🎓 Lesson 21
D5
Specific Energy Consumption (SEC) Benchmarking Across Technologies
Specific Energy Consumption (SEC) tells you how much energy it takes to break one ton of rock—like measuring fuel efficiency, but for blasting.
🎯 Learning Objectives
- ✓ Calculate SEC for a surface blast using explosive energy content and blasted tonnage
- ✓ Analyze SEC trends across blasting, primary crushing, and SAG milling to identify energy bottlenecks
- ✓ Explain how rock strength, fragmentation quality, and equipment selection influence SEC values
- ✓ Apply SEC benchmarks to evaluate the energy performance of a proposed blasting design versus industry best practice
📖 Why This Matters
Mining accounts for ~11% of global industrial energy use—and blasting and comminution consume over 60% of that. SEC is not just an academic metric—it directly impacts operating costs, carbon footprint, and permit approvals. Engineers who master SEC benchmarking can reduce energy intensity by 15–25% through smarter blast design and downstream integration, turning sustainability into competitive advantage.
📘 Core Principles
SEC bridges geomechanics, explosives engineering, and process integration. At its foundation lies the concept that energy is conserved—but not all input energy contributes to useful fragmentation; losses occur via seismic radiation, airblast, flyrock, and oversize generation. SEC must be evaluated system-wide: from explosive energy release (based on TNT-equivalent or calorific value) to delivered energy at the rock face, then propagated through crushing and grinding stages. Critically, SEC is not static—it depends on rock competency (UCS), joint density, burden-to-spacing geometry, and downstream equipment efficiency. High SEC often signals poor fragmentation (increasing secondary crushing load) or suboptimal powder factor, not just inefficient explosives.
📐 Blast-Specific SEC Calculation
This formula computes SEC for the blasting stage only, using net explosive energy and total fragmented tonnage. It enables direct comparison with crushing/grinding SEC and supports integrated energy modeling.
Blast Stage SEC
SEC_blast = (m_explosive × E_energy) / M_fragmentedCalculates specific energy consumption for the blasting operation only.
Variables:
| Symbol | Name | Unit | Description |
|---|---|---|---|
| SEC_blast | Blast-specific energy consumption | MJ/t or kWh/t | Energy consumed per tonne of fragmented material |
| m_explosive | Mass of explosive used | kg | Total charge mass deployed in the blast round |
| E_energy | Energy density of explosive | MJ/kg | Net usable energy per kilogram (e.g., ANFO = 3.0, emulsion = 3.8, dynamite = 6.5) |
| M_fragmented | Total fragmented tonnage | t | Measured or estimated mass of rock broken and ready for loading |
Typical Ranges:
Hard rock surface blasting (UCS > 150 MPa): 1.8 – 3.5 MJ/t
Soft rock or coal surface blasting: 0.8 – 1.6 MJ/t
Underground development heading: 3.0 – 6.0 MJ/t
💡 Worked Example
Problem: A surface mine blasts 12,500 tonnes of granite (UCS = 220 MPa) using 4,800 kg of ANFO (energy density = 3.0 MJ/kg). Calculate SEC in MJ/t and kWh/t.
1.
Step 1: Compute total explosive energy = 4,800 kg × 3.0 MJ/kg = 14,400 MJ
2.
Step 2: Divide by blasted tonnage = 14,400 MJ ÷ 12,500 t = 1.152 MJ/t
3.
Step 3: Convert to kWh/t: 1.152 MJ/t ÷ 3.6 = 0.32 kWh/t (since 1 kWh = 3.6 MJ)
Answer:
The blast SEC is 1.15 MJ/t (0.32 kWh/t), which falls well below the typical range of 1.8–3.5 MJ/t for hard rock surface blasting—indicating high energy efficiency likely due to optimal burden/spacing and low oversize.
🏗️ Real-World Application
At Newmont’s Boddington Mine (Western Australia), engineers reduced overall comminution SEC from 18.7 to 14.2 kWh/t by redesigning blast patterns to improve fragmentation (P80 reduced from 125 mm to 82 mm), thereby decreasing SAG mill load and liner wear. Blast SEC dropped from 2.4 to 1.6 MJ/t (0.44 to 0.44 kWh/t), while downstream crushing SEC fell 22%—demonstrating how upstream SEC optimization cascades through the entire separation train.