PROCESS FOR SEPARATING AMMONIA FROM GASES IN PARTICULAR THE EXHAUST GASES GENERATED BY COMBUSTION PROCESSES

PROCEDE SERVANT A L'EXTRACTION DE L'AMMONIAQUE DE GAZ, PARTICULIEREMENT DE GAZ D'ECHAPPEMENT PRODUITS PAR LA COMBUSTION

English Abstract

ABSTRACT
In a process for separating ammonia from gases, in particular
from the exhaust gases generated by combustion process, in which
the ammonia is either formed or generated, or in which ammonia or
a substance that forms ammonia under the effects of temperature,
is introduced, a substance from the group of zeoliths is added in
finely divided form to the gas that is to be purified as a
treatment medium, this being done by thorough mixing with the
gas. The compounds that are added have the advantage that they
not only remove the ammonia from the exhaust gases very
effectively by absorption, but can bind it very strongly in their
internal structure, which effectively avoids the renewed release
of the ammonia during final disposal.

Claims

PATENT CLAIMS
1. A process for separating ammonia from gases, in particular
from the exhaust gases generated by combustion process, in
which the ammonia is either formed or generated, or in which
ammonia or a substance that forms ammonia under the effects
of temperature is introduced, characterized in that a
substance from the group of zeoliths is added in finely
divided form to the gas that is to be purified as a
treatment medium, this being done by thorough mixing with
the gas.
2. A process for separating ammonia from gases, in particular
from the exhaust gases generated by combustion processes, in
which the ammonia is formed or liberated, on in which
ammonia or a substance that forms ammonia under the effects
of temperature, is added, characterized in that activated
silicon dioxide is added in finely divided form to the gas
that is to be purified as a treatment medium, this being
done by thorough mixing with the gas.
3. A process a defined in claim 1 or claim 2, characterized in
that the treatment medium is added in solid form.
4. A process as defined in claim 1 or claim 2, characterized in
that the treatment medium is added in the form of a
suspension.
5. A process as defined in one of the claims 1 to 4, for
purifying the exhaust gases generated by combustion
processes, characterized in that the treatment medium is
mixed into the fuel.

Description

2~5~
The present invention relates to a process for separating ammonia
from gases, in particular from the exhaust gases generated by
combustion process, in which the ammonia is either formed or
generated, or in which ammonia or a substance that forms ammonia
under the effects of temperature, i5 introduced.
During the treatment of exhaust gases that result from combustion
processes, in order to reduce the concentrations of nitrous
oxide, either ammonia or a reduction catalyst is added to the
flow of gas (SCR process), or else ammonia or a substance that
forms ammonia under the effects of temperature (e.g., urea,
ammonium carbonate [sal volatile]) is sprayed into the gas ~`low
at a temperature range that is above 700 degrees Centigrade (SNCR
process). In both cases, the ammonia that is not used up during
the process that reduces the NOx can be carrled out in the
exhaust gases in the form of so-called ammonia slip
[Ammoniakschlup~--Tr.]. This contaminates not only the
atmosphere, but also any subsequent exhaus~-gas puri~ication
systems, if ammonia or ammonia compounds (ammonium chloride,
ammonium sulphate, ammonium bisulphite) are flush~d out with the
dust from a filter system or in the waste water from a wet-
scrubbing system.
It is true that the above-mentioned ammonium salts, which are
formed in the exhaust-gas section at temperatures in excess of
300 degrees Centigrade, can be removed effectively with cloth
fil~ers; however, problems are encountered when such filter dusts
are subjected to further processing. If they are eventually
wetted with water, the ammonia is driven off once again in
gaseous form and then escapes to the atmosphere, or waste water
that contains ammonium salt will be formed as seepage water in a
dump. This means that hazard-free ultimate disposal of this dust
becomes con;ectural.
.

2~
It is the task of the present invention to describe a process by
which ammonia can be removed from gas that is to be purified,
this being done in such a manner that the substance that either
absorbs or binds the ammonia can be disposed of without risk and
without the ammonia escapinq once again.
This task has been solved by the measures described in claim 1 or
in claim 2. When this is done, the treatment medium can be
introduced either as a solid or in the form of a suspension. If
the exhaust gases that are generated in combustion processes are
to be purified, it is po6sible to either introduce the treatment
medium into the exhaust gases Pither in finely divided form, or
mix it directly into the fuel, when the desired reaction, which
leads to the binding of the ammonia, can start as early as the
time when the ammonia is formed.
The compounds that are proposed possess the advantage that they
not only absorb the ammonia from the exhaust ~ases very well, but
can also bind it very strongly in their internal structure. This
effectively avoids the above-discussed environmental hazards that
are caused by subsequent liberation of the ammonia.
,
~ . :