Study On Modeling Of Naphtha Pyrolysis Furnace

Pyrolysis furnaces are very important in petrochemical industry with theirhigh capacity and high energy consumption. They produce most ethylene,propylene, butadiene and other basic petrochemical materials. Naphtha is themain raw material for pyrolysis furnaces. Development of petrochemicaltechnology and increase of human consumption have brought interests in andresearch into the naphtha pyrolysis furnaces. This thesis focuses on the studyof the process modeling, on-line simulation, and optimization techniques ofnaphtha pyrolysis furnaces. The main contributions and achievements are asfollows:An on-line simulation model for naphtha pyrolysis furnace is developed inthis thesis. It is different from all the other models which can only be usedoff-line. An algorithm to estimate the detailed composition of naphtha basedon the industrial measured data is developed here. Then the important averagephysical characteristics of naphtha such as average molecular, form-heat andspecific heat can be calculated. A stochastic method to adjust the initialselectivity coefficients of the primary reaction is developed in this thesis.Then the molecular kinetic model can be applied on-line to predict the mainproduct yields and the cracking severity index with collecting operatingparameters.An applied free radical mechanism model of naphtha cracking process isdeveloped here based on Rice's free radical chain reaction theory. Thereduced mechanism model is also explored here with the quasi-steady-stateapproximation and other reduction strategies in order to achieve fastcalculation of the free radical model. The calculated results agree well withthe measured data. It can easily be used on-line when combined with thenaphtha detailed composition estimation algorithm.A general naphtha cracker on-line optimization model is developed here. Atwo-step optimization strategy composed of a quasi-finite-element methodand a stochastic method is developed to calculate the optimal operationcondition. Through operational optimization calculation in typical operatingcondition, the total annual profit can be increased by 8.13%. The results showthat traditional process optimization methods and ideas can be modified andintroduced into naphtha pyrolysis furnace operation. An on-line naphthapyrolysis furnace optimization system is also developed in this thesis.The naphtha detailed composition estimation algorithm can be generalized to otherfields. It can be used to estimate the composition of light gas oil and heavy gas oilthrough appending or reducing the species. The detailed composition of HGO,HVGO could be estimated by appending some assumed components and it would behelpful to investigate their cracking model.A dynamic heat-transfer process model of naphtha pyrolysis furnace is developedhere based on the steady-state model. The characteristics of the temperature change ofthe tube wall and process gas inside tube are analyzed under disturbance of theoperating parameters. The dynamic response characteristics can be expressed in theform of transfer functions, which are useful to the research works on the advancedcontrol system design for naphtha pyrolysis furnaces.