Thread Content
The functions of the economizer and the air preheater are the same in terms of energy saving and consumption reduction. Air preheaters offer significant economic benefits in terms of waste heat recovery from flue gas and air, as well as from flue gas and steam. Next, I will introduce them to you one by one. economizer 1, Structure of the economizer: It is generally a coiled-tube heat exchanger, which consists of many parallel coiled seamless steel tubes along with inlet and outlet manifolds. The feedwater pumped by the feedwater pump is fed into the tubes where it exchanges heat with the flue gas outside the tubes, thereby increasing in temperature, and then is sent to the steam drum. Flue gas generally flows from top to bottom, causing the flue gas and water to flow in opposite directions, which increases the heat transfer temperature and improves the heat transfer efficiency. 2. Arrangement of the economizer: at the rear of the boiler where the flue gas temperature is low. Today, suspension-type economizers are commonly used in large boilers. The outlet header pipes of the economizer can be used to suspend both the economizer itself as well as the superheater and reheater. 3. The main functions of the economizer: ① The economizer absorbs the heat from the low-temperature flue gases in the tail flue, reducing the exhaust temperature of the boiler, thereby improving the boiler’s thermal efficiency and saving fuel. ②The use of a economizer increases the temperature of the water entering the boiler drum, reducing the temperature difference between the drum wall and the feedwater. This in turn reduces the thermal stress on the drum, thereby extending its lifespan. 1. Structure of air preheaters: Air preheaters are generally classified into tubular, plate-type, and rotary types; both the tubular and plate-type types utilize partitioned heat transfer. 2. Placement of air preheaters: Air preheaters are usually installed at the outlet of the boiler. Here, the air exchanges heat with the flue gas, and the heated air is sent to the burner to assist in combustion. Electric boilers save electricity, while coal boilers save coal. 3. Functions of the air preheater: ① It uses air with a temperature much lower than that of the feedwater to cool the flue gas, thereby recovering the heat from the flue gas. This helps to further reduce the flue gas temperature and minimize heat losses due to flue gas emissions. Experimental results and theoretical calculations show that for every 10-degree decrease in flue gas temperature, the boiler efficiency can increase by approximately 0.7% ； ②Increasing the temperature of the air fed into the furnace can improve or enhance combustion, ensuring stable ignition at low loads. Thermal tests show that for every 100 increase in the temperature of the combustion air, the theoretical combustion temperature in the furnace can increase by about 30 to 40. The temperature of the hot air supplied into the furnace by the air preheater③ increases, which raises the average flame temperature and thereby enhances radiation heat transfer within the furnace. By meeting the same amount of heat absorption during evaporation, it is possible to reduce the heating surface area of the water wall tubes, thereby saving metal usage ； ④Hot air can also be used as a desiccant in the powder production system. The boiler temperature is high, with the flue gas temperature reaching several hundred degrees; in such cases, an air preheater needs to be installed. It can effectively recover the wasted residual heat for reuse, and in this way it also helps to save coal, electricity, and gas.