Derating Prediction Due to Scaling at Kamojang Geothermal Turbine Using Nozzle Blocking Ratio Calculation

摘要

Kamojang POMU has installed capacity of 375 MW. Kamojang with operation a base load system should ready to supply electricity continuously exclude the requirements of repair or scheduled maintenance. Derating due to scaling is the common problem at geothermal power plant which affect not only an economic and energy losses but also a higher turbine maintenance cost. Turbine scaling in Kamojang POMU is influenced by steam phase changes from saturated to slightly superheated, the temperature of the steam is above the boiling point with temperature rise around 3 to 4 °C. The level of critical scaling on the turbine is commonly referred as Nozzle Blocking Ratio. This parameter has shown us a critical level of scaling in the turbine nozzle without turbine dismantling. Kamojang historical NBR data indicates derating value occurred around 10 – 11 with turbine output ± 53 MW. Based on historical data, derating prediction model by the equation y = 0.0642x-2808.3 with confident level at 87% is for Kamojang and y = 0.035x-1530.9 with confident level at 97% is for Darajat Unit 1. Derating estimation for Darajat Unit 1 is on October 2020, and at Kamojang Unit 2 is on March 2020.