Abstract:
The Ulubelu geothermal field is located in Lampung province in South Sumatra, Indonesia. Ulubelu is a liquid-dominated system with an average enthalpy of 1100 kJ/kg. It is the largest geothermal power plant in Sumatra with 2×55 MWe capacity from two identical units 1 and 2. Both units have been in operation since September 2012. Another 55 MWe plant was recently introduced in July 2016 which should be followed by a fourth 55 MWe unit in July 2017. Based on the steam-field topography and terrain characteristics, units 1-2 used hybrid separation system, which is a combination between satellite and centralized separation plant. Units 3-4 are designed with a central separator station that receives the entire flow of two-phase fluid from all the production sectors of the field. The steam field design for all units includes a separator with integrated water drum with baffle plate type, large diameter two-phase pipeline, direct hot brine injection, scrubbing line system and scrubber vessel for moisture removal. In order to make a flexible operation, all of the units are connected with interconnection lines both in two-phase and steam pipelines. Several technical challenges were experienced in the operation of units 1-2 including; the unknown two-phase flow rate from each production well, water hammer in large two-phase pipeline and brine carry-over at the steam outlet of the separator. Not resolved, these problems are likely to take place during the operation of units 3-4. This work attempts to analyse the cause of problems and provide recommendations for future steam field design in order to optimize and improve the performance of the geothermal field.
