JP6552085B2 - Boiler feed system - Google Patents

Description

  The present invention relates to a boiler water supply apparatus that supplies water to a steam boiler.

As described in Japanese Patent Application Laid-Open No. 2014-219112, water supplied to the steam boiler is supplied to the boiler by pressurizing boiler water with a water supply pump provided in a water supply pipe. At that time, the feed water flow rate to the boiler varies depending on the steam pressure in the boiler. In steam boilers that supply steam, steam with increased saturated steam temperature is supplied by pressurization, and the pressure in the boiler is high when steam is being supplied. Use a lift that can be fed into the boiler. However, water supply to the boiler may be performed even when the pressure in the boiler is low. For example, when starting at the factory and immediately after the boiler operation switch is turned on, or when all blows are periodically drained to clean the inside of the boiler, the boiler should be supplied with water. Start the combustion after raising the water level in the boiler. In this case, there is no steam in the boiler, and water supply is performed in a state where the pressure in the boiler is low. Therefore, the flow rate of the water supply discharged from the water supply pump is larger than that during normal operation.

Even during the operation of the boiler, the steam pressure value in the boiler rises and falls. In the boiler, when the steam pressure value falls to the lower limit pressure value, combustion of the boiler is started to raise the steam pressure, and when the steam pressure value rises to the upper limit pressure value, the combustion is stopped. Therefore, even during combustion, the steam pressure value will fluctuate, and the fluctuation of the steam pressure value will also change the feed water flow rate to the boiler.

If water supply is performed in a state where the boiler internal pressure is low, the water supply flow rate to the boiler increases. In this case, the water supply pump is in a state where cavitation is likely to occur, and when the cavitation occurs, the head of the pump is lowered, and vibration and noise are generated. Also, if the water level in the boiler body rises suddenly due to an excessive feed water flow rate, after the water level reaches the feed water stop water level, it is detected that the feed water stop water level is reached and the operation of the feed water pump is stopped. During this period, the water level may be significantly higher than the water supply stoppage water level. If the water level in the boiler is higher than the normal range, the liquid in the boiler is taken out with the steam, and the steam supplied from the boiler contains a large amount of liquid, which lowers the steam quality. It also causes the problem of causing

Therefore, in the invention described in Japanese Patent Application Laid-Open No. 2014-219122, a steam pressure detecting device for detecting the steam pressure in the boiler and an inverter for controlling the rotation speed of the feed water pump are installed, and the detected steam pressure value is set. The rotational speed of the feed water pump is controlled based on that. When the steam pressure is high, the rotation frequency of the feed water pump is increased by increasing the power supply frequency of the feed water pump with an inverter. When the steam pressure is low, the rotation speed of the feed water pump is decreased by decreasing the power supply frequency of the feed water pump with an inverter. Reduce the number. By doing in this way, even if steam pressure changes, the feed water flow rate supplied to a boiler is made constant.

However, in the case of a water supply apparatus that adjusts the water supply flow rate by changing the rotational speed of the water supply pump based on the pressure in the boiler, there are the following problems. Lowering the rotational speed of the feed pump will lower the discharge pressure, but as the difference between the pressure on the boiler side and the total feed pump head becomes smaller, the feed water flow rate will be large due to a slight change in the rotational speed of the feed pump. It will change and it will be difficult to adjust the constant flow rate. During water supply, it is affected by the resistance of piping and valves provided on the secondary side of the water supply pump, but detection by the steam pressure inside the boiler can does not take into account the influence of other factors. Since the relationship between the steam pressure and the feed pump rotational speed also changes depending on the difference in conditions on the primary side, appropriate flow rate adjustment is difficult in rotational speed control.

JP 2014-219122 A

  The problem to be solved by the present invention is that when water is supplied to a steam boiler whose steam pressure in the boiler changes, fluctuations in the feed water flow due to fluctuations in the steam pressure in the boiler are reduced, cavitation is generated, An object of the present invention is to provide a boiler water supply apparatus capable of preventing problems such as a drop in steam quality due to a rise in water level in the body.

The invention according to claim 1 is a boiler in which a water supply pipe having a water supply pump is connected on the way, and when the water level in the boiler is lowered to a water supply start water level, the water supply pump is operated to supply water. When the water supply pressure detection device is installed between the water supply electric valve and the water supply pump and the water supply electric valve on the secondary side of the water supply pump installation position of the water supply pipe, and the water supply pump supplies water, The operation to start opening the feed water motor operated valve while starting the operation is performed, and the water feed pump discharge detected by the water feed pressure detection device by operating the water feed pump in a state where the opening degree of the water feed motor valve is small. When the side pressure value becomes higher than the target value, the operation of opening the opening of the water supply electric valve based on the difference between the detected pressure value and the target value is performed, and the discharge pressure on the feed water pump detected by the feed water pressure detection device is And characterized in that to adjust the degree of opening of the water supply electric valve to maintain a constant value.

By carrying out the present invention, even when water supply is performed in a state where the pressure in the boiler is low, the water supply flow rate can be maintained substantially constant, and cavitation due to the increase in the flow rate or a rapid rise in water level in the can Problems such as a drop in vapor quality can be prevented.

Flow chart of a boiler according to an embodiment of the present invention Water supply condition explanatory drawing in one example of the present invention

  One embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a flow chart of a boiler according to an embodiment of the present invention, and FIG. 2 is a time chart schematically explaining a water supply condition according to an embodiment of the present invention. The boiler 1 performs combustion in a combustion chamber portion provided in the center, and a combustion device 2 is provided in an upper portion of the combustion chamber. A water supply pipe 6 is connected to the bottom of the boiler, a water supply pump 7 is installed in the middle of the water supply pipe 6, and water supply to the boiler 1 is performed by operating the water supply pump 7. The detection of the water level in the boiler is performed by a water level detection cylinder 8 provided outside the boiler can body. The water level detection cylinder 8 communicates with the boiler body through a water level detection cylinder communication pipe. The steam section in the upper part of the boiler, the upper part of the water level detection cylinder 8, the boiler water part in the lower part of the boiler, and the lower part of the water level detection cylinder 8. Are connected to each other, so that the water level in the boiler can body can be detected by the water level detection tube 8.

The water level detection cylinder 8 is provided with an electrode rod E1 that detects the presence or absence of water at the water supply stop water level (E1 water level) and an electrode rod E2 that detects the presence or absence of water at the water supply start water level (E2 water level). Each water level electrode bar is electrically connected to the operation control device 4 for controlling the operation of the boiler, and the operation control device 4 determines the water level by the signal with or without water detected by the water level electrode bar. And control the operation of the water supply pump 7 according to the water level. When the signal for detecting the absence of water is input from the water level electrode rod E2, the operation control device 4 outputs the water supply pump 7 and supplies water to the boiler. When the water level rises by supplying water and the water presence detection signal is input from the water level electrode rod E1 to the operation control device 4, the operation control device 4 outputs an operation stoppage to the water supply pump 7 to supply water. Stop.

When combustion is performed by the combustion device 2 with the boiler water stored in the boiler 1, the heat generated in the combustion device 2 heats the boiler water in the heat transfer tube of the boiler can body, and steam is generated in the boiler. Do. The generated steam is separated into steam and boiler water in the steam-water separator 5, and the steam is taken out from the top of the steam-water separator 5 and supplied to the steam usage point. The operation control device 4 also controls the amount of combustion in the boiler 1. In the boiler, the steam pressure detection device 3 detects the pressure value in the boiler. When the pressure value in the boiler is low, the boiler performs combustion operation. When the pressure value becomes higher than the upper limit value, combustion in the boiler Stop the operation. When the combustion amount is set in stages such as high combustion and low combustion, the combustion amount is changed according to the steam pressure value detected by the steam pressure detecting device 3, and the steam pressure When the value is high, the combustion amount is decreased, and when the steam pressure value is low, the combustion amount is increased.

The water supply pipe 6 is provided with a water supply electric valve 9 on the boiler 1 side from the position where the water supply pump 7 is installed, and a water supply pressure detection device 10 is provided between the water supply pump 7 and the water supply electric valve 9. The feed water motor operated valve 9 and the feed water pressure detection device 10 are also connected to the operation control device 4, and the value of the pressure in the feed water pipe 6 detected by the feed water pressure detection device 10 is output to the operation control device 4 In the device 4, the opening degree of the feed water motor-operated valve 9 is controlled.

The water supply control to the boiler 1 will be described based on the time chart shown in FIG. The time chart of FIG. 2 describes the water supply situation when the boiler internal pressure is high and low. The first half of the figure is the state where the boiler internal pressure is high, and the second half is the water supply situation when the boiler internal pressure is low. . When the water level in the boiler drops to the water level E2, the operation control device 4 outputs an operation command to the feed water pump 7 to feed water by operating the feed water pump 7. When the feed water pump 7 operates, the feed water motor valve 9 is opened to supply boiler water pressurized by the feed water pump 7 into the boiler 1.

The opening degree of the feed water motor-operated valve 9 at this time is adjusted so that the feed water pump discharge side pressure detected by the feed water pressure detection device 10 becomes a value set as a target. The pressure value on the discharge side of the water supply pump detected by the water supply pressure detection device 10 fluctuates depending on the pressure in the boiler even if the water supply pump operates in the same manner. When the feed water electric valve 9 is set to the same opening degree, the pressure value increases when the pressure in the boiler is high, but the pressure value decreases when the pressure in the boiler is low.

First, the water supply control state in the case where the boiler internal pressure described in the first half of FIG. 2 is high will be described. In FIG. 2, the water level in the boiler is lowered to E2 at time A and the water supply operation is started. At time A, the operation of the water supply pump 7 is started and an operation for starting to open the water supply electric valve 9 is performed. In this embodiment, the discharge of boiler water by the feed water pump 7 is performed earlier than the opening of the water supply electric valve 9, and at the beginning of water supply, the water supply pump 7 is operated with the opening degree of the water supply electric valve 9 being small. ing. Therefore, the feed water pump discharge side pressure detected by the feed water pressure detecting device 10 is temporarily significantly higher than the target value. In the operation control device 4, when the pressure value on the discharge side of the feed water pump is higher than the target pressure, the opening degree of the water supply electric valve 9 is opened, and when the pressure value greatly exceeds the target value, water supply is performed. Open the motorized valve 9 as soon as possible. The pressure on the water supply pump discharge side is larger than the target value at the beginning of water supply start, but thereafter, as the opening degree of the water supply motor operated valve 9 becomes larger, the pressure value decreases and approaches the target pressure. The operation control device 4 reduces the speed at which the feed water motor valve 9 opens when the discharge pressure value of the water supply pump 7 approaches the target value, and when the water discharge pump pressure value becomes equal to the target pressure value at time B The change of the opening degree of the motor operated valve 9 ends. Here, the water supply motor-operated valve 9 is stopped at an opening degree close to full open, and the pressure value is stable at the target value. The feed water flow rate at this time increases as the feed water motor valve 9 opens, but reaches the target value at time B and is stable thereafter. By supplying water, the water level in the boiler rises, and at time C, the water level in the boiler reaches the E1 water level, which is the water supply stop water level, and the operation of the water supply pump 7 is stopped. When the operation of the feed water pump 7 is stopped, the pressure on the discharge side of the feed water pump is reduced, and the feed water to the boiler is stopped. And if the water supply electric valve 9 is closed, it will return to the state before water supply start.

Next, the water supply situation in the state where the boiler internal pressure described in the second half of FIG. 2 is low will be described. In FIG. 2, at time D, the water level in the boiler is lowered to E2, and the water supply operation is started. At time D, the operation of the water supply pump 7 is started and the operation of opening the water supply electric valve 9 is performed. In this embodiment, the discharge of the boiler water by the water supply pump 7 is performed earlier than the opening of the water supply electric valve 9, and at the beginning of the water supply, the water supply pump 7 is in a state where the opening degree of the water supply electric valve 9 is small. Is working. Therefore, even if the pressure in the boiler is low, the feed pump discharge pressure detected by the feed water pressure detection device 10 is temporarily higher than the target pressure. At this stage, the pressure at the discharge side of the feed pump is high because the opening degree of the feed motor valve 9 has not reached the required amount, so the pressure of the feed water rises even if the pressure in the boiler is low. Do. However, since the pressure in the boiler is low this time, the pressure on the discharge side of the feed pump detected by the feed pressure detection device 10 does not rise as in the first half of FIG. 2 where the pressure in the boiler is high.

After that, while the pump discharge side pressure is higher than the target value, the opening degree of the water supply electric valve 9 is increased. Unlike the case where the boiler pressure is high, the difference between the detected value of the pump discharge side pressure and the target value is different. Since it is small, the opening speed of the water supply electric valve 9 becomes slow. Since the pump discharge side pressure reaches the target value at time E, the operation to open the opening of the water supply motor-operated valve 9 stops at time E. The opening degree of the water supply electric valve 9 at this time is smaller than that in the case where the boiler internal pressure is high.

By adjusting the opening degree of the water supply electric valve 9 so that the discharge pressure of the water supply electric valve becomes a target value, the water supply flow rate to the boiler can be set to an appropriate amount. Regardless of the internal pressure of the boiler, if the opening degree of the feed water electronic valve 9 is the same, if the boiler internal pressure is low, the pressure on the discharge side of the feed water pump will not increase so much, so the feed water flow rate is large. Become. In this case, when adjustment is performed to reduce the cross-sectional area of the water supply flow path with the water supply electric valve 9, the resistance increases in the water supply flow path, so that the pressure increases on the discharge side of the water supply pump and passes through the water supply electric valve 9. Water supply flow rate decreases. The feedwater flow rate supplied to the boiler changes even if the pressure in the boiler changes by adjusting the pressure on the discharge side of the feedwater pump to the same pressure when the pressure in the boiler is high and low by the feedwater motor-operated valve 9. It can be adjusted to the same level.

Thereafter, by supplying water at a target flow rate, the water level in the boiler rises, and at time F, the water level in the boiler reaches E1, which is the water supply stop water level, and the operation of the water supply pump 7 is stopped. When the operation of the feed water pump 7 is stopped, the pressure on the discharge side of the feed water pump is reduced, and the feed water to the boiler is stopped. Then, when the feed water motor-operated valve 9 is closed, the state before the water feed start is restored.

By doing as mentioned above, even when the steam pressure in the boiler is different, the feed water flow rate is stabilized. Therefore, even when the pressure in the boiler is low, it is possible to suppress the occurrence of cavitation due to an excessive supply water flow rate, and it is also possible to suppress a drop in steam quality due to a sudden rise in the water level in the can.

In the water supply control in the boiler, water supply is started when the water level drops to the water supply start water level, and water supply is stopped when the water level rises to the water supply stop water level. It was set based on the feedwater flow rate at low pressure of the boiler. This is because when the pressure in the boiler is low, the feed water flow rate increases, so by setting the interval between the feed water start water level and the water supply stop water level large, the frequency of feeding water increases even if the pressure in the boiler is low. Because it was necessary to make it not too much. However, as described above, when the feed water flow rate can be made constant by the feed water flow rate required at high pressure, the water level interval at which the water supply control is performed can be set small. When the water level interval is set large, when the water level is high, the liquid component is taken out with the steam and the steam quality is reduced, and when the water level is low, the water circulation in the can may become insufficient. The However, the water level interval can be narrowed by suppressing the feed water flow rate at low pressure, and the water level fluctuation width in the can can be suppressed to a small level. Therefore, the water circulation state in the can is also stabilized, and high steam quality can be maintained in all regions between the upper limit and the lower limit of the steam pressure.

The present invention is not limited to the embodiments described above, and many modifications can be made by those skilled in the art within the technical concept of the present invention.

DESCRIPTION OF SYMBOLS 1 Boiler 2 Combustion device 3 Steam pressure detection device 4 Operation control device 5 Steam separator 6 Feed water piping 7 Feed water pump 8 Water level detection cylinder 9 Feed water electric valve 10 Feed water pressure detection device E1 Feed water stop water level E2 Feed water start water level

Claims (1)

A water supply pipe with a water supply pump is connected on the way, and when the water level in the boiler falls to the water supply start water level, the water supply pump is operated to supply water. When a water supply pressure detection device is installed between the water supply electric valve, the water supply pump, and the water supply electric valve on the secondary side, and the water supply pump supplies water, the water supply pump is started and closed When the operation to start opening the motorized valve is performed and the feedwater pump is operated in a state where the opening of the motorized water supply valve is small, the pressure value on the discharge side of the feedwater pump detected by the feedwater pressure detecting device is higher than the target value. open the opening of the water supply electric valves on the basis of the difference between the detected pressure value and the target value do, the water supply to the water supply pump discharge pressure that is detected by the water supply pressure detector is kept a predetermined value Boiler feed water and wherein the one which regulates valve operating opening.

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