Carbon dioxide emission tallies for 210 U.S. coal-fired power plants: A comparison of two accounting methods

Figures & data

Figure 1. Annual CO₂ emissions measured by CEMS (CAMD data) vary by ±10.8% (two times the standard deviation) from CO₂ emissions calculated from fuel consumption (EIA data) for 210 U.S. coal-fired power plants during 2009. The percent difference was calculated according to: 100 × (CAMD – EIA)/[(CAMD + EIA)/2].

Figure 2. Annual CO₂ emission rates calculated from CAMD and EIA data for 210 U.S. power plants during 2009 show similar mean values (2,062 and 2,074 lb CO₂/MWh, respectively), but more variable CAMD emission rates compared to EIA emission rates (standard deviations of 178 and 137 lb CO₂/MWh, respectively).

Figure 3. Attenuation bias due to CAMD measurement error is shown by comparison of best-fit lines where (a) EIA CO₂ emission rates are used to predict CAMD rates, and (b) CAMD CO₂ emission rates are used to predict EIA rates (data are for 210 U.S. coal-fired power plants during 2009). Although both lines share the same significance and correlation (P < 0.001, R ² = 0.61), note the larger standard error for (a) and that the slope for (b) is closer to zero.

Table 1. EPA methods used to measure and certify flue-gas flow. Results from the installed measurement system must agree with results from one or more of these methods

Method	Description
2	Assumes laminar flow, no wall effects adjustment
D2H	Assumes laminar flow, default wall effects adjustment
M2H	Assumes laminar flow, measured wall effects adjustment
2G	Assumes inclined flow, no wall effects adjustment
2GH	Assumes inclined flow, measured or default wall effects adjustment
2F	Assumes swirling flow, no wall effects adjustment
2FH	Assumes swirling flow, measured or default wall effects adjustment
2J	Rectangular ducts, assumes laminar flow, measured or default wall effects adjustment
2GJ	Rectangular ducts, assumes inclined flow, measured or default wall effects adjustment
2FJ	Rectangular ducts, assumes swirling flow, measured or default wall effects adjustment

Table 2. The difference between CAMD and EIA CO₂ emissions varied with the method used to certify the CAMD flue-gas flow measurement at 112 power plants during 2009

Method	n ^a	CO2 % difference ^b	^σ %diff. ^c	t-Statistic ^d	P ^e
2	32	+3.0	5.4	−4.5	0.00 ^f
2F	9	+1.6	5.8	−1.3	0.19
D2H	13	−0.2	5.0	−0.4	0.70
2FH	12	−0.8	4.9	0.0	0.96
M2H	17	−3.1	4.2	+1.9	0.06 ^g
2GH	29	−3.0	4.8	+2.5	0.01 ^f
^aNumber of plants.
^bAverage percent difference between CAMD and EIA CO2 emissions, calculated as: 100 × (CAMD – EIA)/[(CAMD + EIA)/2].
^cStandard deviation of the percent difference.
^dTwo-sample, ntotal =210, assuming equal variances.
^e Significance, two-tailed distribution.
^f Method significantly different at 95% confidence.
^g Method significantly different at 90% confidence.

Figure 4. The minimum error of the annual CO₂ emission tally calculated from the EIA fuel consumption data varies between ±1.3% and ±7.2% for 210 U.S. coal-fired power plants during 2009.