A foaming problem in an industrial-size deacidifier (packed column) within the ammonia
hydrogen sulfide circulation scrubbing process (AS process) on a specific site is experimentally
investigated. The foamability of solutions is successfully assessed in a small test cell, and the
Bikermann coefficient is calculated to characterize the foaminess behavior. The investigations
revealed that filtration of the real sour water taken from the specific site does not alter foaming
characteristics. Impurities, especially phenol and its derivatives, cresols, are found to highly
contribute to foaminess behavior. Experiments in a pilot plant revealed higher pressure drop
and lower flood point data. Critical spots of foam formation are identified, and design suggestions
for column internals are given.1. Introduction 8867
Foaming can be a serious problem in the process
industry, reducing throughput and separation perfor-
mance or even causing contamination of products due
to takeover of foam from other vessels.
The starting point of this work is a foaming problem
in an industrial-size packed tower (deacidifier) within
the ammonia hydrogen sulfide circulation scrubbing
process (AS process). The pressure drop of this tower is
observed to rise from steady-state conditions for no
apparent reason. Similar deacidifiers on other sites do
not show that behavior, possibly because of different
sour water compositions, caused by different coal com-
positions or carbonization conditions. Impurities formed
during the carbonization process can cause foaming, and
their contribution to foamability is so far unknown. The
deacidifier is supposed to be redesigned, and maximum
operating parameters (i.e., flood point data) using this
particular sour water with its specific impurities are
requested by the engineers. Studies about foaming in
deacidifiers of the AS process cannot be found in the
literature; an experimental investigation is therefore
necessary. Because of the difficult toxic system and the
required complex equipment, the experimental results
achieved in this academic research are of rare value.
The following chapter gives an overview of foam in
general, foam stabilization due to different forces and
mechanisms, and, finally, foaming in columns. After
that, the determined composition of the sour water will
be presented and its foamability will be assessed in a
small test cell, resulting in a coefficient characterizing
foamability. The contribution of the impurities to foam-
ing behavior will be roughly estimated by experiments
with synthetic solutions.
Pilot-plant experiments with the packing used in the
redesigned tower are carried out to obtain pressure drop
and flood point data. The transferability of test-cellexperiments to the real column is evaluated. The
hydrodynamics inside the column are observed and
presented in different pictures taken from movies. After
the identification of critical spots of foam formation,
design suggestions for column internals are given.
2. Foam Theory
Two foam types are distinguishable. Kugelschaum lies
directly on the surface of the liquid (Figure 1) where,
because of a high liquid fraction (1 æ), different
bubbles do not interact. The surface forces are respon-
sible for the formation of spherical bubbles. Age of foam
rises with height, and gravity forces lead to draining of
the liquid. Thus, the liquid films (lamellae) piding the
different bubbles are thinned and the Kugelschaum is
converted to polyederfoam. In this area coalescence (film
rupturing) prevails. In polyederfoam, three lamellae
intercept in a Plateau border with an angle of 120°
between the lamellae (Figure 2).
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