Cleaning and liquid contact with solids – Processes – Hollow work – internal surface treatment
Reexamination Certificate
2000-05-26
2002-11-12
Markoff, Alexander (Department: 1746)
Cleaning and liquid contact with solids
Processes
Hollow work, internal surface treatment
C134S022100, C134S022190, C134S023000, C134S026000, C134S028000, C134S034000, C134S040000
Reexamination Certificate
active
06478033
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention generally relates to methods for foam cleaning combustion turbines. More specifically, the present invention is directed to methods for cleaning contaminants adhering to the internal surfaces of the compressor, combustion and turbine sections of a combustion turbine by pumping one or more foamed cleaning solutions therethrough. Also discussed is a manifold for temporarily blocking the air intake opening of the compressor section of a combustion turbine to facilitate such cleaning.
II. Description of the Background
Combustion turbines are used in a multitude of applications, including aviation, shipping, chemical processing and power generation. In combustion turbine power generation facilities, efficiency can be improved by supplementing the electrical power generated directly from the combustion turbine with recovery units designed to capture heat from the exhaust gas generated by the turbine. This heat can be used to produce steam to drive a steam turbine, operate steam driven equipment or provide heat to chemical processing facilities, thus improving the efficiency of the power generation facilities.
As used herein, the term combustion turbine refers to any turbine system having a compressor section, a combustion section and a turbine section. The compressor section is designed to compress the inlet air to a higher pressure. Atomized fuel is injected into the combustion section where it is combined with the compressed inlet air and oxidized. Finally, the energy from the hot gasses produced by oxidation of the fuel is converted to work in the turbine section. While fuels typically comprise natural and synthetic gases (mostly methane), other hydrocarbons, including liquified natural gases (LNG), butane, kerosene, diesel and fuel oils may be employed. The expanding combustion gases power the turbine by turning the rotating blades of the turbine sections as they escape the combustion section. The compressor section is mechanically powered by a rotor comprising a rotor shaft with attached turbine section rotating blades and attached compressor section rotating blades. In power generation facilities, the rotor drives an associated electrical generator. Alternatively, the rotor may be used to power chemical process equipment. While the exhaust gas may merely be discarded, preferably it is recovered as additional heat energy often being used to produce steam in power generation facilities.
The overall efficiency of a combustion turbine engine is heavily dependent on the efficiency of the compressor. The pressure ratio of the compressor, i.e., the ratio of air pressure at the compressor outlet to air pressure at the air inlet, is one of the significant parameters which determines the operating efficiency of the compressor. The higher the pressure ratio at a given rotational speed, the greater the efficiency. The higher the air pressure at the outlet of the compressor, the greater the energy available to drive the turbine downstream of the compressor and hence to generate power or produce thrust.
In axial flow compressors, pressurization of air is accomplished in a multiplicity of compressor stages or sections, each stage being comprised of a rotating multi-bladed rotor and a non-rotating multi-vaned stator. Within each stage, the airflow is accelerated by the rotor blades and decelerated by the stator vanes with a resulting rise in pressure. Each blade and vane has a precisely defined airflow surface configuration or shape whereby the air flowing over the blade or vane is accelerated or decelerated, respectively. The degree of air pressurization achieved across each compressor stage is directly and significantly related to the precise air foil surface shape. Unfortunately, the surfaces of the compressor blades and vanes become coated with contaminants of various types during use. Oil and dirt sucked in through the air intake become adhered to the blade and vane surfaces of the compressor.
Deposits build up on compressor blades during normal operation causing reduced airflow through the compressor section of combustion turbines. Such deposits are often the result of the ingestion of hydrocarbon oils and greases, smoke, dust, dirt and other particulate air pollutants through the air intake of the combustion turbine. Upon formation of a hydrocarbon film upon the internal surfaces, including both the rotating blades and stationary vanes, of the compressor, additional particulates pulled through the compressor become trapped. As the airflow through the compressor section diminishes, the compressor discharge pressure drops, resulting in a reduction in compressor efficiency and power output from the turbine. The resulting inefficiency causes an increase in fuel consumption and a loss in power generation output.
Aluminum and other metal substances erode from other parts, e.g., clearance seals of the engine, and are also deposited on the blades and vanes. Metals contained in the fuel, particularly heavy metals such as magnesium and vanadium, deposit on the combustion and turbine blades and vanes. All of these surface deposits alter the ideal air foil surface shape, disturbing the desired air flow over the blades and vanes. This results in a reduction in the pressure rise across each successive turbine stage and a drop in overall turbine efficiency.
Gas turbine compressors have been periodically cleaned to remove the build up of particulates on internal components. Some of this cleaning has been performed without full shutdown of the combustion turbine, while other cleaning methods have required not only full shutdown, but even disassembly of the turbine. Materials used in such cleaning operations have included water, ground pecan hulls, coke particles and chemical cleaning mixtures which have been sprayed, blown or otherwise injected into the inlet of the combustion turbine after it has been configured for such a cleaning operation.
Removal of contaminants from the blades and vanes of in service compressors is desirable to restore compressor and engine efficiency. Since it is both time consuming and expensive to disassemble the engine, methods capable of removing these contaminants without disassembly of the engine are desirable. Furthermore, any method utilized to remove the contaminants must not interfere with the structural or metallurgical integrity of the components of the engine. Acceptable methods must be capable of removing the contaminating materials without attacking engine components constructed of similar materials. Because many liquid solvents also attack the engine components, the injection of liquid solvents into the engine has often proven to be unacceptable.
Abrasive particles impinging upon the contaminated surfaces will also dislodge contaminants. However, abrasive materials have proven to be unsatisfactory. Such materials are often overly abrasive, not only dislodging contaminants but also destroying the surface smoothness of the blades and vanes. Furthermore, some of these abrasive materials generally remain within the engine. If non-combustible, these materials may clog cooling holes of the turbine components and restrict needed cooling airflow. If combustible, these materials may produce residues which clog the cooling holes.
A general discussion of compressor section cleaning may be found in Scheper, et al. “Maintaining Gas Turbine Compressors for High Efficiency,” Power Engineering, August. 1978, pages 54-57 and Elser,“Experience Gained in Cleaning the Compressors of Rolls-Royce Turbine Engines,” Brennst-Warme-Kraft, Sep. 5, 1973, pages 347-348. Several exemplary prior art cleaning methods are described in more detail below.
Many prior art methods merely sprayed water into the air intake of an operating combustion turbine. U.S. Pat. No. 4,196,020 to Hornak, et al. discloses a wash spray apparatus for use with a combustion turbine engine. The apparatus includes a manifold having a plurality of spray nozzles symmetrically disposed about the air intake of a combustion turbine engine. Water is s
Brookhart Walter R.
HydroChem Industrial Services, Inc.
Markoff Alexander
Shook Hardy & Bacon L.L.P.
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