The explosion limit of gas mixture explosion (2)

(2) Factors affecting the explosion limit

Explosion limit is not a fixed value, affected by many factors, the main factors initial temperature, initial pressure, oxygen content halo, ignition energy and the like

1.

The higher the initial temperature of the mixture, the wider the explosion limit range, that is, the lower limit decreases, the upper limit increases, and the danger increases; on the contrary, the explosion limit range narrows

2.

In the case of pressure changes, the explosion limit changes are more complicated

The influence of pressure on the upper limit is more obvious, but the influence on the lower limit is smaller

There are exceptions.

3.

In the mixture, if the inert gas concentration increases, the explosion limit is reduced.

4.

The energy of external energy (such as static sparks, impact friction sparks), hot surface area, contact time between the fire source and the mixture, etc.

Table 13-2 Minimum ignition energy of some common combustible gas and steam

In addition to the above factors, the inner wall material of the container, mechanical impurities, light, surface active substances, etc.

(3) Explosive reaction equivalent concentration

Explosive reaction equivalent concentration refers to the concentration ratio of combustible (explosive) substances and combustion-supporting (explosive) substances in an explosive mixture to the stoichiometric concentration when a complete chemical reaction can occur.

For example, calculate the explosive reaction equivalent concentration of carbon monoxide in the air

If the O ₂ content in the air is 21% (volume fraction) and the content of other gases represented by N2 is 79% (volume fraction), then 1 mol O ₂ in the air is equivalent to 3.

2CO+O ₂ +3.
76N ₂ =2CO ₂ +3.
76N ₂

According to the reaction formula, the total volume of the substances participating in the reaction is 2+1+3.
76=6.
76
.
If the total volume of 6.
76 is taken as 100, the proportion of 2 volumes of carbon monoxide in the total volume is X=2/6.
76×100%=29.
6%
.
Therefore, the complete reaction concentration of carbon monoxide in the air is 29.
6%
.

Although the explosion limit of carbon monoxide is 12.
5%-80.
0%, when its concentration is 29.
6%, under the same temperature and pressure conditions, the explosion risk is the largest, and the explosion power is also the largest, see Table 13-3
.

In the same way, the explosive reaction equivalent concentration of all other combustible (explosive) gases in other combustion-supporting (explosive) gases can be calculated
.

The above actually refers to the theoretical explosive reaction equivalent concentration, and the actual explosive reaction equivalent concentration is equal to or slightly higher than the calculated theoretical explosive reaction equivalent concentration
.

Table 13-3 Combustion and explosion of carbon monoxide and air mixed under the action of fire source