If you think that this entry will be about literature, you’ll be disappointed. It’s about the noise being generated right now around various thermodynamic cycles where heat is converted to work. Recently we’ve seen an upswell of interest in the Kalina Cycle harvest method and a number of companies have been chartered and funded to produce harvest systems for a variety of heat sources (like Exorka and Kalex.)

But just what is Kalina Cycle? Before we answer that, we need to take a look at basic Rankine Cycle (or sometimes called Carnot Cycle) harvest. It is a 4 stage process by which a working fluid is pressurized, heated to prompt phase change from liquid to gas, expanded through a harvest device (typically a turbine,) and then condensed. The cycle is closed loop in nature and forms the basis for virtually all electricity generation involving heat (geothermal, solar thermal, natural gas, coal, and nuclear – for the US, that’s 90+% of generation.)

Attribution: Andrew Ainsworth

A variation on theme is Organic Rankine Cycle which follows the same process as Rankine Cycle with the principal difference being the composition of the working fluid. In straight RC the working fluid is most often water. In ORC the working fluid tends to be a stable compound with a relatively low boiling point (i.e. isobutane or isopentane.) This is less efficient than RC but can harvest energy from heat sources from 75-150C where RC requires 250C and higher temperatures to function well.

Thus we come to Kalina Cycle, really a variation on ORC (and thus RC.) It was proposed by Alexander Kalina about 20 years ago. KC follows the same process as RC, but again changes the composition of the working fluid from a single stable compound with a low boiling point to a two part working fluid (most often ammonia/water mixture) which can, under certain circumstances, increase the efficiency of ORC harvest of relatively low temperature resources.

Of the 3 related conversion cycles, RC and ORC are in wide use today. Kalina Cycle is still gaining steam, so to speak.

This entry was posted on Friday, May 2nd, 2008 at 6:54 am and is filed under Geothermal, Research.