Experimental Research On The Slagging Characteristic Of Blended Zhundong Coal In A 350MW Power Plant Boiler

Zhundong coal is an important kind of coal reserve in China.It is considered as a kind of clean steam coal of igh quality due to its low-to-medium ash yields,low phosphorus and sulphur contents,high volatile matters,and middle-high calorific value However,severe slagging and fouling occur during the combustion of Zhundong coal.Coal fired thermal power plants have been puzzled by fouling,slagging for a long time,which greatly lower the safety of boilers and reduce the boiler efficiency,so that increase the cost of thermal power plants.This experimental research was conducted in a power plant boiler.Firstly,infrared pyrometer and CCD was used to test the fire temperature field in the boiler.The results show that the NOx emission goes down with the increase of SOFA rate significantly but it goes up with the increase of blending ratio.After that,the effects of SOFA rate and blending ratio on furnace temperature field distribution and slagging characteristic was studied by changing the SOFA rate and blending ratio of Zhundong coal.As a result,the flame temperature in primary combustion zone goes down with the increase of SOFA rate,but in secondary combustion zone it goes up and the outlet temperature goes up,too.The temperature in primary combustion zone goes up with the increase of blending ratio,but in SOFA zone it goes down.The slagging in the middle of the burner zone is the most serious when SOFA rate is the highest.With the decrease of SOFA rate,the slagging above SOFA zone becomes more and more serious.With the increase of blending ratio,the slagging in the middle of burner zone and above SOFA zone both become more and more serious.Enrichment of oligoclase and hematite occurs in the inner of slagging samples.With the development of slagging,the content of alkali metal in slagging samples gradually decreases.Whereafter,the slgging characteristic along the flue gas was studied by XRD to analyze the development process of the slagging along the flue gas.Finally,Slagging samples were got by a silicon carbide rod above over fire air and stratified to investigate the transformation of alkali metal elements and mineral conversion during the slagging process of Zhundong coal by CFA,ICP,XRD and SEM,in order to discuss the mechanism of the formation of slagging,as well as the development of the slagging with time and its deposition rate.As a result,coal particles burn in the furnace fully with the precipitation behavior of most Na and K,which attach on heating surface and form initial molten slag film.Slagging keeps developing and forms capture surface.With the capture of ash particles,the melting point of sedimentary layer rises.Ash particles solidify in the sedimentary layer and new capture surface forms.The research proves that temperature and atmosphere are vital to slagging and verifies the significance of alkali metals and ferreous sulfide during the formation of the initial sedimentary layer.Furthermore,the research describes the general process of the formation and development of coal slagging with different kinds of methods from angles of the transformation of alkali metal elements and mineral conversion,as well as the characteristic of microtopography,which has some reference value of solving the fouling and slagging problems during the combustion of Zhundong coal and even other high alkali metal coals in a boiler of thermal power plant.