Estimating carbon dioxide emissions from coal plants
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Four factors are used to estimate the CO2 emissions from coal plants:
- Plant capacity
- Plant capacity factor
- Heat rate of plant (an expression of efficiency)
- Emissions factor of the type of coal used in the plant
Contents
Formula
The CO2 emissions from a proposed coal plant can be calculated with the following formula:
annual CO2 (in million tonnes) = capacity * capacity factor * heat rate * emission factor * 9.2427 x 10^-12
Example for a typical coal plant
- Size: 1,000 MW
- Capacity factor: 80%
- Supercritical combustion heat rate: 8863 Btu/kWh
- Sub-bituminous coal emission factor: 96,100 kg of carbon dioxide per TJ
Based on these parameters, the annual CO2 for the plant is as follows:
Annual CO2 (million tonnes) = 1,000 * .8 * 8863 * 96,100 * 9.2427 * 10^-12 = 6.30 million tonnes
Capacity factor
"Capacity factor" or "load factor," is a measure of the amount of power that a plant produces compared with the amount it would produce if operated at its rated capacity nonstop. A capacity factor of 100% means that a plant is run at its maximum capacity for every hour of the year. Actual capacity factors are lower than 100% because of routine maintenance, fuel availability problems, and variations in demand.
Worldwide
As shown in table below, the average capacity factor for coal plants worldwide, based on the International Energy Agency's estimate for 2017, was 52.8%, down from 59.3% in 2013. Individual countries vary from 37.8% (Russia) to 82.2% (Japan).
| Country or region | Coal-fired electricity generation in 2017 (TWh) |
Coal-fired generating capacity in 2017 (GW) |
Capacity factor |
|---|---|---|---|
| China | 4446 | 981 | 51.7% |
| US | 1320 | 277 | 54.4% |
| India | 1194 | 224 | 60.8% |
| EU | 708 | 170 | 47.5% |
| Japan | 360 | 50 | 82.2% |
| South Africa | 226 | 42 | 61.4% |
| Russia | 172 | 52 | 37.8% |
| World | 9858 | 2130 | 52.8% |
| Country or region | Coal-fired electricity generation in 2014 (TWh) |
Coal-fired generating capacity in 2014 (GW) |
Capacity factor |
|---|---|---|---|
| China | 4146 | 855 | 55.4% |
| US | 1713 | 302 | 64.7% |
| India | 967 | 176 | 62.7% |
| EU | 841 | 177 | 54.2% |
| Japan | 349 | 50 | 79.7% |
| South Africa | 232 | 39 | 67.9% |
| Russia | 158 | 49 | 36.8% |
| OECD | 3478 | 614 | 64.7% |
| World | 9707 | 1882 | 58.9% |
Other Estimates
China: According to the China Electricity Council, the "national average utilization hours for thermal generation" during the first six months of 2013 was 2,412 hours. Compared to the actual number of hours in those months (4380), this suggests a capacity factor of 55.07 percent.[3]
India: For the period April 2011 - December 2011 India's Central Electricity Authority reported an all-India load factor of 72.10 percent.[4] A slightly lower figure of 69.63 percent (still high compared to the worldwide average) was reported by the Central Electricity Authority for the period April 2012 - December 2012.[5]
United States: Average capacity factor for coal plants dropped in the United States from 73 percent in 2008 to 60% in 2013.[6]
Heat rate
A coal plant's heat rate is a measurement of how well a plant performs the task of converting one form of energy (coal) to another form of energy (electricity). Note that in order for various measures of heat rate to be useful for comparative purposes, definitions must be consistent. For this reason the standard way of measuring heat rate is to compare the quantity of energy contained in coal as it enters the plant site to the quantity of energy contained in the electricity that exits the plant site into the grid. (Energy consumed to mine and transport coal is not included, nor is energy lost in moving electricity through the grid.) There are two common ways of expressing heat rate, one using Btu/kWh and the other using kcal/kWh. A plant that was 100 percent efficient at converting all its coal energy into electrical energy would have a heat rate of 860 kcal/kWh or 3412 Btu/kWh; of course, it is not possible for such a plant to exist. The higher the heat rate, the lower a plant's efficiency. Heat rate is determined by the type of combustion technology, the type of coal, and the size of the plant. Additional factors include continuity of operations (starting and stopping a plant degrades efficiency) and ambient temperature (the warmer temperature of the available cooling water will make a plant running in a hot climate less efficient than a plant running in a cold climate).
MIT's Future of Coal study (2007)
In 2007 MIT's Future of Coal study examined the coal combustion technologies used by nearly all coal plants.[7] According to the study, improved technologies (supercritical, ultra-supercritical) deliver significantly better efficiencies. Note that the Sargent & Lundy study (see below) showed more modest differentials among the various technologies.
| Technology | Type of Coal | Plant Capacity (MW) |
Net Heat Rate (kcal/kWh) |
Net Heat Rate (Btu/kWh) |
Net Plant Efficiency |
|---|---|---|---|---|---|
| Subcritical | Illinois #6 (bituminous) | 500 | 2,509 | 9,950 | 34.29% |
| Supercritical | Illinois #6 (bituminous) | 500 | 2,237 | 8,870 | 38.47% |
| Ultra-supercritical | Illinois #6 (bituminous) | 500 | 1,987 | 7,880 | 43.30% |
| Subcritical CFB | Lignite | 500 | 2,474 | 9,810 | 34.78% |
Note: As a U.S. study, it is presumed that the "Future of Coal" studied used the HHV method for calculating heat rates, which results in efficiency estimates approximately 2% to 4% lower than the LHV method used in the rest of the world.
Sargent & Lundy study (2009)
In 2009 the U.S. Environmental Protection Agency commissioned the consulting firm of Sargent & Lundy to make a study of heat rates at various types of coal plant. The study looked at the performance of currently available plant types (subcritical, supercritical, and ultra-supercritical) as well as technology not yet commercially available (advanced ultra-supercritical) or available but not widely deployed (IGCC). Coal types included lignite (Texas), subbituminous (Powder River Basin), and bituminous (Illinois #6). Plant size is measured in terms of gross capacity, i.e. prior to subtracting capacity devoted to internal plant functions. Heat rates were calculated on a net basis, i.e. based on a plant's actual delivery of electricity to the grid. Pollution controls included selective catalytic reduction (SCR), flu gas desulfurization (FGD), activated carbon injection (ACI), and baghouse.[8] As shown in the table, larger plants and higher grade coals result in better plant efficiency. (The sole exception to that principle is IGCC plants, which are expected to perform more efficiently with subbituminous coal than with bituminous coal.) The efficiency figures and heat rates provided by the Sargent & Lundy study were computed using the higher heating value (HHV) method, which is standard for coal plant ratings in the United States, rather than the lower heating value (LHV) method, which is standard outside the United States. The LHV method reflects actual field conditions, since it assumes that the condensate energy in plant steam is lost into the environment. The LHV method is used by the International Energy Agency. To convert HHV efficiencies to LHV efficiencies, two percentage points are added for bituminous coals, three percentage points are added for subbituminous coals, and four percentage points are added for lignite coals, as shown in Table 2.[9]
| Technology | Type of Coal | Plant Capacity (MW) |
Heat Rate Based on HHV Method (kcal/kWh) |
Heat Rate Based on HHV Method (Btu/kWh) |
Plant Efficiency Based on HHV Method |
HHV to LHV Conversion Factor | Plant Efficiency Based on LHV Method | Heat Rate Based on LHV Method (Btu/kWh) |
|---|---|---|---|---|---|---|---|---|
| Subcritical | Bituminous | 400 | 2,357 | 9,349 | 36.50% | 2% | 38.50% | 8,863 |
| Subcritical | Bituminous | 600 | 2,346 | 9,302 | 36.68% | 2% | 38.68% | 8,821 |
| Subcritical | Bituminous | 900 | 2,343 | 9,291 | 36.72% | 2% | 38.72% | 8,811 |
| Subcritical | Subbituminous | 400 | 2,376 | 9,423 | 36.21% | 3% | 39.21% | 8,702 |
| Subcritical | Subbituminous | 600 | 2,363 | 9,369 | 36.42% | 3% | 39.42% | 8,656 |
| Subcritical | Subbituminous | 900 | 2,360 | 9,360 | 36.45% | 3% | 39.45% | 8,648 |
| Subcritical | Lignite | 400 | 2,512 | 9,963 | 34.25% | 4% | 38.25% | 8,921 |
| Subcritical | Lignite | 600 | 2,499 | 9,912 | 34.42% | 4% | 38.42% | 8,880 |
| Subcritical | Lignite | 900 | 2,497 | 9,901 | 34.46% | 4% | 38.46% | 8,871 |
| Supercritical | Bituminous | 400 | 2,284 | 9,058 | 37.67% | 2% | 39.67% | 8,601 |
| Supercritical | Bituminous | 600 | 2,274 | 9,017 | 37.84% | 2% | 39.84% | 8,564 |
| Supercritical | Bituminous | 900 | 2,267 | 8,990 | 37.95% | 2% | 39.95% | 8,540 |
| Supercritical | Subbituminous | 400 | 2,302 | 9,128 | 37.38% | 3% | 40.38% | 8,450 |
| Supercritical | Subbituminous | 600 | 2,290 | 9,080 | 37.58% | 3% | 40.58% | 8,409 |
| Supercritical | Subbituminous | 900 | 2,284 | 9,057 | 37.67% | 3% | 40.67% | 8,389 |
| Supercritical | Lignite | 400 | 2,433 | 9,647 | 35.37% | 4% | 39.37% | 8,667 |
| Supercritical | Lignite | 600 | 2,422 | 9,603 | 35.53% | 4% | 39.53% | 8,631 |
| Supercritical | Lignite | 900 | 2,415 | 9,576 | 35.63% | 4% | 39.63% | 8,609 |
| Ultra-Supercritical | Bituminous | 400 | 2,250 | 8,924 | 38.23% | 2% | 40.23% | 8,480 |
| Ultra-Supercritical | Bituminous | 600 | 2,238 | 8,874 | 38.45% | 2% | 40.45% | 8,435 |
| Ultra-Supercritical | Bituminous | 900 | 2,233 | 8,855 | 38.53% | 2% | 40.53% | 8,418 |
| Ultra-Supercritical | Subbituminous | 400 | 2,268 | 8,993 | 37.94% | 3% | 40.94% | 8,334 |
| Ultra-Supercritical | Subbituminous | 600 | 2,254 | 8,937 | 38.18% | 3% | 41.18% | 8,286 |
| Ultra-Supercritical | Subbituminous | 900 | 2,250 | 8,921 | 38.25% | 3% | 41.25% | 8,272 |
| Ultra-Supercritical | Lignite | 400 | 2,396 | 9,502 | 35.91% | 4% | 39.91% | 8,550 |
| Ultra-Supercritical | Lignite | 600 | 2,383 | 9,449 | 36.11% | 4% | 40.11% | 8,507 |
| Ultra-Supercritical | Lignite | 900 | 2,378 | 9,430 | 36.18% | 4% | 40.18% | 8,491 |
| Advanced Ultra-Supercritical | Bituminous | 400 | 2,105 | 8,349 | 40.87% | 2% | 42.87% | 7,959 |
| Advanced Ultra-Supercritical | Bituminous | 600 | 2,094 | 8,305 | 41.08% | 2% | 43.08% | 7,919 |
| Advanced Ultra-Supercritical | Bituminous | 900 | 2,088 | 8,279 | 41.21% | 2% | 43.21% | 7,896 |
| Advanced Ultra-Supercritical | Subbituminous | 400 | 2,122 | 8,414 | 40.55% | 3% | 43.55% | 7,834 |
| Advanced Ultra-Supercritical | Subbituminous | 600 | 2,109 | 8,363 | 40.80% | 3% | 43.80% | 7,790 |
| Advanced Ultra-Supercritical | Subbituminous | 900 | 2,103 | 8,341 | 40.91% | 3% | 43.91% | 7,771 |
| Advanced Ultra-Supercritical | Lignite | 400 | 2,240 | 8,882 | 38.41% | 4% | 42.41% | 8,044 |
| Advanced Ultra-Supercritical | Lignite | 600 | 2,228 | 8,834 | 38.62% | 4% | 42.62% | 8,005 |
| Advanced Ultra-Supercritical | Lignite | 900 | 2,221 | 8,808 | 38.74% | 4% | 42.74% | 7,984 |
| IGCC | Bituminous | 600 | 2,124 | 8,425 | 40.50% | 2% | 42.50% | 8,029 |
| IGCC | Subbituminous | 600 | 2,033 | 8,062 | 42.32% | 3% | 45.32% | 7,528 |
| IGCC | Lignite | 600 | 2,147 | 8,515 | 40.07% | 4% | 44.07% | 7,742 |
Government of India CO2 Baseline Database (2013)
As part of its participation in the Clean Development Mechanism (CDM) under the Kyoto Protocol to the United Nations Framework Convention on Climate Change (UNFCCC), the government of India Central Electricity Authority publishes an annual report on the carbon dioxide emissions of the country's existing coal plants larger than 25 MW in size. Version 8 of this report, the results of which are shown in Table 3, is based on plants commissioned through 2012 and on 120 samples of coal from different Indian coal fields. While the characteristics of that coal are not included in the study, "Indian coal" typically refers to subbituminous coal.[10]
| Technology | Type of Coal | Plant Capacity (MW) |
Net Heat Rate (kcal/kWh) |
Net Heat Rate (Btu/kWh) |
Net Plant Efficiency |
|---|---|---|---|---|---|
| Unspecified | Indian coal | 67.5 | 3,125 | 12,393 | 27.53% |
| Unspecified | Indian coal | 120 | 2,747 | 10,894 | 31.32% |
| Unspecified | Indian coal | 200-250 | 2,747 | 10,894 | 31.32% |
| Unspecified | Indian coal | 300 | 2,582 | 10,239 | 33.32% |
| "Type 1" | Indian coal | 500 | 2,622 | 10,398 | 32.81% |
| "Type 2" | Indian coal | 500 | 2,545 | 10,093 | 33.81% |
| Unspecified | Indian coal | 600 | 2,545 | 10,093 | 33.81% |
| "Type 1" | Indian coal | 660 | 2,329 | 9,236 | 36.94% |
| "Type 2" | Indian coal | 660 | 2,274 | 9,018 | 37.84% |
| Unspecified | Indian lignite | 75 | 3,125 | 12,393 | 27.53% |
| Unspecified | Indian lignite | 125 | 2,909 | 11,536 | 29.58% |
| Unspecified | Indian lignite | 210-250 | 3,014 | 11,953 | 28.55% |
Global Coal Plant Tracker
For new coal-fired generating units of 400 MW and larger, the Global Coal Plant Tracker uses the following efficiencies and corresponding heat rates:
| ' | Efficiency | Heat Rate (Btu/kWh) |
| Subcritical | 38% | 8979 |
| Supercritical | 42% | 8124 |
| Ultra-supercritical | 44% | 7755 |
Effect of plant age and size on heat rate
Overall, coal plant efficiency is lower in older, small plants than in larger, new ones. According to the International Energy Agency, the efficiency of new subcritical plants may be 38% on a LHV basis, while that of an older subcritical plant may be 20% to 25%.[11]
As of July 2018, the Global Coal Plant Tracker applies a 10% performance penalty to plants older than 9 years, a 15% performance penalty to plants older than 19 years, and a 20% performance penalty to plants older than 29 years. In addition, the GCPT also applies a 10% performance penalty to units smaller than 400 MW and an additional 10% penalty to units smaller than 200 MW. Together, the two penalties may amount to a 45% increase in emissions for the smallest, oldest plants.[12]
| ' | 0 - 349 MW | 350 - 449 MW | 450+ MW |
| 0 - 9 Years | 20% | 10% | 0% |
| 10 - 19 Years | 30% | 20% | 10% |
| 20 - 29 Years | 40% | 30% | 20% |
| 30+ Years | 45% | 35% | 25% |
Emission factor
US Department of Energy
The following carbon dioxide emission factors were estimated by the U.S. Department of Energy for coals in the United States.[13]
- Lignite (i.e. brown coal): 216.3 pounds of carbon dioxide per million Btu
- Subbituminous coal: 211.9 pounds of carbon dioxide per million Btu
- Bituminous coal: 205.3 pounds of carbon dioxide per million Btu
- Anthracite: 227.4 pounds of carbon dioxide per million Btu
It appears that the U.S. values are based on the high heat value approach.
Note that, perhaps counterintuitively, carbon dioxide emission factors are not necessarily lower for higher quality coals. For example, anthracite coal, which is the highest quality coal, produces more carbon dioxide per Btu than low-quality lignite. This is because anthracite lacks hydrogen, which is a small portion of the content of lower grade coals. When burned, hydrogen is transformed into water vapor (H2O) rather than carbon dioxide (CO2). Therefore, nearly all the energy in anthracite comes from the combustion of carbon, resulting in higher carbon dioxide emission rates per unit of energy than when lower grade coals containing some hydrogen are burned. (Of course, on a tonnage basis, higher grade coals do produce more carbon dioxide than lower grade coals.)
IPCC
The following carbon dioxide emission factors for stationary combustion in the energy industries are estimated by the IPCC.[14]
- Lignite: 101,000 kg of carbon dioxide per TJ
- Subbituminous coal: 96,100 kg of carbon dioxide per TJ
- Bituminous coal: 94,600 kg of carbon dioxide per TJ
- Anthracite: 98,300 kg of carbon dioxide per TJ
These figures are based on the low heat value (i.e. net calorific) approach.
Coefficient
9.2427 x 10^-12
This is the product of:
- 1.00 * 10^-9 million tonnes per kg
- 8.76 * 10^6 kWh per MW
- 1.06 * 10^-9 TJ per Btu
It allows the amount of carbon dioxide emitted by a plant to be described in millions of tonnes.
Lifetime
According to unit-by-unit assessment in the Global Coal Plant Tracker (January 2019), coal-fired units have retired at an average of 38 years, and a capacity-weighted average of 39 years, although the average age varies greatly by region:
| Region | Average age of retirement (years) |
| Africa and Middle East | 28 |
| Australia/New Zealand | 42 |
| Canada/United States | 52 |
| East Asia | 23 |
| Eurasia | 51 |
| Latin America | 37 |
| EU28 | 43 |
| non-EU Europe | 46 |
| Southeast Asia | 20 |
| South Asia | 20 |
| China | 23 |
| India | 40 |
| United States | 52 |
| World | 38 |
Articles and resources
References
- ↑ World Energy Outlook 2018, International Energy Agency, Annex A, June 2018 (fee required)
- ↑ World Energy Outlook 2016, International Energy Agency, Annex A, November 2016 (fee required)
- ↑ "2013年1-6月份电力工业运行简况" China Electricity Council, 2014
- ↑ "All India Plant Load Factor," Central Electricity Authority, accessed July 2014
- ↑ "All India Plant Load Factor Thermal," Central Electricity Authority, accessed June 2014
- ↑ "Benchmarking Emissions," Natural Resources Defense Council, 2014, page 2.
- ↑ 7.0 7.1 "The Future of Coal," Massachusetts Institute of Technogy, 2008, Table 3.1: Representative Performance and Economics for Air-Blown PC Generating Units," p. 19.
- ↑ 8.0 8.1 "NEW COAL-FIRED POWER PLANT PERFORMANCE AND COST ESTIMATES," Sargent & Lundy, 2009
- ↑ "High Efficiency Electric Power Generation; The Environmental Role," János Beér, Massachusetts Institute of Technology, undated
- ↑ 10.0 10.1 "CO2 Baseline Database for the Indian Power Sector: User Guide Version 8.0," Central Electricity Authority, January 2013, Appendix B
- ↑ Technology Roadmaps: High-efficiency, low-emissions coal-fired power generation," International Energy Agency, 2012, page 17.
- ↑ A 40% differential between the most efficient new subcritical plants and older subcritical is noted by Ben Caldecott, Gerard Dericks, and James Mitchell of the University of Oxford in their study of subcritical coal."Stranded Assets and Subcritical Coal: The Risk to Companies and Investors," Oxford Sustainable Finance Programme, 2015, p. 14
- ↑ B.D. Hong and E.R. Slatick, "Carbon Dioxide Emission Factors for Coal," U.S. Energy Information Administration, 1994
- ↑ "2006 IPCC Guidelines for National Greenhouse Gas Inventories," Table 2.2 "Default Emission Factors for Stationary Combustion in the Energy Industries," page 2.16
Related SourceWatch articles
External resources
- List of countries by carbon dioxide emissions, Wikipedia
- "All India Plant Load Factor," Central Electricity Authority
- Michael Lazarus and Chelsea Chandler, Coal Power in the CDM: Issues and Options," Stockholm Environment Institute, working paper 2011
- "New Coal-Fired Power Plant Performance and Cost Estimates," Sargent & Lundy, 2009
- Charlotte Hussy, Erik Klaassen, Joris Koornneef and Fabian Wigand, "International comparison of fossil power efficiency and CO2 intensity – Update 2014," Ecofys
