Nexisense Coal Mine Safety Gas Sensors: Liquid CO₂ Fire Prevention System Integration Solution

In the prevention and control of spontaneous combustion in coal mine goafs, liquid carbon dioxide, with an expansion ratio of approximately 600 times (at 15°C, 0.1 MPa), strong heat-absorbing cooling effect, rapid diffusion and filling, and high adsorption characteristics on coal, has become an effective means for inerting, explosion suppression, and inhibiting oxidation of residual coal. In combination with relevant regulations from the National Mine Safety Administration, liquid CO₂ injection systems must be equipped with continuous gas composition monitoring to ensure O₂ concentration is below the asphyxiation threshold, CO₂ in return air does not exceed 1.5%, and in intake air does not exceed 0.5%, preventing secondary asphyxiation risks.

Nexisense series gas sensor modules, with high-selectivity optical and electrochemical principles as the core, support multi-parameter online monitoring, suitable for real-time feedback and closed-loop control throughout the entire liquid CO₂ fire prevention process, and have achieved stable integration in multiple mines with high spontaneous combustion tendency.

Core Application Mechanism of Liquid CO₂ in Coal Mine Fire Prevention

After liquid CO₂ is injected into the goaf, it rapidly vaporizes, producing volume expansion and low-temperature effects (vaporization heat absorption approximately 577.8 kJ/kg), effectively compressing oxygen concentration in the oxidation zone, lowering residual coal temperature, and inhibiting chain oxidation reactions. At the same time, the high adsorption property of CO₂ results in a slower release rate than nitrogen, prolonging the duration of inerting.

Typical processes include surface/underground storage tanks, pressurized delivery pipelines (low-temperature and high-pressure resistant), and release ports arranged in the oxidation zone. During injection, continuous monitoring of gas composition changes in the goaf and return air flow is required to achieve closed-loop concentration regulation.

Role of Sensors in Coal Mine Safety Monitoring and Nexisense Integration Advantages

Coal mine safety monitoring systems (KJ series, etc.) require real-time and continuous monitoring of multiple gases such as CH₄, CO, CO₂, and O₂. Nexisense modules use NDIR (non-dispersive infrared) for high-precision detection of CO₂/CH₄ and electrochemical for CO/O₂, combined with temperature/humidity compensation algorithms, ensuring drift <±3% FS/year in high-dust, high-humidity, wide-temperature (-20~60°C) environments.

Strong system compatibility: Supports RS485 Modbus RTU, 4-20mA analog output, and switch quantity alarms, easy to connect to KJ95, KJ335 and other coal mine safety monitoring substations or PLCs, realizing gas overrun power cutoff and CO₂ concentration-linked ventilation regulation.

Typical Project Application Cases

Goaf Inerting Fire Prevention Project

During the shutdown period of the 1300+ fully mechanized caving face in a large mine in Northwest China, a mobile liquid CO₂ device was used to inject into the goaf. Nexisense CO₂/O₂ sensors were deployed at the return air corner and outside the sealed area, accessing the surface monitoring platform via Modbus protocol, achieving closed-loop control with O₂ dropping to<12% and CO₂ stabilizing in the 1-1.5% range before and after injection. The project verified that injecting 16 t of liquid CO₂ covered approximately 10,400 m³ of space, significantly reducing oxidation zone temperature and restoring residual coal spontaneous combustion indicators to normal.

Coal Bunker and High-Rise Area Emergency Inerting

For coal bunker fire hazards, Nexisense multi-parameter sensors are integrated into mobile fire extinguishing devices, achieving synchronous monitoring of CO, CO₂, and O₂ during injection. The system links automatic ventilation cutoff and activation of local fans for dilution to prevent concentration overrun. In actual applications, response time<10 s, with O₂ concentration rapidly dropping from 21% to below the safety threshold.

Working Face Withdrawal and Sealed Area Opening Monitoring

During withdrawal from spontaneous combustion coal seams, Nexisense sensors are placed at return air roadways and inside/outside sealed walls to monitor CO/CO₂ gradient changes and pressure differences. Data is uploaded to cloud platforms, supporting trend analysis and warning threshold settings to ensure O₂ >18% and CO<24 ppm before opening.

Selection Guide and System Integration Considerations

Key selection parameters:

• Range: CO₂ 0-5%/20% vol (inerting monitoring), O₂ 0-25% vol, CO 0-1000 ppm, CH₄ 0-4% vol.

• Accuracy: ±(30 ppm + 3% reading) or better, response time T90<15 s.

• Interface: RS485 Modbus RTU (default), 4-20mA, switch quantity, LoRa wireless optional.

• Protection: Ex d I Mb / Ex ia I Ma explosion-proof, intrinsically safe, IP65 or above.

• Power consumption:<200 mW, suitable for KJ substation power supply.

Integration considerations:

• Sensor installation location should avoid direct injection zones; recommend sampling pipeline + filter to prevent dust/moisture.

• Pipeline design should minimize dead volume to ensure gas transmission delay<30 s.

• EMC protection: Shielded cables, power isolation to prevent underground frequency converter interference.

• Calibration cycle: Recommend on-site zero/span calibration every 3-6 months, supporting ABC automatic baseline or manual nitrogen/fresh air calibration.

• System linkage: CO₂ overrun (return air >1.5%) triggers increased ventilation or personnel evacuation alarm; O₂<18% links injection stop.

• Data fusion: Integration with fiber optic temperature measurement and bundle tube systems to achieve multi-source data analysis.

Nexisense OEM/Customization and Bulk Supply Advantages

Nexisense focuses on intrinsically safe sensor R&D for coal mines and provides OEM services:

• Custom range, interface protocol (extended Modbus registers, custom protocol), housing material.

• Firmware optimization: Integration of customer-specific compensation algorithms (such as pressure/temperature cross-compensation).

• Bulk delivery: Stable monthly capacity, independently controllable supply chain, delivery in 6-8 weeks.

• Technical support: Complete SDK, 3D models, on-site debugging guidance, 5-10 year lifecycle commitment.

These features help integrators reduce secondary development costs, improve system reliability, and enhance project competitiveness.

Frequently Asked Questions (FAQ)

1. How to prevent personnel asphyxiation risk during liquid CO₂ injection?
   Through Nexisense O₂/CO₂ sensors for real-time monitoring of return air corner and intake/return air flow concentrations, when O₂<18% or="">1.5% (return air), the system automatically alarms and links ventilation adjustment or injection stop to ensure safe working space.

2. How stable is the NDIR CO₂ sensor in high-dust, high-humidity coal mine environments?
   Nexisense modules use hydrophobic optical windows + internal heating + filtered sampling design, combined with dual-channel reference compensation, achieving drift <±0.5% FS/year under humidity 0-99% RH (non-condensing) and dust<100 mg/m³.

3. How to seamlessly integrate sensors with existing KJ coal mine safety monitoring systems?
   Supports standard RS485 Modbus RTU protocol for direct access to substation acquisition modules; provides 4-20mA analog output compatible with older systems; SDK includes sample code supporting RTOS embedded development.

4. What key parameter monitoring is required for goaf inerting effect evaluation?
   Focus on monitoring O₂ concentration decline trend, CO₂ distribution gradient, CO generation reduction, and temperature changes; Nexisense multi-parameter modules can simultaneously collect CH₄, CO, CO₂, O₂ to achieve dynamic division of the “three zones”.

5. Does OEM customization support specific explosion-proof ratings and communication extensions?
   Supports Ex ia I Ma intrinsically safe and Ex d I Mb flameproof customization; can extend LoRa wireless, CAN bus, or Ethernet interfaces to adapt to wireless networking needs in smart mines.

6. How to optimize ventilation control strategy before and after liquid CO₂ system injection?
   Strengthen local ventilation before injection to dilute residual gas; monitor concentration gradient during injection and dynamically adjust air volume to prevent leakage; maintain slight positive pressure ventilation after injection to promote uniform inert gas distribution.

7. How to compensate for zero-point drift during long-term sensor operation?
   Supports ABC automatic baseline calibration (assuming periodic exposure to fresh air) or manual nitrogen zero-point calibration; built-in temperature/pressure compensation algorithms, with on-site verification once every 12 months.

8. How applicable is Nexisense in coal mine emergency rescue scenarios?
   Low-power module design suitable for mobile monitoring equipment; fast response<10 s, supports multi-gas in-situ analysis, providing O₂, CO, CH₄ explosion/toxicity risk assessment basis for rescue decision-making.

Conclusion:

Nexisense is committed to deep cultivation in the field of coal mine gas monitoring technology, assisting system integrators and engineering project parties in building reliable liquid CO₂ fire prevention and safety monitoring systems. We welcome coal mining enterprises, monitoring system vendors, and emergency rescue equipment suppliers to contact us for detailed specification sheets, prototype testing, or customized solution discussions, jointly improving mine disaster prevention and control levels and promoting high-quality development of safe production.