JPH0315085B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a water level control device in a boiler.

In a multi-tube once-through boiler, the liquid level inside the boiler can changes depending on the steam load, and since can water has a high steam content, the water level control device is placed outside the boiler can. Therefore, even if the water level in the water level control device does not change, the liquid level in the boiler can fluctuates because the steam content in the liquid changes depending on the steam load, and when the load is high, the liquid level becomes high.

In order to improve the dryness of steam under high load conditions, the operating water level is set at about 60-70% of the water pipe length. If the boiler is operated at this operating water level, the liquid level in the boiler can will not rise when the load is light, and the water pipes, upper header, etc. will overheat.

The present invention measures the drop in the can water level during low steam load in the boiler as described above by measuring the steam load and controlling the can water level to be near the high water level, thereby increasing the water level indicated by the can water level detector. An object of the present invention is to provide a device that can prevent overheating of water pipes, upper headers, etc. by bringing the actual water level in the can closer to the actual water level in the can.

The present invention includes a steam load measuring device for a boiler, and a water level control device for raising the water level of an operating tank when the steam load of the boiler is low.

Examples of the present invention will be described below.

FIG. 1A is a block explanatory diagram showing the configuration of such a boiler system, and a cross section of the boiler 1 is shown. FIG. 1B is a sectional view taken along the line AA in FIG. 1A.

In the figure, inside a boiler 1, a large number of water pipes 1b are installed along the inner circumferential surface of a wall 1a, and the water pipes 1b are made of a hollow cylindrical body, and the lower end thereof is an annular lower header 1c (water chamber). The upper end portions thereof communicate with the annular upper header 1d (steam chamber), and the lower portions of the lower header 1c and the water pipe 1b,
Canned water is stored.

A combustion chamber 1e is formed in the center of the boiler 1 surrounded by water pipes 1b, and an electric motor 1f is provided above the combustion chamber 1e.
An air passage 1h is provided which communicates with a blower 1g driven by a blower 1g, and a nozzle rod 1i and an electrode rod 1j are vertically provided within the air passage 1h.

The lower end of the combustion chamber 1e communicates with the flue 1k through a hollow space between a large number of water pipes 1b. Upper header 1d
From there, a communication pipe 1l extends outside the wall 1a and communicates with the lower header 1c.

A water level gauge 1m and a water level detector 2 for visually displaying the canned water level are installed in the middle of the communication pipe 1l. A water supply control section 3 is connected to the water level detection section 2, and its output terminal is connected to an electric motor 4a that drives a water supply pump 4. An inlet pipe of the water supply pump 4 communicates with a water source (not shown), and a discharge pipe thereof communicates with the lower header 1c.

Further, a pressure detection section 5 is connected to the upper part of the communication pipe 1l, and its output terminal is connected to a heating control section 6. From the heating control section 6, control signal lines 6'a~
6'c extends and is connected to each of the electric motor 1f, electrode rod 1j, and fuel pump 6'd. An inlet pipe of the fuel pump 6'd communicates with a fuel tank (not shown),
Its discharge pipe communicates with the nozzle rod 1i. and,
A blow pipe 1n extends from the lower header 1c and communicates with a drainage channel (not shown) via a blow stock 1p, and a steam pipe 1q extends from the upper header 1d and communicates with a desired steam load (not shown).

In the configuration of the boiler system described above, when generating steam, the electric motor 1f drives the blower 1g to forcefully feed air into the air passage 1h while applying a high voltage to the electrode rod 1j to generate steam from the tip of the nozzle rod 1i. The injected fuel is ignited and combusted within the combustion chamber 1e. High-temperature combustion gas generated by such combustion enters the middle part of the water pipe 1b from the lower end of the combustion chamber 1e, passes through this, reaches the flue 1k, and is exhausted. During this time, heat exchange takes place and the canned water in the water pipe 1b is heated and turned into steam, which is then transferred to the upper header 1d.
The steam is collected and stored at the steam pipe 1q and supplied to the steam load through the steam pipe 1q.

Regarding heating control, upper header 1d
The steam pressure in the upper header 1d is extracted through the communication pipe 1l and supplied to the pressure detector 5.
When the heating control section detects that the vapor pressure of Send to 6.

When the steam pressure in the upper header 1d drops due to continued steam consumption and a lower limit steam pressure signal is received, the heating control unit 6 starts the electric motor 1f through the control signal line 6'a and starts the blower 1g. Butetsete wind road 1
After purging h with air, a high voltage is applied to the electrode rod 1j through the control signal line 6'b, and at the same time, the fuel pump 6d is started through the control signal line 6'c to ignite the fuel injected from the nozzle rod 1i. When the steam pressure continues to rise and an upper limit steam pressure signal is received from the pressure detector 5, the fuel pump 6'd is stopped via the control signal line 6'c. The combustion is stopped by cutting off the fuel supply, and when the combustion gas is discharged, the electric motor 1f is stopped via the control signal line 6'a, and the air blowing from the blower 1g is cut off.

Therefore, even if the combustion is controlled intermittently, the upper header 1
The vapor pressure within d can be maintained at a pressure value between the two preset pressure values as the upper and lower limit vapor pressures.

In addition, in a simple device, the start/stop control of the electric motor 1f and the combustion pump 6'd, and the application of high voltage to the electrode rod 1j may be performed simultaneously.

Furthermore, regarding the water supply system, changes in the canned water level in the air-water interface in the communication pipe 1l, that is, in the water pipe 1b, are transmitted to the water level detection section 2, and the water level detection section 2 detects the canned water level set in advance. When it is detected that the lower limit water level has been reached, a lower limit water level signal is sent to the water supply control unit 3, and at the same time, when it is detected that the upper limit water level has been reached, an upper limit water level signal is sent to the water supply control unit 3.

When the canned water level in the water pipe drops due to steam consumption and a lower limit water level signal is received from the water level detection unit 2, the water supply control unit 3 starts the electric motor 4a and causes the water supply pump 4 to lower the water pipe through the lower header 1c. 1
When the water supply to b is started, water supply continues, the can water level rises, and an upper limit water level signal is received from the water level detector 2, the electric motor 4a is stopped to cut off the water supply to the water pipe 1b.

Thus, even with the intermittent water supply control, the water level of the canned water in the water pipe 1b can be maintained at a water level between the upper and lower limit water levels preset.

The intermittent control of water supply and the intermittent control of combustion are performed independently of each other.

Also, when blowing canned water, use blowing stick 1.
By opening p, part or all of the canned water in the lower header 1c and the water pipe 1b can be blown out through the drain pipe 1n.

In addition, blower 1g, air passage 1h, nozzle rod 1i,
The burner consisting of the electrode rod 1j is not limited to this, and if necessary, it is sufficient to heat the canned water in the water pipe 1b to generate steam, so generally an electric heater or the like is also used. Any heating device that includes the above may be used.

Similarly, the heating control section 6 may also be of any type as long as it can turn the heating device on and off.

Next, an example of a steam load measuring device according to the present invention will be described. In the present invention, it is not necessary to determine the amount of steam, but it is sufficient to be able to express the steam load in percent years relative to the total load. The state of this change in steam load has already been clarified by the inventors, and a measuring device for heating time and heating stop time has been proposed, and the steam load can be determined from the ratio thereof. FIG. 2 is a control block diagram showing a heating control section, a heating time measuring section, and a heating stop time measuring section.

The pressure sensor 5a outputs a corresponding steam pressure signal _S0 in response to the steam pressure in the upper header 1d guided through the communication pipe 1l. As shown in the figure, when the vapor pressure is higher than the lower limit vapor pressure P _L , the vapor pressure signal S corresponding to the lower limit vapor pressure P _L supplied from the reference voltage source 5d is lower than the reference voltage V _L equal to the lower limit set value of ₀ . Since the vapor pressure signal _S0 is also larger, the first comparator 5b detects this and sets the value Cb- in FIG.
Outputs "1" as shown in 1.

Then, as the steam is consumed or the temperature decreases, the steam pressure decreases, and as shown in Figure 3 Bc-1,
When the lower limit vapor pressure P _L is reached, the vapor pressure signal S ₀ becomes smaller than the reference voltage V _L , so detecting this, the first comparator 5b sets "0" as shown in FIG. 3 Cd-1. Output.

Upon receiving the inversion of the output signal of the first comparator 5b from "1" to "0" at the set terminal, the flip-flop 6b is set to "1", and its positive phase output signal is shown in FIG. 3 De-1. As shown, it is inverted from "0" to "1". Upon receiving this signal, the driver 6c becomes conductive, the relay 6e is excited, the contacts 6e', 6e'', and 6e are closed, and power is supplied to the motor 1f, electrode rod 1j, and fuel pump 6'd. Therefore, canned water is heated.

Thus, while the flip-flop 6b is at "1", heating continues and the vapor pressure continues to rise as shown in FIG. 3Af-1.

Eventually, as _shown in FIG. 3Ag-1, when the vapor pressure reaches the upper limit vapor pressure _P Since it is smaller than the reference voltage V _H which is equal to the upper limit setting value of the pressure signal S ₀ ,
As shown in Fig. 3 Bi-1, the second comparator 5c, which was outputting "0" as shown in Fig. 3 Bi-1,
It will now output "1".

The inversion of the output signal of the second comparator 5c from "0" to "1" is converted by the inverter 6a into an inversion from "1" to "0" and supplied to the reset terminal of the flip-flop 6b.
Reset this to "0".

Then, as shown in FIG. 3 Dj-1, the positive phase output signal of the flip-flop 6b becomes "0", so the relay 6e becomes de-energized, and the contacts 6e',
6e'' and 6e are opened and heating of the canned water is stopped.

In this way, the time Th ₁ (hereinafter referred to as heating time) from when the heating device starts until it stops is specified even when the flip-flop 6b is set to "1", and furthermore, the time Th 1 (hereinafter referred to as heating time) from when the heating device starts until it stops is specified by the time when the flip-flop 6b is set to "1". The time Th ₂ from start to start (hereinafter referred to as heating stop time) is also specified by the time during which the flip-flop 6b is set to "0".

After heating is stopped, as shown in Figure 3 Ak-1, the steam pressure decreases again as steam is consumed or the temperature decreases, until it reaches the lower limit steam pressure P _L.
The flip-flop 6b remains at "0" to form a heating stop time _Th2 , after which the same operation is repeated and the vapor pressure is maintained between the upper limit vapor pressure P _H and the lower limit vapor pressure P _L. dripping

For example, if the amount of steam (steam load) increases in the step of increasing steam pressure, heating of canned water,
The amount of heat flowing into the boiler system due to the supply of canned water,
Where the amount of heat flowing out of the boiler system due to heat radiation is approximately constant for the heating time during steady operation,
The amount of heat flowing out of the boiler system due to evaporation of canned water increases in proportion to the amount of evaporation, so more heat is taken away from the boiler system, and as shown in Fig. 3 Af'-
As shown in Fig. 1, the slope of increase in vapor pressure becomes slower.

Therefore, at the moment shown in Fig. 3 Ac-1, at the same time, the flip-flop 6b is reversed to "1" as shown in Fig. 3 Ee'-1, and the heating time is set.
Assuming that the transition to time Th ₁ occurs, if the amount of evaporation increases, at the time shown in Fig. 3 Ag'-1,
As shown in Figure 3 Ej'-1, the flip-flop 6
Since b is inverted to "0", a heating time Th ₁ ' is formed which is longer than the heating time Th ₁ before the amount of evaporation increases.

A quantitative consideration of the change in the heating time Th ₁ depending on the change in the amount of evaporation is as follows.

Generally, the change dU in the internal thermal energy possessed by a boiler system is expressed as dU = ηB・Hu・dt + Gw・Iw・dt−Gs・Is・dt −Q _R・dt (1).

However, η...Boiler efficiency (excluding heat radiation loss) B...Heating value of fuel Hu...Fuel consumption (flow rate) Gw...Amount of water supplied to the boiler (flow rate) Iw...Enthalpy of water supply Gs...Evaporation Quantity (flow rate) Is...Enthalpy of steam Q _R ...Amount of heat released from the boiler (heat flow rate).

Regarding the right side of equation (1), the first term is the amount of heat flowing into the boiler system due to heating of can water, the second term is the amount of heat flowing into the boiler system due to supply of can water, and the third term is the amount of heat flowing into the boiler system due to the supply of can water.
The term represents the amount of heat flowing out from the boiler system due to evaporation of canned water, and the fourth term represents the amount of heat flowing out from the boiler system due to heat radiation.

By the way, in general, in a boiler system, the variable amount of canned water that is replenished by intermittent control of the water supply system is small compared to the amount of canned water held during operation. Therefore, the amount of water held by the boiler system during operation can be considered to be a constant value unique to each boiler system, so the amount of water held by the boiler system at the start of heating time Th ₁ corresponding to the lower limit steam pressure P _L is The internal thermal energy U _L and the internal thermal energy U _H possessed by the boiler system at the end of the heating time Th ₁ corresponding to the upper limit steam pressure P _H
Each of these values is specific to each boiler system.

Therefore, based on equation (1), the increase in internal thermal energy (U _H − U _L ) generated in the boiler system with the passage of one heating time Th ₁ is U _H − U _L = (η・B・Hu ) Th ₁ + (Gw・Iw) Th ₁ −Gs∫ ^Th1 ₀ Isdt−Q・Th ₁ ...(2) Approximate.

In reality, the difference between the upper and lower vapor pressure limits P _H and _PL is not large, so for simplicity, calculate the average enthalpy value Is ₁ n corresponding to the upper and lower vapor pressure limits and set Is = Is ₁ n. Then, equation (2) becomes U _H − U _L = (η・B・Hu) Th ₁ + Iw∫ ^T1 ₀ Gwdt − (Gs・Is ₁ n) Th ₁ −Q _R・Th ₁ ...(3) .

Furthermore, considering the heating time Th ₁ ,
Within one heating time Th ₁ , water is supplied a number of times according to the amount of evaporation due to the intermittent control of water supply, which is performed independently of heating control. Therefore, during the water supply period, the amount of water supplied ( On the other hand, during the water supply stop period, water is not supplied at all, and the amount of water supplied (flow rate) flowing into the boiler becomes zero.

However, from a long-term perspective over a large number of heating times, in an operating boiler system, the average water supply amount (flow rate) supplied by water supply control is in equilibrium with the evaporation amount (flow rate), so the amount of water held in the boiler is approximately It is kept at a constant value.

Therefore, ∫Gwdt=GsTh ₁ ...(4) holds true.

Then, when calculating the evaporation amount Gs from equations (3) and (4), it becomes Gs=C _B −C _R −Cv/Th ₁ ...(5).

However, C _B = η・B・Hu/Is ₁ n−Iw … (5a) C _R = Q/Is ₁ n−Iw … (5b) Cv=U _H −U _L /Is ₁ n−Iw … ...(5c), and if the feed water enthalpy is constant, both are constants unique to each boiler system.

Therefore, if C=C _B −C _R (6) is set in equation (5), the evaporation amount Gs is expressed as Gs=C−Cv/Th ₁ (7).

Further, C represents the amount of evaporation when the heating time Th ₁ is infinite (continuous heating), that is, the maximum amount of evaporation unique to each boiler system.

Furthermore, the heating time T ₁₀ at Gs=0 is T ₁₀ =Cv/C (8), and even if the amount of evaporation (steam load) is zero, the heating time T ₁₀ is mainly due to heat radiation from the boiler. This is the minimum heating time required to compensate for the thermal energy that flows out and maintain the boiler system in operation.

FIG. 4 is a graph illustrating the relationship between the heating time Th ₁ and the evaporation amount Gs expressed by the above equation (7).

In this way, the heating time Th ₁ of the boiler system is the amount of evaporation
Since it is specified to a value unique to each boiler system according to Gs, if you measure the heating time Th ₁ and specify this,
The evaporation amount Gs can be calculated according to the above equations (5) to (7).

Next, for example, if the amount of evaporation (steam load) increases during the step of lowering the steam pressure, there is no amount of heat flowing into the boiler system due to the heating of the canned water, and furthermore, the amount of heat flowing into the boiler system is increased by the supply of canned water. Where the amount of heat flowing into the system and the amount of heat flowing out from the boiler system due to heat radiation are approximately constant during the heating stop time during steady operation,
The amount of heat flowing out of the boiler system due to evaporation of canned water increases in proportion to the amount of evaporation, so as in the process of increasing steam pressure, more heat is taken away from the boiler system, as shown in Figure 3. Figure 5 corresponds to
As shown in Ak'-1, the downward gradient of vapor pressure becomes steeper.

Therefore, suppose that at the time shown in Fig. 5Ag-1, at the same time, the flip-flop 6b is reversed to "0" and the heating stop time begins, as shown in Fig. 5Ej'-1. Assuming that, if the amount of evaporation increases, at the time shown in Figure 5 Al'-1, the
As shown in Em'-1, the flip-flop 6b is inverted to "1", so a heating stop time Th ₂ ' is formed which is shorter than the heating stop time Th ₂ before the amount of evaporation increases. .

The heating stop time depends on the change in the amount of evaporation.
Quantitative consideration of changes in Th ₂ is as follows.

During the heating stop time, the canned water is not heated, the first term on the right side of equation (1) becomes zero, and the internal thermal energy changes.
dU is expressed as dU＝Gw・Iwdt−Gs・Is・dt−Q _R dt ( ₉ ), and the decrease in internal thermal energy (U _L − U _H )
is expressed as Iw∫ ^Th ₂₀ Gwdt U _L −U _H = (Gs・Is ₁ n) Th ₂ −Q _R Th ₂ ……(10).

In equation (10), if we set ∫ ^Th2 ₀ Gwdt=GsTh ₂ and find the evaporation amount Gs, we get Gs=C′v/Th ₂ −C _R (11).

However, C′v=U _H −U _L /Is ₁ n−Iw=Cv ……(11a) C=Q _R ／Is ₁ n−Iw ……(11b) And heating stop time T ₂₀ at Gs=0 is T ₂₀ = C′v/C _R , and even if the amount of evaporation (steam load) is zero, the heating stop time T ₂₀ is due to the outflow of thermal energy mainly due to heat radiation from the boiler, and the upper limit vapor pressure This is the maximum heating stop time required to reach the lower limit vapor pressure.

Therefore, even when the steam load is no load, the boiler system heating device is controlled intermittently during the heating time T ₁₀ and the heating stop time T ₂₀ .

The graph illustrating the relationship between the heating stop time Th ₂ and the evaporation amount Gs expressed by the above equation (11) is shown in the sixth graph.
It is a diagram.

In this way, the heating stop time Th ₂ of the boiler system is also specified to a value unique to each boiler system according to the evaporation amount Gs, so if the heating stop time Th ₂ is measured and specified, the above (11 ) The evaporation amount Gs can be calculated according to the formula.

Next, returning to FIGS. 2 and 3, the operations of the heating time measuring section TH1 and the heating period calculating section 8-1 will be explained as follows.

During the intermittent control of the heating device, the positive phase output signal of the flip-flop 6b becomes "1" during the heating time _Th1 , for example, as shown in FIG. 3D. In response to this positive phase output signal, AND gate 7b-1 opens only during the heating time, and the clock pulse from clock pulse oscillator 7a-1 is guided to counter 7c-1 for counting.

Then, as shown in FIG. 3 Dj-1, when the flip-flop 6b is inverted from "1" to "0", its positive phase output signal is inverted from "1" to "0", and the AND gate 7b-1 is closed. counter 7
The supply of the clock pulse to c-1 is cut off, and the counter 7c-1 generates a digital code representing the heating time _Th1 , which is output as the heating time signal _S1-1 .

At the same time, the arithmetic unit 8a-1 receives the inversion of the positive phase output signal of the flip-flop 6b from "1" to "0" at the control terminal, and executes arithmetic processing to be described later.

After the arithmetic processing by the arithmetic unit 8a-1 is completed, the monostable multi-channel flip-flop, which was triggered and transitioned to a metastable state, was triggered when the positive phase output signal of the flip-flop 6b was inverted from "1" to "0". Since the vibrator 7d-1 returns to a stable state and sends a clear pulse to the clear terminal of the counter 7c-1, the counter 7c-1 is cleared and ready for the next measurement.

On the other hand, the heating stop time measuring section TH2, which has the same configuration as the heating time measuring section TH1, receives a reset signal from the complementary output terminal of the flip-flop 6b and determines the heating stop time.
Outputs the signal S _2-1 representing Th ₂ and sends it to the storage device MTH2.
The signal is input to the arithmetic unit 8a-1 via.

Before the counter 7c-1 is cleared, the arithmetic unit 8
a-1 calculates Th ₁ /Th ₁ + Th ₂ from the signals S1-1 and S1-2, and calculates the percentage of the steam load preset in the percentage annual load setter 8b-1, which is composed of a digital switch or the like. Compared with the load constant signal _S3-1 representing the year, the calculation unit 8a-1 calculates that the load constant signal is, for example, 20%.
Th ₁ / (Th ₁ + Th ₂ ) compared to Th ₁ / (Th ₁ + Th 2 )
When Th ₂ ) < 20%, a signal S ₅ is generated and sent to the water supply control section.

FIG. 7 is a block diagram showing a water level detection section and a water supply control section.

When the water level is higher than the lower limit water level L, the lower limit water level probe 2a is submerged in water, and conduction is established between the underwater electrode 2c and the underwater electrode 2c,
Since a load circuit consisting of a first current detector 2e, a lower limit water level probe 2a, and an underwater electrode 2c is formed for the AC power source 2d, a current flows through the first current detector 2e, and this is detected. 1 current detector 2
e outputs "1".

Then, when the water level falls and reaches the lower limit water level L, the tip of the lower limit water level probe 2a leaves the water surface and the load circuit for the AC power supply 2d is cut off, so that the current passing through the first current detector 2e decreases. becomes zero, and detecting this, the first current detector 2e
outputs "0".

Upon receiving the inversion of the output signal of the first current detector 2e from "1" to "0" at the set terminal, the flip-flop 3b is set to "1", and its positive phase output signal changes from "0" to "0". 1”.
In response to this signal, the driver 3c becomes conductive, the relay 3e is excited, the contact 3e' is closed, and power is supplied to the motor 4a, so that canned water is supplied to the boiler.

Thus, while the flip-flop 3b is at "1", water supply continues and the water level continues to rise.

When the water level eventually reaches the upper limit water level H, the upper limit water level probe 2b is submerged, and the second current detector 2f, which had been outputting "0" because it was far from the water surface, now outputs "1". It becomes like this.

The inversion of the output signal of the second current detector 2f from "0" to "1" is converted by the inverter 3a into an inversion from "1" to "0" and is supplied to the reset terminal of the flip-flop 3b. ,
Reset this to "0".

Since the positive phase output signal of the flip-flop 3b becomes "0", the relay 3e becomes de-energized, the contact 3e' is opened, and the water supply is stopped.

A signal S5 sent from the heating time calculation unit 8a-1 when the steam load becomes Th ₁ /(Th ₁ +Th ₂ )<20% is amplified by the amplifier 3f and energizes the relay coil Rf. Then, normally closed contact Rf-1 opens, flip-flop 3b is set, and relay 3
e is energized, contact 3e' is closed, pump 4 is operated, and water supply is started. When the water level probe 2b detects a rise in the water level, the current detector 2f outputs an output signal, which resets the flip-flop 3b, deenergizes the relay 3e, and stops the water supply. At the same time, the signal from the current detector 2f is applied to the monostable multivibrator 3G, and the connected monostable multivibrator 3H outputs a signal for a certain period of time after a certain period of time and flips the flip-flop via the normally open contact Rf-2. Since 3b is set, relay 3
e is energized and water supply starts. Therefore, when the steam load becomes 20% or less, only the upper limit water level probe 2b operates and water supply starts after a certain period of time. If the operation time of the monostable multivibrator 3H is made long enough so that it will work even when the water level reaches the upper limit water level probe 2b lands on the water, the signal of the monostable multivibrator 3H will turn off at the same time when the water level is higher than the upper limit water level H. Since the set input to the flip-flop 3b is eliminated and the water supply is stopped because it is immediately reset, it is also possible to control the water level by setting the water level above the upper limit water level H as the upper limit water level.

FIG. 8 is a time chart of the present invention. The left side of the cutting line CL is when the steam load rate is 20% or more, including 20%, and the right side is when it is 20% or less. In the figure, 11 is a line indicating ON-OFF of the pressure switch, and 12 is a line indicating ON-OFF of the heating device operated by it.
Lines 13 and 14 indicate the operation of the heating time timer and heating stop time timer in the computing unit 8a-1; 15 is a line indicating the upper and lower levels of the canned water level; 1
6 and 17 are lines showing the operation of the upper and lower limit water level probes 2b and 2a, 18 is a line showing ON-OFF of the water supply pump 4, and 19 is a line showing the time TMQ1 at which the water level higher than the upper limit water level is controlled by the timer. .

When the steam load rate is greater than Th ₁ / (Th ₁ + Th ₂ )≧20% calculated by heating control, the water level of the can is between the upper limit water level H and the lower limit water level L, as shown on the left side. It changes like this. time 2
At time 1, as shown by line 16, the water supply is stopped due to the upper limit water level probe 2b landing on water, and the water level drops due to the steam load, and at time 22, as shown by line 17, the lower limit water level probe 2a takes off water, and as shown by line 18. Water supply is started and the water level rises until time 23, when water supply is also stopped. These are the ON-
This is done separately from OFF.

The signal due to the rise in vapor pressure at the pressure switch 5a turns on the heating device at time 24 as shown by line 12.
Turn OFF and start calculating the heating stop time as shown by line 14. And when the pressure decreases due to steam consumption,
At time 25, the pressure switch 5a detects the lower limit steam pressure and turns on the heating device. and line 13
The heating time timer starts operating as shown by line 14, and at the same time the heating stop timer shown by line 14 turns OFF.
do. Heating continues until time 26, and time 26
Then, the pressure switch 5a detects the upper limit steam pressure and operates, the heating device is turned off, the heating time timer is turned off, and the heating stop time timer is turned on.
Repeat the same below. Such heating control is the same even when the steam load is Th ₁ /(Th ₁ +Th ₂ )<20%. As already mentioned, Th ₁ / (Th ₁ +
Th ₂ ) is calculated and this value approximately represents the steam load.

As the steam load decreases, the amount of evaporation also decreases, so the gradient of the water level drop becomes smaller as shown by the water level line 15-1. When the steam load becomes 20% or less, Th ₁ / which was calculated by the calculator 8a-1 from one heating time Th ₁ and the following heating stop time Th ₂
Since (Th ₁ +Th ₂ ) is less than 20%, the pump 4 is driven at time 31 as described above. Then, water is supplied exceeding the upper limit water level H until a fixed time 32 determined by the monostable multivibrator 3G, and
3, the water supply pump 4 is stopped, the water supply is cut off for a certain period of time 34 determined by the monostable multivibrator 3H, the water level drops through the high water level H, and water supply is started at a water level H1 near the high water level. If the steam load rate exceeds 20% at this time 35 or the time 36 before that, there will be no signal S5, so the return to the time chart on the left side will be returned to, but the steam load rate will be
If it is less than 20%, the same applies thereafter. When the steam load increases and exceeds 20%, the signal S5 disappears, so the relay Rf is deenergized, the contacts Rf-1 and Rf-2 become inactive, and the lower limit water level probe 2a also comes into operation. In this case, the lower limit water level probe 2a comes into operation even at the same time, so if the water level is currently falling or rising, the state returns to the left side diagram in FIG. 8 when the water level next falls.

In the above explanation, the steam load factor was calculated from the heating time and the heating stop time, but it can also be similarly calculated from the operation of the water supply device during the water supply period and the water supply stop period (Japanese Patent Application Laid-Open No. 107930/1984, etc.) Therefore, calculation of steam load is not limited to calculation from ON/OFF of the heating device, but may be calculated as long as it can be calculated during continuous operation. The water level may also be detected by a level switch.

As described above, the present invention enables the control reference position of the can water level to be raised or lowered depending on the steam load in a boiler in which the can water level is controlled by turning it on and off by a water supply device, and the can water level is adjusted when the steam load is small. Since the water can be controlled based on the upper limit water level, there will be no overheating of the water pipes, upper headers, etc.

[Brief explanation of the drawing]

Figure 1A is a block diagram showing the configuration of a small boiler system to which the configuration of the present invention can be attached.
Figure B is an AA sectional view of the boiler 1 in Figure 1A, Figure 2 is a heating control diagram, and Figures 3 and 5 are
Figure 4 is a graph showing the relationship between heating time Th ₁ and evaporation amount Gs; Figure 6 is a graph showing the relationship between heating stop time Th ₂ and evaporation amount Gs; FIG. 7 is a water level control diagram, and FIG. 8 is a time chart of the present invention. 2a...Lower limit water level detection probe, 2b...Upper limit water level detection probe, S5...Load factor signal.

Claims (1)

[Claims] 1 Water level detection means that detects the can water level and outputs a lower limit/upper limit water level signal, starts a water feed pump that supplies water to the boiler in response to the lower limit water level signal, and stops the water pump in response to the upper limit water level signal. In a boiler system equipped with an intermittent control water supply control means,
A boiler comprising a means for calculating a steam load factor, and a means for controlling a water level near a water level detecting means that receives a signal from the means for calculating a steam load factor and outputs an upper limit water level signal for a water supply control means during low load. water level control device in the system.