(109b) Decision-Making and Optimization of Steam Crackers Using COILSIM1D

Decision-Making
and Optimization of Steam Crackers using COILSIM1D

Abstract:

Steam
cracking is the dominant process for the production of light olefins. With roughly
150 MTon of ethylene being produced each year worldwide, this process is of
extreme importance for the (petro-)chemical industry. Given the extremely high
temperatures at which this process is carried out, it is also highly
energy-demanding, amounting to approx. 8% of the entire chemical industry
energy consumption. In this context, continuous adjustments to the daily
operation are necessary in order to maximize production and margins, while
accounting for variable feed types and qualities, market shifts and the usual
operational limitations that influence the optimal operation point of each
plant.

Steam
cracking furnaces can be divided into two distinctive parts: radiant box and
convection section. In the former, the process feed is cracked in tubular
reactors suspended in a gas fired chamber whereas in the latter, the remaining
energy content of the hot flue gas that results from the fuel combustion is
recovered by preheating the process feed and other utility streams. As is to be
expected, there is a very strong interlinking between radiant and convection
section, hence influencing each other’s operation. Determining settings for
operation of each section that optimize the global process is, therefore, of
utmost importance.

This
paper focuses on the importance of furnace simulations that explicitly account
for a detailed description of the convection section of steam crackers (see
Figure 1), combined with dedicated heat transfer and evaporation models, as
well as accurate physical property estimation methods. When integrated within a
whole-furnace simulator, this level of detail allows to accurately represent
the process, enabling to determine the optimal operation point that maximizes
the combined efficiency of radiant and convection section operations, which is
crucial in order to guide decisions oriented at optimizing the operation of
furnaces.

To
illustrate this, a case study of an ethylene production facility is presented,
in which the operation of radiant and convection sections of the furnaces are
optimized simultaneously. This task is straightforwardly carried out using the
steam cracking simulation package COILSIM1D. This software counts with a detailed
microkinetic model, combined with detailed convection section, furnace, TLE and
steam drum models, enabling to maximize the yield of desired products while
minimizing fuel consumption. This has largely positive economic and
environmental implications in the process.

Figure
1: Schematic representation
of the convection section of a steam cracking furnace. Various tube
arrangements can be implemented.