Study On The High Efficiency And Low NOx Emission Technology Of Local Supporting-Combustion By Membrane Oxygen-Enrichment For The Pulverized Coal Boiler

The coal-fired electricity dominates in the power generation in China. It not only consumes lots of end-energy, but also brings results in serious environment pollution. To save the coal resource and reduce pollutant emission is one of key issues faced by the power plants in China. Hence, it is of great importance to study and develop control technologies on high efficiency, low NOx emission and low load stability combustion, in order for the re-adjustment of power generation structure and the steady sustainable development of the power industry.With application of the advanced techniques such as rich-lean combustion, staging combustion and enrich oxygen combustion, tangential firing has become a general method in pulverized coal boiler in China for its merits in combustion organization. However, further improvement and development are also found necessary for the technology because of the characteristic of power coal used in China. For medium and small-sized lean and bum bituminous coal boiler using staging combustion, NOx emission and coal burnout are two problems which restrict each other. An effective way to solve the contradiction between low NOx emission and high efficiency is to adopt advanced technical reformation of the boiler. On the premise of combustion safety and high efficiency, how to get good air dynamic field and combustion formation to decrease NOx emission are then the primary target of the research.To solve problems such as low thermal efflciency,high NOx emission, slag bonding and high temperature corrosion of a 150t/h pulverized coal boiler, literrature review and analytic demonstration were first carried out on the existing technics of high efficiency and low NOx emission. The thesis then continued with discussion of the formation mechanics of NOx in the combustion process and the control technique of NOx emission of pulverized coal boiler. The flowing field and combustion of pulverized coal were simulated, using k-ε-g turbulence combustion model for computations of the gas phase and two competing reactions for the coal devolatilization. On the basis of experiments of the cold dynamical field and simulation of coal particle trace and velocity field, the technology of local enriched-oxygen supporting combustion (LEOSC) was developed and a system of membrane oxygen-enrichment was designed for the first time. A new idea was proposed to use the enriched-oxygen air as the over flame air (OFA) and the welted edge air, which has been applied in the practice for the first time, and reasonable operational parameters have been obtained under the LEOSC working condition. Models of low NOx combustion and thermal efficiency characteristics were developed in the thesis with artificial neural network, and integral combustion was optimized using heredity algorithm. A software for guidance of boiler operation for high efficiency and low NOx emission combustion was developed to help to achieve the targets under usual operating situations.The practical results proved that the LEOSC technology is good for decreasing of NOx emission with high thermal efficiency through reasonable combustion organization and optimal operation. With this technology, the conflict between NOx emission and coal burnout and problems of slag bonding and high temperature corrosion can be prevented effectively. As the low load stable burning are improved, the reliable, economical and stable operation of the boiler can be guaranteed.