Encyclopedia of Environmental Science and Engineering, Volume I and II

NITROGEN OXIDES REDUCTION 753

Conversion of Emission Standards

As can be seen from the above regulations, NO x standards

come in various units. Some regulations state NO x limits in

ppm, on a dry volume basis, whereas other regulations may

require the emissions in lbs NO x /MBtu. Figures 2–4 have

been developed for converting emission units at different

oxygen percents in the flue gas for natural gas, oil, and coal

fired units, respectively. Figure 2 is based on a typical gaseous

fuel, a US/Texas gas (see Table 10 18,19 ). Figures 3 and 4 were

based on a number of different liquid and solid fuels (see

Tables 11 18,20 and 12 18,21 , respectively). Three Lotus spread-

sheets were utilized to develop Figure 2. First, a spreadsheet

was developed, Table 13, that converts the gas components,

on a percent volume basis, to the elemental component mass

fractions. In addition, the spreadsheet also calculates the

lower and higher heating values of the natural gas based on

the components in the natural gas. The lower heating value

is compared for accuracy to experimental results. Next, the

component mass fractions were read into the second spread-

sheet, Table 14, to calculate the flue gas constituents and

the pounds of flue gas produced per pound of fuel on a dry

weight basis. Using the quantity of flue gas and the higher

heating value of the natural gas, a “K” factor was developed

for all three figures via:

K

HHV V

FG MW

= × M

×

where

HHV  heating value of the natural gas, Btu/lb

FG  volume of flue gas per lb of fuel, dscf/lb

MW  molecular weight of NO 2 , lb/lbmol

V M  molar volume, dscf/lbmol

In this equation, V M is equal to 385.1 dscf/lbmol at 68
F and

29.92 in. Hg. The “K” factors for a new selected fuels are

found in Tables 10–12. As can be seen from the tables, the

“K” factors do not vary widely for each type of fuel, which

implies that Figures 2–4 could be readily applied to a par-

ticular fuel type. The exception to the rule are gaseous fuels

that have a moderately high carbon dioxide content, such

as the natural gas from Germany. Because the carbon diox-

ide does not play a role in the combustion process, a high

carbon dioxide content gas will produce significantly lower

flue gas per pound of fuel, thereby increasing the “K” factor.

The “K” factor was then read into the third spreadsheet to be

used in the following equation to develop the data points for

each conversion graph:

X

K E (20.9 %O )

20.9

  ^2

where

X  NO x concentration, ppmvd

E  lb NO x /Mbtu

%O 2  % oxygen in the flue gas.

TABLE 9^

NO x emission standards for passenger cars and light duty trucks (g/mi)16,17

New York California Federal

PC LDTI^2 LDT2^3 PC LDTI^2 LDT2^3 PC LDTI^2 LDT2^3

5 yr/ 0.4 0.4 1.0 0.4 0.4 1.0 1.0 1.2 1.7

50,000 mi (0.7)^1 (0.7)^1

1993

10 yr/—————————

100,000 mi

5 yr/ 0.4 0.4 1.0 0.4 0.4 0.7–1.0 0.4–1.0 0.4–1.2 0.7–1.7

50,000 mi (0.7)^1 (0.7)^1

1994

10 yr/ — — — 0.6 0.6 0.9 0.6 0.6 0.97

100,000 mi

5 yr/ 0.4 0.4 0.7 0.4 0.4 0.7 0.4–1.0 0.4–1.2 0.7–1.7

50,000 mi

1995

10 yr/ — — — 0.6 0.6 0.9 0.6 0.6 0.97

100,000 mi

1 The standard for in-use compliance for passenger cars and light duty trucks certifying to the 0.4 g/mi NO x standard shall be 0.55 g/mi NO x for 50,000

miles.

2 LDTI refers to light duty trucks from 0–3, 750 pounds loaded vehicle weight.

3 LDT2 refers to light duty trucks from 3,751–5750 pounds loaded vehicle weight, but less than 6,000 pounds gross vehicle weight.

C014_002_r03.indd 753C014_002_r03.indd 753 11/18/2005 1:26:53 PM11/18/2005 1:26:53 PM