Abstract: Recovery of waste heat from flue gas under 180℃ was named as deep recovery in this paper，and thermodynamics characteristics of this process were analyzed.Three recovery modes were proposed and some characteristics of them were also discussed.Especially，a mathematical model was built for split-flow pattern and the result obtained was discussed.There is obvious difference at the thermodynamics characteristics of recovery of waste heat in flue gas for deep and normal recovery，and exist of turn point T_co leads to a constriction for outlet temperature of hot water of single-flow pattern.Split-flow pattern can overcome this limit caused by the turn point，and split-flow ratio x can be determined from temperature of demand hot water and total cost.When cost ratio is higher than a low limit value，optimum split-flow ratio can be found to get the lowest total cost; while the cost ratio is lower than the value，split-flow ratio should be as small as possible to reduce total cost.When outlet water temperature of optimum result is lower than requirement，split-flow ratio should be improved or adjusted to reach demand value.

Key words: flue gas, waste heat, condensation, split-flow

摘要： 将180℃以下的烟气余热的回收利用称为烟气余热的深度回收，分析了深度回收过程中烟气的热力学特性；提出了三种利用模式并分析了不同模式的特点；针对分流模式建立了数学模型并对结果进行了分析。烟气余热深度回收与常规余热回收在热力学特性上有明显区别，转折点Tco的存在使得直流模式的出水温度受到限制；分流模式有利于克服转折点引起的出水温度过低的问题，分流系数可根据实际热水温度需求及成本来确定：成本比高于下限值时可以找到最优分流系数使成本最低，成本比低于下限值时应该根据温度要求尽量降低分流系数以减少成本。

关键词: 烟气, 余热, 冷凝, 分流