GB1594524A

GB1594524A - Apparatus for the removal of undesired components from fluids

Info

Publication number: GB1594524A
Application number: GB16793/78A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-05-12
Filing date: 1978-04-27
Publication date: 1981-07-30
Also published as: DE2820850C2; DE2820850A1; FR2390193B1; IT7823337A0; CA1106777A; IT1095265B; JPS53139278A; FR2390193A1

Description

(54) APPARATUS FOR THE REMOVAL OF UNDESIRED COMPONENTS FROM FLUIDS (71) I, BERNARD J. LERNER, of 727 Orchard Hill Drive, Pittsburgh, Pennsylvania 15238, United States of America, a citizen of the United States of America, do hereby declare the invention for which I pray that a patent may be granted to me and the method by which it is to be performed to be particularly in and by the following statement:- This invention relates to the removal of undesired components from fluids and has particular relationship to such removal where the fluids flow at high velocities between about 1,000 and 2,500 feet per minute. The components which are removed from a fluid, may be soluble, for example soluble salts or acids, such as acetic, nitric or hydrochloric acid, or insoluble or particulate such as sulphur, carbon powder, fly ash or graphite. The components may also be in the form of a mist, either initially present or deliberately injected into the gas to dissolve soluble particulates and to wet and wash down insoluble particulate. Essentially, this invention serves for fluid scrubbing and/or mist elimination for high velocity fluid flow.

Separation and removal of undesirable or contaminant particulates from a fluid flow, such as a gas stream in accordance with the teachings of the prior art has been effected by two principal methods: gas filtering and centrifugal force separation. Gas filters are comprised of porous, foraminous or fibrous media, woven or nonwoven through which the gas is wholly conducted. Filters separate by means of inertial impaction and impingement of the particles on the fibers as the gas containing the particles passes through the filters.

For removal of small particle sizes, the fibers must be fine. While gas filters are reasonably effective in particulate removal, the gas velocity through a filter must be maintained at relatively low levels to avoid excessive and uneconomic gas pressure drops. This is particularly true in thecase of fine particulate filtration, where the particles are in the 1-20 micron size range and the fibers are very fine, typically in the 10 to 200 micron range. Gas pressure drop through a fibrous filter is approximately proportional to the square of velocity of the gas in the turbulent flow regime. Industrial fine particulate filters, such as baghouses, consequently have very large filter surfaces, operating typically at 5 to 50 feet per minute gas face velocity, and are relatively expensive. Further, the optimum ranges of gas velocity through the filter media with respect to the efficiency of particle removal by the mechanisms of interception and impaction are invariably higher than those which can be practically and economically employed with respect to the gas pressure drop across the filter.

While fibrous or filamentary woven or felted gas filter media are applicable to particulate removal, including mist filtration, they do not readily lend themselves to continuous washing in the case of solid particulate removal or to too high liquid loads in the case of mist removal alone. Because of the uniformity and small size of the fluid passages through such filter media, and the competition of liquid and gas flow for these fluid flow passages, the flow capacity of the filter for gas is restricted because of the presence of liquid, or that for liquid because of the presence of the gas. If a filter medium is used which possesses even a moderate degree of dynamic capillarity, under a specific combination of gas and liquid loadings, liquid is retained and gas flow impeded except with extremely high gas-pressure drops. Dynamic capillarity, or the equivalent dynamic liquid hold-up in a medium, is the tendency to retain liquid in the voids or interstics of a filter medium, which exists under certain flow conditions of the fluid and the dynamic rate by which such a flow of the medium takes up liquid.

The capillarity effect is enhanced by the continuous injection of liquid by the flowing gas into the medium. In the case of static capillarity, the only force counteracting the capillary force is gravity. In the case of dynamic capillarity, the capillary force is counteracted in addition by the force exerted by the gas and augmented by the continuous loading of liquid. The effect of appreciable liquid loadings on a capillary filter medium resulting from dynamic capillarity is to make the medium behave as a virtually solid wall with respect to gas flow. For dynamic liquid loads, such as are generated by filter washing, even a small degree of capillarity yields significant gas flow passage obstruction with liquid.

Additionally, if the gas stream contains solid, insoluble particulates, capillary filter media are highly susceptible to clogging by the solids.

United States Patent No. 3,733,789, to Rebours, which is typical of the prior art of this type, uses a sprayed tubular filter cloth to form a continuous stable film of washing liquor on the cloth through which the gas is "micro-sieved". Rebours' data on gas-flow resistance as a function of linear gas velocity illustrates the typically high-resistance/low flow characteristics of the capillary filter media, whether woven cloth or compacted or felted fibrous material. Rebours' teaching is specific for liquid "micromists" and as pointed out by Rebours, solid insoluble particles unfailingly clog the filter after a few hours of operation.

United States Patent No. 3,135,592 to Fairs also discloses an irrigated filter medium but in countercurrent liquid-gas flow. Fairs' gas velocities are about 15 feet per minute and fall into Rebours' range of 4 to 20 feet per minute representing essentially laminar, as distinct from turbulent flow, gas flow. Rebours and Fairs are limited to such low gas velocities because the gas-flow passages are clogged with liquid. Sprayed screen devices such as those of United States Patent No. 3,763,634, in the name of Alliger and United States Patent No. 3,785,127 to Mare, suffer from the same gas flow limitations resulting from the necessity of trying to force both liquid and gas through restricted, uniform-size openings and/or capillary flow spaces in a filter medium. United States Patent No.

3,370,401, in the name of Lucas discloses a teaching similar to that of Fairs, except that the fibrous filter medium is deliberately operated in the flooded condition.

Centrifugal-force separators, such as devices with parallel-vane serpentine or sinusoidal-paths, or chevron or zig-zag passages, are used primarily for mist elimination, in clean gases not containing solid particulate. Such parallel vane separators are commonly used for removing liquid carryover in steam boilers, watercooling towers, and in gas-liquid contacting apparatus such as distillation or fractionation towers, evaporators, gasscrubbing apparatus and the like. Another area of application is the removal of mists from the air intakes of power turbines such as marine-power or propulsion plants. In such separators the fluids carrying the suspended matter is bent or deflected by the vanes and the suspended matter is ejected by centrifugal force. The force exerted on a particle of mass M is Mv2 r where v is the velocity of the particle and r the radius of the path. It is desirable that v should be high or r small.

Centrifugal-force impaction separators operate at much higher velocities than do filter media, and are used for low-load liquid mist removal or for batch particulate removal. In zig-zag or sinusoidal parallelsided passage types of separators, the removed liquid must drain under the influence of gravity without accumulating within the passages or being otherwise subject to reentrainment in the gas. Liquid occurring either as a mist, or as a deliberately-introduced spray wash that has been removed and collected as drops or as a liquid film on surfaces exposed to the flowing gas, is subject to being dragged along in the direction of gas flow by gas friction and momentum transfer. The resulting liquid carrythrough or reentrainment lowers the overall liquid removal efficiency. Various expedients have been suggested to overcome this deficiency.

United States Patent No. 1,616,802, (Hosch) describes a serpentine-passage separator having liquid-collection baffles protruding from the peaks of-the corrugations. Other modifications of the sinusoidal or zig-zagpath vane separators are typically shown by the following United States Patents to Clark No. 2,802,543; Sqkolowski, No. 3,751,886; Hurlburt, No. 3,757,498; Hill, No. 3,813,855 and Regehr No. 3,849,055. These show the use of solid, planar-wall vanes, having various catchments or arrangements to drain the liquid removed. However, such protrusion catchments, particularly those opening up toward the upstream side, are subject to gas impact and momentum transfer to the collected liquid in the exposed pocket. The liquid is unprotected with respect to gas friction and momentum transfer and is picked up and entrained in the gas. On the other hand, turning the catchments or protrusions to the downstream side serves to introduce lowpressure accelerated gas-flow regions immediately downstream of the liquid catchment, which serves to suck or aspirate the liquid out of the protective pocket into the stream. These deficiencies result in limited liquid loading or handling capability and a tendency to reentrain liquid at relatively low gas velocities.

In the prior art, there are also provided gas-permeable structures defining serpentine passages or channels for the gas.

Typical of this prior art are United States Patents to Schaff, No. 2,567,030 and Brixius, No. 2,760,597. Schaff and Brixius disclose particulate filter panels consisting of alternating corrugated layers of paper, fly screen and similar materials. Such filters are for "dry" use, inasmuch as the capillary nature of the internal walls would prevent gas permeation under liquid irrigation or a mist load. The corrugated layers of the Schaff and Brixius filters are horizontally disposed with alternate layers reversely corrugated. If an attempt were made to use such devices for mist removal or other wet application, liquid drainage would be seriously impeded and highly inefficient.

The filter panels of this prior art are specifically disposable and are intended for one-time batch use until plugged, at which time such filters are either discarded or removed from service and re-worked.

This invention seeks to overcome the above deficiencies and drawbacks of the prior art and to provide an apparatus and a method for removing undesired components from fluids flowing at high velocity which apparatus can readily drain the impinging liquid and/or particulate, is readily permeable to the gas, does not become clogged by liquids or particulates and does not require frequent replacement.

According to this invention there is provided an apparatus for removing undesired components from a moving fluid, the apparatus including a flow channel for conducting said fluid in a substantially horizontal stream, and a plurality of substantially vertical fibrous bodies interposed in said flow channel in the path of said stream to remove said components from said stream, the bodies being formed of high-voidage, non-capillary, free-draining material, as herein defined. The fibrousbody means may comprise a plurality of rows of separate fibrous-body baffles with the baffles staggered; i.e., the baffles in each row displaced along its row with respect to the baffles in the rows upstream and downstream with respect to it. The staggering is such that the baffles in each row are aligned with the gaps between the baffles in the rows upstream and downstream from it so that the fluid, typically a gas, is carried to flow in sinuous path sharply curved around the baffles. The fibrous-body means may also be in the form of fibrous strips secured to the walls of sinuous or serpentine or zig-zag vanes in the flow path. The fluid in this case also flows in part through the strips.

In one aspect of the invention, there is also provided a method of removing undesirable components from a fluid flow comprising means to cause the fl-uid to flow in a substantially horizontal stream through a plurality of substantially vertical fibrous bodies of high voidage, non-capillary and free-draining material, as herein defined, interposed in the stream, in which the fluid is a moisture-laden gas and the method comprises capturing the moisture in said bodies and draining the captured moisture downwardly from the fibrous bodies.

Solid particulate may be removed from a dry gas by passing the gas in dry condition through the fibrous-body means and so that the body means used in this way will not ultimately clog, it may be sprayed periodically with sufficient liquid to wash down the captured particulate.

Solid particulate may also be removed by spraying~ the fibrous-body means with a liquid as the contaminated fluid is flowing through it. The sprayed liquid flows in either a counter current direction or in the same direction as the flow or has flow components counter-current or in the direction of the flow. There should be sufficient liquid to dissolve any soluble particulate and wash it down the fibrous bodies and to wash down the insoluble particulate. The liquid may also be injected into the flowing gas as a mist. In this case the mist and any particulate dissolved in it and the insoluble particulate are captured by the fibrous bodies and washed down.

A portion of the gas flow deflected by the baffles or by the vanes flow in an arcuate path and the mist and/or particulate matter is ejected by centrifugal force from the stream, impinging on adjacent baffles or walls whence it is drained. From the portion of the gas that flows through the baffles or fibrous strips, the mist and/or particulate matter is removed and washed down as described. The separate baffle structure has advantages over the vane structure of the prior art particularly in that the resistance to gas flow (pressure drop) is lower in the baffle structure at equal gas velocities.

In this disclosure, the expression "high voltage" is a term of the art, descriptive of light, porous materials of which the internal void space is proportionally high. Such a material is generally understood to mean a material that has an internal void space to fibre ratio greater than 9 to 1 or 90%. The expressions "non-capillary" and "free draining" are considered to be self explanatory. However, by "non-capillary" is to be understood that the pore size of the baffles is of such dimension that the pores do not tend to retain liquid and the expression "free-draining" is equally to be understood to mean that essentially collected liquid can flow freely out of the filter medium to the collection means. Of necessity these properties are closely interdependent and the most suitable pore size is determined by tests. As will be understood, capillarity is effected by the viscosity of the liquid whereas drainage and re-entrainment are observable as a function of gas flow velocity. Any liquid residing in the baffles is due entirely to the dynamic retention of liquid at a given liquid injection rate and gas velocity.

As used herein the word "fibrous" is intended to include "filamentary"; the word "fibrous" is also intended to include fibrous mats, ribbons and wire systems such as steel wool and the like and non-capillary wire mesh. The fibrous-body baffles or strips used in this invention are typically made of bonded non-woven materials, examples of which are typically described in United States Patents No. 3,526,557 to Taylor and No. 3,920,428 to Kinsley or open-celled reticulated polyurethane foam as described by United States Patent No. 3,190,057 in the name of Sinex or of expanded metal. The fibrous-body material may also be formed of many interlaced randomly disposed fibres as disclosed in United States Patents No.

2,784,132 to Maisel or No. 2,958,593 to Hoover. Another typical fibrous-body material is a knitted-mesh pad wherein the individual layers of knitted material have been severely crimped or distorted so as to render the mesh openings non-uniform and non-capillary.

It is essential that the fibrous-body means be free-draining with respect to liquid, not have high wet-gas-flow resistance relative to the dry-gas-flow resistance, and be free from any tendency to fill with retained liquid. To minimize liquid re-entrainment, the fibrousbody means must be of a sufficient thickness along the direction of gas flow to allow rapid protected liquid drainage. Preferably, this thickness should be not less than 1/4 inch, to provide for free drainage of liquid in the interior or downstream side of the baffle or strip. The draining stream on the downstream side is thus protected from excessive friction by the shielding effect of fibrous material on the upstream side of the strip. To optimize this protected-drainage effect, the flow is generally horizontal with the fibrous-body baffles or strips disposed in a substantially vertical position completely across the stream so that no gas flows under the baffles. Liquid drainage then occurs with minimum retardation and frictional drag by the gas flow, and is sufficiently rapid so that the fibrous-body baffles and strips may be continuously spray-irrigated without any significant accumulation of liquid.

The fibrous-body means may, in the practice of this invention, be arranged in different configurations, such as to define serpentine or zig-zag passages with parallel walls or chevron arrangements or as separate baffles in staggered rows or as deflecting panels arranged in series in the direction of flow. Such configurations of whatever form are referred to herein as imparting to the gas a circuitous path. When a serpentine-passage configuration is used, the preferred angle of inclination, of-the longer dimension of the transverse cross section of the strip, with respect to the direction of gas flow is between 20 and 70".

Typically, the pourous bodies are secured to vanes guiding the gas in circuitous paths.

When a staggered baffle arrangement is used, the angle of inclination of the length dimension of the transverse cross-section of the baffle may range from 900 (normal to gas flow direction) to 300. Along their heights the strips or baffles are generally vertical.

In some applications, it may be preferable to employ a fibrous body with anisotropic properties with respect to gas flow and gasflow resistance. For example, a fibrous body constructed or fabricated in layers or sheets generally parallel to the outer surfaces will normally have lower gas flow resistance for flow parallel to such layers than for gas flow normal to such layers. Such an anisotropic fibrous body may be used to afford a higher degree of protection from gas friction of liquid drainage in the interior of the fibrous body by orienting the anisotropic fibrous body so that the high-resistance gas flow path is normal to the exterior surface of major dimension. Alternately, if protection of liquid drainage is a secondary consideration and augmented gas flow through the fibrous body is desired, the preferred orientation of an anisotropic fibrous body would then be such that the low-resistance gas flow path is normal to the exterior surface of major dimension.

Embodiments of this invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a view in perspective with part of the top wall 13 of the duct or conduit 11 broken away, showing an embodiment of this invention Fig. 2 is a plan view showing one stage of fibrous body baffles of the embodiment shown in Figure 1; Fig. 3 is a view in perspective of a bracket used to hold and drain the fibrous-body baffles of the embodiment shown in Figure 1; Fig. 4 is a graph showing the relationship between the pressure drop and gas velocity in the apparatus shown in Figure 1; Fig. 5 is a graph showing the pressure drop through a fibrous body used in the practice of this invention as a function of the velocity; Fig. 6 is a plan view of a modification of this invention including sinuous, zig-zag, or serpentine vanes having fibrous bodies mounted thereon; Fig. 7 is a plan view, generally diagrammatic of another modification of this invention; and Fig. 8 is a plan view, generally diagrammatic, of a further modification of this invention.

The apparatus shown in Figures 1,2 and 3 includes a duct or conduit or flow channel 11 for treating a gas. This duct is in the form of an open-ended box having a top wall 13, a bottom wall 15 and side walls 17 and 19. The top 13 has openings 20 for mounting of the baffles 25, but these openings are closed by plates (not shown) after the baffles 25 are mounted. Within the duct 11 there is fibrous-body means in the form of two stages 21 and 23 of fibrous-body baffles 25, each stage having a plurality of rows 27 and 29 of the baffles 25. While the embodiment shown in Figures 1, 2 and 3 has only two rows of baffles per stage, there may be a larger number of rows per stage. The duct 11 extends horizontally and each baffle 25 is mounted substantially vertically and is of fibrous, high-voidage, non-capillary, freedraining material as previously defined. The baffles 25 in different rows 27 and 29 are staggered with respect to each other, the baffles in row 29 being displaced along the row with respect to the baffles along row 27 so that the baffles 25 of row 29 are coextensive with the spaces between the baffles of row 27.

The fibrous body 30 of each baffle 25 is mounted in a frame 31 formed of a channel section 33 and bars 35 and 37 extending from one lip of the channel and an angle section 39 secured between the extending ends of the bars 35 and 37. The fibrous body 30 is in the form of a rectangular parallelepiped and it abuts the web of the channel section 33 along the thickness dimension of the body 30, the bars 35 and 37 at its upper and lower ends along the width dimension and the angle 39 along one edge (Fig. 1).

The frame 31 is secured by welding or otherwise to the bottom 15 of the duct 11.

The channel 33 extends below the fibrous body 30.

The row 27 requires a different bracket 31 to that for the row 29. The bracket shown in Figure 3 is appropriate for the bodies 25 of the row 29. For the row 27 the bars 35 and 37 and the angle 39 should be on the lefthand side of the channel 33 with reference to Figure 3 (see Figure 2).

As shown in Figure 2, the baffles 25 in the first row 27 are at +450 to the direction of gas flow and the baffles 25 in the second row are at 450 to the direction of gas flow.

Typically, this angle may vary from 900, that is perpendicular to the gas-flow direction, by up to +300 to the gas-flow direction.

Below each stage 21 and 23 there is a tank 41. The projecting ends of the channels 33 extend into the tank. Typically each fibrous body 30 is 243 inches wide, 1 inch thick and 12 inches long. The spacing between adjacent baffles of each row and between the baffle on the first row 27 and the adjacent baffle of a succeeding row 29 is 1 inch. The width may also be referred to as the thickness of the bodies 25. As previously stated, the fibrous body means is of a sufficient thickness in the direction of gas flow to allow for protected liquid drainage.

Since the bodies are aligned at an angle to the gas flow direction, this thickness will be greater than the 1 inch spacing referred to above.

The apparatus includes spray headers 43 to which nozzles 45 are connected. A liquid, typically water, is supplied to the headers 43 and projected as a spray 47 towards the downstream sides of the channel 11. As shown, the spray also impinges on the baffles 25 of the stage 21. A like nozzle may be disposed between the first stage 21 and the second stage 23. In accordance with one aspect of this invention, the nozzles may be provided on the downstream sides of the stages 21 and 23. Such nozzles moisten the baffles 25 so that particulate from dry gas passing through and captured by the fibrous-body means is washed down.

In the use of the apparatus, a fluid, such as a gas (air) at a high velocity is transmitted through the duct in a substantially horizontal stream in the direction of the arrow 51. The gas picks up liquid mist from the sprays 47 and so misted passes through the stages 21 and 23 of baffles 25. As shown by the arrows in Figure 2, the gas partly passes through the fibrous bodies 30 and partly is deflected by the bodies and then is deflected and passes through other fibrous bodies 30. A portion of the gas stream passing through a fibrous body gives up its mist and/or its particulate to the fibers; a portion also impinges on the channel section 33 and gives up its mist and/or particulate to the section 33. The liquid resulting from the captured mist drains through the fibrous body and through the channel section 33 into container 41, whence it may be removed. The bottom 15 is provided with holes under the channels through which the liquid flows into tanks 41.

The gas flowing through- each fibrous body 30 forces a large part of the mist captured by the fibers onto the channel section 33. For this reason the preponderant portion of the liquid resulting from the mist is drained through the channel section 33 into the tank 41. The channel sections 33 extend into the pool 50 formed in the tank 41. The liquid which drains along the channels sections 33 is protected from reentrainment by the upstream portion of the fibrous body 30 and by the base 15 of the duct 11.

The duct 11 is provided with flanges 53 so that a number of double stages may be connected in series. A plurality of ducts 11 as shown in Figure 1 may be stacked to form a high duct. In this case the tanks 41 extend only from the base 15 of the lowermost duct.

Each duct has a bottom for supporting the baffles 25, but only the uppermost duct has a top 13. The baffles 25 along the stacked ducts are coextensive. The liquid drains along the coextensive baffles 25 through the holes 52 in each base 15 or through enclosed horizontal troughs.

The orientation of the fibrous baffles 25 and the thickness of such baffles are both dependent on the density and gas flow resistance of the fibrous baffle material.

The preferred gas linear velocity range of operation of the apparatus shown in Figures 1 to 3 in the practice of this invention is from 1000 to 2500 ft./min., based on the superficial or empty cross-sectional gas flow area. Within this range, it has been discovered that a surprisingly high degree of gas flow is obtained through relatively thick fibrous baffles 25, used in the practice of this invention, at gas pressure drops that are substantially less than those that are obtained withflow through identical solid body baffle configurations. This was determined by the following comparison tests: These tests were carried out with apparatus in accordance with this invention, as shown in Figures 1 through 3 but with only one stage 21 of baffles. The fibrous baffles 25 were each 1" thick, 243 inches wide and 12" long. The baffles were non-capillary, bonded, non-woven, "high-voidage" pads of 40-micron diameter polyester fibers bonded with a polyvinylchloride resin. The duct section containing the baffles was 12" square. In a test, gas flow was supplied by a 7.5 HP blower, ducted to the flow section by a 12" diameter, 5 ft. long, rigid aluminum pipe. Pressure drop was measured by means of an inclined manometer across the test section. For comparison purposes, the operation of the apparatus shown in Figures 1--3 was compared to the operation of similar mock-up apparatus in which the baffles are of solid wood. The results are shown in the following Table I:- TABLE I (a) Wood Baffles AP, in inches Velocity, fpm of H2O 1484 2.7 1625 3.2 1696 3,8 1837 4.5 1660 3.5 1784 4.1 (b) Fibrous Baffle 1682 2.0 1893 2.5 2209 3.0 2436 3.5 These data are plotted in Figure 4, as log of pressure drop vs. log of linear velocity. In this table, log of pressure drop, AP, in inches of water, is plotted vertically and log of gas velocity in feet per minute is plotted horizontally. Curve F is for the fibrous baffles 25 and curve W for the wooden baffles.

Table I .shows that the fibrous-body baffles transmitted a significant fraction of the gas as is manifest from the remarkably lower pressure drop at equal superficial gas velocities. This decrease in pressure drop is substantially greater than was anticipated.

The gas flow through the fibrous-body baffles 25 can be determined approximately on the assumption that pressure drop in turbulent gas flow across an obstructed flow system is proportional to the square of the gas velocity. Figure 4 shows this to be a fair approximation as the slopes of the linear graphs is 2. The relationship is given b.y:-- (APf /APW)=(V, /Vw)2 where APf, AP=Pressure drop across fiber and wood baffles, respectively.

V,/V=Ratio of gas flows external to baffle- bodies, fiber or wood.

D through the fibrous pads can be calculated as: 95=100 [1-(1-fl?] where f=Fraction of gas going through fibrous bodies in one stage 21 or 23 of Fig. 1.

n=Number of stages required for 95% gas transmission through fibrous bodies.

95/100=[1-(1-0.28)"] (0.72)"=0.05 n=9.1 stages Implicit in the above calculation are two off-setting assumptions. First, it is assumed that there is negligible flow resistance for gas flow through the fibrous-body baffles or pads and second, that no pressure-drop correction is necessary for the reduction in inter-baffle passageway velocity resulting from the flow through the fibrous baffles 25.

To arrive at a corrected baffle gas transmission estimate, data were taken on the pressure drop of the fiber-body pad used in the above tests when employed as a direct-filter material (100% gas transmission). This data is presented in the following Table II and is plotted in Figure 5.

In Figure 5 log of pressure drop, AP, in inches of water is plotted vertically and log of velocity in feet per minute horizontally.

TABLE II AP, in inches Linear Velocity, fpm of H2O 1848 2.0 2046 2.5 2288 3.0 2508 3;5 2794 4.0 From Figures 4 and 5 the separate interbaffle gas velocity and the velocity of the gas transmitted through the baffles 25 are obtainable. These values are obtained by trialand-error calculation of the separate component pressure drops based on the assumption that the separate pressure drops should add up to the experimentallydetermined. total pressure drop.

The 2.6 inch pressure-drop at a superficial linear velocity of 2000 fpm (Figure 4) consists of two components: a partial "solidbaffle" pressure drop, AP1, due to the interbaffle velocity, Vj and a pad-flow pressure loss, APf, due to gas flow at Vf feet/minute through the pads. The sum of the two velocities must equal the total velocity of 2000 feet/minute. From the pressure drop data of Figure 4 and the pressure drop behavior of the pad material at 100% gas transmission (Figure 5), it is possible to estimate pad flow by trial-and-error calculations. At the superficial velocity of 2000 feet/minute, it is found that the velocity through the pad is 800 feet/minute, indicating 40% gas-flow transmission through the pad. For this level of flow transmission, 5.9 stages would be required for filtration of 95% of the gas through the pads. This method offers a fairly straightforward technique for choosing the optimum fiber-body pad or baffle thickness, material characteristics, orientation and number of stages.

The effectiveness of the apparatus in accordance with this invention as shown in Figures 1--3 as a mist eliminator was demonstrated as described in the following Example I:- Example I This operation was carried dut with the two-stage apparatus as shown in Figures 1 through 3 with the non-capillary, bonded, high-voidage pads (baffles) 25 of the composition, bonding, and dimensions used in the above test. Air carrying water fog was conducted through this apparatus. The air was supplied at 2000 ft./min linear velocity in the test section. An atomized water fog 47 (Figure 1) was generated by a sonic nozzle 45, No. SDC 125H made by Sonic Development Company. Air pressure of 40 pounds per square inch gauge was used in the nozzle 45, as recommended by the manufacturer, to generate the finest practicable mist. The nozzle 45 injected the mist 47 upstream of the first stage of baffles.

For comparison purposes, wooden baffles were used in place of the fibrous baffles 25.

In addition, the apparatus according to this invention was compared with two stages of a high-velocity commercial vane-type eliminator, the "Euroform" eliminator disclosed by Regehr (Supra) and also in a leaflet entitled munters euroform d-MIST R. Visual methods of assessing water fog penetration were used. In addition, the Tyndall dispersion effect on a strong light beam placed normal to the flow direction at the gas outlet was observed. Typical results are presented in Table III.

TABLE III Visual and Tyndall Beam Determination of Fog Penetration Velocity=2000 ft./min.

Observed Unit Tested Penetration 2-stage Wood Baffles Heavy 2-stage Fiber-Baffles None 2-state vane-type eliminator (see above) Light The vapour emerging from the apparatus constructed in accordance with the invention was observed to be at the air wetbulb temperature and was saturated with water. This indicates that heat and mass transfer in the practice of this invention takes place at a high rate and efficiently in spite of the fact that at the high gas (air) velocity, the residence time of the liquid in the gas is extremely short.

Because of the effectiveness of the apparatus for mist removal and the unique interaction between the liquid droplets and fibers of the pad, the apparatus has advantages as a wet particulate scrubber.

In conventional particulate-removal by wet or spray scrubbing or venturi scrubbers, water is atomized either at a spray nozzle or by gas frictional shear and injection into the gas stream containing the particulates which are to be removed. The gas is confined in a shell or a duct or a conduit and moves at a high velocity relative to the fixed spray nozzle or initial gas-liquid contact region.

The atomized water spray leaving the initial gas-liquid contact region is at a lower velocity than the gas and is rapidly accelerated by the gas stream until the water droplets achieve the velocity of the gas stream a relatively short distance downstream from the nozzle or initial contact zone. Only during the acceleration period do the spray droplets possess a differential velocity relative to the particulates in the gas stream and only during this period do the water droplets offer an impingement target for collision with the particles moving along with the gas at the gas velocity. Collision capture is a function of the relative velocity of the particles and droplets. Obviously, once the droplets attain the same velocity as the particulates, there is virtually no change of particulate collision-capture by the drops, so that venturi and spray scrubbers only operate in the relatively short droplet acceleration zone.

In the practice of this invention, the atomized water droplets, after they have been.partially or wholly accelerated to the velocity of the gas stream, are captured by the fibers composing the fibrous baffle of this invention. Collision and momentary adherence of a droplet to a fiber brings the droplet to a rest position, so that the relative velocity of the particles with respect to the captured droplet is the full velocity of the gas stream passing the fiber. On the outer or upstream fiber layers, the velocity of the gas is essentially that of the free gas stream, while for interior fibers removed from the upstream face, the relative velocity is that of the portion of the gas flowing through the fibrous-body means (baffles 25 or vanes carrying fibrous bodies). At high gas velocities, the droplet tends to either be reentrained by gas friction for subsequent recapture by a deeper fiber, or grow by capture and coalescence with other drqplets.

Those droplets that grow in size by capture coalescence with other drops are rapidly drained off down the fiber under the influence of gravity, or become unstable in the presence of gas frictional forces and shatter into smaller droplets. Because gas friction is moderated in the interior and downstream portions of the fibrous-body baffles, the growth-drainage mechanism dominates in these regions. However, because larger drops 'tend to be quickly removed, the moving gas and the particles it contains are exposed in the practice of this invention to a dynamic drop population in which the smallest drop sizes predominate, and in which a significant portion of these droplets are held at rest or in retarded flight relative to the velocity of the particles. The efficiency of droplet capture of fine particles is governed by the number and size of the targer droplets, as well as the relative particle-droplet velocity. For a given quantity or rate of spray liquid injection, the number of droplet targets is inversely proportional to the size of the drops, so that smaller drops provide a larger number of targets than do larger drops, and the collection efficiency is greater for a smaller mean droplet size. Further, for fine particles a general rule of thumb relating collection efficiency to target size is that the maximum impingement efficiency occurs when the target diameter is approximately 5 to 10 times that of the particle diameter. By controlling the initial drop-size distribution at the spray nozzle, and the fiber count and fiber diameter of the fibrous-body baffle, this efficiency can be optimized for a particulate size or size distribution. This phenomenon only occurs for non-capillary fibrous body means. In the case of capillary bodies the gas flow is blocked by the liquid which fills the pores of the bodies.

Example II The apparatus as shown in Figures 1 to 3 was used to test for particulate-removal efficiency using a fine fly ash obtained from a local power plant of the Duquesne Light Company. The fly ash had been collected from the combustion gas by means of an electrostatic precipitator and microscopic examination showed that it contained a significant fraction of particles having a size of less than I micron. In the apparatus used in this example there were two stages; the first upstream stage 21 serving as a primary irrigated collection stage and a downstream demisting stage 23. Each stage contained three rows of fibrous pads or baffles. The primary collection stage 21 included three rows of stainless steel wire pad elements 25, made from corrugated knitted-mesh wire, each pad 3/4 inch thick and otherwise having the same dimensions as the elements of Example I. The demisting stage 23 consisted of three rows of the fibrous elements used in Example I.

The primary collection stage was sprayed concurrent with gas flow, using a Bete Fog Nozzle Company Type ST6FCN for the spray nozzle 45, operated at 225 psig water pressure, giving a flow rate of 3.4 GPM. Gas flow was 1648 CFM, as determined by pitottube traverses, to arrive at the average velocity and the overall pressure drop was 5" of water. A 250-gram weighed sample of the fly ash was fed into the suction side of the air blower over a period of 45 seconds to yield a high inlet loading of more than 3 grains per standard cubic foot. The water draining from each stage during the test was collected, filtered, and the recovered solids dried and weighed. The weight of the recovered fly ash was 207 grams, representing a weight recovery of 82.8%. In view of the unrecoverable losses to the walls and unwashed parts of the system, and the fact that only one wetted-fibrous body stage 21 was employed, the 82.8% direct recovery is remarkably high.

The apparatus shown in Figure 6 includes a horizontal flow channel or conduit 60 within which a plurality of vertical, generally parallel spaced vanes 61 of serpentine shape are mounted. Typically the vanes are composed of 1/8" thick polystyrene panels and are spaced about 1" apart. Spaced along the opposite faces of each vane 61 there are a plurality of vertical pads 63 of fibrous, high voidage, noncapillary, free-drainage material. The pads 63 may be secured to the vanes by an adhesive. The conduit has a top and a bottom (not shown) and the vanes 61 and pads 63 extend from the top to the bottom.

A high velocity horizontal stream of mist and/or-particle-laden gas passes through the conduit 60. The mist and/or particles are captured by the fibrous pads and washed down through the pads 63 and along the vanes 61 under the pads.

The apparatus shown in Figure 7 includes a horizontal flow channel or duct 71 similar to the duct 11 of Figure 1 within which there are a plurality of vertical baffles 73. Each baffle 73 includes a generally cylindrical screen 75 on the outer surface of which there is an annulus 77 of fibrous, highvoidage, non-capillary free-draining material. The baffles extend between the top and bottom (not shown) of duct 71.

The apparatus shown in Figure 8 includes a horizontal channel or duct 81 similar to duct 11 of Figure 1 within which there are a plurality of baffles 83. Each baffle 83 includes a generally cylindrical screen 85 within which there is a mass 87 of fibrous, high voidage, non-capillary free draining material. The baffles 83 extend between the top and bottom (not shown) of the duct.

In the apparatus of Figures 7 and 8, one stage of two rows of staggered baffles 73 and 83 are shown. There may be any desired number of stages, each stage having a plurality of rows of staggered baffles 73 and 83, the baffles of each row being aligned with the spaces between the baffles of preceding and succeeding rows.

WHAT I CLAIM IS: 1. An apparatus for removing undesired components from a moving fluid, the apparatus including a flow channel for conducting said fluid in a substantially horizontal stream, and a plurality of substantially vertical fibrous bodies interposed in said flow channel in the path of said stream to remove said components from said stream, the bodies being formed df high-voidage, non-capillary, free-draining material, as hereinbefore defined.

2. An apparatus according to claim 1 wherein the bodies have a thickness transversely to the stream of at least + inch and are so mounted as to suppress reentrainment in the fluid stream of the undesired components.

3. An apparatus according to claim 1 or claim 2 wherein the channel has a top and a bottom wherein the bodies extend completely between the top and the bottom so that no fluid flows between the bodies and said top and bottom.

4. An apparatus according to any one of claims 1 to 3, wherein the bodies are mounted so that the fluid flows successively from bodies upstream in the flow channel towards bodies downstream in the flow channel, a portion of the fluid flowing through one or more of the bodies on which it impinges and a portion of the fluid being deflected by one or more of the bodies on which it impinges, the bodies through which the fluid flows removing the undesired components from the fluid flowing through the bodies and the fluid deflected by the bodies following a tortuous path through the flow channel.

5. An apparatus according to any one of claims 1 to 4, wherein the bodies are mounted in rows in the flow channel from the upstream end to the downstream end of the channel, the bodies in each row being offset with respect to the bodies in the adjacent upstream or downstream rows.

6. An apparatus according to any one of the preceding claims, wherein the flow channel has a plurality of generally vertical vanes having a form such as to guide the gas in a tortuous path, the bodies being spaced along at least one surface of each vane.

7. An apparatus according to claim 6

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Claims

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having the same dimensions as the elements of Example I. The demisting stage 23 consisted of three rows of the fibrous elements used in Example I.

The primary collection stage was sprayed concurrent with gas flow, using a Bete Fog Nozzle Company Type ST6FCN for the spray nozzle 45, operated at 225 psig water pressure, giving a flow rate of 3.4 GPM. Gas flow was 1648 CFM, as determined by pitottube traverses, to arrive at the average velocity and the overall pressure drop was 5" of water. A 250-gram weighed sample of the fly ash was fed into the suction side of the air blower over a period of 45 seconds to yield a high inlet loading of more than 3 grains per standard cubic foot. The water draining from each stage during the test was collected, filtered, and the recovered solids dried and weighed. The weight of the recovered fly ash was 207 grams, representing a weight recovery of 82.8%. In view of the unrecoverable losses to the walls and unwashed parts of the system, and the fact that only one wetted-fibrous body stage 21 was employed, the 82.8% direct recovery is remarkably high.

The apparatus shown in Figure 6 includes a horizontal flow channel or conduit 60 within which a plurality of vertical, generally parallel spaced vanes 61 of serpentine shape are mounted. Typically the vanes are composed of 1/8" thick polystyrene panels and are spaced about 1" apart. Spaced along the opposite faces of each vane 61 there are a plurality of vertical pads 63 of fibrous, high voidage, noncapillary, free-drainage material. The pads 63 may be secured to the vanes by an adhesive. The conduit has a top and a bottom (not shown) and the vanes 61 and pads 63 extend from the top to the bottom.

A high velocity horizontal stream of mist and/or-particle-laden gas passes through the conduit 60. The mist and/or particles are captured by the fibrous pads and washed down through the pads 63 and along the vanes 61 under the pads.

The apparatus shown in Figure 7 includes a horizontal flow channel or duct 71 similar to the duct 11 of Figure 1 within which there are a plurality of vertical baffles 73. Each baffle 73 includes a generally cylindrical screen 75 on the outer surface of which there is an annulus 77 of fibrous, highvoidage, non-capillary free-draining material. The baffles extend between the top and bottom (not shown) of duct 71.

The apparatus shown in Figure 8 includes a horizontal channel or duct 81 similar to duct 11 of Figure 1 within which there are a plurality of baffles 83. Each baffle 83 includes a generally cylindrical screen 85 within which there is a mass 87 of fibrous, high voidage, non-capillary free draining material. The baffles 83 extend between the top and bottom (not shown) of the duct.

In the apparatus of Figures 7 and 8, one stage of two rows of staggered baffles 73 and

83 are shown. There may be any desired number of stages, each stage having a plurality of rows of staggered baffles 73 and 83, the baffles of each row being aligned with the spaces between the baffles of preceding and succeeding rows.

WHAT I CLAIM IS: 1. An apparatus for removing undesired components from a moving fluid, the apparatus including a flow channel for conducting said fluid in a substantially horizontal stream, and a plurality of substantially vertical fibrous bodies interposed in said flow channel in the path of said stream to remove said components from said stream, the bodies being formed df high-voidage, non-capillary, free-draining material, as hereinbefore defined.
2. An apparatus according to claim 1 wherein the bodies have a thickness transversely to the stream of at least + inch and are so mounted as to suppress reentrainment in the fluid stream of the undesired components.
3. An apparatus according to claim 1 or claim 2 wherein the channel has a top and a bottom wherein the bodies extend completely between the top and the bottom so that no fluid flows between the bodies and said top and bottom.
4. An apparatus according to any one of claims 1 to 3, wherein the bodies are mounted so that the fluid flows successively from bodies upstream in the flow channel towards bodies downstream in the flow channel, a portion of the fluid flowing through one or more of the bodies on which it impinges and a portion of the fluid being deflected by one or more of the bodies on which it impinges, the bodies through which the fluid flows removing the undesired components from the fluid flowing through the bodies and the fluid deflected by the bodies following a tortuous path through the flow channel.
5. An apparatus according to any one of claims 1 to 4, wherein the bodies are mounted in rows in the flow channel from the upstream end to the downstream end of the channel, the bodies in each row being offset with respect to the bodies in the adjacent upstream or downstream rows.
6. An apparatus according to any one of the preceding claims, wherein the flow channel has a plurality of generally vertical vanes having a form such as to guide the gas in a tortuous path, the bodies being spaced along at least one surface of each vane.
7. An apparatus according to claim 6

wherein the bodies are spaced along the opposite surfaces of each vane.
8. An apparatus according to claim 3, wherein each body is supported in a bracket which mounts each body so that it extends between the top and the bottom, each said bracket having an undesired-componentdraining-member on one side which extends through the bottom of the channel.
9. A method of removing undesired components from a fluid comprising means for causing the fluid to flow in a substantially horizontal stream through a plurality of substantially vertical fibrous bodies of high-voidage, non-capillary and free-draining material as hereinbefore defined, interposed in said stream, in which the fluid is a moisture-laden gas and the method comprises capturing the moisture in the fibrous bodies and draining the captured moisture gravitationally from the fibrous bodies.
10. A method of removing solid particulate from a fluid comprising means for causing the fluid to flow in a substantially horizontal stream through a plurality of substantially vertical fibrous bodies of high-voidage, non-capillary and free-draining material as hereinbefore defined, interposed in said stream, wherein the method includes injecting a liquid spray into the fluid upstream, capturing drops of said spray on the fibres of the bodies, said liquid spray capturing the solid particulate and draining the solid particulate-containing drops gravitationally from the fibrous bodies.
11. A method according to claim 10 wherein the liquid spray is injected upstream of the fibrous bodies.
12. A method according to claim 10 or claim 11 wherein the captured drops of the spray are caused to coalesce into larger drops and said larger drops are drained gravitationally together with large, directly captured drops, at a higher rate than the drainage of smaller captured drops, the higher rate drainage of large drops producing a dynamic drop population on the fibres of said bodies in which smaller drops predominate and in which the solid particulate is captured before the smaller drops are drained from the bodies.
13. A method according to claim 12 wherein a proportion of the larger drops are caused to become unstable and are shattered into smaller drops.
14. A method according to any one of claims 10 to 13 wherein a proportion of the drops formed on the fibres of upstream bodies are re-entrained by the fluid stream and are recaptured by the fibers of downstream bodies.
15. An apparatus for-removing undesired components from a moving fluid substantially as hereinbefore described and with reference to the accompanying drawings.
16. A method of removing undesired components from a fluid substantially as hereinbefore described and with reference to the accompanying drawings.