Direct mixing of geothermal water and condensate into heated groundwater at Nesjavellir power station
Author: Haukur Darri Hauksson
Year: 2023
Supervisors: Einar Jón Ásbjörnsson, Baldur Brynjarsson, Arna Páldsdóttir
Abstract:
The focus of this study is on the Nesjavellir geothermal power station in Iceland, which
plays a vital role in supplying hot water for space heating in the capital area. The power
station operates as a co-generative single-flash geothermal plant, generating electricity using
high-temperature geothermal steam and utilizing geothermal water to heat groundwater for
hot water production. Opportunities exist at the Nesjavellir power station to enhance the
utilization of underutilized flow streams, such as geothermal water and condensate.
The objective of this thesis is to investigate the potential of incorporating a small amount
of geothermal water and condensate into heated groundwater at Nesjavellir in order to im-
prove resource utilization without increasing scaling risks. The study involves analyzing the
scaling tendencies of different mix combinations.
Laboratory experiments were conducted to evaluate the scaling potential of various mixing
ratios. PHREEQC modeling and simulation techniques were employed to determine the
optimal mixing ratio that minimizes scaling while maximizing energy utilization.
The research findings suggest that mixes containing condensate water potentially decrease
the rate of magnesium silicate scaling in laboratory experiments. This indicates that using
condensate water as a component in the mixture can be beneficial in mitigating the formation
of magnesium silicate scale.
Additionally, the PHREEQC modeling results provide further insight into the behavior of
magnesium silicate minerals, specifically Antigorite, Chrysotile, Talc, and Enstatite. The
modeling suggests that the supersaturation of these minerals in the presence of mixes con-
taining condensate water would be either lower or comparable to that observed in 100%
heated groundwater.
By identifying the optimal mixing ratio of geothermal water, condensate, and heated ground-
water, it becomes possible to maximize the utilization of geothermal resources without sig-
nificant modifications to the current production process.