Circulating fluidized bed boiler system burning high-alkali fuel
By installing a fluidized bed desuperheating device and a cyclone separator in the circulating fluidized bed boiler system, the problem of ash accumulation and fouling during the combustion of high-alkali fuels has been solved, achieving efficient flue gas purification and stable combustion.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-08
- Publication Date
- 2026-04-10
AI Technical Summary
When high-alkali fuels are burned in circulating fluidized bed boilers, alkali metals are easily volatilized and condense on low-temperature heating surfaces, leading to serious ash accumulation and fouling problems.
A fluidized bed desuperheating device is installed in the circulating fluidized bed boiler system to reduce the temperature of high-temperature flue gas by using fluidized cold ash and cold air, and to perform gas-solid separation through a cyclone separator to capture gaseous alkali metals and condense them on low-temperature ash particles, thereby achieving flue gas purification.
It effectively reduces flue gas temperature to below 700℃, avoids condensation of gaseous alkali metals, reduces ash accumulation on low-temperature heated surfaces, and achieves stable combustion of high-alkali fuels.
Smart Images
Figure CN121828696A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a combustion technology for high-alkali fuels using a circulating fluidized bed boiler, specifically a circulating fluidized bed boiler system for burning high-alkali fuels, belonging to the field of high-alkali fuel combustion technology. Background Technology
[0002] High-alkali fuels (such as high-alkali coal from Zhundong, Xinjiang, and high-alkali biomass) have high volatility, high calorific value, good combustion characteristics, and huge reserves, showing great application potential. However, during the combustion process in boilers, the alkali metals contained in high-alkali fuels readily volatilize into gaseous substances. These gaseous alkali metals condense upon contact with the low-temperature heating surfaces of the boiler, and also trap tiny particles that fall onto them, forming a fouling layer that typically accumulates and thickens, affecting the normal operation of the boiler. Previous research and engineering practices on high-alkali fuels have focused primarily on pulverized coal boilers with higher combustion temperatures (>1100℃), while less attention has been paid to circulating fluidized bed boilers with relatively lower combustion temperatures (850-900℃). Although the temperature inside the furnace of a circulating fluidized bed boiler does not reach the ash melting temperature of the fuel, the high temperature of the flue gas still causes the alkali metals to volatilize into a gaseous state. This gas then enters the low-temperature heating surfaces of the tail flue, where it condenses, causing severe fouling problems and affecting unit operation. Summary of the Invention
[0003] The technical problem to be solved by this invention is: how to reduce the temperature of the flue gas before it enters the low-temperature heating surface of the tail flue to a reasonable temperature.
[0004] To address the above problems, the present invention provides a circulating fluidized bed boiler system that burns high-alkali fuel, comprising:
[0005] Fluidized beds are used to burn high-alkali fuels; high-alkali fuels include coal or biomass with high alkali metal content.
[0006] A fuel feeder used to supply high-alkali fuel to a fluidized bed;
[0007] An air preheater used to heat the air fed into the furnace of a fluidized bed;
[0008] Primary and secondary air fans used to supply air to the air preheater;
[0009] Dry desuperheater used to collect and cool the gas in a fluidized bed;
[0010] Cyclone separators are used for gas-solid separation in dry desuperheaters; cyclone separators have a high gas-solid separation effect and can recover more than 99% of ash particles to return to the furnace, thereby forming a circulating flue gas.
[0011] A tail flue heat exchanger used to exchange heat between the gas separated by the cyclone separator and the air preheater.
[0012] Preferably, the circulating fluidized bed boiler system that burns 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 using high-alkali fuel further includes a cold slag conveyor for transporting slag from the cold slag cooler to the dry desuperheater. The cold slag conveyor has a particle size sorting function, and the optimal particle size range of the cooled ash fed into the dry desuperheater is between 100 and 500 micrometers.
[0014] Preferably, the circulating fluidized bed boiler system that burns high-alkali fuel further includes a return feeder for collecting the solids separated by the cyclone separator and conveying them to the furnace of the fluidized bed.
[0015] Preferably, the circulating fluidized bed boiler system that burns high-alkali fuel further includes a tertiary air fan for supplying air to the return feeder.
[0016] Preferably, the inner wall of the dry desuperheater is lined with a fire-resistant and wear-resistant material.
[0017] Preferably, the circulating fluidized bed boiler system using high-alkaline fuel further includes a fourth air fan for supplying air to the dry desuperheater. By adjusting the airflow, the fluidization rate within the dry desuperheater can be controlled, thereby achieving the purpose of controlling the material concentration inside the dry desuperheater.
[0018] Preferably, high-alkali fuel enters the fluidized bed furnace from the fuel feeder for combustion. The high-temperature flue gas generated after combustion enters the dry desuperheater. The low-temperature ash contained in the dry desuperheater mixes with the air injected from the fourth blower to form a fluidized state and mixes and exchanges heat with the high-temperature flue gas to reduce the temperature of the high-temperature flue gas. Then, it enters the cyclone separator for gas-solid separation. The pure flue gas separated from the cyclone separator enters the tail flue heat exchanger and air preheater for heat exchange before being 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 flue gas leaving the dry desuperheater is no more than 700°C.
[0020] More preferably, in order to achieve the optimal 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 / m³. 3 .
[0021] This invention involves installing a fluidized bed desuperheating device between a fluidized bed and a cyclone separator. This device uses fluidized cold ash and cold air within the fluidized bed to reduce the high-temperature flue gas at the furnace outlet. Due to the temperature reduction, alkali metal gaseous substances in the high-temperature flue gas condense on the surface of the cold ash particles. Simultaneously, by adjusting the fluidization rate of the fluidized bed desuperheating device, the material concentration within the bed is controlled, thereby altering the mixing degree between the flue gas and the cold ash, achieving the goal of controlling the flue gas temperature. Subsequently, the cooled, ash-containing flue gas enters the cyclone separator for gas-solid separation. Because the cyclone separator has high separation efficiency, most of the material is separated, and the purified flue gas enters the tail flue.
[0022] The fluidized bed desuperheating device arranged at the furnace outlet uses fluidized material medium derived from cooled boiler bottom ash or other waste ash, which is a waste recycling process and therefore has high economic efficiency.
[0023] The invention proposes a solution for circulating fluidized bed boiler systems using high-alkali fuels, which can address the problem of severe ash fouling on the low-temperature heating surface at the tail end. The solution and expected operational results are as follows:
[0024] By installing a desuperheater at the furnace outlet, the temperature of the high-temperature flue gas rich in alkali metals at the furnace outlet is reduced, so that the temperature of the flue gas entering the tail flue is lower than 700°C. At this time, the gas phase no longer contains alkali metals, thus avoiding the phenomenon of condensation of gas phase alkali metals on the low-temperature heating surface.
[0025] The dry desuperheater contains a high concentration of low-temperature ash particles. These ash particles mix with the high-temperature flue gas to cool it down, while also capturing gaseous alkali metals, causing the alkali metals to condense on the low-temperature ash particles. Subsequently, through the gas-solid separation action of the cyclone separator, the pure flue gas enters the tail flue, while most of the ash particles are recycled back to the furnace, thus achieving the purpose of circulating and purifying the flue gas. Attached Figure Description
[0026] Figure 1 This is a schematic diagram of a circulating fluidized bed boiler system that burns high-alkali fuel, as provided by the present invention. Detailed Implementation
[0027] To make the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings.
[0028] Example
[0029] A circulating fluidized bed boiler system that burns high-alkali fuel is characterized by comprising:
[0030] Fluidized bed 1 for burning high-alkali fuels; high-alkali fuels include coal or biomass with high alkali metal content.
[0031] Fuel feeder 13 for supplying high-alkali fuel to fluidized bed 1;
[0032] An air preheater 8 is used to heat the air fed into the furnace of the fluidized bed 1.
[0033] Primary air fan 9 and secondary air fan 10 are used to supply air to the air preheater 8.
[0034] Dry desuperheater 2 is used to collect and cool the gas in fluidized bed 1;
[0035] Cyclone separator 3 is used for gas-solid separation of gas inside dry desuperheater 2; cyclone separator 3 has a high gas-solid separation effect and can recover more than 99% of ash particles to return to the furnace, thereby forming the purpose of circulating flue gas.
[0036] Tail flue heat exchanger 7 is used to exchange heat between the gas separated by cyclone separator 3 and air preheater 8.
[0037] A slag cooler 5 is used to collect slag generated inside the furnace of fluidized bed 1;
[0038] The slag conveyor 6 is used to transport the slag material in the slag cooler 5 to the dry desuperheater 2; the slag conveyor 6 has a particle size sorting function, and the optimal particle size range of the cooled ash slag fed into the dry desuperheater 2 is between 100-500 micrometers.
[0039] The return feeder 4 is used to collect the solids separated by the cyclone separator 3 and transport them to the furnace of the fluidized bed 1.
[0040] A tertiary air blower 11 is used to supply air to the return feeder 4;
[0041] The quaternary air blower 12 is used to supply air to the dry desuperheater 2. By adjusting the air flow rate, the fluidization rate inside 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 lined with fire-resistant and wear-resistant material.
[0043] The working process of the above-mentioned circulating fluidized bed boiler system using high-alkali fuel is as follows:
[0044] High-alkali fuel enters the furnace of fluidized bed 1 from fuel feeder 13 for combustion. The high-temperature flue gas generated after combustion enters dry desuperheater 2. The low-temperature ash slag contained in dry desuperheater 2 mixes with air injected from the fourth blower 12 to form a fluidized state and mixes and exchanges heat with the high-temperature flue gas to reduce the temperature of the high-temperature flue gas. Then it enters cyclone separator 3 for gas-solid separation. During this process, the gaseous alkali metal in the high-temperature flue gas is captured by cold ash slag and separated by the cyclone separator. Most of the ash particles (more than 99%) will be returned to the furnace through return feeder 4 to realize material circulation. The pure flue gas separated from cyclone separator 3 enters the tail flue heat exchanger 7 and exchanges heat with air preheater 8 before being discharged from the system. The dry desuperheater 2 is a fluidized bed device. It uses boiler cold ash slag added from the cold ash conveyor 6 as fluidized material and is fluidized by air blown in from the bottom by the fourth blower 12. The fluidization operation state of the cold ash inside can be adjusted according to different fluidization speeds, i.e., bubbling bed or fast bed fluidization.
[0045] The temperature of the high-temperature flue gas before entering the dry desuperheater 2 is 800-950℃, and the temperature of the flue gas leaving the dry desuperheater 2 is below 700℃.
[0046] To achieve optimal cooling, the fluidization velocity within the dry desuperheater 2 is controlled at 1-6 m / s; the average material concentration within the dry desuperheater 2 is controlled at 50-500 kg / m³. 3 .
[0047] The pure flue gas separated from the cyclone separator 3 has a temperature lower than the gaseous sublimation temperature of alkali metals. Therefore, when it enters the flue gas tail duct, the problem of condensation of gaseous alkali metals upon cooling is greatly reduced, and the ash accumulation and fouling effect on the heating surface is reduced. Thus, the boiler system of the present invention can achieve the fundamental purpose of burning high-alkali fuels without ash fouling on the heating surface.
Claims
1. A circulating fluidized bed boiler system that burns high-alkali fuel, characterized in that, include: Fluidized bed for burning high-alkali fuels (1); A fuel feeder (13) for supplying high-alkali fuel to a fluidized bed (1); An air preheater (8) is used to heat the air fed into the furnace of the fluidized bed (1); Primary air fan (9) and secondary air fan (10) used to supply air to the air preheater (8); A dry desuperheater (2) for collecting and cooling the gas in the fluidized bed (1); Cyclone separator (3) used for gas-solid separation of gas in dry desuperheater (2); Tail flue heat exchanger (7) is used to exchange heat between the gas separated by the cyclone separator (3) and the air preheater (8).
2. The circulating fluidized bed boiler system using high-alkali fuel as described in claim 1, characterized in that, It also includes a slag cooler (5) for collecting slag generated inside the furnace of the fluidized bed (1).
3. The circulating fluidized bed boiler system using high-alkali fuel as described in claim 1, characterized in that, It also includes a slag conveyor (6) for conveying slag material in the slag cooler (5) to the dry desuperheater (2).
4. The circulating fluidized bed boiler system using high-alkali fuel as described in claim 1, characterized in that, It also includes a return feeder (4) inside the furnace for collecting the solids separated by the cyclone separator (3) and conveying them to the fluidized bed (1).
5. The circulating fluidized bed boiler system using high-alkali fuel as described in claim 1, characterized in that, It also includes a tertiary blower (11) for supplying air to the return feeder (4).
6. The circulating fluidized bed boiler system using high-alkali fuel as described in claim 1, characterized in that, The inner wall of the dry desuperheater (2) is lined with fire-resistant and wear-resistant material.
7. The circulating fluidized bed boiler system using high-alkali fuel as described in 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 for burning high-alkali fuel as described in any one of claims 1-7, characterized in that, High-alkali fuel enters the furnace of fluidized bed (1) from the fuel feeder (13) for combustion. The high-temperature flue gas generated after combustion enters the dry desuperheater (2). The low-temperature ash contained in the dry desuperheater (2) mixes with the air injected from the fourth blower (12) to form a fluidized state and mixes and exchanges heat with the high-temperature flue gas to reduce the temperature of the high-temperature flue gas. Then it 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.
9. The circulating fluidized bed boiler system for burning high-alkali fuel as described in claim 8, characterized in that, The temperature of the high-temperature flue gas before entering the dry desuperheater (2) is 800-950℃, and the temperature of the flue gas leaving the dry desuperheater (2) is no more than 700℃.
10. The circulating fluidized bed boiler system for burning high-alkali fuel as described in claim 8, characterized in that, 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 / m³. 3 .