JPH0232525B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a boiler system, and particularly to a boiler system provided with a means for preventing low-temperature corrosion of an economizer.

<Prior art and its problems> When using fuel containing sulfur in the parts that make up a boiler, the exhaust gas contains sulfur dioxide gas (SO ₃ ), and when this exhaust gas comes into contact with low-temperature parts. The steam it contains reaches its dew point and condenses, and SO ₃ dissolves into it to form sulfuric acid, which corrodes the parts and leads to an accident. It is known that such members include air preheaters, energy savers, steel plates forming ducts, and the like. Among these problems, when water leaks due to corrosion in the heat exchanger tubes of the energy saver that heats the pressurized water supply, there is a problem in that the operation must be shut down, the tank shut down, and the energy saver repaired or replaced.

Figure 1 is a diagram of a carbon steel tube with feed water flowing inside, with the horizontal axis representing the sulfur content (%) in heavy oil fuel and the vertical axis representing the minimum tube metal temperature for preventing corrosion. . If there is no scale inside the heat transfer tube, the tube metal temperature can be considered to be approximately the temperature of the fluid inside the tube. Curve A shows the minimum tube metal temperature for preventing corrosion when the fuel does not contain vanadium in the case of a heavy oil-fired boiler, and curve B shows the minimum temperature for preventing corrosion when the combustion residue (ash) contains approximately 3.5% vanadium. Indicates tube metal temperature.

As is clearer from this Figure 1, the medium (water supply)
It is necessary to set the temperature to a point higher than this curve.

In conventional boilers, in order to prevent such low-temperature corrosion, a feed water heater or heating type deaerator is installed as a means to increase the feed water temperature, but there is a problem in that the equipment cost is high.

The present invention solves this problem by providing a simple water supply bypass line and recirculation line for the main water supply line.

<Purpose of the invention> The present invention can be applied to existing boilers without causing such low-temperature corrosion, and the boiler equipment can be easily modified by adding pipes, etc. Moreover, in new boilers, the feed water heater, The purpose of this study is to propose a boiler structure that prevents low-temperature corrosion of the economizer without using a heating type deaerator or the like.

<Summary of Means> In short, the present invention provides a boiler feed pump, a main feed water flow rate control valve, a feed water temperature transmitter at the inlet of the economizer, a economizer, and a feed water temperature transmitter at the outlet of the economizer, in the main water supply pipe. In the boiler provided sequentially from the upstream side, a water supply bypass pipe line with a bypass amount adjustment valve controlled by a temperature transmitter at the outlet of the carbon economizer, which supplies a portion of the feed water to the boiler drum by bypassing the carbon economizer. and a recirculation pump and a recirculation flow control valve controlled by a feed water temperature transmitter at the inlet of the economizer, and a water supply supplying a portion of the feed water at the outlet of the economizer to the inlet of the economizer. This is a boiler device characterized by being provided with a recirculation pipe line.

<Embodiment> FIG. 2 is a diagram of a pipe system and a control system showing an embodiment of the present invention. In this case, water is supplied to the boiler 1 from a water supply tank 2 through a boiler feed pump 4, a main water flow rate control valve 5, and a main water flow rate, which are installed in order in a main water supply pipeline 3 that connects each member to form a main water supply system. A total of six fuels are supplied to the upper shell 1a of the boiler via the economizer 7. The main water supply conduit 3 consists of a conduit 3a that connects the inlet of the economizer 7 and the water supply tank 2, and a conduit 3b that connects the outlet of the economizer and the upper body 1a. The water supply bypass pipe 8 is provided with a bypass amount adjustment valve 9, one end of the water supply bypass pipe 8 is connected to the pipe 3a at a connecting part 8a, and the other end is connected to the drum (upper body) inlet by the pipe 3b. Connect at the nearby connecting part 8b.

The feed water recirculation path 10 also has one end connected to the pipe 3a downstream of the connection 8a for the feed water flow at a connection 10a, and the other end connected to the connection 8b at the upstream connection 10b for the pipe 3b. . This water supply recirculation line 10 is provided with a recirculation pump 11 and a recirculation amount control valve 12 . Combustion gas G is boiler 1
The water flows through the flue 13 to the economizer 7, exchanges heat with the water supply, and is then discharged through the flue 14 and chimney 15.

In such a device, the water supplied in the water supply tank 2 is at almost the outside temperature, and if the temperature is 15°C, the temperature of the heat exchanger tube near the water supply inlet of the economizer will increase regardless of the sulfur content in the fuel, as shown in Figure 1. This will cause low-temperature corrosion.

In this case, the bypass water supply amount is controlled from the connection part 8a via the water supply bypass pipe line 8 and the bypass amount control valve 9, and therefore the water supply amount to the energy saver is also controlled, and the water supply recirculation line 10 is used to save water. This temperature increase can be achieved by increasing the pressure of a portion of the heated feed water extracted from the outlet connection part 10b of the coaler 7 by the recirculation pump 11, controlling its flow rate by the recirculation flow rate control valve 12, and supplying it to the pipe line 3a. By mixing the water supplied from the water supply tank with the water supplied from the water supply tank, the temperature of the water supply at the inlet of the economizer can be increased to prevent low-temperature corrosion.

Furthermore, since the temperature of the feed water at the outlet of the economizer is controlled, the temperature of the water feed water at the outlet of the economizer can be kept below the saturation temperature for the boiler pressure, resulting in the water hammer phenomenon caused by steaming in the main water supply pipe.
This can prevent the occurrence of

Each of these controls is performed by the boiler's main control box 20 which stores signals from the exhaust gas thermometer 21 and temperature signals from the temperature transmitters 16 and 18 and issues command signals. A load signal L is sent to this main control box 20, and a water supply flow rate signal from the main water supply flow meter 6 is also sent. These signals are compared with the stored values in the main control box, and command signals are sent to the main water supply flow rate control valve 5, the bypass amount control valve 9, and the recirculation flow rate control valve 12, and the respective flow rates are adjusted.

<Effects of the Invention> By carrying out this invention, the bypass amount and recirculation amount of the feed water are controlled, and the temperature of the feed water at the inlet of the economizer is controlled to an appropriate temperature higher than the temperature of the low temperature corroding metal, thereby preventing low temperature corrosion of the economizer. This has the effect that it is possible to provide a boiler apparatus that prevents the water hammer phenomenon.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between the metal temperature of steel pipes and the sulfur content in the fuel to prevent low-temperature corrosion, and Fig. 2 is a drawing showing the pipe system and control system of the boiler equipment according to the present invention. It is. 1...Boiler, 3...Main water supply pipe, 3a, 3b
...Pipe line, 8... Water supply bypass pipe line, 9... Bypass amount control valve, 10... Water supply recirculation pipe line, 11...
... Recirculation pump, 12 ... Recirculation amount control valve, 20
...Main control box.

Claims (1)

[Scope of Claims] 1. A boiler feed water pump, a main water supply flow rate control valve, a feed water temperature transmitter at the inlet of the economizer, a economizer, and a feed water temperature transmitter at the outlet of the economizer from the upstream side of the main water supply pipe. In the boilers provided in sequence, a feed water bypass pipe line with a bypass amount regulating valve controlled by a temperature transmitter at the outlet of the economizer, which supplies a part of the feed water to the boiler drum by bypassing the economizer; A feed water recirculation pipe having a circulation pump and a recirculation flow rate regulating valve controlled by a feed water temperature transmitter at the inlet of the economizer, and supplying a portion of the feed water at the outlet of the economizer to the inlet of the economizer. A boiler device characterized by being provided with a passage. 2. Send signals of the exhaust gas temperature at the inlet of the economizer, the water supply temperature at the inlet of the economizer, and the water supply temperature at the outlet of the economizer to the main control box of the boiler that outputs memory and command signals, and send the boiler load signal and the water supply flow rate signal to the main control box. The command signal sent to the control box and compared with the value stored in the main control box controls the bypass amount control valve, the recirculation amount control valve, and the main water supply flow rate control valve, and controls the metal temperature of the energy saver heat transfer tube. 2. The boiler device according to claim 1, further comprising a main control box and a signal circuit that can maintain the temperature at a temperature higher than that at which low-temperature corrosion occurs.