Firetube having thermal conducting passageways

Abstract

A firetube is immersed in a fluid to be heated and transfers heat from hot gases flowing through the firetube to the fluid surrounding the firetube. The firetube has a plurality of thermally conductive passageways which extend through the firetube for increasing the surface area available for heat transfer. Fluid is conducted through the passageways by a thermosiphon effect resulting from a temperature differential in the vessel, the fluid below the firetube being cooler and denser than fluid above the heat exchanger.

1 . A firetube adapted to extend horizontally into a vessel for heating fluid therein, the firetube having a gas inlet, a gas outlet and at least one flowpath therebetween, the firetube conducting hot gases along the flowpath from the gas inlet to the gas outlet, the firetube comprising:
 a plurality of passageways spaced along the flowpath for passing fluid upwardly therethrough, each passageway extending generally upwardly from a fluid inlet at a lower portion of the firetube to a fluid outlet at an upper portion of the firetube and having a thermally conductive wall extending through the flowpath for conducting heat from the hot gases to the fluid passing therethrough.   
     
     
         2 . The firetube of  claim 1  wherein the flowpath is generally U-shaped from the gas inlet to the gas outlet. 
     
     
         3 . The firetube of  claim 2  wherein the generally U-shaped flowpath comprises
 a U-tube conduit having the gas inlet adjacent the gas outlet at a common header wall, the plurality of passageways being spaced along the U-tube conduit. 
 
     
     
         4 . The firetube of  claim 2  wherein the firetube is a hollow body having body walls, the gas inlet being adjacent the gas outlet at a common header wall, the generally U-shaped flowpath comprising:
 at least one dividing wall extending from between the gas inlet and the gas outlet, partially along the hollow body from the common header wall and toward a tube end, wherein 
 the gases are directed to flow along the U-shaped flowpath from the gas inlet, about a distal end of the at least one dividing wall, and to the gas outlet. 
 
     
     
         5 . The firetube of  claim 2  wherein at least some of the plurality passageways are distributed laterally across the flowpath. 
     
     
         6 . The firetube of  claim 4  wherein
 at least some of the plurality of passageways are integral with the at least one dividing wall. 
 
     
     
         7 . The firetube of  claim 6  wherein passageways integral with the at least one dividing wall are substantially aligned and connected therebetween by plates to urge gas along the U-shaped flowpath. 
     
     
         8 . The firetube of  claim 1  wherein the flowpath comprises two side-by-side flowpaths. 
     
     
         9 . The firetube of  claim 8  wherein the firetube is a hollow body having enclosing body walls, the gas inlet being adjacent the gas outlet at a common header wall, the two, side-by-side flowpaths comprise:
 a first dividing wall, intermediate the gas inlet and the gas outlet, and extending from the common header wall toward a tube end,; 
 a second dividing wall extending from the common header wall intermediate the gas inlet; and 
 a third dividing wall extending from the common header wall intermediate the gas outlet, 
 wherein gases flow along the two, side-by-side flowpaths from the gas inlet, about distal ends of the first, second and third dividing walls and to the gas outlet, 
 
     
     
         10 . The firetube of  claim 9  wherein:
 the distal end of the second dividing wall and the distal end of the third dividing wall art are connected; and wherein 
 a first flowpath of the side-by-side flowpaths is formed from the gas inlet, between the first and second divider walls, and to the gas outlet between the first and third divider walls, and 
 a second flowpath of the side-by-side flowpaths is formed from the gas inlet, between the first divider wall and the body walls, and to the gas outlet between the first divider wall and the body walls. 
 
     
     
         11 . The firetube of  claim 1  wherein the thermally conductive passageways are pipes extending substantially vertically through the firetube. 
     
     
         12 . The firetube of  claim 1  further comprising a vortex generator at one or more of the passageway fluid inlets. 
     
     
         13 . A heat exchanger for a vessel comprising the firetube of  claim 1 , wherein
 the vessel is a direct-fired vessel and the fluid is a process fluid to be heated by the firetube, the firetube being immersed in the process fluid.   
     
     
         14 . The heat exchanger of  claim 13  wherein each of the plurality of passageways has a diameter from about 15% to about 18% of a diameter of the inlet. 
     
     
         15 . A heat exchanger for a vessel comprising the firetube of  claim 1 , wherein
 the vessel is an indirect-fired vessel and the fluid is a heat transfer fluid to be heated by the firetube, the heat exchanger further comprising a fluid-to-fluid heat exchanger for flowing a process fluid therethrough, the fluid-to-fluid heat exchanger being immersed in the heat transfer fluid.   
     
     
         16 . The heat exchanger of  claim 15  wherein the heat transfer fluid is glycol. 
     
     
         17 . The heat exchanger of  claim 13  wherein
 the firetube is obround in cross-section and is installed through an obround manway formed in the vessel.