Steam Purity Troubleshooting: The Berlin Geothermal Steam Field, El Salvador

Abstract

Moisture carried with the geothermal steam at the turbine inlet can cause millions of dollars lost in electricity generation. These revenue losses occur due to frequent power plant overhauls, retrofitting and extended turbine maintenance required to remove the scaling out of the turbine blades and diaphragm or replace expensive turbine components (e.g. turbine shaft) damaged by entrained liquid droplets impacting the surfaces at high velocity.
Several technical articles, published since the onset of the geothermal industry, describe practical design techniques and recommendations to improve the steam field design effectiveness, to deliver dry and clean steam to the turbine. These criteria fundamentally refer to primary separation efficiency and steam line scrubbing (or secondary separation). Some of the design recommendations might be valid within a range of physical conditions (e.g. steam pressure or velocity) or applicable only to a specific steam field configuration. The authors consider an opportunity to combine all the design techniques, criteria, and experiences
published to date into an integrated thermofluid model to either validate the well-known recommendations or optimise their results.
The Berlin Geothermal Steamfield (El Salvador) is presently experiencing problems with one of its turbine units due to impurities carried by the steam. LaGeo and the University of Auckland are working together to analyse the problem, develop and calibrate a model to simulate the current steam field, and assess optimisation scenarios to mitigate the steam purity problem.
This paper presents the findings, modelling results, and provide recommendations.