Influence of Elevated Temperature and Gas Atmosphere on Abrasion and Interface Properties in Blast Furnace and Pilot Oven Cokes

This project developed a novel approach using rotational tribology testing to investigate the mechanical properties and abrasion resistance of the coke reactive maceral derived components (RMDC), inertinite maceral derived components (IMDC), and the interfaces between these two phases, at room temperature and at elevated temperatures of up to 950°C. The originality of this approach lay in the ability to apply tribological testing to the porous coke surface at elevated temperatures under a controlled inert or CO2 reactive atmosphere.

Coke wear characteristics were quantified via:

• the application of advanced microscopy techniques and
• analysis of the coefficient of friction during tribological testing.

Two sets of coke samples were selected for this project. These include a bosh coke sample retrieved from an operating blast furnace and a near-matched feed coke, and pilot oven coke samples from three single coals, covering a range of coal rank, petrographic composition and two different coal measures.

Blast Furnace Coke Samples

High temperature abrasion resistance for both the bosh and feed cokes was lower than at room temperature. The reduction in abrasion resistance was observed for both the RMDC and IMDC, and at interfaces.  The bosh coke showed lower resistance to abrasive wear at room temperature compared to the unreacted feed coke samples, indicating that the higher temperature and adverse environment the bosh coke was exposed to in the blast furnace resulted in reduced resistance to abrasion.  Feed coke samples that had been pre-reacted with CO2 showed a similar trend in mean COF over time to the bosh coke samples. This suggests that the CO2 attack during the pre-reaction 'levels' coke properties, to some extent, and effectively overwrites the effects of prior CO2 exposure.  The bosh coke IMDC showed more severe damage than in the corresponding feed coke sample at 950°C, suggesting that the thermal damage to the IMDC is accentuated by prior gasification. In a CO2 atmosphere, the mean COF and wear severity ratings for the bosh coke were within measurement error of the feed coke samples. This suggests that the in-situ reaction with CO2, like the pre-reaction of the feed coke with CO2, 'levels' coke properties and results in the feed coke samples showing a similar trend to the bosh coke.

Pilot Oven Coke Samples

All pilot oven cokes tested showed an increase in progressive macropitting at the sample surface with an increase in the tribological testing temperature from room temperature to 400°C to 950°C. This indicates that deterioration in abrasion resistance was observed even at 400°C, and was accentuated at 950°C.  A relatively low CSR coke, C426, showed more severe wear and damage than high CSR coke C395 following tribological testing of pre-reacted samples at both room temperature and 950°C.  

The new finding from this project is that cokes become increasingly susceptible to abrasion as the temperature is increased, even in the absence of carbon dioxide. This highlights that abrasion of cokes in the blast furnace is more important than hitherto realised, and may need to be directly measured, since differences in abrasion resistance between cokes would affect both the susceptibility of the coke to breakdown and the generation of fines in the furnace.