(260e) Characterization of Particle Flow In Inclined Standpipes

Authors: 
van Ommen, J. R., Delft University of Technology


Characterization of particle flow in inclined
standpipes

Lilian de
Martín and J. Ruud van Ommen

Delft University of Technology, Department of Chemical Engineering,
Product & Process Engineering, Julianalaan 136, 2628 BL Delft, The
Netherlands

In
several chemical processes, such as fluid catalytic cracking (FCC), the
presence of several coupled elements (risers, standpipes, cyclones?)
complicates to have a steady operation. Two main limitations are encountered in
these systems that are associated with the standpipes.

The first
one is commonly found operating at high catalyst recirculation rates. In this condition,
an excess of gas can be transferred down the standpipe with the solids. When
this occurs, the regime in the standpipe changes and there is no longer a
well-defined dense phase [1]. At this point, the apparent density and
consequently the pressure build-up in the standpipe decreases, leading in turn
to the air go up the standpipe and a decrease of the collector efficiency [2].
This undesired situation can be avoided increasing the pressure drop across the
standpipe by increasing the apparent density of the solid.

The
second one comes from the bubbles formed in the standpipe due to the aeration
required to maintain the solid circulating. The maximum catalyst flow rate that
the standpipe can handle is limited by the size of these bubbles [3]. This
limitation is especially a problem when operating with inclined standpipes
because the rising bubbles become large at low solids flow rate and low aeration

In this
work we have characterized the catalyst circulation features in a circulating
fluidized bed (CFB) equipped with an inclined standpipe by means of visual
observation, pressure drop and pressure fluctuations. We have specially focused
on inclined standpipes because they are quite often used in industry, but
seldom studied in academia. Moreover, the hydrodynamics behavior in inclined
standpipes is quite different from that in vertical standpipes or horizontal
transport lines.

The tests
were carried out in a CFB consisting in a riser 0.265 m diameter and 5 m tall.
The standpipe has an inclination of 45o, 0.09 m diameter and it is
made of Perspex. The solid fluidized is FCC catalyst with an average particle
size of 60 μm.

[1] J. R. Grace, A. A. Avidan and
T. M. Knowlton. Circulating fluidized beds. Springer 1996.

[2] D. Geldart, N. Broodryk and A.
Kerdoncuff. Studies on the flow of solids down cyclone diplegs. Powder
Technology, 76 (1993) 175-183.

[3] W.-C Yang. Handbook of
fluidization and fluid-particle system. CRC Press 2003.