Title: Process for the production of a gaseous fuel
Abstract: A process for the production of a gaseous fuel from a waste material and/or a premium fuel, which process comprises: i) providing a processing chamber having therein a plurality of outwardly radiating inclined vanes at a base thereof, an inlet and an outlet; ii) introducing a waste material and/or a premium fuel into the chamber through the inlet; iii) generating an upward flow of a heating fluid through the vanes at the base of the chamber, whereby the waste material and/or the premium fuel circulate about an axis of the chamber in a compact turbulent band and is gasified and/or pyrolysed to produce a gaseous fuel stream, which gaseous fuel stream exits the chamber through the outlet; and iv) feeding at least a portion of the gaseous fuel stream back into the chamber through an entry point adjacent the vanes.
Patent Number: 6,883,442 Issued on 04/26/2005 to Groszek, et al.
| Inventors:
|
Groszek; Martin Alexander (Newbury, GB);
Dodson; Christopher Edward (Reading, GB);
Notebaart; Cornelis Wilhelmus (JA Dieren, NL);
Oudenhoven; Hubertus Petrus Maria (GH Westervoort, NL)
|
| Assignee:
|
Mortimer Technology Holdings Ltd. (Reading, GB)
|
| Appl. No.:
|
110763 |
| Filed:
|
October 25, 2000 |
| PCT Filed:
|
October 25, 2000
|
| PCT NO:
|
PCTGB00/04106
|
| 371 Date:
|
September 16, 2002
|
| 102(e) Date:
|
September 16, 2002
|
| PCT PUB.NO.:
|
WO0130943 |
| PCT PUB. Date:
|
May 3, 2001 |
Foreign Application Priority Data
| Current U.S. Class: |
110/341; 110/204; 110/243 |
| Intern'l Class: |
F23B 007//00; F23G 007//00; B01J 008//18 |
| Field of Search: |
422/139,145,146,147,234
110/101. R,104. R,204,243,244,245
48/197. R,197. FM,210
922/234
|
References Cited [Referenced By]
U.S. Patent Documents
| 3411465 | Nov., 1968 | Shirai.
| |
| 3799077 | Mar., 1974 | Lowe.
| |
| 3920417 | Nov., 1975 | Fernandes.
| |
| 4023280 | May., 1977 | Schora et al.
| |
| 4191539 | Mar., 1980 | Patel et al.
| |
| 4197092 | Apr., 1980 | Bretz.
| |
| 4248164 | Feb., 1981 | Isheim.
| |
| 4298453 | Nov., 1981 | Schoennagel et al.
| |
| 4315758 | Feb., 1982 | Patel et al.
| |
| 4388877 | Jun., 1983 | Molayem et al.
| |
| 4451184 | May., 1984 | Mitchell.
| |
| 4479920 | Oct., 1984 | Dodson.
| |
| 4568362 | Feb., 1986 | Deglise et al.
| |
| 4646637 | Mar., 1987 | Cloots.
| |
| 5033205 | Jul., 1991 | Dodson.
| |
| 5582118 | Dec., 1996 | Atkins et al.
| |
| 5829368 | Nov., 1998 | Cote et al.
| |
| Foreign Patent Documents |
| 12 96 732 | Jun., 1969 | DE.
| |
| 15 71 650 | Jan., 1971 | DE.
| |
| 27 21 237 | Dec., 1977 | DE.
| |
| 29 42 804 | May., 1981 | DE.
| |
| 0 092 622 | Feb., 1983 | EP.
| |
| 8 701 523 | Jan., 1989 | NL.
| |
| WO 9517982 | Jun., 1995 | WO.
| |
Primary Examiner: Rinehart; Kenneth
Attorney, Agent or Firm: Bacon & Thomas, PLLC
Claims
1. A process for the production of a gaseous fuel from a waste material and/or
a premium fuel, which process comprises:
(i) providing a processing chamber having therein a plurality of outwardly radiating
inclined vanes at a base thereof, an inlet and an outlet;
(ii) introducing a waste material and/or a premium fuel into the chamber through
the inlet;
(iii) generating an upward flow of a heating fluid through the vanes at the base
of the chamber, wherein the vanes at the base of the chamber impart a rotational
motion to the heating fluid to circulate the heating fluid about a substantially
vertical axis of the chamber as said fluid rises, whereby the waste material and/or
the premium fuel circulate about an axis of the chamber in a compact turbulent
band and is gasified and/or pyrolysed to produce a gaseous fuel stream, which gaseous
fuel stream exits the chamber through the outlet; and
(iv) feeding at least a portion of the gaseous fuel stream back into the chamber
through an entry point adjacent the vanes.
2. A process as claimed in claim 1, wherein from 10 to 100% by volume of the
gaseous fuel stream is fed back into the chamber.
3. A process as claimed in claim 1, wherein the said at least portion of the
gaseous fuel stream is reintroduced into the chamber at an entry point below the
vanes of the chamber.
4. A process as claimed in claim 3, wherein the said at least portion of the
gaseous fuel stream is reintroduced into the chamber through one or more venturi
inlets positioned below the vanes of the chamber.
5. A process as claimed in claim 1, wherein the said at least portion of the
gaseous fuel stream is mixed with steam prior to being reintroduced into the chamber.
6. A process as claimed in claim 1, wherein the inlet for the waste material
and/or the premium fuel is located adjacent the base of the chamber and the outlet
is spaced downstream from the inlet.
7. A process as claimed in claim 1, wherein the inlet for the waste material
and/or the premium fuel is located at a position above the vanes of the chamber.
8. A process as claimed in claim 1, wherein the waste material and/or premium
fuel comprises a solid and/or liquid material.
9. A process as claimed in claim 1, wherein the waste material comprises one
or more of sewage sludge, by-product waste, waste wood, wood shavings, clean wood,
agricultural waste, animal litter, municipal solid waste and/or refuse-derived fuel.
10. A process as claimed in claim 1, wherein the premium fuel comprises one or
more of coal, petrochemical derivatives and/or residues from refineries.
11. A process as claimed in claim 1, wherein the waste material and/or the premium
fuel is introduced into the processing chamber by injecting it through the inlet
under the influence of a compressed gas or by a gravity feed mechanism.
12. A process as claimed in claim 1, wherein the heating fluid comprises steam
and/or a gas stream produced by combustion of a fuel.
13. A process as claimed in claim 1, wherein the processing chamber contains
a resident bed of particulate material which circulates about an axis of the chamber
when the flow of the heating fluid is generated.
14. A process as claimed in claim 13, wherein the particulate material comprises
a solid absorbent material for removal of acidic gases from the gaseous fuel stream
exiting the processing chamber.
15. A process as claimed in claim 13, wherein the particulate material of the
resident bed comprises a catalytic material.
16. A process as claimed in claim 15, wherein the catalytic material acts to
increase the rate of tar decomposition in the gaseous fuel stream.
17. A process as claimed in claim 13, wherein the particulate material comprises
one or more of dolomite, a nickel-bearing catalyst, a zeolite, a magnesium-calcium
carbonate, and/or a calcined magnesium-carbonate.
18. A process as claimed in claim 1, wherein the heating fluid is at a temperature
in the range of from 300 to 1000° C.
19. A process as claimed in claim 1, wherein a portion of the gaseous fuel stream
which has exited the chamber is collected during each processing cycle.
20. A process as claimed in claim 1, wherein the gaseous fuel stream produced
from the waste material and/or the premium fuel is subjected to one or more further
processing steps selected from particulate removal, drying, compression and/or sweetening.
21. A process as claimed in claim 1, wherein the pressure drop through the chamber
is less than 400 Pa.
22. A process as claimed in claim 1, wherein the said at least portion of the
gaseous fuel stream is fed back into the chamber without the assistance of supplemental
pumping means.
23. An apparatus for carrying out the process as defined in claim 1, the apparatus comprising:
(a) a processing chamber having therein a plurality of outwardly radiating inclined
vanes at a base thereof, an inlet and an outlet;
(b) means for introducing a waste material and/or a premium fuel into the chamber
through the inlet;
(c) means for generating an upward flow of a heating fluid through the vanes
at the base of the chamber, whereby, in use, the waste material and/or the premium
fuel circulate about an axis of the chamber in a turbulent band and is gasified
and/or pyrolysed to produce a gaseous fuel stream, which gaseous fuel stream exists
the chamber through the outlet; wherein the means for generating an upward flow
of a heating fluid is a base with a circular arrangement of overlapping vanes,
wherein each vane is inclined relative to the base and
(d) means for feeding at least a portion of the gaseous fuel stream back into
the chamber through an entry point adjacent the vanes.
24. An apparatus as claimed in claim 23, wherein the vanes radiate outwardly
from a central point toward the vertical wall of the chamber and form part of a
circular disk.
Description
The present invention relates to a process for the treatment of waste materials
and/or premium fuels for the purpose of producing a gaseous fuel.
A number of different processes are known for the recovery of heat values from
waste materials. For example, domestic and factory waste materials such as clean
wood, agricultural waste, refuse-derived fuel, municipal solid waste and sewage
sludge may be treated using a bubbling fluidised bed, a circulating fluidised bed,
a fast fluidised bed, a pressurised fluidised bed, a moving bed or a moving grate.
The main disadvantages of these processes are capital costs, flexibility and tar
production. Flexibility is a particularly important issue for plants handling waste
materials, since the feed material is waste, as opposed to a premium fuel, and
there will therefore be relatively large fluctuations in both its physical and
chemical composition. To accommodate the nature of many waste materials, the processing
unit will also need a high turndown ratio and the ability to come on/off stream
at relatively short notice. In addition it may be necessary to run the facility
on more than one waste stream to make investment in such a system economic.
Additionally, tar production is a major problem for many existing gasification
units. If the organic materials present in the waste are not cracked to simple
molecules during the treatment process, they exist with the product gas stream
and cause major downstream problems. These problems arise when the process gas
temperature or that of the wetted surfaces falls below the dew point of the compounds
concerned, causing them to condense out on surfaces forming liquids which then
cause problems ranging from equipment fouling to occupational health issues. In
addition, liquid tars are difficult to dispose of and can even cause a more serious
disposal problem than that posed by the original waste material.
Most conventional process systems include a unit known as a tar cracker whose
function is to augment the action of the gasifier and break down the large organic
molecules into smaller ones which have higher dew points. Despite the additional
capital costs and complexity associated with supplementary tar crackers, the occurrence
and hence the problems associated with tar are not fully eliminated because the
conventional processes are generally based on a single gas pass, hence the degree
of tar cracking that can be achieved economically is limited.
Recycling gases leaving the processor to produce cracking of the contained
tars within the process reactor itself have not been feasible owing to the high
pressure drop across the conventional process reactors. To alleviate this problem
would necessitate the use of expensive supplemental pumping systems which themselves
would be liable to fouling from condensed tars.
In our European Patent No. 0 068 853 is described and claimed a process whereby
a particulate material to be treated is embedded and centrifugally retained within
a compact, but turbulent, toroidal bed of further particles which circulate about
an axis of the processing chamber. Specifically, the resident or host particles
within the bed are circulated above a plurality of outwardly radiating, inclined
vanes arranged around the base of the processing chamber. The vanes are preferably
arranged in overlapping relationship and the particles are caused to circulate
around the bed by the action of a processing fluid, for example a gas injected
into the processing chamber from beneath and through the vanes.
The present invention aims to address at least some of the problems associated
with the prior art processes for the treatment of waste materials, and to furthermore
provide a process which can also be used to treat premium fuels such as coal and
petrochemical derivatives, plastics and residues from refineries.
Accordingly, in a first aspect the present invention provides a process
for the production of a gaseous fuel from a waste material and/or a premium fuel,
which process comprises:
(i) providing a processing chamber having therein a plurality of outwardly
radiating inclined vanes at a base thereof, an inlet and an outlet;
(ii) introducing a waste material and/or a premium fuel into the chamber
through the inlet;
(iii) generating an upward flow of a heating fluid through the vanes at
the base of the chamber, whereby the waste material and/or the premium fuel circulates
about an axis of the chamber in a compact turbulent band and
- is gasified and/or pyrolysed to produce a gaseous fuel stream, which
gaseous fuel stream exits the chamber through the outlet; and
(iv) feeding at least a portion of the gaseous fuel stream back into the
chamber through an entry point adjacent the vanes.
In the process of the present invention, organic compounds in the waste material
and/or the premium fuel are heated to a temperature sufficient to cause decomposition
thereof, i.e. to cause pyrolysis. In this manner, the material being treated may
be converted into or becomes a gas by gasification.
A portion or all of the gaseous fuel stream which has exited the chamber is advantageously
reintroduced into the chamber at an entry point adjacent the vanes. By recycling
typically from 10 to 100% by volume, more typically from 60 to 90%, still more
typically from 75 to 85%, still more typically approximately 80% of the gaseous
fuel stream exiting the chamber, it is possible to both increase and control the
energy content of the gaseous fuel stream eventually exported. It will be appreciated
that some or all of the gaseous fuel stream may be recycled through the chamber
one or more times before finally being collected for use or for further processing.
During each processing cycle, a portion of the gaseous fuel stream which has exited
the chamber can be collected, whilst the remainder can be reintroduced into the
chamber. Also, one or more passes of the gaseous fuel stream through the hot zone
beneath the vanes facilitates the breakdown of large organic molecules. At elevated
temperatures, and preferably in the presence of steam, many components of tar undergo
shift reactions, in which the large organic molecules are split down into smaller
molecules. By reducing the content of tar compounds exhausted, the need for a separate
tar cracking unit operation can be obviated. In this regard, the pressure drop
across a reactor, such as that described and claimed in EP-B-0 068 853, is small
in comparison with other gas-solid contacting unit operations because the reactor
has a high free area distributor and shallow bed of material which provide a pressure
drop much lower (of an order of magnitude) than conventional fluid beds. Pressure
drops through such a reactor are typically in the range of from 100 to 400 Pa,
more typically 200 to 300 Pa. This attribute is beneficial because it enables the
option of non-mechanical recycling of the hot exhaust gaseous fuel stream. The
gaseous fuel stream may be reintroduced into the chamber at an entry point below
the vanes of the chamber through, for example, one or more venturi inlets positioned
below the vanes. Such inlets produce increased gas velocities within the chamber
resulting in more efficient circulation of the material being treated and of any
inert or catalytic material present in the chamber, which, in the latter case,
produces greater contact with the material being treated and process gases. Alternatively,
a portion or all of the gaseous fuel stream may be reintroduced in the chamber
by mixing it with the heating fluid prior to its entry into the chamber.
Advantageously, a gas-solid separator is provided in the recycle
loop to prevent fouling of the distributor before feeding a portion of the gaseous
fuel stream back into the chamber. This function may be performed by any suitable
gas-solid separation technique such as, for example, a conventional reverse flow
cyclone separator or a rotary separators.
Once at least a portion of the gaseous fuel stream has been recycled through
the chamber at least one time, it may be collected and stored ready for use. Alternatively,
one or more of the following further processing steps may be carried out: particulate
removal using, for example, a cyclone or baghouse; drying to remove, for example,
motive and reaction steam using, for example, alumina beads and/or a condenser;
compression to reduce the cost of transporting the gas to its final destination
by, for example, a compressor or an in-line gas booster; and/or sweetening to remove
any acid gases remaining in the gaseous fuel.
The inlet for the waste material and/or the premium fuel will generally be located
adjacent the base of the chamber and the outlet will generally be spaced downstream
from the inlet. The inlet is preferably located at a position above the vanes of
the chamber. The outlet will generally be vertically spaced above the inlet of
the processing chamber, although the inlet may be located adjacent thereto. Both
the inlet and the outlet may be provided in a top portion of the chamber.
The material to be treated may be introduced into the processing chamber by injecting
it through the inlet under the influence of a compressed gas such as compressed
air and/or an inert gas such as nitrogen, CFC and other noble/mono-atomic gases.
The material to be treated may also be injected with steam. In one preferred embodiment
of the present invention, the inlet is located above the vanes at the base of the
chamber and the material to be treated is introduced into the chamber by a gravity
feed mechanism, for example using an air lock device such as a rotary valve. The
gravity feed mechanism may be provided in a vertical wall of the chamber.
The waste material to be treated may comprise domestic and factory waste materials
including solid and/or liquid materials such as, for example, waste wood, wood
shavings, agricultural waste, animal litter, refuse-derived fuel, municipal solid
waste and sewage sludge. The process of the present invention may also be used
to treat fuels such as premium fuels, for example coal, petrochemical derivatives,
residues from refineries and plastics.
The gaseous fuel produced by the process of the present invention will generally
have the following characteristics:
| |
|
| |
Calorific Value MJ/m3 |
10-15 |
| |
Composition by Volume |
| |
CO2 |
20-30 |
| |
CnHm |
2-4 |
| |
CO |
25 |
| |
CH4 |
12-14 |
| |
H2 |
20-35 |
| |
N2 |
6-10 |
| |
|
The values quoted in the table above relate to the use of oxygen, rather than
air, for the combustion of the organics. The use of substantially pure oxygen or
oxygen-enriched gases minimises the quantity of nitrogen in the final fuel gas
stream therefore improving its quality.
It will be appreciated that the flow of heating fluid may be generated either
before or after the material to be treated is introduced into the chamber. Alternatively,
the flow of heating fluid may be generated at the same time as the material to
be treated is introduced into the chamber.
The heating fluid may comprise steam or a gas stream produced by the direct combustion
of a fuel. In the latter case, the combustion product of a suitable fuel will generally
have the following composition:
| |
|
| |
Component |
Volume % (Wet Basis) |
| |
|
| |
CO2 |
10 |
| |
N2 |
72% |
| |
H2O |
18% |
| |
|
Heated air and/or a heated inert gas may also be used. Heating may be achieved
by any suitable means, such as electrical and/or microwave heating means. Steam
is advantageously used because it enhances the cracking of tars present in the
gaseous fuel stream resulting from treatment of the waste material and/or premium
fuel. Separate heating means may also be provided for heating the processing chamber
and its contents.
The heating fluid is typically heated to a temperature in the range of from 200
to 1100° C., depending upon the nature of the material to be treated. More
typically, the heating fluid is heated to a temperature in the range of from 300
to 1000° C., still more typically from 400 to 900° C.
The flow of the heating fluid through the chamber may be generated in a manner
as described in EP-B-0 382 769 and EP-B-0 068 853, i.e. by supplying a flow of
heated fluid into and through the processing chamber and directing the flow by
means of the plurality of outwardly radiating and preferably overlapping vanes
arranged in the form of a disc and located at or adjacent to the base of the processing
chamber. The vanes are inclined relative to the base of the chamber so as to impart
rotational motion to the heating fluid entering the chamber, hence causing the
heating fluid to circulate about a substantially vertical axis of the chamber as
it rises.
In a preferred embodiment of the process according to the present invention,
the
processing chamber contains a resident bed of particulate material which circulates
about an axis of the chamber when the flow of the heating fluid is generated. The
average density of the particles of the resident bed is such that there is little
or substantially no migration thereof to the outlet. The circulating resident bed
particles provide a turbulent environment within which gas/particles heat and mass
transfer properties are enhanced. This consequently enhances heat transfer to the
material to be treated. A tortuous/labyrinthine flow type path is provided, which
increases the effective residence time of the material to be treated in the processing
chamber, hence increasing the time for gasification and/or pyrolysis. The circulating
resident bed of particles may also act as a heat sink. The material to be treated
will generally enter the chamber below and/or adjacent to the circulating resident
bed particles in order to contact therewith. Alternatively, if the inlet is vertically
spaced above the vanes at the base of the chamber and the circulating resident
bed, then the material to be treated will fall down through the chamber, under
the action of gravity, on to the circulating resident bed. This may be achieved
by, for example, a gravity feed mechanism provided in a vertical wall of the chamber.
In general, the average terminal velocity of a resident bed particle will be
greater
than the average terminal velocity of a particle of the material to be treated,
prior to the latter being introduced in the chamber. However, the process of the
present invention may also be used in circumstances where the terminal velocity
of the particles of the material to be treated decreases during processing.
The particulate material of the resident bed may comprise an inert material,
which acts to increase the time spent by the material to be treated in the processing
chamber. Suitable examples include one or more of sand, alumina, and/or ash from
the material being processed (autogenous). Alternatively, the particulate material
may comprise a solid absorbent material for the additional purpose of removing
acidic gases, such as hydrochloric acid, hydrofluoric acid and/or sulphuric acid,
from the gaseous fuel stream before it exits the processing chamber. Suitable examples
include ceramics, alumina, silica, limestone and zeolite. The particulate material
may alternatively or, in addition, comprise a catalytic material, for example a
catalytic material such as dolomite, a nickel-bearing catalyst, a zeolite, a magnesium-calcium
carbonate, a calcined magnesium-carbonate, which acts to increase the rate of tar
cracking or decomposition in the exiting gaseous fuel stream. The resident bed
particles may be replenished from time to time if required. The resident bed particles
typically have an average size of from about 1 to 6 mm, more typically from about
2 to about 3 mm.
It will be appreciated that char (i.e. non-volatile components in the material
to be treated) may be produced when carrying out the process of the present invention.
Char and other non-volatile components may be removed from the chamber via a central
discharge, which is preferably designed to differentiate char from the resident
bed material. Alternatively, it may be removed with the exhaust gaseous fuel stream
to be subsequently captured in a downstream gas processing stage, for example cyclone separation.
Gasification may be thought of as a generic term covering a number of
individual reactions and process events including: drying, devolatilisation, char
combustion, tar cracking (which can be catalysed by a resident bed). In some circumstances,
each of these reaction/process events require different conditions, such as temperature,
residence time and catalysing medium, for optimum performance. The use of multiple
stages makes it possible to optimise the conditions for each reaction/process event.
Accordingly, the processing chamber according to the first aspect of the present
invention may comprise multiple (i.e. two or more) stages installed within a single
reactor vessel, for example a drying and/or devolatilisation stage, a char combustion
stage, and a tar cracking stage.
Alternatively, multiple (i.e. two or more) stages may be achieved
by the use of multiple reactors connected in series. Accordingly, in a second aspect
the present invention provides a process for the production of a gaseous fuel from
a waste material and/or a premium fuel, which process comprises:
(i) providing first and second processing chambers, each chamber having
therein a plurality of outwardly radiating inclined vanes at a base thereof, an
inlet and an outlet;
(ii) introducing a waste material and/or a premium fuel into the first chamber
through the inlet thereof;
(iii) generating an upward flow of a heating fluid through the vanes at
the base of the first chamber, whereby the waste material and/or the premium fuel
circulate about an axis of the first chamber in a turbulent band and is heated
to produce a gaseous fuel stream and char, said gaseous fuel stream exiting the
first chamber through the outlet thereof;
(iv) feeding at least a portion of the gaseous fuel stream into the second
chamber through an entry point adjacent the vanes;
(v) feeding at least a portion of char generated in the first chamber into
the second chamber through the inlet thereof;
(vi) generating an upward flow of a heating fluid through the vanes at the
base of the second chamber, whereby the char circulates about an axis of the first
chamber in a turbulent band and is heated in a char combustion step to produce
a gaseous fuel stream, which gaseous fuel stream exits the second chamber through
the outlet thereof; and
(vii) optionally feeding at least a portion of the gaseous fuel stream from
the second chamber back into the first chamber through an entry point adjacent
the vanes.
Additionally, in a third aspect, the present invention provides a process
for the production of a gaseous fuel from a waste material and/or a premium fuel,
which process comprises:
(i) providing first, second and third processing chambers, each chamber
having therein a plurality of outwardly radiating inclined vanes at a base thereof,
an inlet and an outlet;
(ii) introducing a waste material and/or a premium fuel into the first chamber
through the inlet thereof;
(iii) generating an upward flow of a heating fluid through the vanes at
the base of the first chamber, whereby the waste material and/or the premium fuel
circulate about an axis of the first chamber in a turbulent band and is heated
to produce a gaseous fuel stream and char, said gaseous fuel stream exiting the
first chamber through the outlet thereof;
(iv) feeding at least a portion of the gaseous fuel stream into the third
chamber through an entry point adjacent the vanes thereof;
(v) feeding at least a portion of char generated in the first chamber into
the second chamber through the inlet thereof;
(vi) generating an upward flow of a heating fluid through the vanes at the
base of the second chamber, whereby the char circulates about an axis of the first
chamber in a turbulent band and is heated in a char combustion step to produce
a gaseous fuel stream, which gaseous fuel stream exits the second chamber through
the outlet thereof;
(vii) generating an upward flow of a heating fluid through the vanes at
the base of the third chamber, whereby said at least portion of the gaseous fuel
stream from the first chamber circulates about an axis of the third chamber in
a turbulent band and is heated in a tar cracking step to produce a gaseous fuel
stream, which gaseous fuel stream exits the third chamber through the outlet thereof;
(viii) optionally feeding at least a portion of the gaseous fuel stream
from the third chamber back into the second chamber through an entry point adjacent
the vanes; and
(ix) optionally feeding at least a portion of the gaseous fuel stream from
the second chamber back into the first chamber through an entry point adjacent
the vanes.
It will be appreciated that the preferred and advantageous features described
herein in relation to the first aspect of the present invention are equally applicable
either singularly or in any combination to the second and third aspects.
The present invention also provides an apparatus for carrying out the process
of the first, second or third aspects as herein described.
The present invention will now be described further, by way of example, with
reference to the accompanying drawings, in which:
FIG. 1 is a schematic illustration of an apparatus suitable for carrying out
one embodiment of the process according to the invention;
FIG. 1
a is a perspective view of an arrangement of vanes in one embodiment
of the present invention;
FIG. 2 is a schematic illustration of the trajectories of particles of material
to be treated through a circulating resident bed of particles;
FIG. 3 is a schematic illustration of an alternative form of the apparatus suitable
for carrying out one embodiment of the process according to the invention;
FIGS. 4(
a-c) are schematic illustrations to show: (a) single
stage multiple gas pass configuration, (b) double stage multiple gas pass configuration,
and (c) triple stage multiple gas pass configuration;
FIG. 5 is a schematic illustration of the general arrangement for Examples 1
and 2 given below; and
FIG. 6 is a schematic illustration of the general arrangement for Example 3
given below.
In FIG. 1, a generally cylindrical processing chamber
1 is shown suitable
for carrying out the process according to the present invention. The processing
chamber
1 has an inlet
5 and an outlet
10 spaced downstream
therefrom. At the base
15 of the chamber
1 there is provided a circular
arrangement of overlapping vanes, wherein each vane is inclined relative to the
base. Two vanes are shown at
20 and
25. The vanes
20,
25
radiate outwardly from a central point towards the vertical wall of the chamber
and form part of a circular disc. A flow of a heating fluid, for example steam,
enters the chamber via an inlet
7 and passes through the vanes
20,
25 at the base
15 of the chamber
1. The arrangement of the
vanes
20,
25 imparts rotational motion to the heating fluid entering
the chamber
1 so that the heating fluid circulates about a substantially
vertical axis of the chamber
1 as it rises. By this process, the heating
fluid swirls around the chamber
1 in a turbulent fashion and then exhausts
from the chamber via outlet
10.
The arrangement of the vanes is more clearly shown in the perspective view shown
in FIG. 1
a, where there is shown a plurality of outwardly radiating incline
vanes
20,
25 at the base
15 of chamber
1, which impart
a rotational motion to the heating fluid to circulate the heating fluid about a
substantially vertical axis of the chamber
1 as the fluid rises.
A resident bed of particles
30 resides in the chamber
1. The particulate
material of the resident bed
30 may comprise, for example, a solid absorbent
material for the purpose of removing acidic gases and/or a catalytic material for
the purpose of increasing the rate of tar decomposition.
A feed hopper
35 and venturi arrangement
40 are provided to supply,
for example, a waste material
45 to be treated, under compressed air injection,
through the inlet
5 into the chamber
1. As the flow of heating fluid
is generated through the vanes
20,
25 at the base
15 of the
chamber
1, the resident bed particles
30 circulate about a substantially
vertical axis of the chamber
1 in an annular region thereof. The waste material
to be treated
45 is then injected into the chamber
1 and contacts
immediately or almost immediately with the circulating resident bed particles
30.
Because of their size and density, there is little or substantially no migration
of the resident bed particles
30 to the outlet
10.
In this manner, substantially all of the waste material
45 is gasified
and/or pyrolysed resulting in a gaseous fuel stream which flows downstream through
the circulating resident bed particles
30, whereby acidic gases are removed
and/or the rate of tar decomposition is increased depending upon the nature of
the resident bed particles
30. Thereafter, the gaseous fuel stream exits
the chamber through the outlet
10, where a portion may be collected and
stored. The remaining portion of the gaseous fuel stream which has exited the chamber
1 is reintroduced into the chamber
1 through, for example, one or
more venturi inlets (not shown) positioned below the vanes
20,
25.
Alternatively, the remainder of the gaseous fuel stream may be fed into inlet
7
to mix with the heating fluid prior to entry into the chamber
1. By recycling
some or all of the gaseous fuel stream exiting the chamber
1, it is possible
to increase and control the energy content of the gaseous fuel stream eventually
exported. Also, multiple passes of the gaseous fuel stream through the hot zone
beneath the vanes
20,
25 helps breakdown large organic molecules.
Because of the relatively low pressure drop through the chamber, the gaseous fuel
stream may be fed directly back into the chamber
1 without recourse to supplemental
pumping means.
In FIG. 2 trajectories
50 of the particles of a waste material to be treated
45 are shown. It can be seen that the circulating resident bed particles
30 provides torturous/labyrinthine paths for the particles of the waste
material to be treated
45. Accordingly, the resident bed particles
30
not only act to remove acidic gases and/or increase the rate of tar decomposition
in the gaseous fuel stream, but also have the effect of increasing the time the
waste material spends in the chamber, hence achieving a greater degree gasification
and/or pyrolysis.
FIG. 3 illustrates an alternative form of the apparatus suitable for carrying
out the process according to the present invention. It can be seen that in this
embodiment the inlet for the material to be treated is provided in a vertical wall
60 of the chamber and is vertically spaced from the resident bed particles
30 and the vanes
20,
25 at the base of the chamber. The material
to be treated
45 is thus introduced into the chamber
1 by a gravity
feed mechanism which includes an air lock, for example a rotary valve
61.
Accordingly, in use, the material to be treated
45 will fall down through
the chamber
1, under the action of gravity, on to the circulating resident
bed particles
30. Char
62 and other non-volatile components in the
material to be treated
45 are removed from the chamber
1 via a central
discharge
63, which is designed to differentiate char
62 from the
resident bed material
30.
FIGS.
4(
a-c) are schematic illustrations to show: (a) single
stage multiple gas pass configuration, (b) double stage multiple gas pass configuration,
and c) triple stage multiple gas pass configuration. As previously indicated, gasification
may be thought of as a generic term covering a number of individual reactions and
process events including: drying, devolatilisation, char combustion, tar cracking
(which can be catalysed by a resident bed). While it is, of course, possible to
carry out gasification according to the present invention in a single chamber as
shown in FIG.
4(
a), for some applications it may be preferable for
the reaction/process events to be carried out in separate chambers. The use of
multiple stages makes it possible to optimise the conditions for each reaction/process event.
FIG.
4(
b) shows a double stage configuration comprising a gasifier
chamber and a char combustion chamber. The gasifier and char combustion chambers
generally have the same features as the processing chambers described above and
shown in FIGS. 1 and 2; the processing conditions in each are, however, adjusted
to optimise the reaction/process events. The feed is introduced into the gasifier
chamber, where it is heated to produce a gas and char. Heating in the gasifier
chamber may also result in drying and/or devolatisation of the feed. The gas and
char are then fed into the char combustion chamber, where they are further heated.
At least a portion of the fuel gas thereby evolved in the char combustion chamber
is fed back into the gasifier chamber. Heated air is passed through the vanes at
the base of the char combustion chamber. The heated air, together with at least
a portion of the fuel gas evolved may be used to provide or contribute to the heating
fluid in the gasifier chamber. If desired, a separate source of heating fluid may
also be introduced through the vanes at the base of the gasifier chamber.
By recycling typically from 10 to 100% by volume, more typically from 60 to 90%,
still more typically from 75 to 85% of the gaseous fuel stream exiting the chamber,
it is possible to both increase and control the energy content of the gaseous fuel
stream eventually exported. It will be appreciated that some or all of the gaseous
fuel stream from the char combustion chamber may be recycled through the gasifier
chamber one or more times before finally being collected for use or for further
processing. During each processing cycle, a portion of the gaseous fuel stream
which has exited the char combustion chamber can be collected, whilst the remainder
can be reintroduced into the gasifier chamber. Also, the gas recycle assists in
producing the heating fluid in the two chambers.
FIG.
4(
c) shows a triple stage configuration comprising a gasifier
chamber, a char combustion chamber and a tar cracking chamber. The chambers generally
have the same features as the processing chambers described above and shown in
FIGS. 1 and 2; the processing conditions in each are, however, adjusted to optimise
the reaction/process events. The feed is introduced into the gasifier chamber,
where it is heated to produce a gas and char. The gas and char are then fed respectively
into tar cracking chamber and the char combustion chamber, where they are further
heated. At least a portion of the fuel gas thereby evolved in the char combustion
chamber is fed back into the gasifier chamber. Heated air is passed through the
vanes at the base of the char combustion chamber. The heated air, together with
at least a portion of the fuel gas evolved may be used to provide or contribute
to the heating fluid in the gasifier chamber. If desired, a separate source of
heating fluid may also be introduced through the vanes at the base of the gasifier
chamber. At least a portion of the fuel gas evolved in the tar cracking chamber
may optionally be fed into the char combustion chamber. Again, the at least a portion
of the fuel gas evolved may be used to contribute to the heating fluid in the char
combustion chamber. Again, it will be appreciated that some or all of the gaseous
fuel stream from the chambers may be recycled one or more times before finally
being collected for use or for further processing. During each processing cycle,
a portion of the gaseous fuel stream which has exited the tar cracking chamber
can be collected, whilst the remainder can be reintroduced into the char combustion
chamber and, in turn, into the gasifier chamber.
EXAMPLES
There is significant interest in premium fuel substitutes. While the heat value
of these low and negative value wastes can be realized via straight combustion,
the process intensity of a gas-solid reactor operated in this mode is limited by
the differential of the gas temperature and the quantity of free water and ash
present. On small to medium scale applications, process intensity is an important
factor, which should ideally be maximized.
One way of increasing the process intensity is to gasify the organics within
the feedstock and then burn them ex-situ as a fuel gas in an existing burner system.
The following example involves the use of wood shavings, which are first gasified
in a reactor system as herein described, and then used to fuel a burner attached
to an existing rotary drier.
Example 1
Wood Shavings Gasification
This Example involves processing of fine waste wood dust to generate a fuel
gas suitable for use in a close-coupled excess air burner.
The reactor was operated with an oxidising atmosphere in the lower (bed) region
and a reducing atmosphere in the upper (freeboard) region (see FIG. 5).
Feed material was metered into the freeboard of the reactor where it came into
contact with hot process gases rising from the gas distributor at the base. In
this reducing region of the reactor, the flash gasification process took place,
generating the fuel gas and a residual char.
While the fuel gases were expelled from the reactor, the char particles continued
their ascent to the bed region. As this region was operated with excess air, the
char particles were substantially completely combusted to CO
2 and water
to generate a reducing atmosphere and produced the heat needed to drive the gasification
process in the freeboard above.
The gas passing through the distributor was ambient air and the interface between
the reducing and oxidising regions within the furnace was controlled by manipulating
the air and feed flow rates.
Tests were undertaken in a T400 (400 mm internal diameter) Torbed (RTM) reactor
fitted with 30% free surface area blades. The flow rate of air passing through
the unit was controlled via a frequency inverter fitted to the forced draught fan.
Air flow rate was quantified by a portable hot-wire anemometer. Feed material was
continuously metered into the Torbed reactor via a frequency inverter controlled
screw conveyor, which had a nominal range of 30 kg/h to 300 kg/h. The unit was
also fitted with a small pilot burner in the region just above the blades to facilitate
start-up. Performance of the unit was gauged by the output of an on-line gas analyser
combined with a subjective visual assessment of the flame in the rotary dryer fire-box
and by the temperature profile in the Torbed reactor.
To prepare the system for gasification, the unit was started-up in combustion
mode. This was achieved by operating at a sub-stoichiometric solids feed-rate with
respect to the oxygen content of the fluidising air. The composition of the wood
fines is given in Table 1-1 and the feed rate required for start-up was 30 kg/h.
The small gas fired pilot burner was employed to initiate combustion.
| TABLE 1-1 |
| Composition (Typical) of Wood Shavings. |
| |
|
Mass % |
|
| |
Typical |
(as received |
Mass % |
| |
Composition |
basis) |
(dry basis) |
| |
| |
Moisture |
15 |
— |
| |
Carbon |
42.5 |
50 |
| |
Hydrogen |
5.1 |
6 |
| |
Nitrogen |
0.9 |
1 |
| |
Oxygen |
36.6 |
43 |
| |
Heat Value |
15,800 kJ/kg |
19,000 kJ/kg |
| |
Once the reactor was heat soaked to around 1000° C., operation was switched
to gasification mode. This transition was achieved by simply increasing the solids
feed-rate. Once the quantity of organics entering the reactor with the feed exceeded
the amount of oxygen available for complete combustion, the atmosphere in the upper
region of the reactor became reducing and the gasification process commenced. This
change of operating mode was also accompanied by a reduction in temperature associated
with the endothermic requirements of the gasification reactions. Further increases
in feed-rate extend the reducing zone and increased the quality of the fuel gas.
At steady state, the flow rate of ambient air into the reactor was around 250
kg/h and the balancing solids feed-rate was around 140 kg/h. The resulting temperature
in the lower section of the reactor was 744° C., while the temperature in
the upper section was 738° C. A composite (21 measurements) assay of the gas
produced under these conditions is given in Table 1-2.
| TABLE 1-2 |
| Exhaust gas composition-Wood Shavings Gasification Trial |
| |
|
Concentration |
| |
Component |
(volume % dry basis) |
| |
| |
CO |
15.2 |
| |
CO2 |
14.9 |
| |
CH4 |
2.9 |
| |
H2 |
6.4 |
| |
O2 |
0.3 |
| |
N2 |
58.6 |
| |
C2H4 |
0.8 |
| |
C2H6 |
0.2 |
| |
C6H6 |
0.3 |
| |
C7H8 |
0.1 |
| |
The calorific value of this gas was of sufficient quality to operate the close-coupled
natural gas burner servicing a rotary dryer. The flame emanating from this burner
was a very intense white colour with flecks of yellow caused by the carry-over
of char particles. Upon completion of the trial, the reactor and duct work were
inspected, however there were no signs of tar.
Example 2
Chicken Litter Gasification
The following example involves the use of chicken litter, which is first gasified
in a Torbed (RTM) reactor based system, and then used to fuel a burner attached
to an existing rotary drier.
The reactor was operated with an oxidising atmosphere in the lower (bed) region
and a reducing atmosphere in the upper (freeboard) region (FIG. 5). Feed
material was metered into the freeboard of the reactor where it came into contact
with hot process gases rising from the gas distributor at the base. In this reducing
region of the reactor, the flash gasification process took place generating the
fuel gas and a residual char.
While the fuel gases were expelled from the reactor, the char particles continued
their ascent to the bed region. As this region was operated with excess air, the
char particles were completely combusted to CO
2 and water to generate
a reducing atmosphere and produced the heat needed to drive the gasification process
in the freeboard above.
The gas passing through the distributor was ambient air and the interface between
the reducing and oxidising regions within the furnace was controlled by manipulating
the air and feed flow rates.
Tests were undertaken in a T400 (400 mm internal diameter) Torbed (RTM) reactor
fitted with 30% free surface area blades. The flow rate of air passing through
the unit was controlled via a frequency inverter fitted to the forced draught fan.
Air flow rate was quantified by a portable hot-wire anemometer. Feed material was
continuously metered into the Torbed reactor via a frequency inverter controlled
screw conveyor, which had a nominal range of 30 kg/h to 300 kg/h. The unit was
also fitted with a small pilot burner in the region just above the blades to facilitate start-up.
Performance of the unit was gauged by the output of an on-line gas analyser
combined with a subjective visual assessment of the flame in the rotary dryer fire-box
and by the temperature profile in the Torbed reactor.
To prepare the system for gasification, the unit was started-up in combustion
mode. This was achieved by operating at a sub-stoichiometric solids feed-rate with
respect to the oxygen content of the fluidising air. The composition of the chicken
litter is given in Table 2-1 and the feed rate required for start-up was 30 kg/h.
The small gas fired pilot burner was employed to initiate combustion.
| TABLE 2-1 |
| Composition (Typical) of Chicken Litter |
| |
|
Mass % |
|
| |
Typical |
(as received |
Mass % |
| |
Composition |
basis) |
(dry basis) |
| |
| |
Moisture |
15 |
— |
| |
Carbon |
40.2 |
47.3 |
| |
Hydrogen |
5.6 |
6.6 |
| |
Nitrogen |
4.6 |
5.4 |
| |
Oxygen |
31.1 |
36.6 |
| |
Sulphur |
0.6 |
0.7 |
| |
Heat Value |
15,800 kJ/kg |
19,000 kJ/kg |
| |
Once the reactor was heat soaked to around 1000° C., operation was switched
to gasification mode. This transition was achieved by simply increasing the solids
feed-rate. Once the quantity of organics entering the reactor with the feed exceeded
the amount of oxygen available for complete combustion, the atmosphere in the upper
region of the reactor became reducing and the gasification process commenced. This
change of operating mode was also accompanied by a reduction in temperature associated
with the endothermic re
