(485a) Real Residence Time Distribution of Solids from Lagrangian Simulation in Openfoam

Real residence time
distribution of solids from Lagrangian simulation in OpenFOAM

Yujian Sun, Milorad P. Dudukovic*

Chemical Engineering Reaction
Laboratory, Washington University in St. Louis, St. Louis, MO 63130

Abstract:

The classic tracer injection-response method to measure residence
time distributions (RTD) is restricted to the close-close boundary
condition which is not met by many practical processes. On the other
hand, most Lagrangian codes like OpenFOAM
has an "age" attribute for individual particles which
records the time spent in the system by each particle. By proper
statistical analysis of data, an age distribution function (ADF) of
solids in the whole system may be obtained. However, such ADF differs
from the real residence time distribution (RTD) of solids in the
specific zones of interest, e.g. the reaction and the regeneration
zones in a circulating fluidized bed reactor. To obtain the solids
RTD in the pre-defined zone, another attribute called "Tres"
(short for residence time) needs to be introduced for individual
particles, in a way similar to how "age" is defined.
However, what is different is the criterion when the time should be
incremented. For Tres, it should start to increase when the position
of the particle "hits" the pre-defined boundary from
outside of the zone to inside, and stop to be incremented when the
particle passes the boundary again leaving the zone. With Tres of
statistically significant amount of particles gathered, the real
solids RTD may be calculated by statistical means which can be
further used in reaction engineering analysis. This work explores
this potential application of Lagrangian simulation, making use of
and adapting the Lagrangian codes in OpenFOAM, to obtain solids RTD
in the riser and the regenerator of a circulating fluidized bed
reactor.