Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The invention relates to an installation for obtaining
energy from solid fossil fuels, especially those high in inerts,
more particularly bituminous coal, the said installation con-
sisting o~ at least one ~lock in which the solid fuels are
converted into gas and containing a gas turbine and a steam
turbine for extracting electrical energy from the gases, the
dust and sulphur being removed from the gases, in the block,
before the gas turbine.
The advantage of a block installation of this kind is
that if the gas-turbine process is correctly combined with the
ste~m-turbine process, greater thermal efficiency is obtained
than in an installation in which the processes are all carried
out separately. The dust-removing operation cleans the gases
to such an extent that they can be fed to the gas turbine in
spite of the fact that ~he coal used is high in inerts. De-
sulphurization is carried out under high pressure and therefore
has advantages over the known pressureless flue-gas desulphuri-
zation, especially since the desulphurizing units are smaller
and since, in adsorptive desulphurizing, the adsorption losses
are reduced by the high pressure. This means ~hat installations
of this kind also cause particularly little pollution.
So-called pressure-gasification in a solid bed is
known. In units of this kind, coal, mostly high in iner~s,
is gasified with some of the available combustion air, and
with steam, under high pressuxe, i.e. it is partly burned.
; The gasification pressure in known units of this kind is about
20 bars. Gasification is carried out in a reactor produciny
lean gas at a temperature of between 500 and 600C which is
cooled and is then fed to dust-removal and desulphurizing units.
The clean lean gas is burned, as fuel gas, in a boiler under
pressure. ~'he flue-gases are used to operate the gas turbine,
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while ~le steam produced in the boiler drives the steam
turbine.
However, coal-gasiEication under pressure produces
a series of losses. Some of these are based upon the large
proportion of unburned mater:ial in the ash removed from the
reactor, hitherlto always amounting to more than 10%. Other
losses are the result of so-called casing steam, i.e evaporation
of the cooling water ed to ~le pressure-gasifier. Other
losses are caused by the evaporation of water during so-called
quenching. Finally, the losses are still further increased
by the fact that much of the water used in washing the gases
is not separated but remains in the fuel gas in the form of
a spray which 1therefore has to evaporated in the firing of
the boiler.
Other disadvantages of coal-gasification under
pressure arise from operating difficulties. For instance,
during tha cooling oiE the lean gas, tars condense and are
deposited upon the par~icles of dust in the gas, producing
a mixture of dust and tar. This easily leads to baked-on
deposits and blockages in the different circuits in which it
occurs, and these must be removed. If substantial heat losses
are to be prevented, the dust-tar mixture must be separated
from the washing medium in a tar-separator or some other
suitable unit, the said mixture being returned to the gas-
producer. This produces special problems, since the dus~y
tar is difiEicult to pump and again produces operational
problems.
Hitherto-known units for gasifying coal under
pressure are also comparatively difficult to cQntrol. For
instance, lthere are fluctuations in the gas-outlet temperature,
in the calorific value, and in the dust and tar contents, these
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fluctuations bein~ mainly attributable to the intermittent
~eeding of coal to the gas-producer. Furthermore it is
impossible to achieve a rapid load increase if an adequetelY
high calorific value of the fuel gases is required at the same
time. These problen-s make it impossible to obtain a sensitive
performance control.
Finally, it should be pointed out that, because of
their low calorific value, the fuel gases cause problems when
they are burned in the boiler, and there are many occasions
when comhustion must be supported by additional fuels, usually
fuel oil.
There has also been proposed an installation of the
kind described at the beginning hereof having a block in which
the fuel is burned and desulphurized in a fluidized layer.
To this end, the ground fuel and the desulphurizer are fed
to the fluidized bed, the fuel being burned, under pressure,
in the suspension. ~Ieat is transferred to the steam process
within the fluidized layer, the combustion temperature being
thus restricted to about 900C. The flue-gas emerging from
the vortex chamber, and containing a considerable amount of
solid material (ash, unburned substances, and partly charged
desulphurzier) must then be passed to a gas turbine. There
has hitherto been no known way of producing a mechanically
cle~ gas from these flue-gases.
If a vortex chamber is used to burn the ground fuel,
this produces a series of disadvantages, since a considerable
amount of unburned substances must also be expected in the
ash in the vortex chambsr. Unfortunately, the unburned
substances are discharged from the vortex chamber with the
10w of flue-gas and thus inevitably reach the subsequent
dust-removal unit. It is extremely difficult to ~eparate the
total ash from the fuel and the partly-charged desulphurizer
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from the flow of flue gas. It is also difEicult to separate
the partly-charged desulphurizer from th~ ash for preparing
the desulphurizer. In addition to this there are wear
problems in connection witn the heating surfaces which have to
be arranged within the fluidized layer. This wear is due mainly
to the inevitable erosion in the fluidized layer. ~ccurate
control of the fluidized-bed temperatures also presents con-
: siderable difficulties. If, for instance, the fluidized-bed
temperature rises too high, the ash softens and the fluidized
bed bakes onto the heating surfaces. On the other hand, if the
fluidized-bed temperature is too low, there is a drop in the
degree of combustion and ~hus a corresponding increase in fuel
losses. Furthermore, low-temperature carbonization sets in,
and this causes the tar to condense and the fluidized bed to
bake onto the heating surfaces.
It is the purpose of the invention to reduce the
losses and operating problems in installations of the kind
described at the beginning hereof, and to design an installation
that can be used as a peak-load power station.
According to the invention, this purpose i3 achieved
in that a melting-chamber boiler, to which the ground fuel
is fed, is pressure fired, and in that the flue-gases pass to
- desulphurizing and dust-removal units before they reach the
gas turbine.
Since combustion takes place in one part of the
installation (partial combustion and post-combustion), the
two processes can be jointly controlled as required for a
peak-load power station~ In other words, the output can be
increased and reduced relatively quickly, and may thus be
adapted to the power taken off, without heat loss and without
supporting the combustion process with oil or other additional
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fuels. Since the fuel is burned in a melting-chan~er boiler
(kettle, vessel), no tar occurs, no equipment is re~uired to
deal with it, and the corresponding difficulties are eliminated.
Ihe pressure in ~e flue-gas side of the melting-chamber boiler
may be 10 bars, for example, and this corresponds approximately
~o t~e gas-turbine pressure.
The main advantage~s of the new installation is that
there is a negligeable amount of unburned substance in the
melting-chamher slag, so little that it cannot be measured.
The thermal efficiency is considerably higher, since there
are no losses by evaporation outside the steam circuit, such
as have hitherto been unavoidable in the gasification of a
fuel. The low water content in the flue-gas also assists in
improving the thermal efficiency. This is the reason for the
low dew-point and the relatively small waste-gas loss.
Another advangtage is that most of the ash is removed
from the melting-chamber boiler in the form of granules and
does not reach the turbine gas. The granular material thus
removed may be further processed and used for other purposes.
Accordiny to another characteristic of the invention
the flue-gases may be removed from bahind the radiating portion
of the boiler. Moreover, heat-exchanger surfaces are provided,
outside the boiler, for the flue-gases thus removed, and may
be used to adjust the flue-gas temperature before the gas
turbine. These heat-exchanger surfaces are used to produce
the steam which is fed to the steam-power process. It is
also desirable to burn the fuel directly under pressure in a
cyclone since, as compared with the gasification technique,
this saves a number of additional units (gas producers) and
requires, for the combustion process, a unit substantially
smaller tham that used in the fluidized-bed technique. It
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is also possible to locate ~e heat--exchanger surfaces, used
to adjust the flue-gas temperature before the gas turbine,
in the flue-gas desulphurizer. The said heat-exchanger
surfaces may also follow the desulphurizer~
The actual desulphuriziny may be carried out with
metal car~onates or oxides, using a solid bed in which the de-
sulphurizer is in the form of pellets or briquettes. On the
other hand, a fluidized becl may be used, or the desulphuriæer
may be injected into the desulphurizing chamber in the form
of a dry dust.
On the flue-gas side, a dry flue-gas dust-removal
unit, operating at the existin~ high pressure, may be inserted
after the said heat-exchanger surfaces~ l~his dust-removal
unit may operate with ceramic candle filters or with separator
nozzles, a hot cyclone bPing used, if necessary, as a pre-
separator before the actual dust-removal process.
~ s regards subsequent equipment, the invention
has the advantage that the heat-exchanger surfaces after
the radiating portion of the boiler are substantially smaller
as compared wi~h those in the proposed fluidized bed, and
this reduces erosion. Furthermore, the desulphurizer is
more easily separated from the ash, since there is considerably
less ash than in the fluidized-bed process. This is also
quite an advantage.
The details, further characteristics, and other
- advantages of the invention may ~e gathered from the
following descriptions of three examples of embodiment o~ the
installation according to the invention, as illustrated
in the drawing attached hereto, wherein :
Fig. 1 is a first example of embodiment of the
installation according to the invention, in which the flue-
gases are desulphurized in a fluidized bed;
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Fig. 2 is an e~ample oE en~odiment using a modified
(injection) desulphuriæing unit;
Eig. 3 is an example of embodiment of the installa-
tion accordiny to the invention using a solid-bed desulphuri-
zing unit.
In the figures, similar parts of the installation
bear the same reference numerals.
Coal containing inerts is fed rom a bunker 1 to a
grindin~ unit 2 which passes thP grouncl fuel, througll a gate
3, to a line 4 running to the cyclone-firing unit of a melting-
chamber boiler (kettle, vessel) marked 5 as a whole.
Id~ntification of the media in the lines corresponds
to German Industrial Standard 2481.
'rhe flue-gases are removed at 7 and pass, in ~he
installation according to Fiy. l to a fluidized-bed desulphuri
zer 8. The desulphurizing agent used may be limestone, for
example, which is fed, through a gate unit 9, to the desul-
phurizing unit at lO and ll. The desulphurizing flue-gases
leave the fluidized bed at 12 and pass to a cyclone which
removas any coarse solids. These solids ara removed at 14 and
are passed to a grading unit 15 consisting of several screens,
fore~mpls. The overflow from the screens is passed on,
through a line 16, for further processiny or use. l`he
material passing through the screens is removed at 17 and
passes, in the example of embodiment illustrated, to a gate
18 to which fine dust is fed through a line 20. The fine-dust
separator ~a separator nozzle or filter) is shown at 21, and
the flue gases from which the coarse solids have been removed
are fed ther.eto.
The flue-gases leave fine separa-tor 21 at a tempera-
ture of bet~leen 800 and 900C, fsr example, and pass, through
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a line 22, to a gas turbine 23 which is followed by a waste-
heat boiler 24. The flue-gases are th~n released to the
atmosphere at 25.
Provision is made, in the example of embodiment
illustrated, for the separated fine dust to be returned, through
gate unit 18, pneumatically ~rough a line 26, to line 4, so
that this part of the dust is returned to melting-chamber
boiler 5.
Dust and ash is removed in the form of a liquid from
boiler ~, and this passes to a hydraulic ash-removal unit and
a crusher for granular material, this portion of the ins-talla-
tion being marked 27. The granular material from the melting-
chamber ash is separated from the transpor~ing water, and is
removed, at a gate 28.
Boiler-feed water, which has been fed at 30 to waste-
heat boiler 24, flows through a line 32 having a branch 34
running the radiating portion of melting-chamber boiler 5.
Steam leaves the boiIer at 35 and, as shown in the example ~ -
of embodiment, it is passed through a heat-exchanger 36
arranged in ~idized-bed desulphurizer 8. This st~am then
passes ~hrough a line 37 to a steam-turbine unit 38 with
in~ermediate superheating 38a, followed by a condenser 39.
As indicated, the fossil fuels, in the form of coal,
are fed directly to the ~ombination block described. This
is also the case in the installations shown in Figs. 2 and 3.
The example of embodiment in Fig. 2 difers from
that in Fig. 1 mainly in the type of desulphurizer to which
the flue-ga~ses pass from line 7. The desulphurizing device
i~ Fig. 2 is marked 40. It uses a dry desulphurizer in the
form of a dust which is injected into desulphurizing vessel
41, at several locations, through nozzles marked 42-44. Again,
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the desulphurizer is passed, with the aid of air from air-
supply line ~7, shown in dotted lines, through a gate unit
.~. 45, to the ~bove-mentioned nozzles.
The sulphur associated with the desulphurizer leaves
vessel 41, in the form of a ~iolid, ~lrouyh a line 48 and is
therefore passed to a gradiny unit 15 which has an overflow at
lS. Part of the desulphurizer is returned to the gate through
a line 49, and part is removed at 16a for processing or further
. use. The amount removed is xeplaced at 16b by the addition
of fresh desulphuxizer.
In the example of embodiment according to Fig. 3,
solid-bed desulphuring is carried in a reaction vessel S0. In
this case, the desulphurizer may be in the form of pellets or
briquettes and may be fed continuously or intermittently
through a gate 51. If any desulphurizer, and the sulphur
associated therewith, is removed from vessel 50, this product
returns at 51 to the screen overflow of grading unit 15, and
so to line 16, fxom which the processed desulphurizer can
be returned to the pxocess at 53.
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