Although there are many fire and explosion accidents in chemical enterprises, there are a lot of lessons learned, and the parts prone to accidents are relatively clear, but there are many factors causing combustion and explosion in the production process, and the scope is also wider, especially the fire source causing combustion and explosion is not easy to figure out, therefore, the prevention of fire and explosion accidents is a detailed and complex work. The focus of fire prevention and explosion prevention should be placed on the control of limiting and eliminating combustible substances, combustion-supporting substances and ignition sources, and do everything possible to avoid the three at the same time in a state of interaction. At the same time, it also requires us to take strict and reliable measures in technology and management to control the expansion of the accident state.

So how to control and do a good job of explosion-proof principle? Let's take a look at the basic principles of explosion protection.

Basic principles of explosion protection

There are many kinds and large quantities of modern fuels used in industrial production, and the production process is complex, so various corresponding protective measures need to be taken according to different conditions. From the formation of the destructive power of the explosion, the explosion generally needs to have five conditions:

(1) Combustible substances that provide energy (release source);

(2) Auxiliary combustion accelerant (oxidizer);

(3) Uniform mixing of combustible substances and accelerants;

(4) The mixture is placed in a relatively closed space (bounding body);

(5) Ignition source with sufficient energy.

Ignition source, combustible substance and accelerant in the above conditions are the three elements of combustion explosion, explosion-proof technology is based on these explosion conditions, take the corresponding technical measures and management measures to achieve the purpose of preventing accidents.

1 The explosive intensity of the combustible concentration is closely related to the concentration of the explosive mixture, the relationship between the explosive intensity and the concentration change is similar to the sine curve, the concentration or low or too high can not explode, the two points are called the lower explosive concentration and the upper explosive concentration. Below the lower explosive limit concentration, the mixture cannot be ignited because the heat of the combustible substance is too low to maintain the minimum temperature required for flame propagation in the mixture; If the concentration gradually increases and exceeds the upper limit of the explosion concentration, although the combustible substance increases, the oxygen concentration of the combustion is lower than the chemical equivalent value, which cannot meet the needs of the complete combustion of the mixture, and there will be no explosion. Therefore, it is possible to prevent the occurrence of explosion accidents by controlling the concentration of fuel, or to minimize the destructive power that may be caused by explosion accidents.

When the inert medium is added to the explosive atmosphere, on the one hand, the oxygen components in the explosive atmosphere can be diluted, reducing the opportunity for the interaction of combustible substance molecules and oxygen molecules, and also isolating the combustible components from oxygen molecules, forming a non-burning barrier between them; When the activated molecule collides with the inert medium particle, the activated molecule loses its activation energy and cannot react. On the other hand, if the combustion reaction has occurred, the free radicals will interact with the inert medium particles, making them inactive, resulting in the interruption of the combustion chain reaction. At the same time, the inert medium will also absorb a large amount of heat released by the combustion reaction, so that the heat can not accumulate, and the combustion reaction will not spread to other combustible component molecules, which will inhibit the combustion reaction. Therefore, the inert medium is added to the combustible/air explosive atmosphere, the explosion range of the combustible component is reduced, when the inert medium increases to a sufficient concentration, the upper and lower limits of the explosion can be made to coincide, and then the concentration of the inert medium is increased, at this time the combustible air mixture will no longer burn.

The control temperature of the ignition source has a particularly significant effect on the chemical reaction speed. For the general reaction, if the initial concentration is equal, the reaction speed is about 2 to 4 times faster every 10℃ increase in temperature. Therefore, temperature (that is, the ignition source usually referred to) is the initial factor to speed up the reaction speed and cause the explosion accident, and the control of the ignition source is one of the important measures to prevent the explosion accident.

One of the important characteristics of the explosion phenomenon is that when the explosive material explodes, the high temperature and high pressure gas products generated expand at a very high speed, causing a sudden increase in the pressure in the encircle body, and then the encircle body explodes, forming a shock wave and causing destructive power. In order to prevent or weaken the sudden increase of pressure in the enclosing body caused by the explosion, the enclosing body should not be relatively closed as much as possible.