H2S
(hydrogen sulfide, sulphide)H2S
(hydrogen sulfide, sulphide) is a toxic, as well as a
flammable gas with the typical rotten egg smell. H2S
is the result of the decomposition process of many sulfurous
organic substances, such as proteins. Hydrogen sulfide also
also occurs in natural gas, as well as in intestinal gasses
(including livestock manure). The typical rotten egg smell
is only perceived in very low concentrations, but in case
of prolonged exposure or in case of higher concentrations
the intensity of the sensation is receding. Because of the
toxicity of this substance, even breathing low
concentrations of hydrogen sulfide for a longer period will
be dangerous, thus the importance of an efficient separation
of this element from industrial emissions. Even a tiny
quantity of this gas can cause odour nuisance (the odor
treshold for this gas is 0,0005 PPM!). The odour treshold in
olfactometry is the lowest concentration leading to odour
nuisance.
Separation of H2S from biogas
by means of biological air scrubbers
For this method gas scrubbers or air scrubbers are used, werein
the H2S
is absorbed from the biogas.
This kind of installation consists of one or more gas
scrubbers (srubbing stages).
Inside the air scrubber, the biogas is brought in contact with water out of the aeration tank, wich is circulated once over the air
scrubbers and reconducted into the aeration tank.
The H2S absorbed will be oxidated in the aeration tank.
For this biological air scrubbing technique, the gas
scrubbers are preferrably installed in the direct
neighbourhood of the aeration tanks ( see installation
overview pictures on top).
Odour removal efficiency of biological air scrubbers
With this method the total removal efficiency is situated
around 95%. This means that
there won't be any odour nuisance left for the surroundings,
fact that can easily be confirmed by basic olfactometry
techniques.
Advantages of biological air scrubbers for the removal of H2S
One of the most important advantages of this odor removal
technique is the very low operating cost (no continuous supply of chemicals
needed).
H2S separation with chemical gas scrubbers
In certain cases, where biological air scrubbing methods
will not be applicable for the separation of hydrogen
sulfide, a one or multistage gas scrubber installation might
be an appropriate solution. In this case, the gas will be
scrubbed by adding chemicals to the water. For an efficient
separation
of H2S out of industrial emissions, several
stages (gas scrubbers) will ne necessary, in practice, to
obtain the required result. A typical multistage gas
scrubbing installation will be a first gas scrubber operated
with cheaper chemicals to separate most of the hydrogen
sulfide and a second gas scrubber operated with more
expensive specialty chemicals to eliminate the last odor
particles.
Odor removal efficiency of chemical gas scrubbers for the separation of H2S
A correct dosage and use of the correct chemicals will allow
to reduce the olfactive nuisance for the surroundings to an
imperceptible level. It goes without saying that basic
olfactometry techniques will allow to bring evidence. |