Relationship Between Natural Gas Inlet Pressure, Air Inlet Pressure, and Combustion Pressure
Combustion is a controlled chemical reaction where fuel and air mix to release heat energy. In industrial boilers, furnaces, and gas turbines, the balance of pressures—natural gas inlet pressure, air inlet pressure, and combustion chamber pressure—plays a critical role in ensuring safe, efficient, and stable operation.
🔍 Combustion Chamber Pressure
- The combustion chamber pressure is primarily determined by downstream equipment such as exhaust fans, induced draft (ID) fans, or tall stacks.
- These systems create a negative draft relative to ambient atmospheric pressure, preventing the flame from moving backward into the air supply.
- In practice, combustion chamber pressure is slightly lower than atmospheric pressure to maintain safe flame direction and proper exhaust flow.
⚙️ Natural Gas Inlet Pressure
- Natural gas must always enter the combustion chamber at a higher pressure than both air inlet pressure and combustion chamber pressure.
- This ensures:
- Proper fuel flow into the chamber.
- Prevention of backflow of air into the gas supply line (which could be hazardous).
- If gas pressure is too low, combustion becomes unstable, and if it is equal to or lower than chamber pressure, dangerous reverse flow may occur.
🌍 Air Inlet Pressure
- Air is supplied by forced draft (FD) fans or natural draft systems.
- The rate of airflow depends on the rate of fuel flow—more fuel requires more air to maintain the correct air-fuel ratio.
- Adequate excess air is necessary for complete combustion.
- If air pressure is too low, incomplete combustion occurs, leading to carbon monoxide (CO) formation, soot deposits, and reduced efficiency.
- Typically, there is a pressure drop across the burner as air mixes with fuel in a high-velocity zone.
🔥 Relationship Between Pressures
1. Natural Gas Pressure > Air Pressure > Combustion Chamber Pressure
- Ensures proper fuel delivery and safe flame stability.
2. Combustion Chamber Pressure
- Controlled by downstream draft equipment.
- Must remain slightly negative relative to atmosphere to prevent flame blowback.
3. Air Pressure
- Must be sufficient to provide excess oxygen for complete combustion.
- Directly linked to fuel flow rate and fan capacity.
4. Gas Pressure
- Must always exceed chamber pressure to avoid contamination and backflow.
📊 Summary Table
📌 Conclusion
The relationship between natural gas inlet pressure, air inlet pressure, and combustion chamber pressure is fundamental to safe and efficient combustion:
- Natural gas pressure must always be higher to ensure proper fuel delivery.
- Air pressure must be sufficient to provide excess oxygen for complete combustion.
- Combustion chamber pressure is controlled by downstream draft equipment and kept slightly negative to maintain flame stability.
By carefully balancing these pressures, industries can achieve efficient combustion, reduced emissions, and safe operation of boilers, furnaces, and gas turbines.