The economizer is a crucial heat exchange device in boiler systems, specifically designed to recover waste heat from tail flue gas and preheat boiler feedwater, thereby significantly improving system thermal efficiency and reducing fuel consumption. Its design and working principle are based on efficient heat conduction and convective heat transfer, making it one of the core components for achieving efficient energy utilization.

 

Economizers realize heat exchange through serpentine tubes or finned tube bundles made of high-temperature resistant materials (such as carbon steel or stainless steel). High-temperature flue gas (typically between 250°C and 500°C) flows outside the tube bundles, while low-temperature feedwater (after deoxygenation treatment) flows inside the tubes. Heat is transferred from the flue gas to the tube wall through heat conduction and convective heat transfer, further heating the feedwater. This process significantly reduces the flue gas temperature (which can drop below 150°C) while increasing the feedwater temperature, which then enters the boiler drum to participate in steam generation. The entire heat exchange process follows the law of energy conservation, and thermal efficiency can be quantified by the ratio of the heat absorbed by the feedwater to the heat released by the flue gas.

 

According to design and application requirements, economizers are mainly classified into the following categories:

- By heating degree: Non-boiling type (feedwater does not reach saturated boiling state) and boiling type (allowing partial water evaporation);

- By material: Cast iron economizers (suitable for boilers with pressure ≤ 2.5MPa) and steel tube economizers (suitable for higher pressure conditions);

- By structural form: Plain tube economizers, finned tube economizers (expanding surface area to improve heat exchange efficiency), spiral tube economizers (extending flue gas path to enhance heat exchange), and heat pipe economizers (utilizing working medium phase change for efficient heat transfer);

- By flow arrangement: Concurrent flow, countercurrent flow, or mixed flow designs, among which countercurrent arrangement usually achieves higher heat exchange efficiency.

 

The application of economizers directly brings multiple benefits:

1. Energy efficiency improvement: By reducing exhaust gas temperature (reducing heat loss by 100–250°C), boiler thermal efficiency can be increased by approximately 10–15%, significantly saving fuel costs;

2. Emission reduction: Low-temperature exhaust gas helps reduce the diffusion of pollutants (such as sulfides and nitrogen oxides) in the flue gas, supporting environmental compliance;

3. Equipment protection: Preheated feedwater can reduce thermal stress on the boiler and extend system lifespan.

 

Economizers are widely used in power station boilers, industrial boiler systems, and extended to waste heat recovery scenarios in chemical, metallurgical and other fields, making them an indispensable part of modern efficient energy utilization. Their efficient and reliable design makes them a key equipment for improving boiler performance and achieving sustainable development.