U.S. patent application number 13/443058 was filed with the patent office on 2012-10-11 for solar boiler system.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Nobuyoshi MISHIMA, Toshihiko Sakakura, Takashi Sugiura.
Application Number | 20120255471 13/443058 |
Document ID | / |
Family ID | 46022063 |
Filed Date | 2012-10-11 |
United States Patent
Application |
20120255471 |
Kind Code |
A1 |
MISHIMA; Nobuyoshi ; et
al. |
October 11, 2012 |
Solar Boiler System
Abstract
It is an object of the present invention to provide a solar
boiler system that can suppress the installation cost for a solar
heat collector and significantly improve gross thermal efficiency
while minimizing a rise in air temperature resulting from the
collected solar heat. The solar boiler system of the present
invention includes a boiler for burning fossil fuel; a primary air
system for pneumatically transporting pulverized fossil fuel to a
burner attached to the boiler; a secondary air system for supplying
preheated air for combustion to the boiler; and a secondary air
superheater provided at the secondary air system, the secondary air
superheater further superheating the preheated air for combustion
with solar thermal energy.
Inventors: |
MISHIMA; Nobuyoshi;
(Hitachi, JP) ; Sugiura; Takashi; (Hitachinaka,
JP) ; Sakakura; Toshihiko; (Hitachi, JP) |
Assignee: |
Hitachi, Ltd.
Tokyo
JP
|
Family ID: |
46022063 |
Appl. No.: |
13/443058 |
Filed: |
April 10, 2012 |
Current U.S.
Class: |
110/347 ;
110/234; 110/265; 110/302 |
Current CPC
Class: |
F23L 2900/15044
20130101; F23L 15/045 20130101; Y02E 20/34 20130101; Y02E 20/348
20130101; F23C 7/08 20130101 |
Class at
Publication: |
110/347 ;
110/234; 110/265; 110/302 |
International
Class: |
F23L 15/00 20060101
F23L015/00; F23D 1/00 20060101 F23D001/00; F23K 3/02 20060101
F23K003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 11, 2011 |
JP |
2011-086905 |
Claims
1. A solar boiler system comprising: a boiler for burning fossil
fuel; a primary air system for pneumatically transporting
pulverized fossil fuel to a burner attached to the boiler; a
secondary air system for supplying preheated air for combustion to
the boiler; and a secondary air superheater provided at the
secondary air system, the secondary air superheater further
superheating the preheated air for combustion with solar thermal
energy.
2. A solar boiler system comprising: a boiler for burning fossil
fuel; a primary air draft fan for generating air for transportation
which allows pulverized fossil fuel to be pneumatically transported
to the boiler; a primary air heater for preheating the air for
transportation sent from the primary air draft fan; a forced draft
fan for generating air for combustion of the boiler; a secondary
air heater for preheating the air for combustion sent from the
forced draft fan; and a secondary air superheater for superheating
the air for combustion at an outlet of the secondary air heater by
using solar thermal energy as a heat source.
3. The thermal boiler system according to claim 2, further
comprising: a plurality of solar light collecting mirrors for
collecting solar light; a heat exchanger for subjecting a heat
medium for heat storage to heat exchange with a heat medium, which
is heated with the solar thermal energy collected by the solar
light collecting mirrors; a low-temperature tank for storing a
low-temperature heat medium for heat storage used for heat exchange
in the heat exchanger; a high-temperature tank for storing a
high-temperature heat medium for heat storage heated in the heat
exchanger; and a changeover valve for switching to allow the heat
medium for heat storage to flow to both the low-temperature tank
and the high-temperature tank.
4. A method of retrofitting an existing boiler system, the existing
boiler system including: a boiler for burning fossil fuel; a
primary air draft fan for generating air for transportation which
allows pulverized fossil fuel to be pneumatically transported to
the boiler; a primary air heater for preheating the air for
transportation sent from the primary air draft fan; a forced draft
fan for generating air for combustion of the boiler; and a
secondary air heater for preheating the air for combustion sent
from the forced draft fan; the method comprising the step of
additionally installing: a solar heat recovery apparatus for
collecting solar thermal energy; and a secondary air superheater
for further superheating the air for combustion at an outlet of the
secondary air heater by using solar thermal energy collected by the
solar heat recovery apparatus as a heat source.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a solar boiler system to
which solar thermal energy is applied.
[0003] 2. Description of the Related Art
[0004] For example, a solar thermal gas turbine as disclosed in
JP-2010-275997-A is used for a thermal power system equipped with a
solar heat recovery apparatus. JP-2010-275997-A proposes the
following system. A solar-heat receiving unit is installed on the
leading end of a tower having a height of approximately 100 m from
the ground. Solar light reflected from a large number of reflecting
mirrors installed on the ground is collected in the solar-heat
receiving unit. High-pressure air supplied from a compressor
installed on the ground is superheated with the solar light thus
collected, with the result that high-temperature air is produced.
This high pressure and high temperature air is made to flow in a
high temperature and high pressure expansion turbine installed on
the leading end of the above-mentioned tower so that a generator is
driven to generate electricity. For this system to superheat air to
approximately 900.degree. C., a large number of the reflecting
mirrors are needed and an area in which flat mirrors are installed
is enormous. Thus, the cost of the solar heat recovery apparatus is
increased. Further, the high temperature and high pressure air
expansion turbine and the generator are inevitably installed on the
tall tower; therefore, there is a problem in that stable operation
is difficult. "Development of High Efficiency Solar Heat Power
Generation System", Mitsubishi Heavy Industries' Technical Review,
Vol. 31, No. 4 (1994-7), P.239-242, discloses an example as below.
A mixed gas of helium and xenon is superheated to 1000.degree. C.
in a solar heat receiving unit by use of solar light collected by a
solar heat collector, with the mixed gas thus superheated being
supplied to a regeneration gas turbine.
SUMMARY OF THE INVENTION
[0005] The system as the above-mentioned conventional technology is
such that solar light is concentrated in the solar heat receiving
unit by means of a large number of flat mirrors installed on the
ground. The solar light thus concentrated superheats the
high-pressure air at the compressor outlet. The high-pressure air
thus superheated is supplied to the high temperature and high
pressure air expansion turbine. To generate high-temperature air of
approximately 1000.degree. C. or higher, the system requires a
large number of flat mirrors. That is, the above-mentioned
conventional technology in which the solar thermal energy is
applied to the gas turbine needs to increase air temperature up to
1000.degree. C. or higher in order to improve efficiency.
Therefore, the conventional technology involves a problem
contradictory to the increase in air temperature up to 1000.degree.
C. or higher in that the installation cost of the solar collector
is significantly increased. It should be noted that the
above-mentioned conventional technologies do not disclose any
application of solar thermal energy to a boiler system.
[0006] Accordingly, it is an object of the present invention to
provide a solar boiler system that can suppress the installation
cost for a solar collector and significantly improve gross thermal
efficiency while minimizing an air temperature rise resulting from
the collected solar heat.
[0007] According to one aspect of the present invention, there is
provided a solar boiler system comprising: a boiler for burning
fossil fuel; a primary air system for pneumatically transporting
pulverized fossil fuel to a burner attached to the boiler; a
secondary air system for supplying preheated air for combustion to
the boiler; and a secondary air superheater provided at the
secondary air system, the secondary air superheater further
superheating the preheated air for combustion with solar thermal
energy.
[0008] The present invention can provide a solar boiler system that
can suppress the installation cost for a solar collector and
significantly improve gross thermal efficiency while minimizing a
rise in air temperature resulting from the collected solar
heat.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a diagram for assistance in explaining a system
connecting a solar collector, a boiler secondary air superheater
and a boiler smoke tunnel system according to an embodiment of the
present invention.
[0010] FIG. 2 is a detailed diagram for assistance in explaining
the solar collector and the secondary air superheater in FIG.
1.
[0011] FIG. 3 is a graph of a gross thermal efficiency progress
rate (estimation) in the embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0012] An embodiment of a solar boiler system according to the
present invention applied to a coal-fired thermal power boiler will
hereinafter be described with reference to the drawings.
Incidentally, equivalent constituent elements are denoted with like
reference numerals throughout all figures.
[0013] The embodiment according to the present invention described
below includes a smoke wind tunnel of a boiler in a steam power
plant; a solar heat recovery apparatus; and a system for inputting
solar heat energy recovered by the solar heat recovery apparatus to
a boiler furnace via a secondary air superheater. The steam power
plant corresponds to one mode of thermal power generation.
Incidentally, the solar heat recovery apparatus is described by
taking a trough type as an example. However, the same holds true
for a tower type. Oil is here used as a heat medium for recovering
solar thermal energy. However, the same hold true for other heat
media containing water. Further, molten salt is exemplarily used as
a heat medium on a side where the recovered solar heat is stored or
radiated.
[0014] FIG. 1 is a system diagram for assistance in explaining a
solar boiler system according to the present embodiment. The solar
boiler system of the present embodiment includes, as a basic
system, a primary air system for a boiler, a secondary air system
for the boiler, a smoke tunnel system for the boiler, and a solar
recovery system.
[0015] Atmospheric air needed for burning in a boiler 10 passes
through a silencer 1 and is divided into primary air and secondary
air. The primary air is increased in pressure by a primary air
draft fan 25 (PAF) and heated by a primary air heater (a primary
air preheater) 28. Thereafter, the heated primary air flows into a
fine grinding mill 29 at a subsequent stage. Further, the fine
grinding mill 29 pulverizes fossil fuel 58 into fine powder. The
pulverized fossil fuel 58 along with the primary air passes through
a fine grinding mill outlet pipe 59 and flows into a wind box 9 of
the boiler 10. In the wind box 9, the boiler primary air, secondary
air and the fine powder fuel pass through corresponding passages of
a plurality of combustor burners (not shown). Thereafter, the
primary air, the secondary air and the fine powder fuel unite with
one another and are burned at fuel combustor burner outlets.
[0016] Boiler secondary air is increased in pressure by a forced
draft fan 2 (FDF) and is heated with steam by a steam-type air
heater 3 (SAH). Thereafter, the heated boiler secondary air flows
into a secondary air heater (a secondary air preheater) 4. In the
secondary air heater 4, the secondary air is heated to
approximately 350.degree. C. and passes through a secondary air
superheater inlet damper 6. The preheated air for combustion flows
through a secondary air superheater inlet duct 22. In addition, in
a secondary air superheater 7 the preheated air is further
superheated to approximately 400 to 500.degree. C. with a heating
medium having solar thermal energy. The superheated air passes
through a secondary air superheater outlet duct 8 and is led to the
wind box 9. In this way, the solar thermal energy is inputted into
the boiler 10 via the boiler secondary air. If operation in which
solar thermal energy is not recovered in the boiler is performed, a
secondary air superheater bypass damper 5 is opened so that the
secondary air flows into a secondary air superheater bypass duct
21, thereby leading the secondary air to the wind box 9.
[0017] Boiler exhaust gas burnt in the furnace of the boiler 10
passes through a boiler outlet duct 11. Thereafter, the exhaust gas
sequentially passes through denitrification equipment 15, a primary
and secondary air heater (a primary and secondary air preheater) 16
(AH), an electric dust precipitator 17 (EP), an inductive draft fan
18 (IDF) and a desulfurizer 19 (DeSox) on the subsequent stage.
Lastly, the exhaust gas flows into a chimney 20 and diffuses to
atmosphere.
[0018] After superheating the secondary air to approximately 400 to
500.degree. C., a low-temperature solar heat medium moves out of
the secondary superheater 7 and passes through the inside of a
secondary air superheater outlet heat medium pipe 40. Thereafter,
such solar heat medium is collected in a heat medium tank 30. The
low-temperature heat medium having moved out of the heat medium
tank 30 is increased in pressure by a primary heat medium
circulating pump 32. Then, the low-temperature heat medium passes
through a three-way valve 34 located at a solar light collecting
mirror group inlet and is led to solar light collecting mirrors 35,
where the low-temperature heat medium is heated and becomes a
high-temperature heat medium. The high-temperature heat medium,
which has heated to as high as approximately 410 to 510.degree.
with sunlight, passes through a three-way valve 36 located at a
solar light collecting mirror group outlet, a solar heat collector
outlet heat medium pipe 37, a secondary air superheater inlet heat
medium pipe 39, a secondary air superheater inlet valve 56, a
secondary heat medium circulating pump 41 and a secondary heat
medium circulating pump outlet heat medium pipe 42. Then, the
high-temperature heat medium is led to the secondary superheater 7.
The high-temperature heat medium supplied as described above
superheats the secondary air to approximately 400 to 500.degree.
C., so that the solar thermal energy is brought into the furnace of
the boiler. If the heat exchanging operation of the secondary air
superheater 7 comes to a stop, control is exercised to close the
secondary air superheater inlet valve 56 and to open a secondary
air superheater bypass valve 55. As a result, the high-temperature
heat medium is diverted to the heat medium tank 30.
[0019] The secondary air superheater bypass valve 55 is disposed in
a secondary air superheater bypass heat medium pipe 38 connected
between the solar heat collector outlet heat medium pipe 37 and the
heat medium tank 30. The secondary air superheater bypass heat
medium pipe 38 bypasses the secondary air superheater inlet heat
medium pipe 39, the secondary air superheater inlet valve 56, the
secondary heat medium circulating pump 41, the secondary heat
medium circulating pump outlet heat medium pipe 42, the secondary
air superheater 7 and the secondary air superheater outlet heat
medium pipe 40.
[0020] FIG. 2 is a diagram for assistance in explaining a detailed
system of the solar heat recovery apparatus and of the secondary
air superheater in FIG. 1. More specifically, the solar boiler
system is such that solar thermal energy is stored during daylight
and a high-temperature heat medium is again supplied to the
secondary air superheater 7 during the hours of darkness, i.e.,
after the sun goes down. Incidentally, a description is given of an
example in which molten salt is used as a heat medium for storing
solar thermal energy.
[0021] Incidentally, solar heat varies largely between day and
night. Because of this influence, electric power facilities making
use of solar heat has a problem in that the output of a turbine
generator varies between day and night. According to the
configuration shown in FIG. 2 this problem will be solved.
[0022] In daytime operation, first, a heat medium is heated to high
temperature with daytime solar thermal energy. Part of the heated
heat medium is circulated by use of the three-way valve 36 located
at the solar light collecting mirror group outlet, a heat medium
supply pipe 49 for heat exchange with molten salt, and a primary
heat medium circulating pump inlet valve 33. This inlet valve 33 is
installed on an accumulator heat-exchanger side. On the other hand,
low-temperature molten salt in a low-temperature molten salt tank
51 is supplied to a molten salt heat exchanger 47 via a
low-temperature molten salt tank outlet changeover three-way valve
45, a solar heat-storing molten salt transfer pump 44 and a molten
salt heat exchanger inlet changeover three-way valve 46. This
low-temperature molten salt is then subjected to heat exchange with
the high-temperature medium supplied from the solar light
collecting mirror group outlet three-way valve 36. The
high-temperature molten salt increased in temperature through this
heat exchange is supplied to a high-temperature molten salt tank
52, and thus solar thermal energy is stored.
[0023] During nighttime hours, the high-temperature molten salt
stored by the heat storage operation during daytime hours is taken
out of the high-temperature molten salt tank 52. The
high-temperature molten salt thus taken out is used as a medium
heating the low-temperature heat medium supplied as a heated medium
(heating medium during daytime hours) to the molten salt heat
exchanger 47. More specifically, to supply the high-temperature
molten salt in the high-temperature molten salt tank 52 to the
low-temperature molten salt tank 51, the molten salt heat exchanger
inlet changeover three-way valve 46 and the low-temperature molten
salt tank outlet changeover three-way valve 45 are switched such
that a solar heat radiation molten salt transfer pump 43 is
activated. This control allows the solar thermal energy stored in
the high-temperature molten salt tank 52 to be radiated to the heat
medium.
[0024] The high-temperature heat medium heated with the daytime
solar thermal energy or the nighttime high-temperature molten salt
passes through the secondary air superheater inlet heat medium pipe
39 and the secondary air superheater inlet valve 56 and is
increased in pressure by the secondary heat medium circulating pump
41. The high-temperature heat medium thus supplied is collected via
the secondary heat medium circulating pump outlet heat medium pipe
42 in a secondary air superheating pipe inlet header 53 installed
in the secondary air superheater 7. The high-temperature heat
medium supplied to the secondary air superheating pipe inlet header
53 sequentially flows in a secondary air superheater heat-transfer
pipe 54 installed in the secondary air superheater 7 toward the
downstream side. During this flow, the high-temperature heat medium
superheats the secondary air of approximately 350.degree. C. at the
outlet of the secondary air heater 4 to approximately 400 to
500.degree. C. After superheating the secondary air for burning
boiler fossil fuel, the heat medium becomes a low-temperature heat
medium. The low-temperature heat medium is collected in a secondary
air superheating pipe outlet header 57 installed in the secondary
air superheater 7. The low-temperature heat medium moves out of the
secondary air superheating pipe outlet header 57, passes through
the secondary air superheater outlet low-temperature heat medium
pipe 40 and is returned to the heat medium tank 30. The
low-temperature heat medium, once again, moves out of the heat
medium tank 30, passes through a circulating pump inlet valve 31
and is increased in pressure by the primary heat medium circulating
pump 32. The low-temperature heat medium thus increased in pressure
is sent to the solar light collecting mirrors 35 or the molten salt
heat exchanger 47 and becomes the high-temperature heat medium
again. The high-temperature heat medium is returned to the
secondary air superheater 7. In this way, the system of the present
embodiment is configured so that the heat medium is circulated
between the solar light collecting mirrors 35 and the secondary air
superheater 7 during daytime hours and is circulated between the
molten salt heat exchanger 47 and the secondary air superheater 7
during nighttime hours.
[0025] FIG. 3 shows a gross thermal efficiency progress rate (an
absolute value) in the present embodiment. A horizontal axis
represents air temperatures (.degree. C.) at the outlet of the
secondary air superheater 7 and a longitudinal axis represents a
gross thermal efficiency progress rate. In general, a secondary air
temperature at the boiler furnace inlet of a coal-fired thermal
power boiler is approximately 350.degree. C. Therefore, an
estimation example in FIG. 3 takes a point where air temperature at
the second air superheater outlet (the boiler furnace inlet) is
approximately 350.degree. C. as a reference point of gross thermal
efficiency.
[0026] In the present embodiment described above, the secondary air
superheater 7 allows solar thermal energy to further superheat the
secondary air (approximately 350.degree. C.) preheated by the
secondary air heater 4. For example, if the secondary air of
350.degree. C. is superheated up to 400.degree. C. by the secondary
air superheater 7, the gross thermal efficiency progress rate is
increased by about 0.8%. If the secondary air is superheated up to
450.degree. C., the gross thermal efficiency progress rate is
increased by about 1.6%. If the secondary air is superheated up to
500.degree. C., the gross thermal efficiency progress rate is
increased by about 2.4%. Incidentally, FIG. 3 shows the example in
which the secondary air is superheated up to 400 to 500.degree. C.
by the secondary superheater 7. However, the secondary air may be
superheated to over 500.degree. C. In this case, the dimensions of
the solar heat recovery apparatus such as the solar light
collecting mirrors 35 are increased according to the magnitude in
temperature which is increased by the secondary air superheater 7.
It is necessary, therefore, to determine the value of temperature
to be superheated by the secondary air superheater 7 after the
discussion on how much the area of a site at which to install the
solar heat recovery apparatus is great.
[0027] According to the embodiment described above, it is possible
to superheat the Boiler secondary air which is air for combustion
of a fossil-fuel-fired boiler to be supplied to the boiler furnace,
by using solar thermal energy of which energy cost is free. More
specifically, the secondary air having a conventional temperature
of approximately 350.degree. C. is superheated with solar heat by
approximately 50 to 150.degree. C. and the resulting secondary air
of approximately 400 to 500.degree. C. is supplied to the boiler
furnace. This can reduce coal heat-input to the boiler for the
entire boiler, thereby reducing boiler fuel consumption. As a
result, gross thermal efficiency can be improved significantly.
General large boilers allows a Ljungstroem air heater to heat air
for boiler combustion to approximately 350.degree. C. with exhaust
gas and the air for boiler combustion thus heated is taken into the
boiler. The solar heat recovery apparatus, which is necessary to
heat this air by approximately 50 to 150.degree. C. with solar
heat, can be downsized in comparison with the system configured to
superheat air to 1000.degree. C. from normal temperature as
described in the related art.
[0028] Incidentally, the gas turbine system that obtains air of
high temperature close to 1000.degree. C. from air of common
temperature through solar heat is as below. The necessary thermal
energy of flat mirrors reflecting and collecting solar heat is
enormous. The number of the necessary flat mirrors reaches half a
million. In addition, a plane area in which necessary sunlight
reflecting mirrors are installed is enormous. On the other hand,
the solar boiler system of the present embodiment just needs the
number of the flat mirrors that increases the secondary air of
approximately 350.degree. C. by approximately 50 to 150.degree. C.
Thus, the installation cost of the solar heat collector can be
suppressed significantly compared with that of the solar gas
turbine system.
[0029] The system based on the conventional technology described
earlier is such that the solar gas turbine and the generator are
installed on the place as high as approximately 100 m. Therefore,
the solar gas turbine or the generator is likely to be unstable in
operation. However, since in the boiler system of the present
embodiment it is not necessary to install on the high place a
rotating machine such as a generator or the like, system's stable
operation can be performed.
[0030] Since the solar heat quantity recovered per day varies from
morning to evening through daytime, the thermal energy of the
secondary air inputted to the boiler furnace varies accordingly.
However, the boiler system of the present embodiment can address
such variation by regulating the heat quantity of coal inputted to
the boiler furnace, i.e., the supply quantity of coal. Even if the
recovered solar heat quantity varies, regulating the quantity of
fuel inputted to the furnace can minimize variations in steam
temperature, in pressure and in quantity of evaporation. Thus, the
solar boiler system (the thermal power system) can be provided that
can operate such that the output of the turbine generator is
constant throughout the day regardless of day or night. The solar
boiler system of the present invention can be applied not only to a
new plant but also to a method of retrofitting an existing
coal-fired thermal power boiler. More specifically, equipment
installed additionally to the existing plant includes the solar
heat recovery apparatus composed of the solar light collecting
mirrors 35, the molten salt heat exchanger 47 and the heat medium
tank 30 and connection pipes and valves therefor. The equipment
also includes the secondary air superheater 7 installed
additionally to the secondary air system. Because of the additional
installation of the secondary air superheater 7, the secondary air
superheater bypass damper 5 and the secondary air superheater inlet
damper 6 are installed between the secondary air heater 4 of the
secondary air system and the wind box 9. As described above, the
existing boiler system is retrofitted to the solar boiler system,
whereby an improvement in efficiency can be achieved without
replacement of the overall boiler system.
* * * * *