Dewatering and drying characteristics of Coffee Pulp
Abstract
The major constraint in the utilisation of coffee pulp is
its high moisture content. For easy storage, the moisture content
of the pulp needs to be lowered to about 15% wet basis. A two
stage process comprising mechanical Dewatering followed by drying
is effective in removing water from the coffee pulp. However,
to design appropriate equipment for dewatering and drying coffee
pulp, the dewatering and drying characteristics of the pulp need
to be known. For this purpose, studies on dewatering and drying
of coffee pulp were undertaken in order to identify and relate
the parameters important to these two stages of processing.
The dewatering process was investigated by subj ecting coffee
pulp samples to consolidated drained (CD) triaxial compression
tests. Four levels of constant cell pressures and continuously
increasing axial pressure were used to vary the dewatering
conditions.
Studies into the drying of coffee pulp were undertaken in
a ventilated laboratory oven. Drying temperatures were between
75°C to l500C because coffee pulp dries fastest within this
range, besides the ease to achieve constant temperature and
relative humidity in the oven. Drying experiments were conducted
at four levels of initial moisture content obtained by mechanical
removal of 0%, 5%, 10% and 20% of the fluid from four separate
coffee pulp samples.
The results indicate that the behaviour of coffee pulp
collected at different times of the picking season is generally
very diverse even when subjected to similar dewatering
conditions. For the increasing pressure conditions the
relationship between expressed fluid and applied pressure was
exponential. No relationship was found between expressed fluid
and rate of applying pressure because the rat.t er varied in
unpredictable manner. However when under constant pressure an
exponential relationship was identified between expressed fluid
and pressing duration. Empirical equations for these
relationships were developed.
A linear relationship was found to exist between expressed
fluid and reduction in sample volume. However, the reduction in
sample volume is bigger than the corresponding expressed fluid.
The drying studies culminated with the development of an
empirical equation for predicting the moisture content of coffee
pulp during drying. However, for this equation to be applicable
in the field, further work is required to establish the
equilibrium moisture content at different conditions of
temperature and relative humidity.
The empirical equations developed for both dewatering and
drying of coffee pulp seem to be dependent on other unknown
factors inherent to the samples besides those covered by this
study. These equations can be refined by studies into the
physical and biological properties of coffee pulp.
Citation
Mburu, J.K(1991). Dewatering and drying characteristics of coffee pulpSponsorhip
University of NairobiPublisher
Department of Agricultural Engineering, University of Nairobi
Description
Msc- Thesis