炼焦荒煤气上升管显热回收换热过程动态特性

Dynamic characteristic of heat transfer process during sensible heat recovery of raw coke oven gas in ascension pipe

煤焦油结焦是制约炼焦荒煤气上升管显热回收换热器长期高效安全运行的主要因素。通过调控荒煤气及上升管管壁温度抑制煤焦油析出是防止结焦的有效措施。基于多孔介质非热平衡模型,建立了内嵌螺旋盘管及多孔填料的荒煤气显热回收套管换热器的一维非稳态热传递模型。结合炼焦周期内荒煤气流量与温度瞬时数据计算得到荒煤气、上升管管壁、填料层、熔融盐温度动态变化,分析了填料层热容、填料层有效导热系数及熔融盐流量对其动态变化的影响,并提出了有效控制荒煤气及上升管管壁温度的方法。结果表明:荒煤气中煤焦油析出及结焦主要发生在炼焦后期荒煤气流量减小时;填料层导热系数是上升管换热器设计时考虑的重要参数,增大填料层导热系数可显著提高余热回收效率,但会使荒煤气与上升管管壁温降增大,设计时应在保证焦油蒸汽不发生冷凝的前提下尽可能增大填料层导热系数;炼焦后期,通过切断熔融盐取热,并合理设计填料层导热系数、填料层热容及熔融盐入口温度等可实现上升管管壁温度调控,从而避免荒煤气中煤焦油析出及结焦。

Carbon deposition of coal tar is the main factor that restricts the long term efficient and safe operation of the ascension-pipe heat exchanger for recovering sensible heat of raw coke oven gas(COG).It is an effective measure to prevent carbon deposition of coal tar by controlling temperatures of raw COG and inner wall of ascension pipe.Based on local non-thermal equilibrium idea of porous media,a one-dimensional unsteady heat transfer model was established for the ascension-pipe heat exchanger with embedded spiral coils and por⁃ous fillers for sensible heat recovery of raw gas.Based on the instantaneous data of raw gas flow and temperature during the coking cycle,the dynamic characteristics of temperatures of raw COG,wall of ascension pipe,packing layer and molten salt were obtained.The effects of the heat capacity of filler layer,effective thermal conductivity of filler layer,and molten salt flow rate on its dynamic changes were ana⁃lyzed.Moreover,a method was proposed to effectively control temperatures of raw COG and wall of ascension pipe.The results show that the coal tar precipitation mainly occur in the late coking period when raw COG output will decrease quickly.The thermal conductivity of packing layer is an important parameter to be considered in the design of the ascension-pipe heat exchanger.Increasing the conductivity of packing layer can improve the heat recovery efficiency,but also make the temperature drops of raw COG and wall of ascension pipe in⁃creased.The thermal conductivity of the packing layer should be increased as far as possible under the premise of ensuring that the tar va⁃por does not condense.In the later stage of coking,the temperature control of the rising pipe wall can be realized by cutting off the molten salt to get heat,and reasonably designing the thermal conductivity of packing layer,the heat capacity of packing layer and the inlet tem⁃perature of molten salt,so as to avoid the coal tar precipitation.