板式通道内含亚微米颗粒低温湿烟气对流冷凝传热机理研究

The direct discharge of wet flue gas from wet desulfurization tower in coal-fired units will cause the waste of energy and water. However, the recuperative heat exchanger is incapable of the recovery due to the quite small temperature difference between flue gas and cold source, since the temperature of flue gas is quite low at the outlet of desulfurization tower. In this research, a new method to recover the heat and water of flue gas is proposed by using regenerative heat exchanger. However, the effect of submicron particles on the convective condensation heat transfer of wet flue gas is not clear, and the research on the two-phase flow in the condensation heat transfer process is not sufficient, and the numerical and analytic models need to be further developed. In this study, a simulated moisture flue gas condensation heat transfer and visualization experimental system will be built. The convective condensation heat transfer process of wet flue gas with submicron particles in plate-channels will be carried out to reveal the influence of fine particles on the heat and mass transfer process of condensation. The influence mechanism of different corrugated structures on the evolution of film shape and gas-liquid flow pattern will be investigated. Convective condensation heat transfer prediction model will be constructed to study the coupling effects of gas-liquid phase transition, multiphase flow and channel structures. The optimization of channel structure parameters will be conducted under specific working conditions. The thermal-hydraulic calculation model of regenerative condensation heat exchanger will be established, and the thermal characteristics of regenerative flue gas condensation heat exchanger will be analyzed. The present study would enrich the theoretical system of convective and condensation heat transfer, and offer scientific evidence and technical route for the efficient recovery of heat and water in low temperature flue gas after desulfurization tower in coal-fired boilers.

燃煤机组脱硫塔出口的饱和湿烟气直接排入大气会造成大量水热资源的浪费。由于脱硫塔出口烟气温度较低，与环境空气换热温压较小，常规间壁式换热器不能满足烟气的水热回收要求。本项目提出采用再生式冷凝换热对低温湿烟气进行水热回收。而前人对亚微米颗粒在湿烟气冷凝传热过程中的影响机制尚不明确，对槽道波纹表面湿烟气冷凝气液两相流动的研究并不充分，且相关数值与解析模型仍不完善。本项目拟通过实验研究含亚微米颗粒湿烟气在板式通道中的对流冷凝传热过程，旨在进一步阐明微细颗粒对冷凝传热传质过程的影响机制；获得不同槽道波纹结构对冷凝液膜形态及气液两相流动的影响规律；并构建对流冷凝传热的多因素耦合预测模型，阐明气液相变、多相流动和通道结构等多因素的耦合影响机制；进而建立再生式烟气冷凝换热计算模型，明确再生式烟气冷凝换热器的热力特性。本项目可丰富对流冷凝传热的理论体系，为燃煤机组低温湿烟气水热高效回收提供技术和理论基础。

本项目提出的再生式冷凝换热器能克服烟气与环境空气换热温压小的困难，可回收低品位湿烟气中大量的水热资源。本项目针对再生式冷凝换热器中复杂的传热传质过程开展研究，通过实验、数值模拟和理论计算，阐明了再生式烟气换热器内颗粒物沉积机理，改进了湿烟气冷凝传热模型，优化了再生式烟气冷凝换热器传热元件结构，构建了再生式烟气冷凝换热器的热力计算模型。本项目研究的主要成果和结论包括：.首先，从实际出发对低温烟道中的沉积物和换热元件进行了测试分析，获得了在颗粒物沉积过程中烟气中的氨气组分的作用机制，阐明了再生式烟气换热器内颗粒物沉积机理；设计了研究诱导颗粒物沉积化合物生成特性的实验系统，研究了不同条件下换热通道壁面上沉积物的沉积规律；提出了改进的烟气系统以应对颗粒物沉积和缓解再生式烟气换热器传热元件因颗粒物沉积导致的堵塞腐蚀问题。.其次，搭建了烟气冷凝实验系统，分别用实验和数值模拟研究了平翅片管换热器对流冷凝换热特性，将数值计算结果与实验结果进行了对比分析，获得了冷凝液对传热的影响；综合考虑对流传质和扩散传质过程，改进了湿烟气冷凝传热模型，并对含尘工况中使用的烟气冷凝传热元件的传热传质特性进行了研究，分析了不同运行参数和结构参数条件下速度场与温度梯度场以及速度与浓度梯度场的协同性；将(火积)耗散极值原理拓展应用于对流传质过程中，定义显热(火积)和潜热(火积)，建立湿烟气对流冷凝传热过程的(火积)平衡方程，获得湿烟气层流对流冷凝传热的场协同方程，研究了矩形通道中的湿烟气的对流冷凝传热过程，得出了矩形通道中烟气层流对流冷凝传热的最优速度场。.最后，建立了再生式烟气冷凝换热器对低温含湿烟气进行水热高效回收的热力计算模型，获得了再生式冷凝换热器的热力特性；查明了烟气温度，蓄热体温度，水蒸气质量分数和冷凝水质量流率的分布规律；对回转再生式换热器的烟气泄漏问题开展了研究，提出了一种烟气低泄漏方案，获得了“清洗烟气”和“隔离烟气”对换热器换热效率的影响；提出了一种含再生式烟气冷凝换热器的新型余热回收系统，对该系统进行了计算分析，表明烟气冷凝换热器可显著提升余热回收系统的技术经济性。.本项目的开展能够为低品位湿烟气的水热高效回收提供理论基础和技术支撑。