JPH0465282B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a once-through boiler system, and more particularly to a water wall system of a once-through boiler system suitable for achieving good load characteristics at startup and during load changes.

The conventional water wall system for this type of once-through boiler equipment is
Generally, as shown in Fig. 1, feed water is pressurized by a boiler feed water pump 1, and then sequentially passed through a boiler feed water flow control valve 2, a boiler (drain) recirculation confluence section 3, an energy saver 4, and a water wall 5, where it is heated. and then steam water separator 6
The water is separated from the water. Among the separated substances, drain is stored in a drain tank 8, then pressurized by a drain recirculation pump 9, and then passed through a drain recirculation flow control valve 10 to the boiler recirculation confluence provided at the inlet of the economizer 4. Returned to part 3.

Further, numerals 12 and 17 in FIG. 1 indicate a drain tank level control system and a boiler feed water control system, respectively, the details of which are shown in FIGS. 2 and 3. First, control of the drain tank level by the control system 12 is normally performed by operating the drain recirculation flow control valve 10 with the function element 21 in proportion to the drain level detected by the detector 11. Function element 21 is drain recirculation flow control valve 1
If the drain tank level still rises even after fully opening 0, the drain tank blow flow control valve 13 is operated by the function element 22 to blow the drain,
It also lowers the level.

On the other hand, the control system 17 normally controls the amount of water supplied to the economizer by operating the boiler water flow control valve 2 so that the amount of water supplied to the economizer detected by the water wall flow rate detector 15 matches the water supply command 18. This is done by However, in order to protect the water wall pipes, water wall 5 must have a flow rate of approximately 30% of the boiler's full load (water wall minimum water supply amount), so water supply command 18 is set at the minimum value. By passing the restricting element 23, the water wall flow rate target value 30 is set. Also, steam generation inside the economizer 4 (causing water hammer, etc.)
In order to prevent this, the water wall pressure detected by the water wall pressure detector 20 is passed through the function element 26 to create the economizer outlet fluid temperature limit value 31, and this and the economizer outlet fluid temperature detected by the detector 19 are Subtraction element 2 based on temperature
7 and a proportional-integral element 28 to obtain an anti-steaming signal 32. This signal is activated by the signal high selection element 2 when the fluid temperature at the outlet of the economizer exceeds the limit value 31.
9 is assigned to selection, which increases the amount of water supply,
It also has the function of lowering the temperature of the fluid inside the economizer.

A once-through boiler with such a configuration operates using a recirculation line (recirculation operation) when generating steam below the water wall minimum water supply amount, and on the other hand, when generating steam exceeding the water wall minimum water supply amount. In some cases, operation is performed without using a recirculation line (once-through operation).
There is a transition point called the Benson Point between them.

However, the conventional once-through boiler with such a configuration has the following drawbacks.

(1) At startup, the amount of blow from the drain tank 8 increases, resulting in large heat loss and therefore a long startup time.

(2) Steam pressure control response is slow during recirculation operation.

(3) Reverse response occurs in steam pressure control near Benson Point.

The drawback of (1) above is due to the following reasons. That is, after the boiler is ignited, the enthalpy of the drain discharged from the steam-water separator 6 gradually increases, and by the time steam is generated, it becomes saturated water. However, when this saturated drain is recirculated to the economizer 4, it is necessary to keep the enthalpy of the feed water at the inlet of the economizer 4 considerably lower than that of saturated water in order to prevent steam generation within the economizer 4. There is. Therefore, for example, even if saturated water close to the water wall minimum water supply flow is flowing out from the steam water separator 6, it is not possible to recirculate the entire amount to the inlet of the economizer 4, and the water flows out from the boiler water flow control valve 2. A considerable amount of cold water needs to flow in. However, under such conditions, the level of the drain tank 11 increases, so
Drain tank blow flow control valve 1 that involves heat loss
The balance must be maintained by continuously blowing saturated water from step 3 onwards. This state continues until the amount of evaporation increases and the amount of drain in the drain tank 8 decreases considerably. Incidentally, it is known that in actual plants, after ignition, the evaporation continues until about 20% of the amount of evaporation occurs when the boiler is at full load. Normally, when a boiler is started, the amount of fuel input is limited due to combustion gas temperature restrictions, etc., so the above heat loss directly becomes a factor in prolonging the start-up time.

Next, the drawback of (2) above is due to the following reason. In other words, vapor pressure basically depends on the amount of evaporation, but
During recirculation operation, the water wall flow rate is kept constant under the minimum water supply amount, so steam pressure control is performed using the fuel amount. However, even if the amount of fuel is changed, the amount of heat absorbed by the water wall that contributes to the amount of evaporation is delayed due to the heat capacity of the water wall metal, etc., and the change remains slow.

Furthermore, the drawback of (3) above is due to the following reason. That is, during once-through operation, the fluid at the inlet of the steam-water separator 6 is usually sufficiently dry steam, so the steam pressure can be controlled by the amount of water supplied. this is,
This is because when the steam pressure decreases, if the amount of water supplied is increased, the amount of evaporation will increase as long as the fluid at the inlet of the steam-water separator 6 is dry. However, an increase in the amount of water supplied decreases the fluid enthalpy at the inlet of the steam separator 6, so in conditions where the fluid at the inlet of the steam water separator 6 has not become sufficiently dry steam, such as near Benson Point, the steam pressure will decrease. If the amount of water supplied is increased in response to a decrease in steam pressure, the fluid at the inlet of the steam-water separator will become a mixed state of steam and water, and the amount of evaporation generated will actually decrease, which may cause a phenomenon called the so-called reverse response of steam pressure control.

In this way, steam pressure control needs to be performed appropriately depending on whether the boiler is in circulation operation or once-through operation, but in the vicinity of Benson Point, the operating status of the boiler changes depending on the control action. This makes steam pressure control difficult.

As a solution to this difficulty, immediately after switching from circulating operation to once-through operation, the water wall water supply amount is intentionally reduced to superheat the fluid at the inlet of the steam-water separator 6, and the steam 7 thus generated is heated to the superheater 101. Conventionally, attempts have been made to compensate for the lack of evaporation by increasing the flow rate of the superheater water injection valve 104 after the steam has passed through the water, but this method inevitably causes a disturbance in the steam temperature at the outlet of the superheater 103. Therefore, it is undesirable.

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned prior art, and to
It is an object of the present invention to provide a once-through boiler device having a water wall system capable of improving load characteristics represented by startup time, steam pressure responsiveness and stability, etc.

As a result of studying a method for securing the minimum water supply amount of water wall during intermediate load operation, the inventor found that the above-mentioned drawbacks can be solved by dividing the water wall into individual water wall pipes and making it possible to freely connect them in series. I found a solution.

The present invention was made based on the above findings, and
Along the wake of the economizer, the water wall, the steam separator,
In a water wall system for a once-through boiler that is equipped with a drain tank, a drain recirculation pump, a drain recirculation flow control valve, a drain recirculation system that reaches the upstream part of the energy saver, etc., the water wall system is adapted to correspond to the water wall pipe. The system is divided into a plurality of systems having the same configuration, and between the divided water wall systems there is provided a series drain guide system that can freely guide the drain generated in the upstream divided water wall system to the water wall of the downstream divided water wall system. It is characterized by having been established.

In a preferred embodiment of the present invention, at least one of the divided water wall systems can be provided with a self-drain recirculation system, and in this case, high temperature condensate can be recirculated, so that the amount of steam evaporation can be reduced if necessary. This makes it possible to increase the amount of energy.

With the above configuration, during steady-state (through-flow) operation, each divided water wall system is operated in parallel according to the usual method, and during intermediate load operation up to once-through operation, the divided water wall systems are operated in series. This makes it possible to solve various problems caused by the minimum water supply amount.

Hereinafter, the present invention will be explained in more detail with reference to embodiments shown in the drawings.

FIG. 4 shows an example of the system of the present invention in which the water wall is divided into two parts.

In this system, water is supplied to the boiler feed pump 1.
After being pressurized in
Thereafter, the water is divided into two routes, sent to the first divided water wall 35 and the second divided water wall 44, and heated. The heated fluids are sent to the first steam/water separator 36 and the second steam/water separator 45 to separate steam and water, and the separated steam is collected at a confluence section 46 and then sent to a superheater (not shown).
sent to.

By the way, this water wall system includes the first steam separator 36
The mode is roughly divided into the following three modes depending on the difference in the drain recovery method in the second steam separator 45.

(1) Parallel operation mode (2) Series operation mode (3) Series operation high temperature fluid concentration mode It goes without saying that there are intermediate modes between these modes. In the parallel operation mode (1), the first drain recirculation series flow control valve 39 provided downstream of the first drain recirculation pump 38 and the second drain recirculation pump 61, respectively, and the second drain recirculation valve 39 for self-drain recirculation are operated. This is the operation mode when the drain recirculation concentrated flow control valve 48 is fully closed, and the first drain tank 3
7 and the second drain tank 47 are controlled by the first drain recirculation parallel flow control valve 40 and the second drain tank, which are branched and provided downstream of the first drain recirculation pump 38 and the second drain recirculation pump 61, respectively. It is controlled by a recirculation dispersed flow control valve 49. Under this condition, the movable nozzle 33 of the flow control valve provided in the water supply system between the economizer 4 and the first divided water wall 35 and the water supply system between the economizer 4 and the second divided water wall 44 are The provided water supply parallel flow regulating valve 42 is, in principle, fully open.

In this mode, two dividing water walls 35 and 4
Since the protective water supply amount is always required separately for each of the divided water walls, the minimum water supply amount for the entire water wall is the sum of the protective water supply amount of each divided water wall. Therefore, the pressure loss in the water wall is small, and for the same reason as in the case of FIG. 1, it is suitable for high load ranges.

Next, the series operation mode (2) is an operation mode when the first drain recirculation parallel flow control valve 40 and the second drain recirculation concentrated flow control valve 48 are fully closed, and each drain tank 37 and 47 The levels of are controlled by a first drain recirculation serial flow control valve 39 and a second drain recirculation distributed flow control valve 49, respectively. Water supply parallel flow control valve 42
The flow rate of the first drain recirculation series flow control valve 39 is
The divided water wall 44 is opened to compensate for the insufficient water supply amount than the protective water supply amount, and the movable nozzle 33 is closed to ensure the differential pressure of the water supply parallel flow control valve 42.

In this mode, two dividing water walls 35 and 4
Since the protective water supply amount for 4 can be shared in a certain proportion, especially under conditions where the amount of evaporation is small, it is possible to reduce the minimum water supply amount for the entire water wall to about half that of the parallel mode.

Next, the series operation high temperature fluid concentration mode (3) is the most characteristic operation mode in the present invention. This mode is similar to the series operation mode described above in that the first drain recirculation parallel flow control valve 40 is fully closed and the level control of the first drain tank 37 is performed by the first drain recirculation series flow control valve 39. However, the difference is that the level control of the second drain tank 47 is performed by a second drain recirculation concentrated flow regulating valve 48. At that time, the flow control valve 48
If the level of the second drain tank 47 does not drop even after fully opening the second drain tank 47, open the second drain recirculation distributed flow control valve 49 to avoid recirculating the drain to the inlet of the energy saver 4 as much as possible. It is desirable to do so.

In addition, the water supply parallel flow control valve 42 and the movable nozzle 3
The operation in step 3 is the same as in the series operation mode.

In this mode, as is clear from Figure 9 below, the water wall protection flow is covered as much as possible by the drain obtained from each steam separator, so the drain that passes through the economizer 4 is recycled. The amount of steam evaporation that makes it possible to stop the circulation is approximately half that in the parallel operation mode. Furthermore, the minimum water supply amount for the entire water wall up to the same stopping point is constant at about half of that in the series operation mode.

The boiler is operated according to such an example of the operation mode, and the control system at that time will be explained below. First, FIG. 5 shows the configuration of the level control system 53 related to the first drain tank 37 shown in FIG. 4, and in this configuration, parallel operation mode = 0 and other modes = 1. The latter outputs 1 from the water wall series/parallel command 62 and the constant element 66.
A complementary signal of the command 62 obtained by subtracting the former from the value of is created, and this complementary signal and the command 62 are multiplied by the output of the function element 64 that gives the valve opening in proportion to the respective drain tank level, and the command thus obtained is The first drain recirculation parallel flow control valve 40 and the first drain recirculation series flow control valve 39 are operated by the signal. In addition, during series operation, etc., when the level rises beyond the position where the function element 64 issues a full open command because the flow control valve 40 is fully closed or has a low opening, the valve sent from the function element 70 When the open command is processed by the high selection element 71 and the opening degree of the flow control valve 40 increases beyond the level at which the function element 70 issues a full open command, the function element 72 causes the high selection element 71 to process the opening command of the flow control valve 40, and then the function element 72 causes the high selection element 71 to process the opening command. The opening degree of the first drain blow flow control valve 52 is increased respectively. By following this series of steps, it is possible to avoid drain blowing as much as possible even when the level is high.

Next, FIG. 6 shows the configuration of the level control system 56 related to the second drain tank 47 shown in FIG. The second drain recirculation concentrated flow regulating valve 48 and the second drain recirculation are operated in the same manner as in the case of FIG. 5 except that the recirculation concentration and dispersion command 63 is used in which the high temperature fluid concentration mode = 1 and the other modes = 0. The dispersed flow control valve 49 and the second drain blow flow control valve 55 provided in the downstream branch system of the second drain tank are operated.

FIG. 7 shows a flow rate control system 57 that operates a water wall parallel water supply flow regulating valve 42 provided in a system that branches from the water supply system downstream of the energy saver and then reaches the second divided water wall.
This shows the circuit of the integrated control system (see Figure 4).
The water supply command 18 sent from the signal constant multiplier 73
The value reduced to 1/2 is processed by the minimum value limiting element 74, and the flow control valve 42 is operated using this as the protection flow rate target value of the second divided water wall 44.

Further, FIG. 8 shows a circuit of the flow rate control system 59 related to the boiler feed water flow control valve 2 that supplies water to the first divided water wall 35, and the concept is the same as that in FIG. Since the water supply flow control valve 2 needs to vary the amount of water supplied to the economizer 4, a steaming prevention circuit including an economizer outlet fluid temperature detector 19 and a water wall pressure detector 20 similar to the conventional technology is used. It has been added.

Although the individual control systems in this embodiment are as shown in FIGS. 5 to 8, it is desirable to operate these under the integrated control system 60 and perform the following control.

(1) At startup, operate in series operation high temperature fluid concentration mode to minimize the total drain blow amount.

(2) During recirculation operation, operate at an intermediate position between series operation and series operation in high temperature fluid mode. At that time, if it is desired to transiently increase the amount of evaporation, it is sufficient to shift to the series operation high temperature fluid concentration mode, and in the opposite case, it is sufficient to shift to the series operation mode.

(3) When switching from recirculation operation to once-through operation, first increase the amount of transient evaporation by shifting from an intermediate state between series and series high temperature fluid concentration mode during recirculation operation to series high temperature fluid concentration mode, This quickly increases the dryness of the fluid at the inlet of the steam/water separator.

Next, after switching to the parallel operation mode and operating it before switching, it is sufficient to switch and shift to the series high temperature fluid concentration mode.

(4) When switching from once-through operation to recirculation operation,
Before switching, first set the series operation to high temperature fluid concentration mode to operate in a state where the recirculation amount at the inlet of the economizer 4 is least likely to occur, and then switch to the series operation mode or further to the parallel operation mode.
It is desirable to quickly lower the fluid dryness at the inlet of the steam/water separator.

Hereinafter, in order to confirm the effects of the embodiments of the present invention, changes in fluid volume in each mode will be considered.

FIG. 9 shows the amount of fluid in each part according to mode. The horizontal axis in the figure is the sum of the amount of steam evaporation generated from each steam separator 36 and 45, point G is a value equal to the protective water supply amount of one divided water wall, and point 2G is parallel operation at twice the amount of point G. The value is equal to the Benson point in the mode. Further, section A shown in the upper part of the figure shows the flow rate structure in the second divided water wall 44, and section B shown in the lower part shows the flow rate structure in the economizer 4, the total drain flow amount, etc. First, to explain section A, the flow rate 75 in the second divided water wall 44 is the protective water supply amount G (constant)
However, the breakdown differs for each mode.
That is, in the parallel operation mode (1), the flow rate from the energy saver to the water supply parallel flow control valve 42 (see horizontal line section 83)
In contrast, in the series operation mode (2), the drain amount of the first steam/water separator 36 shown by the dashed line 77 is covered by the series operation high temperature fluid concentration mode (3).
In addition to the above, since the amount of evaporation from the second divided water wall 44 shown by the broken line 76 is recovered from the second steam/water separator 45 shown by the upper vertical line part 78, the water supply parallel flow control valve is The integrated value of the flow rate passing through 42 is the area corresponding to the horizontal line part 83 in the figure, and the amount is about 1/2 in the parallel operation mode in the series operation mode and 1/4 in the series operation high temperature fluid concentration mode. .

Next, in section B, the broken line 79 is the total flow rate of the economizer 4, which is the protection flow rate G of the first divided water wall 35 and the flow rate passing through the water supply parallel flow control valve 42 indicated by the horizontal line part 83. Therefore, it is reduced in other modes compared to the parallel operation mode. Furthermore, it can be seen that the recirculation flow rate 80 to the inlet of the economizer 4 is also significantly reduced in the other modes compared to the parallel operation mode in which the entire drain of each steam/water separator 36 and 47 is recirculated. . By the way, if we assume that drain blowing is performed to prevent steaming in the economizer in a state where 3/4 or more of the drain is recirculated in the water supply amount of the economizer 4,
The total integrated amount is shown in the shaded area 81. In other words, in series operation and high temperature fluid concentration mode,
Compared to the parallel operation mode similar to the conventional technology, the drain flow amount is about 1/4 and 1/8, respectively.

As described above, according to the present invention, the water wall system is divided into a plurality of systems having the same configuration corresponding to the water wall pipes, and the drain generated in the upstream divided water wall system is separated between each divided water wall system. By providing a series drain guide system that can be freely guided to the water wall of the downstream split water wall system, and preferably by providing a self-drain recirculation system in at least one of the split water wall systems, the start-up time is improved. When the load changes, including the following, it is possible to operate each divided water wall system in parallel operation mode, series operation mode, series operation high temperature fluid concentration mode, or any mode selected from these intermediate modes, thereby significantly reducing the amount of drain blow. It is possible to achieve a reduction in start-up time associated with this, an improvement in steam pressure control response associated with improved controllability of steam pressure, and an elimination of reverse steam pressure response that occurs when switching between circulating and continuous flow operation.

[Brief explanation of the drawing]

Figure 1 is a water wall system diagram for a conventional once-through boiler, Figure 2 is a system diagram of drain tank level control applied to the water wall system in Figure 1, and Figure 3 is the water wall system in Figure 1. The water supply control system diagram, Figure 4, applied to
A water wall system diagram for a once-through boiler according to an embodiment of the present invention, FIG. 5 is a system diagram of the first drain tank level control applied to the water wall system of FIG. 4, and FIG. 6 is a system diagram of the water wall system of FIG. 4. Figure 7 is a system diagram of the second drain tank level control applied to the system, and Figure 8 is a control system diagram of the water wall parallel water supply flow control valve applied to the water wall system of Figure 4.
4 is a control system diagram of the water supply flow regulating valve applied to FIG. 4, and FIG. 9 is a fluid flow rate change diagram according to operation mode for explaining the effects of the embodiment of the present invention. 2... Boiler feed water flow control valve, 3... Drain recirculation confluence section, 4... Energy saver, 5... Water wall, 6... Steam water separator, 8... Drain tank, 9... Drain recirculation Circulation pump, 10... Drain recirculation flow control valve, 13...
... Drain tank blow flow control valve, 18 ... Water supply command, 19 ... Economizer outlet fluid temperature detector, 20 ...
...Water wall pressure detector, 24, 27...Subtraction element, 2
5, 28...Proportional integral element, 26...Function element,
Signal height selection element, 33...Movable nozzle, 35...
First divided water wall, 36... First steam/water separator, 37...
...first drain tank, 38...first drain recirculation pump, 39...first drain recirculation series flow control valve,
40...First drain recirculation parallel flow control valve, 42...
Water supply parallel flow control valve, 44...Second divided water wall, 45...
...Second steam/water separator, 46...Steam confluence section, 47...
...Second drain tank, 48...Second drain recirculation concentrated flow control valve, 49...Second drain recirculation distributed flow control valve, 52...First drain blow flow control valve, 53...
1st drain tank level control system, 55...2nd
Drain tank blow flow control valve, 56...Second drain tank level control system, 57...Water wall parallel water supply flow rate control system, 59...Boiler feed water flow rate control system,
60...General control system, 61...Second drain recirculation pump, 62...Water wall series/parallel command, 63...Recirculation concentration distribution command, 64, 65, 70, 72...Function element, 66... Constant element, 67... Signal subtraction element, 68, 69... Signal multiplication element, 71... Signal height selection element, 73... Signal constant multiplication element, 74...
Minimum value limiting element, 75...Second divided water wall flow rate, 7
6... Second divided water wall evaporation amount, 77... First steam water separator drain amount, 78... Second steam water separator drain amount, 79... Total flow rate of energy saver, 80... Energy saver Inlet recirculation flow rate, 81...Total cumulative amount of drain blow, 8
2...Total evaporation amount, 83...Water supply parallel flow control valve flow rate.

Claims (1)

[Claims] 1. A water wall, a steam/water separator, a drain tank, a drain recirculation pump, a drain recirculation flow control valve, and a drain that reaches the upstream part of the energy saver in sequence along the wake of the energy saver. In once-through boiler equipment equipped with a recirculation system,
The above-mentioned water wall system is divided into a plurality of systems having the same configuration corresponding to the water wall pipes, and the drain generated in the upstream divided water wall system is transferred between the divided water wall systems to the downstream divided water wall system. A once-through boiler device characterized by being provided with a series drain guide system that can be guided freely to the water wall of the boiler. 2. A once-through boiler device according to claim 1, wherein at least one of the divided water wall systems has a self-drain recirculation system.