Biomass boiler oxygen-enriched combustion and biomass fly ash potassium extraction method

Abstract

The invention relates to the technical field of environmental protection, and discloses a biomass boiler oxygen-enriched combustion and biomass fly ash potassium extraction method which comprises the following steps: step 1, high-carbon-dioxide-concentration flue gas generated after biomass is subjected to oxygen-enriched combustion in a boiler is cooled, fly ash is separated, the flue gas enters a flue gas heat exchanger, and low-temperature flue gas and hot air are obtained after heat exchange with cold air; 2, fly ash obtained through separation and water are mixed and stirred, a water-ash mixture is obtained, CO2 is introduced into the water-ash mixture, and the ash mixture and low-temperature flue gas are subjected to a contact reaction; step 3, performing solid-liquid separation on the water-ash mixture after the reaction to obtain a potassium-rich solution A and a filter residue A, dividing the solution A into a solution B and a solution C, returning the solution B to the contact reaction tank for circulation, and enabling the solution C to enter a concentration device; 4, heating and concentrating the solution C through hot air to obtain a solution D; and 5, carrying out solid-liquid separation on the solution D to obtain potassium salt and mother liquor F. The method is simple in process, low in extraction cost and high in product purity.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology, specifically to a method for oxygen-enriched combustion in a biomass boiler combined with potassium extraction from biomass fly ash. Background Technology

[0002] Biomass fly ash is a solid waste produced after biomass combustion. Its main components include Si, Al, Ca, and Mg. The average density of biomass incineration fly ash is close to 1 g / cm³. 3 Biomass fly ash is highly absorbent, and its leachate has a pH value as high as 13, exhibiting strong alkalinity. Because biomass fly ash is alkaline, direct use as fertilizer can negatively impact plant growth. Currently, the common practice in China is to solidify and stabilize biomass fly ash before landfilling. This method results in high overall disposal costs, with the construction and operation of secure landfills being prohibitively expensive for both government and businesses. It not only generates new pollution but also occupies large areas of land, failing to achieve the goals of waste reduction and resource recovery. Furthermore, the potential environmental risks are uncontrollable. Therefore, the utilization of biomass fly ash from biomass power plants has become an urgent problem to be solved.

[0003] As a major agricultural country, my country consumes approximately 11 million tons of potash fertilizer annually. However, biomass fly ash also contains valuable nutrients essential for plant growth, such as potassium (K), phosphorus (P), magnesium (Mg), iron (Fe), zinc (Zn), and manganese (Mn). Potassium (K), in particular, is present in biomass fly ash, with a content ranging from 2% to 8%, indicating significant potential for resource utilization. In recent years, many research institutions and enterprises, including Tsinghua University, Xi'an Jiaotong University, and China Southern Power Grid, have been experimenting with potassium extraction from biomass fly ash.

[0004] In addition, under the dual carbon background, CO2 capture, utilization and storage technologies have received increasing attention, but there is still a lack of effective CO2 disposal and utilization measures. Biomass fly ash is strongly alkaline and contains a large amount of metal oxides, which has great potential for carbon sequestration.

[0005] Currently, there are two main technical routes for potassium extraction from biomass fly ash: water leaching and acid leaching. Water leaching involves crushing and screening the fly ash, mixing it with water, and using the water to leach out potassium (K) from the fly ash. The K is then transferred to the water, resulting in a K-containing aqueous solution. Soluble carbonates or sulfates are added to remove impurities such as calcium and magnesium ions from the aqueous solution, and the solution is then evaporated to obtain potassium salts. Acid leaching uses acidic solutions such as hydrochloric acid or sulfuric acid instead of water as the leaching agent. Alkali or carbonates are added to neutralize the solution, obtaining a potassium-containing aqueous solution and removing impurities such as calcium and magnesium. The potassium-containing aqueous solution is then evaporated to crystallize the potassium salts. The main purpose of using an acidic solution as the leaching liquid is to enhance the dissolution of potassium from the fly ash and increase extraction efficiency. For example, Chinese patent CN119929842 A discloses a method for purifying potassium salts from biomass fly ash, comprising: 1) acid leaching, mixing biomass fly ash with an acid solution, stirring, separating solid and liquid to obtain a potassium-containing acid leaching solution and leached ash residue; 2) impurity removal, adding alkali to the potassium-containing acid leaching solution to adjust the pH to 11-13, adding sodium carbonate and stirring, separating solid and liquid to obtain a potassium-containing solution and metal precipitate; 3) concentration, concentrating the potassium-containing solution; 4) evaporation and crystallization, evaporating and crystallizing the concentrated potassium-containing solution to obtain potassium salts and a remaining sodium-containing solution; 5) drying, drying the potassium salts to obtain a potassium salt product. Additionally, bipolar membrane electrodialysis is used to pass the remaining sodium-containing solution into a bipolar membrane electrodialysis device for bipolar membrane electrodialysis treatment, with the obtained acid solution recycled to step 1) and the obtained alkali recycled to step 2). The main drawback of this method is that it uses acid as the leaching agent in the extraction stage, followed by the use of alkali and sodium carbonate as neutralizing and impurity-removing agents, respectively. The large amount of reagents used in the process results in high extraction costs and poses a risk of corrosion to the equipment. Furthermore, the evaporation and drying of the potassium-containing solution requires a large amount of heat, further increasing the extraction cost. Chinese patent CN 116002720 A discloses a method for extracting potassium salts from biomass fly ash. The method includes the following steps: (1) crushing biomass fly ash to obtain raw material A; (2) mixing raw material A with water, stirring, and separating the solid and liquid to obtain a high-concentration potassium salt solution B and filter residue C; (3) heating the high-concentration potassium salt solution B, stirring, and separating the solid and liquid to obtain a high-concentration potassium salt solution and filter residue D; (4) adding calcium chloride or potassium sulfate to the high-concentration potassium salt solution C, stirring, and separating the solid and liquid to obtain a high-concentration potassium salt solution D; (5) stirring the high-concentration potassium salt solution D, cooling, letting it stand, and separating the solid and liquid to obtain a high-concentration potassium salt solution E and a high-purity potassium salt product. The disadvantage of this method is that water is used as the leaching agent, resulting in low leaching efficiency. It also uses reagents such as calcium chloride and potassium sulfate, which increases the complexity and cost of the process. In addition, heating the solution will consume a large amount of heat source, increasing the extraction cost.Chinese Patent CN 111960438 A discloses a potassium extraction system and method based on biomass fly ash. The system includes: a raw material mixing device for introducing mixing water and fly ash, stirring and mixing to obtain a mixed liquid; a stirring device for introducing the mixed liquid output from the raw material mixing device, stirring evenly to obtain a uniformly stirred mixed liquid; a settling tank for introducing the uniformly stirred mixed liquid, allowing it to settle, and obtaining a supernatant and treated fly ash; wherein the settling tank is equipped with a heat exchange buried pipe for heat exchange of the mixed liquid in the settling tank; and an evaporation and crystallization device for introducing the supernatant, achieving supersaturation of the potassium solution through evaporation, and crystallizing to obtain potassium salt. This method directly mixes water and fly ash, uses external steam heating for solid-liquid separation, and then obtains potassium salt through evaporation and crystallization. The disadvantages of this method are that the heating process consumes a large amount of heat, the extraction efficiency using only water is low, and there is no impurity removal measure, resulting in low product purity. Summary of the Invention

[0006] The present invention aims to provide a method for potassium extraction from biomass fly ash in conjunction with oxygen-enriched combustion in a biomass boiler, in order to solve the problems of complex processes, high extraction costs, and low product purity in the existing biomass fly ash potassium extraction technology.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for oxygen-enriched combustion in a biomass boiler combined with potassium extraction from biomass fly ash, comprising the following steps: Step 1: The high carbon dioxide concentration flue gas produced by the oxygen-enriched combustion of biomass is cooled, fly ash is separated, and then heat is exchanged with cold air to obtain low-temperature flue gas and hot air. Step 2: Mix the separated fly ash with water to obtain a water-ash mixture. Introduce CO2 into the water-ash mixture, and the ash mixture reacts with the low-temperature flue gas. Step 3: After the reaction is completed, the water-ash mixture is separated into a potassium-rich solution A and a filter residue A. Solution A is divided into solution B and solution C. Solution B is returned to the contact reaction tank for circulation, and solution C enters the concentration unit. Step 4: Solution C is brought into contact with hot air in a concentration device and concentrated by heating with hot air to obtain solution D; Step 5: Solid-liquid separation of solution D yields potassium salt and mother liquor F. Preferably, as an improvement, in step one, the flue gas with a high carbon dioxide concentration is cooled to 120~140℃.

[0008] Preferably, as an improvement, in step one, the moisture content of the low-temperature flue gas is 30-40%, and the temperature is 80-90℃; the temperature of the hot air is 80-90℃.

[0009] Preferably, as an improvement, in step two, the mass ratio of water to ash is 3~5:1.

[0010] Preferably, as an improvement, in step two, the CO2 injection rate is 15%.

[0011] Preferably, as an improvement, in step three, the mass ratio of solution B to solution C is 3 to 4.

[0012] Preferably, as an improvement, in step four, the concentration device is a spray-type concentration tower, where solution C exchanges heat with hot air in a countercurrent manner.

[0013] Preferably, as an improvement, in step five, solution D is allowed to cool naturally to precipitate potassium salt.

[0014] Preferably, as an improvement, in step five, the solid-liquid separation device is a centrifugal dewatering machine or a plate and frame filter press.

[0015] The principle and advantages of this solution are as follows: In practical application, this technical solution addresses the problems existing in the fly ash potassium extraction process of current technologies by innovatively utilizing the high-concentration CO2 flue gas from oxygen-enriched combustion in biomass boilers to react with a mixture of biomass fly ash and water: the CO2 in the flue gas dissolves in the water and ionizes to produce CO3. 2- and H + H + This causes potassium oxides in fly ash to be converted into soluble metal ions that enter the water, and CO3. 2- Then with the dissolved Ca 2+ Mg 2+ The reaction of metal ions generates CaCO3 and MgCO3 precipitates, thereby removing some impurities. In addition, the low-temperature flue gas heats the water-ash mixture to 40-60℃ during contact, further increasing the dissolution rate of potassium. Furthermore, the water vapor in the low-temperature flue gas is released during the cooling process, which can also play a role in water replenishment, realizing the resource utilization of water in the flue gas and reducing the amount of water consumed during the extraction process. Moreover, the CO2 in the flue gas is absorbed by the water-ash mixture, playing a role in flue gas decarbonization and carbon fixation.

[0016]

[0017] During the technology development phase, the inventors addressed the issues of uniform distribution during the reaction of flue gas and water-ash mixtures, as well as the slow reaction rate of weakly acidic gas (carbon dioxide). They conducted secondary technical optimization of the process for synergistic potassium extraction using high-concentration CO2 flue gas from oxygen-enriched combustion in biomass boilers, along with biomass fly ash and water. Through synergistic optimization of key parameters such as reaction temperature, the amount of carbon dioxide (flue gas) added, and the water-ash ratio, they achieved a quadruple effect: flue gas waste heat heating, carbon dioxide dissolution and acid production, carbon dioxide reaction with calcium and magnesium for impurity removal, and carbon fixation. Furthermore, compared to the traditional method using dilute hydrochloric acid as an extractant, this technology eliminates the need for additional alkali to adjust the pH after extraction. The inventors had previously attempted to introduce carbon dioxide gas at room temperature, but the extraction effect was poor due to the low temperature.

[0018] In summary, the beneficial effects of this technical solution are as follows: 1. In this technical solution, low-cost heating and impurity removal are achieved in the potassium extraction process from fly ash through the above methods, while improving potassium extraction efficiency. Compared with the traditional acid leaching method for potassium extraction, this method can significantly save on heat energy consumption, water consumption, and reagent consumption, with heat consumption savings exceeding 90%, water consumption savings exceeding 20%, and reagent savings exceeding 50%.

[0019] 2. In this technical solution, the waste heat of boiler flue gas is used to enhance potassium leaching, concentrate the leaching solution and evaporate and crystallize it, avoiding the use of additional heat sources, thereby reducing the energy consumption of potassium extraction from fly ash and realizing the cascade utilization and resource utilization of thermal energy.

[0020] 3. In this technical solution, the high-concentration CO2 flue gas from the oxygen-enriched combustion of the material boiler is reacted with a mixture of biomass fly ash and water. The CO2 in the flue gas is absorbed by the mixture and fixed in the form of carbonate ions, thereby achieving the effects of flue gas decarbonization and carbon dioxide fixation.

[0021] 4. In this technical solution, the inventors found that heating is beneficial to improving the extraction efficiency of potassium; introducing carbon dioxide into the water-ash mixture can also effectively remove the concentration of calcium and magnesium ions in the solution, thereby playing a role in impurity removal; adding dilute hydrochloric acid to the water-ash mixture to adjust the pH value significantly increases the dissolution rate, indicating that acidity can promote potassium extraction. Attached Figure Description

[0022] Figure 1 This is a process flow diagram of oxygen-enriched combustion in a biomass boiler combined with potassium extraction from biomass fly ash in an embodiment of the present invention.

[0023] Figure 2 This is a graph showing the trend of calcium and magnesium ion changes in the solution at different temperatures in an embodiment of the present invention. Detailed Implementation

[0024] The following detailed description provides further details on specific embodiments, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art; the experimental methods used are all conventional methods; and the materials and reagents used are all commercially available.

[0025] Overview of the plan: The basic implementation examples are as follows: Figure 1 The method for potassium extraction from biomass fly ash via oxygen-enriched combustion in a biomass boiler includes the following steps: Step 1: The high-carbon dioxide-concentration flue gas produced by the oxygen-enriched combustion of biomass in the boiler passes sequentially through an economizer and an air preheater for heat recovery, reducing the temperature to 120-140℃. It then enters a dust collector to separate fly ash before entering a flue gas heat exchanger. In the heat exchanger, a fan introduces cold air to cool the flue gas, resulting in low-temperature flue gas at 80-90℃ and a moisture content of 30-40%, and hot air at 80-90℃.

[0026] Step 2: The biomass fly ash separated from the dust collector is mixed with water in a mixing tank to obtain a water-ash mixture, which is then transferred to a contact reaction tank. The mass ratio of water to fly ash in the mixing tank is 3-5:1. In the contact reaction tank, CO2 is introduced into the water-ash mixture, and dilute hydrochloric acid is added to adjust the pH. The CO2 introduction rate is 15%, and the dilute hydrochloric acid addition rate is 0.1-0.6%. Low-temperature flue gas from the flue gas heat exchanger reacts with the water-ash mixture, simultaneously heating the mixture.

[0027] Step 3: When the pH value in the contact reaction tank reaches 7-8, the reaction is complete. The water-ash mixture after the reaction enters the solid-liquid separation device, which separates the water and ash to obtain potassium-rich solution A and filter residue A. Solution A is divided into two parts, solution B and solution C. Solution B is returned to the contact reaction tank for circulation to increase the potassium concentration in the solution, while solution C enters the concentration device. The mass ratio of solution B to solution C is 3-4.

[0028] Step 4: Solution C from the solid-liquid separator enters the concentration unit, which is a spray-type concentration tower. In the concentration unit, solution C is pressurized by a circulating pump and sprayed down from the top of the concentration unit. Hot air from the flue gas heat exchanger enters from the bottom of the concentration unit and comes into countercurrent contact with solution C for heat exchange. After absorbing the heat from the hot air, the water in solution C continuously evaporates into water vapor, which is carried out of the tower by the air, thereby achieving the concentration and reduction of the solution to obtain concentrated solution D.

[0029] Step 5: When the density of solution D reaches the set value, solution D is transferred to a solid-liquid separator by a pump. Inside the separator, solution D cools naturally and potassium salt precipitates. The separator separates solution D into potassium salt and mother liquor F. The potassium salt is collected and stored as the product, while the mother liquor F is returned to the concentration unit. The solid-liquid separator in this step can be a centrifugal dewatering machine or a plate and frame filter press.

[0030] Example 1 A method for potassium extraction from biomass fly ash via oxygen-enriched combustion in a biomass boiler includes the following steps: Step 1: After a biomass boiler is modified for oxygen-enriched combustion, the flue gas temperature at the dust collector outlet is 140 degrees Celsius, the CO2 volume concentration is 57.5%, and the H2O volume concentration is 25.5%. After heat exchange, the flue gas on the flue gas side is cooled to 85 degrees Celsius, and the cold air on the air side is heated to 80 degrees Celsius.

[0031] Step 2: The biomass fly ash from the dust collector has a K2O content of 7.7%. The fly ash is mixed with water at a mass ratio of 1:5. The resulting mixture enters the reaction tank and undergoes a bubbling contact reaction with the flue gas from the flue gas cooler. The reaction lasts for 1 hour, during which the pH value of the mixture decreases from 9.5 to 7.1, at which point the reaction is terminated. During the reaction, some CO2 in the flue gas is absorbed, and the mixture is heated to 60°C. The remaining flue gas is discharged from the top of the reaction tank.

[0032] Step 3: After the reaction is completed, the water-ash mixture is subjected to solid-liquid separation. The separated solution and filter residue have a K ion concentration of 15000~25000 mg / L. 80% of the obtained solution is sent back to the reaction tank to continue dissolving potassium salts and circulating, while the remaining 20% ​​is sent to the concentration device (concentration tower).

[0033] Step 4: In the concentration unit, the solution is pressurized by the circulating pump and sprayed downwards through the spray layer set at the top of the concentration tower. Hot air from the flue gas heat exchanger enters from the bottom of the concentration tower and undergoes countercurrent heat exchange with the solution. The water in the solution is heated and continuously carried away by the hot air, eventually concentrating the solution.

[0034] Step 5: When the solution density in the concentration tower reaches 1.8~2.0 g / mL, the concentrate is transferred to a thickener for cooling and crystallization using a slurry pump. Then, it is transferred to a centrifugal dehydrator to separate the solid potassium salt. The remaining mother liquor is returned to the concentration unit. Testing revealed that the separated potassium salt is mainly composed of potassium carbonate, with a purity exceeding 50%, making it a high-quality potassium resource that can be used as a raw material for potash fertilizer production.

[0035] Example 2 The difference between this embodiment and Embodiment 1 is that: in this embodiment, a method for potassium extraction from biomass fly ash through oxygen-enriched combustion in a biomass boiler includes the following steps: Step 1: After a biomass boiler is modified for oxygen-enriched combustion, the flue gas temperature at the dust collector outlet is 140 degrees Celsius, the CO2 volume concentration is 57.5%, and the H2O volume concentration is 25.5%. After heat exchange, the flue gas on the flue gas side is cooled to 95 degrees Celsius, and the cold air on the air side is heated to 90 degrees Celsius.

[0036] Step 2: The biomass fly ash from the dust collector has a K2O content of 7.7%. The fly ash and water are mixed at a mass ratio of 1:3. CO2 and dilute hydrochloric acid are then introduced into the water-ash mixture at a rate of 15% and 0.5% respectively. The resulting water-ash mixture enters a reaction tank and undergoes a bubbling contact reaction with the flue gas from the flue gas cooler. The reaction lasts for 1 hour, during which the pH of the mixture decreases from 9.5 to 7.1, at which point the reaction is terminated. During the reaction, some of the CO2 in the flue gas is absorbed, and the mixture is heated to 60°C. The remaining flue gas is discharged from the top of the reaction tank.

[0037] Step 3: After the reaction is completed, the water-ash mixture is subjected to solid-liquid separation. The separated solution and filter residue have a K ion concentration of 15000~25000 mg / L. 60% of the obtained solution is sent back to the reaction tank to continue dissolving potassium salts and circulating, while the remaining 40% enters the concentration device (concentration tower).

[0038] Step 4: In the concentration unit, the solution is pressurized by the circulating pump and sprayed downwards through the spray layer set at the top of the concentration tower. Hot air from the flue gas heat exchanger enters from the bottom of the concentration tower and undergoes countercurrent heat exchange with the solution. The water in the solution is heated and continuously carried away by the hot air, eventually concentrating the solution.

[0039] Step 5: When the solution density in the concentration tower reaches 1.8~2.0 g / mL, the concentrate is transferred to a thickener for cooling and crystallization using a slurry pump. Then, it is transferred to a centrifugal dehydrator to separate the solid potassium salt. The remaining mother liquor is returned to the concentration unit. Testing revealed that the separated potassium salt is mainly composed of potassium carbonate, with a purity exceeding 50%, making it a high-quality potassium resource that can be used as a raw material for potash fertilizer production.

[0040] Experiment Example 1: Effect of Temperature on Potassium Salt Extraction Efficiency Experimental method: 100g of fly ash was placed in a beaker and 500g of distilled water was added. The mixture was stirred for 1 hour at 20℃, 40℃, 60℃ and 80℃ respectively. The ion concentration and pH value in the solution were measured. The results are shown in Table 1 below.

[0041] Table 1

[0042] As shown in Table 1, the potassium ion extraction rate gradually increased with increasing temperature, and the solution pH value gradually increased as well. The peak value was reached at 60℃. Further increasing the temperature did not significantly improve the potassium salt extraction efficiency, indicating that high temperature is beneficial for improving the potassium salt extraction rate.

[0043] Experiment Example 2: Effect of CO2 on the Removal of Calcium and Magnesium Experimental method: 100g of fly ash was placed in a beaker, and 500g of distilled water was added. The mixture was heated and stirred at 60℃, and filtered while hot to obtain a solution. 15% CO2 gas was passed into the solution (the solution in Experiment Example 1). The mixture was stirred for 1 hour at 20℃, 40℃, and 60℃ respectively. The concentrations of calcium and magnesium ions in the solution were measured. The results are as follows: Figure 2 As shown.

[0044] Depend on Figure 2 It can be seen that as the reaction temperature increases, the calcium and magnesium ion content in the solution decreases significantly after carbon dioxide is introduced. The original calcium and magnesium ion concentrations were 723.1 mg / L and 53.93 mg / L, respectively. After introducing CO2 at 20℃ for 1 h, the calcium and magnesium ion concentrations decreased to 527.7 mg / L and 32.24 mg / L, respectively. Furthermore, the calcium and magnesium ion concentrations further decreased with increasing reaction temperature, indicating that carbon dioxide can effectively remove calcium and magnesium ions from the solution, and the higher the temperature, the better the removal effect.

[0045] Experiment Example 3: Effect of pH on Potassium Extraction Experimental method: 100g of ash residue was placed in a beaker, 500g of distilled water was added, and 2g, 4g, 6g, 10g, 15g and 20g of dilute hydrochloric acid were added respectively. The mixture was stirred at 20℃ for 1h, and the changes in ion content in the solution were detected. The results are shown in Table 2.

[0046] The test results showed that the content of K, Ca, and Mg ions in the solution increased with the increase of hydrochloric acid. Calculations showed that after adding 2g, 4g, 6g, 10g, 15g, and 20g of HCl, the potassium extraction rates from the ash residue were 20.28%, 22.22%, 24.89%, 25.25%, 31.02%, and 37.05%, respectively. Under the same temperature conditions, adding water resulted in a potassium extraction rate of 14.99%. Increasing acidity helps improve potassium salt extraction, but it also increases the calcium and magnesium ion content, leading to higher subsequent purification costs.

[0047] Table 2

[0048] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for oxygen-enriched combustion in a biomass boiler combined with potassium extraction from biomass fly ash, characterized in that, Includes the following steps: Step 1: The high carbon dioxide concentration flue gas produced by the oxygen-enriched combustion of biomass is cooled, fly ash is separated, and then heat is exchanged with cold air to obtain low-temperature flue gas and hot air. Step 2: Mix the separated fly ash with water to obtain a water-ash mixture. Introduce CO2 into the water-ash mixture, and the ash mixture reacts with the low-temperature flue gas. Step 3: After the reaction is completed, the water-ash mixture is separated into a potassium-rich solution A and a filter residue A. Solution A is divided into solution B and solution C. Solution B is returned to the contact reaction tank for circulation, and solution C enters the concentration unit. Step 4: Solution C is brought into contact with hot air in a concentration device and concentrated by heating with hot air to obtain solution D; Step 5: Solid-liquid separation of solution D yields potassium salt and mother liquor F.

2. The method for potassium extraction from biomass fly ash in conjunction with oxygen-enriched combustion in a biomass boiler according to claim 1, characterized in that: In step one, the flue gas with a high carbon dioxide concentration is cooled to 120~140℃.

3. The method for potassium extraction from biomass fly ash in conjunction with oxygen-enriched combustion in a biomass boiler according to claim 2, characterized in that: In step one, the moisture content of the low-temperature flue gas is 30-40%, and the temperature is 80-90℃; the temperature of the hot air is 80-90℃.

4. The method for potassium extraction from biomass fly ash in conjunction with oxygen-enriched combustion in a biomass boiler according to claim 3, characterized in that: In step two, the mass ratio of water to ash is 3~5:

1.

5. The method for potassium extraction from biomass fly ash in conjunction with oxygen-enriched combustion in a biomass boiler according to claim 4, characterized in that: In step two, the CO2 injection rate is 15%.

6. The method for potassium extraction from biomass fly ash in conjunction with oxygen-enriched combustion in a biomass boiler according to claim 5, characterized in that: In step three, the mass ratio of solution B to solution C is 3 to 4.

7. The method for potassium extraction from biomass fly ash in conjunction with oxygen-enriched combustion in a biomass boiler according to claim 6, characterized in that: In step four, the concentration device is a spray-type concentration tower, where solution C exchanges heat with hot air in a countercurrent flow.

8. The method for potassium extraction from biomass fly ash in conjunction with oxygen-enriched combustion in a biomass boiler according to claim 7, characterized in that: In step five, solution D cools down naturally and potassium salts precipitate out.

9. The method for potassium extraction from biomass fly ash in conjunction with oxygen-enriched combustion in a biomass boiler according to claim 8, characterized in that: In step five, the solid-liquid separation device is a centrifugal dewatering machine or a plate and frame filter press.

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