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Our client refinery has a Crude Heater in the Crude Unit. A Crude Heater is a balanced draft, box type, horizontal tube radiant heater, having a common convection section on top. The heater was originally built in 1968 for 423.2 MM Btu/hr heat duty. The convection section is designed to preheat oil feed and also superheat steam from 371 to 450°F.
The flue gases leaving the steam superheater are further cooled in a combustion air preheater, before being let off in the stack. The Air Preheater supplies preheated air to the furnace for combustion. The flue gas temperature leaving the convection section as per the original design was 550°F. Valero was experiencing stack temperatures as high as 810 to 850°F.
Furnace Improvements performed an engineering study for NOx reduction on this furnace and modeled the furnace with Ultra Low NOx burners. It was found that the radiant tubes in this heater had been suffering from high tube metal temperature and flame impingement. The convection section was inefficient and the air preheater operating temperature was reaching the metallurgical limits.
Furnace Improvements modified the convection section and reduce the relative coking rates. The relative coking rates in the existing convection section and the proposed retubed convection section are shown in the graph below.
Valero accepted our recommendations and immediately assigned Furnace Improvements for the NOx reduction and performance improvement project. |
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