Note: Descriptions are shown in the official language in which they were submitted.
CA 027575322011-10 03
Description
Process and device for treating flue gases
The invention relates to a process for treating a
carbon dioxide-containing flue gas stream, wherein at
least a part of the carbon dioxide present is removed
from the flue gas stream by means of a scrubber,
forming a low carbon dioxide gas stream and a high
carbon dioxide gas stream,. and also to a device for
carrying out the process.
In the utilization of fossil fuels, e.g. coal, mineral
oil or natural gas, in power stations or other
industrial firing plants, carbon dioxide-containing gas
streams, customarily termed flue gases, arise, which
are generally released to the environment. Since carbon
dioxide is what is known as a greenhouse gas, to which,
owing to its climatically harmful action, a substantial
adverse effect on the global climate is assigned,
technical solution-s are required for limiting the
carbon dioxide emission to the environment.
Recently, novel power station designs have been
proposed in which the carbon dioxide (C02) contained in
the flue gas is scrubbed out of the flue gas in a
scrubbing stage designed, e.g., as an absorption
column, downstream of the power station. The power
station in this process need not be converted to oxygen
combustion, as in what are termed "oxyfuel power
stations", but can be operated conventionally with air
combustion. The purpose of these novel designs is to
inject the carbon dioxide formed in the combustion of
fossil fuels and present in the flue gas into suitable
geological formations, in particular into certain rock
layers or saltwater-bearing layers, and thereby to
restrict the carbon dioxide emission to the atmosphere.
CA 027575322011-10-03
2 -
The climatically harmful action of greenhouse gases
such as carbon dioxide should be reduced thereby. This
technology is termed in the specialist field "post
combustion carbon capture technology (PCC)".
Carbon dioxide-containing flue gas streams also arise
in other industrial firing plants which are operated
with fossil fuels. These include, e.g., industrial
furnaces, steam kettles and similar large thermal
plants for generating power and/or heat. It is
conceivable that also in such plants, the carbon
dioxide is separated off from the flue gas streams by
means of a scrubber and fed to utilization or storage
(e.g. by injection underground).
When carbon dioxide is separated off from flue gases by
scrubbing out by means of chemical and/or physical
scrubbing media, a high carbon dioxide gas stream
arises which is present in the water-saturated state.
After a precompression, this gas stream must be dried
in order to correspond to the water contents required
for high carbon dioxide product streams. If the high
carbon dioxide gas. stream is intended to be fed, for
example, via pipelines to a later use, then for
prevention of corrosion and hydrate formation,
generally it is necessary to comply with a water
content of less than 500 ppmv after a final
compression.
The most customary prior art methods to date for
reducing the water content of high carbon dioxide gas
streams downstream of a flue gas scrubber are drying by
means of a molecular sieve absorber station or a glycol
scrubber. However, both known processes have specific
disadvantages:
Elimination of the water by means of a molecular sieve
CA 027575322011-10 03
3 -
adsorber station or a glycol scrubber demands a high
expenditure in terms of apparatus.
In addition to the adsorbers of the molecular sieve
adsorber station, it is necessary to install a
multiplicity of control valves (high expenditure on
piping). The control of the adsorber station is
extensive. For providing the regeneration, additional
thermal energy (heating the CO2 regeneration stream by
means of steam or an electric heater) and electrical
energy (repeated compression of the expanded CO2
regeneration stream) are required.
The structure of a glycol scrubber contains an
absorption column, a regeneration column, a series of
heat exchangers, filters and pumps. In the case of the
glycol scrubber, also, additional thermal energy is
required for the regeneration.
It is therefore an object of the present invention to
configure a process of the type mentioned at the outset
and also a device for carrying out the process in such
a manner that the drying of the high carbon dioxide and
water-saturated gas stream is made possible in an
economical manner without the described disadvantages
of the previous methods.
This object is achieved according to the invention in
terms of the process in that the high carbon dioxide
and water-saturated gas stream formed from the flue gas
stream after removal of the carbon dioxide is cooled by
means of a refrigeration system below the dew point
temperature of the water contained in the gas stream
and dried by condensing and separating out the water.
In this process the possibility of the formation of gas
hydrates (dependent on pressure, temperature and
composition) must be taken into account, which
CA 027575322011-10 03
- 4 -
formation can be avoided by feeding in glycols,
preferably a mixture of monoethylene glycol-water.
In order to separate off water from the high carbon
dioxide gas stream, the gas stream must be cooled below
the dew point temperature of the water (depending on
the pressure of the water-saturated gas). If the
temperature falls below the dew point, the water
condenses out and can be separated off from the gas
stream.
The gas stream including the glycol-water mixture
possibly sprayed in should be able to be cooled for
this, for example to a temperature of below 10 C at a
pressure of >30 bar. In central European regions this
cannot be achieved by cooling water (usual temperatures
around 25 C). In order to provide a cooling medium
having the required inlet temperatures, therefore,
according to the invention the use of a refrigeration
system, in particular a compression or absorption
refrigeration system, is proposed.
In contrast to a compression refrigeration system, the
absorption refrigeration system has a markedly lower
electrical energy consumption, since instead of a
compressor a pump can be used. Therefore, according to
a preferred configuration of the invention, an
absorption refrigeration system is used downstream of
the scrubber for drying the high carbon dioxide and
water-saturated gas stream.
In a particularly advantageous embodiment of the
invention, the absorption refrigeration system is
driven by means of thermal energy, in particular in the
form of steam and/or remote heat and/or direct firing.
In the case of treatment of a flue gas stream from a
CA 027575322011-10 03
-
coal-fired combustion and/or gasification plant, the
thermal energy is expediently obtained from vapours of
a coal -drying stage connected upstream of the
combustion and/or gasification plant or from vapour
5 condensate (if the vapours have already been utilized
in advance in another process). Vapours or- vapour
condensate from coal drying are available as waste heat
at a utilizable temperature level (>100 C). By
utilizing this waste heat for driving the absorption
refrigeration system, electrical energy is only further
required for the circulation pump of the solvent of the
absorption refrigeration system. Considerable savings
of electrical energy are achieved thereby.
To comply with the desired-product requirements for a
CO2 stream intended for further use or storage, the high
carbon dioxide gas stream is dried preferably to a
water content of less than 500 ppmv.
.20 In this case the high carbon dioxide gas stream is
expediently dried at a pressure between 30 and 60 bara,
preferably between 35 and 40 bara.
The present invention is primarily intended for
processing flue gases from conventional combustion
plants. The carbon dioxide-containing flue gas stream
is formed in this case in an industrial firing plant in
which fossil fuels are burnt with combustion air. This
flue gas stream is preferably subjected to a scrubbing
in an absorption column, with subsequent scrubbing
medium regeneration, for separating off carbon dioxide
from the flue gas stream. By expelling gaseous
components during the scrubbing medium regeneration,
the high carbon dioxide gas stream is expediently
formed, whereas the low carbon dioxide gas stream is
taken off from the absorption column.
CA 027575322011-10 03
6 -
Preferably, the carbon dioxide is removed from the
carbon dioxide-containing flue gas stream by means of a
scrubber having a physically and/or chemically acting
scrubbing medium. In this process the scrubbing medium
expediently contains as a component at least one amine.
In a particularly preferred configuration of the
invention, accordingly, the high carbon dioxide gas
stream is formed in a regeneration of a scrubbing
medium used for scrubbing, which scrubbing medium
contains as a component at least one amine.
The carbon dioxide removed from the flue gas stream can
finally be fed to a utilization or storage, in
particular injection underground, whereas the low
carbon dioxide gas stream can be released to the
atmosphere with a considerably reduced climatically
harmful action.
The invention further relates to a device for treating
a carbon dioxide-containing flue gas stream having a
scrubbing appliance for scrubbing out from the flue gas
stream at least a part of the carbon dioxide present,
forming a low carbon dioxide gas stream and a high
carbon dioxide gas stream.
The object in question is achieved in terms of the
device in that a refrigeration system for cooling and
drying the high carbon dioxide gas stream is connected
downstream of the scrubbing appliance. In this case, in
addition, an appliance for spraying in glycols, in
particular a glycol-water mixture, can also be
provided.
A particularly preferred configuration of the device
envisages that the refrigeration system is constructed
as an absorption refrigeration system.
CA 027575322011-10 03
7 -
The invention has a great number of advantages:
Refrigeration systems require considerably lower
capital and operating costs compared with the molecular
sieve adsorber stations or glycol scrubbers customarily
used for drying.
The possibility of utilizing thermal energy
(advantageously waste heat) for generating refrigera-
tion in the absorption refrigeration system is
particularly advantageous. In particular when vapours
from an upstream coal drying stage are used in coal-
fired combustion or gasification plants, the energy
requirement for drying can be considerably reduced.
Instead of vapours, vapour condensate can alternatively
be used, if the vapours have already been used in
another process.
The simple and robust construction is a further
advantage of the use of an absorption refrigeration
system for drying the high carbon dioxide and water-
saturated gas stream.
The invention is suitable for all conceivable
industrial firing plants in which carbon dioxide-
containing gas streams arise. These include, e.g.,
fossil-fuelled power stations, industrial furnaces,
steam kettles and similar large thermal plants for
power and/or heat generation. Particularly
advantageously, the invention can be used in industrial
firing plants which are supplied with air as combustion
gas. In particular, the invention is suitable for coal
power stations in which the C02 is scrubbed out of the
flue gas and injected below ground ("CCS - carbon
capture and storage").
The invention will be described in more detail
CA 027575322011-10 03
8 -
hereinafter with reference to an exemplary embodiment
illustrated diagrammatically in the figure:
The figure shows a block diagram of a processing plant
for a high carbon dioxide and water-saturated gas
stream from a carbon dioxide scrubber of a coal power
station.
In a scrubber which is not shown in the figure, a high-
carbon dioxide gas stream is separated off from a
carbon dioxide-containing flue gas of a coal-fired
power station, which high carbon dioxide gas stream is
intended for storage below ground. The high carbon
dioxide gas stream is precompressed by means of a
compressor 1 and then passed through a heat exchanger 2
where the gas stream is precooled by means of cooling
water KW. A glycol-water mixture is then sprayed in,
wherein the majority of the glycol originates from the
glycol processor .7 (concentration of the glycol-water
mixture separated off in 5). In a downstream heat
exchanger 3 further cooling by means of the absorption
refrigeration system 4 then proceeds. For supplying the
absorption refrigeration system with thermal energy,
vapours BD and vapour condensate BK from an upstream
coal drying stage are used. The glycol-water mixture
condensed out in the heat exchanger 3 as a consequence
of the cooling below the dew point temperature of the
water is separated off in a downstream condensate
separator 5. The gas stream dried to a water 'content of
less than 500 ppmv is finally compressed in a final
compressor 6 to the pressure intended for the further
use of the gas stream (e.g. for injection below
ground).
