沼气工程罐内盘管加热传热速率与效率分析

国内沼气工程中广泛采用的加热方式——罐内盘管加热。从热力学角度出发,基于热力学第一、第二定律,对影响罐内加热的各因素从传热速率与传热效率方面进行分析。研究表明,从传热速率-总传热系数角度分析,选用热导率在15 W·m-1·K-1以上的厚管壁管径,同时采用低转速的搅拌方式能实现最大化的传热速率。另外,从传热效率-有效能角度对传热过程进行能耗分析,在逆流搅拌下,提高冷物料进口温度可以减少换热的不可逆性,可增加传热过程有效能的利用率。研究结果为实现沼气工程罐内加热过程传热速率与效率统一,达到能量的最优化利用提供理论参考。

Analysis of heat transfer efficiency and rate inside fermentation tank with heating coil of biogas projects

Heating coil inside the tank is widely used in biogas projects at home and abroad. The various factors affecting the heating and heat transfer of the tank were analyzed from the heat transfer efficiency and rate based on the first and the second laws of thermodynamics. It was found that from the view of the overall heat transfer coefficient, the thermal conductivity and wall thickness were comprehensive considered and then the maximum heat transfer rate was obtained with low speed mixing method by choosing the thick wall with the value of thermal conductivity of above 15 W·m^-1·K^-1. Meanwhile, the energy consumption of transfer process was analyzed from the view of heat transfer efficiency. It can be obtained that an appropriate increase in the inlet temperature of cold material can reduce the irreversibility of heat transfer and increase the utilization ratio of limited energy for heat transfer process with countercurrent mixing. Therefore, the high-efficient, energy saving and rational theoretical guidance was provided for biogas project using tank heating to achieve the unity of transfer heat rate and efficiency.