Circulating fluidized bed boiler system for burning high-alkali fuel

Abstract

The utility model discloses a circulating fluidized bed boiler system burning high-alkali fuel. The circulating fluidized bed boiler system comprises a fluidized bed used for burning the high-alkali fuel. The fuel feeder is used for providing the high-alkali fuel to the fluidized bed; the air preheater is used for heating air fed into a hearth of the fluidized bed; the dry type desuperheater is used for collecting gas in the fluidized bed and cooling the gas; the cyclone separator is used for carrying out gas-solid separation on gas in the dry type desuperheater; and the tail flue heat exchanger is used for carrying out heat exchange on the gas separated by the cyclone separator and the air preheater. According to the dry type desuperheater, the problem that dust on a low-temperature heating surface at the tail is severely contaminated can be solved, high-concentration low-temperature dust particles exist in the dry type desuperheater, and gas-phase alkali metal can be captured while the dust particles and high-temperature flue gas are mixed for cooling, so that the alkali metal is condensed on the low-temperature dust particles; then gas-solid separation is carried out, and pure flue gas enters a tail flue; most of ash particles circularly return to the hearth; and the purpose of circularly purifying the flue gas is achieved.

Description

Technical Field

[0001] The utility model relates to a technology for burning high-alkali fuel using a circulating fluidized bed boiler, in particular to a circulating fluidized bed boiler system burning high-alkali fuel, belonging to the technical field of high-alkali fuel combustion. Background Art

[0002] High-alkali fuels have high volatility, high calorific value, good combustion characteristics, and huge reserves, offering great application prospects. However, during the combustion process in boilers, the alkali metals contained in these fuels easily evaporate into gaseous substances. These gaseous alkali metals condense upon encountering the boiler's low-temperature heating surfaces and trap tiny particles that fall on them, forming an ash fouling layer that typically accumulates thicker and affects the normal operation of the boiler. Previous research and engineering practice on high-alkali fuels has focused on pulverized coal boilers with higher combustion temperatures (>1100°C), while less attention has been paid to circulating fluidized bed boilers with relatively low combustion temperatures (850-900°C). Although the temperature in the furnace of a circulating fluidized bed boiler does not reach the ash melting temperature of the fuel, the high-temperature flue gas still causes the alkali metals to evaporate into a gaseous state. These alkali metals then enter the low-temperature heating surfaces of the tail flue along with the flue gas and condense on the heating surfaces, causing serious fouling problems that affect unit operation. Utility Model Content

[0003] The technical problem to be solved by the utility model is: how to reduce the temperature of the flue gas before entering the low-temperature heating surface of the tail flue to a reasonable temperature.

[0004] In order to solve the above problems, the utility model provides a circulating fluidized bed boiler system burning high-alkali fuel, which includes:

[0005] Fluidized beds for burning high-alkali fuels such as coal or biomass with a high alkali metal content.

[0006] a fuel feeder for supplying high-alkaline fuel to the fluidized bed;

[0007] an air preheater for heating the air fed into the furnace of the fluidized bed;

[0008] Primary and secondary fans used to supply air to the air preheater;

[0009] A dry desuperheater for collecting and cooling the gas in the fluidized bed;

[0010] The cyclone separator is used to separate the gas from the dry desuperheater; the cyclone separator has a high gas-solid separation effect and can recover more than 99% of the ash particles and return them to the furnace, thereby forming the purpose of circulating flue gas.

[0011] The tail flue heat exchanger is used to exchange heat between the gas separated by the cyclone separator and the air preheater.

[0012] Preferably, the circulating fluidized bed boiler system burning high-alkali fuel further includes a slag cooler for collecting slag generated in the furnace of the fluidized bed.

[0013] Preferably, the circulating fluidized bed boiler system for high-alkali fuel further includes a cold slag conveyor for conveying slag from the slag cooler to the dry desuperheater. The cold slag conveyor has a particle size sorting function, and the optimal particle size range for the cooled ash fed to the dry desuperheater is between 100 and 500 microns.

[0014] Preferably, the circulating fluidized bed boiler system burning high-alkali fuel further comprises a return device for collecting the solids separated by the cyclone separator and transporting the solids to the furnace of the fluidized bed.

[0015] Preferably, the circulating fluidized bed boiler system burning high-alkali fuel further includes a tertiary fan for supplying air to the return device.

[0016] Preferably, the inner wall of the dry desuperheater is covered with fire-resistant and wear-resistant material.

[0017] Preferably, the circulating fluidized bed boiler system using high-alkali fuel also includes a quaternary fan for supplying air to the dry desuperheater. By adjusting the air flow rate, the fluidization velocity within the dry desuperheater can be controlled, thereby achieving the purpose of controlling the material concentration within the dry desuperheater.

[0018] Preferably, the high-alkali fuel enters the furnace of the fluidized bed from the fuel feeder for combustion, and the high-temperature flue gas generated after combustion enters the dry desuperheater. The low-temperature ash contained in the dry desuperheater is mixed with the air injected from the four-stage fan to form a fluidized motion state, and mixed with the high-temperature flue gas for heat exchange to reduce the temperature of the high-temperature flue gas, and then enters the cyclone separator for gas-solid separation; the pure flue gas separated from the cyclone separator enters the tail flue heat exchanger and the air preheater for heat exchange and then is discharged from the system.

[0019] More preferably, the temperature of the high-temperature flue gas before entering the dry desuperheater is 800-950°C, and the temperature of the high-temperature flue gas leaving the dry desuperheater is no more than 700°C.

[0020] More preferably, in order to achieve the best cooling effect, the fluidization velocity in the dry desuperheater is controlled at 1-6 m / s; the average material concentration in the dry desuperheater is controlled at 50-500 kg / m 3 .

[0021] The present invention installs a fluidized bed cooling device between the fluidized bed and the cyclone separator. This device uses the fluidized cold ash and cold air within it to reduce the high-temperature flue gas at the furnace outlet. Due to the reduced temperature, the alkali metal vapor phase in the high-temperature flue gas condenses on the surface of the cold ash particles. Simultaneously, by varying the fluidization velocity of the fluidized bed cooling device, the concentration of material within the bed is controlled, thereby varying the degree of mixing between the flue gas and the cold ash, thereby achieving the purpose of controlling the flue gas temperature. Subsequently, the cooled ash-containing flue gas enters the cyclone separator for gas-solid separation. Due to the high separation efficiency of the cyclone separator, most of the material is separated, and the pure flue gas enters the tail flue.

[0022] The fluidized bed cooling device arranged at the furnace outlet uses the fluidized material medium from the cooled boiler bottom ash or other waste ash, which is a waste recycling and therefore has high economic efficiency.

[0023] The utility model proposes to solve the problem of serious ash contamination on the tail low-temperature heating area by burning high-alkali fuel in the circulating fluidized bed boiler system. The solution and expected operating effects are as follows:

[0024] The desuperheater installed at the furnace outlet reduces the temperature of the high-temperature flue gas rich in alkali metals at the furnace outlet, making the flue gas temperature entering the tail flue below 700°C. At this time, the gas phase no longer contains alkali metals, thus preventing the condensation of gaseous alkali metals on the low-temperature heating surface.

[0025] There is a high concentration of low-temperature ash particles inside the dry desuperheater. These ash particles mix with the high-temperature flue gas to cool it down and capture gaseous alkali metals, causing the alkali metals to condense on the low-temperature ash particles. Subsequently, the gas-solid separation effect of the cyclone separator allows the pure flue gas to enter the tail flue. The vast majority of the ash particles are recycled back to the furnace, achieving the purpose of circulating and purifying the flue gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of a circulating fluidized bed boiler system using high-alkali fuel provided by the utility model. DETAILED DESCRIPTION

[0027] In order to make the present invention more clear and easy to understand, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0028] Example

[0029] A circulating fluidized bed boiler system burning high-alkali fuel, characterized by comprising:

[0030] A fluidized bed 1 for burning high-alkali fuels; high-alkali fuels include coal or biomass with a high alkali metal content.

[0031] a fuel feeder 13 for supplying high-alkaline fuel to the fluidized bed 1;

[0032] an air preheater 8 for heating the air fed into the furnace of the fluidized bed 1;

[0033] A primary fan 9 and a secondary fan 10 for supplying air to the air preheater 8;

[0034] A dry desuperheater 2 for collecting and cooling the gas in the fluidized bed 1;

[0035] The cyclone separator 3 is used to separate the gas in the dry desuperheater 2 from the solids. The cyclone separator 3 has a high gas-solid separation effect and can recover more than 99% of the ash particles and return them to the furnace, thereby forming a circulating flue gas.

[0036] A tail flue heat exchanger 7 for exchanging heat between the gas separated by the cyclone separator 3 and the air preheater 8;

[0037] a slag cooler 5 for collecting slag produced in the furnace of the fluidized bed 1;

[0038] The cold slag conveyor 6 is used to convey the slag in the cooler 5 to the dry desuperheater 2; the cold slag conveyor 6 has a particle size sorting function, and the optimal particle size range of the cooled ash fed into the dry desuperheater 2 is between 100-500 microns.

[0039] a return device 4 for collecting the solids separated by the cyclone separator 3 and conveying them to the furnace of the fluidized bed 1;

[0040] A tertiary fan 11 for supplying air to the return device 4;

[0041] The quaternary fan 12 is used to supply air to the dry desuperheater 2. By adjusting the air flow rate, the fluidization velocity in the dry desuperheater 2 can be controlled, thereby achieving the purpose of controlling the material concentration inside the dry desuperheater 2.

[0042] The inner wall of the dry desuperheater 2 is covered with fire-resistant and wear-resistant materials.

[0043] The working process of the above-mentioned circulating fluidized bed boiler system burning high-alkali fuel is as follows:

[0044] The high-alkali fuel enters the furnace of the fluidized bed 1 from the fuel feeder 13 for combustion, and the high-temperature flue gas generated after combustion enters the dry desuperheater 2. The low-temperature ash contained in the dry desuperheater 2 is mixed with the air injected from the quaternary fan 12 to form a fluidized motion state, and mixed with the high-temperature flue gas for heat exchange to reduce the temperature of the high-temperature flue gas. It then enters the cyclone separator 3 for gas-solid separation. During this process, the gaseous alkali metals in the high-temperature flue gas will be captured by the cold ash and separated by the cyclone separator. Most of the ash particles (more than 99%) will return to the furnace through the return device 4 to realize the circulation of the material; the pure flue gas separated from the cyclone separator 3 enters the tail flue heat exchanger 7 and the air preheater 8 for heat exchange and then is discharged from the system. The dry desuperheater 2 is a fluidized bed device, which uses the boiler cold ash added from the cooler conveyor 6 as the fluidized material, and is fluidized by the air blown in from the quaternary fan 12 at the bottom. The fluidization operation state of the cold ash inside it can be adjusted according to different fluidization speeds, that is, a bubbling bed or a fast bed flow state.

[0045] The temperature of the high-temperature flue gas before entering the dry-type desuperheater 2 is 800-950°C, and the temperature of the high-temperature flue gas leaving the dry-type desuperheater 2 is below 700°C.

[0046] In order to achieve the best cooling effect, the fluidization velocity in the dry desuperheater 2 is controlled at 1-6 m / s; the average material concentration in the dry desuperheater 2 is controlled at 50-500 kg / m 3 .

[0047] The pure flue gas separated from the cyclone separator 3 has a temperature lower than the gaseous sublimation temperature of the alkali metal. Therefore, after entering the flue gas tail duct, the problem of condensation of the gaseous alkali metal when it encounters cold is greatly reduced, and the dust accumulation and contamination effect on the heating surface is reduced, so that the boiler system of the present invention can achieve the fundamental purpose of burning high-alkali fuel without causing dust contamination of the heating surface.

Claims

1. A circulating fluidized bed boiler system burning high-alkali fuel, characterized in that: include: A fluidized bed for burning high-alkaline fuels (1); a fuel feeder (13) for supplying a high-alkaline fuel to the fluidized bed (1); an air preheater (8) for heating air fed into the furnace of the fluidized bed (1); A primary fan (9) and a secondary fan (10) for supplying air to the air preheater (8); A dry desuperheater (2) for collecting gas in the fluidized bed (1) and cooling it; A cyclone separator (3) for performing gas-solid separation on the gas in the dry desuperheater (2); A tail flue heat exchanger (7) is used for performing heat exchange between the gas separated by the cyclone separator (3) and the air preheater (8).

2. The circulating fluidized bed boiler system burning high-alkali fuel according to claim 1, characterized in that: It also includes a slag cooler (5) for collecting slag generated in the furnace of the fluidized bed (1).

3. The circulating fluidized bed boiler system burning high-alkali fuel according to claim 1, characterized in that: It also includes a cold slag conveyor (6) for conveying the slag material in the slag cooler (5) to the dry desuperheater (2).

4. The circulating fluidized bed boiler system burning high-alkali fuel according to claim 1, characterized in that: The invention also comprises a return device (4) for collecting the solid separated by the cyclone separator (3) and conveying the solid to the furnace of the fluidized bed (1).

5. The circulating fluidized bed boiler system burning high-alkali fuel according to claim 1, characterized in that: It also includes a tertiary fan (11) for supplying air to the return device (4).

6. The circulating fluidized bed boiler system burning high-alkali fuel according to claim 1, characterized in that: The inner wall of the dry desuperheater (2) is covered with fire-resistant and wear-resistant material.

7. The circulating fluidized bed boiler system burning high-alkali fuel according to claim 1, characterized in that: It also includes a quaternary fan (12) for supplying air to the dry desuperheater (2).

8. The circulating fluidized bed boiler system burning high-alkali fuel according to any one of claims 1 to 7, characterized in that: High-alkali fuel enters the furnace of the fluidized bed (1) from the fuel feeder (13) for combustion, and the high-temperature flue gas generated after combustion enters the dry desuperheater (2). The low-temperature ash contained in the dry desuperheater (2) is mixed with the air injected from the quaternary fan (12) to form a fluidized motion state, and is mixed with the high-temperature flue gas for heat exchange to reduce the temperature of the high-temperature flue gas. The flue gas then enters the cyclone separator (3) for gas-solid separation; the pure flue gas separated from the cyclone separator (3) enters the tail flue heat exchanger (7) and exchanges heat with the air preheater (8) before being discharged from the system.

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