【作者】 谭力；

【导师】 吕清刚； 李诗媛；

【作者基本信息】 中国科学院研究生院（工程热物理研究所） ， 热能工程， 2014， 博士

【摘要】 燃煤生成的C02对环境的危害已经引起了世界各国的关注。富氧燃烧技术有利于捕集、储存和利用燃煤生成的CO2,被认为是短期内减缓C02排放较为可行的技术,而且能用于现有燃烧设备的改造。循环流化床富氧燃烧技术将循环流化床洁净燃烧技术和富氧燃烧技术有机结合,但其研究起步较晚,还有许多问题需要解决。在当前研究中氧气浓度较低的背景下,本论文在热重-质谱联用仪、鼓泡流化床和循环流化床三个试验平台上开展系统的试验研究,探索了高氧气浓度下循环流化床富氧燃烧技术的可行性,分析了燃烧温度、燃烧气氛、氧气浓度和操作参数等因素对煤的燃烧特性、气体污染物生成特性和传热特性的影响。在热重分析仪和5kW鼓泡流化床富氧燃烧试验系统上,分别进行了02/N2和02/C02气氛下的富氧燃烧试验,研究了朔州烟煤的燃烧特性。研究发现,提高氧气浓度和燃烧温度能明显改善煤的燃烧特性；与02/N2气氛相比,02/C02气氛对煤的燃烧特性略有改善。在鼓泡流化床和热重-质谱联用仪上,同时研究了朔州烟煤富氧燃烧的污染物生成特性。TG-MS试验结果表明,与02/N2气氛相比,02/C02气氛降低了S02、NO、NO2、NH3和HCN等的排放浓度。随着氧气浓度的增大,所有气体的析出时间明显变短,析出峰强度变大。NO呈现双峰析出,N02呈现单峰析出,而S02则由双峰析出向单峰析出转变。鼓泡流化床试验结果表明,氧气浓度增大,NO和N20的排放浓度均降低：温度升高,NO的排放浓度先降低后升高,N2O的排放浓度降低。02/C02气氛抑制了部分S02的生成,钙基脱硫剂对S02的脱除作用明显。添加钙基脱硫剂后,在两种气氛下N20的排放浓度均有降低,NO的排放浓度在02/C02气氛下基本不变,在02/N2气氛下则有较大幅度升高。在0.15MWth循环流化床富氧燃烧试验系统上,进行了高氧气浓度下的循环流化床富氧燃烧试验,研究了炉膛的传热特性。研究表明,0.15MWth循环流化床富氧燃烧试验系统的炉膛总传热系数约为27W/(m2.K),流化速度、一次风率和燃烧气氛对试验系统的炉膛总传热系数几乎没有影响,高氧气浓度下循环流化床富氧燃烧的传热特性与常规循环流化床燃烧的差异很小。在改造后的0.1MWth循环流化床富氧燃烧试验系统上,进行了高氧气浓度下的循环流化床O2/CO2燃烧试验,研究了燃烧温度、整体氧气浓度、过量氧气系数、二次风比例和一次风氧气浓度等因素对煤的燃烧特性和污染物排放特性的影响。研究结果表明,提高燃烧温度和整体氧气浓度,有利于改善煤在循环流化床内的燃烧,CO、SO2与N2O的排放浓度降低,但NO的排放浓度略有升高。过量氧气系数对循环流化床02/CO2燃烧作用明显,过量氧气系数增大,CO的排放浓度显著降低,而NO和N20的排放浓度逐渐升高,SO2的排放浓度略有降低。增大二次风比例可以改善煤的燃烧特性,同时SO2的排放浓度增高。提高一次风氧气浓度降低了SO2的排放浓度,而CO和N20的排放浓度先增大后降低,NO排放浓度先降低后增大,但在一次风氧气浓度超过45%以后,N2O和NO的排放浓度变化很小。在高氧气浓度循环流化床富氧燃烧中,分级燃烧仍然是一个有效控制气体污染物排放的技术。对0.1MWth循环流化床富氧燃烧试验系统进行了改造,添加了烟气再循环系统,探索了高氧气浓度下循环流化床氧气／再循环烟气(O2/RFG)燃烧的启动与切换操作工艺,研究了燃烧温度、燃烧气氛和钙基脱硫剂等因素对于燃烧特性和污染物排放特性的影响。结果表明,0.1MWth循环流化床富氧燃烧系统能够进行O2/RFG燃烧且运行稳定,02/N2气氛向O2/RFG气氛的切换时间约40分钟,从点火启动至达到烟气再循环稳定运行状态的时间约9小时；在一次风氧气浓度为49.6%-55.2%、二次风氧气浓度为45.3%～51.7%的范围内,燃烧后的干烟气中C02浓度在90%以上；与02/C02配气燃烧相比,除NO的排放浓度基本不变外,CO与SO2的排放浓度均有一定程度的增加,N2O的排放浓度则明显降低；在O2/RFG气氛下,飞灰含碳量为26.1%～34.1%,烟气中S02浓度为87～197mg/MJ,N20浓度为48～78mg/MJ, NO浓度仅为19～44mg/MJ。更多还原

【Abstract】 CO2emission from coal combustion is harmful to the environment, which has been greatly concerned in many countries. As one of the feasible technology for CO2mitigation in the short term, oxy-fuel combustion is beneficial to the capture, storage, and utilization of CO2from coal combustion, and can be applied to the existent combustion equipments. The technology of oxy-fuel combustion in circulating fluidized bed (CFB) takes the advantages of circulating fluidized bed combustion (CFBC) and oxy-fuel combustion. However, the research on oxy-fuel CFBC starts late and there are many problems to be solved, and the low concentration of oxygen is usually focused on in the present study, In this paper, three test platforms are used to carry out a series of experiments:thermo gravimetric and mass spectrometric (TG-MS) analyzer, bubbling fluidized bed (BFB) and circulating fluidized bed (CFB). In this paper, the feasibility of oxy-fuel CFBC at high oxygen concentration is explored, and the effects of combustion temperature and atmosphere, oxygen concentration, and operating parameters on the characteristics of coal combustion, gas pollutant formation, heat transfer are investigated.The oxy-fuel combustion experiments were conducted at O2/N2and O2/CO2atmosphere in a5kW oxy-fuel BFBC test platform and a thermo gravimetric analyzer respectively, in order to study the combustion characteristics of Shuozhou bituminous coal. It is found that the increase in the oxygen concentration and combustion temperature can improve the combustion characteristics of bituminous coal, which are slightly better at O2/CO2atmosphere than that at O2/N2atmosphere.Meanwhile, oxy-fuel combustion tests were also conducted at a BFBC test platform and TG-MS analyzer to study the gaseous pollutant generation characteristics of Shuozhou bituminous coal. The results of TG-MS tests show that, compared with O2/N2atmosphere, the emission of SO2, NO, NO2, NH3and HCN reduces at O2/CO2atmosphere. With the increase in the oxygen concentration, all the gases precipitate quickly significantly, and the intensity of precipitation peak increases. NO presents a double peak precipitation, and NO2shows an unimodal precipitation, while SO2shifts from a double peak precipitation to single peak. The results of tests in the BFBC platform reveal that NO and N2O emission decreases with the increase in the oxygen concentration; and when the combustion temperature increases, NO emission first decreases and then increases while N2O emission decreases. At O2/CO2atmosphere, SO2emission is inhibited, and the effect of calcium based sorbent on SO2removal is obvious. With the addition of calcium based sorbent, N2O emission decreases at both atmospheres, and NO emission remains unchanged at O2/CO2atmosphere while increases greatly at O2/N2atmosphere.In order to study the effects on the heat transfer characteristics of the furnace, experimental tests at high oxygen concentration were conducted in a0.15MW4oxy-fuel CFBC test platform. The results demonstrate that the total heat transfer coefficient of0.15MWth oxy-fuel CFBC test platform is about27W/(m2K); The fluidization velocity, the primary air ratio, and the combustion atmosphere has little influence on the total heat transfer coefficient of the test platform. There is little difference of heat transfer characteristics between oxy-fuel CFBC and air CFBC at high oxygen concentration.The CFB O2/CO2combustion tests at high oxygen concentration were carried out in the reformed0.1MWth oxy-fuel CFBC test platform to investigate the effects of the combustion temperature, overall oxygen concentration, excess oxygen ratio, secondary flow ratio and the oxygen concentration in primary flow on the combustion and pollutant emission characteristics. The research results show that the increase in the combustion temperature and overall oxygen concentration is benefit to improve coal combustion in CFB, the emission of CO, SO2and N2O decreases, while NO emission increases slightly. The effect of excess oxygen ratio is noticeable. With its increase, CO emission decreases significantly, SO2emission decreases slightly, while NO and N2O emission increases gradually. When the oxygen concentration in primary flow increases, SO2emission decreases, while CO and N2O emission increases at first and then decreases, NO emission decreases at first and then increases. But when the oxygen concentration in primary flow is over45%, there is little change of in N2O and NO emission. In oxy-fuel CFBC at high oxygen concentration, flow staging and oxygen staging is still an effective method to control the gas pollutant emission.The0.1MWth oxy-fuel CFBC test platform is reformed by adding the flue gas recycle system. The start-up and switch procedures of the O2/recycled flue gas (O2/RFG) combustion at high oxygen concentration in the0.1MWth oxy-fuel CFBC test platform are explored, and the effects of combustion temperature, combustion atmosphere, calcium based sorbent on combustion and pollutant emission characteristics was investigated. The results show that the0.1MWth oxy-fuel CFBC test platform can be used for O2/RFG combustion and operated stably. It takes about40minutes to switch from O2/N2atmosphere to O2/RFG atmosphere, and about9hours from ignition to stable operation of O2/RFG combustion. When the oxygen concentration is in the range of49.6%-55.2%and45.3%-51.7%in the primary flow and secondary flow respectively, CO2concentration in the dry flue gas can be higher than90%. Compared with O2/CO2combustion, NO emission basically remains unchanged, CO and SO2emission increases to some extent, and N2O emission decreases. Under O2/RFG atmosphere, the carbon content of the fly ash is26.1%-34.1%, the SO2emission in flue gas is87-197mg/MJ, N2O emission is48-78mg/MJ, and NO emission is19-44mg/MJ.更多还原