JP4672911B2 - Boiler multi-can installation system to prevent corrosion due to low load operation - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a boiler multi-can installation system having a boiler that performs low-load operation, and relates to a boiler multi-can installation system that prevents corrosion due to low-load operation.
[0002]
[Prior art]
A boiler multi-can installation system is known in which a plurality of once-through boilers are installed instead of a large boiler, and the number of boiler combustions is adjusted according to the load. In the case of a multi-can installation system, the number of boiler combustions is controlled in accordance with the steam requirement, so that high efficiency can be maintained even when the steam requirement is small. In this case, the operation priority is set for the boiler, and combustion is performed in order from the boiler with the highest operation priority. The operation priority is periodically changed to eliminate the bias of the combustion time, It prevents the boiler from reaching the end of its life in a short period of time.
[0003]
In boilers using iron-based materials, corrosion is minimized when the pH value of the can water is maintained at 11.0 to 11.8. Therefore, the pH value of the can water is controlled to be within the appropriate range. is doing. Although the pH value of feed water is lower than the above value, the concentration of can water proceeds by generating steam, and the pH value can be increased by concentration. The once-through boiler supplies water from the lower part and takes out steam from the upper part, and the can water taken out together with the steam is separated from the steam and returned to the lower part of the boiler. Concentration due to evaporation does not occur in the lower part of the boiler, but it is corroded by raising the pH value in the lower part of the boiler by bringing the can water taken out together with the steam and separated from the steam to the lower part of the boiler, and adjusting the pH value of the can water to an appropriate range. Is prevented.
[0004]
However, the circulation amount of can water differs depending on the load factor of the boiler, and corrosion may occur depending on the load factor. In a boiler with a high load factor and a large amount of combustion, the temperature of the entire can water rises and the can water circulates due to the boiling of the can water, so that the pH value in the lower part of the boiler can be kept in an appropriate range. However, if the boiler has a low load factor and a small amount of combustion and is not heated until the temperature of the entire can water is increased, the circulation amount of the can water decreases. Even if the temperature of the entire can water does not rise, if combustion is performed, the temperature of the can water in the heated portion rises to generate steam, and if steam is generated, water is supplied from the bottom of the boiler. Since the pH value of the feed water is low, when water is supplied in a state where the circulation amount of the can water is small, the pH value at the lower part of the boiler is lowered, and if the pH value is out of the proper range, the state becomes susceptible to corrosion.
[0005]
In the case of a boiler multi-can installation system, since the load factor is high in a boiler with a high operation priority, the pH value of the can water at the bottom of the boiler rises and stabilizes, but the operation priority is low and the required steam volume is reduced. Accordingly, in a low-load boiler that burns only for a short time, the pH value of the can water in the lower part of the boiler decreases. FIG. 3 is an explanatory diagram showing a combustion implementation state and a change state of the can water pH value in the lower part of the boiler when three boilers of boiler A, boiler B, and boiler C are installed. The boiler A, which has become the second place from the third place due to the rotation of the operation priority, has a low load factor for performing short-time combustion in small pieces, and thus the pH value of the can water is lowered. If the pH value of the can water continues to decrease, it eventually becomes less than the lower limit of the appropriate range and becomes an environment susceptible to corrosion, in which case the corrosion proceeds. In the multi-can installation boiler, there is a boiler with a high load factor and a boiler with a low load factor, and there is a problem that corrosion progresses with a boiler having a low load factor and a low load order.
[0006]
[Problems to be solved by the invention]
The problem to be solved by the present invention is to prevent a boiler multi-can installation system from lowering the pH value of boiler water that falls in a low load order and deviating from an appropriate range and causing corrosion.
[0007]
[Means for Solving the Problems]
This is a multi-can installation system for boilers that has multiple boilers and a unit control device that controls the number of boilers that burn, and adjusts the steam supply by burning the required amount of steam. The control device calculates the load factor of each boiler, measures the time within the range of the load factor at which the can water pH value decreases , and when the time within the range reaches a predetermined time or more, On the other hand, the time that has been set as the time required to recover the pH value of the can water is controlled by increasing the load factor and changing the operation priority order for adjusting the pH value. When reaching the above, control is performed to return the operation priority to the original state .
[0008]
Since the boiler with a low load factor has a small circulation amount, the pH value of the can water decreases. However, since the boiler with a high load factor has a large circulation amount, the pH value of the can water can be increased. By performing control to increase the load factor with respect to the boiler having a load factor at which the can water pH value decreases, it is possible to prevent the can water pH value from decreasing to a value at which corrosion is likely to occur, and corrosion of the boiler can be prevented.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing a boiler combustion situation and a change situation of a boiler can water pH value in one embodiment of the present invention, and FIG. 2 is a flow chart of a boiler multi-can installation system embodying the present invention. In this embodiment, three boilers 1 are installed, and the three boilers 1 are boiler A, boiler B, and boiler C, respectively. A steam header 4 for collecting steam generated in each boiler is provided and connected to each boiler by a steam pipe 5. The steam generated in the boiler 1 is collected in the steam header 4 and then sent to the steam use location 2, and a pressure detector 6 for detecting the steam pressure is provided in the steam collecting portion. The number control device 3 is provided connected to the pressure detector 6, and each boiler combusts when the number control device 3 instructs each boiler to perform combustion.
[0010]
Each boiler has a large number of water pipes connected between the upper and lower headers, a water supply pipe connected to the lower header, and a steam pipe connected to the upper header. Water is supplied from below and heated in the water pipe section. This is a once-through boiler that extracts steam from the top. A steam separator 7 is provided in the middle of the steam pipe 5, and the canned water taken out from the upper header together with the steam is separated by the steam separator 7 and returned to the lower header, and only the steam is taken out from the boiler. Keep it like that.
[0011]
The number control of the boilers performed by the number control device 3 is performed based on the steam pressure value detected by the pressure detector 6 and the combustion state set for each steam pressure value in the number control device 3. When the steam pressure value detected by the pressure detector 6 is low, the number control device 3 burns many boilers in the order of operation priority, and when the steam pressure value is high, the number of combustion units 3 decreases the number of combustion. Control the supply amount. The number control device also sets operation priorities for each boiler. Since three boilers are installed, the operation priority is changed from the first to the third. The operation priority is periodically rotated, and the boiler operation is changed by changing the operation priority of each boiler in turn. Make sure that the burning time is not biased. The number control device calculates a load factor that is a ratio of the actual combustion amount to the rated combustion amount for each boiler. The amount of combustion within a certain time is calculated for each boiler, and the load factor in each boiler is calculated every certain time.
[0012]
The number of boilers to be burned is determined from the amount of steam used by the steam use point 2, and in this embodiment, it is assumed that one to two boilers have a certain amount of steam that needs to be burned. In this case, among the three installed boilers, one boiler will continue to burn, one boiler will start and stop combustion as needed, and one boiler will not burn at all. . Since the boiler that performs the combustion is determined by the operation priority, the boiler with the first operation priority is always combusted, the boiler that is second is intermittent combustion, and the boiler that is third is always stopped. . In the case of FIG. 1, the operation priority is first from the boiler C, the second from the boiler B, and the third from the boiler A, and starts from the state immediately before the rotation in which the operation priority is changed. In the state before the rotation, the boiler C which is the first place performs continuous combustion, and since the load factor is high, sufficient circulation occurs in the boiler, and the pH value of the can water is stable. Boiler B, which is the second place, repeats short-time combustion, and the pH value of the can water tends to decrease because the load factor is low. Since the boiler C which is the third place does not burn, the pH value of the can water does not change.
[0013]
When rotation of the operation priority change is performed in this state, the boiler C which has been the first operation priority until that time is third, stops combustion, and the boiler B which is second is first. Boiler A, which is the third place and the second place, performs the intermittent combustion. In the case of boiler B, the temperature of the whole can water rises by performing continuous combustion. Therefore, in the boiler B, a sufficient amount of circulation can be secured by boiling of the can water, and the pH value of the can water that has been lowered is increased and stabilized. In the case of boiler A, since it is intermittent combustion, the can water in the water pipe portion is heated to generate steam, but the temperature of the entire can water rises and the can water does not rise. In this case, the pH value of the can lowers because the pH value of the boiler lower can water is larger due to the supply of low pH water than the increase due to the circulation of the concentrated water.
[0014]
The number control device 3 calculates the load factor of each boiler, and if there is a boiler whose load factor is equal to or longer than a predetermined time within a predetermined range, the operation priority order of the boiler is temporarily changed to higher order. The pH value of the boiler is adjusted. The predetermined range of the load factor is a load factor in which the pH value of the lower can water decreases because steam is generated but the circulation of the can water is small. For example, the load factor is 10% to 30%. If the actual load factor is higher than the above range, the circulation amount of the can water will increase, so the pH value of the can water will be stable. Conversely, if the load factor is low, the evaporation amount will decrease and the change in pH value will be small. It is not necessary to perform control for adjusting the pH value. Even if the load factor falls within the above range, it takes time for the amount of decrease in the pH value to reach an amount that needs to be adjusted to adjust the pH value. If the time is over, set the operation priority of the relevant boiler to higher.
[0015]
The number control device 3 calculates the load factor of the boiler within a certain time for each boiler, and when the load factor is within the range of 10% to 30%, the time is accumulated. The number control device 3 detects that the load factor of the boiler A having the second highest operation priority is within a range of 10% to 30%, and the accumulated time within the range is 3 hours or more. Then, the operation priority order is temporarily changed for pH value adjustment. The number control device 3 sets the boiler A, which has been the second highest so far, as the first, which is the highest in the operation priority order, and instead sets the boiler B, which has been the first highest, as the second. If the operation priority of the boiler A whose pH value in the boiler water at the lower part of the boiler tended to decrease due to the low load factor is changed to the first highest load factor, the boiler A will burn continuously. Therefore, the circulation amount of the can water can be secured, and the pH value of the can water in the boiler A increases.
[0016]
When the elapsed time since the change of the operation priority order for adjusting the pH value reaches the time set as the time necessary for recovering the pH value of the can water, the unit control device 3 is given priority to the operation. The order is returned to the original state, and boiler A is second and boiler B is first. The number control device 3 calculates the boiler load factor after that, and temporarily restores the pH value of the can water every time the load factor is within a range of 10% to 30% for 3 hours or more. Change the priority of operation. In addition, when the elapsed time since the rotation has elapsed for the rotation execution interval, rotation is performed to change the operation priority of all the boilers.
[0017]
Even if the pH value of the can water is lowered because the load factor is low, the pH value can be recovered by increasing the load factor of the boiler, and the load factor is reduced before the pH value falls outside the proper range. By raising and raising the pH value, it is possible to prevent the low load boiler from being corroded due to a drop in the can water pH value.
[0018]
In this embodiment, the pH value is adjusted by switching the operation priority between the low load factor boiler and the high load factor boiler, but the low load factor boiler is excluded from the operation priority target and Even if the combustion is forcedly performed at a high load rate regardless of the priority order, the same effect can be obtained.
[0019]
【The invention's effect】
By implementing the present invention, it is possible to prevent a low load order boiler with a small load factor from becoming an environment that is susceptible to corrosion due to a decrease in the can water pH value due to a decrease in the amount of can water circulation, thereby preventing the occurrence of corrosion. be able to.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a boiler combustion state and a change in pH value of the lower can water in the boiler in one embodiment of the present invention. FIG. 2 is a flow diagram of a boiler multi-can installation system embodying the present invention. 3] Explanatory diagram showing changes in boiler combustion status and pH value in lower boiler water in boiler in conventional example [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Boiler 2 Steam use location 3 Unit control device 4 Steam header 5 Steam piping 6 Pressure detector 7 Steam-water separator

Claims (1)

This is a multi-can installation system for boilers that has multiple boilers and a unit control device that controls the number of boilers that burn, and adjusts the steam supply by burning the required amount of steam. The control device calculates the load factor of each boiler, measures the time within the range of the load factor at which the can water pH value decreases, and when the time within the range reaches a predetermined time or more, On the other hand, the operation priority is changed to increase the load factor, and the elapsed time after changing the operation priority for adjusting the pH value is the time required to recover the pH value of the can water A boiler multi-can installation system for preventing corrosion due to low-load operation, characterized in that when the set time is reached, the operation priority is controlled to return to the original state.

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