1. What is CO₂ blasting?
CO₂ blasting (also known as CO₂ rock blasting) — formally referred to as liquid carbon dioxide phase-change fracturing technology — is a purely physical rock-breaking method. Its core principle involves rapidly heating liquid CO₂ inside a sealed fracturing tube, causing it to vaporize within 20–40 milliseconds. This phase change expands its volume by over 600 times, generating high pressure (up to 200–310 MPa). Once this pressure ruptures a preset-pressure shear disc, the high-pressure gas is released through an energy-release nozzle, fracturing the surrounding rock mass.
2. How does the CO₂ blasting system work?
- Charging: Liquid CO₂ is injected into a high-strength, reusable fracturing tube (liquid storage tube) via a charging system.
- Placement: The assembled fracturing tube is inserted into a pre-drilled borehole.
- Activation: An initiator delivers an electric current to the internal heating element (activator), instantly generating high temperature.
- Phase Change & Fracturing: The heat causes the liquid CO₂ to transition into a supercritical state, rapidly increasing pressure. When pressure exceeds the shear disc’s rupture threshold (e.g., 200–300 MPa), the disc fails.
- Energy Release: High-pressure CO₂ gas jets out through the energy-release nozzle at high velocity, impacting the rock and creating radial fractures. The “gas wedge” effect further propagates these cracks, ultimately breaking the rock.
3. What are the key components of CO₂ blasting equipment?
A complete CO₂ blasting system consists of three main subsystems:
- Charging System: Includes CO₂ storage tanks, filling machines, and tightening devices for safe liquid CO₂ loading into fracturing tubes.
- Blasting System: Centered around the fracturing tube, which comprises an energy-charging head, activator (heating tube), storage tube, preset-pressure shear disc, sealing gaskets, and energy-release nozzle. Also includes a high-energy pulse initiator.
- Monitoring System: Instruments for real-time monitoring of temperature, pressure, and ground vibration to ensure operational safety and evaluate effectiveness.
4. What are the main advantages of CO₂ blasting technology?
CO₂ blasting offers significant benefits due to its physical working mechanism:
- Safety: No chemical reactions, open flames, or toxic gases; low vibration frequency (0–60 Hz); minimal environmental impact; minimum safe distance as short as 1 meter.
- Eco-friendliness: Byproducts are primarily CO₂ gas and water vapor—non-polluting.
- Controllability: Energy output and direction can be precisely adjusted by varying CO₂ charge volume and shear disc thickness (which sets rupture pressure).
- Cost-effectiveness: The core fracturing tube (steel) is reusable hundreds of times; only the heating element and shear disc are consumables. Overall operating costs are competitive with, and in some cases lower than, traditional drilling and blasting.
- Efficiency: Concentrated energy release enables effective rock fragmentation. For specific rock types (e.g., granite, as documented), optimized hole patterns (e.g., staggered layout with 2–3 m spacing) achieve high efficiency.
5. In which scenarios is CO₂ blasting applicable?
CO₂ rock breaking and CO₂ mining technologies are widely used in applications requiring strict control over safety, environmental impact, and vibration:
- Mining: Open-pit coal, metal, and quarry stone extraction and presplitting.
- Municipal Engineering: Urban foundation excavation, subway tunneling, road construction — even near buildings.
- Underground Operations: Enhancing permeability for coalbed methane drainage and roadway development in mines.
- Special Applications: Clearing blockages in equipment, emergency rescue operations — anywhere conventional explosives are prohibited.
Summary
CO₂ blasting is an innovative, physical rock-fracturing technique that uses the rapid phase change of liquid CO₂ to generate high-pressure gas for rock breakage. It is safe, environmentally friendly, and highly controllable. The reusable fracturing tube is the technological core, and the process relies on instantaneous heating to trigger pressure buildup and fracture propagation. Compared to conventional explosive blasting, CO₂ blasting offers unique advantages in diverse rock-breaking scenarios, with equipment reusability being a key factor in its cost structure.