Note: Descriptions are shown in the official language in which they were submitted.
1057589t
This inventlon relates to the process of burning
carbonaceous materials under approximately stoichiometric
conditions in a fluid bed, wherein the discharged solids are
recycled to the fluid bed and heat of combustion is dissipated
through cooling surfaces.
Numerous systems have already been used to burn
carbonaceous materials. It is known, inter alia, to use for this
purpose fluidized-bed reactors operated as described herein-
before (see British Patent Specification 784,595 and J.R. GRACE,
"Fluidization and its Application to Coal Treatment and Allied
Processes", AICHE Symposium Series 141, Vol. 70 (197~), pp. 21-26,
and DL.KEAIRNS et al. "DeSign of a Fluidized Bed Combustion
Boiler for Industrial Steam Generation", AICH~ Symposium Series
126, Vol, 68 (1972), pp. 259-266.
The known processes have the disadvantages that the
height of the bed must be comparatively low so that the pressure
loss is kept within reasonable limits, that the presence of
cooling surfaces in the lower part of the reactor space involves
a disturbance of the transverse mixing of the solids in the
fluidized bed so that the inhomogeneities of temperature (over-
heating, formation of crusts) occur, and that the op0ration of the
reactor cannot be satisfactorily adapted to varying power
requirements. An adaptation can be effected virtually by a
fall in temperature in connection with modification by combustion
and fluidization conditions, or by a shut-down of individual
reactor units.
It is an object of the invention to provide a process
in which the known disadvantages, particularly those mentioned
hereinbefore, are avoided.
3o An object of the invention is to provide a process
which can be carried out with minimum structural expenditure
with greater economy and without the disadvantages of the earlier
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~ 057584
systems mentione~ above.
Another object of the invention is to provide an
improved fluid bed combustion system especially for particulate
carbonaceous material.s with greater combustion load per reactor
volume unit, low nitrogen oxide level in flue gases and improved
ability to respond to varying power demands.
St.ill another obJect of the invention is to provide
a combustion system for the purposes described which minimizes
the level of noxious or toxic components in the flue gases.
It is also an object of the invention to provide an
improved system for burning carbonaceous materials which have
been burned only problematically heretofore witll respect to
temperature homogenei.ty.
These objects are attained according to the invention
in that:
(a) combustion is carried out in the presence of
oxygen-containing gases, which are supplied in two partial
streams at different height levels of an upright fluid bed, and
at least one of the partial streams is used as a secondary gas
and fed into the combustion chamber on one plane or a plurality
of su~eriml~osed planes;
(b) the volume ratio of fluidizing gas to secondar~
gas is adjusted to a value in the range of substantially 1:20
to 2:1;
(c) the gas veloci.ty and the ratio of fluidizing gas
to sccondary gas are adjusted to provide above the secondary gas
inlet means a f]uldized bed condition having a mean suspension
density of 15-100 kg/m3;
(d) at least a substantial part of the heat of combus-
tion is dissipated through cooling surfaces disposed in thefree furnace space above the secondary gas inlet means;
1057584
(e) a major part of the carbonaceous material is
fed into the space which is disposed below the secondary gas
inlet means and virtually free of internal fixtures; and
(f) solids are withdrawn from the circulation system
which comprises the fluid-bed reactor, separator, and recycle
conduit.
In one aspect of the invention, there is therefore
provided a process for burning a carbonaceous material to
produce steam, which comprises the steps of:
introducing carbonaceous material into a fluid bed
in an upright reactor;
fluidizing the carbonaceous material in the fluid bed
with a primary fluidizing gas introduced at the bottom of the bed
and a secondary gas introduced in the fluid bed at a level
above that at which the primary gas is introduced and above the
bottom of the fluid bed, at least the secondary gases containing
oxygen;
burning the carbonaceous material with the oxygen;
maintaining the supply of carbonaceous material and
oxygen to the fluid bed at distinct proportions;
maintaining the volume ratio of fl.uidizing gas to
secondary gas at substantially 1:20 to 2:1;
removing thermal energy from the fluid bed by disposing
therein at a level about the location at which the secondary
gas is introduced, cooling surfaces in contact with the fluid
bed and extending into the interior thereof;
cooling the surfaces with water to produce steam;
controll.ing the removal of thermal energy by adjusting
the mean solids suspension density above the location at which the
secondary gas is introduced within the range of 15 to lO0 kg/m3
as a result of the adjusted velocity and the volumé ratio of the
gases;
~ 3 ~
~5'~584
controlling the fluidization of the material in the
bed to preclude the formation of a discrete upper level of the bed
and to ensure a solids density gradient decreasing over
substantially the entire height of the reactor;
maintaining below the level at which the secondary gas
is introduced, a space substantially free of internal obstruction
at which the carbonaceous material is introduced;
separating solids from the gas effluent from the bed
at the top thereof to collect solid particles;
recycling the solid particles to the fluid bed at a
lower portion thereof whereby the fluid bed and the means for
separating and recycling the particles constitute a closed
solids circuit; and
removing excess solids from the circuit, after the
separation thereof from the gas effluent from the bed.
The invention also provides, in a second aspect thereof,
an apparatus for the combustion of a carbonaceous material
comprising:
an upright vertically elongated fluid bed chamber;
means for introducing the carbonaceous material into
a lower portion of the chamber;
means for introdueing a fluidizing gas into the
chamber at the bottom thereof;
means for introdueing a secondary gas into the chamber
at least one meter above the fluidizing gas inlet means and at a
location up to substantially 30% of the total height of the
chamber, at least one of said gases containing oxygen sustaining
combustion within the chamber;
means for removing a flue gas entraining solid
particles from the top of the chamber;
cooling surfaces provided with ducts from a cooling
fluid disposed in the chamber and extending into the bed over
a region thereof above the secondary gas inlet means, the
4 -
lOS'7584
chamber having a substantially free space below the secondary
gas inlet means;
a separator for removing the particles from the flue
gas;
conduit means for recycling the particles separated
from the flue gas to the chamber;
a fluidized bed cooler;
means for removing recirculated particles from the
cycle formedby the chamber, the separator and the conduit
means and introducing same into the cooler;
means for fluidizing the particles in the cooler
with one of the gases prior to introducing same into the
chamber; and
means for passing the other of said gases in indirect
heat-exchanging relation with the fluidized particles in the
cooler prior to introducing the other gas into the chamber.
The solids are carried with the flue gases from the
bed by entrainment and are separated from the flue gases in a
single or multistage separation system, being recycled, at
least in part to a lower portion of the bed.
This lower portion of the bed is, according to a
critical feature of the inventionr free from internal fixtures
as note.d above, including any cooling surface which might
obstruct an undisturbed movement of the solids and gases of the
bed at least from the point of introduction of the primary
fluidizing gas (bottom of the bed) to a point at a safe distance
from the secondary gas inlet. Such lack of disturbance of
lateral solids mixing and of the initial mixing gases and solids
has been found to be essential to a satisfactory practice of
the invention.
However, it is also important and indeed critical to
the present invention that internal cooling surfaces within
the column or shaft of the bed are provided above the free space
-- 5 --
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~ .
` l~)S7584
and preferably over a major fraction of the heightof the bed,
these surfaces being generally in the form of upright fluid-
cooled walls.
It has also been found to be critical to control the
gas velocities and volumes! especially the ratio of fluidizing
gas to secondary gas so as to maintain above the secondary gas
inlet a fluidized bed with a mean solids suspension density
of 15-100 kg/m3. We have found that deviations from the range
result in sharp reductions of heat transfer rates at lower
values and increases in energy consumption for higher values
leading to a loss of efficiency at either end.
From an orthodox fluidized bed, which comprises a
dense phase that is separated from the overlying gas space
by a distinct step in density, the fluidized bed used in
accordance with the invention differs in that it involves states
of distribution which lack a defined boundary layer. There is no
drastic change in density between a dense phase and an overlying
dust-containing space but the concentration of solids in the
reactor decreases continuously in an upward direction to the place
at which the solids are entraii~led out of the reactor in a gas
stream.
When the operating conditions are de~ined by means
of the Froude and Archimedes number, the following ranges are
obtained:
0.1 ~ 3/4 . u . Pg ~ 10
g d Pk g
and 0.01 ~ Ar ~100
where dk g (Pk~Pg)
Pg Y
In the above relations:
~S7584
u = relative gas velocity in m/sec;
Ar = Archimedes number;
Pg = density of the gas in kg/m ;
Pk density of the solid particle in kg/m3;
dk = diameter of the spherical particle in m"
y = kinematic viscosity in m2/sec;
g = constant of gravitation in m/sec.2.
Because all oxygen-containing gases re~uired for the
combustion are divided into at least two partial streams which
are supplied on different levels, the combustion is effected in
two stages. Because of the substoichiometric combustion in a
first lower zone and an afterburning in a second higher zone there
results a "soft" combustion, which eliminates local overheating
so that formation of crusts or clogging is avoided and the
formation of nitrogen oxide is limited to values below 100 ppm.
Because internal blockage in the lower reactor space,
below the secondary gas inlet means, are avoided as far as
possible, a good distribution of the fed carbonaceous material is
instantaneously effected. The rapid mixing with the hot bed
material ensures good degasification and ignition of the fuel.
If the carbonaceous material is fed in A fineyrained
state, e.g., with a mean particle diameter oE 30 - 250 ,u,
it has a large surface area so that short reaction times are
enabled.
It should be noted that the mean particle diameter of
30 - 250 microns applies principally to fine-grain solid
carbonaceous materials which have been found to be particularly
suitable for use with the present invention.
The combustion may be carried out in a fluid-bed
reactor which is rectangular, square, or circular in cross-
section~ The lower part of the fluid-bed reactor may be down-
wardly tapered, e.g., conical; this is particularly desirable
Y, j`,~! ~
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1t)5'~584
with reactors which are large in cross-section or where
an inert fluidizing gas is used.
Under atmospheric pressure, the gas velocities in the
fluid-bed reactor above the secondary gas inlet means are
usually above 5 m/sec. and may be as high as 15 m/sec.
The ratio of the diameter to the height of the fluidized-
bed reactor should be such that gas residence times of 0.5-8.0
sec., preferably 1-4 sec., are obtained.
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lUS75~34
The latter parameters are not critical in the sense
that if deviation from these ranges occur, the system will become
inoperative or pose an environmental hazard. However, it has
been found that a residence time of 0.5-8.0 seconds for the gas
traversing the fluid-bed reactor should be maintained for optimum
results. If the residence time is greater or less than this
range,the system remains operative although various economic
disadvantages arise.
The fluidizing gas may consist of virtually any desired
]0 gas which will not adversely affect the quality of the exhaust
gas. Suitable gases are, e.g., inert gases such as recycled
flue gas (exhaust gas), nitrogen, and water vapor. To increase
the combustion rate, it will be desirable, to supply the reactor
with a fluidizing gas consisting of a partial stream of the
oxygen-containing gases required.
In view of the above, the process can be carried out
in the following ways:
1. An inert gas is used as a fluidizing gas. In this
case the oxygen-containing combustion gas used as secondary gas
must be charged in at least two superimposed planes.
2. Oxygen-containing gas is used as fluid~zinK gas.
In this case it i5 su:Eficient ~o feed secondary gas in one plane,
although the secondary gas also can be fed in a plurality of
planes in this embodiment.
A plurality of secondary gas inlet openings are
preferably provided in each feeding plane.
According to a preferred feature of the invention,
the secondary gas is fed on a level which is up to 30% of the
total height of the fluid-bed reactor, and at least 1 m, over
the fluidizing gas inlet. If in this case the secondary gas is
fed in a plurality of planes, the above level refers to the
level of the uppermost secondary gas inlet. The feeding on this
8 -
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~05758~
level ensures that there is a sufficiently large space for the
first combustion stage, so that the reaction of the carbonaceous
material and the oxygen-containing gas is almost complete in
this stage - whether the oxygen-containing gas is supplied as
fluidized gas or as secondary gas in a lower plane- and enables
the accommodation of sufficiently large cooling surfaces in the
upper reaction space disposed over the secondary gas inlet means.
The cooling surface area can be further increased if,
in accordance with another preferred feature of the invention,
additional cooling surfaces are installed on the wall of the
fluid~bed reactor. These cooling surfaces may cover also the
wall of the lower part of the reactor because this will not
adversely affect the mixing of solids. The wall itself may
constitute a cooling surface.
The cooling surfaces consist generally of rectangular
tube plates, which are cooled by a force-fed fluid and are spaced
at least 150 mm. preferably 250-500 mm, apart. Such Gooling
surfaces are used also in cooling walls. The axes of the tubes
should be parallel to the direction of flow of the gas-solids
suspension because this results in a minimum of erosion, Whereas
this results in a slightly lower heat transfer per unit of cooling
surface area than an arrangement of tubes having a horizontal
axis, which is at right angles to the direction of flow, the
smaller heat transfer is not significant because the process
according to the invention permits of an accommodation of large
cooling surfaces in the fluid-bed reactor and, if desired, in
the succeeding separating and recyclinG unit.
If the carbonaceous materials have only a low content
incombustibles, it is not economical to utilize their sensible
heat after their withdrawal from the circulation system compris-
ing the fluid-bed reactor, the separator, and the recycle
conduit. On the other hand, if the content of incombustibles
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~)57584
is high, the heat content will desirably be utilized. To this
end, the solids may be cooled in a fluidized-bed cooler. An
improved heat balance can be obtained if, in accordance with
a preferred feature of the invention, the solids are cooled in
a fluidized-bed cooler which preferably comprises a plurality of
chambers flown through in succession, and in which gas serving
as fludizing gas and/or secondary gas in the fluid-bed reactor
is heated, so that the heat content of the solids is returned
to the combustion process.
It will also be desirable to extract heat from the
exhaust gas from the fluid-bed reactor used for the combustion.
To this end conventional steam boiler technology waste-heat
recovery may be adopted or, in a particularly desirable manner,
the exhaust gas may be fed as fluidizing gas to a fluidized-bed
cooler. The fluidized-bed cooler may be of the Venturi type
and may be rectangular or square or circular in cross-section
and may consist of tube plates. Heat may alternatively be ex-
changed with a coolant flowing in tube bundles. Water is most
desirably used as a coolant because the water is thus heated
and is then fed to the cooling surfaces of the fluid-bed reactor
used for the combustion and is evaporated and/or superheated there.
To minimize the sulfur content of the exhaust gas,
the combustion process is preferably carried out in the presence
of fine-grained desulfurizing agents such as lime, dolomite and
the like. The desulfurizing agents should have approximately
the same particle size as the solid carbonaceous material and
are simply fed jointly with the latter or are introduced scpa-
rately in the fluid-bed reactor.
For a reactor having given dimensions, the capacity can
be increased in accordance with a further preferred feature of
the invention in that the combustion process is carried out
- with oxygen-enriched air rather than with air and/or under
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10575~4
superatmospheric pressure, preferably up to 20 kg/cm gauge.
In this case the cooling surface area must be larger
than for an operation with air and/or under atmospheric pressure.
This may be accomplished, e.g., by the installation of additional
cooling registers in the furnace space above the secondary gas
inlet means.
If oxygen-enriched air is used, the density of the
suspension in the reactor space above the secondary gas inlet
means should lie in the upper part of the range from 15 to lO0
kg/m3 because the heat flow densities are higher and a higher
solids concentrations yield higher coefficients of heat transfer.
The main advantage of the process according to the
invention resides in that it can be adapted in a very simple
manner to the power requirement, which varies substantially in
practice. According to a preferred feature of the invention
this is accomplished in that the combustion rate is controlled
by a control of the density of the suspension in that part of
the furnace space of the fluid-bed reactor which is disposed
above the secondary gas inlet means.
Given operating conditions, including given flui-
dizing gas and secondary gas volume rates and a gtven resulting
mean average density of the suspension, are accompanied by a
distinct coefficient of heat transfer at the cooling surfaces.
The heat transfer will be increased if the density of the suspen-
sion is increased by an increase of the fluidizing gas rate and,
if desired the secondary gas rate, At a virtually constant
combustion temperature in the whole cyc]e, the increased heat
transfer enables the dissipation of the heat at the rate which
corresponds to the higher combustion rate. The higher o~ygen
requirement which is due to the higher combustion rate is virtu-
ally automatically met by the fact that the fluidizing gas and,
if desired, secondary gas are fed at higher rates to increase
1)
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l~St~584
the density of the suspension.
~ or an adaption to a lower power reauirement, the
combustion rate can be controlled by a decrease of the density
of the suspension in that part of the furnace space of the fluid-
bed reactor which is disposed above the secondary gas inlet.
The decrease of the density of the suspension results in a decrease
of the heat transfer so that less heat is dissipated from the
fluid-bed reactor and the combustion rate can be decreased sub-
stantially without a decrèase in temperature,
The carbonaceous material is fed in the conventional
manner, most desirably through a single lance or a plurality of
lances and preferably by pneumatic blowing. Owing to the good
lateral solids mixing, a relatively small number of lances are
sufficient and in fluid-bed reactors having small dimensions
even a single lance will suffice.
The solid combustion residues entrained by the exhaust
gases from the fluid-bed reactor are recycled by means of cyclone
separators or baffles or impingement separators in which the
gas stream is deflected, The walls of the recycling means are
provided, if desired, with coolin~ surface~ which are ~re~erably
approached by ~arallel flows.
The final purification of the gases may be accomplished
in a conventional way, e,g,, by means of an electrostatic precip-
itator. The solids which are thus collected may by recycled
into the fluid-bed reactor to minimize the carbon content.
The process according to the invention is particularly
suitable for the combustion of coal of any kind, of coal-washing
refuse, retort residue, oil shale, fuel oil and mixtures thereof.
Where fuel oil.is used as the carbonaceous material, a bed material
is required which consists, e.g. of fine-grained lime or dolomite
or other mineral substances having approximately particle sizes
in the range of 30 - 250 microns.
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~57S~9~
The essential advantage afforded by the process
according to the invention resides in that the temperature
throughout the circulation system comprising the fluid-bed
reactor, separator, and recycling means is more constant than in
any previous processes of burning carbonaceous material. The
intense motion of solids precludes temperature gradients so that
an overheating of individual solid particles is avoided.
In the preferred embodiment of the process, comprising
the addition of desulfurizing agents, the fact that temperatures
are constant has a beneficial effect also on the desulfurization
ef~iciency of the exhaust gases. As a result of the constant
temperatures, the desulfurizing agents retain their activity
and their capacity to take up sulfur and low ~toichi~metric ratios
of Ca:S (less than 2) are needed.
This aclvantage is supplemented by the small particle
size of the desulfurizing agent because the sulfur-combining
velocity depends mainly on the diffusion velocity and is particu-
larly promoted by the existing relation of surface area to volume.
The process according to the invention also enables
a complete combustion of the carbonaceous material. In the
preferred embodiment of the invention with oxygen rates only
slightly above the stoichiometric requirement e.g., not above
an excess of 30 % preferably not above 10 % such results are
obtained.
The invention will now be explained more ~ully and
by way of example with reference to the accompanying drawing
and the Examples, In the drawing:
Fig. 1 is a diagrammatic sectional view showing a
fluid-bed reactor having a square reactor space;
Fig. 2 is a diagrammatic sectional view showing a
fluid-bed reactor having a cylindrical reactor space which has
a conical lower part;
1a~5-7~
Fig, 3 is a diagrammatical sectional view showing the
fluid-bed reactor of Fig. 1 and the equipment connected thereto.
A fluid~bed reactor l is provided with cooling surfaces
3 disposed above a secondary gas inlet 2. ~dditional cooling
surfaces 4 and 5 are disposed on the wall of the fluid-bed
reactor 1 and of a separator 6, which is structurally combined
with the fluid-bed reactor 1. To show the arrangement of the
cooling surfaces more clearly, the several tubes have a horizontal
orientation, which differs from the preferred embodiment in which
the tubes run vertically.
In operation, the fluid-bed reactor l is fed with
carbonaceous material through a lance 7, with fluidizing gas
through inlet 8, and with secondary gas through inlet 2. A rela-
tively dense fluidized bed is disposed between the secondary gas
inlet 2 and the fluidizing gas inlet ~ and has a density of sus-
pension which may attain a value as high as the bulk density of
the bed material. The mean density of the suspension above
the secondary gas inlet 2 is 15 - lO0 kg/m3.
The solids entrained by the exhaust gas from the
fluid-bed reactor l are collected from the exhaust ~as in the
separator 6 and are recycled throu~h conduit 9 into the ~luid-bed
reactor 1. The surplus solids produced are withdrawn through
conduit 10.
The fluid-bed reactor shown in Fig. 2 has a conical
lower portion. In this case, secondary gas is fed through in-
lets 2a, 2b, and 2c, 2d disposed on different levels. The other
reference characters are the same as in Fig. 1.
In the embodiment shown in Fig. 3, the arrangement
shown in Fig. l is succeeded in the exhaust gas path by a waste-
heat boiler 11 and an electrostatic precipitator 12. A fluidized-
bed cooler 14 provided with cooling registers 13 serves to cool
the solids discharged through conduit lO.
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1~5~7584
In the waste-heat boiler 11, which consists of a
fluidized-bed cooler, additional sensible heat is extracted from
the exhaust gas from the separator 6 of the fluid-bed reactor.
A fine purification of the exhaust gas is effected in the electro-
static precipitator 12. Solids which are thus collected are
conducted in conduit 15 and combined with the solids discharged
through conduit 10. The combined solids are then fed to the
fluidized-bed cooler 14,
The fluidized-bed cooler 14 comprises four chambers,
which are flown through in succession, and is supplied with
oxygen-containing fluidizing gas through conduit 16. The gas is
collected in the hood and is fed through inlet 2 as secondary
gas to the fluid-bed reactor 1. By the cooling registers 13,
the solids are indirectly cooled with a gas, which is supplied
through conduit 17 and which may contain oxygen, if desired.
Except for a partial stream, the gas leaving the cooling registers
13 is supplied through conduit 8 as fluidizing gas to the fluid-
bed reactor 1. The branched-off partial stream is used for
pneumatically feeding the carbonaceous material through lance 7.
In Figs. 1-3 the feed line 7 for the carbonaceous
material is shown to be provided with a blower 7a through which
a carrier air or gas can be introduced and which entrains particles
of a desulfurizing agent from a dispenser 7b and particles of a
carbonaceous material from a dispenser 7c. A valve 7d permits a
portion of the primary fluidizing gas to be used as part of the
carrier gas or allows part of the carbonaceous material or the
carrier gas to be introduced at the bottom of the fluid-bed.
Example 1 (with reference to E`i~. 1)
Coal was burned with air. The fluid-bed reactor 1 used
for this purpose had a base area of 1 x 1 m2 and a height of
12 m, The reactor was provided throughout its inside wall with
a cooling surface 4 having an area of 60 m2. Besides, the reactor
1~)57584
space contained plane vertical cooling surfaces 3 having an
additional cooling surface area of 27 m2 and disposed above
the secondary gas inlet 2. The fuel lance 7 was disposed 0.2
m over the grate and the secondary gas inlet 2 was disposed
2.5 m over the grate.
Coal having a calorific value Hu = 7170 kcal/kg
(= 30.0 MJ/kg) and a mean average particle diameter of 0.1 mm
was pneumatically fed at a rate of 1 metric ton/h by means of
air at a rate of 150 standard m3/h. The fluid-bed reactor 1
was fed through the grate with 4000 standard m3/h air at 300
C and through inlet 2 with 4300 standard m3/h air at 300C.
The mean density of the suspension in the reactor space was
300 kg/m3 below the secondary gas inlet 2 and 50 kg/m3 above
the inlet. The temperature throughout the circulation system
was about 850C.
The combustion residues were collected from the
exhaust gas in the separator 6 and were recycled into the
fluid-bed reactor 1. A partial stream was discharged at 10
and so controlled that the amount of residues recycled per
hour was five times the amount of solids contained in the
fluid-bed reactor.
Under the above-mentioned process conditions,
coefficients of heat transfer amounting to 120 watts/m2C were
obtained. Of the total heat supplied at a rate of 9.2 x 106
watts, heat at a rate of 5.8 x 106 watts was dissipated
through the cooling surfaces and used to generate saturated
steam at 60 bars. The utilization of the fuel was 99~. The
CO content in the exhaust gas was less than 0.1~.
Example 2 (with reference to Fig. 1)
Coal was burned with oxygen-enriched air. The fluid-
bed reactor 1 described in Example 1 was used for this purpose.
In that reactor the area of the cooling surfaces disposed in
the upper reactor space had been increased to 37 m2. Besides,
ti ? /b
1057~4
additional cooling surfaces having an area of 15 m2 had been
installed in the separator 6 on the walls thereof.
During operation under full load, coal having a
calorific value H = 7170 kcal/kg and a mean particle diameter of
0.1 mm was pneumatically fed at a rate of 2.7 metric tons/h by
means of 300 standard m3/h oxygen-containing gas, which contained
60% by volume oxygen and was at 300 C. The density of the
suspension was about 300 kg/m3 in the reactor space below the
secondary gas inlet 2 and about 90 kg/m3 in the reactor space above
the secondary gas inlet 2. The temperature throughout the
circulation system was about 850 C. The solids collected from
the exhaust gas in the separator 6 were recycled to the fluid-
bed reactor 1 at such a rate that the amo~lnt of solids recycled
per hour was eight times the solids content of the reactor. The
remainder was discharged through conduit 10.
The coefficients of heat transfer obtained under these
conditions amounted to 290 watts/m2 C. Of the total heat
supplied (23.4 x 106), heat corresponding to 18.7 x 106 watts
was dissipated through cooling surfaces and used to generate
saturated steam at 60 bars.
Owing to a reduc~d power requirement, it was desired to
operate the plant at one-third of the steam generation rate.
Whereas the fluid-bed reactor 1 and the installed cooling surfaces
4 and 5 were not changed, the coal-feeding rate was reduced to
0.9 metric ton/h. Coal was fed through lance 7 by means of 100
standard m3/h air. The same fluidizing and secondary gases as
described hereinbefore were fed at reduced rates of 400 and 2200
standard m3/h, respectively.
Under the above-mentioned conditions, the concentration
of solids was increased to about 530 kg/m3 in the lower reactor
space and was decreased to about 30 kg/m3 in the upper reactor
- space. The coefficients of heat transfer were decreased to 100
watts / m2 C. I~
,~ - ~6 -
10575~
It is apparant that an adaptation to the power require-
ment was accomplished by the mere change of the rates at which
coal, fluidizing gas and secondary gas were fed. The solids
content throughout the fluid-bed reactor and the temperature of
850 (+10) C in the circulation system were not changed.
Only a very short time was required to run up the
reactor to a higher power or to full load.
Example 3 (with reference to Fig. 1)
Fuel was burned with air under superatmospheric pressure.
For this purpose, the fluid-bed reactor 1 was used which has been
described in Example 1 and had been provided with cooling surfaces
having a total area of 132 m2 60 m2 of said area were provided
on the inside wall of the reactor space, 25 m2 on the walls of
the separator 6, and 47 m in the free reactor space disposed over
the secondary gas inlet 2. The fluid-bed reactor contained a
sufficiently large amount of limestone as bed material.
Fuel oil having a calorific value of 96~0 kcal/kg
(= 40.2 MJ/kg) and an S content of 3.2 % by weight was fed at a
rate of 1.5 metric tons per hour through lance 7. Limestome
which contained about 97% by weight CaC03 and had a mean particle
diameter of about 0.1 ~ 0.2 mm was pneumatically fed as a bed
material and as sulfur-combining agent at a metered rate of
278 kg/h, corresponding to a molar ratio of 1,8 moles CaO per
mole of sulfur in the fuel oil, by means of 50 s-tandard m3/h air.
The fluid-bed reactor was fed through the grate with
10,500 standard m3/h air and through the secondary gas inlet 2
wit;h 7000 stnndard m3/h air. The air in both streams was under
a pressure of 5 bars and at a temperature of 300 C. A tempera-
ture of 850 C was obtained in the circulation system. The
withdrawal of solids through conduit 10 and the recycling of
solids through conduit 9 were controlled so that the amount of
solids recycled per hour was about eight times the solids content
- Jd~ .
lOS75~
of the fluid~bed reactor.
Under these conditions of operation, the mean density
of the suspension in the reactor space was 300 kg/m3 below the
secondary gas inlet 2 and 60 kg/m3 above the secondary gas inlet
2. The coefficient of heat transfer was about 150 watts/m2 C
Of the total heat supplied at a rate of 18.6 x 106 watts, heat
at a rate of 11.4 x 106 watts was dissipated by the cooling sur-
faces formed by tubes and was utilized to generate sa-turated
steam at 60 bars.
The utilization of the fuel amounted to 99%. The C0
content in the exhaust gas was below 0.1% by volume and the N0
content below 100 ppm. A desulfurization of 90% was effected.
Example 4 ¦with reference to Fi~. 3.)
Coal-washing refuse was burned with oxygen-enriched
air. For this purpose, the f]uid-bed reactor 1 was used which
has been described in Example 1 and which had been provided with
cooling surfaces of 60 m2 area on its inside wall, of 58 m2 area
in the upper reactor space and of 25 m2 area in the separator 6.
Coal-washing refuse containing 67% by weight ash, a
combustible content of 30% by weight, a moisture content of 3 %
by weight, a mean particle size of 0.08 mm, and a calorific
value of 2000 kcal/kg (-8.4 MJ/kg) was fed through lance 7 at
a rate of 9.1 metric tons/h by means of 1000 standard m3/h
conveying gas, which had an oxygen content of 60 % by volume
and a temperature of 450 C. The reactor was fed through the
grate with 4000 standard m3/h fluidizing gas and -through the
secondary gas inlet 2 with 2700 standard m /h secondary gas.
Each of said gas streams had an oxygen content of 60 % by volume
and a temperature of 450 C.
The mean density of the suspension amounted to about
250 kg/m3 below the secondary gas inlet 2 and to about 70 kg/m3
above the secondary gas inlet 2.
1S
, ;, ~ --
~057S84
Ash was recycled at such a rate that ten times the
reactor content was recycled per hour. m e remainder was dis-
charged through conduit 10. The temperature throughout the
circulation system was at about 850 C.
The hot incombustible residue discharged through
conduit 10 was fed to a fluidized-bed cooler 14, which comprised
four chambers and interconnected cooling registers 13 immersing
into the several chambers. The fluidizing gas at a rate of
2700 standard m3/h had an oxygen content of 60 % by volume and
the indirect coolant at a rate of 500 standard m3/h consisted
of a gas having the same composition. These gases were heated to
450 C and were supplied to the fluid-bed reactor 1 as secondary
gas, as a fluidizing gas and as a feeding gas, respectively.
The incombustible residue was discharged from the
fluidized-bed cooler 14 at a temperature of 150 C. Under these
conditions, coefficients of heat transfer amounting to 200
watts/m C were obtained. Of the total heat supplied at the
rate of 22.6 x 106 watts, heat at a rate of 16.6 x 10 watts was
dissipated through the cooling surfaces and used to generate
saturated steam at 60 bars.
1'-` -~ -
