Patent ID: 8490581

Claim:
A fired heater unit comprising: a forced draft blower unit for supplying ambient air to the fired heater unit under positive pressure such that the fired heater unit is maintained under positive pressure; an air preheater unit operatively connected to the forced draft blower unit; at least one radiant heating section, wherein each of the at least one radiant heating section having a heating element located therein for heating flue gas entering the radiant heating section, and a plurality of vertically extending radiant tubes having process fluid flowing therethrough spaced from the heating element, wherein the air preheater unit is operatively connected to the at least one radiant heating section; a convection section operatively connected and laterally positioned with respect to the at least one radiant heating section, wherein the convection section having a plurality of parallel vertically oriented convection tubes, wherein each convection tube being operatively connected to the at least one radiant heating section, wherein each convection tube having an inner tube operatively couple to one of the radiant tubes and having process fluid flowing therethrough, wherein each inner tube having more than one vertically extending section such that each inner tube making more than one pass through the convection section, and at least one outer tube extending along a predetermined portion of the inner tube, wherein each vertically extending section of the inner tube is laterally spaced and substantially parallel to the vertically extending radiant tubes, wherein each vertically extending section having an outer tube associated therewith, and each outer tube being spaced from the inner tube to form a vertical flow path therebetween, wherein the flow path having a first open upper end and a second open lower end, wherein the first open upper end of the vertical flow path is operatively connected to the at least one radiant heating section, wherein flue gas from radiant heating section enters the flow path through the first open upper end from the at least one radiant heating section and travels in a downwardly direction through the vertical flow path to the second open lower end.