【作者】 杨建国；

【导师】 岑可法；

【作者基本信息】 浙江大学 ， 工程热物理， 2010， 博士

【摘要】 石油与煤炭均是人类宝贵的和有限的一次能源及资源,为了保证资源的可持续利用,电厂锅炉节油和提高燃料利用率已越来越被重视。电厂锅炉煤粉气流空气富氧直接点火技术即是应此而生的一项全新的无油点火技术。煤粉气流空气富氧直接点火的概念是常温的高氧浓度煤粉气流在常温环境下直接点火,并不需要外部热源而稳定着火燃烧。其基本原理是利用煤粉在高氧浓度下显著增加的燃烧放热速度和单位体积烟气焓来保证合适的火焰温度、回流热量和着火距离,促使火焰自稳定着火燃烧。针对煤粉气流空气富氧直接点火新概念和新技术,需要从基本燃烧理论到实际工程应用的全方位进行研究。因此本文从以下几个方面开展了研究：(1)利用热分析技术研究了煤粉在不同氧浓度条件下的燃烧特性,得出在高氧浓度下,煤粉的着火温度、着火热有所降低,但并不能克服煤种之间的差异,而呈倍数关系提高的燃烧速度、理论燃烧温度、烟气焓,为煤粉气流冷态条件下自稳燃提供了可行性。同时研究了煤焦的热分析燃烧特性,采用数学优化方法(差分进化算法DE)计算煤焦燃烧的动力学参数。并建立了DE分离法,对热分析TG曲线进行分离,研究了煤焦在高氧浓度下分段燃烧的动力学参数。(2)在大型卧式燃烧试验炉上进行了煤粉气流空气富氧直接点火的试验研究,分别试验了旋流燃烧器、直流燃烧器空气富氧直接点火的可行性,并进行了燃烧参数的测试。旋流燃烧器在一次风氧浓度为30.1%时,旋流二次风氧浓度在23.2%以上时,冷炉冷风煤粉气流可以直接用火把点燃,此时综合氧浓度为25.1%。直流燃烧器冷炉冷风成功直接点火的最低氧浓度为27.9%,最低煤粉浓度为0.32kgC/kgA.在富氧条件下,煤粉气流离开喷口即迅速着火,火焰炽亮,火焰发展也较为迅速。(3)从节约点火费用角度出发,提出了两种富氧方式：局部富氧与整体富氧。局部富氧是在燃烧器中心钝体边缘加入氧气,整体富氧是在一次风管道中加入氧气,局部富氧比整体富氧大幅度节省了氧气消耗量(1:3)。以125MW机组锅炉直流燃烧器为原型,设计了空气富氧直接点火直流燃烧器,对该燃烧器的燃烧特性进行了数值计算模拟。得出局部富氧点火的一次风速、煤粉浓度、氧气流速均存在最佳值。整体富氧随着氧浓度的提高显著提升煤粉气流的燃烧强度。(4)在电厂125MW机组中储式直流燃烧锅炉上进行了煤粉气流空气富氧直接点火技术的工程开发、应用与试验。煤粉气流空气富氧直接点火技术获得了成功。富氧燃烧器无论局部富氧或整体富氧均可以实现冷炉冷风直接点火,煤粉气流燃烧稳定,火炬明亮,燃烧无明显黑烟。试验表明,富氧点火的燃烧效率可达90%以上；采用富氧点火能满足锅炉升温升压的要求,锅炉升温升压过程中,富氧点火的煤粉燃烧效率达到87%(非精确采样),优于其它无油点火技术；富氧燃烧器能满足锅炉正常负荷运行要求,可作为主燃烧器安全使用；富氧燃烧器具有很好的低负荷适应能力,在发电功率25MW以上均能保持不投油、不投氧稳定燃烧；富氧燃烧器改造对一次风系统运行无明显影响。(5)与其它无油(微油)点火技术相比,采用富氧直接点火技术可以减少投资费用。由于提高了点火期间的煤粉燃尽率,而辅助燃料(氧气、油、电)费用相近,因而更加节约锅炉点火综合运行费用。(6)对空气富氧燃烧状态下的煤灰结渣特性进行了分析研究,结果表明富氧燃烧的煤灰灰熔点会有所提高,富氧点火燃烧对锅炉结渣无明显的不利影响。采用热分析方法研究了煤灰的熔融过程,结果表明不同气氛对煤灰中矿物质熔融特征温度影响不明显,主要影响了矿物质的熔融程度。并以热分析特征温度为依据,进一步研究了煤灰熔融过程中的矿物质演变机理。更多还原

【Abstract】 The primary energy resource of oil and coal are valuable and limited. For the sustainable utilization of the energy resource, saving oil and improving coal utilization efficiency have got more and more attention in power plant. Against the background, a novel technique of no-oil ignition——pulverized-coal direct ignition with oxygen-enriched air, was proposed and investigated in the paper.The concept of pulverized-coal direct ignition with oxygen-enriched air was described as: the oxygen-enriched pulverized-coal flow is ignited directly in cold conditions and able to combust stably without other heat source. And the basic principle is that the combustion heat release rate and the heat capacity of flue gas per unit volume, both of which are bound to increase greatly responsible for high concentration of oxygen in pulverized coal flow, preserve a proper level of flame temperatures, backflow heat and ignition distance, and thus provoke a steady combustion.Given that the brand new concept and technique of pulverized-coal direct ignition with oxygen-enriched air, the basic theories of combustion and practical application in engineering are studied thoroughly and in detail in the paper. The related work includes:(1) The combustion characteristics of the pulverized-coal with different oxygen concentrations are studied by thermal analysis technology. Conclusions can be drawn that, ignition temperature and ignition heat of pulverized coal are reduced at high oxygen concentrations. But it is limit between the differences of coal quality. The combustion rate, theoretical combustion temperature and heat capacity of flue gas which increasing more times enabled the spontaneous and stable combustion of pulverized coal in cold conditions. Meanwhile, the combustion characteristics of coal char are studied with thermal analysis. Combustion kinetic parameters of coal char are calculated by the mathematic optimization Algorithm (Differential Evolution, DE). The DE separation method was proposed and the kinetic parameters of the coal char combustion with multi-stage at high oxygen concentration were studied. (2) Experimental study was done in a large horizontal furnace, which was involved with testing the feasibility of pulverized-coal direct ignition with oxygen-enriched air by using swirl burner and straight burner, as well as tuning the combustion parameters. In the cold furnace, the cold pulverized-coal flow from the swirl burner could be ignited by a torch when the primary air oxygen concentration is above 30.1% and the secondary air oxygen concentration is above 23.2%. In this case, the mixed air oxygen concentration was 25.1%. Furthermore that from the straight burner was ignited directly, with the minimum oxygen concentration 27.9% and the minimum pulverized-coal concentration 0.32kgC/kgA. In the oxygen-enriched air condition, the pulverized-coal flow was ignited rapidly after leaving the nozzle. The flame was singular bright and completed more quickly.(3) For cutting down the consumption of oxygen, two oxygen enrichment modes were proposed:partial oxygen enrichment and overall oxygen enrichment. By adding oxygen into the center of the flow from the edge of the blunt body, partial oxygen enrichment consumed oxygen only one third of that of overall oxygen enrichment which adding oxygen into the primary air pip. Based on the straight burner of an 420t/h boiler, an oxygen-enriched straight burner was specially designed for direct ignition with oxygen-enriched air. The combustion characteristics of the new straight burner were simulated by means of numerical computation. The result shows that the primary air velocity, pulverized-coal concentration and the flow velocity of oxygen for the partial oxygen enrichment burner have their own optimum values, while for the overall oxygen enrichment burner, the combustion of the pulverized-coal flow is strengthened significantly with the increasing of oxygen concentration.(4) The technique of pulverized-coal direct ignition with oxygen-enriched air was studied on its project development, engineering application and experiments in a storage pulverized-coal boiler of 125MW unit with straight combustion burners. It deserved great success. Either partial oxygen enrichment or overall oxygen enrichment, the oxygen-enriched burner can both be ignited directly in cold conditions; the combustion of the pulverized-coal flow is steady with bright flame and absence of black smoke. Some meaningful results can be obtained from the experiments. The combustion efficiency of oxygen-enriched ignition exceeds 90%. The requirements of raising temperature and boosting pressure of the boiler could be completed with oxygen-enriched ignition burner, which has a higher combustion efficiency of 87% (non-exact sampling) than other no-oil ignition techniques. Oxygen-enriched burner was qualified as the main burner to bear the designed load of the boiler. What’s more, oxygen-enriched burner owns a good ability to adapt to the low loads to 25MW without additional oil or oxygen help. Finally, there was obscure influence on the primary air system operating.(5) Pulverized-coal direct ignition with oxygen-enriched air leads to fewer investment cost than other techniques of no-oil (or tiny-oil) ignition if it was used on more than one boiler in plant. Because of the higher coal combustion efficiency with the oxygen-enriched burner, there are also fewer operating costs, except the obscure difference of the auxiliary fuel (oxygen, oil, and electricity) costs.(6) The coal ash was produced under the condition of oxygen-enriched combustion and studied on the slag characteristics. The results show that the oxygen-enriched combustion increases somewhat the ash fusion point and that the oxygen-enriched ignition does not result in a significant deterioration of slag trends. The fusion procedure of the coal ash was investigated with the method of thermal analysis. The results indicated that the atmosphere mainly affects the fusion degree of the mineral matters rather than the characteristic temperature of mineral matters in coal ash. Further investigation on the evolution of mineral matters in the course of fusion was performed based on the characteristic temperatures of thermal analysis.更多还原