Coal tar residue harmless treatment system and method based on microwave-hot carrier gas synergistic cracking

Abstract

The invention relates to the technical field of hazardous waste treatment, and discloses a harmless treatment method and system for coal tar residues. The method comprises the following steps: mixing coal tar residues and ash according to a ratio, and extruding and granulating to form a porous particle material; sending the particles into a microwave cracking furnace, cracking organic matters in the coal tar residue particles into oil gas under the synergistic effect of microwave radiation and hot carrier gas at 400-800 DEG C, taking the oil gas out by the carrier gas, and condensing and separating to obtain cracked oil; the oil content of residues is less than 0.2%. The method solves the problems of coking, wall sticking and secondary pollution in traditional treatment, and realizes oil resource recovery and residue harmlessness.

Description

Technical Field

[0001] The present invention relates to a hazardous waste resource processing technology, and in particular to a microwave-assisted hot-carrier gas cracking processing system and method for coal tar residue, belonging to the technical field of waste material processing and resource utilization. Background Art

[0002] Coal tar residue is a hazardous waste (HW11 category) generated during the process of coal coking and coal gasification. It has the characteristics of high viscosity, high toxicity and complex composition. The traditional treatment methods have the following key problems:

[0003] Incineration treatment method: secondary pollution is serious. Incomplete combustion produces dioxins and polycyclic aromatic hydrocarbons, and the emission concentration is likely to exceed the standard. The flue gas contains SO 2 , NOx, heavy metal vapor (such as arsenic, mercury), requiring a complex tail gas purification system (investment cost increased by more than 30%). Waste of resources, coal tar residue has a high calorific value (20-30 MJ / kg), direct incineration only recovers heat energy, and oil resources are not utilized; the residual carbon content in the residue ash is >15%, and the calorific value is not fully released.

[0004] Landfill treatment: Long-term environmental risk. BTEX, phenols, and heavy metals (such as Cd and Pb) in oil residue will seep into the soil and groundwater, and the cost of remediation is high. Pretreatment is required to reduce the oil content to less than 5%, and traditional dehydration / solidification technology is difficult to meet the standard. Land resources are occupied, landfill site selection is difficult, and disposal costs continue to rise.

[0005] Solvent extraction method: Solvent residue and toxicity transfer, commonly used organic solvents are easy to remain in the extraction residue, forming new hazardous waste; the extract needs to be further distilled and separated, which consumes a lot of energy. The economic efficiency is poor, the solvent recovery rate is less than 90%, the processing cost is high, and it is only suitable for oil residues with high oil content.

[0006] Traditional pyrolysis: coking and equipment blockage, strong stickiness of oil residue, forming a coking layer on the inner wall and pipeline of the pyrolysis furnace, requiring frequent shutdown for cleaning; intermittent operation leads to low processing efficiency. Low product quality: pyrolysis oil contains coke powder and asphaltene (>10%), which requires deep refining before use; the oil content of the residue is generally>3%, which is still a hazardous waste (HW11). Summary of the invention

[0007] The present invention proposes a technology of using inorganic ash to modify coal tar residue, microwave and hot carrier gas for synergistic cracking, aiming to solve the problems of how to completely degrade organic matter in coal tar residue; how to avoid coking and equipment wall sticking during the cracking process; and how to achieve low energy consumption and high efficiency production.

[0008] The core of the present invention lies in the full process design of "ash granulation-microwave carrier gas synergistic cracking-product high value", which specifically includes the following steps:

[0009] Ash mixing and granulation: Mix coal tar residue with dry and loose inorganic ash (such as lime, carbide slag) with a moisture content of ≤5wt% in a mass ratio of 15%-40%.

[0010] The ash content must meet the following requirements: specific surface area ≥ 20 m² / g, adsorbing oil; non-cohesive, such as industrial waste slag with a CaO content ≥ 50%; formed into particles (spherical / cylindrical) with a diameter of 5-50mm and a porosity of ≥ 30% by an extruder, and the particle compressive strength must be ≥ 5MPa.

[0011] Microwave-hot carrier gas synergistic cracking, the particles are sent into the microwave cracking furnace, and the following are applied simultaneously: microwave radiation: power density 5-50 kW / m³, frequency 915MHz or 2450 MHz; hot carrier gas sweep: temperature 400-800℃ (preferably 600℃), flow rate 0.25-2m / s, penetrating the particle layer from top to bottom; under the synergistic effect of microwave internal heating (molecular vibration cracking) + hot carrier gas external heating (heat transfer and oil and gas carrying), the organic matter is completely cracked within 10-40 minutes.

[0012] Product separation and utilization: After condensation (primary 80℃, secondary -10℃), the cracking gas is obtained to obtain cracking oil (yield 18-25%), which can be cracked again to produce carbon black; residue characteristics: oil content <0.2%; fixed carbon ≥50%, calorific value ≥23 MJ / kg, which can be directly used as a substitute fuel for cement kilns.

[0013] Compared with the prior art, the present invention has the following innovative breakthroughs:

[0014] Ash granulation controls material properties: ash absorbs oil to reduce viscosity, and the particle porosity ≥ 30% ensures smooth airflow, solving the problems of wall sticking and coking in traditional technologies;

[0015] Energy-coupled cracking mechanism: microwaves selectively heat polar components, hot carrier gas provides a uniform thermal field and instantly takes away oil and gas, increasing cracking efficiency by more than 40%;

[0016] Dynamic anti-coking design: carrier gas instantly sweeps oil and gas to avoid deposition on the furnace wall;

[0017] Static pyrolysis: through granulation, the pyrolysis products have strength, the whole pyrolysis process is static, there is no softening flow in the pyrolysis process, no wall adhesion, the pyrolysis oil and gas quickly leave the microwave zone with the hot carrier gas, and no coking is produced;

[0018] No dioxins are produced during the entire process and the residues are completely harmless.

[0019] The present invention can achieve:

[0020] Environmental protection: The oil content of the residue is less than 0.2%, meeting the admission requirements of the "Hazardous Waste Landfill Standard" (GB 18598-2019);

[0021] Economical: Low processing cost, the value of pyrolysis oil and residual fuel can offset more than 60% of the cost;

[0022] Industrial feasibility: The equipment can run for a long time without decoking, and the processing capacity is ≥100 kg / h. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a process flow chart of the present invention;

[0024] Figure 2 It is a schematic diagram of the system structure, including the following contents: 1 mixing unit, 2 granulation and feeding unit, 3 microwave cracking furnace, 4 carrier gas heating device, 5 microwave source, 6 condensation separator, 7 coal tar residue, 8 ash, 9 carrier gas, 10 hot carrier gas, 11 cracking gas, 12 residue discharging device, 13 cracking oil, and 14 non-condensable gas. DETAILED DESCRIPTION Embodiment 1

[0025] Take coal tar slag with an oil content of 25% and mix it with lime (water content 5wt%, specific surface area 30㎡ / g), with the lime ratio of 15wt%;

[0026] Extruded into Φ50mm cylindrical particles with a porosity of 45%;

[0027] The mixture was sent to a microwave cracking furnace with a microwave power of 5 kW and nitrogen gas at 800°C and a nitrogen flow rate of 1 m / s for 10 minutes.

[0028] The obtained residue had an oil content of 0.21% and a pyrolysis oil yield of 18.7%. Embodiment 2

[0029] Raw material pretreatment: Take high-viscosity coal tar residue after centrifugal separation with an oil content of 32% and a dynamic viscosity of ≥5000 mPa·s and mix it with kaolin powder with a specific surface area of ​​35m² / g at a ratio of 40wt%; after mixing, the viscosity of the material drops to 800 mPa·s.

[0030] Granulation: The mixed material is made into cylindrical particles with a diameter of 5mm and a length of 10-15mm using a double-roll extruder, with a stacking void ratio of 40% and a particle compressive strength of 5MPa. The surface of the particles is sprayed with 0.05mm thick lime powder to further reduce adhesion;

[0031] Microwave-hot argon synergistic cracking: 100 kg of particles were fed into a microwave cracking furnace, and the microwave power was adjusted to 50 kW / m³ (frequency 915 MHz); 400°C hot argon was introduced (flow rate 0.25 m / s), and a porous distributed argon inlet (aperture 3 mm, opening rate 40%) was set in the cracking furnace to ensure that the airflow evenly penetrated the particle layer; the cracking time was 40 minutes.

[0032] Product processing and analysis: After the cracking gas was condensed in two stages (first stage at 80℃, second stage at -10℃), the cracking oil yield reached 22.1% (accounting for 69.2% of the total oil in the raw material); the residue had a porous structure and an oil content of 0.18%; the fixed carbon content was 58.3%, and the calorific value was 23.5 MJ / kg, which met the solid fuel standard of GB / T 30725-2014.

[0033] The obtained pyrolysis oil was heated in a secondary pyrolysis reactor (450°C, N 2 The yield of carbon black was 19.4%. Under the same conditions, when coal tar residue without ash was directly pyrolyzed, the coal tar residue collapsed and adhered when heated, resulting in blockage of the air flow channel, and the oil content of the residue was as high as 12.7%; the yield of pyrolysis oil was only 5.3%, and there was serious coking in the furnace. Embodiment 3

[0034] Take low-oil coal tar residue with an oil content of 8.2% and a moisture content of 15%, mix it with dry calcium carbide slag and synthetic resin adhesive in a mass ratio of 4:1:0.3. After mixing, the moisture content of the material drops to below 3% and the fluidity is significantly improved.

[0035] A ring die extruder is used to form spherical particles with a diameter of 10mm and a stacking porosity of more than 30%. The cracking furnace adopts pulse microwave mode (5s on / 2s off) with a power of 15kW (microwave frequency 2450MHz) to avoid local overheating. Water vapor at a temperature of 600℃ is introduced (flow rate 0.5m / s) and the cracking time is 18 minutes. The oil content of the residue is 0.09% and the fixed carbon content is 62.4%. The cracking oil yield is 4.8% (accounting for 58.5% of the raw oil content), and the calorific value of the gas is 18 MJ / Nm³. It saves 37% energy compared with traditional pyrolysis. Embodiment 4

[0036] Take 1 ton of coal tar slag from the bottom of the tar dehydration tank of the coking plant, and then take 0.3 tons of factory waste lime powder (CaO content ≥ 90%, specific surface area 40㎡ / g), and mix them in a closed mixer for 1 hour.

[0037] A twin-screw extruder (L / D=15:1, die head aperture 8 mm) was used for granulation to produce honeycomb cylindrical particles with a diameter of 8 mm, a length of 10 mm, and a porosity of 45%.

[0038] The particles were fed into a microwave cracking furnace with a microwave frequency of 915HNz and a power density of 10 kW / m³, and carbon dioxide gas at 720°C and a flow rate of 2 m / s was introduced at the same time. The cracking time was 18 minutes.

[0039] The granular residue after cracking is crushed and carbon black is prepared in a rotary kiln; the cracking oil gas produced during cracking is condensed to obtain cracking oil, which can be sprayed into a vertical carbon black reactor to prepare carbon black.

[0040] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A system and method for harmless treatment of coal tar residue based on microwave-hot carrier gas synergistic pyrolysis, characterized in that The following steps are involved: ❶Mix coal tar residue with dry and loose inorganic ash, with the ash accounting for 15%-40wt%; ❷ Extrude the mixed material into porous particles with a particle size of 5-50mm; ❸ The coal tar residue particles are fed into a microwave cracking furnace and cracked for 10-40 minutes under the conditions of microwave power of 5-50kW / m³, while hot carrier gas at a temperature of 400-800℃ and a flow rate of 0.25-2m / s is introduced; ❹ The cracking gas is condensed and separated to obtain cracking oil, and the oil content of the residue is less than 0.2%.

2. The method according to claim 1, characterized in that: The particles are spherical or cylindrical, with a stacking void ratio of ≥30% and a compressive strength of ≥5MPa.

3. The method according to claim 1, characterized in that: The ash may be lime powder, kaolin or carbide slag, with a specific surface area of ​​≥20m² / g and a moisture content of ≤5wt%.

4. The method according to claim 1, characterized in that: The hot carrier gas passes through the gaps between the granular materials from top to bottom and penetrates the material particle layer, thereby forming synergistic heating with the microwave radiation.

5. The method according to claim 1 or 4, characterized in that: The hot carrier gas may be nitrogen, carbon dioxide, argon, water vapor, or the like.

6. A coal tar residue harmless treatment system based on microwave-hot carrier gas synergistic pyrolysis comprises: Mixing unit, granulation and feeding unit, carrier gas heating device, microwave cracking furnace, microwave source, condensing oil and gas separator, residue discharging device.

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