Technical description of boiler economizer and air preheater

I. Economizer design and layout features

Layout and heat exchange method: In the lower part of the double flue, the economizer is arranged in series to exchange heat with the flue gas in a countercurrent manner. At the same time, H-type finned tubes are selected to improve the heat exchange performance.

Water supply process: The water is collected through the economizer inlet collection box and transported to the front and rear economizer inlet headers respectively. After being heated by the horizontal finned economizer, it enters the hanging tube inlet header and then forms 4 rows of hanging tubes upward. These hanging tubes undertake the important task of hanging the horizontal superheater and horizontal reheater in the tail flue. Each header leads to 95 hanging tubes. The ends of the 4 outlet headers of the hanging tubes are connected to two descending hanging tubes to supply the tube water to the lower header of the water-cooled wall.

Protection design: The top row of economizers are equipped with comb-shaped protective covers, flue gas flow baffles are arranged between the economizer tube group and the flue synchronous wall and waterfall wall, and wind damage protection plates are set within the working range of the soot blower to ensure the stable operation of the economizer. It adopts the standard household size of 3mm×90mm×195mm.

II. Advantages and disadvantages of finned economizers

Advantages: The finned economizer significantly increases the heat exchange area, which can reach 4-5 times that of ordinary economizers, effectively reducing the volume of economizers and reducing the use of consumables.

Disadvantages: In an ash-containing environment, the ash accumulation problem is more serious, so the economizer must be equipped with effective soot blowing equipment.

III. The role of air preheater

Reducing exhaust heat loss: Using air with a temperature lower than the feed water temperature to cool the flue gas, recover the heat of the flue gas, and effectively reduce the exhaust temperature. Experiments and theoretical calculations show that for every 10℃ reduction in exhaust temperature, the boiler efficiency can be increased by about 0.7%.

Improve combustion stability: Increasing the temperature of the air sent into the furnace can improve and strengthen the combustion process and ensure stable ignition when the boiler is running at low load. Thermal tests show that for every 100℃ increase in the temperature of the combustion-supporting air, the theoretical combustion temperature of the furnace increases by about 30-40℃.

Save metal consumption: As the temperature of the hot air entering the furnace rises, the average temperature of the flame increases, enhancing the radiation heat transfer effect in the furnace. Under the condition of meeting the same evaporation heat absorption, the heating surface of the water-cooled wall tube can be reduced, reducing metal consumption.

Acting as a desiccant: Hot air can be used as a desiccant in the powder making system to ensure the normal operation of the powder making system.

IV. Characteristics of rotary air preheater

Advantages: The rotary air preheater has the characteristics of small shape and light weight, and the heat transfer element allows large power, which is especially suitable for large-capacity boilers.

Disadvantages: There are problems of large air leakage and complex structure. In practical applications, the plate type, material and thickness of the heat transfer element should be reasonably selected according to the results of coal quality and ash content analysis and calculation; at the same time, the structural form and size of the air preheater should be determined in combination with the boiler type, pulverizing system form and main parameters of boiler auxiliary equipment.