| Oxygen blast furnace(OBF) is an ironmaking process, where oxygen is used in stead of hot blast in traditional blast furnace. It has the advantages of high PCI rate, low coke rate, high productivity, and high top gas calorific value, and this will lead to a great revolution of blast furnace ironmaking process. Furthermore, without emission of NOx, OBF is aslo an environment-friendly blast furnace.Due to the great changes of the operation conditions, particularly the top gas recycling, high PCI rate, as well as the possible hot burden charging, the status of various regions in the furnace and the mass flow and energy flow in the process will be tremendously different from traditional blast furnace. It is thus necessary to study the regional and overall mass and heat balances, the gas flow in the furnace, the combustion behavior of PIC in the raceway area, as well as the possible hot top gas reforming for development and optimization of oxygen blast furnace process. Under such a background, the main content of this work are as follows.(1) A mathematical model of mass and heat balances is developed to calculate the mass and heat flows of OBF process. The model consists of a raw materials composition and slag quantitu and composition module, a top gas recycling module, a blast volume and gas composition module, dual balance module, a high temperature zone module and a shaft zone module.The calculation results show that, adiabatic combustion temperature of OBF process with top gas recycled to the furnace shaft is too high and the adiabatic combustion temperature of OBF process with top gas recycled to the furnace hearth is a little too low when the energy balance for the whole furnace and different zones are all satisfied. For OBF process with top gas recycled both the furnace shaft and hearth, when recycle gas volume is 550Nm3/tHM, and the recycle gas partition to hearth and shaft is 1:1, the heat partition in all regions of furnace and the adiabatic combustion temperature attain to a proper condition for furnace running. Hot burden charging can not decrease the coke ratio, but can improve the reduction condition in the shaft and increase the productivity of the furnace, and it can also make the operation adjustment of the furnace more flexible.(2) Taking a 2100m3 blast furnace as a example, and considering the distribution of voidage in the bueden bed. a three-dimensional mathematical model is developed to calculate the gas flow in the furnace. The gas velocity field is calculated with this model. The resisdence time distribution (RTD) of gas is also obtained by the nonsteady-state calculation of a tracer gas.The calculation results show that the gas flow in 2100m3 OBF is close to piston flow. As blast velocity increases from 200m/s to 307m/s, the mean residence time of gas in the furnace decreases from 14.5s to 9.7s, and the fraction of dead zone increases from 0.8% to 5.3%.(3) A mathematical model is developed to calculate the combustion of injected pulverized coal in and around the raceway. The combustion space of PC is devided into raceway zone, deadman zone and dripping zone. All the heterogeneous reactions of coal powder with oxygen, carbondioxide and steam are taken into account in the model. The combustion reaction of coke bed is also taken into account.The calculation results showed that, the blast forms a recirculation flow in the raceway and the gas velocity decreases dramatically from 160m/s to 3m/s in the coke bed. The coal particle follow with the recirculation flow of gas. have a residence time of 20ms to 50ms in the raceway. With the increase of oxygen enrichment in blast, the positions where the devolatilization of coal particles and maximum consumption devolatilized carbon take place shift toward tuyere exit, and this makes the pulverized coal combustion more completely.(4) An experiment platform for high temperature gas reforming is constructed. The influences of composition, temperature, carbon size and flowrate of gas to be reformed on the reforming effect experimentally studied. The results show the temperature of gas reforming plays a decisive role in the gas reforming.(5) An one-dimensional kinetic model for gas reforming though a carbon based packed bed is developed to simulate the reforming process. The calculation results show that, the reformed gas temperature increases with the increase of raw gas temperature and the decrease of raw gas oxidation degree at fixed bed height, but it can be controlled to meet the required temperature by addition of water vapour. With the increase of gas temperature, the carbon monoxide and hydrogen molar fraction of reformed gas increase as long as the oxidation degree of raw gas is high enough. The effects of bed height and particle size of carbon material are also studied. |
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