Performance Deterioration of Gas Turbine Engines - Research Paper Example

Gas Turbine Engine Deterioration Number Introduction Gas turbine engine’s performance can be evaluated by steady-state paced performance models. The engines normally deteriorate in performance when they are in use and begin to accumulate operating time when working due to erosion and wear and fouling. Presently, there exists intense competition on the production of efficient working gas turbines. This paper seeks to cover the recoverable and unrecoverable performance deterioration of gas turbine engines. The mechanisms of deterioration include turbine fouling, erosion, increased clearances, seal distress, compressor, mitigation process along with their manifestation and the rules of thumb. It is equally important also to cover the aspects of permanent deterioration (Meher-Homji, Chaker and Motiwala, 2001). There are several gas turbines utilized in combined cycles, and the recovery of steam generator performance is made. The use of high-performance gas turbine engines has resulted in an increase in fuel costs making it essential for maintaining high working efficiencies of the engines. It is important to understand the basic design and aerodynamic principles in regard to gas turbines. The factors that affect deterioration include the temperature control on the materials, rotor speeds and the stress levels, and the fluid dynamic characteristics that includes, chocking, dissolution, stall and infuse. In order to attain sufficient thermodynamic efficiency, there is necessary need for heat to be added at high temperatures (Meher-Homji, Chaker and Motiwala, 2001). Accordingly, there shall be a mechanism for cooling to be included. The cooling characteristics can in turn affect the complete thermal efficiency of the engine. For that reason, the losses that culminate the cooling flow can have detrimental effects causing a cycle penalty. Thus, there are several forms of deterioration that can alter the cooling flow and the overall working efficiency of the gas turbine. The compressor can accumulate dust during its working cycles on the field. The dust eventually finds its way into the tiny cooling holes in the hot areas of the blades. This will in turn lead to blade distress due to the impaired cooling caused by the dust blocking the vents of the blades. This gives an example of how performance degradation is linked to the mechanical behavior and consistency of a gas turbine engine. On the other hand, higher firing ratios increase pressure ratios. Accordingly, high-performance gas turbine engines that have high-pressure ratios, cyclic temperatures, tight tip clearances and stage loadings are more vulnerable to performance deterioration. In view of that, the following issues closely relate to the mechanical aspects of performance (Meher-Homji, Chaker and Motiwala, 2001). a. Rotor Speeds The blade stresses are determined by the difference in variation of the square tip and speed and the mass flow rate. b. Mass Flow Present gas turbine engine performance is up-scaled by increased flow rate through zero staging. Accordingly, the output is increased at a minimal cost without the risk of damaging the gas turbine. The initial stages comprise of transonic processes that require special transonic blades that experience fewer losses as opposed to transonic blading (Rybnikov, Getsov and Leontiev, 2005). Accordingly, high velocities increase erosion rates in the presence of hard particle in the thermodynamic flow. c. The Compressor Surge and Stall Compressor surge and stall are a factor that leads to performance deterioration. High operation speeds that result in inadequate pressure ratio can also lead to the drop in density. This in turn leads to a choke condition at the rear of the compressor leading to a stall in the early stages. Consequently, the compressor deterioration ultimately leads to surge damage. d. Turbine Engine Design The design of gas turbines has not been a challenge due to the lack of diffusing air flow that is not present. Therefore, the turbine is regarded at the component that outlines the gas turbine operating line and any changes on the nozzle area will affect the match point of the engine affecting its overall output and performance. Problem Statement Gas turbines deteriorate as a result of the different mechanisms involved in the eroding process. Also, there exist the unforeseen faults that are nearly impossible to predict. For that reason, the turbine erosion can eventually be determined over time by tracking. This is given by the combination of the diagnosis and the time evolution prognosis of a system’s performance. The Aim of the Study The research aims at developing the prognostic methodology that will be able to determine and predict degradation as single parameter with the assistance of past recordings. Since the behavior of a machine is inherent due to its operating uncertainties, the most preferred method of use shall be through the Monte Carlo Statistical Process to give a scope of the future trends. Accordingly, the simulation method will provide precise statistics based on the oncoming points of failure in the future and repair (Venturini and Puggina, 2012). Background Every machine has a known finite number of states. For that reason, the processes of transfer in between states can be anticipated to be known. The system’s behavior can be measured by evaluating the time alteration of the state vector B in the point state space. In the formula each state can be identified by a “state indicator” variable b S[B] = S[B1(t),b2(t),..,bnc (t)] Examples Performance and Mechanical Deterioration in Gas Turbines Gas turbine deterioration falls under two categories namely performance and mechanical deterioration. Further, the classification of deterioration can be broken down to include recoverable, unrecoverable and permanent deterioration. A. Recoverable Deterioration i) Compressor fouling Compressor fouling and its limitations is the most predominant area that heavily influences gas turbine deterioration. Also, fouling on the axial flow compressors results in catastrophic effects in the operation of gas turbines. In addition, compressor fouling results in a drop of airflow and the compressor isentropic efficiency (Ogbonnaya, 2011). This results in a “rematching” of the gas turbine’s compressors resulting in a fall in thermal efficiency and power output. Fouling is caused by airborne salt, gas turbine exhaust injection, mineral deposits, insects and impure air. ii) Turbine Section Fouling Turbine section fouling is caused by contaminants that enter the gas turbine through the air inlet section. Also, the hot turbine areas, the presence of hot gasses, ashes, and non-combusted hydrocarbons can be deposited. A drop in static temperature is experienced when hot combusting products pass through the nozzles. Accordingly, a substantial amount of ashes is dumped on the nozzle blades (Ma and Zhu, 2009). This causes a drop in the size of the nozzle area resulting in a reduction in gas turbine performance. B. Unrecoverable Deterioration Unrecoverable deterioration can be caused by a combination of factors that include but are not limited to flow path damage, surface erosion, airfoil roughness, compressor corrosion, tip and seal clearance increase, drift control calibrations, and the malfunctioning of the compressor bleed valves (Carcasci, Costanzi and Pacifici, 2014). D. Permanent Deterioration Permanent deterioration will lead to a decline in performance of the gas turbine as a result of the following reasons. i) The distortion of the casing ii) The increase in leakages iii) Roughness increase on the surface iv) The untwist of the airfoil Degradation Modeling The performance degradation of the gas turbine can take shape in many forms in accordance with the behavior of the machine and the stochastic sequence of the preceding trends. Venturini, M. and Puggina, N. (2012). Prediction Reliability of a Statistical Methodology for Gas Turbine Prognostics. The presence of two random numbers will give the stochastic characteristic of the slope and its intercept. Also, as time elapses, the trend intercept decreases due to the incomplete recovery as a result of the residual loss increase. Accordingly, the postulate of the linear trend will not be resistive because there shall be the need for the incorporation of the points of failure and repair (Venturini and Puggina, 2012). The Degradation Scenarios The Degradation Scenarios in Relation to Time to Failure Venturini, M. and Puggina, N. (2012). Prediction Reliability of a Statistical Methodology for Gas Turbine Prognostics. The figures of the failures and repairs can be altered by changing the Qthr. On the other hand, the scenario case number two, and the medium threshold only has five trends that permit Q> Qthr. For that reason, there can be four events that are obtainable in this event as follows: a. Every repair will eventually be followed by a failure b. The number of the failures and repairs has to be equal The TTFmax denotes the time elapsed between a single repair and failure that is predominant on the first data trend. Results and Discussion 1. The set-up of the methodology It can be determined that the degradation prediction turn out to be more reliable due to the existence of large sample numbers when the values of the parameters are increased. Accordingly, the influence is considered to be negligible in the command of ± 0.3 %. Venturini, M. and Puggina, N. (2012). Prediction Reliability of a Statistical Methodology for Gas Turbine Prognostics. There is a noticeable increase in the computational time that ranges from seconds and gradually increases to hours. 2. The availability estimation Venturini, M. and Puggina, N. (2012). Prediction Reliability of a Statistical Methodology for Gas Turbine Prognostics. The availability decrease of 1.00 to 0.75 is recorded over the period of 57 days due to the degrading of the machine over time. Accordingly, the availability decrease is not notable because of the similarity of the shapes of the data trends. The time frame will entirely depend on the threshold values. Therefore, t (given time), at any threshold will result in the decrease in availability courtesy of additional trends for the calibration methodology. Summary The methodology determined a suitable health index by the use of limited computational resources. However, there exists a notable variation of the time frame in relation to the selected scenario. For that reason, the authenticity of the study is dependable on data trend considered. Accordingly, the methodology proved to be dependable since it was marginally inclined by the well-thought-out data trends. Bibliography Carcasci, C., Costanzi, F. and Pacifici, B. (2014). Performance Analysis in Off-design Condition of Gas Turbine Air-bottoming Combined System. Energy Procedia, 45, pp.1037-1046. Ma, Z. and Zhu, Z. (2009). Thermodynamic Modelling and Efficiency Analysis of a Class of Real Indirectly Fired Gas Turbine Cycles. Therm. sci., 13(4), pp.41-48. Meher-Homji, C., Chaker, M. and Motiwala, H. (2001). Gas Turbine Performance Deterioration. Proceedings of the 30th Turbomachinery Symposium, pp.139-176. Ogbonnaya, E. (2011). Gas Turbine Performance Optimization Using Compressor Online Water Washing Technique. Engineering, 03(05), pp.500-507. Rybnikov, A., Getsov, L. and Leontiev, S. (2005). Failure Analysis of Gas Turbine Blades. MAM, 11(S02). Venturini, M. and Puggina, N. (2012). Prediction Reliability of a Statistical Methodology for Gas Turbine Prognostics. J. Eng. Gas Turbines Power, 134(10), p.101601. Read More