US2403545A

US2403545A - Dust arrester liquid level control

Info

Publication number: US2403545A
Application number: US489857A
Authority: US
Inventors: Nutting Arthur
Original assignee: American Air Filter Co Inc
Current assignee: American Air Filter Co Inc
Priority date: 1943-06-05
Filing date: 1943-06-05
Publication date: 1946-07-09
Anticipated expiration: 1963-07-09
Also published as: GB646148A

Abstract

646,148. Washing gases. AMERICAN AIR FILTER CO., Inc. July 11, 1947, No. 18461. Convention date, June 5, 1943. Addition to 646,147. [Class 55(ii)] To enable dust arrestor devices according to the parent Specification to operate efficiently when air flows are other than normal, they are provided with a liquid level control means for maintaining the liquid in the suction side of the bath at a predetermined high level during air flows varying within the operating range, while permitting the low liquid level to vary, the control means causing the volume of liquid swept through the baffle zone to increase and then decrease as the air flow increases through the said range. In the form shown, the control means consists of a box 10 divided into three vertical chambers, a low level chamber 11 communicating with bath 3 and open to atmosphere, a high level chamber 12 communicating with bath 3 through chamber 11 and closed at the top. the top air space being connected by a pipe 19 to the outlet air space 6 of the arrestor so that the liquid level in chamber 12 corresponds to the high level in bath 3. These levels are controlled by a weir 17 across which excess liquid can flow to the third chamber, which is divided into an overflow compartment 13 connected by a sealed standpipe 20 to a drainage chamber 14. When the plant is started up a solenoid valve opens to allow a small continuous flow of make up water to enter chamber 12 through pipe 27. With normal air flow, part of this water passes to tank 3 to make up evaporation loss and part escapes over weir 17. To compensate for air flows above or below normal, which would cause flooding or starving of the baffle zone of water, the low level of the tank is permitted to alter to render available less or more water for passage through the zone, whilst the high level is held constant.

Description

July 9, 1946. A. NUTTING DUST ARRESTER LIQUID LEVEL CONTROL Filed June 5, 1943 Fig. 1.

Worma/ H/ '9/7 Ops/army Aeuel rm! low Operating Level Norma! Lou Oper'df/ng Level Fig.5. Normal "h" Cu/zo/n 152GB 600 700 600 .900 low //aa /200 I300 /4oo 6.1. M

o a 5 4 4 & om .B Q musux xbwm INVENTOR ARTHUR Nun-mg BY (b e W ATTORNEY and during that time the arrester will operate inefliciently and may operate, more or less dr y. long enough to cause the arrester to clog up. 66

Patented July 9, 1946 UNITED STATES PATENT OFFICE I DUST ARREsTER lj Q lflif LEVEL CONTItOL Arthur Nutting, Louisville, Ky

assignor to American'Air Filter Company, Inc.,ILouisville, Ky., a

corporation or Delaware p 8 Claims. 1

There are presently available a number of dif- I ferent dust arresters of. the type wherein air passes downwardly through the inlet air side of thearrester and impinges against a water bath as it turns to pass upwardlythrough a baflle zone into the clean air side thereof, the air propelling a stream of water into the battle zone at a rate depending upon the velocity of the air and the "head" of water available in the impingement area. Dust arresters of this general type are designed for operation at a predetermined air flow and provided with a predetermined static liquid level. When operation is instituted, the static level drops on the inlet side and rises on the outlet side, reaching the proper operating level when the proper air fiow is reached. At the proper air flow, the proper operating level on the inlet side provides an available head" of proper proportion and thus insures a proper water flow. Since some water is lost during operation, it is customary to install a water level control on the inlet side of the arrester in order to maintain an operating level correspondingto the proper air flow.

Generally speaking, these controls are designed to add make-up water to the bath when the low operating level falls below normal and to drain water from the bath when it rises above normal. They have not been entirely satisfactory for a number of reasons. For example, the drains clog from time to time. Also the controls waste considerable water when the arrester is shut down due to the fact that the drainage outlet is set at the low operating level and therefore tends to prevent the Water from rising to the static level unless the drain is closed at that time by a valve. Since this valve should be operated automatically, its provision increases the amount of control equipment necessary while dirt often prevents the automatic closure of the drain.

Another objection to this type of control arises from its inability to cope with substantial variations in the air fiow from the predetermined flow. For example, should the air fiow rapidly increase to a value substantially above normal, the low 0pcrating level will rapidly drop to a value substantially below normal. -mentary surge of excess water into the baille zone.

As it drops, there is a mo- When it reaches the lower level, there is a def ficient water flow. Assuming the excess air flow continues indefinitely, the deficient water flow will last for a period of time depending upon the speed with which the control adds'make-up water certainly Now when the make-up water is added to raise the deficient operating level to the normal low level for the predetermined air flow, too much water becomes available for the increased air flow. As a result, the arrester is more or less flooded and its resistance greatly increased. The increased resistance, of course, cuts down the. air flow somewhat but an equilibrium will be established with an excess flow of both air and water at the normal low operating level.

On the other hand, should the air flow rapidly decrease from the excess flow to normal, the low operating level surges upwardly above the normal level supplying excess water to the battle zone for an interval depending upon the drainage rate of the excess water.

Should the air flow rapidly decrease below normal, the low operating level again surges above normal but is ultimately returned to normal as the Water drains. When the normal low operat ing level is restored with a deficient air flow, a deficient .water flow results.

A more important objection arises when the arrester is installed and operated at a constant air flow above or below the predetermined flow for which it was designed. This Often occurs in service due to various reasons. For example, it is not uncommon to find the user installing, with the arrester, a fan or blower either larger or smaller than the one recommended for the arrester. When this occurs the fan or blower will tend to maintain an abnormal air flow while the controls will attempt to maintain the normal low opera ing level. As a. result, too much or too little water is supplied rendering the operation of the arrester unsatisfactory until the controls are readjusted. This usually necessitates one or more service calls by the manufacturer of the dust arresting equipment, although the fault was not occasioned by his equipment.

In summary, it may be said that the foregoing water level controls permit satisfactory operation of the dust arrester only when the air flow variations are held within narrow limits, and, beyond such limits, cause deficient and excess water flows with deficient and excess air flows. The present invention relates to an improved water level control.

The principal object is to provide a control which not only avoids most, if not all, of the foregoing objections, but also maintains good operating conditions generally, and good water flow Another object is to provide an extremely simple and relatively tool-proof control.

A further object is to provide, in a water-level control having a drainage outlet communicating with the liquid bath of an arrester, a make-up water supply which is interposed between the drain and bath whereby relatively little dirt or sludge is carried into the drain and clogging of the drain is correspondingly prevented.

A further object is to provide openly-accessible, readily removable, drain protecting screens whereby the incentive for maintenance is prometed.

An embodiment of the invention is illustrated in the accompanying drawing wherein:

Figures 1 is vertical section showing the relation or the control to a suitable form of arrester;

Figure 2 is a side elevation of the control mechanism taken at right angles of Figure 1;

Figure 3 is an exaggerated view illustrating changes in water level on the low level side of the arrester; and

Figure 4 is a graph showing the resistance characteristic of an arrester equipped with my 7 control in relation to the resistance correspondingly of the same arrester equipped with a waterlevel control on the dirty side and also indicating the wide air-flow limits of the arrester with my control.

The control is illustrated in connection with an arrester l of the type described and illustrated in my co-pendlng application flied September 15, 1942, and serially numbered 458,426, new Patent .No. 2,373,330, dated April 10, 1945. In this arrester, a stream or column of air flows downwardly through inlet chamber 2 and impinges against the upper surface of water bath 3 as it turns to enter the slot-like entrance of the baiile zone formed by baiiies 4 and 5 which form part of a structure dividing the upper portion of the bath into high pressure and low pressure (or suction) sides and dividing the air space overlying the bath into an inlet chamber 2 and an outlet chamber 6. The air passes upwardly through the air cleaning conduit formed by bailles l and 6 in the bafile zone and discharges into outlet chamber 8. The baflles 4 and 5 constrain the air column in the baflle zone, to pass in the form of a ribbon from the slot entrance upwardly along a path of s-shape. The air moves along the S-path at a velocity effective to subject the ribbon of air to intensive centrifugal action in both the upper and lower halves of the S-path.

As the air flow rises from zero to normal, when operation is first instituted, the static level drops on the inlet side, and rises on the outlet side, respectively to the normal low and high operating levels indicated. the diflerence between which is proportional to the resistance of the baille zone.

The flow of air further depresses the normal low 7 operating level adjacent the entrance to the S-path, causing such level to assume a slope of the character indicated. The head h created by this depression tends to maintain a continuous and relatively constant free flow of water into the entrance of the path. The air flow propels this stream of water upwardly entirely through the path and, in doing so, forces the stream to new in the form of a water film, along each concave wall in each half of the path to the upper end or each half, and in the form of a water curtain, across the air column from the end of each half, the flrst curtain extending to the beginning or the second film and the second curtain projecting constant rate suificient to form continuous films and curtains. With prior low level controls, when the air either flows continuously at some other rate or otherwise varies from the predetermined rate, the water flow varies likewise occasioning the operating difficulties heretofore mentioned.

I have discovered that these dlfliculties may be substantially eliminated, and a wide range of air flows accommodated, simply by controlling the normal omrating level on the high side while permitting the level on the low side to vary at will. While this may be done in various ways, it can be accomplished simply and effectively by combining an over-flow weir on the high side with suitable means for maintaining a small and continuous stream of make-up water preferably supplied adjacent the weir. Furthermore, while the weir may be positioned at one side of the bath. it preferably is arranged in a chamber separate and apart from. but having liquid-sealed communication with, the bath with the make-up water discharging into the chamber preferably at some point between the bath and the weir.

Accordingly, I provide a control box it which is divided by two vertical partitions into three vertical chambers comprising: a low level or screen chamber H, a high level or weir chamber l2, and a third compartment which is additionally divided by a horizontal partition into an upper overflow compartment l3 and lower drainage chamber 94. The screen chamber ll openly communicates at its lower end with the bath 3 and at its upper end with the atmosphere so that its water level will rise and fall with the operating level on the low side of the cleaner. When the inlet chamber 2 is exposed to atmosphere, the screen chamber level will be the same as the low operating level, but when the inlet chamber is connected to a duct, these levels will be differcut by an amount corresponding to the resistance of the duct.

The weir chamber l2 openly communicates at its lower end with the lower end of the screen compartment II and, through it, with the bath 3. This chamber could, of course, communicate directly with the bath but an interposed screen compartment II is preferred in order to provide between the weir chamber and the bath, a convenient space to accommodate a dewatering louver l5 and a pair of screens I8, all of which may be readily removed through the open top of the screen chamber II. A weir I1 is interposed between (weir and overflow): compartment 12 and chamber l3, which openly communicate with each other above the weir and which are not only sealed, at the top, by a plate I! but placed in communication with the outlet air space 8 on the clean air side of the arrester by a pipe 19. With this arrangem nt, the level in the weir compartment l2 rises and falls with the level on the high side of the arrester, while the overflow passes over weir l1 into the overflow chamber l3.

The bottom of overflow chamber l3 communicates, through an overflow standpipe 20, with the bottom of drainage chamber ll, which contains a liquid seal II, for the lower end of the stand- 7 pipe 20, and an overflow outlet 2! leading from suming the upper levels of the liquid seal through a three-way valve 23, in its "run" position, to the sewer. The upper end of drainage chamber I I is open to atmosphere. with this arrangement, the liquid level in the standpipe is a measure of the total pressure of the system plus the air flow resistance encountered in the baffle zone.

The make-up water is supplied from a supply pipe 24 through a strainer 25 and solenoid valve 26, the solenoid of which is electrically connected (by means not shown) to open and close the valve automatically when the operation of the arrester is started and stopped respectively. The normally open solenoid valve 26 is adjusted to permit a small continuous stream of make-up water to flow. While the make-up water may be introduced at any point, it is arranged to discharge through opening 21 at a point between the screens l6 and the weir IT. The make-up water is supplied at a rate, sufiicient, under normal operating conditions, to compensate for evaporation and to provide a small continuous overflow. Consequently, there will normally be a continuous flow of clean water from opening 21 to both the bath 3 and the weir l1.

The supply pipe 24 is also connected through a normally closed manually operable valve 28 to discharge through opening 29 into the weir chamber l2. This latter supply provides a rapid flow of water for the purpose of filling the arrester when it is empty. The arrester may be emptied in any suitable way as through drainage outlet 30 leading from the weir compartment l2 through the three-way valve 23. The valve 23 in its drain position connects the drainage outlet 30 to the sewer and in its run position connects the overflow outlet 22 to sewer. I

When the arrester is first installed, the valve 23 is placed in the run" position, connecting the overflow to the sewer, and the valve 28 opened to supply bath water. When the water reaches the static level, the valve 28 is closed and thereafter remains closed except poses. When the fan '(not shown) is started, air will be drawn through the arrester and, as-

that the air flows at the predetermined value for which the arrester was designed, the bath water level will fall on the inlet or low side and rise on the outlet or high side to the normal low and high operating levels indicated in the drawing. The solenoid valve 26 opens, simultaneously with the institution of fan operation, to supply small continuous streams of water to the bath 3 and the weir chamber l2 and, so long as the high level coincides with the upper edge of the weir I1, the weir portion of the make-up water will simply pass upwardly through the weir chamber l2 and overflow continuously into the overflow chamber l3.

Should the air flow rise above the predetermined value, the operating level on the low side will fall below normal, while that on the high side will tend to rise above normal creating xcess water which quickly drains overthe weir I1. As a result of the foregoing action, the rate, at which water flows from the low level through the baiiic zone to the high level, is affected by changes in the flow of air and the head h.

Since the flow of air has increased to a supernormal value, the water flow tends to increase because the air propels the available water through the baflie zone at a faster rate.

On the other hand, since the low operating level has dropped to a subnormal value, the water flow tends to decrease because the head h is decreased to a subnormal value (see Fig. 3). In fact, the decrease in the head It is greater with high level control than it'would be without level control. For example, without level control, the low level drops and the high level rises, to values such that their diflerence is proportional to the resistance of the battle zone. With high level control, the high level cannot rise above normal; hence the low level must continue to drop until the difference between levels again becomes proportional to the baliie zone resistance.

The net effect is that, as the air flow progressively increases through the supernormal range, the water flow progressively decreases until an upper air flow limit is reached at which the water.

flow becomes deficient. The decrease in water flow, however, proceeds the upper air flow limit is normal air flow.

When the air flow falls below the predetermined rate, the low level rises above and the high level falls below the normal operating levels. The overflow now ceases until the make-up water restores the high level. When the high level is restored, the low level is slightly increased over what it would otherwise be. Here again the same flactors affect the rate at which water flows through the battle-zone. For example: the subnormal airflow propels the "available water at a slower rate; while the ri caused by the subnormal air flow and the additional rise in that level, caused by the restoration of the deficient high level to normal, increases the head h, rendering more water "available. The net effect is that, as the air flow progressively decreases through the subnormal substantially above the range, the water flow progressively decreases unfor bath water supply purtil a lower limit is reached at which the water flow again becomes deficient. Here again, however, the decrease in water flow proceeds at a slow rate so that the lower air flow limit is substantially below the normal flow.

The effect of a high level control may be illustrated by reference to the curves shown in Figure 4. Here curve N indicates the resistance characteristic of an arrester of the type shown in Figure 1 equipped with the aforesaid high level control, while graph W indicates the rate of water flow. The predetermined air flow for this C. F. M. At this flow, maximum water flow conditions were obtained while the resistance, in inches of water, was 4.65. Good Water flow conditions were still maintained when the flow varied over a range of 800 C. F. M. ex-

shows the resistance varying from 3.0" at 855 C. F. M. to 6.5" at 1090 C. F. M., a resistance variation of 3.5" with an air flow variation of 235 C. F. M. All of the foregoing values are, of course, approximate.

The high level control illustrated has the further advantage of supplying make-up water between the bath 3 and the weir I1. This normally maintains a flow of water into the bath, substantially minimizes the reverse flow of bath water at a slow rate so that.

se in the low level into the drainage end of the control and correspondingly avoids the clogging of the drains. Furthermore, when bath water does flow into the weir compartment, the louver reduces the disturbance oi the sludge and settled material in the bath proper while the screens operate to strain the water and thus minimize the amount of dirt carried over to the sewer. The maintenance of the screens and louvers is promoted by the ease with which they may be removed from and replaced in the screen chamber.

For the sake of clarity in the claims, the high pressure or low level side of the bath is designated as either or both the pressure side and the low level side while the low pressure or high level side is designated as either or both the suction side and the high level side.

Having described my invention, I claim:

1. The combination with a dust arrester of the type comprising: a casing wherein an air stream or column is adapted to move downwardly through an air inlet chamber to impinge against a bottom liquid bath as it turns to enter and pass upwardly through a baiiie zone and thence into an outlet chamber; an element and member mounted on the casing and constructedand arranged to define, in said zone, the opposite sides of an upright sinuously-curved air-cleaning conduit of slot-like cross-sectional area constraining the air to pass through said zone in the form of a shallow sinuous ribbon from a slot-like air inlet at the bottom of the zone which communicates horizontally with the air inlet chamber to an air outlet slot at the top of the zone which discharges the air laterally into the outlet chamber at an angle to the vertical, said element extending upwardly in position to divide the upper portion of the bath into pressure and suction sides having operating levels respectively below and above the static level of the bath and being arranged to present a concavely-curved air-directing wall which defines the convex side of the lowermost curved portion of said conduit and which slopes, at its lower end, downwardly into the bath to form the lower side of said inlet slot at a level providing; at the slot entrance, a head oi liquid which progressively decreases as the air flow through the conduit progressively increases through its operating range, said member extendirig upwardly in position to divide the air space above the bath into said air inlet and outlet chambers and being arranged to present a lower convexly-curved air-directing wall forming the concave side of said lowermost curved portion of said conduit and an upper concavely-curved air-directing wall forming the convex side of the uppermost curved portion of said conduit; the arrester being designed to receive an operating range of air ilows which tend to lowe the bath level on the pressure side and raise it on the suction side in proportion to the air flow resistance of conduit and which operate to propel a stream of liquid from the low level or pressure side of the bath through the conduit into the outlet chamber; of control means for maintaining the suction side of the bath at a predetermined high level during such operating air flows while permitting the low level on the pressure Side of the bath to vary at will, said control means being operative to cause the volume of the liquid stream in the conduit to increase progressively to a maximum and\then decrease progressively from the maximum as the air flow increases progressively through its operating range, said control means including: drainage means for draining excess 8 liquid from the high level side of the bath when the high level tends to exceed the predetermined value; and make-up means for supplying makeup water to raise the high level side of the bath to said predetermined value.

2. The combination of claim 1 wherein the drainage 'means comprises an overflow weir arranged to overflow at said predetermined level.

3. The combination of claim 1 wherein: the make-up meansis arranged to supply a continuous stream of make-up liquid during the operation of the arrester; and means are provided operatively to connect and disconnect said make-up means at the beginning and end of each operative period of said arrester.

4. The combination with a dust arrester of the type comprising: a casing wherein an air stream or column is adapted to move downwardly through an air inlet chamber to impinge against a bottom liquid bath as it turns to enter and pass upwardly through a bafiie zone and thence into an outlet chamber; an element and member mounted on the casing and constructed and arranged to define, in said zone, the opposite sides of an upright S-shaped air-cleaning conduit oi slot-like cross-sectional area constrainin the air to pass through said zone in the form of a shallow sinuous ribbon from a slot-like air inlet at the bottom of the zone which communicates horizontally with the air inlet chamber to an air outlet slot at the top of the zone which discharges the air laterally into the outlet chamber at an angle to the vertical, said element extending upwardly in position to divide the upper portion of the bath into pressure and suction sides having operating levels respectively below and above the static level of the bath and being arranged to present a concavely-curved air-directing wall which defines the convex side of the lower half of said conduit and which slopes, at its lower end, downwardly into the bath to form the lower side of said inlet slot at a level providing, at the slot entrance, a head of liquid which progressively decreases as the air flow through the conduit progressively increases through its operating range, said member extending upwardly in position to divide the air space above the bath into said air inlet and outlet chambers and being arranged to present an air-directin wall having a convexly-curved section forming the concave side of said lower half of said conduit and a concavely-curved section forming the convex side of the upper half of said conduit; the arrester being designed to receive an operating range of air flows which tend to lower the bath level on the pressure side and raise it on the suction side in proportion to the air flow resistance of conduit and which operate to' propel a stream of liquid from the lower level or pressure side of the bath through the conduit into the outlet chamber; of control means for maintaining the suction side of the bath at a predetermined high level during such operating air flows while permitting the low level on the pressure side or the bath to vary at will, said control means being operative to cause the volume of the liquid stream in the conduit to increase progressively to a maximum and then decrease progressively from the maximum as the air flows increase progressively through its operating range, said control means including: means providing a high level compartment separate from the bath but having a liquid column which joins the bath liquid and an overlying air space which is connected to said air outlet chamber and subject to the air pressure thereof so that said liquid column, while separate from the a bath, rises and falls with the high level side of the bath, the high level compartment being arranged to overflow when the high level side of the bath tends to rise above the predetermined level; drainage means for draining the overflow; and make-up means for supp ying make-up liquid to the bath to raise its high level when such level tends to fall below the predetermined value.

5. The combination of claim 4 wherein: the make-up means is arranged to supply make-up liquid directly to said liquid column.

6. The combination of claim 4 wherein: the make-up means is arranged to supply, during the operation of said arrester, a continuous stream of make-up liquid directly to said liquid column; and means are provided operatively to connect and disconnect said make-up means at the beginning and end of each operative period of said arrester.

'7. The combination of claim 4 wherein the drainage means comprises: means forming an overflow chamber within the high level compartment, the overflow chamber being separated from the liquid column in said compartment by a partition forming an overflow weir and the air space of the compartment above the column and the overflow chamber being sealed except for its communieation with the air outlet chamber; and means providing a liquid sealed drainage outlet for the overflow chamber.

8. The combination of claim'4 wherein: means are provided to form a screen chamber which is interposed between the bath and the high level compartment and arranged to communicate at its upper end with the atmosphere and, adjacent its lower end, with both the bath and the high level compartment.

ARTHUR NUTTING.