| Coal-fired utility boiler is one of major sources of dust, SO2and NOx in china. In order to meet the less and less NOx emission limit of<Emission Standard of Air Pollutants for Thermal Power Plants>(GB13223-2011), effective NOx control technology would be applied to the pulverized coal boiler. Lower NOx combustion in the furnace and post-combustion removal process such as SCR system have been widely used to control NOx emission for most power plants. In this paper two the utility boilers burning Shenhua coal have been studied on lower-NOx combustion technology. Opposed firing boiler which is supercritical once-through boiler has been numerically simulated to propose air staging modification. And numerical simulation and experiment have been done to present and finish lower-NOx combustion modification for tangential firing boiler which is subcritical controlled circulation boiler.Firstly combustion and NOx emission of Russian-made800MWe supercritical once-through boiler have been numerically simulated. It’s a T type opposed firing boiler. Based on actural performance, analysing simulating results, lower-NOx combustion technology of air staging have been proposed. Over-fire air rate, over-fire air nozzle elevation and main burner nozzle elevation have been optimized by numerical simulations. And then lower-NOx combustion solution has been recommended for the special kind of boiler.Key parameter of rate of NOx, which directly reveal law of NOx generation and reduction in the furnace, has been analyzed particularly, connected with O2concentration, temperature distribution and char burnout rate. Controlling factors have been found in different combustion zones for NOx formation. O2concentration is major control factor in main combustion zone and temperature is key factor in burnout zone.Secondly combustion and NOx emission of600MWe subcritical controlled circulation boiler has been numerically studied. Shenhua coal is main fuel. Based on real operating condition, Analyzed slagging character, compound air staging technology solution has been proposed to control NOx emission. The solution is expected to decrease NOx formation by vertical air staging along furnace height and horizontal air staging in main combustion zone.In the numerical simulating research of compound air staging, iso characteristics surface has been introduced to analysis important parameters such as rate of NOx etc. Compound air staging technology solution has been optimized considering on the result that O2concentration is major control factor in main combustion zone and temperature is key factor in burnout zone by numerical simulating. Velocity deviation and the temperature deviation at furnace outlet have been discussed for the tangential coal fired boiler before and after modification. Outlet temperature and burnout of pulverized coal have also studied.Lastly600MWe subcritical controlled circulation boiler have been transformed with the above compound air staging. Experimental research has been done after modification of lower NOx combustion technology. NOx emission has been measured before and after modification to evaluate NOx reduction. Temperature distribution, boiler efficiency and CO/H2S content nearing water wall have been analyzed to evaluate combustion characteristics, slagging in the furnace and high-temperature corrosion. Experimental data showed compound air staging technology recommended in last chapter decreased NOx emission greatly. After modification burning efficiency of boiler decreased slightly but the boiler thermal efficiency increased. |
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