Method for co-processing waste cathode carbon blocks in a power plant

Abstract

This invention discloses a method for co-processing waste cathode carbon blocks in power plants, belonging to the field of solid waste resource utilization technology. The method includes the following steps: crushing and coarsely grinding the waste cathode carbon blocks to obtain coarse powder; mixing the coarse powder with coal to obtain mixed fuel; and feeding the mixed fuel into the boiler furnace of a power plant for high-temperature combustion. During the high-temperature combustion process, the high-temperature flue gas generated by boiler combustion and the alkaline components in the coal ash cause in-situ mineralization of the fluorides in the waste cathode carbon blocks, generating stable fluoride mineral phases and fixing them in the coal ash. Specifically, the crushing and coarsely grinding step involves feeding the waste cathode carbon blocks into a ball mill for grinding. Through specific pre-crushing and coarse grinding processes combined with high-temperature mineralization, the method overcomes the processing obstacles of high-hardness materials while achieving efficient resource utilization of waste cathode carbon blocks and fixing fluorides in situ during combustion.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization technology, specifically relating to a method for co-processing waste cathode carbon blocks in power plants. Background Technology

[0002] During the electrolytic aluminum production process, a large amount of waste cathode carbon blocks are generated due to major overhauls of electrolytic cells. These blocks mainly consist of graphitized carbon and fluorides, have a high calorific value, and possess excellent potential as a fuel substitute.

[0003] However, existing technologies for the resource utilization of waste cathode carbon blocks still have some shortcomings: First, there is the challenge of hazardous waste environmental treatment. The fluorides in waste cathode carbon blocks are chemically active and are easily volatilized with flue gas or leached by leachate during conventional heat treatment or landfilling, causing serious secondary environmental pollution and making it difficult to meet the increasingly stringent requirements for the harmless disposal of hazardous waste. Second, there is the challenge of physical processing and utilization. Waste cathode carbon blocks have high Mohs hardness and high density. This high hardness characteristic makes it difficult to be directly and efficiently crushed and uniformly blended with coal when entering the traditional pulverizing system of power plants, which limits its large-scale industrial co-firing application as fuel in power plants.

[0004] Therefore, how to utilize the high calorific value of waste cathode carbon blocks while overcoming the material processing obstacles caused by their high hardness, and how to achieve high-temperature in-situ solidification of fluorides, are technical problems that urgently need to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a method for co-processing waste cathode carbon blocks in power plants. Through pre-crushing and coarse grinding and high-temperature mineralization reaction of a specific process, the method overcomes the obstacles of processing high-hardness materials, realizes the efficient resource utilization of waste cathode carbon blocks, and fixes fluorides in situ during combustion.

[0006] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution: A method for co-processing waste cathode carbon blocks in a power plant includes the following steps: The waste cathode carbon blocks are crushed and coarsely ground to obtain coarse powder; The coarse powder is mixed with coal to obtain a mixed fuel; The mixed fuel is fed into the boiler furnace of the power plant for high-temperature combustion; During the high-temperature combustion process, the high-temperature flue gas generated by the boiler combustion and the alkaline components in the coal ash are used to cause the fluorides in the waste cathode carbon blocks to undergo an in-situ mineralization reaction, generating stable fluoride mineral phases and fixing them in the coal ash residue.

[0007] In one or more embodiments of the present invention, the step of crushing and coarsely grinding the waste cathode carbon block specifically includes: Waste cathode carbon blocks are fed into a ball mill for grinding. The ground powder is then screened through a drum screen. The qualified fine powder that passes through the screen is used as the coarse powder and enters the next process. The large particles on the screen are returned to the ball mill for further grinding.

[0008] In one or more embodiments of the present invention, the particle size of the qualified fine powder is controlled to be from 0.074 mm to 0.6 mm.

[0009] In one or more embodiments of the present invention, the amount of coarse powder mixed with coal is not greater than 30% of the total processing capacity of the corresponding single medium-speed coal mill.

[0010] In one or more embodiments of the present invention, the mixed fuel is fed into the lower coal mill of the power plant boiler and then enters the furnace for combustion by the lower burner.

[0011] In one or more embodiments of the present invention, the ball mill is of type MQY1870, with a designed output of 6-16 tons / hour, a rated motor power of 210kW, and an operating voltage of 380V.

[0012] In one or more embodiments of the present invention, the method adopts an intermittent operation system, with a continuous daily operation time of 8 hours and an annual processing capacity of 17,000 tons of waste cathode carbon blocks.

[0013] In one or more embodiments of the present invention, the specific process of the in-situ mineralization reaction is as follows: Cryolite (Na3AlF6) and sodium fluoride (NaF) in waste cathode carbon blocks react with calcium oxide (CaO) and silicon dioxide (SiO2) in coal ash under the high temperature environment of 1200℃~1500℃ in power plant boilers to generate chemically stable calcium fluoride (CaF2), which then melts and solidifies in the bottom slag and fly ash.

[0014] A system for co-processing waste cathode carbon blocks in power plants, comprising, in sequence: Raw material storage silos, belt feeders, ball mills, drum screens, finished product storage tanks, pneumatic ash conveying devices, coal bunkers, and medium-speed coal mills; The discharge port of the raw material storage silo is connected in sequence to the feed port of the ball mill via a belt feeder. The discharge port of the ball mill is connected to the inlet of the drum screen. The fine powder outlet of the drum screen is connected in sequence to the finished product storage tank and the pneumatic ash conveying device. The output end of the pneumatic ash conveying device is connected to the coal bunker. The discharge port of the coal bunker is connected to the medium-speed coal mill.

[0015] In one or more embodiments of the present invention, the ball mill is an MQY1870 type, with a motor rated power of 210kW and an operating voltage of 380V; the power input of the ball mill in the system does not depend on the modification of the 6kV high-voltage switchgear.

[0016] Compared with existing technologies, the method for co-processing waste cathode carbon blocks in power plants of this invention effectively overcomes the physical processing barriers caused by the high hardness and high density of waste cathode carbon blocks through pre-processing crushing and coarse grinding. This allows the blocks to be easily pulverized and uniformly blended with coal, overcoming the obstacle of directly pulverizing high-hardness materials in traditional processes. More importantly, during the high-temperature combustion of the mixed fuel in the boiler, the high-temperature environment of the boiler and the alkaline oxides rich in the coal ash promote the in-situ mineralization reaction of volatile and easily leached fluorides in the waste cathode carbon blocks, generating a chemically stable calcium fluoride mineral phase, which is firmly fixed in the coal ash. This not only eliminates secondary environmental pollution caused by fluorides in conventional hazardous waste disposal but also fully releases the high calorific value of approximately 5000 kcal in the waste cathode carbon blocks, effectively converting them into fuel to replace coal. Thus, under the premise of meeting stringent environmental protection requirements, it achieves the deep harmless and resource-based co-processing of hazardous waste. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of the material pretreatment and coarse grinding process for the co-processing of waste cathode carbon blocks in power plants according to the present invention. Figure 2 This is a flowchart of the fine powder co-firing and high-temperature mineralization process for the co-processing of waste cathode carbon blocks in power plants according to the present invention. Figure 3 This is a logical layout diagram of the coal mill workshop according to the present invention; Figure 4 This is a logic diagram of the factory area location for this invention; Figure 5 This is a schematic diagram of the structure of the present invention for the co-processing of waste cathode carbon blocks in power plants. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0020] Example 1: This example provides a method for co-processing waste cathode carbon blocks in power plants. This method addresses the processing obstacles of high-hardness materials from two dimensions: pretreatment and combustion, and achieves in-situ solidification of fluorides.

[0021] First, the waste cathode carbon blocks produced by the electrolytic aluminum plant are unloaded into a discharge hopper by transport vehicles and then conveyed to a raw material storage silo via an NE100 bucket elevator. Next, a belt feeder at the bottom of the raw material storage silo quantitatively feeds the material into an MQY1870 ball mill for coarse grinding. This step is specifically designed to address the high hardness of the waste cathode carbon blocks, utilizing the impact grinding principle of the ball mill to initially crush them, thus solving the problem of large amounts of coke and gravel being discharged if the material were directly fed into a medium-speed mill.

[0022] The ground mixed powder enters a drum screen for sieving. This step sieves out qualified fine powder with a particle size controlled between 0.074 mm and 0.6 mm, while the larger particles on the screen are returned to the ball mill for further grinding via a reflux device to ensure that the output particle size meets the combustion requirements.

[0023] The qualified fine powder is screened and fed into the NE30 bucket elevator, which lifts it to a height of 30 meters and has an output of 30T / H. The powder is then sent to the finished product storage tank for centralized collection.

[0024] Next, a pneumatic conveying device is used to quantitatively transport the waste cathode carbon block powder from the finished product storage tank to the coal bunker through a sealed pipeline. During this stage, the amount of waste cathode carbon block powder mixed with the original coal is strictly controlled, and the mixing ratio is no more than 30% of the total processing capacity of the coal mill, which is approximately 10 tons per hour.

[0025] Finally, the mixed fuel is fed into the lower coal mill of boiler No. 4 in the power plant. After being further finely ground by the medium-speed mill, it is injected into the boiler furnace by the lower burner for combustion.

[0026] To coordinate with the power plant's production scheduling and reduce the plant's power load, this process adopts an intermittent operation system, running continuously for only 8 hours per day, approximately 365 days per year. It can process a total of about 17,000 tons of waste cathode carbon blocks, which means that the waste cathode carbon blocks processed annually can replace 17,000 tons of coal. Based on a raw coal price of 500 yuan / ton, the annual fuel cost savings can reach 8.5 million yuan.

[0027] Example 2: This example provides a system for the co-processing of waste cathode carbon blocks in power plants.

[0028] The system is arranged in series as follows: raw material storage silo → belt feeder → ball mill → drum screen → bucket elevator → finished product storage tank → pneumatic ash conveying device → coal bunker → medium-speed coal mill.

[0029] To avoid overburdening the existing dust removal system of the thermal power plant, a sealed dust collection hood is installed at the discharge point of the ball mill to work in conjunction with the drum screen. In this embodiment, the ball mill is the MQY1870 model, with a designed output of 6~16 T / H, equipped with a 210kW motor and a rated operating voltage of 380V. Because it uses 380V low-voltage power supply, there is no need to modify the power plant's existing 6kV high-voltage switchgear; it can be directly connected to the power plant's existing low-voltage plant power system, greatly reducing investment in electrical equipment. This system has a compact structure, small footprint, and utilizes finished product storage tanks and a pneumatic ash conveying system to isolate the coarse grinding process from the existing units, ensuring safety and reliability.

[0030] Example 3: In this example, the waste cathode carbon blocks contain approximately 20% fluoride, primarily in the form of cryolite (Na3AlF6) and sodium fluoride (NaF). After the waste cathode carbon block powder is fed into a coal-fired boiler, the furnace center temperature reaches 1200℃~1500℃. Under this high-temperature, high-oxidation environment, the following physicochemical changes occur: Cryolite first undergoes thermal decomposition, producing sodium fluoride and aluminum fluoride (Na3AlF6→3NaF + AlF3).

[0031] Boiler combustion flue gas and high-temperature coal ash are rich in calcium oxide (CaO) and silicon dioxide (SiO2). NaF, in its molten state at high temperatures, undergoes a vigorous chemical reaction with CaO and SiO2 to produce highly stable calcium fluoride (CaF2, i.e., fluorite) and sodium silicate (Na2SiO3). 2NaF + CaO + SiO2 → CaF2 (melt solidification) + Na2SiO3 (slag composition) The generated CaF2 has a melting point of over 1420℃. It is in a molten or semi-molten state inside the boiler. When it is discharged from the furnace along with the bottom ash and fly ash, it is trapped and fixed in the glassy coal ash network.

[0032] Through the high-temperature mineralization reaction disclosed in this invention, fluorides are transformed from a volatile free state into a stable crystalline form that is extremely difficult to leach. Subsequent testing according to national hazardous waste leaching toxicity standards showed that the fluoride ion leaching concentration in the solidified ash residue was far below the standard limit, achieving complete harmless treatment of hazardous waste.

[0033] Most existing power plants and related enterprises use the old-style ball mill pulverizing system, which is a DTM350 / 600 type ball mill with an output of 30T / H. This old equipment is equipped with a 1000kW high-power motor and requires a 6000V high-voltage power supply. This not only requires a dedicated 6kV high-voltage switchgear and a large-capacity transformer, resulting in extremely high infrastructure investment, but also leads to an abnormally high plant power consumption rate due to the continuous operation of the high-power motor.

[0034] The MQY1870 steel ball coal mill selected in this invention, after optimization, can achieve a capacity of 10 T / H, with a motor power of only 210 kW. This is calculated based on an annual processing capacity of 7300 tons of waste cathode carbon blocks. The old equipment operates for approximately 243 hours per year, consuming about 243,000 kWh of electricity, and requires additional costs of hundreds of thousands of yuan for the infrastructure renovation of the 6kV switchgear and subsequent high maintenance costs for the high-voltage equipment.

[0035] This equipment operates for approximately 730 hours per year, consuming about 153,000 kWh of electricity. It uses conventional 380V low-voltage electricity and can be directly connected to the existing plant power system without the need for additional 6KV high-voltage upgrades, thus significantly reducing infrastructure investment.

[0036] Meanwhile, since the high hardness of the waste cathode carbon blocks is borne by the upstream steel ball mill, the downstream power plant's existing medium-speed coal mill no longer needs to invest in high-wear-resistant materials. Considering the electricity costs, depreciation, and maintenance costs over the system's entire life cycle (LCC), the total operating cost of this invention is more than 60% lower than the solution using the old-style high-power steel ball mill. It is evident that this invention, employing a specific combination of low-power, low-voltage power supply equipment and an intermittent operation system, has produced significant economic and technical benefits in terms of system energy consumption and infrastructure investment.

[0037] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this disclosure. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0038] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for co-processing waste cathode carbon blocks in a power plant, characterized in that, Includes the following steps: The waste cathode carbon blocks are crushed and coarsely ground to obtain coarse powder; The coarse powder is mixed with coal to obtain a mixed fuel; The mixed fuel is fed into the boiler furnace of the power plant for high-temperature combustion; During the high-temperature combustion process, the high-temperature flue gas generated by the boiler combustion and the alkaline components in the coal ash are used to cause the fluorides in the waste cathode carbon blocks to undergo an in-situ mineralization reaction, generating stable fluoride mineral phases and fixing them in the coal ash residue.

2. The method for co-processing waste cathode carbon blocks in power plants according to claim 1, characterized in that, The specific steps of crushing and coarsely grinding the waste cathode carbon blocks are as follows: Waste cathode carbon blocks are fed into a ball mill for grinding. The ground powder is then screened through a drum screen. The qualified fine powder that passes through the screen is used as the coarse powder and enters the next process. The large particles on the screen are returned to the ball mill for further grinding.

3. The method for co-processing waste cathode carbon blocks in power plants according to claim 2, characterized in that, The particle size of the qualified fine powder is controlled to be between 0.074 mm and 0.6 mm.

4. The method for co-processing waste cathode carbon blocks in power plants according to claim 1, characterized in that, The amount of coarse powder mixed with coal shall not exceed 30% of the total processing capacity of the corresponding single medium-speed coal mill.

5. The method for co-processing waste cathode carbon blocks in power plants according to claim 4, characterized in that, The mixed fuel is fed into the lower coal mill of the power plant boiler and then enters the furnace for combustion via the lower burner.

6. The method for co-processing waste cathode carbon blocks in power plants according to claim 2, characterized in that, The ball mill is model MQY1870, with a designed output of 6-16 tons / hour, a rated motor power of 210kW, and an operating voltage of 380V.

7. The method for co-processing waste cathode carbon blocks in power plants according to claim 1, characterized in that, The method adopts an intermittent operation system, with a continuous operation time of 8 hours per day and an annual processing capacity of 17,000 tons of waste cathode carbon blocks.

8. The method for co-processing waste cathode carbon blocks in power plants according to claim 1, characterized in that, The specific process of the in-situ mineralization reaction is as follows: Cryolite (Na3AlF6) and sodium fluoride (NaF) in waste cathode carbon blocks react with calcium oxide (CaO) and silicon dioxide (SiO2) in coal ash under the high temperature environment of 1200℃~1500℃ in power plant boilers to generate chemically stable calcium fluoride (CaF2), which then melts and solidifies in the bottom slag and fly ash.

9. A system for co-processing waste cathode carbon blocks in power plants, characterized in that, In order, they include: Raw material storage silos, belt feeders, ball mills, drum screens, finished product storage tanks, pneumatic ash conveying devices, coal bunkers, and medium-speed coal mills; The discharge port of the raw material storage silo is connected in sequence to the feed port of the ball mill via a belt feeder. The discharge port of the ball mill is connected to the inlet of the drum screen. The fine powder outlet of the drum screen is connected in sequence to the finished product storage tank and the pneumatic ash conveying device. The output end of the pneumatic ash conveying device is connected to the coal bunker. The discharge port of the coal bunker is connected to the medium-speed coal mill.

10. The system for co-processing waste cathode carbon blocks in power plants according to claim 9, characterized in that, The ball mill is an MQY1870 model, with a rated motor power of 210kW and an operating voltage of 380V; the power input of the ball mill in the system does not depend on the modification of the 6kV high-voltage switchgear.

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