JP3960467B2 - Water supply method in unit control operation of multi-pipe once-through boiler - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a water supply method in a multi-tube once-through boiler control operation, and more specifically, in the number control of a plurality of multi-tube once-through boilers that supply water to a boiler body via a steam separator. The present invention relates to a method for correcting a water level in a water level detector with a steam / water separator in a boiler in a transient operating state in response to a combustion load rapid increase command.
[0002]
[Prior art]
The multi-pipe once-through boiler includes an upper header, a lower header, and a number of water pipe groups connected between the upper header and the lower header. In this type of boiler, vertical water pipes are arranged in multiple layers so as to surround the combustion chamber, and water pipes that exchange heat with the supplied exhaust gas are densely arranged.
[0003]
In any case, when it is a once-through boiler and a steam separator for removing residual water droplets and dissolved impurities in the generated steam is provided, the reference water level is lower than the upper end of the water pipe. Is set as follows. As a result, all the evaporation pipes (water pipes) function as rising pipes, and the entire interior is not filled with canned water, and a vapor phase is generated in the upper part of the water pipe.
[0004]
When the boiler is in normal operation, the air / water turbidity generated in the water pipe is introduced from the upper pipe to the water / water separator, and the steam after the saturated water is separated is sent to the steam header through the steam pipe. . The steam separator is indispensable for small multi-tube once-through boilers, and is installed at a higher position than the boiler body, which is in communication with the lower header. It is naturally circulated through the boiler body.
[0005]
During operation of the boiler, naturally, the can water in the main body evaporates and decreases, and the water level of the steam separator also decreases. By the way, when water is supplied to the boiler body via the air / water separator, a water level detector that detects a drop in the water level is attached to the air / water separator to supply can water. Then, the water level control device operates based on the water level detected by the water level detector, and the water supply pump is started and stopped by an on / off command from there.
[0006]
The water level detector is provided with a feed water pump off water level detection electrode for detecting the set upper limit water level and a feed water pump on water level detection electrode for detecting the set lower limit water level, and the detection signal of each electrode is input to the water level control device. . For example, when there is a water supply command, water is supplied until the set upper limit water level is reached, and the water supply is stopped when the water supply pump-off water level detection electrode outputs a water detection signal that has reached the upper limit position. When the water level falls and the feed pump on water level detection electrode outputs a signal indicating that there is no canned water at the lower limit position, the water supply is resumed. In this way, the can water is kept between the set lower limit water level and the set upper limit water level.
[0007]
By the way, when a large amount of evaporation is required, instead of covering it with a single boiler, multiple small-capacity or medium-capacity boilers are arranged, and the number of these is controlled to cope with a wide range of load fluctuations. It is often done to be able to. In this case, in a boiler that has received a low load command and continues in a low combustion state, or a boiler that does not supply air but maintains pressure and is on standby to prepare for an increase in load, the reference water level is slightly higher than the set lower limit water level. .
[0008]
[Problems to be solved by the invention]
In the above-mentioned number control operation, when several small capacity boilers, for example, those with an evaporation amount of about 2 tons / hour are arranged, three-position control is performed such that each is 0, 50, 100%. If three boilers are used in such intermittent control, after each boiler exits the low-pressure interlock, it is possible to cope with a change in load that increases or decreases in increments of {(50/300) × 100}%. . However, when controlling the number of units in three positions with a boiler with a large evaporation capacity of 4 tons / hour, it becomes difficult to deal with fine loads, and when it is necessary, PI control (proportional integral control) Will be introduced.
[0009]
In the unit control based on the PI control, as in the case of the three-position control, the control is not based on the pressure of the boiler body, but based on the pressure condition in the steam header required according to the load. That is, in the number control, only one steam header is provided, and steam is sent from the steam separators of all the boilers. On the other hand, changes in the load at the steam supply destination are easily reflected in the entire system. Therefore, based on the load command corresponding to the pressure command value from the steam header, the combustion amount is controlled for one or a plurality of boilers selected to bear the increase / decrease in the evaporation amount.
[0010]
However, if the piping heat capacity between the boiler and the number control pressure detection unit in the steam header is large, it takes time until the pressure fluctuation in the control pressure detection unit reaches the boiler. It is not always the best mode for the boiler. If there is a sudden load increase command in such a situation, the boiler water in the water pipe will transiently expand at once, increasing the amount of evaporation (void), thereby raising the water level and causing carryover. Let the wet steam flow to the steam separator. As a result, the water level rises excessively in the steam / water separator, and the water level detector also exceeds the set upper limit water level.
[0011]
This is thought to be due to the fact that steam is swirling for the steam-water separation action, but in the once-through boiler, the diameter of the steam-water separator is regulated so as not to exceed a certain size. Therefore, it is not always possible to increase the size of the steam separator according to the boiler capacity, sudden introduction of wet steam and forced mixing of water containing voids, Several factors, such as the occurrence of foaming and bubbling due to the above, may cause the water level detector to appear at a level far from the actual level.
[0012]
When such a situation occurs, the water level is first set to the set upper limit water level L as indicated by the one-dot chain line A in FIG. _H When the voids and the like are extremely few, the time exceeding the actual water level is significantly longer than the actual water level represented by the broken line B. In addition, the set lower limit water level L descends from the high water level. _L It may take a lot of time to get close to.
[0013]
However, the set lower limit water level L _L When the water is reached and water is supplied, the void drops at this point and the water level is L _D Plunges to a low water level. This is the lower limit water level L _L This is because the water level does not exhibit the actual water level commensurate with the amount of canned water until it reaches the point, and suddenly returns to the actual water level when water is supplied.
[0014]
This happens only when special conditions overlap, but it means that the low water level has been raised before the set lower limit water level is reached. Water supply will start when the set lower limit water level is exceeded, but it will take time for water supply because the canned water is too low, or the generation of steam will stagnate or decrease, making the number control response worse. There is a problem.
[0015]
The present invention has been made in view of the above problems, and its purpose is to apply a combustion load with a large increase based on a rapid increase in load to a boiler subject to unit control not only in three-position control but also in PI control. In the unit control operation of a multi-tube type once-through boiler, the water level detector prevents the occurrence of a water level far from the actual situation, avoids the delay in recovery of canned water volume, and realizes unit control with good response. It is to provide a water supply method.
[0016]
[Means for Solving the Problems]
The present invention is provided with a steam / water separator that receives steam from the boiler body and returns saturated water separated from the steam to the boiler body, and supplies water to the boiler body through the steam / water separator. Among the multiple tubular once-through boilers, the load corresponding to the pressure condition of the steam header where steam is collected from the steam separator of each boiler for the boiler whose combustion amount is to be changed in response to the load change This is applied to the unit control operation method in which the burnup is controlled based on the command. The feature is that, referring to FIG. 1, FIG. 2 and FIG. 4, the increase range of the load command value from the steam header 4 for the boiler 1A whose combustion amount is to be changed is determined in advance. When it is above (S2), even though the water supply pump 3A of the boiler is off (S5), the set upper limit water level L in the water level detector 7A _H If the detection of the water level exceeding S is continued (S6), and the setting lower limit water level L during the continuation _L If a higher water level continues to be detected (S12), a predetermined time integration value (K) of the load commanded during the continuation exceeds a preset load integration limit value (S13). Length of time (t _c ), The feed water pump 3A is driven to replenish boiler water via the steam separator 2A (S16).
[0017]
A predetermined length of time (t _c ) Instead of setting the time when the feed water pump is driven to be the time when the time integral value of the load exceeds a preset load integration limit value, the set upper limit water level L in the water level detector 7A _H The time Ta from the time when the water level was detected exceeding the preset time limit (t _b ) May be exceeded.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Below, the water supply method in the unit control operation of the multi-tube once-through boiler according to the present invention will be described in detail with reference to the drawings. FIG. 2 shows a system diagram in the case where the number of three multi-tube once-through boilers 1A, 1B, 1C is controlled. Each boiler is provided with steam / water separators 2A, 2B, and 2C that receive steam from the boiler body and return naturally separated saturated water separated from the steam to the water pipe of the boiler body. Since water is supplied to the boiler body through this steam separator, each of the feed water pumps 3A, 3B, 3C is connected to each steam separator.
[0019]
The steam generated from these multitubular once-through boilers is collected in one steam header 4 after passing through each steam separator. Therefore, it is possible to control the burnup based on the load command corresponding to the pressure condition of the steam header by the command from the unit control device 5 so that the boiler whose combustion amount is to be changed in response to the load change of the steam supply destination. It can be done.
[0020]
The number control device is a microcomputer, and when the pressure command value of the steam header 4 is read and calculation necessary for the number control is performed, a signal for defining the combustion amount is output to the combustion devices 6A, 6B, 6C of each boiler. It is supposed to be. The water supply pumps 3A, 3B, and 3C are started and stopped by water level controllers 8A, 8B, and 8C that receive detection signals from the water level detectors 7A, 7B, and 7C attached to the respective steam separators. Incidentally, 9A, 9B, and 9C in the figure are water level meters, which are used for visualizing the water levels of the water level detectors 7A, 7B, and 7C.
[0021]
When a once-through boiler with a steam amount of, for example, 4 tons / hour is used in the unit control system having such a device configuration, PI (proportional integral) control is adopted for the operation control, and the combustion amount that closely corresponds to the load change. Consideration will be given to increase or decrease. According to this PI control, various combustion loads can be commanded to any boiler, but in order to simplify the following explanation, the boilers 1B and 1C are currently operated at 100% load, It is assumed that the boiler 1A is in a steady operation with a 40% load. Therefore, there is an increase allowance of 60% until the total amount of steam corresponding to the maximum 300% is generated.
[0022]
Next, a supplementary water supply method in the unit control operation will be described. Referring also to FIG. 1A, as described in the section of the prior art, the alternate long and short dash line A indicates the set lower limit water level L. _L However, in the present invention, the water level is not set to the set lower limit water level L instead of eliminating the void by normal water supply. _L Another water supply is forcibly performed at a very early stage before reaching the water level, and the expansion of the can water in the water level detector 7A is extinguished in advance by this supplementary water supply, and the water level is corrected.
[0023]
Here, an outline of the main part of the operation in the present method will be described in advance in order to facilitate understanding of the later description. Point M on the dot-and-dash line A, that is, the water level is still the set upper limit water level L _H At a certain time, a water supply command is input from the number control device 5 to the water level controller 8A, and based on this, the water supply pump 3A is operated for a short time. Regardless of the presence or absence of voids, _D The time t until the amount corresponding to _d Are the same, the water level after being fed at point M follows a solid line C descending towards point N.
[0024]
This solid line C is the set lower limit water level L _L When reaching the water level controller 8A, the water level controller 8A operates the water supply pump 3A to start regular water supply. After that, the water level is the set lower limit water level L _L As long as it recovers as described above and a command to change the combustion amount is not issued, the operation is continued with the water level within the allowable range. The generated steam is led to the steam header 4 together with steam from the other boilers 1B and 1C through the steam separator 2A.
[0025]
A little more detail. First, the above-described boiler 1A is a boiler that is in a standby operation in the unit control operation or is already in a steady operation based on a combustion amount corresponding to a load. And this boiler is handled as the object of the combustion amount increase / decrease at the time of load change control of unit control. In this case, the water levels of the boiler main body, the steam separator 2A, and the water level detector 7A are initially set at the reference water level L as shown in the left part of the alternate long and short dash line A in FIG. _R It is in.
[0026]
Now, as shown in FIG. 1B, the combustion load is suddenly reduced to, for example, 100% based on the pressure command value of the steam header 4 with respect to the boiler 1A in a steady operation with a load of 40% from the unit control device 5. Suppose a high combustion command is issued. Because it is dominated by PI control, even if it does not increase step by step to 100%, a gradual increase command is given from 40% to 100% continuously or in 3% increments in a short time (See line X).
[0027]
Thus, since the startup of 60% requires a rapid increase in the burnup, the rapidly heated boiler water expands at once, the evaporation becomes active and at the same time the voids increase, thereby greatly increasing the water level. As described in the section of the prior art, in the water level detector 7A, as shown in FIG. _H Over. Now, if the load increase range is up to 20%, there is no problem, but if it is known in advance that an abnormal water level will appear in the steam separator 2A and then the water level detector 7A, the above 60% increase range is obvious. It is in the area where the abnormal water level appears.
[0028]
The above numerical value such as 20% is unique to each boiler, and may be determined in advance when introducing software for controlling the number of units. The value will be referred to as a load increase reference value hereinafter. The above explanation is that when the increase width of the load command value from the steam header 4 for the boiler 1A is equal to or greater than the load increase reference value, that is, When the combustion command is received from the current burnup to the corresponding burnup so that the boiler operates in accordance with the load increase command value, the following other conditions also overlap The replenishment water supply control comes to work.
[0029]
The other conditions are that the feed water pump 3A of the boiler 1A is off, and the set upper limit water level L that is the pump-off command water level in the water level detector 7A. _H The detection lower limit water level L is continuously detected and the pump-on command water level is exceeded. _L This means that higher water levels continue to be detected. That is, the former teaches that the expansion of can water is severe, and the latter teaches that no water has been supplied until this monitoring time.
[0030]
In addition, about the latter, it can replace with monitoring a water level and can also monitor the presence or absence of activation of a water supply pump. When the water pump is not activated, the water level is the set lower limit water level L _L If the pump has been activated even once, the supplementary water supply control must be executed after that unless the load command value exceeds the load increase reference value again. Because there is no possibility.
[0031]
By the way, in the above control, the water level is the set upper limit water level L. _H How long it lasts for the replenishment water supply is appropriate, and what is the replenishment water supply time. One of the determinations of the former is, in the simplest case, only to find out empirically the allowable duration (hereinafter referred to as the waiting time limit) specific to the boiler. By folding it into the control software, the replenishment water supply can be started when the standby limit time has elapsed. This operation will be briefly described later with reference to FIGS.
[0032]
The number control device is a microcomputer as described above, and the following control can be introduced by utilizing the high-speed calculation function. It is the set upper limit water level L _H The time integral value of the commanded load is calculated while exceeding the limit value, and when this exceeds the preset load integration limit value, the undesired behavior of the can water caused by voids by driving the feed pump It is intended to calm down. Needless to say, the actual water level is corrected by this, and thereafter, the operation for 100% load is continued with the on / off control of the feed water pump 3A.
[0033]
The operation of the pump for replenishing water supply may be determined in advance to be given a time of, for example, 10 seconds. This replenishment water supply time may be determined based on the capacity for storing canned water in the steam separator 2A, the discharge performance of the water supply pump 3A, etc., and does not require a long time. The operation of driving the water supply pump to dissipate voids when the load integration limit value is exceeded will be described below using the flowcharts of FIGS. 4 and 5.
[0034]
When the load increase command based on the pressure command value from the steam header is issued during the unit control operation, the combustion amount change command is issued for the boiler 1A in the 40% load operation state (step of the flowchart of FIG. 4). 1, hereinafter referred to as S1). First, it is determined whether the increase range of the load command value is equal to or greater than the load increase reference value (S2). If it is equal to or greater than 20% as described above, a calculation storage value K described later is set to 0 ( S4).
[0035]
At this time, whether or not the feed water pump 3A is moving, that is, the feed water pump on water level detection electrode 10L shown in FIG. _L ) Is not cut (S5), the water level continues to be the set upper limit water level L. _H , That is, the feed water pump-off water level detection electrode 10H has a pump-off command water level (set upper limit water level L _H It is checked whether or not the above water level is detected (S6). Incidentally, reference numeral 10E in FIG. 3 is a lower limit water level detection electrode for detecting the operation limit water level. If no water detection signal is output from now on, the burner of the corresponding boiler is stopped and airing is prevented. The
[0036]
Current water level is set upper limit water level L _H If it exceeds, the control mode for the supplementary water supply is entered for the first time at this point. Since the counter i is set to 0 in step 3, the counter i is incremented by 1 (S 7), i is confirmed to be 1 (S 8), and the unit control device 5 determines the current load command value LC _i (= LC ₁ ) Is read (S9). Even if the load command increases from 40% to 100% as described above, it is increased so that it gradually increases, for example, 43, 46, 49, 52%. Time is T ₀ Even if (see (a) of FIG. 1), the water level is the set upper limit water level L _H Time to exceed _a (T ₀ + T _a ) Load command value LC at time ₁ Is read.
[0037]
Load command value LC just read ₁ Is multiplied by a predetermined time of, for example, 0.2 seconds, and the calculated storage value F becomes a strip-shaped area in FIG. ₁ Is required (S10). And that F ₁ Is added to the previous K, and a new K is set (S11). At that time, the current water level is again the set lower limit water level L _L Is checked (S12). Setting lower limit water level L _L Since the feed water pump 3A will operate if it is turned off, the current control is no longer necessary, and the flowchart returns and waits for the next load increase command.
[0038]
Setting lower limit water level L _L If not, it is determined whether the current K exceeds the load integration limit value (S13). At present, only one load command value has been read, and since the load integration limit value is not exceeded, control is returned to step 5. Thereafter, steps 6 and 7 are followed. Since the counter i has been incremented to 2, the process proceeds to step 14 via step 8 where the standby state is kept until 0.2 seconds of the predetermined time elapses from the previous reading of the load command value. It should be noted that this 0.2 second is assumed that the control returns to step 5 from step 9 to step 13 processed earlier, and that 0.2 seconds is not consumed until the current step 14 is reached. It is a value set by standing.
[0039]
After the elapse of 0.2 seconds, in step 9 the current load command value LC ₂ Is read and multiplied by a predetermined time of 0.2 seconds to obtain the calculated stored value F ₂ Is required (S10). The value of K in step 11 is F ₁ + F ₂ Then go to Steps 12 and 13. It is assumed that this operation is repeated until i = 170. K obtained at this time is the sum of the area of 170 strips 0.2 × ΣLC _i (I = 1, 2,... 170).
[0040]
This value is given by the area with vertical stripes in FIG. This K ₁₇₀ If the load integration limit value is exceeded (S13), the number control device 5 commands the operation of the water supply pump 3A through the water level controller 8A, and supplementary water supply is started (S15). In FIG. 1 (a), the time until the load time integral value reaches the load integration limit value is indicated by t. _b (= 0.2 seconds × 170 = 34 seconds).
[0041]
When the time is counted and, for example, 10 seconds, which is the specified replenishment water supply time, has elapsed (S16), the water supply pump 3A is stopped. In FIG. 1 (a), the replenishment water supply time zone is t. _c It is expressed as When the replenishment water supply ends (S17), the control is returned to step 1.
[0042]
During this control, the set lower limit water level L _L When a water level lower than S is detected (S12) or when a negative answer is made in Steps 5 and 6, the time integral value of the load that has been calculated so far can be cleared. In step 4, K is reset to zero.
[0043]
0.2 × ΣLC mentioned above _i Since (i = 1, 2,... 170) is the time integral value of the load, it is clear from the equation that LC _i == constant, the calculation in this control can also be applied to intermittent control (see line Y) that changes stepwise, such as three-position control, as shown in FIG. .
[0044]
Incidentally, the load integration limit value described above is the area of the vertical stripe portion in both cases (b) and (c) of FIG. 1, and it goes without saying that it is the same. In the figure, the time required to reach the load integration limit value t _b However, it is shorter in (a) corresponding to the case of (c) than that shown in (a) corresponding to the case of (b).
[0045]
In the flowcharts of FIGS. 6 and 7, the time Ta from when the water level detector detects a water level exceeding the set upper limit water level (S26) is a preset waiting time limit t. _b (S33), the supplementary water supply specified time t _c In this example, the water supply pump is driven for 10 seconds (S38) and the expansion of the can water caused by the voids is calmed down. Steps 27 to 31 and 34 to 36 calculate the time during which the water level exceeding the set upper limit water level continues based on the time read from the clock.
[0046]
The standby limit time is a simple time such as 40 seconds, for example, but the time can be changed in proportion to the magnitude of the load command value exceeding the load increase reference value. If you add it to the software, you can avoid falling into something unique. However, since the load integration limit value in the flowcharts of FIGS. 4 and 5 is determined based on the input energy, the control accuracy is better than in the case of FIGS. 6 and 7.
[0047]
【The invention's effect】
As can be seen from the above detailed description, according to the present invention, when there is a demand for high combustion based on the load command due to the unit control, an excessively long high water level is generated due to the occurrence of voids and the like. However, it can be solved by replenishing water that is secured separately from regular water supply. That is, the water level in the steam separator or the water level detector can be corrected in advance so as to indicate the actual water level. Therefore, the situation where the water level has already become low when the water level falls below the set lower limit water level can be avoided.
[0048]
If the low water level caused by the large load increase is resolved, the behavior of the boiler body during normal operation is maintained, and evaporation of water and stagnation during the unit control can be avoided, and as a result Unit control without sacrificing performance.
[0049]
Whether the replenishment water supply is necessary or not based on the integrated time value of the load or on the basis of the standby limit time, the water level that appears as the combustion load suddenly increases is appropriately determined. It can be corrected to the actual water level at any time. When using the time integral value of the load, improvement of control accuracy is expected, and when based on the standby limit time, simplification of control is expected.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 explains a water supply method in a unit control operation of a multitubular once-through boiler according to the present invention, wherein (a) is a graph showing a temporal change of a water level in a water level detector, and (b) is a PI. The graph which shows the calculation point of the time integral value of the load in control, (c) is a graph at the time of applying to intermittent control.
FIG. 2 is an overall system diagram when three multi-pipe once-through boilers are operated in a unit-controlled manner.
FIG. 3 is a schematic diagram showing the internal structure of a water level detector.
FIG. 4 is a flowchart showing a procedure for supplying supplementary water based on a time integral value of a load.
FIG. 5 is a flowchart following FIG. 4;
FIG. 6 is a flowchart showing a procedure for supplying supplementary water based on a length of time exceeding a set upper limit water level.
FIG. 7 is a flowchart following FIG. 6;
[Explanation of symbols]
1A, 1B, 1C ... multi-pipe once-through boiler, 2A, 2B, 2C ... steam separator, 3A, 3B, 3C ... feed pump, 4 ... steam header, 5 ... number control device, 6A, 6B, 6C ... combustion 7A, 7B, 7C ... Water level detector, 10H ... Feed water pump-off water level detection electrode, 10L ... Feed water pump on water level detection electrode, L _H ... Set upper limit water level (pump-off command water level), L _L ... Setting lower limit water level (pump-on command water level), L _R ... reference water level, LC _i ... Load command value, t _b ... Time to reach load integration limit value during PI control, and standby limit time during intermittent control, t _c ... replenishment water supply time.

Claims (2)

A multi-pipe once-through boiler is provided with a steam-water separator that receives steam from the boiler body and returns saturated water separated from the steam to the boiler body, and supplies water to the boiler body through the steam-water separator. Based on the load command according to the pressure condition of the steam header in which steam is collected from the steam separator of each boiler, for the boiler that is subject to combustion amount change in response to the load change, In the unit control operation method to control the burnup,
When the increase range of the load command value from the steam header for the boiler whose combustion amount is to be changed is greater than or equal to a predetermined increase range, the water supply pump of the boiler is off If the water level detector continues to detect the water level that exceeds the set upper limit water level and continues to detect a water level that is higher than the set lower limit water level, the time integral value of the load commanded during the continuation is preset. A multi-tube system characterized in that when a predetermined load integration limit value is exceeded, a predetermined time length water supply pump is driven to replenish boiler water via a steam-water separator. Water supply method in unit control operation of once-through boiler. The start of driving the time water supply pump of a predetermined length according to claim 1 is replaced with a time when the time integral value of the load exceeds a preset load integration limit value. The multi-tube according to claim 1, wherein a time from when a water level exceeding a set upper limit water level is detected by the water level detector is a time point when a preset standby limit time is exceeded. Water supply method in the unit control operation of the type once-through boiler.

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