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The aviation fuel oil (the mainstream is jet fuel No.3, that is, aviation kerosene) left in the fuel system inside the fuselage can not be simply discharged or discarded after the civil aviation aircraft has reached its service life and officially retired due to aircraft type elimination or accident damage. It belongs to flammable dangerous chemicals, which are volatile, flammable and explosive, and harmful to the environment. The treatment process must strictly follow the principles of safety first, environmental compliance, resource maximization, and whole process control, and implement standardized and professional treatment processes in accordance with the Civil Aviation Administration's norms, hazardous chemicals management regulations and environmental protection standards, so as to prevent safety accidents and environmental pollution, and at the same time realize rational utilization of resources.

1. Pretreatment before retirement: initial fuel emptying and safety control.

Before the aircraft officially enters the dismantling or sealing process, the initial emptying of the fuel system must be completed, which is the basis for subsequent treatment. The whole process should be carried out in the explosion-proof area of the special apron, dismantling base or aircraft cemetery to prevent fire, static electricity and illegal operation.

1. Remaining fuel consumption in flight phase.
If the aircraft has flight capability, the retired flight will accurately calculate the range, consume most of the fuel in the air as much as possible, and reduce the amount of oil left on the ground; If it is impossible to fly or need emergency retirement, it will directly enter the ground emptying process, and it is strictly forbidden to store a large amount of residual fuel for a long time.

2. Ground professional pumping operation
The explosion-proof special oil pump and closed oil collection equipment are used to connect the oil drain interface of the aircraft fuel tank, and a negative pressure oil pumping system is established. First, most of the liquid fuel in the main fuel tank and auxiliary fuel tank is pumped. During operation, the pumping speed is strictly controlled to avoid electrostatic accumulation caused by excessive flow speed. All equipment shall be properly grounded, and the pressure difference shall be controlled within 0.05MPa to prevent the tank structure from being deformed. At the same time, the oil and gas concentration shall be monitored in the whole process to ensure that the combustible gas concentration in the working environment is less than 10% of the lower explosion limit, and emergency equipment such as fire foam and dry powder fire extinguishers shall be equipped.

3. Fuel system pressure relief and pipeline residual oil collection
After the oil pumping is completed, the fuel pipeline, oil pump, oil filter and other components are depressurized, and the residual fuel in the pipeline is collected through the oil drain at the low point of the pipeline and the sedimentation tank, so as to prevent the fuel from staying in the dead corner of the pipeline and subsequently volatilizing to form a safety hazard. The preliminarily extracted fuel will be uniformly loaded into a sealed and clearly marked special oil storage tank, and the source, oil quantity and oil type will be recorded, waiting for subsequent testing and classified disposal.

2. Deep cleaning of oil tank: trace residual oil and oil film are completely removed.

After the initial emptying, oil film and trace residual oil will still adhere to the inner wall, compartment and gap of the aircraft fuel tank. Although the amount of such residue is small, it is highly volatile, and it is easy to cause deflagration when it meets sparks and high temperature. It is also a core safety hazard in the dismantling process and must be thoroughly cleaned.

1. Inert gas replacement
Nitrogen with purity ≥99.5% is introduced into the fuel tank for inert gas replacement, so as to reduce the oxygen concentration in the tank to below 8%, completely eliminate the risk of oil and gas explosion, and create a safe environment for subsequent cleaning operations. During the replacement process, the oxygen and oil and gas concentrations are monitored in real time to ensure that the next operation is carried out after reaching the standard.

2. Gradient heating and centrifugal separation
Aiming at the composite fuel tank, a step-by-step heating method (the temperature rise is not more than 5℃ per hour) is adopted to reduce the viscosity of residual fuel and make it easier to leave the inner wall of the fuel tank. Then, the residual oil and impurities are separated by centrifugal separation equipment to further reduce the residual fuel in the fuel tank.

3. Steam purging and adsorption cleaning
Purge the inside of the oil tank with high-temperature steam in all directions to dissolve and peel off the stubborn oil film; Then use special absorbent cotton, activated carbon and other absorbent materials to wipe and absorb the remaining trace fuel and oil pollution in the fuel tank. Finally, use explosion-proof endoscope to check to ensure that the thickness of the residual oil film is less than 2mm, which meets the standard of safe disassembly.

4. volatile oil gas collection and treatment
The fuel vapor volatilized in the cleaning process is collected by negative pressure pumping system, treated by activated carbon adsorption, catalytic oxidation or condensation recovery device, and discharged after reaching the standard, so as to avoid VOCs (volatile organic compounds) from polluting the air and recover some liquefied fuel components.

III. Classified disposal of extracted fuel: qualified reuse and unqualified harmless treatment.

The fuel extracted from retired aircraft needs to undergo professional quality inspection, distinguish between qualified usable and polluted deterioration, and implement different disposal schemes respectively to achieve the balance between resource utilization and environmental protection treatment.

1. Qualified fuel: recycling.
If the extracted fuel is not polluted, and all indexes (density, flash point, freezing point, water segregation index, impurity content, etc.) meet the use standards of aviation fuel, it can re-enter the civil aviation fuel supply system after settling, filtering, draining and full-scale inspection. According to the civil aviation industry standard, this kind of recovered fuel can be mixed with brand-new aviation fuel at the proportion of no more than 10% of the total receiving oil tank, which can be used for refueling of in-service aircraft to realize resource recycling and avoid waste.

2. Slightly polluted fuel: purification and regeneration
If the fuel is mixed with a small amount of water and impurities, or slightly contaminated by microorganisms, it can be treated by multistage filtration, dehydration, sedimentation, purification and other processes to remove water and impurities and restore fuel performance. Test again after purification, and reuse according to qualified fuel flow after reaching the standard; It can also be used as industrial fuel and boiler fuel after modification, thus expanding the utilization ways.

3. Unqualified fuel: harmless disposal
If the fuel cannot be purified up to the standard due to long-term storage, chemical pollution, excessive additives and other reasons, it belongs to hazardous waste, and it is strictly prohibited to dump and burn it at will. It needs to be handed over to a professional organization with the qualification of hazardous chemicals disposal, and treated by standardized incineration and pyrolysis processes according to the national hazardous waste treatment standards, so as to control the waste gas and waste residue in the whole process, ensure the discharge up to the standard, and prevent soil, water and air pollution.

Fourth, the whole process of compliance control: qualification, standards and record traceability

The fuel treatment of retired civil aviation aircraft is a high-risk special operation, which is supervised by the Civil Aviation Administration, the Emergency Management Department, the Ministry of Ecology and Environment and other departments, and must meet strict compliance requirements.

1. Job qualification requirements
Enterprises undertaking fuel treatment must have IATA aircraft disassembly qualification, hazardous chemicals management and disposal qualification and ISO14001 environmental management system certification. Operators must hold hazardous chemicals operation certificate and aviation fuel treatment special training certificate, hold relevant certificates throughout the whole process, and be equipped with A-class chemical protective clothing, anti-static gloves, positive pressure breathing apparatus and other protective equipment.

2. Implement standard specifications
Strictly follow the standards such as the Quality Control and Operation Procedure of Civil Aviation Fuel (MH/T 6020—2025), ICAO's Guide to Aircraft Disassembly and Environmental Management, and EU's Directive on Scrap Aircraft Recycling, clarify the indicators of emptying, testing, disposal and environmental protection, and put an end to illegal operations.

3. Record and trace the whole process
From pumping, cleaning, testing to final disposal, each link needs to be recorded in detail, including fuel quantity, quality inspection report, disposal process, operators, environmental emission data, etc., and a complete traceability file should be established, which should be subject to third-party audit and inspection by regulatory authorities to ensure traceability and verifiability throughout the process.

V. Difference of fuel treatment in different decommissioning scenarios

According to the final destination of the aircraft after retirement, the focus of fuel treatment is slightly different:

1. Aircraft dismantling and scrapping: It is necessary to carry out thorough emptying and deep cleaning to ensure that there is no residue in the fuel system, and then disassemble the fuselage. All residual oil and oil stains are treated as hazardous wastes, and the parts are recycled.

2. The aircraft is sealed for standby: after most of the fuel is drained, the fuel system is sealed and inerted, and the residual trace fuel is regularly monitored to prevent deterioration and leakage. During the sealing period, the oil and gas control is well done, and the fuel system is re-tested when it is subsequently put into use.

3. Aircraft refitting or exhibition: After the fuel is thoroughly cleaned and harmlessly treated, the fuel tank shall be sealed and anticorrosive to eliminate potential safety hazards and ensure that there are no fuel-related risks during refitting and exhibition.

Vi. Key points of core safety and environmental protection

1. Safety prevention and control: put an end to naked fire, static electricity and high temperature in the whole process, divide the work area into explosion-proof grades, and equip with emergency fire fighting and ventilation equipment to prevent explosion, fire and personnel poisoning accidents.

2. The bottom line of environmental protection: It is strictly forbidden to leak or directly discharge fuel oil. All residual oil, greasy dirt and oily wastes shall be managed as hazardous wastes, and waste gas and wastewater shall be discharged after reaching the standard, so as to protect soil and water sources.

3. Resource conservation: give priority to recycling qualified aviation fuel, realize recycling, reduce resource consumption and practice the concept of green civil aviation.

To sum up, the treatment of aviation fuel oil for retired civil aviation aircraft is a systematic project integrating safe operation, professional testing, classified disposal and environmental protection compliance, and every link can not be sloppy. Only by strictly following the standard process can we not only ensure the safety of operation, put an end to environmental pollution, but also realize the rational utilization of resources and complete the green closed loop of decommissioning and disposal of civil aviation aircraft.