Pushing the boundaries of CFD simulations with ANSYS FLUENT. Investigation of 2-phase evaporative reacting flows in micro-scale.
Nowadays, there is a growing need to investigate thoroughly complex physical phenomena taking place in large scale engineering applications in order to optimize their design and increase their efficiency. However, this need is often not met due to the inability to measure small scale phenomena in real-time or to reproduce realistic operating conditions in experimental laboratories. A similar problem arises in the petroleum industry, especially the Fluid Catalytic Cracking reactors (FCC), where the conversion of heavy hydrocarbons to lighter ones, relies on the mixing and evaporation of injected gasoil droplets and their collisions with catalytic particles inside the reactor, i.e. a chaotic and unsteady phenomenon, which starts from the micro-scale and affects the large scale behaviour. In these reactors, product selectivity can vary greatly due to petroleum composition uncertainty, while catalyst deactivation owed to non-evaporated liquid which blocks the catalyst pores contribute to the decrease of FCC unit efficiency. Injection strategy may benefit from the investigation of single droplet–catalyst collisions and the accurate prediction of products yield.
For this reason, ANSYS FLUENT CFD 2D/3D simulations of single droplet-catalyst and droplet-catalyst cluster collisions under different collision scenarios were performed. The non-isothermal, surface reacting two phase flow was simulated with the standard models of ANSYS Fluent accompanied by the development of an interphase evaporation model and the extension of the provided basic grid refinement technique towards a dynamic one, both using User Defined Functions (UDFs). Grid refinement can now be applied at any distance from any iso-surface. The analyzed collision scenarios gave an important insight into the droplet heat-up and lifetime, as well as the formation underlying physics of cracking products. Moreover, the influence of important process parameters as such of temperature, particle size of the solid catalyst and the initial impact velocity on both the quantity of the produced chemical compounds as well as the collision outcome were examined. The results showed that collisions between droplets and hot catalysts of equal size are expected to improve conversion, while also limit the possibility of liquid-pore blocking.
This is one of the very first models that investigate such complicated physical phenomena at extreme real-life reactor elevated temperature conditions. With the aid of the developed model, the estimation of cracking products yield is available. Any possible collision scenario can be simulated. Important computational time is saved by the implementation of the dynamic grid refinement technique. This work was awarded in the ANSYS Hall of Fame 2016 international competition with one the Best Award in Show: Academic.
- Nikolopoulos1,2, I. Malgarinos1,2, M. Gavaises2
1Centre for Research & Technology Hellas /
Chemical Process and Energy Resources Institute (CERTH/CPERI)
4th km. Ptolemaida Mpodosakio Hospital Area, GR-50200 Ptolemaida
2School of Engineering and Mathematical Sciences, City University London, Northampton Square, EC1V 0HB London, UK
Dr. Nikolopoulos Nikos studied Mechanical Engineering at NTUA from 1996 till 2001, while afterwards made his PhD at Laboratory of Aerodynamics, Fluid Section under the supervision of Prof. Bergeles. Since 2007 he works for CERTH/CPERI and is a Senior Researcher working on the field of CFD and last few years on Mechanical stresses. In 2013 he was awarded with a Marie-Curie Fellowship (Individual) in CITY University of London. He leads a group of 5 people working on those fields of research.