Encyclopedia of Environmental Science and Engineering, Volume I and II

752 NITROGEN OXIDES REDUCTION

and federal governments. 33,34,35 NO x control options have been

applied to fired process heaters^34 whose uncontrolled emis-

sions are in the range of 0.10 to 0.53 lb/10^6 Btu. The percent-

age reductions attained for key control technologies include,

(1) Low NOx burners (25–65%)

(2) Selective Catalytic Reductions (SCR) (65–90%)

and

(3) Combined Low NOx and SCR (70–90%)

Additional factors involved in choosing a desired technology

include capital, operating and maintenance costs.^35

Mobile Source Regulations

In addition to stationary combustion, mobile sources, such as

passenger cars and trucks, contribute almost 50% of the NO x

produced in the United States. To reduce the emissions from

these sources, federal and State governments have imple-

mented standards on tailpipe emissions of NO x. Typically,

vehicles are divided into three main weight categories:

(1) light duty, (2) medium duty, and (3) heavy duty. Vehicles

are further subdivided in each main category; emission

limits are applied to these subcategories. Emission limits are

expressed two different units: (1) g/mi, grams per mile, or

(2) g/bhp-hr, grams per brake horse-power-hour. In the federal

and California regulations, standards are expressed in g/mi for

light and medium duty vehicles, whereas g/bhp-hr is used for

heavy duty vehicles. As a comparison of some of the emission

limits, Table 9 shows the federal, California and New York 16,17

standards for passenger and light duty vehicles.

To further reduce air pollutant emissions from vehi-

cles, the federal and State governments have implemented

a number of other programs. One such program is the

Clean-Fuel Vehicles Fleet Program which is designed to

reduce emissions, in highly polluted regions, from vehicles

belonging to a fleet. Tailpipe emissions generally account

for 60% of the total vehicle emissions.^16 Thus, governments

are beginning to focus on the other emission forms asso-

ciated with vehicles. These include evaporative emissions,

CO emissions at cold temperatures, air toxics emissions,

emissions testing and procedures, and emissions control

diagnostics systems. Regulating emissions is not the only

method to curb NO production. The composition of the fuel

has also been a target of regulations. Requirements have

been promulgated to establish the use of reformulated gaso-

line, oxygenated gasoline, reduced volatility gasoline, and

cleaner diesel fuel.

Thus, the federal and state governments have taken

active role in the limiting of NO x emissions. Depending on

the political climate in the United States, these gulations may

become less or more stringent over the next few years.

TABLE 4

NYS DEC NO x RACT emission limits for very larger

boilers (lbs NO x /MBtu)^14

Boiler configuration

Primary fuel type Tangential Wall Cyclone Stokers

Gas only 0.20 0.20 NA NA

Gas/oil 0.25 0.25 0.43 NA

Coal wet bottom 1.00 1.00 0.60 NA

Coal dry bottom 0.42 0.45 NA 0.30^1

1 The limit is 0.33 lbs NOx/MBtu when 25% of other solid fuels, on a

Btu basis, are utilized.

TABLE 5^

NYS DEC NO x RACT emission limits for large boilers

(lbs NO x /MBtu)^14

Primary fuel type Emission limit

Gas only 0.20

Gas/oil 0.30

Pulverized coal 0.50

Coal (overfeed stoker) 0.30^1

1 The limit is 0.33 lbs NO x /MBtu when 25% of other solid fuels, on a

Btu basis, are utilized.

TABLE 7^

NYS DEC NO x RACT emission limits for combustion turbines

(ppm, corrected to 15% O 2 )^14

Combustion turbine and fuel types Emission limit

Simple cycle and regenerative

Gas only 50

Multiple fuels 100

Combined cycle

Gas only 42

Oil only 65

TABLE 6^

NYS DEC NO x RACT emission limits for

mid-size boilers (lbs NO x /MBtu)^14

Primary fuel type Emission limit

Gas only 0.10

Distillate oil 0.12

Residual oil 0.30

TABLE 8^

NYS DEC NO x RACT emission limits for internal combustion

engines (gms NO x /brake HP-hr)^14

Engine and fuel types Emission limit

Rich burn 2.0

Lean burn

Gas only 3.0

Other fuels 9.0

1 Rich burn engine—O 2 by volume is less that 1.0% in the

exhaust.

2 Lean burn engine—O 2 by volume is greater than or equal to

1.0% in the exhaust.

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