Wear of coal logs in pipe

The wear characteristics of small (49 mm diameter) coal logs (i.e. compacted coal cylinders) having an approximate length of 76 mm were tested in a steel pipe in the laboratory. For each individual test, three identical coal logs were compacted from the same batch of materials under the same compaction conditions. Six factors that affect coal log wear were varied in the tests, one at a time, to assess their individual effects. These factors include: coal type, binder concentration, coal log diameter, compaction temperature, water pressure encountered by coal logs, and pipe interior roughness. The results showed that logs made of subbituminous coal were more resistant to abrasion than logs made of bituminous coal. The addition of 0.5 wt.% binder to coal mixture made logs six times more wear resistant than binderless logs. Coal logs prepared with larger diameter ratio and tested at lift-off velocity performed better than smaller diameter-ratio logs tested at the same velocity. Lift-off velocity is the minimum mean velocity of the fluid (water) at which the coal logs are completely suspended (levitated) by the flow in the pipe. An optimal compaction temperature of the order 80°C resulted in more wear-resistant logs than the other compaction temperatures tested. Testing coal logs in a pressurized pipe resulted in more durable and less abrasive coal logs. Finally, coal logs tested in a rough pipe encountered more wear than coal logs tested in a smooth pipe. The results of this study suggest that coal can be compacted at coal mines into strong cylinders (logs) for transportation to power plants by using large-diameter underground steel pipelines.