Geothermal energy is categorized as a “green energy”, with low emission of approximately 5% of carbon dioxide, 1% H2S, 1% sulfur dioxide and less than 1% of the nitrous oxide of an equal sized fossil or coal power plant. Concentrations of each environmentally disruptive gases are controlled by temperature, composition of fluid, and geological setting. Although most of the geothermal emissions commonly come from existing geothermal resource gas, some percentage of the emission also comes from various processes of the energy conversion process. Non-condensable gases are also emitted as a part of high temperature process of geothermal energy conversion.
According to various studies, the type of geothermal power plant design would really impact the production rate of the mentioned gasses. The selection between open-loop and closed (binary)-loop system is essential while taking into consideration air emission. Geothermal plants to this date are commonly separated into three main cycle design: dry-steam, flash-steam or binary –the first two extensively generate more greenhouse gasses (GHGs) compared to the last. In a binary loop system, gases which are removed from the system will not be transferred to the open atmosphere, instead, after transferring the heat gasses will be run through back to the ground, and result in minimal air pollution. In contrary, open-loop system emits all of the emission gas contained such as hydrogen sulfide, carbon dioxide and many more. There are also different factors which cause the technology to emits gases that are naturally present in the fluid such as fluid chemistry/composition, fluid phase, and geological setting to temperature.
The main types of air emission or contamination within the application of geothermal energy are commonly found to be carbon dioxide and hydrogen sulfide. Hydrogen sulfide reacts to produce SO2 once touched with the atmosphere. SO2 is known for its hazardous nature to health and environment, causing acid rain and respiration problem. Even though the concentration of this gas emission is significantly smaller than a conventional fuel power plant, reduction of hydrogen sulfide emission is still desirable for any conditions. Types of condensers installed to the design determines the ratio between the condensable and non-condensable gas. Consequently, with the right selection of condenser as well as implementing other reduction plans such as installation of adsorption tower, etc, hydrogen sulfide emission could be minimized.