Abstract

This work deals with the off-design performance analysis of gas turbines. Two gas turbine power stations in Rivers state, Nigeria were used as case studies. Ambient temperature-induced off-design calculations were carried out. This is because no gas turbine operates at its design point in the field and ambient temperature is one of the parameters that changes more frequently in gas turbine operation. Off-design performance models were developed to estimate the power output, thermal efficiency and the exhaust gas temperature at different ambient temperature values. Input data were obtained from the two gas turbine operations and engine adaptation results from previous researches. The power output and the thermal efficiency drops with increase in ambient temperature while the exhaust gas temperature increases with increase in ambient temperature. On the average, power output drops by 1.13 MW when ambient temperature increases by 10 ◦C for the first gas turbine power plant and the value obtained for the second gas turbine power plant which is smaller is 0.473 showing that the power drop is dependent on the power output of the plant. For the same range of ambient temperature increase, thermal efficiency drops by 0.637 % and 0.583 % respectively for the two power plants. Larger drop in power output as well as thermal efficiency occurs at the lower temperature values. The exhaust gas temperature increases with ambient temperature almost uniformly with average value of 1.29 K and 1.21 K respectively for 1◦C increase in ambient temperature. The simulated results closely matched the results obtained from the field at different ambient temperatures. The results of this work will guide power plant operators in economic analysis by estimating the power output beforehand.

Highlights

  • Engine performance parameters such as power output, specific fuel consumption and thermal efficiency are provided at the design point of the engine

  • Variation of ambient conditions alone will make gas turbines to operate at conditions outside the design conditions

  • Power output drops with increase in ambient temperature, with greater magnitude of power drop occurring at lower temperatures

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Summary

Introduction

Engine performance parameters such as power output, specific fuel consumption (sfc) and thermal efficiency are provided at the design point of the engine. Engine parameters such as pressure ratio, shaft speed, mass flow rate and the power output are specified usually with the ambient conditions at the design point. Design point performance calculations which usually involves estimating the overall plant efficiency and the air flow rate required to obtain the design power can be carried out. The design point of gas turbine specified by engine manufacturers is usually at sea level, ambient temperature and pressure of 15◦C and 1 atmosphere respectively and relative humidity of 60 % [1]. The estimation of the performance parameters such as the power output at off-design point is crucial since power plants are installed based on the amount of power the unit could produce

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