NZ628393B2 - Rotary plough for gasifiers - Google Patents
Rotary plough for gasifiers Download PDFInfo
- Publication number
- NZ628393B2 NZ628393B2 NZ628393A NZ62839312A NZ628393B2 NZ 628393 B2 NZ628393 B2 NZ 628393B2 NZ 628393 A NZ628393 A NZ 628393A NZ 62839312 A NZ62839312 A NZ 62839312A NZ 628393 B2 NZ628393 B2 NZ 628393B2
- Authority
- NZ
- New Zealand
- Prior art keywords
- rotary
- plough
- rotation
- ash
- component
- Prior art date
Links
- 239000007787 solid Substances 0.000 claims abstract description 16
- 239000002184 metal Substances 0.000 claims abstract description 7
- 229910052751 metal Inorganic materials 0.000 claims abstract description 7
- 239000003575 carbonaceous material Substances 0.000 claims description 7
- 210000003371 Toes Anatomy 0.000 claims description 3
- 238000002309 gasification Methods 0.000 description 33
- 239000002245 particle Substances 0.000 description 32
- 241000234295 Musa Species 0.000 description 30
- 235000018290 Musa x paradisiaca Nutrition 0.000 description 30
- 238000000605 extraction Methods 0.000 description 16
- OKTJSMMVPCPJKN-UHFFFAOYSA-N carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 13
- 239000003245 coal Substances 0.000 description 13
- 230000003628 erosive Effects 0.000 description 12
- 239000002699 waste material Substances 0.000 description 9
- 239000007789 gas Substances 0.000 description 8
- 239000002028 Biomass Substances 0.000 description 6
- 238000007790 scraping Methods 0.000 description 5
- 239000000463 material Substances 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- 238000006748 scratching Methods 0.000 description 4
- 230000002393 scratching Effects 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 3
- 239000003795 chemical substances by application Substances 0.000 description 3
- 238000005552 hardfacing Methods 0.000 description 3
- 235000008733 Citrus aurantifolia Nutrition 0.000 description 2
- 229910000831 Steel Inorganic materials 0.000 description 2
- 235000015450 Tilia cordata Nutrition 0.000 description 2
- 235000011941 Tilia x europaea Nutrition 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 230000003247 decreasing Effects 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 239000004571 lime Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000002441 reversible Effects 0.000 description 2
- 239000002893 slag Substances 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- 230000037250 Clearance Effects 0.000 description 1
- 241000565356 Fraxinus pennsylvanica Species 0.000 description 1
- 229910000760 Hardened steel Inorganic materials 0.000 description 1
- 229910000990 Ni alloy Inorganic materials 0.000 description 1
- 239000003082 abrasive agent Substances 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000011449 brick Substances 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 230000035512 clearance Effects 0.000 description 1
- 239000000571 coke Substances 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- -1 iron-chromium-nickel Chemical compound 0.000 description 1
- 238000004519 manufacturing process 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
- 239000011236 particulate material Substances 0.000 description 1
- 230000037361 pathway Effects 0.000 description 1
- 230000002093 peripheral Effects 0.000 description 1
- 230000000630 rising Effects 0.000 description 1
- 239000004449 solid propellant Substances 0.000 description 1
- 239000011800 void material Substances 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
- C10J2300/00—Details of gasification processes
- C10J2300/09—Details of the feed, e.g. feeding of spent catalyst, inert gas or halogens
- C10J2300/0913—Carbonaceous raw material
- C10J2300/093—Coal
-
- 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
- F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
- F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
- F23G5/24—Incineration of waste; Incinerator constructions; Details, accessories or control therefor having a vertical, substantially cylindrical, combustion chamber
- F23G5/26—Incineration of waste; Incinerator constructions; Details, accessories or control therefor having a vertical, substantially cylindrical, combustion chamber having rotating bottom
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
- F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
- F23G5/24—Incineration of waste; Incinerator constructions; Details, accessories or control therefor having a vertical, substantially cylindrical, combustion chamber
- F23G5/28—Incineration of waste; Incinerator constructions; Details, accessories or control therefor having a vertical, substantially cylindrical, combustion chamber having raking arms
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23H—GRATES; CLEANING OR RAKING GRATES
- F23H15/00—Cleaning arrangements for grates; Moving fuel along 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
solids handling equipment rotary plough (200) includes an elongate metal body (201) with a leading face (210) and a trailing face (212). The body (201) is configured to be mounted to a rotary component for rotation about an axis of rotation at least in one direction which is an operative forward direction such that the leading face (210) leads the trailing face (212). At least the leading face (210) has at least two major operatively upwardly and outwardly extending surfaces (202.1, 204.1) which are not coplanar. A first major surface (202.1) is angled operatively rearwardly and upwardly relative to the forward direction of rotation at an angle of at least 1° to the vertical. A second major surface (204.1) is angled operatively forwardly and outwardly at an angle of at least 1° relative to a radius of a circle described in use by the rotary plough (200) when rotating in the operative forward direction. irection such that the leading face (210) leads the trailing face (212). At least the leading face (210) has at least two major operatively upwardly and outwardly extending surfaces (202.1, 204.1) which are not coplanar. A first major surface (202.1) is angled operatively rearwardly and upwardly relative to the forward direction of rotation at an angle of at least 1° to the vertical. A second major surface (204.1) is angled operatively forwardly and outwardly at an angle of at least 1° relative to a radius of a circle described in use by the rotary plough (200) when rotating in the operative forward direction.
Description
ROTARY PLOUGH FOR GASIFIERS
Field of the Invention
THIS INVENTION relates to gasifiers. In particular, the invention relates
to a solids handling equipment rotary plough, to a rotatable grate assembly for a
gasifier for gasifying carbonaceous material producing ash and to a gasifier for
gasifying carbonaceous material.
Background of Invention
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 pressurised 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 rotatable 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 rotatable grate assembly is also used to distribute
gasification agent (typically a mixture of steam and oxygen) into the bed of
carbonaceous material.
Typically, a conventional rotatable grate assembly comprises of a number
of components, principally an upper roughly conical-shaped rotatable grate component,
a lower rotatable support structure rigidly connected to the upper rotatable grate
component at an upper periphery of the rotatable support structure so that the rotatable
grate component and the rotatable support structure rotate together about a common
axis of rotation 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 rotatable 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
rotatable grate assembly.
As the rotatable grate assembly is rotated, one or more symmetrically
circumferentially spaced ploughs which are rigidly connected to an outer periphery of
the upper rotatable grate component act to remove the ash from the bottom of the
gasifier. Ash consists of dry coarse ash and clinkers, which are by-products of the
gasification process. Clinkers are solid agglomerates of particles of melted ash.
Clinkers need to be crushed in order efficiently to be removed from the gasifier. The
ploughs continuously scrape the ash through an ash discharge passageway which is
defined between the upper rotatable grate component of the rotatable grate assembly
and a wall of the gasifier. As the rotatable grate assembly rotates, the clinkers are
crushed between shield plates mounted on the upper rotatable grate component and
wear bricks mounted on the wall of the gasifier. The ash and clinkers fall under force of
gravity from the ash discharge passageway into an ash lock which is in communication
with the ash discharge passageway, to exit the gasifier.
The operation of and the removal of ash from a fixed bed gasifier are well
known in the art and described in detail in .
The inventor has experience with two existing plough designs. The first is
a conventional “short straight plough” and the second is the Sasol® Banana Plough™
which is currently in commercial use in South Africa in the Sasol® FBDB™ gasifier.
The major differences between the short straight plough and the Sasol®
Banana Plough™ is that the short straight plough has planar leading and trailing faces,
whereas the Sasol® Banana Plough™ has curved leading and trailing faces, with the
leading and trailing faces curving in the same direction, resembling to some extent a
banana. Both the short straight plough and the Sasol® Banana Plough™ are mounted
on the upper rotatable grate component of the rotatable grate assembly at an angle to
the direction of rotation, such that the leading face of the plough functions to scrape ash
particles from an ash bed in a gasification chamber radially inwardly via a central ash
discharge passageway or annulus into an ash chamber disposed below the rotatable
grate assembly. Usually a number of ploughs, e.g. four ploughs, are symmetrically
mounted on the rotatable grate assembly. Thus, during forward rotation of the rotatable
grate assembly, the leading faces of each plough remove ash and crushed clinker
particles from the gasifier by a scraping and cutting motion which causes the ash
particles to follow a radially inward pathway from the wall of the gasifier to the central ash
discharge annulus and into the ash chamber.
In the operation of the short straight plough, severe erosion on the
ploughs and other components of the rotatable grate assembly has been observed.
This lead to the making of improvements in the materials of construction of the rotatable
grate assembly, e.g. by introducing custom made hard-facing to mitigate erosion, as
well as by introducing a number of changes in the geometry of the plough and other
wear surfaces exposed to ash particles. These changes, amongst others, lead to the
development of the Sasol® Banana Plough™ which is in current commercial operation
and has been for about 40 years.
The inventor has subsequently learned that the mode of ash removal with
the Sasol® Banana Plough™ causes erosion of certain components of the rotatable
grate assembly, ploughs and gasifier walls exposed to ash. Discrete element modelling
has shown surprisingly that the forward rotation of a rotatable grate assembly on which
the Sasol® Banana Plough™ is mounted causes the leading face of a trailing plough to
force ash particles onto the trailing face of a preceding plough. Thus, ash particles
become compressed between the trailing face of a leading plough, the gasifier wall and
the leading face of a trailing plough. This causes an accumulation and compression of
ash particles between the two ploughs, which leads to outward forces on the gasifier
walls. Ash particles wedged between the ploughs and the gasifier wall cause erosion
patterns on the gasifier walls and on the components of the grate assembly.
In an attempt to free the wedged ash particles, a grate may temporarily be
operated in the reverse mode. This action however induces high torque loads on the
drive systems which may eventually lead to mechanical equipment failure.
Furthermore, erosion is increased during periods of reverse operation and ash
extraction rates are also vastly reduced. Erosion leads to increased maintenance costs,
equipment downtime and production loss. These are major operational inefficiencies
caused by the inability of the ploughs of the prior art to remove ash in both the forward
and the reverse operational modes of a rotatable grate assembly.
describes the components and the operation of a fixed
bed coal gasifier. It discloses the use of the Sasol® Banana Plough™ in a fixed bed
gasifier and its reverse mode of operation. The state of the art Sasol® Banana
Plough™ is attached to a rotatable grate component such that the Sasol® Banana
Plough™ passes with limited clearance over an ash collection surface. Ash is
continuously withdrawn from the bottom of a gasification zone by rotation of the
rotatable grate component and the Sasol® Banana Plough™ continuously discharges
ash through an ash discharge passageway. discloses the location
and use of the Sasol® Banana Plough™ but is silent on the functional design of the
Sasol® Banana Plough™. also does not disclose any operational
problems associated with the Sasol® Banana Plough™ or methods to solve them.
specifically focuses on the grate component of a fixed
bed coal gasifier and discloses information on the operation of the ash extraction
assembly. It also discloses the use of the Sasol® Banana Plough™ which is
operational in the reverse mode but does not disclose any information on its method of
functioning.
US 4,014,664 describes the components and operation of a rotary grate
component assembly for a fixed bed coal gasifier, and the assembly appears to be
similar to the grate assembly described in and .
US 4,014,664 discloses that the scrapers are located on the periphery of the grate
component and that the scrapers are operational in the reverse mode.
GB 389251 describes improvements in the mechanism of ash discharge in
a Kerpely gas producer (Kerpely gas producers were often used for under firing coke
ovens). GB 389251 discloses that scrapers are located at the periphery of a grate
component and are arranged at an angle to the radius so that their rotation sweeps ash
towards the centre of the grate component and into an ash discharge hopper.
US 5,230,716 describes the components and operation of a reversible
rotary grate component for a fixed bed coal gasifier. US 5,230,716 discloses that
scoops (ploughs) are located on an upper surface and near an apex of a conical grate
component. In addition, each scoop is positioned at an angle to the radius of the
gasification chamber and discharges ash from the central region of a gasification zone
in the gasification chamber towards the peripheral region of the grate component to the
ash discharge passageway. The location and operation of the scoop is therefore
different to the state of the art Sasol® Banana Plough™ hereinbefore described.
US 5,138,957 describes a bottom feed biomass gasification system that
does not recirculate gases through a fixed bed. The gases are directed to a secondary
heating chamber to maintain the desired operating temperature in a primary heating
chamber. US 5,138,957 discloses that the ash discharge system has four
symmetrically spaced paddles that are mounted on the periphery of a rotary band which
rotates in a clockwise direction. The paddles comprise “generally radial front walls”
which appear to be vertical. The paddle surface (radial front walls) sweeps the ash
forwardly to an ash discharge passageway located between the chamber wall and ash
discharge system. When clinkers are formed, they are broken down between the rear
walls of the paddles and the walls of the reaction chamber. There is no mention of ash
being lodged between the ploughs or erosion of the paddles or chamber walls in
US 5,138,957.
JP 2011083773 describes a process for the removal of melted ash
produced in a biomass gasification process. A rotary scraper spans the horizontal
surface of a floor of a reaction chamber. A “scratching finger” is connected to ends of
the rotary scraper. Slag is directed forwardly by the “scratching finger” and after a
single revolution of the rotary scraper; the slag is discharged through a discharge outlet
located between the wall of the reaction chamber and the rotary scraper. The design of
the “scratching finger” is undisclosed, however, a top view of the “scratching finger”
leads to the conclusion that it is rectangular in shape with vertical faces.
GB 548082 describes a mechanism for keeping a rotating plough in a
rotatable gas generator stationary. In normal operation the plough rotates with an ash
pan and gas producer and does not turn out ash. When the mechanism is engaged and
the plough is held stationary, ash will be removed from the producer. The ash plough
itself is not shown nor is its design or specific functioning described.
CN 2518061 describes the extraction of block-shaped lime from a vertical
lime kiln. The extraction device is rotatable and reversible and has six scrapers that are
symmetrically located around its circumference. CN 2518061 discloses that the
scrapers are “triangle” in shape and “scrapes the ash inwardly to an ash discharge
tube”. The reverse mode of operation is required to “break the furnace conditions”.
CA 2188736 describes a fixed bed biomass gasification system, of which
a primary chamber has a raised table for supporting the bed of biomass. The waste
removal system consists of four ploughs that are symmetrically located at the periphery
of a ring member on a rotating table and removes ash and waste from the chamber to
accumulate in a channel that spans the chamber wall. The ash and waste material are
then pushed to a waste aperture located in the floor of the chamber. Two of the
ploughs are formed with scraping members that extend inwardly towards an apex of the
table to scrape ash from the annular zone to the waste aperture. The scraping
members also break up clinkers that form on the edge of the table. From a top view of
the waste disposal system, it appears that the ploughs are fin-shaped and the scraping
members are rectangularly shaped. CA 2188736 however does not provide any actual
description of the design or shape of the ploughs. CA 2188736 is also silent on the
reversibility of the waste disposal system.
GB 141056 relates to improvements to rotary grates employed in gas
producers. The ash grates disclosed are conical in shape and attached to a top surface
of the grate are radial projections with the leading surface of the projection rising
rearwards from the leading edge. The front surfaces of the projections are convex and
when the grate rotates will raise the combustible material and ash above the grate to
prevent clinkering. These projections do not remove ash from the ash bed. The conical
shape of the grate also causes ash to move to the sides where an annulus is provided
with stationary scrapers attached to the inside of vessel wall of the gas producer for ash
removal. The ash grate projections in GB 141056 serve for clinker breaking and mixing
above the grate. GB 141056 is silent on the functional design of the scraper itself. As
ash is removed toward the periphery in GB 141056, no surface is provided for
displacing ash radially inward.
EP 0159420 describes the gasification of solid fuel in a fixed bed system.
There are two different sets of scrapers in the fixed bed gasifier for the extraction of ash.
Radially extending walls continue downwards and extend inwardly into the chamber
above a grate component to form “upper scraper members”. These scrapers are fixed
to the chamber walls. In addition, there are a set of scrapers attached below the grate
component that are described as “vertically reciprocable scrapers”. From the
longitudinal section view of the gasification system, each “vertically reciprocable
scraper” appears to span the left and right bottom surface of the grate and extends to
the apex of the grate and central portion. The oscillating rotary motion of the grate
component and the “vertically reciprocable scrapers” is controlled to be slightly more or
less than the circumferential angle of 30°. The “vertically reciprocable scrapers” sweep
ash over the periphery of the grate component to the ash discharge tube. The design
aspects of the scrapers are undisclosed in EP 0159420.
A plough that at least ameliorates the problems associated with the
ploughs of the prior art and is preferably able effectively to remove ash in both the
forward and reverse operational modes of a rotatable grate assembly would be
desirable.
Summary of the Invention
According to one aspect of the invention there is provided a solids
handling equipment rotary plough, the rotary plough including
an elongate metal body having a leading face and a trailing face and being
configured to be mounted to a rotary component for rotation about an axis of rotation at
least in one direction which is an operative forward direction such that the leading face
leads the trailing face, at least the leading face having at least two major operatively
upwardly and outwardly extending surfaces which are not coplanar, a first major surface
being angled operatively rearwardly and upwardly relative to the forward direction of
rotation at an angle of at least 1° to the vertical and a second major surface being
angled operatively forwardly and outwardly at an angle of at least 1° relative to a radius
of a circle described in use by the rotary plough when rotating in the operative forward
direction.
By “major surfaces” of a face is meant that there are no other surfaces on
the face which are larger than the major surfaces. Each major surface is typically
planar.
In this specification, unless clearly intended otherwise in the context used,
the term “radius” or “radially” is used to describe a direction or position relative to or
coinciding with the radius of a circle in use described by the rotary plough when rotating
in a plane through which said axis of rotation extends. Thus, a radially outer or radially
outward object or part is further away from said axis of rotation of the metal body of the
rotary plough than a radially inner or radially inward object or part. It is however to be
noted that “outwardly” means outwardly away from said axis of rotation, although not
necessarily along a radius of said circle, unless so specified, with the term “inwardly”
having an opposite meaning.
Typically, in use, said plane through which said axis of rotation extends is
a horizontal plane.
The metal body may be of hardened steel. Alternatively, the metal body
may be of casting steel, e.g. a specially modified heat resistant iron-chromium-nickel
alloy of ASTM A297 Grade HF. The major surfaces may be clad in a specially
hardened material, e.g. a hardfacing such as PRO 100 (trade name) hardfacing.
The trailing face may have at least two major surfaces which are not
coplanar, a first major surface being angled forwardly and upwardly relative to the
forward direction of rotation at an angle of at least 1° to the vertical and a second major
surface being angled rearwardly and outwardly at an angle of at least 1° relative to a
radius of a circle described in use by the rotary plough when rotating in the forward
direction.
The first and second major surfaces of the leading face may share a
common periphery or edge between them. In other words, the first and second major
surfaces may be adjacent to and bordering each other.
The common periphery or edge of the first and second major surfaces of
the leading surface may be linear and may extend downwardly in an outward direction.
The common periphery or edge of the first and second major surfaces of
the leading surface may be angled forwardly relative to a radius of a circle described in
use by the rotary plough when rotating in the forward direction.
The common periphery or edge of the first and second major surfaces of
the leading surface may define at least a portion of a top periphery of the second major
surface.
The common periphery or edge of the first and second major surfaces of
the leading surface may define at least a portion of a bottom periphery of the first major
surface.
The first and second major surfaces of the trailing surface may share a
common periphery or edge between them.
The common periphery or edge of the first and second major surfaces of
the trailing surface may be linear and may extend downwardly in an outward direction,
and may be angled rearwardly relative to a radius of a circle described in use by the
rotary plough when rotating in the forward direction.
The angle of the first surface to the vertical may be in the range of from
about 1° to about 35°, e.g. about 15°.
The angle of the second surface relative to said radius of said circle
described in use by the rotary plough when rotating in the forward direction may be in
the range of from about 1° to about 18°, e.g. about 6°.
The second surface may extend operatively vertically.
The trailing face of the body of the rotary plough may be a mirror image of
the leading face of the body of the rotary plough. Thus, the trailing face and the leading
face may be mirrored about a radius plane defined by the rotary plough in use.
The body may have a linear centre line, or may be configured to be
mounted such that it extends radially outwardly from where it is mounted to a rotary
component. A spine may be defined between the leading and trailing faces. The spine
may be planar and the spine may coincide in use with a radius of said circle described
by the rotary plough when rotating in the operative forward direction. The spine may
have a curved upper periphery over at least a portion of the length of the spine. In one
embodiment of the invention, a radially outer portion of the upper periphery of the spine
is flat and a radially inner portion of the upper periphery of the spine is convexly curved.
A radially outward portion of the body may have an increased height
compared to a radially inward portion of the body. Preferably, a bottom surface of the
body drops down radially outwardly to end in a rounded upwardly curved toe.
According to another aspect of the invention, there is provided a rotatable
grate assembly for a gasifier for gasifying carbonaceous material producing ash, the
grate assembly including
a rotary component configured for rotation about an upwardly extending axis of
rotation, the rotary component being configured for rotation at least in one direction
which is an operative forward direction; and
a plurality of rotary ploughs as hereinbefore described, the rotary ploughs being
mounted to the rotary component for rotation together with the rotary component about
said axis of rotation and the rotary ploughs extending outwardly away from said axis of
rotation.
The rotary component may be an upper rotatable grate component, the
rotatable grate assembly further including a lower rotatable support structure fastened
to the upper rotatable grate component for rotation together with the upper rotatable
grate component, the lower rotatable support structure being configured to be drivingly
rotated about an axis of rotation which coincides with said axis of rotation of the upper
rotatable grate component.
Typically, said axis of rotation of the upper rotatable grate component is
vertical.
The rotary component may be configured for rotation in both said
operative forward direction and an operative reverse direction. Thus, the grate
assembly may be operable in both said forward direction and said reverse direction.
The rotary ploughs may extend radially away from said axis of rotation.
Thus, an end of a rotary plough where the rotary plough is mounted to the rotary
component may be radially in line with a free end of said rotary plough.
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.
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.
The rotary ploughs may be equiangularly spaced. Thus, for example,
when only two rotary ploughs are present, they may be about 180° apart, when three
rotary ploughs are present, they may be about 120° apart, when four rotary ploughs are
present, they may be about 90° apart, and when six rotary ploughs are present, they
may be about 60° apart. It may however be that the arrangement of the rotary ploughs
is not symmetrical due to construction constraints (other components in the way, etc.),
particularly when the rotary plough of the invention is retrofitted to an existing rotatable
grate assembly. Large variations in spacing between rotary ploughs, e.g. up to 60°
variation, may be employed.
It is expected that up to six rotary ploughs may be mounted to the rotary
component.
According to a further aspect of the invention, there is provided a gasifier
for gasifying carbonaceous material, the gasifier including a rotatable grate assembly as
hereinbefore described, the rotatable grate assembly being 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 a pressure of between 5 bar(g) and
100 bar(g) and a temperature of between 400°C and 1600°C.
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.
Brief Description of the Drawings
The invention will now be further described, by way of example, with
reference to the accompanying diagrammatic drawings in which:
Figure 1 shows a vertically sectioned view of a rotatable grate assembly,
installed in a fixed bed dry bottom coal gasifier;
Figure 2 shows a three dimensional view of a rotary plough in accordance with
the invention;
Figure 3 shows a plan view of the rotary plough of Figure 2;
Figure 4 shows a side view of the rotary plough of Figure 2;
Figure 5 shows an end view of the rotary plough of Figure 2;
Figure 6 shows a vertical section through the rotary plough of Figure 2, taken at
VI-VI in Figure 4;
Figure 7 shows a vertical section through the rotary plough of Figure 2, taken at
VII-VII in Figure 4;
Figure 8 shows a vertical section through the rotary plough of Figure 2, taken at
VIII-VIII in Figure 4;
Figure 9 shows the velocity of ash particles displaced by a short straight plough
in (A) the forward and (B) the reverse direction;
Figure 10 shows the velocity of ash particles displaced by a Sasol® Banana
Plough™ in (A) the forward and (B) the reverse direction; and
Figure 11 shows the velocity of ash particles displaced by a rotary ash plough in
accordance with the invention having mirror image leading and trailing faces, in both the
forward and reverse directions.
Detailed Description of a Preferred Embodiment
With reference to Figure 1 of the drawings, reference numeral 10
generally refers to a grate assembly installed in a gasification vessel 100 of a fixed bed
dry bottom coal gasifier. The gasification vessel 100 defines a gasification chamber 102
(a pressure vessel) 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,
connected to a lower rotatable support structure 12 by a plurality of connecting bolts 15.
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 rotary metal ash 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. The
ploughs 17 may be of the short straight type or the Sasol® Banana Plough™ as
hereinbefore described, or an improved rotary ash plough according to the present
invention. Conveniently, the upper rotatable grate component 11 is configured to allow
the ploughs 17 to be readily interchangeable.
The upper rotatable grate component 11 is provided with shield plates 22,
arranged in terrace fashion.
In use, the grate assembly 10 is rotated about a vertical 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 lower edges of 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 Figures 2 to 8 of the drawings, reference numeral 200
generally indicates a rotary ash plough in accordance with the present invention. The
plough 200 has an elongate hardened, wedge-shaped in plan view, steel body 201
defining an operative leading face 210 and an operative trailing face 212. The trailing
face 212 is a mirror image of the leading face 210.
Although not shown in the drawings, the plough 200 typically includes
mounting formations, e.g. bolt receiving apertures, towards the right hand end of the
body 201 as shown in Figure 4, to allow mounting of the plough 200 to the rotatable
grate component 11.
Each of the leading face 210 and the trailing face 212 defines two angled
or sloped major planar surfaces 202.1, 202.2 and 204.1, 204.2. The surfaces 202.1,
202.2 are constructed at an angle to the vertical, such that a bottom leading edge 206 of
the leading face 210 is radially in front of a top leading edge 208 in an operative forward
direction of rotation 203, which in this embodiment is counter-clockwise. The surface
202.1 is thus angled rearwardly relative to the forward direction of rotation 203, and
upwardly away from a horizontal plane in which the plough 200 in use rotates. For the
trailing face 212, the opposite is true in respect of the surface 202.2 when the plough
200 is rotated counter-clockwise as indicated by the arrow 203.
The faces 202.1, 202.2 are typically formed by a 30° angled cut 220 (see
Figure 6), i.e. a 15° cut to the vertical each (when the plough 200 is viewed in an
operative condition). However, the angle 220 may be anywhere in the range of from
about 2° to about 70°. The angle 220 can thus be decreased to approach about 2° or
increased to approach about 70°; however, ash extraction efficiency may be negatively
impacted by a too narrow or a too wide angle 220.
The second surface 204.1 is in use a vertical planar surface which is
angled forwardly and outwardly at an angle relative to a radius 222 (see Figure 3) of a
circle (not shown) described in use by the rotary plough 200 when rotating in the
forward direction 203. Being a mirror image of the surface 204.1, the opposite is thus
true for the surface 204.2 when the plough is rotated in the forward direction 203.
The surfaces 204.1, 204.2 are typically cut by a 12° radial cut, indicated by
an angle 224 (see Figure 3), such that the body 201 of the plough 200 widens in a
direction away from a radially inner edge 214 of the body 201. The radial cut or angle
224 of the surfaces 204.1, 204.2 may be anywhere in the range of from about 2° to
about 36°. The angle 224 can thus be decreased to approach about 2° or increased to
approach about 36° but the ash extraction efficiency may also be negatively impacted
by a too wide or a too narrow angle 224.
The body 201 has a centre plane coinciding with the radius 222, defining a
spine 226 between the leading and trailing faces 210, 212. The spine 226 is planar and
has a curved upper periphery 228 in a radially inner portion of the body 201 and a flat
periphery 230 in a radially outer portion of the body 201.
As can be seen in Figure 4 of the drawings, a radially outer portion of the
body 201 has an increased height compared to a radially inner portion of the body 201,
with a bottom surface 232 of the body 201 dropping radially outwardly before curving
upwardly again to define a rounded or curved toe 234.
In use, one or more ploughs 200 are bolted to the upper rotatable grate
component 11 of the grate assembly 10 by fastening means (not shown) near said
radially inner edge 214 of the body 201. As the grate assembly 10 and thus the plough or
ploughs 200 are rotated in a forward direction 203 through the ash particles in the ash
bed of the gasification chamber 102, the angled surfaces 202.1 and 204.1 result in forces
on the ash particles of which the contact vectors are axially upward and inwards towards
the axis of rotation.
Discrete element modelling surprisingly identified a problem not previously
identified in the operation of a grate assembly fitted with ploughs of the prior art. During
rotation of the grate, a compression of particles between two successive ploughs
occurs, resulting in erosion of the components of the grate assembly and the gasifier
walls. The inclusion of two angled surfaces 202.1 and 204.1 on the leading face 210 of
the plough 200 surprisingly overcomes this problem and reduces the compressive effect
discovered in the operation of the short straight plough or the Sasol® Banana Plough™
of the prior art. The angled surface 202.1 lifts ash particles vertically upwards to fill void
spaces in the ash bed which are caused by variable ash particle sizes. The surface
204.1 induces an inward displacement of the ash particles towards the axis of rotation
relative to the normal (i.e. 90°) contact vector, thus ensuring removal of the particles via
the ash discharge annulus 19. By lifting and displacing the ash particles inwardly
towards the axis of rotation, the angled surfaces 202.1 and 204.1 enable ash particles to
have particle-to-particle contact surfaces, thus minimizing wear on the plough 200 and on
other surfaces, e.g. the shield plates 22 or the gasifier wall 18. The number of ploughs
200 employed will be determined by the required ash extraction rate. Typically, up to six
ploughs 200 would be utilized.
Modelling has also shown that extraction efficiency of the plough 200 is
increased over ploughs of the prior art, in both the forward direction 203 and in a reverse
direction of operation.
The plough 200 is designed such that the leading face 210 (comprising
both angled surfaces 202.1 and 204.1) and the trailing face 212 (also comprising angled
surfaces 202.2 and 204.2) are mirror images of each other. This enables the plough
200 effectively to remove ash when rotated in the forward direction 203 or in a reverse
direction, without a reduction in the ash extraction efficiency or a change in the erosion
characteristics. This extends the working life of the plough 200 greatly and prevents
high wear and loss of extraction when operating the grate assembly 10 and plough 200
in a reverse mode.
Example
The inventor has conducted modelling studies to determine the solids flow
characteristics of the short straight plough and the Sasol® Banana Plough™ of the prior
art as well as the plough 200. The results are reflected in Figures 9, 10 and 11. In
these figures, the shade indicates the velocity of the ash particles at a point, with the
light grey shades representing slow moving or stationary ash particles, and the darker
shades representing particles which have a faster velocity.
Referring in particularly to Figure 9A (short straight plough) and Figure
10A (Sasol® Banana Plough™), it can be seen that in forward operation (indicated by
reference numerals 301 and 401) the ash particles at the leading face of the plough
move the fastest and are therefore also responsible for the greatest degree of wear on
the plough and the gasifier walls. When the short straight plough is operated in reverse
mode (indicated by reference numeral 302 in Figure 9B), almost all of the ash particles
remain stagnant, which clearly shows the inability of the short straight plough to operate
in reverse mode.
As shown in Figure 10B, the Sasol® Banana Plough™ operated in
reverse mode along the direction of arrow 402 causes ash to be displaced outwardly
towards the gasifier wall. This results in an increase in the degree of wear or erosion on
the gasifier wall.
Referring to Figure 11 of the drawings, the velocity of ash particles is
shown when displaced by a plough 200 in accordance with the invention. Figure 11
represents operation of the plough in either the forward or the reverse direction. The
contrasting factor in the operation of the plough 200 when compared to the Sasol®
Banana Plough™ (Figure 10) and the straight short plough (Figure 9) is that the plough
200 has a constant moving layer of ash on the leading face. This is because the plough
200 creates a stagnant layer of ash particles ahead of it, as it is mounted on the grate in
a direction perpendicular to the direction of rotation, i.e. radially extending. With a
constant stagnant layer built up ahead of the plough 200, ash-on-ash friction ahead of
the plough improves and promotes solid flow and thus prevents erosion on the plough
200.
During the modelling exercise, the performance of the plough 200 was
compared with the short straight plough and the Sasol® Banana Plough™ of the prior
art. The results are reflected in the table hereunder.
Short straight Sasol® Banana
Forward Operation Plough 200
plough Plough™
Extraction rate
1.6 1.2 0.93
(m /rev)
Torque (kN.m) 62.0 76 70
Short straight Sasol® Banana
Reverse Operation Plough 200
plough Plough™
Extraction rate
0.6 0.2 0.93
(m /rev)
Torque (kN.m) 99.0 120 70
The extraction rate of the plough 200 in the reverse direction is higher
than that of the short straight plough or the Sasol® Banana Plough™ and at a much
reduced torque. It is also clear from the data that the ploughs of the prior art show
severe drop-off in performance when the rotational direction is reversed, whereas
performance of the plough 200 remains unchanged.
Similar torque and extraction rates are achieved in the forward or reverse
operational modes of the plough 200, which is a notable improvement over those
achieved by the Sasol® Banana Plough™ and the short straight plough. The major
distinguishing factor in the operation of the plough 200 when compared to the Sasol
Banana Plough and the short straight plough is that the plough 200 has a constant
moving layer of ash on the plough face. This is because the plough 200 creates a
stagnant layer of particles ahead of it as it is mounted normal to the contact direction.
Solids flow is thereby promoted and improved.
A grate assembly 10, as illustrated, incorporating one of more ploughs
200, as illustrated, will yield benefits in respect of reduced erosion on the ploughs, wear
plates, grate components and gasifier walls, which will improve the life of the
mechanical equipment. Furthermore, ash and clinker particles are more efficiently
extracted from the gasifier as the plough 200 can operate in both the forward and
reverse directions without a reduction in the extraction efficiencies or any noticeable
increase in equipment wear. The reduced torque associated with operation in both the
forward and reverse operating modes is beneficial in that equipment failure is mitigated.
Claims (12)
- WHAT WE CLAIM IS: 5 1. A solids handling equipment rotary plough, the rotary plough including an elongate metal body having a leading face and a trailing face and being configured to be mounted to a rotary component for rotation about an axis of rotation at least in one direction which is an operative forward direction such that the leading face leads the trailing face, at least the leading face having at least two major operatively 10 upwardly and outwardly extending surfaces which are not coplanar, a first major surface being angled operatively rearwardly and upwardly relative to the forward direction of rotation at an angle of at least 1° to the vertical and a second major surface being angled operatively forwardly and outwardly at an angle of at least 1° relative to a radius of a circle described in use by the rotary plough when rotating in the operative forward 15 direction.
- 2. The solids handling equipment rotary plough according to claim 1, in which the angle of the first surface to the vertical is in the range of from 1° to 35° and the angle of the second surface relative to said radius of said circle described in use by 20 the rotary plough when rotating in the forward direction is in the range of from 1° to 18°.
- 3. The solids handling equipment rotary plough according to claim 1 or claim 2, in which the second surface extends operatively vertically. 25
- 4. The solids handling equipment rotary plough according to any one of claims 1 to 3, in which the first and second major surfaces of the leading face share a common periphery or edge between them.
- 5. The solids handling equipment rotary plough according to claim 4, in 30 which the common periphery or edge of the first and second major surfaces of the leading surface is linear and extends downwardly in an outward direction, and in which the common periphery or edge of the first and second major surfaces is angled forwardly relative to said radius of said circle described in use by the rotary plough when rotating in the forward direction.
- 6. The solids handling equipment rotary plough according to any one of claims 1 to 5, in which the trailing face of the body of the rotary plough is a mirror image of the leading face of the body of the rotary plough.
- 7. The solids handling equipment rotary plough according to any one of claims 1 to 6, in which the body is configured to be mounted such that it extends radially outwardly from where it is mounted to said rotary component. 10
- 8. The solids handling equipment rotary plough according to any one of claims 1 to 7, in which a radially outward portion of the body has an increased height compared to a radially inward portion of the body.
- 9. The solids handling equipment rotary plough according to claim 8, in 15 which a bottom surface of the body drops down radially outwardly to end in a rounded upwardly curved toe.
- 10. A rotatable grate assembly for a gasifier for gasifying carbonaceous material producing ash, the grate assembly including 20 a rotary component configured for rotation about an upwardly extending axis of rotation, the rotary component being configured for rotation at least in one direction which is an operative forward direction; and a plurality of rotary ploughs according to any of claims 1 to 9, the rotary ploughs being mounted to the rotary component for rotation together with the rotary component 25 about said axis of rotation and the rotary ploughs extending outwardly away from said axis of rotation.
- 11. The rotatable grate assembly according to claim 10, in which the rotary component is configured for rotation in both said operative forward direction and an 30 operative reverse direction, and in which the rotary ploughs extend radially away from said axis of rotation.
- 12. The rotatable grate assembly according to claim 10 or claim 11, in which the rotary component is an upper rotatable grate component, the rotatable grate
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
ZA2012/00591 | 2012-01-24 | ||
ZA201200591 | 2012-01-24 | ||
PCT/IB2012/056798 WO2013110981A1 (en) | 2012-01-24 | 2012-11-28 | Rotary plough for gasifiers |
Publications (2)
Publication Number | Publication Date |
---|---|
NZ628393A NZ628393A (en) | 2015-08-28 |
NZ628393B2 true NZ628393B2 (en) | 2015-12-01 |
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