WANG Yongying;YANG Shi;ZHANG Shen;

• 1:China Coal Research Institute Company of Energy Conservation
• 2:State Key Laboratory of High Efficient Mining and Clean Utilization of Coal Resources
• 3:National Energy Technology & Equipment Laboratory of Coal Utilization and Emission Control
• 4:Jinan Heating Group Co.

Abstract：

Possessing the advantages of burning stability and low burn-out rate,the double-cone combustion chamber with independent space is suitable for industrial boilers which start-stop frequently.with the increase of market demand for high-capacity boilers,the combustion chamber volume and number increase,and the adoption of water cooling method will lead to problems such as difficult installation and complex water system.Therefore,it is urgent to develop new cooling methods.Air cooling technology has the advantages of simple structure and combustion stability. Whether this technology can be used in the combustion chamber with independent space needs to be explored.In order to determine the combustion and wall cooling of the air-cooled combustion chamber,the three-dimensional modeling of the combustion chamber and furnace of 14 MW industrial boiler was carried out by using numerical simulation technology. The internal combustion,metal wall temperature,exit flame shape and furnace fullness were obtained under the different ratio of internal and external secondary air distribution under 50% and 100% load.The results show that: at the conditions of constant excess air coefficient,the temperature of the inner region decreases gradually with the increasing of inner secondary air ratio,the average temperature of metal wall also shows a decreasing trendwith the increase of the ratio of internal secondary air at 50% load,while first decreased and then increased at100% load,which is the result of the combined effect of combustion supporting by internal secondary air and cooling by external secondary air; With the increase of the proportion of the internal secondary air,the high temperature area of the metal wall gradually moves backward and focuses on the exit area of the back cone; when the inner secondary air ratio is 0.4,the temperature of metal wall is maximum( 930 K)at 50% load,and when the inner secondary air ratio is 0.2,the temperature of metal wall is maximum( 835 K) at 100% load.The two temperatures all appear in the behind cone,at this time,the air volume of secondary air distribution is 2 600 Nm3/h,which should be avoided.According to the maximum temperature,the wall material is selected as 0 Cr18 Ni9; The average temperature of the combustion chamber,the average temperature and maximum temperature of the metal wall under 50% load are all higher than that under 100% load,which is the working condition that air cooling structure needs to focus on.As the inner secondary air ratio increases,the length of flame increases at first and then decreases.When the internal secondary air is too small,the outlet gas velocity is small,and the external secondary air has a velocity component toward the center,and the flame is mainly concentrated in the front of the furnace.With the increase of the ratio of internal secondary air,the exit velocity increases and the flame becomes longer and thinner.However,as the proportion continues to increase,the axial speed of the external secondary air becomes smaller,and the swirl strength of the exit flame is completely determined by the secondary air.The increase of the swirl strength of the exit leads to the flame becoming shorter and thicker.Under two loads,the flame is longer when the ratio of internal secondary air is 0.4-0.5.The ratio internal and external secondary air is 0.5 ∶ 0.5,the flame's fullness in furnace is the best,the combustion situation and wall temperature in the combustion chamber are also uniform and stable,and the fullness of the flame in the furnace is the best,which is the mostsuitable working parameter for both loads.

Key Words： air cooling;pulverized coal combustion chamber;flame shape;temperature of metal wall;numerical simulation

Abstract:

Keywords:

Foundation: 中国煤炭科工集团科技创新创业资金资助项目(2018-TD-ZD001)

Authors: WANG Yongying;YANG Shi;ZHANG Shen;

DOI: 10.13226/j.issn.1006-6772.20012002

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