• 한국연소학회:학술대회논문집
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• 1999.10a
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• pp.149-154
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• 1999

The influences of air staging on NOx emission and burnout of coal flames were investigated using 1MWth combustion test facility. The experiments showed that variation of overall excess air ratio led to a relatively higher NOx emission level for ${\lambda}=1.2.$ When air staging was applied to the combustion air, it was confirmed that a fuel rich primary combustion zone was established and unburned char was burened completely by mixing with the staged air supplied radially around the flame. The NOx emissions were redued by increasing the staged air flow rate, and staging air was suggested to be more than 40% of the total combustion air for the substantial NOx reduction.

• Korean Chemical Engineering Research
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• v.59 no.1
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• pp.127-137
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• 2021

Air emission charge for nitrogen oxide as a precursor of fine dust has been introduced and implemented within the country from 2020. Therefore, the development of economical combustion technology for NOx reduction has got more needed urgently. This study investigated the air-staging effect as a way to reduce the NOx during combustion of domestic unused forest biomass, recently possible to secure REC (Renewable Energy Certification) as a substitute for overseas wood pellets in a 0.1 MWth circulating fluidized bed combustion test-rig. Operating conditions were comparison with and without air-staging, the supply position of tertiary air (6.4 m, 8.1 m, 9.4 m in the combustor) and variation of air-staging ratio (Primary air:Secondary air:Tertiary air=91%:9%:0%, 82%:9%:9%, 73%:9%:18%). NO and CO concentrations in flue gas, profiles of temperature and pressure at the height of the combustion, unburned carbon in sampled fly ash and combustion efficiency on operating conditions were evaluated. As notable results, NO concentration with air-staging application under tertiary air supply at 9.4 m in the combustor reduced 100.7 ppm compared to 148.8 ppm without air-staging while, CO concentration increased from 52.2 ppm without air-staging to 99.8 ppm with air-staging. However, among air-staging runs, when tertiary air supply amount at 6.4 m in the combustor increased by air-staging ratio (Primary air:Secondary air:Tertiary air=73%:9%:18%), NO and CO concentrations decreased the lowest 90.8 ppm and 66.1 ppm, respectively. Furthermore, combustion efficiency at this condition was improved to 99.3%, higher than that (98.3%) of run without air-staging.

• Journal of Mechanical Science and Technology
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• v.16 no.9
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• pp.1112-1120
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• 2002

Numerical investigations on air staging and fuel staging were carried out with a newly designed coaxial cyclone combustor, which uses the method of two stage coal combustion composed of pre-combustor and main combustor. The pre-combustor with a high air/fuel ratio is designed to supply gas at high temperature to the main combustor. To avoid local high temperature region in this process, secondary air is injected in the downstream. Together with the burned gas supplied from the pre-combustor and the preheated air directly injected into main combustor, coals supplied through the main burner react rapidly at a low air/fuel ratio. Strong swirling motion of cyclone combustor keeps the wall temperature high, which makes slagging combustion possible. Alaska, US coal is used for calculations. Predictions were made for various coal flow rates in the main combustor for fuel staging and for the various flow rate of secondary air in the pre-combustor for air staging. In-scattering angles are also chosen as a variable to increase residence times of coal particles. Temperature fields and particle trajectories for various conditions are described. Predicted temperature variations at the wall of the combustor are compared with corresponding experimental data and show a similar trend. The in-scattering angle of 20° is recommended to increase the combustion efficiency in the main chamber.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.1
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• pp.32-38
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• 2003

Staged combustion, such as air- and fuel-staging, is a relatively well-known technique fur reduction of NOx emission and used in combination with other techniques nowadays. However, the design variables are still selected depending upon operating conditions. There are many variables tested to investigate the NOx emission characteristics fur changing of fuel or air velocity, swirl intensity, and staging ratio of air and fuel in multi-staged burner. In air-staging case, the fuel-rich condition of the primary combustion zone is very helpful to reduce NOx emission and its range is known to be restricted by the increase of carbon monoxide. However, in many cases carbon monoxide level is not too high to be restricted operating condition. So we tried to expand the equivalence ratio range to the richer condition in the primary combustion zone and certificate the function of each burner component and its contribution to the overall NOx production.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.10
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• pp.637-644
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• 2016

The purpose of this study is to understand the characteristics of unburned carbon (UBC) and NOx emissions for pulverized coal when air staging combustion is applied. A two-staged drop tube furnace capable of applying air staging combustion was designed and installed. The combustion of sub-bituminous (Tanito) has been investigated. UBC and the NOx concentration were measured under various temperatures and stoichiometric ratios in unstaged and staged combustion. As a result, UBC decreased and the NOx concentration increased with an increase in stoichiometric ratio and temperature. In particular, the NOx reduction mechanism was activated when the temperature in the fuel rich zone increased. Both UBC and the NOx concentration decreased as the temperature increased in the fuel rich zone. A high NOx reduction effect was obtained, compared to the UBC increase, when the air staging technique was applied.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.167-171
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• 2001

Air-staging combustion is a relatively well-known technique to reduce NOx emission and used in combination with other techniques nowadays. However, the design variables are still selected depending upon operating circumstances. Though the fuel-rich condition of the primary combustion zone is very helpful to NOx reduction, its range is known to be restricted by the increase of carbon monoxide. However, in many cases carbon monoxide level is so low not to be the restriction at all. So we tried to expand the equivalence ratio range to the richer condition in the primary combustion zone and make the function of each burner component and its contribution to the overall NOx production clear.

• Journal of the Korean Society of Combustion
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• v.13 no.2
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• pp.7-13
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• 2008

The aim of this work is to identify application of ultra low NOx and CO combustor. To achieve this, we developed the premixed oxidizer-staging combustor using a cyclone flow. Various factors such as equivalence ratio for the combustion condition and swirl type for secondary air injection have been tested experimentally for flame stability and NOx, CO emission characteristics. Before to do this, we had been tested cyclone premixed combustor in advance. it is similar to first combustor of premixed oxidizer-staging combustor. As a result, cyclone premixed flame shows the very high flame stability and low NOx emission. however, it can be identified that there were some problems such as a little high CO emission and thermal resistance of combustor wall. Cyclone premixed oxidizer-staging combustor can resolve those of problems. In our combustor, we can found out optimal condition that the secondary air injection method is swirl type, swirl direction is co-swirl and equivalence ratio of first combustor is 1.3. Quantitatively, we can achieve 10.8 ppm for NOx and 30.2 ppm for CO emissions respectively. Form this result, we can identified that cyclone premixed oxidizer-staging combustor can apply to ultra low NOx and CO combustor.

• 한국연소학회:학술대회논문집
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• 2004.06a
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• pp.235-241
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• 2004

Computations were performed to investigate the effects of air staging on combustion in three stage heavy-oil fired combustion burner. The burner was designed for 3 MW. Different amounts of air are introduced into each 3 three stages by means of each dampers. The goal of the study is to understand combustion phenomena according to each air stage mass ratios through CFD. Air flow rates at three inlets are adjusted by dampers inside a burner. Here, injection conditions of liquid fuel are kept constant throughout all simulations. This assumption is made in order to limit the complexity of oil combustion though it may cause some disagreement. In case of cold flows, only longitudinal velocities arc considered, On the other hand, flow, temperature and NOx generations are taken into account for reactive flows. Simple parametric study was conducted by setting 1'st air stage mass ratio as a parameter. And an optimal operation condition was found. The computational study is based on k-e model, P-1 radiation model(WSGGM) and PDF, and is implemented on a commercial code, FLUENT.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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• pp.591-596
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• 1995

In order to investigate the reduction of NO emissions, natural gas was fueled for two-stage combustion apparatus. NO and CO emissions were described by five variables: total air ratio, primary air ratio, secondary air injection position, secondary air injection velocity, and swirl ratio. It was mainly observed that, as the primary air ratios of 0 and 0.4 NO emission decreased with increasing the secondary air injection position and secondary air injection velocity. The effect of weak swirl on NO emission was found to be insignificant.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.11
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• pp.1464-1472
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• 1999

Design and operation of $1MW_{th}$ pulverized coal combustion testing facility are described. Also the influence of air staging on NOx emission and burnout of coal flames was investigated in this facility. The test facility consisted of coal feeding system, firing system and flue gas treatment system. A top-fired externally air staging burner was adopted in order to avoid influence of gravity on the coal particles and for easy maintenance. Distribution of temperature and chemical species concentration of coal flames could be measured in vertical pass of furnace. Main fuel was pulverized (83.4% less than $80{\mu}m$) Australian high bituminous coal. From variety of test conditions, overall excess air ratio was selected at 1.2(20% excess air). Tho study showed that increasing the staged air resulted in lower NOx omission, and it was suggested to be more than 40% of the total combustion air for the substantial NOx reduction. Sufficient burnout was not achievable when NOx emission was less than 500ppm. Also, the amount of core air did not influence tho NOx reduction.