U.S. patent application number 14/077732 was filed with the patent office on 2014-09-18 for steam turbine power plant.
This patent application is currently assigned to Hitachi, Ltd.. The applicant listed for this patent is Hitachi, Ltd.. Invention is credited to Naohiro KUSUMI, Kenichiro NOMURA, Fumiyuki SUZUKI, Yuichi TAKAHASHI, Masaaki TOMIZAWA, Kazunori YAMANAKA, Tatsuro YASHIKI, Takuya YOSHIDA, Yasuhiro YOSHIDA.
Application Number | 20140260254 14/077732 |
Document ID | / |
Family ID | 49582628 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140260254 |
Kind Code |
A1 |
YOSHIDA; Yasuhiro ; et
al. |
September 18, 2014 |
Steam Turbine Power Plant
Abstract
A steam turbine power plant includes heat-source equipment that
heats a low-temperature flow by applying a heat medium and thus
generates a high-temperature flow, a steam generator using the
high-temperature flow generated by the heat-source equipment, a
steam turbine driven by the steam generated by the steam generator,
an electric generator that converts rotational motive power of the
steam turbine into electric power, a heat-medium controller that
controls a supply rate of the heat medium supplied to the heat
source equipment, a low-temperature flow controller that controls a
supply rate of the low-temperature flow supplied to the heat-source
equipment, a prediction device that predicts startup constraints of
the steam turbine from control input variables of the controllers
when the steam turbine is started, and a control input variables
setter so as to prevent data predictions by the prediction device
from exceeding limit values of startup constraints.
Inventors: |
YOSHIDA; Yasuhiro; (Tokyo,
JP) ; YOSHIDA; Takuya; (Tokyo, JP) ; YASHIKI;
Tatsuro; (Tokyo, JP) ; KUSUMI; Naohiro;
(Tokyo, JP) ; NOMURA; Kenichiro; (Tokyo, JP)
; YAMANAKA; Kazunori; (Tokyo, JP) ; TOMIZAWA;
Masaaki; (Tokyo, JP) ; TAKAHASHI; Yuichi;
(Tokyo, JP) ; SUZUKI; Fumiyuki; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hitachi, Ltd. |
Tokyo |
|
JP |
|
|
Assignee: |
Hitachi, Ltd.
Tokyo
JP
|
Family ID: |
49582628 |
Appl. No.: |
14/077732 |
Filed: |
November 12, 2013 |
Current U.S.
Class: |
60/664 |
Current CPC
Class: |
Y02E 10/46 20130101;
Y02E 20/16 20130101; F01K 7/165 20130101; F01K 13/02 20130101; F01D
19/02 20130101; F22B 35/00 20130101 |
Class at
Publication: |
60/664 |
International
Class: |
F01K 13/02 20060101
F01K013/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 15, 2013 |
JP |
2013-054056 |
Claims
1. A steam turbine power plant, comprising: heat source equipment
that heats a low-temperature flow by applying a heat medium to
generate a high-temperature flow; a steam generator that generates
steam using the high-temperature flow generated by the heat source
equipment; a steam turbine driven by the steam generated by the
steam generator; an electric generator that converts rotational
motive power of the steam turbine into electric power; a heat
medium controller that controls a supply rate of the heat medium
supplied to the heat source equipment; a low-temperature flow
controller that controls a supply rate of the low-temperature flow
supplied to the heat source equipment; a prediction device that
predicts startup constraints of the steam turbine from control
input variables of the heat medium controller and the
low-temperature flow controller when the steam turbine is started;
a control input variables setter that sets the control input
variables of the heat medium controller and the low-temperature
flow controller from limit values of the startup constraints as
well as from a value predicted by the prediction device; and a
control signal output device that outputs command values to the
heat medium controller and the low-temperature flow controller in
response to the control input variables.
2. The steam turbine power plant according to claim 1, wherein the
prediction device computes at least one of a thermal stress and
differential thermal expansion of the steam turbine that occur
during a previously set prediction time period, as a predicted
value of the startup constraints.
3. The steam turbine power plant according to claim 2, wherein the
prediction time period is set to be long with respect to a response
time of the startup constraints relative to control of the heat
source equipment.
4. The steam turbine power plant according to claim 1, further
comprising: a measuring instrument that measures at least one of a
pressure and temperature of the steam supplied to the steam
turbine; wherein correction of a predicted value of the startup
constraints is based upon a value measured by the measuring
instrument.
5. The steam turbine power plant according to claim 1, wherein: the
heat source equipment is a gas turbine, the heat medium is a fuel,
and the low-temperature flow is a flow of air.
6. The steam turbine power plant according to claim 5, wherein:
when a load value of the gas turbine equals a previously set point,
the control input variables setter holds for a previously set time
the command values that are output to the heat medium controller
and the low-temperature flow controller.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to steam turbine power
plants.
[0003] 2. Description of the Related Art
[0004] It is being demanded that a starting time of a steam turbine
power plant be further reduced for suppressed instability of the
electric power in a grid-connected power system by connecting
renewable energy, represented by wind power generation or solar
power generation, to the power system. When the steam turbine is
started up, however, steam abruptly increases in both temperature
and flow rate. A consequential sudden increase in a surface
temperature of the turbine rotor relative to an internal
temperature thereof augments a radial temperature gradient and thus
increases a thermal stress. An excessive thermal stress could
shorten a life of the turbine rotor. In addition, if the change in
the temperature of the steam is significant, differential thermal
expansion due to a difference in heat capacity occurs between the
rotor and casing of the turbine. If the differential thermal
expansion increases, this could lead to contact between the
rotating turbine rotor and the stationary casing, and hence to
damage to both thereof. Accordingly, a starting state of the steam
turbine needs to be controlled to prevent the thermal stress of the
turbine rotor and the differential thermal expansion thereof with
respect to that of the casing from exceeding respective maximum
permissible levels (refer to Japanese Patent No. 4723884, shown as
Patent Document 1 below, and JP-2009-281248-A, shown as Patent
Document 2 below).
SUMMARY OF THE INVENTION
[0005] In Patent Documents 1, 2, however, the flow rate of the
steam supplied to the steam turbine is controlled by a control
valve to regulate the thermal stress and the differential thermal
expansion, so the thermal stress and the differential thermal
expansion are only regulated in a range that the control valve can
control the flow rate of the steam. Another problem exists with
energy efficiency since surplus steam is given away via a bypass
valve for reduced supply of the steam to the steam turbine.
[0006] The present invention has been made with the above in view,
and an object of the invention is to provide a steam turbine power
plant adapted to start operating very efficiently in an extended
control range of its startup constraints such as a thermal
stress.
[0007] In order to attain the above object, the present invention
includes heat source equipment that heats a low-temperature flow by
applying a heat medium to generate a high-temperature flow, a steam
generator that generates steam using the high-temperature flow
generated by the heat source equipment, a steam turbine driven by
the steam generated by the steam generator, an electric generator
that converts rotational motive power of the steam turbine into
electric power, a heat medium controller that controls a supply
rate of the heat medium supplied to the heat source equipment, a
low-temperature flow controller that controls a supply rate of the
low-temperature flow supplied to the heat source equipment, a
prediction device that predicts startup constraints of the steam
turbine from control input variables of the heat medium controller
and the low-temperature flow controller when the steam turbine is
started, and a control input variables setter that controls the
heat medium controller and the low-temperature flow controller so
as to prevent data predictions by the prediction device from
exceeding limit values of the startup constraints.
[0008] In accordance with the present invention, a steam turbine
power plant starts operating very efficiently in an extended
control range of thermal stresses and other startup
constraints.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic block diagram of a steam turbine power
plant according to a first embodiment of the present invention;
[0010] FIG. 2 is a flowchart that represents a starting control
sequence relating to the steam turbine power plant according to the
first embodiment of the present invention;
[0011] FIG. 3 is a supplemental explanatory diagram of the starting
control sequence relating to the steam turbine power plant;
[0012] FIG. 4 is a flowchart that shows details of step S104 in the
sequence of FIG. 2;
[0013] FIG. 5 is a schematic block diagram of a steam turbine power
plant according to a second embodiment of the present
invention;
[0014] FIG. 6 is a schematic block diagram of a steam turbine power
plant according to a third embodiment of the present invention;
[0015] FIG. 7 is a diagram showing an example of an operating
pattern for heat source equipment; and
[0016] FIG. 8 is an explanatory diagram of a method for controlling
heat source equipment of the steam turbine power plant according to
the first embodiment of the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0017] Hereunder, embodiments of the present invention will be
described using the accompanying drawings.
First Embodiment
1. Steam Turbine Power Plant
[0018] FIG. 1 is a schematic block diagram of a steam turbine power
plant according to a first embodiment of the present invention.
[0019] The steam turbine power plant shown in FIG. 1 includes heat
source equipment 1, a steam generator 2, a steam turbine 3, an
electric generator 4, a heat medium flow controller 12, a
low-temperature fluid flow controller 14, and a steam turbine
starting control device 21. An example in which the heat source
equipment 1 in the present embodiment is a gas turbine, that is,
the steam turbine power plant is of a combined-cycle type, is
described below.
[0020] The heat source equipment 1 uses the amount of heat
possessed by a heat medium (in the present example, a gas fuel, a
liquid fuel, a hydrogen-containing fuel, or the like), to heat a
low-temperature flow (in the example, a flow of air burned with the
fuel) and supply this heated flow as a high-temperature flow of
fluid (in the example, a combustion gas that has been used to drive
the gas turbine) to the steam generator 2. The steam generator 2
(in the present example, a waste heat recovery boiler) heats feed
water by heat exchange with the heat held by the high-temperature
fluid flow which has been generated by the heat source equipment 1,
and thereby generates steam. The steam thus generated by the steam
generator 2 is next used to drive the steam turbine 3. The electric
generator 4 is coaxially coupled to the steam turbine 3, and the
generator 4 converts rotational driving force of the steam turbine
3 into electric power. The electric power that the generator 4 has
generated is output to, for example, an electric power system (not
shown).
[0021] The heat medium flow controller 12 (in the present example,
a fuel control valve) is provided on a heat medium supply route
leading to the heat source equipment 1, and the heat medium flow
controller 12 controls a flow rate of the heat medium supplied to
the heat source equipment 1. The low-temperature fluid flow
controller 14 (in the present example, IGV) is provided on a
low-temperature fluid supply route leading to the heat source
equipment 1, and the low-temperature fluid flow controller 14
controls a flow rate of the low-temperature fluid supplied to the
heat source equipment 1. The controllers 12, 14 are each fitted
with a control input variables measuring instrument 11 or 13, by
which is measured a control input variable (in the present example,
a valve opening angle) of the controller 12, 14. The control input
variable of the controller 12, 14 that the control input variables
measuring instrument 11, 13 has measured is input to the steam
turbine starting control device 21.
2. Steam Turbine Starting Control Device
[0022] The steam turbine starting control device 21 includes a
prediction device 22, a control input variables setter 23, and
control signal output devices 24, 25. These elements are described
in order below.
(1) Prediction Device
[0023] During the startup of the steam turbine 3, the prediction
device 22 predicts, from the control input variable of the
controller 12, 14, future values of the startup constraints
estimated to be imposed upon the steam turbine 3 when a preset time
period elapses from the current time of day, and outputs the
predicted values to the control input variables setter 23 (in the
present example, a gas turbine controller). The preset time period
here refers to a prediction period (described later herein) or a
period that has been set to be longer than the prediction period.
The startup constraints refer to those changes in physical
quantities due to abrupt increases in steam temperature, steam
pressure, or the like, that will appear when the steam turbine 3 is
started. The physical quantities are a magnitude of a thermal
stress applied to a turbine rotor of the steam turbine 3, that of
axial differential thermal expansion in the turbine rotor and a
casing accommodating the turbine rotor, and other variables
developing during the start of the turbine. Hereinafter, when the
wording "thermal stress" is used, this simply means the thermal
stress upon the turbine rotor, and when the wording "differential
thermal expansion" is used, this simply means the axial
differential thermal expansion of the turbine rotor and the
casing.
[0024] The startup constraints computed by the prediction device 22
include at least one of the thermal stress and differential thermal
expansion of the steam turbine 3 that appear during the prediction
period. The prediction of the thermal stress, in particular, is
described below by way of example in the present embodiment. In
addition, the prediction period is a time that includes a response
time from a start of controlling the controller 12, 14 and
imparting a change to the amount of heat that the heat source
equipment 1 generates, until the steam turbine 3 has suffered a
change in startup constraint. That is to say, the prediction period
is the response time or a time that has been set to be longer than
the response time. The prediction period differs according to the
kind of startup constraint. For example, a time required for a
thermal stress to start changing for a reason such as a delay in
heat transfer is shorter than a time required for differential
thermal expansion to start developing for a reason such as the
delay in heat transfer.
[0025] Startup constraints can be calculated in accordance with the
known rules of thermodynamics and/or the rules of heat transfer
engineering. Thermal-stress calculation sequences that the
prediction device 22 executes are set forth below by way of
example.
[0026] Sequence A1
[0027] The control input variable of the controller 12, 14
corresponds to the supply rates of the heat medium and
low-temperature fluid to the heat source equipment 1 and is
therefore closely related to a thermal load state of the heat
source equipment 1. Accordingly, first a process in which heat and
matter propagate from the heat source equipment 1 through the steam
generator 2 to the steam turbine 3 is calculated from the control
input variable of the controller 12, 14 that the control input
variables measuring instrument 11, 13 has measured. Next, a flow
rate, pressure, temperature, and other plant physical quantities of
the steam that are estimated to be reached at an entrance of the
steam turbine 3 after the preset time period has elapsed are
further calculated from a result of that calculation. Predictive
computation of the plant physical quantities can be conducted by
first assuming that current change rates of the heat medium flow
rate and the low-temperature fluid flow rate (i.e., change rates of
the control input variable of the controller 12, 14) remain
invariant from the current time to the preset time period, then
calculating, from the value measured by the control input variables
measuring instrument 11, 13, a value that the control input
variable of the controller 12, 14 is estimated to take after the
elapse of the preset time period, and computing the plant physical
quantities from the calculated value of the control input variable
in the manner described above.
[0028] Sequence A2
[0029] Next on the basis of the calculation results in sequence A1,
pressures, temperatures, heat transfer coefficient, and other
variables at various stages of the steam turbine 3 are calculated
allowing for a pressure drop at a first stage of the steam turbine
3.
[0030] Sequence A3
[0031] Heat transfer of the steam to the turbine rotor is
calculated from the calculation results in sequence A2, and after
that, a temperature distribution in a radial direction of the
turbine rotor is calculated from a result of that calculation.
[0032] Sequence A4
[0033] Finally, a thermal stress estimated to occur after the
elapse of the preset time period is calculated from the calculation
result in sequence A3, pursuant to the rules of materials
engineering that use a coefficient of linear expansion, Young's
modulus, Poisson ratio, and/or the like.
[0034] The prediction device 22 executes the above sequences to
compute startup constraints at a predetermined sampling cycle, then
store the computed startup constraints, and output prediction time
periods of time-series data to the control input variables setter
23 for each prediction time period.
(2) Control Input Variables Setter
[0035] The control input variables setter 23 calculates control
input variables of the controller 12, 14 so that the data
predictions that have been input from the prediction device 22 fall
within a range of the limit values which have been set beforehand
in the process of starting the steam turbine 3. These control input
variables are calculated from deviations between the limit values
and a predicted value (e.g., a peak value) of the startup
constraints time-series data that has been input from the
prediction device 22, and the calculations are conducted so that,
for example, the predicted value does not overstep or approach the
limit values. The control input variables to reach the heat medium
flow controller 12 are output to the control signal output device
24 in advance, and the control input variables to reach the
low-temperature fluid flow controller 14 are output to the control
signal output device 25 in advance.
(3) Control Signal Output Devices
[0036] The control signal output device 24 computes a command value
addressed to the heat medium flow controller 12, from the control
input variables that the control input variables setter 23 has
calculated, and outputs the computed command value to the heat
medium controller 12. The command value to the heat medium
controller 12 is determined by numerically represented device
characteristics. In the present embodiment, the command value is
calculated from a fuel flow rate that satisfies a gas turbine load
command (MWD), for example. After the command value has been
output, the heat medium controller 12 executes PID control so that
the control input variable measured by the control input variables
measuring instrument 11 will be controlled to approach a target
value (set point) of the control input variable.
[0037] The control signal output device 25 computes a command value
addressed to the low-temperature fluid flow controller 14, from the
control input variables that the control input variables setter 23
calculated, and outputs the computed command value to the
low-temperature fluid flow controller 14. The command value to the
low-temperature fluid flow controller 14 is also determined by the
numerically represented device characteristics. In the present
embodiment, the command value is calculated from an air flow rate
that satisfies a gas turbine speed command, for example. After the
command value has been output, the low-temperature fluid flow
controller 14 executes PID control so that the control input
variable measured by the control input variables measuring
instrument 13 will be controlled to approach a target value (set
point) of the control input variable.
3. Starting Control Sequence
[0038] FIG. 2 is a flowchart representing a starting control
sequence that the steam turbine starting control device 21 conducts
for the steam turbine 3, and FIG. 3 is a supplemental explanatory
diagram of the starting control sequence.
[0039] Steps S101 to S103
[0040] Steps S101 to S103, shown in FIG. 2, constitute a startup
constraints prediction data-sampling sequence that the prediction
device 22 executes. That is to say, the steam turbine starting
control device 21 starts the data-sampling sequence to start the
steam turbine 3, and after this, the controller 21 activates the
prediction device 22 to compute the plant physical quantities that
the plant is estimated to have after the elapse of the preset time
period (step S101), and then compute startup constraints from the
computed plant physical quantities (step S102). The plant physical
quantities computation sequence and the startup constraints
computation sequence are as described above. In addition, since the
present embodiment assumes that as described above, the control
input variable of the controller 12, 14 changes at a current rate
of change within the preset time period to ensure a lighter
processing load, the startup constraints are calculated assuming
such linear changes in startup constraint (in the present example,
thermal stress) 201 that are shown in FIG. 3.
[0041] After the calculation of the startup constraints, the
prediction device 22 determines whether the prediction period has
passed from the start of the steam turbine (step S103), and next
until the prediction period has passed, repeats steps S101-S103 to
sample computed startup constraint values at fixed cycles
(processing cycles of steps S101-S103). After the sampling of the
computed startup constraint values corresponding to the prediction
period, the steam turbine starting control device 21 shifts
sequence control to steps S104 to S107.
[0042] Steps S104 to S107
[0043] Steps S104 to S107 constitute a sequence that the control
input variables setter 23 executes, and this sequence is a control
sequence executed for the controller 12, 14.
[0044] In step S104, the control input variables of the controllers
12, 14 are computed from the prediction period of predicted startup
constraints time-series data that was obtained in the sampling
sequence of steps S101-S103. In step S105, command values are
output to the controllers 12, 14 via the control signal output
devices 24, 25 and the corresponding control input variables of the
controllers 12, 14 are corrected. In the present embodiment, as
indicated by an arrow 202 in FIG. 3, a time 203 at which the
command values are output to the controllers 12, 14 in step S105 is
short relative to the prediction period, only occupying an initial
certain time of the prediction period (this certain time is
hereinafter referred to as the control input update interval). A
plurality of programs to execute here the sequence shown in FIG. 2
are active at cycles of the control input update interval, with
time differences. Accordingly the command values are newly imparted
to the controllers 12, 14 at the cycles of the control input update
interval by the programs active with the time differences. Thus the
command values based on the predicted startup constraints data
corresponding to the prediction period longer than a response time
of the startup constraints are imparted to the controllers 12, 14
at a cycle shorter than the prediction period. If the number of
programs which execute the sequence of FIG. 2 with the time
differences is taken as A, the prediction period equals a value
obtained by multiplying the control input update interval by A, so
this enables overlapped output of the same command value to be
avoided while ensuring continuity of the output of the command
values.
[0045] After the output of the command signals to the controllers
12, 14, whether startup completion conditions are satisfied is
determined in step S106. If the conditions are satisfied, the
sequence in FIG. 2 is completed, and if the conditions are not
satisfied, sequence control is returned to a very beginning (START)
of the starting control sequence, as shown in FIG. 2. The startup
completion conditions here are conditions that become a basis for
determining whether the steam turbine power plant has shifted to
rated operation (e.g., whether the fuel flow rate, the turbine
output, the generator output, and the like have reached respective
ratings), and these conditions are defined on a plant-specific
basis. This means that up until the startup completion conditions
have been satisfied, that is, during the starting control sequence,
the steam turbine starting control device 21 will execute the
sequence of FIG. 2 at the cycle of the prediction period.
[0046] Look-ahead control of the physical quantities of the steam
generated by the steam generator 2 will be conducted by repeated
execution of the above sequence.
4. Control Input Variables Computation Sequence
[0047] FIG. 4 is a flowchart that shows details of step S104 in the
sequence of FIG. 2.
[0048] In the flowchart of FIG. 4, whether the startup constraints
are less than respective threshold values (set points) is
determined first (step S104a). Each of the threshold values differs
according to the kind of startup constraint, and is a value that
has been set to be smaller than a corresponding limit value, for
example, a value of 90% of the limit value. If the startup
constraints are less than the threshold values, the control input
variables of the controllers 12, 14 are set to increase the flow
rates of the heat medium and the low-temperature fluid (steps
S104b, 104c). If the startup constraints are equal to or greater
than the threshold values, the control input variables of the
controllers 12, 14 are set to reduce the flow rate of the heat
medium (step S104d) and maintain that of the low-temperature fluid
(step S104e). Based on differences between, for example, the peak
values and limit values (set points for each startup constraint) of
the time-series data obtained within the prediction period, control
input variables are set so that the startup constraints occurring
after the elapse of the preset time period will fall within the
ranges of the limit values. After execution of steps S104b, S104c
or steps S104d, S104c, step S104 is finished and then control is
shifted to step S105. Order of execution of steps S104b, S104c may
be reversed. The same also applies to steps S104d, S104e.
5. Beneficial Effects
[0049] The present embodiment yields the following beneficial
effects.
(1) Rapid Start of the Steam Turbine
[0050] In accordance with the present embodiment, the amount and
temperature of steam generated by the steam generator 2 can be
controlled by controlling at least one of the flow rates of the
heat medium and low-temperature fluid supplied to the heat source
equipment 1, an element provided at a front stage of the steam
generator 2. For example, the steam temperature can be mainly
controlled by operating the heat source flow controller 12 and
controlling the flow rate of the heat medium. This is because the
steam temperature changes with a temperature of a high-temperature
fluid supplied to the steam generator 2. Additionally, the flow
rate of the steam can be mainly controlled by operating the
low-temperature fluid flow controller 14 and controlling the flow
rate of the low-temperature fluid. This is because controlling the
flow rate of the low-temperature fluid controls that of the
high-temperature fluid, hence changing the amount of steam
generated in the steam generator 2.
[0051] Thus, the flow rate and temperature of the steam that are
the physical quantities closely associated with the startup
constraints such as a thermal stress and differential thermal
expansion can both be regulated. This in turn enables the steam
flow and the steam temperature to be controlled flexibly according
to a particular state of the steam turbine 3, and thus allows the
steam turbine 3 to be started rapidly in an appropriate way.
[0052] In addition, since the amount of steam generated can itself
be increased, a starting time of the steam turbine can be reduced
relative to a conventional configuration in which a flow rate of
steam which has already been generated in a steam generator is
controlled by a control valve and then the flow rate of the steam
supplied to a steam turbine is regulated. In the conventional
configuration, the flow rate of the steam is limited to a narrow
regulating range, so while the flow of the steam might be capable
of being throttled down with the control valve, the flow rate of
the steam cannot be increased.
(2) Suppressed Energy Loss
[0053] In the present embodiment, since the amount of steam
generated in the steam generator 2 can itself be controlled, the
steam temperature and the amount of steam generated can be
controlled flexibly in response to operating conditions. This
enables energy loss to be suppressed relative to the conventional
configuration in which a surplus of the steam which has already
been generated is given away via a bypass valve for regulated steam
flow.
(3) Highly Efficient and Accurate Predictive Calculation
[0054] In a case of a general configuration in which a thermal
stress and the like are predicted and a supply rate of steam
supplied to a steam turbine is controlled with a control valve,
predictive calculation is usually executed in a plurality of
patterns for one output operation on a command value for an opening
angle of the control valve. This calculation method is intended to
raise adequacy of control by adopting predictive calculation
results of the patterns as a choice or option. This method,
however, applies an extremely significant calculation load due to
executing the predictive calculation of the patterns, makes it
absolutely necessary to impart a margin to a calculation capacity
of a control panel or switchboard so that the predictive
calculation follows a change in startup constraint, and/or requires
a high level of know-how for construction of an algorithm for
increasing a calculation speed.
[0055] In a case of the present embodiment, on the other hand,
faster predictive calculation can be implemented by limiting a
transition assumed of the change rates of the values measured by
the control input variables measuring instruments 11, 13, to one
pattern, and applying this pattern to the predictive calculation
only. As a result, a sampling period at which the predicted values
of the plant physical quantities can be enhanced and the control
input variables can be correspondingly controlled more frequently.
This provides high prediction accuracy, and yet suppresses
calculation throughput, so reducing restrictions on a memory, clock
frequency, and other factors of a control panel or switchboard.
High contribution to application and operation of an easy-to-mount
and stable actual machine is anticipated as well. Furthermore, if a
time longer than the response time of the startup constraints is
set as the prediction period, this improves prediction accuracy of
the intended startup constraints.
Second Embodiment
[0056] FIG. 5 is a schematic block diagram of a steam turbine power
plant according to a second embodiment of the present invention. In
the figure, substantially the same elements as in the first
embodiment are each assigned the same reference number as on the
shown drawings, and description of these elements is omitted
herein.
[0057] As shown in FIG. 5, the present embodiment differs from the
first embodiment in that the former includes a function that
corrects the predicted values of the plant physical quantities. To
be more specific, the steam turbine power plant shown in the figure
includes a pressure gauge 15 and a temperature gauge 16 on a steam
line connecting the steam generator 2 and the steam turbine 3. The
pressure and temperature of the steam supplied to the steam turbine
3 are measured by the pressure gauge 15 and the temperature gauge
16, respectively, and then input with the values measured by the
control input variables measuring instruments 11, 13 to the
prediction device 22. The prediction device 22 then uses the
measurements by the pressure gauge 15 and the temperature gauge 16
to correct the plant physical quantities that have been predicted
from the values measured by the control input variables measuring
instruments 11, 13.
[0058] During plant operation, for example, a certain correlation
is likely to occur between the predicted values and measured values
of the steam pressure and the steam temperature. For example, the
predicted value may be calculated as a certain level higher or
lower than the measured value. Such a correlation is stored as a
relational expression or a table in a data storage region of the
prediction device 22. When the prediction device 22 conducts a
predictive calculation of the plant physical quantities in
accordance with sequence A1, the predicted values that have been
calculated from the values measured by the control input variables
measuring instruments 11, 13 are corrected on the basis of the
values measured by the pressure gauge 15 and the temperature gauge
16. The prediction device 22 conducts the correction in accordance
with the above correlation. After the correction, the device 22
executes sequences A2-A4 and calculates the predicted values of the
startup constraints on the basis of the plant physical quantities
obtained after the correction.
[0059] All other factors, including the configuration and the
control sequences, are substantially the same as in the first
embodiment.
[0060] The present embodiment yields substantially the same
beneficial effects as those of the first embodiment. In addition,
enhancing the accuracy of the predicted values of the plant
physical quantities by the correction also improves the prediction
accuracy of the startup constraints and ensures adequate starting
control of the steam turbine 3.
[0061] While an example of correcting the predicted values of both
the steam temperature and the steam pressure has been described in
the present embodiment, the pressure gauge 15 and the temperature
gauge 16 may be omitted to correct only one of the two values.
Third Embodiment
[0062] FIG. 6 is a schematic block diagram of a steam turbine power
plant according to a third embodiment of the present invention. In
the figure, substantially the same elements as in the first and/or
second embodiment are each assigned the same reference number as on
the shown drawings, and description of these elements is omitted
herein.
[0063] The present embodiment differs from the first and second
embodiments in that operation depends upon an operation mode of the
heat source equipment 1. More specifically, a control input
variables setter 26 in the present embodiment has a command hold
function, that is, when the load (gas turbine load) upon the heat
source equipment 1 reaches a preset load value (e.g., a load value
predefined during plant operation planning), command values
addressed to the controllers 12, 14 are held for a fixed time by
the above hold function of the setter 26.
[0064] In general, a plurality of specific bands on which the load
is to be held are set for the gas turbine and this load often needs
to be held for a preset time with each arrival of the load at one
of the bands. When a power plant equipped with a gas turbine having
such an operational restriction is started, load hold and a load
change are repeated as shown in FIG. 7. The present embodiment is
geared to such a restriction on a starting control method.
[0065] FIG. 8 is an explanatory diagram of a method for controlling
the heat source equipment 1 by use of the control input variables
setter 26.
[0066] During the starting control sequence, the control input
variables setter 26 computes the load of the heat source equipment
1. The heat source load 1 can be computed from the heat source flow
rate (the value measured by the heat source flow controller 12)
and/or the like. The control input variables setter 26 determines
at all times whether the load of the heat source equipment 1 has
reached any one of various load set points, and if the load of the
heat source equipment 1 has reached one of the load set points and
needs to be held for operational reasons, the setter 26 sets a load
hold time as shown in an example of FIG. 8A. For example, when a
difference derived by subtracting a peak value of a predicted
thermal stress from a thermal stress limit value is expressed as
AG, if AG in the example of FIG. 8A is a plus value, the load hold
time is set to be shorter with greater AG, and if AG is a minus
value, the load hold time is set to be longer with greater
.DELTA..sigma.. Additionally, the control input variables setter 26
outputs the current control input variables as target values to the
control signal output devices 24, 25 without depending upon the
predicted values that are input from the prediction device 22.
After that, the setter 26 holds the settings of the target control
input variables until the preset time has passed. After the preset
time has passed, control is shifted to variable control of the load
of the heat source equipment 1. When the operation state of the
heat source equipment 1 is a load change, the control input
variables setter 26 executes the variable control of the load of
the heat source equipment 1 without executing the control input
variables hold sequence described above.
[0067] When the control input variables setter 26 executes the
variable control of the load of the heat source equipment 1, the
setter 26 sets a load change rate command value (control input
variables) as shown in FIG. 8B, and outputs the command value to
the control signal output devices 24, 25. For example, if the value
of AG is plus, the load change rate is set to be greater according
to the particular value of AG, and if the value of AG is minus, the
load change rate is set to be smaller according to the value of AG.
When the load of the heat source equipment 1 reaches another set
point as a result of such variable control, the preset time is held
once again and the control of the control input variables is
returned to variable control.
[0068] Thus, even if the heat source equipment 1 has operational
restrictions on the transition of the load, the present embodiment
provides substantially the same beneficial effects as those of the
first and second embodiments.
Other Examples
[0069] While examples of calculating a thermal stress as a startup
constraint with the prediction device 22 have been described in the
first to third embodiments, differential thermal expansion or both
of a thermal stress and differential thermal expansion may be
calculated as a control input variable(s). Examples of calculation
sequences relating to the calculation of differential thermal
expansion are shown as sequences B1 to B5 below.
[0070] Sequence B1
[0071] The flow rate, pressure, temperature, and other factors of
the steam that are estimated to be reached at the entrance of the
steam turbine 3 after the preset time period has elapsed are
calculated in substantially the same manner as that of thermal
stress calculation.
[0072] Sequence B2
[0073] On the basis of calculation results obtained in sequence B1,
the pressures, temperatures, heat-transfer coefficients, and other
factors of various sections of the turbine rotor and the casing are
calculated allowing for pressure drops at the various sections of
the turbine rotor and the casing.
[0074] Sequence B3
[0075] Temperatures of various sections of the turbine rotor and
casing as cut in an axial direction of the turbine are calculated
by heat-transfer calculation based on results of the calculation in
sequence B2.
[0076] Sequence B4
[0077] The amounts of axial thermal change (expansion) of the
turbine rotor and casing are calculated from results of the
calculation in sequence B3.
[0078] Sequence B5
[0079] On the basis of calculation results obtained in sequence B4,
differential thermal expansion of the turbine rotor and casing
after the elapse of the preset time period is calculated in
accordance with, for example, the rules of materials engineering
that uses a coefficient of linear expansion.
[0080] In addition, while a combined-cycle power plant has been
taken by way of example, the present invention can be applied to
substantially all types of power plants including steam turbines,
represented by steam power plants and solar thermal power plants.
Sequences to be used to start these power plants are also
substantially the same as in the embodiments.
[0081] For example, when the present invention is applied to a
steam power plant, coal or natural gas is equivalent to the heat
source, air or oxygen to the low-temperature fluid, a fuel control
valve to the controller 12, 14, a boiler furnace to the heat source
equipment 1, a combustion gas to the high-temperature fluid, a
boiler heat transfer section (steam-generating section) to the
steam generator 2, and a boiler load controller to the control
input variables setter 2.
[0082] For example, when the present invention is applied to a
solar thermal power plant, solar light is equivalent to the heat
source, a heat-collecting panel drive to the heat medium flow
controller 12, a heat-collecting panel to the heat source equipment
1, a heat-collecting panel direction/angle measuring instrument to
the control input variables measuring instrument 11, an oil, a
high-temperature solvent salt, or any other appropriate
solar-energy conversion and hold medium to the low-temperature
fluid and the high-temperature fluid, an oil flow control valve to
the low-temperature fluid flow controller 14, and a control input
variables setter to the control input variables setter 23.
[0083] Alternatively, the steam pressure, steam temperature, and
fuel flow rate that are entered in a predictive calculation method
32 may only be replaced by steam pressure or steam temperature and
a predictive calculation of a thermal stress may be conducted.
[0084] Furthermore, the plant physical quantities may include a
temperature, pressure, flow rate of exit steam as well as those of
entrance steam, the steam flowing into the steam turbine 3.
Increasing the number of kinds of information about the plant
physical quantities allows startup constraint prediction accuracy
to be improved. Besides, while the values measured by the control
input variables measuring instruments 11, 13 have been adopted as
the control input variables of the controllers 12, 14 that are to
be used for the predictive calculation of the startup constraints,
those measured values may instead be replaced by the command values
that are output to the controllers 12, 14.
* * * * *