In compliance with industry standards (such as GB 15577 Safety Regulations for Dust Explosion Prevention, NFPA 652/654 standards) and the special working conditions of grain depots, this proposal ensures safety, efficiency, and regulatory compliance:
I. Design Objectives
Explosion-Proof Safety: Prevent dust explosions (grain dust has an explosive lower limit of 20-60g/m³ and a minimum ignition energy <100mJ).
Efficient Dust Removal: System air volume ≥3000m³/h, vacuum degree ≥25kPa, covering silo operation areas and conveying corridors.
Automated Control: Minimize manual intervention, equipped with safety interlocks and real-time monitoring.
Standard Compliance: Meet requirements of GB 50016, GB 15577, and ATEX/IECEx explosion-proof certifications.
II. Core Components of the System
1. Vacuum Cleaning System
Model: Water-ring vacuum pump (explosion-proof grade: Ex d IIB T4)
Advantages: Oil-free design to avoid dust adsorption; water medium isolates ignition sources.
Air Volume/Vacuum Degree: 3500m³/h @ 28kPa (selected based on silo capacity; recommended for 5000-ton single silos).
Explosion-Proof Structure: All-stainless-steel casing with explosion relief discs (when Pmax ≤0.1MPa, relief area ≥1m² per 10m³ container).
2. Dust Removal Unit
Primary Cyclone Separator:
Separation efficiency ≥95% (for dust particles >30μm), made of metal (antistatic treated).
Secondary Explosion-Proof Cartridge Dust Collector:
Filter material: PTFE-coated antistatic filter cartridges (surface resistance <10⁹Ω) with filtration precision of 0.3μm.
Cleaning method: Pulse backblowing (nitrogen inerting protection to prevent dust resuspension during cleaning).
Explosion relief devices: Flameless explosion vent (Q-BEV) + flame arrester valve (installed at pipe inlet).
3. Pipe Network and Suction Port Design
Pipe Layout:
Main pipeline: DN150 stainless steel (wall thickness ≥2mm), inclined ≥30° to prevent dust accumulation.
Branch pipelines: Cover silo discharge ports, conveyor transfer points, and ground cleaning points.
Suction Hoses:
Antistatic wear-resistant hoses (resistance <10⁶Ω) with quick-connect explosion-proof plugs.
Suction Tools:
Explosion-proof suction nozzles (copper alloy material), universal suction arms (fixed interfaces at silo tops).
4. Explosion Suppression and Monitoring System
Explosion Suppression:
Chemical isolators installed in pipelines (trigger time <15ms).
Monitoring:
Dust concentration sensors: Real-time monitoring of pipeline concentration (alarm threshold: 20% of lower explosion limit).
Temperature/spark detection: Infrared spark probes (response time ≤0.1s) linked to nitrogen fire extinguishing.
Static grounding monitoring: Ensure system grounding resistance <10Ω.
5. Intelligent Control Cabinet (Explosion-Proof Type)
Functions:
One-button start/stop, fault diagnosis, variable frequency air volume adjustment (energy-saving mode).
Interlock Control:
Excessive dust concentration → automatic shutdown → triggering inerting (N₂ injection).
Data Recording:
Stores operating parameters, supports OPC UA protocol for integration with grain depot DCS systems.
III. Key Explosion-Proof Measures
Eliminate Ignition Sources:
All motors/electrical components meet Ex d IIB T4 (surface temperature ≤135℃).
Pipeline flange bonding resistance <0.03Ω.
Control Dust Concentration:
Pipeline wind speed ≥20m/s (to prevent deposition), designed at 23m/s.
Explosion Relief Protection:
Flameless explosion vents installed on dust collector tops (relief area calculated).
Outdoor pipelines equipped with explosion relief ducts leading to safe zones.
Inerting Protection:
Nitrogen pulses used for cartridge cleaning (oxygen content reduced to below 8%).
