Impact of coal density on heavy equipment efficiency in mining operations: A case study of silicified and low rank coal

Abstract

The operational efficiency of heavy equipment in surface mining is fundamentally influenced by the physical characteristics of the extracted material. Variations in coal density, particularly the presence of highly abrasive silicified coal and low-rank (low-calorific value) coal, directly affect excavator cycle times, bucket fill factors, and machine productivity measured in tons per hour. This study addresses the challenge of quantifying how these specific material properties impact the utilization efficiency of heavy equipment (excavators) in open pit mining operation. Data collection involved direct time studies of excavator cycle times (digging, swinging, dumping, returning) across two distinct material types: highly dense, silicified coal and lower density, low-rank coal. The study found a significant inverse correlation between coal density and the efficiency metrics of heavy equipment. In this case digging time for a single pass on silicified coal increase by 183% compared to soft coal and the digging time per pass is minimal on low rank coal. For a PC1250 excavator with a 7.5 m³ bucket capacity, the elevated cycle time results in an hourly output far below that of low-rank coal. Specifically, production drops to 471 m³/hour, which is only 46% of the standard PC1250 production rate (1,018 m³/hour based on a standard cycle time of 26.5 s per pass). Conversely, Low Rank Coal with faster digging rates than silicified coal, Low rank coal achieves a shorter total cycle time per production cycle. The estimated productivity reaches 881.25 m³/hour, or 86.5% of the PC1250 standard capacity.