Rankine cycles advantage

The Rankine cycle diagram placed adjacent the Brayton cycle in Figure 9-15 is indicated as a simple steam cycle with superheat, but no reheat and no multi-pressure steam generation. The thermodynamic advantage of the Rankine bottoming cycle is the lowered temperature of heat rejection, in the steam condenser, from the overall combined cycles. 

Another advantage is that the IGCC system generates electricity by both combustion (Brayton cycle) and steam (Rankine cycle) turbines. The inclusion of the Brayton topping cycle improves efficiency compared to a conventional power plant s Rankine cycle-only generating wstem. Typically about two-thirds of the power generated comes from the Brayton cycle and one-third from the Rankine cycle. 

What are the advantages of a Rankine cycle in the compression process ... 

There are situations where it is desirable to combine several cycles in series in order to take advantage of a very wide temperature range or to utilize what would otherwise be waste heat to improve efficiency. Such a cycle is called a cascaded cycle. A cascaded cycle made of three Rankine cycles in series is shown schematically in Fig. 5.1. The cascaded cycle is made of three subcycles. Subcycle A, 1-2-3-4-1, is the topping cycle subcycle B, 5-6-7-8-S, is the middle cycle and subcycle C, 9-10-11-12-9, is the bottom cycle. The waste heat of the upstream cycle is the heat input of the downstream cycle. Since the net work output is equal to the sum of the three outputs and the heat input is that of the topping cycle alone, a substantial efficiency increase is possible. 

COMMENTS The advantage of using reheat is to reduce the moisture content at the exit of the low-pressure turbine and increase the net power of the Rankine power plant. The one reheat Rankine basic cycle shown in Fig. 2.13 can be expanded into more than one reheat if desired. In this fashion it is possible to use higher boiler pressure without having to increase the maximum superheater temperature above the limit of the superheater tubes. 

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