Fired heaters flame impingement

Startup heaters - electrical or direct-fired types - are used to heat synthesis gas for the converter dining startup. Some of the problems encountered with these heaters are hydrogen-induced tracks, overheating and flame impingement, thinning at bends, and furnace explosions. Normally, SS321 is used for startup heater coils and the downstream pipeline88. 

Operators use furnace cameras to remotely view burners in the numerous fired heaters that are heating this oil to spot such performance defecfs as flame impingement, flames that are burning too low, clogged burners, irregular flame patterns, flashback, flames thaf are producing too much pollution, or oil spillage. 

Camera approach Visually observe the waterwall or refractory wall directly to be certain flames are not touching the walls, causing potentially catastrophic leaks at sites like crude oil (fired) heaters. Besides spotting flames contacting the external tube surface inside the firebox, the camera can also spot other signs of impingement like tubes with a cherry-red color or bulges in the tube walls [12]. 

Flame Impingement. The most common reliabihty hazard for fired heaters. 

Operators understand the importance of maintaining fired heaters in a safe and rehable condition. The response from operators to this priority could go to another extreme run fired heaters with too much excess air. The result of much excess air is much reduced flame length and thus the risk of flame impingement is minimized. 

I feel the need to provide additional comments on excess air as many plants have an O2 reduction program. O2 reduction (or minimum excess air) must be built upon the basis of proper draft control. Minimum excess air for the fired heater can be obtained when it is reduced to the point where combustibles begin to appear in the stack. For modern fired heaters, this occurs at 8% excess air equivalent to 1.8% of oxygen level in the flue gas. However, practical constraints prevent achieving this minimum excess air in operation, and these constraints include variations in fuel quality, feed rates, and other process variables. Thus, operation without flame impingement sets the limit for practical minimum excess air. The optimal flue... 

Figure 8.3 Classical tube rupture of a fired heater from flame impingement on a blocked-in heater tube.

The types of problems a fired heater or furnace system typically encounters include flame impingement on tubes, coke buildup inside the tubes, hot spots inside the furnace, fuel composition changes, burner flameout, control-valve failure, and feed-pump failure. 

During normal operations, checklists and samples are collected as advanced instrumentation monitors the process. The types of problems a fired heater or furnace system typically encounter include flame impingement on tubes, coke buildup inside the tubes, hot spots inside the furnace, fuel composition changes, burner flameout, control valve failure, and feed-pump failure. Other problems may include incorrect temperature indicator readings, failure of oxygen analyzers, oxygen leaks on the furnace, and the unexpected shutdown of downstream equipment. A fired heater system is designed to run almost continuously, 24 hours a day, 7 days a week. The operational team is in place to ensure that the equipment and systems operate safely, effectively, and produce a quality product that meets or exceeds customer expectations. 

Why do operators often run with too much air and hence waste energy For one thing the flame temperature is reduced. Also, more excess air produces more flue gas. This increases heat pickup in the convective section. Finally, flame length is shortened and flame impingement is reduced. These factors make it easier to fire the heater without overheating the tubes. Unfortunately, the price must be paid in lost furnace efficiency and wasted energy. 

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