JP3762098B2 - Control method of once-through boiler - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for controlling a once-through boiler. More specifically, the present invention calculates the superheat degree of the evaporation pipe during the steady-state operation of the once-through boiler (hereinafter referred to as steady operation), and aims to maintain this constant. The present invention relates to a method for economically operating a once-through boiler by controlling the amount of water discharged from a steam separator.
[0002]
[Prior art]
In general, a once-through boiler is provided with a large number of evaporation pipes on the wall inside the heating furnace, and when the desalted water is supplied to the evaporation pipes from a water supply amount control valve through a economizer, the outlet of the evaporation pipes is provided. The steam is adjusted so as to become wet saturated steam, that is, saturated steam containing mist-like water droplets. The wet saturated steam at the outlet of the evaporator tube is guided to the steam separator and separated from the steam, and then supplied to the superheater as dry saturated steam, that is, saturated steam containing no water droplets. Condensed water from the steam separator is extracted as blown water by an extraction water amount control valve.
[0003]
In the operation of once-through boilers, it is important to improve the economic efficiency of steam generation while preventing abnormal overheating of each evaporator tube. , Referred to as “moisture”), that is, the ratio of mist-like water droplets contained in superheated steam.
[0004]
As a method for controlling the moisture of the wet steam at the outlet of the evaporator pipe, there is a method of setting the ratio of the boiler main feed water flow rate to the dry steam flow rate after this steam is separated into steam and water. However, it is difficult to say that the optimum operation is being performed because the boiler manufacturer's recommended values and user experience values are currently used.
[0005]
[Problems to be solved by the invention]
As a method of balancing the moisture of saturated steam at the outlet of each evaporator, the water supply is reduced until the outlet steam temperature of all the evaporators reaches a superheated area with a constant boiler load, and the temperature is kept within a certain range. There is a method in which the throttle valve is manually adjusted so that it is kept uniform. However, in this method, even after adjusting the throttle valve, the moisture of the steam separator inlet steam and the moisture of each evaporator outlet steam, especially the lowest one of the evaporator moisture (hereinafter referred to as the lowest moisture), Steady operation will be carried out without sufficiently improving the deviation. Here, the steam moisture at the inlet of the steam separator can be easily calculated from the mass balance such as the ratio of the amount of water withdrawn and the amount of feed water. It is not possible to calculate the moisture of the outlet steam of each evaporator tube from the moisture of the separator. Therefore, in the steady operation, only the steam moisture at the inlet of the steam separator is managed, but the steam moisture at the inlet of the steam separator and the evaporation pipe are changed due to the scaling of the throttle valve and the change in the heat balance in the heating furnace. Since the correlation with the minimum moisture at the outlet also changes, if the evaporator tube is always managed so as not to be overheated abnormally, the set value of the moisture gradually increases, which causes uneconomical operation. Therefore, there is a demand for a control method that manages the evaporator tube so that it does not overheat and prevents the set value of the moisture from becoming uneconomical operation.
[0006]
In view of the above, it is an object of the present invention to provide a method for controlling a once-through boiler capable of economical operation at as high a temperature as possible while preventing abnormal overheating of the evaporation pipe.
[0007]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems of the prior art, the present inventors pay attention to the fact that the amount of change in the outlet temperature of the evaporator tube increases as the overheated state is reached. Appropriate moisture by calculating the superheat degree of the evaporation pipe by appropriately calculating the temperature change amount, and controlling the amount of water supply and the amount of water extracted from the steam / water separator so as to maintain this superheat degree constant The present invention has been found to be manageable.
[0008]
That is, the gist of the present invention is that a feed water system capable of adjusting a feed water flow rate, a heating furnace having a plurality of evaporation pipes each connected to the feed water system via a throttle valve, and an amount of discharged water connected to the evaporation pipe In a method for controlling a once-through boiler comprising a steam separator having a control valve,
In each control cycle, the temperature of the outlet steam or the amount of change in the temperature of the one evaporation tube where the amount of change in the temperature is maximum is detected,
A predetermined calculation is added to the detected amount of change in temperature to calculate the degree of superheat of the evaporation tube,
The present invention resides in a method for controlling a once-through boiler, characterized in that the amount of water supplied and / or the amount of water extracted from the steam separator is adjusted to maintain the degree of superheat of the evaporator pipe in the vicinity of a target value.
[0009]
According to the control method for the once-through boiler of the present invention, the degree of superheat of the evaporator pipe is determined based on the maximum value of the temperature change of the evaporator pipe, and the evaporator pipe showing this maximum value is most likely to cause abnormal overheating. Therefore, it is easy to monitor the abnormal overheating of the evaporator tube. Therefore, while suppressing the abnormal overheating of the evaporator tube, it is possible to maintain an appropriate degree of superheat with less moisture, and it is possible to economically operate the boiler.
[0010]
Here, the target value of the evaporation pipe superheat degree can be determined by, for example, a trial and error method. In this case, the amount of water absorption can be reduced during normal operation, and the degree of superheat of the evaporator tube immediately before the evaporator tube is abnormally overheated can be obtained and selected as the target value. The predetermined calculation can be performed by applying the detected temperature change amount in each control cycle to a first-order lag filter or a moving average filter. In this case, the degree of superheat of the evaporator tube suitable for economic operation can be obtained.
[0011]
When the detected change in temperature is a negative value, it is also a preferred aspect of the present invention to replace the negative change with its absolute value or zero. In this case, particularly steep changes in operating conditions can be avoided.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail. FIG. 1 schematically shows a configuration example of a once-through boiler including a control system for carrying out the method of the present invention. In the figure, reference numeral 1 denotes a heating furnace, and a large number (for example, about 60) of evaporation tubes 2 are arranged on the inner wall surface. Each evaporation pipe 2 is provided with a throttle valve 3, and by adjusting each throttle valve 3, the amount of water supplied to the corresponding evaporation pipe 2 can be adjusted individually. The supplied water is introduced into the heating furnace 1 from the pipe 4 through the water supply amount adjusting valve 5, the economizer 6 and the pipe 7, and is evaporated in the evaporation pipe 2 to become wet saturated steam. This wet saturated steam is led to the steam separator 9 via the pipe 8, where it is separated into dry saturated steam and water. The separated water is extracted from the pipe 11 through the extraction water amount control valve 10. The dry saturated steam is extracted from the pipe 12 through the superheater 13, the superheat reducer 14 (the amount of sprayed water is adjusted by the sprayed water amount control valve 15) and the superheater 16 while adjusting the enthalpy, and various kinds of boiler generated steam are used. Served for use.
[0013]
The temperature of the outlet steam of each evaporation pipe 2 is constantly monitored by a steam thermometer 17, and the temperature data is input to a computer 18. Similarly, data relating to the amount of water supplied to the heating furnace, the flow rate of dry saturated steam at the outlet of the steam separator, and the flow rate of water discharged from the steam separator are input to the computer 18. Here, the water flow rate withdrawn from the steam / water separator may be measured directly, or may be calculated from the opening degree of the withdrawing water amount control valve and its valve characteristics. The moisture of the steam at the inlet of the steam / water separator obtained from these data is output by the computer 18 to the internal control device 19 of the boiler, whereby the moisture set value in the boiler internal control device 19 is changed. In the boiler internal control device 19, the amount of water supply and / or the amount of withdrawal is adjusted according to the changed set value of moisture, and moisture control of saturated steam at the inlet of the steam separator is performed.
[0014]
Next, a method for calculating the degree of superheat will be described.
(1) First, the amount of change in temperature within a predetermined time of the outlet steam of each evaporator tube during steady operation is obtained. As the amount of change in temperature, it is desirable to use the difference between the temperature of each evaporator tube in the previous control cycle and the temperature of each evaporator tube in the current control cycle.
(2) The maximum amount of change is selected from the amount of change in the temperature of the outlet steam obtained for each evaporator tube.
(3) If the maximum amount of change is a negative number, replace it with its absolute value or zero.
{Circle around (4)} An appropriate filter is applied to the maximum temperature change obtained in each control cycle, and the value is smoothed to calculate the degree of superheat of the evaporation pipe. Examples of the filter include a first-order lag filter and a moving average filter.
[0015]
Control is performed to maintain the calculated degree of superheat of the evaporation pipe in the vicinity of the target value. In general, the set target value varies depending on the boiler. For this reason, as the target value initially determined in a specific boiler, the water supply is gradually decreased before the start of control, and the degree of superheat immediately before reaching the overheat state is adopted. Thereafter, the vehicle is actually operated and the target value is corrected based on the result.
[0016]
In order to maintain the superheat degree of the evaporation pipe in the vicinity of the target superheat degree, the water supply amount and / or the steam / water separator discharge water amount adjustment valve is adjusted. This can also be replaced by adjusting the target value of steam moisture at the steam separator inlet. The adjustment of the moisture of the steam at the steam separator inlet is usually performed by a water supply amount and / or a discharge water amount adjustment valve.
[0017]
In (1), the amount of change in the temperature of the outlet steam of each evaporator tube is obtained for all the evaporator tubes, and this method is generally preferred for calculating the degree of superheat of the evaporator tube. However, in order to reduce the computer load, it can be substituted by obtaining an evaporation tube showing the highest temperature from each of the evaporation tubes and obtaining the amount of change in the temperature of the evaporation tube.
[0018]
As described above, in the method of the present invention, in the control of the once-through boiler, the amount of water supply and / or the amount of water discharged from the steam / water separator is maintained so that the evaporation pipe superheat degree, which is the maximum superheat degree of the evaporation pipe, is maintained at the target value. By controlling this, the boiler is economically operated. The adjustment of the water supply amount is mainly performed by a control valve that adjusts the water supply amount to the entire heating furnace.
[0019]
Here, by directly controlling the maximum superheat degree of the vapor at the outlet of the evaporation pipe, it is possible to quickly and safely increase the moisture automatically and appropriately even in the event of an abnormal overheating of the evaporation pipe in the event of an emergency. Can be treated.
[0020]
【Example】
FIG. 1 is a graph showing an example of a result of carrying out the once-through boiler control method of the present invention, and shows the progress of moisture (%), the maximum temperature of the evaporator tube (° C.), and the degree of superheat of the evaporator tube. In this embodiment, the conventional control with a constant moisture is performed before the start of the control according to the method of the present invention, and after the control is started with the method of the present invention, the evaporation tube superheat is first set to the first set value. Next, control is performed so as to maintain the second set value. After the start of the control according to the present invention, it can be understood that in both the first and second set values, the moisture is drastically reduced compared to before the start of the control according to the present invention, and an economical operation is performed. . It can also be understood that if the evaporative tube superheat degree is maintained at a high target value, economical operation with less moisture is performed. In this example, the evaporator tube having the highest temperature is selected from all the evaporator tubes, the amount of change in the temperature is calculated, and the degree of superheat of the evaporator tube is calculated therefrom. Here, when the temperature change amount is a negative number, this is replaced with zero, the temperature change amount is passed through a first-order lag filter, and the value is smoothed to obtain the degree of superheat of the evaporation tube.
[0021]
As mentioned above, although this invention was demonstrated based on the suitable embodiment example, the control method of the once-through boiler of this invention is not limited only to the structure of the said embodiment example, From the structure of the said embodiment example. Various modifications and changes are also included in the scope of the present invention.
[0022]
【The invention's effect】
As described above, the control method for the once-through boiler according to the present invention obtains the superheat degree of the evaporation pipe as a control value while monitoring the abnormal superheat of the evaporator pipe during the steady operation of the once-through boiler, and sets the superheat degree to the target value. By performing the control to maintain the current, the once-through boiler can be operated economically and economically.
[Brief description of the drawings]
FIG. 1 is a schematic block diagram showing a configuration of a once-through boiler including a control system for carrying out a control method according to an embodiment of the present invention.
FIG. 2 is a graph showing an operation result obtained in an example of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Evaporation pipe 3 Throttle valve 5 Water supply amount adjustment valve 6 Eco-saving device 9 Steam / water separator 10 Extraction water amount adjustment valve 13, 16 Superheater 14 Superheat reducer 17 Steam thermometer 18 Computer 19 Boiler internal control device

Claims (3)

A water supply system capable of adjusting the water supply flow rate, a heating furnace having a plurality of evaporation pipes each connected to the water supply system via a throttle valve, and a steam / water separator having an extraction water amount adjustment valve connected to the evaporation pipe In a method for controlling a once-through boiler comprising:
In each control cycle, the temperature of the outlet steam or the amount of change in the temperature of the one evaporation tube where the amount of change in the temperature is maximum is detected,
A predetermined calculation is added to the detected amount of change in temperature to calculate the degree of superheat of the evaporation tube,
A method for controlling a once-through boiler, characterized in that the amount of water supplied and / or the amount of water extracted from a steam / water separator is adjusted to maintain the degree of superheat of the evaporator pipe in the vicinity of a target value. The method of controlling a once-through boiler according to claim 1, wherein the predetermined calculation is performed by applying a first-order lag filter or a moving average filter to a temperature change amount in each control cycle. The method for controlling a once-through boiler according to claim 1 or 2, wherein when the detected change amount of the temperature is a negative value, the negative change amount is replaced with an absolute value or zero.

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