Abstract:
A scrubber for removing pollutants from a gas comprising a housing for conducting the gas therethrough, a mechanism for introducing pollutant-reactive filtering agent into the housing, a sump for collecting the filtering agent and having a first volume, and an intermediate sump for collecting the filtering agent and channeling the filtering agent into the sump, the intermediate sump having a second volume that is less than the first volume.

Description:
This application is a division of application Ser. No. 08/946,134, filed Oct. 7, 1997, now U.S. Pat. No. 6,068,686. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to the field of pollution control systems. 
     More particularly, this invention relates to apparatus for removing contaminants from fluid. 
     In a further and more specific aspect, the present invention relates to a system and method for removing pollutants from a fluid. 
     2. Prior Art 
     Industrialized processes normally produce undesirably large measures or quantities of contaminants or pollutant material that can be toxic to the environment and highly odoriferous. Normally, the pollutants are carried within fluid that may be in the form of a liquid or a gas. In this regard, to control the odoriferous and toxic pollutants, various apparatus and systems have been devised to filter or otherwise remove pollutants from fluid. 
     Of particular concern are waste treatment facilities located near municipalities. Although necessary for the proper treatment of municipal wastewater and other potential waste material, waste treatment facilities produce large amounts of toxic and highly odoriferous gaseous emanations. In this regard, odor scrubbers have been devised to remove undesirable toxic and odoriferous pollutants from the gaseous emanations produced from waste treatment facilities for substantially eliminating foul smells, reducing worker exposure to hazardous compounds and reducing corrosion to the facility equipment. 
     The largest odor component released by waste treatment facilities is hydrogen sulfide. Other odorous compounds that may be generated when treating waste material include mercaptans, dimethyl sulfide, dimethyl di-sulfide and other uncharacterized organic sulfide based constituents. In addition to the foregoing toxic and odoriferous constituents, toxic volatile organic compounds (VOCs) may also be produced. Nevertheless, the foregoing odorous and non-odorous compounds are treated using some form of removal technique. In this regard, most waste treatment plants are forced to deal with these compounds in addition to a variety of other air-borne contaminants that can be detrimental to the operation of odor removal systems. The current trend is to minimize releases into the atmosphere that may cause odor complaints from residential communities surrounding the waste treatment plant. Local air quality boards are also generating more stringent air quality guidelines due to increased federal requirements. 
     Current odor removal systems are expensive, difficult to construct and difficult to maintain. Although considerable effort has been invested toward the improvement of scrubber systems, existing scrubber system technology requires large amounts of energy, water, chemical reagents and maintenance in order to ensure proper operation. Therefore, the foregoing and other deficiencies replete throughout the art necessitate certain new and useful improvements. 
     It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art. 
     Accordingly, it is an object of the present invention to provide a new and useful scrubber system and method for removing toxic and/or odoriferous pollutants from a fluid. 
     Another object of the present invention is to provide a scrubber system that is easy and relatively inexpensive to construct. 
     And another object of the present invention is to provide a scrubber system that utilizes a simple and efficient multi-stage scrubbing system. 
     Still another object of the present invention is to provide a scrubber system that is highly efficient. 
     Yet another object of the instant invention is to provide a scrubber system that is easy and inexpensive to maintain. 
     Yet still another object of the instant invention is to provide a scrubber system that conserves chemical reagents. 
     And a further object of the invention is to provide a scrubber system that is safe for workers and for municipalities. 
     Still a further object of the immediate invention is to provide a scrubber system that is dependable and requires little monitoring. 
     Yet a further object of the invention is to provide a scrubber system that conserves utilities and natural resources. 
     And still a further object of the invention is to provide a scrubber system that occasions no adverse environmental impacts as a result of operation. 
     Another object of the present invention is to provide a method of cleaning a sensor for monitoring a polluted fluid. 
     And another object of the present invention is to provide a method of monitoring a sensor for monitoring a polluted fluid. 
     SUMMARY OF THE INVENTION 
     Briefly, to achieve the desired objects of the instant invention in accordance with a preferred embodiment thereof, provided is a scrubber for removing pollutants from a fluid and having an inlet for receiving the fluid and an outlet for emitting the fluid. The scrubber is generally comprised of a primary scrubber assembly coupled with the fluid intermediate the inlet and the outlet for removing a primary measure of pollutants from the fluid, and a secondary scrubber assembly coupled with the primary scrubber assembly intermediate the inlet and the outlet, the secondary scrubber assembly for removing a secondary measure of pollutants from the fluid. 
     The primary scrubber assembly may be comprised of a first stage scrubber coupled with the fluid intermediate the inlet and the outlet for removing a first measure of pollutants from the fluid, and a second stage scrubber coupled with the first stage scrubber intermediate the inlet and the outlet, the second stage scrubber for removing a second measure of pollutants from the fluid. In a particular embodiment, the first stage scrubber may include a housing, a source of a filtering agent coupled with the housing in fluid communication, and means for communicating the filtering agent into the housing, the filtering agent reactive with the pollutants to remove the first measure of pollutants from the fluid. The means for communicating the filtering agent into the housing of the first stage scrubber may include a pump mounted with the source of a filtering agent and the housing in fluid communication, and at least one dispersing element mounted for communicating the filtering agent from the pump into the housing. The present invention may further include a control assembly for monitoring the measure of pollutants present within the fluid adjacent the inlet and for actuating the pump to either increase or decrease the amount of filtering agent supplied to the housing in response to the measure of pollutants. 
     Regarding a preferred embodiment, the second stage scrubber may include a housing, a source of a filtering agent coupled with the housing in fluid communication and means for communicating the filtering agent into the housing, the filtering agent reactive with the pollutants to remove the second measure of pollutants from the fluid. Regarding the second stage scrubber, the means for communicating the filtering agent into the housing may include a pump mounted with the source of a filtering agent and the housing in fluid communication, and at least one dispersing element mounted for communicating the filtering agent from the pump into the housing. Further regarding the second stage scrubber, the present invention may also provide a control assembly for monitoring the measure of pollutants present within the fluid intermediate the second stage scrubber and the secondary scrubber assembly and for actuating the pump to either increase or decrease the amount of filtering agent supplied to the housing in response to the measure of pollutants. 
     The secondary scrubber assembly of the present invention may be comprised of a housing and a plurality of filtering layers carried by the housing, the plurality of filtering layers cooperating together to remove the secondary measure of pollutants from the fluid. The plurality of filtering layers are preferably mounted with the housing in substantially vertical series and are each comprised of a plurality of trays removably carried by the housing, and filtering media removably carried by each of the plurality of trays. 
     Consistent with the foregoing scrubber system, a method of removing pollutants from a fluid may also be provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and further and more specific objects and advantages of the instant invention will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment thereof taken in conjunction with the drawings in which: 
     FIG. 1 illustrates a perspective view of a scrubber system for removing pollutants from a fluid including a wet stage scrubber assembly and a dry stage scrubber assembly, in accordance with a preferred embodiment of the present invention; 
     FIG. 2 illustrates a sectional view taken along line  2 — 2  of FIG. 1, in accordance with a preferred embodiment of the present invention; 
     FIG. 3 illustrates a perspective view of a liquid delivery system for supplying liquid to the wet stage scrubber assembly of the scrubber system of FIG. 1, in accordance with a preferred embodiment of the present invention; 
     FIG. 4 illustrates a nozzle assembly operative for communicating liquid from the liquid delivery system of FIG. 3 to the wet stage scrubber assembly of FIG. 1, in accordance with a preferred embodiment of the present invention; 
     FIG. 5 illustrates a fragmented partially exploded perspective view of the dry stage scrubber assembly of FIG. 1, in accordance with a preferred embodiment of the present invention; 
     FIG. 6 illustrates a top plan view of the scrubber system of FIG. 1, in accordance with a preferred embodiment of the present invention; 
     FIG. 7 illustrates an end elevational view of the scrubber system of FIG. 1, in accordance with a preferred embodiment of the present invention; 
     FIG. 8 illustrates a rear elevational view of the scrubber system of FIG. 1, in accordance with a preferred embodiment of the present invention; 
     FIG. 9 illustrates a block diagram of a control assembly for controlling the operation of the scrubber system of FIG. 1; and 
     FIG. 10 illustrates a vertical sectional view of a wet stage scrubber assembly being generally representative of the wet stage scrubber assembly introduced in combination with FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the drawings, in which like reference characters indicate corresponding elements throughout the several views, attention is first directed to FIG. 1 which illustrates a perspective view of a scrubber system generally designated by the reference character  20 . Scrubber system  20  is of a type for removing pollutants from a fluid such as a gas and perhaps a liquid. In a preferred application, scrubber system  20  is more particularly of a type that may be used at municipal wastewater treatment facilities and various industrial facilities for removing pollutants from the gases produced from the treatment of the wastewater and from industrial processes. However, scrubber system  20  may be employed in other similar applications if desired. For the purposes of the ensuing discussion, pollutants will be hereinafter collectively referred to as pollutants. 
     In general, scrubber system  20  is generally comprised of a structure  21  having an inlet  22  for receiving contaminated gas or gas having pollutants in the direction indicated by the arrowed line A. Also included is an outlet  23  for emitting clean gas or gas substantially free from pollutants in the direction indicated by the arrowed line B. From inlet  22 , gas initially enters into a primary or wet stage scrubber assembly  24  in which a primary measure of pollutants are removed from the fluid. In the present embodiment, wet stage scrubber assembly  24  is comprised of a first stage scrubber  25  and a second stage scrubber  26  coupled in series intermediate inlet  22  and outlet  23 . In this regard, gas entering inlet  22  passes consecutively through first stage scrubber  25  and second stage scrubber  26  and is wetted or otherwise treated with one or more liquid chemical reagents supplied from a liquid delivery system  28 , further details to be discussed as the detailed description ensues. The gas will then pass from the wet stage scrubber assembly  24  into a secondary, third stage or dry stage scrubber assembly  27  where the gas will conduct through a dry filtering media to remove a secondary measure of pollutants from the fluid which will thereafter conduct or emit outwardly through outlet  23 . 
     It will be generally understood that scrubber system  20  utilizes a multi-stage scrubber assembly comprised of first and second wet stage scrubbers  25  and  26  and a dry third stage scrubber  27 . In this regard, scrubber system  20  may include less than or more than two wet stage scrubbers and perhaps more than one dry stage scrubber as desired in order to effectuate the desired removal of pollutants consistent with the teachings herein. Accordingly, the first and second wet stage scrubbers  25  and  26  and the dry third stage scrubber  27  of scrubber system  20  are set forth merely for the purposes of example in light of a preferred embodiment and are not intended to be limiting features. 
     Consistent with the foregoing and ensuing discussions, it will be generally understood that for gas to pass from inlet  22  to outlet  23 , the gas must be flowing. In this regard, the flowing movement of the gas may be accomplished from a location remote from scrubber system  20  or may be accomplished by a motorized or otherwise mechanical mechanism carried by scrubber system  20 . Furthermore, gas entering inlet  22  is generally considered to be contaminated with a measure of pollutants. The measure of pollutants may be considered to be an amount or level of pollutants or perhaps one or more specific types of pollutants. 
     Having described the general structural and functional characteristics of scrubber system  20 , attention is now directed to FIG. 2 illustrating a sectional view taken along line  2 — 2  of. FIG.  1 . As evidenced in FIG. 2, contaminated gas enters inlet  22  in the direction indicated by the arrowed line A and enters into first stage scrubber  25 . First stage scrubber  25  is generally comprised of a housing  40  that, as best seen in FIG. 1, is generally cubical in shape, although this is not essential. Housing  40  bounds or otherwise defines a chamber  41  within which is carried a media  42 . In the specific example shown in FIG. 2, media  42  extends throughout substantially the entire extent of chamber  41 , although this is not an essential feature. Consistent with conventional practice, media  42  is preferably comprised of a low-density material to allow gas to easily pass therethrough and may be comprised of low density polypropylene, a cellular or foam packing material or other suitable low density/high surface area packing media. 
     As previously indicated, gas passing into and through chamber  41  of first stage scrubber  25  is wetted or otherwise treated with a liquid chemical reagent supplied from a first liquid delivery assembly  43  of liquid delivery system  28 . With momentary reference to FIG. 3, first liquid delivery assembly  43  of liquid delivery system  28  is generally comprised of a receptacle  44  coupled with chamber  41  of first stage scrubber  25  in fluid communication by virtue of a conduit assembly  45 . Consistent with conventional practice, receptacle  44  carries, and is operative as a source of, a liquid chemical reagent. The chemical reagent is operative as a filtering agent and is drawn out of receptacle  44  and into and through conduit assembly  45  by virtue of a conventional pump  48  coupled with conduit assembly  45 , receptacle  44  and housing  40  of first stage scrubber  25  in fluid or otherwise liquid chemical reagent communication. To communicate the liquid chemical reagent from conduit assembly  45  into chamber  41  (not shown in FIG. 6) of housing  40 , conduit assembly  45  branches out from pump  48  and terminates at a plurality of locations with a corresponding plurality of nozzle assemblies  49  mounted with housing  40  at a generally elevated location, also shown in FIG.  2 . In this regard, and consistent with normal operation, each nozzle assembly  49  facilitates the communication and dispersion of the liquid chemical reagent into chamber  41  of housing  40 . Upon introduction of the liquid chemical reagent within chamber  41 , it will descend through media  42  and engage, wet or otherwise treat the contaminated gas flowing therethrough, further details to be presently discussed. 
     With momentary attention to FIG. 4, illustrated is a perspective view of one of the plurality nozzle assemblies  49  first discussed in combination with FIG.  6 . As evidenced in FIG. 4, each nozzle assembly  49  includes a base plate  50  engagable with housing  40  by virtue of rivets, bolts, screws or other conventional fastening mechanism. Also included is an inverted substantially conical member  51  mounted with base plate  50  in spaced relation by virtue of a plurality of rods  52 . Conical member  51  includes a substantially conical sidewall  51 A having a substantially conical first major surface  51 B, a substantially conical second major surface  51 C, a continuous upper edge  57  and a nadir  54 . At each of the terminating points of conduit assembly  45  previously introduced, conduit assembly  45  extends through base plate  50  and terminates with an open end  55  -extending inwardly into chamber  41  through housing  40  at a location spaced from conical member  51 . In this regard, base plate  50  and rods  52  merely operate as a means of suspending conical member  51  within chamber  41  in spaced relation from open end  55 . Therefore, and consistent with the nature and scope of the present invention, other mechanical structures may be used for suspending conical member  51  within housing  41  in spaced relation relative open end  55  if desired. 
     In the foregoing manner of construction of nozzle assembly  49 , liquid chemical reagent passing through conduit assembly  45  will pass through and emerge through each respective open end  55  in the direction indicated by the arrowed line C in FIG.  4  and impact substantially conical first major surface  51 B of conical member  51 . Upon impaction with substantially conical first major surface  51 B, the liquid chemical reagent will deflect therefrom and spatter and disperse outwardly from edge  57  in the directions generally indicated by the arrowed lines D. The simple and efficient design of conical member  51  and its orientation relative open end  55  contributes to the ability of conical member  51  to act as a highly efficient dispersing element for dispersing liquid chemical reagent into housing  41  without the risk of becoming clogged or otherwise blocked with extraneous contamination buildup which is otherwise common with convention and well known nozzle assemblies currently in use in combination with scrubber systems of the type herein described. 
     As previously mentioned, base plate  50  of each nozzle assembly  49  may be mounted with housing  40  by virtue of rivets, bolts, screws or other conventional fastening mechanism. Nevertheless, base plate  50  is preferably detachably mounted with housing  40  by virtue of either bolts, screws or other suitable engagement mechanism operative for facilitating the detachable engagement of base plate  50  with housing. The preferred detachable engagement of base plate  50  with housing allows users to easy access, remove, replace and/or repair each nozzle assembly  49  from an exterior location. 
     Consistent with conventional practice, the liquid chemical reagent that may be used to wet or otherwise treat the contaminated gas passing through chamber  41  of first stage scrubber desirably operates to react with the pollutants to either dissolve them or form precipitates to pull or otherwise remove the pollutants from the gas. Because odoriferous contaminates are primarily comprised of hydrogen sulfide and other sulfide-based compounds or constituents, the liquid chemical reagent may be comprised of sodium hydroxide or other similar and suitable caustic substance having a relatively high pH level on the order of 10-11. When introduced into chamber  41 , the sodium hydroxide or other similar substance will react with the hydrogen sulfide and other sulfide-based compounds to form precipitates which fall out of the contaminated gas. Thus, first stage scrubber  25  operates to desirably remove a first measure of pollutants from the total measure of pollutants carried by the contaminated gas. The first measure of pollutants removed by first stage scrubber  25  may be either one or more specific types of pollutants or perhaps an amount or quantity of the total measure of the pollutants carried by the contaminated gas. 
     With attention directed back to FIG. 2, from first stage scrubber  25 , the contaminated gas will pass through a passageway or opening  56  and enter second stage scrubber  26 . Although not an essentially limiting feature, opening  56  may be obstructed by a low density screen or filter and is preferably located somewhat subjacent inlet  22  to facilitate the efficient flow of the contaminated gas from first stage scrubber  25  to second stage scrubber  26 . Like first stage scrubber  25 , second stage scrubber  26  is generally comprised of a housing  60  that, as best seen in FIG. 1, is generally cubical in shape, although this is not essential. Housing  60  bounds or otherwise defines a chamber  61  within which is carried a media  62 . In the specific example shown in FIG. 2, media  62  extends throughout substantially the entire extent of chamber  61 , although this is not an essential feature. Consistent with conventional practice, and like media  42 , media  62  is preferably comprised of a low-density material to allow gas to easily pass therethrough and may be comprised of low density polypropylene, a cellular or foam packing material or other suitable low density/high surface area packing media. 
     As previously indicated, gas passing into and through chamber  61  of second stage scrubber  26  is wetted or otherwise treated with a liquid chemical reagent supplied from first liquid delivery assembly  43  and a second liquid delivery assembly  63  of liquid delivery system  28 . With momentary reference to FIG. 6, receptacle  44  of first liquid delivery assembly  43  is coupled with chamber  61  of second stage scrubber  26  in fluid communication by virtue of a conduit assembly  64 . In this regard, receptacle  44  is generally intended to be included within the scope of second liquid delivery system  63 . Furthermore, and as also shown in FIG. 3, second liquid delivery assembly  63  of liquid delivery system  28  is further comprised of a receptacle  65  coupled with chamber  61  of second stage scrubber  26  in fluid communication by virtue of conduit assembly  64 . Consistent with conventional practice, receptacle  65  carries, and is operative as a source of, a liquid chemical reagent which may be different from the liquid chemical reagent carried by receptacle  44 . The chemical reagent carried by receptacle  65  is operative as a filtering agent and is drawn out of receptacle  65  and into and through conduit assembly  64  by virtue of a conventional pump  66  coupled with conduit assembly  64 , receptacle  65  and housing  60  of second stage scrubber  26  in fluid or otherwise liquid chemical reagent communication. To communicate the liquid chemical reagent from conduit assembly  64  into chamber  61  (not shown in FIG. 6) of housing  60 , conduit assembly  64  branches out from pump  66  and terminates at a plurality of locations with a corresponding plurality of nozzle assemblies  67  mounted with housing  60  and extending into chamber  61  at a generally elevated location (also shown in FIG.  2 ). In this regard, and consistent with normal operation, each nozzle assembly  67  facilitates the communication and dispersion of the liquid chemical reagent into chamber  61  of housing  60 . Upon introduction of the liquid chemical reagent within chamber  61 , it will descend through media  62  and engage, wet or otherwise treat the contaminated gas flowing therethrough. Each nozzle assembly  67  is substantially identical to nozzle assembly  49  discussed in combination with first stage scrubber  25 , further details of which will not be further discussed. The chemical reagent carried by receptacle  44  of first liquid delivery system  43  may be drawn therefrom into and through conduit assembly  64  by virtue of a conventional pump  68  coupled with conduit assembly  64  intermediate receptacle  44  and housing  60  of second stage scrubber  26  in fluid or otherwise liquid chemical reagent communication. 
     The purpose of wetting or otherwise treating the contaminated gas passing through chamber  61  of second stage scrubber is to enhance the effectiveness of the removal of the pollutants from the contaminated gas. In this regard, in addition to the sodium hydroxide supplied from receptacle  44  of the first liquid delivery assembly  43 , receptacle  65  preferably carries sodium hypochlorite which is also added to chamber  61  to wet or otherwise treat the contaminated gas passing through chamber  61  of second stage scrubber  26 . Treating the contaminated gas with a selected combination of sodium hydroxide and sodium hypochlorite operates to not only dissolve or precipitate hydrogen sulfide and other sulfide-based compounds from the contaminated gas, but also operates to enhance the dissolution or precipitation of sulfide-based compounds other than hydrogen sulfide in order to remove a second measure of pollutants from the contaminated gas. In this manner, when introduced into chamber  61 , the sodium hydroxide and the sodium hypochlorite will react with the hydrogen sulfide and other sulfide-based compounds to dissolve the compounds or form precipitates which fall out of the contaminated gas. Thus, second stage scrubber  26  operates to desirably remove a second measure of pollutants from the total measure of pollutants carried by the contaminated gas. Like the first measure of pollutants removed by first stage scrubber  25 , the second measure of pollutants removed by second stage scrubber  26  may be either one or more specific types of pollutants or perhaps an amount of the total measure of the pollutants carried by the contaminated gas. 
     Although sodium hydroxide and sodium hypochlorite have been disclosed as preferred liquid chemical reagents, those of ordinary skill will readily appreciate that other chemical reagents may be used if desired depending on the type of pollutants carried by the contaminated gas. Furthermore, although the sodium hydroxide and the sodium hypochlorite are each channeled into and through conduit assembly  64  for communicating each into chamber  61  of second stage scrubber  26 , those having regard toward the relevant art will readily appreciate that the direct mixing of sodium hydroxide with sodium hypochlorite would result in a violent chemical reaction that may not only occasion damage to scrubber system  20  but also prove hazardous to workers. As a consequence, and although not herein specifically shown, conduit assembly  64  is configured in a manner such that the sodium hydroxide and the sodium hypochlorite are mixed together in the presence of water to thereby eliminate the potential of a violent chemical reaction. This aspect of the present disclosure is well known by those having regard toward the relevant art and is a feature common to prior art scrubbers of the type herein disclosed, further details of which will not be herein further discussed as they will readily occur to the skilled artisan. 
     Regarding FIG. 2, the pollutants removed from the contaminated gas by first stage scrubber  25  and second stage scrubber  26  fall into a sump  70  located at the bottom of first and second stage scrubbers  25  and  26  bound by each respective housing  40  and  60  thereof. Sump  70  contains a predetermined amount or level of water, for instance 1000-3000 gallons, supplied from a water source (not shown). The water carried by sump is normally constantly circulated through conduit assemblies  45  and  64  of first and second stage scrubbers  25  and  26 , respectively, by virtue of conventional pumps  71  and  72  coupled with housings  60  and  40  of wet stage scrubber assembly  24 , respectively (shown only in FIG.  6 ). Furthermore, the water in sump  70  is either continuously or periodically replenished from a make-up water source (not shown) operative for maintaining the water level at a predetermined and desired level. In this manner, precipitated and dissolved toxic and odoriferous pollutants falling within sump  70  may be desirably contained within the water carried in sump  70  in accordance with conventional practice. 
     With attention directed back to FIG. 2, from second stage scrubber  26 , the contaminated gas will pass through a passageway or opening  78  and enter third stage scrubber  27 . Although not an essentially limiting feature, opening  78  may be obstructed by a low density screen or filter and is preferably located somewhat subjacent opening  56  to facilitate the efficient flow of the contaminated gas from second stage scrubber  25  to third stage scrubber  27 . Third stage scrubber  27  is generally comprised of a housing  80  that, as best seen in FIG. 1, is generally cubical in shape, although this is not essential. Upon entrance into third stage scrubber  27 , the contaminated gas will impact an angled platform  81  changing the flow of the contaminated gas from a substantially horizontal path as indicated by the arrowed line A to a substantially vertical path as indicated by the arrowed line B. After impacting platform  81 , the contaminated gas will flow into and through a mist eliminator  84  and into and through a filtering assembly  85  where a third measure of the pollutants is removed. As previously discussed, the third measure of pollutants may be either one or more types of pollutants or perhaps an amount or quantity of the total measure of pollutants carried by the contaminated gas. In any event, upon removal of the third measure of pollutants, further details to be discussed presently, the gas will be substantially free from pollutants and will safely emit through outlet  23 . 
     With attention directed to FIG. 5 illustrating a fragmented partially exploded perspective view of third stage scrubber  27 , housing bounds or otherwise defines a chamber  82  within which are carried in series a plurality of filtering layers  83  that comprise filtering assembly  85 . Consistent with a preferred embodiment, filtering layers  83  (also seen in FIGS. 1 and 2) are carried in substantially vertical series commensurate with the directional flow of the contaminated gas. Furthermore, although three layers  83  are evidenced in the present example, less or more may be employed without departing from the nature and scope of the present invention as herein specifically described. 
     Each filtering layer  83  is generally comprised of a plurality of trays  90  mounted and removably carried by housing  80  in a substantially horizontal or otherwise perpendicular orientation relative the directional flow of the contaminated gas. Each filtering layer  83  includes a total of nine individual trays  90 , although less or more may be used consistent with the teachings contained herein. Each tray  90  carries filtering media  91 . Filtering media  91  is preferably dry and may be comprised of a carbon-based media or other suitable dry filtering media. Although not herein specifically shown, trays  90  may be mounted on rails, platforms or other suitable mechanism that may be supplied with housing  80  in order to facilitate the installation and removal of trays  90  into and from chamber  82  of housing  80 . 
     The purpose of constructing each filtering layer  83  with a plurality of trays  90  operative for carrying filtering media  91  is so that each tray  90  may be easily installed and removed manually without the need of employing additional equipment such as vacuum removal equipment and the like. Trays  90  may be removed and installed much like the drawers of a conventional chest of drawers. In this regard, each tray  90  may be easily transported when full of filtering media  91  by an ordinary man or woman without considerable difficulty. Therefore, in operation, the filtering media  91  carried by each of the trays  90  of each filtering layer  83  will collect or otherwise filter the third measure of pollutants from the contaminated gas as it flows through the filtering layers  83 . Over time, the filtering media will become spent and have to be replaced. In this regard, rather than shutting down the entire scrubber system, the trays  90  of each filtering layer  83  may be individually and easily removed. Once removed, a user may discard the spent filtering media  91  to be replaced with fresh filtering media  91 . Upon installation of fresh filtering media  91 , the trays  90  of one of the selected filtering layers  83  may be reinstalled and the process repeated with the other filtering layers  83  if desired. In this regard, each filtering layer  83  may be easily and independently maintained with fresh filtering media  91  without having to shut down the entire scrubber assembly  20 . Additionally, individual trays  90  from each filtering layer  83  may also be selectively and independently removed, maintained and re-installed as desired to ensure proper operation. 
     To facilitate proper gas flow through third stage scrubber  27 , each tray  90  is preferably constructed of a low density material. Furthermore, and as evidenced in FIG. 5, each tray may be provided with a removable lid  92  for allowing a user to easily access each tray for removing and replacing filtering media  91  as required for proper maintenance of scrubber assembly  20 . Mist eliminator  84 , although not an essential feature of the present invention, is a conventional apparatus operative for removing moisture from the contaminated gas prior to its flow into and through filtering assembly  85 . The moisture collected by mist eliminator  84  will fall and collect upon platform  81  which will funnel the moisture downwardly into a drain  86  (FIG.  2 ). 
     As previously indicated, for gas to pass from inlet  22  to outlet  23  of scrubber assembly  20 , the gas must be flowing. In this regard, the flowing movement of the gas may be accomplished, as previously intimated, from a location remote from scrubber system  20  or may be accomplished by a motorized or otherwise mechanical mechanism carried by scrubber system  20 . Regarding the latter, and as shown in FIG. 2, FIG. 5, FIG.  6  and FIG. 7 illustrating an end elevational view of scrubber system  20  of FIG. 1, outlet  23  may be provided with a conventional blower or fan  93  operative for drawing gas inwardly from inlet  22  and outwardly from outlet  23 . The placement of fan  93  at outlet  23  is not an essential feature. In this regard, fan  93  may be located at other suitable locations with scrubber assembly  20  without departing from the nature and scope of the present invention as herein specifically described. 
     As previously mentioned, first, second and third stage scrubbers  25 ,  26  and  27 , respectively, each operate to remove first, second and third measures of pollutants, respectively, from the contaminated gas entering inlet  22  so that the gas emitted from outlet  23  is substantially free from pollutants. To enhance the efficiency of scrubber system  20 , the present invention includes the provision and method for controlling the amount of liquid chemical reagents added to the first and second stage scrubbers  25  and  26  in order to effectuate the efficient removal of the maximum respective measures of pollutants from the contaminated gas when passing through the first and second stage scrubbers  25  and  26 . To carry out this task, a control assembly  120  may be provided. 
     Control assembly  120 , a block diagram of which may be seen in combination with FIG. 9, is generally comprised of a first sensor  100  (shown also in FIGS. 1,  2 ,  3 ,  6  and  8 ) which may be coupled with inlet  22  adjacent first stage scrubber  25  and a second sensor  101  (shown also in FIG. 2) coupled with opening  78  intermediate second stage scrubber  26  and third stage scrubber  27 . Sensor  100  of control assembly  120  operates to directly monitor and sample the gas passing through inlet  22  prior to entering first stage scrubber  25  to determine the level, measure and/or amount of pollutants present in the contaminated gas at inlet  22 . Similarly, sensors  101  of control assembly  120  operates to directly monitor and sample the gas passing through opening  78  prior to entering third stage scrubber  27  to determine the level, measure and/or amount of pollutants present in the contaminated gas at each respective location. For the purposes of the ensuing discussion, the level, measure and/or amount of pollutants present within the contaminated gas passing through scrubber system may be hereinafter collectively referred to as the concentration of pollutants for ease of discussion. 
     Consistent with the foregoing, sensor  100  and sensor  101  of control assembly  120  may also be coupled with a controller  121  mounted with structure  21  by virtue of conventional electrical interconnections  122  and  123 , respectively. Although controller  121  may be located anywhere along structure  21  and perhaps at a location remote from structure  21 , the present embodiment illustrates controller  120  located at third stage scrubber  27  as illustrated in combination with FIG. 2, although this is not an essential feature. Although not herein specifically described, controller  121  includes conventional electrical circuitry and a conventional microprocessing unit and logic circuitry operative for receiving signals from sensors  100  and  101  and for responding to the signals in a manner to be presently described, controller  121  being programmable by virtue of conventional programming operations for allowing a user to control the operation of scrubber system  20  in a predetermined and selected fashion. 
     As evidenced in FIG. 9, controller  121  may be coupled with pump  48  by virtue of conventional electrical interconnection  124  and to pumps  66  and  68  by virtue of conventional electrical interconnection  125 . In this regard, and as previously intimated, sensor  100  will operate to monitor the concentration of pollutants in the contaminated gas at inlet  22  prior to entry into first stage scrubber  25  and communicate this information in the form of a signal to controller via electrical interconnection  122  to controller  121 . If the concentration of pollutants monitored by sensor  100  are high, controller  121  will send a signal to pump  48  via electrical interconnection  124  to actuate and control pump  48  to correspondingly increase the amount of chemical reagent added to chamber  41  of first stage scrubber  25  to thereby increase the cleaning intensity of first stage scrubber  25  in response to the concentration of pollutants entering first stage scrubber  25  from inlet  22 . Furthermore, if the concentration of pollutants monitored by sensor  100  are low, controller  121  will send a signal to pump  48  via electrical interconnection  124  to actuate and control pump  48  to correspondingly decrease the amount of chemical reagent added to chamber  41  of first stage scrubber  25  to thereby decrease the cleaning intensity of first stage scrubber  25  in response to the concentration of pollutants entering first stage scrubber  25  from inlet  22 . 
     Those having regard toward the relevant art will appreciate that control assembly  120  operates to conserve the liquid chemical reagent supplied from receptacle  44  by selectively actuating pump  48  to add only so much liquid chemical reagent as is necessary to effectively remove the first measure of toxic and/or odoriferous contaminates consistent with normal operation of first stage scrubber  25 . In addition, with sensor  100  located at inlet  22  adjacent first stage scrubber  25 , variations in the measure of pollutants will be immediately detected for effecting the desired and virtually instantaneous actuation of pump  48  to either increase or decrease the amount of liquid chemical reagent supplied to housing  40  in order to accommodate the increased or decreased measure of pollutants in the contaminated gas. Consistent with the present teachings, sensor  100  may be provided as an electrical and conventional hydrogen sulfide sensor/analyzer or other suitable and conventional sensor/analyzer operative for detecting pollutants. 
     Like sensor  100 , sensor  101  will operate to monitor the concentrations of pollutants in the contaminated gas at opening  78  intermediate second stage scrubber  26  and third stage scrubber  27  prior to entry into third stage scrubber  27  and communicate this information in the form of a signal to controller  121  via electrical interconnection  123 . If the concentration of pollutants monitored by sensor  100  are high, controller  121  will send a signal to pump  66  and/or pump  68  to actuate and control pump  66  and/or pump  68  to correspondingly increase the amount of chemical reagent added to chamber  61  of second stage scrubber  26  to thereby increase the cleaning intensity of second stage scrubber  26  in response to the concentration of pollutants present in the fluid passing through opening  78 . Furthermore, if the concentration of pollutants monitored by sensor  100  are low, controller  121  will send a signal to pump  66  and/or pump  68  to actuate and control pump  66  and/or pump  68  to correspondingly decrease the amount of chemical reagent added to chamber  61  of second stage scrubber  26  to thereby decrease the cleaning intensity of second stage scrubber  26  in response to the concentration of pollutants present in the fluid passing through opening  78 . 
     Those having regard toward the relevant art will readily appreciate that control assembly  120  operates to conserve the liquid chemical reagent supplied from receptacle  44  and/or receptacle  65  by selectively actuate pump  66  and/or pump  68  to add only so much liquid chemical reagent as is necessary to effectively remove the second measure of toxic and/or odoriferous contaminates consistent with normal operation of second stage scrubber  26 . In addition, with sensor  101  located at opening  78  intermediate second stage scrubber  26  and third stage scrubber  27 , variations in the measure of pollutants passing through opening  78  will be immediately detected for effecting the desired and virtually instantaneous actuation of pumps  66  and  68  to either increase or decrease the amount of liquid chemical reagent supplied to housing  60  in order to accommodate the increased or decreased concentration of pollutants in the contaminated gas passing through opening  78 . Consistent with the present teachings, sensor  101  may be provided as an electrical and conventional hydrogen sulfide sensor/analyzer or other suitable and conventional sensor/analyzer operative for detecting pollutants. 
     With continuing reference to FIG. 9, the present invention may also be provided with a first sump sensor  130  operative for monitoring the concentration of chemical reagent in the water carried by sump  70  in chamber  41  of first stage scrubber  25 , and a second sump sensor  131  operative for monitoring the concentration of chemical reagents carried by sump  70  in chamber  61  of second stage scrubber  26 . Consistent with conventional practice, sump sensor  130  may be provided as a conventional pH sensor operative for monitoring the relative pH of the water carried by sump  70  in chamber  41 , the relative pH corresponding to the concentration of sodium hydroxide present within the water. Sump sensor  131 , on the other hand, may be provided as a combination pH/oxidation-reduction-potential sensor operative for monitoring not only the pH but also the available oxygen in the water carried by sump  70  in chamber  61 , the amount of available oxygen corresponding to the level of sodium hypochlorite present within the water. 
     In this regard, sump sensor  130  will operate to monitor the concentration of chemical reagent in the water carried by sump  70  in chamber  41  of first stage scrubber  25  and communicate this information in the form of a signal to controller  121  via electrical interconnection  132 . In response to the concentration of chemical reagent monitored by sump sensor  130 , controller  121  may use not only the information provided from sensor  100  but also the information provided from sump sensor  130  to correspondingly send selected signals to pump  48  to either increase the amount of chemical reagent to chamber  41  if the concentrations of pollutants at inlet  22  are high and the concentrations of chemical reagent in the water located in sump  70  within chamber  41  are low, or decrease the amount of chemical reagent to chamber  41  if the concentrations of pollutants at inlet  22  are low the concentrations of chemical reagent in the water located in sump  70  within chamber  41  are correspondingly high. 
     Similarly, sump sensor  131  will operate to monitor the concentration of chemical reagent in the water carried by sump  70  in chamber  61  of second stage scrubber  26  and communicate this information in the form of a signal to controller  121  via electrical interconnection  133 . In response to the concentration of chemical reagent monitored by sump sensor  131 , controller  121  may use not only the information provided from sensor  101  but also the information provided from sump sensor  131  to correspondingly send selected signals to pump  66  and/or pump  68  to either increase the amount of chemical reagent to chamber  61  if the concentrations of pollutants at opening  78  are high the concentrations of chemical reagent in the water located in sump  70  within chamber  61  are low, or decrease the amount of chemical reagent to chamber  61  if the concentrations of pollutants at opening  78  are low the concentrations of chemical reagent in the water located in sump  70  within chamber  61  are correspondingly high. 
     Those skilled in the art will readily appreciate that controller assembly  120  provides a redundant system of directly monitoring the concentrations of pollutants at inlet  22  and at opening  28 , and the concentrations of chemical reagents in sump  70  for facilitating immediate and efficient responses in the amount of chemical reagents added to first stage scrubber  25  and second stage scrubber  26  and to allow a user to ascertain the operating efficiency of wet stage scrubber assembly  24 . Control assembly  120  further operates to optimize the operation of first and second stage scrubbers  25  and  26 , respectively. As a result, the life or longevity of the filtering media  91  carried by the filtering layers  83  in the third stage scrubber  27  may be maximized to inhibit premature build up or saturation of the filtering media  91  with pollutants. 
     To provide flexibility in the operation of scrubber system  20 , the microprocessing unit of the controller  121  may be programmed for actuating pump  48  and pumps  66  and/or  68  in response to predetermined and selected threshold concentrations of pollutants present in the contaminated gas as monitored by sensors  100  and  101 , and in response to predetermined and selected threshold concentrations of chemical reagents present within sump  70  both in first stage scrubber  25  and second stage scrubber  26 . For instance, if a user requires scrubber system  20  to respond to small fluctuations in the concentration of pollutants entering inlet  22  and passing through opening  78 , and/or to small fluctuations in the concentration of chemical reagents with the sump  70  located in first and second stage scrubbers  25  and  26 , a user may program controller  121  to respond accordingly. On the other hand, if a user requires scrubber system  20  to respond only to large fluctuations in the concentration of pollutants entering inlet  22  and passing through opening  78 , and/or to respond only to large fluctuations in the concentrations of chemical reagents with the sump  70  located in first and second stage scrubbers  25  and  26 , a user may program controller  121  to respond accordingly. The ability of a user to program controller  121  in the foregoing manner will save on the cost of chemical reagents, provide flexibility and minimize waste. To carry out this programming, a conventional keypad  140  may be provided and coupled with controller by virtue of conventional electrical interconnection  141 , keypad  140  operative for manual manipulation to allow a user to program desired information into controller  121  to facilitate desired operating parameters of scrubber system  20 . Keypad  140  may be mounted either with structure  21  adjacent controller  121 , or perhaps at a remote location. 
     Over a period of operating time of scrubber system  20 , sensors  100  and  101  will be constantly subjected to high levels pollutants. As a result, sensors  100  and  101  may experience reduced response ability and perhaps total sensor failure over a certain period of operating time. This is particularly true with conventional hydrogen sulfide sensors. Accordingly, the present invention provides a method of periodically cleaning sensors  100  and  101  to substantially eliminate reduced sensor response and sensor failure. The foregoing method may be carried out through the selective programming of controller  121 . In this regard, controller  121  may be programmed such that during operation of scrubber assembly  20 , controller  121  will send a signal to each sensor  100  and  101  via electrical interconnection  122  and  123 , respectively, to actuate a first switch or solenoid carried by each sensor  100  and  101  to toggle each sensor  100  and  101  from monitoring the contaminated gas to monitoring a zero- or fresh-fluid source such as the ambient air. The controller  121  will maintain each sensor  100  and  101  to monitor the fresh-fluid source for a predetermined amount of time, such as ten minutes in a preferred embodiment or other selected and predetermined amount of time, during which sensors  100  and  101  will essentially undergo a cleaning process purging out built up contaminants. After the foregoing predetermined amount of time has passed, controller  121  will send a signal to each sensor  100  and  101  via electrical interconnection  122  and  123 , respectively, to actuate the first switch or solenoid carried by each sensor  100  and  101  to toggle each sensor  100  and  101  from monitoring the fresh-fluid source to the contaminated gas in accordance with normal operation of scrubber system  20 . The foregoing process may be carried out every hour, daily, or at other predetermined intervals during the operation of scrubber system  20  as determined by the user and programmed into controller  121 . 
     In addition to the foregoing, it may also be desirable to monitor sensors  100  and  101  periodically to ascertain whether they are operating within predetermined and selected parameters in accordance with the normal operation of scrubber system  20 . Accordingly, the present invention provides a method of periodically monitoring sensors  100  and  101  that may be carried out through the selective programming of controller  121 . In this regard, controller  121  may be programmed such that during operation of scrubber assembly  20 , controller  121  will periodically send a signal to each sensor  100  and  101  via electrical interconnection  122  and  123 , respectively, and actuate a second switch or solenoid carried by each sensor  100  and  101  to toggle each sensor  100  and  101  from monitoring the contaminated gas to monitoring a calibration source  150  to which each sensor may be coupled. Although calibration source  150  is shown as being common to both sensors  100  and  101 , this is not an essential feature and each sensor  100  and  101  may each be coupled with an individual calibration source consistent with the present teachings. Calibration source  150  may be comprised of a selected and predetermined fluid, such as a 10 PPM (parts/million) hydrogen sulfide gas or other selected gas having a predetermined PPM level of calibration material such as hydrogen sulfide. Sensors  100  and  101  will each monitor the calibration source to determine the relative PPM of the calibration material and will conduct this information in the form of signal via electrical interconnections  122  and  123  to controller  121 . 
     The controller  121  will then compare the monitored PPM values sensed by each sensor  100  and  101  and compare the monitored PPM values with a predetermined and selected range of values that may be programmed into controller  121  by a user. If the monitored PPM values fall within the predetermined and selected range of values programmed into controller  121  by the user, controller will subsequently send a signal back to each sensor  100  and  101  via electrical interconnections  122  and  123 , respectively, actuating the second switch or solenoid of each sensor  100  and  101  to toggle each sensor  100  and  101  from calibration source  150  and back to the contaminated gas at inlet  22  and opening  78 , respectively, to resume normal operation of scrubber system  20 . If, on the other hand, the monitored PPM values fall outside the predetermined and selected range of values programmed into controller  121  by the user, controller will subsequently send a signal back to each sensor  100  and  101  via electrical interconnections  122  and  123 , respectively, actuating the second switch or solenoid of each sensor  100  and  101  to toggle each sensor  100  and  101  from calibration source  150  and back to the contaminated gas at inlet  22  and opening  78 , respectively, to resume normal operation of scrubber system  20 . However, controller  121  will also actuate an indicator (such as a light or an audible alarm carried by controller  121 ) for alerting the user that the sensor  100 . and/or sensor  101  requires recalibration and/or maintenance. The foregoing process may be carried out daily, weekly, monthly or at other predetermined intervals during the operation of scrubber system  20  as determined by the user and programmed into controller  121 . 
     The present invention has been described above with reference to a preferred embodiment. However, those skilled in the art will recognize that changes and modifications may be made in the described embodiments without departing from the nature and scope of the present invention. For instance, scrubber system  20  may be provided with a walkway  103  (shown in FIGS. 1,  2 ,  6 ,  7  and  8 ) coupled with structure  21  upon which workers may walk and access scrubber system  20  as needed for maintenance and repair. Furthermore, and as shown in FIG. 8 illustrating a rear elevational view of scrubber system  20 , receptacles  44  and  65  of liquid delivery system  28  may each be provided with a transparent fluid level indicator  104  and  105 , respectively, for allowing users to easily ascertain the level of liquid chemical reagent within each receptacle  44  and  65 . Each receptacle  44  and  65  may also be provided with a conventional fill and drain port  106  and  107 , respectively, for allowing users to easily fill and drain each receptacle  44  and  65  as needed for the normal operation of scrubber system  20 . Furthermore, housing  80  may be provided with a door  151  as shown in FIG.  1  and accessible for accessing a storage compartment (not shown) bound by housing  80  of third stage scrubber  27  in which selected tools and other selected items may be desirably stored. 
     In addition to the foregoing, housings  40  and  60  of first and second stage scrubbers  25  and  26  may be provided with removable access panels that may preferably extend along substantially the entire width of each housing  40  and  60 , respectively, and operative for allowing the easy installation and removal of media as required for normal and efficient operation of scrubber assembly  20 . Consistent with the foregoing, and as shown in FIG. 1, housings  40  and  60  may each be provided with removable first or top panels  110  located on top of each housing  40  and  60  and removable second or bottom panels  111  located toward the bottom of each housing  40  and  60 . Top and bottom panels  110  and  111  may be detachably mounted with each housing  40  and  60  by virtue of convention nut and bolt fasteners or other suitable fasteners operative for facilitating easy installation and removal. In this manner of orientation of panels  110  and  111 , top panels  110  may be removed and media easily introduced through openings occluded by the top panels  110  and then reinstalled when full. Furthermore, bottom panels  111  may be removed and media easily removed through openings occluded by the bottom panels  111 . With the bottom panels  111  located proximate the bottom of each housing  40  and  60 , gravity will cause the media contained by each housing  40  and  60  to fall outwardly from the openings occluded by the bottom panels  111  without the need of enlisting additional mechanical equipment to facilitate removal. When each housing  40  is empty, bottom panels  111  may be reinstalled prior to filling housings  40  and  60  with fresh media. Because each housing  40  and  60  includes top and bottom panels  110  and  111 , the media of each individual housing  40  and  60  may be independently maintained in the foregoing manner. 
     Those having regard toward the art will readily appreciate that because the volume of water located within sump  70  may be on the order of perhaps 1000-3000 gallons, variations in pH and oxygen in the water corresponding to the concentrations of chemical reagents present within sump  70  at first stage scrubber  25  and second stage scrubber  26  occur very slowly. To enhance the ability to more accurately assess the concentrations of chemical reagents present within sump  70  at first and second stage scrubbers  25  and  26 , attention is directed to FIG. 10 illustrating a vertical sectional view of a wet stage scrubber generally designated at  160  and of which is intended to be generally representative of first stage scrubber  25  and second stage scrubber  26 . Like first and second wet stage scrubbers  25  and  26 , wet stage scrubber  160  includes a housing  161  bounding a chamber  162  and a sump  163 . Also included is at least one nozzle  164  mounted with housing  161  for communicating chemical reagent into chamber  162  in the manner and form previously described in combination with first and second wet stage scrubbers  25  and  26 . As illustrated, located within chamber  162  is an intermediate sump  165  located spaced from or otherwise elevated from sump  163 . Also included is a partition or intermediate floor  166  dividing chamber  162  into a first chamber portion  167  of which may be filled with media  170  (much like media  42  and media  62  previously discussed) and a second chamber portion  168  encompassing sump  163 . Intermediate sump  165  encompassing a volume of perhaps 100-200 gallons or other predetermined volume substantially less than the total volume of sump  163 . 
     During operation, the water and chemical reagents dispersed into and through first chamber portion  167  from nozzle  164  will fall through media  170  and conduct into intermediate sump  165  by virtue of partition  166  and then outwardly through a drain  172  formed with intermediate sump  165  for receipt by sump  163 . Because intermediate sump  165  encompasses a volume substantially less than the volume of sump  163 , variations in the concentrations of chemical reagents corresponding to variations in pH and/or available oxygen concentrations will occur rapidly and be relatively dramatic as compared to the variations in concentrations of chemical reagents within sump  163 . Accordingly, it may be desirable to locate sump sensors within intermediate sump  165  to more accurately, quickly and efficiently discern variations in concentrations of chemical reagents present within sump  163 . Thus, first and second wet stage scrubbers  25  and  26  may each be fitted with partition  166  and intermediate sump  165  in accordance with the foregoing discussion. Sump sensor  130  may then be correspondingly located within the intermediate sump of first wet stage scrubber  25  and sump sensor  131  located within the intermediate sump of second wet stage scrubber  26 . In this manner of placement, sump sensors  130  and  131 , in combination with each respective intermediate sump, will operate to immediately detect variations in pH and/or available oxygen concentrations, rather than if located within sump  70 , and communicate the information to controller  121  of control assembly  120  as previously discussed in accordance with normal operation. Because intermediate sump  165  allows sump sensors  130  and  131  to measure acute variations in the concentrations of chemical reagents, a user may use sump sensors  130  and  131  in control assembly  120  in the foregoing manner independently of sensors  100  and  101  if desired. 
     Various changes and modifications to the embodiment herein chosen for purposes of illustration will readily occur to those skilled in the art. To the extent that such modifications and variations do not depart from the spirit of the invention, they are intended to be included within the scope thereof which is assessed only by a fair interpretation of the following claims.