Research on Water Seal Flame Arrestors and Explosion Venting - RTO System Project

In the process of coal mine gas extraction and transmission, ensuring safety requires maintaining high-concentration gas extraction for utilization while avoiding explosion risks at the discharge end, as well as preventing contact between ignition sources and low-concentration gas. Common foreseeable ignition sources in gas extraction systems include:

1. Lightning strikes on exhaust pipes;
2. Backfire at the gas utilization end;
3. Static electricity in gas transmission pipelines;
4. Artificial sparks on the ground.

Although lightning protection, grounding, and pipeline bonding can reduce ignition risks, additional protective devices are still necessary to prevent explosions from damaging equipment or spreading underground.

Relevant Standards:

• GB 50471-2008 "Code for Design of Coal Mine Gas Drainage Engineering"stipulates that when utilizing gas, the pipeline system on the discharge side of the extraction pump must be equipped with safety devices to prevent backfire, backflow, and explosions.
• GB 40881-2021 "Design Code for Safety Assurance Systems of Low-Concentration Gas Pipeline Transportation in Coal Mines"requires that safety facilities for low-concentration gas pipelines include flame arrestor and explosion venting, explosion suppression, and explosion blocking devices based on different principles. Water seal flame arrestors and explosion venting devices should be prioritized.
• AQ 1072-2009 "Technical Specifications for Water Seal Flame Arrestor and Explosion Venting Devices in Gas Pipeline Transportation" specifies requirements, test methods, inspection rules, labeling, packaging, transportation, and storage.

Principle of Water Seal Flame Arrestor and Explosion Venting Devices

The device prevents backfire and explosions by using water to isolate flames, confining them to the explosion site, and preventing the ignition of gas on the intake side. Meanwhile, the pressure generated by the explosion is released through venting components, mitigating the explosion's impact.

Structure and Operation:

                                                   a.Single-Barrel Structure                                                                 b. Double-Barrel Structure
1—Inlet End;
2—Outlet End;
3—Explosion Venting Component;
4—Sealing Water;
5—Water Level Controller;
6—Glass Tube Water Gauge;
7—Metal Flow Distribution Screen

• • Under regular operation, gas flows from left to right. The water seal submerges the left intake pipe, allowing gas to pass through the water seal into the internal space of the device before exiting through the right outlet.
  • During an explosion(e.g., at the utilization or discharge end), the shockwave propagates backward (right to left). High-pressure gas first impacts the venting components to release pressure, while flames entering the water-seal barrel are blocked by the water-sealed intake, preventing further propagation and thus stopping the explosion.

To minimize pressure loss, the flow area must match the pipeline diameter. For large-diameter pipelines, the barrel size becomes unwieldy, complicating manufacturing, transportation, and installation.

High-speed gas flow agitates the water surface, carrying droplets into the outlet pipe, necessitating frequent replenishment.

Improved Double-Barrel Design:

• Most water droplets agitated by the gas settle in the left barrel while any remaining droplets carried into the venting barrel return via a connecting pipe, reducing water loss and the need for frequent replenishment.

Key Parameters in Standards

1. Venting Pressure

• Explosions generate overlapping shockwaves, creating extreme pressure at the tail end. Venting ports are designed to rapidly release this pressure.
• Tests show venting pressures often exceed 100 kPa. AQ 1072-2009specifies a venting pressure range of 90–120 kPa, significantly higher than normal gas transmission pressure, ensuring safety.
  2. Water Seal Height
• A balance is needed: sufficient height to block flames but not excessive pressure loss. Gas extraction pumps (e.g., water-ring vacuum pumps) operate at low outlet pressures (a few kPa). Excessive water seal height increases pump load.
• AQ 1072- 2009 mandates that the effective water seal height block flames while keeping the device's pressure loss below 2.0 kPa. Minimizing height is recommended where safety permits.
  3. Flow Distribution Screen
• Observations show that gas flow causes violent water surface fluctuations, creating large gas gaps that may allow flames to bypass the water seal.
• The intake pipe's bend creates uneven flow velocities (higher on the outer radius), leading to non-uniform water surface impact and potential flame transmission.
• AQ 1072- 2009 requires installing a stainless-steel flow distribution screen (mesh count ≥ 4) to ensure uniform gas velocity and water surface impact, preventing large gas gaps.

Conclusion

Water seal flame arrestors and explosion venting devices are critical for coal mine gas extraction safety, isolating flames and venting pressure to protect systems. Standards define key parameters like venting pressure (90–120 kPa), water seal height (balancing flame blocking and low-pressure loss), and flow uniformity (via screens) to ensure effectiveness.

Future advancements may integrate smart sensors and automation for real-time monitoring and adjustment, enhancing safety. Multi-principle protection systems (e.g., combining suppression and blocking) could further strengthen pipeline safety, driving safer and more efficient gas extraction and utilization.

Innovation and standardization will continue to bolster coal mine safety and gas resource utilization.