Location: NPCC, US only - Northeast Power Coordinating Council, US part only
This dataset represents the production of high voltage electricity and heat in a combined cycle natural gas power plant with CHP (combined heat and power) in US - Northeast Power Coordinating Council in 2012.
In a combined cycle power plant, a gas turbine is followed by a steam turbine. The dataset refers to a combined cycle power plant of 400MWe class with a gas turbine 260MWe and a steam turbine 140MWe.
For electricity production with natural gas, four different datasets relying to different power plant types exist:
- conventional power plant with / without CHP
- combined cycle power plant with / without CHP
At the moment, these datasets differ in nothing but the efficiency. High voltage electricity (at the busbar) is the reference product, whereupon heat is a by-product in CHP plants. Out of all fossile fuels, natural gas holds worldwide the highest share of CHP plants besides peat. Furthermore, natural gas power plants are today often designed with combined cycles. The advantages of a combined cycle power plant are for example:
- a higher efficiency (approximately between 50-60% compared to ca. 33% for a conventional power plant)
- high operating flexibility
- lower emissions due to higher efficiency
- lower cooling water need.
The approximate share of combined cycle natural gas power plants in US - Northeast Power Coordinating Council amounts to ca. 36%. About 27% are combined heat power plants (calculations made with IEA/OECD statistics and own assumptions).
The efficiency calculations are based on IEA/OECD statistics (fuel inputs, electricity produced) and some own calculation assumptions. Reducing factors such as contaminations of important plant parts, cooling conditions or part load have been taken into account. Even if efficiencies vary with different surrounding temperatures, a medium efficiency is assumed for all countries. Temperature adjustments would be related to high uncertainties.
Water is used for wet cooling and as feed water in the steam circuit. In this dataset, 100% wet cooling and no once-through cooling is assumed.
EMISSIONS:
Different sources served as basis for assumption of average emissions. Where possible, the most recent sources were taken into account, whereas older sources were taken in order to determine the remaining data gaps. The emissions have been fixed for the former UCTE region* and have been overtaken as such for all countries without value adaptation (adaptation of the uncertainty). See ecoinvent report 'Erdgas' given as main source for details (Tab. 11.15). In the following a short overview:
- Emissions of NOx, CO, CO2, SO2, particles, N2O and CH4 are mainly taken from CORINAIR 2001, EPA, and a variety of other data sources
- NOx emissions are a major challenge in natural gas power plants. With rising temperature, emissions also rise; band widths of NOx emissions in literature are correspondingly large. There are several methods to diminish these emissions.
- CO is a result of incomplete burning. For economic and technical reasons, plant combustion is optimized and CO emissions are low.
- CO2 and SO2 emissions are dependent on the composition of the used fuel. Due to the low sulfur content of the used natural gas, no desulfurization has to take place.
- Organic compound emissions are estimated on the basis of EPA 1998.
- Particles are assumed to be smaller than 2.5 micro-m
former UCTE: Union for the Coordination of the Transmission of Electricity, since 2009 replaced by ENTSO-E European Network of Transmission System Operators for Electricity.
Sources:
- CORINAIR 2001. EMEP/CORINAIR 2001: Joint EMEP/CORINAIR Atmospheric Emission Inventory Guidebook, Third Edition. Copenhagen: European Environment Agency, 2001. http://reports.eea.eu.int/technical_report_2001_3/en.
- EPA 1998. US Environmental Protection Agency (1998). Compilation of Air Pollutant Emission Factors, AP-42, Fifth Edition, Volume I: Chapter 1: External Combustion Sources, Natural Gas Combustion - Final Section - Supplement D , July 1998. CHIEF (Clearinghouse for Inventories and Emission Factors). Research Triangle Park, North Carolina. http://www.epa.gov/ttn/chief/ap42/.
- Rentz O., Karl U., Peter H. (2002). Ermittlung und Evaluierung von Emissionsfaktoren für Feuerungsanlagen in Deutschland für die Jahre 1995, 2000 und 2010. Deutsch- Französisches Institut für Umweltforschung, Uni Karsruhe. Endbericht. Im Auftrag des Umweltbundesamtes. Forschungsbericht 299 43 142. Umweltbundesamt. Berlin.
Undefined unit processes (UPRs) are the unlinked, multi-product activity datasets that form the basis for all of the system models available in the ecoinvent database. This is the way the datasets are obtained and entered into the database by the data providers. These activity datasets are useful for investigating the environmental impacts of a specific activity (gate-to-gate), without regard to its upstream or downstream impacts.