Utilization of Waste Brine to Enhance an Existing Production Through Hydrothermal Turbine and Double Flash Cycle (Back Pressure) in Lahendong Geothermal Field, Indonesia

Abstract

Currently in Indonesia, most of geothermal sources had a two phase dominated fields and brine from production wells or separator just to maintain reservoir through reinjection wells. In unit V and VI Lahendong field, we had steam fraction about 20% each and the rest is waste product (hot brine). Then the steam flows into turbine to generate electricity 2 x 20 MW. This paper will focus on how to enhance production from waste brine through designing a secondary turbine with hydrothermal turbine and double flash cycle (back pressure) before waste product toward into reinjection wells. The process design and simulation will use pipe size 6” schedule 40 as brine supply facility either to flash separator or hydrothermal turbine to avoid disturbance of operation. From the optimization, first, the double flash cycle (back pressure turbine) resulting power output 2447.56 kW with differential pressure between flasher valve and separator 3.8 bara. Second, the boiling liquid applied into two phase expander (turbo expander type). The turbo expander able to generate electricity about 282.23 kW with outlet pressure 5.924 bara, which is the atmospheric pressure around 0.924 bara. This type has way to expand the energy, it is should remove the vapor energy from the system. The aim of pressure setting in this research is to reach silica saturation index (SSI) less than 1 after had some processes.