combined laser-induced fluorescence and absorption spectroscopy were applied to detect indium atoms in the TMI seeded flame and the measured atomic indium concentration was found to be at the ppm level. This method of seeding organometallic vapor like TMI to a reactive gas flow demonstrates the feasibility for quantitative spectroscopic investigations that may be applicable in various fields, e.g., chemical vapor deposition applications or temperature measurement in flames with two-line atomic fluorescence.

Parametric Study of Emissions from Low Calorific Value Syngas Combustion, with Variation of Fuel Distribution, in a Prototype Three Sector Burner

The emission composition is measured for a prototype burner while varying the equivalence ratio in discrete portions of the burner. The burner is a three sector system, consisting of a separate igniter, pilot/stabilizer and main burner. The design allows for discrete control of equivalence ratio in each of the three sectors. The ignition sector, designated RPL (Rich- Pilot-Lean), operates from rich to lean equivalence values, and serves to ignite the pilot sector, which, in turn, stabilizes the main combustion sector. All three burner sections are premixed. The burner is operated at atmospheric pressure with inlet flows heated to 650 K (±8 K). Tests were performed for three gases: methane, a model syngas (10% CH4, 22.5% CO, 67.5% H2), and dilute syngas. The dilute gas includes sufficient nitrogen to lower the heating value to 15 MJ/m3. The model syngas and diluted syngas are representative of fuels produced by gasification process. The burner emissions, specifically, CO, CO2, O2 and NOx, are measured while holding the RPL equivalence value constant and varying the equivalence ratio of the pilot and main sectors. The equivalence ratios for pilot and main sectors are chosen such that the total burner equivalence ratios remain constant during a test sequence. The target total equivalence ratio for each gas is chosen such that all experiments should have the same flame temperature. (Less)

Experimental and Reactor Network Study of Nitrogen Dilution Effects on NOx Formation for Natural Gas and Syngas at Elevated Pressures

Gas turbines emissions, NOX in particular, have negative impact on the environment. To limit the emissions gas turbine burners are constantly improved. In this work, a fourth generation SIT (Siemens Industrial Turbomachinery) burner is studied to gain information about the formation of NOX emissions. The gas mixtures for the full burner are limited to natural gas with different nitrogen dilutions. The dilutions vary from undiluted to Wobbe index 40 and 30 MJ/m3. In addition to the full burner, the central body (the RPL – Rich/Pilot/Lean) is investigated. Methane is used to characterize standard gas turbine operation, and a non-standard fuel is explored using a generic syngas (67.5 % Hydrogen, 22.5 % Carbon monoxide and 10% Methane). Both these gases are also investigated after dilution with nitrogen to a Wobbe index of 15 MJ/m3. The experiments are performed in a high-pressure facility. The pressures for the central body burner are 3, 6 and 9 bar. For the full burner the pressures are 3, 4.5 and 6 bar. The combustion air is preheated to 650 K. The emission measurements are sampled with an emission probe at the end of the combustor liner, and analyzed in an emission rack. The results are compared with previous investigations made at atmospheric conditions. The burner is modeled using a PSR and plug flow network to show which reaction paths are important in the formation of emissions for the burner under the experimental conditions. The measurement results show that the NOX concentration increases with pressure and flame temperature. With increasing dilution the NOX concentration is decreased. For rich mixtures PSR calculations show that the NOX concentration decreases with pressure. (Less)

Experimental Investigations of an Industrial Lean Premixed Gas Turbine Combustor With High Swirling Flow

In the interest of understanding the prospects and restrictions of fuel flexibility in prototype industrial gas turbine combustion an experimental study is performed. Methane is used to characterize standard gas turbine operation; in addition a non-standard fuel is explored, generic syngas (67.5 % Hydrogen, 22.5 % Carbon monoxide and 10 % Methane). Both these gases are also investigated after dilution with Nitrogen to a Wobbe index of 15 MJ/m3. All measurements are conducted at a preheat temperature of 650 K to mimic gas turbine conditions. The pressure is atmospheric. The burner examined is a downscaled industrial 4th generation DLE burner. This swirl-stabilized burner features three concentric sectors: the RPL (rich-pilot-lean), the Pilot and the Main. The burner is designed to be coupled with a quartz combustion liner allowing a variety of laser and optical diagnostics, including PIV (Particle Image Velocimetry) and OH-pLIF (planar Laser Induced Florescence). The mentioned techniques are used herein for identification of combustion and flow phenomena. For this study the measurement region is located at the burner recirculation zone. CFD (RANS) calculations are compared with the OH-pLIF images to identify the zones of active combustion. CFD is also used to see the effect of recirculation zone position when moving towards the lean blow out limit. Additionally, integral scales are calculated for each of the combustion cases and from these, the Kolmogorov scales are derived. The flow field, imaged by PIV, show that the recirculation zone location along the major flow axis is strongly dependent on the presence of combustion. A combustion case, near lean blow out, shows that the recirculation zone has moved up-streams closer to a non-combustion case for some of the measurement sessions.

Experimental Investigation of Laminar Flame Speeds for Medium Calorific Gas with Various Amounts of Hydrogen and Carbon Monoxide Content at Gas Turbine Temperatures

It is expected that, in the future, gas turbines will be operated on gaseous fuels currently unutilized. The ability to predict the range of feasible fuels, and the extent to which existing turbines must be modified to accommodate these fuels, rests on the nature of these fuels in the combustion environment. Understanding the combustion behavior is aided by investigation of syngases of similar composition. As part of an ongoing project at the Lund University Departments of Thermal Power Engineering and Combustion Physics, to investigate syngases in gas turbine combustion, the laminar flame speed of five syngases (see table) have been measured. The syngases examined are of two groups. The first gas group (A), contains blends of H-2, CO and CH4, with high hydrogen content. The group A gases exhibit a maximum flame speed at an equivalence ratio of approximately 1.4, and a flame speed roughly four times that of methane. The second gas group (B) contains mixtures of CH4 and H-2 diluted with CO2. Group B gases exhibit maximum flame speed at an equivalence ratio of 1, and flame speeds about 3/4 that of methane. A long tube Bunsen-type burner was used and the conical flame was visualized by Schlieren imaging. The flame speeds were measured for a range of equivalence ratios using a constrained cone half-angle method. The equivalence ratio for measurements ranged from stable lean combustion to rich combustion for room temperature (25 degrees C) and an elevated temperature representative of a gas turbine at full load (270 degrees C). The experimental procedure was verified by methane laminar flame speed measurement; and, experimental results were compared against numerical simulations based on GRI 3.0, Hoyerman and San Diego chemical kinetic mechanisms using the DARS v2.02 combustion modeler. On examination, all measured laminar flame speeds at room temperature were higher than values predicted by the aforementioned chemical kinetic mechanisms, with the exception of group A gases, which were lower than predicted. (Less)

Flame investigation of a gas turbine central pilot body burner at atmospheric pressure conditions using oh plif and high-speed flame chemiluminescence imaging

Experiments were performed on the central pilot body (RPLrich- pilot-lean) of Siemens prototype 4th generation DLE burner to investigate the flame behavior at atmospheric pressure condition when varying equivalence ratio, residence time and co-flow temperature. The flame at the RPL burner exit was investigated applying OH planar laser-induced fluorescence (PLIF) and high-speed chemiluminescence imaging. The results from chemiluminescence imaging and OH PLIF show that the size and shape of the flame are clearly affected by the variation in operating conditions. For both preheated and non-preheated co-flow cases, at lean equivalence ratios combustion starts early inside the burner and primary combustion comes to near completion inside the burner if residence time permits. For rich conditions, the unburnt fuel escapes out through the burner exit along with primary combustion products and combustion subsequently restarts downstream the burner at leaner condition and in a diffuse-like manner. For preheated co-flow, most of the operating conditions yield similar OH PLIF distributions and the flame is stabilizing at approximately the same spatial positions. It reveals the importance of the preheating co-flow for flame stabilization. Flame instabilities were observed and Proper Orthogonal Decomposition (POD) is applied to time resolved chemiluminescence data to demonstrate how the flame is oscillating. Preheating has strong influence on the oscillation frequency. Additionally, combustion emissions were analyzed to observe the effect on NOX level for variation in operating conditions. (Less)

Investigation of a Premixed Gas Turbine Combustor Central Body Burner Using OH Planar Laser Induced Fluorescence at Elevated Pressures

Experiments were performed on the central body rich-pilotlean (RPL) burner of a Siemens Industrial Turbomachinary 4th generation DLE combustor to observe the combustion changes that may occur when using fuels other than natural gas. Measurements were taken of temperatures at multiple points along the RPL body while hydroxyl (OH) radical distribution extending from the dump plane of the burner was imaged by planar laser induced fluorescence (PLIF). The RPL burner was run using four fuels; methane, a generic syngas (67.5% H2, 22.5% CO and 10% CH4) and dilutions of these with nitrogen to a Wobbe index of 15 MJ/m3. Each of the fuels was operated at several equivalence ratios ranging from f = 0.80 to f = 1.80, for combustion pressures of 3, 6 and 9 bar. It was found that the flame position in the RPL, determined from temperature measurement at the thermocouple positions, was dependent on the fuel, equivalence ratio and to a lesser extent pressure. A link was established between the OH distribution in the post burner region and RPL temperature profiles based on the expected flame behavior inside the RPL. For all measurement points some combustion occurred within the burner volume, indicated by thermocouples at the burner exit. (Less)

Experimental Investigations of Lean Stability Limits of a Prototype Syngas Burner for Low Calorific Value Gases

The lean stability limit of a prototype syngas burner is investigated. The burner is a three sector system, consisting of a separate igniter, stabilizer and Main burner. The ignition sector, Rich-Pilot-Lean (RPL), can be operated with both rich or lean equivalence values, and serves to ignite the Pilot sector which stabilizes the Main combustion sector. The RPL and Main sectors are fully premixed, while the Pilot sector is partially premixed. The complexity of this burner design, especially the ability to vary equivalence ratios in all three sectors, allows for the burner to be adapted to various gases and achieve optimal combustion. The gases examined are methane and a high H2 model syngas (10% CH4, 22.5% CO, 67.5% H2). Both gases are combusted at their original compositions and the syngas was also diluted with N2 to a low calorific value fuel with a Wobbe index of 15 MJ/m3. The syngas is a typical product of gasification of biomass or coal. Gasification of biomass can be considered to be CO2 neutral. The lean stability limit is localized by lowering the equivalence ratio from stable combustion until the limit is reached. To get a comparable blowout definition the CO emissions is measured using a non-dispersive infrared sensor analyzer. The stability limit is defined when the measured CO emissions exceed 200 ppm. The stability limit is measured for the 3 gas mixtures at atmospheric pressure. The RPL equivalence ratio is varied to investigate how this affected the lean blowout limit. A small decrease in stability limit can be observed when increasing the RPL equivalence ratio. The experimental values are compared with values from a perfectly stirred reactor modeled (PSR), under burner conditions, using the GRI 3.0 kinetic mechanism for methane and the San Diego mechanism for the syngas fuels. (Less)

Operability and performance of central (Pilot) stage of an industrial prototype burner

An investigation on the central-pilot stage of a Siemens Industrial Turbomachinery 4th Generation DLE prototype test burner has been performed to understand the emission performance and operability. The core section, which is defined as RPL (Rich premixed lean) plays an important role for full burner combustion operation by stabilizing the main and pilot flames at different operating condition. Optimal fuel-air flow through the RPL is critical for multiple stages mixing and main flame anchoring. Heat and radical production from the central stage provides the ignition source and required heat for burning the main flame downstream of the RPL section. Surrounding the RPL outside wall cooling air has been blown through an annular passage. The cooling air protects the RPL wall from overheating and provides the oxygen source for the secondary combustion downstream of the RPL. At rich operation unburned hydrocarbon/radicals can pass the RPL and burns by the coflow air entrainment. To determine the flame stabilization and operability, an atmospheric pressure test has been accomplished using methane as a fuel. Primary flame zone can be identified by a thermocouple placed outside the RPL wall and secondary combustion zone at the exit has been examined by chemiluminescence imaging. Emission measurement and LBO (Lean blow out) limits have been determined for different equivalence ratios from 1.8 to LBO limit. Co-flow air temperature was changed from 303 K to 573 K to evaluate the secondary combustion and RPL wall heat transfer effect on flame stability/emission. It is found that equivalence ratio has strong effect on the RPL flame stabilization (primary/secondary flame). Emissions/radical generation were also influenced by the chemical reaction inside the RPL. It can be noticed that coflow air temperature has a significant role on emission, LBO and flame stabilization for the central-pilot stage burner due to the heat loss from the flame zone and RPL wall. A chemical kinetic network (ChemkinTM) and CFD modelling approaches (Fluent) are employed to understand in detail the chemical kinetics, heat transfer effect and flow field inside the RPL (combustion and heat loss inside and emission capability). Experiment shows that the low CO and NOx levels can be achieved at lean and rich condition due to lower flame temperature. Present experimental results by changing equivalence ratio, residence time and co-flow temperature, creates a complete map for the RPL combustion, which is key input for full 4th Generation DLE burner design. (Less)