The aim of this work is to gain fundamental understanding of coke formation under typical industrial reactor conditions.
Light olefins such as ethylene and propylene are the most important basic chemicals for the petrochemical industry. The dominant process to manufacture them is the thermal cracking in the presence of steam. Coke deposition on the inner wall of the tubular cracking reactors is the main drawback of this process. The resulting coke layer reduces the cross-sectional area of the tubular reactors, causing a continuous increasing pressure drop. Thus, bi-molecular reactions gain ground, leading to lower olefin selectivity. In addition, the resistance to heat transfer from the furnace to the feed is increased. All the above lead to higher tube metal temperatures and eventually, to process shutdown in order to decoke the reactors. This negatively affects the desirable production and the economics of the process.
The reactor material is one of the most important factors affecting the deposition of coke. However, only a limited number of studies have been carried out evaluating the effect of metal surface technologies, including the use of low-coking alloys and coatings. For feedstocks heavier than ethane fundamental understanding of the relation between the materials composition/state and coke formation on is limited to non-existing. Ideally a model could be developed that predicts the coking rates (initial and asymptotic coking rate) for different materials and coatings, taking into account feedstock composition of the used, as well as the operating conditions and the surface composition. This will help to optimize the runlength of steam crackers, determine optimal pretreatment conditions, and maximize its profit.
Experimental thermogravimetric investigation of coke formation on desired samples of coated/uncoated metal to evaluate:
- The influence of temperature (up to 886 ℃)
- The desired material composition, coating and surface morphology (roughness)
- Difference in feed composition (naphtha versus ethane, naphtha composition) using surrogate feedstocks
The coated or uncoated metals will be examined using:
- Physical analysis of the coke (SEM) to understand the structure of the coke.
- Chemical analysis of the coke (EDX) and gas phase composition of feed and effluent Chemical composition and structural analysis of the reactor material surface after coking.
With the above information a model will be developed that describes the coking rate taking into account process conditions, reactor material composition, and reactor material surface/ coating morphology for different feed compositions.
Scale-up to a real industrial plant by modeling and experimental tests on pilot plant and bench scale.