PROCEDE ET EQUIPEMENT DE NETTOYAGE D'EMANATIONS INDUSTRIELLES

PROCESS AND EQUIPMENT FOR CLEANING INDUSTRIAL FUMES

Abrégé anglais

"PROCESS AND EQUIPMENT FOR CLEANING INDUSTRIAL FUMES"
A b s t r a c t
In a process and equipment for cleaning industrial fumes
of the type wherein the fumes are submitted to a first washing
stage in a cyclonic-scrubber operating as a saturator, wherein the
fumes, flowing along a spiral path, are sprayed by a washing
liquid, and to a second stage, wherein the fumes, leaving the
saturator, flow through a Venturi-scrubber, the cleaning efficiency
is considerably improved, both with regard to dusts collection and
chiefly to the capture of polluting gases (such as SOx, NOx, C12,
F , and so forth), by providing, downstream the Venturi-scrubber, a
further washing stage in a second cyclonic-scrubber.

Revendications

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A process for industrial fumes or gases
cleaning, in which the fumes and gases are submitted to a
first washing with water in a first cyclonic-scrubber
operating as a saturator, and then to a second washing with
water in a Venturi scrubber, wherein:
(a) the fumes or gases exiting the Venturi scrubber
are washed with water in a second cyclonic-
scrubber;
(b) the exhaust water exiting the first cyclonic
scrubber is purified and sent to a settling tank;
(c) the second cyclonic-scrubber is fed with the
purified water exiting said settling tank;
(d) the water exiting the Venturi scrubber, is fed to
the first cyclonic scribber, and
(e) the exhaust water exiting the second cyclonic
scrubber is fed to the Venturi scrubber.
2. An e~uipment for industrial fumes or gases
cleaning, comprising:
(a) a first cyclonic scrubber in which the fumes or
gases are washed with wash water;
(b) a Venturi scrubber downstream of (a), in which the
fumes or gases are also washed with wash water;
and
(c) a second cyclonic scrubber downstream of (b), in
which the fumes or gases are ~urther washed with
wash water;
wherein said first and said second cyclonic scrubbers are
two discrete axially superposed sections composing a single
cyclonic washing tower, each individual section having a
sloped bottom wall for collecting and draining the wash

water.
3. This equipment according to claim 2, further
comprising an axially installed spray tube for each section
of said cyclonic washing tower to deliver radial water jets,
and fume- or gas-inlet fitting in each of said sections,
said fitting being arranged in such a manner as to impart a
helical motion to the fumes or gases along the respective
washing tower section.

Description

~19097
,
-- 1
"PROCESS AND EQUIPMENT FOR CLEANING INDUSTRIAL FUMES"
This invention concerns industrial fumes cleaning and more
specifically the capture of polluting dusts and gases (such as SOx,
NOx, C12, F , and so forth).
Ai,long known processes and equipments for the same purpose,
~hose disclosed by Italian Patent N. 9~1,166 and 1.045.466 to the
same Applicant's name, can be mentioned.
In such patents process and equipment for cleaning fumes
at least partially combustible and carrying dusts (essentially
metal oxydes) and chiefly the fumes developed by steelmaking are
described.
The said processes consist of a post-combustion stage of
combustible gases and a dust collection stage by washing (with
water or other liquids) in two steps: first step of pre-washing in
a saturator and second step of end washing in a Venturi scrubber.
In the frame of the processes and equipments subject
matter of the above mentioned Patents, a washing tower is
described, divided in two separate parts by a baffle, having the
following features:
- a tangential fitting for the inlet of the fumes to be cleaned in
the upper portion of the washing tower, which operates as a
saturator;
- a header with nozzles spraying water in cross-current to the
fumes rising according to spiral flow pattern, as in a cyclone
washer;
- a Venturi scrubber outside the tower and connected to this latter
by two elbow ducts: the upper one between the saturator outlet
and the convergent portion of the Venturi pipe, the lower between
the divergent portion of the Venturi pipe and the tangential
inlet into the lower part of the washing tower;
~k '

1319097
- a tangential inlet for the cleaned fumes in the lower
portion of the tower in order to collect the finest
droplets.
Inasmuch as the industrial fumes, especially the
flue gases from combustion of coal and/or fuel oil, e.g. in
the production of steam and/or electrical power, contain
dusts, prevailingly metal oxides, and acid gases, the
industrial and social importance of any improvement of the
cleaning degree become evident.
In accordance with the invention, it has been
discovered that if a third cyclone-type washing stage is
added to the process and equipment as disclosed in the above
said Italian Patents downstream the Venturi scrubber,
further improvements of the cleaning degree are achieved
with minimum additional operating costs and no increase of
washing water cansumption.
ThereEore, the present invention provides a process
for industrial fumes or gases cleaning, in which the fumes
and gases are submitted to a first washing with water in a
cyclonic-scrubber operating as a saturator, and then to a
second washing with water in a Venturi scrubber, wherein:
(a) the fumes or gases exiting the Venturi scrubber
are washed with water in a second cyclonic-
scrubber;
(b) the exhaust water exiting the first cyclonic
scrubher is purified and sent to a settling tank;
(c) the second cyclonic-scrubber is fed with the
puri~ied water exiting said settling tank;
(d) the water exiting the V~nturi scrubbar is fed to
the first cyclonic scrubber, and
(e) the exhaust water exiting the third cyclonic
scrubber is fed to the Venturi scrubber.
The invention also provides an equipment for
industrial fumes or gases cleaning, comprising:

~3~9097
(a) a first cyclonic scrubber in which the fumes or
gases are washed with wash water;
(b) a Venturi scrubber downstream of (a), in which the
fumes or gases are also washed with wash water;
and
(c) a second cyclonic scrubber downstream of (b), in
which the fumes or gases are further washed with
wash water;
wherein said first and said second cyclonic scrubbers are
two discrete axially superposed sections composing a single
cyclonic washing tower, each individual section having a
sloped bottom wall for collecting and draining the wash
water.
The typical features and advantages of this
invention are cleared up by the following detailed
description, reEerring to the accompanying drawing, which
shows diagrammatically and exemplary embodiment of the
equipment according to the invention.
Having now reference to the drawing, a washing
tower 1 is shown, partitioned by a sloping baffle 2 in an
upper washing section lA and a lower washing section lB.
The baffle 2 is sloping in æuch a way as to convey
water falling on it to a drain 3. The reference numeral 4
indicates the inlet of the fumes to be cleaned and the
reference numeral 5 indicates the outlet from the section lA
for the fumes processed inside the same section.
The washing of the fumes is made by a æpraying
pipe 6 which delivers radial jets of water, fed through the
pipe 8 by the pump 7.
From the outlet 5 the fumes go through an elbow 5A
into the Venturi scrubber 9 consisting of an upstream, or
convergent,

i319~97
section 9B~ a narrow section 9A to which wash water is fed through
the pipe 10 by the pump 11 and a downstream, or divergent, section
9C.
From the elbow 13A of the Yenturi scrubber the water
separated due to centrifugal effect is collected and discharged
into a tan~ 12 from which it is drawn by the pump 7.
The fumes or gases from the outlet 13 of the Venturi
scrubber 9 enter the lower section 18 of the washing tower 1 where
a washing process, almost in the same way as in the upper section
lA, is carried out by the spraying pipe 14 fed with pressure water
through the pipe 15 by the pump 16.
The water collected on the sloping bottom 17 o~ the
section lB feeds the pump 11 and the cleaned fumes intaken by the
fan 18 through the duct 20 are exhausted to the atmosphere through
the stack 19.
The wash water discharged from the first cyclone washing
device (section lA) goes to a tank 21, wherein it is preferably
neutralized with an alkaline reagent, e.g. lime, and is sent to a
settliny and washing tank 22 whose water feeds the pump 16 through
the reservoir 23, whilst the sludges are removed and disposed of in
the usual way.
Finally through the tube 24 it is possible to restore the
washing water.
From the above stated description two important features
of this invention appear clearly:
a) an improvement of the cleaning degree of the fumes, which
approach 99-99,5X referred to the dusts and 92-98X referred to
the polluting gases and vapours, whilst by the prior art a
cleaning degree of g8-99% for the dusts and 60-92% for the gases
and vapours was achieved;

- l3~as7
h) a subs~antial saving of water9 as the wash water is recycled
from the one to the other washing stage, clear water being
used in the final high-level cleaning stage.
In this connection, it should be observed, however, that, if
necessary, water recycled to the various stages can undergo
particular cleaning treatments.
Concerning the operation and process conditions, reference can
also be had to the aforementioned Italian Patents, since the third
stage of the cyclone-washing takes place in a way similar to that of
the first washing stage.
In order that the features and advantages of the invention may be
better understood, two practical embodiments of the relevant proce-
dure will be illustrated hereinafter.
EXAMPLE 1
The apparatus and the procedure of the invention are used to purify
the fumes coming from a coal-fired power station: a typical
concentration of dusts (ash) in the fumes is in the order of
magn;tude of 20,000 milligrams (mg) per normal cubic meter (Nm ).
By adopting the installation and the procedure outlined hereinbefore,
the final dust concentration in the flues drastically drops to as
little as 40 mg/Nm .
By comparison, with the prior art installations and procedures,
including those referred to above, the dust-stripped flues still
contained as many as 100 mg/Nm3 of dusts. This means that the
purifying efficiency of the procedure and installation accord~ng to
the present lnvention is more than twice that of the prior art
approaches: stated another way, the degree of dust removal is as high
as 99,8% with the instant process and installation, as compared with
99,5% obtainable with the prior art methods and installations.

. ~319~7
As regards the removal of sulphur dioxide, the prior art arrived at
removing, from an initial S02 content in the flues of 4,000 mg/Nm ,
only an amount corresponding to a final S02 concentration of
800-1,000 mg/Nm , corresponding to 80%-70% removal, respectively,
whereas the process and the installation according to the present
invention permit to obtain final concentrations of sulphur dioxide as
low as 400 mg/Nm , corresponding to a 90% removal.
Also in this case, therefore, the removal efficiency of the process
and installation according to the present invention is at least twice
that obtainable with the prior art teachings.
EXAMPLE 2
. . _
The fumes ex;ting a purification installation for Fe-Si alloys
usually contain 15,000 mg/Nm of dusts: these can be reduced, with
the process and installation according to the invention, to as few as
30 mg/Nm , that which corresponds to a degree of stripping as high as
99,8%, as compared with 99% removal of the prior art, that is, 150
mg/Nm3: it is observed, incidentally, that the dust removal difficul-
ty is the more serious~ the smaller the dust particle size is.
As regards gaseousSiF4, from dn initial content of 500 mg/Nm , the
invention permits to arrive at as few as 5 mg/Nm3, that which is
tantamount to say that the remoYal efficiency is at least 99,0%, as
compared with the 95% removal of the prior art, that is 25 mg/Nm ~f
residual SiF4.
Modifications and changes can be introduced in the process and the
installation according to this invention without depar~ing from the
scope thereof: if so desired or nècessary, for example, it is well
possible to supplement alkaline reagents not only to the tank 21, but
also to the reservoir 23 and to the tank 12.

Dessin représentatif