What is the typical thermal efficiency range for subcritical plants?

Subcritical plants, which operate below the critical pressure of water, typically exhibit thermal efficiency in the range of 30% to 40%. The thermal efficiency is influenced by various factors, including the design of the plant, the type of fuel used, and operational conditions.

The correct answer reflects this characteristic range, as subcritical plants do not reach the higher efficiencies associated with supercritical or ultra-supercritical technologies, where efficiencies can exceed 40%.

In subcritical systems, the thermal efficiency is limited due to the way heat is transferred and the higher specific enthalpy of steam used in the cycle compared to supercritical cycles. Therefore, placing the typical efficiency range for these plants at 38%-40% is accurate and aligns with industry standards for conventional steam cycles. This option represents the upper side of what can be reasonably achieved in terms of efficiency in subcritical steam generation, factoring in operational efficiencies and design constraints.