What are the main energy consumption and environmental impacts in the production process of graphitized petroleum coke?

Analysis of Main Energy Consumption and Environmental Impacts in the Production of Graphitized Petroleum Coke

I. Main Energy Consumption Processes

1. High-Temperature Graphitization Treatment
   Graphitization is the core process, requiring temperatures to reach 2,800–3,000°C to convert non-graphitic carbon in petroleum coke into a graphite crystal structure. This stage is extremely energy-intensive, with traditional Acheson furnaces consuming 6,000–8,000 kWh per ton of electricity. New continuous vertical furnaces reduce this to 3,000–4,000 kWh per ton, though energy costs still account for 50%–60% of total production expenses.
2. Long Heating and Cooling Cycles
   Traditional processes take 5–7 days per batch, while new furnaces shorten this to 24–48 hours. However, cooling still requires 480 hours of natural still air cooling. Frequent furnace startups and shutdowns lead to thermal energy waste, further increasing energy consumption.
3. Energy Consumption in Auxiliary Processes
   • Crushing and Grinding: Petroleum coke must be crushed to a particle size of 10–20 mm, with grinding consuming significant electrical energy.
   • Purification (Acid Washing): Chemical reagents are used to remove impurities, adding process complexity without direct electricity consumption.
   • Gas Protection: Inert gases like argon or nitrogen are continuously supplied to prevent oxidation, requiring sustained operation of gas supply equipment.

II. Environmental Impact Analysis

1. Waste Gas Emissions
   • Low-Temperature Stage (Room Temperature–1,200°C): Calcium oxide (CaO) in the filler material (calcined petroleum coke) reacts with carbon to produce carbon monoxide (CO), while thermal decomposition generates methane (CH₄) and other hydrocarbon emissions.
   • High-Temperature Stage (1,200–2,800°C): Sulfur, ash, and volatile matter decompose, producing particulate matter and sulfur dioxide (SO₂). Without effective treatment, SO₂ emissions contribute to acid rain, while particulate matter degrades air quality.
   • Mitigation Measures: A combination of cyclone separators, three-stage alkaline scrubbers, and baghouse filters ensures treated emissions meet regulatory standards.
2. Wastewater and Solid Waste
   • Wastewater: Acid washing generates acidic wastewater requiring neutralization, while equipment cooling water contains oil contaminants necessitating separation and recovery.
   • Solid Waste: Screened-out filler material with substandard resistivity is bagged for sale or landfill disposal, posing soil contamination risks if mishandled.
3. Dust Pollution
   Dust is generated during crushing, screening, and furnace cleaning. Without enclosed collection systems, it endangers worker health and pollutes the environment.
   Control Measures: Dust is captured using suction cranes, hoods, and baghouse filters before being discharged through exhaust stacks.
4. Resource Consumption and Carbon Emissions
   • Water Resources: Significant water is used for cooling and cleaning, exacerbating water stress in arid regions.
   • Energy Structure: Reliance on fossil fuel-based electricity leads to CO₂ emissions. For example, producing one ton of graphite electrodes consumes 1.17 tons of standard coal, indirectly increasing carbon footprints.

III. Industry Response Strategies

1. Technological Upgrades
   • Promote new continuous vertical furnaces to shorten cycles and reduce energy consumption (electricity use drops to 3,500 kWh per ton).
   • Adopt microwave graphitization technology for ultra-fast heating (<1 hour) with focused energy delivery.
2. Environmental Governance
   • Waste Gas Treatment: Combust emissions at low temperatures and employ enclosed collection with multi-stage purification at high temperatures.
   • Wastewater Recycling: Implement water reuse systems to minimize freshwater intake.
   • Solid Waste Valorization: Repurpose substandard filler material as recarburizers for steel plants.
3. Policy and Industrial Synergy
   • Comply with regulations such as the Air Pollution Prevention and Control Law and Water Pollution Prevention and Control Law to enforce strict emission standards.
   • Advance integrated anode material projects by building in-house graphitization capacity to reduce reliance on external suppliers and minimize transportation-related pollution.

IV. Conclusion

The production of graphitized petroleum coke is a highly energy-intensive and polluting process, with energy consumption concentrated in high-temperature graphitization and environmental impacts spanning waste gas, water, solid waste, and dust pollution. The industry is mitigating these effects through technological advancements (e.g., continuous furnaces, microwave heating), environmental governance (multi-stage purification, resource recycling), and policy alignment (emission standards, integrated production). However, sustained optimization of energy structures—such as integrating renewable electricity—remains critical for achieving sustainable development.