scholarly journals The Effects of Coke Parameters and Circulating Flue Gas Characteristics on NOx Emission during Flue Gas Recirculation Sintering Process

Energies ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 3828 ◽  
Author(s):  
Juntao Han ◽  
Guofeng Lou ◽  
Sizong Zhang ◽  
Zhi Wen ◽  
Xunliang Liu ◽  
...  
Keyword(s):  
Flue Gas ◽  
Coke Consumption ◽  
Reduction Rate ◽  
Combustion Efficiency ◽  
Nox Emission ◽  
Nox Emissions ◽  
Content Increase ◽  
Gas Treatment ◽  
Flue Gas Recirculation ◽  
Gas Recirculation

The new process of flue gas recirculation, which reduces coke consumption and reducing NOx emissions, is now extensively used. Compared with traditional sintering, the characteristics of circulating flue gas and coke parameters significantly affect the combustion atmosphere and coke combustion efficiency. Based on the actual complex process of sintering machine, this study proposes a relatively comprehensive one-dimensional, unsteady mathematical model for flue gas recirculation research. The model encompasses NOx pollutant generation and reduction, as well as SO2 generation and adsorption. We focus on the effects of cyclic flue gas characteristics on the sintering-bed temperature and NOx emissions, which are rarely studied, and provide a theoretical basis for NOx emission reduction. Simulation results show that during sintering, the fuel NOx is reduced by 50% and 10% when passing through the surface of coke particles and CO, respectively. During flue gas recirculation sintering, the increase in circulating gas O2 content, temperature, and supply-gas volume cause increased combustion efficiency of coke, reducing atmosphere, and NOx content in the circulating area; the temperature of the material layer also increases significantly and the sintering endpoint advances. During cyclic sintering, the small coke size and increased coke content increase the char-N release rate while promoting sufficient contact of NOx with the coke surface. Consequently, the NOx reduction rate increases. Compared with the conventional sintering, the designed flue gas recirculation condition saves 3.75% of coke consumption, i.e., for 1.2 kg of solid fuel per ton of sinter, the amount of flue gas treatment is reduced by 21.64% and NOx emissions is reduced by 23.59%. Moreover, without changing the existing sintering equipment, sintering capacity increases by about 5.56%.

Lean Blowout Limit and NOx-Production of a Premixed Sub-ppm NOx Burner With Periodic Flue Gas Recirculation

2004 ◽  
Author(s):  
Jochen R. Kalb ◽  
Thomas Sattelmayer
Keyword(s):  
Natural Gas ◽  
Flue Gas ◽  
Gas Content ◽  
Stable Operation ◽  
Reacting Flow ◽  
Nox Emissions ◽  
Lean Blowout ◽  
Fresh Mixture ◽  
Flue Gas Recirculation ◽  
Gas Recirculation

The technological objective of this work is the development of a lean-premixed burner for natural gas. Sub-ppm NOx emissions can be accomplished by shifting the lean blowout limit (LBO) to slightly lower adiabatic flame temperatures than the LBO of current standard burners. This can be achieved with a novel burner concept utilizing periodic flue gas recirculation: Hot flue gas is admixed to the injected premixed fresh mixture with a mass flow rate of comparable magnitude, in order to achieve self-ignition. The subsequent combustion of the diluted mixture again delivers flue gas. A fraction of the combustion products is then admixed to the next stream of fresh mixture. This process pattern is to be continued in a cyclically closed topology, in order to achieve stable combustion of e.g. natural gas in a temperature regime of very low NOx production. The principal ignition behavior and NOx production characteristics of one sequence of the periodic process was modeled by an idealized adiabatic system with instantaneous admixture of partially or completely burnt flue gas to one stream of fresh reactants. With the CHEMKIN-II package a reactor network consisting of one perfectly stirred reactor (PSR, providing ignition in the first place) and two plug flow reactors (PFR) has been used. The effect of varying burnout and the influence of the fraction of admixed flue gas have been evaluated. The simulations have been conducted with the reaction mechanism of Miller and Bowman and the GRI-Mech 3.0 mechanism. The results show that the high radical content of partially combusted products leads to a massive decrease of the time required for the formation of the radical pool. As a consequence, self-ignition times of 1 ms are achieved even at adiabatic flame temperatures of 1600 K and less, if the flue gas content is about 50%–60% of the reacting flow after mixing is complete. Interestingly, the effect of radicals on ignition is strong, outweighs the temperature deficiency and thus allows stable operation at very low NOx emissions.

Effects of Flue Gas Recirculation on NOx Emissions from Gas-Fired Utility Boilers

2021 ◽  
pp. 319-337
Author(s):  
Nikola Tanasić ◽  
Mirjana Stamenić ◽  
Vladimir Tanasić
Keyword(s):  
Flue Gas ◽  
Nox Emissions ◽  
Flue Gas Recirculation ◽  
Utility Boilers ◽  
Gas Recirculation

On the Influence of Fuel Mixing and Flue Gas Recirculation on the Emissions of a Fuel Flexible Gas Turbine Combustor

2015 ◽  
Author(s):  
Stefan Fischer ◽  
David Kluß ◽  
Franz Joos
Keyword(s):  
Nitric Oxide ◽  
Flue Gas ◽  
Nox Emissions ◽  
Combined Effects ◽  
Fuel Gas ◽  
Flue Gas Recirculation ◽  
Mixing Behavior ◽  
Nitric Oxide Emissions ◽  
Fuel Mixing ◽  
Gas Recirculation

The main benefits of operating a combustor under flue gas recirculation conditions are the increase in efficiency of the post combustion carbon capture and storage process and the potential to reduce NOX emissions while keeping the thermal load of the gas turbine constant. The latter is primarily caused by the change in thermodynamic properties of the combustive mixture with increasing vitiation. As a result, the dominant NOX formation pathways change with increasing FGR ratio. In a partially premixed combustor, the formation of NOX emissions can also be influenced by the fuel mixing behavior. Different setups lead to combustive mixtures with different degrees of homogeneity as well as influencing the distribution of the mixture within the combustion chamber. In this paper the combined effects of the variation of mixture homogeneity and the flue gas recirculation ratio on the NOX emissions and the stability range is experimentally investigated for different fuel gases. The experiments are performed on the atmospheric laboratory test rig, which is equipped with a partially premixed combustor. The burner is equipped with modular fuel gas nozzles allowing for the variation of the fuel mixing behavior. Exhaust gas measurements are performed to evaluate the influence of the parameters on the emissions profile of the combustor and to compare the results to a theoretical study. The results of this study show that the level of nitric oxide emissions as well as the potential to decrease said emissions with FGR operation is dependent on the mixing behavior of the combustor. Furthermore, the combined effects of fuel gas nozzle and FGR operation lead to a proposal of an operational strategy for the combustor which combines the advantages of low nitric oxide emissions and a broad range of stability.

Dynamic Model Construction of an Industrial Flue Gas Recirculation (FGR) Furnace for Real-Time NOx Emission Control

2003 ◽  
Author(s):  
Q. Jiang ◽  
C. Zhang ◽  
J. Jiang
Keyword(s):  
System Identification ◽  
Numerical Simulations ◽  
Dynamic Model ◽  
Flue Gas ◽  
Dynamic Models ◽  
Nox Emission ◽  
Flue Gas Recirculation ◽  
Frequency Responses ◽  
Dynamic Relationships ◽  
Gas Recirculation

Flue gas recirculation is one of the most effective ways to reduce nitric oxides (NOx) emission in conventional industrial furnaces. To design an effective control scheme, one has to understand the dynamic relationships among different furnace inputs and outputs. This paper concentrates on the construction of such dynamic models for an industrial furnace using numerical simulations and frequency domain system identification techniques. The numerical simulations are based on the conservation equations of mass, momentum, and energy. The inputs to the furnace consist of the pressure head of the flue gas recirculation fan, the temperature of the combustion air, and the flow rate of the combustion air. The outputs considered herein are NOx and oxygen (O2) concentrations. To obtain a dynamic model for this multi-input and multi-output system, low amplitude sinusoidal signals of different frequencies are administrated at the furnace input. The dynamic relationships among the inputs and outputs at these frequencies are established in terms of frequency responses (magnitude and phase) around a particular furnace operating point. These frequency responses are further processed by a least squares based system identification technique to convert them to a set of parametric models. The result of the system identification is a set of the transfer functions with the order ranging from 3rd to 6th. Studies have been carried out to verify the validity of these dynamic models by comparing the responses generated from these models with those obtained from the full-scale numerical solution. These dynamic models provide a starting point for the design of realtime optimal feedback control systems for minimizing NOx emission.

Flue Gas Recirculation in Gas Turbine: Investigation of Combustion Reactivity and NOX Emission

2009 ◽  
Author(s):  
Felix Guethe ◽  
Marta de la Cruz Garci´a ◽  
Andre´ Burdet
Keyword(s):  
Gas Turbine ◽  
Flue Gas ◽  
Gas Turbines ◽  
Nox Emission ◽  
Moderate Increase ◽  
Fuel Injector ◽  
Flue Gas Recirculation ◽  
Combustion Reactivity ◽  
Gas Recirculation ◽  
The Impact

Flue gas recirculation (FGR) is a promising technology for the optimization of post-combustion CO2 capture in natural gas combined cycle (NGCC) plants. In this work, the impact of FGR on lean gas turbine premix combustion is predicted by analytical and numerical investigations as well as comparison to experiments. In particular the impact of vitiated air condition and moderate increase of CO2 concentration into combustion reactivity and NOx emission is studied. The influence of inlet pressure, temperature and recirculated NOx are taken as parameters of this study. Two different kinetic schemes are used to predict the impact that FGR has on the combustion process: the GRI3.0 and the RDO6_NO, which is a newly compiled mechanism from the DLR Stuttgart. The effects of the FGR on the NOx emissions are predicted using a chemical reactor network including unmixedness as presumed probability density function (PDF) to account for real effects. The magnitude and ratio of prompt to post-flame thermal NOx changes with the FGR-ratio producing less post flame NOx at reduced O2 content. For technical mixtures (i. e. an industrial fuel injector), NOx emission can be expected to be lower with the vitiation of the oxidizer. This is due to several effects: at low O2 concentration, the highest possible adiabatic flame temperatures for stoichiometric conditions decreases resulting in lower NOx when averaged over all mixing fractions. Further effects result from lower post flame NOx production and the role of “reburn” chemistry, actually reducing NOx (recirculated from the exhaust), which might become relevant for the high recirculation ratios, where parts of the flame would operate at rich stoichiometry at given unmixedness. Therefore in general for each combustor technical mixing could decrease NOx with respect to perfect mixing at high FGR-ratio assuming the engine can still be operated. Although the findings are quite general for gas turbines the advantage that reheat engines have in terms of operation are highlighted. For reheat engines this can be understood as an extension of the “reheat concept” and used as the next step in the goal to achieve minimal emissions at increasing power. In addition, NOx emission obtained in FGR combustion reduces even further when the engine pressure ratio increases, making the concept particularly well suited for reheat engines.

Combustion Under Flue Gas Recirculation Conditions in a Gas Turbine Lean Premix Burner

2010 ◽  
Author(s):  
Andre´ Burdet ◽  
Thierry Lachaux ◽  
Marta de la Cruz Garci´a ◽  
Dieter Winkler
Keyword(s):  
Gas Turbine ◽  
Flue Gas ◽  
Gas Turbines ◽  
Nox Reduction ◽  
Nox Emission ◽  
Stable Operation ◽  
Engine Operation ◽  
Flue Gas Recirculation ◽  
Gas Recirculation ◽  
Co Emission

An EV burner as installed in Alstom’s dry low NOx gas turbines was experimentally investigated under different Flue Gas Recirculation (FGR) and engine conditions. FGR enables the reduction of the high exhaust volume flow while significantly increasing the exhaust CO2 concentration. This may substantially improve the post-combustion capture of CO2. However, FGR introduces consequent changes in the gas turbine combustion process mainly because of the oxygen depletion and CO2 increase within the oxidizer. N2 and CO2 were mixed with air in order to obtain at the burner inlet a synthetic oxidizer mixture reproducing O2 and CO2 levels spanning different FGR levels of interest for engine operation. In addition, various degrees of unmixedness of the reactive mixture were investigated by varying the ratio of fuel injected at different port locations in the investigated burner set. Stable operation was achieved in all tested conditions. The lean premix flame shifts downstream when O2 is depleted due to the decrease of the reactivity, although it always stays well within the combustion chamber. The potential for NOx reduction when using FGR is demonstrated. Changes of the NOx formation mechanism are described and compared to the experimental data for validation. Unmixedness appears to be less detrimental to NOx emission when under high FGR ratio. However, CO emission is shown to increase when FGR ratio is increased. Meanwhile, with the present gas turbine combustor, the CO emission follows the equilibrium limit even at high FGR ratio. Interestingly, it is observed that when the burner inlet pressure is increased (and consequently the inlet burner temperature), the increase of CO emission due to FGR is lowered while the NOx emission stays at a very low level. This present an argument for using a higher cycle pressure in gas turbines optimized for FGR operation.

Characteristics and flame appearance of oxy-fuel combustion using flue gas recirculation

Fuel ◽  
2021 ◽  
Vol 297 ◽  
pp. 120775
Author(s):  
Mohsen Abdelaal ◽  
Medhat El-Riedy ◽  
Ahmed M. El-Nahas ◽  
Fathy R. El-Wahsh
Keyword(s):  
Flue Gas ◽  
Fuel Combustion ◽  
Flue Gas Recirculation ◽  
Gas Recirculation
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