U.S. patent application number 11/937775 was filed with the patent office on 2008-07-10 for method of and arrangement for co-combustion of biomasses and/or organic wastes as secondary fuel in a coal dust firing system.
This patent application is currently assigned to RWE POWER AKTIENGESELLSCHAFT. Invention is credited to Rolf Hauk.
Application Number | 20080163804 11/937775 |
Document ID | / |
Family ID | 38961179 |
Filed Date | 2008-07-10 |
United States Patent
Application |
20080163804 |
Kind Code |
A1 |
Hauk; Rolf |
July 10, 2008 |
METHOD OF AND ARRANGEMENT FOR CO-COMBUSTION OF BIOMASSES AND/OR
ORGANIC WASTES AS SECONDARY FUEL IN A COAL DUST FIRING SYSTEM
Abstract
The invention concerns a method of and an arrangement for
co-combustion of biomasses and/or organic wastes as secondary fuel
in a coal dust-fired boiler of a vapor generator. The secondary
fuel is dried directly or indirectly with the flue gas of the
boiler. The vapors produced in the drying operation are fed to the
combustion chamber of the boiler as final combustion air and/or
secondary air.
Inventors: |
Hauk; Rolf; (Unna,
DE) |
Correspondence
Address: |
GROSSMAN, TUCKER, PERREAULT & PFLEGER, PLLC
55 SOUTH COMMERICAL STREET
MANCHESTER
NH
03101
US
|
Assignee: |
RWE POWER
AKTIENGESELLSCHAFT
Essen
DE
|
Family ID: |
38961179 |
Appl. No.: |
11/937775 |
Filed: |
November 9, 2007 |
Current U.S.
Class: |
110/224 |
Current CPC
Class: |
F23C 6/047 20130101;
F23C 2900/01001 20130101; F23G 5/04 20130101; F23D 1/00 20130101;
F23G 5/08 20130101; F23G 7/10 20130101; Y02E 20/348 20130101 |
Class at
Publication: |
110/224 |
International
Class: |
F23G 5/04 20060101
F23G005/04 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 10, 2006 |
DE |
10 2006 053 337.2 |
Claims
1. A method of co-combustion of biomasses and/or organic wastes as
secondary fuel in a boiler of a vapor generator, which is fired
with coal in grain and/or dust form as primary fuel, wherein the
secondary fuel is dried directly or indirectly with the flue gas of
the boiler, and wherein the vapors from the drying of the secondary
fuel are added to the combustion air fed to the boiler.
2. A method as set forth in claim 1 wherein in which the combustion
air is added to the boiler in a stepped configuration over a
plurality of levels characterised in that the vapors are at least
partially added in the combustion air level which is last
downstream in the flow direction of the flue gas.
3. A method as set forth in claim 1 characterised in that the
addition of the fuel to the combustion air is regulated in
dependence on the demand for output power of the drier for the
secondary fuel in such a way that optionally a partial amount of
the vapors is also added to the next combustion air level which is
disposed upstream in relation to the flue gas.
4. A method as set forth in claim 2 characterised in that the
amount of air required for the drier for the secondary fuel
corresponds to the design amount for the last combustion air level
in the downstream direction.
5. A method as set forth in claim 1 characterised in that the
energy required for the drier for the secondary fuel is coupled out
of the flue gas flow downstream of an air preheater.
6. A method as set forth in claim 5 characterised in that a partial
amount of the air flow is branched off downstream of the air
preheater for drying the secondary fuel.
7. A method as set forth in claim 5 characterised in that a partial
amount of the air flow is fed to the boiler downstream of the air
preheater as primary and secondary air.
8. A method as set forth in claim 7 characterised in that the
primary air which is branched off downstream of the air preheater
is fed to the boiler by way of at least one coal mill.
9. A method as set forth in claim 2 characterised in that final
combustion air is added to the combustion air level which is last
in the downstream direction.
10. A method as set forth in claim 1 characterised in that direct
drying is effected in the air flow in the drier for the secondary
fuel.
11. A method as set forth in claim 1 characterised in that indirect
drying is effected in the drier for the secondary fuel.
12. An arrangement for co-combustion of biomasses and/or organic
wastes as secondary fuel in a coal dust firing system, comprising
at least one drier for the secondary fuel, wherein the drier is
connected downstream of an air preheater for conditioning of
combustion air and/or mill air and wherein the vapors outlet of the
drier is connected to the final combustion air feed and/or the
secondary air feed of the boiler.
Description
[0001] The invention concerns a method of and arrangement for
co-combustion of biomasses and/or organic wastes as secondary fuel
in a coal dust firing system.
[0002] Such a method is known for example from DE 196 49 986 A1.
The method described in DE 196 49 986 provides that sludge is
introduced in the form of a suspension tangentially into a cyclone
combustion chamber and dried and degassed on a spiral path with a
heat transfer medium. The fuel gas produced in that way, the vapors
and the degassed fine sludge dust are fed to the combustion chamber
and/or the flue gas suction return system and/or an injection
burner. The degassed coarse sludge dust is separated by centrifugal
action from the cyclone combustion chamber and distributed to the
carbon mill and/or the carbon burner line.
[0003] That method is comparatively complicated and expensive in
terms of energy technology, especially as the cyclone combustion
chamber is operated by means of an oil or gas burner.
[0004] DE 101 56 616 A1 discloses a method of co-combustion of
sludge in a fluidised bed boiler with a stationary or slightly
expanding fluidised bed, wherein mechanically dewatered, pumpable
sludge is fed on to the fluidised bed in the fluidised bed
combustion chamber of the fluidised bed boiler immediately above
the fluidised bed at a plurality of locations over the periphery of
the fluidised bed combustion chamber, by means of injection lances,
and wherein the introduction is effected in each case by means of
compressed air so that scattering of the sludge over the fluidised
bed is effected. In the method described in DE 101 56 616 the
sludge introduced into the fluidised bed is also carried by the
fluidised bed, mixed with the fluidised bed material and finally
undergoes joint combustion therewith.
[0005] Direct introduction of the sludge into the firing chamber of
a boiler without previous treatment in that way, as is described by
way of example in DE 196 49 986, is only possible in the case of a
fluidised bed firing system.
[0006] Organic materials which are to be introduced into a
dust-fired boiler require preliminary drying depending on their
respective moisture content. That applies in any case to
mechanically dewatered sludges.
[0007] Biomasses and waste which have a comparatively high water
content are being increasingly used in coal-fired power stations
with dust firing.
[0008] DE 196 49 986 A1 already presupposes that the direct
distribution of moist biomasses to coal dust mills is known. In
fact moist biomasses and waste are being increasingly distributed
directly to the coal mills. In the case of a direct feed to the
coal mills, only a limited amount can be used as the drying
reserves of the mills are limited and in most cases the coal mills
are also not suitable for comminuting moist, fibrous substances.
Depending on the biomasses used, for example when dealing with
moist wood, a drying operation is necessary prior to a fine
comminuting step. A certain grain size of the biomasses to be used
is not to be exceeded because of a possible adverse effect on the
dust firing system.
[0009] Previous methods of co-combustion of biomasses and other
organic wastes in coal dust firing systems therefore provide, as is
also described in DE 196 49 986, for drying with natural gas or
petroleum. That involves comparatively high energy costs.
[0010] It is known from the drying of brown coal prior to the
combustion thereof that the energy required for the drier is to be
branched out of the water vapor circuit of the power station
process. That is linked to a comparatively high level of apparatus
complication and expenditure, which is not in any way related to
the energy yield which can be attained when drying biomasses and
other organic waste.
[0011] At any event post-treatment of the drier vapors and fumes is
complicated and expensive. Under some circumstances when
condensation of the drier vapors and fumes takes place effluent
reprocessing is required.
[0012] Therefore the object of the invention is to provide a method
of and an arrangement for co-combustion of biomasses and/or organic
wastes in a coal dust firing system, with which the aforementioned
problems are avoided.
[0013] To attain the object of the invention there is provided a
method of co-combustion of biomasses and/or organic wastes as
secondary fuel in a boiler of a vapor generator, which is fired
with coal in grain and/or dust form as fuel, wherein the secondary
fuel is dried directly or indirectly with the flue gas of the
boiler, and wherein the vapors from the drying of the secondary
fuel are added to the combustion air fed to the boiler.
[0014] An advantage of that operating procedure is that
condensation of the vapors with downstream-disposed effluent
reprocessing and possibly concomitant odor annoyance are not
required.
[0015] In a preferred variant of the invention in which the
combustion air is added to the boiler in a stepped configuration
over a plurality of levels it is provided that the vapors are at
least partially added in the combustion air level which is last
downstream in the flow direction of the flue gas.
[0016] To state that in different terms, the method according to
the invention involves co-combustion of moist biomasses and organic
wastes as secondary fuel in a coal dust firing system, wherein the
secondary fuel is pre-dried, the energy required for the drying
operation is coupled directly out of the flue gas flow and the
vapors produced in the drying operation--primarily water vapor--are
added again to the flue gas still in the boiler upstream in the
direction of flow of the flue gas before the ancillary heating
surfaces. The dried secondary fuel can be allocated to the coal
mills and introduced with the primary air into the boiler.
[0017] Such coal mills can be for example in the form of known
roller bowl-type mills in which the energy of the flue gas is used
for pre-drying the crushing material and the flue gas is used for
transporting that material.
[0018] Desirably the addition of the vapors to the combustion air
is effected in dependence on the demand for output power of the
drier for the secondary fuel in such a way that optionally a
partial amount of the vapors is added to the next combustion air
level which is disposed upstream in relation to the flue gas.
Desirably the amount of air required for the drier for the
secondary fuel corresponds to the design amount for the last
combustion air level in the downstream direction. If the demand for
output power of the drier for the secondary fuel is higher than the
air required in the last downstream combustion air level, for
example in the form of final combustion air, cascade-like
distribution of the vapors can be effected in a direction towards
the next combustion air levels disposed in the upstream
direction.
[0019] In a preferred embodiment of the method according to the
invention the energy required for the drier for the secondary fuel
is coupled out of the flue gas flow downstream of an air
preheater.
[0020] Desirably in that case a partial amount of the air flow is
branched off downstream of the air preheater for drying the
secondary fuel. Another partial amount of the air flow can be fed
to the boiler downstream of the air preheater as primary and/or
secondary air.
[0021] The primary air which is branched off downstream of the air
preheater is desirably fed to the boiler by way of at least one
coal mill. There the energy thereof is used for drying the primary
fuel.
[0022] In a preferred variant of the method according to the
invention final combustion air is added to the combustion air level
which is last in the downstream direction. The vapors of the drier
can be completely supplied as the final combustion air. In the case
involving a stepped combustion air feed without the addition of
final combustion air, the vapors can be fed to the boiler as
secondary air.
[0023] Preferably direct drying is effected in the air flow in the
drier for the secondary fuel.
[0024] As an alternative thereto it is possible that indirect
drying is effected in the drier for the secondary fuel.
[0025] Compression and removal of dust from the vapors can be
provided downstream of the drier. In that case compression serves
to compensate for the pressure losses of the drier.
[0026] The object of the present invention is further attained by
an arrangement for co-combustion of biomasses and/or organic wastes
as secondary fuel in a coal dust firing system, comprising at least
one drier for the secondary fuel, wherein the drier is connected
downstream of an air preheater for conditioning of combustion air
and/or mill air and wherein the vapors outlet of the drier is
connected to the final combustion air feed and/or the secondary air
feed of the boiler.
[0027] The invention is described hereinafter by means of three
embodiments by way of example illustrated in the drawings in
which:
[0028] FIG. 1 shows an arrangement of a dust-fired boiler with air
preheater and drier for secondary fuel in accordance with a first
embodiment of the invention,
[0029] FIG. 2 shows a diagrammatic view of a method implementation
modified in comparison to the FIG. 1 embodiment in accordance with
a second embodiment of the invention, and
[0030] FIG. 3 shows a diagrammatic view of a third embodiment of
the invention.
[0031] The embodiment illustrated in the drawings has a dust-fired
boiler 1 which is operated for example with hard coal as primary
fuel. The coal with which the boiler 1 is operated is ultimately
not critical to the invention, it can equally be fired with brown
coal.
[0032] Of the boiler 1, only the combustion chamber is illustrated,
the upper region of the boiler with the ancillary heating surfaces
not being shown for the sake of simplicity in the flow chart. The
boiler 1 is in the form of a boiler with stepped combustion air
feed. The individual combustion air levels are denoted by
references 2 through 6, wherein the lowermost combustion air level
2 represents the infiltrated air feed to the combustion chamber,
the following combustion air level 3 represents the primary air
feed, the combustion air level 4 disposed downstream thereof
represents the secondary air feed, the combustion air level 5 in
adjoining relationship downstream in relation to the flow gas
represents the upper air feed and the last downstream combustion
air level 6 represents the final combustion air level. Reference 7
denotes the flue gas flow out of the combustion chamber or the
boiler 1.
[0033] As can be seen in particular from FIG. 1 the flue gas flow
is passed by way of an air preheater 8 in the form of a rotary air
preheater--referred to hereinafter as the preheater. The preheater
8 is connected in known manner to a fresh air feed 9. The fresh air
is heated in the preheater 8 directly or indirectly with flue gas
from for example 35.degree. C. to about 350.degree. C. At about
350.degree. C. the heated air flows through the drier 10 in which
biomasses in the form of for example moist wood chips or the like
are dried in direct contact with the heated air.
[0034] The vapors outlet 11 of the drier 10 is directly connected
to the combustion chamber of the boiler 1. In the described
embodiment 100% of the vapors is fed to the boiler 1 as final
combustion air 6. The dried material withdrawn from the drier is
allocated to the coal mills (not shown) which are arranged in the
primary air feed 3 to the combustion chamber.
[0035] Alternatively the biomasses can be ground downstream of the
drier 10 in a separate mill and after the grinding operation
injected separately or jointly with the coal into the boiler.
[0036] In accordance with a further variant it can be provided that
the biomass is crushed prior to the drying operation in a separate
mill. Finally the biomasses can already be present in comminuted
form so that additional grinding is unnecessary.
[0037] Whether separate grinding of the biomasses is required
optionally prior to or after the drying operation is predominantly
a question of the physical properties of the biomass in regard to
grindability thereof.
[0038] When injecting the biomasses jointly with the coal it is
appropriate for it to be allocated to the coal mills in which
intensive thorough mixing of biomass and coal and possibly also
post-crushing of the biomass are achieved.
[0039] Downstream of the preheater 8 and upstream of the drier 10
heated air is distributed in known manner by way of the combustion
air levels of the combustion chamber of the boiler 1, wherein the
primary air feed 3 is passed in known manner by way of one or more
coal mills which are not illustrated here.
[0040] Regulation provides that, with an increased demand for
output power of the drier 10, a partial amount of the vapors is
added cascade-like to the upper air 5 and possibly also the
secondary air 4.
[0041] By way of the final combustion air feed 6 and/or the upper
air feed 5 and/or the secondary air feed 4, the vapors pass out of
the drier 10 into the flue gas flow 7 and finally into the flue gas
outlet 12. To compensate for any pressure losses in the drier 10, a
vapors compressor 13 is connected downstream of the drier 10. A
filter can also be connected downstream of the vapors compressor
13, if required, such a filter is not shown in the simplified view
of the operating procedure of the method.
[0042] The embodiment illustrated in FIG. 2 approximately
corresponds to that of FIG. 1, with the difference that the drier
10 is in the form of an indirect drier and has two outlets 11a,
11b, the outlet 11a serving as a vapors outlet and the outlet 11b
in contrast passing the cooled heat exchange medium of the drier
10. The outlets 11a and 11b are brought together again upstream of
the vapors compressor 13.
[0043] In other respects identical parts are denoted by the same
references in the various Figures.
[0044] That also applies to the embodiment which is illustrated in
FIG. 3 and which differs from the preceding embodiments insofar as
the drier 10 is in the form of an indirect drier which however has
a separate circuit 15 for the heat exchange medium. That heat
exchange circuit 15 is closed in itself. Provided therein is a
compressor 16 in order to produce the circulatory flow of the heat
exchange medium.
[0045] Provided for heating the heat exchange medium is a heat
exchanger 17, the outlet 11b of which is combined downstream of the
drier 10 with the vapors outlet 11a of the drier 10.
[0046] In the embodiment described with reference to FIG. 2 by way
of example the drier 10 could be in the form of a fluidised bed
drier with inwardly disposed heating surfaces.
[0047] In the embodiment described with reference to FIG. 3 it
would be possible to provide for example vapor, nitrogen or flue
gas as the heat exchange medium. The cooled air from the outlet 11b
of the heat exchanger 17 is added together with the vapors to the
final combustion air or introduced into the combustion chamber of
the boiler 1 as a final combustion air feed.
LIST OF REFERENCES
[0048] 1 boiler [0049] 2 infiltrated air feed to the combustion
chamber [0050] 3 primary air feed to the combustion chamber [0051]
4 secondary air feed to the combustion chamber [0052] 5 upper air
feed to the combustion chamber [0053] 6 final combustion air feed
to the combustion chamber [0054] 7 flue gas flow [0055] 8 air
preheater [0056] 9 fresh air feed to the air preheater [0057] 10
drier [0058] 11 vapor outlet [0059] 11a vapors outlet [0060] 11b
drier outlet/heat exchanger outlet [0061] 12 flue gas outlet [0062]
13 vapors compressor [0063] 14 secondary fuel flow [0064] 15 heat
exchanger circuit [0065] 16 compressor [0066] 17 heat exchanger
* * * * *