NZ621271B2 - Gasification of carbonaceous material - Google Patents
Gasification of carbonaceous material Download PDFInfo
- Publication number
- NZ621271B2 NZ621271B2 NZ621271A NZ62127112A NZ621271B2 NZ 621271 B2 NZ621271 B2 NZ 621271B2 NZ 621271 A NZ621271 A NZ 621271A NZ 62127112 A NZ62127112 A NZ 62127112A NZ 621271 B2 NZ621271 B2 NZ 621271B2
- Authority
- NZ
- New Zealand
- Prior art keywords
- grate
- support structure
- gasifier
- rotatable
- component
- Prior art date
Links
- 239000003575 carbonaceous material Substances 0.000 title claims abstract description 12
- 238000002309 gasification Methods 0.000 title claims description 38
- 230000001702 transmitter Effects 0.000 claims abstract description 27
- 238000006073 displacement reaction Methods 0.000 claims abstract description 18
- 239000000789 fastener Substances 0.000 claims abstract description 11
- OKTJSMMVPCPJKN-UHFFFAOYSA-N carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 22
- 239000003245 coal Substances 0.000 claims description 21
- 239000002028 Biomass Substances 0.000 claims description 14
- 239000002699 waste material Substances 0.000 claims description 4
- 239000000463 material Substances 0.000 claims description 3
- 229910052799 carbon Inorganic materials 0.000 claims 1
- 230000000875 corresponding Effects 0.000 description 7
- 239000003795 chemical substances by application Substances 0.000 description 5
- 239000007789 gas Substances 0.000 description 5
- 238000009826 distribution Methods 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 239000002893 slag Substances 0.000 description 3
- 230000000712 assembly Effects 0.000 description 2
- 230000000295 complement Effects 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 230000000116 mitigating Effects 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000006011 modification reaction Methods 0.000 description 2
- 230000000750 progressive Effects 0.000 description 2
- 238000007790 scraping Methods 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- 230000003068 static Effects 0.000 description 2
- 241000565356 Fraxinus pennsylvanica Species 0.000 description 1
- 239000003082 abrasive agent Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000011449 brick Substances 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 238000005304 joining Methods 0.000 description 1
- 210000001699 lower leg Anatomy 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- MYMOFIZGZYHOMD-UHFFFAOYSA-N oxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 239000011236 particulate material Substances 0.000 description 1
- 238000009420 retrofitting Methods 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 238000010008 shearing Methods 0.000 description 1
- 230000035882 stress Effects 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10J—PRODUCTION OF PRODUCER GAS, WATER-GAS, SYNTHESIS GAS FROM SOLID CARBONACEOUS MATERIAL, OR MIXTURES CONTAINING THESE GASES; CARBURETTING AIR OR OTHER GASES
- C10J2200/00—Details of gasification apparatus
- C10J2200/09—Mechanical details of gasifiers not otherwise provided for, e.g. sealing means
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10J—PRODUCTION OF PRODUCER GAS, WATER-GAS, SYNTHESIS GAS FROM SOLID CARBONACEOUS MATERIAL, OR MIXTURES CONTAINING THESE GASES; CARBURETTING AIR OR OTHER GASES
- C10J3/00—Production of combustible gases containing carbon monoxide from solid carbonaceous fuels
- C10J3/02—Fixed-bed gasification of lump fuel
- C10J3/20—Apparatus; Plants
- C10J3/34—Grates; Mechanical ash-removing devices
- C10J3/40—Movable grates
- C10J3/42—Rotary grates
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23H—GRATES; CLEANING OR RAKING GRATES
- F23H17/00—Details of grates
- F23H17/08—Bearers; Frames; Spacers; Supports
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23H—GRATES; CLEANING OR RAKING GRATES
- F23H2700/00—Grates characterised by special features or applications
- F23H2700/005—Rotary grates with vertical axis
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23H—GRATES; CLEANING OR RAKING GRATES
- F23H2700/00—Grates characterised by special features or applications
- F23H2700/009—Grates specially adapted for incinerators
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23H—GRATES; CLEANING OR RAKING GRATES
- F23H9/00—Revolving-grates; Rocking or shaking grates
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23H—GRATES; CLEANING OR RAKING GRATES
- F23H9/00—Revolving-grates; Rocking or shaking grates
- F23H9/02—Revolving cylindrical grates
Abstract
grate assembly (10) for a gasifier for gasifying carbonaceous material producing ash includes an upper rotatable grate component (11) and a lower rotatable support structure (12) fastened to the upper rotatable grate component (11) by a plurality of removable fasteners (15) acting to prevent vertical displacement of the upper rotatable grate component (11) and the lower rotatable support structure (12). The lower rotatable support structure (12) is configured to be drivingly rotated about a common vertical axis of rotation (21) shared with the upper rotatable grate component (11). The assembly (1) further includes at least two key torque transmitters (16) spaced angularly relative to the common axis of rotation (21) and engaging the upper rotatable grate component (11) and the lower rotatable support structure (12) to transfer torque from the lower rotatable support structure (12) to the upper rotatable grate component (11) when the lower rotatable support structure (12) is driven. cal displacement of the upper rotatable grate component (11) and the lower rotatable support structure (12). The lower rotatable support structure (12) is configured to be drivingly rotated about a common vertical axis of rotation (21) shared with the upper rotatable grate component (11). The assembly (1) further includes at least two key torque transmitters (16) spaced angularly relative to the common axis of rotation (21) and engaging the upper rotatable grate component (11) and the lower rotatable support structure (12) to transfer torque from the lower rotatable support structure (12) to the upper rotatable grate component (11) when the lower rotatable support structure (12) is driven.
Description
GASIFICATION OF CARBONACEOUS MATERIAL
THIS INVENTION relates to gasification of carbonaceous material. In
particular, the invention relates to a grate assembly for a gasifier for gasifying
carbonaceous material and to a gasifier for gasifying carbonaceous material.
For some gasifiers, such as the Sasol® FBDB™ gasifier, it is necessary
intermittently or continuously to load and unload particulate material, such as particulate
carbonaceous material (e.g. coal) and ash. Thus, for example, in the case of a
pressurized gasifier (e.g. a fixed bed dry bottom gasifier), particulate carbonaceous
feedstock, e.g. coal, is loaded into a gasification chamber of the gasifier to form a bed
(in the case of a fixed bed gasifier), and gasified at elevated temperatures and
pressures, and after gasification any remaining ungasified material is removed from the
gasifier as ash via a rotatable grate assembly and an ash lock.
The grate assembly has two main mechanical functions. Primarily it is used
to extract ash from the bottom of the gasification chamber, but it is also used to crush
and remove any ash agglomerates (clinkers) that may be formed in the gasification
process. The grate assembly is also used to distribute gasification agent (typically a
mixture of steam and oxygen) into the bed of carbonaceous material.
The grate assembly comprises of a number of components, principally an
upper roughly conical-shaped rotatable grate component, a lower rotatable support
structure fixedly connected to the upper rotatable grate component at an upper
periphery of the rotatable support structure and a ring gear connected at a lower
periphery of the rotatable support structure. A lowermost stationary support structure is
provided on which the rotatable components are supported. In use, the grate assembly
is rotated when the ring gear which is drivingly connected to the lower rotatable support
structure is driven via a motor and gearbox assembly which turns the rotatable
components of the grate assembly.
In the grate assembly of the prior art, the rotatable grate component is fixedly
connected to the rotatable support structure with a plurality of bolts located in
corresponding bolt holes and a single key torque transmitter is located in a
corresponding keyway. The connecting bolts are intended to prevent vertical
separation of the upper rotatable grate component from the lower rotatable support
structure. In use, the key functions as a torque transmitter between the adjacent
components in order to transmit the drive force from the ring gear, through the lower
rotatable support structure to the upper rotatable grate component. In the grate
assembly of the prior art, a single key is used as a torque transmitter. The key is
designed to withstand the entire radial load or shear force experienced by the grate
assembly in an upset condition. It is commonly believed in the prior art that, in use, a
single key will always seat before other keys and will carry the entire radial load or
shear force and therefore the use of multiple keys is regarded as superfluous.
It has been found that, in use, the connecting bolts and, on occasion, the key
itself fail in upset conditions where the free rotation of the grate assembly is obstructed.
Such an upset condition may occur where hard ash agglomerates (clinkers) are present
and become lodged in an ash discharge annulus defined between the rotatable grate
component and a wall of the gasification chamber. In such an instance, the free
rotation of the upper rotatable grate component is restricted, whilst the motor and ring
gear continue to rotate and act on the lower rotatable support structure. It will readily
be appreciated that in such an event the torque on the rotatable grate component
increases and that the load transferred from the gearbox, though the ring gear to the
lower rotatable support structure and to the upper rotatable grate component is carried
by the key torque transmitter. Failure of the connecting bolts is thus an unexpected
failure since the key is designed to resist the radial forces associated with an upset
condition wherein the free rotation of the upper rotatable grate component is hindered.
In use, the connecting bolts are in effect protected by the key and are accordingly not
designed to carry any of the tangential shear loads associated with upset conditions.
When the connecting bolts shear, the upper rotatable grate component and
the lower rotatable support structure separate and the grate assembly can no longer
remove ash from the gasifier. This results in the shutdown of the gasifier which is
clearly undesirable as it may severely impact on production levels and income
generated from the gasifier. The prior art design thus results in inefficient operation
and reduction of this inefficiency would be beneficial.
In order to mitigate functional failure arising from failure of the connecting
bolts, attempts were made to use larger and/or stronger connecting bolts. Attempts
were also made to weld the key to the two interfacing components (i.e. the rotatable
grate component and the rotatable support structure) as it was firmly believed that the
displacement of the key out of position was the main cause leading to failure of the
connecting bolts. Both approaches have, however, proven in practice to be
unsuccessful in mitigating functional failure of the grate assembly as described
hereinbefore.
Investigations have revealed that the failure of the grate assembly in upset
conditions is partly due to a design flaw in the manner in which the connecting bolts and
key torque transmitter connect the rotatable grate component and the rotatable support
structure. Surprisingly, it has been found that, taking into account the dynamic
mechanical loads in the grate assembly during an upset condition, a relative movement
between the rotatable grate component and the rotatable support structure is
introduced, i.e. one component (typically the rotatable support structure) continues to
rotate while the other component in the assembly (typically the rotatable grate
component) remains stationary, its rotation being hindered by the ash agglomerates
trapped in the ash discharge annulus. In this event, a relative rotation around the key
torque transmitter occurs, i.e. rotation of the rotatable grate component is hindered by
the ash agglomerate(s) in the ash discharge annulus and it consequently pivots around
the key torque transmitter.
In operation it is crucial that the axis of rotation of the two connected
rotatable components coincides. Relative movement of the adjacent components
around the key leads to a displacement of the connecting bolts relative to the
corresponding bolt holes and of the key relative to the keyway. This leads to a
displacement of the axis of rotation of one of the rotating components. Displacement of
the axis of rotation leads to a progressive increase of the shear stresses on the bolts,
and ultimately failure of the bolts. With the bolts not able to prevent the relative
movement of the two adjacent components, the rotatable components of the grate
assembly separate leading to a functional failure of the assembly.
In the course of the investigations, it was discovered surprisingly that the
connecting bolt failure was not due to insufficient strength of the connecting bolts in the
vertical plane (i.e. substantially parallel to the axis of rotation of the grate assembly), but
due to misalignment of the rotatable grate component and rotatable support structure in
the horizontal plane (i.e. in a plane substantially perpendicular to the axis of rotation)
due to the relative rotation of the components around the key torque transmitter.
attempts to overcome the problem of segregation of
particulate coal feedstock fed into a fixed bed coal gasifier which results in gasifier
operational instability and “hot spots” as a result of preferential gas flow through a non-
homogenous coal bed so produced. This document discloses a fixed bed gasifier and a
method of operating a fixed bed gasifier to overcome the aforesaid problems. The
gasifier has a static coal distribution device inside a gasification chamber of the gasifier
and a rotatable grate having at least one upwardly projecting finger above an ash outlet
of the gasification chamber. The combination of the static coal distribution device and
the rotatable grate component with projecting finger are claimed to improve the radial
and axial distribution of coal and ash particles in the fixed bed of coal, thereby to
homogenise the bed and improve gasifier operation and stability.
describes two alternative grate assemblies which are suitable for accomplishing its
stated objective. Nowhere in is there any mention of the problem of
the misalignment between upper and lower grate components, relative rotation of upper
and lower grate component around a key torque transmitter, or the functional failure of a
grate assembly due to the shearing of the connecting bolts between upper and lower
grate components. is in fact directed at an entirely different problem
than the problem the present invention is directed at.
CN 201762288 is a Chinese utility model and relates to a co-current, air-
blown, fixed bed biomass gasifier. A prior art biomass gasifier described by
CN 201762288 has a furnace, an ash chamber, a grate, supports and an ash discharge
mechanism. The grate is a flat structure which is installed horizontally below the
furnace. The grate has a plurality of holes extending through it to allow combustible gas
and ash-slag to pass therethrough. CN 201762288 identifies that the problems
associated with grates of the prior art include inter alia (i) that ash accumulates on the
grate thus resulting in low gasifier efficiency, (ii) that ash blocks the holes in the grate
thereby preventing combustible gas from exiting the furnace through said holes and
inhibiting gas production capacity, (iii) that the holes in the grate lead to material
leakage, and (iv) that existing grates are poorly suited to the gasification of a variety of
types of biomass as the holes in the grate do not lend themselves to be adapted to the
gasification of different types of biomass. Alternative gasifiers are thus proposed and
illustrated in Figures 2 – 13 of CN 201762288. Although a component (13) is present in
the gasifiers proposed in CN 201762288 and is termed a grate, it is not a rotatable
grate in the conventional sense, but is in fact a stationary device positioned below the
furnace. The grate (13) is designed to support a bed of biomass-derived ash and to
allow combustible gas and ash-slag produced in the furnace to pass through holes in
the grate (13), although apparently the majority of ash-slag is discharged through an
ash-discharge annulus between the grate (13) and an inner wall of the furnace. An ash-
agitating mechanism is provided to agitate ash collecting on top of the grate (13) and to
push the ash into the ash-discharge annulus. The ash agitating mechanism is thus the
only fully rotatable component in any of the biomass gasifiers described in
CN 201762288. CN 201762288 further describes that it would be advantageous to be
able to adjust the size of the holes in the grate (13) thereby to render the biomass
gasifier adaptable to the gasification of various types of biomass. CN 201762288
discloses that one method of adjusting the size of the holes in the grate (13) is to
provide an adjustment plate (19) having a substantially similar construction to the grate
(13), i.e. being disc-like and having a plurality of holes disposed therethrough, installed
coaxially with and underneath the grate (13) in the furnace. The adjustment plate (19)
is rotatable to a limited extent so that, in a first position, the adjustment plate (19) is
positioned relative to the grate (13) such that holes (13a) and holes (19a) overlap thus
defining a plurality of channels extending through both components (13) and (19), or in
a second or subsequent position, the adjustment plate (19) can be rotated slightly
relative to the grate (13) such that the holes (19a) and the holes (13a) do not overlap
(i.e. are offset), thus effectively reducing the size of the holes or channels extending
through the grate (13) and adjustment plate (19). In this manner, the effective size of
the holes (13a) in the grate (13) of the biomass gasifiers of CN 201762288 are
adjustable such that various types of biomass can be gasified in the gasifier simply by
rotating the adjustment plate (19) slightly relative to the grate (13). In order to
limit the relative movement of the adjustment plate (19) relative to the grate (13),
CN 201762288 describes a plurality of arcuate formations (29) projecting from the
bottom surface of the grate (13) which slot into complementary arcuate depressions
(28) in the adjustment plate (19) located beneath the grate (13). By fitting the
projections (29) on the underside of the grate (13) into the complementary depressions
(28) provided on an upper face of the adjustment plate (19) limited rotational movement
of the adjustment plate (19) relative to the stationary grate (13) is allowed. The four
arcuate projections (29) thus do not function as key torque transmitting members. The
projections (29) and depressions (28) are merely included to guide, and to limit the
range of, relative rotation between the stationary grate (13) and the rotatable adjustment
plate (19). No torque whatsoever is transferred by the projections (29).
According to one aspect of the invention, there is provided a grate assembly
for a gasifier for gasifying carbonaceous material producing ash, the grate assembly
including:
an upper rotatable grate component; and
a lower rotatable support structure fastened to the upper rotatable grate
component by a plurality of removable fasteners acting to prevent vertical displacement
of the upper rotatable grate component and the lower rotatable support structure, the
lower rotatable support structure being configured to be drivingly rotated about a
common vertical axis of rotation shared with the upper rotatable grate component,
the assembly further including at least two key torque transmitters spaced
angularly relative to said common axis of rotation and engaging the upper rotatable
grate component and the lower rotatable support structure to transfer torque from the
lower rotatable support structure to the upper rotatable grate component when the lower
rotatable support structure is driven.
In this specification, the term “component” is intended to include an
assembled component including more than one part, such as a rotatable grate
component comprising a number of parts assembled to form the grate component.
Unless the context clearly requires otherwise, through the description and the
claims, the words “comprise”, “comprising”, “including” and the like are to be construed
in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in
the sense of “including, but not limited to”.
It was surprisingly discovered that the introduction of a plurality of keys
mitigates the functional failure experienced with the grate assembly of the prior art.
The inclusion of a plurality of keys in accordance with the invention is thus not intended
simply to strengthen the grate assembly as may be understood to be the case, but
rather to maintain the geometrical integrity of the grate assembly.
The keys may be equiangularly spaced. Thus, for example, when only two
keys are present, they may be about 180º apart, when three keys are present, they may
be about 120˚ apart, and when four keys are present, they may be about 90˚ apart. It
may however be that the arrangement of the keys is not symmetrical due to
construction constraints (other components in the way, etc.) and the arrangement may
thus be slightly offset, e.g. 170º and not 180º. In this specification, “equiangularly” is
thus intended to mean that the angles differ by no more than 30º, preferably by no more
than 10º, more preferably by no more than 5º.
Preferably, the keys are arranged in sets of two, with the two keys in a set
being positioned in diametrically opposed positions in a horizontal plane about said
common vertical axis of rotation.
The keys may be arranged in a circle, and may be interspaced by at least
one fastener between adjacent keys, the fastener acting to inhibit or prevent vertical
displacement of the upper rotatable grate component and the lower rotatable support
structure. The fasteners may be in the form of nut and bolt arrangements.
Typically, the keys are unthreaded and do not act to inhibit or prevent vertical
displacement of the upper rotatable grate component and the lower rotatable support
structure.
Preferably, the keys are not circular cylindrical.
The keys may be tapered from a wider operatively upper end to a narrower
operatively lower end or vice versa.
The keys may be elongate and may be polygonal in outline in end view, e.g.
square. It is to be understood that the end view is taken in a direction along a
longitudinal axis of the elongate key.
The keys may be sturdier than the fasteners so that a shank portion of a
fastener has a maximum transverse dimension which is less than a minimum transverse
dimension of a key.
The rotatable grate component may have an upwardly inwardly tapering
outer surface. The upwardly inwardly tapering outer surface may be staggered or
stepped when seen in vertical cross-section, defining vertically and radially spaced
terraces. The terraces may be covered by shield plates to protect the rotatable grate
component from abrasive material, e.g. ash.
According to another aspect of the invention, there is provided a gasifier for
gasifying carbonaceous material, the gasifier including a grate assembly as
hereinbefore described mounted within a gasification chamber defined by a gasification
vessel with the lower rotatable support structure of the grate assembly being connected
to drive means.
The gasifier may be a fixed bed gasifier, in particular a fixed bed dry bottom
gasifier.
The gasifier may be a coal, waste or biomass gasifier, or a gasifier
configured to gasify a combination of two or more of coal, waste and biomass. Typically
however, the gasifier is a coal gasifier operating at an elevated pressure of between 5
bar(g) and 100 bar(g) and a temperature of between 400ºC and 1600ºC.
The rotatable grate component typically has a vertical dimension and a radial
direction and is rotatable about a vertical axis of an ash discharge outlet of the
gasification chamber, with a lower periphery of the rotatable grate component being
below an apex or upper end of the rotatable grate component.
In one embodiment of the invention, in use, the grate component is rotated
about the vertical axis of said ash discharge outlet. Carbonaceous feedstock, e.g. coal,
is fed batch-wise into a top of the gasifier and gasification agent is fed into a bottom of a
reaction zone defined by the gasification vessel through gasification agent outlets
underneath lower edges of the outer shield plates of the rotatable grate component,
thereby to gasify coal located in a slow moving bed within the gasification chamber.
Ash is continuously withdrawn from the bottom of the gasification chamber through an
annular ash discharge passageway being provided between a wall of the gasification
chamber and the rotatable grate component. Ploughs are rigidly connected to the
rotatable grate component which continually rotates in operation, the ploughs scraping
the ash through said ash discharge passageway, whereafter the ash flows under force
of gravity into an ash lock located beneath the gasifier vessel. As the grate assembly
rotates, clinker crushing is performed between the shield plates of the rotatable grate
component and wear bricks located on the wall of the gasifier vessel.
The invention will now be described by way of example with reference to the
accompanying diagrammatic drawings in which:
Figure 1 shows a vertically sectioned view of a grate assembly in accordance
with the invention, installed in a fixed bed dry bottom coal gasifier in accordance with
the invention;
Figure 2 shows a plan view of a lower rotatable support structure of the grate
assembly of Figure 1;
Figure 3 shows a plan view representation of the relative rotation of the rotating
grate component and the rotating support structure in an upset condition in a grate
assembly of the prior art; and
Figure 4 shows a plan view representation of the rotation of a grate assembly
according to the present invention.
With reference to Figure 1 of the drawings, reference numeral 10 generally
refers to a grate assembly in accordance with the invention installed in a gasification
vessel 100 of a fixed bed dry bottom coal gasifier in accordance with the invention. The
gasification vessel 100 defines a gasification chamber 102 within which the grate
assembly 10 is located. The gasification chamber 102 has a wall 18.
The grate assembly 10 comprises an upper rotatable grate component 11,
fixedly connected to a lower rotatable support structure 12 by a plurality of connecting
bolts 15 and at least two key torque transmitters 16. The lower rotatable support
structure 12 is drivingly connected to a ring gear 13 which is in turn connected through a
gearbox to an electric motor (not shown). In use, the electric motor and gearbox are
used to rotate the rotatable components 11, 12 and 13 of the grate assembly 10.
The rotatable components 11, 12 and 13 are supported by a stationary
support structure 14 above an ash discharge outlet or passageway 20 of the gasification
vessel 100. One or more ploughs 17 are connected to a radially outermost periphery of
the upper rotatable grate component 11. The ploughs 17 are used to scrape ash from
an ash bed within the gasification chamber 102 through an ash discharge annulus 19
which is defined between the outer periphery of the upper rotatable grate component 11
and the wall 18 of the gasification chamber 102.
In use, the grate assembly 10 is rotated about an axis of rotation 21, which
corresponds with the centre line of the ash discharge passageway 20 which is also the
centre line of the grate assembly 10. Coal is fed batch-wise into the top of the gasifier
(not shown) and gasification agent is fed into a lower portion of the gasification chamber
102 through gasification agent outlets 23 underneath the lower edges of the outer shield
plates 22, thereby to gasify coal located in a slow moving bed within the gasification
chamber 102. Ash is continuously withdrawn from the bottom of the gasification
chamber 102 through the ash discharge annulus 19 provided between the wall 18 of
the gasification chamber 102 on the one hand and the upper rotatable grate component
11 on the other hand, and through the ash discharge passageway 20. The ploughs 17
rotate with the upper rotatable grate component 11 thereby discharging ash by scraping
it through the ash discharge annulus 19. As the upper rotatable grate component 11
rotates, clinker crushing is performed between the shield plates 22 of the upper
rotatable grate component 11 and the wall 18 of the gasifier chamber 102.
With reference to Figure 2 of the drawings, a plan view of the rotatable
support structure 12 of the grate assembly 10 of Figure 1 is shown. A plurality of bolts
(not shown) corresponding to a plurality of bolt holes 32 are used to fixedly but
removably connect the upper rotatable grate component 11 to the lower rotatable
support structure 12. The bolts are designed vertically to connect the adjacent
components 11 and 12 and are not designed to withstand radial shear forces. At least
two diametrically opposed keyways 34 are provided in which corresponding keys (not
shown) are snugly located. The keys are designed to act as torque transmitters,
transferring the driving force from the electric motor and gearbox (not shown) via the
ring gear 13 and the rotatable support structure 12 to the upper rotatable grate
component 11.
In use, upset conditions may occur where ash agglomerates become wedged
in the ash discharge annulus 19 located between the upper rotatable grate component
11 and the vessel wall 18 as shown in Figure 1. The grate assembly 10 is designed to
crush the agglomerates wedged in the ash discharge annulus 19. However,
circumstances may arise where the agglomerates cannot easily be broken for removal
via the ash discharge annulus 19 and ash discharge passageway 20 and the rotation of
the upper rotatable grate component 11 is hindered. In such cases, the ring gear 13
continues to drivingly rotate the rotatable support structure 12 which is fixedly
connected to the upper rotatable grate component 11. The rotational force is
transferred to the rotatable grate component through the key torque transmitters located
in the keyways 34 as described.
Investigations have revealed that, when only one key torque transmitter is
used, in the event of the rotation of the upper rotational grate component 11 being
restricted, a relative rotation around the key in the keyway 34 occurs, i.e. the upper
rotatable grate component 11 which is restricted from rotating by the ash agglomerate
tends to pivot around the key in the keyway 34. The relative movement of the two
adjacent components 11, 12 around the key leads to a displacement of the connecting
bolts relative to the corresponding bolt holes 32 and of the key relative to the keyway
34. This leads to a displacement of the axes of rotation, marked A and B in Figure 3 of
the drawings.
In Figure 3, the direction of rotation is shown by arrow 30. The rotational
profile of the stationary component (i.e. the upper rotatable grate component 11) is
shown generally as reference numeral 110. A key (not shown) is located in the keyway
34. The rotational profile of the rotating component (i.e. rotatable support component
12) is shown generally as reference numeral 120. The axis of rotation of the profile 110
is shown as point A, whereas the axis of rotation of the profile 120 is shown as point B.
The inventors have found that, in operation, it is critical that the axes of
rotation A and B of the rotatable grate components coincide, i.e. that points A and B
overlap along a common axis of rotation 21 as shown in Figure 1. In an upset
condition, the axis of rotation represented by point B becomes offset from the common
axis of rotation 21 and accordingly no longer overlaps with the axis of rotation
represented by point A. The displacement of point B from the central axis of rotation 21
as a result of a relative rotation of the support component 12 around the key in the
keyway 34, leads to a progressive increase of the shear forces acting on the connecting
bolts located in the bolt holes 32. As the connecting bolts fail sequentially, the area
available to transmit the driving force of the ring gear 13 diminishes and as a
consequence there are fewer connecting bolts to carry the load, leading finally to the
failure of all the connecting bolts. With the connecting bolts not able to prevent the
relative movement of the two connected rotatable components 11 and 12, the rotatable
components 11 and 12 of the grate assembly 10 separate leading to a functional failure
of the grate assembly 10.
Figure 4 shows a diagram of the rotational profiles of the rotatable grate
components 11, 12 according to the present invention. The introduction of additional
symmetrically spaced keys located in corresponding keyways 34 prevents any
displacement of the axis of rotation, which is a common problem in the grate assembly
of the prior art wherein a single key and keyway 34 is provided between the upper
rotatable grate component 11 and the lower rotatable support structure 12. Thus, the
inclusion of one or more sets of keys provides that the axes of rotation represented by
points A and B overlap, coinciding with the axes 21, even in the upset condition
described hereinbefore.
Preferably one set of keys (i.e. two keys) spaced substantially diametrically
opposite one another can be used, more preferably two sets of keys (i.e. four keys) can
be used. Each set of keys is spaced substantially opposite one another such that the
keys are substantially orthogonal and equiangularly spaced around the circumference of
the rotatable support structure 12 which attaches to the upper rotatable grate
component 11. In instances where the upper rotatable grate component 11 and the
lower rotatable support structure 12 do not consist of an equal number of segments
(typically the components of the grate assembly 10 are constructed by joining together
three or more segments to make up the part), a minimum of one key per segment is
acceptable.
The additional keys will, in use, provide an additional connecting and torque
transfer mechanism which will prevent the relative displacement of the axes of rotation
A and B. In mitigating the displacement of the axes or rotation A and B to keep them
coaxial with the axis 21, the transfer of rotational loads onto the connecting bolts is
prevented and ultimately separation of the connected rotatable components 11 and 12
and functional failure of the grate assembly 10 is avoided.
The grate assembly 10 of the invention, as illustrated, thus provides for a
reduction in lost production due to greater availability of equipment and a reduction in
operating costs due to a reduction in maintenance required to repair functional failures
of the grate assembly. Furthermore, advantageously, minor modifications only are
required to retrofit the solution provided by the invention to existing equipment. In other
words, retrofitting of existing grate assemblies to obtain the advantages of the invention
is thus achieved by means of relatively minor modifications to the existing equipment.
Claims (15)
1. A grate assembly for a gasifier for gasifying carbonaceous material producing ash, the grate assembly including: 5 an upper rotatable grate component; and a lower rotatable support structure fastened to the upper rotatable grate component by a plurality of removable fasteners acting to prevent vertical displacement of the upper rotatable grate component and the lower rotatable support structure, the lower rotatable support structure being configured to be 10 drivingly rotated about a common vertical axis of rotation shared with the upper rotatable grate component, the assembly further including at least two key torque transmitters spaced angularly relative to said common axis of rotation and engaging the upper rotatable grate component and the lower rotatable support structure to transfer 15 torque from the lower rotatable support structure to the upper rotatable grate component when the lower rotatable support structure is driven and wherein the key torque transmitters are unthreaded and do not act to inhibit or prevent vertical displacement of the upper rotatable grate component and the lower rotatable support structure.
2. The grate assembly of claim 1, wherein the key torque transmitters are equiangularly spaced in a horizontal plane about the common vertical axis of rotation. 25
3. The grate assembly of claim 1 or claim 2, wherein two key torque transmitters are provided and are spaced 170 - 190º apart.
4. The grate assembly of claim 1 or claim 2, wherein three key torque transmitters are provided and are spaced 110 - 130˚ apart.
5. The grate assembly of claim 1 or claim 2, wherein the key torque transmitters are arranged in sets of two, with the two key torque transmitters in a set being positioned in diametrically opposed positions about the common vertical axis of rotation.
6. The grate assembly of any of claims 1 to 5, wherein the key torque transmitters are arranged in a circle and are interspaced by at least one fastener between adjacent key torque transmitters, the fastener acting to inhibit or 5 prevent vertical displacement of the upper rotatable grate component and the lower rotatable support structure.
7. The grate assembly of claim 6, wherein the fasteners are in the form of nut and bolt arrangements.
8. The grate assembly of any of claims 1 to 7, wherein the key torque transmitters are tapered from a wider operatively upper end to a narrower operatively lower end. 15
9. The grate assembly of any of claims 1 to 8, wherein the key torque transmitters are elongate and polygonal in outline in end view.
10. A gasifier for gasifying carbonaceous material, the gasifier including a grate assembly as claimed in any of claims 1 to 9 mounted within a 20 gasification chamber defined by a gasification vessel with the lower rotatable support structure of the grate assembly being connected to drive means.
11. The gasifier of claim 10, which is a fixed bed gasifier 25
12. The gasifier of claim 10 or claim 11, which is a fixed bed dry bottom gasifier.
13. The gasifier of claim 12, which is a coal, waste or biomass gasifier, or a gasifier configured to gasify a combination of two or more of coal, waste 30 and biomass.
14. The gasifier of claim 13, which is a coal gasifier operating at an elevated pressure of between 5 bar(g) and 100 bar(g) and a temperature of between 400ºC and 1600ºC.
15. A grate assembly for a gasifer for gasifying carbon access material producing ash substantially as herein before described with reference to any one of the embodiments described with reference to
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB1114700.6A GB2493957A (en) | 2011-08-25 | 2011-08-25 | Grate assembly for a gasifier with at least two key torque transmitters |
GB1114700.6 | 2011-08-25 | ||
PCT/IB2012/053758 WO2013027133A1 (en) | 2011-08-25 | 2012-07-24 | Gasification of carbonaceous material |
Publications (2)
Publication Number | Publication Date |
---|---|
NZ621271A NZ621271A (en) | 2015-06-26 |
NZ621271B2 true NZ621271B2 (en) | 2015-09-29 |
Family
ID=
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