• Journal of Mechanical Science and Technology
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• 제16권9호
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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.

• 대한기계학회논문집B
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• 제25권11호
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• pp.1616-1623
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• 2001

A basic experimental study has been carried out to find out the design parameters of fuel 2-staging atomizers in order to reduce nitrogen oxides(NOx) rate emitted from the steam boilers used the liquid fuel. The heavy fuel oil(B-Coil) and fuel 2-staging Y-jet twin-fluid atomizers were adopted in this study. The results of this paper were obtained from the real as well as the model scale atomizers. In the case of model atomizers test, NOx reduction rate was strongly dependent on the staged fuel rate, but it was weakly dependent on the injection hole arrangement and air swirl conditions. The real scale atomizers was designed and manufactured on the base of these test results, and those was mounted and operated in the real boiler generates 185 ton steam per an hour. The reduction rate of the model and real plant was reached 10∼30% of base NOx by atomizers. but dust was sharply increased in the low O$_2$combustion region of the real plant.

• 대한기계학회논문집B
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• 제27권1호
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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.

• 대한기계학회논문집B
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• 제34권3호
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• pp.283-290
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• 2010

이 연구의 목적은 NOx 저감을 위한 연료희박 재연소 기법과 산화제 다단 연소 기법의 혼합 기법의 실험적 연구를 목표로 한다. 실험용 연소로에서 재연소 연료 분율, 재연소 노즐 직경, 산소부하도 및 재연소 연료 분사 위치등을 고려한 실험을 수행 하였다. 또한, 산화제 다단 연소를 통하여 생성된 유동장이 NOx 저감에 미치는 영향을 연료희박 기법의 NOx 저감율과 비교하는 실험을 수행하였다. 실험을 통하여 연료희박 재연소와 산화제다단연소 기법의 혼합 기법이 NOx 저감에 미치는 긍정적인 효과를 관찰 하였다.

• 대한기계학회논문집B
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• 제32권1호
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• pp.7-14
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• 2008

It has been reported that partially premixed interacting flame could be sustained till sonic exit velocities if eight small nozzles are arranged optimally and one nozzle on the center is fed small amount of fuel. But the equivalence ratios in this experiments were 20-60. In this research, experiments were conducted to know the effects of lean-rich staging in multiple jet flames on the blowout velocity. The fuel mole tractions in the fuel-air mixture, the nozzle exit velocity and the diameter between adjacent nozzles were alternatively changed. When the lower mole fraction fuel was fed to the nozzles located near the center and small amount of fuel to the center nozzle, flame was not extinguished even at the nozzle exit velocity of 200m/s. Also the interacting flame could be sustained till that velocity when four small size nozzles for lean mixture were located within the arrangement of four nozzles for rich mixture and configured optimally.

• Bulletin of the Korean Chemical Society
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• 제17권10호
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• pp.885-892
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• 1996

The effects of NOx reduction by advanced fuel staging in a small scale combustor (6.6 kWT) have been investigated using propane gas flames laden with ammonia as fuel-nitrogen. The variables which had the greatest influence on NOx reduction were temperature, reducing stoichiometry (relate to main combustion zone stoichiometry, air fraction and reburning fuel fraction) and residence time of reducing zone. NOx reduction was best at the reburning zone temperature of above 1,000 ℃ and reburning zone stoichiometry was 0.85. In terms of residence time of the reburning zone, NOx reduction was effective when burnout air was injected at the point where the reburning zone had been already established. In the advanced fuel staging NOx reduction was relatively large at the burning of higher Fuel-N concentration in the fuel. Under optimum reburning conditions, fuel nitrogen content had a relatively minor impact on reburning efficiency.

• 대한기계학회논문집B
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• 제40권10호
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• pp.637-644
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• 2016

본 연구의 목적은 석탄 입자 연소 시 공기 다단 연소 적용에 따른 UBC(Unburned Carbon) 및 질소 산화물(NOx) 배출 특성을 분석하는 것이다. 이를 위해 공기 다단 연소가 가능한 2단 하향 분류층 반응기(Two Staged Drop Tube Furnace, Two Staged DTF)를 설계 및 제작하였다. 아역청탄(Tanito)의 단일 및 다단 연소 실험을 진행하여 UBC 및 NOx 배출 특성을 분석하였다. 그 결과, 단일 연소 조건에서 온도 및 공기비가 증가함에 따라서 UBC 함량이 감소했지만 NOx의 농도는 증가했다. 특히 과농 연료 연소 영역에서 NOx 저감 반응이 일어났으며, 이때 반응 온도가 증가할수록 NOx 저감 반응이 활성화 될 뿐아니라 UBC는 감소되었다. 공기 다단 연소 실험의 경우 석탄 입자의 UBC 증가량에 비해 높은 NOx 저감 효과를 얻을 수 있었다.

• Environmental Engineering Research
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• 제14권3호
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• pp.158-163
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• 2009

It is difficult for a burner to achieve an increase in combustibility and a reduction of NOx emission, simultaneously. The reason is because thermal NOx could be reduced at low temperature, while the combustibility should be decreased. To solve this problem, an externally oscillated staging burner was developed, and experiment was conducted according to effective parameters. The combustibility could be improved through the accelerated transfer of heat, mass and momentum obtained by external oscillation. Also, NO is reduced by the decrease of residence time of burning gas in the local highest-temperature spot, which is decreased by the external oscillation and fuel staging. Experiments on variables were conducted to determine the reference flame, and the flame generating the lowest NO concentration was selected. The conditions of reference flame were oscillation frequency 250 Hz, sound pressure 1 VPP, and air ratio 1.1, and NO and CO concentrations were 1ppm and 20 ppm, respectively.

• 한국연소학회:학술대회논문집
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• 한국연소학회 1999년도 제19회 KOSCO SYMPOSIUM 논문집
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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.

• 한국대기환경학회:학술대회논문집
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• 한국대기환경학회 1999년도 추계학술대회 논문집
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• pp.473-474
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• 1999

일반적으로 NOx배출은 연소과정에 의해 강력하게 지배되고 있으며, NOx 저감 기술은 1970년대 후반부터 많은 연구들이 수행되어, 그 이론들이 확립되고 있다. 석탄 연소시스템에서는 공기 다단(air staging, OFA), 연료다단(fuel staging, reburning) 및 배기가스 재순환(FGR) 등이 대표적인 NOx 저감 기술이며 [1∼4], 그 중 배기가스 재순환법은 저산소 배기가스를 연소용 공기에 재혼입시키므로써 NO의 생성속도를 저하시켜 NOx를 저감시키는 기법이다.(중략)