InfluenceofCoal-feedRatesonBituminousCoalIgnitioninAFull-scaleTiny-oilIgnitionBu.doc

本科毕业论文外文文献及译文文献、资料题目：Influence of Coal-feed Rates on Bituminous Coal Ignition in A Full-scaleTiny-oil Ignition Burner文献、资料来源：期 刊文献、资料发表（出版）日期：2009.8.5院 （部）： 热能工程学院专 业： 热能与动力工程外文文献Influence of Coal-feed Rates on Bituminous Coal Ignition in A Full-scale Tiny-oil Ignition BurnerA B S T RACTA tiny-oil ignition burner has been proposed to reduce oil consumption during the firing-up process and partial-load operations. To investigate the influence of different feed rates on bituminous coal ignition in the tiny-oil ignition burner, full-scale reacting-flow experiments were performed on an experimental setup.The ignition burner was identical to that normally used in an 800-MWe utility boiler. Gas temperature distributions in the burner were obtained at coal-feed rates of 2, 3, 4, and 5 tonnes/h. Char burnout and release of C and H were observed at the exit of the burner nozzle. Gas compositions such as O2 and CO were measured in the center of the burner. A change in resistance was obtained within the burner. A saving of 90% over previous oil consumption was gained in the firing-up process by using the new oil-gun technology.Key words: Tiny-oil ignition burner ；Coal-burning utility boiler；Coal-feed rates1. IntroductionTo fire-up a boiler, oil is primarily used to pre-heat the combustion chamber of a furnace bringing it to its operating temperature.Generally, oil is delivered under high pressure by an oil-gun with a delivery capacity of about 1 tonne/h. Therefore, in the initial firingup process of a bituminous coal-fired 300 MWe utility boiler, about 100 tonnes of fuel oil would be consumed. Concerns over increasing economic costs in pulverized coal-fired power stations arising from oil consumed in the firing-up process and partial-load operations has spurred interest in developing oil-free and tiny-oil ignition burners. Various investigators have reported studies of oil-free ignition burners. Masaya et al. studied the stabilization of pulverized coal combustion using a plasma-assisted burner, while Kanilo et al. investigated the ignition and combustion of pulverized coal using a microwave-assisted burner. In China, Zhang et al. described their application of plasma ignition technology in bituminous coal-fired boilers. However, for such burners, two main problems arise: difficulties in extending the capacity of the burner and the frequent maintenance required during operation. Li et al. investigated induction-heating ignition of a pulverized coal stream. Induction-heating can supply a reliable convenient source of energy to ignite the pulverized coal stream, but this technology has not been previously reported to have been used in any utility boiler.An alternative tiny-oil ignition burner has been developed and tiny-oil ignition, centrally fuel-rich burners proposed (see Fig. 1). The burner features two oil-guns arranged in the central pipe and the firing-up process is summarized as follows. Atomized oil from one oil-gun, called the main oil-gun, ignites and burns in an adiabatic chamber. Subsequently, an oil flame ignites the atomized oil from the other oil-gun, called the auxiliary oil-gun. Cone separators are installed in the primary aircoal mixture duct to concentrate the pulverized coal into the central zone of the burner. The fuel-rich primary aircoal mixture passes into the first combustion chamber whereby the fuel-rich primary aircoal mixture is ignited by a high-temperature oil flame formed by both main and auxiliary oil-guns. Next, the burning pulverized coal and oil flame from the first combustion chamber is directed into the second combustion chamber where the coal is ignited. After the boiler has been fired-up, both main and auxiliary oil-guns are then shut down and the burner switches operations to becoming a centrally fuelrich burner . Characterized by high combustion efficiency and low NOx emission. The influence of coal-feed rates on the bituminous coal ignition in the full-scale tiny-oil ignition burner was investigated.2. Experimental set-upFig. 1 shows the tiny-oil ignition apparatus. The ignition burner was identical to the burner that had been used in an 800-MWe utility boiler and its operation is briefly described as follows. The feeder supplies pulverized coal by primary air from the blower. The pulverized coal is then carried to the tiny-oil ignition burner by primary air. Oil is drawn from the oil tank and sent to the main and auxiliary oil-guns atomizing the oil mechanically and by air. Although compressed air enters the oil-guns, a small fraction is also consumed in oil combustion, the main body of which is supplied by another blower. The pulverized coal is ignited in the primary air duct. In the experimental set-up there was no separation into inner and outer secondary air.All gas temperatures were measured at the center of the burner as well as the exits of the first and the second combustion chambers. Ash samples were sampled at the exit of the tiny-oil ignition burner. Gases were sampled using a water-cooled stainless steel probe and analyzed online on a Testo 350M instrument 5. The probe, consisting primarily of a water-inlet pipe, water-outlet pipe, sampling tube, outer pipe and supporting components, was bracket-mountedat the exit of the burner. A sample of the high-temperature gas is collected in the sampling tube and cooled by high pressure cool water delivered through the water-inlet pipe cooling the sampling tube and after heat change flows out via the water-outlet pipe. A water pump provided continuous water circulation. When gas enters the sampling tube, temperatures decease rapidly and the pulverized coal stops burning. Samples are drawn up by a pump through filtrating devices into a Testo 350M gas analyzer for subsequent analysis. The accuracy of the analyzer for each species measurement is 1% for O2 and 5% for CO. Each sensor was calibrated before measurement. COmax is 10,000 ppm in this experiment.The difference in pressure before and after ignition is called the burner resistance. A static pressure method was used to measure ignition resistance at the position of the straight section (See Fig. 1). One end of the u-tube differential manometer was connected with a static pressure hole, and the other end was open to atmospheric conditions.Table 1 lists equipment used along with their technical characteristics. Table 2 lists operating parameters. Table 3 lists the final analysis and other characteristics of 0 # light diesel oil used inthe experiments. Table 4 records the characteristics of the bituminous pulverized coal used in the experiments. The methods used to measure calorific value, proximate analysis and ultimate analysis were in accordance with 213-2003, 212-2001 and 476-2001 of the Chinese standards code, respectively. The pulverized coal fineness was R90 = 9.2%, i.e. 90.8% of all particles pass through a 90 lm aperture sieve.3. Result and discussion3.1. The gas temperature distributionFig. 2 depicts gas temperature profiles measured along the burner center line; here x is the measured distance from the central pipe exit (See Fig. 1). Using the two oil-guns in the absence of coal during firing-up, gas temperatures decreased from 1044 _C to 856 _C with increasing distance. Most of the oil from both main and auxiliary oil-guns burnt out in the central pipe. High-temperature gas was then formed. As the gas flowed toward the burner nozzle, cold air diffuses into it resulting in a gradual decrease in gas temperatures. Using the two oil-guns in the presence of coal during firing-up, the high-temperature oil flame ignited the pulverized coal releasing heat as it continuously burned. As a consequence, gas temperatures increased along the direction of the primary air flow, i.e. along the burner center line.Fig. 3 shows the gas temperature profile measured at the exits of the first and second combustion chambers, at a radius of r1 and r2, respectively, from the center line of the burner (See Fig. 1). During firing-up with the two oil-guns operating in theabsence and then later in the presence of coal, gas temperatures were observed to be largest along the center line. As the radius increased, gas temperatures decreased gradually. Wall temperatures of the first and the second combustion chambers were less than 116 _C and 127 _C, respectively. At low temperatures, the burner wall was safe.During firing-up with the two oil-guns operating in the absence of coal, gas temperature distributions were similar at the exits of the first and the second combustion chamber. The oil-flow rate of auxiliary and main oil-guns was 65 and 35 kg/h, respectively (See Table 2). The oil-flow rate of auxiliary oil-gun was higher than that main oil-gun. The released heat on the side of the auxiliary oilgun (r1 0 and r2 0 and r2 0). Hence gas temperatures on the side of the auxiliary oil-gun were higher than those on the side of themain oil-gun. For example, at the first combustion chamber exit, gas te eratures at r1 = _57 and _114 mm, where the auxiliary oil-gun was mounted, were 1005 _C and 767 _C, respectively, and at r1 = 57 and 114 mm, where the main oil-gun was mounted, were 601 _C and 203 _C, respectively. Gas temperatures at the second combustion chamber exit are lower than those at the first combustion chamber exit. Most of the oil of the main and auxiliary oilgunsburned out in the central pipe. As the gas flowed from the first combustion chamber to the second, it mixed with cold air, thus gradually decreasing gas temperatures.During firing-up with the two oil-guns in the presence of coal, the pulverized coal burned adequately releasing heat in the process. Gas temperatures at the second combustion chamber exitwere higher than those at the first combustion chamber exit. By increasing coal-feed rates, more heat was absorbed by the pulverized coal thereby decreasing its temperature. At the same time,much more coal ignited; the released heat of combustion thereby increased and in the process the temperature of the pulverized coal would then increase. When coal-feed rates increased from 2 to4 tonnes/h, the released heat of combustion is more than the absorbed heat. Thus at equivalent measuring points at the exits of the first and second combustion chambers and on the burner center line (see Fig. 2) gas temperatures gradually increased. When the coal-feed rate was increased to 5 tonnes/h, the released heat from coal combustion was less than the absorbed heat. Thus gas temperatures at equivalent points decreased. However, pulverized coal can be successfully ignited. Oil from the main oil-gun was ignited by a high-energy igniter and burnt in an adiabatic chamber. Subsequently, the oil flame formed by the main oil-gun ignited the atomized oil from the auxiliary oil-gun. Afterward, the igniter was closed, and the oil flamewas maintained by the two oil-guns and burned steadily. During firing-up using the two oil-guns in the presence of coal, instantaneous ignition was achieved by the oil flame and a steady burn of the pulverized coal developed. The flame formed by the two oil-guns and pulverized coal was bright and steady during the whole process. Fig. 4 shows photos of the oil and coal flame.3.2. Char burnout and release rate of C and H at the exit of the burnerFig. 5 shows the char burnout and release rate of C and H at the exit of the tiny-oil ignition burner. Char burnout was calculated using=1-（wk/wx）/(1-wk)where w is the coal burnout factor, wk is the ash weight fraction in the input coal, and wx is the ash weight fraction in the char sample.is the percentage release of components (C and H), which wascalculated by=1-(wix/wik)(wk/wx)where wix is the weight percentage of the species of interest in the char sample and wik is the weight percentage of the species of interest in the input coal 6.The distributions of char burnout and release rates of C and H were similar at the different coal-feed rates. The char burnout and the release rates of C and H were largest along the burner center; as the radius increased, they decreased with the increase of coal-feed rates. At the center of the burner (r2 = 0), char burnout and release rates of C and H decreased from 83%, 81%, 95% to 75%, 72%, 87% as coal-feed rates increased from 2 to 5 tonnes/h.3.3. Gas compositions and the burner resistanceTable 5 lists gas compositions at the center of the burner exit as well as the burner resistance. For coal-feed rates of 2, 3, 4, 5 tonnes/ h, O2 concentrations were in the range 0.010.04% and CO concentrations were more than 10,000 ppm. The O2 concentration at the center point of the burner exit was almost exhausted. When the primary air temperature and velocity were 15 _C and 23 m/s, respectively, with oil-flow rate at 100 kg/h, the burner resistance while the two oil-guns were in operation increased 190 Pa in the absence of coal and in the presence of coal were 500, 600, 600, 550 Pa for coal feeding rates of 2, 3, 4, 5 tonnes/h, respectively.3.4. Consumed oilUsing the tiny-oil ignition burner, total oil-flow rate decreased from 1000 to 100 kg/h, thus saving 90% of the oil usually consumed in the firing-up process.4. Conclusion(1) When the primary temperature and velocity air were 15 _C and 23 m/s, respectively, ignition was successful with an oil-flow rate of 100 kg/h and the bituminous coal-feed rate was increased from 2 to 5 tonnes/h. Wall temperatures of the first and the second combustion chambers were less than 116 _C and 127 _C, respectively. At the low temperature, the burner wall was safe. O2 concentrations at the exit of the burner were 0.010.04%. During firing-up, the burner resistance increased to 190 Pa with coal absent and to 500600 Pa with coal present. A saving of 90% of the oil normally consumed in the firing-up process represents a significant economic benefit.(2) Temperatures along the center line of the burner gradually increased along the direction of the primary air flow in the presence of coal. As coal-feed rates increased from 2 to 4 tonnes/h, gas temperatures at equivalent points at the exits of the first and second combustion chambers and on the center line increased gradually. A further increase of the coal-feed rate to 5 tonnes/h decreased temperatures at these points.(3) Distributions of char burnout and release rates of C and H were similar for different coal-feed rates; as the radius increased, they decreased with the increase of coal-feed rates. Finally, increasing coal-feed rates decreased char burnout and release rates of C and H at equivalent points at the exits. Acknowledgements This work was supported by the Hi-Tech Research and Development Program of China(Contract No.2007AA05Z301), Post-doctoral Foundation of Heilongjiang Province (LRB07-216), Heilongjiang Province via 2005 Key Projects (Contract No. GC05A314), and the Hi-Tech Research and Development Program of China (863 program) (Contract No.2006AA05Z321).References1 Masaya S, Kaoru M, Koichi T, Oleg PS, Masao S, Masakazu N. Stabilization of pulverized coal combustion by plasma assit. Thin Solid Films 2002;407:18691.2 Kanilo PM, Kazanesev VI, Rasyuk NI, Schunemann K, Vavriv DM. Microwave plasma combustion of coal. Fuel 2003;82:18793.3 Zhang XY, Luo ZB, Zhang SK, Zou GW, Jiang BH. Application testing and study of plasma combustion technology in coal fired boilers with double inlet and outlet tube mill and whirl burner. China Power 2003;36:259 in Chinese.4 Li WJ, Cen KF, Zheng CG, Zhou JH, Cao XY. Induction-heating of pulverized coal stream. Fuel 2004;83:21037.5 Li ZQ, Jing JP, Chen ZC, Ren F, Xu B, Wei HD, et al. Combustion characteristics and NOx emissions of two kinds of swirl burners in a 300-MWe wall-fired pulverized-coal utility boiler. Combust Sci Technol 2008;180(7):137094.6 Costa M, Silva P, Azevedo JLT. Measurements of gas species, temperature, and char burnout in a low-NOx pulverized-coal-fired utility boiler. Combust Sci Technol 2003;175:27189.中文译文：在全面微油点火燃烧器中给煤率对烟煤燃烧的影响摘要：微油点火燃烧器在冷炉启动和低负荷稳燃中减少油耗的方法已经被建议。为了研究不同给煤率对微油燃烧器点燃烟煤的影响，在设计的实验台上对燃烧器全面流场进行了实验研究。点火燃烧器同样的被广泛应用于800WMe的电站锅炉。分别得到了在给煤速率为2t/h、3t/h、4t/h、5t/h时燃烧器内的温度分布。焦炭燃烧和挥发分的析出能在燃烧器喷嘴出口被观测到。对燃烧器中心的气体成份像O2、CO2进行了测量，获得了燃烧器内的阻力变化情况。通过使用新型的油枪技术，使得在点火过程中相对原来的油耗量可以减少百分之九十。关键词：微油点火燃烧器、燃煤电站锅炉、给煤率1简介点燃锅炉时，油主要被用来预热燃烧室的内壁，以使之达到其相应的运行温度。通常来说，油通过输送容量为1吨/小时的油枪在高压下被释放出来。因此，在最初的点火过程中，300MWe的燃煤锅炉大约有100吨的燃料油将会被消耗掉。在燃煤电厂中，锅炉冷炉启动和低负荷稳燃中的石油消耗使得经济成本增加，这就增加了我们在开发无油和微油点火燃烧器方面的兴趣。Masaya以及许多科研人员已经研究并报道了有关无油点火燃烧器的不同成果。【1】研究煤粉通过使用活性组分燃烧器的稳定燃烧情况【2】使用微波煤粉锅炉来研究煤粉的点火和燃烧【3】描述在煤粉燃烧锅炉中关于等离子点火技术的应用。然而，对于这些燃烧器，存在着在扩大燃烧器容积和运行期间需要经常维修这两个主要的问题【4】研究感应加热点燃煤粉流。感应加热可以提供可靠的、方便的能源去点燃煤粉流，但是这种技术先前还没有报道过被应用于任何的电站锅炉中。另一种微油点火燃烧器已经被开发并用来点火，并计划应用于中心燃料丰富的燃烧器内（见图1）。燃烧器在中央导管处安置的两条油枪的作用很大。点火过程依下列各项被总结出来：雾化的油从一个油枪中喷出，这个油枪叫做主油枪。在绝热室内进行点火和燃烧。随后，燃油被点燃。从另一个油枪中喷出雾化的石油，这根油枪叫做辅助油枪。锥形燃烧器安装在输送空气和煤的主管道中，以用来聚集煤粉使之进入燃烧器的中心区域。燃料丰富的一次风煤混合物进入第一燃烧室，据此，富燃料一次风煤混合物被来自主油枪和辅助油枪的高温火焰所点燃。然后，来自第一燃烧室的燃烧着的煤粉和石油火焰直接进入第二燃烧室，在这里煤被点燃。在锅炉被点燃后，主油枪和辅助油枪关闭。与此同时，燃烧器调整开关，成为一个富燃料中心燃烧器。【5】燃烧效率高和低氮氧化物排放的特点在全面微油点火燃烧器中给煤率对烟煤燃烧的影响已经被研究。图1 实验装置2实验装置图1表示微油点火装置，点火燃烧器同样的已经被应用于800MWe的电站锅炉的中。同时，它的操作被简述如下：给煤机通过送风机提供的一次风补给煤粉，与此同时，煤粉被一次风携带到微油点火燃烧器内。油从油箱内被带出到主油枪和辅助油枪，在这里通过空气机械雾化。压缩空气虽然进入油枪，但一小部分的油在燃烧中还是被消耗掉。主体则通过另一台送风机提供。煤粉在一次风管道中被点燃，实验装置中没有分离进入内部和外部的二次风。所有气体温度都在燃烧器的中心以及第一燃烧室和第二燃烧室的出口被测量出。灰样品在微油量点火燃烧器的出口被提取。气体通过使用水冷不锈钢探针在Testo350M仪器上在线分析，抽取样品探针，主要包括一个进水管、出水管、收集管、外管以及支持组件，在燃烧器的出口展开。被抽取的高温气体被收集到收集管内，并被高压冷却水冷却。