What are some disadvantages of using a regenerator in a gas turbine cycle?

The correct answer identifies key disadvantages of using a regenerator in a gas turbine cycle. Regenerators are used to recover heat from exhaust gases, thus improving the cycle's efficiency. However, they also introduce some challenges.

Increased capital costs arise due to the need for additional materials and design complexity involved in incorporating a regenerator into the system. This investment is essential for enhanced efficiency but can significantly raise the initial costs of the gas turbine system.

The pressure drop is another significant downside. The regenerator requires a certain flow resistance, which can reduce the pressure of the working fluid entering the turbine. This drop can lead to a decrease in overall system performance as it may require more energy to maintain the desired flow rates.

Although the coating of heating surfaces and other factors, like temperature drop reductions, are valid concerns, the option that addresses the increased capital costs and pressure drop is focused and highlights the economic and operational impacts specifically relevant to the question's context. Thus, the answer clearly points to some of the major practical disadvantages that engineers must consider when designing and operating gas turbine systems with regenerators.