Abstract:
A resistive heating system for a combustion turbine susceptible to inlet air filter house component and compressor icing includes a plurality of heating panels (bundles) arranged in a substantially-planar array, adapted to be located on or adjacent to the turbine&#39;s inlet air filter house. Each heating panel is provided with one or more electrically-resistive heating elements; and a controller for selectively activating the resistive heating elements on each of the plurality of heating panels.

Description:
BACKGROUND 
       [0001]    The present application relates generally to combustion turbine plants and more particularly, to an anti-icing heating system arrangement for a combustion turbine inlet filter house. 
         [0002]    Combustion turbine engines typically include a compressor for compressing incoming air, a combustor for mixing fuel with the compressed air and igniting a fuel/air mixture to form a high temperature gas stream, and a turbine section driven by the high temperature gas stream. 
         [0003]    Combustion turbines are utilized globally for electric power generation or as mechanical drives for operating pumps and compressors, under a variety of climatic conditions. Operation during cold ambient temperature and high humidity conditions oftentimes causes ice to build up on the turbine inlet filter house components. Frequently this ice build-up on air filtration elements (bird screens, moisture separators, coalescer filters, and filtration modules) is severe enough to restrict air flow and to increase the inlet air pressure drop across the filter house thus leading to combustion turbine performance loss or even shut down. Precipitating icing forms when water ingested as liquid or solid at temperature near or below freezing (wet snow, freezing rain, etc.) adheres to most exposed surfaces, causing ice buildup. Also, ice formation occurs when saturated cooled air comes in contact with colder filter house surfaces. The common approach to manage inlet ice build-up is to remove the moisture separators and coalescer filters installed in weather hood and heat the ambient air upstream of the air filter modules using hot air or, heating coils supplied either with steam or hot water/glycol mixture. 
         [0004]    Some available methods use the existing turbine Inlet Bleed Heat (IBH) system to provide heat for anti-icing. Based on environmental conditions and filter house design parameters, this is often insufficient. In such cases, an independent anti-icing system is sometimes retrofitted into the filter house. With coil-based systems, heating coils are designed and placed ahead of the inlet filters to provide heating during ambient conditions that promote formation of ice on the air filters, interior filter house walls, as well as on downstream gas turbine components such as inlet guide vanes and compressor first stage blades. For coil-based systems, heating is supplied to the coils in the form of hot water water/glycol mixture or low pressure (LP) steam. 
         [0005]    These commonly-utilized solutions are capital-cost-intensive and negatively impact production efficiency through the operating year due to the addition air flow restriction (pressure drop) imposed by, for example, the heating coils. 
         [0006]    Accordingly, there remains a need for a relatively simple but effective, low-cost system for preventing ice build-up on bird screen and/or moisture separators and air filters in the filter house of combustion turbine plants, particularly when operating in cold, humid environments. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    In one exemplary but nonlimiting embodiment, the present invention relates to a resistive heating system for a combustion turbine susceptible to inlet air filter house component and compressor icing, the system comprising a plurality of heater bundles arranged in a substantially-planar array, adapted to be located on or adjacent the turbine inlet air filter house; each heater bundle provided with one or more electrically-resistive heating elements; and a controller for selectively activating the resistive heating elements on each of the plurality of heater bundles. 
         [0008]    In another exemplary but nonlimiting aspect, the invention relates to a turbine inlet filter house incorporating an anti-icing heating system comprising an inlet filter house having an air inlet and an air outlet, a bird screen and/or moisture separator and an air filter downstream of the bird screen and/or moisture separator; one of the bird screen and/or moisture separator and the air filter provided on a surface thereof with at least one electrically-resistive heating element shaped and arranged to raise a surface temperature of the bird screen and/or moisture separator and the air filter. 
         [0009]    In still another exemplary but nonlimiting aspect, the invention provides a turbine inlet filter house incorporating an anti-icing system comprising an inlet filter house having an inlet and the outlet and supporting at least one filter at or near the inlet; an elongated electrically-resistive heating element supported on a heater bundle located upstream of the inlet filter house; at least one temperature sensor supported on the heater bundle; and a control system for activating the electrically-resistive heating element as a function of surface temperature of the heater bundle as determined by the at least one temperature sensor. 
         [0010]    The invention will now be described in greater detail in connection with the drawings identified below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a partial schematic of a combustion turbine inlet filter house; 
           [0012]      FIG. 2  is a schematic diagram of an exemplary but nonlimiting anti-icing-resistive heating system applied to an inlet filter or bird screen and/or moisture separator in accordance with the invention; 
           [0013]      FIG. 3  is a partial schematic of a combustion turbine inlet filter house incorporating an anti-icing-resistive heating system in accordance with a second exemplary but nonlimiting embodiment; and 
           [0014]      FIG. 4  is a simplified schematic view illustrating a resistive heating system in accordance with an exemplary but nonlimiting embodiment, combined with a conventional Inlet Bleed Heat (IBH) system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]      FIG. 1  illustrates in simplified schematic form a typical elevated combustion turbine filter house  10  including an air inlet  12 , a filter section  14  and outlet duct section  16  leading to the compressor (not shown). The filter section may include one or more arrays (modules)  18 ,  20  of stacked, vertically-oriented air filters described further below. The inlet section  12  may include a vertically-arranged weather hood  22 , each fitted with a plurality of horizontally-oriented bird screen and/or moisture separators  24  (sometimes referred to herein simply as a “screen”), also described further below. The bird screen and/or moisture separators  24  and air filters  18 ,  20  ensure that only filtered air reaches the internal components of the turbine. The bird screen and/or moisture separators  24  are exposed to atmosphere and are particularly vulnerable to ice-build-up when the turbine is operating in cold and humid ambient, conditions. 
         [0016]      FIG. 2  illustrates one exemplary but nonlimiting embodiment of a resistive heating system for use with the filter house shown in  FIG. 1 . More specifically, and with reference to a single, otherwise conventional bird screen and/or moisture separator  24 , the resistive heating system is arranged to include plural, independent heating subsections or zones, exemplified by subsections or zones  26 ,  28 , recognizing that there may be, for example, two vertically aligned rows of seven or more subsections or heating zones for each bird screen and/or moisture separator or air filter. Other configurations are within the scope of the invention, it being understood that different inlet house configurations, dimensions, etc. will require variations in screen and/or filter layouts. Each subsection or zone may include one or more electrical resistance elements, such heat-tracing cables  30 ,  32 , respectively, laid out in predetermined patterns on the screen  24  to ensure sufficient heating of the respective zones to substantially eliminate or prevent the build-up of ice on the screen. It will be appreciated that similar resistive heating elements may be provided in designated heating zones on each of the bird screen and/or moisture separators  24  at the inlet to the filter house. It will also be understood that the cables are applied directly to the screen filtering media, e.g., wires rods or wire mesh, etc.). 
         [0017]    The resistive heat-tracing cables  30 ,  32  (or other suitable resistive heating elements) within each heating zone may be powered by a redundant electrical power source  34  and be automatically controlled by a surface temperature thermostatic system. In the exemplary but nonlimiting example, thermocouples  35  may be used to monitor surface temperature sensors (or other Thermally Resistive Devices (RTDs)) within the designated screen sections or zones  26 ,  28 . A thermostatic control system  36  will continuously monitor the inlet air screen surface temperatures at multiple locations (i.e., within the various heating zones  26 ,  28  etc.) and will energize the resistive heat-tracing cables  30 ,  32  in the assigned zones as needed. The control system  36  will interface with the power plant control system (not shown) so as to provide control capability from the plant control center. Alternatively, separately controlled heat-tracing cable arrangements may be installed within the individual zones. Thus, the resistive heating system is thermostatically controlled with the ability to automatically or manually raise or lower the surface temperature to compensate for ambient excursions in the variously designated zones or in subdivided areas of those zones. 
         [0018]    It will be appreciated that a similar resistive heating arrangement may be employed with respect to the inlet air filters  18  and/or  20 , so that for ease of understanding, the bird screen and/or moisture separator  24  in  FIG. 2  may also be regarded as an inlet filter  18  or  20  for purposes of understanding the invention described herein. In addition to the extent a bird screen and/or moisture separator is in fact a coarse filter, the term “filter” as used herein broadly embraces both air filters and bird screen and/or moisture separators used in turbine inlet filter houses, with resistive heating elements applied to the filter media. 
         [0019]    In an example embodiment, the resistive heating system might increase the ambient air temperature at the inlet house from, e.g., 20-22° F. to&gt;32° F. but the threshold temperatures for activating and deactivating the resistive system may also vary. 
         [0020]      FIG. 3  illustrates a second exemplary but nonlimiting embodiment. Here, a resistive heating system  38  is located in a separate steel structure in front of or upstream of the inlet  40  to the filter house  42 . The structure is preferably electrically isolated from the filter house for both personnel and operational safety. In the specific embodiment shown, two horizontal rows  44 ,  46  of heater panels  48  are located, one above the other, with each row again comprised of seven heater bundles. It will be understood that the number of rows and the number of heater bundles in each row may vary with requirements as already noted above. 
         [0021]    Each heater bundle  48  includes one or more electrical resistance heater element  50 , again laid out in a predetermined pattern on the panel to ensure sufficient heating to substantially eliminate or prevent the build-up of ice on the bird screen and/or moisture separators and air filters behind or downstream of the heating bundles. Alternatively, each bundle  48  may include plural (for example, nine) independently controlled heater sets each comprised of (for example, three) heater elements  50 . The electric power to each heater bundle is supplied from an electric panel  56 . In an exemplary embodiment, each panel  56  may be 48″H×36″W×10″D. The panels should be UL or CE approved and “climate controlled” to ensure a range of operation and storage temperatures of −20 to 122 deg. F. 
         [0022]    Each heater bundle incorporates an independently controlled closed loop temperature controller to maintain the air temperature gradient at the compressor bellmouth within required limits, e.g., plus or minus 5 F independent of combustion turbine load and filter house physical configuration (symmetrical or non-symmetrical), and air velocity profile. 
         [0023]    Each heater bundle is supplied with a temperature sensor (e.g., a thermocouple, one shown at  52 ) to measure air temperature downstream of the respective heater bundle. As shown in  FIG. 3 , the fourteen bundles are electrically connected via conduits  54  (enclosing fourteen X nine electrical circuits) to control panels  56  located at ground level, below the elevated inlet filter house. An exemplary electrical rating requirement for each heater bundle is 275 kW, 400V/3 phase. The control panels  56  include individual temperature control modules for controlling the respective heater bundles  48 , and their respective plural heating elements. The exact location of the control panels may vary with specific applications. In use, a signal from the temperature sensor  52  is routed to the temperature controller mounted in the control panel  56 . The controller turns the power on and off in a pre-specified sequence or regulates the voltage of electrical supply to each heater element set  50  to maintain the exit air temperature downstream of the heater bundle at the desired setpoint to insure that air humidity ratio is less than a pre-specified threshold for each temperature. A 4-20 mA output signal is available from the controller that could be used to display heating rate of each heater bundle in terms of percent full capacity. 
         [0024]    Each heating element  50  is supplied also with an over-temperature-detection-and-control to prevent overheating of heating elements in absence of air flow. 
         [0025]    The above described features/operation applies as well to the first described embodiment shown in  FIGS. 1 and 2 . It will also be understood that the heater bundles  48  located upstream of the bird screen and/or moisture separator could also be located within the filter house, upstream of the air filters (and downstream of the bird screen and/or moisture separators). Such a system is shown as  FIG. 4  where a resistive heating system  58  as described herein (either the system of  FIG. 2  or the system of  FIG. 3 ) is located adjacent or within the inlet portion  64  of a filter house  62 . Within the filter house inlet portion, there is a conventional IBH system  66  in which a main pipe header from the turbine supplies a hot compressor air to a pipe manifold. The manifold routes the heated air to an array of pipes that are located within (or adjacent to) the inlet to thereby heat the inlet air. Here, the resistive heating system controller  60  communicates with the IBH system controller  68  so as to integrate the systems and apportion the inlet heating function as desired or needed. 
         [0026]    Still other applications are possible. For example, the resistive heating system described herein could be employed for zonal control of a bleed-heat injection system if so equipped. 
         [0027]    Additional commercial advantages include simplicity in that the system can be designed and operated without the need to provide additional process controller to accommodate the additional sequencing required for integration into the existing plant-control system; and lower cost, e.g., the cost to install and maintain typical inlet heating coil systems may extend into the millions of dollars, far more than required for the exemplary resistive heating system described herein. In addition, the currently-used coil system often requires filter house structural modifications such as removal of the hood and bird screen and/or moisture separators. The resistive heating system described herein will require shorter downtime for installation and operation. In addition, the presently-described invention does not include the reduced performance penalty of coils which increase pressure drop and negatively affect the turbine performance. Finally, the cycle time for installation of an inlet heating coil system typically is approximately 45 weeks whereas in the case of the resistive heating system described herein, the period from design to operation may be reduced to as few a ten weeks. 
         [0028]    It will be further appreciated that the electrical heating system as described herein is not limited to use in cold climates. It may also be used as a de-fogger in warmer climates where fogging can lead to a caking effect on air filters. 
         [0029]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.