Harmful gas exhaust system for limited space of cable trench

Abstract

The invention provides a harmful gas exhaust system for a limited space of a cable trench, and the harmful gas exhaust system for the limited space of the cable trench is characterized in that the interior of the cable trench is divided into a plurality of sub-regions, and the top and bottom of each sub-region are respectively provided with a plurality of sensors which are electrically connected with an exhaust device in the sub-region; the sensors detect the concentration of harmful gas, the sensors at the upper part and the lower part of the cable trench are opposite in position, and the plurality of sensors are distributed in a rectangle in a vertical plane; and each sensor independently detects whether the concentration of the harmful gas reaches an early warning threshold C2 or not. The method has the beneficial effects that precise prevention and control are realized through spatial layered monitoring and a dynamic risk algorithm. According to the system, gas sensors are arranged at the top and the bottom of each cable trench area in pairs to form a rectangular monitoring network in the vertical direction. When it is detected that the concentration of the harmful gas breaks through a threshold value, a risk quantification model is started, risk assessment is conducted on the accumulated harmful gas, and a corresponding risk response mechanism is started.

Description

Technical Field

[0001] This invention relates to the field of hazardous gas ventilation technology, and more specifically to a hazardous gas ventilation system for confined spaces in cable trenches. Background Technology

[0002] Cable trenches, as critical infrastructure in power systems, are underground conduit structures used for laying and protecting power and communication cables, commonly found in substations, power plants, and urban power grids. Their structural forms mainly include rectangular, circular, and arched shapes, typically constructed primarily of concrete or brick, with an openable cover to facilitate cable installation, maintenance, and replacement. The core function of cable trenches is to provide physical protection for cables, shielding them from mechanical damage, soil erosion, and external environmental interference, ensuring the stability and safety of power transmission. However, traditional cable trenches struggle to adapt flexibly to the bends and undulations of cables in complex terrain, and drainage relies on pumps, resulting in low efficiency. In recent years, prefabricated cable trenches have been increasingly adopted, using factory-produced prefabricated components for on-site assembly to improve construction efficiency and reduce resource consumption; however, environmental control within the trench remains a challenge.

[0003] The generation of harmful gases in cable trenches primarily stems from anaerobic decomposition within their semi-enclosed environment and the infiltration of external pollutants. Long-term accumulation of silt, rainwater, and decaying plant and animal remains within the trenches, under poor ventilation conditions, undergoes anaerobic microbial fermentation and decomposition, continuously generating a mixed gas primarily composed of hydrogen sulfide (H2S) and carbon monoxide (CO). Especially in the high temperatures of summer, microbial activity is enhanced, significantly increasing the gas generation rate. Furthermore, leaks from nearby natural gas pipelines may introduce hydrocarbon gases such as methane and ethane, while underground seepage from chemical plants may bring ammonia and volatile organic compounds. These gases tend to accumulate in low-lying areas within the trenches, and the complex structure of cable trenches further restricts gas diffusion, exacerbating localized concentration increases.

[0004] The accumulation of harmful gases poses multiple threats to the safety of cable systems and the health of personnel: First, there is the risk of explosion and fire. When the concentration of flammable gases such as methane reaches the lower explosive limit, they may cause a flash explosion when they come into contact with electrical sparks, static electricity, or short-circuit arcs in cable joints. The shock wave can damage cable supports, covers, and even the surrounding building structure. Second, it causes corrosion and equipment failure. H2S dissolves in water to form a weak acid, which accelerates the corrosion of the cable's metal armor layer and supports, shortening the equipment's lifespan. High concentrations of CO2 or methane may also crowd out oxygen, creating an oxygen-deficient environment that endangers personnel's lives. In addition, corrosion can cause secondary disasters: If the cable insulation layer is exposed to harmful gases after corrosion or high-temperature aging, it will release toxic substances such as hydrogen chloride and dioxins, polluting the environment and expanding the power outage area.

[0005] The enclosed nature of cable trenches and the metabolism of organic matter inside create a breeding ground for harmful gases. The hazards extend throughout the entire chain from facility safety to ecological pollution, and risk management urgently needs to be achieved through measures such as dynamic monitoring, forced ventilation, and structural protection. Summary of the Invention

[0006] To address the problem of harmful gas accumulation in cable trenches; This invention provides a hazardous gas exhaust system for a confined space in a cable trench. The cable trench is divided into multiple sub-regions. Multiple sensors are arranged at the top and bottom of each sub-region and electrically connected to the exhaust device in that sub-region. The sensors detect the concentration of hazardous gases. The sensors at the top and bottom of the cable trench are positioned opposite each other, and the multiple sensors form a rectangular distribution in the vertical plane. Each sensor individually detects whether the concentration of hazardous gases has reached the warning threshold C2. When C > C2 in the current sub-region, the hazardous gas risk value R of the sensor in the lower part of the sub-region is... 下 =W 下 ×[0.6×(C / C2)+0.4×((ΔC / Δt) / V 10 )]; When C > C2 in the upper sub-region, the risk value R of harmful gases from the sensor in the upper part of the sub-region is... 上 =W 上 ×[0.5×(C / C2)+0.5×((ΔC / Δt) / V 10 )]; H=(ΣR 下 +ΣR 上 )×K×P; in: W 下 W represents the lower weighting coefficient. 上 The upper weighting coefficient is denoted by C; C is the detected concentration; ΔC / Δt is the rate of change of the harmful gas concentration; V 10 The safety threshold for the rate of change of harmful gas concentration; ΣR 下 ΣR is the sum of the hazardous gas risk values ​​of all lower sensors within a sub-region; 上 The sum of hazardous gas risk values ​​of all upper sensors within a sub-region; K is the time-series weight, which is 0.8 when only the upper sensor is triggered, 1.1 when only the lower sensor is triggered, 1.3 when both upper and lower sensors are triggered simultaneously, and 1.5 when the lower sensor is triggered within 30 seconds of the upper sensor being triggered; P is the percentage of sensors that are triggered within a sub-region. The assessed value H within the sub-region is calculated, and this value is used to determine which risk level it falls into: Level 1: When H < 0.2, only passive ventilation is used; Level 2: When 0.2 ≤ H < 0.4, the exhaust system in the sub-area will activate active exhaust at 30% intensity; Level 3: When 0.4 ≤ H < 0.7, the exhaust system in the sub-area will activate active exhaust at 60% intensity; Level 4: When 0.7 ≤ H < 1.0, the exhaust system in the sub-area will activate full-intensity active exhaust. Level 5: When H≥1.0, the exhaust devices in the sub-area and adjacent areas will be activated at full intensity for exhaust. Level 6: When three or more consecutive sub-areas have H≥1.0, the entire cable trench area will be fully ventilated and fire-fighting measures will be activated.

[0007] As a preferred embodiment, the sensor includes a CO concentration sensor and an H2S concentration sensor, each sensor individually detecting the CO concentration C_ CO Has the warning threshold C been reached? 21 and the concentration of H2S C_ H2S Has the warning threshold C been reached? 22 ; C_ of the current subregion CO >C 21 At that time, the risk value R of CO in the lower sub-region 下_CO =W 下 ×[0.6×(C_ CO / C 21 )+0.4×((ΔCO / Δt) / V 11 )]; C_ of the current subregion H2S >C 22 At that time, the risk value R of the lower sub-region H2S 下_H2S =W 下 ×[0.6×(C_ H2S / C 22 )+0.4×((ΔH2S / Δt) / V 12 )]; When the C_ of the upper subregion CO >C 21 At that time, the risk value R of CO in the upper sub-region 上_CO =W 上 ×[0.5×(C_ CO / C 21 )+0.5×((ΔCO / Δt) / V 11 )]; When the C_ of the upper subregion H2S >C 22 At that time, the risk value R of H2S in the upper sub-region 上_H2S =W 上 ×[0.5×(C_ H2S / C 22)+0.5×((ΔH2S / Δt) / V 12 )]; in: ΔCO / Δt is the rate of change of CO concentration; ΔH2S / Δt is the rate of change of H2S concentration; C 21 The safe threshold for CO concentration; C 22 The safe threshold for H2S concentration; V 11 V is the safe threshold for the rate of change of CO concentration. 12 The safe threshold for the rate of change of H2S concentration; The calculated CO assessment value H _CO =(ΣR 下_CO +ΣR 上_CO )×K×P, and use this to determine which risk level it falls into; The calculated H2S evaluation value H _H2S =(ΣR 下_H2S +ΣR 上_H2S )×K×P, and use this to determine which risk level it falls into; Where ΣR 下_CO This is the sum of the CO risk values ​​of all lower sensors within a sub-region; ΣR 上_CO This is the sum of the CO risk values ​​of all upper sensors within a sub-region; ΣR 下_H2S This is the sum of the H2S risk values ​​of all lower sensors within a sub-region; ΣR 上_H2S The sum of H2S risk values ​​for all upper sensors within a sub-region; The risk values ​​of the two hazardous gases are calculated separately. Both gases can trigger exhaust ventilation; if both are triggered, the strategy based on the highest risk level will be implemented.

[0008] As a preferred embodiment, the W 下 The value is 0.6, and the W value is... 上 It is 0.4.

[0009] As a preferred embodiment, the sensor collects data every 10 seconds.

[0010] The beneficial effects of this invention are as follows: 1. This invention achieves precise prevention and control through spatial layered monitoring and dynamic risk algorithms. The system deploys gas sensors in pairs at the top and bottom of each cable trench area, forming a vertical rectangular monitoring network. When the concentration of harmful gas exceeds a threshold, a risk quantification model is activated to assess the risk of the accumulated harmful gas and initiate a corresponding risk response mechanism. A six-level progressive strategy is employed, escalating from passive ventilation to regional coordinated defense.

[0011] 2. This invention employs a multi-gas classification and treatment approach, using differentiated risk algorithm parameters for CO and H2S. A more stringent rate-of-change threshold is set for highly toxic H2S, increasing sensitivity by 50% compared to CO, ensuring a rapid response to highly toxic substances. When multiple harmful gases are triggered simultaneously in the trench, the system automatically selects the execution strategy with the higher risk level, preventing the combined toxicity effect from being underestimated. Attached Figure Description

[0012] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein... Figure 1 This is a schematic diagram of the sensor arrangement of the present invention; Detailed Implementation To illustrate the features of the present invention, the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0013] Example 1: Please refer to the following: Figure 1 This invention is deployed in a cable trench system of a 220kV substation. The cable trench has a total length of 150.4m × width of 1.8m × depth of 2.2m, and is divided longitudinally into 24 standard sub-areas of 6m each and one end area of ​​6.4m. A monitoring matrix is ​​constructed for each sub-area: GDS60 CO / H2S composite sensors (range 0-2000ppm / resolution 1ppm) based on the NDIR principle are arranged at 0.44m below the trench top cover and at 1.54m below the trench top cover, respectively, in a 2×3 matrix, forming 6 monitoring nodes in the vertical direction (vertical spacing 1.1m / horizontal spacing 2m). The detection data from each node is connected to the local PLC control box via armored shielded cables. Each sub-area is equipped with two GD-5K explosion-proof axial flow exhaust fans as ventilation devices. The fan inlet is located 0.6m above the monitoring surface at the bottom of the trench, and the outlet extends to the ground pressure relief tower. The CO safety threshold C... 11 =40ppm, H2S safety threshold C 22 =8ppm; the safety threshold for the rate of change of gas concentration is set at V according to OSHA standards. 11 =2ppm / min (CO), V 12 =1ppm / min (H2S); Spatial weighting coefficient characteristic assigned to W 下 =0.6, W =0.4.

[0014] 1) Calculate the bottom risk component: When the sensor at the bottom of the trench in the sub-region detects H2S=10ppm (ΔH2S / Δt=2ppm / min) and CO=45ppm (ΔCO / Δt=3ppm / min) at time t0; R 下_H2S=0.6×[0.6×(10 / 8)+0.4×((2) / 1)]=0.93; R 下_CO =0.6×[0.6×(45 / 40)+0.4×((3) / 2)]=0.765; 2) Calculate the top risk component: At time t0, the sensor at the top of the trench in the sub-region detects H2S = 8 ppm (ΔH2S / Δt = 1 ppm / min) and CO = 40 ppm (ΔCO / Δt = 2 ppm / min). R 上_H2S =0.4×[0.6×(8 / 8)+0.4×((1) / 1)]=0.4; R 上_CO =0.4×[0.6×(40 / 40)+0.4×((2) / 2)]=0.4; 3) Calculate the evaluation values ​​of H2S and CO (top trigger 18 seconds after bottom trigger, K is 1.5; 3 out of 6 nodes exceed the threshold, P=3 / 6=0.5): H _H2S =(0.93+0.4)×1.5×0.5=0.9975; H _CO =(0.765+0.4)×1.5×0.5=0.87375; 4) Based on H_ H2S =0.9975, H_ CO =0.87375 triggers a level 4 response.

[0015] This embodiment achieves precise prevention and control through spatial layered monitoring and dynamic risk algorithms. The system deploys gas sensors in pairs at the top and bottom of each cable trench area, forming a vertical rectangular monitoring network. When the concentration of harmful gas exceeds a threshold, a risk quantification model is activated to assess the risk of the accumulated harmful gas and initiate a corresponding risk response mechanism. A six-level progressive strategy is employed, escalating from passive ventilation to regional coordinated defense.

[0016] Furthermore, this embodiment also employs a multi-gas classification approach, using differentiated risk algorithm parameters for CO and H2S. A more stringent rate-of-change threshold is set for highly toxic H2S, increasing sensitivity by 50% compared to CO, ensuring a rapid response to highly toxic substances. When multiple harmful gases are triggered simultaneously in the trench, the system automatically selects the execution strategy with the higher risk level to avoid underestimating the combined toxicity effects.

[0017] The above embodiments and accompanying drawings are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. The present invention has been described in detail with reference to preferred embodiments. Those skilled in the art should understand that any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the present invention do not depart from the spirit of the present invention and should also fall within the protection scope of the claims of the present invention. Other related technical structures not disclosed in detail in the present invention are existing technologies in the art.

Claims

1. A hazardous gas exhaust system for confined spaces in cable trenches, characterized in that, The cable trench is divided into multiple sub-regions. Multiple sensors are arranged at the top and bottom of each sub-region and electrically connected to the ventilation device in the sub-region. The sensors detect the concentration of harmful gases. The sensors at the top and bottom of the cable trench are positioned opposite each other, and the multiple sensors form a rectangular distribution in the vertical plane. Each sensor individually detects whether the concentration of harmful gases has reached the warning threshold C2. When C > C2 in the current sub-region, the hazardous gas risk value R of the sensor in the lower part of the sub-region is... 下 =W 下 ×[0.6×(C / C2)+0.4×((ΔC / Δt) / V 10 )]; When C > C2 in the upper sub-region, the risk value R of harmful gases from the sensor in the upper part of the sub-region is... 上 =W 上 ×[0.5×(C / C2)+0.5×((ΔC / Δt) / V 10 )]; H=(ΣR 下 +ΣR 上 )×K×P in: W 下 W represents the lower weighting coefficient. 上 The upper weighting coefficient is denoted by C; C is the detected concentration; ΔC / Δt is the rate of change of the harmful gas concentration; V 10 The safety threshold for the rate of change of harmful gas concentration; ΣR 下 ΣR is the sum of the hazardous gas risk values ​​of all lower sensors within a sub-region; 上 The sum of hazardous gas risk values ​​of all upper sensors within a sub-region; K is the time-series weight, which is 0.8 when only the upper sensor is triggered, 1.1 when only the lower sensor is triggered, 1.3 when both upper and lower sensors are triggered simultaneously, and 1.5 when the lower sensor is triggered within 30 seconds of the upper sensor being triggered; P is the percentage of sensors that are triggered within a sub-region. The assessed value H within the sub-region is calculated, and this value is used to determine which risk level it falls into: Level 1: When H < 0.2, only passive ventilation is used; Level 2: When 0.2 ≤ H < 0.4, the exhaust system in the sub-area will activate active exhaust at 30% intensity; Level 3: When 0.4 ≤ H < 0.7, the exhaust system in the sub-area will activate active exhaust at 60% intensity; Level 4: When 0.7 ≤ H < 1.0, the exhaust system in the sub-area will activate full-intensity active exhaust. Level 5: When H≥1.0, the exhaust devices in the sub-area and adjacent areas will be activated at full intensity for exhaust. Level 6: When three or more consecutive sub-areas have H≥1.0, the entire cable trench area will be fully ventilated and fire-fighting measures will be activated.

2. The hazardous gas exhaust system for confined spaces in cable trenches according to claim 1, characterized in that: The sensors include a CO concentration sensor and an H2S concentration sensor, each sensor individually detecting the CO concentration C_. CO Has the warning threshold C been reached? 21 and the concentration of H2S C_ H2S Has the warning threshold C been reached? 22 ; C_ of the current subregion CO >C 21 At that time, the risk value R of CO in the lower sub-region 下_CO =W 下 ×[0.6×(C_ CO / C 21 )+0.4×((ΔCO / Δt) / V 11 )]; C_ of the current subregion H2S >C 22 At that time, the risk value R of the lower sub-region H2S 下_H2S =W 下 ×[0.6×(C_ H2S / C 22 )+0.4×((ΔH2S / Δt) / V 12 )]; When the C_ of the upper subregion CO >C 21 At that time, the risk value R of CO in the upper sub-region 上_CO =W 上 ×[0.5×(C_ CO / C 21 )+0.5×((ΔCO / Δt) / V 11 )]; When the C_ of the upper subregion H2S >C 22 At that time, the risk value R of H2S in the upper sub-region 上_H2S =W 上 ×[0.5×(C_ H2S / C 22 )+0.5×((ΔH2S / Δt) / V 12 )]; in: ΔCO / Δt is the rate of change of CO concentration; ΔH2S / Δt is the rate of change of H2S concentration; C 21 The safe threshold for CO concentration; C 22 The safe threshold for H2S concentration; V 11 V is the safe threshold for the rate of change of CO concentration. 12 The safe threshold for the rate of change of H2S concentration; The calculated CO assessment value H _CO =(ΣR 下_CO +ΣR 上_CO )×K×P, and use this to determine which risk level it falls into; The calculated H2S evaluation value H _H2S =(ΣR 下_H2S +ΣR 上_H2S )×K×P, and use this to determine which risk level it falls into; Where ΣR 下_CO This is the sum of the CO risk values ​​of all lower sensors within a sub-region; ΣR 上_CO This is the sum of the CO risk values ​​of all upper sensors within a sub-region; ΣR 下_H2S This is the sum of the H2S risk values ​​of all lower sensors within a sub-region; ΣR 上_H2S The sum of H2S risk values ​​for all upper sensors within a sub-region; The risk values ​​of the two hazardous gases are calculated separately. Both gases can trigger exhaust ventilation. If both are triggered, the strategy is implemented according to the highest risk level.

3. The hazardous gas exhaust system for confined spaces in cable trenches according to claim 1 or 2, characterized in that: The W 下 The value is 0.6, and the W value is... 上 It is 0.

4.

4. The hazardous gas exhaust system for confined spaces in cable trenches according to claim 1, characterized in that: The sensor collects data every 10 seconds.

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