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.