Various options for reducing the TMT of a vacuum heater, such as changing the transfer line size and adding extra surface area in the radiation and convection sections, are examined here. The best option generally depends on the limitations under which the heater operates with regard to the process requirements and the downstream equipment limitations and flexibility.
In a Saudi Aramco refinery, a vacuum furnace was found to be operating at a high tube metal temperature (TMT) and was forced to shut down before the normal run length of five years. The coke laydown was also found to be substantial. An evaluation revealed that the furnace outlet temperature and pressure were operating at much higher values, compared to the design values, to maintain the same flash zone conditions at the vacuum tower.
This scenario was the result of a change in furnace location, which increased the transfer line length by 200 meters (m). The increase in transfer line length resulted in an additional pressure drop of 120 millimeters (mm) of mercury, which increased the fur
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