Combustion characteristics of anthracite in a vertical cyclone combustor

Isothermal, gas combustion and coal tests were undertaken in order to characterise a vertical cyclone combustor for burning anthracite. Inert particles (alumina cement) were used during the first two series of tests, in order to characterise chamber temperatures, material collection efficiencies and size distribution of particles. Mixture ratios from 0.4 up to 1.6 were tested in steps of 0.2. Under isothermal conditions, an optimum penetration length of vortex finder into the combustion chamber was found to be approximately 10% of the chamber length. The highest temperature can be obtained in the lower section of the combustion chamber both in gas and in coal combustion. The collection efficiency of the cyclone combustor in the various modes of operation was found to be excellent. For coal tests, mixed firing with coal and gas was adopted to sustain the flame in the combustor. The mixed fuels investigated here contain 60, 70 and 80% by mass of coal, and the 70% case was found favorable in the context of carbon burnout and collection efficiency.     

An experiment analysis of MILD combustion with liquid fuel spray in a combustion vessel

Mild combustion is characterized by its distinguished features, such as suppressed pollutant emission, homogeneous temperature distribution, reduced noise, and thermal stress. Recently, many studies have revealed the potential of MILD combustion in various power systems but most studies have been focused on gas phase fuel MILD combustion. Therefore, further study on MILD combustion using liquid fuel is needed for the application to a liquid-fueled gas turbine especially. In this work, we studied experimentally on the formation of liquid fuel MILD combustion under the condition of high dilution by burnt gas generated from a first premixed flame in two stages combustor which consists of the first premixed burner and secondary combustor. In particular, the effects of burnt gas velocity and oxygen level of burnt gas on the formation of liquid fuel MILD combustion were investigated. The results show that as the burnt gas velocity through the nozzle becomes higher, the color of flames was changed from yellow to pale blue and flames became very short. The OH radical measured by ICCD camera was uniformly distributed on the pale blue flame surface and its intensity was very low compared to conventional liquid diffusion flame. As burnt gas velocity is increased, local high-temperature region appeared to be diminished and the flame temperature became spatially uniform. And CO emission was sampled around 1 ppm and NOx emission was measured around 10 ppm under the overall equivalence ratio of 0.8 to 0.98 for 40 mm or less diameter of velocity control nozzle. This low NOx emission seems to be attributed to maintaining the average temperature in secondary combustor below the threshold temperature of thermal NOx formation. In view of the uniform temperature distribution, low OH radical intensity and low NOx emission data in the secondary combustor, formation of stable MILD combustion using kerosene liquid fuel could be verified at high burnt gas velocity.

     

Experimental investigations on combustion characteristics of a swirl-stabilized premixed burner

Experimental investigations have been conducted to understand the combustion characteristics of a swirl-stabilized double-cone pre-mixed burner used for industrial gas turbines for power generation. NOx and CO emissions, extinction limit, combustion noise, pressure loss, and wall temperature distributions were measured for various operating conditions. Results show that NOx emissions are decreased with increasing air/fuel ratio or decreasing air load unless the air load is too small. CO emissions are also decreased with increasing air/fuel ratio, leading to a positive correlation between NOx and CO emissions. Flame extinction limit is reduced with increasing air flow rate as the flow residence time is reduced. Combustion noise has its peak amplitude at the frequencies of 150 or 300 Hz, which are considered to be the resonance frequencies of the longitudinal mode of the combustor. The noise level at the peak frequency is maximized when the flame is considered to be located near the burner exit. Pressure loss is decreased with the A/F ratio as the flame moves downstream out of the burner.

     

四角切圆锅炉炉内煤粉燃烧过程数值模拟

利用计算流体动力学软件PHOENICS 3.5对一台200 MW四角切圆水平浓淡燃烧煤粉炉进行数值模拟研究,采用多流体两相流动模型及煤粉燃烧综合模型,计算得出在垂直方向不同二次风风量分布的工况下,炉内各截面处的烟气温度、燃料浓度、燃烧产物组分浓度以及炉内辐射热流的分布。结果表明,在燃烧器出口处出现了高煤粉浓度和烟气高温区,并出现气固两相分离的现象,使得煤粉着火及时,燃烧器区域维持较高温度,并防止水冷壁结渣,炉内温度、炉膛出口氧量和飞灰可燃物的计算结果和试验结果相比,吻合较好。二次风分级配风工况下,下部燃烧器区烟气温度升高,但氧气推迟混入,相应位置飞灰可燃物有所增加。计算模型能够合理地模拟水平浓淡煤粉气流在大型锅炉炉膛内的燃烧过程,适用于运行工况的优化和炉内污染物的控制。     

Measurements of Non-reacting and Reacting Flow Fields of a Liquid Swirl Flame Burner

The understanding of the liquid fuel spray and flow field characteristics inside a combustor is crucial for designing a fuel efficient and low emission device.Characterisation of the flow field of a model gas turbine liquid swirl burner is performed by using a2-D particle imaging velocimetry(PIV)system.The flow field pattern of an axial flow burner with a fixed swirl intensity is compared under confined and unconfined conditions,i.e.,with and without the combustor wall.The effect of temperature on the main swirling air flow is investigated under open and non-reacting conditions.The result shows that axial and radial velocities increase as a result of decreased flow density and increased flow volume.The flow field of the main swirling flow with liquid fuel spray injection is compared to non-spray swirling flow.Introduction of liquid fuel spray changes the swirl air flow field at the burner outlet,where the radial velocity components increase for both open and confined environment.Under reacting condition,the enclosure generates a corner recirculation zone that intensifies the strength of radial velocity.The reverse flow and corner recirculation zone assists in stabilizing the flame by preheating the reactants.The flow field data can be used as validation target for swirl combustion modelling.     

Ignition and combustion characteristics of the gas turbine slinger combustor

This paper describes the ignition and combustion characteristics of a gas turbine slinger combustor with rotating fuel injection system. An ignition test was performed under various airflow, temperature and pressure conditions with fuel nozzle rotational speed. From the test, there are two major factors influencing the ignition limits: the rotational speed of the fuel nozzle, and the mass flow parameter. Better ignition capability could be attained through increasing the rotational speed and air mass flow. From the spray visualization and drop size measurement, it was verified that there is a strong correlation between ignition performance and drop size distribution. Also, we performed a combustion test to determine the effects of rotational speed by measuring gas temperature and emission. The combustion efficiency was smoothly enhanced from 99% to 99.6% with increasing rotational speed. The measured pattern factor was 15% and profile factor was 3%.     

An experimental study on combustion efficiency of low grade anthracite in AFBC

This is the basic study to develop a fluidized bed combustion boiler which can use low grade anthracite. In this study, the anthracite of about 3400 kcal/kg was burned in the bench scale non-recycling atmospheric fluidized bed combustor of 200mm diameter and 2215mm height with the static bed height of 250mm and the combustion temperature range of 800–950°C. During the combustion, the effect of factors such as the superficial gas velocity in bed, the air ratio, the coal supply location and the coal particle size on the combustion efficiency, the elutriation ratio and the unburned carbon content both in elutriated ash and in drained ash was thoroughly analyzed. When the superficial gas velocity in bed is 0.7～2.2m/s, the air ratio is 1.0～1.6 and coal supply locations are 300,500 and 700mm above the air distributor, the combustion efficiencies range from 66% to 83.5% for the mean coal particle size of 0.209mm, and from 71% to 88% for the case of 0.265mm. The combustion efficiency decreases as the superficial gas velocity in bed and the air ratio increase. The lower the coal supply location is, the better the combustion efficiency becomes in general.     

适用于燃用贫煤1 025 t/h锅炉的中心给粉旋流燃烧器

提出了中心给粉旋流煤粉燃烧器,并针对某厂采用EI-DRB型燃烧器设计燃用贫煤的1 025 t/h锅炉稳燃能力差,不能燃用设计煤质的问题,进行了实验室冷态试验及锅炉冷、热态试验,得出了新型的燃烧器结构,并将下层8只燃烧器改造为新型燃烧器.试验表明,中心给粉燃烧器的回流区最大直径、长度与燃烧器最外层直径之比分别为1.40和1.89,可卷吸足够的高温烟气及时点燃煤粉,得出了外二次风叶片角度、一次风量、二次风量及三次风对燃烧器出口射流的影响规律;在实际运行参数下,EI-DRB型燃烧器没有回流区,不利于稳定燃烧.得出了二次风挡板开度和给粉机转数对燃烧器出口处温度场的影响规律.采用新型燃烧器后,锅炉效率提高,当电负荷降至140 MW时,锅炉可以不投油稳定运行,在燃用贫煤、无烟煤和贫煤的混煤时(混合比为11),锅炉在高负荷和低负荷下均可稳定运行.锅炉NOx排放下降.     

一种船用液体燃料蜗壳旋流器的数值研究与性能验证

为实现船用液体燃料蜗壳旋流器的可靠性点火,提高其燃烧的稳定性和燃烧效率,采用RNG k-ε双方程湍流模型,设计出一种满足船用特殊需要的蜗壳旋流器,列举了7组不同戊烷和空气进口流量,对该具体尺寸的蜗壳旋流器的液雾燃烧过程进行了数值模拟和试验验证,得到了蜗壳旋流器内部流场以及出口处的烟气温度场和燃烧产物的组分浓度分布。分析对比这7组进口流量对该蜗壳旋流器的出口温度和出口气体组分的影响,找到了满足船用需要的该具体尺寸蜗壳旋流器对应的最佳燃料进口流量。该模拟和试验结果为蜗壳旋流器的结构设计提供了理论依据。     

空气分级炉膛煤粉燃烬模型及实炉试验对比

传统的炉膛分区段传热设计模型忽略了煤粉燃烬计算，适用于非空气分级燃烧。随着空气分级低NOx燃烧技术的普遍应用，在炉膛分区段传热计算中引入煤粉燃烧模型以确定沿炉膛高度燃烬分布，对于提高炉膛上部屏式或辐射受热面蒸汽温度设计准确性有较为重要的意义。建立了改进型分区段传热计算和煤粉燃烧相耦合的空气分级炉膛燃烬和传热模型，对一台空气分级低NOx燃烧锅炉进行了全负荷工况试验，采用该模型对试验工况进行燃烬和传热模拟，得到空气分级锅炉炉膛煤粉燃烧过程的物理图景以及煤粉沿炉膛高度燃尽分布，并研究了燃烧模式和表面反应动力学参数等对燃烬度分布的影响。结果表明，炉膛出口煤粉颗粒燃烬度数值解与大部分测试数据吻合较好，煤粉颗粒燃烧后期灰分引起热退火抑制效应以及炉内局部烟气含氧量分布不均匀是引起模型误差的主要因素，所建立的燃烧和传热耦合模型与传统的炉膛分区段传热模型计算量相当，适合工程应用。     

Conjugated heat transfer and temperature distributions in a gas turbine combustion liner under base-load operation

Prediction of temperature distributions on hot components is important in development of a gas turbine combustion liner. The present study investigated conjugated heat transfer to obtain temperature distributions in a combustion liner with six combustion nozzles. 3D-numerical simulations using FVM commercial codes, Fluent and CFX were performed to calculate combustion and heat transfer distributions. The temperature distributions in the combustor liner were calculated by conjugation of conduction and convection (heat transfer coefficients) obtained by combustion and cooling flow analysis. The wall temperature was the highest on the attachment points of the combustion gas from combustion nozzles, but the temperature gradient was high at the after shell section with low wall temperature.     

A study on combustion characteristics of superadiabatic combustor in porous media

Because of the energy resource exhaustion, the aggravating environmental air pollution, the smoke phenomena and so on, the recent trends and targets in designing combustor are reduction of pollutant emissions and improvement of combustor efficiency. Therefore many combustion methods and emission control technologies have been proposed by many researchers through numerical and experimental analyses, One of the most available and effective combustion methods is the excess enthalpy combustion, so called, the superadiabatic combustion. In this study, the superadiabatic combustion with the reciprocating flow in a porous media has been investigated with the variation of equivalence ratio, flow velocity and reciprocating cycle time. In this system, the flow direction is reversed regularly by the solenoid valves. The results of this study show that the maximum gas temperature is remarkably higher than the theoretical adiabatic flame temperature and the emission characteristic is very excellent. The analyses reveal several attractive characteristics of the flame and the proposed idea is promising to burn mixtures of low heat content in a reciprocating type combustor. This combustor can be applied to the elimination of unburned compound, with more intensive and continuous study.     

An overview of liquid spray modeling formed by high-shear nozzle/swirler assembly

A multi-dimensioanl model is being increasingly used to predict the thermo-flow field in the gas turbine combustor. This article addresses an integrated survey of modeling of the liquid spray formation and fuel distribution in gas turbine with high-shear nozzle/swirler assembly. The processes of concern include breakup of a liquid jet injected through a hole type orifice into air stream, spray-wall interaction and spray-film interaction, breakup of liquid sheet into ligaments and droplets, and secondary droplet breakup. Atomization of liquid through hole nozzle is described using a liquid blobs model and hybrid model of Kelvin-Helmholtz wave and Rayleigh-Taylor wave. The high-speed viscous liquid sheet atomization on the pre-filmer is modeled by a linear stability analysis. Spray-wall interaction model and liquid film model over the wall surface are also considered.     

An experimental study on the combustion characteristics of a low nox burner using reburning technology

The combustion characteristics of a low NO_x burner using reburning technology have been experimentally studied. The reburn burner usually has three distinct reaction zones which include the primary combustion zone, the reburn zone and the burnout zone by provided secondary air. NO_x is mainly produced in a primary combustion zone and a certain portion of NO_x can be converted to nitrogen in the reburn zone. In the burnout zone, the unburned mixtures are completely oxidated by supplying secondary air. Liquefied Petroleum Gas (LPG) was used as main and reburn fuels. The experimental parameters investigated involve the main/ reburn fuel ratio, the primary/secondary air ratio, and the injection location of reburn fuel and secondary air. When the amount of reburn fuel reaches to the 20-30% of the total fuel used, the overall NO reduction of 50% is achieved. The secondary air is injected by two different ways including vertical and parallel injection. The injector of secondary air is located at the downstream region of furnace for a vertical-injection mode, which is also placed at the inlet primary-air injection region for a parallel-injection mode. In case of the vertical injection of the secondary air flow, the NO_x formation of stoichiometric condition at a primary combustion zone is nearly independent of the reburn conditions (locations, fuel/air ratios) while the NO_x emission of the fuel-lean condition is considerably influenced by the reburn conditions. In case of the parallel injection of the secondary air, the NO_x emission is sensitive to the air ratio rather than the fuel ratio and the reburning process often coupled with the multiple air-staging and fuel-staging combustion processes.     

微型发动机燃烧室的模拟研究

简要介绍了微型发动机的研究意义和应用前景。采用模拟软件对微型发动机燃烧室中的燃烧现象进行了模拟,并对影响燃烧的主要因素进行了分析,为微型燃烧室的设计提供了依据。     

涡轮喷气发动机燃烧室中的传热过程及气膜冷却效应的实验研究

本文叙述与讨论了涡轮喷气发动机火焰筒在单管燃烧室试验器上壁温测量的试验结果。其主要内容包括：（1）试验装置及测量方法的叙述（2）燃烧室气流进口参数（总压,总温及流量）及余气系数对火焰筒壁温沿轴向分布的影响（3）有气膜冷却的火焰筒和无气膜冷却的火焰筒在相同工作状态下壁温分布的比较。报告还推荐了一种火焰筒传热过程及气膜冷却壁温计算方法,对火焰筒壁温进行了计算,并与实验结果作了比较,提出了编者的看法。     

Spray and combustion characteristics of a dump-type ramjet combustor

Spray and combustion characteristics of a dump-type ram-combustor equipped with a V-gutter flame holder were experimentally investigated. Spray penetrations with a change in airstream velocity, air stream temperature, and dynamic pressure ratio were measured to clarify the spray characteristics of a liquid jet injected into the subsonic vitiated airstream, which maintains a highly uniform velocity and temperature. An empirical equation was modified from Inamura’s equation to compensate for experimental conditions. In the case of insufficient penetration, the flame in the ram-combustor was unstable, and vice versus in the case of sufficient penetration. When the flame holder was not equipped, the temperature at the center of the ram-combustor had a tendency to decrease due to the low penetration and insufficient mixing. Therefore, the temperature distribution was slanted to the low wall of the ramcombustor. These trends gradually disappeared as the length of the combustor became longer and the flame holder was equipped. Combustion efficiency increased when the length of the combustor was long and the flame holder was equipped. Especially, the effect of the flame holder was more dominant than that of the combustor length in light of combustion efficiency.     

Analysis of the combustion oscillation in a silo-type gas turbine combustor and its suppression

The characteristics of combustion oscillation of a silo-type 79.5 MW gas turbine combustor in commercial operation and its suppression have been investigated. The oscillation of the lean premixed gas turbine combustor resulting from the combustion instability occurred at near full load operation. An FFT analysis of the combustion dynamics showed that the dominant frequency of the oscillation would be that of the 1st longitudinal acoustic resonance mode of the combustor. To suppress the combustion oscillation, a passive control technique for reducing the combustion instability was employed; that is, the fuel to the combustor was redistributed by adjusting the operational schedule of one of six fuel control valves, which would lead the increase of the local operational equivalence ratio near the central recirculation zone of the combustor. By doing so, the oscillation was successfully reduced to the permissible level while the amount of NO_x emission met proper regulatory level set by the local government.     

A numerical study on the flow characteristics in the mixing region of the catalytic combustor

Catalytic combustion is usually accomplished by a chemical reaction at the catalyst surface. Therefore, it is important that the fuel and air stream be well mixed and supplied uniformly. In this study, a perforated plate is used to enhance the mixing and flow uniformity for stable catalytic combustion. Also, a numerical simulation is performed to investigate the variation of flow characteristics according to various parameters. The results show that the uniformity of mixing and flow can be effectively improved for most of the cases by using a well-designed perforated plate.     

Effect of swirling flow by normal injection of secondary air on the gas residence time and mixing characteristics in a lab-scale cold model combustor

The present study investigates gas residence time and mixing characteristics for various swirl numbers generated by injection of secondary air into a lab-scale cylindrical combustor. Fine dust particles and butane gas were injected into the test chamber to study the gas residence time and mixing characteristics, respectively. The mixing characteristics were evaluated by standard deviation value of trace gas concentration at different measurement points. The measurement points were located 25 mm above the secondary air injection position. The trace gas concentration was detected by a gas analyzer. The gas residence time was estimated by measuring the temporal pressure difference across a filter media where the particles were captured. The swirl number of 20 for secondary air injection angle of 5° gave the best condition: long gas residence time and good mixing performance. Numerical calculations were also carried out to study the physical meanings of the experimental results, which showed good agreement with numerical results.