CN209991442U - Water loss protection structure of circulating fluidized bed boiler - Google Patents

Abstract

The utility model provides a circulating fluidized bed boiler desiccation protection structure, be provided with PCV valve and relief valve at boiler superheater outlet pipe way, still set up the control valve that releases on this superheater outlet pipe way, the take-off pressure of this control valve that releases is less than PCV valve and relief valve, and the control valve that releases, connect on safety power supply, the control valve that releases can discharge a large amount of steam that produces in the boiler with certain speed rapidly when the circulating fluidized bed boiler takes place the loss of moisture accident, thereby guarantee that heating surfaces such as boiler water-cooling wall are not super-warm, the higher urgent water charging system of fungible investment, need not extra maintenance at ordinary times.

Description

Water loss protection structure of circulating fluidized bed boiler

Technical Field

The utility model belongs to the equipment safety protection device of circulating fluidized bed boiler, especially the device that the protection receives the hot side and does not overtemperature when the loss of coolant accident takes place.

Background

The circulating fluidized bed boiler has been widely used in China due to its advantages of wide fuel adaptability, combustibility of low calorific value fuel and other special fuels, low pollutant control cost, etc. The technology of the circulating fluidized bed in China is developed rapidly, and the circulating fluidized bed boiler is the country with the largest number of operating circulating fluidized bed boilers in the world. In recent years, 350 MW-grade CFB units with dozens of supercritical parameters are put into operation in China, and the largest supercritical circulating fluidized bed unit in the world is the second-stage 600MW unit in white horse in China.

One of the important differences between the circulating fluidized bed boiler and the pulverized coal furnace is that the gas-solid two-phase heat transfer to the heated surface is mainly performed in the hearth, a large amount of circulating material solid particles exist in the hearth, the hearth has large refractory material consumption, and the hearth has large thermal inertia. Therefore, when the boiler loses water, the possibility that the heating surfaces such as the water-cooled wall and the like are over-heated and damaged because the bed materials continuously release heat to the heating surfaces exists. Therefore, when the ALSTOM type CFB boiler was introduced in the early days, an emergency water supplement system was introduced at the same time as one of its necessary configurations.

The emergency water replenishing system is a special configuration system of the circulating fluidized bed boiler and comprises an emergency water replenishing pump, an emergency water replenishing tank and the like. The heating surface can be protected when water supply is lost, and the heating surface is prevented from being burnt out.

Because the emergency water replenishing pump has high pressure and large flow, and a diesel engine needs to be configured to deal with the power loss condition of the whole plant, the diesel engine is configured with high power and generally needs to be imported, and the investment is large.

However, the probability of water supply loss caused by power loss of the whole plant is extremely low, and the emergency water supply system needs to be put into use immediately after the occurrence of the water loss accident and needs to be regularly operated in a trial mode, so that the daily operation and maintenance cost is high.

SUMMERY OF THE UTILITY MODEL

The utility model provides a technical problem provide a dedicated steam control valve of releasing when the dehydration condition takes place at circulating fluidized bed boiler promptly, in time will be heated the working medium in the face according to setting for the logic and release with controlled rate to prevent to receive the hot side overtemperature, play the purpose that the protection received the hot side.

The technical means adopted by the utility model are as follows.

A water loss protection structure of a circulating fluidized bed boiler is provided with a PCV (positive pressure control) valve and a safety valve on an outlet pipeline of a boiler superheater, and is characterized in that at least 1 discharge control valve is further arranged on the outlet pipeline of the superheater, the tripping pressure of the discharge control valve is lower than that of the PCV valve and the safety valve, and the discharge control valve is connected to a safety power supply; an emergency water replenishing system is not arranged in the circulating fluidized bed boiler unit.

The discharge control valve is electrically or hydraulically controlled.

The tripping of the relief control valve is automatically controlled, and the return seat is automatically or manually controlled.

The opening and closing differential pressure of the discharge control valve is more than 10% of the take-off pressure.

When the number of the discharge control valves is 2 or more than 2, the jump-up pressure or the recoil pressure is set in a step-type ascending or descending manner.

The beneficial effects of the utility model are as follows.

1. After a boiler water loss accident, particularly a boiler water loss accident caused by power loss of a whole plant, accumulated bed materials, castable in a boiler and the like can be transferred to heat of working media in a heating surface, the heat is taken out of a boiler body at a controlled mass flow rate, the phenomenon that the heating surface is over-heated due to the fact that the heat cannot be taken out of the boiler in time is avoided, meanwhile, a safety valve of a superheater and a PCV (pressure gradient valve) cannot jump, the service lives of the safety valve and the PCV are prolonged, and meanwhile, waste of the working media is reduced.

2. The utility model discloses only set up mode simple structure, non-maintaining, the investment of special relief control valve very low, can replace conventional urgent water charging system completely, practice thrift a large amount of initial investments and fortune dimension expense, simplify the emergency management of power plant, reduced the human cost.

3. The existing emergency water replenishing system is not only complex, but also needs regular trial operation at ordinary times, but has few used opportunities, so that the cost performance is extremely low. After water loss occurs, some power plants worry that a large amount of low-temperature water supplement enters the heating surface and the heating surface is damaged. The unit of the utility model can not have the condition that low-temperature water enters the heating surface of the boiler, and is a structural design with high economical efficiency.

4. The utility model discloses a desiccation protection architecture can be used to the circulating fluidized bed boiler of each grade parameter such as subcritical, supercritical, super supercritical, the range of application is wide.

Drawings

Fig. 1 is a schematic diagram of the system structure of the present invention.

Detailed Description

A superheater 3 (or a water wall) of the boiler is followed by a superheater outlet line 1, and a safety valve and a PCV valve are provided on the outlet line 1. After the loss of coolant accident happens, the steam pressure rises, and the PCV valve and the safety valve quickly jump after reaching the jump-off pressure, so that the steam is discharged. When the vapor pressure falls back to the set recoil pressure, the PCV valve and the safety valve recoil.

Since the PCV valve and the safety valve are provided for protecting the superheater, the capacity and the tripping pressure of the PCV valve and the safety valve are also selected according to the safety principle for protecting the superheater, and the parameter settings of the PCV valve and the safety valve are specified by national standards and cannot be changed at will, the existing valve body cannot be provided for discharging the steam in the heated surface at an optimal discharge rate so as to protect the heated surface.

The utility model discloses a focus on, set up 1 at least dehydration and protect dedicated control valve 2 of releasing on this over heater outlet pipeline 1, and this control valve 2 of releasing take-off pressure is less than PCV valve 4 and relief valve 5, control valve 2 of releasing, PCV valve 4 and relief valve 5's order and quantity can be decided according to actual unit needs, set up under the condition of a plurality of control valves of releasing, can set up the jump-off pressure numerical value of ladder nature, control valve 2 of releasing adopts electric control or hydraulic control, use current valve body can, control valve 2 of releasing need connect on safety power supply, the jump-off of control valve 2 is automatic, the seat is automatic or manual all can, the relation of the jump-off pressure of control valve 2 and seat back pressure is different with conventional relief valve or PCV valve, the pressure differential of opening and close of relief valve 5 is generally 4% ~ 7% of jump-off pressure, the biggest is not more than 10%, and the pressure differential of opening and close of dehydration protection control valve 2 is generally greater than 10%.

The take-off pressure, the recoil pressure, the capacity and the like of the discharge control valve 2 are all set adaptively according to the parameters of different circulating fluidized bed units, and can be obtained by calculation by a person skilled in the art without specific limitation.

After a loss of water accident occurs in any situation, the tripping pressure of the loss of water protection discharge control valve 2 is lower than that of the PCV valve and the safety valve, so that the steam pressure rises, the loss of water protection discharge control valve trips firstly, the discharge rate of the loss of water protection discharge control valve can ensure that the steam pressure does not rise continuously any more, under the condition that a plurality of discharge control valves with different tripping pressures are arranged, the gradually rising pressure sequentially reaches the tripping pressures of the plurality of discharge control valves, the rising rate is gradually reduced until the steam pressure does not rise continuously, and the tripping of the PCV valve and the safety valve is not triggered. When the steam pressure is reduced to the back seat pressure, the water loss protection discharge control valve 2 returns to the seat, and returns to the seat in turn according to the step back seat pressure value under the condition of a plurality of discharge control valves, and then the steam pressure continues to rise, the water loss protection discharge control valve jumps, and the steam pressure is reduced and returns to the seat. After the process is circulated for a plurality of times, the temperature of bed materials, casting materials and the like in the boiler is reduced, the heat transfer rate to working media in a heating surface such as a water-cooled wall is reduced, water is not changed into steam any more, the pressure and the temperature of the steam are not increased, the heat absorption of the working media in the heating surface is little, and the heating surface is not over-heated, so that the heating surface is effectively protected. In the process of rising or falling of the steam pressure, the situation that the falling steam pressure rises instead of reaching the lowest return seat pressure value of the relief control valve may occur, and at the moment, the plurality of relief control valves are repeated to jump and release the steam pressure in sequence, so that the process is a flexible process and has different changes and adjustments according to different unit parameters and different events.

After a loss of water accident caused by power loss of a whole plant occurs, the three fans are stopped completely, the circulating material quickly falls back to the air distribution plate, the temperature of the circulating material, castable in the furnace and the like is still as high as about 850 ℃, heat is released to heating surfaces such as a furnace water-cooled wall and the like in a radiation and heat conduction mode, working medium water continuously absorbs heat in the water-cooled wall and is changed into steam, and a main steam valve of the steam turbine and a steam inlet valve of an intermediate pressure cylinder are completely closed, so that steam pressure is increased. The working medium in the furnace is continuously converted into steam from water, the steam continuously absorbs heat, the pressure and the temperature are increased, and the overheating damage of the heating surface is caused to a certain degree. At the moment, the water loss protection discharge control valve 2 is connected with a security power supply, so that the boiler can normally work under the condition of power loss, discharge steam, reduce the steam pressure and temperature and effectively protect the heating surface of the boiler.

The water loss protection discharge control valve 2 is specially designed and selected according to the water loss accident working condition of the circulating fluidized bed boiler, and the discharge rate, the take-off pressure and the recoil pressure are selected according to the principle that the heating rate of the heating surface is the minimum, so that the safety of the heating surface can be guaranteed most effectively.

Taking a certain 350MW supercritical circulating fluidized bed boiler as an example, a water loss protection discharge control valve is arranged, and the rated discharge capacity is 117 t/h. After water loss, the discharge control valve automatically jumps when the steam pressure reaches 27MP, and is manually closed when the recoil pressure value is reached. The set values of the recoil pressure for different operating conditions are shown in the following table.

And selecting the reseating pressure of the discharge control valve operated by different hands.

(1) Working condition a:

after a power failure accident occurs, the pressure of working media in the water-cooled wall begins to rise until the jump starting pressure of the discharge control valve reaches 27MPa, the discharge control valve automatically jumps to discharge the working media, and the discharge control valve is manually closed when the pressure is reduced to 20 MPa. Within 12000s after power loss, the working medium pressure is in a rapid oscillation process with approximate equal amplitude. The temperature of the working medium shows a tendency of oscillation and rising until the working medium and the material on the bed side reach thermal equilibrium. Under the control condition, the overtemperature phenomenon can never occur on the pipe wall, namely, under the condition of power loss, the discharge control valve is automatically opened, and when the pressure of the working medium is reduced to 20MPa, the discharge control valve is manually closed, the discharge of the working medium is stopped, and an emergency water supply system is not required to be equipped on the 350MW supercritical CFB boiler.

After the relief control valve is repeatedly operated for 31 times, the steam pressure can not reach the take-off pressure of 27MPa any more.

(2) Working condition b:

after a power failure accident occurs, the pressure of working media in the water-cooled wall begins to rise until the tripping pressure of the discharge control valve reaches 27MPa, the discharge control valve automatically trips to discharge the working media, and the discharge control valve is manually closed when the pressure is reduced to 15 MPa. Within 10000s after power loss, the working medium pressure is in a rapid oscillation process with approximate equal amplitude. The temperature of the working medium shows a tendency of oscillation and rising until the working medium and the material on the bed side reach thermal equilibrium. Under the control condition, the overtemperature phenomenon of the pipe wall still can not occur, and by adopting the control strategy, an emergency water supply system does not need to be arranged on the 350MW supercritical CFB boiler.

However, as the recoil pressure decreases, the average discharge rate increases, the number of valve trips decreases, and the bleed control valve is operated 12 times repeatedly.

(3) Working condition c:

and the working condition c is obtained by further reducing the recoil pressure on the basis of the working condition b, the pressure and the temperature of the working medium oscillate reciprocally along with the opening and the closing of the discharge control valve, the quality of the working medium in the water-cooled wall is reduced in a step manner, when a power loss accident happens for 7407 seconds, the wall of the pipe reaches the allowable temperature, and the water-cooled wall is burnt out at an overtemperature.

The bleed control valve is tripped 6 times.

Therefore, the drainage protection can be realized by reasonably selecting the drainage control valve and the take-off pressure thereof, particularly the manual recoil pressure according to the actual condition of the unit.

Claims (5)

1. A water loss protection structure of a circulating fluidized bed boiler is characterized in that a PCV (PCV) valve (4) and a safety valve (5) are arranged on an outlet pipeline (1) of a boiler superheater, at least 1 discharge control valve (2) is further arranged on the outlet pipeline (1) of the superheater, the tripping pressure of the discharge control valve (2) is lower than that of the PCV valve (4) and the safety valve (5), and the discharge control valve (2) is connected to a safety power supply; an emergency water replenishing system is not arranged in the circulating fluidized bed boiler unit.

2. The boiler water loss protection structure of the circulating fluidized bed according to claim 1, wherein the discharge control valve (2) is electrically or hydraulically controlled.

3. The circulating fluidized bed boiler water loss protection structure of claim 1, wherein the tripping of the drain control valve (2) is automatically controlled and the reseating is automatically or manually controlled.

4. The water loss protection structure of a circulating fluidized bed boiler according to claim 1, wherein the open/close pressure difference of the discharge control valve (2) is more than 10% of the tripping pressure.

5. The circulating fluidized bed boiler water loss protection structure of claim 1, wherein when the number of the discharge control valves (2) is 2 or more than 2, the take-off pressure or the recoil pressure is set to be increased or decreased in a stepwise manner.

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