第五章气体成分检测选读.ppt

* * LEL and UEL We saw that every substance has got a certain explosive range and that is only possible when the situation is complete with a mixture of gases. That mixture must contain combustible gas and oxygen. This only fact is not enough, because this mixture must be in the right proportion as well. When the proportion between combustible gas and oxygen is not between two known parameters, there is no beginning of combustion. The third parameter in this story is the ignition. With the right ignition energy the right temperature will be reached, so that the reaction can take place. * * Explosive limits of several combustible gases in air Methane is lighter than air and should not be looked for on the ground. Nonane and Propane are heavier than air. Below Lower Explosive Limit - not enough fuel to ignite Above Upper Explosive Limit - not enough oxygen Between LEL and UEL -atmosphere is explosive CO and H2S are not only combustible, but above all very toxic! When the combustible gas detector gives an alarm, the concentration is far above the STEL and TWA values. It is even more dangerous; When the display is coming up from zero, the concentration is already above the STEL and TWA value. Never use a combustible measuring device for measuring these substances, Immediate danger for life!! Note: Carbon Monoxide is senseless, tasteless and colorless, an invisible enemy. Hydrogen Sulfide has a strong smell, but also the property to paralyze the nasal organ. So, you smell it …. not anymore! * * Measuring methods Combustible gas can be measured in different ways and the values of those measurements can be given in different ways too. Measure combustible gas by catalytic combustion with both portable as permanent instruments. Measure combustible gas by thermal conductivity, especially in case of huge concentration of gas and in case of inert situations. Measure combustible gas by amplified catalytic combustion in case of leak detection in PPM-range and by s