Note: Descriptions are shown in the official language in which they were submitted.
WO95/01~7 ~16 ~ 4 7 ~ PCT/SE94/00643
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METHOD FOR CLEANING A GAS FLOW
This invention relates to a method for cleaning a
humid gas flow containing gaseous impurities, such as an
exhaust-air flow containing volatile solvents and origi-
nating from a spray booth in a painting plant, in which
method the gas flow is dehumidified by cooling, the cool-
ed gas flow is reheated to subsequently be conducted
through a device for the adsorption of gaseous impuri-
ties, a desorption-gas flow is heated to form a hot-gas
flow, which is conducted through the adsorption device in
order to clean the latter and entrain impurities accumu-
lated therein, the contaminated hot-gas flow is conducted
to a combustion device in order to be burnt, and hot com-
bustion gases are LemJved from the combustion device in
order to take part in at least one of the heating pro-
cesses.
The above method is used in a painting plant forcleaning an exhaust-air flow containing paint particles
and volatile solvents and originating from a spray booth
in the plant. In this prior-art method, the gas flow is
conducted through a dust separator, where particulate
impurities are separated from the gas flow, which is
cooled when leaving the dust separator. Part of the gas
flow leaving the dust separator is conducted, as cooling-
gas flow, through the adsorption device in order to cool
those parts of this device that have been heated by the
hot-gas flow, whereupon the cooling-gas flow is used as
desorption-gas flow. Hot combustion gases from the
combustion device are conducted through a heat exchanger
in order there to emit heat to the desorption-gas flow,
which also is conducted through the heat ~h~nger.
Further, a heat exchanger is used for reheating the
cooled gas flow leaving the dust separator.
The object of the present invention is to provide a
cleaning method in which the energy consumption is lower
WO95/01~7 PCT/SE94/00643
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and there is less need of heat exchangers than in the
above prior-art method, and which thus is less expensive
to implement than the prior-art method.
According to the invention, this object is attained
by a method which is of the type stated by way of intro-
duction and is characterised in that hot combustion gases
from the combustion device are introduced into and mixed
with the cooled gas flow and the desorption-gas flow.
It will be appreciated that the two heat exchangers
required for implementing the above prior-art method can
be dispensed with when utilising the method according to
the invention. The cooling-gas flow, which in the prior-
art method is dimensioned to serve as hot-gas flow as
well and thus is llnn~cPssarily large, may, if used in
a corresponding fashion when implementing the method
according to the invention, be advantageously reduced to
merely fulfil the cooling function, hot combustion gases
being supplied to the desorption-gas flow so as to form
the hot-gas flow.
The invention will now be described in more detail
with reference to the accompanying drawings, in which
Fig. 1 schematically illustrates a plant which is
intended for implementing the inventive method and in
which use is made of an incinerator with a recuperative
heat exchanger; and
Fig. 2 schematically illustrates a plant which is
intended for implementing the inventive method and in
which use is made of an incinerator with a regenerative
heat exchanger.
In Figs 1 and 2, the encircled numerals at the dif-
ferent flow arrows indicate a flow value for the respec-
tive flows, this flow value bearing a relation to the air
flow which prevails in a spray booth and whose flow value
has been set at lOO. The temperature of the respective
flows is also indicated at some flow arrows.
Both the plant illustrated in Fig. 1 and that illu-
strated in Fig. 2 are used for cleaning the exhaust-air
WO 95/01827 ~ 1 S ~ 4 7 8 PCT/SE94/00643
flow cont~; n; ng paint particles, volatile solvents and
water vapour that leaves a spray booth 1 in a plant for
painting vehicle bodies. Via an air conditioner 2, an air
flow is blown into the spray booth 1 by means of a fan 3.
The major part (about 90%) of the air blown into the
spray booth 1 is air that is circulated in the system in
a manner to be described in more detail below, whereas
the remainder (about 10%) is taken from the surrounding
atmosphere. The air is conditioned in the air conditioner
2 in such a manner that an air flow having a temperature
of about 23C and a relative humidity of about 60% is
obtained in the spray booth 1.
The air flow leaving the spray booth 1 and having
a temperature of about 18C is conducted through a dust
separator 4, such as a wet electrostatic precipitator,
where particulate impurities, such as paint particles,
are separated from the air flow. When leaving the dust
separator 4, the air flow is dehumidified by cooling in
a cooler 5.
The cooled air flow leaving the cooler 5 is, as will
be described in more detail below, supplemented with an
additional flow with which it is conducted, by means of a
fan 6, through a device 7' (Fig. 1) or 7" (Fig. 2) for
the adsorption of gaseous impurities, such as volatile
solvents. The adsorption device 7' or 7", which is of
known design, consists of a rotor composed of a plurality
of segment-shaped adsorption elements cont~ ; ng a
suitable adsorbing agent, which is zeolite in the rotor
7' shown in Fig. 1 and active carbon in the rotor 7"
shown in Fig. 2. US-A-5,057,128, for instance, discloses
a rotor of this type.
The flow path through the rotor 7' or 7" is, by
means of fixed channel walls (not shown), divided into
three sectors, namely a gas-cleaning sector, which covers
most of the circular cross-sectional area of the rotor
and through which is conducted the main part of the gas
flow to be cleaned, and two minor sectors, of which one
WO95/01~7 PCT/SE94/00643
216~78-`
is a cooling sector through which a minor part of the gas
flow to be cleaned is conducted in order to cool the
adsorption elements, and the other is a desorption sector
through which a hot-gas flow is conducted in order to
clean the rotor and entrain impurities accumulated there-
in. The cooling-air flow is regulated by means of a
register 8. The rotor 7' or 7" rotates during use, so
that the portion thereof situated opposite to the gas-
cle~n;~g sector of the flow path is gradually inserted
into the desorption sector of the flow path so as to be
cleaned, and then inserted into the cooling sector of the
flow path in order to be cooled.
The major part of the cleaned yas flow leaving the
adsorption device or the rotor 7' or 7" is, as mentioned
above, recycled to the air intake of the fan 3, whereas
the remainder of the gas flow is discharged into the sur-
rounding atmosphere.
The hot-gas flow, which has a high solvent concen-
tration when leaving the adsorption device 7' or 7", is
conducted to a combustion device 10' or 10" by means of
a fan 9.
In the Example illustrated in Fig. 1, the combustion
device 10' is an incinerator of the type described in
e.g. DE-A1-30 41 269 and DE-A1-30 43 286 and has a com-
bustion chamber 11 and a recuperative heat exchanger 12through which the heavily contaminated hot-gas flow is
introduced into the combustion chamber 11. The combustion
gases from the combustion chamber 11 are removed through
the heat ~X~h~nger 12, where they emit heat to preheat
the hot-gas flow, so that their temperature is reduced
from about 730C to about 350C.
A part (about 40%) of the thus-cooled combustion
gases is conducted, via a flow-regulating register 13, to
the desorption sector there to be mixed with the cooling-
air flow from the adsorption device 7' and form, togethertherewith, the hot-gas flow. The cooling-air flow leaving
the adsorption device 7' has a temperature of about 60C
W095/01~7 PCT/SE94/00643
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and is mixed with combustion gases having a temperature
of about 350C in such proportions (6:4) that the hot-gas
flow obtains a temperature of about 180C. When leaving
the adsorption device 7', the hot-gas flow has a tempera-
ture of about 90C.
A part (about 30%) of the combustion gases cooled
in the heat exchanger 12 forms the above-mentioned
additional flow and is conducted to the outlet of the
cooler 5 to be mixed with the cooled air flow leaving
this device. The cooled air flow leaving the cooler 5 has
a temperature of about 15C and is mixed with combustion
gases having a temperature of about 350C in such propor-
tions (100:3) that a gas flow having a temperature of
about 25C is obt~inP~.
The remainder (about 30%) of the combustion gases
cooled in the heat ~ch~nger 12 is conducted through a
heat-recovery device 14 before being let out into the
surrounding atmosphere.
The plant illustrated in Fig. 2 differs from that
illustrated in Fig. 1 in that active carbon, and not
zeolite, is used in the adsorption device, as mentioned
above, and in that an incinerator with a regenerative
heat exchanger, and not a recuperative heat exchanger, is
used as combustion device. The in~;n~rator employed is of
the type described in e.g. SE-A-8403330-7 and SE-A-
8802791-7.
The hot-gas flow, which has a high solvent concen-
tration when leaving the adsorption device 7", is con-
ducted to the combustion device 10", i.e. the regene-
rative incinerator, where combustion takes place. Thecombustion gases removed from the combustion device 10"
have a temperature of about 206C. A part (about 45~) of
the combustion gases is conducted, via a register 13,
to the desorption sector there to be mixed with the
cooling-air flow from the adsorption device 7" and form
therewith the hot-gas flow. The cooling-air flow leaving
the adsorption device 7" has a temperature of about 50C
W095/01827 ~ PCT/SE94/00643
2165i7~
and is mixed with combustion gases having a temperature
of about 206C in such proportions (5.5:4.5) that the
hot-gas flow obtains a temperature of about 120C. When
leaving the adsorption device 7", the hot-gas flow has a
temperature of about 70C. The remainder (about 55%) of
the combustion gases is conducted to the outlet of the
cooler 5 to be mixed with the cooled air flow leaving
this device. This air flow, which has a temperature of
about 15C as in the plant illustrated in Fig. 1, is
mixed with combustion gases having a temperature of about
206C in such proportions (100:5.5) that a gas flow hav-
ing a temperature of about 25C is obtained. In the plant
illustrated in Fig. 2, the energy contained in the com-
bustion gases is utilised to the full, for which reason
there is no need of any special heat-recovery device.
