JPH0226122B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a once-through boiler, and in particular to a water supply control device thereof.

Normally, a once-through boiler has a pipe line between the water supply inlet and the steam outlet, and the evaporation section does not form a circulation circuit, as in, for example, a drum boiler.
That is, in a once-through boiler, feed water preheated by an economizer is sent to an evaporator, and flows through to the evaporator outlet due to the pushing pressure of the feed water pump. During this time, the feed water is heated and evaporated, and the generated steam is led to a superheater. Since this once-through boiler does not have a drum that holds a large amount of water, it has a small heat storage capacity and takes a short time to start up. It also has excellent load followability, and can therefore be made smaller and lighter. It has characteristics. For this reason, once-through boilers are often used for intermediate load thermal power generation and exhaust gas energy recovery plants. For the above-mentioned exhaust gas energy recovery, the energy of exhaust gas that was previously wasted in waste incinerators and diesel engines is recovered by a once-through boiler, and the steam obtained here is used to drive, for example, a turbine and power There are also examples of attempts to recover energy as electricity. That is, electric power is recovered by driving a generator with a steam turbine, and power is recovered by driving a propulsion main shaft with a steam turbine in a ship or the like.

There is a so-called combined plant that combines a gas turbine and a once-through boiler that uses the gas turbine's exhaust gas as a heat source, and uses the steam generated from the boiler to drive a steam turbine to recover power or electric power. Recently, it has attracted particular attention as a plant suitable for making use of the advantages of turbines while improving their disadvantage of poor thermal efficiency.

Furthermore, unlike ordinary single-fire boilers, the heating intensity of boilers that use exhaust gas from waste incinerators, diesel engines, gas turbines, etc. as their heat source is determined by other factors and cannot be adjusted freely. This is because the degree of heating can be controlled by adjusting the amount of fuel sent to the burner in a normal dedicated boiler, but in a boiler that uses exhaust gas as a heat source, the exhaust gas boiler supplies the load to a diesel engine, gas turbine, or waste incinerator. The degree of heating of the boiler depends on the amount and quality of the waste, and cannot be freely adjusted. Therefore, the main role of a control device for an exhaust gas boiler is to control the amount of water supplied to the boiler in accordance with the energy of the exhaust gas, unlike a control device for a normal dedicated boiler.

However, in a once-through boiler, if the heating is too strong compared to the amount of water supplied, the flow becomes unstable, which not only prevents the boiler from producing stable steam but also burns out the boiler pipes. Flow instability tends to occur more easily when the feed water temperature is low. Conventional once-through boilers are designed to prevent the phenomenon of unstable flow by inserting a restriction in the middle of the pipe to increase pressure loss in the pipe. However, if the load changes suddenly or the feed water temperature drops due to a malfunction in the feed water heater, etc., and the flow deviates from the planned conditions, flow instability is likely to occur, especially when the boiler load is high. It appears strongly.

The control devices for once-through boilers that use exhaust gas as a heat source are not able to adequately deal with the above-mentioned flow instability. If the water supply temperature drops, there is a risk of unstable flow phenomena. This will be further explained in detail below with reference to the drawings regarding a conventional example.

FIG. 1 is an example of a pipe system diagram of the above-mentioned combined plant. Exhaust gas from a gas turbine 1 passes through a duct 2 and reaches a once-through boiler 3, where it is heated and discharged from a stack 4 to the outside of the system. On the other hand, the feed water is pressurized by a water feed pump 5 and its flow rate is adjusted by a water feed valve 6, and then passed through a pipe _7a to be supplied to the once-through boiler 3. The water channel in the once-through boiler 3 is constituted by a pipe line _7b , and the feed water is heated by the exhaust gas of the gas turbine 1 and turned into superheated steam, which is sent to the steam-water separator 8 via the pipe line _7c . The steam separator 8 and the steam turbine 9 are connected via a pipe _7d and a main steam valve 10, and superheated steam is sent to the steam turbine 9 to drive a load (not shown). The steam that has passed through the steam turbine 9 is condensed in a condenser 11, pumped out by a condensate pump 12, sent to a drain tank 13, heated in a feed water heater 14, and then transferred to a feed water pump 5.
The water is sent to the water supply facility and used again as a water supply.

50 is a conventional control device for the once-through boiler 3, which includes a rotation speed meter (rotation speed of the low-pressure compressor of the gas turbine) 20 of the gas turbine 1, an intake air temperature meter 21 of the gas turbine, an exhaust gas temperature meter 22 of the gas turbine,
The control signal is outputted to the water supply valve 6 by inputting the output signals of the exhaust gas thermometer 23 of the once-through boiler and the steam thermometer 24 at the outlet of the once-through boiler, respectively. That is, since the water supply pump 5 is operated at a constant rotation, the amount of water supplied to the once-through boiler 3 is adjusted by adjusting the opening degree of the water supply valve 6.

Here, the control device 50 will be explained in detail based on FIG. 2 showing an example of the configuration of a conventional block connection diagram.The amount of air passing through the gas turbine 1, that is, the amount of exhaust gas can be estimated with high accuracy from the rotation speed of the low-pressure compressor of the gas turbine. It has been known. Here, the function generator 101 in the control device 50 receives the rotation speed N ₁ from the low-pressure compressor rotation speed meter 20 and the intake air temperature meter 21.
The temperature output T ₀ is input and the exhaust gas flow rate is determined based on the predetermined characteristics of the gas turbine.
Estimate and output G _g . Note that the intake air temperature gauge 2
The temperature output T ₀ of 1 is used as a parameter to estimate the exhaust gas flow rate G _g with higher accuracy.
On the other hand, the temperature output T 3 of the exhaust gas thermometer 22 of the gas turbine 1 and the temperature output T ₂ of the exhaust gas thermometer ₂₃ of the boiler
is input to the subtractor 103, and its temperature difference ΔT is calculated and output. Exhaust gas flow signal G _g and temperature difference △T
is multiplied by a multiplier 102 to output a boiler heat reception (expected) signal G _g ·ΔT which is proportional to the boiler heat reception, and this value is input to the next function generator 104.

The function generator 104 has a function shape set in advance based on the characteristics of the boiler, and has a function of calculating the generated steam amount signal G _s from the boiler received heat amount signal. The temperature output T ₃ of the exhaust gas thermometer 22 of the gas turbine 1 is input to the function generator 105 as well as the subtractor 103, where the set value T^ ₄ of the steam temperature at the boiler outlet is calculated. Note that the function generator 105 has a function shape set in advance so that the plant efficiency is maximized. The output temperature _T4 of the steam thermometer 24 at the boiler outlet and T^, which is the output of the function generator 105, are compared in a subtracter 106, and the difference _ΔT4 is calculated using a known proportional plus integral type amplifier.
It is input to the adder 108 as a corrected steam amount signal via the PI controller 107, and the adder 108 calculates the water supply amount from the generated steam amount and the corrected steam amount, and supplies water to the water supply valve 6 so as to supply water commensurate with this water supply amount. Outputs control signal S _c1 .

Next, the operation of the control device 50 illustrated in FIG. 2 will be explained. When the load on the gas turbine 1 changes, the flow rate of exhaust gas and the temperature at the entrance and exit of the once-through boiler 3 change accordingly, and the heating of the once-through boiler 3 changes accordingly. The degree is also affected. Such a change in the operating state of the boiler is detected by the control device 50, and the amount of water supplied is adjusted. That is, the function generator 101 generates the exhaust gas flow rate signal G _g , and the subtractor 103 generates the gas temperature difference △ at the inlet and outlet of the boiler.
The boiler received heat amount (expected) signal G _g and ΔT, which is the output of the multiplier 102 where T is output, respectively, indicates the amount of heat received in the new operating state of the boiler. The amount of water to be supplied corresponding to this new amount of received heat is calculated by the function generator 104, and the generated steam amount signal G _s and the PI controller 10
The water supply valve 6 is supplied via an adder 108 so as to supply water commensurate with the sum of the corrected steam amount signal from 7.
The water supply control signal S _c1 is output.

Due to changes in the operating conditions of the boiler, the steam temperature _T4 at the boiler outlet changes, but the function generator 105 also changes the set value of the steam temperature according to the exhaust gas temperature output _T3 of the gas turbine 1, so the steam temperature remains at the optimum steam temperature. constantly adjusted to suit conditions. Note that the water supply valve 6 is a known valve that can adjust the amount of water supply according to the water supply control signal S _c1 .

Here, when fluctuations in the feed water pump 5 due to external disturbances such as fluctuations in output due to fluctuations in rotational speed or fluctuations in feed water temperature are small, or when load fluctuations in the gas turbine are slow, the control device 50 illustrated in FIG. To control a boiler stably and accurately. but,
If the fluctuations due to the above-mentioned disturbances or the fluctuations in the load of the gas turbine are large, it cannot be said that sufficient control is achieved.

Gas turbines have the characteristics of being easy to start and stop and have excellent load followability, so the load often changes suddenly, but once-through boilers need to operate stably even in such cases. There is. In this control device 50, when the load on the gas turbine 1 suddenly increases, for example, the multiplier 102
The amount of heat received by the boiler (estimated) which is the output of G _g・△T
increases, and the feedwater control signal S _c1 also increases immediately, but the steam output temperature T ₄ at the boiler outlet does not change immediately due to the heat storage capacity of the boiler itself, and on the other hand, the gas turbine Exhaust gas temperature output of gas turbine as load increases in 1.
Since T ₃ increases immediately, the deviation ΔT ₄ which is the output of the subtractor 106 shows a large negative deviation. This large negative deviation △T ₄ acts in the direction of restricting the water supply, so the amount of water supply becomes extremely small compared to the boiler received heat amount (expected) G _g · △T, causing flow instability.

Furthermore, this tendency is also affected by the feed water temperature T ₁ . For example, if the feed water temperature T ₁ becomes low due to a failure of the feed water heater 13, not only will it not be possible to obtain optimal steam conditions, but the flow will also be affected. It can also cause instability.

On the other hand, if the load on the gas turbine 1 suddenly decreases, a phenomenon opposite to the above-mentioned case of a sudden increase will occur. In other words, as the amount of heat received by the boiler (expected) G _g △T decreases, the feed water control signal S _c1 decreases accordingly, but due to the heat storage capacity of the boiler itself, the output temperature of steam at the boiler outlet T ₄ changes quickly. On the other hand, as the load on the gas turbine 1 decreases, the exhaust gas temperature output _T3 of the gas turbine immediately decreases, so the deviation _ΔT4 , which is the output of the subtractor 106, shows a large positive deviation. This large positive deviation △
T ₄ acts in the direction of increasing water supply.

The once-through boiler, which is temporarily supplied with more water than necessary, supplies steam with a low degree of superheat to the steam turbine. That is, when the feed water temperature is low or when the rate of decrease in the load on the gas turbine 1 is excessive, wet steam is supplied to the steam turbine 9. Steam with a low degree of superheat or wet steam not only deteriorates the efficiency of the steam turbine but also damages the turbine blades due to drain attack. This tendency is particularly noticeable in combined plants where the exhaust gas temperature is low and the degree of superheat is low.

The present invention was made to solve the above-mentioned problems in once-through boilers, and by adding a few parts to existing equipment, it is possible to prevent flow instability even when the boiler heating amount suddenly changes, and to prevent steam The purpose is to provide a control device that does not cause drain attack on the turbine, that is, a means for calculating the amount of heat received by the boiler from the flow rate of exhaust gas for heating the boiler and the temperature difference between the exhaust gas at the inlet and outlet of the boiler, and a method for calculating the amount of heat received by the boiler. means for calculating the amount of steam generated from the steam temperature; and means for calculating the corrected steam amount from the deviation between the set value of the steam temperature at the boiler outlet calculated from the exhaust gas temperature at the boiler inlet and the measured value of the steam temperature at the boiler outlet; A control device for a once-through boiler that adjusts the amount of water supply and has means for calculating the amount of water supply from the amount of steam generated and the amount of corrected steam, comprising means for calculating the amount of stable water supply from the amount of heat received by the boiler, and a means for calculating the amount of water supply from the amount of heat received by the boiler; means for comparing the water supply amount and selecting the larger value as the calibrated water supply amount; means for calculating the minimum water supply amount of the boiler from the heat received by the boiler and the water supply temperature; and the minimum water supply amount and the calibration water amount. Compare the amount of water supplied,
This is a control device for a once-through boiler, characterized in that it is equipped with a means for shutting off a steam passage supplying a load when the minimum water supply amount is large and this state continues for a certain period of time or more, and the following is an embodiment of the present invention. will be explained with reference to the drawings.

FIG. 3 is a block connection diagram showing Embodiment 51 of the control device of the present invention. In addition to the circuit configuration of the conventional control device shown in FIG.
and 114, high-level selector 111, comparator 11
2. A timer 113 is added, and the boiler feed water temperature _T1 of the feed water thermometer 25 attached to the pipe _7a is added as an input signal, and in addition to the feed water control signal 2nd stage S _c2 , the turbine trip water supply system is It is configured to output an abnormal signal E _s .

Here, the boiler received heat amount (estimated) G _g ·ΔT and the boiler feed water temperature T ₁ which are the output signals of the multiplier 102 are input to the function generator 110 . The function generator 110 calculates a stable water supply amount to the boiler with a slight margin to the limit at which unstable flow occurs in the boiler.
G _snio is calculated and output to the high-level selector 111. The specific value of the function of the function generator 110 varies depending on the type and size of the boiler, and is calculated based on the design of each boiler or determined based on the value obtained as a result of factory test operation. The unstable flow phenomenon becomes more likely to occur as the heating of the boiler increases, as the feed water temperature T ₁ decreases, and as the water supply decreases, so generally speaking, the amount of heat received by the boiler (expected) G _g The boiler stable water supply amount G _snio also increases as the temperature increases, and if the water supply temperature T ₁ decreases, the boiler stable water supply amount G _snio increases.

In addition to the above-mentioned stable water supply amount G _snio , the high-level selector 111 receives a water supply control signal S _c1 which is the output of the adder 108.
is connected, and the signal with the larger value of these two is selected as the calibrated water supply amount, and the water supply control signal is sent to the second stage.
Output as S _c2 .

The function generator 114 contains the amount of heat received by the boiler (estimated)
G _g・△T and feed water temperature T ₁ are input, and this T ₁
Here, the minimum water supply amount G _fnio of the boiler is calculated using the value of as a parameter, and is output to the comparator 112.

The steam conditions at the boiler outlet are determined by the heat balance between the amount of water supplied to the boiler and the amount of heating by the boiler. That is, C _p・G _g・△T=G _f (is-if) ...Equation (1) where C _p is the specific heat of gas (Kcal/Kg℃) G _g is the exhaust gas flow rate (Kg/sec.) △T is Differential temperature of gas at boiler inlet and outlet (℃) G _f is water supply amount (Kg/sec.) is is boiler outlet enthalpy (Kcal/Kg) if is feed water enthalpy (Kcal/Kg) (Feed water enthalpy if is feed water temperature T (approximately equal to ₁ ) If the enthalpy at the boiler outlet falls too much, drain attack will occur in the steam turbine as described above, so the enthalpy at the boiler outlet will decrease.
is has a permissible lower limit value, and that value is defined as i _snio .
The allowable lower limit value i _snio of the enthalpy at the boiler outlet is a value unique to the steam turbine that depends on the type of steam turbine, the material and shape of the blades, etc. From the above equation (1), the minimum water supply amount G _fnio of the boiler is determined by the following equation (2).

G _fnio = C _p・G _g・△T/i _snio −T ₁ …(2) Formula The function generator 114 combines a subtracter, a divider, and a coefficient unit, and calculates the boiler heat received (expected) G _g・△T The minimum water supply amount G _fnio may be calculated from two inputs: and the water supply temperature T ₁ using the value of T ₁ as a parameter. Also, using equation (2) above, the minimum water supply amount is
The relationship between G _fnio , boiler heat received (expected) G _g ·ΔT, and feed water temperature T ₁ may be calculated in advance, and a known function generator may be used in combination with a plurality of diodes, resistors, and amplifiers.

The comparator 112 is connected as input to the water supply control signal 2-stage S _c2 which is the output of the high-level selector 111 and the minimum water supply amount G _fnio of the boiler which is the output of the function generator ₁₁₄ . When the timer 113 is large, the timer 113 of the next stage is set.

The timer 113 is constituted by, for example, a known on-delay motor timer, and outputs a water supply system abnormality signal _Es when the set state continues for a certain period of time or more. The water supply system abnormality signal _Es is transmitted through another drive circuit (not shown) to fully close the main steam valve 10 in FIG. 1, fully open the bypass valve 14, and output an alarm such as a buzzer.

Next, the operation of the control device shown in FIG. 3 will be explained. In the boiler load settling state, adder 1
The water supply control signal S _c1 , which is the output of the function generator 110, is larger than the boiler stable water supply amount G _snio , which is the output of the function generator ₁₁₀ .
The output S _c1 of is selected. Further, since the second stage water supply control signal S _c2 is larger than the minimum water supply amount G _fnio which is the output of the function generator 114, the timer 113 is not set. Here, when the load on the gas turbine 1 increases rapidly, the boiler received heat amount (estimated) G _g ·ΔT, which is the output of the multiplier 102, increases, and the generated steam amount signal G _s increases accordingly. On the other hand, although the exhaust gas temperature output _T3 of the gas turbine 1 increases rapidly, the boiler outlet steam temperature _T4 does not increase immediately, so the temperature deviation _ΔT4 , which is the input to the PI controller 107, becomes a large negative value. It acts in the direction of reducing the amount of water supplied. Therefore, the water supply amount is extremely small compared to the boiler heating amount, and the water supply control signal S _c1 is the boiler stable water supply amount which is the output of the function generator 110.
G becomes smaller than _snio . Here, the high-level selector 111
Since the stable water supply amount G _snio , which is the output of the function generator 110, is selected as the calibrated water supply amount and output as the water supply control signal 2-stage S _c2 , the once-through boiler operates stably without unstable flow. can.

As time passes and the boiler outlet steam temperature T ₄ rises, the deviation ΔT ₄ of the output of the subtractor 106 becomes smaller and the feed water control signal, which is the output of the adder 108, decreases.
When S _c1 increases and becomes larger than the boiler stable water supply amount G _snio of the output of the function generator 110, the state is the same as that during boiler settling operation, and the output S _c1 of the adder 108 is selected, and this value is used as the water supply control signal in the second stage. Output as S _c2 . In addition, in the case where the boiler stable water supply amount G _snio , which is the output of the function generator 110, is smaller than the minimum water supply amount G _fnio , which is the output of the function generator 114, the output G of the function generator 110 is determined by the high-level selector 111. When the value of _snio is selected, timer 113
It goes without saying that the water supply system abnormality signal E _s is output after a certain period of time has elapsed after the is set.

When the load on the gas turbine 1 suddenly decreases, the output generated steam amount signal G _s of the function generator 104 becomes smaller, but the temperature deviation △ which is the output of the subtractor 106 decreases.
Since _T4 becomes a large positive value, the feed water control signal S _c1 , which is the output of the adder 108, does not decrease much, and the amount of water fed to the boiler becomes excessive compared to the heating, and the degree of superheating of the steam at the boiler outlet decreases. , in some cases becoming wet steam. In this situation, function generator 1
Since the value of the output G _fnio of 14 is larger than the water supply control signal S _c1 , the timer 113 is set by the comparator 112, and after a certain period of time, the water supply system abnormality signal E _s is output, and the main steam valve 10 in FIG. At the same time, the bypass valve 15 is fully opened and surplus steam is dumped into the condenser 11, so that the steam turbine 9 is protected from drain attack. Note that this timer 113 is provided to prevent erroneous operation of the water supply system abnormal signal, and even if the output G _fnio of the function generator 114 becomes large within a very short period of time, it will be stopped due to the heat storage capacity of the boiler itself. Since the degree of superheating of the steam at the boiler outlet does not decrease much, timer 113
By setting a time limit on the operation, the transmission of the water supply system abnormality signal is delayed and the accuracy of the alarm is increased.

In the above explanation, the exhaust gas flow rate signal is determined from the intake air temperature T ₀ of the gas turbine 1 and the low pressure compressor rotation speed N1.
Although the value of G _g is estimated, a known anemometer may be provided in the middle of a circuit such as an exhaust gas duct, and the exhaust gas flow rate signal G _g may be directly detected from the output of this anemometer.

In addition, when using diesel engine exhaust gas, the exhaust gas flow rate signal G _g is determined by the engine intake pressure, supercharger rotation speed, or fuel rack position.
may be estimated.

FIG. 4 shows another embodiment 52 of the control device of the present invention, and the difference between this embodiment and the embodiment shown in FIG. The configuration of the container 110' is
In this embodiment, the _multiplier 1
Boiler heat received (preheating) G _g・△ which is the output of 02
Only the value of T is used, and the feed water temperature T ₁ is not used as an input. This is an embodiment that can be advantageously used in a boiler where the point at which flow instability occurs is not greatly affected by the value of the feed water temperature, and the function generator 110'
The form of the function is set to a value that allows a margin for the fluctuation of the supply water temperature T ₁ in advance. Here, when the load of the gas turbine 1 suddenly increases, the output of the function generator 110' is increased with a margin, so the stable water supply amount G _snio , which is the output of the function generator 110', is selected at a high level relatively early. Since the water supply control signal S _c2 is the output of the function generator 111, the efficiency is slightly lowered, but the structure of the function generator 110' can be simplified and the control device can be made inexpensive. In this case, the time during which the stable water supply amount G _snio of the boiler, which is the output of the function generator 110', is selected as the second stage water supply control signal S _c2 is small compared to the total operating time, so the decrease in efficiency is ignored. I can do it.

As described above, the once-through boiler control device according to the present invention is an inexpensive control device that requires only slight modifications to the conventional control device, even when there is a fluctuation in the amount of exhaust gas due to sudden load fluctuations of the engine, gas turbine, etc. Also, the once-through boiler provides a control device that can continue stable operation without causing flow instability and can protect the steam turbine from drain attack.

[Brief explanation of drawings]

Fig. 1 is a piping system diagram of a conventional example of a combined plant, Fig. 2 is a block connection diagram of a control device of a conventional example of a once-through boiler, and Fig. 3 is a block connection diagram of an embodiment of the control device of a once-through boiler of the present invention. 4 is a block connection diagram of another embodiment of the once-through boiler control device of the present invention. 1...Gas turbine, 2...Duct, 3...Once-through boiler, 4...Stack, 5...Water pump,
6... Water supply valve, 7 _a , 7 _b , 7 _c , 7 _d ... Pipe line, 8
...Steam water separator, 9...Steam turbine, 10...
Main steam valve, 11... Condenser, 12... Condensate pump, 13... Drain tank, 14... Feed water heater, 15... Bypass valve, 20... Revolution meter, 2
DESCRIPTION OF SYMBOLS 1... Gas turbine intake air temperature meter, 22... Gas turbine exhaust gas thermometer, 23... Once-through boiler exhaust gas temperature gauge, 24... Once-through boiler outlet steam thermometer, 2
5... Boiler feed water temperature gauge, 50, 51, 52...
Control device, 101, 104, 105, 110, 1
10', 114...function generator, 102...multiplier, 103,106...subtractor, 107...PI
Controller, 108... Adder, 111... High level selector, 112... Comparator, 113... Timer.

Claims (1)

[Scope of Claims] 1. Means for calculating the amount of heat received by the boiler from the flow rate of exhaust gas for heating the boiler and the temperature difference between the exhaust gas at the inlet and outlet of the boiler, and means for calculating the amount of generated steam from the amount of heat received by the boiler; Means for calculating the corrected steam amount from the deviation between the set value of the steam temperature at the boiler outlet calculated from the exhaust gas temperature at the boiler inlet and the measured value of the steam temperature at the boiler outlet, and the method for calculating the corrected steam amount from the generated steam amount and the corrected steam amount In a control device for a once-through boiler that adjusts the amount of water supplied, the control device includes a means for calculating a stable water supply amount from the amount of heat received by the boiler, and a value obtained by comparing the stable water supply amount and the water supply amount. means to select the larger of the above as the calibrated water supply amount; a means to calculate the minimum water supply amount of the boiler from the heat received by the boiler and the water supply temperature; and a means to calculate the minimum water supply amount by comparing the minimum water supply amount and the calibrated water supply amount. 1. A control device for a once-through boiler, characterized in that it is provided with means for shutting off a steam passage supplying a load when the amount of steam is large and this state continues for a certain period of time or more. 2. The once-through boiler control device according to claim 1, wherein the means for calculating the stable water supply amount uses the supply water temperature as a parameter.