Abstract:
A waterproof and salt repellant media for use in a gas turbine intake filter is provided. The media includes a first composite material layer having a polypropylene melt-blown layer and a polypropylene spun-bond layer, and a second composite material layer having a polyester spun-bond material coated with PTFE.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of U.S. Provisional Application Ser. No. 61/583,426 filed Jan. 5, 2012, the contents of which are incorporated herein. 
     
    
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    N/A 
       FIELD OF THE INVENTION 
       [0003]    The present invention generally relates to a waterproof and salt repellant media and a filter formed from the media. 
       DESCRIPTION OF THE PRIOR ART 
       [0004]    A large variety of filters are utilized to remove particulates, pollutants and other undesirable materials from fluids, such as liquids or gas. The filters come in a variety of shapes and can include one of many types of filter media. 
         [0005]    One known filter media is disclosed in U.S. Publication No. 2008/0302074 (“the &#39;074 Publication”). The &#39;074 Publication describes a multiple layer filter media for removing particulates from a fluid stream. The media includes a composite having a first thermoplastic layer, a second thermoplastic layer, and an expanded PTFE or ePTFE (expanded Polytetrafluoroethylene) membrane layer sandwiched between the first and second thermoplastic layers. 
         [0006]    PTFE membranes are formed from stretching a PTFE film. Filters with PTFE membranes have several drawbacks. For example, PTFE membranes are very expensive. In this regard, the filter media disclosed in the &#39;074 Publication is extremely expensive given the use of the PTFE membrane in the composite. 
         [0007]    Filters are needed, in particular, for gas turbines. Such turbines include air-intake components. However, contaminates in the air can cause problems with the turbine if not removed. For example, small particles in the intake air may deposit on the blades of the turbine and cause fouling of the compressor. Accordingly, it is necessary to provide an adequate filter system to remove such pollutants. 
         [0008]    The common contaminants come from three main sources: water, dust and emissions. These contaminants can cause erosion, fouling, particle fusion and corrosion. Particularly the present invention is used for coastal, marine or offshore applications in which a high concentration of moisture and salt exist in the atmosphere. Salt is a primary cause for corrosion in a gas turbine. Also, a high concentration of salt can lead to fouling of the compressor blades. Conventional high efficiency filters do not prevent water penetration. Therefore, the water can pass through the filter media to the inlet of the gas turbine. This water can dissolve dry salt particles into salt solution, and transfer them from one side of the filter to the other, releasing them into the gas turbine. Additionally, the moisture can load the filters causing a remarkably high pressure drop. It is critical to design a high efficiency filter with moisture resistant and water control. 
         [0009]    The present invention is designed to overcome problems associated with prior designs and provide an enhanced media and filter for high concentration of moisture and salt applications. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention provides a cost effective filter media that is waterproof and repels salt solutions. Moreover, the present invention provides low flow restriction and is low cost in comparison with existing filter technology. 
         [0011]    The filter media of the present invention is particularly useful as a gas turbine air intake filter. Specifically, the filter is designed to remove water droplets and salt solutions that may occur in harsh conditions or environments, such as offshore platforms and tropical high moisture areas. 
         [0012]    In accordance with an embodiment of the invention, a filter media is provided having a first composite material layer and a second composite material layer. The first composite material layer includes a melt-blown material layer and a spun-bond material layer. The second composite material layer includes a material with a hydrophobic coating. 
         [0013]    In accordance with another embodiment of the invention, an improved filter media is provided having a first composite material layer and a second composite material layer. The first composite material layer includes a layer of polypropylene melt-blown and a layer of polypropylene spun-bond attached to the polypropylene melt-blown layer. The second composite material layer includes a polyester (i.e., PET) spun-bond with a hydrophobic treatment. Preferably, the hydrophobic treatment includes providing a hydrophobic coating, such as a PTFE coating, on the polyester spun-bond material. The hydrophobic coating provides a hydrophobic property such that salt water solution or tiny water aerosols will be stopped by the low surface tension of the media. 
         [0014]    The first composite material layer is positioned on top of the second composite material layer. The filter media is positioned so that air flow contacts the top or first composite material layer first and then travels through the second composite material layer. 
         [0015]    The composite material layers are bound together. Preferably, the composite material layers are laminated by an ultra-sonic bonding technique. 
         [0016]    The filter media can be pleated and be utilized in a filter cartridge. The filter cartridge housing the media can then be utilized in a variety of equipment, such as the air-intake of a gas turbine machine. 
         [0017]    Coating the polyester layer with a hydrophobic coating, such as a PTFE coating, is less expensive than providing a full membrane layer of ePTFE. Accordingly, the cost of the present filter media is significantly less than the prior media utilizing ePTFE membranes. Such membranes can range from 4 to 10 times the cost of a polyester spunbond with a hydrophobic coating. 
         [0018]    The hydrophobic coating can be one of two types. The coating can be a fluorochemical coating, or an organic silicone type coating. 
         [0019]    Further aspects of the invention are disclosed in the description of the invention, including the Figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    To understand the present invention, it will now be described by way of example, with reference to the accompanying drawings in which: 
           [0021]      FIG. 1  is a schematic diagram of a partially exploded cross-section of filter media made in accordance with the present invention, the diagram also showing the direction of airflow. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    While this invention is susceptible of embodiments in many different forms, there is shown in the drawings what will herein be described in detail preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments illustrated. 
         [0023]    As illustrated in the partially exploded cross-sectional view of  FIG. 1 , a filter media  10  is provided having a first composite material layer  12  and a second composite material layer  14 . Arrows  16  show the fluid flow direction through the composite material layers  12 ,  14  of the filter media  10 . The filter media  10  is typically pleated for use in a filter cartridge or panel filter or holder. 
         [0024]    The first composite material layer  12  can be a thermoplastic fibrous material forming a spun-bond scrim. The thermoplastic materials can be polypropylene, nylon, polyester or polyethylene. Preferably, the first composite material layer  12  is formed from a polypropylene melt-blown  18  and a polypropylene spun-bond  20  on top of the melt-blown. The polypropylene spun-bond layer  20  will protect the melt-blown layer  18  during pleating and handling of the material. 
         [0025]    The polypropylene spun-bond layer  20  has a low surface energy. This will facilitate repelling water droplets. 
         [0026]    The polypropylene melt-blown layer  18  functions to coalesce small water droplets into bigger droplets. Gravity then pulls the large droplets to drain down vertically from the filter media  10 . 
         [0027]    The melt-blown layer  18  also functions to trap contaminants. The melt-blown layer includes randomly laid small fibers, typically in the range of 1 to 7 microns. The fibers form a tortuous path and add depth to the composite material layer  12 , which increases the contaminant holding capacity of the filter media  10 . 
         [0028]    The melt-blown layer  18  is formed to have a thickness of 0.40 to 0.70 millimeters (preferably 0.46 to 0.66 millimeters) and a basis weight of 10-60 grams per square meter (preferably 20-40 grams per square meter). 
         [0029]    The second composite material layer  14  can be a thermoplastic fibrous media and wetlaid paper. The thermoplastic fibrous material can be spunbond, hydroentangles, and carded media. The material can be Polypropylene, Polyethylene, Polyester, and Nylon. The wetlaid paper can be fiberglass paper and cellulose paper. Preferably, the second composite layer  14  is formed from a polyester spun-bond with a hydrophobic treatment or coating  22 . Preferably, the polyester spun-bond is coated with a hydrophobic coating, such as a PTFE coating having hydrophobic properties. The hydrophobic properties lower the surface tension of the material and increase water repellency. 
         [0030]    There are several methods for coating the spun-bond media with a material having a hydrophobic property. In accordance with one method a fibrous media is immersed in a PTFE bath, that is, a solution containing fluorocarbon chemicals, and is then dried with heat. 
         [0031]    The spun-bond media with hydrophobic coating has a water entry pressure greater than a 10 inch water column (W.G.). Preferably, the pressure is greater than 20 inch W.G. 
         [0032]    The second composite material layer  14  is formed to a thickness of 0.30 to 0.50 millimeters (preferably 0.38 to 0.43 millimeters), and a basis weight of 70 to 300 grams per square meter (preferably 170 grams per square meter). The polyester layer with the hydrophobic coating has an air permeability of 10 to 50 cfm (preferably 23 cfm). 
         [0033]    The first composite material layer  12  is bound together with the second composite material layer  14 . Preferably, the first and second composite material layers  12 ,  14  are laminated together. This can be done with an ultra-sonic bonding technique. 
         [0034]    Many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood within the scope of the appended claims the invention may be protected otherwise than as specifically described.