Layout scheme of gas detector in production device area of chemical plant

The production equipment area is the core area of chemical plant, with dense equipment and complex technology, and usually involves high temperature and high pressure environment. The layout of gas detection in this area cannot be “cast net”, but must be based on the principle of fluid mechanics and process characteristics, and the strategy of “precise locking and three-dimensional defense” must be implemented.

Core principle: accurately lock the release source
The detectors in the production unit area should not be distributed blindly and evenly, but should focus on covering the “second type release source”, that is, the parts where leakage may occur during normal operation. The key control points include dynamic sealing points, such as the sealing parts of centrifugal pumps and compressors, which are the highest frequency leakage points; Operating components, such as frequently operated valve groups, sampling ports, condensate discharge ports and vent ports; And static sealing points, such as flanges and bellows expansion joints that are often disassembled.

In terms of distance control, the toxic gas detector should not be more than 1 meter away from the release source to ensure that the alarm is given before reaching the lethal concentration; The combustible gas detector should not be more than 4m (outdoor) or 2m (indoor/poorly ventilated) away from the release source.

Plane layout: wind direction and spacing
In the plane layout of the device area, it is necessary to carry out gridding or targeted layout in combination with local meteorological conditions and device scale.

The first is the wind direction strategy. The detector should be arranged on the windward side of the minimum frequency wind direction of the release source, and the leaked gas should be blown to the detector by natural wind. If it is arranged on the downwind side, it is necessary to shorten the distance from the release source.

Followed by the spacing standard. The spacing between detectors in outdoor device area should be about 15 meters; Because gas is easy to accumulate in indoor or enclosed workshops, the spacing should be encrypted to within 7.5 meters. In addition, for pits and cable trenches where gas may accumulate, separate detectors must be added.

Vertical layout: the decisive role of density
The installation height is the most critical parameter in the scheme and must be determined according to the relative density of the target gas (compared with air).

For gases heavier than air, such as liquefied petroleum gas, benzene, hydrogen sulfide, chlorine gas, etc., the detector should be installed at a distance of 0.3 m to 0.6 m from the floor and close to the ground to catch the sinking gas cloud.

For gases lighter than air, such as hydrogen, methane, ammonia, etc., the detector should be installed at a position 0.5 to 2 meters higher than the release source, or directly installed at the top of the factory building and under the beam.

For gases with similar air density, such as carbon monoxide, ethylene, etc., the detector should be installed at a distance of 1.5 meters to 1.8 meters from the floor, that is, the height of people’s breathing zone.

Special scene layout strategy
Compressor room and pump room belong to high-risk closed space. In addition to the routine layout, it is suggested to add detectors at the exhaust port to monitor whether the exhaust gas exceeds the standard. If there is a trench or cable tunnel in the workshop, detectors must be set in the trench, especially for heavy gas monitoring.

For high-temperature or high-pressure pipelines, for high-temperature pipelines (such as hot oil), the gas will rise due to heat after leakage. Even if the gas itself is heavier than air, it is recommended to increase the installation height appropriately or install it above the pipeline side.

For multi-layer pipe gallery, if there are flanges or valves in the lower layer, detectors should be set under the lower layer pipes; If it is a fully enclosed pipe gallery, it needs to be set every 15 meters according to indoor standards.

Environment and protection requirements
The installation position should be away from strong electromagnetic fields (such as near high-power motors), high-temperature radiation sources (such as near heating furnaces) and places where water drops and oil stains directly drop. The detector shall be installed at a position convenient for personnel to observe, debug and maintain, and avoid being installed at a dead corner rarely reached by personnel or at a height where scaffolding needs to be erected frequently, unless the telescopic rod is used for maintenance.

The device area is usually explosive, and the equipment must have corresponding explosion-proof grade (such as EX D IIC T6); If it is in a corrosive environment (such as acid-base tank farm), the shell should be treated with anti-corrosion.

Through the above scheme, the gas leakage in the production device area can be ensured to be captured at the first time, and precious “golden time” can be won for emergency treatment.