This document discusses methods for sampling gases. It explains that gas sampling is important for characterizing chemical and thermal properties and for assessing air quality. Sampling gases is more difficult than liquids or solids since gases are invisible and mix easily. The document describes static and dynamic sampling methods. The static method uses a sample probe, container, and delivery line to extract and collect a gas sample by evacuating and filling the container multiple times. The dynamic method continuously flows gas through the container to flush out residual gases without needing evacuation.
2. Why Sampling of gases required?
o Gas sampling is done to characterize the chemical, thermal, and hydrological properties of
a surface or subsurface hydrothermal system.
o To assess the air quality.
o Due to presence gases and vapors of inorganic as well as organic which could be hazardous
for the health conditions of workers.
3. Sampling of Gases
o Quite difficult to sample gases than sampling of solids and liquid.
o It could be different for different gases.
o As gases are not visible, they are miscible with each other. So separating them could be a
difficult task.
o It may get contaminated by the gases or others present in the atmosphere.
o Concentrations of gases changes with time and circumstances.
4. Gases are present in
PIPE LINES GAS WELL PROCESS
PLANT
STORAGE
TANKS
OPEN
ATMOSPHERE
6. Method of sampling on the basis of physical
state
1. Ambient sampling
2. Stack sampling
o Static method
o Dynamic method
7. Static sampling method
o Apparatus required for the removal of gas samples consists
of:
1. Sample probe – They extract sample gas from the process stream and supply it to the
analysis system. They remove undesirable particulates at the sampling point and avoid
cold spots thus preventing false measurements.
2. Sample container – Enlarged, cylindrical, rectangular having tubes at both ends and it is
made of glass, steel, and iron material. Gas sample is collected in the container.
3. A delivery line – for the sample.
4. A mercury trap – An arrangement connected to the sample container which consists of tube
dipped in a vessel containing Mercury. It acts as a trap for excess gas.
8. Static sampling method
o A, B, C,D are stopcocks or valves of the
apparatus sample container.
o Open B and C valves to evacuate the
sample container.
o Keep all other stopcocks closed.
o After evacuation close stopcock B and
open D through which sample container
gets filled.
o Excess gas is let out through E.
o The process is repeated number of
times to get desired accuracy in
sampling.
9. Dynamic sampling method
o Apparatus required for the removal of gas samples consists of:
1. Sample probe – They extract sample gas from the process stream and supply it to the
analysis system. They remove undesirable particulates at the sampling point and avoid
cold spots thus preventing false measurements
2. Sample container – Enlarged, cylindrical, rectangular having tubes at both ends and it
is made of glass, steel, and iron material. Gas sample is collected in the container.
3. A delivery line – for the sample.
4. A mercury trap – An arrangement connected to the sample container which consists of
tube dipped in a vessel containing Mercury. It acts as a trap for excess gas.
10. Dynamic sampling
method
o A, B, C,D are stopcocks or valves of the
apparatus sample container.
o No need to evacuate Sample container.
o Stopcock B is closed A, C, D is kept
open.
o Gas from source is admitted into
sample container at steady rate.
o Flush the container by passing the gas
for longer time which removes any
residual gases present in the container.
