Geothermal Power Generation

Developments and Innovation

Ron DiPippo, Ron DiPippo

• Éditeur: Woodhead Publishing
• Année: 2016
• ISBN:
  9780081003442
• Sujet: Technik & Maschinenbau
• Sous-sujet: Regenerative Energieressourcen

Geothermal Power Generation: Developments and Innovation provides an update to the advanced energy technologies that are urgently required to meet the challenges of economic development, climate change mitigation, and energy security.

As geothermal resources are considered renewable and can be used to generate baseload electricity while producing very low levels of greenhouse gas emissions, they can play a key role in future energy needs.

This book, edited by a highly respected expert, provides a comprehensive overview of the major aspects of geothermal power production. The chapters, contributed by specialists in their respective areas, cover resource discovery, resource characterization, energy conversion systems, and design and economic considerations.

The final section provides a range of fascinating case studies from across the world, ranging from Larderello to Indonesia. Users will find this to be an essential text for research and development professionals and engineers in the geothermal energy industry, as well as postgraduate researchers in academia who are working on geothermal energy.

• Provides readers with a comprehensive and systematic overview of geothermal power generation
• Presents an update to the advanced energy technologies that are urgently required to meet the challenges of economic development, climate change mitigation, and energy security
• Edited by a world authority in the field, with chapters contributed by experts in their particular areas
• Includes comprehensive case studies from across the world, ranging from Larderello to Indonesia

1

Introduction to geothermal power generation

L.Y. Bronicki     Ormat Technologies Inc., Reno, Nevada, United States

Abstract

Geothermal energy is the only alternative energy source which can supply base-load or dispatchable power, independent of climate and weather. Although not evenly distributed geographically, geothermal energy potential is substantial in many countries. Today, more than 10 GW of geothermal power plants are in operation around the world.

Unlike fossil fuel power plants, in geothermal power generation most of the capital costs are incurred up front in the development of the resource. The risks and challenges are all related to exploration, drilling, and managing the resource. Geothermal fluids come in a wide range of temperatures and consist of steam, brine of different chemical properties, as well as noncondensable gases.

Power conversion is the most predictable part of a geothermal project, as it consists of well-established engineering designs. Most plants use steam turbines, and about 20%, use the Organic Rankine Cycle. The economic exploitation of a geothermal fluid of given characteristics is achieved by choosing the power station configuration so as to maximize the exergy efficiency of the whole system (resource and plant) and not only the thermal efficiency of the plant.

The promising engineered geothermal systems aim at exploiting hot rock sources that are not accessible via conventional geothermal technology. Commercialization of this technology could unlock many thousands of megawatts of power, 100 GW in the United States alone.

Keywords

Geothermal energy; Engineered geothermal systems; Reservoir engineering; Organic Rankine cycle (ORC); Renewability; Sustainability

 

Geothermal energy is the only alternative energy source that can supply base-load or dispatchable power, independent of the climate. Although not evenly distributed geographically, geothermal energy potential is very important, particularly if research and development into technology such as engineered geothermal systems (EGS) will be actively pursued.

Chapters included in this publication cover subjects dealing with the nature of geothermal energy resources, their utilization, conversion technologies, as well as its future development. The chapters also highlight the greatest challenge in geothermal development, namely, the geothermal resource. Power conversion is the least uncertain part of a geothermal project but requires designs to ensure an economic exploitation of the resource over the designed life of the project. The risks and challenges are related to exploration, drilling, and managing the resource. Optimization depends on the manner in which the power station configuration is adapted to the available resource.

The distribution of geothermal resources is irregular due to unequal distribution of volcanoes, hot springs, and heat manifestations at specific locations over the Earth's surface. Geothermal resources are a reflection of the underlying global, local geological, and hydrological frameworks. The most thermally rich resources tend to concentrate in environments with abundant volcanic activity and tend to be controlled by plate tectonic processes or spreading centers evident as volcanic chains associated with subduction zones and hot spots. The local geological characteristics that favor useful resources include relatively shallow resource depths to high permeability in the rocks surrounding the resource, and adequate resource fluids.

Exploration starts with the analysis of available geological information to identify the potential target. Once the target is identified, geochemical studies and core drilling are undertaken. These studies are complimented or sometimes preceded by geophysical surveys including aeromagnetic or resistivity studies and remote infrared and hyper spectral techniques.

Hydrothermal systems have differing types of chemical properties which in turn impact the choice of materials and design of the power plant. The source of heat is usually a magma chamber a few kilometers below the surface. Fluid origin is meteoric, namely rain water, which infiltrates the ground to depths of a few kilometers. The permeability and degree of fracturing of this cap rock vary from site to site according to the intensity and abundance of the surface hydrothermal systems manifestations, such as hot springs, steam vents, geysers, etc.

In the early stages of exploration of a hydrothermal system when there is only surface evidence, the aim of a geochemical survey is the generation of a model that evaluates the temperature and chemical conditions of the fluid at depth.

Drilling of the wells for extracting geothermal energy resources is a niche within the larger drilling services industry that focuses primarily on oil, gas, and minerals. In particular, deep drilling required in most exploration programs for geothermal power generation projects will likely use large drill rigs typical in oil and gas extraction.

There are several aspects unique to geothermal drilling. Mainly, geothermal formations, by their nature, involve elevated temperatures, which are usually significantly higher than those experienced when drilling for oil and gas. The rock that hosts these formations are typically harder (granite, granodiorite, quartzite, basalt, volcanic tuff), more abrasive, highly fractured, and underpressured. Caustic elements may be present that can cause corrosion and scaling in the wellbore.

These unique characteristics present challenges in dealing with geothermal wells, which, unlike oil and gas wells, do not produce economically until used through electric generation or direct uses. For power production, geothermal wells must be of a larger diameter than oil and gas wells to produce sufficiently high flow rates for commercial production. Depths of geothermal wells vary according to location and can reach over 3000 m and even more for EGS projects.

Reservoir engineering is the comprehensive integration of all available surface and underground information regarding geology, geophysics, geochemistry, well drilling-testing, exploitation data, information concerning the geothermal developer, and objectives of a geothermal development (eg, market targets, costs, and finance), so it is the most powerful tool to evaluate the feasibility of a project. As in any scientific or engineering activity, results derived from reservoir engineering depend on the quantity and quality of the information, as well as the associated processing and interpretation of the information. Reservoir engineering is not limited to the final numerical tool but also includes acquisition of information which allows prediction of the impacts on a geothermal resource 20–30 years into the future.

Geothermal reservoir monitoring is the means for maintaining a sustainable geothermal field during operation. Using techniques such as downhole monitoring, surface monitoring, and introducing the collected data into the numerical model of the reservoir, the impact on the long-term sustainability of a geothermal field can be closely evaluated to ensure that the resource is not prematurely cooling and that any cooling or adverse impact can be mitigating by drilling makeup wells correctly located.

The promising engineered geothermal systems (EGS) aims to exploit hot rock not accessible via conventional geothermal technology. Commercialization of this technology could unlock many thousands of megawatts of power. For example, the estimate of the technical potential for EGS in the United States is estimated at 100 GWe, which is more than 30 times the total current installed geothermal capacity in the United States from current sources. As of the end of 2014 there has been some success in particular on engineered injection wells of existing plants, but no actual electricity production using both engineered production and injection wells on the same plant. Once EGS becomes commercialized, the system needs to demonstrate sustainability.

As with any other geothermal energy source, EGS development involves some impact on the environment. Geothermal resources are environmentally important as natural thermal features. Typically, the most significant environmental impacts are associated with the exploitation of high-temperature, liquid-dominated geothermal systems for electric power generation. However, the majority of these impacts can be avoided or minimized with appropriate techniques. Moreover, as geothermal energy generally offsets use of fossil fuels, the use of geothermal resources is more likely to improve air quality and overall water quality.

Geothermal power conversion are the techniques used for the conversion of thermal energy content of geothermal fluid into mechanical power to drive a generator and produce electrical power. Power conversion is the most predictable part of a geothermal project, as it consists of well-established and straightforward engineering design with work executed by experienced manufacturers, engineering firms, and contractors.

Today, more than 10 GW of geothermal power plants are in operation in the world, and a majority of them use steam turbines that operate on dry steam or steam produced by single- or double-flash with about 1.5 GW using organic Rankine cycles (ORC) or geothermal combined cycles. However, to widen the range of resources suitable for power generation beyond dry steam and flashed steam plants, ORC cycles have been implemented in the last 30 years and will probably continue to grow as a common technology driving future development of geothermal resources.

Operational experience confirms the advantages of ORC power stations, not only for low-temperature, liquid-dominated resources but also for certain high-temperature resources where the brine is aggressive or the fluid contains a high percentage of noncondensable gas. The higher installation cost of these systems, where economically feasible, is justified by environmental and long-term resource management considerations.

From the concept of sustainability and renewability of geothermal systems and the relationship between renewable and sustainable capacities, it is possible to estimate the commercial, sustainable, and renewable capacities of a geothermal system. Sustainability is defined as the ability to economically install and maintain power capacity over the amortized life of a power plant. This is done by taking practical steps, such as drilling “makeup” wells as required to compensate for resource degradation. Renewability is defined as the ability to maintain an installed power capacity indefinitely without encountering any resource degradation. Typically, the renewable power capacity at a geothermal site is generally too small for commercial development of electrical power capacity but may be adequate for district heating or other direct uses of the geothermal energy.

The cost of production for geothermal electric generation is important. In particular, the levelized cost of power is the applicable measurement for the cost of geothermal energy. Unlike fossil fuel power plants, most of the capital costs are incurred upfront in the development of the resource. Power cost is an objective criterion that favors geothermal solutions compared to other alternative energy sources. However, the costs are heavily tied to the resource and the need for makeup well drilling to maintain full generation capacity over the planned period of operation to provide an adequate return on investment.

Part One

Resource exploration, characterizationand evaluation

Outline

2. Geology of geothermal resources

3. Geophysics and resource conceptual models in geothermal exploration and development

4. Application of geochemistry to resource assessment and geothermal development projects

5. Geothermal well drilling

6. Characterization, evaluation, and interpretation of well data

7. Reservoir modeling and simulation for geothermal resource characterization and evaluation

2

Geology of geothermal resources

W.A. Elders¹, and J.N. Moore^{2 1}University of California, Riverside, CA, United States ²University of Utah, Salt Lake City, UT, United States

Abstract

Geological investigations are essential during the exploration, economic assessment, and production of geothermal resources. This chapter reviews the environments where these resources occur and the geological techniques used in their investigation. While the local geological setting, s...