Combination of Primary Measures on Flue Gas Emissions in Grate-Firing Biofuel Boiler

Increasingly stringent limits for NOx and SO2 emission are forcing the investigation of new reduction methods. This study was conducted to determine the combination of primary measures, i.e., flue gas recirculation (FGR) and excess air effects on sulfur, nitrogen and hydrocarbon emissions, in boiler flue gas. Experimental research was performed using an experimental, small-scale (20 kW) model of an industrial biofuel boiler. During combustion of sunflower seed hulls at different FGR ratios and incomplete combustion regimes, the composition of flue gas (NO, NO2, N2O, HCN, NH3, SO2, SO3, H2S, CO, and CxHy) was compared, allowing an explanation of the determinants of emission concentration changes to be provided. Increasing the flue gas recirculation ratio in the primary air had a positive effect on reducing NOX and CO with certain organic compounds. However, an opposite effect on SO2 was observed. NOX and SO2 concentrations were found to be approximately 500 mg/m3 and 150 mg/m3 under a regular combustion regime. When the FGR ratio of 50% NOX concentration decreased by 110 mg/m3, the SO2 concentration increased by 60 mg/m3. The incomplete combustion regime reduced NOX concentration by 70 mg/m3, whereas SO2 concentration increased by 100 mg/m3. The influence of primary measures presented an unclear relationship to hydrocarbon emissions, with concentrations not exceeding 18 mg/m3.

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Effects of Flue Gas Recirculation on Emissions from a Small Scale Wood Chip Fired Boiler

Energy Procedia ◽

10.1016/j.egypro.2015.02.034 ◽

2015 ◽

Vol 66 ◽

pp. 65-68 ◽

Cited By ~ 3

Author(s):

Qun Chen ◽

Xiaohui Zhang ◽

Jue Zhou ◽

Vida N. Sharifi ◽

Jim Swithenbank

Keyword(s):

Flue Gas ◽

Wood Chip ◽

Small Scale ◽

Flue Gas Recirculation ◽

Gas Recirculation

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

Fuel ◽

10.1016/j.fuel.2021.120775 ◽

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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Experiment investigation of coal MILD-Oxy combustion integrated with flue gas recirculation at a 0.3 MW th furnace

Fuel Processing Technology ◽

10.1016/j.fuproc.2017.04.002 ◽

2017 ◽

Vol 162 ◽

pp. 126-134 ◽

Cited By ~ 13

Author(s):

Zhihui Mao ◽

Liqi Zhang ◽

Xinyang Zhu ◽

Chuguang Zheng

Keyword(s):

Flue Gas ◽

Flue Gas Recirculation ◽

Gas Recirculation

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

Volume 1: Turbo Expo 2004 ◽

10.1115/gt2004-53410 ◽

2004 ◽

Cited By ~ 4

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.

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658 NO_x formations in coal combustion with flue gas recirculation

The Proceedings of Conference of Tokai Branch ◽

10.1299/jsmetokai.2011.60._658-1_ ◽

2011 ◽

Vol 2011.60 (0) ◽

pp. _658-1_-_658-2_

Author(s):

Ryo YOSHIIE ◽

Takuya KAWAMOTO ◽

Yasuaki UEKI ◽

Ichiro NARUSE

Keyword(s):

Flue Gas ◽

Coal Combustion ◽

Flue Gas Recirculation ◽

Gas Recirculation

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Low NO x Combustion of DME by Means of Flue Gas Recirculation

Challenges of Power Engineering and Environment ◽

10.1007/978-3-540-76694-0_233 ◽

2007 ◽

pp. 1247-1251 ◽

Cited By ~ 2

Author(s):

Ryosuke Matsumoto ◽

Mamoru Ozawa ◽

Shinya Terada ◽

Takenori Iio

Keyword(s):

Flue Gas ◽

Flue Gas Recirculation ◽

Gas Recirculation

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Modelling the Effect of External Flue Gas Recirculation on NOx and CO Emissions in a Premixed Gas Turbine Combustor With Chemical Reactor Networks

Volume 4B: Combustion, Fuels, and Emissions ◽

10.1115/gt2018-76548 ◽

2018 ◽

Cited By ~ 1

Author(s):

V. Prakash ◽

J. Steimes ◽

D. J. E. M. Roekaerts ◽

S. A. Klein

Keyword(s):

Gas Turbine ◽

Flue Gas ◽

Recirculation Zone ◽

Chemical Reactor ◽

Inlet Temperature ◽

Part Load ◽

Flue Gas Recirculation ◽

Reactor Networks ◽

Gas Recirculation ◽

The Impact

The increasing amount of renewable energy and emission norms challenge gas turbine power plants to operate at part-load with high efficiency, while reducing NOx and CO emissions. A novel solution to this dilemma is external Flue Gas Recirculation (FGR), in which flue gases are recirculated to the gas turbine inlet, increasing compressor inlet temperature and enabling higher part load efficiencies. FGR also alters the oxidizer composition, potentially leading to reduced NOx levels. This paper presents a kinetic model using chemical reactor networks in a lean premixed combustor to study the impact of FGR on emissions. The flame zone is split in two perfectly stirred reactors modelling the flame front and the recirculation zone. The flame reactor is determined based on a chemical time scale approach, accounting for different reaction kinetics due to FGR oxidizers. The recirculation zone is determined through empirical correlations. It is followed by a plug flow reactor. This method requires less details of the flow field, has been validated with literature data and is generally applicable for modelling premixed flames. Results show that due to less O2 concentration, NOx formation is inhibited down to 10–40% and CO levels are escalated up to 50%, for identical flame temperatures. Increasing combustor pressure leads to a rise in NOx due to thermal effects beyond 1800 K, and a drop in CO levels, due to the reduced chemical dissociation of CO2. Wet FGR reduces NOx by 5–10% and increases CO by 10–20%.

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