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Methods and technology of clearing the atmospheric air from
aerosols by means of pulsed and DC corona discharge
A.Z.Ponizovsky*, V.N.Ivanov**, A.V.Savchenko**
* FSUE-MBPP “Salut”, Moscow, Russia
** IEM SPA “Typhoon”, Obninsk, Russia
It is known that main technical parameters determining efficiency of a
device cleaning air from aerosols are:
·
efficiency of air cleaning in a wide range of fragment sizes (η, %)
·
specific power inputs (Wsp W*h/m3*mg)
·
hydraulic resistance
·
relation of air flow to the volume of refining device.
The most efficient devices for cleaning air from aerosols according
to the first three parameters are electric precipitators (EP), where
fragments are charged and then removed by action of high direct voltage
(HVDC). At the same time the fourth parameter, even in the best samples
of EP with separate charging and extraction chambers, is sufficiently lower
than in filters with solid filtrating material or in different kinds of cyclone
collectors. This is connected with the fact that the speed of air in an EP is
determined by time of aerosol charging in a HVDC corona (t s), which
essentially depends on time of presence of a particle in the zone of a
corona discharge, i.e. time of contact (fig. 1).
Fig. 1
Dependence of relative aerosol charging (Q/Qlim) on the time of presence
of a particle in the zone of a HVD corona discharge
From fig. 1 it follows, that the operation of a standard EP
will be efficient at dwell-times of a fragment in the zone of
corona discharge about 1 seconds. As the time of drift of a
aerosols in an EP at a maximum charge is about 0,1 s an essential
increase of value G can be reached only at the expense of
decrease of charging time.
We have found out, that an essential decrease of charging
time can be attained, using for this purpose the high voltage
pulse streamer (HVPS) corona discharge rather than HVDC
corona discharge. In an EP of the standard configuration having
inter electrode spacing about 0,2m, the HVPS streamer corona
generated under operating of voltage pulses with amplitude 100
kV and durations of about 10-7 s creates a pulsed current with
density about 1000 A/m2, that surpasses current density in a
HVDC corona by 5 orders of magnitude. For creation not only
high-density of current in a pulse, but also its high average value,
it is necessary to supply a high frequency of following of corona
flashes. Simple calculations demonstrate, what even at
pulse
repetition frequency of 50 Hz the mean charge, introduced in the
inter electrode space is more than by one order of magnitude
higher than at a HDV corona.
These considerations served us as a base
for designing
high-performance experimental – industrial plants for purification
of air from aerosols.
The purification process of vent gases from aerosols is
realized in a tube-type EP fed by very short high-voltage pulses
superimposed on high constant voltage which results in a
combined HVDC and HVP corona discharge. The charging of
aerosols of any dispersion, practically up to the greatest possible
value, is performed during a flash of a HVP corona. The removal
of aerosols from the air flow occurs in time spaces between
pulses, due to the HVDC corona discharge.
For realization of this process we have designed a HV pulse
generator, allowing to superimpose short high voltage
pulses
with big repetition rate on HVDC. This generator was patented
and
awarded a bronze medal on Brussels Exibition of the
Developments, Inventions and KNOW-HOW "BRUXELLESEURECA-95".
The principal circuit diagram of the device is shown on fig.2.
Fig.2
Circuit diagram and layout of the device for removal of aerosols by means
of HVP and HVD
The device involves a controlled HVDC source, a pulsed HV
generator, on the base of Fitch diagram, and a tubular EP. The device
allows to change the pulse repetition rate from 0 (the HVDC) up to 800
Hz. Dimensions of tubular EP are as follows: diameter of the pipe - 100
mm, length - 1000 mm.
Fig. 3 presents results of experiments on cleaning ventilation surge
from chrome anhydride aerosol with initial concentration of the order of
0.5mg/m3 and the flow rate 200 m3/h, flow velocity 20 m/s. The pulse
amplitude were 80 kV, their duration 100 ns, HVDC was equal 30 kV.
Fig.3
Cleaning ventilation surge from chrome anhydride aerosol
1-efficiency, 2- power consumption
From fig.3 it follows that increase of pulse repetition frequency from
HVDC to 50 Hz results in increasing of cleaning rate from 40 up to 99,2 %
practically without increase of power consumption. Increasing of pulse
repetition rate allows to attain practically full air cleaning however with
sufficient increase of power consumption.
Thereby using multifunction system of EP power supply makes it
possible already by pulse repetition rate 50 Hz attain practically maximum
charging of aerosols and as a result, almost full air cleaning from
specified aerosol.