Effect Of Dry Coal Size Distribution On Coke Quality And Its Mechanism

Since Japan’s Nippon Steel Corporation developed a dry coal pre-pressing system（DAPS）that reduces the moisture content of coal to 2%-4%in 1992,the dry coal coking process has effectively reduced coking heating fuel and improved coal loading.The advantages such as conditions,prolonging furnace life,shortening coking time and improving coke quality are widely concerned.However,in addition to the moisture content of the loaded coal,the factors affecting the quality of coke include the coal quality,fineness,bulk density,and coking process.At present,most coking plants in China use a coal preparation process followed by powder preparation,which does not take into account the hardness differences of the individual coals,and cannot make the individual coals fully utilize their coking performance during the coking process.At the same time,in China’s coking production,the granularity characteristics of the incoming coal materials are generally expressed only by the fineness,and this concept can only explain the mass percentage of coal particles smaller than 3 mm in the coal materials to the total coal,it cannot represent the uniformity of the coal particle size distribution.Therefore,in order to further optimize the coking process of dry coal,by studying the influence of the particle size and particle size distribution of dry coal coking blended coal on the properties of the colloidal layer,the coke optical structure and coke quality,it is of great significance for the rational use of coal resources,optimization of the coal blending structure,and improvement of coke quality.In this thesis,based on the industrial analysis,total sulfur analysis,and determination of the adhesion index of ten single coals,the experiment of the colloidal layer was carried out on ten kinds of single dry coals with different particle sizes（2%moisture）,and the influence of particle size of dry coal on the colloidal layer index was obtained.Then,from the microscopic perspective,the changes in the content of the coke-forming optical structure of different coal samples and the particle size of dry coal in the optical structure of a single coal coke were studied.Finally,based on the above experiments,a reasonable coal blending scheme was designed.A 5 kg small coke oven coal blending coking experiment was performed on the blended coal in the dry condition.The obtained cold coke samples were analyzed for cold strength,thermal performance,and SEM.Based on coke characteristics formed under different particle sizes of single coal,the in-depth study of the fineness and particle size distribution of dry coal combined with the coke crushing strength and abrasion resistance,coke reactivity and strength after reaction and the mechanism of influence.Through the above studies,the following conclusions are mainly drawn:（1）As the particle size of dry coking coal changes,the colloidal layer index varies with the type of coal.The maximum thickness Y of the colloidal layer generally increases first and then decreases;the final volume shrinkage X value increase trends typically.（2）As the degree of coal metamorphism increases,the content of the mosaic structure increases first and then decreases,and the content of fibrous and lamellar tissue increases.Moreover,the dried coal particle size has different effects on the optical microstructure content and OTI index of single coal.With the increase of particle size of most dry coals,the OTI index decreases,the anisotropy content decreases,and the coke quality decrease.（3）In the case of coking of dry coal,the proper blending of coal fineness and reasonable particle size distribution is conducive to improving coke quality.Under the premise that the moisture content is 2%and the test coal blending ratio,changing the blending ratio of different particle sizes can be determined,when the dry blended coal has a fineness of 90%and a particle size of 0-0.5 mm,0.5-1 mm,1-2 mm,2-3 mm,and>3 mm,the proportions are 17.50%,20%,31.5%,21.25%and 10%,the coke mechanical strength,coke reactive CRI and post-reaction strength CSR are the best.（4）Compared with the wet coal coking scheme,various performance indexes of the coke obtained from the dry coal coking scheme are significantly improved.When the coal particle size is moderate,the generation of crack centers can be effectively reduced.A reasonable particle size distribution can also reduce coke pores,smooth the surface,thicken the pore walls,reduce the contact area with CO₂,and reduce the thermal reactivity of coke.