Abstract:
Contaminated hot gases are first cooled and then the flow is divided between a plurality of identical modules for removal or contaminants. There are two stages of treatment in each module, starting with submergence of the flow under the surface of an agitated liquid neutralizing solution in a reservoir under a pair of counter rotating separator deflectors. Above the deflectors the flow is propelled upward through a venturi restrictor chamber, then into a collector pressure chamber. This completes the first stage of treatment, the second stage being the same as the first stage. Between these first and second stages the flow is passed through an electronic air cleaner. Upon leaving the second stage of treatment the cleaned gas flow joins the flows from the other modules in a fresh air distributor. Filters are provided for the liquid neutralizing solutions and nozzles for washing, rinsing and drying the separator deflectors, these elements being controlled so that no more than one module is taken out of operation at any time.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a pollution control system for air or gas, or air or gas containing microparticles such as smoke. 
     Air pollution is a long-standing menace particularly in regard to foundry operations, various manufacturing industries, field burning and exhaust from power plants and internal combustion engines where the exhausts are released to the atmosphere. 
     In addition to particulates such as smoke and dust the most objectionable polluting gases are sulfur dioxide, hydro-carbons, oxides of nitrogen, methane, freons, carbon dioxide, carbon monoxide, methyl chloroform and carbon tetrachloride. 
     Various types of pollution control devices exist in the prior art. Schwartz U.S. Pat. No. 4,690,697 describes a system in which hot flue gas is cooled before passing it to an enclosure for removing noxious gases. Two such enclosures are provided allowing the gas flow to be transferred from one to the other. 
     Jackson U.S. Pat. No. 3,729,901 describes pollutant recovery apparatus in which exhaust gases are bubbled through liquid in one or the other of two tanks so that one tank may be cleaned while the other is operating to collect contaminants. 
     Schimpke U.S. Pat. No. 3,347,535 describes a gas-liquid contact apparatus having two air washer housings mounted side-by-side on a single liquid tank. 
     Schouw U.S. Pat. No. 3,683,594 describes a modular fume scrubber having three modules, one on top of the other and connected in parallel to triple the capacity of the system without increasing the required floor space required for a single unit. 
     Panzica U.S. Pat. No. 3,299,621; Howick U.S. Pat. No. 3,557,535; Howick U.s. Pat. No. 3,702,048 and Harmon U.S. Pat. No. 2,007,759 describe air gas washers having an upward flow through spray generators, impeller blades and baffles. 
     These devices do not have the capability to accomplish a &#34;no detection&#34; result. They may be effective to a certain extent but lack the ability to completely remove the contaminant. 
     SUMMARY OF THE INVENTION 
     In the present system a plurality of modules is provided so that the operation of any one module may be interrupted for cleaning without impairing the operation of the rest of the system. Hot air or gases are first cooled to a suitable temperature and then submerged in a liquid neutralizing solution in a reservoir under the module. The liquid is agitated by an oscillating vane agitator. 
     The air/gas flow emerging from the liquid is drawn through a pair of counterrotating separator deflectors which remove droplets of liquid and particulate matter. This upward movement of the air/gas stream is produced by a plurality of counterrotating propellers in a tapered venturi restrictor chamber beneath a collector pressure chamber. The reservoir, agitator, separator deflector elements, propellers and venturi chamber and the collector pressure chamber constitute a first stage of the module. 
     From the collection pressure chamber of the first stage of the module the air/gas is passed through an electronic separator and thence into a second stage of the module having all the elements described in the first stage. The cleaned air/gas is then discharged from the second stage into a fresh air distributor, then to open space or channeled into a factory fresh air system. 
     Nozzles are provided for applying wash water, rinse water and drying air to the separator deflectors in a cleaning cycle. During the cleaning cycle the rotation speed of the separator deflectors is reduced to a slow speed. These operations in the cleaning cycle are controlled by a motor speed resistor control, a master automatic reset timer and three secondary automatic reset timers. 
     Initiation of the cleaning cycle is controlled by an air venturi in the inlet to the module and an air venturi in the air/gas flow out of the collector pressure chamber, through vacuum sensors responsive to said venturis. The vacuum sensors are adjusted to the altitude above or depth below mean sea level. At the completion of the wash, rinse and air dry operations the rotation of the separator deflectors is returned to normal operating speed. 
     During a cleaning cycle in one of the modules the remaining modules continue in operation so that the operation of the system is not interrupted. The effectiveness of the system has been reliably tested and qualifies under a &#34;no detection&#34; rating. 
     The invention will be better understood and the foregoing features and advantages will become apparent from the following description of the preferred embodiment illustrated in the accompanying drawings. Various changes may be made in the details of construction and arrangement of parts and certain features may be used without others. All such modifications within the scope of the appended claims are included in the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front elevation view of a system according to the invention having two modules. 
     FIG. 2A is a schematic view on the line 2A--2A in FIG. 1 showing air flow patterns in the system. 
     FIG. 2B is a view on the line 2B--2B in FIG. 2A. 
     FIG. 3 is a vertical sectional view showing the air flow pattern through one of the modules. 
     FIG. 4A is an enlarged view of the first stage in the lower part of the module in FIG. 3. 
     FIG. 4B is an enlarged view on the line 4B--4B in FIG. 4A. 
     FIG. 4C is an enlarged view on the line 4C--4C in FIG. 4A. 
     FIG. 4D is a sectional view on the line 4D--4D in FIG. 4C. FIG. 4E is an enlarged view on the line 4E--4E in FIG. FIG. 4F is a sectional view on the line 4F--4F in FIG. FIG. 5 is an enlarged sectional view on the line 5--5 in FIG. 4A. FIG. 6 is a sectional view on the line 6--6 in FIG. 5. FIG. 7 is a sectional view on the line 7--7 in FIG. 8. FIG. 8 is a sectional view on the line 8--8 in FIG. 7. FIG. 9 is a view on the line 9--9 in FIG. 8. FIG. 10 is a sectional view on the line 10--10 in FIG. 8. FIG. 11 is a sectional view on the line 11--11 in FIG. 7. FIG. 12 is a schematic view of the piping arrangement for a neutralizing solution for the two modules through filter cartridge packages to the recovery distribution tanks. 
     FIG. 13 is a schematic diagram of a typical filter cartridge package in FIG. 12. 
     FIG. 14 is a schematic diagram of the control of the initiation of the wash cycles in the first and second stages in the two modules by certain venturis and vacuum sensors, and the pressure wash spray control system for the nozzles in FIG. 7. 
     FIG. 15 is a view on the line 15--15 in FIG. 2A. 
     FIG. 15A is an enlarged sectional view through a portion of FIG. 15. 
     FIG. 16 is an enlarged sectional view on the line 16--16 in FIG. 15A. 
     FIG. 17 is an enlarged sectional view on the line 17--17 in FIG. 15A. 
     FIG. 18A is an enlarged sectional view of one of the vacuum sensors in FIG. 14 showing the parts in open circuit position. 
     FIG. 18B is a similar view showing the parts in different positions. 
     FIG. 19 is a front diagrammatic view of the two modules showing the positions of the air venturis. 
     FIG. 20 is a similar side view showing the positions of the air venturis in the two modules. 
     FIG. 21 is a general diagram of the control system for the wash cycles for the separator deflectors in the first and second stages of the two modules. 
     FIG. 22 is a diagram of details in the control system for the first stage in both modules in FIG. 21. 
     FIG. 23 is a diagram of details in the control system for the second stage in both modules in FIG. 21. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIGS. 2A and 2B, the contaminated air or gas, if it is at a high temperature, is introduced through a pipe or tube 10 to a cooling unit 12. Cold air is supplied to cooling unit 12 by a plurality of vortex tubes 14. Vortex tubes 14 are manufactured by the Vortec Corporation in Cincinnati, Ohio. In a typical operation air/gas at a temperature of 350° F. is cooled to a temperature in the range of 90° F., to 80° F. 
     The cooled air or gas is then drawn into the system inlet 15, 16, and divided by flow divider 18 to flow into the two modules 20 and 21 in housing 23. A passageway 22 directs the incoming air/gas flow downward under the surface 24 of a liquid neutralizing solution in reservoir 26 in each module as seen in FIGS. 3 and 4A relating to module 20. 
     The composition of this solution depends upon the nature of the contaminants. It may be plain water. It may contain synthetic wetting agents, detergents, emulsifiers, aminos, water soluble solvents, biodegradable composition water, baking soda and related types, enzymes, etc. 
     Reservoir 26 contains an oscillating vane agitator 28 mounted on the vertical shaft 30 in FIG. 5. The agitator is oscillated by a link 32 connected at one end to a pin in a disc 34 on the agitator and connected at the other end to a pin in a disc 36 on a shaft 38 driven by the motor 40 in FIG. 4A. 
     Above the surface 24 of the liquid in reservoir 26 in FIG. 4A are lower and upper counter rotating separator deflectors 42 and 44 shown in greater detail in FIGS. 7-11. Each of these separator deflectors is pan shaped with a flat imperforate bottom plate 46, an outwardly sloping side wall 48 and a flat horizontal peripheral rim 50. The side wall 48 is corrugated as shown in FIG. 10 and slotted at 52 as shown in FIGS. 9 and 10. These slots are from 0.007 to 0.015 inch in width in a typical example. 
     These corrugations and slots are inclined as shown in FIG. 9 to act as fins for propelling the air/gas inward and downward through the side wall 48 when the separator deflector is rotated. Since the two separator deflectors 42, 44 rotate in opposite direction the corrugations and slots in lower separator deflector 42 are inclined in a direction opposite to the inclination for the upper separator deflector 44 shown in FIG. 9. 
     The lower separator deflector 42 is supported by its rim 50 on the bearing block 54 in FIG. 8 and the upper separator deflector 44 is supported and rotated by shaft 56 in FIG. 4A. As seen in FIG. 8 the rim 50 of the lower separator deflector has teeth 58 on the upper side of its rim 50 and the upper separator deflector 44 has teeth 60 on the underside of its rim 50. Four idler pinion gears 62 supported by a slotted peripheral jacket 64 engage these gear teeth to rotate the lower separator deflector 42 in the opposite direction of rotation relative to the upper separator deflector 44, as shown in FIGS. 8 and 9. Shaft 56 is driven by the motor 66 in FIG. 3 at a typical speed of 3600 r.p.m. 
     The counter rotation of the two separator deflectors produces a sharp shearing effect on the upward air/gas flow which is very effective in removing fine particulates. 
     The separator deflectors 42 and 44 are washed, rinsed and air dried by the nozzles 68 in FIGS. 7 and 11 in a cleaning cycle to be described hereinafter. 
     Above the separator deflectors 42, 44 the air/gas flow is propelled through tapered venturi restrictor chamber 70 by three propellers 72, 74 and 76 on the shaft 56 as seen in FIG. 4A. Propellers 72 and 76 are connected directly to this shaft while propeller 74 is driven in the opposite direction of rotation by the reversing gear unit 78 shown in FIG. 4E. 
     Propeller blades 74 are mounted on an outer ring hub 80 which is driven through pinion gears 82 from gear 84 on the shaft 56, the pinions 82 being mounted for rotation on studs 86 in stationary cover plates 88, the lower one of which is supported by brackets 90 mounted on the wall of chamber 70. The air/gas flow from venturi restrictor chamber 70 establishes a desired pressure in collector pressure chamber 92 in FIG. 4A. 
     The propellers 72, 74 and 76 are designed for high efficiency quiet operation with curved blades as shown in FIG. 4D. Again, the counter rotation of the three propellers produces sharp shearing effects on the upward air/gas gas flow which is effective in removing fine particulates. 
     Collector pressure chamber 92 discharges through a passageway 94 to an electronic filter 96 as shown in FIGS. 15 and 15A. This filter has sections of grid wires oriented in different directions relative to each other as shown in FIGS. 16 and 17. Suitable electronic filters for this purpose are made by Honeywell in North Golden Valley, Minn. The cross section of passageway 94 is smaller than the cross section at the narrowest point in tapered chamber 70 in order to maintain the desired pressure in chamber 92. manifold 118 in the first stage of module 20 supply the four sets of nozzles 68 shown in FIG. 11, and venturi wash and spray nozzles to be described, through harness pipes 125 in FIGS. 4A and 21. Cleaning solution is supplied to the manifold by a pipe 126 under the control of solenoid valve 128, rinse water is supplied by pipe 130 under the control of solenoid valve 132 and air under pressure is supplied by pipe 134 under the control of solenoid valve 136. 
     The cleaning solution valve 128 is opened for an interval of 30 seconds by a timer 138, the rinse water valve 132 is opened for an interval of 30 seconds by a timer 140 and the air valve 136 is opened for an interval of 30 seconds by a timer 142. These timers are activated in sequence by a master timer 144 which has an operating cycle of two minutes and 30 seconds. 
     The operation of master timer 144 is initiated by switch 147 in a relay 146 controlled by venturis and vacuum sensors to be described. A power supply line 148 operates the timers 138, 140 and 142 and master timer 144, and a power supply 150 operates the three solenoid valves 128,132 and 136. The circuit 152 is controlled by the vacuum sensors mentioned above, through a programmable alternating control system 328. At the start of a cleaning cycle a second master timer 306 reduces the speed of the separator deflectors 42 and 44 to 20 r.p.m. and at the completion of the cycle returns the speed to normal operating speed. These controls will be described. manifold 118 in the first stage of module 20 supply the four sets of nozzles 68 shown in FIG. 11, and venturi wash and spray nozzles to be described, through harness pipes 125 in FIGS. 4A and 21. Cleaning solution is supplied to the manifold by a pipe 126 under the control of solenoid valve 128, rinse water is supplied by pipe 130 under control of solenoid valve 132 and air under pressure is supplied by pipe 134 under the control of solenoid valve 136. 
     The cleaning solution valve 128 is opened for an interval of 30 seconds by a timer 138, the rinse water valve 132 is opened for an interval of 30 second by a timer 140 and the air valve 136 is opened for an interval of 30 seconds by a timer 142. These timers are activated in sequence by a master timer 144 which has an operating cycle of two minutes and 30 seconds. 
     The operation of master timer 144 is initiated by switch 147 in a relay 146 controlled by venturis and vacuum sensors to be described. A power supply line 148 operates the timers 138, 140 and 142 and master timer 144, and a power supply 150 operates the three solenoid valve 128, 132 and 136. The circuit 152 is controlled by the vacuum sensors mentioned above, through a programmable alternating control system 328. At the start of a cleaning cycle a second master timer 306 reduces the speed of the separator deflectors 42 and 44 to 20 r.p.m. and at the completion of the cycle returns the speed to normal operating speed. These controls will be described. 
     The wash cycle for the separator deflectors 42 and 44 in FIGS. 8 and 11 is activated by a plurality of air/gas venturis and vacuum sensors as shown in FIGS. 18A and 18B. The air/gas venturi 154 having an inlet screen 155 is connected through a tube or pipe 156 to a connection 158 on the vacuum sensor 160. Connection 158 communicates with one end of cylinder 162 containing a piston 164 on piston rod 66. 
     A bridging contact disc 168 on an insulating disc 169 is adjustably mounted on piston rod 166 by screw 167 to close a circuit between a pair of contacts 170 connected to circuit wires 172. The movement of the disc 169 and bridging contact 168 toward contacts 170 is stopped by an adjustable stop screw 174 behind one of the contacts 170. Contacts 170 have spring ends 171 to stop the upward movement of disc 169. Screw 167 holds a leaf spring 173 against a pin 175 frictionally engaging piston rod 166, allowing the piston rod to slide through disc 169. 
     Piston 164, piston rod 166 and disc 169 are pressed downward toward the stop screw 174 by compression spring 176 in cylinder 162 as shown in FIG. 18A. In normal operation the air/gas pressure in pipe 156 from venturi 154 sufficiently reduces the pressure in cylinder 162 to overcome the compressive force of spring 176 so that piston 164 moves upward causing bridging contact 168 to open the circuit through contacts 170 as shown in FIG. 18B. When an accumulation of particulate matter on screen 155 reduces the vacuum in the venturi the increase in pressure in cylinder 162 closes the circuit through bridging contact 168 to start a cleaning cycle. Stop screw 174 limits the downward movement of parts 168, 169 to avoid damage to the flexible contact fingers 170. 
     FIGS. 18A and 18B show the wide range of adjustment available for use under different pressure conditions either in the vacuum sensors themselves or atmospheric pressures ranging from elevations below sea level to very high elevations above sea level. Each vacuum sensor is adjusted in installation according to the atmospheric pressure at the location where it will be used. 
     FIGS. 19 and 20 diagrammatically show in one front view and one side view the locations of the venturis in the two modules 20 and 21. Venturi 178 is in the common air/gas inlet 16 for both modules and venturi 180 is in the common duct 103 leading to the outlet 104 for both modules. Venturi 182 in module 20 and 184 in module 21 are in the pressurized collector chamber areas and venturi 186 in module 20 and 188 in module 21 are in the upper ends of passageways 94 in FIG. 15A leading to the upper section of each module. 
     Venturi 178 is connected through vacuum line 190 to vacuum sensor 192 and venturi 180 is connected through vacuum line 194 to vacuum sensor 196. Venturi 182 is connected through vacuum line 198 to vacuum sensor 200 and venturi 184 is connected through vacuum line 202 to vacuum sensor 204. Venturi 186 is connected through vacuum line 206 to vacuum sensor 208 and venturi 188 is connected through vacuum line 210 to vacuum sensor 212. All the vacuum sensors are contained in a housing outside of the modules. 
     As will be explained hereinafter these vacuum sensors operate to control the initiation of the cleaning cycle involving the spraying of cleaning solution, rinse water and drying air through the nozzles 68 in FIG. 11 as previously described with reference to FIG. 22. 
     The nozzles 68 are supplied by the manifold 118 through harness 125 and solenoid valves 128, 132 and 136 in FIG. 21. In the first phase of the cleaning cycle cleaning solution from tank 216 flows through distribution pipe 218 and pipe 220 to the valve 128, propelled by air through pipe 222 from air compressor 224. 
     After 30 seconds valve 128 is closed by sequential timing unit 234 which then opens valve 132 to supply rinse water through pipe 228 from water supply tank 230 to wash out the cleaning solution. Then after 30 seconds the sequential timing unit 234 closes valve 132 and opens valve 136 for 30 seconds to supply an air flow through pipe 232 directly from the air compressor 224 for the drying phase of the cleaning cycle. The cleaning cycles are the same for the first and second stages of both modules in FIG. 21. These piping connections will not be described in detail. 
     In FIG. 14 the sequential timing unit 234 described in reference to FIG. 22 controls the wash cycle for the first stage of the first module 20. The sequential timing unit 236 operates in the second stage of the first module, sequential timing unit 238 operates in the first stage of the second module 21 and sequential timing unit 240 operates in the second stage of the second module. 
     Air venturi 178 in inlet 16 controls vacuum sensor 192 to provide a measure of particulate contaminated air/gas inflow. Venturi 182 in the approach to the outlet of pressure collector chamber 92 in FIG. 5A similarly controls vacuum sensor 200. These values are compared in a computer associated with sequential timing units 234 and 236 to measure the reduction of air/gas flow through venturi 178 resulting from the accumulation of buildup of solid material on the separator deflectors 42, 44. When excessive contamination accumulation is indicated, the wash and air spray cycle described in connection with FIG. 22 is activated. 
     Also in this cycle pipe lines 242 and 244 in FIG. 14 supply nozzles to clean the two venturis with liquids and air from outlet 124 in manifold 118 in FIG. 22. The wash cycle controls for the second stage in the first module and both stages in the second module are similar to the foregoing description with reference to further details in FIGS. 22 and 23. 
     FIG. 12 is a diagram of the pipelines conveying the liquid cleaning solution 24 in first stage reservoir 26 and solution 25 in second stage reservoir 100 in FIG. 3 and includes the second module 21. First stage reservoir 6 in the first module 20 is supplied from solution tank 246 by booster pump 248 and pipeline 250. The solution is circulated out of reservoir 26 through discharge pipeline 252 by discharge pump 254 to a pipeline 256. This pipeline connects to the two filters 106 and 108 through the normally open manually actuated solenoid valves 110 and 112 as also shown in FIG. 13. Pipeline 256 is also connected to a conventional type of liquid flow sensor 258. 
     The outflows from filters 106 and 108 are similarly passed through manually actuated normally open solenoid valves 114 and 116 to a common pipeline 260 which is also connected to a conventional type of liquid flow sensor 262. From pipeline 260 a return flow booster pump 264 passes the filtered solution back through pipeline 268 to the first stage solution tank 246 for the first module 20. 
     In a similar manner solution from the second stage solution tank 270 for the first module 20 is pumped by booster pump 272 through pipeline 274 to the second stage reservoir 100 in the first module 20. Solution is removed from reservoir 100 through pipeline 276 by discharge pump 278 which passes the flow to a pipeline 280 through a pair of normally open manually actuated solenoid valves and a pair of filters the same as described in connection with the discharge from the first stage reservoir 26. Pipeline 280 is connected to a conventional liquid flow sensor 282 and discharge pipeline 284 is connected to a conventional liquid flow sensor 286. The flow in pipeline 284 is returned by booster pump 288 through pipeline 290 to the second stage solution tank 270 for the first module 20. 
     In normal operation, all the valves 110, 112, 114 and 16 are open to pass the solution from both the first stage reservoir 26 and second stage reservoir 100 back to their respective solution tanks 246 and 270 in the first module 20. When the liquid flow sensors 282, 286, 258 and 260 indicate, by signal lights, reduced flows as a result of excessive accumulation of contaminants, the manual valves 110, 112, 114, 116 for one of the filters are closed for replacement of that filter, while the other filter of the pair remains in operation. Then the solution flow is diverted through the new filter while the other filter is being replaced. After both filters of a pair have been replaced, solution flow is restored through both filters. 
     The operation of the solution filter system for the second module is the same as just described for the first module. There may be any number of pairs of such modules as may be needed to handle the pollution load in a particular installation. FIG. 12 includes a solution tank 292 for the first stage and a solution tank 294 for the second stage of the second module. The first stages in both modules share one pair of filters and the second stages share the other pair. Solution tank 292 is served by pipelines 251 and 269 and tank 294 is served by pipelines 251 and 269 and tank 294 is served by pipelines 275 and 291. 
     As the pollution control system is in operation for a period of time, venturi 178 in the inlet 16 begins to accumulate an emission buildup of particulates and residues on the screen 155 of the venturi in FIGS. 18A and 18B. When this accumulation starts to close off the flow to the orifice in the venturi, the degree of vacuum in the venturi is reduced in the vacuum line 190 and sensor 192, causing the increase of pressure in the sensor to close its circuit to relay switch 316 in FIG. 22 in the circuit 148 for the startup operation of the cleaning cycle for the nozzles 68. 
     This relay switch is connected to a power line 317. The relay is manufactured by Synchro-Start Products, Inc. in Skokie, Ill. 
     Venturis 182 and 184 located in the pressure collector chambers 92 in the two modules similarly respond to any accumulation of particulates and residues that have passed through the first stage of the cleaning operation, closing the switches in the sensors 200 and 204. This closes circuits 324 and 326 to a relay circuit inside a programmable alternating control system 328 that starts operation of one or the other of the cleaning systems sequential timing units 234 or 236 in the first stages of the two modules. This programmable alternating control system 328, powered by a supply source 329, controls the cleaning cycle operations of the first and second modules. The system 328 is manufactured by Texas Instruments, Inc. 
     When the programmable alternating control system 328 starts operation it selects the appropriate module 20 or 21, only one module being cleaned at a time. After the programmable alternating control system 328 selects one module, it closes relay switch 146, 147 inside the sequential timing unit 234 or 236 which starts its master timer 144. Timer 144 activates the cleaning cycle as previously described. 
     Timer 306, started by relay switch 147, controls relaty switch 304 to slow down the speed of drive motor 66 from 3600 r.p.m. to 20 r.p.m. The motor is switched from full power circuit 300, 308 to resistor circuit 314, 312, 310. When the cleaning cycle is completed, timer 306 operates relay 304 to return motor 66 to normal operating speed. The control of motor 67 in the second module is the same. 
     The first stage system also activates the second stage system simultaneously for complete one module cleaning. Circuit wires 330 and 332 connect programmable alternating control system 328 with the corresponding wires in system 334 in FIG. 23 for cleaning the second stage of the module selected by system 328. 
     A second stage backup system in FIG. 23 utilizes venturis 186 and 188 in the two modules, located in the air passage tube 94 in FIG. 15a. As the air/gas cleaned in the first stage enters into the air passage tube 94 it passes by venturis 186 and 188. Any accumulation of particulates and residues starts to close off the flow to the orifices in these venturis which in turn reduces the vacuum in the vacuum lines 206 and 210 between the venturis and the vacuum sensors 208 and 212. As the degree of vacuum begins to drop in the sensors, these sensors close their switches to wires 209 and 213 to relay switch 336 in FIG. 23 in the circuit 148 for the startup operation. 
     Venturi 180 located in the outlet flue 103 receives the final passage of clean air before discharge from the modules. Should an accumulation occur, restricting the air flow to the orifice in venturi 180, this in turn will close the switch in sensor 196 by reduction of vacuum in line 194. This action signals the programmable alternating control system 334 through wire 197 to select and activate sequential timing units 234, 236, 238 and 240 in sequence, module 20 first and then module 21, to activate the cleaning cycles for the first and second stages of module 20 and then the first and second stages of module 21. The system 334 is manufactured by Texas Instruments, Inc. 
     Thus the backup system in FIG. 23 provides a safety feature to insure the washing of separator deflectors 42 and 44 in the event of failure of the primary control system in FIG. 22. 
     When there are more than two modules, the cleaning cycles for each additional pair are controlled as shown in FIGS. 22 and 23.