JPH08285204A - Forced circulation type electric heating water tube boiler - Google Patents

Abstract

PURPOSE: To improve reliability on operation of a boiler and a plant by preventing the occurrence of a boiler trip due to the occurrence of cavitation. CONSTITUTION: A feed water pump 2 is connected to a feed water tank 1 and the feed water pump 2 is connected to a steam drum 4 through a delivery piping 5. The piping on the outlet side for high temperature fluid of the steam drum 4 is connected to a circulation pump 7 through first and second heat- exchanges 20 and 21, and and a circulation pump 7 is connected to a steam generator 8 through the first heat-exchanger 20. The steam outlet side of the steam generator 8 is connected to the steam drum 4, a steam outlet in the steam drum 4 is connected to a steam reservoir 10, and the steam outlet side of the steam reservoir 10 is connected to a steam use load 11. A circulation water temperature is reduced by the second heat-exchanger 21 on the suction side of the circulation pump 7, a cavitation occurring condition is relaxed, the temperature of circulation water flowing in the steam generator 8 is increased through the first heat-exchanger 20, and the heat loss of a boiler is not generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forced circulation type electrically heated water tube type boiler used for a steam supply auxiliary boiler installed in a boiling water nuclear power plant.

[0002]

2. Description of the Related Art Generally, a boiling water nuclear power plant is equipped with an auxiliary boiler as a steam supply facility for indoor tank humidification, waste treatment process, and turbine gland seal at plant start / stop. There is. This auxiliary boiler does not generate smoke like heavy oil boilers, and
A forced circulation type electrically heated water tube type boiler with a simple equipment configuration is used.

The equipment configuration of a conventional forced circulation type electrically heated water tube type boiler will be described with reference to FIG. In FIG. 4, boiler feed water from a water feed tank 1 indicated by reference numeral 1 flows through a discharge pipe 5 by a water feed pump 2 and flows into a steam drum 4 via a deaerator 3. In order to prevent heating operation of the water supply pump 2, a minimum flow pipe 6 connected to the water supply tank 1 is branched and provided in the discharge pipe 5 of the water supply pump 2, and the water supply pump 2 is operated while the water supply pump 2 is operating. The minimum allowable flow rate is returned to the water supply tank 1.

The feed water flowing into the steam drum 4 is sent to the evaporation tube group of the steam generator 8 by the circulation pump 7, and the transformer 9 connected to the steam generator 8 directly applies the three-phase alternating current to the evaporation tube group. As a result, the heat generated in the evaporation tube group is added to become heated water (high temperature / high pressure) of the gas-liquid two-phase flow, and returns to the steam drum 4 again.

The heated water of the gas-liquid two-phase flow that has flowed into the steam drum 4 is separated into steam and high-temperature liquid by the gas-liquid separation device in the steam drum 4, and the steam is loaded through the steam sump 10 into various steam use loads. The high-temperature liquid supplied to 11 is circulated through the steam generator 8 and the steam drum 4 by the circulation pump 7.

A blow pipe 16 for continuously discharging a fixed amount of about several percent of the rated evaporation amount is connected to the steam drum 4 in order to prevent corrosion due to concentration of feed water quality components flowing into the steam drum 4. , This blow piping 16 is a blow water cooler 17
And is drained after being cooled by the cooling water of the cooling system 18 in the plant.

The steam used on the side of the steam use load 11 has a steam storage capacity even if the amount of use changes in the design plan.
A pressure control device 12 provided at 10 controls the steam output of the steam generator 8 so that the generated steam pressure becomes substantially constant.

[0008] A trap for automatically discharging drainage when condensed water is generated by a steam drain pipe 13 so that condensed water generated by heat radiation does not stay in the steam reservoir 10 below the steam reservoir 10.
It is connected to the drain cooler 15 via 14 and is drained after being cooled by the cooling water of the cooling system 18 in the plant.

[0009]

As described above, if the change in the amount of steam used on the load side is normal within the design plan, the generated steam pressure can be maintained at a substantially constant pressure. However, in the unlikely event that the steam usage load 11 side causes an abnormal increase in steam usage outside the design plan, the pressure in the steam drum 4 suddenly drops.

In this case, since the pressure in the steam drum 4 is lowered in the circulation pump 7 into which normally high-temperature and high-pressure circulation water flows, cavitation is generated at the inlet of the circulation pump 7 and water is not sent to the steam generator 8. It becomes possible and the boiler stops. Therefore, there is a problem that the supply of steam is stopped, which hinders the operation to the side of the steam use load 11 and causes the plant to stop.

The present invention has been made in order to solve the above problems, and by effectively reducing the temperature of the circulating water flowing into the circulating pump during normal operation without reducing the boiler efficiency as much as possible, steam should be used. If the pressure inside the steam drum drops sharply due to an abnormal increase in steam usage outside the design plan on the working load side, prevent the boiler from stopping due to cavitation at the inlet of the circulation pump, and operate the boiler and plant. The purpose of the present invention is to provide a forced circulation type electrically heated water tube type boiler that can improve reliability.

[0012]

According to the present invention, water is supplied from a water supply tank to a steam drum through a deaerator by a water supply pump,
The feed water that has flowed into this steam drum is sent to the evaporation tube group of the steam generator by a circulation pump, a voltage is applied by a transformer connected to the steam generator, and the heat generated in the evaporation tube group causes gas-liquid two It becomes a phase flow and returns to the steam drum, and after the heated water of the gas-liquid two-phase flow that has flowed into the steam drum is separated into steam and high-temperature liquid by the gas-liquid separation device in the steam drum, the steam is stored in the steam reservoir. Supply to various steam use load through, circulates the high temperature liquid by the circulation pump through the steam generator and the steam drum, connects the blow pipe to the steam drum, and connects the blow pipe to the blow water cooler. In the forced circulation type electrically heated water pipe type boiler connected, a heat exchanger is provided in the suction pipe and the discharge pipe of the circulation pump.

[0013]

In the forced circulation type electrically heated water pipe type boiler, the circulating water cooling second heat exchanger is provided on the suction side of the circulating pump, and the circulating water heating first unit is provided on the discharge side of the circulating pump.
Install a heat exchanger.

The second heat exchanger provided on the suction side of the circulation pump lowers the temperature of the circulating water flowing into the circulation pump to relieve the cavitation generation condition. On the other hand, the temperature of the circulating water flowing into the steam generator is raised by the first heat exchanger provided on the discharge side of the circulation pump to prevent heat loss of the boiler as much as possible.

The circulating water has its water temperature lowered by a second heat exchanger using the feed water as cooling water and a first heat exchanger using the circulating water cooled by this second heat exchanger as cooling water. To do. Further, the circulating water once having a low temperature is subjected to heat recovery by the first heat exchanger and becomes a high temperature again before flowing into the steam generator.

Since the temperature of the circulating water flowing into the circulating pump is low even if the amount of steam used increases abnormally, boiler trip due to cavitation can be prevented, and the reliability of boiler and plant operation can be improved.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a forced circulation type electrically heated water tube type boiler according to the present invention will be described with reference to FIG. In FIG. 1, the same parts as those in FIG. 4 are designated by the same reference numerals and the description of the overlapping parts will be omitted. Explaining the difference between the first embodiment and the conventional example, the suction pipe 30 of the circulation pump 7 is steam in the order of the pipe side of the first heat exchanger 20 and the pipe side of the second heat exchanger 21. It is connected between the drum 4 and the circulation pump 7.

The discharge pipe of the circulation pump 7 is connected to the steam generator 8 via the body side of the first heat exchanger 20.
The pipe 22 branched from the discharge pipe 5 of the water supply pump 2 is connected to the body side inlet of the second heat exchanger 21, and the pipe 23 provided at the body side outlet of the second heat exchanger 21 is the water supply tank 1 It is connected to the.

As described above, in the above-described embodiment, the circulating water having a high temperature from the steam drum 4 uses the feed water having a temperature lower than the water temperature as the refrigerant, the first heat exchanger 20 and the second heat exchanger.
The water temperature is lowered in the first heat exchanger 20 using the low-temperature circulating water cooled by 21 and sent from the circulating pump 7 as a refrigerant.

Since the circulating water once having a low temperature passes through the first heat exchanger 20, heat is recovered by the high temperature circulating water before being cooled, so that the circulating water flowing into the steam generator 4 is The temperature rises again and avoids a decrease in boiler efficiency. Also,
Since the pipe 22 and the pipe 23 connected to the second heat exchanger 21 are provided, a flow rate higher than the minimum flow rate of the water supply pump 2 can always be secured, so that the conventional minimum flow pipe 6 shown in FIG. 4 is unnecessary. Become.

In the first embodiment, the first heat exchanger 20 for exchanging heat between the suction fluid of the circulation pump 7 and the fluid on the discharge side of the circulation pump 7 and the cooling water are supplied from the water supply pump 2. Although the second heat exchanger 21 used has been described, the present invention is not limited to this embodiment,
What is essential is that it has a piping system provided with a heat exchanger that cools the circulating water flowing into the circulation pump 7 and a heat exchanger that heats the circulating water sent from the circulation pump 7.

Next, a second embodiment of the present invention will be described with reference to FIG. The second embodiment shown in FIG. 2 is a diagram in which the fluid of the cooling system 18 used for the drain cooler 15 and the blow water cooler 17 in the suction pipe of the circulation pump 7 in the first embodiment is used as cooling water. A heat exchanger 24 corresponding to the first heat exchanger 20 shown in 1 is provided. The discharge pipe of the circulation pump 7 is provided with a heat exchanger 31 corresponding to the second heat exchanger 21 using the hot blow water flowing from the steam drum 4 through the pipe 32 as a heating fluid.

On the outlet side of the heating fluid of this heat exchanger 31, a pipe 33 connected to the water supply tank 1 and a pipe 34 branched from this pipe 33 and connected to the blow water cooler 17 via a flow rate setting valve 35. Is provided. The steam drum 4 and the heat exchanger 31 are connected by a pipe 32.

The suction water of the circulation pump 7 is cooled by the heat exchanger 24, and the discharge water of the circulation pump 7 is heated by the heat exchanger 31. The high-temperature fluid introduced from the steam drum 4 is cooled by a blow water cooler 17 through a pipe 33, a pipe 34 branched from the pipe 33, and a flow rate setting valve 35 for a predetermined fixed amount. After that, it is discharged to the drainage system 19, and the remaining part returns to the water supply tank 1 through the pipe 33.

Therefore, according to this embodiment, as compared with the conventional example, the amount of high-temperature fluid introduced from the steam drum 4 increases, but the increased amount returns to the water supply tank 1, so the amount discharged to the discharge system 19 changes. Without, it also has the effect of increasing the temperature of the water supply.

Next, a third embodiment of the present invention will be described with reference to FIG. In the third embodiment, a heat exchanger 24 similar to that of the second embodiment is provided in the suction pipe of the circulation pump 7. The discharge pipe of the circulation pump 7 is provided with a heat exchanger 25 that uses self-generated steam that flows in from a lower part of the steam reservoir 10 via a pipe 26 as a heating fluid, and is connected to the water supply tank 1 on the outlet side of the heating fluid. The pipe 27 is provided.

The suction water of the circulation pump 7 is cooled by the heat exchanger 24, and the discharge water of the circulation pump 7 is heated by the heat exchanger 25. The self-generated steam introduced from the lower part of the steam sump 10 heats the discharge water of the circulation pump 7 and then returns to the water supply tank 1 as condensed water.

Therefore, according to the present embodiment, the self-generated steam is consumed as compared with the conventional example, but the condensed water thereof is collected in the water supply tank 1, and the drain cooler and the conventional one provided therefor are also collected. This has the effect of eliminating the need for cooling water pipes and traps.

[0029]

According to the present invention, a heat exchanger is provided in each of the suction and discharge pipes of the circulation pump to reduce the temperature of the circulating water flowing into the circulation pump without reducing the boiler efficiency as much as possible. As a result, if an abnormal increase in steam usage occurs on the steam usage load side and the pressure in the steam drum drops sharply, it is possible to prevent the boiler from stopping due to cavitation at the inlet of the circulation pump. Therefore, the reliability of the operation of the boiler is improved, and the reliability of the operation of the steam use load, that is, the operation of the plant is improved.

[Brief description of drawings]

FIG. 1 is a system diagram showing a first embodiment of a forced circulation type electrically heated water tube type boiler according to the present invention in a partial block diagram.

FIG. 2 is a system diagram showing a second embodiment of a forced circulation type electrically heated water tube type boiler according to the present invention in a partial block diagram.

FIG. 3 is a system diagram showing a third embodiment of a forced circulation type electrically heated water tube type boiler according to the present invention in a partial block diagram.

FIG. 4 is a system diagram showing a block diagram of a conventional forced circulation type electrically heated water tube type boiler.

[Explanation of symbols]

1 ... Water tank, 2 ... Water pump, 3 ... Deaerator, 4 ... Steam drum, 5 ... Discharge pipe, 6 ... Minimum flow pipe, 7
... Circulation pump, 8 ... Steam generator, 9 ... Transformer, 10 ... Steam storage, 11 ... Steam usage load, 12 ... Pressure control device, 13 ... Steam drain piping, 14 ... Trap, 15 ... Drain cooler, 16 ... Blow piping, 17 ... Blow water cooler, 18 ... Cooling system, 19 ... Drainage system, 20 ... First heat exchanger, 21 ... Second heat exchanger, 2
4, 25, 31 ... Heat exchanger, 22, 23, 26, 27, 28, 29, 32, 3
3, 34 ... Piping, 30 ... Suction piping, 35 ... Flow rate setting valve.

Claims (4)

[Claims] 1. A water supply tank supplies water to a steam drum through a deaerator by means of a water supply pump, and the water supply flowing into this steam drum is sent by a circulation pump to an evaporation pipe group of a steam generator, and then to the steam generator. A voltage is applied by the connected transformer, and the heat generated in the evaporation tube group causes a gas-liquid two-phase flow to return to the steam drum. The heated water of the gas-liquid two-phase flow that has flowed into the steam drum is transferred to the steam drum. After separating into steam and high temperature liquid by a gas-liquid separator inside, the steam is supplied to various steam use loads through a steam reservoir, and the high temperature liquid is supplied to the steam generator and the steam drum by the circulation pump. In the forced circulation type electrically heated water pipe type boiler, in which a blow pipe is connected to the steam drum and the blow pipe is connected to a blow water cooler, the suction pipe and the discharge pipe of the circulation pump are A forced circulation type electrically heated water tube type boiler characterized in that a heat exchanger is provided in the tube. 2. A heat exchanger for exchanging heat between the suction side fluid of the circulation pump and the discharge side fluid of the circulation pump is provided in the circulation lines of the water tank, the steam drum, the circulation pump and the steam generator. The forcedly heated electrically heated water tube type boiler according to claim 1. 3. The forced circulation type electrically heated water pipe type according to claim 1, wherein a heat exchanger that uses boiler feed water or cooling water for boiler auxiliaries as a cooling fluid is provided on the suction side of the circulation pump. boiler. 4. The cooling water of the heat exchanger provided on the suction side of the circulation pump is used as discharge water of the boiler feed water pump, and is branched from a cooling line for flowing the cooling water and a discharge pipe of the water supply pump to the water supply tank. 3. The forced circulation type electrically heated water tube type boiler according to claim 1, wherein it is also used as a connected minimum flow line.