Answer :
Final answer:
Intercept valves on reheat turbines protect against low pressure scenarios that could lead to turbine overspeed and failure, while isolation and temperature control valves ensure safe and efficient operation of plant equipment during normal and maintenance circumstances.
Explanation:
Intercept valves provided on reheat turbines are crucial safety components designed to protect the turbine and associated equipment from damage. These valves can close if the pressure reaches a dangerously low point, which might be indicative of equipment failure elsewhere in the plant.
For reheat turbines, this is especially important during instances such as a quick shutdown or a failure in the heat exchange system, where steam pressure and temperature could rapidly drop, leading to insufficient force on the turbine blades which might cause the turbine to overspeed and potentially fail. Therefore, intercept valves act as a safeguard against such scenarios, ensuring that the turbines are protected from operating under conditions that may cause mechanical stress or equipment failure.
In addition, the use of temperature control valves (TCVs), including direct and pilot actuated valves, ensures proper temperature regulation. This is crucial in chemical processes, such as in a pressurized water nuclear reactor scenario mentioned, where precise temperature control impacts the efficiency and safety of the operation. As shown in Figure 15.24 and similar diagrams, the proper functioning of thermal regulators within a pressurized water nuclear reactor system is necessary to avoid overheating and to maintain a stable reactor core temperature.
Without appropriate isolation valves, as discussed in the chemical factory example, the plant would face serious issues when maintenance is required, or if a unit operation needs to be shut down, thereby underscoring the critical need for proper valve selection and installation in process engineering.