Desulfurization thermodynamics experiment of stainless steel pickling sludge

A technical idea of returning stainless steel pickling sludge to smelting process so as to recycle valuable metals of Fe, Cr, and Ni was proposed, expecting to realize sludge detoxification and resource utilization. Thermodynamics calculation showed that not only most valuable elements including Fe, Cr and Ni, but also the harmful element of sulfur in pickling sludge can be enriched into molten metal. As a result, a theoretical study on desulfurization thermodynamics of sludge pretreatment was conducted, and results indicated that complete desulfurization temperature of pure pickling sludge was above 1400℃. When 0.5-0.8% carbon was added as reducing agent, the complete desulfurization temperature was reduced to 1000℃ or below. Desulfurization roasting experiment indicated that desulfurization rate at 1400℃ under inert environment was 78.74% and maximum desulfurization rate at 1000℃ under reducing environment was 91.62%.

Volatilization behaviour and volatilization kinetics of CaF2-Na2O-CaOSiO2-Al2O3-MgO-B2O3 synthetic mould flux

To reduce the volatilization of the volatile-containing slags and obtain accurate measurement results of slag performance,the volatility degree and deviation mechanism must be determined.Non-isothermal thermogravimetric analysis at different heating rates was used to establish the volatilization kinetic model,and it reveals the volatilization mechanism of CaF2-Na2O-CaO-SiO2-Al2O3-MgO-B2O3 synthetic sodium-containing fluoride mould flux.The results demonstrated that the evaporation of NaF and SiF4 was the decisive factor that led to the change in composition and deviation of properties of the tested slags.The most probable kinetic mechanism function for the evaporation of volatile component from sodiumcontaining fluoride mould flux could be expressed by g(α)=[—ln(1-α)]^2/3,with an apparent activation energy of 164.866 kJ mol^-1 and pre-exponential factor of 2.13×10^-4 s^-1,where α is the conversion rate at any time step in the volatilization process.The reaction mechanism was random nucleation followed by growth,which was the limiting factor for the volatilization of synthetic sodium-containing fluoride mould flux.The method of increasing heating rate and adding protection gas in the measurement system will help to obtain more accurate results of slag performance.

Interaction mechanism between coal combustion products and coke in raceway of blast furnaces

The interaction mechanism between the combustion products of pulverized coal injected and coke in the raceway of blast furnace was studied through thermodynamic calculation and experiments.The results indicated that additives significantly affected the melting property of coal ash in high temperature zone.Although the unburnt char,raw coal ash,and catalyzed coal ash failed to wet the coke surface,the wettability of the catalyzed coal ash on the coke was greater than that of the raw coal ash.Since the unburnt char had weak reaction with the coke surface,it showed little influence on the surface morphology of the coke.The interaction between the raw coal ash and the coke gave rise to the increase in the pore size on the coke surface.However,the raw coal ash only affected the coke surface and the entrances of the pores owing to its poor fluidity.After being melted,the catalyzed coal ash was expected to immerge into the inside part of the coke and then react with the coke,resulting in an expansion and increase of coke cavities.The raw coal ash and the unburnt char reduced the coke reactivity,while the catalyzed coal ash improved the coke reactivity.Thereinto,the coal ash containing Fe2O3 exhibited a larger influence on the reactivity than that containing CaO.

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.

Effects of microstructural evolutions of pyrolysis char and pulverized coal on kinetic parameters during combustion

Pyrolysis chars have potential as fuels for pulverized coal injection(PCI);however,their proper and efficient utilization requires evaluation of char combustion kinetics.The combustion characteristics of two chars(F-char and M-char)and two pulverized coals(H-PCI and P-PCI)were analyzed herein using thermogravimetric analysis–mass spectrometry.The apparent activation energy(Ea)of the sample under non-isothermal combustion conditions was obtained using the Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods,and the reaction mechanism for the fuels was established using the Malek method.Additionally,changes in the microscopic pore structure and carbon chemical structure of the fuels at different stages of combustion were characterized using N2 adsorption and X-ray diffraction to analyze the relationship between microstructural evolution and Ea.The results suggested that Ea of the sample first rapidly decreased and then became stabilized during combustion.Compared with pulverized coals,the two chars presented more developed micro-scopic pore structure,less-ordered carbon chemical structure and lower Ea during reaction.During combustion,the stacking height of the aromatic layer first decreased and then increased,whereas the specific surface area first increased and then decreased.The volatile content significantly influenced Ea only during the initial stage of combustion.During the middle stage,Ea was controlled more by the microscopic pore structure and the carbon chemical structure,and those influences disappeared in the later stage.The transition point of the structures affecting Ea occurred at a combustion rate between 52.9%and 72.0%.In general,the microscopic pore structure and the carbon chemical structure influenced kinetic parameters more than the volatile content.

Analysis of energy consumption for lump coal degradation in melting gasifier

The volume hypothesis,a theory about the energy scale of comminution,was adopted to analyze the degradation behavior of lump coal under different heating time.The breakage energy of chars was determined by a compression test,and the results show that the ultimate strength of chars decreased at the early stage during the heating process,resulting in a decrease of the char breakage energy.At the late stage during the heating process,the char breakage energy increased with the increase of heating time.The power consumption coefficients CKof different chars were determined by a drum experiment,and then the char degradation behavior under different power consumptions was predicted.In addition,agasification experiment was conducted to determine the gasification activation energy（with CO_2）of lump coal heated for different time.The results show that the gasification activation energy increased greatly at the early stage during the heating process,which showed opposite change to the breakage energy of chars.Furthermore,the internal temperature and heat changes of the bonded coal briquette were calculated by using an unsteady heat conduction equation.The large difference between the surface and the center temperatures of coal and the large amount of heat absorption at the early stage during the heating process may have a negative effect on the breakage energy of chars.