裂解制乙烯装置中急冷锅炉的结焦及传热模型

COKING AND HEAT TRANSFER MODEL OF PYROLYZER QUENCH HEAT EXCHANGERS

在裂解制乙烯装置的急冷锅炉中,焦是通过结焦母体在高温区的气-固反应结焦与低温区的液-固冷凝结焦两个途径形成的。本文对结焦母体的冷凝结焦提出了母体的冷凝速率公式,并用实际生产数据确定了公式中的诸常数;对反应结焦,沿用了我们提出的动力学公式与数据。据此所得的结焦与传热模型,可用来计算沿急冷锅炉换热管长度,随运转天数而变的焦层厚度、油气温度、管壁温度、压力降,以及急冷锅炉的高压水蒸气产量等工艺参数。用本模型计算得的急冷锅炉出口的油气升温曲线与工厂实际运转情况很接近,可用于预测、指导生产,并可供设计参考。

A coking and heat transfer model combined with a kinetic model of gasphase cracking reactions for two-stage quench heat exchangers is purposed.For the coking section in the model,the coke deposited on the tube wallis considered to be formed in two ways:(1) A small part of the macromole-cules of coke precursor diffusing to the tube wall converts into coke immedi-ately through gas-solid reactions on the tube wall of high temperature region;while (2) the other great part of them is cooled and condensed into amor-phous pitch-like liquid drops on the tube wall of lower temperature region,and finally converts into coke through liquid-solid reactions.For heat transfer section,the rate equation of cooling and condensationof the coke precursor and its vapor pressure-vs.-temperature relation havebeen successfully developed,other heat transfer formulas are carfully selec-ted.Using the overall model,we have computed the thickness of coke layerinside the tube, the temperature of the gas, the pressure drop, etco all alongthe whole tube length in the full operating period. The computed results arewell comparable with the actual commercial data.