Heat recovery and power generation from industrial process streams

A method of recovering work from a process having at least a first and a second process stream which comprises:

• (1) transferring heat in a first heat exchange zone in a first temperature range from the first process stream to a selected working fluid comprising at least two components to yield a heated and pressurized vapor-containing working fluid at a first temperature and a cooled first process stream, wherein the selected working fluid has a given composition;
• (2) work expanding the heated and pressurized vapor-containing working fluid in an expansion turbine to generate work, and withdrawing therefrom a cooled expanded working fluid;
• (3) transferring heat from the cooled expanded working fluid to the second process stream in a second heat exchange zone in a second temperature range which is lower than the first temperature range, thereby heating the second process stream and condensing at least a portion of the cooled expanded working fluid to yield a condensate-containing working fluid;
• (4) returning the condensate-containing working fluid to the first heat exchange zone to provide the selected working fluid of step (1);
• and
• (5) changing the given composition of the selected working fluid in response to a change in the first temperature range, a change in the second temperature range, or changes in both the first and second temperature ranges.