Note: Descriptions are shown in the official language in which they were submitted.
B'~
The present Inventlon relates to a devlce for the
purlflcatlon of gas, especlally combustlon gas. Combustlon gases
from a furnace contaln a certaln amount of heat energy, whlch
cannot be reclalmed In the combustlon plant, or In conventlonal
heat exchangers. There /s a/so corros/ve matter, such as sulphur
compounds, dust partlc/es and other contamlnants, whlch are dlf-
flcult to remove, and whlch may cause envlronmental troub/e.
The present Inventlon prov/des a devlce, whlch permlts
an effIclent utlllzatlon of the resldual heat In combustlon gases
for heatlng alr, and slmultaneously makes It posslble to purlfy
the latter, comprlslng neutrallzatlon of corroslve/acld compounds
and collectlng gas entralned ashes, partlcle-bound heavy meta/s
and certaln gaseous mercury compounds. rhe rest product wlll be
a chemlcally stable compound, whlch may be eas/ly d/sposed of.
Accordlng to the present Inventlon there Is prov/ded a
dev/ce for alr preheatlng and the purlflcatlon of gas, especlally
combustlon gas, and Includlng a regeneratlve heat exchanger con-
nected to a plant produclng contam/nated gas, sald heat exchangercomprls/ng at least two ll~e unlts for a/ternate use In purlflca-
t/on of gas and preheatlng of alr, respect/ve/y, each unlt havlng
a storage space holdlng heat storlng bodles, the heat exchanger
belng provlded wlth sw/tch-over valves guldlng the f/ow of gas
and alr so they wlll pass In opposlte dlrectlons through the
storage spaces, each storage space belng provlded wlth connec-
tlons at Its /ower part and further connectlons at Its upper
part, and holdlng a quantlty of baslc granules, each unlt and the
gas Inlet connect/on thereto belng arranged so the temperature
wlthln the assoclated storage space wlll be reduced to below the
dew polnt of the combustlon gases occaslonally passlng thereto,
and each storage space belng provlded wlth Internal, perforated
partltlon walls, dlvldlng the space Into at least two chambers,
permlttlng a baslcally transverse f/ow of the gas, and alr,
respectlvely, In relatlon to the granules wlthln the storage
space.
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Thus, the devlce Includes a regeneratlve heat exchanger
connected to a plant produclng contamlnated gas, sald heat
exchanger comprlslng at /east two unlts for alternate use and
each havlng a storage space holdlng heat storlng bodles and belng
provlded wlth connectlons permlttlng the passage of combustlon
gas and alr, respect/vely. The Inventlon Is character/zed In
that the heat storlng bodles Include a certa/n quantlty of baslc
granu/es, each unlt belng provlded wlth connect/ons at Its /ower
end and further connect!ons at Its upper end, as well as swltch-
over va/ves guldlng the flow through the storage spaces, so con-
tamlnated gas wlll pass In one dlrectlon and alternatlvely alr
wlll pass In the opposlte dlrectlon, whereln each unlt and the
gas Inlet connectlon thereto are arranged so the temperature
wlthln the storage space wlll be reduced to below the dew polnt
for molsture In the combustlon gases.
The molsture wlll blnd fly ashes, partlcle-bound heavy
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metals and certain gaseous mercury compounds, and will
expedite the reaction between the sulphur dioxide and the
basic granules.
The connections to the storage space are preferably
arranged so the gas will pass the storage space from above,
downwardly, whereas the air will pass from below, upwardly.
Alternatively, the connections may be arranged so the gas
will pass from the interior at the storage space and out-
wardly, whereas the air will pass from the exterior and
inwardly. The storage space is advantageously provided with
internal, perforated portion walls, dividing the space into
at least two chambers, permitting a basically transverse
flow of the gas, and air, respectively.
The heat exchanger is preferably combined with an appa-
ratus for cleaning the basic granules, as well as means for
transporting the granules from the storage space to the
appratus and back to the storage space, and for removing
spent material therefrom. The cleaning apparatus preferably
includes a rotating, heated drum. This may be provided with
a connection for receiving part of the heated air, so the
chemical reaction continues. Hereby calcium sulphite bound
to the granules will be further oxidized into calcium sul-
phate. This is a stable and inert rest product, which may
be deposed without noticeable inconvenience. The chemically
spent surface layer of the granules will be ground off
while the drum is rotated, so fresh material is available,
when the granules are transferred back to the heat
exchanger for re-use.
Part of the heated air may be transferred to the burner
of a furnace, where the contaminated gas is prod~ced.
During certain operating conditions an exces~ of heated
air is produced in the heat exchanger. This may advan-
tageously be transferred to the gas exhaust duct in order
to increase the rising properties of the gases.
The heat exchanger is advantageously provided with
means to measure the content of sulphur dioxide in the com-
bustion gas ef~luent, and for govering the transfer of
~ranules from and to the storage space to maintain a
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predetermined value of reaction intense basic contact
surface.
The invention will below be described with reference -to
the accompanying drawings, in which
Figure l shows a cross section through a heat exchanger
according to the invention connected to a furnace,
and a regeneration apparatus, which are schemati-
cally denoted, and
Figures 2 - 4 schematically shows different arrangements
of the storage ~pace and the passages therein.
In Figure 1 reference 10 denotes a furnace ~orming part
of a boiler provided with a burner 11 for gaseous, liquid
or solid fuel, which is supplied with heated air from a
combustion gas purifier/heat exchanger through a conduit
12. The combustion gas conduit directly connected to the
boiler/furnace is denoted by 13.
In order to reclaim residual heat in the combustion
gases, and to render undesirable emissions therein harm-
less there are heat exchangers/filters l~. These will
alternatively be passed through by combustion gases, which
give off part of their residual heat, and by air, which
will be heated. The plant therefore includes at least two
similar units, even if one only is shown in the drawing.
Preferably a third unit is held as a reserve, which makes
it possi~le to cut out each unit in turn for cleaning and
overhaul.
The shape of the heat exchanger units may vary, and the
size will of course depend upon the capacity of the combus-
tion plant. A pre~rred embodiment comprises a tower-like
structure, where the base measures are less than the
height, and which encloses a storage space 15 containing
basic granules 16. This advantageousl~ contains crushed
limestone, or similar matter, but may possibly consist of
macadam or some other carrier, provided with a basic
surface coating.
In the embodiment shown, the storage space is provided
with a bo~tom 17, which from a central, longitudinally run-
ning slot 18 is inclined downwardly to both sides, towards
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exits 19. These may be closed by lids 20, and adjacent to
the slot 18 there is a flap valve 21.
The stora~e space 15 is provided with internal, as well
as external partition walls 22 and 23, respectively. The
internal partition walls 22 are mounted above the slot 18,
and from a wedge-shaped void above the latter. The external
partition ~alls 23 are parallel to the internal w~lls,
whereby wedge-shaped voids remain between the external
walls and the side walls of the unit.
The ridge-shaped roof of the unit is provided with con-
nections for the air conduit 12 to the burner and the com-
bustion gas conduit 13, respectively, and within the roof
there is a second flap valve 24. The final gas effluent is
denoted by 25, and issues from the a space below the bottom
17.
The intention is that the storage space shall alterna-
tively be passed by combustion gas and air, respectively,
and with two units in operation in a plant one will be
supplied with gases for heating the granules, while the
other unit is supplied with air which is heated by pre-
viously heated granules. After some time of operation the
flows of fluids are reversed.
In the operating position shown in the drawing the heat
exchanger 14 is passed by air, utilizing the heat absorbed
by the granules in a previGus stage.
Air enters through an opening 26 to one side of the
space below the bottom 17, which is located opposite to the
connection for the combustion gas conduit 25. The flap
valve 21 is swung (to the right in the drawing~ so a con-
nection is obtained from the opening 26, by way of slot 18,
to the space between the internal partition walls 22.
Due to the design of the partition walls the air - and
later the combustion gas - will pass substantially horizon-
tally through the layers o~ granules, which have about uni-
form thickness.
The upper flap valve 24 is turned so i~ closes t~le
connection to the combustion gas conduit 13, but maintains
the-connection with the air conduit open. When the flap
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valves 24 and 21 are turne~ to their alternative positions
connections for combustion gases in, and out, respectively
are opened, while the air passage is cut of~.
~ here is always some moisture in the combustion gases,
and in conventional plants the gas exit temperature is
maintained so high, that no risk for condensation upon the
heating surfaces of the boiler occurs. This means that
there is rather much residual heat in the effluent.
The storage space 15 and the connection ~o the combus-
tion gas e~it is according to the invention arranged so
condensation of steam occurs within the storage space. The
precipitated moisture greatly enhances the reaction between
the sulphur dioxide content in the combustion gases and the
basic granules into calcium sulphite. The moist and sticky
granules prevalent in a large portion of the storage space
has a high capaclty for catching fly ash, as well as
particle-bound heavy metals and certain gaseous mercury
compounds.
Beside the air preheating a good purification of the
gases will be obtained. When air later on passes through
the granules and is heated the calcium sulphite, initally
formed, will at least partly be fur~her oxidized towards
the more stable, final product calcium sulphate.
After some time of use ~he surface layer of the granu-
les will be less reaction active. The mass of granules is
made to slowly pass downwards in the unit, 50 spent
material is removed at its bottom, while new, reaction-
inclined material is supplied at the top.
~ n the drawing reference 27 denotes a rotatable drum
enclosed in a casing (not shownl, to which the granules are
supplied by some suitable transport means 28. Transfer o~
granules from the opposite side of the unit will occur hy
some similar means - the transpor~ part is indicated by the
broken line 29.
A regeneration and a mechanical cleaning of the
granules occurs in the drum 27. The surface layers of ~he
granules are worn off and separated, ~or instance by the
drum being perforated, wholly or in part. ~ereby powdery
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stuff and smaller pieces from the granules will be removed
while the cleaned granules are fed out of the drum by
suitable means (not shown).
The cleaning apparatus is preferably common to the two
heat exchanger units and contains an excess of granules,
which is being treated while both storage spaces remain
filled.
Transfer back to the storage spaces occurs by means of
some suitable device 30, for instance a bucket or screw
conveyor. A device 31 connected to the combustion gas
effluent senses the content of sulphur dioxide in ~he
combustion gases leaving the plant, and will govern the
circulation of granules so the sulphur dioxide content does
not exceed a predetermined value.
The heat content o the combustion gases is usually
higher than what it is possible to utilize for heating the
air to the burner. The surplus of air can be transferred to
the drum 27 by way of conduit 32. The hot air promo-tes the
oxidation of the calcium sulphite on the granules into
calcium sulphate, which is a stable rest product, which can
easily be separated from the granules by mechanical wear,
or washing. The air leaving the drum may carry a certain
amount of dust and is preferably transerred to the combus-
tion gas conduit 13 or directly to the units 14, so the
contaminated air must pass the granule store, where the
dust will be collected.
On these occasions when the excess of air is not needed
in the cleaning apparatus 27 part o the air may be trans-
ferred to the combustion gas effluent 25 by way of a con-
duit 33 terminating in a nozzle 34, in order to lncrease
the rising properties of the combustion gases.
Figures 2 - 4 schematically show some alternative
embodiments of granule stores, and the combustion gas and
air conduits connected thereto. In all figures the air
paths are shown in full lines, while the paths of combus-
tion gases are shown in broken lines.
The embodiment according to Figure 2 largely corre-
sponds to that of Figure 1, but the storage space 15a has a
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form more li~e an inverted V. The partition walls 22a, 23a
are inclined about corresponding to, or slightly exceeding
the natural angle of repose of the granules.
Elere comparatively small surfaces on the cold side are
exposed towards -the possibly still corrosive gases~
Figure 3 shows a modification where the walls 22b, 23b
defining the storage space has the form o~ a regular V.
Here the surfaces at the cold side will be correspondingly
bigger than in the previous example, but on the other hand
there are small surfaces only at the warm side, which must
be insulated to prevent condensation.
As is evident from Figure 4, the partition walls 22c,
23c can be located vertically. In this manner two parallel
part storage shafts 15c are obtained, which may be comple-
tely separated, or may be interconnected by supply and
feeding-out means for the granules. The combustion gases
will pass from within and outwardly, while air passes from
without and inwardly.
The embodiments above described and shown in the
drawings are to be regarded as examples only, and the com-
ponents thereof may be varied in many ways within the scope
of the appended claims. The storage space may be formed as
a single shaft - located between two partition walls, and
the bottom 17 can be formed so its sides slope towards the
centre. These will ensure a simpler feeding-out of the
granules.
Instead of the rotating drum 27, a shaking screen or
some similar device may be used, where the granules will be
subjected to mechanical wear and the influence of air,
while simultaneously smaller particles are removed.
The invention is described as used in connection with a
furnace, but it is evident that it may also be used in con-
nection with industrial processes, where hot, contaminated
gas is produced.
