A PROCESS FOR THE CONDITIONING OF FLUE GASES

METHODE POUR LE CONDITIONNEMENT DES GAZ DE CARNEAU

English Abstract

A process for the conditioning of flue gases polluted with
solids, particularly from incinerating plants, for subsequent
flue gas purification, preferably with dry additives, by spraying
water into the gas stream, wherein said water is sprayed into the
gas stream through a preceding spray drying installation, prefer-
ably having a rotating atomizer.

Claims

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C l a i m s :
1. A process for the conditioning of flue gases from inciner-
ating plants polluted with solids for subsequent flue gas
purification with dry additives by spraying water into the
gas stream, characterized in that said water is sprayed
into the gas stream through a spray drying installation
having a rotating atomizer.
2. The use of spray drying installations having a rotating
atomizer for the conditioning of flue gases from incinerat-
ing plants polluted with solids for subsequent flue gas
purification with dry additives, for spraying water into
the gas stream.

Description

~ 2141302
SMB
A Process for the Conditioning of Flue Gases
The object of the present invention is a process for the con-
ditioning of flue gases polluted with solids, particularly from
incinerating plants, for subsequent flue gas purification,
preferably with dry additives, by spraying water into the gas
stream.
For the purification of flue gases, it is necessary in general
to condition the flue gas in terms of temperature and steam con-
tent. In wet flue gas purification processes, for instance, this
conditioning takes place in a quencher. For the purification of
flue gases with dry additives, water is conventionally sprayed
into the flue gas stream by means of spray lances. Subsequent
~lue gas purification with dry additives then causes elimination
of acidic components, such as HCl, HF, SO2, and NOx. If the flue
gases are polluted by solids, the latter are considerably en-
riched in the quencher and thus channeled out of the process. In
the flue gas purification with dry additives, the solid impur-
ities are channeled out of the process and hence removed from the
flue gas along with the dry additives. If the flue gases are
conditioned by spraying in water by means of spray lances, high
solids pollutions result in undesirable and obtrusive sticking
and caking which may also interfere with the subsequent purifica-
tion with dry additives. Such sticking and caking is observed in
particular in cases when spraying of the water is done in an
uneven manner and larger droplets get into the flue gas stream
as well in addition to fine mists.
Unsufficient conditioning of the flue gases will result in un-
sufficient purification. Overdosing of the water will result in

2141302
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sticking and caking of the solids present in the flue gas and in
addition can cause the dry additives to cake as well.
The object of the invention is to provide a process for the
conditioning of flue gases polluted with solids, particularly
from incinerating plants, for subsequent flue gas purification,
which process will avoid the observed obstructions especially in
the flue gas purification with dry additives, and still to ensure
good and even conditioning which can be readily controlled.
This problem can be solved surprisingly well by spraying the
water into the gas stream through a preceding spray drying
installation, preferably having a rotating atomizer.
To date, spray drying installations have been used uniquely to
dry solutions or dispersions of solids. Spray drying is a
relatively tedious but gentle drying method and therefore is used
primarily to dry temperature sensitive solids of high quality.
In addition, spray drying installations have also been used
already for quasi-dry flue gas purification by spraying solutions
or dispersions of absorbing agents with water. At the end of the
spray tower, a newly dried absorbing agent was then separated
which additionally contains the impurities of the flue gas that
are to be removed. However, spray drying installations have not
been used to date to condition flue gases, because the require-
ments with respect to instruments and process engineering seemed
much too high. Surprisingly, it has now been found, however, that
sticking and caking can be avoided with flue gases polluted with
solids, particularly from incinerating plants, while still allow-
ing a perfect, reproducable conditioning which can be readily
controlled.
The subsequent flue gas purification can then be performed, for
instance, by spraying in dry additives. In particular, alkali
metal and alcaline earth metal hydroxides can be considered for
the purification of flue gas. However, other absorbing agents,
especially active charcoal, can be used as well as dry additives.

2l~l3n2
In principle, it is also possible, of course, to condition flue
gases polluted with solids, particularly from incinerating
plants, according to the invention and then to add dry additives
thereto and optionally to further subject them to wet purifica-
tion. Thereby it is possible to separate the solids of the flue
gas from the flue gas in a dry form.
In case of spray drying installations, in principle all spray
drying installations can be used that are conventionally used for
spray drying and especially for flue gas purification. Prefera-
bly, spray drying installations with rotating atomizers are
employed, since they allow for a particularly good and even
distribution of the liquid phase in the gas stream.
Spray drying installations with rotating spray atomizers have
originally been developed for the recovery of milk powder, but
are employed to a considerable extent for quasi-dry flue gas
purification as well. With flue gases polluted with solids,
particularly from incinerating plants, however, this method can
lead to obstructions and unsatisfactory results.
Hence, an object of the present invention is first a process for
the conditioning of flue gases polluted with solids, particularly
from incinerating plants, for subsequent flue gas purification,
preferably with dry additives, by spraying water into the gas
stream, characterized in that the water is sprayed into the gas
stream through a preceding spray drying installation, preferably
having a rotating atomizer. A further object of the invention is
the use of spray drying installations for the conditioning of
flue gases polluted with solids, particularly from incinerating
plants, for subsequent flue gas purification, preferably with dry
additives, by spraying water into the gas stream.
Preferably, spray drying installations with rotating atomizers
are employed.

~ 21~1302
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The subsequent flue gas purification, for instance by blowing in
dry alkali metal and alcaline earth metal hydroxides, is rendered
substantially more reliable and efficient according to the
invention.
The seemingly excessively high requirements of a spray drying
installation with respect to instruments and process engineering
just for the conditioning of the flue gases eventually leads to
such improved results, however, that the overall plant works
better and more economically.
A critical advantage is the improved security of the process, for
it works in a more flexible way when more or less water is
required or when more or less water is supplied. There is no
sudden break but rather a slow increasing or decreasing of the
amount of water supplied which is introduced in the flue gas.
Therefore, it is also easier for the process to be controlled.
Spray lances tend to get obstructed and thereby to suddenly
interrupt the water supply. This results in severe obstructions
of the process.
A typical spray drying installation which can also be used for
abrasive aqueous liquids is described in U.S. Patent 4,530,822
and is sold, for instance, by the firm of NIRO. These installa-
tions can be used for the present invention as well.