ENCYCLOPEDIA OF ENVIRONMENTAL SCIENCE AND ENGINEERING - NITROGEN OXIDES REDUCTION pdf

Typically, nitric oxide, NO, and nitrogen dioxide NO 2 , both of which are formed as a by-product during combustion.. If these predictions are accurate, then it becomes even more importa

INTRODUCTION

Nitrogen oxides are one of the most persistent categories of

globally emitted air pollutants because they are combustion

products of both stationary and mobile sources By far the

highest concentration of the oxides formed during

combus-tion are NO and NO 2 Given time, and in the presence of O 2

either in the flue gases or in the atmosphere most of the NO

is converted to NO 2

There are six commonly encountered oxides of nitrogen:

(1) nitric oxide (NO); (2) nitrous oxide (N 2 O); (3) nitrogen

dioxide (NO 2 ); (4) nitrogen trioxide (N 2 O 3 ); (5) nitrogen

tetroxide (N 2 O 4 ); (6) nitrogen pentoxide (N 2 O 5 ) Typically,

nitric oxide, NO, and nitrogen dioxide NO 2 , both of which

are formed as a by-product during combustion Nitric oxide

is a colorless, odorless, toxic, nonflammable gas which is

slightly soluble in water Nitrogen dioxide, however, is a

reddish-brown gas that is toxic and highly corrosive with

a pungent odor This gas can contribute to highly visible

plumes Emissions of nitrogen oxides are of concern due to

their potential role in ozone formation, acid rain deposition,

health effects, and formation of toxic air pollutants

EFFECTS OF NO

X

Human and Animal Health Effects

Of the two compounds, nitrogen dioxide is the most toxic and

dangerous to humans A variety of studies has been performed

to observe the effects of NO 2 on humans and animals Most of

these studies have been performed using pure NO 2 Effects of

acute NO 2 exposure have been reported as nose and eye

irri-tation, obliterative bronchiolitis, pulmonary congestion and

edema, pneumonitis, and death Most of these reactions, such

as pulmonary edema and obliterative bronchiolitis, can occur

at extremely high concentrations (150–500 ppm) for short

periods of time minutes to an hour It appears, however, that

mixtures of oxides tend to lessen the discomfort and the

poten-tial to contract severe disorders It has also been shown that

chronic, intermittent exposure to NO 2 (10–40 ppm) can result

studies, continuous exposure to NO 2 for 90 days at 5 ppm has

resulted in the deaths of 18% of the rats, 13% of the mice and

66% of the rabbits. 1 On the other hand, intermittent exposure

for 18 months at the same level (5 ppm) did not result in any deaths In addition to the chronic and acute effects, it appears that daily exposure to NO 2 concentrations of 5 ppm can lead to slightly accelerated lung tumor formation, but not at a level of any statistical significance

On the other hand, exposure strictly to nitric oxide has not been reported to result in human poisoning probably due to its relatively low toxicity and its conversion to NO 2 The relative toxicity can be seen in the exposure standards set by NIOSH (National Institute for Occupational Safety and Health) and OSHA (Occupational Safety and Health Administration) For nitric oxide, the threshold limit value (TLV) for an 8-hour time weighted average (TWA) expo-sure is 25 ppm. 2 For nitrogen dioxide, the TLV is 1 ppm for

a short-term exposure limit (STEL) The short-term sure limit is a 15-minute TWA exposure that should not be exceeded at any time during a workday Likewise, the imme-diately dangerous to life or health (IDLH) concentration for nitric oxide is 100 ppm, whereas for nitrogen dioxide, the concentration is 50 ppm. 2 Toxicologists have reported that nitric oxide can be a mild nose, eye and throat irritant At high concentrations, nitric oxide can lead to a progressive depression of the central nervous system. 1

Environmental Effects

Not only does NOx affect the human population, but it also has an adverse effect on the environment, in particular vege-tation Gaseous pollutants damage plants by entering through the stomata during the respiration cycle. 3 The pollutants can disrupt the photosynthesis process and can destroy plant chlorophyll Experiments have shown that concentrations of

NO 2 as low as 0.5 ppm can result in reduced plant growth by

as much as 35% In particular, it appears that plants are more susceptible to nitrogen dioxide effects at night than during the day Scientists feel that NOx has played a significant role

in the deforestation of central Europe

Not only does direct exposure to nitrogen oxides result

in plant deterioration, but nitrogen oxides combine with certain hydrocarbons to form ozone and peroxyacyl nitrates (PAN’s), two compounds that have been found be more toxic towards plants than nitrogen oxides alone Exposure to these compounds has been shown to result in plant growth suppression, bleaching, glazing and silvering on the lower surface of the leaves. 3

In addition to vegetative kill, nitrogen dioxide is an

extremely corrosive gas that can have deleterious effects on

a wide range of materials such as plastics, fabrics, rubber

and metals Studies on Nylon-6 and Kevlar have revealed

that the ultimate tensile strengths of these materials are

0.5–0.8% volume concentration

Global Warming/Greenhouse Effect

The greenhouse effect occurs due to the buildup of gases

which can absorb heat The earth maintains a constant

aver-age temperature by radiating heat to space; thus, greenhouse

gases absorb a portion of this heat and radiate it to the lower

atmosphere Scientists believe that the heat is trapped in the

lower atmosphere, resulting in global warming, rising sea

level and global climatological alterations There is

consid-erable debate over the global warming issue when viewed

from the geologic time scale In any case, there has been

considerable research done in this field and it will continue

to be a topic of concern for years to come

Principally, carbon dioxide is the most important

green-house gas, contributing to roughly half of the global warming

that has been reported The other half of the global warming

has been attributed to approximately 20 other gases, most

notably methane, chlorofluorocarbons (CFC-11 and CFC-12),

ozone, nitrous oxide, and nitrogen dioxides Some scientists

have estimated that a 50% increase in the current

concentra-tion of N 2 O will result in a mean global temperature increase

of 0.2–0.5
C. 4 Of the nitrous oxide emissions, 25% has been

attributed to fossil fuel combustion If these predictions are

accurate, then it becomes even more important to control

the emissions of nitrogen oxides from combustion related

processes

Acid Rain Deposition

Acid rain forms when sulfur dioxide and nitrogen oxides

mix with water vapor to form sulfuric and nitric acid In

par-ticular, nitrogen oxides are transformed into nitric acid by

the following reactions: 5

On an annual basis, nitric acid is responsible for approximately

30% of the acidity of rainfall This percentage increases to

around 50% during the winter Acid rain is one of the most

damaging effects of NOx emissions It leads to the

destruc-tion of ecosystems in lakes, deforestadestruc-tion, and the stripping

of organic material in soils, creating erosion and potentially

substantially to the acid pulse in snowmelt, which in turn

severely impacts the freshwater ecosystem Therefore, acid

rain is yet another reason for controlling and limiting NOx

emissions to the atmosphere

Ozone Formation

In addition to being a cause of acid rain, nitrogen oxides are also considered one of two precursors to the formation of pri-mary ozone, O 3 Ozone is thought to be formed from the com-plex reaction of certain hydrocarbons and nitrogen oxides

The role of nitrogen oxides in ozone formation is significant because of the health effects associated with ele-vated levels of ozone Ozone exposure can lead to coughing and chest discomfort, headaches, upper respiratory illness, reduced pulmonary function, eye irritation, and increased asthma attacks For ozone, the NIOSH ceiling exposure limit

is 0.1 ppm; the OSHA threshold limit value (TLV) for an 8-hour time weighted average (TWA) exposure is 0.1 ppm

immediately dangerous to life or health (IDLH) tion for ozone is 10 ppm, which is five times less than the IDLH for nitrogen dioxide and nitric oxide, respectively In addition to human health effects, studies have shown that ozone damages agricultural crops and forest ecosystems

NOx REGULATIONS

Stationary Source Regulations

Because of the harmful effects associated with nitrogen oxides, governments around the world have established increasingly stricter regulations over the past few decades

par-ticular, the United States federal government enacted the Clean Air Act (CAA) to protect the nation’s air quality The CAA was first passed into legislation in 1970, with substan-tial amendments being added in 1977 and most recently in

1990 The amendments in 1990 greatly increased the scope

of the existing CAA The CAA is divided into seven primary Titles, I–VII Some of he new major points in these Titles are as follows: 6, 7

• Title I —A new system was established to

deter-mine if an area is classified as either an ozone attainment or an ozone nonattainment area The CAA effectively divides the United States into attainment and nonattainment areas, based on the level of criteria pollutants in the area’s ambient air Because of the formation of ozone from vola-

requires more stringent requirements for these two classes for compounds

• Title II —Clean fuel requirements and increased

restrictions on motor vehicle emissions were introduced in Title II Under Title II, new vehicle tailpipe emissions of NOx were to be reduced by 60%, starting with 40% of all new vehicles in the

1994 model year and increasing to 100% by the

1998 model year

• Title III —Emission limitations for 189

hazard-ous air pollutants (HAP’s) are to be set by the

United States Environmental Protection Agency (USEPA) The National Emissions Standards for Hazardous Air Pollutants (NESHAP’s) set in ear-lier versions of the CAA will remain intact, but the USEPA will now be required to use the best dem-onstrated emissions control practices in a particu-lar industry to regulate sources for that industry

Under standards set by the USEPA, major sources will be required to apply Maximum Available Control Technology (MACT) A major source is defined as one that emits 10 tons/year of a HAP or

25 tons/year of any combination of HAPs

• Title IV —Under Title IV, the USEPA is required

to establish a program to reduce the occurrence of acid rain Because SO 2 and NOx are the two main contributors to acid rain, facilities that fall under control of Title IV will be forced to meet certain standards and will be required to obtain an acid rain permit

• Title V —A comprehensive operating permit

pro-gram was established for all significant air emission sources

• Title VI —Under this Title, a new national program

was developed to phase out the use of carbons (CFCs) and similar compounds to protect the stratospheric ozone layer

• Title VII —The USEPA’s enforcement ability was

greatly enhanced with more criminal and civil powers

Included in the Title I requirements are the National Ambient

Air Quality Standards (NAAQS), which specify the maximum

allowable concentrations for six criteria pollutants These pollutants are: (1) carbon monoxide; (2) lead; (3) nitrogen oxides; (4) ozone; (5) particulates ( 10 microns diameter);

and (6) sulfur oxides There are two types of NAAQS, which are defined in the USEPA 40 CFR Part 50 Regulations:

• primary—standards are designed to protect the public health

public from a pollutant’s effects on visibility, sonal comfort, properly, etc

If an airshed area exceeds the ambient air concentrations of one of these pollutants, then that area is considered to be

in nonattainment For nitrogen oxides, the primary and ondary National Ambient Air Quality Standards expressed

sec-as annual arithmetic mean concentration are 0.053 parts per

million (100 m g/m 3 ). 8 This limit should not be exceeded, during any 12 consecutive month period, for the annual aver-age of the 24-hour concentrations Figure 1 9 shows the con-trol technologies required by facilities to meet the NAAQS

The three main categories are BACT, LAER, and RACT

BACT or Best Available Control Technology, is defined by the CAA as “ … an emission limitation based on the maxi-mum degree of reduction of each pollutant … which the per-mitting authority … ” 9 considers appropriate BACT applies

to new or modified sources of emissions in attainment areas

LAER or Lowest Achievable Emission Rate applies to new

or modified sources in nonattainment areas It refers to the most stringent emission limitation achieved by a similar facility or a particular source category. 9 RACT or Reasonably

NAAQS

Sources in attainment areas

New or modified sources

Best Available Control Technology Lowest Achievable Emission Rate Reasonably Available Control Technology

Maximum Achievable Control Technology

Generally Available Control Technology

New or modified sources Areas sources

NESHAP

Major sources

Sources in attainment areas

non-New or modified sources

Existing sources

Case by case

Fewer than

30 sources More than or equal

to 30 sources

FIGURE 1 Relationships between control technologies and standards 9

Available Control Technology applies to existing sources in

nonattainment areas RACT has been defined by the USEPA

as “the lowest emission limitation that a particular source is

capable of meeting by the application of control technology

that is reasonably available considering technological and

economic feasibility”. 9

One of the ways the CAA provides for regulation

of emissions is through the New Source Performance

Standards (NSPS), which is also a component of Title I

The USEPA continually promulgates new standards, under

the 40 CFR Part 60’s, to regulate the emissions of criteria

pollutants from new or substantially modified stationary

sources These new sources may also have to undergo a

New Source Review (NSR) permitting process Under this

process, the regulating agency determines whether the

facility can begin operation and under what conditions

The following is a list of new source performance

stan-dards that pertain to facilities that are regulated for NOx

emissions: 10

• Subpart D-Fossil Fuel Fired Steam Generators

(facilities that began construction after 8/17/71)

(250 MBtu/hr) 10

• The NOx emission limits are found in Table 1

E n  NOx limit (ng/J heat input)

w  % of total heat input derived from lignite

x  % of total heat input derived from gaseous fossil

• Subpart Da-Electric Utility Steam Generating

Units (facilities that began construction after 9/18/78) (250 MBtu/hr) 10

E n  NOx limit (ng/J heat input)

w  % of total heat input derived from combustion of

fuels subject to the 86 ng/J heat input standard

x  % of total heat input derived from combustion of

fuels subject to the 130 ng/J heat input standard

y  % of total heat input derived from combustion of

fuels subject to the 210 ng/J heat input standard

z  % of total heat input derived from combustion of

fuels subject to the 260 ng/J heat input standard

v  % of total heat input derived from combustion of

fuels subject to the 340 ng/J heat input standard

• Subpart Db-Industrial-Institutional Steam rating Units (facilities that began construction after 6/19/84) ( 100 MBtu/hr) 10

(facili-ties that began construction after 12/2/89) (250

• Subpart GG-Stationary Gas Turbines (facilities

that began construction after 10/3/77) 10

tur-bines are given by two equations For units with a

per hour, the allowable NOx emission at 15% O 2 , dry is given by the following equation:

E

n =0 0075 (14 4 )+

For units with a heat input peak load of 10.7 GJ (10 MBtu)

with a base load at ISO conditions of 30 MW or less, the

TABLE 1 USEPA 40 CFR Part 60 Subpart D-Fossil-fuel fired steam

generators NO x emission limits 10

Fuel type

NOx emission limits, ng/J(lb/

MBtu) (expressed asNO2) for heat input (1) Gaseous fossil fuel 86 (0.20) (2) Liquid fossil fuel 129 (0.30) (3) Liquid fossil fuel  wood residue 129 (0.30) (4) Gaseous fossil fuel  wood residue 129 (0.30) (5) Solid fossil fuel 1 300 (0.70) (6) Solid fossil fuel  wood residue 1 300 (0.70) (7) Lignite, except (9) 260 (0.60) (8) Lignite  wood residue, except (9) 260 (0.60) (9) Lignite mined in North Dakota, South

Dakota, or Montana, and which is burned in a cyclone-fired unit

340 (0.80)

1 Except liginite or a solid fossil fuel containing 25%, by weight, or more coal refuse

The NO emission limits are found in Table 3

The NO emission limits are found in Table 2

allowable NOx emission at 15% O 2 , dry is given by the

E n  NOx limit (% by volume, dry)

Y  mfg.’s rated heat rate at mfg.’s rated peak load or

the actual measured heat rate based on lower heating value of fuel as measured at actual peak load for the facility The value of Y shall not exceed 14.4 kJ per watt hour

F  defined according to the nitrogen content of the

fuel as follows:

Fuel-bound nitrogen (% by weight) F (NOx % by volume)

0.015  N  0.1 0.04 (N) 0.1  N  0.25 0.004  0.0067 (N-0.1)

N > 0.25 0.005

In addition to NSPS and NAAQS, the USEPA is

reduc-ing NOx emissions through Title IV, the Acid Rain Program

The regulations under this program were published as final

in the April 13, 1995 Federal Register and became effective

on May 23, 1995 The regulations are aimed directly at coal fired utility plants in which the combustion of coal on a BTU basis exceeds 50% of its annual heat input The type of boil-ers used at these plants has been subdivided into Group 1 and Group 2 boilers Group 1 boilers include tangentially fired boilers or dry bottom wall-fired boilers Group 2 boilers include wet bottom wall-fired boilers, cyclone boil-ers, vertically fired boilers, arch-fired boilers, or utility boilers (i.e fluidized bed or stoker boilers) In addition, the CAA has set standards based on Phase I and Phase II

In the acid rain regulations, NOx emission limits have been established for Phase I coal fired utility units with tangentially fired boilers (95 units) or with dry bottom wall-fired boilers (84 units), which were to be effective January 1, 1996 For tan-gentially fired boilers, the limit is 0.45 lb/MBtu of heat input on

an annual average basis For dry bottom wall fired boilers, the

NOx limit is 0.50 lb/MBtu of heat input expressed on an annual average basis The facilities that cannot meet the requirements will be allowed to apply for a less restrictive emission standard

or to join an “averaging pool,” through which the overall sions limit average is attained Phase I standards for Group 2 boilers are scheduled to be set by January 1, 1997 with imple-mentation by January 1, 2000 Phase II standards for Group 1 and 2 boilers are required to be established by 1997. 11

Similar to the federal government under the Clean Air Act, State governments have the authorization to enact regulations that maintain ambient air quality and to set limits for sources

of air pollution In New York State, the agency charged with

TABLE 2 USEPA 40 CFR Part 60 Subpart Da-electric utility steam generating units NOx emission limits 10

Emission limit for heat input

Any fuel containing more than 25%, by weight, lignite not subject

to the 340 ng/J heat input emissions limit 2

260 0.60

1 Exempt from NOx standards and NO x monitoring requirements

2 Any fuel containing less than 25%, by weight, lignite is not prorated but its % is added to the % of the predominant fuel

enforcing these regulations is the New York State Department

of Environmental Conservation (NYSDEC) The USEPA has

delegated authority to the NYSDEC to issue permits to

con-struct to sources for the modification or concon-struction of any

stationary source subject to federal NSPS, NESHAPS, or

PSD (Prevention of Significant Deterioration) requirements,

and to implement and enforce the federal standards and PSD

requirements where they apply. 12 The NYSDEC requires that

any new or modified air emission source acquire a permit to

construct and a certificate to operate under the requirements of

6 NYCRR Part 201 Any air contamination source subject to

the NSPS, NESHAPS, or PSD requirements must be in

com-pliance with the federal standards as well as any applicable

State standards, such as New York State Ambient Air Quality

Standards (NYSAAQS) or New York State performance

stan-dards The NYSAAQS for NO 2 is 0.053 ppm (100 m g/m 3 ) 13

with the same averaging period as that of the USEPA NAAQS

Recently, the NYSDEC made revisions to the 6 NYCRR

Part 200, 201, and 227 air pollution regulations In particular,

these revisions included Subpart 227–2 entitled “Reasonably

Available Control Technology (RACT) for Oxides of Nitrogen

(NOx).” 14 This subpart requires operators of existing major

sta-tionary sources of NO x to use RACT to limit NO x emissions

A source is classified as a major source if it has the potential to

emit 100 tons NOx per year or if it has the potential to emit 25

tons NOx per year in a “severe” ozone nonattainment area The

major stationary sources as defined in Subpart 227–2 are: 14

MBtu/hr

MBtu/hr

nonattainment areas; 400 HP in all other areas

where, Q MAX is equal to the maximum heat input capacity

to maintain a log book containing process information Other

the specific sources above were required to submit a RACT proposal detailing the technology and potential emissions to the NYSDEC by May 31, 1995

Outside of state and federal regulations, certain cities promulgate their own air pollution control regulations

The New York City Department of Environmental Protection (NYC DEP) revised their air pollution code in March, 1992 This document contains guidelines for obtain-ing local permits and certificates as well as standards for air

DEP set a limit for boilers with a capacity of 500 MBtu/hr

depending on whether the boiler was completed before (150 ppmv NOx) or after (100 ppmv NOx ) August 20, 1971. 15

The petrochemical and refinery sectors have been subjected

to stringent regulatory requirements in recent years by state

TABLE 3 USEPA 40 CFR Part 60 Subpart Db-industrial/commercial/institutional steam generating units

NO x emission limits 10

Fuel/steam generating unit type

NOx emission limits, ng/J(lb/MBtu) (expressed as NO2) for heat input

(1) Natural Gas and distillate oil, except (4) (i) Low heat release rate 43 (0.10) (ii) High heat release rate 86 (0.20) (2) Residual oil

(i) Low heat release rate 130 (0.30) (ii) High heat release rate 170 (0.40) (3) Coal

(i) Mass-feed stoker 210 (0.50) (ii) Spreader stoker and fluidized bed combustion 260 (0.60) (iii) Pulverized coal 300 (0.70) (iv) Lignite, except (v) 260 (0.60) (v) Lignite mined in North Dakota, South Dakota, or

Montana, and is combusted in a slag tap furnace

340 (0.80)

(vi) Coal-derived synthetic fuels 210 (0.50) (4) Duct burner used in a combined cycle system

(i) Natural gas and distillate oil 86 (0.20)

Tables

and federal governments. 33,34,35 NOx 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,

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

and

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

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

16,17

standards for passenger and light duty vehicles

To further reduce air pollutant emissions from cles, the federal and State governments have implemented

vehi-a number of other progrvehi-ams One such progrvehi-am 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

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 NOx RACT emission limits for large boilers

Coal (overfeed stoker) 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 7 NYS DEC NOx RACT emission limits for combustion turbines

Primary fuel type Emission limit

Distillate oil 0.12 Residual oil 0.30

TABLE 8 NYS DEC NOx RACT emission limits for internal combustion

Conversion of Emission Standards

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

come in various units Some regulations state NOx limits in

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

x

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

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

18,20 and 12 18,21 , respectively) Three Lotus sheets were utilized to develop Figure 2 First, a spreadsheet

spread-on a percent volume basis, to the elemental compspread-onent 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-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:

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

“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 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

diox-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:

TABLE 9

NOx emission standards for passenger cars and light duty trucks (g/mi) 16,17

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

1994

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

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

fuel, a US/Texas gas (see Table 10

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

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

Tables 11

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

) Figures 3 and 4 were

Oxygen in Fluegas (Excess Air),%

(0.1)

(42) (50)

(75-145)

TURBINES BOILERS

- New Source Performance Standards (NSPS)

- > 100 MBtu/hr in size -50 - 100 MBtu/hr in size

- Depends on heat rate (NSPS)

- Simple cycle and regenerative combustion turbines

- Combined cycle combustion turbines

1 2 3

4 5 6

- > 500 MBtu/hr in size, after 8/20/71

- > 500 MBtu/hr in size, before 8/20/71

7 8

FIGURE 2 Conversion of emission units and comparison of various standards for NOx natural gas units.

Oxygen in Fluegas (Excess Air),%

(0.28)

(0.3)

(0.43)

1 2

- NSPS-Subpart D- >250 MBtu/hr

- Dry bottom cyclone boiler

- Dry bottom wall utility boilers

- Dry bottom tangential & wall boilers-> 250 MBtu/hr 4

3

NJ DEP - utility boiler NYS DEC - >250 MBtu/hr

5 - Dry bottom tangential utility boilers

FIGURE 3 Conversion of emission units and comparison of various standards for NOx oil-fired units.

Oxygen in Fluegas (Excess Air),%

(0.55)

(0.42) (0.38)

(0.5) (0.45)

1 - NSPS - Subpart D - > 250 MBtu/hr

2 - NSPS - Subpart Da - > 250 MBtu/hr (bituminous & anthracite coal)

3 - Dry bottom cyclone utility boilers

4 - NSPS - Subpart Da - > 250 MBtu/hr (subbituminous coal)

5 - Dry bottom wall utility boilers

6 - Dry bottom tangential boilers

7 - Dry bottom tangential utility boilers

FIGURE 4 Conversion of emission units and comparison of various standards for NOx coal-fired units.