DryVac technology provides a cost effective
integrated process for dewatering and drying, handling both organic and
inorganic waste streams.
In a single operation involving two stages the liquid waste is first mechanically dewatered
and then dried. The DryVac unit
looks like a standard plate filter press. However, plates are replaced by DryVac elastic
envelope modules (DEEMs) which
expand and contract according to pressure applied externally or internally.
Instage onedewatering
takes place very like with a
conventional plate press with conditioned sludge being
pumped into the sludge chambers lined with filter cloths.
Solids are retained in the press and liquid flows out.
The DEEM
is hollow
with elastic walls.
The
DEEM inflates
under internal pressure.
But in stage
two, the drying stage, the DryVac process
is different. In this stage low-pressure steam is used to
inflate the DEEMs and at the same time a vacuum is
applied to the filtrate ports. The cake is squeezed
as the DEEMs inflate, and the combination of heat transferred
to the filter cake and the pulling of a vacuum on the
filter chamber results in the remaining water vapourising
at low temperature. The walls of the expanding DEEMs remain in contact with the sludge
ensuring effective heat transfer. By controlling the duration of the drying stage,
the dry solids of the end product can be carefully and accurately controlled. Because
the cake is much drier
than with a conventional press, the solids drop out
as a dry cake when the press is opened at the end
of the drying cycle.
The process is energy efficient
and there is wide flexibility
of design with the possibility of retrofit to existing presses.
The DryVac system consists of DEEM’s (patent applied
for), steam energy conversion modules, frames and
support units. There is a range of DEEM sizes
(up to 2m x 2m) and press capacity can be as low as
0.06m3 or as high as 18m3 and more. The system is supplied in modular formats for
ease of installation
and to provide maximum flexibility. Fully mobile units
can also be supplied.
Stage 1 - Feed Conditioned sludge is fed
into the chambers with the
feed pump.
Stage
1 Pressure and
Air Blow Pressurised air is introduced
into the steam chamber to
squeeze the cake.
Pressurised air is blown
through the cake to
remove water.
Stage
2 - Drying Steam is applied to the
steam chamber.
Vacuum is drawn on the
'cake' via the filtrate ports.
Discharge Steam and vacuum are
turned off and DEEMs deflate.
