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Example for purification of a biogas
and obtaining pure biomethane
This
innovative "One-pot" process consists in capturing gaseous
pollutants in a physicochemical treatment whose liquid
effluents are subsequently digested by the aerobic bio-purification
process in the treatment plant.
(A)
Simultaneous
process of absorption (capture) and organic chemical
modification of Volatile Organic Compounds (organic
and inorganic).
This operation is carried out in a single operation
on a collection installation by physicochemical washing.
(B) The
final destruction of the capture products after the
simultaneous process of absorption and chemical modification
This ultimate operation (B) is carried out in a biological
treatment plant. The organic compounds present and formed
During the condensation reaction are digested by the
process of natural aerobic bio-purification of the purification
plant.
The
originality of the process resides firstly in the choice
of the reagent which combines with the pollutants to
be treated and secondly in the final natural destruction
in the wastewater treatment plant that does not generate
any new gaseous pollution.
The
example below describes the treatment of 100 m3 of biogas
from the methanisation of sludge from an urban sewage
treatment plant. (test on a biogas line for sludge drying).
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EQUIPMENT USED:
- Absorption
column 800 liters (column + tank), height: 3
m., base area: 0,28 m2 (diameter 60 cm), tray
lining, demister out of air.
-
Fluid circulation pump adjustable from 0 to
25 m3 / H.
- Adjustable
pollutant effluent gas supply valve from 0 to
1000 m3 / h.
AVERAGE COMPOSITION OF THE BIOGAS TO BE TREATED:
Air
flow with a flow rate of 100 m3 / h. containing:
- Methane:
98.6% (98.6 m3)
- Miscellaneous
impurities (minority compounds): 0.4% (0.4 m3)
of which:
-
H2S: 10.618 mg / m3
- Mercaptans:
207 mg / m3 (Ethanethiol, methanethiol,
propane and butanethiol)
- Eventually
traces of siloxanes
The
base and reagent quantities are calculated from
the attached spreadsheet.
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Matériel
type
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OPERATIVE
CHARGE FOR DEMONSTRATION
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Water: 400 L.
- 30%
soda:
33.5 kg
- 40%
reactive: 36.9 kg
VALIDATION
OF THE DEMONSTRATION OF TREATMENT
This demonstration allowed an expected run time of 4
hours.
During this period of operation, regular checks of the
effectiveness verified the absence of H2S at the exit
of the industrial installation in place.
Results:
Absence of H2S validated at the column exit.
Cost
materials of the treatment: 26 € for the 4 h. Operating.
By way of comparison, a conventional treatment with
bleach would have cost 127 €
The
operation was carried out over a period of 4 hours with
a gas flow rate of 100 m3 / h.
The end of the reaction is controlled by pH-metry (about
pH = 9) and the absence of H2S verified with lead acetate
paper. The reaction medium is colorless and odorless.
CONCLUSIONS
OF THE DEMONSTRATION
Total
elimination of H2S and mercaptans during a 4 hr operating
period.
In this test, it is clear that for the destruction of
sulfur impurities, treatment with bleach is 2.5 times
more expensive than treatment with the GASWASH process.
- This
example of biogas treatment includes:
- Complete
elimination of H2S and mercaptans.
- Lowering
the 4% water of methanation to 40 ° C. (1 to 1.5%)
- Total
elimination of siloxanes and organochlorines or fluorinated
if present in trace amounts.
In this example, the GASWASH system was used to purify
100 m3 of biogas, which supplied 98 m3 of pure biomethane
but also of H2S and mercaptans.
TREATMENT
REVIEW
The
98 m 3 of methane obtained with purity greater than
98.5% (biomethane) obtained can be used as an energy
source or as a precursor for the manufacture of biohydrogen,
for example with the VABHYOGAZ process.
Cost
for treatment with the GASWASH process:
Treatment
of 100 m3 of biogas: 26 € Either for a production of
98 m3 of methane for: 0,265 € / m3 or 2,68 cts. € /
kWh
ANNEXE
Energy equivalence
See
also the examples of the DAVID Process - Odors
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Valorisation
