ANS:D - none of these

The sensible heat of hot industrial flue gases can be recovered by various heat recovery devices such as economizers, regenerators, and ceramic recuperators. These devices are designed to transfer heat from the hot flue gases to a fluid (such as water or air) that can be used for other purposes, such as preheating feedwater or air for combustion.

• Economizers: These devices preheat the boiler feedwater using the heat from the flue gases before it enters the boiler. They are commonly used in steam power plants to improve overall efficiency by reducing the amount of fuel needed to produce steam.
• Regenerators: Regenerators are heat exchangers that cyclically absorb and release heat from a moving fluid stream. They are often used in processes where a high-temperature fluid stream is used to preheat a cooler fluid stream before entering a process. While regenerators are typically associated with cyclic processes, they can also be used for continuous heat recovery applications.
• Ceramic recuperators: Recuperators are heat exchangers that recover heat from the flue gases by transferring it to a separate fluid stream. Ceramic recuperators use ceramic materials for their heat transfer surfaces, which offer advantages such as high thermal efficiency, resistance to corrosion, and ability to operate at high temperatures.