Center firing indirect heat exchanger for spray drying and controls for same

An apparatus for providing continuous heated process air to a spray dryer, said device transferring heat from combustion air to process air, said combustion air travelling along a combustion air path, and said process air travelling along a process air path, said apparatus comprising:

• A) an elongate center firing tube in the center of said apparatus, said elongate center firing tube having an inlet end and an outlet end, a longitudinal axis, and also having a cylindrical firing tube outer wall assembly defining a portion of said combustion air path;
• B) an elongate outer annular sleeve assembly having a longitudinal axis substantially parallel to said longitudinal axis of said elongate center firing tube, said elongate outer annular sleeve assembly facilitating heat transfer therein from combustion air to process air and including:
• 1) A cylindrical annular sleeve outer wall assembly, said cylindrical annular sleeve outer wall assembly combining with said cylindrical firing tube outer wall assembly to define an annular heat transfer space therebetween, said annular heat transfer space having a first end and a second end and defining a part of said combustion air path and also defining a part of said process air path;
• and
• 2) A plurality of elongate heat transfer tubes within said annular heat transfer space and having heat transfer tube walls intermediate said two paths such that said heat transfer tube walls define part of said combustion air path and also define part of said process air path, such that heat may be transferred through said heat transfer tube walls from said combustion air to said process air;
• C) a redirection member configured to accept combustion air exiting said outlet end of said elongate center firing tube and to redirect said combustion air in an opposite direction into said inlet end of said annular heat transfer space of said elongate outer annular sleeve assembly,
• such that said combustion air path begins at said inlet end of said elongate firing tube, then passes out of said outlet end of said elongate firing tube, is then redirected in a substantially opposite direction into said first end of said annular heat transfer space, then passes through the inside of said plurality of elongate heat transfer tubes within said annular heat transfer space, and then exits said second end of said annular heat transfer space, and
• such that said process air path enters through said second end of said annular heat transfer space and receives heat upon entering and contact with the inside of said plurality of elongate heat transfer tubes before exiting said first end of said annular heat transfer space.

An apparatus for providing continuous heated process air to a spray dryer, said device transferring heat from combustion air to process air, said combustion air travelling along a combustion air path, and said process air travelling along a process air path, said apparatus comprising:

• A) an elongate center firing tube in the center of said apparatus, said elongate center firing tube having an inlet end and an outlet end, a longitudinal axis, and also having a cylindrical firing tube outer wall assembly defining a portion of said combustion air path;
• B) an elongate outer annular sleeve assembly having a longitudinal axis substantially parallel to said longitudinal axis of said elongate center firing tube, said elongate outer annular sleeve assembly facilitating heat transfer therein from combustion air to process air and including:
• 1) A cylindrical annular sleeve outer wall assembly, said cylindrical annular sleeve outer wall assembly combining with said cylindrical firing tube outer wall assembly to define an annular heat transfer space therebetween, said annular heat transfer space having a first end and a second end and defining a part of said combustion air path and also defining a part of said process air path;
• and
• 2) A plurality of elongate heat transfer tubes within said annular heat transfer space and having heat transfer tube walls intermediate said two paths such that said heat transfer tube walls define part of said combustion air path and also define part of said process air path, such that heat may be transferred through said heat transfer tube walls from said combustion air to said process air;
• C) a redirection member configured to accept combustion air exiting said outlet end of said elongate center firing tube and to redirect said combustion air in an opposite direction into said inlet end of said annular heat transfer space of said elongate outer annular sleeve assembly,
• D) a recirculation apparatus which accepts at its inlet a recirculated portion of combustion air from said second end of said annular heat transfer space, and inserts said recirculated portion into said inlet end of said elongate center firing tube to be combined with other combustion air entering said inlet end of said elongate center firing tube,
• such that said combustion air path begins at said inlet end of said elongate firing tube, then passes out of said outlet end of said elongate firing tube, is then redirected in a substantially opposite direction into said first end of said annular heat transfer space, then passes through the inside of said plurality of elongate heat transfer tubes within said annular heat transfer space, and then exits said second end of said annular heat transfer space, and
• such that said process air path enters through said second end of said annular heat transfer space and receives heat upon entering and contact with the inside of said plurality of elongate heat transfer tubes before exiting said first end of said annular heat transfer space, and
• such that said recirculated portion of combustion air from said second end of said annular heat transfer space is inserted into said inlet end of said elongate center firing tube to be combined with other combustion air entering said inlet end of said elongate center firing tube.