Q&A: Is it a normal practice to shut down some burners when operating at low capacity?
Our experts’ recommendations for fired heaters:
In normal practice, for fired heaters, it is recommended to operate all the burners at lower capacity so that all passes and all tubes can get equal heat. However, due to some constraints in the heater (e.g. due to higher than required heat release even at burner turndown or unacceptable fuel pressure when operating below burner turndown), it may not be possible to operate or control all the burners. In case a few burners may be shut-down, ensure that all the operated burners are being rotated periodically, so that all passes and consequently all tubes are equally heated. In case burners have to be turned off, their air register shall be closed.
Our expert’s recommendations for Steam Methane Reformers:
The principle is very similar to the one of fired heaters, since usually SMR run a few hundred degrees hotter than fired heaters, even at turndown conditions. As a general rule, it is recommended not to turn the burners off. Despite this recommendation, in case burners have to be turned off, the air register shall be left open to some degree in order to cool down the burner fuel tips which do not benefit any longer from cold fuel flow.
There are mainly two types of SMR (side-fired and top-fired).
- Side-fired SMR: the single burner tip has a big size of nozzle which is conceived as a black body which absorbs a lot of heat, and excess heat should be avoided as this can lead to tips cracking.
- Top-fired SMR: due to the buoyancy effect even if air is coming up to the burner tips, there is still heat from the box that’s coming up. Therefore, even if the air register is open, those tips will not see the air.
Standard Turndown practice: Pay special attention during burners test to maintain the flame stability at low turndown rates.
William Han, Syngas Technology Director ROC Americas
Amit Gupta, Director Furnace Technology and Proposal, ROC Americas