Note: Descriptions are shown in the official language in which they were submitted.
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Continuous fuel supply system for a coal gasification reactor
[0001] The invention relates to a process for the controlled continuous
supply of
fine-grain to pulverised fuel materials into a pressurised feed tank in a
pressure gasifi-
cation process in which finely ground or pulverised (< 0.5 mm) fuel materials
such as
coal, petrol coke, biological waste or fuels are converted in suspension with
low particle
load (< 50 kg/m3; no fluidised bed) by reaction with gasifying agents
containing oxygen,
under elevated pressure at temperatures above the slag melting point.
[0002] In the course of pressure gasification processes a carbon-
containing fuel
material is converted by means of an oxygen-containing gas, wherein the oxygen-
containing gas is supplied in a substoichiometric ratio so that a carbon
monoxide con-
taining product gas is obtained. If the reaction gas contains water vapour,
the product
gas is of synthesis gas character and contains major portions of hydrogen. To
achieve
a conversion that is as complete as possible under substoichiometric
conditions, the
fuel material must be fed to the reactor in finely ground condition. The
reaction normally
takes place under elevated pressure.
[0003] Since gasification reactions are operated economically only if
operated con-
tinuously for an extended period of time, the amount of finely ground fuel
material sup-
plied per time unit should be as constant as possible to ensure trouble-free
operation.
The transfer of the fuel material to the required pressure level and the
supply of the fuel
material under pressure are problems yet to be solved in coal gasification
reactions.
For this reason, coal gasification plants always include plant equipment which
serve to
ensure trouble-free supply of fuel to the reactor. Such equipment usually
consists in
special dosing tanks and lock hopper assemblies operated by gravity flow.
[0004] Using dosing tanks is not always a means to completely eliminate
the pies-
sure variations occurring when loading the reactor. This may result in
pressure varia-
tions during the carbon gasification reaction which will temporarily change
the composi-
tion of the synthesis gas. Especially the discontinuous filling of the dosing
tank from the
pressure locks generates pressure variations which are of unfavourable effect
on the
pressure difference which serves as driving force for the conveyance between
dosing
tank and burner.
[0005] Introducing the fuel material by gravity flow as done when
supplying the
coal gasification reactors with fuel material is also a potential source of
error. As the fi-
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nely ground fuel material may clog or plug depending on its quality and degree
of dry-
ing, conveyance will sometimes proceed batchwise only or with unexpected
periodic in-
terruptions. In addition, lock hopper systems based on gravity flow frequently
require
sophisticated design solutions since tanks between which conveyance is to be
achieved must be arranged on top of each other.
[0006] Fuel feed systems according to the state of the art are
expenditure-
intensive and not always reliable in operation. In the case of large-capacity
plants, the
spatial separation of grinding and gasification units involves considerable
additional
expenditure as regards the transport of finely ground fuel materials from the
grinding
unit to the fuel feed system. This makes it necessary to provide additional
equipment
(conveying vessels or pneumatic pumps, filters, buffer tanks above the feed
systems).
In addition, considerable expenditure is incurred by piping, instrumentation
and con-
struction work, the latter especially because of the exposed position of the
buffer tanks
at the highest elevation of the gasification unit. Furthermore, lock hopper
systems
which operate according to the gravity flow principle have proven to be
inadequately re-
liable in operation. Additional equipment will at any rate increase the risk
of failure.
[0007] Apart from this commonly known fact, the principle of lock hopper
gravity
feed involves specific functional risks. Despite many very diverse approaches,
it has
proven to be extremely difficult to carry out the process of vessel
pressurising carefully
enough to keep the internal stress of the bulk material sufficiently low. In
many cases,
the bulk material is locally compacted to such a degree that the gravity flow
to the feed
tank is subsequently not induced at all or only to an inadequate extent. The
solid mate-
rial inventory of the feed tank hence diminishes, which frequently causes a
limited out-
put or may even cause the failure of the gasification unit.
[0008] The problem aggravates if oversizing owing to a high plant capacity
comes
up against the construction limits and if the gasification unit is to be
designed for a
higher pressure (typically 4 MPa) than that of the units which have been in
operation
for many years (typically 2.5 MPa).
[0009] Lock hopper gravity feed from the lock hopper into the feed tank
will pro-
duce very high transfer mass flow rates, provided the desired gravity flow is
achieved,
and thus comparatively short transfer periods. The transfer of solids during
lock-hopper
feeding will raise the filling level in the feed tank. The filling level will
then continuously
decrease again by the amounts of fuel supplied to the burners and increase
again by
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=
the next lock hopper transfer operation. In this way, the feed tank is
subjected to tem-
porarily changing conditions which may even affect the steady delivery from
the feed
tank. It is considerably more advantageous to keep the pressure conditions,
the filling
level and the pulsed feed into the bulk fill by dropping-in material, for
instance, as con-
stant as possible with regard to time.
[0010] Some embodiments of the present invention may solve these
problems by a
dosing tank which contains the finely ground fuel material under pressure and,
according
to some embodiments of the invention, has a nearly constant fuel filling
level. Such
almost constant filling level in the feed tank is ensured according to some
embodiments of
the invention by supplying solid material continuously from at least two lock
hoppers via at
least one jointly used continuous supply line which is suited for dense-flow
conveying. As
the continuous supply line is not operated by gravity, it is further possible
to install the feed
tank and the supplying lock hoppers at different geodetic elevations and, in
addition, at a
greater distance from one another, as may be, for example, in a different
building. =
[0011] Known are dosing devices for fuel materials that feed the fuel
material to
the reactor via a dosing tank with upstream lock hopper system. US 5143521 A
de-
scribes a system for the feeding of fuel material into a feed tank which
stores pressur-
ised fuel material and is supplied continuously with finely ground fuel
material by a sys-
tem of lock hoppers. The lock hoppers are connected by a line and pressurised
alter-
nately. The pressure of the expansion gas of the one lock hopper may be used
via a
system of expansion turbines, Venturi tubes and compressors to pressurise the
other
lock hopper. In this way, it is possible to adjust the pressure of finely
ground coal at at-
mospheric conditions to a level suited for coal gasification. Nitrogen is used
as pressur-
ising gas.
[0012] DE 102005047583 Al describes a process and a facility for dosing and
feeding pulverised fuel materials under pressure to a coal gasification
reactor. To en-
sure a constant the feed of fuel material to the coal gasification reactor
over a given pe-
riod of time, the fuel is stored intermediately in a dosing tank, in the lower
part of which
a dense fluid bed is generated above the tank bottom by feeding in gas,
through which
the pulverised fuel material is supplied continuously via burners to a
pressurised gasifi-
cation reactor. Actual feeding to the burners is here implemented by the so-
called high-
speed conveyance, wherein the supply of auxiliary gas to the feed line
downstream of
the burner is used to generate a pressure difference by which the fuel
material is then
transported to the burners. The dosing tank is supplied with fuel material
from two locks
which transport the fuel material by means of gravity and a star feeder into
the dosing
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tank. This is, however, susceptible to failures and requires structures of
high altitudes.
A use of grinding devices is not mentioned.
[0013] The
present invention describes an integrated process for comminuting a
carbonaceous fuel material, pressurising the fuel by means of a suitable gas,
distribut- =
ing and transporting the fuel to a feed tank and feeding it to the reactor.
Transport, dis-
tribution of the fuel and feeding to the reactor are implemented by dense-flow
convey-
ing in a so-called continuous supply line. In this way, the complete fuel
supply chain of
the reactor can be carried out without gravity flow. The gasification reactor
outlet tem-
peratures are preferably above the slag melting point in a range between 1200
and
2000 C and the pressure is preferably between 0.3 and 8 MPa.
[0014] Dense-
flow conveying in this context signifies a pneumatic conveying which
does not transport the fuel material particles as individual particles but in
a dense flow
in the form of dense packings or plugs which fill in the entire cross-
sectional area of the
pipe. The dense-flow conveying flow rates are generally between 4 and 5 m/s,
wherein
a high transport volume is achieved despite the high solid load of the gas
flow. Dense-
flow conveying is characterised by gentle transport of the material and is
especially lit-
tle susceptible to failures by adhering or moist conveying material. The
present pneu-
matic dense-flow conveying process is carried out preferably with solid
densities of at
least 100 kg/m3 and at a differential pressure of at least 0.5 bar.
[0015] Special claim is laid
to a process for supplying finely ground fuel materials
to a cooled reactor (15) for gasification by means of oxygen-bearing gasifying
agents
under pressure, wherein
= the gasifier outlet temperatures are above the slag melting point in the
range
between 1200 and 2000 C and the pressure is between 0.3 and 8 MPa,
= and the finely ground
fuel material is pressurised via a lock system to a pres-
sure level above the gasifier pressure, transferred to at least one feed tank
and from there dosed in dense flow via at least one fuel line to one or more
gasification burners of one or several gasifiers, and
= the conveying gas volume supplied at the discharge of lock hopper is
recovered
in feed tank and returned to lock hopper by means of a device for pressure
increase, and
= the transfer from at least two lock hoppers to at least one feed tank is
carried out
by using a pneumatic continuous supply line jointly,
simultaneously = or
successively at solid material densities of at least 100 kg/m3 and a
differential
pressure of at least 0.5 bar.
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[0016] In an embodiment of the process, the transfer from the lock
hoppers to the
feed tank or tanks is controlled by at least one connection device and at
least one uni-
fying element and the transfer from the unifying element to the feed tank is
imple-
mented by means of individual connection devices or by means of additional
unifying
elements with transferring connection devices.
[0017] The transferring connection devices are designed in an exemplary
fashion
as continuous supply lines suited for dense-flow conveying. By installing
unifying ele-
ments downstream of the lock hoppers, the fuel material is conveyed from the
lock
hoppers to the feed tanks via a number of continuous supply lines which is
smaller than
the number of lock hoppers. It is also possible to direct the solid material
from the out-
lets of the lock hoppers not directly into the unifying elements but via
connection ele-
ments so that it is passed via lines into the unifying elements first and then
into the con-
tinuous supply line. Here, the number of unifying elements is smaller than the
number
of lock hoppers and it may be identical with the number of continuous supply
lines. The
unifying elements are provided as closely to the outlet nozzles as possible
and ar-
ranged as symmetrically to them as possible to ensure a smooth solid flow.
[0018] In a preferred embodiment of the process, the fuel material is
processed
into a finely ground form by mean of a mill or a suitable grinding device. For
this pur-
pose, the fuel material can be made available in any form. It is possible to
deliver fuel
material that has already been finely ground. In such case, claim is only laid
to the
pressurisation of the fuel material and the transport into the reactor.
Usually, however,
the grinding process is an integral part of the process according to the
invention, espe-
cially if the grinding device is arranged in local proximity to the reactor.
In a preferred
embodiment of the invention, the coal milling and drying (CMD) unit is an
integral part
of the coal gasification plant.
[0019] To carry out the transfer function, the lock hoppers are
pressurised with a
gas. Recycled process gas may be used, for example. It is also possible to use
an inert
gas. Pressurising is performed advantageously with inert gases (e.g. nitrogen,
carbon
dioxide) or by means of process gases or recycle gases. To configure the
transfer
process in an advantageous way, pressurising of the lock hoppers by supplied
gas is
preceded by a mutual partial pressurisation of the lock hoppers. To keep the
process
conditions as constant as possible, the lock hoppers are pressurised and
depressur-
ised alternately.
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[0020] In an additional embodiment of the process, the grinding
circuit is blanketed
with inert gas and for blanketing the grinding circuit with inert gas, the
expansion gases
from the lock hoppers are used. The latter are depressurised at regular
intervals for
carrying out the transfer process, wherein the discharged gas can be recycled
to the
grinding devices. This may make the process reliable in operation and keep the
plant
= operating cost at a reasonable level. The gas of the grinding circuit is
additionally de-
dusted. For this purpose a dust separator is used which may also be used to
dedust
the expansion gases from the lock hoppers. The pressurisation or expansion gas
may
be dedusted by means of a dust separator in basically any place of the
process.
[0021] The finely ground fuel material is then preferably fed to a feed
tank. In this
way it is possible to store the fuel material in accordance with the
availability and to
= temporarily buffer the raw material flow. It is thus possible to adjust
bottlenecks which
are compensated by refilling at a later date.
[0022] To run the process according to the invention, all solid,
carbonaceous fuel
materials that can be divided into small particles by milling or grinding may
be used.
These may especially be all kinds of carbon, wherein hard coal, brown coal and
basi-
cally coals of all carbonization kinds are suitable. Suitable as fuel
materials are also
biological fuel materials such as wood, biomasses and other fuel materials
such as
plastic waste and petrol coke or mixtures of these. To run the process
according to the
invention, it should merely be possible to crush the fuel materials into a
finely ground
form which is suitable for dense-flow conveying.
[0023] Subsequent to the comminuting process and the storage in
the feed tank,
the solid material is passed to the lock hopper system in which the solid
material is
pressurised with supplied gas to carry out the gasification reaction. In a
preferred em-
bodiment of the invention the feed tank is atmospheric. Conveyance of the
solid mate-
rial into the lock hoppers is advantageously performed by gravity.
[0024] To run the process according to the invention, the lock
hopper system con-
sists of at least two lock hoppers. In this way, it is possible to connect the
discharging
operations in series and to ensure a nearly continuous material flow. In an
advanta-
geous embodiment the lock hoppers are pressurised individually.
.
[0025] In an embodiment of the process according to the
invention two lock hop-
pers are used to ensure a continuous material flow. The investment cost for
the plant is
thus low. In a further embodiment of the invention, it is also possible to use
three or
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more lock hoppers. This is especially recommended in the case of high plant
through-
puts.
[0026] It is possible to use a plurality of lock hoppers and a
plurality of unifying
elements. In principle, the facility according to the invention may consist of
lock hop-
s pers and unifying elements of any number. The number of lock hoppers is
determined
by the throughput of the plant. The number of unifying elements is determined
by the
number of lock hoppers and the number of continuous supply lines. Different
arrange-
ments of theoretically any number are possible. The interconnection of the
lock hop-
pers and the unifying elements may basically also be carried out as desired.
For this,
any number of connection devices may be used. Preferred connection devices are
pipelines. Possible as well are hoses or flanges, for example. The mode of
spatial in-
terconnection may also be selected as desired.
[0027] Subsequent to pressurising the tanks, the contained fuel
material is dis-
charged in dosed quantities and the pressure in the tanks is then expanded. In
an ad-
vantageous embodiment of the invention the expansion gas is used to partially
pressur-
ise the next lock hopper in the cycle. In order to improve the efficiency,
this may be im-
plemented by introducing the expansion gas directly into the tank to be
pressurised.
[0028] To reduce the dust load of the expansion gas, the
expansion gas is advan-
tageously introduced into the dust separator which is also used to dedust the
gas from
the storage tank or from the grinding process. In principle, it is also
possible to clean
the gas from solid material dusts by means of several independent dust
separators. To
keep the investment cost low, it is advantageous to use only one dust
separator.
[0029] The material flow from the lock hoppers is routed to the
feed tank via at least
one unifying element and the continuous supply line. To utilise the advantage
of some
embodiments of the invention, the lock hoppers are emptied one after the other
in such a
way that a nearly continuous fuel material flow to the feed tank is achieved.
In this way,
the subsequent feed tank for the gasification reactor can be supplied with a
continuous
material flow of a pressure that is suitable for the gasification reaction,
wherein the filling
level of the feed tank remains nearly constant. The filling level of fuel
material in the
feed tank can be adjusted according to the advantageous embodiment of the
process
such that it does not vary by more than 30 % over a given period of time. If
the proc-
ess according to the invention is run by specialists, it is easily possible to
keep the fill-
ing level variations of the feed tank in a range of not more than 10 A over
an ex-
tended period of time.
=
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[0030] The filling level of the feed tank may also be kept constant by
controlling
the continuous supply of finely ground fuel material from the lock hoppers by
adjusting
the pressure difference between lock hopper and feed tank. The inlet or outlet
of gas
into the free space of the lock hoppers influences the pressure difference
between lock
hopper and feed tank and is used as control parameter for the solid material
transport.
[0031] To run the process, the finely ground fuel materials are
preferably of a par-
ticle size which is smaller than 0.5 mm. This is achieved in a grinding and
comminuting
process. The discharge of solid material from the lock hopper may be
facilitated by the
addition of gas into the lock hopper in the immediate vicinity of the
discharge nozzle.
The density in the continuous supply line is adjusted advantageously by adding
gas
into the continuous supply line or into the unifying element or into both. The
addition of
gas at this point may also be used to purge the continuous supply line or the
unifying
element. The connection elements between lock hopper and unifying element may
also
be supplied with gas.
[0032] The conveying gas volume supplied at the discharge of the lock
hopper is
recovered in the feed tank in an advantageous embodiment of the invention and
re-
turned into the lock hopper by means of an injector. The returned conveying
gas and
the propellant gas of the injector are jointly used as replacement gas for the
emptying
lock hopper and thus also for maintaining the pressure of the lock hopper
during the
conveying process.
[0033] To suit certain requirements, it may be of advantage that two or
more lock
hoppers discharge solid material simultaneously or temporarily simultaneously
into a
conveying line. Gas balancing between the feed hoppers may advantageously be
achieved by a gas connection line between the lock hoppers.
[0034] The process according to the invention may also include processes
which
are subsequent processes of the coal gasification process according to the
invention.
Also included in the process according to the invention are process steps
which are re-
quired for a routine operation of the reactor. These may, for instance, be
cleaning
steps. These may as well be supporting process steps such as the supply of gas
for
loosening plugs. Possible as well are process steps for measuring parameters
such as
filling levels, flow rates, pressures or temperature. The invention especially
also de-
scribes a facility to run this process. The facility according to the
invention may include
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=
all plant units that are required for operating a coal gasification plant
according to the
process of the present invention.
[0035]
Claim is also laid to a facility used to supply solid fuel materials to a
reactor
for the gasification of solid fuel materials, comprising
=
= a grinding device,
= a dust separator,
= a storage tank,
= at least two lock hoppers,
= at least one connection device for dense-flow conveying,
= a feed tank,
= a gasification reactor, wherein
= the grinding device is connected to a storage vessel by means of
connection
devices, wherein a dust separator is installed between the grinding device and
the storage tank, and
= a device for pressure increase is provided which returns conveying gas from
feed
tank to lock hopper,
= the storage tank is connected to the lock hoppers via connection devices
which are
suited for gravity flow or dense-flow conveying, and
= the lock hoppers are connected to a feed tank by means of jointly used
connec-
.
=
tion devices which are suited as continuous supply line for dense-flow convey-
ing, and this feed tank is connected to the gasification reactor via further
fuel
material lines.
[0036] The
dense-flow conveying from the lock hopper system to the feed tank al-
lows to install the feed tank at the same or different geodetic height as the
lock hopper
system. In the case of the gravity lock hopper systems known to date it is
indispensa-
ble to install the lock hoppers above the feed tank. By this measure it is
possible to re-
duce the constructional height of the overall plant to a considerable degree.
It is also
possible to locate the lock hopper system and the feed tank and the reactor in
separate
buildings. The invention also involves the advantage that lower constructional
heights
may be selected for the respective units. The various plant components may be
ar-
ranged as desired so that the spatial layout of the plant can be done in a
flexible way.
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[0037] The transfer of the fuel material from the lock hoppers to the
feed tank or
tanks is implemented via at least one connection device and at least one
unifying ele-
ment, and the transfer from the unifying element to the feed tank via
individual continu-
ous supply lines for dense-flow conveying. The transfer from the lock hopper
to the
feed tank may be implemented via further unifying elements with transferring
connec-
tion devices.
[0038] Depending on the embodiment of the process, 2 or more lock hoppers
are
used to pressurise the fuel material. This is especially recommended for
plants with
high fuel material throughputs or if the lock hopper system is to be
pressurised to
to higher pressures. The inlet sides of the lock hoppers are connected to a
feed tank
which conveys the fuel material into the lock hoppers by the aid of both dense-
flow
conveying and gravity conveying. For this purpose, a star feeder or a material
manifold
may be installed in a suitable place between the storage tank and the lock
hoppers. It
is also possible to install intermediate vessels, bulb-shaped vessels or gas
feeding de-
vices between the storage tank and the lock hoppers.
[0039] The fuel material supply system of the coal gasification plant may
also in-
clude a grinding device or a mill which may be of any type desired. The mill
in turn may
also include additional comminuting devices such as shredders for wood or
crushers
for coal. The mill or crusher may also be supplied with gas or blanketed with
inert gas.
In a preferred embodiment of the facility according to the invention the lock
hoppers are
spatially integrated into the grinding unit and are filled by gravity flow
from at least one
storage vessel for finely ground fuel.
[0040] To run the process according to the invention, the lock hopper
system con-
sists of two or more lock hoppers which may be pressurised from outside. The
lock
hopper system is connected to an upstream storage tank which supplies the lock
hop-
per system by gravity conveyance with finely ground fuel material. The
conveying or
transport of the solid material is influenced advantageously by introducing
gas so that
gas introduction devices which influence the conveying or transport of solid
material
may be installed in any place of the lock hopper system, the dense-flow
conveying
lines or the feed tank.
[0041] The lock hoppers may be of any design desired. They may be
provided in
the form of cylinders or as spheres. Preferably they are provided with a
downward dis-
charge cone, the angle of which is determined by the properties of the bulk
material to
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counteract arching and to ensure a uniform material flow. For this reason,
they are ta-
pered towards the bottom in the ideal case. The fuel material hence exits
downwards in
gravity direction. The storage tanks as well as the downstream feed tanks are
also of
this preferred design. The lock hoppers are fitted with inlet valves via which
the lock
hoppers may be pressurised. The lock hoppers are equipped with nozzles,
shutoff and
control valves according to the state of the art which serve to control the
flow of solid
material, to depressurise and pressurise or carry out pressure compensation.
[0042] In an advantageous embodiment of the invention the expanded gases
may
be recycled to the grinding device and/or the fuel storage tank. To separate
the gas
from dust before it is discharged from the system or recycled for being used
in the
plant, the lines are preferably routed via dust separators. The latter
separate the dust
and pass it to a proper disposal or recycle it to the storage tank, for
example. It is theo-
retically possible to install devices by which the gas flow can be separated
from solid
material or dust in any place of the lock hopper system, the dense-flow
conveying line,
the fuel lines or the expansion lines. It is therefore of advantage to provide
for a gas-
sided connection of the lock hoppers with the feed tank.
[0043] The lines may be provided with gas introduction devices in any
place de-
sired. These may be so-called "boosters", for example. Especially the
discharge de-
vices for solid material, however, which are prone to caking, plugging or
arching, may
include additional gas introduction devices by which the solid material can be
loosened.
The lock hoppers as well may be provided with gas introduction devices in any
place
desired.
[0044] In such case, the material discharge of the lock hoppers is
fitted with a
connection element via which the material flow from the lock hoppers is passed
to the
unifying element. These elements shall be designed for high pressures as the
fuel is at
a pressure level above that of the gasification reactor during the whole
conveying proc-
ess from the lock hopper to the feed tank. To ensure controlled material flow,
the lock
hoppers are mounted advantageously such that they are arranged symmetrically
to the
unifying element so that the connection elements between the lock hoppers and
the
unifying element are preferably of the same length.
[0045] The unifying elements may be of any type desired. Preferably
these are
devices which assume the function of mixing elements. These may be, for
example,
pipe manifolds or Y-manifolds but also so-called "pipe headers". Examples of
suitable
unifying elements are given in EP 340 419 B1; here the elements described are
re-
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versed in their function and used as unifying elements. The connection devices
as well
may be of any type desired. Preferably used are pipes. Possible as well are
hoses or
flanges.
[0046] The connection devices or the unifying element may also be
supplied ad-
vantageously with gas for material distribution. If a plurality of unifying
elements is pro-
vided, they may be supplied with gas individually. For this purpose, the
unifying ele-
ment is preferably provided with a gas introduction device. The feed tank as
well is pro-
vided with gas injection devices or gas introduction devices in an embodiment
of the
invention.
[0047] The pipeline for supplying solid material to the feed tank normally
ends a-
bove the solid material filling level and, depending on the properties of the
bulk mate-
rial, it may also enter the feed tank below the solid material level in an
embodiment of
the invention. As the solid material level is subject to only slight
variations if the process
is run advantageously, this may be at a lower or central height position of
the feed tank.
In this way it is possible to achieve a low bulk density in the feed tank if
the solid mate-
rial shows good gas-retaining properties, which reduces the additional amount
of gas
required for conveyance to the burners.
[0048] The facility according to the invention may be provided with
plant equip-
ment required for the operation of a solid fuel supply system in any place
desired. This
may be pumps but may also be heating or cooling devices. Also included are
valves or
shutoff devices. These may theoretically be installed in any place. The
integration of in-
jectors is also possible. Here, so-called "boosters" (gas injectors) may be
used, for ex-
ample, but also possible are gas jet pumps. Finally the facility according to
the inven-
tion also includes thermometers or flow sensors for gases and solid materials,
pressure
sensors, level meters or other measuring devices.
[0049] The design type of dense-flow conveying from the lock hoppers and from
the feed tank may allow to construct the whole plant construction at low
height. As
the conveyance is independent of gravity, the plant equipment may be installed
in any
place desired. By this system, the space requirement can be reduced to a
considerable degree. The system of several lock hoppers and the upstream
storage
tank as well as the constant-level feed tank may allow to achieve trouble-free
and very
constant conveying of fuel to the feed tank over a given period of time, even
for an
extended period of time. This may contribute to the reliability of the plant
and ensures
a constantly high product quality.
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[0050] The facility according to the invention is illustrated in more
detail by means
of two drawings, the embodiment not being limited to these drawings.
[0051] FIG. 1 shows the process flow of a coal gasification plant which
is equipped
with a facility for the supply of fuel material according to the invention.
Fuel material 1 is
supplied and introduced into a mill or suitable grinding device 2. The finely
ground fuel
material is then passed via a dust separator 3 and fuel line 3a into a storage
tank 4,
where the fuel is stored intermediately. Subsequently the fuel is supplied to
lock hop-
pers 5. The represented example shows two of them 5a, 5b. Lock hoppers 5 serve
to
pressurise the fuel batch by batch by supplying gas. For this purpose, lock
hoppers 5
are provided with gas introduction devices 6a, 6b above the filling and gas
introduction
devices 6'a, 6'b into the filling. Between lock hoppers 5 there is a
compensation line 7
which may be opened in the case of need. An expansion line 8 for
depressurisation
leaves lock hoppers 5, via which the expanded gas may be used completely or
only
partially for blanketing grinding device 2. The expanded gas, however, may
also be
used for blanketing storage tank 4 with inert gas. To adjust recycle gas 8c of
grinding
device 2 recycled by means of blower 8b to adequate temperatures, the line may
be
provided with a heat exchanger 8d or another suitable device for supplying
heat.
Downstream of lock hoppers 5a, 5b the finely ground fuel material is
discharged via
suitable connection devices 9a, 9b and passed to unifying element 10. Unifying
ele-
ment 10 may be supplied with gas via gas line 11. The finely ground material
is then
routed via continuous supply line 12 to a feed tank 13.
[0052] In the exemplary variant shown in FIG. 1, two lock hoppers 5a, 5b
make
use of a continuous supply line 12 via unifying element 10. This is achieved
advanta-
geously in such a way that lock hoppers 5a, 5b feed the solid material
alternately into
dense-flow conveying continuous supply line 12 via unifying element 10. To
minimise
the interim time for switching from one lock hopper to the other 5a, 5b and to
ensure an
almost uninterrupted conveying of solid material, it is advantageous to couple
both lock
hoppers 5a, 5b in timely overlapping manner to unifying element 10. Helpful in
this re-
spect is pressure compensation via compensation line 7 between that lock
hopper that
is almost empty already and the other lock hopper that is still full 5a, 5b.
It goes without
saying that it is also possible and advantageous to implement the described
procedure
with more than two lock hoppers S. If there are more than two lock hoppers 5,
it is also
possible to use the expansion gas of that lock hopper 5 that has just been
emptied and
shall now be depressurised for being loaded with solid material from
atmospheric stor-
age tank 4, for partial pressurisation of a lock hopper 5 which is still under
atmospheric
CA 02716621 2010-08-23
10826 14
condition. Connection device 9a, 9b is provided with two valves (not shown),
one close
to the hopper discharge, one close to unifying element 10. After a lock hopper
5 has
been emptied to a minimum level and shut off from unifying element 10 by the
valve in
proximity to unifying element 10, it is recommended to purge or blow free by
gas injec-
tion 9'a, 9'b at connection device 9a, 9b, before the second valve is closed.
[0053] In the ideal case, a constant filling level 13a prevails in feed
tank 13. The
pressure of feed tank 13 can be kept constant by excess gas 21 or feed gas 22
by a
gas compensation process. From feed tank 13, the solid material is routed via
fuel li-
nes 14a, 14b to coal gasification reactor 15 with one or more burners 16a,
16b. In this
case, the entire facility for the supply of solid fuel is located in a
separate plant unit, the
building of grinding unit 17a. Coal gasification reactor 15 and feed tank 13
are located
in another building, the building of gas production unit 17b.
[0054] The advantages of the invention already mentioned which
especially in-
volve a considerable reduction of the number of equipment items, the
construction
height and hence the investment cost as well as an increase in plant
reliability, are ob-
tained for a moderate increase in the demand for pressurising gas. This is due
to the
fact that that part of the gas used for dense-flow conveying of the solid
material in con-
tinuous supply line 12 which has been used to reduce the solid material
density to a
value below the one prevailing in feed tank 13, cannot be used as feed gas for
coal
gasification reactor 15 since it is excess gas, see FIG. 2. If no additional
devices are
available, this part is to be removed unused as excess gas 21. At the same
time, many
times the amount of gas is required in lock hopper 5, which is the active
transferring
hopper, as a replacement for the discharged amount of solid material. It
therefore sug-
gests itself to reduce the demand for gas by recycling excess gas 21 from feed
tank 13
as recycle gas 20 to the lock hopper and using it for a partial substitution
of the gas
consumed for replacement. This may be implemented by a blower or another
device
for pressure increase. Owing to the low pressure difference to be overcome
between
feed tank 13 and lock hopper 5 at simultaneously high system pressure, an
injector 18
suggests itself, especially a gas jet pump. In addition, the pump is also
capable of con-
veying dust-bearing gas, dust separation is not required. As propellant gas
serves the
pressurising gas used for the purpose of replacement, which is available at
significantly
higher pressure. The pressure side of injector 18 is switched over to the
currently ac-
tive lock hopper 5. Under typical operating conditions the portion of recycle
gas
amounts to about 25% of the amount of replacement gas. At the same time the
supply
pressure of propellant gas 23 is about 10 bar higher than the pressure of the
lock hop-
CA 02716621 2010-08-23
10826 15
per, whereas the pressure of recycle gas 20 is only about 1-2 bar above the
pressure
of the lock hopper. These numerical relationships make it obvious to the
specialist that
injector system 18 is fully operative under the specified conditions.
[0055] Gas recycling is integrated into the pressure control system of
feed tank 13
in the following way: Based on the consideration that, at constant operating
conditions,
excess gas 21 is to be removed from feed tank 13, the pressure increase in
feed
tank 13 is avoided by having injector 18 suck off the released amount of gas
and feed it
to lock hopper 5. If the pressure in feed tank 13 continues to rise, the
excessive pres-
sure amount is removed as excess gas 21. This gas as well can be used
beneficially if
to required, e.g. for substituting purge gases which are fed to the
gasification reactor in
various places. Should a pressure increase of feed tank 13 be required
especially dur-
ing the start-up procedure, which cannot be achieved by excess gas 21, with
closed
valves in the lines for recycle gas 20 and excess gas 21, the shortage is
compensated
by fresh feed gas 22.
[0056] The pressurising gas used as propellant gas 23 for injector 18 is
compen-
sation-controlled by the pressure controller of lock hopper 5. Depending on
the position
of the throttling valve in the propellant gas line, the amount of propellant
gas ranges be-
tween 70 and 100% of the gas amount required for replacement. The set value of
the
lock hopper pressure is determined via a cascade (not shown) from the level of
feed
tank 13 (or from its weight). With regard to the level, a fixed set value
(e.g. 50%) is
given. If this set value is exceeded, the value of pressure difference between
lock hop-
per 5 and feed tank 13 controlled by the controller cascade is reduced so that
the sub-
sequently fed solid mass flow decreases, and if the level drops below the set
value, the
controllers operate vice versa.
[0057] Fig. 3 to 8 show, by way of example, arrangements with a varying
number
of lock hoppers 5 and unifying elements 10. These are connected by pipelines
in differ-
ent ways.
[0058] FIG. 3 shows a facility according to the invention which includes
three lock
hoppers 5 and one unifying element 10, wherein each lock hopper 5 is connected
to
unifying element 10 via a connection device 9, and unifying element 10 is
connected to
feed tank 13 via a continuous supply line 12. Unifying element 10 can be
supplied with
gas via gas line 11.
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10826 16
[0059] FIG. 4 shows a facility according to the invention which includes
three lock
hoppers 5 and two unifying elements 10, wherein two lock hoppers 5 are
connected to
the first unifying element 10a via connection devices 9a, 9b, and the first
unifying ele-
ment 10a is connected to the second unifying element 10b via another
connection de-
s vice, and the third lock hopper 5 is directly connected to the second
unifying ele-
ment 10b via a connection device 9c, and the second unifying element 10b is
con-
nected to feed tank 13 via a continuous supply line 12.
[0060] FIG. 5 shows a facility according to the invention which includes
four lock
hoppers 5 and three unifying elements 10, wherein two lock hoppers 5 each are
con-
nected to one unifying element 10 each via connection devices 9a-9d, these
unifying
elements 10 being connected to the third unifying element 10c via further
connection
elements 9e, 9f, and the third unifying element 10c being connected to feed
tank 13 via
a continuous supply line 12.
[0061] FIG. 6 shows a facility according to the invention which includes
six lock
hoppers 5 and two unifying elements 10, wherein three lock hoppers 5 each are
con-
nected to one unifying element 10 each via connection devices 9, these
unifying ele-
ments 10 being connected to feed tank 13 via separate continuous supply
lines 12a, 12b.
[0062] FIG. 7 shows a facility according to the invention which includes
eight lock
hoppers 5 and two unifying elements 10, wherein four lock hoppers 5 each are
con-
nected to one unifying element 10 each via connection devices 9a, 9b, these
unifying
elements 10 being connected to feed tank 13 via separate continuous supply
lines 12.
[0063] FIG. 8 shows a facility according to the invention which includes
eight lock
hoppers 5 and three unifying elements 10, wherein four lock hoppers 5 each are
con-
nected to one unifying element 10a, 10b via connection devices 9, these
unifying ele-
ments 10a, 10b being connected to the third unifying element 10c via further
connec-
tion devices 9, and the third unifying element 10b being connected to feed
tank 13 via
a continuous supply line 12.
CA 02716621 2010-08-23
10826 17
[0064] List of references used
1 Fuel material
2 Grinding device
3 Dust separator
3a Fuel line
4 Storage tank
5,5a,5b Lock hoppers
6,6a,6b Gas introduction devices
6'a,6'b Gas introduction devices
7 Compensation line
8 Expansion line
8a Expansion gas line
8b Blower
8c Recycle gas
8d Heat exchanger
9a-9f Connection devices
9'a,9'b Gas injection
10, 10a-10c Unifying elements
11 Gas line
12, 12a, 12b Continuous supply line
13 Feed tank
13a Filling level
14a,14b Fuel lines
15 Coal gasification reactor
16a,16b Burners
17a Building of grinding unit
17b Building of gas production unit
18 Injector
19 Gas
20 Recycle gas
21 Excess gas
22 Feed gas
23 Propellant gas
Ap Pressure as control parameter
PC Pressure controllers
