Page 134 - Sustainable On-Site CHP Systems Design, Construction, and Operations

112 CHP B a s i c s

Ranking of the various fuels in terms of their emissions production potential, in the order of
the least to the highest emissions is as follows: natural gas, biogas, diesel/fuel oil No. 2, and
coal. Similar ranking of the various CHP power generation technologies in terms of their
emissions production potential is as follows: fuel cells, combustion turbines, microturbines,
natural gas–fired engines, diesel engines, and coal-fired boilers. Therefore, the use of natu-
ral gas in fuel cells produces the least emissions, while the use of coal in boilers to produce
steam for use in steam turbines to produce power produces the most emissions.

Emissions of Reactive Organic Gases
In addition to the emissions of CO , CO, NO , and SO , environmental permitting pro-
2 x x
cess also requires estimates of other criteria pollutants, such as trace organic compounds,
as discussed in Chap. 13. The reactive organic gases (ROGs), also known as volatile
organic compounds (VOCs), are estimated by the sum of all the speciated organic com-
pounds minus those that are methane and ethane.
Examples of uncontrolled emissions, including ROGs/VOCs, for four-stroke rich
8
and lean burn engines can be found at the following link: http://www.epa.gov/ttn/
chief/ap42/ch03/final/c03s02.pdf (see Ref. 8).
Emissions Calculator
The Midwest CHP Application Center has developed a simple spreadsheet-based emis-
9
sions calculator. The emissions calculator estimates expected emissions from the
various classes of power generation technologies (i.e., natural gas–fired reciprocating
engines and natural gas–fired turbines) used in CHP systems. The emissions calculator
does not provide an estimate of emissions from any specific manufacturer’s model of
the power generator. For emission estimates for a specific manufacturer model, please
refer to the manufacturer’s specification sheet for that piece of equipment.
The emissions calculator utilizes the AP-42 emission factors compiled by the U.S.
EPA and can be downloaded from the following URL: http://www.chpcentermw.org/
pdfs/030123-PermitGuidebook-EmCalc_IL.xls. It allows approximation of the expected
emissions from five power generation technology classes:

1. Diesel engine less than 600 hp
2. Diesel engine greater than 600 hp
3. Natural gas–fired engine
4. Gasoline-fired engine less than 250 hp
5. Natural gas–fired turbine

Table 7-3 shows samples of the emissions calculator’s results for the above prime
movers. The left side of the table shows the information for the case when the prime
mover is planned to be located in an attainment area. The various columns display the
following:

• The first column shows the pollutants being estimated.
• The second column provides the AP-42 emission factors utilized by this
emissions calculator.
• The third column provides the estimated emission levels in tons per year for each
pollutant, taking into account the operating hours per year and the fuel input.