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HomeMy WebLinkAboutgreenhousegases77MARCH / APRIL 2003 Climate Change Research his article updates a previous Bloomfield and Moore (1999) esti- mate of the quantity of carbon diox- ide (CO2), hydrogen sulfide (H2S), meth- ane (CH4) and ammonia (NH3) emitted dur- ing geothermal power generation. Since that estimate in 1999, more geothermal power generation capacity has been added in the United States, primarily in the Impe- rial Valley of southern California. Formal reporting required for fossil-fuel power pro- duction provide updated estimates of emis- sions from generation by those sources. Greenhouse Gas Emissions and Climate Impacts For the last century, human activities have been altering the global climate. Ob- servations show that the Earth’s surface has warmed by approximately 0.6 oC (1.1 oF) during the 20th century (CCSP, 2003). At- mospheric abundances of the major, hu- man-generated greenhouse gases, i.e. CO2, CH4, and nitrous oxides (NOx), reached their highest recorded levels in modern history CO2 Emissions from Geothermal Energy Facilities are Insignificant Compared to Power Plants Burning Fossil Fuels By K. Kit Bloomfield (INEEL), Joseph N. Moore (EGI), and Robert M. Neilson, Jr. (INEEL) by the year 2000 and are continuing to rise. About 37 percent of incremental atmo- spheric CO2 accumulation is caused by electric power generation, mainly from the burning of fossil fuels (EIA, 2000). To counteract these climatic effects, delegations from more than 150 countries met in Kyoto, Japan in December of 1997 to complete negotiations on a United Na- tions treaty to reduce their emissions of certain greenhouse gases. That agree- ment—the Kyoto Protocol—calls on devel- oped nations to reduce their use of carbon- emitting fossil fuels. In the United States, CO2 emissions account for roughly 85 per- cent of the total for the world. If the Kyoto Protocol is ratified by the U.S. Senate, the United States will have to limit emissions of CO2 and five other gases by 2008-2012 to 93 percent of 1990 emissions. This target appears to be fairly mod- est, at least until U.S. Department of En- ergy (DOE) projections of energy use and emissions for 2010—based on normal busi- ness-as-usual energy and economic growth expectations—are considered. Under this scenario, the United States will have to re- duce emissions by nearly one-third of pro- jected emissions to reach the target values (EIA, 2000). The emissions reduction target is very ambitious, and will require unprecedented action for the United States to get the job done in such a short period of time. It means Americans will have to slash their energy use or select green energy sources quickly and comprehensively (or that production and process efficiencies will have to in- crease dramatically). The use of geother- mal energy can be a significant contributor to reducing energy related CO2 emissions. Government Activities Former U.S. President Clinton issued a directive on April 15, 1999, requiring an annual report summarizing CO2 emissions produced during electric power generation by both utilities and non-utilities in the United States. In response, DOE and the U.S. Environmental Protection Agency jointly submitted the first report on Octo- ber 15, 1999 (DOE/EPA, 2000). With two major policy actions, President Bush has also emphasized the importance of tech- nology in stabilizing greenhouse gas con- centrations in the atmosphere. The Na- tional Climate Change Technology Initia- tive (NCCTI) announcement on June 11, 2001 included tax incentives for energy efficiency improvements and renewable technologies for buildings, light-duty ve- hicles and electric generation. To improve research support for decision making and to increase accountability, President Bush T Table 1. Comparison of Geothermal and Fossil Fuel CO2 Emissions. Geothermal Coal Petroleum Natural Gas Emissions 0.20 2.095 1.969 1.321 (lbs. CO2/kW-hr) Table 2. Geothermal “Greenhouse Gas” Emissions CO2 H2S CH4 NH3 Emissions 0.20 1.87E-04 1.66E-03 1.39E-04 (lbs./kW-hr) 78 GRC B ULLETIN Climate Change Research announced on Feb. 4, 2002, the establish- ment of a new, high-level structure for coordinating federal climate change sci- ence and technology development. Geothermal CO2 Sequestration and Government Activities The federal government has funded a number of activities to investigate seques- tration of CO2 created by electric power generation. The Integrated Sequestration and Hydrogen Research Initiative is a $1 billion government/industry partnership to design, build and operate a nearly emission- free coal-fired electric and hydrogen pro- duction plant. The 275-megawatt (MW) prototype plant will serve as a large-scale engineering laboratory for testing new clean power, carbon capture and coal-to-hydro- gen technologies. The experience of geothermal plant operators with non-condensable gas injec- tion into their reservoirs is relevant to CO2 sequestration research and development (R&D). Coso Operating Co. (China Lake, CA) has experimented with injecting or sequestering non-condensable gases mixed with spent geothermal fluids. Operationally, the injection of non-condensable gases met with partial success. The gases communi- cated very rapidly with some production wells, but not at all with others. Also, cor- rosion of injection well tubulars increased with the water/gas mixture. Although there are no engineering bar- riers to injection of CO2 into geothermal reservoirs, careful placement of CO2 injec- tors that will not communicate with geo- thermal fluid production wells is essential. Water injection is critical to reservoir man- agement to sustain fluid production. It is apparent that CO2 and water cannot be in- jected into the same well. Therefore, a com- pression and transport system is needed to move CO2 to non-communicating wells, and premium construction materials may be needed due to corrosion considerations.. U. S. Geothermal Greenhouse Gas Emissions The most commonly cited reference on gaseous emissions from U.S. geother- mal power plants was written by Goddard and Goddard (1990), which determined emissions based on data from utility power producers. This data was mainly gathered at The Geysers in northern Cali- fornia, because Pacific Gas & Electric owned the power plants at the time. How- ever, in estimating geothermal emissions it is important to consider both utility and non-utility power operations, and the mix of dry steam, flashed steam, and binary technology facilities. More importantly, improved and in- creased injection to sustain reservoir re- sources has diminished the CO2 released from geothermal power plants. Benoit and Hirtz (1994) reported that CO2 emissions from the Dixie Valley geothermal plant in northern Nevada had decreased from 0.152 pounds of CO2 per kilowatt-hour (kWh) of electricity produced in 1988 to 0.093 lbmCO2/kWh in 1992. Steam that feeds dry-steam and flash-steam plants can contain several weight-percent of non-condensable gases. In these plants, gases contained in reservoir fluids pass through turbines with the steam—but unlike the steam, the gases do not condense at the turbine ex- haust outlet. These non-condensable gases are either exhausted to the atmo- sphere or to a primary abatement system where H2S is removed. The quantity of gases present in the geothermal fluid and subsequently emitted depends on several factors, including the characteristics of the resource (dry steam or liquid, reser- voir fluid composition, temperature), the method of electrical generation (flash, bi- nary, or combined cycle), and plant char- acteristics (efficiency and H2S abatement equipment). Binary power plants release no non-condensable gases because their geothermal fluids are not exposed to the atmosphere (Blaydes, 1994). There are no federal emission limits for CO2 Under the Clean Air Act of 1990. Consequently, formal reporting of CO2 emissions is not required by regulatory agencies, denying such data for geothermal power plants to the public domain. Regu- latory agencies commonly require an emis- sion source compliance test for other gases, however, including H2S, NH3 and CH4. Data on CO2, CH4, NH3 and H2S emissions presented here were obtained from geother- mal power plant operators, utilities, and state air-quality control boards. The pri- mary sources of electrical production and CO2 emissions data for this article were operators of geothermal dry steam and flash plants. Measurement of non-condensable gases in geothermal fluids is critical dur- ing initial well testing for power plant design and regulatory concerns. Non- condensable gas content is a major fac- tor in designing condensers, non-con- densable gas ejector systems, and H2S abatement systems for geothermal power plants. Non-condensable gases can be a major regulatory and permitting concern that may result in large capital and op- erational costs. Although there is no legal require- ment for the collection of CO2 emission data, it is collected during required com- pliance tests for regulated emissions. Since production of non-condensable gases is often used as a reservoir moni- toring tool and an indicator of power plant energy conversion efficiency, CO2 data may also be collected during opera- tions. Data supplied by power plant op- erators included total steam flow to the plant in mass per hour; the mass ratio of steam to total non-condensable gas; net Figure 1. CO2 emissions (lbs. CO2/kW-hr). 79MARCH / APRIL 2003 capacity of the plant in MW; and con- centrations of gaseous components. Several assumptions were made in performing emission calculations. It was assumed that CH4, H2S, NH3, and CO2 are quantitatively ejected to the atmosphere, i.e., there is no partitioning between the atmosphere and the condensate. Because some solution of these gases will occur in cooling tower condensate, the calcu- lations slightly overestimate the quanti- ties of gases emitted from plants where condensate is injected. In contrast, data on the CO2 contents of injected fluids at The Geysers was provided, and the ef- fect of this injection was considered when CO2 emissions from that geothermal field were calculated. This correction was not made for emissions from flashed-steam plants. Emissions reported in Tables 1 and 2 are weighted average values for all geo- thermal capacity, including binary power plants that do not emit CO2. Data cannot be reported by power plant type because some of it is proprietary nature, but binary plants represented only 14 percent of ca- pacity in the weighted average. Table 1 compares CO2 emissions from geothermal power plants to those from fossil-fuel plants. CO2 emission values for coal, pe- troleum and natural gas plants are calcu- lated using data from DOE’s Energy In- formation Administration (EIA, 2002). Ta ble 2 shows emissions of greenhouse gases from geothermal plants per unit of geothermal electricity produced. Recently, International Geothermal Association (IGA - Pisa, Italy) Executive Director Ruggero Bertani reported on emis- sions from 85 geothermal power plants cur- rently operating in 11 countries (Bertani, 2002). His findings, with a weighted aver- age CO2 emission of 122 g/kWh (0.29 lbs/ kWh), were similar to the rate calculated for this article. In 2001, EIA reported that coal, natural gas and oil provided 72 per- cent of electric power generation. Based on Ta ble 1, these sources had a weighted av- erage CO2 emissions rate of 1.926 lbs/kWh. Note also that SOx and NOx emissions are not considered for fossil-fuel electric power production, nor are other life-cycle costs such as emissions incurred during transpor- tation of coal to power plants. Conclusions Our results reveal that geothermal power production has a significant en- vironmental advantage over burning fos- sil fuels for electrical power production. Electrical production from geothermal fluids results in an order of magnitude less CO2 per kilowatt-hour of electricity produced compared to burning fossil fu- els. Thus, the data clearly demonstrate that increased geothermal utilization can help the United States reduce green- house gas emissions, assisting National Climate Change Technology Initiative goals while helping to meet increasing power demands. Acknowledgment This manuscript was authored by a contractor of the U.S. Government under DOE Contract DE-AC07-99ID13727. Ac- cordingly, the U.S. Government retains a nonexclusive, royalty-free license to pub- lish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes. References Benoit, D., and P. Hirtz, 1994. “Non-Condensable Gas Trends and Emissions at DixieValley,” Geothermal Resources Council Transactions, v. 18, pp. 113-117. Bertani, R., 2002. “Geothermal Power Generating Plant CO2 Emission Survey, International Geothermal Association IGA News, n. 49. Blaydes, P.E., 1994. “Environmental Advantages of Binary Power Plants Can Enhance Development Opportunities,” Geothermal Resources Council Transactions, v. 18, pp. 121-125. Bloomfield, K.K., and J.N. Moore, 1999. “Production of Greenhouse Gases from Geothermal Power Plants,” Geothermal Resource Council Transactions, v. 23, pp. 221-223. Our Changing Planet. Climate Change Science Program and the Subcommittee on Global Change Research, 2003, 132 p. DOE/EPA, 2000. Carbon Dioxide Emissions from the Generation of Electric Power in the United States, 21 p. EIA, 2001. Electric Power Annual 2000, v. I, DOE/EIA- 0348(2001)/1, 66 p. EIA, 2001. Electric Power Annual 2000, v. II, DOE/EIA- 0348(2002)/2, 136 p. Goddard, W.B., and C.B. Goddard, 1990. “Energy Fuel Sources and Their Contributions to Recent Global Air Pollution Trends,” Geothermal Resources Council Transactions, v. 14, pp. 643-649. One of the most valuable services that the GRC performs for its members is to pro- vide forums like the Bul- letin to help them keep up with indus- try trends and technologies — and to share good news. To do our job well, the GRC needs to hear from YOU! How can you keep us informed? It’s easy. Add us to your mailing list for press releases, newsletters and other publications. Call, or drop a note by e- mail or fax to let us know about new projects, technologies, products and personnel. And be sure to send us cop- ies of newspaper or magazine articles that feature geother- mal energy, re- source devel- opment, and renewable en- ergy issues. Geothermal Resources Council P.O. 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