U.S. patent application number 14/434791 was filed with the patent office on 2015-08-13 for fuel preparation apparatus and method.
This patent application is currently assigned to DOOSAN BABCOCK LIMITED. The applicant listed for this patent is DOOSAN BABCOCK LIMITED. Invention is credited to Agnieszka Magdalena Kuczynska, Konrad Jerzy Kuczynski.
Application Number | 20150226426 14/434791 |
Document ID | / |
Family ID | 47359101 |
Filed Date | 2015-08-13 |
United States Patent
Application |
20150226426 |
Kind Code |
A1 |
Kuczynski; Konrad Jerzy ; et
al. |
August 13, 2015 |
FUEL PREPARATION APPARATUS AND METHOD
Abstract
An apparatus and method for fuel preparation for example by
milling and drying to produce a pulverous fuel supply are
described. The apparatus includes a fuel preparation unit adapted
to receive a mixture of fuel and a gas and to prepare the fuel for
combustion in a pulverous state; an output conduit defining an
output flow path for a mixture of pulverous fuel and gas from the
fuel preparation unit; a phase separator disposed to receive the
mixture from the output conduit and to separate the mixture into a
gas phase comprising at least a major part of the gas from the
mixture and a fuel phase comprising the pulverous fuel; a gas phase
conduit defining a flow path for the gas phase from the separator;
a heat exchanger preferably being a process fluid heat exchanger
such as a feed water heat recovery heat exchanger fluidly connected
to the gas phase conduit and adapted to receive and dry the gas
phase. The method applies the principles embodied in the
apparatus.
Inventors: |
Kuczynski; Konrad Jerzy;
(Renfrew, GB) ; Kuczynska; Agnieszka Magdalena;
(Renfrew, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DOOSAN BABCOCK LIMITED |
Crawley, Sussex |
|
GB |
|
|
Assignee: |
DOOSAN BABCOCK LIMITED
Crawley, Sussex
GB
|
Family ID: |
47359101 |
Appl. No.: |
14/434791 |
Filed: |
October 18, 2013 |
PCT Filed: |
October 18, 2013 |
PCT NO: |
PCT/GB2013/052725 |
371 Date: |
April 10, 2015 |
Current U.S.
Class: |
110/346 ;
110/222; 110/224; 110/234; 110/347 |
Current CPC
Class: |
F23G 5/442 20130101;
F23K 3/02 20130101; F23K 2201/1003 20130101; F23G 5/033 20130101;
F23K 1/00 20130101; F23K 2201/103 20130101; F23K 2201/20 20130101;
F23K 2201/30 20130101; F23K 2900/01041 20130101; F23G 5/04
20130101 |
International
Class: |
F23G 5/033 20060101
F23G005/033; F23G 5/44 20060101 F23G005/44; F23G 5/04 20060101
F23G005/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 18, 2012 |
GB |
1218747.2 |
Claims
1. An apparatus for preparation and drying of a fuel to produce a
pulverous fuel supply comprising: a fuel preparation unit adapted
to receive a mixture of fuel and a gas and to prepare the fuel for
combustion in a pulverous state; an output conduit defining an
output flow path for a mixture of pulverous fuel and gas from the
fuel preparation unit; a phase separator disposed to receive the
mixture from the output conduit and to separate the mixture into a
gas phase comprising at least a major part of the gas from the
mixture and a fuel phase comprising the pulverous fuel; a gas phase
conduit defining a flow path for the gas phase from the separator;
a heat exchanger fluidly connected to the gas phase conduit to
receive and dry the gas phase.
2. An apparatus in accordance with claim 1 wherein the fuel
preparation unit is a mill adapted to receive a mixture of fuel and
a gas and to mill the fuel to a pulverous state.
3. An apparatus in accordance with claim 1 wherein the heat
exchanger is a process fluid heat exchanger.
4. An apparatus in accordance with claim 1 wherein the heat
exchanger is a heat exchanger disposed to exchange heat with a
process fluid and supply the same for use in an industrial
process.
5. An apparatus in accordance with claim 4 wherein the heat
exchanger is adapted to supply the process fluid to an industrial
process in such manner as to make use of the sensible heat
therein.
6. An apparatus in accordance with claim 4 wherein the process
fluid is feedwater for a steam generator.
7. An apparatus in accordance with claim 1 wherein the phase
separator is adapted to separate substantially all of the gas
output from the mill is separated into the gas phase,
8. An apparatus in accordance with claim 1 further comprising a
fuel source and a gas source together configured to supply a
mixture of fuel and gas to the mill.
9. An apparatus in accordance with claim 8 wherein the gas source
supplies a gas at elevated temperature.
10. An apparatus in accordance with claim 9 wherein the gas source
comprises a source of optionally preheated air and a supply of flue
gas from a combustion chamber.
11. An apparatus in accordance with claim 8 wherein fuel source
comprises a supply of a low-rank fuel with a moisture content of at
least 25% on average.
12. An apparatus in accordance with claim 1 further comprising a
storage volume and a supply conduit to receive the fuel phase and
supply the fuel phase to the storage volume.
13. An apparatus in accordance with claim 1 further comprising a
steam generator and a supply conduit to receive the fuel phase and
supply the fuel phase to the steam generator.
14. An apparatus in accordance with claim 13 wherein the supply
conduit is configured to supply the fuel phase directly to one or
more burners of the steam generator.
15. An apparatus in accordance with claim 14 wherein the supply
conduit is configured to supply the fuel phase to a storage silo of
a steam generator.
16. A method of preparation of a fuel to produce a pulverous fuel
supply comprising the steps of: supplying a mixture of fuel and a
gas to a fuel preparation unit adapted to prepare the fuel for
combustion in a pulverous sate; outputting from the fuel
preparation unit a mixture of pulverous fuel and gas; separating
the mixture into a gas phase comprising at least a major part of
the gas output and a fuel phase comprising the pulverous fuel;
passing the gas phase to a heat exchanger to dry the gas phase.
17. A method in accordance with claim 16 applied as a method of
milling and drying of a fuel to produce a pulverous fuel supply, in
that the fuel preparation unit is a mill applied to receive a
mixture of fuel and a gas and to mill the fuel to a pulverous
state.
18. A method in accordance with claim 16 wherein the heat exchanger
is a process fluid heat exchanger.
19. A method in accordance with claim 16 wherein the heat exchanger
is a heat exchanger disposed to exchange heat with a process fluid
for use in an industrial process and the method comprises using the
heat exchanger to effect condensation of the water vapour and
thereby recover at least some of the latent heat from the drying
process.
20. A method in accordance with claim 19 comprising the further
step of using the process fluid in an industrial process in such
manner as to make use of the sensible heat recovered in the heat
exchanger.
21. A method in accordance with claim 20 wherein the process fluid
is feedwater for a steam generator and the step of using the
process fluid in such manner as to make use of the sensible heat
recovered in the heat exchanger in that the sensible heat recovered
in the heat exchanger effects preheating of the feedwater.
22. A method in accordance with claim 16 wherein substantially all
of the water vapour laden gas output from the mill is separated
into the gas phase and diverted away to the heat exchanger.
23. A method in accordance with claim 16 wherein the step of
supplying a mixture of fuel and a gas to a mill comprises the
supply of a gas at elevated temperature.
24. A method in accordance with claim 23 wherein the step of
supplying a gas at elevated temperature comprises the supply of a
mixture of optionally preheated air and flue gas from a combustion
chamber.
25. A method in accordance with claim 16 wherein the step of
supplying a mixture of fuel and a gas to a mill comprises the
supply of a low-rank fuel with a moisture content of at least
25%.
26. A method in accordance with claim 16 comprising a method of
producing a pulverous fuel supply for a steam generator such as a
boiler for example of a thermal power plant.
27. A method in accordance with claim 26 further comprising the
additional step of supplying the fuel phase to the steam
generator.
28. A method in accordance with claim 27 further comprising the
additional step of supplying the fuel phase directly to one or more
burners of the steam generator.
29. A method in accordance with claim 28 further comprising the
additional step of supplying the fuel phase to a storage silo of a
steam generator.
30. A method in accordance with claim 16 comprising the further
step of passing the fuel phase for storage.
Description
[0001] The invention relates to a fuel preparation process used on
power plants for the preparation for example by milling and drying
of pulverous fuel and in particular carbonaceous fuel such as
pulverised coal and to an apparatus embodying the process. The
invention is in particular applied in the context of milling and
drying of pulverous fuel for supply as a fuel source to a thermal
power plant. The invention is in particular applied to the process
for fuel milling and drying for lignite power plants or biomass
power plants. Additionally the invention is relevant to waste to
energy plants.
[0002] The process aims to improve the standard/conventional
process for the preparation for example by milling and drying of
coal for coal power plants.
[0003] The process aims to improve the standard/conventional
process for fuel preparation and drying applied for biomass power
plants.
[0004] The process aims to improve the standard/conventional
process for fuel preparation for waste to energy power plants.
[0005] In one conventional approach the mill dries the coal and
then the product is directly transported to the combustion furnace.
There are two significant disadvantages that are present, if the
mills (for example fan-beater mills) are used for processing
lignite, that impact significantly the power plant process
efficiency.
[0006] Firstly, in such a conventional process the mill dries the
fuel and then the product is directly transported to the combustion
furnace. This approach is proven in the industry. However it has
reduced process efficiency because of the water vapour that has
been created by drying the fuel and passed to the combustion
furnace. This vapour increases the Induced Draft (ID) fan power
required to extract the flue gas from the furnace and pass it to
the chimney. Secondly, the heat consumed by moisture evaporation is
irreversibly lost.
[0007] In another conventional approach the fuel processed by the
mill is held in intermediate storage silo, from which it is
transported to the furnace. In this process arrangement the water
vapour does not enter the furnace, and therefore the plant
efficiency is increased, however the heat consumed by the mill for
drying the fuel is still lost.
[0008] Current efforts to improve lignite plant efficiency are
focused on pre-drying the coal, and removing the moisture prior to
its introduction to the milling system. Therefore the plant
efficiency is increased by maximum amount at the expense of
significant investment in the drying system. Such systems are
present on the market and are tested on various full size power
plants across the world (i.e. WTA or DryFining process with
fluidized bed dryers). The known processes based on fluidised bed
dryers require an additional milling stage to prepare the coal,
otherwise the fluidised phenomenon will not be achieved. This
further increases the capital investment of the system.
[0009] The invention seeks to provide a process methodology that
addresses initial problems and potentially increases plant
efficiency whilst limiting and ideally avoiding the use of capital
expensive pre-drying technology.
[0010] In accordance with the invention in a first aspect, a method
of preparation of a fuel to produce a pulverous fuel supply, in
particular for supply as fuel to a steam generator such as a boiler
for example of a thermal power plant comprises the steps of:
[0011] supplying a mixture of fuel and a gas to a fuel preparation
unit adapted to prepare the fuel for combustion in a pulverous
sate;
[0012] outputting from the fuel preparation unit a mixture of
pulverous fuel and gas;
[0013] separating the mixture into a gas phase comprising at least
a major part of the gas output and a fuel phase comprising the
pulverous fuel;
[0014] passing the gas phase to a heat exchanger preferably being a
process fluid heat exchanger such as a feed water heat recovery
heat exchanger to dry the gas phase.
[0015] The fuel preparation unit is preferably a fuel pulveriser
such as a mill adapted to receive a mixture of fuel and a gas and
to mill the fuel to a pulverous state. The apparatus in such case
is therefore a method of milling and drying of a fuel to produce a
pulverous fuel supply, in particular for supply as fuel to a steam
generator such as a boiler for example of a thermal power plant
comprises the steps of:
[0016] supplying a mixture of fuel and a gas to a mill;
[0017] outputting from the mill a mixture of pulverous fuel and
gas;
[0018] separating the mixture into a gas phase comprising at least
a major part of the gas output from the mill and a fuel phase
comprising the pulverous fuel;
[0019] passing the gas phase to a process fluid heat exchanger such
as a feed water heat recovery heat exchanger to dry the gas
phase.
[0020] In accordance with the invention in a second aspect, an
apparatus for the preparation of fuel for example by milling and
drying to produce a pulverous fuel supply, in particular for supply
as fuel to a steam generator such as a boiler for example of a
thermal power plant comprises:
[0021] a fuel preparation unit adapted to receive a mixture of fuel
and a gas and to prepare the fuel for combustion in a pulverous
state;
[0022] an output conduit defining an output flow path for a mixture
of pulverous fuel and gas from the fuel preparation unit;
[0023] a phase separator disposed to receive the mixture from the
output conduit and to separate the mixture into a gas phase
comprising at least a major part of the gas from the mixture and a
fuel phase comprising the pulverous fuel;
[0024] a gas phase conduit defining a flow path for the gas phase
from the separator;
[0025] a heat exchanger preferably being a process fluid heat
exchanger such as a feed water heat recovery heat exchanger fluidly
connected to the gas phase conduit and adapted to receive and dry
the gas phase.
[0026] The fuel preparation unit is preferably a fuel pulveriser
such as a mill adapted to receive a mixture of fuel and a gas and
to mill the fuel to a pulverous state. The apparatus in such case
is therefore an apparatus for milling and drying of a fuel to
produce a pulverous fuel supply, in particular for supply as fuel
to a steam generator such as a boiler for example of a thermal
power plant comprises:
[0027] a mill adapted to receive a mixture of fuel and a gas and to
mill the fuel to a pulverous state;
[0028] a mill output conduit defining an output flow path for a
mixture of pulverous fuel and gas from the mill;
[0029] a phase separator to separating the mixture into a gas phase
comprising at least a major part of the gas output from the mill
and a fuel phase comprising the pulverous fuel;
[0030] a gas phase conduit defining a flow path for the gas phase
from the separator;
[0031] a process fluid heat exchanger such as a feed water heat
recovery heat exchanger fluidly connected to the gas phase conduit
to receive and dry the gas phase.
[0032] The apparatus of the second aspect of the invention is an
apparatus to implement the process of the first aspect, and
preferred embodiments of each aspect will be understood from the
following discussion.
[0033] The gas phase is used for example to dry and/or transport
and/or facilitate the storage of the combined fuel and gas phase.
The gas phase becomes laden with water vapour. The invention
separates at least a major part of the water vapour laden gas phase
that has been created by the milling and drying and/or transport
and/or storage of the fuel. The water vapour is not passed to the
combustion furnace. This avoids the penalty of increased ID fan
power demand. The invention uses a heat exchanger preferably being
a process fluid heat exchanger such as a feed water heat recovery
heat exchanger downstream of the phase separator to effect
condensation of vapour moisture. Latent heat consumed by the drying
process is in the preferred case recovered and transferred to a
process fluid for recovery of sensible heat for use in an
industrial process, and in particular is used to preheat feed
water. This further increases the process efficiency.
[0034] In the preferred case the invention is applied to a combined
milling and drying apparatus and method for the milling and drying
of coal of high moisture content, and examples are discussed
hereinbelow in such a context. However the skilled person will
appreciate that this invention can be applied to both coal milling
and drying systems and other milling/fuel preparation and drying
systems presenting similar problems so that the increase of
efficiency of a power cycle can be achieved without dedicated
pre-drying facility and the examples will be interpreted and the
principles of the invention understood accordingly.
[0035] In an example combined milling and drying apparatus and
method the milled fuel is dried by a gas supplied in mixture with
the fuel to be milled. Preferably the gas is at elevated
temperature above ambient. It may be a mixture of optionally
preheated air and flue gas from a combustion chamber. In such case
in the method the step of supplying a mixture of fuel and a gas to
a mill comprises the supply of a gas at elevated temperature and
optionally the step of supplying a gas at elevated temperature
comprises the supply of a mixture of optionally preheated air and
flue gas from a combustion chamber, for example a combustion
chamber of a steam generator.
[0036] Preferably an apparatus in accordance with the invention
includes a fuel source and a gas source together configured to
supply a mixture of fuel and gas to the mill. Preferably the gas
source is adapted to supply a gas at elevated temperature. For
example the gas source comprises a source of optionally preheated
air and a supply of flue gas from a combustion chamber, for example
a combustion chamber of a steam generator.
[0037] In accordance with the invention, at least a major part of
the water vapour laden gas phase and of the water vapour laden gas
output from the mill that has been created by the milling and
drying process is diverted away as the gas phase supplied to the
heat exchanger, which effects condensation of the water vapour and
in the preferred case thereby recovers at least some of the latent
heat from the drying and evaporation process. In a preferred case
substantially all of the water vapour laden gas output is diverted
away as the gas phase supplied to the heat exchanger. In a
preferred case the phase separator is adapted to separate
substantially all of the gas output from the mill into the gas
phase.
[0038] A particular virtue of the invention is that it is
potentially applicable to a range of milling technologies. The
method of the first aspect of the invention and the apparatus of
the second aspect of the invention includes a milling step or
apparatus in which the fuel is milled to a pulverous state for
drying and supply for combustion or storage. Any suitable mill may
be envisaged for use in accordance with the invention to mill the
fuel to a pulverous state, for example including without limitation
ball mills, horizontal and vertical roller mills, beater mills
etc.
[0039] In a possible embodiment, the mill comprises a fan beater
mill, for example comprising in familiar manner a housing for
receiving fuel to be pulverised, a rotary milling shaft, a beater
formation carried on the shaft to effect pulverising of fuel within
the housing, and an impeller.
[0040] The mill in accordance with the invention may be adapted for
direct or indirect supply of pulverous fuel to a combustion
chamber, for example a combustion chamber for a steam generator
such as a boiler for example of a thermal power plant.
[0041] The apparatus and method of the invention is in particular
an apparatus and method for the processing of carbonaceous fuel
having relatively high fuel moisture content prior to milling, for
example at least 25%, for example for use in a combustion
apparatus. The apparatus and method of the invention is in
particular an apparatus and method for the processing of low-rank
fuel, for example for use in a combustion apparatus. The invention
in particular incorporates a carbonaceous fuel and for example
low-rank fuel drying process and system.
[0042] Low-rank fuels are characterised by higher fuel moisture
content (typically 25-60% or more). To avoid the inefficiencies
inherent in combustion of fuel with a high moisture content, the
low-rank fuel is milled to a pulverous state and dried. In a
preferred case, moisture content may be reduced to around
10-20%.
[0043] The present invention relates to the processing by milling
and drying, especially for combustion, of carbonaceous fuel having
relatively high moisture content prior to milling, for example
low-rank fuels, which term is used herein to refer to those fuels,
including fuels sometimes called peat, lignites, brown coals or
sub-bituminous coals, or biomass, which have a higher fuel moisture
content (typically 25-60% or more) than bituminous coals. Thus, in
the preferred case, the apparatus of the invention comprises a
supply of such fuel for milling to pulverous form, and the method
of the invention comprises the milling of such as required by the
combustion furnace.
[0044] Additionally this invention may be applied to waste
combustion plants.
[0045] In accordance with the invention a heat exchanger preferably
being a process fluid heat exchanger is fluidly connected to the
gas phase conduit downstream of the phase separator to receive and
dry the gas phase. Latent heat consumed by the mill for drying or
otherwise in the gas phase is recovered and transferred to heat the
process fluid.
[0046] The process fluid may be a process liquid or air or other
gases. The process liquid may be any liquid or combination of
liquids useable for heat exchange, including water, ammonia,
alcohols, hydrocarbons and the like. Preferably, the process liquid
is wholly or substantially water, optionally including one or more
additives or other minor components known in the art.
[0047] The process fluid stream may be heated by any direct or
indirect thermal exchange, method, device, unit or apparatus.
[0048] In a possible embodiment of the present invention, the
process fluid is water and/or steam and is for example water and/or
steam for/from a steam generator or boiler of a steam generating
process. In a possible embodiment of the present invention, the
process fluid is feedwater for a steam generator. Such a steam
generator may be a boiler, optionally comprising one or more
boilers, and optionally including an integral steam generator
economiser known in the art.
[0049] Latent heat consumed by the mill for drying or otherwise in
the gas phase is in this case recovered and used to preheat feed
water by means of the heat exchanger.
[0050] Such feedwater may be provided directly or indirectly from a
feedwater stream. Preferably, a portion of such a feedwater stream
is provided as the process liquid for the system of the present
invention. Such a portion may be provided as a slip stream of such
a feedwater stream, such a slip stream generally being a minor
portion of the full feedwater stream.
[0051] Thus in such a case the heat exchanger of the apparatus of
the invention is preferably a process fluid heat exchanger and is
for example a heat exchanger disposed to exchange heat with a
process fluid and supply the same for use in an industrial process.
In particular the heat exchanger is adapted to supply the process
fluid to an industrial process in such manner as to make use of the
sensible heat therein. For example the process fluid is feedwater
for a steam generator and the the process fluid is supplied in such
manner as to make use of the sensible heat recovered in the heat
exchanger is effected in that the sensible heat recovered in the
heat exchanger effects preheating of the feedwater.
[0052] By analogy in the method of the invention the heat exchanger
is a process fluid heat exchanger and the method comprises supply
of process fluid to the heat exchanger. In particular the heat
exchanger is a heat exchanger disposed to exchange heat with a
process fluid for use in an industrial process and the method
comprises using the heat exchanger to effect condensation of the
water vapour and thereby recover at least some of the latent heat
from the drying process. Preferably the method comprises the
further step of using the process fluid in an industrial process in
such manner as to make use of the sensible heat recovered in the
heat exchanger. In a particularly preferred case the process fluid
is feedwater for a steam generator and the step of using the
process fluid in such manner as to make use of the sensible heat
recovered in the heat exchanger, effected in that the sensible heat
recovered in the heat exchanger effects preheating of the
feedwater.
[0053] The heat exchanger may be any suitable form of direct or
indirect heat exchanger of familiar or bespoke design. The heat
exchange is in the preferred case a process fluid heat exchanger
from which sensible heat can be recovered for utilisation within an
industrial process, and for example within a steam generation
process. In a possible more complete aspect of the invention, the
method comprises a method of milling and drying of a fuel to
produce a pulverous fuel supply in accordance with the first aspect
of the invention, and further comprises the additional step of
supplying the fuel to a combustion apparatus. A combustion
apparatus is for example a combustion chamber of a steam generator
such as a boiler, for example comprising the boiler of a thermal
power plant.
[0054] In a possible embodiment, the fuel phase is supplied
directly to the burners. In another possible embodiment, the fuel
phase is supplied indirectly for example via a storage silo.
[0055] In an alternative more complete aspect of the invention, the
method comprises a method of milling and drying of a fuel to
produce a pulverous fuel supply in accordance with the first aspect
of the invention, and the further step of passing the dried fuel
for storage.
[0056] The method comprises passing the gas phase to a heat
exchanger preferably being a process fluid heat exchanger to dry
the gas phase, and preferably further comprises using recovered
sensible heat from the heat exchanger, for example as a means of
heating a process fluid which may be a liquid, gas or mixture, in
an additional industrial process. The additional industrial process
is for example a process of operation of a thermal power plant. The
process fluid in such a case is for example a process fluid which
may be a liquid, gas or mixture used in the operation of a thermal
power plant, and is for example feedwater or air.
[0057] By analogy, in accordance with a further more complete
aspect of the invention, an apparatus is provided for milling and
drying of a fuel to produce a pulverous fuel supply, which
apparatus further comprises a combustion apparatus and a fuel
supply conduit to supply the fuel phase comprising the pulverous
fuel to the combustion apparatus. The combustion apparatus is for
example the combustion chamber of a steam generator such as a
boiler for example of a thermal power plant and the supply conduit
is adapted to supply the fuel phase comprising the pulverous fuel
to a combustion chamber within the steam generator. Optionally the
supply conduit is configured to supply the fuel phase directly to
one or more burners of the steam generator. Alternatively the
supply conduit is configured to supply the fuel phase to a storage
silo for example being a storage silo of an indirectly fired steam
generator.
[0058] In accordance with an alternative further more complete
aspect of the invention, an apparatus in accordance with any
preceding claim further comprises a storage volume and a supply
conduit to receive the fuel phase and supply the fuel phase to the
storage volume.
[0059] The invention will now be described by way of example only
with reference to FIGS. 1 and 2 of the accompanying drawings in
which:
[0060] FIG. 1 is an example system for the supply of pulverous fuel
directly to the burners for combustion in combustion furnace
embodying the principles of the invention;
[0061] FIG. 2 is an example system for the indirect supply of
pulverous fuel embodying the principles of the invention.
[0062] The following discussion considers processes applied in
particular to a standard state of the art milling system such as a
fan-beater mill used for processing fuel for combustion into
pulverous form. It will be appreciated that this is an example
only. FIG. 1 shows the supply of pulverous fuel directly to the
burners of a combustion furnace and FIG. 2 shows the indirect
supply of pulverous fuel to a combustion furnace. To the extent
that features of the embodiment of the invention and of the milling
system and combustion furnace are common, like reference numerals
are used.
[0063] The proposed system is used in conjunction with the state of
the art milling system such as a fan-beater mill. The process
incorporates the use of a feed water heat recovery heat exchanger
to dry the gas phase of fan-beater mill product stream and thereby
also to recover at least some of the latent heat input from the
drying process.
[0064] Fuel for combustion, for example comprising a carbonaceous
fuel of relatively high moisture content such as a lignite or other
low-rank fuel, is delivered from a fuel supply 2 and combined with
a hot gas stream comprising a mixture of cold or preheated air 4
and flue gas 6. The mixture is supplied to a beater mill 8 to be
milled into pulverous form suitable for combustion. The hot gases
within the mill dry the fuel to a more suitable state for
combustion. For example a moisture content of 25 to 60% is reduced
to 5 to 10%. Water vapour from the fuel passes into the gas phase.
However if the product of the mill is directly transported to the
combustion furnace including the water vapour that has been created
by drying the fuel this may reduce the process efficiency because
the water vapour that has been created by drying the fuel is passed
to the combustion furnace.
[0065] Instead, the stream that leaves the beater mill is first
separated at the phase separator 12 into a pulverised and dried
fuel phase, and a gas phase. Secondly, the gas phase is passed
through a feed water heat exchanger 10 where the condensation of
vapour moisture is carried out. This enables the plant to reduce
the ID fan power demand, hence increase power plant energy sales.
Additionally the process efficiency increases as the gas leaving
the power plant will have less moisture and therefore a smaller
heat capacity, what will result in less heat being lost through the
chimney. Additionally the process efficiency increases as the
latent heat consumed by the mill for drying is recovered and
transferred to pre-heat the feed water. Importantly, this will
reduce the fuel consumption while the power plant output will
remain unchanged.
[0066] The pulverised fuel phase, substantially denuded of the gas
and water vapour mixture, is passed to the burners 13 of a
combustion furnace 14 of a steam generator. In FIG. 1 the
pulverised fuel phase is supplied directly. FIG. 2 is an example
system for the indirect supply of pulverous fuel to a silo 11 for
onward supply to the burners 13 of a combustion chamber 14 of a
steam generator. The steam generator may be on any suitable
conventional or bespoke design.
[0067] The process calculation of the described solution, shows
that assumed 50% latent heat recovery in the system the power plant
net efficiency will increase by 2.65% p, and if 90% of heat
recovery is achieved, the application of the invention will improve
the net efficiency by 3.84% p. The amount of heat recovery is
driven by the economic factors that influence the design to
increase cost effectiveness of the system.
[0068] The dried fuel product separated from the gas phase in
separator is passed directly to the burners for combustion in
combustion furnace as presented on FIG. 1, or is safely stored in
intermediate storage device (i.e. silo) and then transferred to the
burners for combustion as presented on FIG. 2.
[0069] In another application current invention could be used to
dry the raw fuel and store the product for transportation (i.e.
shipping) and combustion on remote location.
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