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Research Papers: Heat Transfer in Manufacturing

Coupled Heat Transfers in a Refinery Furnace in View of Fouling Prediction

[+] Author and Article Information
T. Pedot

CERFACS,
42 Avenue G. Coriolis,
Toulouse 31170, France
e-mail: thomas.pedot@gmail.com

B. Cuenot

CERFACS,
42 Avenue G. Coriolis,
Toulouse 31170, France
e-mail: cuenot@cerfacs.fr

E. Riber

CERFACS,
42 Avenue G. Coriolis,
Toulouse 31057, France
e-mail: riber@cerfacs.fr

T. Poinsot

CERFACS and IMFT,
2 Al. Pr. C. Soula,
Toulouse 31400, France
e-mail: poinsot@cerfacs.fr

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received June 8, 2015; final manuscript received March 9, 2016; published online April 12, 2016. Assoc. Editor: Laurent Pilon.

J. Heat Transfer 138(7), 072101 (Apr 12, 2016) (10 pages) Paper No: HT-15-1409; doi: 10.1115/1.4033096 History: Received June 08, 2015; Revised March 09, 2016

In industrial refinery furnaces, the efficiency of thermal transfer to heat crude oil before distillation is often altered by coke deposition inside the fuel pipes. This leads to increased production and maintenance costs, and requires better understanding and control. Crude oil fouling is a chemical reaction that is, at first order, thermally controlled. In such large furnaces, the predominant heat transfer process is thermal radiation by the hot combustion products, which directly heats the pipes. As radiation fluxes depend on temperature differences, the pipe surface temperature also plays an important role and needs to be predicted with sufficient accuracy. This pipe surface temperature results from the energy balance between thermal radiation, convective heat transfer, and conduction in the solid material of the pipe, meaning that the thermal behavior of the whole system is a coupled radiation–convection–conduction problem. In this work, this coupled problem is solved in a cylindrical furnace, in which the crude oil flowing in vertical pipes is heated. The thermal radiation of combustion gases is modeled using the discrete ordinate method (DOM) with accurate spectral models and is coupled to heat conduction in the pipe to predict its wall temperature. The flame is described with a complex chemistry combustion model. An energy balance confirms that heat transfers are effectively dominated by thermal radiation. Good agreement with available measurements of the radiative heat flux on a real furnace shows that the proposed approach predicts the correct heat transfers to the pipe. This allows an accurate prediction of the temperature field on the pipe surface, which is a key parameter for liquid fouling inside the pipe. This shows that the thermal problem in furnaces can be handled with relatively simple models with good accuracy.

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Figures

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Fig. 1

Left: Sketch of a typical cylindrical refinery furnace. Right: Sketch of the different energy contributions in the radiant section.

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Fig. 2

Sketch of heat fluxes budget to the pipes

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Fig. 3

Axisymmetric diffusion jet flame configuration

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Fig. 4

Coupling algorithm to solve the thermal problem

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Fig. 5

Left: Cross-sectional view of the Feyzin furnace. Right: Sketch of the oil flow path in one-quarter of the Feyzin furnace (vertical expanded view).

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Fig. 6

Fields of temperature (left), CO2 (middle), and radiative source term (right) of the jet flame computed with CANDLE in a vertical plane cut. Stoichiometric line is drawn in white. ⊗ symbols locate incident radiative flux probes.

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Fig. 7

Structure of the diffusion flame at atmospheric pressure computed with grimech 3.0 full chemistry and transport: temperature (left scale) and main species molar fraction (right scale) profiles. Strain rate is 105 s−1. The vertical dashed line marks the stoichiometric mixture fraction zst.

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Fig. 8 Left

Radial profiles of temperature, radiative source term, and net radiative flux at x=3 m. Right: Incident radiative heat flux: simulation versus measurements.

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Fig. 9

Net radiative flux and pipe wall temperature along a path (tubes 1–20)

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Fig. 10

Net heat flux on a pipe section (tube 2) versus angle at four different heights; 0 deg (respectively, 180 deg) defines the highest exposure to the flame (respectively, refractory furnace wall)

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Fig. 11

Net heat flux on a pipe section (tube 20) versus angle at four different heights; 0 deg (respectively, 180 deg) defines the highest exposure to the flame (respectively, refractory wall)

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