Study On Kinetics Of Pulverized Coal During Mixed Injection Of Coal-Sludge In Blast Furnace

Pulverized coal injection into blast furnace is the main technical means of iron-making operation.Coal injection into blast furnace tuyere not only can be conducive to adjust furnace temperature and improve productivity,but also reduce the cost of iron-making and the utilization of coke resources.Due to the different physical properties of bituminous coal and anthracite,there are some problems about full combustion of pulverized coal in large coal injection operation.Sludge is a kind of iron-containing dust produced in iron and steel production.Fe and C elements in such sludge are recyclable resources.With the increasing attention to environmental and resource issues,it is particularly significant to strengthen the utilization of these resources.Based on two kinds of coal injection provided by a certain steel company and sludge as raw material,dynamical problems of bituminous coal,anthracite pulverized coal blending and sludge were studied.In addition,non-isothermal kinetic model of pulverized coal combustion process by the method of thermal analysis were established to explore the combustion performance,dynamics and mechanism of pulverized coal and sludge.To respond to the national environmental protection policy,this study considered the safety and economy to obtain the best mixture of pulverized coal and sludge.The main conclusions of this paper are as follows:(1)Anthracite A and bituminous B are the two types of coal selected for injection in the test.The fixed carbon content of A was 77.72%,the volatile content was 10.57%,and the sulfur content was 0.66%.The main mineral compositions of sludge were magnetite and kirschsteinite.The content of TFe was up to 59.14%,and it contained CaO,MgO and other minerals involved in smelting slag,which had a high utilization value.However,sludge also contained a small amount of Cl,S,Zn,K and other harmful elements,so the influence should be considered in the process of use.Compared with pulverized coal,the particle size of sludge was relatively fine.At the same time,sludge had a large specific surface area(S),a small median particle size(D50)and an appropriate particle size distribution dispersion.Several kinds of powder particle size distribution of discrete degree(eta)were small(<4.0),and the graded uniform degree satisfied the requirement of injection.(2)At a certain heating rate,with the increase of sludge content in pulverized coal,the DTG curve of pulverized coal combustion moved to the low temperature zone,and the temperature Tm corresponding to the maximum combustion rate decreased.The maximum combustion rate Rmax increased first and then decreased.The addition of 3%～5%content of sludge had larger Rmax,lower temperature and the most obvious change of thermal analysis curve;which promoted the combustion process of pulverized coal.(3)At a certain heating rate,with the increase of sludge content in coal powder,the ignition temperature Ti of coal powder slightly increased the burnout temperature Th decreased,the burnout index Df increased,and the time taken for burnout was shortened.The burnout process was more complete,and the addition of 3%～5%sludge made the pulverized coal burnout process more obvious,indicating that it can promote the burnout effect of pulverized coal and improve the combustion reactivity of pulverized coal.(4)At a certain heating rate,with the increase of the proportion of sludge,the calorific value Q of pulverized coal combustion first increased and then decreased,and the combustion intensity DSCmax increased first and then decreased,among which 3%～5%content of sludge The heat release of coal powder was increased more,and the intensity change was more obvious.Therefore,the sludge of this content improved the comprehensive heat release characteristics of coal powder,and effectively improved the thermal efficiency of coal powder combustion.(5)At a certain heating rate,with the increase of sludge in coal powder,the total activation energy of pulverized coal combustion reaction decreased,and the number of activated molecules increased.According to the formula k=Aexp(-E/RT),it was found that adding dedusting sludge with a content of 3%～5%increased the coal powder reaction rate constant.It showed that adding 3%～5%sludge improved the kinetic conditions of pulverized coal combustion.(6)The components of the sludge were mainly iron oxides,gangues,and a small amount of dopant with alkali metals.At a certain heating rate,it was found that adding Fe3O4,K2CO3 and CaO present in the sludge improved combustion performance of pulverized coal.From the perspective of reaction kinetics,the 5%content of Fe3O4 and the 3%content of K2CO3 reduced the kinetic activation energy of pulverized coal,increased the reaction rate constant and the possibility of reaction.Therefore,discovering from pulverized coal combustion performance and molecular activation,the promotion of pulverized coal combustion by sludge was related to the content of Fe3O4 and K2CO3 in the sludge.(7)Most iron oxides have strong catalytic oxidation performance.Due to the introduction of iron oxides in sludge,there were Fe2O3,Fe3O4,FexO and other substances in the combustion process of pulverized coal,which accelerated the cracking reaction of pulverized coal itself and made the reaction proceed quickly.Therefore,the promotion of pulverized coal combustion resulted from iron oxide in sludge.The best proportion of sludge was 3%～5%,which can make the best combustion effect of pulverized coal.Therefore,sludge can also be used to realize comprehensive utilization of resources.