🎓 Lesson 9
D5
Energy Efficiency Benchmarking Workshop
Energy efficiency benchmarking is measuring how much useful work (like rock breakage) you get from each unit of blasting energy used.
🎯 Learning Objectives
- ✓ Calculate specific energy consumption (MJ/m³) for a given blast design using measured charge weight and excavated volume
- ✓ Analyze fragmentation distribution (P80) versus specific energy to identify optimal energy dosage for target ore recovery
- ✓ Apply the Energy Efficiency Index (EEI) to compare blast performance across different rock types and explosive systems
- ✓ Explain how burden-to-spacing ratio and stemming length influence energy coupling and efficiency loss
📖 Why This Matters
Every kilogram of explosive costs money—and generates vibration, flyrock risk, and environmental impact. In open-pit mines, 15–25% of total operating cost stems from drilling and blasting. Yet studies show up to 40% of explosive energy is wasted due to poor coupling, excessive burden, or suboptimal timing. Benchmarking energy efficiency isn’t just about saving dollars—it’s about predictable fragmentation, reduced shovel wear, lower crushing energy downstream, and meeting sustainability KPIs like CO₂e per tonne of ore. This workshop equips you to turn blast data into actionable insight—not guesswork.
📘 Core Principles
Energy efficiency in blasting hinges on three interdependent domains: (1) Energy Input—determined by explosive type (ANFO vs. emulsion), density, and detonation velocity; (2) Energy Coupling—the fraction transferred effectively into rock via borehole confinement, stemming, and burden geometry; and (3) Energy Utilization—how well that coupled energy achieves desired outcomes (fragmentation, displacement, low backbreak). Rock mass rating (RMR), joint spacing, and weathering control energy absorption and dissipation. Efficient blasts maximize near-field stress wave transmission while minimizing far-field energy leakage—requiring precise alignment of burden, spacing, and delay timing. The concept of ‘energy dose’ (MJ/m³) replaces simplistic ‘powder factor’ because it accounts for both explosive energy content and rock resistance.
📐 Specific Energy Consumption (SEC)
SEC expresses total explosive energy delivered per unit volume of rock broken. It enables direct comparison across blast designs, rock types, and sites—unlike powder factor (kg/t), which ignores explosive energy density and rock strength. SEC must be paired with P80 and crusher feed analysis to assess functional efficiency.
Specific Energy Consumption (SEC)
SEC = (W × E_{spec}) / VMeasures energy intensity of blasting in megajoules per cubic meter of broken rock.
Variables:
| Symbol | Name | Unit | Description |
|---|---|---|---|
| SEC | Specific Energy Consumption | MJ/m³ | Energy delivered per unit volume of fragmented rock |
| W | Total explosive mass | kg | Mass of explosives loaded in the blast |
| E_{spec} | Specific energy of explosive | MJ/kg | Energy released per kilogram (e.g., ANFO ≈ 3.0, heavy ANFO ≈ 3.3, emulsion ≈ 3.8) |
| V | Blasted volume | m³ | Measured volume of muck pile after blast (via LiDAR or photogrammetry) |
Typical Ranges:
Hard granite (RMR > 70): 0.5 – 0.8 MJ/m³
Weathered sandstone (RMR 40–55): 0.3 – 0.5 MJ/m³
Ore with high clay content: 0.6 – 1.0 MJ/m³
💡 Worked Example
Problem: A 12-m bench blast uses 1,850 kg of ANFO (energy density = 3.0 MJ/kg). Post-blast survey measures 9,200 m³ of fragmented muck. Calculate SEC and interpret against typical range for hard granite.
1.
Step 1: Compute total energy input = 1,850 kg × 3.0 MJ/kg = 5,550 MJ
2.
Step 2: Divide by excavated volume = 5,550 MJ ÷ 9,200 m³ = 0.603 MJ/m³
3.
Step 3: Compare to typical SEC range for competent granite (0.5–0.8 MJ/m³): 0.603 falls within optimal band, suggesting good energy utilization.
Answer:
The result is 0.603 MJ/m³, which falls within the safe and efficient range of 0.5–0.8 MJ/m³ for hard granite.
🏗️ Real-World Application
At Newmont’s Boddington Mine (Western Australia), engineers benchmarked SEC across four pit sectors over six months. Sector C showed SEC = 1.1 MJ/m³—35% above fleet average—with concurrent P80 > 120 mm and 22% shovel downtime due to oversized material. Root-cause analysis revealed under-stemmed holes and 12% higher than designed burden. After redesigning stemming height (+1.8 m avg.) and reducing burden by 0.7 m, SEC dropped to 0.72 MJ/m³, P80 improved to 78 mm, and shovel availability increased by 17%. This demonstrated direct linkage between SEC reduction and downstream operational gains.