8. The desulphurizing apparatus
The absorbent described above must be brought into immediate
contact with the gas. This takes place in closed purification chambers. They can
be made of steel, gas-tight brickwork or concrete.
Size of the chamber
The area perpendicular to the gas-flow or cross section of the
chamber is important. If it is too small, the gas will flow too quickly through
the absorbent and the contact time is too short. If the gas flow is too fast
channels will open in the absorbent. The gas then flows through these channels
and is not properly purified.
The volume (if the cross section is fixed then the height) of
the chamber is also important. The chamber must contain enough absorbent for the
gas to be in contact with the absorbent over a sufficient distance. Apart from
this the purification chamber must be large enough so that it does not
constantly need to be refilled.
Dimensioning method
A method for calculating the required size of purification
chambers is included at the end of this manual.
Intermediate trays
The purification chamber contains several intermediate trays. A
layer of absorbent cat 20-30 cm thick is placed on each tray. This avoids
compacting of the absorbent under its own weight.
The intermediate tray floors are permeable to the biogas. They
are made from perforated steel sheet or wooden slats. Wickerwork can also be
used.
The individual, intermediate trays do not rest upon the
absorbent in the tray below, but are supported by small spacers attached to the
tray underneath. The layers of absorbent that lie between should not be
compacted.
Inserting absorbent
The absorbent should be placed on the trays in such a way that
it is not compressed or packed down. It should be piled up higher at the chamber
walls to avoid the preferable gas penetration at this position.
The chamber corer
The chamber cover should be designed to give access to the whole
chamber cross section. This allows the removal of the intermediate trays from
the chamber.
Sealing the cover
The cover must be sealed with the chamber. A rubber seal made
from foam rubber' old bicycle inner tubes or a water hose would be suitable.
Fixing
The cover is fixed on to the chamber with clamps or bolts.
Control valves
Control valves are installed in the feed and exit pipes of the
purification chamber. These are used to disconnect the chamber from the gas flow
while the absorbent is being exchanged.
Scavenging vent
In addition, a scavenging vent is installed. It is used for
flushing air out of the chamber with new biogas after exchanging the absorbent
and sealing the chamber.
Caution: Danger of fire and explosion
When scavenging. the chamber there is a danger of fire and
explosion, due to the gas emerging from the scavenging vent. For this reason the
vent exit should be installed high up and away from buildings. Open flames and
smoking must be prohibited during all work on the purification chamber.
When scavenging is completed, that is, when two or three times
the volume of the chamber has been vented, the valve to the user can be
re-opened.
The H2S content of the gas can also be checked via
the scavenging vent even during plant operation (see Section 5).
Desulphurization chamber for biogas
Cylindrical purification chamber
Rectangular purification chamber
Construction of intermediate trays,
cross section; The intermediate trays can be made
from
