JPH0694207A - Feedwater controller for boiler - Google Patents

Abstract

PURPOSE:To prevent crack due to thermal stress of an inlet header of an economizer by feeding water directly to a drum, etc., by using an economizer by-pass tube at the time of starting a boiler and hot banding. CONSTITUTION:A by-pass feedwater tube 20 for feeding water to a drum 5, etc., by by-passing an economizer 3 is provided in a main piping system for feeding water from a feedwater pump 1 to the drum 5 through a feedwater heater 2 and the economizer 3. An economizer by-pass valve 13 is opened at the time of starting a boiler and hot banding, an economizer inlet vale 14 is closed, and low temperature water is fed directly to the drum 5 by an economizer by-pass tube 20. After a turbine is ventilated, the valve 13 is closed, and the valve 14 is opened. Thus, generation of a temperature difference between an interior and an exterior of the tube in an inlet header of the economizer can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a natural circulation boiler suitable for preventing cracks due to thermal stress in the inlet port of the economizer when starting or hot banking.

[0002]

2. Description of the Related Art Conventionally, a boiler has been equipped with a economizer for the purpose of heating the feed water to the boiler by utilizing the preheating of the flue gas to increase the thermal efficiency of the entire boiler plant. Figure 3
(A) and (b) show the structure of a conventional boiler and water and steam piping. In the figure, a water supply pump 1, a water supply heater 2 that heats the water supply by using the extracted air from the high-pressure turbine 7, a economizer 3 that heats the water supply by using the residual heat of the flue gas from the boiler, A furnace 4 having a water-cooled wall structure into which water supply from the economizer 3 is introduced, a drum 5 for separating steam-water mixed steam from the furnace 4 into water and steam, and superheated saturated steam separated by the drum 5. And superheater 6 to turn into superheated steam
It is composed of a high-pressure turbine 7 that rotates by using steam from the engine as a drive source. At the time of boiler startup and hot banking, the gas temperature in the boiler is high, and therefore, for example, the economizer inlet header 15 shown in FIG.
However, since the feed water heater 2 is not operated, the boiler feed water temperature is low (about 60 ° C.). Therefore, thermal stress due to the temperature difference is generated at the connection portion of the economizer stub tube 18 which is a structural discontinuity of the economizer inlet pipe header 15. For example, as shown in FIG. There was a problem that cracks were likely to occur in the vicinity of the stub tube welded portion 19 of the container stub tube 18. 4 (b) and 4 (c) show the welded structure of the coal economizer inlet pipe header and the typical crack occurrence.
Note that FIG. 4C is a cross-sectional view taken along the line AA of FIG. As known examples of boiler feed water temperature control, there are JP-A-59-81401, JP-A-60-69407, and JP-A-60-63407.
-21402, 63-180002, etc. are mentioned.

[0003]

As described above, in the prior art, thermal stress is generated in the connecting portion of the economizer stub pipe due to the temperature difference generated during low temperature intermittent water supply at boiler startup and hot banking. Cracks tend to occur in the stub tube, and no consideration has been given to preventing it. For example, as shown in FIG. 5 (a),
There is a problem that the temperature difference (ΔT) inside and outside the stub pipe at the inlet of the economizer is large. It should be noted that FIG. 6B shows changes in the drum pressure (A), the continuous water supply amount (B), and the intermittent water supply amount (C).

An object of the present invention is to provide a pipe for bypassing the economizer and supplying water directly to the drum at the time of starting the boiler and hot banking, so that cracking due to thermal stress in the inlet port of the economizer is generated. An object is to provide a boiler device capable of preventing the above.

[0005]

To achieve the above object of the present invention, in a natural circulation boiler, a economizer bypass pipe that can supply water to the drum from the feed water heater outlet of the boiler is provided, and the boiler is started and hot. When banking,
By providing a control means for directly supplying water to the drum etc. by using the above economizer bypass piping, the temperature difference between the inside and outside of the economizer inlet pipe approaching portion is reduced, and in the economizer stub pipe connection part, etc. It effectively prevents the occurrence of cracks.

[0006]

[Operation] By using the economizer bypass piping and directly supplying water to the drum during boiler startup and hot banking, low-temperature water does not flow into the economizer inlet pipe draw part, and It is possible to reduce the occurrence of the temperature difference between the inside and the outside in the pipe drawing portion. That is, since the low-temperature feed water does not flow into the hot coal economizer inlet pipe header, there is no temperature difference in the pipe economizer, thus suppressing the occurrence of cracks in the economizer inlet pipe stub and the like. It becomes possible to do. Since the nozzle of the water supply pipe of the drum has a thermal sleeve structure, thermal stress due to the temperature difference is small even if low-temperature water supply flows in.

[0007]

Embodiments of the present invention will be described below in more detail with reference to the drawings. 1 (a) is a schematic diagram showing an example of the configuration of the boiler device of the present invention, FIG. 1 (b) is a diagram showing the water and steam piping system of the boiler, and FIG. 1 (c) is a valve switching operation pattern. It is a figure which shows an example. In the figure, the temperature difference generated between the inside and outside of the economizer inlet header 15 is caused by the intermittent water supply operation of low temperature water for drum level recovery performed at boiler startup and hot banking. In order to prevent this, a economizer bypass pipe 20 is provided, and low-temperature water is directly supplied to the drum 5 by the economizer bypass pipe 20 at the time of intermittent water supply during boiler startup and hot banking. Since the low-temperature water is controlled by using the bypass piping only when the boiler is started and hot banking, the economizer bypass valve 13 and the economizer inlet valve for switching the main piping system and the bypass piping system are used. 14 is provided. The switching timing of the piping system is (1) when transitioning from intermittent water supply to continuous water supply, and (2) when the difference between the temperature of the coal economizer inlet header 15 and the temperature of the water supply becomes small. Will be described below. (1) Water supply control operation when shifting from intermittent water supply to continuous water supply. Up to turbine ventilation, the amount of steam generated in the boiler is small, so the supply of water is intermittent for the drum level recovery. However, the amount of steam consumed by the turbine increases as the load increases after turbine ventilation. Switch to continuous water supply. At boiler startup and hot banking, the economizer bypass valve 13 is opened and the economizer inlet valve 14 is closed. After the turbine is ventilated, the economizer bypass valve 13 is closed and the economizer inlet valve 14 is opened. FIG. 4C shows a valve switching operation pattern of the bypass piping system and the main piping system. (2) Water supply control operation when the temperature difference between the inlet of the economizer and the temperature of the water supply becomes small. A thermometer is attached to the outer surface of the economizer stub pipe 18 of the economizer inlet inlet port 15, and the bypass piping system is used when the difference between the stub pipe temperature and the feed water temperature of the feed water heater 2 outlet is about 70 ° C or more. Then, water is supplied to the drum 5, and when the temperature is lower than about 70 ° C., water supply operation is performed using the main piping system. Fig. 2 shows the economizer bypass valve 13 in the above bypass piping system and main piping system.
And a switching water supply control system of the economizer inlet valve 14 is shown. Also,
By connecting the economizer bypass pipe 20 to the downcomer pipe of the boiler or the lower pipe drawer of the water cooling wall, the thermal stress of the pipe can be reduced by supplying water to a large diameter part of the pipe. The same effect as the example can be obtained.

[0008]

As described above in detail, by providing the boiler with the coal economizer bypass water supply control piping system of the present invention, when the boiler is started or hot banking, the coal economizer inlet pipe draw part having a high temperature is introduced. Since water is supplied directly to the drum, etc. through the economizer bypass pipe without supplying low-temperature water, it is possible to prevent the occurrence of a temperature difference between the inside and outside of the economizer pipe at the inlet port of the economizer, and to connect the stub pipe. There is no cracking in parts and the like, and the life of the boiler is extended.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration (a) of a boiler device, water of a boiler, a steam pipe system (b) and a valve switching operation pattern (c) exemplified in an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a valve switching water supply control piping system in the bypass piping system and the main piping system of the boiler device illustrated in the embodiment of the present invention.

FIG. 3 is an explanatory view showing a configuration of a conventional boiler device (a) and a water and steam piping system (b).

FIG. 4 is an explanatory view showing a configuration (a) of a economizer of a conventional boiler device, a structure (b) of an economizer inlet header, and a crack generation state (c) of a stub pipe.

FIG. 5 is a graph showing a state of occurrence of a temperature difference between the inside and outside of a stub pipe at a coal economizer inlet pipe drawing portion at the time of starting a conventional boiler (a) and a relationship between a drum pressure and a water supply amount (b).

[Explanation of symbols]

 1 ... Water supply pump 2 ... Water supply heater 3 ... Economizer 4 ... Furnace 5 ... Drum 6 ... Superheater 7 ... High pressure turbine 8 ... Reheater 9 ... Low pressure turbine 10 ... Condenser 11 ... Low pressure heater 12 ... Deaerator 13 ... coal-saving device bypass valve 14 ... coal-saving device inlet valve 15 ... coal-saving device inlet pipe 16 ... coal-saving device pipe 17 ... coal-saving device outlet pipe 18 ... coal-saving device stub pipe 19 ... stub pipe weld 20 … Economizer bypass piping 21… Crack occurrence location 22… Economizer stub temperature 23… Water supply temperature

Claims (1)

[Claims] 1. A boiler having a main piping system for supplying water to a drum from at least a water supply pump through a water supply heater and a economizer, wherein the economizer is bypassed and a drum, a downfall pipe, or a water cooling wall pipe is provided. Provide a bypass water supply control pipe connected to the draw part, and install thermometers at the outlet of the water heater and the inlet of the economizer, and if the temperature difference by the thermometer is greater than or equal to the set value, bypass water A means for controlling water supply using a control pipe and a means for performing water supply control by the main piping system by closing the bypass water supply control pipe when the temperature difference is less than a preset value Boiler water supply control device.