1 conditions for explosion of explosive mixture

Explosion refers to the material from a state, through physical or chemical changes, and suddenly turned into another state and emit huge amounts of energy, and the resulting light and heat or mechanical work. In this case, the explosion of the explosive mixture, that is, the explosion of all flammable gases, vapors, and the explosive mixture of dust and air. The explosions also have three conditions can occur: first, there must be explosive or flammable substances; second, to a combustion supporting material, is mainly the oxygen in the air; third, there is also the source of ignition (such as spark, arc and dangerous temperature), it provides the necessary to ignite the mixture the energy. Only when these three conditions exist at the same time, there is the possibility of explosion, in which one of the conditions do not have, there will be no combustion and explosion. Therefore, take appropriate measures, so that the three conditions do not have the same time to achieve the purpose of preventing the explosion. Because the explosive mixture exists in coal, petroleum, chemical industry, textile, food processing and other industries, production, processing, storage and transportation and other places, such as explosion is harmful. As a result, a variety of technical methods have been adopted to prevent the formation and explosion of explosive hazardous environments.

2 basic explosion-proof type

(1) flameproof type "d""

Flameproof type is the device may ignite explosive gas mixture components are enclosed in a shell, the shell can withstand any joints or through the shell structure gap, penetrate into the shell of combustible mixture in internal explosive without damage, and will not cause the light from an external explosive environment, a variety of gas or vapor form (see the GB 3836 standard. 2).

The parts which may produce sparks, arcs and dangerous temperatures are placed inside the flameproof enclosure, which separates the inner space of the equipment from the surrounding environment. The flameproof enclosure gap by osmosis gas and electrical equipment to the internal respiration, there may be explosive gas mixture, when the explosion occurred, the shell can withstand the explosion pressure without damage, while the shell structure gap can be flame cooling and reduce flame propagation speed or acceleration chain termination, the flame or danger the resultant flame cannot pass through the gap of explosion-proof ignition of an external explosive environment, so as to achieve the purpose of explosion.

Flameproof type "d" according to the type of explosive gas environment allowed to be divided into I and IIA, IIB, IIC class.

The explosion-proof type equipment is suitable for places 1 and 2.

(2) increased safety type "e"

Increased safety type is a kind of electrical equipment to produce electric arc, spark is not in normal operating conditions to take additional measures to improve the safety level, to prevent the possibility of explosion proof type internal and external components may be dangerous temperature, arc and spark. It does not include a spark or arc in the case of normal operation of the equipment (see GB 3836. 3).

In normal operation does not produce electric spark and arc equipment structure and dangerous temperature, by taking measures to reduce or control the working temperature, ensure the reliability of electrical connection, increase insulation effect and improve the degree of protection of enclosure, in order to reduce the possibility of pollution caused by moisture and dirt into other measures, reduce the possibility of failure may cause fire improve the equipment, normal operation and fault rules (e.g., motor rotor) under the condition of safety and reliability. "JP"

This type of equipment is mainly used in 2 areas of dangerous places, some types can be used in the 1 areas, such as the appropriate protection of the safety of low-voltage induction motors, junction boxes, etc..

(3) intrinsically safe "i"

Intrinsically safe explosion-proof type is all circuits inside the device are made in standard conditions (including fault condition and regulations), any spark or any thermal effects are not intrinsically safe circuits to ignite explosive gas environment provided by the. "HTH" "I." "HT" level of electrical equipment is working properly and applying two fault conditions of a fault and any combination, are not caused by the intrinsically safe electrical equipment ignited; "HTH" "IB" "HT" level of electrical equipment is working properly and applying a fault condition that cannot cause the intrinsically safe electrical equipment lit (see GB 3836. 4).

Intrinsically safe type is starting from the energy limiting circuit, through the control circuit parameters will be reliable the potential to reduce energy spark ignition energy gas mixture below a specified wire and components of surface heating temperature limit in gas mixture ignition temperature under the provisions of the.

This type of protection can only be applied to electronic equipment, this type of equipment is suitable for 0, 1, 2 (or 1, 2. Exi) area (Exib).

(4) positive pressure type "P""

Explosion proof type of electrical equipment. It is a kind of electrical equipment to achieve security by keeping the equipment inside the shell gas pressure is higher than the surrounding explosive environment pressure measures (see GB 3836. 5).

Positive pressure equipment protection type can use different methods. One method is to protect the static pressure in the system, and the other is to maintain a continuous flow of air or inert gas to limit the combustible mixture into the housing. The two methods need to be used in the equipment before the start of the protective gas to flush the shell, take off the equipment inside the non positive pressure state into the shell of combustible gas, to prevent the formation of combustible mixture in the shell. The key point of these methods is the monitoring system, and the timing of ventilation to ensure that the system