The CHAT cycle

A modification of the HAT cycle has been proposed by Nakhamkin [11], which is known as the cascaded humid air turbine (CHAT). The higher pressure ratios required in humidified cycles led Nakhamkin to propose reheating between the HP and LP turbines. Splitting the expansion in this way is paralleled by splitting the compression, and enables the HP shaft to be non-generating, as indicated in Fig. 6.15. This implies that the capital cost of the plant can be reduced, but the cycle is still complex. 

---

The CHAT cycle may be seen as a low loss evaporative development of the dry intercooled, reheated regenerative cycle [CICBTBTX]. It offers some thermodynamic advantage—increase in turbine work (and heat supplied ) with little or no change in the compressor work, leading to an increased thermal efficiency and specific work output. 

Macchi et al. did not undertake parametric studies of the CHAT cycle and there appears to be no comparably thorough examination of this cycle in the literature but Nakhamkin describes a prototype plant giving a thermal efficiency of some 55% at a very high pressure ratio, i.e. about 70, compared with the dry CICBTBTX cycle optimum of about 40 shown in Fig. 6.17. 

---