Patent Application
20130193127
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.
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.
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.
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.
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.
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.
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.
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.
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.
The invention will now be described in greater detail in connection with the drawings identified below.
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.
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
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>32° F. but the threshold temperatures for activating and deactivating the resistive system may also vary.
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.
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.
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
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.
The above described features/operation applies as well to the first described embodiment shown in
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.
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.
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.
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.
