Optimal Process Design for the Thermal Cracking Process
Systematic methods and tools for managing the complexity
Process Synthesis & Design - II (T4-1b)
Keywords: Thermal cracking, process design, optimal reaction path, steam cracking
Over the last forty years the thermal cracking technology has developed from an empirical understanding of operations and of the performance of cracking furnaces, to on-line use of rigorous models based on first-principles reaction kinetics to optimise plant operations. The models have predictive capability with respect to what is happening in the cracking coils, given the coil configuration, the feed conditions and the incoming heat fluxes.
The main issue is whether the fundamental understanding and the reaction kinetic models for thermal cracking that were obtained over the last forty years can be successfully applied to develop new options for thermal cracking units.
In the past the processes for manufacturing of ethene from hydrocarbon feedstocks have been derived from existing technology in an evolutionary way. The main focus of the process development on these processes was on how to modify these to produce ethene. For example, the current state of the art thermal cracking furnace can be considered as an upgraded fired heater. The direct heating processes are derived from acetylene manufacturing processes. The fluidized bed technologies find their origin in the fluid catalytic cracking technologies. Generally, a process that can add a large amount of energy at a high temperature level in a short period of time can be used for thermal cracking. Through this kind of evolutionary process development, the approach has always been on what the existing technology can do and how this should be modified to obtain a good process for ethene.
A next phase in the development of the thermal cracking process could be a move from modification of existing technology to a fundamental design of the reaction environment to yield ethene as efficient as possible. We no longer take the external conditions for granted but try to find the best external conditions and the resulting configurations, exploiting fundamental insights captured in the available first-principles models. That is, the external conditions are considered as free design decision variables that can be manipulated to find much better cracking performance. With the optimal reaction path known there is an avenue to discover the optimal equipment wherein this process can be conducted.
Finding the optimal reaction path amounts to establishing knowledge on the intrinsic reaction conditions to achieve optimal performance in terms of product yields. We will examine the process of a small volume of reaction mixture along the reaction coordinate, using fundamental kinetic schemes. By means of dynamic optimisation the optimal temperature, concentration, and heat flux profiles are determined as a function of the residence time.
Added to this has been the non-uniformity of the reactor volume. The complexity of this optimisation problem was caught by some common sense approaches in order to yield practically valid recommendations for the operation path of this process. The results and their analysis will be presented as a desired operationg procedure, and as guidelines for the development of the reactor design.
See the full pdf manuscript of the abstract.
Presented Tuesday 18, 16:20 to 16:40, in session Process Synthesis & Design - II (T4-1b).
