Flue gases can leave at high temperatures. We can recover some of this heat using a(n):

The recovery of heat from flue gases is effectively achieved through the use of an economizer. An economizer is a heat exchanger that captures waste heat from hot flue gases before they are expelled into the atmosphere. This waste heat can then be used to preheat the incoming feedwater to a boiler, which improves overall energy efficiency.

By utilizing the heat that would otherwise be wasted, economizers significantly enhance the boiler's efficiency, reduce fuel consumption, and lower greenhouse gas emissions. They are commonly found in industries that rely on large boiler systems, where optimizing the performance of these systems is crucial for both operational efficiency and cost-effectiveness.

In contrast, other options like a flash tank or an open feedwater heater serve different functions within the steam and heating systems. A flash tank is designed to separate steam from water, whereas an open feedwater heater is used for preheating water using steam, but it does not specifically target the recovery of heat from flue gases. An air compressor, on the other hand, is used for compressing air and has no relation to heat recovery from flue gases.

Thus, the economizer is the correct choice as it directly addresses the recovery of heat from flue gases, enhancing the efficiency of thermal