Stable & Clean Combustion Of Pulverized Coal-Fired Boiler Under All Loads Based On High Temperature Air Ignition

Energy saving and pollution reducing are important measures to achieve sustainable development of the nationfil economy,especially for power industry.This article focuses on resolving three major issues of current pulverized coal fired boilers in power stations from ignition of start-up to 100%MCR load,which are closely related to energy saving and environmental protection.As the main research of the project,the study is financed by National '863 Program'(The National High Technology Research and Development Program of China) project(No.2003AA529280):'The Research and Application of Operation Technology to Clean and Efficiently Control the Coal-fired Boiler on the Ultra-low Load'.The assembled technology for a 200MW utility boiler was developed to realize the stable and clean operation in the whole range of the boiler's load,it is based on the ignition technology of high temperature air,and is organically combined with the other two technologies,one is of horizontal bias burner,the other is three dimensional air staged combustion technology.According to the structural characteristics of the high-temperature air ignition burner and its ignition requirement,several different designs of concentrators were proposed.Numeric studies were done to simulate the gas solid two phase flow under the different schemes.This research provided a reference to the selection of the schems in the subsequent engineering applications.The numeric simulations were done to study the ignition characteristics of a single-stage ignition burner and three-stage ignition burner under conditions of different parameters,and thus find the laws of how the main parameters influence the ignition process.The ranges of the optimal parameters were given for specific utility boiler and quality of its fired coal.Key technical problems were discussed related to the 200MW utility boiler started up by the oil-free ignition of high temperature air.The start-up scheme was programmed.Numeric predictions of the combustion process in the furnace were carried out to study the start-up processes when the four ignition burners were put into operation one by one.It is proposed that the burners should be switched timely during the start-up in industrial applications.The prediction results showed that the start-up scheme could meet the requirements of the start-up curve of boiler.The results agreed well with the curve getting from the industrial application.A retrofit scheme applied for stabilizing the combustion was put forward,which combined high temperature air ignition burner with horizontal bias burner.Numeric predictions of the combustion process in the furnace were done under 30%-50%MCR conditions when the combined scheme was applied to 200MW utility boiler.Forecasts showed that the stable effect of the combined combustion technology is significant.By means of the stable ability of horizontal bias burner,the load point under which the high temperature air heater could be halted was put forward during the actual operation,reducing the cost of power generation and the pollutant emissions.The three dimensional air staged combustion technology was applied to the utility boiler,which combined the Concentric Firing System(CFS),horizontal bias combustion and the air-staged combustion alone vertical direction of whole furnace.On the base,a set of retrofit scheme was proposed to reduce the NO_x emissions.The method combined cold model experiment with numeric simulation was adopted to study the selection of the key retrofit parameters and operation parameters in the scheme.The assembled technology scheme was carried out for specific structure utility boiler and quality of its fired coal,and the systematic research route was formed.The main contents of the technical program had a retrofit application to the actual utility boiler. The results showed that the Ringelmann blackness of flue-gas is less than one class under the ultra-low load.The retrofit reduced soot emission by 90%during the start-up, and the combustion was stable,30%NO_x emission was reduced under the low load.The assembled technology has significant economic and environmental benefits,and has applicability in similar units.