Consider the following statements regarding Reheat Rankine steam cycle:

1. The main purpose of reheat in Rankine cycle is to increase the efficiency of the cycle.

2. In practice, the reheat is generally limited to one point of expansion.

3. Due to reheat, the steam rate (specific steam consumption) is reduced.

Which of the above statements are correct?

Reheating in the Rankine cycle:

• In a simple cycle, after the isentropic expansion in the turbine, steam is directly fed into condenser for the condensation process. But in the reheat system, two turbines (high-pressure turbine and low-pressure turbine) are employed, to increase the quality of steam at the turbine exit.
• Steam, after expansion from the high-pressure turbine, is sent again to the boiler and heated until it reaches a superheated condition. It is then left to expand in the low-pressure turbine to attain condenser pressure. The reheat cycle has been developed to take advantage of the increased efficiency with higher pressures, and yet avoid excessive moisture in the low-pressure stages of the turbine.
• With reheat the mean temperature of heat addition Tm increases and so efficiency and work output increase but the steam rate decreases.

Steam Rate: It is the amount of steam consumed to produce 1 kW of power output.

\(Steam\;Rate = \frac{{3600}}{{{W_{net}}}}\;kg/kW - hr\)

Since the net-work achieved by the same mass flow rate of steam is increased the steam rate will be decreased.

The reheat pressure is limited to 20-25% of the high-pressure turbine. 

The main purpose of reheating is to increase the quality of the steam at the turbine exit, not to increase the efficiency.