(58ac) Evaluating the Impact of Higher Emissivity Technologies on Steam Cracking Furnaces, By Means of COILSIM1D Simulations

Evaluating
the impact of higher emissivity technologies on steam cracking furnaces, by
means of COILSIM1D simulations

Session: 30th
Ethylene Producers’ Conference

Authors:
Andrés
E. Muñoz G.¹, David J. Brown¹

1.      AVGI
bvba

Abstract:

Olefin
production by thermal cracking is a mature process and so major innovations are
comparatively rare. However, because of both the huge scale and the steady
growth of the ethylene industry worldwide, several technologies are being developed
that reduce energy consumption of cracking furnaces. For some years already,
one of the fields of focus for improvement has been the enhancement of emissivity
of the furnace refractory lining (the ‘hot face’) and the outside surface of
the radiant coils by applying coatings.

The
principle is simple: Higher emissivity in the radiant box ensures more
efficient heat transfer to the process gas and, therefore, less energy
(expressed, for example, as fuel flow rate) is required in order to maintain
the same cracking severity, when compared to a normal emissivity furnace.
However, because of a lower amount of flue gas being generated, the arch
temperature will be lower (see Figure 1) and the heat recovery taking place in
the convection section will be less, offsetting the beneficial effect
originally expected from the increase in radiant efficiency. Consequently, an
adequate balance of the overall effect of enhanced emissivity is of the utmost
importance when considering the application of this technique.

This paper
illustrates the impact of increasing emissivity in the radiant section, by
means of COILSIM1D simulations. COILSIM1D can model accurately all the
interacting and competing effects within an industrial furnace. Combining a
detailed microkinetic model to describe the chemistry taking place in the reactor,
with a coupled radiant box – convection section furnace model, the global
effect of increasing emissivity can be studied.

The
conclusion of the study is that high-emissivity coatings can be very beneficial
but that a proper evaluation must made, case-by-case, to choose the right
candidates.

Figure
1: Arch and Coil Outlet Temperature as a function
of emissivity, for a constant firebox fired duty