Method for recycling waste metal fly ash collected by cloth bag dust removal

Abstract

The application provides a near-zero waste recycling method of waste metal fly ash captured by cloth bag dust removal, belongs to hazardous waste resource utilization, and specifically belongs to the energy-saving and environmental protection industry in the national strategic emerging industry. The application provides a recycling method of waste metal fly ash, which comprises the following steps: fly ash captured by a cloth bag dust remover in an oil residue filter cake metal recovery process is returned to a middle combustion zone of a multi-chamber furnace for combustion, so that metal ash first-class products are obtained. The application re-introduces waste fly ash captured by the cloth bag dust remover into a metal recovery main process, improves the comprehensive recovery rate of the metal ash products without increasing the load of additional treatment of the filter cake, significantly reduces the fly ash discharge amount, and the reduction is greater than or equal to 90%, thereby greatly reducing the solid waste disposal cost; the return system does not affect the stable operation of the multi-chamber furnace, the product indexes are qualified and are first-class products, the metal ash yield is increased, the benefit is significant, and the application provides a near-zero waste technology path for the oil residue hydrogen production filter cake metal recovery process.

Description

Technical Field

[0001] This invention provides a method for reusing waste metal fly ash collected by bag filters, which belongs to the category of hazardous waste resource utilization. Specifically, it relates to a near-zero waste recycling method for fly ash from bag filters in an oil residue hydrogen production metal recovery process. Background Technology

[0002] Oil residue-to-hydrogen metal recovery technology, a key technology for resource recycling in the petrochemical industry, generates a large amount of fly ash containing heavy metals while recovering valuable metals such as nickel (Ni), vanadium (V), and molybdenum (Mo). This fly ash is classified as hazardous waste, and the traditional "collection-landfill disposal" model has the following prominent problems: (1) Serious waste of resources: Actual measurement data shows that the Ni content in fly ash is 5.36 wt%, V content is 9.04 wt%, and Mo content is 21.62 wt%, with metal grades significantly higher than the threshold for industrial use. Direct landfilling leads to secondary loss of valuable metals. (2) Significant environmental risks: Fly ash contains heavy metals and combustibles, and long-term storage poses a risk of leakage and occupies a large amount of land resources; (3) Technical bottlenecks: Existing technologies lack effective means to safely reuse fly ash in the main process. The return process is prone to causing suspended combustion in multi-hearth furnaces, secondary dust generation, and temperature field disturbances, which affect the stable operation of the system.

[0003] Therefore, developing a reuse technology that can achieve near-zero waste of fly ash and deep recovery of valuable metals is of great practical significance and urgency for promoting the green and low-carbon transformation of the petrochemical industry and alleviating the shortage of strategic metal resources. Summary of the Invention

[0004] This invention provides a method for reusing waste metal fly ash collected by bag filters. The method of this invention achieves deep recovery of valuable metals from metal fly ash in oil residue hydrogen production.

[0005] This invention provides a method for reusing waste metal fly ash collected by bag filters, comprising the following steps: The fly ash collected in the bag filter of the metal recovery system is returned to the central combustion zone of the multi-hearth furnace used in the metal recovery system for combustion to obtain metal ash.

[0006] Preferably, the return feeding includes: conveying the material to the secondary air inlet of the central combustion zone using a single-pipe peristaltic feeding method, and then blowing it into the central combustion zone under the action of secondary air.

[0007] Preferably, the pipeline used for conveying is equipped with a pneumatic clamp valve.

[0008] Preferably, the frequency of the pneumatic clamp valve is 0.2~1.8 Hz.

[0009] Preferably, the control method for the damper at the secondary air inlet includes: using the overall load of the multi-hearth furnace and the oxygen quantity at the multi-hearth furnace outlet as feedforward quantities, using the temperature of the central combustion zone as tracking quantities to calculate the temperature difference between the actual temperature and the set temperature, and adjusting the opening of the damper according to the result of the temperature difference calculation.

[0010] Preferably, the metal recycling system includes a bag filter and a bag conveying pump connected to the bag filter. The bag conveying silo pump is also connected to a bag ash conveying air storage tank to provide air for conveying fly ash. Ash storage area, used to store excess fly ash; Secondary air fan and multi-hearth furnace.

[0011] Preferably, the temperature of the central combustion zone is 400~560℃.

[0012] Preferably, when the number of layers in the multi-hearth furnace is 17, the central combustion zone is the 14th layer.

[0013] This invention significantly improves the overall recovery rate of metal ash products by reintroducing fly ash collected by bag filters into the main metal recovery process without increasing the additional processing load. The fly ash discharge volume is reduced by ≥90%, greatly reducing solid waste disposal costs. The return system does not affect the stable operation of the multi-hearth furnace, and the product indicators are qualified and are first-class products, providing a "near-zero waste" technical path for the metal recovery process of oil residue hydrogen production filter cake.

[0014] This invention is applicable to all valuable metal recovery devices, such as oil residue filter cake, equipped with multi-hearth furnaces and bag filters, and is particularly suitable for low-cost retrofitting of existing projects. With increasingly stringent environmental policies and rising value of metal resources, this "fly ash internal circulation" technology will be widely adopted in the field of metal ash recovery both domestically and internationally, offering significant economic and environmental benefits and promising broad application prospects. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the device used in the embodiment; Figure 2 The terms refer to fly ash, finished ash before fly ash reuse, and finished ash after fly ash reuse. Detailed Implementation

[0016] This invention provides a method for recycling metallic ash, comprising the following steps: The fly ash collected in the bag filter of the metal recovery system is returned to the central combustion zone of the multi-hearth furnace used in the metal recovery system for combustion to obtain metal ash.

[0017] In this invention, the metal recovery system preferably includes an oil residue metal recovery system; the metal recovery system preferably includes a bag filter; a bag conveying silo pump connected to the bag filter; the bag conveying silo pump is also connected to a bag ash conveying air storage tank for providing air for conveying fly ash; an ash silo for storing excess fly ash; a secondary air fan and a multi-hearth furnace.

[0018] In this invention, the return feeding preferably includes: conveying the fly ash to the secondary air inlet of the central combustion zone using a single-pipe peristaltic feeding method, and then blowing it into the central combustion zone under the action of secondary air; the pipeline used for conveying is preferably equipped with a pneumatic clamp valve, and the pipeline is preferably an ash conveying pipeline lined with wear-resistant ceramic; the frequency of the pneumatic clamp valve is preferably 0.2~1.8 Hz. By adopting a single-pipe peristaltic feeding method to return the fly ash to the central combustion zone of the multi-hearth furnace, the conveying process ensures the formation of discrete ash plugs, slowly pushing the fly ash into the furnace.

[0019] In this invention, the temperature of the central combustion zone is preferably 400~560℃.

[0020] In this invention, the preferred method for controlling the damper at the secondary air inlet includes: calculating the temperature difference between the actual temperature and the set temperature using the overall load of the multi-hearth furnace and the oxygen content at the multi-hearth furnace outlet as feedforward quantities, and the temperature of the central combustion zone as the tracking quantity; and adjusting the damper opening based on the calculated temperature difference. This control method enables precise temperature control of the central combustion zone (fluctuation within ±5℃), ensuring that the furnace volumetric heat load is unaffected by return material and that the heat load of the central combustion zone is precisely controlled.

[0021] In this invention, when the multi-hearth furnace has 17 layers, it is preferable to return the fly ash to the 14th layer of the multi-hearth furnace. In this invention, the fly ash returned to the 14th layer of the multi-hearth furnace (out of 17 layers) is located in the combustion roasting zone, without disrupting the primary air distribution for complete combustion of the original gas lance; the oxygen required for the combustion of the powder and fly ash returned material in the 14th layer is provided by secondary air.

[0022] The selection of this furnace inlet point (the furnace inlet point refers to the 14th layer when the multi-hearth furnace has 17 layers) and the creeping feeding method effectively avoid the problems of suspended combustion and secondary dust caused by continuous two-phase airflow (fly ash and secondary air).

[0023] The following detailed description of the metal ash recycling method provided by the present invention, in conjunction with embodiments, should not be construed as limiting the scope of protection of the present invention.

[0024] Figure 1 A schematic diagram of the structure of a portion of the device used in the embodiment: a bag filter; a bag conveying pump connected to the bag filter; The bag conveying silo pump is also connected to a bag ash conveying air storage tank to provide air for conveying fly ash. Ash storage area, used to store excess fly ash; Secondary air fan and multi-hearth furnace.

[0025] Example 1 The filter cake with a carbon content of 16% and a moisture content of 70% was continuously fed into a multi-hearth furnace at a rate of 6t / h (the temperature of each layer of the multi-hearth furnace is shown in Table 1) for combustion. The resulting flue gas was purified and dust removed by a bag filter to obtain fly ash (the composition content is shown in Table 1). The fly ash is transported to the 14th layer of the multi-hearth furnace at a speed of 0.2t / h and a frequency of 0.2~1.8Hz by the bag conveying silo pump and the bag ash conveying air storage tank. Under the action of the secondary fan, it is burned together with the filter cake product. The resulting flue gas is purified and bag dust is removed to obtain recycled metallic ash (referred to as recycled fly ash metallic ash product).

[0026] Table 1 Temperature of each layer in the multi-hearth furnace

[0027] Table 2. Components and content of fly ash and recycled metal ash, and their yield

[0028] Figure 2 The images show fly ash, finished ash before fly ash reuse, and finished ash after fly ash reuse: from left to right, the first is fly ash collected by bag filter, the second is finished ash before fly ash reuse, and the third, fourth, fifth, and sixth are finished ash after fly ash reuse.

[0029] Depend on Figure 2 As shown in Table 2, compared with the finished ash under normal operating conditions, the finished ash after fly ash recycling shows no difference in composition except for a slightly lighter color, and does not affect product quality. The slightly lighter color is due to the extremely low combustible content of the fly ash after high-temperature burning in the secondary combustion chamber. However, a key evaluation indicator for first-grade finished ash is a combustible content of less than 3%, so the recycled ash actually has a positive effect.

[0030] Based on the analysis of laboratory data and product appearance comparison, the finished fly ash is grayish-black in appearance, with particle size and flowability consistent with the original product, and exhibits no clumping or secondary pollutant generation. After fly ash reuse, the production of metallic ash increases, while the amount of fly ash discharged decreases by 90%, achieving a comprehensive effect of increased production, reduced waste, and energy conservation.

[0031] The innovative point of this invention is: (1) Innovation of return material location: The 14th layer (combustion zone) of the multi-hearth furnace was selected as the fly ash return point, which not only ensures the full combustion of combustibles, but also avoids interference with the temperature field of the main combustion zone, thus achieving "return material without backfire"; (2) Innovative feeding method: The pneumatic clamp valve peristaltic feeding technology is adopted with a frequency of 0.2~1.8 Hz to form discrete ash plugs instead of continuous airflow, which fundamentally solves the problem of secondary dust and suspended combustion in the return process; (3) Temperature control strategy innovation: Establish a precise temperature control system with feedforward-feedback composite control as the core, using multi-hearth furnace load and outlet oxygen quantity as feedforward and return material layer temperature as feedback to achieve precise temperature control within ±5℃; (4) System integration innovation: Construct a closed-loop circulation system of "bag dust removal - silo pump conveying - peristaltic return - multi-hearth furnace reuse" to realize the on-site disposal and resource utilization of fly ash.

[0032] Significant technical effects of the present invention: (1) Significant environmental benefits: The amount of fly ash discharged has decreased by ≥90%, and the amount of hazardous waste landfilled has been reduced by about 1,680 tons per year (calculated at 0.15 t / h and 8,400 h / a), which has greatly reduced the cost of solid waste disposal and environmental risks; (2) Outstanding economic benefits: Without increasing the additional filter cake processing load, the metal ash production increased by 2.5% (from 6.0 t / h to 6.15 t / h). Based on 8,400 hours of operation per year and a metal ash value of RMB 100,000 per ton, the annual increase in benefits is RMB 126 million. (3) Excellent product quality: The recycled metal ash product meets the first-class product standard (combustible material <3%), the recovery rate of Ni, V and Mo is significantly improved, and the product appearance, particle size and flowability are consistent with the original product. There is no clumping or secondary pollutant generation. (4) Stable system operation: The return process does not affect the stable operation of the multi-hearth furnace, the furnace temperature field distribution is reasonable, and the flue gas purification system operates normally; (5) High promotion value: It is applicable to all oil residue filter cake metal recovery devices equipped with multi-hearth furnaces and bag dust collectors, especially suitable for low-cost retrofitting of existing projects, providing the industry with a replicable and scalable "near-zero waste" technology paradigm.

[0033] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for recycling waste metal fly ash collected by a bag filter, characterized in that, Includes the following steps: The fly ash collected in the bag filter of the metal recovery system is returned to the central combustion zone of the multi-hearth furnace used in the metal recovery system for combustion to obtain metal ash.

2. The reuse method according to claim 1, characterized in that, The return feeding includes: conveying the material to the secondary air inlet of the central combustion zone using a single-pipe conveying peristaltic feeding method, and then blowing it into the central combustion zone under the action of secondary air.

3. The reuse method according to claim 2, characterized in that, The pipeline used for transportation is equipped with a pneumatic clamp valve.

4. The reuse method according to claim 3, characterized in that, The frequency of the pneumatic pinch valve is 0.2~1.8Hz.

5. The reuse method according to claim 2, characterized in that, The control method for the damper at the secondary air inlet includes: calculating the temperature difference between the actual temperature and the set temperature using the overall load of the multi-hearth furnace, the oxygen quantity at the multi-hearth furnace outlet as feedforward quantities, and the temperature of the central combustion zone as tracking quantities; and adjusting the opening of the damper based on the results of the temperature difference calculation.

6. The reuse method according to claim 1, characterized in that, The metal recycling system includes a bag filter and a bag conveying pump connected to the bag filter. The bag conveying silo pump is also connected to a bag ash conveying air storage tank to provide air for conveying fly ash. Ash storage area, used to store excess fly ash; Secondary air fan and multi-hearth furnace.

7. The reuse method according to claim 1, characterized in that, The temperature of the central combustion zone is 400~560℃.

8. The reuse method according to claim 1, characterized in that, When the multi-hearth furnace has 17 layers, the central combustion zone is the 14th layer.

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