Note: Descriptions are shown in the official language in which they were submitted.
CA 02860362 2014-06-23
Gas Absorption Granular Material
The invention relates to a compressed gas absorption granular material for
separating gaseous chlorine and sulphur compounds - also referred to below as
HCI and SOx
gases - from exhaust gases, in particular from SO2 and/or SO3 from combustion
gases of
thermally processes, in particular for use in a solid matter exhaust gas
reactor, such as a
packed bed filter, fixed bed absorber, moving bed absorber or the like,
connected
downstream of a combustion unit, said granular material predominantly
containing
compressed bodies which have at least one calcium compound in the form of
hydrated lime
and/or powdered limestone. The compressed bodies of the gas absorption
granular material
may be shaped bodies produced by compression moulding - also referred to below
as
compressed parts - of any geometric three-dimensional shape, for example
spherical,
cuboid, conical, prismatic shape, or flakes or grains of granular material -
referred to below
as compressed grains - created by comminution or crushing of the compressed
shaped
bodies and having a compacted structure produced by the compression.
Buildup-agglomerated granules are known which absorb SO x gases and include
exclusively hydrated lime as active substance. Use thereof in a solid matter
gas reactor
connected downstream of a combustion zone has shown that the theoretical
absorption
capacity of a granule is not attained. SO x is absorbed in a shell form in a
relatively thin outer
shell zone, forming calcium sulphate (CaSO4). The hydrated lime in the
interior of the granule
remains unused for example up to 40 %. Obviously the diffusion of the SO gas
is prevented
by the calcium sulphate formation in the outer shell zone.
EP 2 103 338 Al discloses that, in the relatively dry SO x exhaust gas
purification
processes with hydrated lime in powder form, higher degrees of separation can
be achieved
by increasing the relative humidity of the exhaust gas because in this case
directly around
the hydrated lime a reactive zone of relatively high humidity is formed in
which SO x gas is
initially dissolved before it reacts with the CaO of the hydrated lime. In
accordance with this
phenomenon, the document proposes the use of a moist hydrated lime with
adsorbed
moisture content between 3 and 25 % by weight for the dry SO x exhaust gas
purification.
DE 10 2009 045 278 Al describes mineral, calcium-based, buildup-agglomerated
porous granules which have a core (parent grain) containing at least 80 % by
weight calcium
carbonate (CaCO3) as well as at least one buildup agglomeration layer
containing calcium
hydroxide (Ca(OH)2) and surrounding the core, wherein the granules contain a
calcium
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CA 02860362 2014-06-23
hydroxide fraction of at least 60 % by weight, based on the total dry weight
of the granules,
and have a substantially spherical configuration as well as a BET surface of
at least 8 m2/g.
These known granules should have micropores, mesopores and macropores.
Moreover the
water content of the known granules may be 2 to 20 % by weight.
In the context of the present invention it has been recognised that the high
water
content and the porosity of these known granules also do not provide the
expected high SOx
separation yield and that, as in the case of the hydrated lime granules
without "parent grain",
an outer absorption region is formed which impedes the progress of the
separation and a
relatively large amount of unconsumed or unused hydrated lime is still present
in the interior
of the granules. Clearly the water adsorbed at room temperature in the
granules is not, as in
the case of powdered hydrated lime having adsorptively bound water, is
available to promote
reaction at the high temperatures at which the absorption processes or the
exhaust gas
purification proceed. These high temperatures are known to be generated by
exhaust gas
temperatures for example between 100 and 900 C. It appears that a type of
blocking by the
calcium sulphate formation in the outer edge regions of the granules takes
place, so that the
further penetration of gas into the interior of the granules is hindered.
The object of the invention is to create granules having at least one SON-
absorbing
calcium compound, in which the progress of absorption into the interior during
the exhaust
gas purification is not significantly hindered and which thus ensure a higher
degree of
utilisation for the SON separation.
The object of the invention is achieved by the features of Claim 1.
Advantageous
embodiments of the invention are set out in the claims which are dependent
upon this claim.
In the context of the invention the expression "compressed shaped bodies" -
also
referred to below as pressings - are understood to be bodies which are
produced by pressing
or compacting or compressing finely divided substances using mechanically
operated
presses with shaping tools. As already specified above, the shaped bodies can
have any
three-dimensional shapes. The volumes are for example between 0.03 and 40, in
particular
between 0.04 and 5 cm3. The same applies with respect to the volumes,
preferably also for
the pressed grains produced by breakage of the shaped bodies.
The SON-absorbing calcium compounds used within the context of the invention
are
preferably products which contain calcium hydroxide (Ca(OH)2) - also referred
to below as
hydrated lime - in quantities above 80 % by weight and/or finely divided
calcium carbonate
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(CaCO3) - also referred to below as powdered limestone - in quantities above
90 % by
weight.
Within the context of the invention the expression "powdered" also includes
powder,
dust or the like with particle sizes up to 250, in particular up to 90 pm.
The invention provides for the presence of hydrated lime and/or powdered
limestone
in a compressed part or in the compressed grains for SO x separation out of
exhaust gases
from thermal processes. It is within the scope of the invention to use, in
addition to these
essential constituents, further desulphurisation agents, for example magnesium
hydroxide
and/or calcium oxide in the form of white fine lime and/or sodium hydrogen
carbonate in the
compressed parts or in the compressed grains. These further constituents
should be
contained in the compressed parts or grains at no more than 20 % by weight.
The
compressed parts or the compressed grains may also contain for example up to
20 % by
weight of further adsorption and/absorption agents such as for example
activated carbon or
coke or the like, so that for example other pollutants or polluting gases such
as mercury can
be removed from exhaust gases which are to be purified.
The compressed parts according to the invention or the compressed grains may
also
contain binding agents which effect a stabilisation of the compressed parts
the compression.
Examples of this are carboxyl methylcellulose, starch, glucose, alginates,
molasses,
lignosulphonates, clay minerals, in particular bentonite. Accordingly the
compressed grains
may also contain these binding agents.
The invention is substantially characterised in that the compressed parts and
compressed grains contain, in addition to hydrated lime and/or powdered
limestone particles,
defibrated cellulose fibres in the form of defibrated paper material and/or
defibrated
cardboard material and/or defibrated or ground wood. Within the context of the
invention the
expressions "defibrated paper material" and "defibrated cardboard material"
include a
material made of paper or cardboard fibres, wherein the material is produced
for example
from paper or cardboard which in the dry state is defibrated by comminution
machines to a
high degree of fineness. The high degree of fineness means that the fibre
length is for
example between 0.1 and 5 mm, in particular between 0.1 and 2 mm at a
slenderness ratio
of the fibres (length to diameter) for example between 10 to 1 and 5 to 1. The
wood fibres are
for example between 1 and 5 mm long at a slenderness ratio like the paper
fibres. The wood
flour has for example fibres with lengths between 0.1 and 1 mm at of a
slenderness ratio for
example of 1.0 mm.
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Paper fibres 0 - 2 mm with a high slenderness ratio of the fibres
Paper fibres 0 - 5 mm with a high slenderness ratio of the fibres
Wood flour 0 - 1 mm with a low slenderness ratio of the fibres
Thus the invention relates in particular to a gas absorption granular material
formed
for use as HCI and SO x absorption granular material preferably in a solid
matter exhaust gas
reactor which is connected downstream of a combustion unit, and which has
shaped bodies
produced from finely-divided material using a compression method and/or a
granulated
material produced from compressed shaped bodies by comminution, wherein the
shaped
bodies of the granular material and the comminuted grains of the granulated
material have in
their matrix hydrated lime and/or limestone powder, as an SO x absorption
agent, and finely
divided defibrated paper material and/or finely-divided defibrated cardboard
material and,
moreover, preferably adsorbed water, in particular a water content up to 30 %
by weight
relative to the quantity of absorption agent and the defibrated material.
A gas absorption granular material with the following compositions based of
the
mixture of absorption agent and defibrated material is advantageous:
hydrated lime and/or powdered limestone 99.5 to 90, in particular 99 to 95 %
by weight
defibrated material 0.5 to 10, in particular 1 to 5 % by weight.
The defibrated cellulose material, in particular the defibrated paper material
and the
defibrated cardboard material, - also referred to below merely as defibrated
material - have
the capacity to store water for example by capillary action in the compressed
parts and the
grains in such a way that even at higher temperatures, such as occur for
example in exhaust
gas purification systems connected downstream of combustion units, water is
available in
sufficient quantity in the compressed parts or the grains and in a known
manner can favour
the reaction between the SO,, gas and the hydrated lime particles and/or the
powdered
limestone particles, in that for example water is also stored in the
defibrated paper material
and the defibrated cardboard material for dissolving SO, gases and a formation
of calcium
sulphate out of the solution can take place. In any case the defibrated
material which stores
the water effects an increase in the degree of separation of the SO x gases.
It is also provided synergistically that almost the entire calcium-based
absorption
agent of a compressed part or a compressed grain can react with the SO x gas
to calcium
sulphate, without external reaction layers significantly blocking the progress
of the reaction.
"Blocking" such as occurs in the case of compressed parts or compressed grains
without
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defibrated material can be avoided. A substantial further synergistic effect
is that the
defibrated material promotes the compression process in the production of
compressed parts
as an aid to compression, in that less pressing force is necessary is for the
production of
compressed parts of specific strength. This effect of defibrated paper and
defibrated
cardboard in the production of briquettes from finely divided substances is
known from EP
621 800 B2. This prior art describes inter alia the briquetting of burnt lime
using paper fibres
from newsprint paper comminuted to a high degree of fineness.
It is known from DE 11 12 003 A2 to briquette hydrated lime with 6 until 7 %
water by
pressing and to burn the shaped parts in a shaft furnace.
The granules according to the invention are produced and used for example with
bulk
densities between 0.6 and 1.3, in particular between 0.7 and 1.1. The
compressed parts and
the compressed grains advantageously have adsorptively bound water in
quantities between
0 and 30, in particular between 5 and 25 % by weight. They have a sufficient
strength, in
particular a sufficient abrasion resistance, so that they can be used for SO x
separation in the
known exhaust gas purification systems operated with granules, without
disruptive dust being
produced.
The use of the defibrated material results in particular in the following
advantages:
= A porosity or capillarity is achieved which improves the diffusion of
harmful
gases into the interior of the compressed shaped bodies or. the compressed
broken grains
and thus also improves the separation yield;
= A water reservoir is created which contributes to an increase in the
separation
yield;
= Waste products in the form of waste paper and/or cardboard material can
be
used.
It is within the scope of the invention, before the compression or during the
compression to selectively admix additives with the mixtures, such as for
example starch,
glucose, methylcellulose, alginates and molasses, clay minerals, in particular
bentonite, for
example for increasing the strength of the compressed parts and/or the
abrasion resistance
of the compressed parts or the compressed grains. However, the additives
should not
constitute more than 10 % by weight, in particular no more than 7 % by weight,
in a
compressed part or in a broken compressed grain of the granular material.
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The following table contains, in % by weight, preferred dry powdered doses of
components for compression for the production of shaped bodies according to
the invention.
The details with respect to the defibrated material should be understood to
mean that in any
case at least one defibrated material must be present in the specified
quantities, wherein the
quantity is also determined inter alia according to the required water storage
capacity. It is
not obligatory to use the additives. However, when they are used they are used
in the
specified quantities, wherein a plurality of additives can also be used in one
dose. The
specified upper limit for the respective quantity of a defibrated material
applies in particular
for the maximum quantity if only this one material is included. The rest, if
any, to make up
100 % by weight is obtained from the addition of an additive and/or another
defibrated
material. For the additive it is the case that the specified quantity is the
upper limit, when the
respective additive is added alone.
Table
Absorber Defibrated material
Additive
hydrated lime 90 - 99 defibrated 0.5 - 10 starch 0 -
5
waste paper
powdered defibrated
90 - 99 1 - 10 glucose 0 -
5
limestone cardboard
hydrated lime
powdered 90 - 99 wood fibres 0.5- 10 methylcellu lose
0 - 1
limestone
wood flour 1 -10 alginate 0 -
3
molasses 0 -
3
lignosulphonate 0 -
5
clay mineral 0-
10
bentonite 0 -
10
The doses according to the invention are mixed and a water content up to 30,
in
particular between 5 and 25 % by weight, is set, based on the absorber and the
defibrated
material, e.g. before the pressing, e.g. before or during the mixing. Thus the
setting of the
water content may take place by moistening the dry constituents of the mixture
in the mixer.
However, the setting may also take place by the use of a mixture constitutent
or a plurality of
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mixture constituents which already have a specific quantity of adsorptively
bound water
before the incorporation into the mixture. It is advantageous to use hydrated
lime which has
between 5 and 30, in particular between 15 and 25 % by 'weight of adsorbed
water and/or to
use a ,defibrated material which has up to 15, in particular up to 10 % by
weight of adsorbed
water.
After the mixing, shaped bodies are produced from the mixture by compression
or
compaction in a pressing device. The compression advantageously takes place in
continuously or discontinuously operating compression devices for non-plastic
substances,
for example with roller presses or stamping presses. By way of example, flakes
can be
produced by roller presses, and these shaped parts are comminuted by crushing
and then
classified, resulting in a gas absorption granular material of compressed
grains according to
the invention. Or shaped bodies with regular or irregular geometric three-
dimensional shape
can be produced in the form of compressed parts, for example by means of
stamping
presses, wherein these shaped bodies then form the granular material according
to the
invention. However, these compressed shaped bodies with the regular or
irregular three-
dimensional shapes can also be comminuted, in order to produce a granular
material from
compressed grains of a specific grain size.
The crushed grains of the granular material have grain size distributions
produced by
sieving, for example as follows:
0 - 2 mm 0 to 20 % by weight, in particular 5 to 15 % by weight
2 - 12 mm 80 to 100 % by weight, in particular 85 to 95 % by
weight
0 - 12 mm 0 to 20 % by weight, in particular 0 to 10 % by weight
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