A New Mathematical Simulation Approach for Thermal Cracking Furnace Studies

Thermal cracking of hydrocarbons for olefin production is normally carried out in long reactor tubes suspended in a large gas fired furnace. In this paper, a coupled furnace-reactor mathematical model based on a computational fluid dynamics (CFD) technique is developed to simulate the complex fluid dynamics phenomena in the thermal cracking furnace. The model includes mass transfer, momentum transfer, and heat transfer, as well as thermal cracking reactions, fuel combustion and radiative heat transfer. The rationality and reliability of the mathematical model is confirmed by the approximate agreement of predicted data and industrial data. The coupled furnace-reactor simulation revealed the details of both the transfer and reaction processes taking place in the thermal cracking furnace. The results indicate highly nonuniform distribution of the flue-gas velocity, concentration and temperature in the furnace, which cause nonuniform distribution of tube skin temperature and heat flux of the reactor tubes. Profiles of oil-gas velocity, pressure, temperature and product yields in the lengthwise direction of the reactor tube are obtained. Furthermore, in the radial direction steep velocity and temperature gradients and relatively slight gradients of species concentration are found. In conclusion, the model can provide more information on the fluid dynamics and reaction behavior in the thermal cracking furnace, and guidance for the design and improvement of thermal cracking furnaces.

U-model Enhanced Dynamic Control of a Heavy Oil Pyrolysis/Cracking Furnace

This paper proposes a case study in the control of a heavy oil pyrolysis/cracking furnace with a newly extended U-model based pole placement controller(U-PPC). The major work of the paper includes: 1) establishing a control oriented nonlinear dynamic model with Naphtha cracking and thermal dynamics; 2) analysing a U-model(i.e., control oriented prototype) representation of various popular process model sets; 3)designing the new U-PPC to enhance the control performance in pole placement and stabilisation; 4) taking computational bench tests to demonstrate the control system design and performance with a user-friendly step by step procedure.

Oxidation of Fe-Cr-Ni Alloys in a Low Oxygen Partial Pressure Atmosphere to Mitigate Coke Formation

Anti-coking oxide films were prepared on a 25Cr35Ni and 35Cr45Ni alloy surface under the low oxygen partialpressure atmosphere of a H2-H2O mixture. The composition and phase structure of the oxide films were analyzed by energydispersive spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The anti-cokingperformance of a mini tube made of a HP40 (25Cr35Ni) alloy was evaluated on a bench scale pyrolysis and coking test unit.The results showed that the surface Fe and Ni content decreased after the oxidation of the two alloys in a low oxygen partialpressure atmosphere. The oxide films were mainly composed of MnCr_(2)O_(4) and Cr_(2)O_(3). The average mass of coke in the minitube with oxide film decreased by 87% relative to that of a tube without an oxide film when the cracking temperature was 900℃. The ethylene, propylene, and butadiene yields in the pyrolysis tests were almost the same for the mini tubes withand without an oxide film. The oxide film on the alloy surface effectively inhibited catalytic filamentous coke formation.An industrial test showed that the run length of the cracking furnace with the in-situ coating technology was significantlyextended.

Simulation of Whole Periodic Operation of Naphtha Pyrolysis

A simulation strategy based on a simplified Lobo Evans zone method for a radiant box and an approach for the local pressure drop along the reaction tube in an industrial cracking furnace was established. A rigorous approach including a set of molecular reactions, radiation and coke formation models was used to simulate the naphtha pyrolysis in the cracking furnace. The simulation predicted the periodic operating state of the cracking furnace. The profiles of main product yields, coke layer thickness, tube skin temperature, and other operation parameters were studied with respect to time. The simulation showed that the calculated results were in good agreement with the real working plant experience.