Ensuring complete combustion of graphite petroleum coke is a complex process involving multiple steps. Petroleum coke, a byproduct of oil refining, is high in carbon, sulfur, and volatile matter, making its combustion more challenging than coal. Incomplete combustion results in energy waste, toxic emissions such as carbon monoxide (CO), and residual unburned carbon.
To achieve complete combustion, the classic "3T + 1E" combustion principle must be met simultaneously, adjusted to the characteristics of petroleum coke. The following are key conditions for ensuring complete combustion of graphite petroleum coke:
I. Core Combustion Principles (3T + 1E)
1. Temperature
Sufficiently High Temperature: The furnace temperature must be maintained sufficiently high (typically above 1200°C) to ensure that the petroleum coke particles are rapidly heated to their ignition point (petroleum coke has a high ignition point, approximately 450-600°C) and maintain a stable combustion reaction.
Uniform Temperature: The temperature distribution within the furnace should be as uniform as possible to avoid localized low-temperature zones, which would otherwise result in incomplete combustion of the petroleum coke in those areas.
2. Time
Sufficient residence time: Petroleum coke particles and their volatile components must remain in the high-temperature zone for a sufficient period of time to ensure complete combustion. Due to the low volatile content of petroleum coke, combustion is primarily focused on the burning of fixed carbon, a relatively slow process.
Measures: Ensure adequate flue gas travel and duration within the furnace by optimizing furnace design and adjusting burner position and angle. In fluidized bed boilers, material circulation can be used to extend the particle residence time.
3. Turbulence
Sufficient air mixing: This is one of the most critical conditions. Strong turbulence must be provided to ensure thorough and rapid mixing of air and petroleum coke particles.
Measures:
Rational air distribution: Utilize segmented air supply (e.g., primary, secondary, and tertiary air). Primary air is used to stabilize ignition and fluidization (in a fluidized bed), while secondary air, the main combustion air, is injected at high velocity to create strong turbulence and ensure mixing with the combustibles.
Optimize burner design: Use swirl burners or specially designed nozzles to create strong recirculation zones and vortices to enhance mixing. Ensure Sufficient Furnace Space: Provide ample space for air and fuel to mix.
4. Excess Air
Optimal Excess Air Ratio: Provide slightly more air than the theoretical air volume to ensure that every fuel particle has access to oxygen. However, excessive excess air should be avoided, as this will lower the furnace temperature, negatively impact combustion efficiency, and increase flue gas heat loss and sulfur oxide formation.
Control Range: For petroleum coke, the oxygen content in flue gas is typically controlled between 2.5% and 4.5% (the specific value depends on equipment and fuel characteristics), corresponding to an excess air ratio of approximately 1.15 to 1.25.
Summary: Checklist for Ensuring Sufficient Combustion
Fuel Preparation: Is the petroleum coke ground to a sufficient fineness? Is the feed material stable?
Temperature: Is the furnace temperature sufficiently high and uniform (>1200°C or 850-950°C for CFB)?
Time: Does the furnace design ensure sufficient residence time?
Turbulence/Mixing: Is staged air supply used? Is the secondary air sufficiently strong to penetrate the flue gas?
Excess air: Is the excess air ratio controlled within the optimal range based on flue gas analysis (O₂ and CO)?
Key indicator monitoring: Are CO levels and fly ash carbon content monitored in real time, used as a basis for adjustments?
By systematically meeting the above requirements and focusing on optimizing petroleum coke's difficult-to-burn properties, we can maximize its complete combustion and achieve highly efficient, low-pollution energy utilization.
