Abstract:
An air treatment system and method that uses inertial moisture separators in two stages for removing moisture present in intake air entering the air treatment system, thereby increasing the effectiveness and lifespan of high efficiency filters that otherwise may become clogged by accumulating moisture.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to air filtration and demoisturizing systems for gas turbines. 
     Gas turbines include inlet air treatment systems that remove dust and moisture from air that is channeled to the compressor of the gas turbine. Some inlet air treatment systems include moisture separators and coalescing pads that remove moisture from intake air, and pre-filters and final filters that remove dust and debris from the intake air. During normal operating conditions, it is desired to have the inlet air treatment system channel clean, dehydrated air to the gas turbine compressor with minimal airflow disruption and air pressure drop. Eventually, used coalescers and filters become clogged and cause an excessive air pressure drop under normal operating conditions. Over time, the pressure drop across these air treatment elements results in reducing the operating efficiency of the gas turbine. In some instances, the reduced air pressure may cause a compressor surge that may damage the compressor. 
     Accordingly, it is desirable to provide an air treatment system and method that minimizes clogging of air treatment elements, such as air filters, to avoid a reduced air pressure that may cause a compressor surge. Moisture removal systems currently operate either 1 or 2 vane banks that use inertial separation to remove water. One bank of these vanes is placed in front of the filters to remove bulk water, and then a second bank (if used) is place behind the last filter to prevent moisture from reaching the gas turbine. 
     The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. 
     BRIEF DESCRIPTION OF THE INVENTION 
     An air treatment system and method that uses inertial moisture separators in two stages for removing moisture present in intake air entering the air treatment system, thereby increasing the effectiveness and lifespan of high efficiency filters that otherwise may become clogged by accumulating moisture. In one embodiment, the layout of the vane banks is rearranged to place the second bank behind the first set of filters and place the final filters behind this second bank. In this arrangement the final filters are kept away from any water that may be in the intake system. An advantage that may be realized in the practice of some disclosed embodiments of the air treatment system is improved air filtration efficiency and reduced maintenance frequency for air filtration elements in an air treatment system. Also, the final filters do not have to be hydrophobically treated and the issues with water reaction on the final filters is diminished. 
     In one embodiment, a multi-stage filtration system is disclosed. The system comprises a first inertial moisture separator in a first stage of the filtration system for removing moisture present in air entering the filtration system, a coalescing first filter in a second stage of the filtration system for removing particulate matter and for coalescing moisture present in the air that has passed through the first stage of the filtration system, and a second inertial moisture separator in a third stage of the filtration system for removing coalesced moisture present in the air that has passed through the second stage of the filtration system. 
     In another embodiment, a filter house is disclosed. The filter house comprises an air intake hood, a first inertial moisture separator in a first stage of the filter house behind the air intake hood, the inertial moisture separator configured to remove water droplets from intake air entering the filter house, a coalescing pre-filter in a second stage of the filter house configured to remove particles in the air that has passed through the first stage of the filter house and to coalesce water droplets in the air that has passed through the first stage of the filter house, and a second inertial moisture separator in a third stage of the filter house configured to remove from the air that has passed through the second stage of the filter house water droplets coalesced by the coalescing pre-filters. 
     In yet another embodiment, a method of filtering air to be used in a gas turbine is disclosed. The method comprises removing water droplets from incoming air using a first inertial moisture separator, after the step of removing the water droplets, filtering particles from the incoming air and coalescing water droplets that have passed through the first inertial moisture separator, and after the step of filtering particles and coalescing water droplets, removing water droplets from the incoming air using a second inertial moisture separator. 
     This brief description of the invention is intended only to provide a brief overview of subject matter disclosed herein according to one or more illustrative embodiments, and does not serve as a guide to interpreting the claims or to define or limit the scope of the invention, which is defined only by the appended claims. This brief description is provided to introduce an illustrative selection of concepts in a simplified form that are further described below in the detailed description. This brief description is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features of the invention can be understood, a detailed description of the invention may be had by reference to certain embodiments, some of which are illustrated in the accompanying drawings. It is to be noted, however, that the drawings illustrate only certain embodiments of this invention and are therefore not to be considered limiting of its scope, for the scope of the invention encompasses other equally effective embodiments. The drawings are not necessarily to scale, emphasis generally being placed upon illustrating the features of certain embodiments of the invention. In the drawings, like numerals are used to indicate like parts throughout the various views. Thus, for further understanding of the invention, reference can be made to the following detailed description, read in connection with the drawings in which: 
         FIG. 1  is a schematic view of an exemplary air filtering system; 
         FIG. 2  is a schematic view of an exemplary multi-stage filter assembly that may be used with the exemplary air filtering system shown in  FIG. 1 ; and 
         FIG. 3  is a flowchart of a method of operating the air filtering system shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates an embodiment of a portion of an air treatment system  100 , e.g., a filter house, that generally includes a housing  101 , a plurality of air intake hoods  102  that are vertically spaced and mounted to the front of the housing  101  and are open to the atmosphere via openings  103  at their bottom portions. Intake air  104  is drawn through these openings  103  and through a plurality of spaced apart air treatment elements  105 , then into a narrowing portion of air conduit  106 , such as an air duct, that channels clean dehydrated air in a downstream direction  107  toward a gas turbine, for example. The air treatment elements  105  may be sufficiently separated to allow service personnel to enter between them for replacement and/or repair of the air treatment elements  105 . 
     A first stage of the plurality of air treatment elements  105  may include demoisturizing elements which, in one embodiment, include inertial moisture separators  108 , also known as marine vane separators, positioned to remove water droplets from intake air  104 . This first stage of the air treatment system  100  may be configured to capture water droplets having a size on the order of about 5 μm (microns) and greater. Such captured water droplets may be allowed to drain downward by force of gravity wherein the captured water may eventually be channeled to a drainage system. 
     In one embodiment, a second stage of the air treatment system  100  may include coalescing pre-filters  109  that provide a coarse filtration to remove larger particles from the intake air  104  and to coalesce the smaller water droplets that have passed through the first stage into larger water droplets. The filter media in the second stage coalescing pre-filters  109  may be configured to admit finer particles, e.g. less than about 1-2 μm while trapping the coarser particles. Because the larger droplets coalesced by the second stage of the air treatment system often clog, or “blind”, finer filter media, a third stage of the air treatment system  100  may be configured to include a second bank of inertial moisture separators  110 , in the form of marine vane separators  108 , as in the first stage, to further dehydrate the intake air  104  by removing the coalesced water droplets. A fourth stage of the air treatment system  100  may include finer air filters  111  configured to remove fine dust and other particles on the order of about 0.1 μm or larger in size. This final filtering stage may alternatively be configured as a dual stage filter utilizing an intermediate filter bank for removing particles from the intake air  104  on the order of 0.3 μm to 0.4 μm or larger in size followed by the 0.1 μm filter. Because of the redundant inertial moisture separators  110  in the third stage (redundant with the first stage inertial moisture separators  108 ), the final finer filter stage  111  operates more efficiently and requires less maintenance due to less moisture clogging the filter media therein. After this fourth stage of the air treatment system  100  the intake air  104  may pass into conduit  106  in the downstream direction  107  toward a gas turbine, for example. The gas turbine typically provides the suction force for drawing the intake air  104  through intake hood openings  103  and through the air treatment elements  105 . 
       FIG. 2  generally illustrates the progressive stage treatment of the intake air flow  104  as the air treatment elements  105  remove water and contaminants therefrom. Ambient air entering the air treatment system  100  includes moisture of various droplet sizes  208  that is partially captured by the first stage  220  inertial moisture separator  108  which removes the larger sized water droplets, such as those sized from approximately 5 μm and larger, from intake air  104 . This leaves smaller sized droplets  209  in the intake air  104  continuing through the air treatment system  100  into a second stage  222  coalescing pre-filter  109  which acts to coalesce the smaller sized water droplets  209  which have passed through the first stage  220 . A portion of the smaller water droplets  209  are coalesced into larger sized water droplets  210  as the air flow  104  passes through the coalescing pre-filter  109 . In addition to coalescing smaller sized droplets  209  the coalescing pre-filter  109  also filters dust particles and other debris, e.g. on the order of about 1-2 μm and larger in size, from the air flow  104 . 
     A third stage  224  inertial moisture separator  110  again captures larger water droplets, e.g., on the order of about 5 μm in size and greater, leaving sufficiently demoisturized intake air  104  with a small amount of miniscule water droplets  211  that preserves the efficient operation of the final stage  226  of air filtration. Air filter  111  removes fine debris and dust particles from the intake air  104 , e.g. on the order of about 0.1 μm and larger. As described above, this final filtration stage  226  may include dual filters which removes fine dust and debris via a two stage filter. The filter media used in the fourth stage  226  is often treated with a hydrophobic coating which acts to resist moisture from becoming clogged therein. However, over time, as the hydrophobic treatment wears off, water tends to clog, or “blind”, the finer filter  111  which reduces its effectiveness and increases a differential pressure across the final filter  111 , potentially shortening its life, requiring more frequent replacement, and negatively affecting operation of the downstream gas turbine. Such high efficiency air filters can have a severe reaction to water and cause a large differential air pressure drop requiring a shutdown of downstream gas turbines. Thus, there is an advantage when using these filter media to keep them as dry as possible. The redundant inertial moisture separators  108 ,  110  reduce these deleterious effects. 
       FIG. 3  illustrates a flow chart representing a method of operating  300  the air treatment system  100 . In the first step  301 , water droplets are removed from intake air  104  using inertial moisture separators  108  in a first stage  220  of the air treatment system  100 . In the next step  302 , dust particles are removed from intake air  104  and moisture that passed through the first stage  220  is coalesced using coalescing pre-filters  109  in a second stage  222  of the air treatment system  100 . In the next step  303 , coalesced water droplets are again removed from intake air  104  using inertial moisture separators  110  in a third stage  224  of the air treatment system  100 . In the next step  304 , finer dust particles are removed from intake air  104  using a high efficiency filter  111  in a fourth stage  226  of the air treatment system  100 . The fourth stage may alternatively include an intermediate filter just prior to the final fine filter for a dual-filter implementation in the fourth stage. 
     In view of the foregoing, embodiments of the invention avoids unnecessary differential pressure increases, improves air filtration efficiency, and reduces maintenance frequency for air filtration elements in an air treatment system. A technical effect is an air treatment system that maximizes up time for gas turbine compressors. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.