Reduction of atmospheric emissions due to switching from fuel oil to natural gas at a power plant in a critical area in Central Mexico

Figures & data

Figure 1. Location of the Tula-Vito-Apaxco industrial corridor (TVAIC) in central Mexico. The dark color corresponds to urban areas; the MCMA corresponds to the gray spot in the center that extends north of Mexico City.

Table 1. Maximum permissible emission levels for thermoelectric indirect heating combustion equipment, NOM-085-SEMARNAT-2011 (DOF 2012).

Thermal capacity (GJ/h)	Fuel type	PM (mg/m^3)	SO2 (ppmv)	NOx (ppmv)	CO (ppmv)
More than 530 (More than 15,000 CC)	Solids & liquids	250	600	110	400
	Gases	-	-	110	450

Figure 2. Temporal annual average air pollutant reduction from 1990 to 2017 within the MCMA.

Table 2. Emission factors used in this study for criteria pollutants, calorific values and sulfur contents for fuel oil and natural gas.

CRITERIA POLLUTANT EMISSION FACTORS
			Fuel Oil^a Calorific value 9965 (± 21) x 10^3 kcal/m^3 Sulfur content 3.38– 4.00%		Natural Gas^a Calorific value 8.528 (± 0.31) x 10^3 kcal/m^3 Sulfur content 3.5 x 10^–4%
Configuration	Pollutant	Formula	Emission Factor (lb/10^3 gal) ^b	Emission Factor Rating	Emission Factor (lb/10^6 ft^3) ^b	Emission Factor Rating
All Types	Sulfur dioxide	SO2	154.3 S ^c	A	0.6	A
Normal Firing	Nitrogen Oxides	NOx ^d	47	A	190	A
Tangential Firing			32	A	170	A
Normal Firing	Carbon Monoxide	CO ^e	5	A	84	B
Tangential Firing			5	A	24	C
All Types	Lead	Pb	1.51E^−03	C	5.00E^−04	D
All Types	Total Particles	PM	8.3A ^f	C	7.6	D

Notes. ^aCalorific values and sulfur content are obtained as average and 95% interpercentile range from daily consumption information provided by CTFPR between November 1, 2010 and February 8, 2011.

^bAP-42 emission factors are presented in lb/10³ gal for fuel oil and in lb/10⁶ ft³ for natural gas; the appropriate conversions were done to obtain emissions in kg/d (emission estimations) and in g/s (CALPUFF model inputs).

^c S is the sulfur content of the fuel in percentage, which must be multiplied by the given value. This is the only emission factor specifically available for Mexican power plants (Cureño, Bravo, and Sosa 2010). The rest is from AP-42.

^dIt has been observed that about 95% of NOx is emitted as NO.

^eCO emissions can increase by factors of 10 to 100 if units are operated incorrectly or are not well maintained.

^fThe emission factor for particulate matter without control equipment is a function of fuel grade and sulfur content of the fuel. For No. 6 grade fuel oil the A value is obtained from the following equation A = 1.12( S ) + 0.37.

Table 3. Technical specification of the generating units at the CTFPR.

		UTM coordinates (km)
Generating unit	Stack	X	Y	Diameter (m)	Height (m)	Gas exit temperature (K)
1	1	470.961	2217.813	3.4	65.00	460.13
	2	470.961	2217.803	3.4	65.00	460.13
2	3	470.958	2217.783	3.4	65.00	445.45
	4	470.957	2217.772	3.4	65.00	445.45
3	5	470.952	2217.695	5.3	65.00	453.65
4	6	470.949	2217.667	5.3	65.00	440.76
5	7	470.947	2217.599	5.4	56.00	430.78

Figure 3. Comparison of the total annual emissions (sum of the five generating units) during 2010, for fuel oil and natural gas consumption at the CTFPR.

Figure 4. Comparison of total daily emissions of SO₂, CO, NOx, Pb, PM and CO₂, for fuel oil and natural gas consumption during 2010. SO₂ and PM have logarithmic y-axis scales.

Figure 5. Wind roses for the cold-dry, warm-dry and warm-wet seasons in the CECATI station in Tepeji del Río, March 2010 – February 2011.

Figure 6. Wind roses for the cold-dry, warm-dry and warm-wet seasons for the northern part of the MCMA, January – December 2010.

Figure 7. Hourly SO₂ concentrations (μg/m³) estimated by CALPUFF for fuel oil consumption at the CTFPR, December 13, 2010 (12:00 LT). The CECATI meteorological station and CTFPR power plant are indicated in red.

Figure 8. Comparison of measured (CECATI station) and modeled (CALPUFF) SO₂ emissions for fuel oil consumption between March 4, 2010 and February 9, 2011.

Figure 9. Temporal profile of CALPUFF simulated SO₂ concentrations during 2010 for receptors > 15 km south of the CTFPR. The orange line corresponds to the Mexican AQS for 24 hr averages.

Figure 10. Box-whisker plot of simulated maximum 24 hr SO₂ mass concentrations from fuel oil consumption at the CTFPR during March-December 2010 and January-February 2011.

Figure 11. Spatial distribution of the 2010 daily average SO₂ concentration in µg/m³ at 12 monitoring stations within the MCMA.

Figure 12. Box-Whisker plot of monthly distributions of 24 hr SO₂ concentration at 6 northern monitoring stations (see Figure 11) within the MCMA during 2010.

Figure 13. MCMA affectation due to SO₂ emissions from the CTFPR, estimated by the AQFS-CdMX system for selected days and hours: (a) January 14, 2018 (10:00 LT), (b) March 14, 2018 (06:00 LT) and (c) April 2, 2019 (07:00 LT).

Figure 14. Annual average sulfate concentrations (µEq/L) in atmospheric wet deposit during 2010, in different sites of the MCMA: IBM Legaria (IBM), Laboratorio de Analisis Ambiental (LAA) and Tlalnepantla (TLA) at the NE; Chapingo (CHA), Netzahualcóyotl Sur (NTS), Cerro del Tepeyac (TEC) and Xalostoc (XAL) at the NW; Museo (MCM) at the Center; Diconsa (DIC), Ecoguardas Ajusco (EAJ), Ex-convento Desierto de los Leones (EDL), Lomas (LOM), Parres (PAR), San Nicolás Totolapan (SNT) at the SW; Corena (COR) and Milpa Alta (MPA) at the SE.

DOF . 2012. Contaminación atmosférica - Niveles máximos permisibles de emisión de los equipos de combustión de calentamiento indirecto y su medición. NOM-085-SEMARNAT-2011, Diario Oficial de la federación, 02/ 02/2012. http://www.dof.gob.mx/nota_detalle.php?codigo=5232012&fecha=02/02/2012.

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