JPH0117041B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to temperature control of interbed heat exchanger tubes in a fluidized bed boiler, and more particularly to a method for preventing burnout of heat exchanger tubes during emergency shutdown of a fluidized bed boiler.

A fluidized bed boiler uses the heat of the fluidized bed to generate steam and supplies this steam to equipment that uses steam such as a steam turbine. Heat transfer tubes such as vessels are placed in the fluidized bed. In this fluidized bed boiler, in the case of equipment that uses steam, such as the above-mentioned steam turbine trip, the supply of steam to the turbine is immediately stopped by closing the main steam valve, and the supply of fuel to the fluidized bed is also stopped to remove unnecessary steam. It is necessary to reduce the occurrence of In this case, the inside of the fluidized bed is at a high temperature of about 850° C. during operation, and the fluidized medium has a large amount of heat, so the high temperature is maintained for a considerable time after the furnace is stopped. For this reason, if the amount of water supplied to the evaporator tube remains unchanged during operation, a large amount of steam will be generated due to residual heat within the layer, and this steam will need to be discharged to the steam reservoir or outside the system. On the other hand, if the supply of water to the evaporator pipe is stopped, the residual water in the pipe will evaporate, and the water in the pipe will turn into steam with a low specific heat, resulting in almost no flow, and there is a risk that the pipe wall will become excessively heated, causing the pipe to burn out. . The above problems also apply to the intralayer superheater tube. These problems can be solved to some extent by using a stainless steel metal as the constituent material of the interlayer heat exchanger tube, but there is a problem in that the material cost is extremely high.

The purpose of this invention is to eliminate the above-mentioned drawbacks of the prior art, to reduce the amount of steam discharged outside the system during emergency shutdown of a fluidized bed boiler, and to eliminate the risk of burnout even if the intrabed heat exchanger tubes are constructed of ordinary steel pipes. There is no way to provide that.

In short, this invention stops the supply of water or steam to the intrabed heat exchanger tubes during an emergency stop of a fluidized bed boiler, and prevents the heat exchanger tubes from burning out from a cooling water system that is separate from the gas cylinder. The amount of cooling water to be obtained is supplied, and the steam generated by residual heat in the layer is gradually discharged to the outside of the system while the pressure inside the pipes is detected.

On the same day as the filing date of this invention, a method was proposed to prevent burnout of heat transfer tubes by using boiler water in the gas cylinder of the boiler as a cooling medium for the heat transfer tubes and also sending the boiler water to the superheater. (Patent Application No. 54-135299) The amount of boiler water supplied is determined by detecting the temperature of the tube wall of the superheater tube, sending the detected temperature signal to the control box, and controlling the amount of boiler water supplied according to the command from the control box. The evaporator tube, which is being controlled, is supplied from the gas cylinder as during operation, and is converted into steam and sent to the gas cylinder according to the amount of heat that the evaporator tube receives from the fluidized medium, and is not particularly controlled.

Therefore, in the event of an emergency shutdown, there is a risk of excessive steam being generated, which should be vented via a safety valve or other relief means.

On the other hand, the present invention focuses on the fact that the saturated steam pressure (that is, the saturated steam temperature) corresponds to the tube wall temperature of the heat transfer tube, and utilizes a pressure detector in the steam discharge pipeline, and also provides a separate head tank to maintain low temperature. Cooling water, in which latent heat can be utilized, is supplied from this head tank to the heat exchanger tubes by controlling the supply amount. Cooling water has a lower temperature than boiler water and can utilize latent heat, so it has a large cooling effect, and it prevents already heated boiler water from being wasted and released, thereby preventing loss of thermal energy.

First, a fluidized bed boiler for carrying out the method according to the present invention will be explained.

In FIG. 1, 1 is the main body of the fluidized bed boiler, and 2 is the gas cylinder. Water is supplied to the gas cylinder 2 by a water pump 3 via an economizer 4. An air chamber 5 is formed in the lower part of the main body 1, and air is supplied to the fluidized bed 8 through a perforated plate 6. An evaporator tube 9 and a superheater tube 10 are arranged in the fluidized bed 8 as intrabed heat transfer tubes. Steam in the superheater tube 10 is sent to a steam turbine 31 via a steam pipe 30. Coal is classified in advance and supplied to this fluidized bed, and is supplied to the fluidized bed via a coarse coal hopper 20 and a screw feeder 24, while pulverized coal is passed through pulverized coal supply pipes 21a and 21b to air. The air is transported by A and reaches the burners 22a and 22b, where it is burned within the layer. Note that reference numerals 23a and 23b represent a group of evaporator tubes that exchange heat with the combustion gas.

If a failure occurs in the turbine 31 in the fluidized bed boiler 1 described above, a turbine trip signal is sent to the control box 32. Based on this signal, the control box 32 completely closes the main steam valve 33 provided in the steam pipe 30 to immediately stop the supply of steam to the turbine 31, and also fully closes the valve 35 provided in the steam pipe 34 to completely close the main steam valve 33 provided in the steam pipe 30 to completely close the steam supply from the gas cylinder 2. steam also stops. At the same time, the valves 37a and 37b provided in the steam pipes 36a and 36b connecting the evaporation pipe 9 and the gas cylinder 2 are also fully closed, and the circulating flow of steam between the evaporation pipe 9 and the gas cylinder 2 is also stopped. Following this operation, the cooling water pipe 41 connecting the head tank 40, the superheater pipe 10, and the evaporator pipe 9
The valve 42 is slightly opened to allow cooling water to gradually flow into these intralayer heat transfer tubes, thereby exchanging heat with residual heat in the layer to prevent burnout of the heat transfer tubes. The steam in the evaporation pipe 9 is gradually made to flow into the steam exhaust pipe 45 by slightly opening the valve 44 provided in the steam exhaust pipe 43. On the other hand, the steam in the superheater tube 10 flows from the steam supply tube 30 into the steam exhaust tube 45. As a result, the steam exhaust pipe 4
The valve 47 is operated while detecting the pressure inside the pipe by the pressure sensor 46 provided at 5, and the steam generated by the residual heat of the fluidized bed is discharged to the outside of the system. The pressure inside the pipe is almost 0
When the temperature is reached, the valve 47 is fully opened to completely release the steam in the pipe and the work is completed.

According to this invention, after the fluidized bed boiler is stopped, cooling water is passed through the heat exchanger tubes in the bed, so that even if the heat exchanger tube structure is made of inexpensive steel pipes, no burnout occurs, and moreover, no steam is discharged outside the system. It is also possible to reduce the amount of heat and improve cooling efficiency. Note that instead of the signal of the released steam pressure, a tube wall temperature measuring device may be attached to the heat transfer tube and the temperature signal may be used for control.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a fluidized bed boiler for carrying out the method according to the invention. 1... Fluidized bed boiler body, 2... Gas cylinder, 9...
Evaporation pipe, 10...Superheater tube, 31...Steam turbine, 32...Control box, 33...Main steam valve, 35,
37a, 37b, 42, 44, 47... valve, 40
...Head tank, 41...Cooling water pipe, 43...
Steam exhaust pipe, 45... Steam exhaust pipe, 46... Pressure detector.

Claims (1)

[Claims] 1. When heat transfer tubes are arranged in a fluidized bed to supply steam to various equipment, when the main steam valve is shut off in an emergency, the water supply from the gas cylinder to the heat transfer tubes in the bed is stopped and cooling water is stored. Cooling water is introduced from the head tank into the heat transfer tube, and the steam generated by the residual heat of the fluidized bed is controlled by the control box, which detects the saturated steam pressure inside the tube corresponding to the tube wall temperature and receives the pressure signal, to control the amount of cooling water. A method for preventing burnout of in-layer heat transfer tubes using a head tank, characterized by controlling a pressure control valve provided in a pipe line for discharging generated steam to the outside of the system.