JP6349946B2 - Boiler system - Google Patents

Description

  The present invention relates to a boiler system.

  Conventionally, as a boiler system, by controlling the opening of a water supply motor valve and continuously supplying water collected in a drain tank to an economizer, the drain is prevented from boiling in the economizer. Yes (see, for example, Patent Document 1).

  In the conventional boiler system, when the water level in the boiler is lowered, the opening degree of the water supply motor valve is merely adjusted so that the target flow rate is obtained. Although the target flow rate is set according to the combustion state of the burner, it is difficult to make it an appropriate amount when a change in the feed water temperature occurs, such as during cold start.

  Usually, the water supply temperature of the drain is high (for example, 130 ° C.), but may be low (for example, 20 ° C.) at the time of cold start. At this time, if water is supplied to the boiler with the target water supply determined based on the high temperature of the water supply, there is a problem that the water supply exceeds the amount of evaporation in the boiler, and conversely the water level rises (2 points in FIG. 3). This is indicated by a line connecting chain circles, which is a line indicating a target flow rate when the volume flow rate is constant and 130 ° C. as a reference). This problem is particularly noticeable in the case of small boilers.

JP 2012-2385 A

  This invention makes it a subject to reduce the water level in a boiler reliably, preventing drain boiling in heat exchangers, such as an economizer, irrespective of the difference in feed water temperature.

As a means for solving the above problems, the present invention provides:
With a boiler,
A heat exchanger for preheating water supplied to the boiler with exhaust gas from the boiler;
A flow rate adjusting means for adjusting the amount of water supplied to the heat exchanger;
A water level sensor for detecting the water level in the boiler;
After the water level detected by the water level sensor reaches the upper limit water level, the target water supply amount is changed between the actual evaporation amount and the boiling limit amount according to the water supply temperature to the heat exchanger while the lower limit water level is exceeded. Control means for controlling the flow rate adjusting means based on the target water supply amount ;
A boiler system characterized by comprising:

  With this configuration, the flow rate is adjusted within a range that does not exceed the actual evaporation amount, so the water level in the boiler can be lowered. Moreover, since the flow rate is adjusted in a range exceeding the boiling limit amount, boiling in the heat exchanger can be surely prevented. In particular, because the amount of water supply is adjusted according to the difference in the temperature of the water supply to the heat exchanger, the water level in the boiler is lowered, and boiling in the heat exchanger is more appropriately prevented. can do.

  In this case, it is preferable that the control means controls the flow rate adjusting means so that the amount of water supplied to the heat exchanger decreases as the temperature of the water supplied to the heat exchanger decreases.

  With this configuration, it is possible to more reliably prevent supercharging water in a state where the water temperature is low, such as during cold start.

  The control means is a range in which the amount of water supplied to the heat exchanger exceeds a lower limit value of water supply that is larger than the boiling limit amount, does not exceed the upper limit value of water supply that is smaller than the actual evaporation amount and larger than the lower limit value of water supply. It is preferable to control the flow rate adjusting means so that

  With this configuration, it is possible to reliably reduce the water level in the boiler and prevent boiling in the heat exchanger, and no malfunction occurs.

  If the water supply to the boiler is drain collected in a closed manner, the effect of the above configuration becomes more effective.

  According to the present invention, the amount of water supplied to the heat exchanger is adjusted according to the difference in the water supply temperature to the heat exchanger within the range of the actual evaporation amount and the boiling limit amount. Regardless, it is possible to reliably reduce the water level by suppressing the amount of water supplied to the boiler while preventing boiling in the heat exchanger.

It is a schematic explanatory drawing of the boiler system which concerns on this embodiment. It is a flowchart which shows the processing content performed with the control apparatus of FIG. It is a graph which shows the relationship between feed water temperature and the amount of feed water.

  Embodiments according to the present invention will be described below with reference to the accompanying drawings. In addition, the following description is only illustrations essentially and does not intend restrict | limiting this invention, its application thing, or its use. Further, the drawings are schematic, and the ratio of each dimension is different from the actual one.

  FIG. 1 shows a boiler system according to this embodiment. In this boiler system, steam generated in the boiler 1 is supplied to a load device 3 such as a heat exchanger via a steam header 2, and the drain generated in the load device 3 is supplied to a drain tank 4 via a steam trap 3a. It is configured to collect and return to the boiler 1.

  As the boiler 1, for example, a multi-tube once-through boiler is used, and a pressure sensor 5 for detecting the internal pressure and a water level sensor 6 for detecting the internal water level are provided therein. The output of each sensor is input to a control device 14 (for example, a microcomputer) described later. An economizer 7 is attached to the boiler 1. The economizer 7 is an example of a heat exchanger for preheating (preheating) the water supplied to the boiler 1 with the exhaust gas from the boiler 1. The boiler 1 is supplied with fuel via a fuel supply line 1b having a flow rate adjusting valve 1a.

  The steam header 2 is provided for temporarily storing steam generated in the boiler 1 and supplying the steam to the load device 3.

  The load device 3 includes, for example, a heat exchanger that uses the heat of steam supplied from the boiler 1 to make the heat available to other devices.

  The drain tank 4 is a closed type sealed type, and the bottom thereof and the bottom of the economizer 7 are connected by a water supply pipe 8. In the middle of the water supply pipe 8, a water supply pump 9, a flow sensor 10, a water supply motor valve 11, and a check valve 12 are provided in this order from the drain tank 4 side. The inlet temperature of the economizer 7 is detected by the temperature sensor 13. The upper part of the drain tank 4 is connected to the upper part of a makeup water tank 16 to be described later via a pressure regulating valve 15, and the generated flash steam is discharged. Note that flash steam refers to a part of condensed water that becomes steam when high-temperature and high-pressure condensed water (also called condensate or drain water) is exposed to a low-pressure atmosphere. be called.

  The control device 14 receives input of various detection signals from the water level sensor 6, the flow rate sensor 10, the temperature sensor 13, and the like, and drives and controls the water supply pump 9, the water supply motor valve 11 and the like.

  Reference numeral 16 denotes a makeup water tank, which is connected to the drain tank 4 via a water pump 17 and a check valve 18. When the amount of drain used is large and the water level in the drain tank 4 falls below the lower limit water level, the water supply pump 17 is driven to supply the makeup water from the makeup water tank 16 to the drain tank 4. The makeup water tank 16 is connected to the boiler 1 via a water pump 19 and a check valve 20. When the water level of the drain tank 4 is lowered and water supply to the boiler 1 is not in time, water can be directly supplied from the makeup water tank 16 to the boiler 1.

  Next, the operation of the boiler system configured as described above will be described with reference to the flowchart of FIG.

  In the standby state where the burner is not burned in the boiler 1, there is no fear that the drain boils in the economizer 7. Fully closed.

  Further, if the burner in the boiler 1 is in a state of being burned (for example, two stages of high or low, three stages of high, medium or low, etc.), the water supply motor valve 11 is operated as follows. Adjust the opening.

  That is, first, a detection signal from the water level sensor 6 that detects the water level in the boiler 1 is read (step S1), and the presence or absence of a water supply request is determined based on the read detection water level (step S2). Whether or not there is a water supply request is determined by determining whether or not the water level detected by the water level sensor is equal to or lower than a preset lower limit water level.

  If the detected water level is equal to or lower than the lower limit water level (step S2: YES), it is determined that there is a water supply request, a water supply signal “present” is transmitted to the water supply motor valve 11, and the water supply pipe 8 is fully opened (step S3). ). Thereby, the water level in the boiler 1 rises. Here, it is determined whether or not the detected water level has reached the upper limit water level (step S4). And the water supply in the state which fully opened the water supply piping 8 is continued until the water level in the boiler 1 reaches an upper limit water level.

  If the detected water level exceeds the upper limit water level (step S4: YES), it is determined that there is no water supply request, a water supply signal “None” is transmitted to the water supply motor valve 11, and the opening of the water supply pipe 8 is as follows. Adjust. That is, the target water supply amount is determined so that the water supply amount changes between the actual evaporation amount and the boiling limit amount according to the difference in the water supply temperature, and the water supply amount for adjusting the opening of the water supply pipe 8 based on the target water supply amount A quantity adjustment process is executed (step S5). This water supply amount adjustment process is continued while the detected water level exceeds the lower limit water level (step S2: NO).

  Specifically, as shown in the graph of FIG. 3, the actual evaporation amount (shown by a line connecting the black squares (♦) in FIG. 3) and the boiling limit amount (black triangles in FIG. And a linear function (indicated by a solid line in FIG. 3) that changes between the two graphs is determined as a target water supply amount for a certain water supply temperature. When the feed water temperature is changed, the actual evaporation amount is obtained in advance through experiments or the like to determine the feed water amount that reaches the evaporation amount at the feed water temperature. When the feed water temperature is changed, the boiling limit amount is obtained in advance through experiments or the like to obtain the feed water amount that reaches the saturation temperature at the outlet of the economizer 7 at the feed water temperature. The linear function may be, for example, a straight line connecting an intermediate value of the water supply amount at the maximum water supply temperature and an intermediate value of the water supply amount at the minimum water supply temperature. However, the method of determining the linear function is not limited to this, and any straight line may be used as long as it does not intersect the graph of the actual evaporation amount and the boiling limit amount. Further, not limited to the linear function, for example, it may be determined as what percentage of the difference between the actual evaporation amount at a certain feed water temperature and the boiling limit amount.

  As described above, when there is no water supply request and it is necessary to lower the water level in the boiler 1 when burning in the boiler 1, the water supply amount is adjusted so as not to exceed the actual evaporation amount. This requirement can be met. That is, even if the water supply temperature changes, the target water supply amount is changed to an appropriate value according to the change. Therefore, even if the feed water temperature becomes high, the feed water amount can be set so as not to exceed the actual evaporation amount. Moreover, even if the water supply temperature is lowered, the amount of water supply can be made according to the temperature drop. As a result, it is possible to reliably prevent the supercharging water to the boiler 1 regardless of the difference in the feed water temperature. Moreover, the boiling in the economizer 7 can be prevented by adjusting the target water supply amount to exceed the boiling limit amount. Also in this case, since the water supply amount can be adjusted according to the change in the water supply temperature, it is possible to reliably prevent boiling in the economizer 7 even when the water supply temperature is high and the boiling limit amount is close to the actual evaporation amount. Is possible.

  In particular, in the small closed drain tank 4 (for example, the weight of the drainable storable water is about 10 kg), the water supply temperature is close to the saturation temperature in the operating pressure range. It is possible to reliably prevent supercharging water regardless of the difference in water supply temperature, while preventing boiling inside.

  In addition, this invention is not limited to the structure described in the said embodiment, A various change is possible.

  For example, in the above embodiment, the actual evaporation amount and the boiling limit amount are determined by experiments or the like. However, the actual evaporation amount and the boiling limit amount may be determined using a mathematical formula with the feed water temperature as a variable. In short, it is only necessary to be able to grasp the actual evaporation amount and the boiling limit amount that change depending on the difference in the feed water temperature.

  In the above embodiment, the target water supply amount is determined by aiming at the approximate median of the actual evaporation amount and the boiling limit amount. However, it is preferable to set the target water supply amount to a smaller value as the water supply temperature is lower. . And by controlling the drive of the water supply motor valve 11 based on this target water supply amount, the water supply amount to the boiler 1 can be suppressed as the water supply temperature is lower. According to this, in the state where the water temperature is low, such as at the time of cold start, the amount of water supplied to the boiler 1 through the economizer 7 becomes excessive and the occurrence of a problem that the water level rises more reliably. Can be prevented.

  In the above embodiment, the target water supply amount is changed between the actual evaporation amount and the boiling limit amount according to the difference in the water supply temperature, but the water supply upper limit value and the water supply lower limit value are determined and changed between them. You may make it make it. The supply water upper limit value may be a value smaller than the actual evaporation amount by a predetermined value (for example, 50 kg / h). The water supply lower limit value may be a value smaller than the water supply upper limit value and larger than the boiling limit amount by a predetermined value (for example, 50 kg / h).

  According to this, if the target water supply amount is changed between the water supply upper limit value and the water supply lower limit value, even if it is a change that becomes the water supply upper limit value or the water supply lower limit value, the change to the boiler 1 even temporarily. It is possible to reliably prevent the actual water supply amount from exceeding the actual evaporation amount or from falling below the boiling limit amount. That is, it is possible to reliably prevent the state of supercharged water in which the water level in the boiler 1 rises and the state in which the drain is boiled by the economizer 7.

  Moreover, in the said embodiment, although the economizer 7 was demonstrated as an example of a heat exchanger, if the amount of water supply to the boiler 1 can be suppressed, preventing the boiling inside, other types of heat exchangers However, it can be adopted.

DESCRIPTION OF SYMBOLS 1 ... Boiler 2 ... Steam header 3 ... Load equipment 4 ... Drain tank 5 ... Pressure sensor 6 ... Water level sensor 7 ... Economizer (heat exchanger)
8 ... Water supply piping 9 ... Water supply pump 10 ... Flow sensor 11 ... Water supply motor valve (flow rate adjusting means)
12 ... Check valve 13 ... Temperature sensor 14 ... Control device (control means)
DESCRIPTION OF SYMBOLS 15 ... Pressure regulating valve 16 ... Supply water tank 17 ... Water pump 18 ... Check valve 19 ... Water pump 20 ... Check valve

Claims (4)

With a boiler,
A heat exchanger for preheating water supplied to the boiler with exhaust gas from the boiler;
A flow rate adjusting means for adjusting the amount of water supplied to the heat exchanger;
A water level sensor for detecting the water level in the boiler;
After the water level detected by the water level sensor reaches the upper limit water level, the target water supply amount is changed between the actual evaporation amount and the boiling limit amount according to the water supply temperature to the heat exchanger while the lower limit water level is exceeded. Control means for controlling the flow rate adjusting means based on the target water supply amount ;
A boiler system characterized by comprising   2. The boiler system according to claim 1, wherein the control unit controls the flow rate adjusting unit so that the amount of water supplied to the heat exchanger decreases as the temperature of the water supplied to the heat exchanger decreases. .   The control means is a range in which the amount of water supplied to the heat exchanger exceeds a lower limit value of water supply that is larger than the boiling limit amount, does not exceed the upper limit value of water supply that is smaller than the actual evaporation amount and larger than the lower limit value of water supply. The boiler system according to claim 1 or 2, wherein the flow rate adjusting means is controlled so that   The boiler system according to any one of claims 1 to 3, wherein water supplied to the boiler is drain collected by a closed system.

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