2016年-世界发展银行全球_Greenhouse_Gases_from_Geothermal_Power_Production_52页_717kb

Summary of "GREENHOUSE GASES FROM GEOTHERMAL POWER PRODUCTION"

Core Content

This document provides an overview of greenhouse gas (GHG) emissions from geothermal power production and outlines methods for assessing these emissions. It is prepared by the Energy Sector Management Assistance Program (ESMAP) of the World Bank and serves as a technical note to guide the evaluation of GHG emissions from geothermal projects at different stages of development.

The report emphasizes that geothermal energy is a renewable source that can be used for heating or power production. While GHG emissions from geothermal power are generally low compared to fossil fuel-based power generation, they can be significant in certain geothermal systems, particularly those with high GHG concentrations in the reservoir fluid.

Main Points

• GHG Emissions from Geothermal Power Plants

  • GHG emissions are primarily composed of CO₂ and CH₄, with CO₂ being the dominant component.
  • CO₂ is typically more than 95% of the total non-condensable gas (NCG) in geothermal fluids.
  • CH₄ has a higher global warming potential than CO₂, but data on its emissions are limited.
  • The global average for operational CO₂ emissions from geothermal power production is 122 gCO₂/kWh, based on data from 2001, with country-specific values ranging from 34 gCO₂/kWh (Iceland) to 330 gCO₂/kWh (Italy).

• Emission Trends and Variability

  • There is a gradual decline in NCG concentration over time due to the reinjection of gas-free brine into the reservoir.
  • Some geothermal power plants, particularly those in carbonate-rich rock areas, may emit significantly higher levels of GHGs, such as the Menderes and Gediz grabens in Turkey and Mount Amiata in Italy.
  • High emission outliers can exceed even the emissions of conventional fossil fuel power plants, with values up to 1,300 gCO₂/kWh.

• Emission Factors and Estimation Methods

  • The report proposes an interim methodology for estimating GHG emission factors for geothermal projects.
  • For pumped binary power plants, the emission factor is 0 gCO₂e/kWh.
  • For projects in carbonate-rich areas, the emission factor is estimated at 790 gCO₂e/kWh.
  • For projects in volcanic or unknown geological settings, the global average of 128 gCO₂e/kWh is used.
  • If Plant Cycle emissions are included, a value of 10 gCO₂/kWh is recommended for a 30-year project lifetime.

• Knowledge Gaps and Recommendations

  • There are uncertainties regarding long-term emission trends and the impact of geothermal production on natural surface emissions.
  • The report recommends:
    • Systematic data collection from geothermal projects to monitor changes in emission factors over time.
    • Conducting baseline studies of surface GHG emissions before production starts.
    • Performing periodic surveys to assess the effect of geothermal power production on gas emissions.
    • Conducting feasibility studies for GHG capture and treatment, especially for projects that may emit more than the grid emission factor.

Key Information

• Geothermal Systems Classification

  • Geothermal systems are categorized based on reservoir temperature into low (<100–150°C), intermediate (100–150°C to 200°C), and high (>200°C) systems.
  • Low and intermediate temperature systems are liquid-dominated, while high temperature systems can be vapor-dominated or steam zones, leading to higher gas emissions.

• Geological Influences on GHG Emissions

  • Volcanic systems are the most common source of high-temperature geothermal energy.
  • CO₂ emissions can originate from:
    1. The geothermal fluid itself.
    2. Host rocks, especially carbonate rocks, which can release large amounts of CO₂.
    3. Deep crustal or mantle sources, or magma bodies.

• Natural Sources and Sinks of CO₂

  • CO₂ is naturally emitted through steam vents and diffuse soil emission, and can be dissolved in groundwater.
  • The geothermal cycle includes both natural and anthropogenic sources and sinks of GHGs.

• Technical Options for Mitigation

  • The report outlines technical options to mitigate CO₂ emissions, including:
    • Energy conversion technologies (e.g., binary systems, conventional turbines).
    • Gas sequestration technologies for capturing and treating GHGs.

Conclusion

This document is a comprehensive guide for assessing GHG emissions from geothermal power projects, highlighting the importance of understanding the geological context, reservoir characteristics, and energy conversion technologies in estimating emission factors. It also emphasizes the need for systematic data collection, baseline studies, and mitigation strategies to address knowledge gaps and ensure environmentally sustainable geothermal energy development.