What Is a Boiler Economizer?
A boiler economizer is a heat exchanger that recovers heat from combustion gases in boilers, which use combustion heat to generate steam. Typically used in steam boilers that combust fuels like oil, coal, or gas, these economizers heat water to generate steam.
Also known as “coal economizers,” these devices are named for their ability to conserve coal in coal-fired steam boilers.
Uses of Boiler Economizers
Boiler economizers are primarily used to preheat the feed water to steam generators. Their advantages include reducing heat loss in combustion gas, thereby improving boiler efficiency. For instance, a 20°C recovery in combustion gas temperature can enhance boiler efficiency by approximately 1%. They also help in decomposing gases in feed water, reducing thermal stress in drum-type boilers.
Apart from boilers, economizers also find use in recovering heat from diesel engine exhaust gases to generate steam, beneficial for diesel generators and marine engines.
Boiler Economizer Principle
A steam boiler comprises several heat exchangers, including the economizer, which recovers heat from combustion gases. The key components include:
1. Superheater:
Generates high-temperature, high-pressure steam from recovered heat, used in power plants to drive turbines for electricity generation. –
2. Reheater:
Reheats steam post-turbine rotation for use in medium or low-pressure turbines.
3. Economizer:
Recovers additional heat energy from combustion gas to preheat water supplied to the superheater, thereby boosting boiler efficiency.
Types of Boiler Economizers
1. Classification by Combustion Gas and Feed Water Flow Direction:
Includes parallel flow, counter-current flow, and mixed-flow types, with counter-current offering the highest efficiency.
2. Classification by Degree of Heating:
Divided into non-evaporative (common in economizers) and evaporative types. Non-evaporative economizers keep the feed water temperature below saturation at the outlet, while evaporative types partially heat water to evaporation.
Structure of Boiler Economizer
Boiler economizers generally comprise steel tubes, either bare or finned, arranged for continuous water flow from inlet to outlet. These tubes are often U-shaped for efficient heat transfer.
Other Information on Boiler Economizers
Standards: Relevant standards include JIS B0126 (Glossary of terms for thermal power plants-Boilers and auxiliary equipment) and JIS B8201 (Steel boilers for land use-Stationary steel boilers-Construction).