Patent Application
20160290214
Exemplary embodiments of the present invention relate to the art of turbomachines and, more particularly, to a heat pipe cooling system for clearance management in a turbine.
Turbomachines include a compressor operatively connected to a turbine that, in turn, drives another machine such as, a generator. The compressor compresses an incoming airflow that is delivered to a combustor to mix with fuel and be ignited to form high temperature, high pressure combustion products. The high temperature, high pressure combustion products are employed to drive the turbine.
Simple and combined cycle gas turbine systems are designed to use a variety of fuels ranging from gas to liquid, at a wide range of temperatures. In some instances, the fuel might be at a relatively low temperature when compared to the compressor discharge air temperature. Utilizing low temperature fuel impacts emissions, performance, and efficiency of the gas turbine system. To improve these characteristics, it is desirable to increase the fuel temperature before combusting the fuel.
By increasing the temperature of the fuel before it is burned, the overall thermal performance of the gas turbine system may be enhanced. Fuel heating generally improves gas turbine system efficiency by reducing the amount of fuel required to achieve the desired firing temperature. One approach to heating the fuel is to use electric heaters or heat derived from a combined cycle process to increase the fuel temperature. However, existing combined cycle fuel heating systems often use steam flow that could otherwise be directed to a steam turbine to increase combined cycle output.
Gas turbine buckets have a running clearance to the shroud blocks. This clearance is a leak path to the hot gases and is a source of inefficiency, however there is a practical limit to the minimum clearance due to component differential expansion as well as start-up and shut-down transients in physical position. As such, there is a need for active management of this running clearance. A number of methods are known in the art for active clearance control including fan-driven and compressor bleed driven air cooling of localized areas of the turbine shell. Additionally, prior art teaches water cooled casings, however negative attributes of water or glycol cooling includes the substantial challenge of accommodating activating the system with a hot casing due to boiling given the high casing surface temperatures.
In an aspect of the present invention, a turbomachine includes a compressor configured to compress air received at an intake portion to form a compressed airflow that exits into an outlet portion. A combustor is operably connected with the compressor, and the combustor receives the compressed airflow. A turbine is operably connected with the combustor, and the turbine receives combustion gas flow from the combustor. The turbine has a turbine casing. A cooling system is operatively connected to the turbine casing. The cooling system includes a plurality of heat pipes attached to and in thermal communication with the turbine casing. The plurality of heat pipes are operatively connected to one or more manifolds. The plurality of heat pipes and the one or more manifolds are configured to transfer heat from the turbine casing to a plurality of heat exchangers.
In another aspect of the present invention, a cooling system for a turbomachine is provided. The turbomachine includes a compressor, and a combustor operably connected with the compressor. A turbine is operably connected with the combustor, and the turbine has a turbine casing. The cooling system is operatively connected to the turbine casing. The cooling system includes a plurality of heat pipes attached to and in thermal communication with the turbine casing. The plurality of heat pipes is operatively connected to one or more manifolds. The plurality of heat pipes and the one or more manifolds are configured to transfer heat from the turbine casing to a plurality of heat exchangers.
In yet another aspect of the present invention, a method of extracting heat from a turbine casing of a turbomachine includes the step of passing combustion gases through a turbine. The turbine casing forms an outer shell of the turbine. An extracting step extracts heat from the turbine casing by thermally conducting the heat to a plurality of heat pipes. The plurality of heat pipes have a molten salt heat transfer medium including one or combinations of, potassium or sodium. A conducting step conducts heat from the plurality of heat pipes to a heat pipe heat exchanger, and the heat pipe heat exchanger is configured to transfer heat to a fuel heating heat exchanger. The heat pipe heat exchanger may be operably connected to a circuit including a heat recovery steam generator heat exchanger.
One or more specific aspects/embodiments of the present invention will be described below. In an effort to provide a concise description of these aspects/embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with machine-related, system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
When introducing elements of various embodiments of the present invention, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Any examples of operating parameters and/or environmental conditions are not exclusive of other parameters/conditions of the disclosed embodiments. Additionally, it should be understood that references to “one embodiment”, “one aspect” or “an embodiment” or “an aspect” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments or aspects that also incorporate the recited features.
A cooling system 250 is operatively connected to the turbine casing 132. For example, a plurality of heat pipes 252 are attached to the turbine casing and the heat pipes are also in thermal communication with the turbine casing. The heat pipes 252 may be circumferentially located around the turbine casing and attached thereto by welds, fasteners, bolts, welded brackets, clamps or any other suitable attachment mechanism. The heat pipes 252 are operatively connected to one or more manifolds 254, and the heat pipes 252 and manifolds 254 are configured to transfer heat from the turbine casing 132 to a plurality of heat exchangers 240.
The heat pipes 252 absorb heat from the turbine casing 132. As the turbine 130 operates, hot combustion gases flow through the various turbine stages (three are shown). Some of the heat is transferred to the turbine casing, and this heat may be harvested by the heat pipes 252. In one example, the heat pipes are welded to the turbine casing, and the heat pipes are configured to maintain close contact with the exterior surface of the turbine casing (to improve heat transfer). In other embodiments, the heat pipes 252 may be contoured to follow the shape of the turbine casing, or the heat pipes may be embedded into the turbine casing.
The manifold 254 is connected to multiple heat pipes 252, and the heat pipes 252 may be arranged circumferentially about the turbine casing/shell 132. The heat pipes 252 include a heat transfer medium 253 which may be a liquid metal, molten salt or Qu material. As examples only, the heat transfer medium may be one or combinations of, aluminum, beryllium, beryllium-fluorine alloy, boron, calcium, cobalt, lead-bismuth alloy, liquid metal, lithium-chlorine alloy, lithium-fluorine alloy, manganese, manganese-chlorine alloy, mercury, molten salt, potassium, potassium-chlorine alloy, potassium-fluorine alloy, potassium-nitrogen-oxygen alloy, rhodium, rubidium-chlorine alloy, rubidium-fluorine alloy, sodium, sodium-chlorine alloy, sodium-fluorine alloy, sodium-boron-fluorine alloy, sodium nitrogen-oxygen alloy, strontium, tin, zirconium-fluorine alloy. As one specific example, the heat transfer medium 253 may be a molten salt comprising potassium and/or sodium. The outer portion of the heat pipes may be made of any suitable material capable of serving the multiple purposes of high thermal conductivity, high strength and high resistance to corrosion from the heat transfer medium.
The heat pipes 252 may also be formed of a “Qu-material” having a very high thermal conductivity. The Qu-material may be in the form of a multi-layer coating provided on the interior surfaces of the heat pipes. For example, a solid state heat transfer medium may be applied to the inner walls in three basic layers. The first two layers are prepared from solutions which are exposed to the inner wall of the heat pipe. Initially the first layer which primarily comprises, in ionic form, various combinations of sodium, beryllium, a metal such as manganese or aluminum, calcium, boron, and a dichromate radical, is absorbed into the inner wall to a depth of 0.008 mm to 0.012 mm. Subsequently, the second layer which primarily comprises, in ionic form, various combinations of cobalt, manganese, beryllium, strontium, rhodium, copper, B-titanium, potassium, boron, calcium, a metal such as aluminum and the dichromate radical, builds on top of the first layer and forms a film having a thickness of 0.008 mm to 0.012 mm over the inner wall of the heat pipe. Finally, the third layer is a powder comprising various combinations of rhodium oxide, potassium dichromate, radium oxide, sodium dichromate, silver dichromate, monocrystalline silicon, beryllium oxide, strontium chromate, boron oxide, B-titanium and a metal dichromate, such as manganese dichromate or aluminum dichromate, which evenly distributes itself across the inner wall. The three layers are applied to the heat pipe and are then heat polarized to form a superconducting heat pipe that transfers thermal energy with little or no net heat loss.
The valves 1081 and bypass lines 1080 (if connected on all heat exchangers) allow for improved control over fuel heating and machine efficiency. For example, heat exchangers 1040 and 1044 may be connected in a loop to only heat the water input to the HRSG. Heat exchangers 1040 and 1042 may be connected in a loop to pre-heat the fuel supply. This configuration may greatly reduce or eliminate the steam withdrawn from the HRSG, and will permit more steam to be directed into a steam turbine (not shown). As another example, heat exchangers 1040, 1042 and 1044 could be connected in a loop. This configuration will pre-heat fuel 1060 and heat water 1070 going into the HRSG. Heat exchangers 1040, 1042 and 1046 may be connected in a loop and this will maximize the fuel heating potential. Alternatively, all heat exchangers may be connected in a loop so that all heat exchangers will benefit from the heat removed from the compressor discharge airflow.
The cooling and fuel heating system of the present invention provides a number of advantages. Turbomachine efficiency may be improved and a reduced steam demand for fuel heating results in improved combined cycle heat rate. The turbine section buckets, wheels and combustion gas transition pieces may have improved lifespans due to the cooler turbine discharge airflow.
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 languages of the claims.
