Typical Steam Cycle

Figure 32 Rankine Cycle With Real v.s. Ideal

Thermodynamics Heat Transfer and Fluid Flow Volume 1 of 3
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SECOND LAW OF THERMODYNAMICS Thermodynamics The same loss of cycle efficiency can be seen when two Rankine cycles are compared (see Figure 33). Using this type of comparison, the amount of rejected energy to available energy of one cycle can be compared to another cycle to determine which cycle is the most efficient, i.e. has the least amount of unavailable energy. An h-s diagram can also be Figure 34 h-s Diagram used to compare systems and h e l p d e t e r m i n e t h e i r efficiencies. Like the T-s diagram, the h-s diagram will show (Figure 34) that s u b s t i t u t i n g n o n - i d e a l components in place of ideal components in a cycle, will result in the reduction in the cycles efficiency. This is because a change in enthalpy (h) always occurs when work is done or heat is added or removed in an actual cycle (non-ideal). This deviation from an ideal constant enthalpy (vertical line on the diagram) allows the inefficiencies of the cycle to be easily seen on a h-s diagram. Typical Steam Cycle Figure 35 shows a simplified version of the major components of a typical steam plant cycle. This is a simplified version and does not contain the exact detail that may be found at most power plants. However, for the purpose of understanding the basic operation of a power cycle, further detail is not necessary. The following are the processes that comprise the cycle: 1-2: Saturated steam from the steam generator is expanded in the high pressure (HP) turbine to provide shaft work output at a constant entropy. 2-3: The moist steam from the exit of the HP turbine is dried and superheated in the moisture separator reheater (MSR). 3-4: Superheated steam from the MSR is expanded in the low pressure (LP) turbine to provide shaft work output at a constant entropy. HT-01 Page 90 Rev. 0

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