Explosion, heater firebox

The correct way to prevent this sort of firebox explosion is to use firebox purge steam. A typical heater firebox might have a half dozen 3-in purge steam connections. The idea is to displace the air in the firebox with steam. Then, the flows of combustible process liquid and fuel gas may be safely stopped, without fear of entering the explosive region. This purge steam is different from the purge steam used in the heater s tubes. 

Fired heaters are extensively used in the oil and gas industry to process the raw materials into usable products in a variety of processes. Fuel gas is normally used to fire the units which heat process fluids. Control of the burner system is critical in order to avoid firebox explosions and uncontrolled heater fires due to malfunctions and deterioration of the heat transfer tubes. Microprocessor computers are used to manage and control the burner system. 

Fires involving liquid process streams are the most common heater loss. Most involve a ruptured process stream tube leading to a firebox fire or a pool fire under or near the heater. The two most common causes are failure of the tubes due to overheating and rupture of the tubes as the result of a fire box explosion. 

What will happen is that flames and black smoke will pour out of the heater s stack. It looks very bad, very dangerous, but it is really not. There is not enough excess oxygen in the firebox to cause a very high temperature. The combustion gases, or flue gas, are too fuel-rich to explode. We say that the flue gas is above the explosive region. 

The lighting of fired heaters has the potential to create an explosion. Two issues are of particular concern. The first is that the firebox is filled with a flammable mixture of hydrocarbon gas and air (oxygen). If a burner is ignited, an explosion will occur. The second concern is that a furnace is operating normally, and then the fuel gas supply fails thus causing the burner flames to go out. If the fuel gas supply is then restored, an unbumed mixture of gas and air can enter the hot fire box and ignite. 

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