Critical factors in understanding the mechanism of ash agglomeration in fluidized bed systems

Aditi B. Khadilkar, Peter L. Rozelle, Sarma V. Pisupati

Research output: Contribution to conferencePaper

1 Scopus citations

Abstract

A simple mathematical model was developed to study ash agglomerate growth in fluidized bed systems. The model can trace the temporal evolution of ash particle size distribution in the system. It evaluates every possible two-particle collision for sticking based on the Stokes' criterion. Agglomeration occurs when there is viscous dissipation of the particle kinetic energy by the slag-liquid formed on ash particles. Several chemical and physical parameters such as fuel chemistry, ash surface properties, slag rheology and particle hydrodynamics affect agglomeration. An integrated model capable of making predictions based on both the fuel composition (chemistry) as well as the reactor configuration (physics), under a given set of operating conditions has been developed as a useful tool for the industry. It would help to predict and prevent agglomeration during combustion and gasification in fluidized beds, including advanced combustion technologies such as chemical looping combustion. The slag-liquid formation tendencies were studied through the use of FactSage™ thermodynamic equilibrium simulation software. Using this technique, the slag-liquid formation tendencies for Pittsburgh seam coal were predicted under both combustion and gasification gaseous atmospheres and experimentally validated using TGA/DTA, XRD and Thermo mechanical analysis (TMA). The hydrodynamics were studied through the use of MFIX-Multiphase Flow with Interphase eXchanges, a computational fluid dynamics software. The kinetic theory of granular flow was utilized to calculate a distribution of collision frequencies for a given particle size distribution. Using this mathematical modeling approach, theoretical predictions of particle hydrodynamics and particle growth kinetics were made. The simulations were run for combustion and gasification of density-separated Pittsburgh seam coal fractions in a laboratory-scale bubbling fluidized bed reactor. This unique two-particle collision model tracks the changes in the number of particles and simultaneous changes in particle dynamics with time. It uses Eulerian methods to compute the hydrodynamics but at the same time considers particle-level variations in the system by modeling particle collisions. The use of Eulerian methods helps to decrease the computational demands over discrete element methods while the collision model helps to maintain accuracy. The model has enabled the consideration of interlinked effects of particle hydrodynamics with particle size increase. Broadly, it also facilitates more accurate predictions through the mathematical integration of chemical and physical parameters that influence agglomeration.

Original languageEnglish (US)
StatePublished - Jan 1 2014
Event31st Annual International Pittsburgh Coal Conference: Coal - Energy, Environment and Sustainable Development, PCC 2014 - Pittsburgh, United States
Duration: Oct 6 2014Oct 9 2014

Other

Other31st Annual International Pittsburgh Coal Conference: Coal - Energy, Environment and Sustainable Development, PCC 2014
CountryUnited States
CityPittsburgh
Period10/6/1410/9/14

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology
  • Geotechnical Engineering and Engineering Geology

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    Khadilkar, A. B., Rozelle, P. L., & Pisupati, S. V. (2014). Critical factors in understanding the mechanism of ash agglomeration in fluidized bed systems. Paper presented at 31st Annual International Pittsburgh Coal Conference: Coal - Energy, Environment and Sustainable Development, PCC 2014, Pittsburgh, United States.