Design of Fired Heater Tube Protection in Oil Production Application

Photo of Austin Godfrey, Jaron Guevara, Bryan Philpott, Sigmund Sognesand Students: Austin Godfrey, Jaron Guevara, Bryan Philpott, Sigmund Sognesand

Sponsor: Chevron

Date: Spring 2013

Requirements:
Two important constraints on the design are the required temperatures on the external and internal surfaces of the tubes. The temperature of the external tube wall should stay above the dew point of the sulfur gases in the flue stream, around 280°F, to prevent acids from condensing onto and corroding the heater tubes. The temperature of the internal fluid film temperature must remain below about 225°F, the temperature at which serious internal corrosion and deposits start to form. Satisfying these temperature constraints should increase the service life of the heater tubes to a minimum of 5 years. The coating or lining should not unduly restrict the flow: the flow must remain turbulent and the pressure drop must be minimized. Relative cost, efficiency, and lead-time are also important considerations for any final design.

Problem:
Design an internal tube protection system for an all-convection direct fired heater in an oil-water separation application, including coating or lining thickness, material options, and possible manufacturing methods, with the goal that the coating or lining will provide sufficient thermal and material resistance to eliminate the existing corrosion and deposit issues inside and outside the heater tubes.

Solution:
The team analyzed the heater transfer characteristics of the heater system and identified the types of internal coating systems that can provide the required temperature control. Using a single thickness coating throughout the heater was shown to be inefficient if not impossible due to temperature constraints. However, by varying coating thickness row by row, a more thermally efficient coating distribution can be implemented on the interior of the tubes that not only protects the interior from corrosion, but also raises the exterior temperatures to 280°F or higher in order to prevent corrosion. The team also recommends that Chevron investigate the possibility of fabricating the heater tubes out of materials that are more corrosion-resistant; this by itself could extend the life of the tube bundles. A thermal analysis application was developed to design a coating system. Once a material and coating are selected, the material properties of each may be used to calculation an appropriate coating distribution inside the heater.

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