Kent H. Casleton

Assessment of Rich-Burn, Quick-Mix, Lean-Burn Trapped Vortex Combustor for Stationary Gas Turbines

This paper describes the evaluation of an alternative combustion approach to achieve low emissions for a wide range of fuel types. This approach combines the potential advantages of a staged rich-burn, quick-mix, lean-burn (RQL) combustor with the revolutionary trapped vortex combustor (TVC) concept. Although RQL combustors have been proposed for low-Btu fuels, this paper considers the application of an RQL combustor for high-Btu natural gas applications. This paper will describe the RQL/TVC concept and experimental results conducted at 10 atm (1013 kPa or 147 psia) and an inlet-air temperature of 644 K (700°F). The results from a simple network reactor model using detailed kinetics are compared to the experimental observations. Neglecting mixing limitations, the simplified model suggests that NOx and CO performance below 10 parts per million could be achieved in an RQL approach. The CO levels predicted by the model are reasonably close to the experimental results over a wide range of operating conditions. The predicted NOx levels are reasonably close for some operating conditions; however, as the rich-stage equivalence ratio increases, the discrepancy between the experiment and the model increases. Mixing limitations are critical in any RQL combustor, and the mixing limitations for this RQL/TVC design are discussed.

SYSTEM ISSUES AND TRADEOFFS ASSOCIATED WITH SYNGAS PRODUCTION AND COMBUSTION

The purpose of this article is to provide an overview of the basic technology of coal gasification for the production of syngas and the utilization of that syngas in power generation. The common gasifier types, fixed/moving bed, fluidized bed, entrained flow, and transport, are described, and accompanying typical product syngas compositions are shown for different coal ranks. Substantial variation in product gas composition is observed with changes in gasifier and coal feed type. Fuel contaminants such as sulfur, nitrogen, ash, as well as heavy metals such as mercury, arsenic, and selenium, can be removed to protect the environment and downstream processes. A variety of methods for syngas utilization for power production are discussed, including both present (gas turbine and internal combustion engines) and future technologies, including oxy-fuel, chemical looping, fuel cells, and hybrids. Goals to improve system efficiencies, further reduce NOx emissions, and provide options for CO2 sequestration require advancements in many aspects of IGCC plants, including the combustion system. Areas for improvements in combustion technology that could minimize these tradeoffs between cost, complexity, and performance are discussed.

Chemiluminescence study of methane—fluorine combustion: Observation and analysis of HCF A 1A″-X1A′

Abstract The chemiluminescent emission which results from excited state product formation upon the intimate mixing of CH4 with F2 is shown to be dominated by visible emission from CH*(A 2Δ-X2Π), C*2 (A 3Πg-X 3Πu), HCF* ( A 1A″- X 1A′) and vibrationally excited HF†(X 1Σ+). The corresponding reaction mixture CD4 + F2 produces the deutero analogs. This study represents the first observation of the HCF emission spectrum from a CH4/F2 flame. The observation of the HCF A 1A″- X 1A′ emission spectrum and the corresponding DCF system allows the unequivocal assignment of these visible transitions to a progression dominated by the excited state bending mode. Transitions (0, υ′2,0) → (0,0,0), υ2 = 1−5 for HCF and υ′2 = 2 − 6 for DCF are observed. An analysis of the spectra yields the electronic and vibrational parameters T0 = 17274 ± 6.8 cm−1. ωe = 1024 ± 6.4 cm−1, ωeχe = −7.7 ± 1.2 cm−1 for HCF and T0 = 17281 ± 8 cm−1, ωe = 787.5 ± 4.4 cm−1, ωeχe = −3.86 ± 0.5 cm−1 for DCF. Each vibrational transition shows resolved K-type subbands characteristics of near-symmetric rotor. Although this structure is highly perturbed for the entire HCF system, a partial rotational analysis has been obtained for two bands in the DCF spectrum. The derived rotational parameters are also consistent with the observation of the excited state bending mode.

Demonstration of a reheat combustor for power production with CO2 sequestration

Concerns about climate change have encouraged significant interest in concepts for ultralow or “zero”-emissions power generation systems. In a concept proposed by Clean Energy Systems, Inc., nitrogen is removed from the combustion air and replaced with steam diluent. In this way, formation of nitrogen oxides is prevented, and the exhaust stream can be separated into concentrated CO2 and water streams. The concentrated CO2 stream could then serve as input to a CO2 sequestration process. In this study, experimental data are reported from a full-scale combustion test using steam as the diluent in oxy-fuel combustion. This combustor represents the “reheat” combustion system in a steam cycle that uses a high and low-pressure steam expansion. The reheat combustor serves to raise the temperature of the low-pressure steam turbine inlet, similar to the reheat stage of a conventional steam power cycle. Unlike a conventional steam cycle, the reheat enthalpy is actually generated by oxy-fuel combustion in the steam flow. This paper reports on the unique design aspects of this combustor, as well as initial emissions and operating performance.

Pressure Effect on NOx and CO Emissions in Industrial Gas Turbines

In order to determine the effect of pressure on emissions and stability limit, an experimental and modeling study has been performed jointly by UTRC and DOE-FETC. Experiments have been performed at lean conditions in 100–400 psi range with two different nozzles. Measured NOx and CO concentrations have been modeled with a PSR Network using detailed chemistry. Good agreement between the data and model predictions over a wide range of conditions indicate the consistency and reliability of the measured data and validity of the modeling approach.Experiments were conducted at the DOE-FETC facility in Morgantown. A simple refractory combustor liner with a fuel-air-premixing nozzle was used to map stability margins, emission levels of NOx, CO and combustion efficiency. Each experimental nozzle had a centerbody and wall pilot for flame stabilization. Data was collected at four different pressures of 100, 200, 300 and 400 psi, and at different diffusion pilot and moisture levels. The premixing nozzle hardware could be easily lit and operated over a broad range of flame temperatures with minimal combustion generated noise. Two different nozzles designed at UTRC were used to determine pressure and nozzle effects.Computations were made for comparison with the experiments. GRI Mech 2.11 kinetics and thermodynamic database was used for modeling the flame chemistry. A Perfectly Stirred Reactor (PSR) network code developed internally at UTRC was used to create a network of PSRs to simulate the flame and combustor. A total of 10 to 15 reactors were used in the network. Residence time varied with the flow rates (air was fixed while fuel flow rate was varied in order to obtain the required equivalence ratio, ϕ).Good agreement between the measured and modeled NOx (5–10%) was obtained, but the agreement for CO (model predictions are higher by 30–50%) was not as good as for NOx. The experimental data and the modeling predictions indicate that the NOx emission functionality with pressure is dependent on both equivalence ratio and absolute pressure. The CO levels tend to go down with increase in pressure as P−0.5, at different equivalence ratios, consistent with an equilibrium analysis.Copyright

NOx Scaling Characteristics for Industrial Gas Turbine Fuel Injectors

An experimental and numerical investigation into the effects of nozzle scale was undertaken at the U.S. Federal Energy Technology Center in conjunction with the United Technologies Research Center. Experiments were conducted at operating pressures from 6.8 to 27.2 atm., and at primary zone equivalence ratios from 0.4 to 0.75. Results reported herein summarize tests at 6.8 atm., and with zero and 4% piloting levels (expressed as mass fractions of total fuel). Computations used to compare to the experimental data were made using the GRI Mech 2.11 kinetics and thermodynamics database for flame chemistry modeling. A perfectly stirred reactor network (PSR) was used to create a network of PSRs to simulate the flame. From these investigations, concentrations of NOx and CO expressed in parts per million (ppm) were seen to increase and remain virtually unchanged, respectively, when comparing a Quarter to Full Scale Bluff-Body (Tangential Entry) nozzle. Simple heat transfer modeling and CO emissions refuted that any variations in thermal characteristics within the combustors were solely responsible for the observed NOx variations. Using PSR network modeling, the NOx trends were explained due to variations in macroscopic mixing scales which increased with nozzle size, thereby creating progressively less uniform mixing, and hence higher NOx levels.Copyright

Low NOx Advanced Vortex Combustor

A lean-premixed advanced vortex combustor (AVC) has been developed and tested. The natural gas fueled AVC was tested at the U.S. Department of Energy’s National Energy Technology Laboratory in Morgantown, WV. All testing was performed at elevated pressures and inlet temperatures and at lean fuel-air ratios representative of industrial gas turbines. The improved AVC design exhibited simultaneous NOx /CO/unburned hydrocarbon (UHC) emissions of 4/4/0 ppmv (all emissions corrected to 15% O2 dry). The design also achieved less than 3 ppmv NOx with combustion efficiencies in excess of 99.5%. The design demonstrated marked acoustic dynamic stability over a wide range of operating conditions, which potentially makes this approach significantly more attractive than other lean-premixed combustion approaches. In addition, the measured 1.75% pressure drop is significantly lower than conventional gas turbine combustors, which could translate into an overall gas turbine cycle efficiency improvement. The relatively high velocities and low pressure drop achievable with this technology make the AVC approach an attractive alternative for syngas fuel applications.

Assessment of RQL Trapped Vortex Combustor for Stationary Gas Turbines

This paper describes the evaluation of an alternative combustion approach to achieve low emissions for a wide range of fuel-types. This approach combines the potential advantages of a staged Rich-burn, Quick-mix, Lean-burn (RQL) combustor with the revolutionary Trapped Vortex Combustor (TVC) concept. Although RQL combustors have been proposed for low-BTU fuels, this paper considers the application of an RQL combustor for high-BTU natural gas applications. This paper will describe the RQL/TVC concept and experimental results conducted at 10 atmospheres (1013 kPa or 147 psia) and an inlet-air temperature of 644K (700°F). The results from a simple network reactor model using detailed kinetics are compared to the experimental observations. Neglecting mixing limitations, the simplified model suggests that NOx and CO performance below 10 parts-per-million could be achieved in an RQL approach. The CO levels predicted by the model are reasonably close to the experimental results over a wide range of operating conditions. The predicted NOx levels are reasonably close for some operating conditions, however, as the rich-stage equivalence ratio increases, the discrepancy between the experiment and the model increases. Mixing limitations are critical in any RQL combustor, and the mixing limitations for this RQL/TVC design are discussed.Copyright

Ultra-Low NOx Advanced Vortex Combustor

An ultra lean-premixed Advanced Vortex Combustor (AVC) has been developed and tested. The natural gas fueled AVC was tested at the U.S. Department of Energy’s National Energy Technology Laboratory (USDOE NETL) test facility in Morgantown (WV). All testing was performed at elevated pressures and inlet temperatures and at lean fuel-air ratios representative of industrial gas turbines. The improved AVC design exhibited simultaneous NOx/CO/UHC emissions of 4/4/0 ppmv (all emissions are at 15% O2 dry). The design also achieved less than 3 ppmv NOx with combustion efficiencies in excess of 99.5%. The design demonstrated tremendous acoustic dynamic stability over a wide range of operating conditions which potentially makes this approach significantly more attractive than other lean premixed combustion approaches. In addition, a pressure drop of 1.75% was measured which is significantly lower than conventional gas turbine combustors. Potentially, this lower pressure drop characteristic of the AVC concept translates into overall gas turbine cycle efficiency improvements of up to one full percentage point. The relatively high velocities and low pressure drops achievable with this technology make the AVC approach an attractive alternative for syngas fuel applications.

Response of two-phase droplets to intense electromagnetic radiation

The response of two-phase droplets to intense radiant heating is studied to determine the incident power that is required for causing explosive boiling in the liquid phase. The droplets studied consist of strongly absorbing coal particles dispersed in a weakly absorbing water medium. Experiments are performed by confining droplets (radii = 37, 55, and 80 microm) electrodynamically and irradiating them from two sides with pulsed laser beams. Emphasis is placed on the transition region from accelerated droplet vaporization to droplet superheating and explosive boiling. The time scale observed for explosive boiling is more than 2 orders of magnitude longer than published values for pure liquids. The delayed response is the result of energy transfer limitations between the absorbing solid phase and the surrounding liquid.