Melissa Wilcox

Engine Distress Detection in Gas Turbines With Electrostatic Sensors

Failures in gas turbines such as fretting at combustor assembly interfaces, blade rub, Thermal Barrier Coating (TBC) spalling, minor amounts of domestic or foreign object damage can be detected by mechanical vibration or gas turbine performance degradation, but it is usually too late for damage control by the time the failure is significant enough to be detected with these methods. Electrostatic charge sensors present a potential method for identifying the failure modes at an earlier stage before significant damage has occurred. In a gas turbine, there are potentially two sources of electrostatic charge in the exhaust gas flow stream: ionized plasma that is a natural byproduct of high temperature combustion, and any form of debris that has originated either in the compressor, combustor, or turbine sections of the gas turbine engine as a result of vibration or fatigue. For this reason, the electrostatic charge monitor becomes a very useful device for monitoring both combustion performance problems as well as potential damage related to debris in the exhaust stream. Electrostatic sensing technology has been proven to work in detecting ingested debris and engine debris on aerospace jet engines. However, the use of the sensors in industrial applications has shown that much research is still required especially in the areas of sensor placement and failure identification. This paper discusses results from testing conducted to identify the optimal placement location for the electrostatic charge sensors in a gas turbine exhaust stream. The results are presented for various sensor locations on small (112 kW) and medium (1.185 MW) frame gas turbines to evaluate distance, velocity, radial location, and gas turbine geometry effects. These tests are completed with the gas turbine ingesting varying amounts of TBC upstream of the compressor and administering power level changes to the gas turbine. The results of this experimental program demonstrate a clear sensitivity to sensor placement along the exhaust duct of a gas turbine as well as the radial location. There are variations in the particle flow pathlines in the exhaust duct at different gas turbine operating conditions. These variations influence the sensors response. Best results are obtained when the sensors are placed at the location with the fastest and hottest exhaust gas. Multiple sensors may be required to obtain comprehensive coverage for practical event detection.Copyright

Technology Review of Modern Gas Turbine Inlet Filtration Systems

An inlet air filtration system is essential for the successful operation of a gas turbine. The filtration system protects the gas turbine from harmful debris in the ambient air, which can lead to issues such as FOD, erosion, fouling, and corrosion. These issues if not addressed will result in a shorter operational life and reduced performance of the gas turbine. Modern day filtration systems are comprised of multiple filtration stages. Each stage is selected based on the local operating environment and the performance goals for the gas turbine. Selection of these systems can be a challenging task. This paper provides a review of the considerations for selecting an inlet filtration system by covering (1) the characteristics of filters and filter systems, (2) a review of the many types of filters, (3) a detailed look at the different environments where the gas turbine can operate, (4) a process for evaluating the site where the gas turbine will be or is installed, and (5) a method to compare various filter system options with life cycle cost analysis.

Mechanical Performance of a Two Stage Centrifugal Compressor under Wet Gas Conditions

As subsea compression becomes a vital technology to the successful production of gas reserves in the North Sea, several technology issues will come to the forefront of the oil and gas industry. One of these important subjects is the capability to compress gas which includes a significant amount of liquids. Compressing wet gas requires knowledge in areas such as the prediction of turbomachinery performance with the mixed phase flow as well as the mechanical reliability of machinery in the same environment. This paper presents experimental results from a wet gas test campaign which, among other goals, is focused on characterizing the mechanical performance of a two stage compressor operating under wet gas conditions. Various mechanical parameters are monitored in the test program including rotor radial and axial vibration, rotor thrust, and shaft torque. A full array of wet gas conditions are tested with a suction pressure of 20 bar (300 psia) and liquid volume fractions in the range of 0.5 to 5%. The operating fluids are air and water, and the two stage compressor is operated at three speed lines ranging from high flow to low flow conditions. Significant variations are noted in the axial thrust, axial vibration and shaft torque. Thrust variations range from seemingly neutral thrust conditions at very low water injection rates to significant thrust increases (as compared to dry condition) for very high water injection rates. Rotor axial vibration is characterized by large amplitude and very low frequency, especially for the case in which the rotor thrust is balanced by the water injection. During higher levels of water injection, rotor axial vibration is generally characterized by relatively large amplitude and slightly higher frequency, although still very low as a percent of running speed. Variations in radial vibration are also noted, but to a much lesser extent.

Successful Selection And Operation Of Gas Turbine Inlet Filtration Systems

A gas turbine inlet filtration system is important for successful operation. The filtration system minimizes the occurrence of foreign object damage, erosion, fouling, and corrosion. The selection of the inlet filtration system is a challenging process which involved choosing multiple filtration stages based on the desired performance of the gas turbine and the local operating environment. This tutorial walks through the factors that should be considered when selecting an inlet filtration system: 1) The characteristics of filters and filter systems, 2) A review of the many types of filters, 3) A detailed look at the different environments where the gas turbine can operate, 4) A process for evaluating the site where the gas turbine will be or is installed, and 5) A method to compare various filter system options with life cycle cost analysis.

Development of Test Stand for Measuring Aerodynamic, Erosion, and Rotordynamic Performance of a Centrifugal Compressor Under Wet Gas Conditions

As the oil and gas industry addresses technology challenges for accessing gas reserves and enhancing the production of existing installations, wet gas compression becomes an important technology focus. When liquid is introduced into a compressor flow stream, the performance of the compressor is significantly influenced. Therefore, a concentrated effort is required to develop the tools to adequately predict the performance of the compressor when subjected to wet gas conditions. A series of tests were performed on a single stage compressor in a wet gas environment in order to provide empirical data for understanding how to predict wet gas performance. The compressor underwent aerodynamic, erosion, and rotordynamic performance testing. The tests were completed with a mixture of air and water at suction pressures of 10, 15, and 18.5 bar. The compressor was subjected to a multiphase flow with liquid volume fractions ranging from 0 to 3% (corresponding to a mass fraction of 73%) at three Mach numbers. Transient tests with liquid load variation were also done. This paper describes the test stand that was developed and operated for testing of the compressor in a wet gas environment. This includes a review of the overall test set-up, description of key test components and of the instrumentation installed on the compressor and the test loop. An overview of main test results is eventually shown.Copyright

Measured Performance of Two-Stage Centrifugal Compressor Under Wet Gas Conditions

The oil and gas industry is moving forward to access the most remote gas reserves and enhance the exploitation of the existing installation or postponing their tail-end. To achieve these accomplishments several technology challenges are being unveiled. In topside upstream application both offshore and onshore, one important technology issue is the capability to compress gas with a significant amount of liquids and it assumes a special interest in case of the facilities revamping. Nevertheless is in the subsea environment where this technology issue becomes really challenging. In order to properly design and size a compressor/motor system for subsea wet gas compression, one must be able to adequately predict the compressor performance with mixed phase flow.This paper presents the results from an experimental test program which investigated the performance of a centrifugal compressor at various wet gas conditions with elevated suction pressure. Performance tests are completed on a two stage centrifugal compressor with a mixture of air and water at suction pressures of 20 bar (300 psi). The compressor is subjected to flow with liquid volume fractions ranging from 0 to 5% along three speedlines.The performance measurements are made in accordance with ASME PTC-10 specifications with an additional torque measurement on the shaft between the compressor and gearbox. At each test condition, once the liquid is injected in the air flow, an increase in pressure ratio occurs. This testifies the compressor is still able to work in presence of water. However, increasing the amount of liquid injected a decreased polytropic head together with an increased absorbed actual power by the compressor cause a deterioration of its efficiency. Moreover when liquid is introduced into the flow, the discharge temperature of the compressor reduces significantly.The performance results and trends mentioned above are reviewed in the detail in this paper.Copyright

Gas Turbine Inlet Filtration System Life Cycle Cost Analysis

Gas turbine inlet filtration systems play an important role in the operation and life of gas turbines. There are many factors that must be considered when selecting and installing a new filtration system or upgrading an existing system. The filter engineer must consider the efficiency of the filtration system, particles sizes to be filtered, the maintenance necessary over the life of the filtration system, acceptable pressure losses across the filtration system, required availability and reliability of the gas turbine, and how the filtration system affects this, washing schemes for the turbine, and the initial cost of any new filtration systems or upgrades. A life cycle cost analysis provides a fairly straightforward method to analyze the lifetime costs of inlet filtration systems, and it provides a method to directly compare different filter system options. This paper reviews the components of a gas turbine inlet filtration system life cycle cost analysis and discusses how each factor can be quantified as a lifetime cost. In addition, an example analysis, which is used to select a filtration system for a new gas turbine installation, is presented.Copyright

Dynamic Pipeline System Simulation of Multi-stage Compressor Trains

An oil and gas company was facing process and mechanical related problems on the multiple-stage compressor trains at two important booster installations. The frequency of these problems has increased lately, and this has led to frequent trips and shut downs. These interruptions affect the operation of the plant leading to a loss in production and consequences of lost revenue for the company. The two platforms each contain one compressor train comprising a four-stage compressor with a gas turbine driver. Each train is fitted with an integrated turbine compressor control panel.Thus, a detailed dynamic pipeline system simulation of the subject compressor trains was performed in order to provide a series of recommendations that would improve the safe operation and increase the reliability of the compression systems. The analysis included a review of the existing compression systems including all the equipment and hardware related with the compression anti-surge system. In addition, a site visit was performed to review and understand the existing anti-sure control system at each facility. A detailed dynamic model of the multi-stage compression system was built for each train. These models included compressor performance maps, gas compositions for each stage and train, piping yard, recycle, isolation, check and blowdown valves, scrubbers, separators, and coolers.Several simulation cases were conducted for both the platform systems. These cases evaluated the effect of the delay and travel times of the existing anti-surge valves, delay the coast down action, failure of the non-return valves (NRVs), action of a blowdown valve on the emergency shutdown (ESD) sequences, recycle valve bypasses, check valve arrays, and process upset conditions. In addition, parametric studies were conducted for each of the most important parameters of the system to quantify their effect of any possible modification.The results of this analysis provide recommendations to solve some of the existing issues while understanding more of the dynamics of the system. It was found that any propose recommendation or change in the sequence or timing of one stage will affect the surrounding stages since they are not only connected through the piping as they are driven by the same gas turbine shaft. Therefore, a very comprehensive analysis was conducted for each train to provide recommendations that would be feasible for implementation while reducing the constant risk of mechanical failure and surge events. Thus, results of the analysis and some of the recommendations obtained are presented in this paper.© 2012 ASME

Development of Test Procedure for Quantifying the Effects of Salt and Water on Gas Turbine Inlet Filtration

Inlet filtration on a gas turbine strongly influences the performance degradation and life of the turbine. The inlet filtration system must have a diverse set of stages to remove the contaminants present in various phases (gas, liquid, and solid). Filters for gas turbine filtration systems are currently classified using one of three standards: ASHRAE 52.2, EN 779, or EN 1822. These standards measure the performance of filters in the dry state and do not consider the performance of the filter when wet (saturated with water). Many locations where gas turbines operate, experience conditions where the filter can be dampened or saturated which can significantly influence the filter’s performance. In addition, if soluble particles, such as sodium chloride, are captured by the filter, then there is a potential for the soluble particles to be carried by the water through the filter and into the gas turbine. In order to understand the performance of a filter with water present, a procedure is being developed. This procedure intends to quantify the effects of water and salt on the performance of filters. The procedure has been written, and a series of preliminary validation tests have been completed. The results of the preliminary validation testing show that a change can be observed in the filter’s performance when salt and water are introduced into the flow stream. In addition, the preliminary validation testing revealed many areas where the test procedure could be improved.© 2012 ASME

Filter Failure During High Humidity Conditions

The operation of a gas turbine, by its basic design, requires it to ingest enormous quantities of air. Even in relatively clean environments, a gas turbine may ingest hundreds of pounds of foreign matter each year of various sizes. Also, the more advanced the turbine design, the more sensitive it is to the quality of the air ingested. Filtration is applied to the inlet air to provide protection against the effects of contaminated air. Filters used with gas turbines are designed to remove a specified amount of particular contaminants. One type of filter is the high efficiency filter. These are often installed in order to capture particles less than ten microns. These filters are sometimes susceptible to water penetration. If the filter is not designed to remove water, then water can absorb soluble contaminants and carry them through the filter into the inlet of the gas turbine. In the case where harmful contaminants travel through the filter with the water, this can be potentially damaging to the gas turbine. For example, salt is soluble and can lead to hot corrosion in the turbine section. If water is allowed to reach the high efficiency filters then the water may carry contaminants through the gas turbine. In order to mitigate this phenomenon, many filter systems have mist removal systems. Even with a good mist removal system, humidity can reach the high efficiency filters. As humid air flows past the high efficiency filters, the decrease in air pressure can lead to water condensing on the filters. A procedure is presented in this paper which shows that filters that have been fully or near fully loaded with contaminants may experience condensation in an environment with high humidity. This paper reviews a thermodynamic analysis that is used to determine the conditions that must be met in order to experience this phenomenon. The possible occurrence of condensation further demonstrates the criticality of replacing inlet filters as soon as the filter pressure loss shows an upward trend.© 2010 ASME