World Geothermal Congress
May 21-26, 2021

Theistareykir Geothermal Power Plant, Description of the Steam Supply System: Design, Operation and Experience Gained

Freyr HARDARSON, Sigurgeir B. GEIRSSON, Karl E. SVEINSSON, J. Gardar EINARSSON, Arni V. SIGURDSSON, Sigurgeir B. GEIRSSON, Valur KNUTSSON

[Mannvit, Iceland]

The steam supply for Theistareykir Geothermal Power Plant is a single flash cycle providing steam for 2x45 MWe turbine units whereas the separated water is mixed with steam condensate from the units and reinjected. The steam supply has been in operation from end of 2016. This paper describes the design and layout of the steam supply, the characteristics of the steam wells, operation and control strategy of the steam supply and its ability to cope with variable load. Furthermore, the paper will report on the experience gained from mixing steam condensate with the separated water, the effect of condensate mixing on the permeability of the reinjection wells and operational history for the first years of operation. The steam supply system comprised of the steam wells, steam pipelines, steam gathering pipelines, steam separators, main steam pipelines, steam control valves, mist eliminators, reinjection pipeline, condensate mixing system and reinjection wells. The steam wells are located on five drilling areas from where most of the wells are directionally drilled. The average length of the wells is 2 500 m and their vertical depth ranges from 1 800 – 2 400 meters, each well producing steam in the range equivalent to 5-21 MWe of electrical power. In the operation of the wells, some of the wells have been shown to have fluctuation in the output and some decline has been noted. The operation of the steam supply must facilitate the operation of the units at variable load and handle abrupt changes in the power output of the turbine/generator units without any delay in the operation of the units due to instability or transient behavior of the steam supply system. The paper describes some the events that can occur and how the steam supply system is able to robustly negate these events. The separated water from the steam separators is reinjected into wells at a depth of approximately 400 meters at the boundary of the geothermal field. To increase the permeability of the wells and reduce scaling, the geothermal water from the steam separators is mixed with condensate from the condensers of the turbines to cool and dilute the water. The experience of condensate mixing has shown large increase in the permeability of the reinjection wells without any adverse effects after about 2 years of operation.

        Topic: Production Engineering, Steam Gathering Systems Paper Number: 25007

         Session 8E: Production Engineering 1 -- Measurements and Operations [Saturday 22nd May 2021, 03:00 pm]
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