B-1N
B-1
B-6N
B-2N
B-2
B-4
B-5N
B-3N
B-3
B-4N
Figure 3 Burner reconfiguration
refinery fuel gas rich in heavier components to very light ‘hydrogen-rich’ fuel gas.1 Another commonly seen occurrence is burner flames reaching the arch location. This is especially prevalent in older furnaces, where burner deterioration over the years of combustion may not give the same level of optimised operation and flame shape. To make the situation worse, tramp air leakage in old furnaces may force the arch oxygen analyser to indicate a false sense of excess air operation, although the burners may actually be starved. In practice, this situation forces the burner flames to rise higher in the furnace box, searching for alternate sources of oxygen, such as tramp air. See Figure 2 , wherein flames almost touching the internal crossover tubes could be viewed from the arch level peep doors. During one of these critical revamps, the heater operation was limited due to high BWT, especially during the end-of-run operating days. A detailed assessment revealed that, apart from the burner tips being worn out over a long period of operation, the heater was constantly operated at a higher duty than its design allowed. The existing burners had been in operation for more than 20 years, and the increased heat duty meant that the flame height could have gone higher. This forced a burner reconfiguration during the revamp. The number of burners was increased from four to six, all fitting within the same firebox. Adequate care was taken to ensure that the burner-to- burner spacing, burner-to-tube spacing, and the ratio of the burner circle diameter to the tube circle diameter criteria were met according to the latest American Petroleum Institute (API) guidelines (see Figure 3 ).
pressurisation. Thus, instead of going for a full- fledged, elaborate furnace revamp, a simpler option of auxiliary equipment replacement could resolve the issue. An important point to consider is the impact of this flue gas quenching on the metallic components of the cast APH and ID fan, as well as downstream locations. It is possible that the metal at these locations was operating near or below the flue gas dew point, which, in the long run, can lead to rapid corrosion. At times, monitoring the system may help achieve not just the unit capacity, but also help in damage prevention and increased equipment life. High firebox or Bridgewall temperature leading to limitation in firing Firebox temperature, also known as Bridgewall temperature (BWT) in fired heater parlance, is the most common indication of fired heater health. As fever is an indication of an unhealthy human body, an elevated BWT is the same for a fired heater. The BWT can be elevated due to multiple reasons. The most common reasons include a high degree of coke formation inside the heater coil or even a minor inorganic layer of deposit outside the coil. However, there can be many other reasons. One such reason is the transition of furnace fuel from traditional Figure 2 Flames observed up to convection to the radiant internal crossover lines
Refining India
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