Danger level of the operating environment is the most important consideration in selecting explosion-proof gensets. It is generally divided according to the frequency and duration of presence of the explosive mixture.
(1) Division of explosive gas hazardous areas
Explosive gas hazardous areas are divided into ZONE 0, ZONE 1 and ZONE 2:
- ZONE 0: locations where explosive gas mixture is present continuously or lastingly
- ZONE 1: locations where explosive gas mixture is likely to be present during normal operation
- ZONE 2: locations where explosive gas mixture is unlikely to be present or is present occasionally for a short time
(2) Division of combustible dust hazardous areas
Combustible dust hazardous areas are divided into ZONE 20, ZONE 21 and ZONE 22:
- ZONE 20: locations and inside of containers where combustible dust is present continuously or frequently during normal operation, and the volume is enough to form a combustible mixture of dust and air and/or is likely to form an uncontrollable thick dust layer
- ZONE 21: locations where dust present is likely to form a combustible mixture of dust and air during normal operation, but not enough to be classified as ZONE 20. It includes places directly adjacent to dust charging or discharging sites, places where dust layer is present or a combustible mixture of dust and air with combustible concentration is likely to be present during normal operation.
- ZONE 22: locations where combustible dust is present occasionally and briefly or combustible dust deposits occasionally or dust layer is likely to be present and a combustible mixture of dust and air is formed. If the combustible dust deposit or dust layer cannot be guaranteed to be eliminated, then it shall be classified as ZONE 21.
To ensure safe diesel genset operation under dangerous environment, the uppermost is to control sources of ignition and electric arc and sparks generated by electrical components. This is to prevent them from igniting the surrounding explosive and combustible gas and dust
Common sources of ignition are divided into 4 categories:
- Mechanical fire source: such as friction, impact and adiabatic compression, etc.
- Thermal fire source: hot surface, heat rays, etc.
- Electric fire source: electric sparks, static electricity sparks and lightning, etc.
- Chemical (or physical) fire sources: flames, chemical energy, heating and spontaneous combustion, etc
According to the classification above, the sources of ignition for diesel gensets can be classified into 6 categories as follows:
- Diesel engine manifold is directly connected to the combustion chamber, and the flame of burning may rapidly return to the ambient atmosphere through the intake system.
- Diesel engine exhaust system discharges flames and sparks.
- Even if the fuel supply is cut off, diesel engine may continue to operate with inhaled combustible materials, even speeding out of control may happen.
- Surface temperature of the hot diesel engine exhaust system and other parts up to 300 ~ 500°C may be over the minimum ignition temperature of many flammable substance.
- Arc and sparks generated by electrical components.
- Static electricity sparks generated by friction or collisions
In a word, it must take full control of the sources of ignition to meet the explosion-proof requirements of gensets. So Aosif’s explosion-proof diesel gensets use modified explosion-proof diesel engine, explosion-proof generator and anti-static accessories. All electrical components have been processed with explosion-proof treatment. Aosif’s explosion-proof gensets have the following characteristics: Effective control over the genset sources of ignition. CHALWYN’s pneumatic safety device is adopted for explosion-proof pneumatic starting method. Combustible gas, smoke and heat detection linkage system is also introduced. Genset with a maximum level of security can be provided as long as the application environment and area are given by the user.