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Boiler Economizer

Boiler economizer is used for the heat energy recovered by the waste heat recovery system


The economics of waste heat recovery from flue gas is a sensitive topic. How to recover investment in the shortest time and achieve maximum economic benefit is the issue that users are most concerned about. This problem needs to be specifically analyzed based on the specific issues of the available temperature difference of the flue gas and the purpose of recovering heat:


1. Flue gas waste heat recovery system applied to the flue of the power plant boiler


The heat energy recovered by the waste heat recovery system of the flue gas is low in temperature and the quality is not high, usually only about 100°C. This part of the recovered heat energy can not be calculated using the equivalent conversion method, but should be equivalent conversion method or thermal balance calculation to determine the effective use of heat recovery value (the second law of thermodynamics).


2. Flue gas waste heat recovery device used in other industrial boilers


(1) Advantages of boiler economizer 


◆ Improve cycle efficiency and reduce coal consumption;


◆ Improve the dust removal efficiency (pre-installation of the dust collector);


◆ reduce the desulfurization tower evaporation, save water.


(2) Problems and solutions caused by installation of flue gas residual heat exchanger in the flue gas duct of the boiler


◆ Low temperature corrosion solution


☆ Choose a reasonable metal wall temperature when designing, and use the metal surface temperature control technology to control in real time


☆ Choose corrosion resistant materials


ND Steel (09CrCuSb) - currently the most ideal "sulfuric acid-resistant low-temperature dew point corrosion" steel used at home and abroad.


Comparison of corrosion rate of ND steel, mg/cm2.h (soaked in 70°C 50% H2SO4 solution for 24 hours):


☆ Use low oxygen combustion


☆ Acceptable limited corrosion rate: Corrosion rate ≤ 0.2 mm/year


◆ Wear solution


◆ The main factors that affect wear:


a. Fly ash particle characteristics and concentration: high SiO2 content, increased wear


b. Arrangement and flushing method of tube bundles: sequence: first row; wrong column: second row


c. The maximum wear position: The first row of 45° - 60° (the central angle on both sides of the windward side) is staggered in the second row: 30° - 45°


d. Direction of air flow: gravity effect


e. Tube Wall Material and Wall Temperature: Increased Hardness of Oxide Film on Increasing Wall Temperature


☆ Choose a reasonable flue gas flow rate: no less than 6m/s


☆Use anti-wear device


1. Wear-resistant tile 2. Wear protection curtain


☆Expansion of heating surface comprehensive utilization technology


For H-shaped finned tubes, a reasonable fin height and fin pitch are selected. When the flue gas flows through the finned tube, an adherent layer is formed on the ribbed surface under the action of the viscous force, and a smaller vortex appears. In the area, large-grain fly ash cannot contact the surface of the base pipe. In addition, under the action of the fins, the horizontal erosion of the flue gas does not converge like the light pipe is in the range of 45°, but is relatively evenly distributed along the surface of thepipe, reducing the outer surface of the pipe partial wear.


◆ Ash solution:


☆ Choose a reasonable flue gas flow rate (not less than 6m/s)


☆Use soot blowing device


☆ The heat transfer surface adopts a reasonable layout: staggered arrangement, proper pitch - enhanced air flow disturbance


☆Heat exchange element with multiple strokes -H type fin tube


◆ The solution of smoke resistance:


☆ The balance of the induced draft fan


☆ Arranging pipes rationally to reduce resistance to an acceptable range


☆ Placed before the induced draft fan



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