Industry: Chemical industry

Monitoring scheme for toxic and hazardous gases in chemical plants

Industry Pain Points

Chemical plants are core locations for the national "major hazard sources" control and management — reactors, storage tank areas, loading and unloading platforms, tank area cofferdams, flare systems, plant areas, and tank top breather valves, each facing the combined risks of flammability, toxicity, oxygen deficiency, high temperature, and high pressure. Common gas types span over 50 types: chlorine (phosgene synthesis/chlor-alkali), HCl/hydrogen fluoride (fluoride production), hydrogen cyanide (VCM process), benzene series (BTX plants), acrylonitrile, ethylene oxide, phosgene, hydrogen sulfide, CO, ammonia, methanol, ethylene, propylene, butadiene... According to the public statistics of hazardous chemical accidents in 2024 alone: 80% involved gas leaks as the initial incident, with volatile organic compounds (VOCs) accounting for 42%. Regulatory requirements are strict — GB 30871 for confined space operations, GB 50493 for automatic alarms, GB 18218 for major hazard source identification, HSE's "three simultaneous" review, the Emergency Management Bureau's "dual control mechanism", and the long-distance pipeline law — each involves monitoring points. A major chemical accident (such as the Tianjin Port explosion in 2015) often results in social impact, fines, and compensation in the billions.

Solution Overview

Yourian provides a full process chain + full gas type + multi-level monitoring solution for chemical plants: ① **Plant area**: Fixed electrochemical + PID + infrared multi-principle probes are deployed above the reaction kettle, on pipeline flanges, valve groups, and sampling ports to specifically monitor high carcinogens such as toluene, benzene, VCM, and acrylonitrile at PPM levels using PID; ② **Tank area**: Each tank top + tank bottom + cofferdam at 4-6 points are equipped with pressure/level/temperature combined monitoring, meeting the design requirements of Class I hazardous areas in GB 50493; ③ **Loading and unloading platform**: Fixed LEL + H2S + VOC + grounding wire status four-in-one to eliminate the risk of static electricity ignition; ④ **Flare system**: Flare burnout rate gas monitoring, environmental compliance + carbon emission measurement; ⑤ **Central SIS/DCS interlock**: Multi-level SIL gas probes are connected to the safety instrumented system according to GB 21109, with ultra-high alarm automatically initiating ESD emergency shutdown + tank area interlock shut-off valve + accident pool preparation + surrounding personnel positioning and evacuation broadcast. Equipment explosion-proof grade is Ex d IIC T6 (the highest level).

## Recommended Configuration Matrix (By Process Unit)

– **Chlor-Alkali / Chlorination Process**: Cl2 / HCl electrochemical sensor (range 0-10 ppm, PC-TWA 1 ppm) + phosgene-specific probe (range 0-1 ppm, IDLH at only 2 ppm, extremely hazardous)
– **Styrene/Acrylonitrile Plant**: Benzene + Acrylonitrile PID Composite Probe (PID Sensitivity at PPB Level) + Flash Point Interlock
– **Ethylene/Propylene Storage Tank**: LEL + Infrared CH4 Dual Probe (with explosion-proof design to prevent PID failure in high humidity environments)
– **VCM (Vinyl Chloride Monomer) unit**: dedicated PID for VCM (strong carcinogen, PC-TWA 7.5 mg/m³) + simultaneous measurement of hydrogen chloride and HCN
– **Ammonia synthesis unit**: NH3 + H2 + high-pressure leak detection (infrared imaging + laser remote sensing combination)
– **Methanol/Ethanol Distillation Area**: LEL + Benzene + Formaldehyde (intermediate product of methanol oxidation)
– **Tank farm cofferdam**: Each cofferdam is equipped with LEL + H2S + toxic gas sensors, depending on the product, and is 0.3m higher than the cofferdam itself
– **Loading dock**: oil and gas recovery monitoring + static electricity alarm + grounding wire monitoring + air detection before drivers exit the cabin
– **Flare system**: flare tail gas SO2 / NOx / VOC / flame photoelectric signal (flame extinction detection, prevention of direct emission)

## Key Technical Specifications

– Explosion-proof grade: Ex d IIC T6 (the highest level in the chemical industry, covering Class IIC gases such as hydrogen and acetylene)
– Protection: IP66 / IP67 (outdoor tank area + coastal humid and hot environment)
– SIL level: SIL 2 – SIL 3 (integrated into SIS safety instrumented system)
– Range: PPM-level sensitivity for toxic gases, 0.01 ppm; LEL 0-100% with three-level alarms at 10%, 25%, and 50%
– Response time: T90 < 15 seconds (toxic gas)
– Operating temperature: -40℃ ~ +75℃ (outdoors in tank areas during winter in the north and summer in the south)
– Communication: HART + Modbus + Profibus, compatible with DCS / SIS safety instruments

## Implementation Essentials (Determining Project Success)

1. **Mandatory for SIL Assessment**: Identify the SIL level (SIL2 = failure rate ≤ 10⁻³) of each monitoring circuit according to GB 21109-2007 / IEC 61508, and the probe selection must meet the standards
2. **Interlock Logic Levels**: Low Alarm → On-site Announcement; High Alarm → DCS Shuts Off Feed + Closes Tank Farm Valves; Ultra-High Alarm → ESD Emergency Shutdown + Activates Accident Water Pool + Notifies Emergency Rescue
3. **VOC LDAR Legal Requirements**: The plant area must conduct flange/valve leak detection (infrared imaging or PID inspection) at least four times a year, and the data must be reported to the local environmental protection bureau
4. **Calibration + Standard Gas Management**: Highly toxic gases (phosgene / chlorine / hydrogen fluoride) are scarce and highly hazardous, requiring high-purity standard gas cylinders + automatic dilution and dispensing stations
5. **Emergency Linkage**: Integrating with the plant's GIS map and wind direction and speed data, it automatically calculates the diffusion range after a leak, determines the affected personnel locations, and recommends evacuation routes

## Regulatory Basis (The Strictest for Chemical Industry)

– GB 50493-2019 "Design Standard for Combustible Gas and Toxic Gas Detection and Alarm in Petrochemical Industry"
– GB 18218-2018 "Identification of Major Hazard Installations for Dangerous Chemicals"
– GB 30871-2022 "Safety Code for Special Operations in Hazardous Chemical Enterprises"
– GB 21109 series "Functional Safety of Safety Instrumented Systems in the Process Industry Sector"
– HJ 1093-2020 "Continuous Monitoring System for Pollution Source Flue Gas"
– AQ 3013 General Specification for Safety Standardization of Hazardous Chemicals Employers
– GBZ 2.1-2019 Limit Standards

## Applicable Customers

Large petrochemical groups (Sinopec / PetroChina / CNOOC); coal chemical industry (Shenhua Coal Chemical / Middling Coal Shaanxi Yulin / Yankuang Yulin); fine chemical industry (Wanhua / BASF / Cabot / Rhodia); fluorine chemical industry / chlor-alkali (Juyuxin Materials / Binhua / Xinjiang Zhongtai); pharmaceutical active pharmaceutical ingredients (Huahai / Prolo / Hisun); enterprises in chemical industrial parks + central supervision platform of the park.

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