High voltage electrical apparatus for removing ecologically noxious substances from gases

Electrical apparatus for removing ecologically noxious substances from gases which includes an electrical precipitator having a reaction chamber through which a stream of the gases to be cleaned passes, and which includes an elongated electrode extending into said reaction chamber for producing a corona discharge within the chamber. The apparatus of the invention includes a multi-stage Fitch generator connected to the electrode which produces a high level pulsating voltage superimposed on a constant direct current voltage. The pulsating voltage causes the electrode to produce the corona effect in the chamber, and the constant direct current voltage sets up an electrostatic field which removes unwanted products of the corona discharge from the gas stream passing through the chamber. The Fitch generator is adapted to provide pulsating voltages of sufficient amplitude and steepness to produce a high density, high energy corona discharge within the chamber. In this application, the Fitch generator allows the apparatus to operate for long periods of time without consuming excessive amounts of electricity.

BACKGROUND 
1. Field of the Invention 
The present invention relates to methods and means incorporating 
electrostatic precipitators for cleaning air and industrial and domestic 
gases contaminated with ecologically noxious substances. More 
particularly, it provides an improved method and highly efficient 
electrical apparatus for that purpose. 
2. Prior Art 
In the prior art, gas cleaning is usually carried out in electrical 
precipitation reaction chambers in which contaminated gases flow through 
an electrode system.. The electrode system of such electrical 
precipitators is activated by short, high voltage electrical pulses 
superimposed on a constant, high, direct-current voltage. The pulses give 
rise to so-called streamer corona discharge within the reaction chamber 
causing a flow of high-speed electrons which activate or ionize gas 
molecules to produce non-noxious aerosols and solid particles within the 
chamber. The aerosols and solid particles are removed from the gases in 
the reaction chamber by the electrostatic conductive field created by the 
constant direct-current voltage existing between the electrodes of the 
electrode system. 
The efficiency of the cleaning process depends on the density and the 
energy of the electron flow generated by the streamer corona discharge. 
Both of these parameters rise with an increase in pulse amplitude and with 
an increase in the steepness of the pulses. The pulse steepness is an 
important factor because the pulse amplitude that can be achieved without 
electrical breakdown of the inter-electrode space in the reaction chamber 
is a function of pulse steepness. 
Based on these considerations, it is an objective of the present invention 
to provide an improved waste stream cleaning method and apparatus which 
embody a high voltage power supply capable of generating voltage pulses of 
the high amplitude and steepness required for producing a high density 
energy flow within a precipitation reaction chamber, and also of producing 
a constant, high, direct-current voltage on which the pulses are 
superimposed. 
Another object is to provide a power supply for use with such a method and 
apparatus which is extremely efficient from an energy consumption point of 
view so that the apparatus may operate normally for long periods of time. 
A further object of the invention is to provide a precipitation reaction 
chamber for such use which includes a high voltage corona-producing 
electrode that responds to the high voltage pulses from the power supply 
to generate a pulse streamer corona of sufficiently high current to enable 
the transfer of the required amount of electrical power into the gases in 
the precipitation chamber so as to activate or ionize the gas molecules to 
produce non-noxious aerosols and solid particles. 
A still further object is to provide a reaction chamber constructed to 
permit the application without electrical breakdown of a constant 
direct-current voltage from the power supply which is sufficiently high 
for the removal of the resulting non-noxious aerosols and solid particles 
from the gases flowing through the reaction chamber. 
There are two main groups of prior art apparatus for cleaning waste stream 
pollutants by means of electric discharge in a precipitation reaction 
chamber. A first group involves the use of a pulse transformer for the 
generation of high voltage pulses. Typical examples of the prior art 
apparatus of the first group are described in U.S. Pat. Nos. 4,016,060 and 
4,808,200. A second group of prior art apparatus involves the use of a 
direct discharge by appropriate switching means of a power storage unit, 
such as a capacitor or a pulse-forming L-C line, to produce the high 
voltage pulses. Typical examples of the prior art apparatus of the second 
group are described in U.S. Pat. Nos. 4,183,736 and 4,713,093. 
A disadvantage of apparatus using a pulse transformer, such as the 
apparatus of the first group, is the necessity of providing two separate 
power supplies, one for producing the constant direct-current high voltage 
for the reaction chamber, and a second for energizing the pulse-generating 
system, the second power supply being connected to the primary coil of the 
pulse transformer. Another disadvantage of the prior art apparatus of the 
first group resides in the fact that a pulse transformer capable of 
generating voltage pulses of the amplitude, power, duration and frequency 
required for producing a streamer corona is a very complicated and 
expensive device. 
A disadvantage of the prior art apparatus of the second group is the 
impossibility of obtaining a pulse voltage with an amplitude greater than 
double the charge voltage. These devices are incapable of producing 
electrons with sufficiently high energy to perform an efficient gas 
cleaning operation in the reaction chamber. 
Another disadvantage of the second group of prior art devices stems from 
the requirement that in order to avoid short circuits of the power supply, 
the power storage unit must be isolated from the power supply by a 
resistor or an inductance coil having high resistivity. However, in the 
periods when the capacitor in the power storage unit is being charged, the 
resistor or inductance coil dissipates as much power as is stored in the 
power storage unit, resulting in low efficiency. 
Still another disadvantage inherent in the prior art apparatus of the 
second type lies in the fact that due to high resistivity of the 
inter-electrode space in the reaction chamber, only a part of the power 
stored in the power storage unit is inserted into the gas flowing through 
the reaction chamber. The remaining part of the power is dissipated in the 
resistivity of the overall circuit. This results in a further reduction in 
efficiency. 
From the foregoing, it will be appreciated that another object of the 
subject invention is to provide a method and means for removing pollutants 
from a gas or liquid waste stream which avoid or overcome the various 
previously mentioned disadvantages of the prior art electrostatic cleaning 
methods and precipitators. 
It is well known in the prior art that various processes for the removal of 
ecologically harmful substances from waste gas and liquid streams can be 
carried out or enhanced by treating the streams with conventional 
oxidizing agents, such as ozone. Certain prior art electrostatic 
precipitators are designed to produce ozone to enhance the oxidation 
process. 
The efficiency of the oxidation of the pollutant molecules depends on their 
chemical structure and concentration and on the reactance of the 
particular oxidant or oxidants. By way of comparison, the reaction rate 
constants K.sub.298 for several standard reactions involving typical 
inorganic and organic industrial pollutants in the presence of the most 
common oxidant-reagents at room temperature are set forth in the following 
Table 1. 
TABLE 1 
______________________________________ 
Reaction K.sub.298, cm.sup.3 /molecule .multidot. sec 
______________________________________ 
O.sub.3 
+ SO.sub.2 .fwdarw. 
SO.sub.3 
+ O.sub.2 
&lt;8 .multidot. 10.sup.-24 
OH + SO.sub.2 .fwdarw. 
HOSO.sub.2 1.1 .multidot. 10.sup.-12 
HO.sub.2 
+ SO.sub.2 .fwdarw. 
HO + SO.sub.3 
&lt;1 .multidot. 10.sup.-18 
O.sub.3 
+ NO .fwdarw. 
NO.sub.2 
+ O.sub.2 
1.8 .multidot. 10.sup.-14 
OH + NO .fwdarw. 
HONO 6.7 .multidot. 10.sup.-12 
HO.sub.2 
+ NO .fwdarw. 
NO.sub.2 
+ OH 6.6 .multidot. 10.sup.-12 
O + NO .fwdarw. 
NO.sub.2 1.9 .multidot. 10.sup.-12 
O.sub.3 
+ NO.sub.2 .fwdarw. 
NO.sub.3 
+ O.sub.2 
3.2 .multidot. 10.sup.-17 
OH + NO.sub.2 .fwdarw. 
HNO.sub.3 1.1 .multidot. 10.sup.-11 
O + NO.sub.2 .fwdarw. 
NO + O.sub.2 
5 .multidot. 10.sup.-12 
O.sub.3 
+ R-CH.dbd.CH.sub.2 
.fwdarw. 
products 10.sup.-18 -10.sup.-17 
O + R-CH.dbd.CH.sub.2 
.fwdarw. 
products 10.sup.-13 -10.sup.-11 
OH + R-CH.dbd.CH.sub.2 
.fwdarw. 
products 10.sup.-12 -10.sup.-11 
______________________________________ 
Experience has demonstrated that many of the harmful and noxious substances 
most frequently encountered in the modern industrial environment tend to 
display a relatively low rate of reaction with ozone. Analysis of the 
K.sub.298 values set forth in Table 1 confirms that the reactions 
involving ions or radicals (O, OH, HO.sub.2) are much more rapid than 
those of the same pollutants with ozone. To take advantage of these 
phenomena, it is another object of the present invention to provide an 
effective method and electrical apparatus for producing primarily highly 
active intermediate substituents (e.g., O, OH, HO.sub.2 ions), rather than 
ozone. 
SUMMARY OF THE INVENTION 
The method and apparatus of the present invention overcome the 
disadvantages of the prior art apparatus of the first and second groups 
described above in several ways: 
(1) The high voltage pulses are generated in the apparatus of the present 
invention by a Fitch pulse generator which is energized by the same power 
supply as is used for producing the constant direct-current voltage. The 
Fitch pulse generator, as will be described, includes an odd number (three 
or more) of series-connected power storage units. Each three sequential 
power storage unit forms a stage of the generator, with each third unit of 
each stage also forming the first unit of the subsequent stage. 
Accordingly, an n-stage Fitch pulse generator produces high voltage pulses 
superimposed on a constant charge voltage, with the amplitude of the high 
voltage pulses being 2n+l times as high as the constant charge voltage. 
The Fitch pulse generator is connected directly in parallel with the 
precipitation reaction chamber. The first power storage unit of the Fitch 
generator is connected directly to the output of the power supply without 
any isolating elements such as resistors or inductance coils. This 
arrangement avoids the power losses which occur in such elements in the 
prior art apparatus and protects the power supply from the high voltage 
pulses. 
(2) A phase shifting network and a frequency divider are included in the 
apparatus of the invention enabling the generation of a switching pulse at 
the moment the rectified voltage of the power supply approaches zero, thus 
avoiding short circuits in the power supply during the time the switch is 
open, or in the case of electrical breakdown. 
(3) Air spark dischargers, vacuum dischargers, or gas filled discharge 
tubes (thyratrons) are used as switches in the Fitch pulse generator. In 
the first two cases an isolating capacitor having a capacitance greater 
than that of the individual power storage units is connected in series 
with each switch in the Fitch generator in order to enable the closure of 
the switches to occur before the complete discharge of the corresponding 
power storage unit. Due to the presence of this capacitor the closure of 
each switch occurs after a short number of oscillations, and when the 
voltage across the isolating capacitor becomes equal and opposite in sign 
to the voltage of the power storage unit. 
In the case of the thyratron, the device is connected directly in series 
with the power storage unit, the anode being connected with the initially 
positively charged output of the unit. As a rule, triggering elements in 
oscillatory circuits must have bidirectional conductivity. Air spark and 
vacuum dischargers are such elements. Commonly, thyratrons are used as 
elements having unidirectional conductivity. In the present invention, the 
physical characteristics of the gas discharge in a thyratron allow us to 
use the thyratron in oscillatory circuits as a bidirectionally conductive 
element for the first half-period of oscillation before the voltage 
applied across the tube changes its sign and switches the current off. The 
pulse duration required for generation of a pulsed streamer corona is in 
the range of 100-400 ns. During this very short period the gas discharge 
in the thyratron is not fully extinguished and the device remains 
bidirectionally conductive. This enables the sign of the power storage 
unit voltage to change completely during the first half of the 
oscillation. 
A recuperation circuit comprising a diode connected in the direction 
opposite the positively charged output of the power storage unit and an 
inductance is inserted in each stage of the Fitch pulse generator thereby 
enabling the restitution of the initial state of the generator after 
closure of the thyratron. 
The invention produces a pulsed streamer corona with electron energy 
greater than 10 eV. This is sufficient to ionize O.sub.2 and N.sub.2 as 
well as most admixture pollutant molecules. The concentration of ionized 
species in the vicinity of a high voltage electrode is approximately 
10.sup.15 cm.sup.-3 for ions and approximately 10.sup.17 cm.sup.-3 for 
radicals. The main electron-to-molecule attachment process at high 
electric field strengths (volts/cm) is attachment+dissociation of O.sub.2, 
H.sub.2 O and CO.sub.2, whose concentrations are therefore the dominant 
parameter for defining the value of the attachment coefficient. At lower 
electric field strengths, for example, where the average electron energy 
is lower than the dissociation threshold, the main attachment process is 
the oxygen three-body attachment. 
The reaction rate for these reactions is relatively high. The initial fast 
electrons produced by the apparatus of the invention react quickly with 
O.sub.2, N.sub.2, etc. to produce the secondary ions and radicals referred 
to earlier. The reaction time of these groups of chemical reactions is 
generally lower than a few tens of microseconds. Following these, the 
slower chemical reactions involving the secondary radicals take place. 
Additionally, during this period the low concentration components 
(NO.sub.x, SO.sub.2, NH.sub.3, organics, etc.) complete with active 
particles (oxygen atoms, etc.) reducing the production of oxygen. 
Nevertheless, the 2-3 seconds the waste stream remains in the reaction 
chamber of the apparatus of the invention are sufficient to enable the 
oxidants to destroy the admixture pollutant molecules. 
The main ion and neutralization molecular reactions outlined in Table 1 
are: 
N.sub.2.sup.+ +H.sub.2 O.fwdarw.H.sub.2 O.sup.+ +N.sub.2 ; N.sup.+ +H.sub.2 
O.fwdarw.H.sub.2 O.sup.+ +N; O.sub.2.sup.+ +H.sub.2 O.fwdarw.H.sub.2 
O.sup.+ +O.sub.2 ; O.sup.+ +H.sub.2 O.fwdarw.H.sub.2 O.sup.+ +O; 
CO.sub.2.sup.+ +H.sub.2 O.fwdarw.H.sub.2 O.sup.+ +CO.sub.2 ; H.sub.2 O 
.sup.+ +H.sub.2 O.fwdarw.H.sub.3 O.sup.++OH; N.sub.2.sup.+ +O.sub.2 
.fwdarw.O.sub.2.sup.+ +N.sub.2 ; O.sup.+ +CO.sub.2 .fwdarw.O.sub.2 .sup.+ 
+CO; CO.sub.2.sup.+ +O.sub.2 .fwdarw.O.sub.2.sup.+ +CO.sub.2 ; e.sup.- 
+O.sub.2 .fwdarw.O.sub.2.sup.- ; e.sup.- +CO.sub.2 .fwdarw.CO.sub.2.sup.- 
; O.sub.2.sup.- +CO.sub.2 .fwdarw.CO.sub.2 .sup.- +O.sub.2 ; e.sup.- 
+X.sup.+ .fwdarw.X.sup..cndot. ; CO.sub.2.sup.- +H.sub.3 O.sup.+ 
.fwdarw.H+H.sub.2 O+CO .sub.2 ; and O.sub.2.sup.+ +CO.sub.2.sup.- 
.fwdarw.CO+O.sub.2 +O. 
The main ion-to-molecular reactions for O.sub.3 production and decay are: 
EQU O.sup.- +O.sub.2 .fwdarw.O.sub.3 +e; O.sub.2.sup.+ +O.sub.3.sup.- 
.fwdarw.O.sub.3 +O.sub.2 ; and O.sup.- +O.sub.3 .fwdarw.2O.sub.2 +e. 
The main neutral particle reactions for O.sub.3 production and decay are: 
EQU O+O.sub.2 +O.sub.2 .fwdarw.O.sub.3 +O.sub.2 ; O(.sup.3 P)+O.sub.3 
.fwdarw.2O.sub.2 ; O(.sup.1 D)+O.sub.3 .fwdarw.2O.sub.2 ; H+O.sub.3 
.fwdarw.OH+O.sub.2 ; and OH+O.sub.3 .fwdarw.HO.sub.2 +O.sub.2. 
In the presence of admixture molecules (M) a competitive reaction (O, HO, 
HO.sub.2, etc. )+M.fwdarw.products takes place. 
In the subject invention, the waste stream passes through an electrostatic 
process that substantially increases the rate of production of highly 
reactive atoms, radicals and active reagents other than O.sub.3. As a 
result, under similar conditions the invention is ten times more efficient 
than the chemical treatment with ozone alone in removing admixture 
pollutants from a waste stream. 
As will become apparent from a reading of the following detailed 
description of a preferred embodiment of the invention, in addition to the 
removal of different kinds of harmful admixtures (e.g., NO.sub.x, 
SO.sub.2, NH.sub.3, organics, etc.) from waste gaseous and liquid streams, 
the invention may be adapted for a variety of other purposes, such as the 
destruction of substances with bad odors (mercaptans, etc.), the disposal 
of noxious or poisonous substances, the sterilization of instruments, and 
the removal of bacteria, viruses, and similar contaminents from 
ventilating air streams and tap water.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The electrical apparatus of the invention includes an electrostatic 
precipitator which serves to remove impurities from a stream of gases 
flowing through the reaction chamber 5 of the electrostatic precipitator 
from the inlet I to the outlet O of the chamber. 
The circuitry of FIG. 1 includes a frequency convertor 1 for converting 
3-phase 50-60 Hz AC line voltage into approximately 400 Hz single-phase AC 
voltage. Frequency convertor 1 may be any conventional frequency convertor 
of the type presently available on the market. 
A single-phase high voltage transformer 2 is connected to the output of 
convertor 1, and this transformer raises the 400 Hz AC voltage from 
convertor 1 to a voltage having an amplitude of, for example, 30-100 Kv. 
The AC voltage from transformer 2 is rectified in a rectifier 3. The 
negative output terminal of rectifier 3 is grounded, and the positive 
terminal is connected to a Fitch pulse generator 7, which is connected to 
reaction chamber 5. 
The reaction chamber 5 of the electrostatic precipitator includes a 
grounded cylindrical casing 6 formed, for example, of stainless steel. An 
elongated corona-producing collector electrode 4, likewise formed of 
stainless steel, extends coaxially with the cylindrical casing 6 into the 
reaction chamber. Electrode 4 is mounted in the grounded casing 6 by an 
insulating member 9 which causes the electrode to be insulated from the 
casing. The casing forms a second electrode for the electrostatic 
precipitator. 
Fitch pulse generator 7 is an n-stage pulse generator. It is connected 
between collector electrode 4 of precipitator and ground. The Fitch 
generator includes 2n+1, an odd number of power storage units 8.1-8.(2n+1) 
connected in series. Typically, each of the power storage units may be a 
single, high voltage (50 Kv) industrial capacitor having a capacitance of 
approximately 0.15 mf, or it may comprise a group of such capacitors. 
The odd number connecting points of the power storage units 8.1 . . . 
8.(2n-1) are connected to electrode 4 through respective oscillation 
damping diodes 10.1-10.n and through series-connected inductance coils 
9.1-9.n. The even number connecting points of the power storage units 8.2 
. . . 8.2n are connected to ground through series-connected inductance 
coils 11.1 . . . 1.n, and oscillation damping diodes 12.1 . . . 12.n. The 
positive terminal of rectifier 3 is connected to the common junction of 
diode 10.1 and inductance coil 9.1. Frequency converter 1, transformer 2, 
and rectifier 3 form the power supply for the apparatus. 
Triggering circuits, including switches 13.1-13.n having respective first 
main electrodes connected in series with respective capacitors 14.1-14.n 
and resistors 15.1-15.n, have their first and second main electrodes 
connected in parallel with the even power storage units 8.2 . . . 8.2n, 
through the capacitors, resistors, and discharge inductances 22.1-22.n. 
The latter can be simply the inductances of the electrical connections in 
the circuit. Each of the switches 13.1-13.n has a trigger electrode 
connected to one terminal of corresponding secondary windings 16.1-16.n of 
a pulse transformer 17. The first main electrodes of switches 13.1-13.n 
are each connected to the other terminal of the corresponding secondary 
windings 16.1-16.n of transformer 17. 
The primary winding 18 of pulse transformer 17 is connected to the output 
of an ignition pulse generator 19 whose controlling input circuit is 
connected to the output of a frequency divider 20. The controlling input 
circuit of frequency divider 20 is connected to the output of a phase 
shifting network 21 which, in turn, is connected to frequency convertor 1. 
Referring to FIG. 1a, the anodes of thyratrons 13.1-13.n are connected in 
series with discharge inductances 22.1-22.n which are connected in turn 
with odd-numbered power storage units 8.1-8.(2n-1). The cathodes are 
connected to respective even-numbered power storage units 8.2-8.2n. 
Secondary windings 16.1-16.n of the pulse transformer 17 are connected 
between the cathodes and control grids of thyratrons 13.1-13.n. Earthing 
inductances 11.1-11.n are connected across adjacent pairs of power storage 
units 8.1+8.2, . . . , 8.(2n-1)+8.2n. The anodes of damping diodes 
12.1-12.n are connected with intermediate points of inductances 11.1-11.n, 
dividing them approximately in the ratio 1:2, whereas the cathodes of 
diodes 12.1-12.n are connected with odd-numbered power storage units 
8.1-8.n. 
The phase shifting network 21 is shown in circuit detail in FIG. 2. This 
network produces an output pulse each time the AC voltage from convertor 1 
(appearing across the primary winding of transformer 2) approaches zero. 
The phase shifting network 21 of FIG. 2 includes a transformer 32 whose 
primary winding is connected across the output of frequency convertor 1. 
Transformer 31 includes two independent secondary windings 33a and 33b 
which are connected to respective rectifier bridges 36 and 37 which are 
included in independent phase shifting networks 34, 35. The rectifying 
bridges each provide a two-cycle rectified voltage of positive polarity 
with double the frequency of the output voltage from frequency convertor 
1, that is, 800 Hz. The negative terminals of rectifier bridges 36 and 37 
are grounded. The positive terminal of bridge 36 is connected through 
resistors 45 and 46 to the anodes 38 and 39 of a double triode 40, and the 
positive terminal of bridge 37 is connected to the left side control grid 
41 of triode 40. 
Control grid 41 is connected through a resistor 47 to the negative terminal 
of a DC biasing source so that the left side of triode 40 is normally 
non-conductive. The right side control grid 42 of triode 40 is connected 
through a resistor 48 to the positive terminal of the DC biasing source so 
that the right side of triode 40 is normally conductive. The cathodes of 
triode 40 are grounded. Anode 38 is coupled through capacitor 49 to 
control grid 32, and anode 39 is coupled through capacitor 50 to a 
grounded resistor 51, the resistor being connected across the input 
terminals of frequency divider 20. 
The operation of the circuits of FIGS. 1, 1a, and 2 will now be described 
with reference to the timing curves of FIGS. 3(a)-3(g). For simplified 
descriptive purposes, the curves of FIGS. 3(a)-(g) relate to a particular 
apparatus embodying the invention in which n equals 1, that is, to a Fitch 
pulse generator with three power stage units 8.1, 8.2 and 8.3. The 400 Hz 
output voltage Ua from frequency convertor 1 is represented by curve A in 
FIG. 3(a). During the first half cycle of the output voltage Ub from 
rectifier 3 (curve B in FIG. 3(b)) power storage units 8.1, 8.2, 8.3 are 
charged to an amplitude U.sub.2. If at the end of the half cycle there is 
no ignition pulse, then during the next half cycle the voltage Ub remains 
approximately equal to U.sub.2, as shown in curve B. 
At the same time a positive half-cycle voltage from phase shift network 34 
(FIG. 2)in phase shifting network 21, shifted backwards by 90 degrees 
(curve C of FIG. 3(c)), is applied to the anodes 38, 39 of triode 40. 
Accordingly, a peak voltage is applied to the anodes 38, 39 at the moment 
output voltage Ua from frequency convertor 1 is zero (curve A). Another 
positive half-cycle voltage Ud from phase shift network 35 (FIG. 2) is 
applied to grid 41 of triode 40. This voltage, as shown by curve D of FIG. 
3(d), is shifted backwards by p degrees depending on the volt-ampere 
characteristics of triode 40 and on the amplitude of the negative bias 
voltage applied to control grid 41. The value of p degrees must be 
adjusted so that the non-conductive left side of triode 40 is rendered 
conductive at the moment of zero voltage of the voltage Ua (curve A). 
When the left side of triode 40 is rendered conductive, a negative pulse Ue 
(curve E of FIG. 3(e)) occurs at the anode 38 and is applied to the right 
side grid 42 to render the right side of the triode 40 conductive. This 
produces a positive pulse Uf (curve F of FIG. 3(f)) at anode 39 and at the 
output of phase shifting network 21 which is applied to the input of 
frequency divider 20. The voltage at anode 39 remains near zero until the 
voltage Ud applied to grid 41 becomes sufficiently low to return the left 
side of triode 40 to its non-conductive state. Then the cycle recommences. 
Accordingly, for the major part of the cycle the left side of triode 40 is 
non-conductive and immune from electrical disturbances. 
Frequency divider 20 increases the time between two sequential pulses in 
wave form F of FIG. 3(f). The wave form G of FIG. 3(g), which represents 
the output of frequency divider 20, contains pulses Ug which correspond to 
each of the pulses Uf of wave form F, or to every second pulse (k=2) (as 
shown), or every third pulse, etc. This allows an easy control of the 
operating power of the system of FIG. 1. 
When a pulse Ud from the pulse train wave form F from frequency divider 20 
enters the input of the ignition pulse generator 19, the pulse generator 
introduces a voltage pulse across the primary winding 18 of pulse 
transformer 17. This results in a high voltage pulse appearing across the 
secondary winding 16.1 which is introduced between the second of the main 
electrodes and the ignition electrode of switch 13.1, and in the case of a 
thyratron between the cathode and the control grid of the thyratron. This 
results in a breakdown of the switch and causes an oscillating circuit to 
be formed which includes power storage unit 8.2 and discharge inductance 
22.1. An oscillatory action is set up in the oscillation circuit which 
recharges the capacitors in power storage unit 8.2 with a cycle of 100-400 
ns depending upon the capacitances and inductances involved in the 
oscillation circuit. 
As the time constant of the circuits formed by power storage units 8.1 and 
8.3 and inductance coils 9.1 and 11.1 is several times larger than the 
cycle of the Fitch pulse generator oscillation during the first period of 
this oscillation, the voltage on the power storage units 8.1 and 8.3 
remains approximately constant, and the voltage on the power storage unit 
8.2 after one-half of the main oscillation period changes its sign and the 
full output voltage of the first stage of the Fitch power generator 
becomes a sum of approximately three charged voltages. 
It can be seen that in general a Fitch pulse generator having n stages, 
i.e., 2n+1 power storage units charged to a voltage U superimposes over 
the constant DC charged voltage a pulsating voltage (curve 2B) which has 
an amplitude approximately equal to 2nU. This pulsating voltage and the 
constant DC voltage (curve U.sub.2) are applied to the corona-producing 
electrode 4 and give rise to a streamer corona discharge in chamber 5 with 
current pulse amplitude and duration depending on the geometry of the 
chamber and on the steepness and amplitude of the voltage pulse. 
FIG. 4 represents an example of an oscillogram of a single-stage Fitch 
pulse generator voltage pulse (U) and a corona streamer current pulse (I) 
produced in the electrostatic precipitator chamber 5. The corona streamer 
discharge produces a high density high energy electron flow in the gas 
stream flowing through the chamber which initiates chemical reactions. 
These chemical reactions result in the conversion of the noxious 
substances in the gas into aerosols or solid particles which are removed 
from the gas by the constant DC voltage fed to the electrode 4. 
The Fitch power generator pulse duration is much shorter than the period of 
the AC input voltage. During the time the Fitch pulse generator 
oscillates, the AC input voltage remains near zero and does not produce 
any external current to feed the discharge in the switches. After several 
Fitch power generator oscillations, the voltages of power storage units 
8.2 . . . 8.2n become approximately equal and opposite in sign to the 
voltage of the corresponding isolating capacitors 14.1 . . . 14.n. This 
results in approximately zero voltages on switches 13.1 . . . 13.n, and 
the elimination of switch discharges. Numerical calculations show that at 
this moment the residual voltages on the capacitors do not exceed 
one-third of the initial charge voltage. 
In the case of a thyratron, the oscillations stop after the first 
half-period due to the automatic closure of the thyratron. The voltage of 
the even-numbered power storage units 8.2-8.2n remains opposite in sign to 
the charge voltage. 
Simultaneously with the main oscillatory process, additional oscillations 
occur in the Fitch power generator with frequencies depending upon the 
capacitances of capacitors 8.1-8.(2n+1) and the inductances of inductance 
coils 9.1-9.n and 11.1-11.n, these frequencies being much lower than the 
main Fitch power generator frequency. The diodes 10.1-10.n and 12.1-12.n 
serve to damp the additional oscillations after their first half cycle. In 
the case of a thyratron, a recuperation circuit comprising diodes 
12.1-12.n and inductances 11.1-11.n causes the residual power of the 
even-numbered storage units 8.2-8.2n to be redistributed among the other 
storage units 8.1-8.(2n-1) without oscillations and hence without 
substantial attenuation. Thus during the time necessary for the extinction 
of switch discharges the power storage unit voltages do not fall very low 
as compared with the charge voltage, thus providing during this time the 
DC voltage necessary for the removal of the reaction products from the 
flow of gases in the chamber 5 of the electrostatic precipitator. 
After all oscillations have terminated, the output voltage of the Fitch 
power generator returns, due to the leakage of residual charges across the 
power storage units, to a level dependent upon the power fed into the 
reaction chamber 5 by the corona streamer current from the collector 
electrode 6, and the power stored in the capacitors 14.1-14.n. This level 
of restored voltage can attain 60% of initial charge voltage. The values 
of resistors 15.1-15.n are selected to insure the full discharge of 
separating capacitors 14.1-14.n in the interval between successive Fitch 
power generator pulses. The power dissipated in resistors 15.1-15.n does 
not exceed 30% of the power supplied to the Fitch power generator from the 
electrical mains. 
From the foregoing description it will be seen that operating in 
conjunction with a single power supply, the Fitch pulse generator 17 
supplies high voltage pulses to the electrostatic precipitator which are 
superimposed on a constant DC voltage. The high voltage pulses have the 
required frequency and amplitude to establish a corona discharge in 
chamber 5 of the electrostatic precipitator which has sufficient intensity 
to ionize the noxious substances in the gases flowing through the chamber, 
and the constant DC voltage has sufficient amplitude to remove the 
resulting substances from the gases. 
The principal advantages of the methods and means comprising the present 
invention may be summarized as follows: 
(1) Relatively high efficiency of the gas cleaning process in the 
electrostatic precipitator of reaction chamber 5; 
(2) Relatively low electric power consumption due to quick closure of the 
switches 13.1 . . . 13.n in the Fitch generator, and conservation of a 
considerable part of power which is stored in the generator, and the 
absence of extraneous elements dissipating any part of the power taken 
from the power supply 3; 
(3) Good control of consumed power due to easy achievement of a required 
frequency and amplitude of the pulse voltage which is superimposed over 
the constant voltage; 
(4) Good protection of the power supply from short circuits and harmful 
action of the output high voltage pulses; and 
(5) Simplicity of construction and large-scale use of industrially 
fabricated conventional devices and elements. 
It will be appreciated that while a particular embodiment of the invention 
has been shown and described, modifications may be made. It is intended in 
the following claims to cover all such modifications which fall within the 
true spirit and scope of the invention.