Note: Descriptions are shown in the official language in which they were submitted.
1037Z27
r~his inveIltion is concerned with improvements in or relat-
ing to a proc~ss ~or the purii`ication of flue gas and other
g~ases which contain sulphur clioxide.
In this connection reference can be made to the flue ~rases
from coal-fired power stations from which, in order to prevent
pollution of the atmosphere, sulphur dioxide in particular must ~ -
be removed, but other gases to be ~Ln into consideration are
for example the waste gases from refuse incinerators, which can -
contain inter alia hydrogen chloride, or the waste gases from
10. moulding operations which may contain phenol and formaldehyde.
i~; Hydrogen fluoride, dust and other inert,solid particles can
also be removed from flue gases and waste gases in accordance
with the process of the invention.
It is known for the removal of sulphur dioxide and the
other above-mentioned materials from flue gases and other
gases to bring the gas into contact with a circulating wash-
ing fluid. The washing fluid contains calcium carbonate and/or
calcium hydroxide as well as water. During the circulation
calcium sulphate and if appropriate further difficultly soluble
20. and/or insoluble materials are separated from the washing
~ fluid. ~he substitution of the calcium separated from the
; circulation takes place as a rule in that milk of li~e is
introduced into the circulation in the appropriate amount.
The known process has the disadvantage that the purifi- ;
cation effect is insufficient, for example only about 7C~o
of sulphur dioxide is removed from a normal flue gas. In
; addition deposits are formed in the pipes and vessels in
- which the circulation of the washin~ fluid takes place, the
deposits consisting substantially of calcium carbonate.
.
30. ~hese deposits considerably impair and make difficult the
operation of the purification plant and reduce its efficiency
and the degree of utilisation of the introduced lime.
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1037227
~" It is an object of the invention to provide a process in which
- these disadvantages are avoided.
According to the invention there is provided a process for the
removal of sulphur dioxide from flue gas and other waste gas in which the
gas is brought into contact with a circulating washing fluid having a pH
of 8 or more before contact and less than 7 after contact, said washing
fluid containing calcium carbonate, calcium hydroxide or a mixture thereof
and water, introducing air into said washing fluid to oxidize calcium
sulfite formed as a result of said contact, separating from said washing
fluid subsequent to said introduction of air calcium sulphate and any
n;. .,
- further materials which are insoluble or have a low solubility and regener-
ating said washing fluid by only adding thereto calcium oxide or a mixture
of calcium oxide and chloride ion releasing compound and where required
. water.
` Accordingly in that only calcium oxide, in place of milk of lime,
: is added to the washing fluid, the purification effect of the process is
- enhanced and a greater portion of the sulphur dioxide contained in the gases
is removed. When chloride ions are present in the circulation up to 99%
of the sulphur dioxide contained in the gases can be removed, and in
n addition, any precipitation, particularly precipitation of calcium carbonate,
- in the apparatus in which the circulation of the washing fluid takes place
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: is substantially completely avoided and the introduced lime is substantially
completely utilized.
The introduction of chlorine ions into the washing fluid suitably
takes place through the addition of calcium chloride. Other chlorides or
- hydrochloric acid can however be added. ;
An optimum purification effect and the minimum deposition are
attained when the pH value of the washing fluid before contact with the gas -
` amounts to 8 or more and the pH value of the washing fluid after contact
` 30 with the gas amounts to less than 7, preferably 6 to 7.
C ~ - 2 _
. 1037227
~ A part of the washing fluid can be extracted from the circulation
.- preferably after the pre-separation of the solid materials. ~lis extraction
:: is particularly suitable when gases are purified which have a high content ;
. of hydrogen
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:: 1037ZZ'7
chloride. In -this cc~se, -through the withdrawal of washing fluid
from tne circulating fluid chlorine ions are removed from the
circulating fluid.
~ he solid materials separated from tlle circulating fluid
can be ~l~ther treated by heating to a gypsiferous mixture.
According to the composition of the waste gases to be purified
the separated solid matter contains a more or less high pro- ;
portion of calcium sulph~lte. r~he gysiferous mixture can be
further treated by the addition of filling materials and/or
10. binding materials to form structural material, for exarnple
bricks. ~he filling material can be fly ash, for example fly
ash which has been separated from flue gas before the flue gas
is purified by the process in accordance with the invention.
One embodiment of the process according -to the invention
is described below by way of ex~mple with reference to the
accompanying drawings.
~ he gas to be purified enters at 2 into the purification
vessel 1 and leaves it at 3. In the purification vessel 1 there
can be used as the countercurrent washer illustrated in the
.,~ ... .
20. drawing any known device which serves the purpose of bringing ;
the gas to be purified into contact with a washing fluid.
Particularly well suited for this purpose are Venturi-Washers
- in which the washing fluid is finely atomised and brought into
very close contact within the gas to be purified. ~urther -;
; devices can be arranged in front of the gas inlet 2, for example
devices for the cooling of gases, devices which serve the
.
purpose of removing materials from the gas, the removal of
which is not effected by the process according to the present
invention and also devices for increasing pressure or speed.
30. In addition kno~ndevices can also be attached to the gas out-
let 30 `
Circulation of the washing fluid commences at 4. At the
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~037Z27
outlet 4 the pII value ol the washing fluic' is measured ~y means
of a measuring instrurneIlt 5. '~he washing fluid flows from the
outlet 4 tnrougll a conduit 6 to a mixing vessel 7. A metering
device 8 is arranged above the mixing vessel 7. ~he metering
device 8 serves the purpose of introducing burnt lime in the
requisite amount into the mixing vessel 7. Additionally air
ca-n be introduced into the mixing vessel 7 through a conduit
9. ~he washing fluid flows from the mixing vessel 7 through
a pipe 10 into a separator 11. ~he separator 11 can for
00 example be a double-jaeketed depositing separa-tor- Above the
separator 11 is a metering device 12 for introducing ealcium
chloride in the requisite amount into the washing fluid in the
separator. The washing fluid freed from a portion of solid
material ir the separator 11 flows through a conduit 13 and
: . .
a pump 14 back to the purification vessel 1 and i~ sprayed
into that at 15. A measuring inst~nent 16 is provided for
measuring the pH value of the washing fluid entering the pur-
i~ieation vessel at 15.
~he washing fluid entering the purification vessel 1 at
20. 15 contains, inter alia, ealeium chloride. Caleium chloride
~; reacts with the sulphur dioxide eontained in the gas to be
purified forming ealeium sulphite and h~clroehlorie aeid. In
- the mixing vessel 7 the ealeiurn sulphite is eonverted to eal-
eium sulphate under the aetion of air. The hydrochloric acid
in the washing fluid reacts in -the mixing vessel 7 with the
burnt lime, introduced there b~ the me-tering device ~, with
the formation of calcium chloride ancl water. ~he calci~un
sulphate eontained in tne washing fluid is separ-ted for -tne
most part in the separator 11 from the washing fluid and to a
30. smaller extent remains in the circulating washing fluid.
If inert solid materials exist in the gas to be purified,
for example dust, then these are meehanicall~ removed through
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~ 10372Z7
the washing liquicl and reach the separator 11. If -the ~as to be
purified contains org~ic s-ubs-tlnces, especiall~ phenol ~nd form-
aldehyde,then these are reacted with the calcium hydroxide con-
tained in the washing fluid or are deposited on the calcium
sulphite resultin~ in the purification vessel 1 and pass with
this in-to the separator 11.
Since the washing fluid entering the puri~ication vessel 1
at 15 contains in addition to calcium chloride calcium 'nydroxide
and possibly calcium carbonate, hydrogen chloride ancl hydrogen
fluoride are removed also in the purification vessel from the
gas to be purified.
The addition of burnt lime through the me-tering clevice 8
and if necessary of calcium chloride through the metering
device 12 is so measured that the washing fluid at 15 has a p~
value which is 8 or higher, whilst i-t should show at 4 a pH
value of 7 or below that, preferably between 6 and 7.
The solid materials in the separator 11 flow from this
together with a small part of the washing fluid into a sep-
,
arating device 17. A centrifuge can, for example, be used as
200 the separating device 17. In the separating device 17 the solid
materials are removed ~rom the washing fluid. When the solid
materials have to be free from chlorides for further working
up they are washed by the addition of water. The calcium
chloride containing filtrate can so far as is necessary be
.: . .
returned at 12 into the circulation of the washing fluid.
Furthermore the filtrate collecting in 17 can be diluted and
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- led into waste water conduits or the filtrate can be evaporated.
~; The solid materials collecting in the separating device
.
: 17 and freed by washing from chlorides can be further worked
30. up into structural materials. The solicl materials which COll- :~
sist essentially of calcium sulphate are heated, whereby
gypsum substantially resul-ts and an~ organic substances
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` 103722~7
existiI~g in tlle soli~l mater;als are subs-t~ tially des-troyed.
~he further WOl'l.~i.ll{, Up to bricl;s or si.~ilar constructionSll
--~ elerlents taXes place for e~am~!?le bJ- the addition of binding
a~ents and/or fillin agents. Cement is a sui'ca-Dle boinding agent
; and a suitable filling material is fl~y ash which is collected in
the purification of flue glses from coal power s-tations.
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