Explanation on Explosion Protection of Sodium Hypochlorite Generator Equipment

Explanation on Explosion Protection of Sodium Hypochlorite Generator Equipment

I. Interpretation based on GB 50058-2014 "Code for Design of Electrical Installations in Explosive Atmospheres":

2.0.10 Explosive Gas Atmosphere

An atmosphere in which a mixture of flammable substances in the form of gas or vapor with air, under atmospheric conditions, can ignite and sustain combustion after ignition.

Note: Based on the explosive range of hydrogen, it is known that a mixture of hydrogen and air with a volume fraction of 4% to 75% constitutes an explosive gas under this project.

3.2 Classification of Hazardous Areas in Explosive Gas Atmospheres

3.2.1 Explosive gas atmospheres shall be classified into Zone 0, Zone 1, and Zone 2 based on the frequency and duration of the occurrence of explosive gas mixtures, as follows:

Zone 0: An environment where explosive gas mixtures are continuously present or present for long periods.

Zone 1: An environment where explosive gas mixtures are likely to occur during normal operation.

Zone 2: An environment where explosive gas mixtures are unlikely to occur during normal operation and, if they do occur, will only exist for a short duration.

3.2.2 An area may be classified as a non-explosive hazardous area if one of the following conditions is met:

The maximum possible concentration of combustible substances does not exceed 10% of the lower explosive limit (LEL).

Note: For example, in general, open-flame equipment such as boilers use balanced ventilation, where the exhaust fan extracts slightly more flue gas than the amount of air supplied by the fan and the gas generated by coal combustion. This maintains negative pressure in the boiler furnace, preventing combustible substances from diffusing near the equipment and forming explosive mixtures with air. Therefore, areas near open-flame equipment are considered non-hazardous, including instruments and other facilities within the boiler itself.

Similar to the boiler design concept, in our company's safe hydrogen discharge design process, the maximum possible concentration of hydrogen is far below 10% of its LEL (i.e., 0.4%). Therefore, according to this clause, the sodium hypochlorite generation system can be classified as a non-explosive hazardous area.

3.2.3 Release sources shall be classified based on the frequency and duration of release of combustible substances into continuous grade, primary grade, and secondary grade release sources. A secondary grade release source is one where release is not expected during normal operation and, if release occurs, it is only occasional and short-term. The following situations may be classified as secondary grade release sources:

Seals of pumps, compressors, and valves that do not release combustible substances during normal operation;

Flanges, connectors, and pipe joints that do not release combustible substances during normal operation;

Safety valves, vents, and other openings that do not release combustible substances into the atmosphere during normal operation;

Sampling points that do not release combustible substances into the atmosphere during normal operation.

Note: Based on the operational characteristics of the equipment, the sodium hypochlorite generation system should be considered a secondary grade release source.

3.2.4 Ventilation is considered adequate if the air flow in the explosive hazardous area can quickly dilute combustible substances to below 25% of the LEL.

3.2.5 The classification of explosive hazardous areas shall be determined based on the release source grade and ventilation conditions. Areas with secondary grade release sources may be classified as Zone 2, and the classification may be adjusted based on ventilation conditions as follows: If ventilation is adequate, the classification of the explosive hazardous area may be reduced.

3.3.3 If positive pressure or continuous ventilation dilution measures are adopted in workshops within explosive gas atmospheres, preventing the formation of an explosive gas environment, the workshop may be downgraded to a non-explosive hazardous environment.

Note: In Jinchuan's safe hydrogen discharge design process, combustible substances are quickly diluted to below 10% of the LEL, which should be considered adequate ventilation. Clause 3.2.5 stipulates that the hazardous area classification may be further reduced if ventilation is adequate, meaning Zone 2 may be further downgraded. Combined with Clause 3.3.3, the sodium hypochlorite generation system may be downgraded to a non-explosive hazardous environment.

II. Conclusion

According to GB 50058-2014 "Code for Design of Electrical Installations in Explosive Atmospheres," in a safe hydrogen discharge design, the sodium hypochlorite generation system can be considered a non-explosive hazardous environment. Equipment within the equipment room does not require explosion-proof selection.

III. Jinchuan's Design Explanation

Jinchuan's explosion-proof zoning classification is as follows:

The space above the electrolyzer interior,

The space above the liquid level in the dehydrogenation tank,

The dehydrogenation pipeline, and

Within a 3-meter radius of the hydrogen discharge outlet are classified as Zone 2.

These areas are internal to the generation system. The equipment room can be classified as a safe area, and related electrical equipment does not require explosion-proof specifications. Equipment used in explosion-proof areas far exceeds the design requirements for Zone 2 instruments, minimizing potential explosion risks to the greatest extent.

Jinchuan strictly adheres to GB 50058-2014 "Code for Design of Electrical Installations in Explosive Atmospheres" and other relevant design standards for explosion-proof safety design. Jinchuan's safe hydrogen discharge design process has been validated in nearly 1,000 practical projects and has passed the explosion-proof certification of TÜV Rheinland, a leading European third-party authority.