AbstractsEngineering

Laboratory evaluation of combustibility of coals for blast furnace pulverised coal injection

by Hongyu Li




Institution: University of Newcastle
Department:
Degree: PhD
Year: 2014
Keywords: coal combustion; pulverised coal injection; reactivity
Record ID: 1054972
Full text PDF: http://hdl.handle.net/1959.13/1051120


Abstract

Research Doctorate - Doctor of Philosophy (PhD) The concern about pulverised coal injection (PCI) into ironmaking blast furnaces has increased because of environmental issues and the shortage of coking coal resources. PCI technology incorporates the advantages of saving energy and cost, improving productivity and potentially reducing CO₂ release. However, injecting unsuitable coals affects the operation of blast furnaces negatively. One of the resulting problems is that unburnt char blocks the passage of fluid and gas transportation, therefore changing the distribution of gas and temperature in the blast furnace. Under these circumstances, it has been addressed that how to evaluate coals before being injected into a blast furnace. Direct evaluation of the combustibility of PCI coals in ironmaking blast furnace is difficult. Different test rigs have been used in the assessment, such as a pilot-scale PCI rigs firing at 25-69 kg/h, a laboratory-scale drop tube furnace (DTF) firing at 4 g/h. A PCI rig is designed to replicate the conditions in the blowpipe, tuyere and raceway of a blast furnace. Although a PCI rig can give a prediction of coal burning behaviour, it is costly and complicated and not always available. Alternatively, a DTF, with the advantages of low cost and easy operation, has been commonly used in the research of coal combustion. However, differences in temperature, heating rate and residence time exist in the two rigs. Significant influence on the devolatilisation of coal and combustion of residue char by these parameters has been suggested in the literature. This thesis therefore investigates coal combustion behaviour by burning coals of different ranks in a laboratory-scale DTF with an as-ground particle size distribution used in PCI industry, with some coals which have previously been combusted in a PCI test rig. This work is built on the hypothesis: a DTF can substitute for a PCI rig in the evaluation of PCI coals by ranking coal combustion performance against coal rank as quantified by the volatile matter (VM) content, and can identify coals that perform better or worse than expected. The objectives are specifically to: Compare the combustion performance of a range of coals combusted in a pilot-scale PCI rig and a laboratory-scale DTF. Establish the methodology to find if the ranking of coal combustion performance in PCI can be predicted by DTF tests on the same coals. Identify coals not fitting the ranking of combustion performance in the PCI rig and suggest reasons, including the clarification of combustion process in the PCI rig by a single particle combustion model. Twelve coals have been tested in the DTF (nine of them have corresponding combustion data in the PCI rig). The gas temperature of the DTF was set at 1450 °C, and coal feed rate was about 4 g/h. The yields of VM in devolatilisation and coal burnouts (at 21%, 22.6% and 26% O₂) were measured, respectively. The measured burnouts from the DTF were compared with the data previously obtained from the PCI rig. It was found that a linear…