Comparison of semi-coke with traditional pulverized coal injection and iron ore sintering fuels based on chemical structure and combustion behavior

Substantial semi-coke has been produced through the industrialized low-temperature pyrolysis process,which has great potential as an alternative fuel for pulverized coal injection(PCI)and iron ore sintering.X-ray diffraction,Raman spectroscope,and thermal analysis were used to compare the carbon chemical structure and combustion reactivity of semi-coke,pulverized coal,and coke breeze.The results show that the average volatile matter content in 46 types of semi-cokes is 8.94 wt.%.The fluctuation range of the characteristic parameters of the semi-coke chemical structure is d_(002)=(0.352–0.379)nm and A_(D1)/A_(G)=(2.51–7.92),while the fluctuation range of the characteristic parameters of pulverized coal is d_(002)=(0.348–0.373)nm and A_(D1)/A_(G)=(1.71–9.03)(where d_(002)means the interlayer spacing between the aromatic planes,and A_(D1)/A_(G)is an index that characterizes the degree of disorder of the char structure through the area ratio of the defect peak band D1 to the perfect graphite peak band G);the overlap between these ranges is relatively high.Contrarily,the fluctuation range of the characteristic parameters of coke breeze is d_(002)=(0.343–0.350)nm and A_(D1)/A_(G)=(0.75–2.51),which is markedly different from that of semi-coke.Semi-coke combustion reactivity is close to that of pulverized coal,but considerably better than that of coke breeze.In terms of chemical structure and combustion reactivity,semi-coke can be used as an alternative fuel for PCI;however,when used for sintering alternative fuel,matching of the heat supply and demand in the later sintering stage must be scrupulously analyzed.

3D model study of coal/coke combustion in a blast furnace effects of coal properties

A three-dimensional mathematical model of the combustion of pulverized coal and coke has been developed.The model is applied to the blowpipe-tuyere-raceway-coke bed region in an ironmaking blast furnace in one computational domain,which includes two parts:pulverized coal combustion model in the blowpipe-tuyere-raceway cavity and the coal/coke combustion model in the surrounding coke bed.The effects of coal properties are examined comprehensively,in terms of coal burnout and gas species distributions.The results indicate that using a coal of fine particle size or high VM content could improve burnout and would affect the gas composition considerably.The burnout is examined in two ways:compared with burnout along tuyere axis,burnout over the raceway surface is a more sensitive and sensible parameter to describe the amount of unburnt char entering the coke bed.The model is useful for examining the flow-thermo-chemical characteristics of the pulverized coal injection (PCI) process under various conditions in a blast furnace.

Thermal analysis and kinetic modeling of pulverized coal combustion accompanied with coke breeze

Pulverized coal injection technique has been widely used as a means of reducing coke consumption during ironmaking process.Owing to the increasing shortage of fossil fuels,other substitutes such as biomass,plastic,and waste tires have been studied in recent years.Coke breeze as one of the by-products of coking industries has been investigated as a substitute for partial pulverized coals.The combustion characteristics of blended fuels were estimated based on the flammability index C and the combustion characteristic index S.For different coke breeze additions,the combustion was divided into two stages,and the apparent kinetic parameters of the two stages were estimated by fitting the experimental data to the shrinkage reaction model and shrinkage diffusion model,respectively.Results showed that with the increase in coke breeze addition from 15% to 60%,the indexes C and S decrease,and the activation energy of the first stage remains almost constant,while that of the last stage increases from 16.89 up to 67.18 kJ mol^(-1),which indicates that adding coke breeze decreases the combustion efficiency of pulverized coal.Comparing the combustion and kinetic parameters under different coke breeze addition conditions,the optimal addition amount is suggested to be within 15%.