ANALISIS PENGARUH PERUBAHAN TEKANAN VAKUM KONDENSOR TERHADAP EFISIENSI TURBIN UAP UNIT 01 DI PLTU PT. BINTAN ALUMINA INDONESIA

Abstract

Unlike previous studies focusing on isolated steam-turbine units, this study investigates condenser-pressure and turbine-performance behavior under a common main steam header and multi-unit load-sharing configuration. The objective is to analyze the quantitative and qualitative impacts of condenser absolute pressure variations on the turbine isentropic efficiency and operational performance of the 30 MW condensing steam turbine Unit 01 at PLTU PT Bintan Alumina Indonesia. Primary operational logsheet data collected over 12 daily observations from the Distributed Control System (DCS) were evaluated under IAPWS-IF97 thermodynamic standards. Measured vacuum gauge pressures were explicitly converted to condenser absolute pressure (𝑃 con,abs ). Simple linear regression and multivariable linear regression modeling were conducted to isolate the net influence of back-pressure while controlling for substantial steam flow variations (47.80 to 99.58 T/h). Simple linear regression yielded 𝑦 = 0.3225𝑥 + 64.025 (𝑅 = 0.1775,𝑝 = 0.172), proving that univariate back pressure alone is insufficient due to heavy steam load confounding. Controlling for steam flow CORRESPONDENCE Phone: +62 (0751) 12345678 E-mail: [email protected] (𝑀) and inlet parameters (𝑃,𝑇) in a multivariable model (𝜂= 10.747 +0.8518 ⋅ 𝑃 , − 0.0107 ⋅ 𝑀−1.3689⋅𝑃+0.1170⋅𝑇) significantly improved model fit (𝑅 = 0.9888,Adjusted 𝑅 = 0.9824,𝑝 < 0.0001) and confirmed a statistically significant net sensitivity of 0.8518% efficiency change per 1 kPa increase in absolute pressure (𝑝 < 0.0001). Thermodynamically, lower condenser absolute pressure results in a lower calculated isentropic exhaust quality within the investigated operational range, indicating a potentially higher moisture fraction under theoretical expansion conditions. Operationally, the central main steam header dynamics demonstrate that refinery load demand and steam mass flow dictate condenser thermal loading and back-pressure performance rather than back-pressure directly driving turbine electrical output. This study contributes by: (1) quantifying the relationship between condenser absolute pressure and turbine isentropic efficiency; (2) evaluating the influence of steam-flow variation on this relationship using multivariable analysis; and (3) identifying the operational implications of a common main steam header configuration. Maintaining condenser absolute pressure stability through preventive tube cleaning, cooling-water filter backwashing, and air ingress mitigation is essential to preserve peak thermal efficiency.