During coal-to-oil boiler operation, unburned fuel is a key risk factor for explosion. The key to this is controlling the synergistic effect of combustible material concentration and ignition sources within the furnace. Unburned fuel accumulates in the form of droplets or flammable gases. When the concentration reaches the explosive limit and encounters hot surfaces, open flames, or static sparks, it can easily cause deflagration or even explosion. Therefore, a protective system must be established encompassing four dimensions: fuel supply, combustion control, safety monitoring, and emergency response.
The tightness of the fuel system is the first line of defense against leaks. After a coal-to-oil boiler conversion, the raw coal pulverized pipeline must be completely dismantled. Fuel lines should be welded using seamless steel pipe to prevent minor leaks at flange joints. Fuel storage tanks should be equipped with level alarms to prevent overflow due to excessive oil levels. Breather valves should also be installed to balance the internal pressure and prevent tank collapse or rupture due to blockage. A check valve should be installed at the fuel pump outlet to prevent fuel backflow when the pump is shut down, causing pipeline vibration and loosening of joints.
Burner performance directly impacts fuel atomization and combustion efficiency. Coal-to-oil boilers require mechanical or air-atomizing burners that match the furnace structure. Ensure that the fuel particle diameter is less than 50 microns to shorten the volatile analysis time. Burner nozzles should be inspected regularly to prevent atomization angle deviation due to carbon deposits or wear, which could cause the oil mist to directly impact the water-cooled walls and cause localized oil accumulation. Fuel temperature must be controlled within the appropriate viscosity range, no less than 40°C for light fuel and no less than 120°C for heavy fuel, to avoid poor atomization due to excessive viscosity.
The air-to-coal ratio is a key parameter for controlling combustion completeness. During operation, the primary and secondary air ratios must be adjusted based on the fuel's calorific value to ensure rapid mixing of the fuel with the air upon entering the furnace. A staged air supply strategy should be adopted during initial startup: initially introducing a small amount of secondary air to stabilize the flame, then gradually increasing the air volume to enhance combustion. During low-load operation, the secondary air damper opening can be adjusted to maintain the furnace outlet oxygen level between 3% and 6% to prevent carbon particles from adsorbing on the heating surfaces and causing secondary combustion due to oxygen deficiency.
Monitoring furnace negative pressure is a key measure for preventing deflagration. Coal-to-oil boilers should be equipped with a high-precision negative pressure gauge to monitor furnace pressure changes in real time. If the negative pressure fluctuates by more than ±50 Pa, the burner operation or fuel supply system must be checked immediately. Excessively low negative pressure can cause flame spillage and trigger an external deflagration; excessively high negative pressure can allow cold air to leak in, lowering furnace temperature and affecting combustion stability. Furthermore, pressure transmitters must be calibrated regularly to prevent instrument errors from causing safety thresholds to fail.
Ignition and flameout protection are the final defense against the accumulation of combustibles. When starting a coal-to-oil boiler, the "ignition first, then fuel addition" sequence must be followed. The ignition gun energy must meet the fuel ignition requirements, and ignition must be maintained for 3-5 seconds before adding the main fuel. If flameout occurs during operation, the fuel supply must be immediately shut off, and the furnace must be purged at 30% of the rated air volume for at least 5 minutes to ensure that the combustible concentration is below the lower explosion limit. The fuel quick-shut valve must be calibrated monthly to ensure that the fuel supply is shut off within 0.5 seconds.
Routine maintenance is fundamental to ensuring the long-term safety of the system. Coal-to-oil boilers require regular cleaning of burner nozzle carbon deposits, inspection of the fuel filter pressure differential, and timely replacement of clogged filter elements. The furnace interior should undergo quarterly endoscopic inspections to remove ash and coke deposits from the heating surfaces to prevent localized overheating due to increased thermal resistance. Safety accessories such as safety valves and pressure gauges must also be regularly calibrated to ensure timely activation in the event of overpressure.
The safe operation of a coal-to-oil boiler depends on the coordinated function of the fuel system, combustion equipment, monitoring instrumentation, and operating procedures. By strengthening equipment sealing, optimizing combustion control, improving the monitoring system, and strictly adhering to operating regulations, the risk of explosions caused by unburned fuel can be effectively reduced, ensuring the long-term stable operation of the boiler after the coal-to-oil conversion.
