- Title
- Pulverised coal injection into blast furnace: a practical study of an integrated iron and steel works
- Creator
- Du, Shan-Wen
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2015
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The economic benefits of pulverised coal injection (PCI) into blast furnace include a reduction in the cost of hot metal, resulting primarily from decreased coke consumption and an increase in hot metal production. Since coal is consumed directly, without going through the cokemaking plant, PCI is also thought to be environmentally friendly. Therefore, PCI has become a standard practice in many blast furnaces worldwide. To improve the performance of PCI operation, a comprehensive understanding of pulverised coal combustion behaviours are required. The goal of this thesis was to study the coal burning characteristics in the regions of blowpipe, tuyere and raceway through both numerical and experimental methodology. From the validation of model, the calculation region and the application of calculated results in practice, the PCI combustion model was developed through 4 phases in this work: (1) validation of the coal combustion model by comparing its predictions with experimental data; (2) investigation into the influence of operation conditions to coal burnout in the regions of blowpipe and tuyere; (3) performance evaluation of coal blend injection in terms of pressure loss caused by combustion within a simplified raceway space; and (4) examination of combustion characteristics of oxy-coal injection technology in the regions of blowpipe, tuyere and raceway, which is a porous space featured by Eulerian-Eulerian multi-fluid approach. In the first phase, the performance of coal devolatilisation models and kinetic parameters were validated by comparing predicted gas temperature profiles with the experimental results of Burgess et al. (1983). It is found that the kinetic parameters proposed by Ubhayakar et al (1976) for the two competing devolatilisation model permit a reasonable simulation of the measured results for blast furnace conditions. The coal combustion in the regions of blowpipe and tuyere was modelled under the conditions of CSC’s N⁰3 blast furnace in the second phase. The influence of operation conditions to coal burnout was comprehensively studied. It is found early ignition can be achieved with higher coal burnout when the double lance is employed instead of the single one. Accordingly, the injection lance used at CSC was changed from the single to the double air-cooled coaxial lance arrangement in 2002. In the third phase, the calculation was extended to the raceway with simplified configuration. The performance of coal blend injection was examined. As indicated in the calculation results, a decrease in coal burnout is found with decreasing the coal volatile content, while the pressure loss within the raceway can be abated due to less volatile released to gas and moderate gas expansion in the combustion region. With improved permeability, more hot blast air can be introduced into the blast furnace for higher productivity. Consequently, the high volatile coal injection was replaced by the coal blend (mixtures of high and low volatile coals) injection at CSC in 2003. In the last phase, the Eulerian-Eulerian multi-fluid model was employed for the prediction of raceway configuration with consideration of coke combustion in all coke operation. Validation work against measured raceway shape and gas composition distribution by Nogami et al. (2005) indicates that the model is acceptable for the simulation. The calculation results show the oxy-coal lance injection enables to fulfil two contradictory conditions at the same time: (1) to retard the coal combustion for moderating the pressure loss in the upstream of coal plume; and (2) to enhance coal combustion and reduce unburnt char generation in the downstream of coal plume. Taking these advantages from the oxy-coal lance injection, blast furnaces can be operated with more blast for higher productivity, or with higher PCI rate for lower fuel cost, thereby achieving the goal of hot metal production with energy saving. In this work, a drop tube furnace has been established and used to provide fundamental insights on PCI coal combustion behaviours. The experiments were carried out in three stages. In the first stage, the volatile release and the generation of char particle and tiny aerosols in the region of coal plume were studied. Only the tested low volatile coal (HGI=85) with larger size (100-200 mesh) exhibits fragmentation during heating. This may encourage the use of low volatile coals in granular coal injection. Significant char agglomeration is found for both tested high and low volatile coals with smaller size (200-325 mesh). It implies that excessive grinding may be avoided in PCI operation. Considering the generation of tiny aerosols composed of soot particles and tar droplets, it is mainly determined by the content of volatile matter and elemental oxygen. In the second stage, a technology has been developed and employed at CSC to evaluate the combustion efficiency of PCI coals. It is found that the coal burnout increases with decreasing the fuel ratio (FC/VM), except for certain coals departing from the general trend. It can be explained by the effect of maceral content to coal combustion. When the coal size is smaller than 200 mesh, the burnout can not be improved further, resulting from the agglomeration of fine particles. In the PCI operation at CSC, the coal quantity passing through 200 mesh has been reduced from 80 to 60%. The experiments for the last stage aim to gain a fundamental insight into the combustion characteristics of pulverised biofuels under conditions pertinent to the raceway of blast furnace. From the van Krevelen diagram, it is found that the rate of hydrogen release from biomass fuels is faster than that of oxygen during the pre-treatment. An increase in pretreating temperature almost linearly decreases the burnout of biofuels. As revealed in the experimental results, the fuel properties, such as fuel ratio, burnout, and ignition temperature, of biomass torrefied at 300 °C or pyrolysed between 400 and 500 °C, are between a high-volatile bituminous coal and a low-volatile one. Therefore, the pretreated biomass can partially replace the coals consumed for PCI and blends with coals to keep reasonable burnout in raceways. It is emphasised that, due to the objectives of this thesis, some results or countermeasures obtained from the comprehensive experimental and numerical studies have been taken into PCI operation at CSC. This seems as a limitation of this study, but it may have a wide range of applications for the improvement of PCI operation.
- Subject
- pulverised coal injection; blast furnace raceway; coal devolatilation and combustion; torrefaction and carbonization of biomass; computational fluid dynamics; drop tube furnace; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1310029
- Identifier
- uon:21976
- Rights
- Copyright 2015 Shan-Wen Du
- Language
- eng
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