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Study of Method and Facilities for Transfering from Hot Air to Exhaust Air Converying System

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Tutor: QinYuZuo;SunShaoZeng
School: Harbin Institute of Technology
Course: Thermal Power Engineering
Keywords: exhaust air converying system,NO_x control,ejector,coal converying system,cold-s
CLC: TK223.25
Type: Master's thesis
Year:  2008
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Abstract:
Pollutant NOx emission by coal combustion in power plants is an increasing threat to environment. At present, the bin and hot air feeding system for pulverized coal is widely used in thermal power plants and other power plants burning lean coal and anthracite coal in China. The hot air feeding system goes against the control of NOx emission, because it leads some phenomenons, like high furnace temperature. To solve the kind of problems, the exhaust and hot air ejector with injection principle was designed. In the innovational plan, the hot air feeding system will be changed to the exhaust air feeding system, on the purpose of reducing the NOx emission of power plants. The main content of the Paper is the design and the optimization of the exhaust air and hot air ejector to insure the ejector’s structure that it is suitable for various conditions.Firstly, the check of the original system and the design of final one were calculated in this Paper, to identify the imPact of the composition of primary air and the feeding system’s resistance, caused by different exhaust air quantities, with two mills working or not. The results showed that, in the common condition, with two mills working, the mass ratio hot air to exhaust air was 1.216. According to one-dimensional ejector design principles, taking 1.216 as ejector ratio, the exhaust air and hot air ejector’s the structural Parameters were determined.Numerical study was to optimize the structure of the exhaust air and hot air ejector by using specialized CFD code FLUENT, and to determine the diameter and the position of the work nozzle on the exhaust air and hot air ejector performance imPacts. The results showed that when the working nozzle diameter (dp1) was 190 mm, the change of system resistance caused by the exhaust air feeding system is little. Working nozzle position of ejector is one of the key design Parameters., which has been optimized by numerical simulation, and according to the design structure, the results showed that: when the distance (lc) between the working nozzle’s exit and the mixed section’s entrance was less than 950 mm, the lateral shift (d) from the working nozzle was zero; d augmented as lc increasing, but d did not exist, when lc was more than 1200 mm. Moreover, the influence of the change of lc on the resistance of the exhaust air and hot air were little, which can be neglected.According to the optimized working nozzle diameter, taking 1:4.06 as scale factor, the single-phase test-bed of the exhaust air and hot air ejector was built, attention on the influence of the exhaust air jet deflect due to the change of the working nozzle location, to solve the erosion and wear problems in primary air piping. The results showed that: the simulation results accorded with the test results well, which verified the rationality of the exhaust air and hot air ejector’s structure and the accuracy of the model selected, and provided the theory basis for simulation to establish the exhaust air feeding system ejector’s key design Parameters.
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