ORC生物质成型燃料链条炉燃烧及系统性能研究

【作者】 陈蓉；

【导师】 王华； 王辉涛；

【作者基本信息】 昆明理工大学 ， 冶金能源工程， 2014， 博士

【摘要】 地球上生物质资源相当丰富,据估算,地球上蕴藏的生物质达18000亿吨,2013年我国可开发为能源的生物质资源约为4亿吨,且随着农林业的发展,生物质资源将越来越多。据估计,到21世纪中叶,采用新技术生产的各种生物质替代燃料将占全球总能耗的40%以上。目前我国生物质燃料成型技术已比较成熟,生物质成型燃料生产能力不断提高,研究进一步扩大生物质成型燃料的应用范围及生物质成型燃料的高效利用技术已成为亟待解决的问题。本文提出采用生物质成型燃料导热油链条炉作为有机朗肯循环(Organic Rankine Cycle, ORC)的驱动热源,将生物质能转换为电能,实现生物质成型燃料的高效利用。为了提高ORC生物质成型燃料导热油链条炉系统的效率,本文完成了如下主要内容的研究：(1)通过热重试验,分析了生物质成型燃料燃烧过程中水分蒸发、挥发分析出及燃烧、固定碳燃烧3个过程的基本反应机理,结合计算流体力学、传热学、化学反应动力学等方面的理论和方法,建立了单颗粒生物质成型燃料燃烧过程的二维计算模型,并进行了模拟计算,得到了单颗粒生物质成型燃料燃烧过程的气体成分以及温度分布变化情况。通过试验结果与计算结果的对比,验证了该模型的准确性。单颗粒生物质成型燃料燃烧过程的模拟研究为构建生物质成型燃料导热油链条炉的床层燃烧计算模型奠定了基础。(2)构建了生物质成型燃料导热油链条炉的床层燃烧和炉膛燃烧一体化的综合模型,对床层和炉膛的流动、传热和传质过程进行了耦合计算。为验证模型的准确性,采用气相色谱仪测量了某链条炉中生物质床层表面的气体成分分布,并与模拟结果进行对比分析,结果吻合较好。基于该模型,研究了空气预热温度、料层厚度、炉排前进速度、颗粒直径和配风方式对生物质床层燃烧和炉膛燃烧的影响规律,为运行提供了理论依据。(3)结合传热学、热力学、流体力学和火用分析方法,建立了生物质成型燃料链条炉系统热力性能的数学模型。应用该模型研究了导热油入口温度、导热油入口流量、二次风温度和二次风速度等影响因素对生物质成型燃料导热油链条炉最终排烟温度、热效率、导热油出口温度、火用效率等主要性能指标的影响规律。研究结果表明各影响因素与系统性能之间存在比较复杂的非线性数学关系,为提高锅炉的性能指标,需要对系统进行多参数的并行优化。(4)运用数学规划理论,基于蚁群算法,建立了生物质成型燃料链条炉系统的多参数优化模型,提出了单目标优化、多目标优化或火用经济优化方法,并以系统最终排烟温度、导热油出口温度、热效率、火用效率、年度总成本、年度化净利润评价指标对生物质成型燃料链条炉系统进行了优化,使该系统的有关性能得到极大改善和提高,如经过初步优化设计后系统供热量同为13.95MW的生物质成型燃料链条炉系统的年度化总成本比原设计下降近8.8%,年度化净利润提高近7%。更多还原

【Abstract】 Biomass resources are very rich and the biomass is about1.8trillion tons on the earth. There are about400million tons biomass resources can be developed into energy in China in2013, and with the development of agroforestry, the biomass resources will be more and more. It is estimated that various kinds of biomass alternative fuels will account for more than40%of total global energy consumption. The production capacity of biomass briquette fuel is increasing with the forming technology is more and more mature, and the next hot issues of the biomass briquette fuel are expansioning the application range and inproving the utilization efficiency. In this paper, the biomass briquette fuel heat-conducting oil chain boiler, which is convert the biomass to the electricity, is used as the driving heat source of organic rankine cycle. This boiler can realize the effective utilization of biomass briquette fuel. In order to improve the efficiency of ORC biomass briquette fuel heat-conducting oil chain boiler system, the main contents are studied in this paper are as follows:(1) The reaction mechanisms of water evaporation process, volatile devolatilization and combustion process and fixed carbon combustion process in biomass briquette fuel combustion are analysed according to the thermal test. The two-dimensional mathematical model of combustion process of single particle biomass briquette fuel is established based on the theories and methords of computational fluid dynamics, heat transfer, chemical reaction dynamics. The combustion process of single particle is simulated with this model, and the gas composition and temperature distribution is obtained. The accuracy of this model is verified by comparing the test results with the calculation results. The simulation study of single particle biomass briquette fuel combustion process is the base of the construction of mathematical model in bed of biomass briquette fuel heat-conducting oil chain boiler.(2) The comprehensive mathematical model of bed and furnace in biomass briquette fuel heat-conducting oil chain boiler is developed, the process of flow, heat and mass transfer are simulated with this model. In order to verify the model, the distribution of gas component in bed furnace was measured by chromatographic instrument, and the simulated results are in good agreement with the test results. The influence of secondary air temperature, bed thickness, chain velocity, particle size and air distribution mode on combustion of bed and furnace is studied based on this model. This study provides a theoretical basis for the operation.(3) The mathematical model of thermal properties of biomass briquette fuel heat-conducting oil chain boiler is developed according to the theories of heat transfer, thermodynamics, fluid mechanics and the method of exergy analysis. The influence of heat-conducting oil temperature and flow, secondary air temperature and velocity on the flue gas temperature, thermal efficiency, outlet heat-conducting oil temperature, exergy efficiency of biomass briquette fuel heat-conducting oil chain boiler was studied with this model. The results indicate that the relationship between the factors and the system performance is a complex nonlinear mathematical relationship. In order to improve the performance of chain boiler, the parallel optimization of multi parameters is necessary.(4) By application of mathematical programming theory and ant colony algorithm (ACA), optimization model of biomass briquette fuel heat-conducting oil chain boiler system was suggested, single-objective, multi-objective and exergoeconomic optimization methods were discussed. Optimization design of biomass boiler system was done, the optimization objectives include exhaust temperature, outlet temperature of the heat conduction oil, thermal efficiency and exergy efficiency, annual total cost index, annual net benefit index.The performances of biomass briquette fuel heat-conducting oil chain boiler system were remarkably improved by means of the proposed optimization design method. For example, in a13.95WM biomass briquette fuel heat-conducting oil chain boiler system, the annual total cost came nearly down8.8%and annual net benefit was raised upabout7%after optimized by this method.更多还原