Where is the final evaporator located in a once-through boiler?

The final evaporator in a once-through boiler is located in a zone of lower flue gas temperature because this placement allows for optimal heat transfer efficiency as the water is converted to steam. Once-through boilers operate with water flowing in one direction through the system, and the placement of the final evaporator helps to ensure that the water has fully absorbed the necessary heat before it exits the system as steam.

By positioning it in a zone where the temperature is lower, the final evaporator can capture the residual heat from the flue gases more effectively, maximizing steam production while minimizing the risk of overheating or damaging the boiler components. This setup is essential for maintaining the overall efficiency of the boiler while ensuring safety and reliability in steam generation.