Methods for Estimating Fugitive Emissions

The USEPA has established a number of methods for estimating fugitive emissions (USEPA 1988, 1995). The methods vary in the time and expense they require and as would be expected, the more time‐consuming and costly methods result in a more accurate estimate of emissions. The least accurate and least costly method for estimating fugitive emissions is to count all the potential sources of releases and apply an average “emission factor,” according to the formula:

(3.4)

where E is the emission rate of VOCs from a component, m_voc is the mass fraction of VOC in the stream serviced by the component, and f_av is the average emission factor.

Portable gas leak imaging cameras are also a new technology that can be used to improve leak detection and repair, leading to reduced fugitive emissions. The cameras use infrared imaging technology to produce video images in which invisible gases escaping from leak sources can be clearly identified. The average emission factors for fugitive emissions from synthetic organic chemical manufacturing industry (SOCMI), including petroleum refining and natural gas plants, are given in Table 3.11.

EXAMPLE 3.4 ESTIMATING FUGITIVE EMISSIONS USING EMISSION FACTORS

A component count of equipment in an acrolein manufacturing facility found that there were 1400 valves, 3048 flanges and other connectors, 27 pumps, 20 pressure‐relief valves, 21 open‐ended lines, and 20 sampling connections (Berglund et al. 1989). Determine the fugitive acrolein emissions in pounds per year using the average SOCMI emission factors from Table 3.11. Assume that the process fluid is composed almost entirely of VOCs and that the equipment contains 87% by mass. Of the valves, 168 are in gas service; all other valves and pumps are in light liquid service.

SOLUTION

For valves in the gas service, estimated acrolein emissions are

• (0.87 lb acrolein/lb VOC)(1400 − 168)(0.005 97 kg VOC/h valve)(2.2046 lb/kg)(24 h/day)(365 day/year) = 16 850 lb/year for all valves in gas service.
• (0.87 lb acrolein/lb VOC)(1400 − 168)(0.004 03 kg VOC/h valve)(2.2046 lb/kg)(24 h/day)(365 day/year) = 83 400 lb/year for all valves in light liquid service.

Summing these values gives the total estimated acrolein emissions from valves, which is about 100 250 lb acrolein/year.

Results for flanges, pumps, pressure‐relief valve, open‐ended lines, and sampling connections for light liquid services were similarly calculated and presented in Table 3.12.

Table 3.11 Average fugitive emission factors from SOCMI^a facilities – refineries and natural gas plants.

Source: Adapted from Allen and Rosselot (1997).

			Emission factors (kg/h/source)
Equipment	Service	SOCMIa	Refineryb	Gas plantc
Valves	Hydrocarbon gas	0.005 97	0.027	—
	Light liquid	0.004 03	0.011	—
	Heavy liquid	0.000 23	0.000 2	—
	Hydrogen gas	—	0.008 3	—
	All	—	—	0.020
Pump seals	Light liquidd	0.019 9	0.11	—
	Heavy liquid	0.008 62	0.021	—
	Liquidd	—	—	0.063
Compressor seals	Hydrocarbon gas	0.228	0.63	—
	Hydrogen gas	—	0.050	—
	All	—	—	0.204
Pressure‐relief valves	Hydrocarbon gas	0.104	0.16	—
	Liquid	0.007 0e	0.007 0e	—
	All	—	—	0.188
Flanges and other
Connectors	All	0.001 83	0.000 25	0.001 1
Open‐ended lines	All	0.001 7	0.002	0.022
Sampling connections	All	0.015	—	—

^a SOCMI: Synthetic Organic Chemical Manufacturing Industry.

^b USEPA (1985a) except as noted.

^c USEPA (1993) except noted.

^d This factor can be used to estimate the leak rate from agitator seals.

^e USEPA (1985b).

Table 3.12 Acrolein emissions estimated using average emission factors.

Equipment type	Emissions (lb/year)	Percent of emissions by equipment type
Valves	100 250	47.52
Flanges	93 717	44.42
Pumps	9 027	4.28
Pressure‐relief valves	2 352	1.11
Open‐ended lines	600	0.28
Sampling connections	5 040	2.38
Total	211 000	100