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Influence of the Secondary Air Angle on the Airflow Field in a Down-Fired Boiler

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Tutor: ZhuQunYi;LiZhengQi
School: Harbin Institute of Technology
Course: Thermal Power Engineering
Keywords: W-shaped boiler,secondary air declination,OFA
CLC: TK229
Type: Master's thesis
Year:  2008
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Abstract:
W-shaped boilers are suitable to burning low volatile fuel like anthracite because of the high temperature in furnace, long-flame, etc. At present, near sixty W-shaped boilers are operating in many Chinese large-scale power stations. Many operation experiences are accumulated in China, yet there are some problems to be solved.Aimed at high heat loss due to solid unburned combustibles, combustion dis-stability, superheater temperature excursion, quantity desuperheat water, etc, in a 1025t/h full-scale utility W-shaped boiler which was designed and produced by DongFang Boiler Works according to the technique introduced from F&W Co. Ltd of USA, the aerodynamic fields were studied on the single-phase cold model, which was built on the Similarity Theory by 1:15. An IFA300 constant-temperature anemometer system was used to measure the air velocity in the model. The experimental results reveals that there is a W-shaped flame in the furnace under the present work condition, but the pulverized coal flows too short to burn out, and the dregs under the arch is caused by the back-coming eddies near the burner. Flame journey increased, furnace using rate enhanced that will advance pulverize coal burnout and ameliorate slag through increasing F-secondary air declination angle. However, large jet angle will easily arouse eroding furnace hopper, arch slag, etc. Entering some E-secondary air will be good for mix between primary and secondary air, pulverize coal ignition in time, protect side wall no to erode by flue gas better, and air grade. Yet, when the E-secondary air was supplied too more, flame will short and arch will be erode.This W-shaped boiler has a large NOx emission because of the combustion characteristic, so that after declination secondary air to increase pulverize burnout, OFA on the burnout chamber must be supplied to reduce NOx emission. In this thesis, OFA spouts are fit in the test-bed to study the flow field. The results show that the flow field keep primary position that Flame journey increased, furnace using rate enhanced, and slag feasibility reduced, etc, due to OFA air influenced flow field little.
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