TRADUCTION NON-DISPONIBLE

PROCESS FOR THE PREPARATION OF A SUBSTANTIALLY HOMOGENEOUS LIME WATER SOLUTION

Abrégé anglais

CANADIAN PATENT APPLICATION
OF
STIG ARVID HENRIKSON
FOR
PROCESS FOR THE PREPARATION OF A
SUBSTANTIALLY HOMOGENEOUS LIME
WATER SOLUTION
Abstract of the Disclosure
In the preparation of homogeneous lime water solution for use
in the purification of waste water, a lime water suspension is used
as starting material. The lime water suspension is supplied at the
bottom of a compartment in which it is caused to rise in order to
leave at the upper part, while passing lamellas during its upward
movement. The lamellas are arranged in such a way that they will
create a sludge zone at their lower part in the compartment, in which
zone the rising lime suspension is filtered, whereas they create at
their upper part in the compartment a clarification zone in which
fine particles are separated.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for the preparation of a substantially homo-
geneous lime water solution intended for use in the purification
of waste water and like liquids, the starting material for the
homogeneous lime water solution consisting of a lime suspension,
comprising introducing the lime suspension at the bottom of a
compartment in which it is caused to rise in order to leave at
the top thereof, said lime suspension during its upward flow
being caused to pass lamellas which create a sludge zone at
their lower end in the compartment, in which zone the rising
lime suspension is filtered, while said lamellas create at their
upper end in the compartment a clarification zone in which fine
particles are separated.
2. A process as claimed in claim 1, wherein the sludge
zone for the rising lime suspension is obtained in that the
surface load on the lamellas is substantially higher at the
lower part than is the surface load on the lamellas at the
upper part forming the clarification zone.
3. A process as claimed in claim 2, wherein the surface
load on the lamellas at the lower part forming the sludge zone
is about twice the surface load on the lamellas at the upper
part forming the clarification zone.
4. A process as claimed in claim 3, wherein the surface
load on the lamellas at the lower part forming the sludge zone
is about 2.5 m3/m2/h while the surface load on the lamellas at
the upper part forming the clarification zone is about 1.25
m3/m2/h.

5. A process as claimed in claim 1, claim 2 or claim 3,
wherein the lime sludge which flows away from the lamellas and
sinks to the bottom of the compartment is wholly or partly
recycled to be incorporated with the lime suspension serving as
starting material.

Description

~lQ~3~33
The present invention relates to a process for the
preparation of a substantially homogeneous lime water solution
intended for use in the purification of waste water and like
liquids, the starting material for the homogeneous lime water
solution consisting of a lime suspension. Characteristic of this
process is that the lime suspension is introduced at the bottom
of a compartment in which it is caused to rise in order to leave
at the top thereof, said lime suspension during its upward flow
being caused to pass lamellas which create a sludge zone at
their lower end in the compartment, in which zone the rising lime
suspension is filtered, while said lamellas create at their upper
end in the compartment a clarification zone in which fine par-
ticles are separated. By means of this invention there is
obtained a lime water preparation which, on one hand, makes
complete use of the flocculating properties of the lime so that
only a minimum amount of lime will have to be supplied to achieve
optimum flocculation and, on the other hand, prevents inconvenient
carbonate-formation, etc., which would produce deposits on
machine equipments, tanks, conduits and pipes. There is also
gained the advantage that the rest content of calcareous small
particles in the effluent purified water will be very small.
The invention will be more fully described hereinbelow
with reference to the accompanying drawings which illustrate the
apparatus for carrying out the process and in which:
Fig. 1 schematically shows a complete purification
plant including the apparatus for carrying out the process;
Fig. 2 shows in greater detail and on a larger scale a
section of the apparatus of the invention, i.e. a lime-water
- 2 - ~
X~

110~3~33
preparing apparatus; and
Fig. 3 is a plan view of the same apparatus.
The purification plant according to Fig. 1 comprises
six series-connected tanks 1-6 which, in turn, are passed by
the water being purified. The tank 1 includes a sand trap and
a machine-cleaned screen. The tank 2 is an aeration tank to
which active sludge is added. The tank 3 is an intermediary-
sedimentation tank. To the tank 4 there is supplied the lime
water solution obtained by the process of the present invention,
in which the lime water solution has been prepared by the
apparatus designated 7. Reference numerals 5 and 6 designate
respectively a flocculation tank and a flotation tank from which
latter the purified water issues. The purification plant may of
course be modified in various ways without affecting the process
of the present invention.
The apparatus 7 comprises the lime dissolving means 8
and the lime water preparing means 9. The lime dissolving means
8 includes a dissolving vessel for dissolving dry, slaked or
quick lime. In this vessel a stirring means 10 mixes the lime
into the added dissolving water. As dissolving water there may
be used the effluent purified waste water having a pH of 10-12,
biologically purified waste water or tap water. The amount of
dissolving water is to be about one litre water per 1.7 g lime.
From the dissolving vessel 8 the lime suspension is
allowed to flow to the lime water preparing means ~ into which
it passes through the pipe 11 and enters centrally at the bottom
of conical compartment 12 serving as a lime sludge hopper. From
this compartment the lime suspension flows upwardly while passing
- 3 -

3~33
a number of lamellas 13 and 14, where-upon it flows away on
either side of a spillway crest 15 to grooves 16.
The lamellas 13 and 14 are of varying length. In the
case shown in the drawings every second lamella 13 is long where-
as intermediate lamellas 14 are short. Thus, the lamellas 13are 2 m long and spaced from each other by a distance of 15 cm,
while the lamellas 14 are only 1 m long but equally spaced by a
distance of 15 cm.
The zone covered by the long lamellas 13 alone, i.e.
the lower half of the pack of lamellas, has been dimensioned so
as to form a stationary sludge zone in this area. The upwardly
flowing lime suspension is filtered by this sludge zone. The
j lamella area which is situated above said sludge zone and has
a double number of lamellas 13 and 14 forms a clarification
zone where fine particles are separated as the lime water flows
upwardly.
The sludge zone for the rising lime suspension is
formed because the surface load on the lamellas 13 is substan-
tially higher at the lower part than is the surface load on the
lamellas 13 and 14 at the upper part forming the clarification
zone. Thus, the surface load on the lamellas 13 at the lower
part forming the sludge zone is about twic~ the surface load
on the lamellas 13 and 14 at the upper part forming the clarifi-
cation zone. The surface load on the lamellas 13 at the lower
part forming the sludge zone should preferably be about 2.5
m3/m2/h, while the surface load on the lamellas 13 and 14 at the
upper part forming the claraficiation zone should preferably be
about 1.25 m3/m2/h. The surface load is calculated on the basis

110~383
of the projected surface of the lamellas.
The sludge, which runs along the lamellas and is
collected in the bottom cone 12, has a density which is about
10-15 times that of the sludge water in the sludge zone and it
occupies about a tenth of the space between the lamellas 13.
The lime sludge collected in the bottom cone 12 is partially
recycled by pumping to the lime dissolving vessel 8 while
remaining lime sludge runs off by gravity to the units before
the point of addition of lime water to the waste water (for
instance the pre-treatment apparatus) at the waste water treat-
ment plant. The volume of lime sludge recycled to the dissolving
vessel 8 must be practically determined in every particular case,
depending int. alia on the amount of sand and inpurities in the
lime used. Reference numeral 17 designates the lime sludge
pump which returns lime through the pipe 18 to the lime
dissolving vessel 8 and which returns lime through the pipe 19
to the pre-treatment apparatus.
The dosage of lime takes place at 20 and the dosage
of lime water solution to the waste water takes place at 21.
The invention is not restricted to the embodiments
described above and shown in the drawings but may be modified
within the spirit and scope of the appended claims.
_ 5 _