(532e) Scale-up of Oscillatory Baffled Reactors (OBRs)

Scale-up
of oscillatory helically baffled reactors (OHBRs)

Safaa M.R. Ahmed, Anh N. Phan,
Adam P. Harvey

School
of Chemical Engineering and Advanced Materials, Newcastle University

Newcastle
upon Tyne - NE1 7RU

Mobile:+44
7774101215

E-mail: 
s.m.r.ahmed@newcastle.ac.uk

Keywords:
Oscillatory baffled reactor, scale-up, residence time distribution

Abstract

An
Oscillatory Baffled Reactor (OBR) is an intensified design of continuous plug flow
reactor (PFR) in which plug flow behaviour can be achieved at very low net
flows (laminar flow regime). OBRs consist of tubes with periodically spaced
baffles of various designs (orifice, helical, integral etc. baffles). There is
a net flow through the reactor, and a superimposed oscillatory flow. The
oscillatory flow interacts with the baffles to produce flow structures (usually
vortices) that provide mixing. The mixing in the OBR is therefore independent
of the net flow. As a result, the OBR’s niche application is to operate “long”
reactions in continuous mode. This is usually impractical in conventional
tubular reactors.

Scale-up
in conventional reactors, i.e. stirred tank reactors, is unpredictable due to
the non-uniform mixing at large scale, leading to large variations in
concentration, temperatures etc. This means that optimum conditions obtained
from laboratory scales cannot be directly used at large scales, therefore
process development/ product-to-market time would increase. However, scale-up
of OBRs should be more predictable, as the flow structures can be reproduced
across length scales.

Recent
studies on oscillatory helically baffled reactors (OHBRs) at small scales
(millilitre volume) found that the helical baffled design could provide high
degree of plug flow across a wide operating window due to the  combined effect
of vortex formation and swirl flow. It was found that the behaviour of
residence time distribution remained the same at all tested scales (10mm
diameter to 25mm diameter, corresponding to volume 0.078L to volume 0.834L)
when the similarity in geometric and dynamic parameters was maintained. The
degree of plug flow was quantified in terms of number of tanks-in-series (N). At
a fixed geometry, a scale-up correlation was established and validated over a
range of operating conditions such as oscillatory conditions (Strouhal number, St,
and oscillatory Reynolds number, Re_o) and the velocity ratio
of oscillatory flow and net flow (ψ).

Where,