Dickinson's state-of-the-art low-pressure steam central energy plant delivers steam and chilled water to heat and cool two-thirds of the buildings on campus, a more efficient system for heating and cooling buildings than using individual boilers and condensers. The plant’s two 800 horsepower boilers are dual-fuel, meaning they can burn either heating oil or natural gas. Because it is less costly and less polluting, the boilers are run on natural gas most of the time. The system uses flue gas recirculation and low NOx burners to control emissions of air pollutants.

Annual emissions of nitrogen oxides (NOx), sulfur dioxide (SO2), carbon monoxide (CO), particulate matter (PM), volatile organic compounds (VOC), lead and mercury from the combustion of natural gas in Dickinson’s central energy plant are estimated using national average emission factors from the USEPA’s Technology Transfer Network Clearinghouse for Inventories & Emissions Factors database (Table 1). Emissions of the greenhouse gases carbon dioxide (CO2) and nitrous oxide (N2O) are accounted for in Dickinson’s Greenhouse Gas Inventory and are not reported here.

The methodology provides a rough approximation of emissions as actual emissions per unit of natural gas combusted by a particular boiler can differ significantly from the national average. The estimates do not use direct measurements of emissions from Dickinson’s central energy plant.

Table 1. Emission factors for external combustion boiler; 10 million to 100 million Btu/hr; flue gas recirculation and low NOx burners

 

Emission Factors

Pollutant

Lbs/1000 cubic ft natural gas

Lbs/million Btu natural gas

Nitrogen oxides (NOx)

32

0.031

Sulfur dioxide (SO2)

0.6

0.00058

Carbon monoxide (CO)

9.4

0.009

Particulate Matter (PM)

7.6

0.0074

Volatile organic compounds (VOC)

5.5

0.0054

Lead

0.0005

4.864 E-7

Mercury

0.00026

2.529 E-7

Source: USEPA, Technology Transfer Network Clearinghouse for Inventories & Emissions Factors, accessed 1/19/2018. WEB SOURCE.

The emission factors in Table 1 are applied to Dickinson’s annual use of natural gas from 2008 through 2016 to estimate emissions of air pollutants. Estimates are reported in Table 2 and displayed in Figure 1.

Table 2: Estimated emissions of air pollutants, 2008 – 2016, tons/year

  2008 2009 2010 2011 2012 2013 2014 2015 2016
NOX 1.26 1.12 1.04 1.09 0.92 1.23 1.39 1.39 1.22
SO2 0.02 0.02 0.02 0.02 0.02 0.02 0.03 0.03 0.02
CO 0.37 0.33 0.31 0.32 0.27 0.36 0.41 0.41 0.36
PM 0.30 0.27 0.25 0.26 0.22 0.29 0.33 0.33 0.29
VOC 0.22 0.19 0.18 0.19 0.16 0.21 0.24 0.24 0.21
Lead 0.00002 0.00002 0.00002 0.00002 0.00001 0.00002 0.00002 0.00002 0.00002
Mercury 0.00001 0.00001 0.00001 0.00001 0.00001 0.00001 0.00001 0.00001 0.00001

 

Figure 1:

Annual Emissions

 

Prepared by: Neil Leary, Center for Sustainability Education, January 19, 2018.