Knowledge Management System Of Institute of process engineering,CAS
|关键词||高含水含氮 生物质废弃物 双流化床解耦燃烧 工业应用 白酒糟|
我国轻工行业每年产生大量高含水含氮生物质废弃物，且富含纤维素、分布集中，利用潜力巨大，而大规模、资源化处理技术的缺乏，使其成为轻工业的重要污染源之一。通过燃烧将高含水含氮生物质废弃物转化为轻工行业所需的过程蒸汽，既高效简便，又能满足工业生物质废弃物快速、清洁、大规模处理的行业要求，但其较高的含水率和氮含量成为燃烧处理技术的主要瓶颈。针对高含水含氮生物质燃料传统燃烧技术存在的燃烧温度低、燃烧不完全和烟气NOx排放超标等问题，开发了双流化床解耦燃烧技术，利用双流化床反应系统将燃料燃烧过程分解为燃料热解和热解产物燃烧两个子过程，并根据再燃技术原理优化热解产物燃烧，消除了燃料含水率对燃烧过程的影响，实现了低NOx排放。本文围绕该双流化床解耦燃烧工艺的开发和工业应用，以白酒糟为原料，开展了白酒糟鼓泡流化床热解及其半焦燃烧实验，为工业示范装置设计和操作参数确定提供参考依据；建立5万吨/年白酒糟双流化床解耦燃烧示范工程，验证了双流化床解耦燃烧技术对高含水含氮燃料的适应性和低NOx排放的技术优势，并通过ASPEN模拟优化了工业示范装置反应器结构和操作参数。本文主要研究内容和研究结果如下：1. 白酒糟鼓泡流化床热解特性。热解温度对白酒糟热解产物收率有显著影响，随着热解温度增加，白酒糟半焦和焦油收率迅速下降，热解气收率增加。热解过量空气系数对半焦收率影响较小，但过量空气系数增加使得热解气产率和CO2含量增加，还原性组分含量在稀释作用下有所降低。低温热解条件下(500?600 oC)，焦油产率随过量空气系数增加而快速降低，而在高温热解条件下(700?800 oC)，过量空气系数对焦油产率和组成影响较小。为保证较高的热解速度和转化率，工业示范装置中鼓泡床热解器操作温度应控制在600?800 oC之间，颗粒停留时间不低于9.9 s。2. 白酒糟半焦燃烧特性。热解温度和过量空气系数的增加，促进了白酒糟半焦中小芳环结构的脱氢和芳香环的增长，使6个或更多融合苯环的芳香化合物和交联结构含量逐渐增加，高反应性的小芳环结构含量降低，从而导致了半焦稳定燃烧阶段缩短、燃尽阶段延长、燃尽速度和着火点降低等现象。对于热解温度为800 oC、热解过量空气系数0.2的白酒糟半焦，其900 oC燃烧灰渣仍含有较多的未燃烧的碳，难以燃尽。因此，鼓泡床热解器最佳温度操作范围为600?700 oC，过量空气系数为0.1左右，而提升管燃烧温度应高于900 oC，以促进白酒糟半焦中低反应性碳结构燃烧，且颗粒燃烧停留时间不低于10 s。3. 白酒糟双流化床解耦燃烧示范工程。根据白酒糟热解及半焦燃烧基础研究，确定了工业示范装置的操作参数，并建立了5万吨/年白酒糟双流化床解耦燃烧示范工程。通过对比白酒糟直接燃烧和解耦燃烧装置运行结果，验证了双流化床解耦燃烧技术有效克服含水30 wt.%白酒糟直接燃烧存在的：燃烧区上移、燃烧不稳定、气相CO等不能完全燃尽、返料阀结渣等问题，且氮氧化物排放低于100 mg/m3，无需任何脱硝设施即达到环保部门规定的排放标准。同时，双流化床解耦燃烧工业示范装置可以在不同负荷、加料量和操作条件下稳定运行，当白酒糟进料量应大于1.45 t/h，锅炉负荷率不低于70%时，烟气中NOx排放量在220 mg/m3以下，燃料N转化率不高于2.87%。4. 双流化床解耦燃烧ASPEN模拟。基于工业示范装置运行结果，建立了白酒糟双流化床解耦燃烧ASPEN模型。鼓泡床热解器模拟结果表明：在保证鼓泡床热解器一定反应温度时，循环床料温度和白酒糟含水率对热解器所需颗粒循环量有很大影响。示范工程装置采用颗粒流分配阀代替传统颗粒流返料阀，灵活调控了进入热解器的床料量、有效控制了控制反应温度，同时避免了提升管燃烧器温度和压力的波动。热解器固体停留时间过长不能显著增加热解气中还原性组分含量以及半焦部分气化C转化率，同时引起反应器体积过大等问题，因此，采用小体积、高通量输送床热解器替代原鼓泡床热解器，大大降低了热解器床层压降和料仓回火风险，同时减小了动力消耗，缩短了热解器预热和启动时间。高通量输送床热解器的成功应用也证明了输送床热解器+输送床燃烧器组合更适于以燃烧为主反应的双流化床解耦燃烧技术。提升管燃烧器和锅炉换热系统模拟结果表明：锅炉效率和蒸汽产量随着排烟温度升高而逐渐降低。锅炉效率和蒸汽产量随着白酒糟含水率而逐渐降低，但当白酒糟含水率低于35 wt.%时，含水率对蒸汽产量影响减弱，对锅炉效率已无明显影响，控制白酒糟最佳含水率应保持在30?35wt.%之间。
The industrial biomass waste with high water and nitrogen content is a kind of solid residue from light industry in China. With massive production, being rich in cellulose and concentrated distribution, there is a huge potential in resource utilization of those biomass waste. While the lack of large?scale and resourceful treatment technology leads to those biomass waste becoming the primary pollution source of light industry. And it seems very efficient and convenient to combust the high water?containing and nitrogen?containing biomass waste to produce steam with meeting the industrial requirement for rapid, clean and large?scale treatment as well. But the high water and nitrogen content in industrial biomass waste becomes the major bottleneck for combustion technology and limites its application. Considering the problems existing in traditional combustion of biomass waste with high water and nitrogen content, such as low combustion temperature, incompleted combustion and NOx emission exceeding standard seriously, the so?called dual fluidized bed decoupling combustion (DFBDC) was researched and developed in this study. This technology divides the traditional combustion into fuel pyrolysis and combustion of pyrolysis products and then improves the combustion process of pyrolysis products based on the reburning theory, thus eliminating the influence of water content in fuel and reaching low NOx emission. For developing the DFBDC process, distilled spirit lees (DSL) was used as the matrial in this study, and bubbling fluidized pyrolysis of DSL and char combustion were conducted to support the reactor design and operating conditions definition. An industrial demonstration plant with a DSL treatment capacity of 50,000 tons/year was established to verify the technical advantages and flexibility to the biomass waste with high water and nitrogen content. A DFBDC ASPEN model was established to optimize reactor structure and operating conditions.The main results from this study are summarized as follows:1. DSL pyrolysis in bubbling fluidized bed (DFB). The pyrolysis temperature had a significant effect on the yields of pyrolysis products, and an increasing temperature leaded to an obvious decrease in the yield of char and tar but increased the yields of pyrolysis gas. The excess air ratio (ER) had a little influence on char yield, while raising ER would increase the pyrolysis gas yield and CO2 content in pyrolysis gas remarkably, followed by reducing compositions content decreasing as a result of CO2 dilution. ER increasing resulted in the decrease of tar yield under low?temperature pyrolysis (500?600 oC) but had an insignificant effect on tar yield and compositons under high?temperature pyrolysis (700?800 oC). The pyrolysis temperature and water content in DSL had a significant effect on pyrolysis reaction rate. In order to obtain a high pyrolysis reaction rate and conversion, the operating temperature of industrial BFB pyrolyzer should be controlled within 600?800 oC with particle residence time no less than 9.9 s.2. Char combustion characteristics. The increase of pyrolysis temperature and ER improved the dehydrogenation of small aromatic rings and growth of aromatic rings, thus leading to the increase of aromatics with ring number more than 6 and cross?linked structure as well as the decrease of small aromatic rings with high reactivity. Those carbon structure changes reduced the stable combustion stage of char and extended the burnout stage, and it also attributed to the decrease of burnout reaction rate and ignition temperature. Especially for the char with pyrolysis temperature of 800 oC and ER of 0.2, its ash still contented a lot of unreacted carbon even combusting at 900 oC. Therefore, the optimal operating temperature and ER of industrial BFB pyrolyzer were 600?800 oC and 0.1 respectively. The combustor temperature should be no less than 900 oC with particle residence time more than 10 s to promote the combustion of low reactive carbon structure and decrease carbon content in fly ash.3. Industrial demonstration plant operation. According to the fundamental researches about DSL pyrolysis and its char combustion, the design and operating parameters of reactors were determined, and an industrial demonstration plant with treatment capacity of 50,000 tons/year was also established. Comparison of direct combustion and decoupling combustion of DSL showed that decoupling combustion technology could solve the problems existing in CFB direct combustion of high?water containing DSL, such as combustion zone decreasing and moving upward, instable combustion, incompleted combustion of CO and volatiles in gaseous phase and serious slagging in loop seal. Besides, the NOx emission in flue gas for decoupling combustion was no more than 100 mg/m3, which reeached the emission standard without any denitrification treatment. This industrial plant of DFB decoupling combustion could also keep stable operation under different boiler loads, feeding rates and operating parameters. And the NOx emission and fuel?N conversion could be controlled below 220 mg/m3 and 2.87% respectively, as feeding rate of DSL and boiler load were no less than 1.45 t/h and 70% respectively.4. ASPEN simulation of DFBDC process. Based on the operation results of industrial demonstration plant, an ASPEN model of DFBDC process was established. The simulation results of BFB pyrolyzer showed that the temperature of circulating bed material and water content in DSL had a significant effect on particle circulating rate for keeping pyrolyzer at a certain temperature. Therefore, a granular flow partition valve was applied in industrial plant instead of traditional loop seal, thus realizing the flexible adjustment of the bed material entering into pyrolyzer for controlling reaction temperature and avoiding the fluctuation of the temperature and pressure in combustor simultaneously. The oversize volume of pyrolyzer could not increase the reducing compositions content in pyrolysis gas and carbon conversion of char partial?gasification significantly. Thus, a novel riser pyrolyzer with small volume and high?throughput was applied in industrial plant instead of the previous BFB pyrolyzer, which reduced the bed pressure, power consumption and tempering risk greatly as well as shortened the preheating and start?up time of pyrolyzer. The successful application of riser pyrolyzer aslo proved that the combination of riser pyrolyzer and riser combustor was more suitable for DFBDC technology with combustion as the primary reaction. The simulation results of riser combustior and heat exchange system showed that the boiler effiency and steam output reduced with the increasing of flue gas temperature. And an economizer was installed in flue to slove the problem of high exhaust gas temperature, making heat loss ratio caused by exhaust gas reduce from 8.2% to 4.6%. Although the boiler effiency and steam output reduced with the increasing of water content in DSL, the influence of water content was weakened significantly as water content was lower than 35 wt.% and 30?35wt.% was the optimal water content in fuel for dual fluidized bed decoupling combustion.
|韩振南. 高含水含氮生物质废弃物双流化床解耦燃烧基础及工业应用[D]. 北京. 中国科学院研究生院,2017.|
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