Economizer: Working, Purpose, Classification and Advantages
Table of Contents
What is an Economizer?
A type of heat-exchanging device is an economizer. Mechanical devices known as “economizers” are created to conserve energy or carry out a specific task, like preheating a process fluid. Depending on the size of the boiler and the available space, an economizer may be installed directly on the boiler close to the flue gas outlet in a vertical, horizontal, or cylindrical orientation.
What is the Purpose of an Economizer?
The efficiency of a boiler is raised by 10-12% with the addition of an economizer. Furthermore, fuel consumption and costs are decreased because less energy is needed for heating. An economizer, as its name suggests, is a device used in thermal power plants to reduce energy consumption during the production of electrical power.
Construction and Working Principles of Boiler Economizer
The construction and use of the boiler economizer are easy and simple. The water is fed to the economizer at room temperature through a horizontal inlet pipe at the bottom of the device. At the top of the economizer, there is another horizontal pipe installed. The bottom and top pipes, which are two horizontal pipes, are connected by a number of vertical pipes. An outlet valve is installed on the top horizontal pipe to supply hot water to the boiler. The vertical pipes of the economizer receive flue gases from the boiler furnace.
The flue gasses transfer residual heat to the water through the surface of the vertical pipe as the water rises through the vertical pipes to the top horizontal line. The economizer uses the heat from the flue gasses to warm the water before it enters the boiler to make steam. Ash particles will be present in the flue gas and will be deposited on the vertical pipe surfaces. So If extra care is not taken, a thick layer of soot will build up on the surfaces, blocking the passage of heat into the water.
Each vertical pipe has a scraper attached to it that is moved up and down by a chain pulley system in order to remove the soot. The soot is scraped all the way to the bottom of the economizer, to the soot chamber. Then, soot is collected from the soot chamber. This is how a boiler economizer works. This boiler economizer is of the most basic design. An economizer in a thermal power plant warms fluids or recovers heat from the flue gasses, which are the combustion product, before they are expelled through the chimney.
So The combustion exhaust gases produced by power plants are called flue gasses, and the main components of these gases are nitrogen, carbon dioxide, water vapor, soot, and carbon monoxide. The preheated boiler feed water is then used to create superheated steam using the recovered heat. Since we are essentially collecting waste heat and directing it to where it is needed, we are reducing fuel consumption and optimizing the process as a result. So All pulverized coal-fired boilers must have an air pre-heater, which can economically recover the heat from exhaust flue gasses.
The Function of the Boiler Economizer
The Heat Transfer Principle underlies the operation of the Economizer in a boiler.Normally, heat transfer takes place from hot to cold temperatures. In the case of boilers, the water that needs to be preheated is cold, while the flue gases or exhaust from the boiler outlet are hot. As a result, an increase in feed water temperature is caused by the temperature difference between water and flue gasses. Economizers can be either smoke tube type or water tube type of design, depending on the type of operations.
The smoke tube type has water on the shell side and flue gasses inside the tubes. In contrast, in a water tube type, flue gasses are on the shell side and water is inside the tube.
So In a thermal power plant, an economizer recovers some of the heat lost in the flue gasses that are expelled up the chimney and uses it to warm the boiler’s feed water. So It is merely a heat exchanger with a long heating surface, like Fins or Gills, hot flue gas on the shell side, water on the tube side, and that’s all there is to it.
Economizers in Power Plants
Economizers must be sized for
- Flue gas volume and temperature.
- The fuel type utilized by the boiler.
- The maximum pressure drop went through the stack.
- How much energy needs to be recovered?
The boiler boils the water, creating superheated steam that is then delivered to the turbines. After passing through the steam condenser of the turbine, where the exhaust steam from the turbine blades is condensed, the condensed water is then heated in the feed water heater before being fed back into the boiler. Between the boiler’s exit and the chimney’s entrance, there are economizers installed in the flue gas passage. So In this arrangement, a large number of thin-walled tubes with small diameters are sandwiched between two headers. The flue gases typically flow in opposing directions outside of the tubes.
Classification of Economizer
Economizer is classified into various categories
Based on Construction
The economizers are classified into two categories Based on Construction. They are
- Plain Tube-Type Economizers
- Gilled Tube-Type Economizers
Plain Tube-Type Economizers
The exterior of the economizer tubes are kept clean and soot-free by soot scrapers that move up and down the tubes. If not, economizer efficiency will drop and heat transfer resistance will rise.
Gilled Tube-Type Economizers
To increase the heat transfer surfaces, rectangular gills are provided on the bare tube walls.
Based on Part of Steam Generation
The economizers are classified into two categories Based on Part of Steam Generation. They are
- Steaming Type Economizers
- Non-Steaming Type Economizers
Steaming Type Economizers
During its passage through the economizer, some of the water (about 5 to 7%) will be converted into steam.
Non-Steaming Type Economizers
When using a non-steaming economizer, the feed water is heated to a temperature that is 75% of the saturation temperature of the boiler.
Based on the Location of Economizers
The economizers are classified into two categories Based on Part of Steam Generation. They are
- Independent Economizers
- Integral Economizers
Independent Economizers
Economizer is installed outside the boiler house at any convenient place
Integral Economizers
Economizer is installed close to the boiler
Based On Boiler Efficiency
The economizers are classified into two categories Based on Part of Steam Generation. They are
- Non-Condensing Economiser
- Condensing Type Economizer
Non-Condensing Economiser
The most prevalent kind of economizer used in thermal power plants is the non-condensing thermal power plant. So They are heat exchanger tubes that are housed inside the duct near the boiler’s exit point and have spiral fins all around them. By transferring heat from the flue gas to the feed water inside the tubes, this economizer helps the boiler use less flue gas. So These are employed in thermal coal-fired power plants where the flue gas temperature can be brought down to 120 °C or less. Efficiency is increased by 3-6% with this kind of Economizer.
Condensing Type Economizer
They are utilized in thermal power plants powered by gas. So They decreased the flue gas temperature to as low as 25 degrees Celsius, which is below the condensation temperature. By 10% to 15%, they increase boiler efficiency. So Sulfur should not be present in the fuel used in the condenser.
Waste Heat Recovery Concept of Boiler Economizer
Boilers are commonly used to generate steam from water. By transferring both sensible and latent heat, water is converted to steam. Sensible heat is the quantity of heat needed to raise the temperature of water at constant pressure without changing its liquid state, whereas latent heat is the quantity of heat needed to convert water from a liquid to a vapor at constant temperature and pressure. If no heat recovery devices are installed after the boiler, there are significant losses from the boiler because its exhaust is typically in the 200°C to 250°C range. So If the exhaust gases that are leaving the boiler at such high temperatures are passed through the economizer to provide the sensible heat needed to heat the feed water to raise its temperature, the heat load on the boiler will be reduced to a greater extent.
Advantages of Economizers
The advantages of economizers are as follows.
- It reduces fuel consumption.
- It increases the efficiency of the boiler.
- As a result of flue gas emissions, heat losses are decreased. Due to a smaller temperature differential, the temperature of flue gasses, which ranges between 370°C and 540°C, reduces thermal stresses in the boiler.