Shell and coil heat exchanger

A heat exchanger comprising:

• a shell having:
• a tubular outer wall having a first and second end, a tubular inner wall having a first and second end coaxial with said outer wall, and first and second end plates attached to the first and second ends of the outer and inner walls to form an enclosed tubular shell cavity therebetween having a first and second end;
• means for admitting a first fluid into said shell cavity;
• means for removing the first fluid from the shell cavity;
• a spiral coil of tubing having a first and second end sealingly exiting through the shell cavity wall for carrying a second fluid therebetween, said spiral coil lying within the shell cavity and having a plurality of spiral windings formed about the axis thereof, the spiral coil sized to fit between the inner and outer shell wall with limited radial clearance to allow limited axial flow of the first fluid, said winding axially spaced from one another to define a spiral flow path therebetween for the first fluid, said radial clearance and axial spacing relatively sized to induce the first fluid to travel in a substantially spiral motion to enhance the heat transfer between the first and second fluids;
• an auxiliary coil of tubing having a first and second end sealing extending through the shell cavity for carrying a third fluid therebetween, said auxiliary coil lying within the shell cavity and having a plurality of windings formed about the axis thereof and axially spaced apart from the spiral coil, for transferring heat between the first and third fluids;
• and
• a divider plate dividing the shell cavity into two coaxial cylindrical regions, a primary region in which lies the spiral coil and an auxiliary region in which lies the auxiliary coil, and means to admit and means to remove a fourth fluid from the auxiliary region.