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Episodic Air Pollution 

Control Measures: 

Analysis of Potential Options 

for Industrial Sources 

Report 

January 2008 

Prepared for: 

U.S. Environmental Protection Agency 

Office of Policy, Economics and Innovations 

Sector Strategies Division 

Work Assignment Manager: Barry Elman 

elman.barry@epa.gov 

Prepared by: 

ICF International 

9300 Lee Highway 

Fairfax, VA 22031 

(703) 934-3000 

Project Manager: Bansari Saha 

bsaha@icfi.com 

 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

Table of Contents 

List of Exhibits ....................................................................................................ii 

List of Acronyms................................................................................................ iii 

Acknowledgements............................................................................................iv 

Executive Summary ...................................................................................ES – 1 

1. Introduction....................................................................................................1 

I. Background on the Issue ....................................................................................................1 

II. Purpose of this Report ........................................................................................................ 1 

 III. Selection of Sectors: Research Scope and Bounds ........................................................... 2 

 IV. Methodology, Data Sources, and Caveats ......................................................................... 3 

 V. Report Outline..................................................................................................................... 4 

 

2. Sector Options and Analyses .......................................................................5 

I. Pulp & Paper ...................................................................................................................... 5 

 a. Overview of the Pulp & Paper Manufacturing Process and its Emissions .................. 5 

 b. Location ........................................................................................................................ 7 

 c. Potential Episodic Control Measures ........................................................................... 9 

 d. Opportunity Assessment of Potential Episodic Control Options ................................ 17 

 II. Iron & Steel ....................................................................................................................... 18 

 a. Overview of the Iron & Steel Manufacturing Process and its Emissions ................... 18 

 b. Location ...................................................................................................................... 20 

 c. Potential Episodic Control Measures ......................................................................... 22 

d. Opportunity Assessment of Potential Episodic Control Options ................................ 27 

III. Cement.............................................................................................................................. 28 

 a. Overview of the Cement Manufacturing Process and its Emissions.......................... 28 

 b. Location ...................................................................................................................... 30 

 c. Potential Episodic Control Measures ......................................................................... 32 

d. Opportunity Assessment of Potential Episodic Control Options ................................ 39 

IV. Implications for Other Sectors........................................................................................... 40

a. Implications for Industrial Boilers................................................................................ 40 

 b. Implications for Other Industrial Sources ................................................................... 42 

 c. Implications for Electric Utilities.................................................................................. 43 

3. Summary of Findings & Next Steps ...........................................................44 

I. Findings............................................................................................................................. 44 

 II. Next Steps......................................................................................................................... 46 

Appendix: Examples of Reactions by Industrial Sectors 

To the California Outages of 2001 and 2005 ...................................................48 

i 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

List of Exhibits 

Exhibit 1: Point Source Emissions from Selected Manufacturing Sectors as a Percentage of All 

Manufacturing Sectors 

Exhibit 2: Basic Pulp & Papermaking Process 

Exhibit 3: Primary Fuel Inputs as Fraction of Total Energy Supply for the Pulp & Paper Industry in 2002 

(fuel use only) 

Exhibit 4: Process Specific Emissions in 2002 

Exhibit 5: Location of Pulp and Paper Mills in Relation to 8-Hour Ozone Nonattainment and Maintenance 

Areas 

Exhibit 6: Location of Pulp and Paper Mills in Relation to Counties Violating the 24-Hour PM2.5 NAAQS 

Exhibit 7: Opportunity Assessment – Pulp & Paper 

Exhibit 8: Basic Iron & Steel Production Process 

Exhibit 9: Primary Fuel Inputs as Fraction of Total Energy Supply for the Iron & Steel Industry in 2002 

(fuel use only) 

Exhibit 10: Location of Iron and Steel Mills in Relation to 8-Hour Ozone Nonattainment and Maintenance 

Areas 

Exhibit 11: Location of Iron and Steel Mills in Relation to Counties Violating the 24-Hour PM2.5 NAAQS 

Exhibit 12: Opportunity Assessment – Iron & Steel 

Exhibit 13: Basic Cement Production Process 

Exhibit 14: Primary Fuel Inputs as Fraction of Total Energy Supply for the Cement Industry in 2002 (fuel 

use only) 

Exhibit 15: Location of Cement Plants in Relation to 8-Hour Ozone Nonattainment and Maintenance 

Areas 

Exhibit 16: Location of Cement Plants in Relation to Counties Violating the 24-Hour PM2.5 NAAQS 

Exhibit 17: Opportunity Assessment – Cement 

Exhibit 18: Industrial Boiler Inventory – Boiler Capacity (Number of Boiler Units in Parenthesis) 

ii 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

List of Acronyms 

AF&PA American Forest & Paper Association 

AIRS Aerometric Information Retrieval System (EPA) 

AISI American Iron and Steel Institute 

AQM Air Quality Management (subcommittee of EPA’s Clean Air Act Advisory Council) 

BOF Basic oxygen furnace 

Btu British thermal units 

CAA Clean Air Act 

CAAAC Clean Air Act Advisory Council (EPA) 

CAP Criteria air pollutant 

CKD Cement kiln dust 

CO Carbon monoxide 

DOE US Department of Energy 

EAF Electric arc furnace 

EPA US Environmental Protection Agency 

ESP Electrostatic precipitator 

FGD Flue gas desulfurization 

GIS Geographic Information System 

lb Pound 

LPG Liquified petroleum gas 

MMBtu Million Btu 

NAAQS National Ambient Air Quality Standard 

NAICS North American Industrial Classification System 

NEI National Emissions Inventory (EPA) 

NESCAUM Northeast States for Coordinated Air Use Management 

NESHAP National Emissions Standard for Hazardous Air Pollutant 

NH3 Ammonia 

NOx Nitrogen oxides 

O&M Operation and maintenance 

OAQPS Office of Air Quality Planning and Standards (EPA) 

OPEI Office of Policy, Economics, and Innovation (EPA) 

PCA Portland Cement Association 

PM Particulate matter 

PM2.5 Particulate matter that is 2.5 micrometers or smaller in size 

PRB Powder River Basin (coal) 

SCAQMD South Coast Air Quality Management District 

SIC Standard Industrial Classification 

SIP State Implementation Plan 

SNCR Selective Non-Catalytic Reduction 

SO2 Sulfur dioxide 

SSD Sector Strategies Division (EPA) 

TDF Tire derived fuel 

TRI Toxics Release Inventory (EPA) 

VOC Volatile organic compound 

iii 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

Acknowledgements 

We would like to thank the following individuals for providing technical information on the 

industry sectors, pointing us to other experts and sources of information, and reviewing sections 

of this report: Timothy Hunt of the American Forest & Paper Association; Arun Someshwar and 

John Pinkerton of the National Council for Air and Stream Improvement; Lawrence

Kavanagh and Bruce Steiner of the American Iron & Steel Institute; Paul Sheehan of the 

Sponseller Group, Inc. (Chair of the Environmental Technology Operating Committee of the 

Association for Iron and Steel Technology); and Tom Carter of the Portland Cement 

Association. Full responsibility for the contents of this report remains, however, with ICF 

International and EPA. 

iv 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

Executive Summary 

The Air Quality Management (AQM) Subcommittee of EPA’s Clean Air Act Advisory Committee 

(CAAAC) recently recommended expanding the use of episodic control measures to help attain 

and maintain National Ambient Air Quality Standards (NAAQS) in areas where all reasonable 

continuous (i.e., year-round) and seasonal control measures have already been required.1

 

Episodic control measures may be particularly useful in areas that are at risk of exceeding the 

8-hour ozone NAAQS and/or the 24-hour fine particle (PM2.5) NAAQS only on a limited number 

of days each year. 

This study seeks to help EPA, states, communities, and other stakeholders assess the potential 

use of episodic control measures by industrial sources. For purposes of this analysis, episodic 

control measures are defined as measures that could be implemented intermittently, on 24-

hours advance notice, and for a total of up to 10 continuous or non-continuous days per year, to 

help attain or maintain the short-term NAAQS for ozone or PM2.5. 

Three industry sectors were selected as case studies for this analysis: pulp and paper; iron and 

steel; and cement. We researched specific technological options for achieving additional 

emission reductions on an episodic basis within the three selected sectors and assessed the 

implications of these options for emission sources in other industry sectors. The options fell into 

the following categories: 

• Fuel switching, i.e., replacing current fuel sources with alternate fuels that result in lower 

emissions of one or more priority pollutants; 

• Low cost retrofits and enhanced use of existing control equipment, i.e., installing low 

capital cost control devices, or using existing control devices more aggressively (or in 

alternate ways); 

• Scheduling changes, e.g., implementing short-term curtailments or targeted outages; 

• Dispatch changes, e.g., shifting load from one boiler to another which has a more effective 

control device or uses a less polluting fuel; 

• Combustion optimization (or re-optimization), e.g., using sensors, controls or cleanburning combustion modifications to reduce emissions; 

• Sector-specific opportunities, e.g., increasing use of cogeneration units at pulp & paper 

facilities. 

We identified and assessed these options through literature reviews and web research on 

manufacturing processes and control methods. The main information source for this study, 

however, has been discussions with sector experts, including industry analysts at ICF and EPA, 

members of trade associations, independent consultants, corporate environmental managers 

and plant-level operators. 

This study finds there are a number of potential episodic control measures available for each of 

the three sectors analyzed. 

• All three sectors possess some fuel switching capabilities and may be able to shift to lower 

emitting fuels to reduce NOx, SO2, and/or PM on an intermittent basis for short periods of 

time. The manner and extent to which short-term fuel switching could be employed, 

 

1

 See Recommendations to the Clean Air Act Advisory Committee: AQM Subcommittee Phase II Report, 

June 2007, http://www.epa.gov/air/caaac/aqm/phase2finalrept2007.pdf. 

ES - 1 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

however, varies from sector to sector. Since facilities typically select their fuels so as to 

minimize production costs and meet other operational objectives, switching to more 

expensive fuels on a continuous basis would be untenable for many facilities. However, 

because fuel switching under an episodic control program would only be invoked on a 

limited number of days each year, the total incremental costs may be within acceptable 

levels for many facilities. 

• Installation of low capital cost retrofits, such as selective non-catalytic reduction (SNCR) 

and gas reburn systems (for NOx control), and lime injection systems (for SO2 control) 

appears to hold promise in the context of an episodic control program. Although the high 

operation and maintenance (O&M) costs associated with these retrofits (e.g., due to the 

significant consumption of reagent or natural gas) may make them cost prohibitive for use 

on a continuous basis at many facilities, they may be suitable for use at some facilities as an 

episodic control measure. 

• Opportunities may exist to modify and thereby enhance the use of existing pollution 

control equipment on a temporary basis to control for additional pollutants (i.e., in addition 

to the main pollutant(s) these controls are intended for). For example, many industrial 

boilers and furnaces have venturi scrubbers. These scrubbers are generally installed as PM 

control devices but may also remove some SO2 from the exhaust stream of the combustion 

unit. Some industry analysts and regulatory experts believe there may be an opportunity to 

enhance the SO2 removal efficiency of venturi scrubbers in some situations by adding alkali 

reagent. This may be technically feasible and economically viable where a unit already has 

such a device and is able to obtain significant incremental SO2 reductions on a short-term 

basis with the addition of the reagent. 

• Opportunities may also exist to run existing pollution control devices more aggressively

for short intervals to achieve incremental emission reductions. Some industry analysts 

thought that in some cases it might be possible to temporarily increase the control efficiency 

of a variety of NOx, SO2, and PM control systems on days when high air pollution 

concentrations occur and where, for cost or other reasons, existing permit conditions do not 

require these control devices to be utilized at their maximum performance levels. 

 

• While scheduling changes involving temporary shutdowns and curtailments that could 

disrupt core production processes were generally deemed inadvisable, there may be 

opportunities to curtail certain operations or rearrange production schedules on a short-term 

basis to move high emitting processes to times when they are less likely to exacerbate air 

quality problems. For example, because steel mini mill operation is generally batch in 

nature, some mini mills may be able to reschedule melting operations from daytime to 

nighttime hours to reduce VOC and NOx emissions, as well as reduce electrical demand, 

during critical daylight hours when ozone formation is likely to occur. There may also be 

opportunities to defer certain ancillary activities at cement plants, such as quarrying activities 

and finishing mill operations, to reduce emissions as well as electrical demand on a shortterm basis. 

• Dispatch changes involving boilers at large pulp and paper mills with excess boiler capacity 

appear to be a feasible episodic control strategy in some instances. 

ES - 2 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

• Additionally, there may also be other sector-specific opportunities for achieving additional 

emission reductions on an episodic basis, such as increasing the use of cogeneration units 

in the pulp and paper sector, which require further exploration. 

• Episodic control measures related to combustion reoptimization techniques appeared less 

viable for the selected industry sectors. Most facilities in these sectors use sophisticated 

computer controlled equipment on highly inter-connected and synchronized production 

processes. Industry experts were reluctant to entertain the idea of altering the already 

optimized processes, as they might make the processes less efficient and/or more polluting. 

While this study has focused primarily on facilities in the pulp and paper, iron and steel, and 

cement manufacturing sectors, our research and information gathering indicates that a wide 

variety of episodic control measures may be available for use by sources in other industrial 

sectors as well. 

• Several episodic control measures that are applicable to industrial boilers in the pulp and 

paper or the iron and steel sectors, may also be broadly applicable to boilers in other 

industrial sectors. For example, some industrial boilers in other industries may be able to 

install low capital cost retrofit technologies (such as SNCR or gas reburn for NOx control, or 

lime injection for SO2 control), to reduce boiler emissions on a short-term basis. Other 

boilers may be able to temporarily reduce emissions by switching to a lower emitting fuel for 

limited periods of time. In addition, some boilers that have already been retrofitted with 

control devices may have the ability to increase the control efficiencies of those devices by 

modifying their operation or running them more aggressively for short time intervals. 

• As with industrial boilers, a number of the episodic control measures applicable to other 

units and processes in the three selected industries may be applicable to similar units or 

processes in other industries as well. Examples include fuel switching at furnaces and 

process heaters, installation of low capital cost retrofits, enhanced use of existing control 

equipment, and certain scheduling changes. Some sectors may also be able to provide 

additional, sector-specific opportunities for achieving emission reductions on an episodic 

basis. 

• Several of the episodic control measures examined in relation to the three selected industry 

sectors involve the rescheduling of electricity-intensive processes to times when they are 

less likely to exacerbate air quality problems. Other industrial sectors may have similar 

opportunities to temporarily halt, curtail or defer electricity-intensive processes as part of an 

episodic control program. These measures could be especially helpful on high electricity 

demand days when electric utilities may rely on very high emitting generating units in order 

to meet peak demand for electricity. Reducing peak electricity demand, or shifting that 

demand from daytime to nighttime hours (when lower-emitting generating capacity is 

available and the resultant emissions may have less ozone or PM2.5 forming impact), could 

provide significant air quality benefits. Electric utilities may also have the ability to employ a 

variety of other episodic control measures to reduce NOx, SO2 and/or PM emissions on 

days with high air pollution concentrations. 

This report is intended to provide a preliminary assessment of the wide array of episodic control 

measures that may be available to industrial sources. The potential measures identified in this 

report should be studied further as EPA, states, communities, and other stakeholders consider 

ES - 3 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

the potential role that episodic control measures could play in helping to meet ozone and PM2.5 

air quality goals. For example: 

• To better assess the technical feasibility, emission reduction potential and cost of 

prospective episodic control measures, it will be necessary to conduct detailed engineering 

and cost analyses of specific measures. Because of the heterogeneity across facilities 

within a sector, as well as across sectors, these analyses will need to take into account sitespecific and process-level emissions, as well as other source-specific considerations at 

individual facilities. 

• Because the ambient impact of episodic control measures is likely to be spatially 

differentiated, location-specific air quality modeling will be necessary to determine the actual 

impact that short-term emission reductions from any particular industrial source or sector 

would have on local and/or regional air quality problems. 

• In order to evaluate the potential utility of episodic control measures it will also be necessary 

to review state-of-the-art practices pertaining to the prediction of ozone and PM episodes. 

The effectiveness of episodic control measures would in part depend on the degree of prior 

notice that can be provided to plant operators, which is in turn a function of the ability of 

regulatory agencies and/or other institutions to predict air pollution episodes. 

Another key step in the further exploration of episodic control measures is to quantify the costeffectiveness of these measures on a dollar-per-ton of pollutant removed basis. Our 

discussions with industry analysts indicated this is a major unknown because episodic 

measures for industrial sources have traditionally been overlooked in the air pollution control 

literature. It must be emphasized that comparisons to cost-per-ton estimates based on 

continuous control programs would provide an erroneous picture, as the acceptable costeffectiveness range for an episodic control program is likely to be substantially higher than the 

corresponding range for a continuous program. Thus, a better understanding of the range of 

cost-effectiveness values that could be appropriate given the benefits of an episodic control 

program needs to be carefully developed. 

A number of critical policy issues will also need to be addressed before episodic control 

measures can be systematically implemented, including whether these measures should be 

mandated by regulation, negotiated as part of the permitting process, or pursued by individual 

facilities on a purely voluntary basis.

ES - 4 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

1. Introduction 

I. Background on the Issue 

The Air Quality Management (AQM) Subcommittee of EPA’s Clean Air Act Advisory Committee 

(CAAAC) recently recommended expanding the use of episodic control measures to help attain 

and maintain National Ambient Air Quality Standards (NAAQS) in areas where all reasonable 

continuous (i.e., year-round) and seasonal control measures have already been required.2

 A 

number of communities have already developed programs to reduce emissions by individuals 

and businesses (e.g., from vehicle use, road construction, open burning and other activities), on 

specific days when high ozone or particulate matter (PM) concentrations are expected. To date, 

however, few efforts have been made to apply episodic control measures to industrial sources.3

 

Industrial source episodic control measures–-measures that can be implemented intermittently 

for short periods of time–-could provide an expanded set of control options for states and 

communities. These options may be particularly useful in areas that are at risk of exceeding the 

8-hour ozone NAAQS and/or the 24-hour fine particle (PM2.5) NAAQS only on a limited number 

of days each year. A variety of measures that could not be implemented on a continuous or 

seasonal basis could potentially prove suitable and acceptable for episodic use. By reducing 

peak concentrations on the highest pollution days, episodic control measures can provide 

considerable health and environmental benefits.4

 

II. Purpose of this Report 

The Sector Strategies Division (SSD) within EPA’s Office of Policy, Economics, and Innovation 

(OPEI) undertook this study to help EPA, states, communities, and other stakeholders assess 

the potential use of episodic control measures by industrial sources. Three industry sectors 

were selected as case studies for analysis: pulp and paper; iron and steel; and cement. 

This study builds on a previous analysis conducted by ICF International in 2006 to identify and 

qualify a subset of industry sectors as candidates for further episodic control research. Our goal 

in this current study is to identify, through research and discussions with industry experts 

nationwide, potential episodic control measures for the three selected sectors that may be 

technically feasible, practical, and cost-effective, and to assess the implications of these 

approaches for other industry sectors. 

For purposes of this analysis, episodic control measures are defined as measures that could be 

implemented intermittently, on 24-hours notice, and for a total of up to 10 continuous or noncontinuous days per year, to help attain and maintain NAAQS for ozone or PM2.5. 

 

2

 See Recommendations to the Clean Air Act Advisory Committee: AQM Subcommittee Phase II Report, 

June 2007, http://www.epa.gov/air/caaac/aqm/phase2finalrept2007.pdf. 3

 Memorandum from Art von Lehe to Barry Elman, EPA Sector Strategies Division, Re: Episodic Control 

Measures, August 11, 2006 

4 The AQM Subcommittee recognized that legal restrictions currently limit EPA’s ability to provide State 

Implementation Plan (SIP) credit for stationary source episodic control measures. The Subcommittee did, 

however, recommend expanding the use of such measures as “backup insurance mechanisms” (outside 

the scope of an approved SIP) for areas working to attain or maintain the short-term ambient air quality 

standards.

1 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

III. Selection of Sectors: Research Scope and Bounds 

In 2006, ICF International conducted an analysis for SSD to identify industry sectors that 

warrant further study with regard to their ability to use episodic control measures to help states 

and local communities meet their ozone and PM2.5 attainment goals.5

 We used three metrics 

as screens for that analysis: plant location vis-à-vis nonattainment designations, emissions of 

relevant criteria air pollutants, and energy consumption. 

• Plant Location. Using a Geographic Information System (GIS) framework, we analyzed 

sectors based on their geographic distribution and correspondence with current short-term 

ozone and PM2.5 nonattainment designations. Information on nonattainment status came 

from the EPA Green Book.6

 The resulting visual representation allowed us to determine 

sectors that could potentially provide significant episodic emission reductions in 

nonattainment areas. 

• Criteria Air Pollutant (CAP) Emissions. We analyzed air emissions profiles for all 28 

industry sectors included in the 2001 Aerometric Information Retrieval System (AIRS) and 

estimated their relative contributions to total CAP emissions (i.e., VOC, NOx, SO2, and 

PM2.5) that contribute to ozone and PM2.5 air quality problems. 

• Energy Consumption. Building on SSD’s on-going analysis of strategies to promote 

environmentally-preferable energy outcomes in selected manufacturing sectors,7

 we 

analyzed the energy intensities and fuel mix for those selected sectors to determine whether 

there may be short-term changes in fuel use and combustion equipment that may offer 

significant potential for episodic emission reductions. 

Based on these screening assessments, we identified a number of sectors as good candidates 

for further study of potential episodic control measures, including the pulp and paper, iron and 

steel, and cement sectors. Section 2 of this report provides updated location maps for these 

three sectors, while Exhibit 1, below, provides updated emissions data. 8

 

 

5

 “Selecting Sectors for Analysis of Potential Episodic Control Measures”, ICF technical memorandum to 

Barry Elman, EPA Sector Strategies Division. September 29, 2006. 

6

 See http://www.epa.gov/oar/oaqps/greenbk/index.html. 7

 See March 2007 final report, Energy Trends in Selected Manufacturing Sectors: Opportunities and 

Challenges for Environmentally Preferable Energy Outcomes, prepared by ICF for SSD, 

http://www.epa.gov/ispd/energy/index.html. 

8

 While the three sectors selected for case studies all have manufacturing facilities located in ozone 

and/or PM2.5 nonattainment areas, and they all emit significant quantities of criteria pollutants and 

operate energy intensive processes, further analysis (including assessment of site-specific emissions, 

stack parameters, air chemistry, atmospheric transport and other factors) would be necessary in order to 

fully characterize the air quality impacts of any individual facility or industry sector. 

2 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

Exhibit 1: Point Source Emissions from Selected Manufacturing 

Sectors as a Percentage of All Manufacturing Sectors 

Sector VOC NOx SO2 PM2.5 

Pulp & Paper* 8% 14% 15% 12% 

Iron & Steel** 1% 4% 3% 7% 

Cement*** 1% 15% 8% 6% 

All Manufacturing Sectors**** 100% 100% 100% 100% 

* Pulp and Paper is defined as NAICS codes 32211, 322121 and 322122, or SIC codes 261 and 262 

** Iron & Steel is defined based on a list of facilities developed by EPA’s Sector Strategies Division 

*** Cement is defined based on a list of facilities developed by EPA’s Sector Strategies Division 

**** All Manufacturing Sectors is defined as NAICS codes 31-33, or SIC codes 20-39 

Source: U.S. EPA’s Final v2 2002 National Emission Inventory (NEI) for Criteria Air Pollutants from Point 

Sources 

IV. Methodology, Data Sources, and Caveats 

Building upon our 2006 analysis, we researched specific technological options for achieving 

intermittent, short-term emission reductions across the target sectors. These options fell into the 

following categories: 

• Fuel switching, i.e., replacing current fuel sources with alternate fuels that result in lower 

emissions of one or more priority pollutants; 

• Low cost retrofits and enhanced use of existing control equipment, i.e., installing low 

capital cost control devices, or using existing control devices more aggressively (or in 

alternate ways); 

• Scheduling changes, e.g., implementing short-term curtailments or targeted outages; 

• Dispatch changes, e.g., shifting load from one boiler to another which has a more effective 

control device or uses a less polluting fuel; 

• Combustion optimization (or re-optimization), e.g., using sensors, controls or cleanburning combustion modifications to reduce emissions; 

• Sector-specific opportunities, e.g., increasing use of cogeneration units at pulp & paper 

facilities. 

We identified and assessed these options through literature reviews and web research on 

manufacturing processes and control methods. The main information source for this study, 

however, has been discussions with sector experts, including industry analysts at ICF and EPA, 

members of trade associations, independent consultants, corporate environmental managers 

and plant-level operators. Within the constraints of time and resources, we conducted a limited 

set of interviews, seeking information and expert opinions to vet the technical feasibility, 

practicality and cost-effectiveness of these potential options. As a result, some information is 

anecdotal, and there are technical points on which knowledgeable opinions vary. 

Clearly, consideration of episodic control measures for industrial sources is in its formative 

stage. This report is intended to provide a preliminary basis for assessing the wide array of 

options that may be possible. Based on this analysis, however, we cannot say definitely which 

measures will or will not be viable, or what benefits they will provide. The potential measures 

3 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

identified in this report should be studied further as EPA, states, communities and other 

stakeholders consider options for achieving ozone and PM2.5 attainment goals. 

V. Report Outline 

The major sections of this report are organized as follows: 

• Section 2, Sector Options and Analyses, explores potential episodic control measures for 

each of the three sectors selected as case studies for this analysis, and considers the 

applicability of these measures to other industrial sources. 

o The first three subsections present the results of our research on the three selected 

sectors: 2.I, pulp and paper; 2.II, iron & steel; and 2.III, cement. We begin each sector’s 

discussion by presenting an overview of its manufacturing processes and related 

emissions, as well as by providing maps that show the location of the sector's facilities in 

relation to nonattainment areas for ozone and PM2.5. We then provide our detailed 

analysis of potential episodic control measures, followed by summaries of our main 

findings in text boxes. 

o Section 2.IV highlights the implications of our analysis for other sectors, focusing on 

potential measures for industrial boilers, as well as for electric utilities and other 

industrial sources.

• Section 3, Summary of Findings & Next Steps, summarizes our findings across the three 

selected sectors, as well as the implications for other sectors, and presents consolidated 

next steps. 

• The Appendix describes the effects that the 2001 and 2005 rolling blackouts in California 

had on the performance of several industry sectors, to inform discussion on how these or 

other sectors might react to unscheduled outages in the context of an episodic control 

program. 

4 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

2. Sector Options and Analyses 

I. Pulp and Paper 

a. Overview of the Pulp & Paper Manufacturing Process and its Emissions 

Pulp and paper manufacturing can be broken down into five significant steps: 9

• Wood preparation involves removing the bark from logs and then breaking down the 

debarked logs into wood chips of uniform size. The uniformity in the chip size maximizes the 

quality and efficiency of the subsequent pulping process. 

• Pulping then converts the fibrous wood material into a slurry of fibers. Pulping involves 

cooking the wood fibers, washing, and screening to remove unwanted materials. Three 

different types of pulping technologies are used, depending on the desired properties of the 

final product and the corresponding amount of lignin that needs to be removed from the 

paper.10 Chemical pulping removes the most lignin, semichemical pulping removes some 

lignin, while mechanical pulping does not remove any lignin. 

• Chemical recovery, which is part of the pulping process, enables the recovery and reuse of 

chemicals used in the chemical and semichemical pulping process. Steam and electricity 

generated during the recovery process also help offset the large energy requirements of 

pulp and papermaking. 

• Bleaching is a chemical process used to whiten or brighten the pulp before it is used in 

papermaking. Different bleaching techniques are used depending on the specific pulping 

process and the residual lignin left in the pulp. 

• Papermaking is the final stage consisting of four steps: 

o Preparing a homogeneous pulp slurry (stock); 

o Dewatering the slurry; 

o Pressing and drying to manufacture the paper; and 

o Finishing the manufactured paper. Depending on the final product desired, 

finishing can involve one or more of the following processes – rewinding the 

paper onto a reel, trimming, coating, printing, saturation, and box-making. 

Exhibit 2 presents a simple flow diagram of the basic pulp and paper manufacturing process, 

applicable for all three types of pulping processes – chemical, semichemical, and mechanical 

pulping. 

 

9

 The following overview of the pulp and paper manufacturing process and emissions is taken from the 

DOE/ITP report on the pulp and paper industry; (Energy and Environmental Profile of the U.S. Pulp and 

Paper Industry, US DOE, Office of Energy Efficiency and Renewable Energy, Industrial Technologies 

Program, December 2005). This overview describes the process at an integrated pulp and paper mill. 

The industry also has a large number of non-integrated mills that purchase pulp to make paper and 

others that obtain and process recycled fibers for papermaking. 10 Wood lignin holds the wood fiber together and adds strength and stiffness to trees, but also results in 

weaker paper that yellows with age. 

5 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

Exhibit 2: Basic Pulp & Papermaking Process

 Source: Smook, 1992 (from EPA Sector’s Notebook, November, 2002) 

Exhibit 3 below shows the relative shares of the different fuel types used in the pulp and paper 

industry in 2002. The “Other” fuel category, which primarily includes biomass, is the dominant 

fuel at about 54 percent of the total. Biomass fuel includes spent liquor or black liquor11

(approximately 70 percent of the “Other” category) and wood residues and byproducts 

(approximately 27 percent of the remainder). The next biggest fuel source is natural gas at 21 

percent, followed by coal and electricity at 10 percent and 9 percent, respectively. 

Exhibit 3: Primary Fuel Inputs as Fraction of Total Energy Supply for the 

Pulp & Paper Industry in 2002 (fuel use only)

Coal Other Net Electricity Natural Gas Fuel Oil 

10% 54% 9% 21% 5% 

Source: Energy Trends in Selected Manufacturing Sectors, EPA Sector Strategies Division, March 

2007, based on DOE/EIA Manufacturing Energy Consumption Survey, 2002 Data Tables. Totals may 

not add to 100 percent due to rounding. 

Net electricity provides a rough approximation for purchased power and includes purchased 

electricity, transfers in, and generation from noncombustible renewables, and excludes electricity 

transferred out or sold. 

 

11 Black liquor is a byproduct generated in the chemical pulping process. Boilers fired with black liquor 

have an efficiency of about 70 percent, compared to 80-85 percent for coal- or natural gas-fired boilers of 

same size. (Source: Characterization of the U.S. Industrial/Commercial Boiler Population, Oak Ridge 

National Laboratory, May 2005.) 

6 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

Air Emissions 

The biggest emission sources in a pulp and paper mill are the power boilers used to generate 

steam and electricity for sustaining the pulp and papermaking process. These power boilers 

consume all of the coal used by this sector and produce significant amounts of SO2 (about 83 

percent of the total for this industry) and NOx (about 77 percent of the total), and some VOC. 

The second biggest emission source is the kraft recovery furnace. While recovery furnaces 

generate significantly lower SO2 and NOx emissions than the power boilers, their VOC 

emissions are similar to those from the power boilers. Power boiler PM emissions are generally 

well controlled through venturi scrubbers, baghouses or ESPs, while ESPs are by far the 

dominant PM control device on kraft recovery furnaces. Exhibit 4 presents process-specific 

emissions from the pulp and paper industry. 

Exhibit 4: Process Specific Emissions in 2002

Pulp and Paper Emissions

0

50000

100000

150000

200000

250000

300000

Bleaching

Kraft Pulping

Kraft Recovery

Papermaking

Power Boilers

Ancillary Ops

Control

Fugitives

Other

Wastewater

Source

Tons per Year

SO2

NOx

VOC

Total HAP

PM-10 PRI

Source: SO2 and NOx Emissions from U.S. Pulp and Paper Mills, 1980-2005. National Council for Air 

and Stream Improvement (NCASI) analysis (based on Draft 2002 NEI data). 

b. Location 

There were 425 pulp and paper mills, including 148 integrated mills, operating in the U.S. in 

2005.12 The location of mills and facilities appears to be largely driven by the location of wood 

sources, rather than energy sources. For example, pulp mills that use virgin woods tend to be 

in regions where trees are harvested, including the Southeast, Northwest, Northeast, and North 

Central regions. Pulp mills that rely on recycled fiber are located near sources of waste paper. 

Nonintegrated paper mills often are located near pulping operations, since this is their primary 

input.13 Exhibit 5 below presents the location of pulp and paper mills in relation to 

nonattainment and maintenance areas for the current 8-hour ozone NAAQS, as of October 

 

12Pulp and Paper Mill Emissions of SO2, NOx, and Particulate Matter in 2005, Special Report No. 06-07, 

National Council for Air and Stream Improvement (NCASI), December 2006. 13 Analysis of Energy Usage in Selected Industrial and Commercial Sectors, US EPA, Sector Strategies 

Division, May 24, 2006. 

7 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

2007.14 15 Exhibit 6 presents the location of pulp and paper mills in relation to counties violating 

the current 24-hour PM2.5 NAAQS, based on 2004-06 monitoring data.16 While these exhibits 

indicate that a number of pulp and paper mills are located in or near areas that currently violate 

the short-term standards for ozone or PM2.5, it should be noted that many of these areas are 

projected to attain the standards in the near term while other areas are at risk of violating the 

standards in the future. It should also be emphasized that source-specific factors, including 

process-level emissions, stack parameters, topography, meteorology, and air chemistry, would 

need to be taken into account when assessing the air quality impact of any individual facility or 

sector on local or regional air quality problems. 

Exhibit 5: Location of Pulp and Paper Mills in Relation to 

8-Hour Ozone Nonattainment and Maintenance Areas 

Sources: Pulp and paper mill locations obtained for facilities listed with SIC codes 261 and 262, or 

NAICS codes 32211, 322121 and 322122, in 2002 (v2) National Emissions Inventory (NEI) CAP 

Point Source Dataset. Nonattainment and maintenance areas for the current 8-hour ozone NAAQS 

obtained from EPA’s Green Book: Nonattainment Status for Each County by Year, October 2007.

 

14 The locations of pulp and paper mills were obtained for facilities listed with SIC codes 261 and 262, or 

NAICS codes 32211, 322121 and 322122, in 2002 (v2) National Emissions Inventory (NEI) CAP Point 

Source Dataset. Data on nonattainment and maintenance areas for the current 8-hour ozone NAAQS 

were obtained from EPA’s Green Book: Nonattainment Status for Each County by Year, October 2007, 

available at http://www.epa.gov/oar/oaqps/greenbk/map8hrnm.html and 

http://www.epa.gov/oar/oaqps/greenbk/anay.html.

15 EPA proposed tightening the 8-hour ozone NAAQS on July 11, 2007. See: 

http://www.epa.gov/air/ozonepollution/pdfs/20070711_proposal_fr.pdf. 

16 The locations of pulp and paper mills were obtained for facilities listed with SIC codes 261 and 262, or 

NAICS codes 32211, 322121 and 322122, in 2002 (v2) National Emissions Inventory (NEI) CAP Point 

Source Dataset. Data on counties violating the current 24-hour PM2.5 NAAQS were obtained from EPA’s 

Air Quality System (AQS) as of July 11, 2007, available at http://www.epa.gov/airtrends/values.html. 

8 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

Exhibit 6: Location of Pulp and Paper Mills in Relation to 

Counties Violating the 24-Hour PM2.5 NAAQS 

Sources: Pulp and paper mill locations obtained for facilities listed with SIC codes 261 and 262, or 

NAICS codes 32211, 322121 and 322122, in 2002 (v2) National Emissions Inventory (NEI) CAP 

Point Source Dataset. Counties violating the current 24-hour PM2.5 NAAQS (based on 2004-06 

monitoring data) obtained from EPA’s Air Quality System (AQS) as of July 11, 2007. 

c. Potential Episodic Control Measures 

We focused our analysis on five categories of potential episodic control measures for the pulp 

and paper sector: 

• Fuel switching; 

• Low cost retrofits and enhanced use of existing control equipment; 

• Dispatch changes; 

• Scheduling changes; and 

• Cogeneration. 

i. Fuel switching 

Several short-term fuel switching options appear to have potential as episodic control measures 

for the pulp and paper industry: 

The pulp and paper industry uses a large number of power boilers and coal is a major fuel 

source for many of these boilers. Coal accounts for a disproportionate share of the SO2 and 

NOx emissions from power boilers, and there appears to be some potential for switching from 

9 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

coal to other lower emitting fuels, such as biomass or natural gas, for short time periods in many 

power boilers. 17

Most power boilers in this industry are “combination boilers” capable of burning multiple fuel 

types. Combination boilers can shift between fuel types on short notice and are generally 

designed to run up to 100 percent on any of the fuels they are designed to handle. According to 

industry analysts, many combination boilers routinely burn coal and biomass, with the 

percentage breakdown between the two fuel sources varying over time and across facilities. 

Typically, facilities that burn biomass have at least a one week onsite supply of biomass fuel. 

Thus, facilities burning both coal and biomass in a combination boiler may have the flexibility to 

increase their use of biomass, or even to use biomass as the only fuel source, for short periods, 

if needed. Industry analysts felt that if biomass was used to displace coal there should be 

significant SO2 and NOx emission reduction benefits. Further analysis is, however, needed to 

confirm that facilities with combination boilers have the ability to shift on short (i.e., 24-hours) 

notice to a higher share of biomass in their fuel mix (i.e., up to 100 percent biomass) for short 

periods of time, since current permit limitations and/or operational constraints could restrict such 

changes. Further analysis is also needed to determine the magnitude of the SO2 and NOx 

emission reductions that short-term fuel switching from coal to biomass could provide, as well 

as the impact on other pollutants, and to more fully assess the cost and operational impacts on 

individual facilities. 

Another potential short-term fuel switching option for power boilers is switching from coal to 

natural gas. Switching to natural gas on a short-term basis appears to be technically viable for 

many facilities since most boilers have natural gas firing capability. The key issue with regard to 

this fuel switching option appears to be cost. Facilities may have to make limited capital 

expenditures to prepare for using natural gas, and would have to establish operational 

procedures, train staff and maintain equipment on an ongoing basis in order to ensure 

“operational readiness” to switch over to natural gas on short notice. Moreover, facilities would 

need to secure a reliable natural gas supply, and this would likely entail a significant price 

premium (over the already high cost of natural gas) in order to ensure sufficient access to 

natural gas on short notice. Nevertheless, some industry analysts thought it was conceivable 

that the cost of shifting to natural gas on a limited number of days with high air pollution 

concentrations could be less than the cost of installing further add-on controls. This would need 

to be confirmed through further analysis, as would the magnitude of the SO2 and NOx 

reductions, and the operational impacts on individual facilities, that would result from 

implementing this strategy. 

In addition, industry analysts also noted that some pulp and paper mills in the Midwest use high 

sulfur coal and may be good candidates for switching to lower sulfur coal on days with high air 

pollution concentrations, such as coal from the Powder River Basin (PRB). Although such a 

switch might entail additional fuel and/or transportation costs, the proximity of these mills to PRB 

in Wyoming and lower rail tariffs resulting from railway deregulation may make this switch a 

viable and cost-effective episodic control strategy for some mills.18 Pulp and paper mills that 

employ this strategy would need to stockpile and manage a secondary coal supply, which would 

 

17 The combustion of coal and biomass both result in higher PM emissions than the combustion of natural 

gas and together they account for most of the PM emitted from power boilers in the pulp and paper 

sector. 

18 Industry analysts pointed out there may also be costs associated with equipment modifications needed 

to burn subbituminous versus bituminous coal and there may be technical feasibility constraints to the use 

of PRB coal in cyclone boilers. 

10 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

further increase operating costs and could potentially raise other logistical or operational issues. 

Moreover, unlike electric utilities, pulp and paper facilities are not primary purchasers of coal 

and may be restricted by existing long-term coal contracts.19 Therefore, they may be 

constrained in their ability to obtain (or replenish) low sulfur coal supplies. Nevertheless, 

switching from high- to low-sulfur coal on short (i.e., 24 hours) notice warrants further 

exploration as a potentially viable and cost-effective episodic control strategy for some 

Midwestern mills that currently burn high sulfur coal. 

Another fuel switching option that might work for smaller mills is switching from residual oil to 

natural gas. Most small mills have package boilers designed to burn fuel oil and/or natural gas. 

According to industry analysts, many of these boilers currently burn residual oil but can switch to 

natural gas on short notice. This switch can provide significant SO2 and NOx emission reduction 

benefits. Switching from residual oil to natural gas may be a particularly attractive option for 

small mills located in or near urbanized areas experiencing air quality problems. There are 

several concerns, however, with burning more natural gas at small facilities; these concerns 

relate to accessibility, availability, and cost. 

• Some small mills may not have access to a natural gas pipeline and would therefore be 

unable to switch over to this fuel on days with high air pollution concentrations. 

• Because natural gas is in high demand for heating purposes during the winter, as well as on 

high electrical demand days during the summer, particularly in the Northeast where a 

number of small mills are located, issues related to availability and price would need to be 

assessed to determine the true viability of this option for small mills.20 

For small mills with package boilers that burn residual oil, an alternative strategy could be to 

switch to LPG or propane instead of natural gas. Our discussions with industry analysts 

indicated that some mills might be able to store a limited supply of LPG onsite for use on days 

when high air pollution concentrations occur. Alternatively, with a 24-hour lead time, mills might 

be able to arrange to have LPG tanker(s) brought onsite to supply enough LPG to replace 

residual oil for a short period of time (e.g., 8-12 hours). Our discussions indicated that this 

might be a viable and cost-effective strategy for a number of small mills given the nature of their 

operations, even though modest capital expenditures may be required (e.g., to install new 

burners) before a boiler would be equipped to burn LPG.21 Further research is needed on the 

costs and operational impacts of implementing this strategy. In addition, permitting restrictions 

may need to be addressed in order to allow mills to store and/or use LPG as an episodic control 

measure. 

 

19 Primary purchasers of coal are those facilities/industries that are the main buyers of coal, and may 

therefore have some influence on the type of coal being shipped as well as delivery schedules. 

20 Mills might need to pay a price premium to secure a guaranteed, as-needed supply. 21 Switching from residual oil to distillate oil or diesel fuel may also be feasible with the installation of new 

burners and a separate fuel storage tank. 

11 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

Summary: Fuel Switching 

There appear to be several potential fuel switching options for achieving significant short-term SO2

and NOx emission reductions from power boilers as part of an episodic control strategy for the pulp 

and paper industry. 

For bigger mills, the most promising short-term fuel switching opportunities would occur at 

combination boilers. Many of these boilers use large quantities of coal and may have the capability to 

temporarily use more biomass or natural gas in its place to achieve significant emission reductions. 

There might also be opportunities to switch from high- to low-sulfur coal for short intervals at some 

Midwestern mills. 

For small mills, short-term shifts from residual oil to natural gas or LPG/propane in package boilers 

seem to hold promise. This strategy might be particularly useful where small mills are located in or 

near urbanized areas with air quality problems.

ii. Low-cost retrofits and enhanced use of existing control equipment 

Another set of episodic control measures we considered entails the use of add-on control 

equipment. Although most pollution control retrofits require significant capital expenditures for 

installation, there are some that have relatively low installation costs but higher operation and 

maintenance (O&M) costs. Such low-capital, high O&M retrofits may be cost-effective to 

operate for short time periods during an episodic air pollution event. Similarly, where control 

technologies are already deployed, it may be possible to run them more aggressively for short 

intervals, or in other ways that would not be feasible or cost-effective on a continuous basis. 

We identified four control technologies that seemed to have potential as episodic control 

measures for the pulp and paper industry: 

• Selective non-catalytic reduction (SNCR) 

• Gas reburn 

• Venturi scrubbers 

• Lime injection 

SNCR for NOx Control 

A number of industry analysts suggested that the use of SNCR systems may be a viable 

episodic control measure for reducing NOx emissions from facilities in the pulp and paper 

industry, particularly for base-loaded boilers (i.e., boilers that run continuously, or close to it). 

SNCR systems can be used with base-loaded boilers firing any fuel (coal, wood, gas, etc.). 

Some analysts have stated, however, that if the boiler load fluctuates significantly, there may be 

technical problems with installing SNCR systems on such boilers. According to these analysts, 

SNCR is not a proven technology on industrial boilers with fluctuating loads. However, one 

SNCR vendor we spoke with has stated that SNCR has been demonstrated on many industrial 

boilers with fluctuating load and that the cycling boilers in the pulp and paper industry do not 

present special technological challenges.22 Thus, the use of SNCR systems as an episodic 

control measure holds promise for base-loaded boilers in the pulp and paper industry. However, 

 

22 This vendor said that it would guarantee the performance of SNCR on cycling boilers at pulp and paper 

mills, although site-specific modeling would be required before a guarantee could be issued with regard to 

any specific installation. 

12 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

the extent to which these systems can be used as an episodic control measure for cycling 

boilers would need to be further analyzed to reconcile the differing viewpoints.23 

In those instances where the use of SNCR systems is technically feasible, the limiting factor is 

generally the cost of implementing these systems. According to industry analysts and 

technology vendors, the cost of purchasing and installing an SNCR system may be on the order 

of $1 million or more for a large industrial boiler. However, for large boilers, most of the total 

annualized costs associated with an SNCR system is for the reagent used (urea or aqueous 

ammonia). Therefore, the cost burden associated with installing and operating an SNCR 

system could be reduced significantly under an episodic control program. For example, in the 

case of a large boiler it might be possible to reduce the total cost burden of an SNCR system by 

50 percent or more if the system were installed and run at an intermediate (e.g., 30 percent) 

control level on a continuous basis, and then ramped up to full capacity (e.g., 50 percent control 

efficiency) on days with high air pollution concentrations. The cost burden could be further 

reduced if the SNCR system were kept on standby and used only on days with high air pollution 

concentrations. 

A major concern expressed by industry analysts was that once an SNCR system is installed and 

available for use as part of an episodic control program, regulators and/or community activists 

may demand that it be run at full capacity on a continuous basis. Further analysis of the 

technical feasibility, emission reduction potential and cost of this option with respect to different 

boiler types, fuels and operating conditions is required. 

Gas Reburn for NOx Control 

Another NOx control technology that might be viable as an episodic control measure for this 

sector is natural gas reburn. According to industry analysts, stoker wood-fired boilers in the 

pulp and paper industry may be ideal candidates for additional NOx control using intermittent 

gas reburn. Since most facilities may have access to natural gas (for use as a boiler starter 

fuel, for example), the incremental costs of using gas reburn may be limited to the costs of 

installing additional burners and using natural gas. Because the strategy would only be used 

intermittently and for short periods, however, mills would require relatively limited quantities of 

natural gas. Thus, the total incremental costs may be within acceptable levels for many large 

mills.24 

Venturi scrubbers for SO2 Control 

About 25 percent of the combination boilers in the pulp and paper industry that burn both coal 

and wood have venturi scrubbers. These scrubbers are installed for PM control but may also 

have the capability to further reduce SO2 emissions by as much as 80 percent when alkali 

reagent is used. Some mills already use alkali reagent in their venturi scrubbers to reduce SO2

emissions, however, the vast majority do not. The main reason why venturi scrubbers have not 

been widely utilized as an SO2 abatement strategy is because they are generally not considered 

to be efficient or cost-effective for that purpose – according to one industry analyst they may 

waste about half the reagent used.25 The use of alkali reagent to achieve additional SO2

 

23 Another issue needing further evaluation according to some industry analysts is the potential for 

ammonium sulfate formation in the case of boilers with high sulfur fuels. 

24 Although natural gas reburn has fallen out of favor as a continuous control strategy in the current 

scenario of high gas prices, its use as an episodic strategy may still be a worthwhile avenue of research. 25 Facilities that need to scrub SO2 on a continuous basis would generally install packed tower scrubbers 

or other SO2 control technologies that are more efficient in their use of alkali reagent, and are capable of 

achieving SO2 reductions of 90 percent or more. 

13 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

emission reductions may, however, be technically feasible and cost-effective as an episodic 

control measure for those facilities that have already installed venturi scrubbers, insofar as they 

could achieve a significant incremental reduction in SO2 emissions on a short-term basis for a 

modest cost with the addition of alkali reagent.26

Lime injection for SO2 Control 

Mills that use baghouses or electrostatic precipitators (ESP) for PM control may have the option 

to inject dry lime powder into the duct that carries exhaust gases from a power boiler to the PM 

control device, to get additional SO2 removal. The costs for implementing this control strategy 

could include the cost of installing storage, transfer and injection systems for the lime, and the 

cost of the lime reagent itself. For kraft mills with existing baghouses or ESPs on their boilers, 

this strategy may be particularly attractive and cost-effective because lime is already available 

at the mill (although the particle size distribution that is needed for lime injection may not be 

easily available). Moreover, in the case of baghouses, caking of the lime on the baghouse walls 

would provide enhanced control efficiency for SO2, with over 70 percent control efficiencies 

possible according to one expert. For mills that use ESP for PM control, the absence of caking 

on the walls would imply that their control efficiencies would be lower, thereby increasing the 

cost-per-ton of SO2 removed. Even with ESPs, however, lime injection may still be able to 

achieve significant short-term SO2 reductions at modest cost. 

Summary: Low Cost Retrofits and Enhanced Use of Existing Control Equipment 

Most industry analysts agree that it is technically feasible to install SNCR systems on base-loaded 

boilers in the pulp and paper industry. Because of the relatively low capital costs and the limited use 

of reagent, installing and using SNCR systems as part of an episodic NOx control program may be a 

cost-effective strategy for these boilers. There is some dispute, however, as to the technical feasibility 

of installing SNCR systems on pulp and paper industry boilers with vacillating load. Further analysis 

of the technical feasibility and cost of this option with respect to different types of boilers and operating 

conditions is required. 

Another NOx control technology that may warrant further consideration as an episodic control 

measure is natural gas reburn. Although the high price of natural gas makes this technology less 

appealing for use on a continuous basis, it may be cost-effective for use as an intermittent, short-term 

control strategy. 

The addition of alkali reagent to venturi scrubbers to achieve further SO2 reductions appears to be a 

promising episodic control measure for mills that have already installed these scrubbers for PM control 

purposes. These mills would need to incur the additional cost (O&M) of using reagent only on a 

limited number of days when high air pollution concentrations occur (as well as the cost of installing an 

alkali addition system for those mills that do not presently have such a system). Its effectiveness, 

however, would vary depending on the fuel mix used in the boilers and other site-specific factors. 

For those mills that use baghouses or ESPs for PM control, lime injection may be a viable and costeffective episodic SO2 control measure. 

 

26 The SO2 reduction resulting from the addition of alkali reagent would also depend on the coal/wood fuel 

mix in the boilers. If the boiler burns mostly coal and very little wood (say 90-10 ratio), then adding 

reagent can provide up to 80 percent SO2 reduction. 

14 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

iii. Dispatch changes 

According to industry analysts, a typical large, integrated mill may have several power boilers, 

e.g., two large combination boilers and two smaller package boilers designed to burn fuel oil 

and/or natural gas. One or more of these boilers would likely be base-loaded and the others 

cycled as needed. In some cases, an integrated mill may also have an idle package boiler that 

could be brought online to burn natural gas with as little as one hour of lead time. Thus, at any 

given moment, a mill may have some excess boiler capacity, and this capacity could occur at a 

boiler that burns cleaner fuel or has a more efficient control device than a boiler that is currently 

being utilized. Most boilers within a facility are inter-connected so that load can be shifted from 

one to another. Therefore, from a theoretical standpoint, mills may have some ability to dispatch 

different boilers at different times to attain episodic emission reduction goals. Further research 

is needed, however, to determine the magnitude of the emission reductions that could result 

from short-term dispatch changes, and to more fully assess the cost and operational impacts on 

individual facilities. 

Another possible dispatching strategy for pulp and paper mills involves generating more steam 

at recovery furnaces, on a short-term basis, to reduce the load on power boilers. Most of the 

steam that is required at an integrated mill is provided by burning black liquor in the recovery 

furnace. Although the recovery furnace is typically operated at a high utilization rate, there may 

be some ability to further increase its capacity utilization on a temporary basis. For example, a 

recovery furnace that is operating at 85 percent of its maximum capacity could be ramped up to 

90 or 95 percent for a short interval in order to reduce the demand for steam from boilers, 

thereby reducing the need to run the boilers to generate steam. Based on our discussions, it 

appears that recovery furnaces can be readily cycled up or down, and most mills have a 

sufficient stockpile of black liquor to allow for a one or two day increase in the furnace’s 

utilization rate. 27 Because black liquor has lower fuel heat content than coal, more black liquor 

would be needed to generate the same amount of energy. Nevertheless, due to the lower SO2

and NOx emissions generally resulting from black liquor combustion compared with most fossil 

fuels, it may be possible to achieve a net reduction in SO2 and NOx emissions. Further 

research is needed to determine the magnitude of the emission reductions that could be 

achieved by increasing steam generation at the recovery furnace on a short-term basis, and to 

more fully assess the cost and operational impacts on individual facilities. 

Summary: Dispatch Changes 

Changing boiler dispatch as an episodic control strategy may work for some integrated pulp and paper 

mills to the extent that they have excess capacity at low emitting boilers on days with high air pollution 

concentrations. In addition, integrated mills may be able to temporarily increase steam production at 

their recovery furnace in order to reduce their reliance on higher emitting power boilers to generate 

steam. 

 

27 In addition, many recovery furnaces have load-carrying oil or gas burners that could be used to produce 

additional steam. Use of auxiliary oil would not increase SO2 emissions due to capture of the oil sulfur by 

sodium fumes inside the furnace. Additional NOx from auxiliary gas or oil burning in the furnace would 

still be less than the NOx produced from coal combustion on a lb/lb steam produced basis. However, 

there could be air permitting issues associated with increased auxiliary fuel burning.

15 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

iv. Scheduling changes 

Short-term scheduling changes appear to be the least viable episodic strategy for pulp and 

paper mills, as they almost always strive to operate at constant capacity in order to maintain 

maximum production efficiency. Industry analysts indicated that short-term changes to mill 

operations would likely reduce production efficiency and therefore be cost prohibitive. 

Moreover, short-term disruptions in mill operations could increase emissions intensity 

(emissions per unit of production), and potentially increase net emissions from a facility. 

Summary: Scheduling Changes 

Industry analysts agreed that scheduling changes would generally not be effective as an episodic 

strategy for pulp and paper mills. 

v. Cogeneration 

The pulp and paper industry is one of the largest cogeneration applications among all industry 

sectors. Cogeneration is considered an environmentally preferable generating technology, 

because the simultaneous production of thermal and electric energy from the same fuel source 

is more efficient than generating just electricity. Onsite electricity generation also eliminates 

energy losses associated with transmission and distribution of power over the electric grid. 

According to industry analysts, a significant portion of the pulp and paper industry’s 

cogeneration is considered emission neutral, because it uses primarily the steam generated 

from the pulping process. More than 65 percent of the industry’s electricity needs are met 

through cogeneration processes.28 

Most analysts we spoke with agreed that the pulp and paper industry may have the ability to 

further increase its electricity generation through its cogeneration systems on a short-term basis 

(i.e., provide a “surge capacity”), but this would need to be studied further. Moreover, any 

strategy that involves increasing electricity generation from the pulp and paper industry for short 

time intervals would need to evaluate the tradeoffs associated with displacing electricity 

generated by power plants. While it is possible that increased electricity generation at pulp and 

paper mills could displace generation from high emitting electrical utility units on high electricity 

demand days, further research is needed to determine the extent to which net emission 

reductions would result from this strategy, and to more fully assess the cost and operational 

impacts on individual mills. 

 

Summary: Cogeneration 

Pulp and paper mills already lead all industry sectors in cogeneration, but they may still have some 

excess capacity to increase their electricity generation on days when high air pollution concentrations 

occur. However, any strategy to increase the pulp and paper industry’s electricity generation would 

need to consider the tradeoffs associated with displacing electricity generated by power plants. 

Moreover, concerns exist in how increased cogeneration would impact the pulp and paper industry’s 

relationship with power plants and electricity rates. More analysis is needed to determine whether this 

can be a viable episodic strategy. 

 

28 Analysis of Energy Usage in Selected Industrial and Commercial Sectors, US EPA, Sector Strategies 

Division, May 24, 2006.

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EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

d. Opportunity Assessment of Potential Episodic Control Options 

Exhibit 7 summarizes the potential viability of the five primary options for further reducing 

emissions on days with high air pollution concentrations. 

Exhibit 7: Opportunity Assessment – Pulp & Paper

Option Viability as Potential Episodic Control Measure 

Fuel switching Promising – Several short-term fuel switching options appear to have 

potential as episodic control measures (for SO2 and NOx reductions) 

Low cost retrofits and 

enhanced use of existing 

control equipment 

Promising – SNCR for base-load boilers (for NOx reductions); venturi 

scrubbers and lime injection (for SO2 reductions) 

Needs further study – Gas reburn (for NOx reductions) 

Dispatch changes 

Possible – For large mills with multiple power boilers and/or a recovery 

boiler operating below maximum capacity on days when high air pollution 

concentrations occur (for SO2 and NOx reductions) 

Scheduling changes Unlikely 

Increased cogeneration Needs further study

17 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

II. Iron & Steel 

a. Overview of the Iron & Steel Manufacturing Process and its Emissions 

As detailed in Exhibit 8, the iron and steel manufacturing process can be broken down into the 

following four major steps: cokemaking, ironmaking, steelmaking, and forming and finishing.29 

• Cokemaking uses coal to generate coke, coke oven gas, and by-product chemicals from 

compounds released from the coal. Coke is produced by heating metallurgical coal (also 

called “coking coal”) in such a manner as to drive off the volatile substances commonly 

present in coal, producing a carbon-rich coke. 

• In the traditional method of ironmaking, iron-bearing materials are reduced to molten 

metallic iron (called “pig iron”) in a blast furnace, using carbon present in coke as a reducing 

agent. The iron-bearing materials are pellets or sinter made from iron ore and other 

materials at ore agglomeration facilities. The pellets or sinter are charged with coke in the 

blast furnace, and hot blast air is blown through tuyeres in the lower part of the furnace. The 

hot gas from coke combustion creates a reducing atmosphere in which the iron oxides are 

converted and melted to molten pig iron. Metallic iron also can be produced without using 

coke in a direct reduction process, generating the necessary reducing atmosphere directly 

with coal or natural gas. Pig iron contains 3 to 4 percent carbon and direct-reduced iron 

commonly contains 1 to 3 percent carbon. 

• Steelmaking removes carbon and other impurities by controlled oxidation of the iron 

charged into a steelmaking furnace. In addition to hot metal from a blast furnace, iron and 

steel scrap or direct-reduced iron can be charged into a steelmaking furnace. Additional 

elements, chromium or nickel for example, may be added to steel in the furnace or in the 

ladle after the furnace to produce special alloy steels. The principal steelmaking processes 

used in the US are: 

o Basic oxygen furnace (BOF) – molten iron from the blast furnace is refined by 

injecting high purity oxygen and adding fluxing materials. BOF offers superior 

energy efficiency with high throughput. Steelmaking facilities that use this 

technology are supplied with molten iron from a blast furnace, along with up to 30 

percent steel scrap. These facilities, which may also include a coke plant and 

finishing facilities, are collectively known as integrated mills. 

o Electric arc furnace (EAF) – steel scrap is melted and refined using electric energy, 

so no cokemaking or ironmaking operations are required.30 EAF permits charging 

with high levels of scrap, which reduces or eliminates the need for access to hot 

metal from the blast furnace. Steel facilities that use this technology are referred to 

as mini mills. 

 

29 The following discussion of the basic iron and steelmaking process is summarized from two sources – 

EPA Sector Notebook on Iron and Steel, 1995, and Gas Research Institute, Environmentally Driven 

Threats and Opportunities for Natural Gas in the Iron and Steel Industry, (prepared by ICF/EEA), 

November 1994. 

30 Some EAF facilities use scrap substitutes (e.g., pig iron or direct reduced iron) as well as scrap. 

18 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

• In the Forming and Finishing stage, once the molten steel has attained the desired 

chemical composition in the steelmaking furnace, it is tapped (poured) into a ladle. 

Additional chemical adjustment may occur in the ladle with the addition of alloying material 

or the removal of unwanted constituents from the molten steel. The next step is the casting 

of the molten steel. There are two types of casting used today: continuous casting and ingot 

casting. Continuous casting accounts for about 97 percent of total steel produced. In 

continuous casting, molten steel is shaped directly from the ladle to form semi-finished steel 

products known as blooms, billets, and slabs. These semi-finished steel products are rarely 

used as final products. They usually serve as raw materials in the manufacturing of final 

steel products. The semi-finished products undergo various processes including hot rolling, 

cold rolling, forging, and drawing to form the finished products. 

Exhibit 8: Basic Iron & Steel Production Process

Source: EPA Sector Notebook 

Exhibit 9 shows the relative share of the different fuel types used in the iron and steel sector in 

2002. Coke and breeze generated in the manufacturing process was the dominant fuel source 

at 36 percent. The industry also used significant amounts of natural gas (27 percent). The 

“Other” fuel category (21 percent) was largely composed of byproduct fuels such as coke oven 

19 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

gas and blast furnace gas. (All of the coke and breeze and most of the fuels classified as 

“other” are coal-based in origin.) 

Exhibit 9: Primary Fuel Inputs as Fraction of Total Energy Supply for the Iron & 

Steel Industry in 2002 (fuel use only)

Coal Other* Net Electricity Natural Gas Coke & Breeze* 

3% 21% 13% 27% 36% 

Source: Energy Trends in Selected Manufacturing Sectors, EPA Sector Strategies Division, March 

2007, based on DOE/EIA Manufacturing Energy Consumption Survey, 2002 Data Tables. Totals may 

not add to 100 percent due to rounding. 

Net electricity provides a rough approximation for purchased power and includes purchased 

electricity, transfers in, and generation from noncombustible renewables, and excludes electricity 

transferred out or sold. 

*All of the coke and breeze, and most of the fuel inputs classified as “other” (i.e., byproduct fuels such 

as coke oven gas and blast furnace gas), are coal-based in origin. 

Air Emissions 

The cokemaking process is a large source for air emissions, including fine particles of coke 

generated during the process and sulfur compounds emitted from the coke oven stacks. 

However, because the expulsion of volatile substances from coal is the purpose of cokemaking, 

fugitive VOCs are the most important source of air emissions. These emissions include various 

complex hydrocarbons, such as benzene and polycyclic aromatics, as well as other VOCs. 

Ironmaking is also significant from an air pollution perspective, as it generates significant 

amounts of NOx, some SO2, and particulates.31 Air emissions are generated from the crushing 

and handling of the ore and from fuel combustion in the furnace. Ore crushing is the largest 

source of uncontrolled PM in the iron and steel industry. The emissions from crushing 

operations, while considerable, are effectively controlled by conventional PM technologies. 

Steelmaking generates some amounts of NOx as a by-product of CO combustion in the exhaust 

of both furnaces. The EAF process also generates additional NOx at the arc. Emissions of 

VOCs and other pollutants depend on the quality of material charged into the furnace. VOC 

emissions are derived primarily from the scrap charge, which is greater in the EAF. 

b. Location 

There are currently 18 integrated steel mills operating in the U.S., mostly in the Great Lakes 

region. In addition, there are mini mills operating in approximately 70 locations across the 

country, with a large concentration in the Great Lakes region as well.32 Exhibit 10 below 

presents the location of iron and steel mills in relation to nonattainment and maintenance areas 

for the current 8-hour ozone NAAQS, as of October 2007.33 34 Exhibit 11 presents the location 

 

31 Energy and Environmental Profile of the U.S. Iron and Steel Industry, US Department of Energy, Office 

of Industrial Technologies, August 2000. 

32 List of iron and steel facilities prepared by U.S. EPA Sector Strategies Division. 33 The locations of iron and steel mills were obtained from the American Iron and Steel Institute. Data on 

nonattainment and maintenance areas for the current 8-hour ozone NAAQS were obtained from EPA’s

Green Book: Nonattainment Status for Each County by Year, October 2007, available at 

http://www.epa.gov/oar/oaqps/greenbk/map8hrnm.html and 

http://www.epa.gov/oar/oaqps/greenbk/anay.html.

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EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

of iron and steel mills in relation to counties violating the current 24-hour PM2.5 NAAQS, based 

on 2004-06 monitoring data.35 While these exhibits indicate that a number of iron and steel 

mills are located in or near areas that currently violate the short-term standards for ozone or 

PM2.5, it should be noted that many of these areas are projected to attain the standards in the 

near term while other areas are at risk of violating the standards in the future. It should also be 

emphasized that source-specific factors, including process-level emissions, stack parameters, 

topography, meteorology and air chemistry, would need to be taken into account when 

assessing the air quality impact of any individual facility or sector on local or regional air quality 

problems. 

Exhibit 10: Location of Iron and Steel Mills in Relation to 

8-Hour Ozone Nonattainment and Maintenance Areas

Sources: Iron and steel mill locations obtained from U.S. EPA Sector Strategies Division. 

Nonattainment and maintenance areas for the current 8-hour ozone NAAQS obtained from EPA’s 

Green Book: Nonattainment Status for Each County by Year, October 2007. 

 34 EPA proposed tightening the 8-hour ozone NAAQS on July 11, 2007. See: 

http://www.epa.gov/air/ozonepollution/pdfs/20070711_proposal_fr.pdf. 

35 The locations of iron and steel mills were obtained from the American Iron and Steel Institute. Data on 

counties violating the current 24-hour PM2.5 NAAQS were obtained from EPA’s Air Quality System (AQS) 

as of July 11, 2007, available at http://www.epa.gov/airtrends/values.html. 

21 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

Exhibit 11: Location of Iron and Steel Mills in Relation to 

Counties Violating the 24-Hour PM2.5 NAAQS

Sources: Iron and steel mill locations obtained from U.S. EPA Sector Strategies Division. Counties 

violating the current 24-hour PM2.5 NAAQS (based on 2004-06 monitoring data) obtained from EPA’s 

Air Quality System (AQS) as of July 11, 2007. 

c. Potential Episodic Control Measures 

We focused our analysis on four categories of potential episodic control measures for the iron 

and steel sector: 

• Fuel switching; 

• Low cost retrofits and enhanced use of existing control equipment; 

• Scheduling changes; and 

• Dispatch changes. 

i. Fuel switching 

For integrated iron and steel mills that produce coke, little opportunity exists to switch from coal 

to other fuels in the coke-making process. Since coke-making is one of the most polluting 

processes in this industry, integrated mills may, however, reduce their reliance on coke by 

burning pulverized coal as an auxiliary fuel in the blast furnace. This would decrease the 

amount of coke they need to produce and yield a corresponding decrease in emissions from the 

coke-making process. There are technical limits, however, on the extent to which pulverized 

coal can be used to displace coke in a blast furnace. Moreover, once a mill has made the 

considerable capital investment necessary to use pulverized coal, it would be expected to use 

that fuel (which is less expensive than coke) to the maximum extent possible. Therefore, there 

appears to be little opportunity to increase the use of pulverized coal in a blast furnace as part of 

a strategy to reduce coke oven emissions on days with high air pollution concentrations. Some 

22 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

blast furnaces may, however, be able to use natural gas as an auxiliary fuel on an episodic 

basis. Using natural gas would likely result in NOx, SO2, and PM emission reductions. More 

research is needed, however, to assess the economic and technical feasibility of this option. 

Most boilers at integrated iron and steel mills are designed to burn multiple fuels and are able to 

switch among these fuels on a few hours notice. Consequently, another short-term fuel 

switching option that might hold some promise for reducing NOx, SO2, and VOC emissions at 

integrated mills is to switch from coke oven gas to natural gas in boilers on days with high air 

pollution concentrations. Most integrated mills have some capability to store unused coke oven 

gas but must flare any unused gas that they are unable to store.36 Depending on the storage 

capacity of their gas holders, and how much of that capacity is unutilized at the time, mills may 

be able to increase the use of natural gas in their boilers for a limited period of time, while 

saving the displaced coke oven gas for later use. As discussed below, mills may also be able to 

slow the operation of their coke ovens as part of an episodic control strategy, which would 

decrease the amount of coke oven gas that is available for use in the boilers. This shortfall 

could then be made up by burning more natural gas. Further analysis is needed to determine 

the extent to which integrated mills could shift from coke oven gas to natural gas in boilers, and 

the degree to which such shifts would reduce NOx, SO2, and VOC emissions.37 Emission and 

cost impacts would need to be assessed on a plant-by-plant basis. 

Because mini mills do not have any significant fuel needs and depend primarily on grid-supplied 

electricity, there do not seem to be any fuel switching options for mini mills. 

Summary: Fuel Switching 

Integrated mills may be able to temporarily slow down the coke-making process to decrease coke 

oven emissions and decrease the supply of coke oven gas to the boilers. The boilers could 

compensate by burning more natural gas which would result in reduced boiler emissions of NOx, SO2, 

and VOC. There may also be opportunities to store a limited amount of coke oven gas in gas holders, 

which would enable mills to temporarily increase their use of natural gas at boilers while saving the 

displaced coke oven gas for later use. 

 

Some integrated mills may also be able to use natural gas as an auxiliary fuel in the blast furnace to 

achieve short-term reductions in NOx, SO2, and PM emissions. This could also allow for a temporary 

decrease in coke production and a corresponding decrease in emissions from the coke-making 

process. 

These potential fuel switching options for integrated mills need to be studied at the plant-level, as their 

infrastructural needs, operational impacts and subsequent costs may vary by plant. 

No fuel switching options were identified for mini mills. 

 

36 Indications are that most integrated mills may have gas holders to store limited quantities of unused 

coke oven gas (e.g., one or two days supply). 

37 Our initial discussions with industry analysts seemed to point towards a significant emission reduction 

benefit if mills were to switch from coke oven gas to natural gas. 

23 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

ii. Low-cost retrofits and enhanced use of existing control equipment 

Another set of episodic control measures we considered entails the use of add-on control 

equipment. Although most pollution control retrofits require significant capital expenditure for 

installation, there are some controls that have relatively low installation costs but higher 

operation and maintenance (O&M) costs. Such low-capital, high O&M retrofits may be costeffective to operate for short periods when high air pollution concentrations occur. Similarly, 

where control technologies are already deployed, it may be possible to run them more 

aggressively for short intervals, or in other ways that would not be feasible or cost-effective on a 

continuous basis. 

• We identified one control technology that seemed to have potential as an episodic control 

measure for iron and steel mills: Selective Non-Catalytic Reduction (SNCR). 

SNCR for NOx Control

Some analysts we spoke with felt that SNCR may hold promise as a short-term control measure 

for reducing NOx emissions from integrated iron and steel mills. While SNCR technology has 

been in use for many years in some industries, no SNCR system has yet been installed at an 

iron or steel mill. The limiting factor has been the cost of implementing these systems. 

According to industry analysts and technology vendors, the cost of purchasing and installing an 

SNCR system may be on the order of $1 million or more for a large industrial boiler. However, 

for large boilers, most of the total annualized cost associated with an SNCR system is for the 

reagent used (urea or aqueous ammonia). Therefore, the cost burden associated with installing 

and operating an SNCR system could be reduced significantly under an episodic control 

program. For example, in the case of a large boiler it might be possible to reduce the total cost 

burden of an SNCR system by 50 percent or more if the system were installed and run at an 

intermediate (e.g., 30 percent) control level on a continuous basis, and then ramped up to full 

capacity (e.g., 50 percent control efficiency) on days with high air pollution concentrations. The 

cost burden could be further reduced if the SNCR system were kept on standby and used only 

on days with high air pollution concentrations. 

A major concern expressed by industry analysts was that once an SNCR system is installed and 

available for use as part of an episodic control program, regulators and/or community activists 

may demand that it be run at full capacity on a continuous basis. Further analysis of the costs 

of this option and other site-specific considerations is required. 

Summary: Low Cost Retrofits and Enhanced Use of Existing Control Equipment 

Some analysts felt that an SNCR system may hold promise as an episodic control measure for reducing 

NOx emissions from large boilers at integrated mills and warrants further research. Because of the 

relatively low capital cost and the ability to limit reagent consumption, installing and using SNCRs as part 

of an episodic control program may be a cost-effective strategy for this industry. 

iii. Scheduling changes 

Integrated mills 

Industry analysts felt there might be opportunities to curtail cokemaking operations at integrated 

facilities for short periods in order to reduce VOC, NOx, SO2, and PM emissions. Facilities can 

generally lengthen the coking cycle (e.g., from 16 hours to up to 24 hours) without disrupting 

other parts of the production process, where they have sufficient onsite coke inventories or the 

24 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

ability to buy additional coke from merchant coke manufacturers. There is indication that some 

facilities may already have permit provisions that require them to use longer coking cycles in 

response to upset conditions. As discussed above, slowing down the coking cycle would also 

reduce the production of coke oven gas, allowing facility operators to increase the use of natural 

gas in boilers, which would yield additional NOx, SO2, and VOC emission reductions. 

Integrated facilities might also be able to increase scrap usage in the basic oxygen furnace for 

short periods of time and on short notice. Basic oxygen furnaces typically charge between 10 

and 30 percent scrap, with the permissible range varying from product to product. Within this 

range, the choice of hot metal versus scrap is primarily based on price. Therefore, there may 

be limited opportunity at some mills to temporarily shift to a higher scrap utilization rate within 

the permissible range for a product, or to switch to production of a product that permits a higher 

scrap utilization rate. 

Another possible option would be to slow down or delay batch operations in the blast furnace for 

short intervals. Industry analysts emphasized, however, that operational stability is very 

important for blast furnaces. For this and other reasons, they believed that episodic control 

measures that target scheduling changes in coke oven operations and/or increased scrap 

utilization rates in the basic oxygen furnace may hold more promise for integrated steel mills 

than scheduling changes affecting the blast furnace. 

Options for rescheduling production activities at integrated mills need to be assessed with 

regard to their potential costs and emission reduction benefits, and evaluated further with plant 

operators to understand their effectiveness and the tolerable levels of disruption for integrated 

mills. 

Mini mills 

Because mini mill operation is generally batch in nature, there may be opportunities to 

rearrange production schedules on a short-term basis to move high emitting processes to times 

when they are less likely to exacerbate air quality problems. For example, rescheduling melting 

operations from daytime to nighttime hours could significantly reduce emissions of VOC and 

NOx during critical daylight hours when ozone formation occurs. Similarly, rescheduling melting 

operations from one time period to another could potentially shift PM and NOx emissions to a 

period when those emissions would be less likely to contribute to a PM2.5 violation. 

Since mini mills consume extremely large amounts of grid-supplied electricity, rescheduling 

melting operations could be particularly useful on high electricity demand days when electric 

utilities may utilize very high-emitting generating units to meet peak load requirements. Shifting 

mini mill electricity consumption from daytime to nighttime hours (when lower-emitting 

generating capacity is available and the resultant emissions may have less ozone or PM2.5 

forming impact), could therefore provide significant air quality benefits. 

Note that during the rolling blackouts in California in 2001 and 2005 (see the Appendix), some 

mini mills with interruptible power contracts switched to firm contracts with their power suppliers 

because the power curtailments were deemed too costly. Others, however, rescheduled their 

melting operations to off-peak hours to take advantage of the cheaper electricity rates during 

those times and still allow for the interruptible contracts to continue.38

 

38 Mini mills pointed out that an unscheduled stoppage that occurs during the course of the melting 

operation is extremely dangerous to workers and could cause equipment destruction. 

25 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

According to industry analysts, many mini mills in other parts of the country also have 

interruptible power contracts so that electricity can be temporarily curtailed or halted when there 

is a surge in electricity demand. There is also evidence that some mills in other parts of the 

country run at night to take advantage of cheaper off-peak electricity rates. 

Further analysis is needed to determine the extent to which mini mills may have additional 

opportunities to shift production to off-peak electricity generation periods, and the magnitude of 

the SO2 and NOx emission reductions that such short-term scheduling changes could provide. 

Further analysis is also needed to more fully assess the cost and operational impacts of these 

changes on individual facilities. 

Summary: Scheduling Changes 

Integrated steel mills might be able to implement longer coking cycles for short time periods if they have 

adequate onsite coke inventories or access to merchant coke. These mills may also be able to increase 

the use of scrap in their basic oxygen furnaces. Scheduling changes in blast furnaces, while technically 

feasible, appear to be more disruptive for these facilities. 

Due to the batch nature of mini mill operations, many mini mills already use interruptible power contracts, 

or schedule their melting activities during off-peak hours, and there may be opportunities to make 

additional scheduling changes to shift melting and other high emitting processes to times when they 

would be less likely to exacerbate air quality problems. The deferral of melting operations from daytime 

to nighttime hours could be particularly useful on high electricity demand days, since it may enable 

utilities to avoid the use of very high-emitting generating units that would otherwise be needed to meet 

peak load requirements. 

iv. Dispatch changes 

According to industry analysts, most integrated steel mills have at least two boilers with some 

flexibility to shift load from one boiler to another on just a few hours notice. Analysts expressed 

their doubts on whether such a change in boiler dispatch would be worthwhile, however, since 

all boilers typically have the capability to use all the available fuel types, and fuel switching 

within the same boiler may generally be a more effective option. 

Summary: Dispatch Changes 

Because integrated mills have access to multiple boilers, changing boiler dispatch may be theoretically 

possible, but may not be practically effective. Most boilers can use all available fuel types, so switching 

fuel within the same boiler may be more effective than changing boiler dispatch. 

26 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

d. Opportunity Assessment of Potential Episodic Control Options 

Exhibit 12 summarizes the potential viability of the four primary options for further reducing 

emissions on days with high air pollution concentrations. 

Exhibit 12: Opportunity Assessment – Iron & Steel

Option Viability as Potential Episodic Control Measure 

Fuel switching 

Promising – Several short-term fuel switching options appear to have 

potential at integrated facilities (for NOx, SO2, PM, and VOC reductions), 

but coke oven gas storage options, and the ability to link slowdowns in 

the coke-making process with increased use of natural gas at boilers, 

need to be evaluated 

Unlikely – At mini mills 

Low cost retrofits and 

enhanced use of existing 

control equipment 

Promising – SNCR on large boilers (for NOx reductions) 

Scheduling changes Promising – For both integrated facilities and mini mills 

Dispatch changes 

Needs Further Study – While it is likely that some integrated facilities 

could shift load among boilers on short notice, it is unclear if this would 

be an effective control measure 

27 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

III. Cement 

a. Overview of the Cement Manufacturing Process and its Emissions 

Cement manufacturing requires the “thermochemical processing of substantial amounts of 

limestone, clay, and sand in large kilns” at very high and sustained temperatures (over 2,750o

F) 

to produce an intermediate product called clinker.39 Clinker is ground up with small quantities of 

gypsum to create Portland cement, the predominant variety of cement manufactured in the U.S. 

Portland cement is used as a binding agent in virtually all concrete.40 The process of Portland 

cement manufacturing can be broken down into the following four steps:41

• Quarrying and crushing the rock; 

• Grinding the carefully proportioned materials to high fineness; 

• Subjecting the raw mix to thermochemical processing in a kiln; and 

• Grinding the resulting clinker to a fine powder. 

Cement is manufactured in four different types of kilns:42

• Long wet kilns; 

• Long dry kilns; 

• Dry kilns with preheaters; and 

• Dry kilns with precalciners. 

Processes that take place within each kiln type include drying and preheating, which comprises 

evaporation of free water, dehydration of clay minerals, and increasing the temperature of the 

raw materials to over 1,650 oF; calcining, a process of decomposing the carbon compounds, 

which occurs when the raw materials reach about 1,650 oF; and heating the calcined raw 

materials to about 2,750 oF, where they are sintered to form clinker. The same raw materials are 

used in the wet and dry kilns, however, the moisture content and processing techniques differ, 

along with kiln designs.43 

• Wet process kilns are generally longer to allow them to dry the wet raw material mix (also 

known as slurry) as it is fed into the kiln. 

• Long dry kilns are more energy efficient than wet process kilns but produce exit gases at 

very high temperatures. 

• Preheater kilns differ from the traditional long wet and long dry kilns because they have a 

series of cyclones where the dry raw material is intimately mixed with the hot combustion 

gases. These kilns use about half of the fuel that a wet kiln uses to produce clinker because 

the preheater system efficiently recovers process heat. 

 

39 Assessment of Control Technology Options for BART-Eligible Sources, prepared by NESCAUM, March 

2005. 

40 Energy Trends in Selected Manufacturing Sectors, prepared by ICF for EPA’s Sector Strategies 

Division, March 2007. 

41 Assessment of NOx Emissions Reduction Strategies for Cement Kilns – Ellis County – Final Report, 

prepared for Air Quality Planning Section, Texas Commission on Environmental Quality, July 14, 2006. 42 Ibid. 43 The following description of the cement manufacturing process and emissions profile is taken from the 

EPA Sector Notebook on Stone, Clay, Glass, and Concrete Products Industry (including cement), 

September 1995. 

28 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

• Precalciner kilns have a calciner vessel inserted between the preheater and the kiln. In a 

precalciner kiln about 40 percent of the fuel is fired in the kiln and the rest is fired in the 

calciner. Firing a large amount of the fuel in the calciner significantly reduces thermal NOx 

emissions because the fuel is burned at less than 2,000o

F and normally fuel consumption for 

a precalciner kiln is 10 percent less than a preheater kiln. 

The clinker produced in the kiln is cooled in a traveling grate using ambient air and the cooled 

clinker is transferred to storage. The clinker is then mixed with four to six percent gypsum and 

ground to produce a homogeneous cement powder, which is typically sent to a bulk storage 

area and then shipped by truck or rail. 

Exhibit 13 presents a simple flow diagram of the traditional cement production process using a 

long wet kiln. 

Exhibit 13: Basic Cement Production Process

Source: Report to Congress on Cement Kiln Dust (obtained from the EPA Sectors Notebook, 

September, 1995). 

Exhibit 14 shows the relative shares of the different fuel types used in the cement sector in 

2002. Coal was the dominant fuel at about 58 percent of the total, not only because it was 

relatively inexpensive but also because the resulting coal ash contains minerals that chemically 

combine with the raw material to make clinker. The “Other” fuel category included petroleum 

coke as well as waste materials that were incinerated for fuel, such as tire derived fuel (TDF). 

Tires made up 3 percent of the total fuel use by this sector in 2004.44 

 

44 See Table 22 in Energy Trends in Selected Manufacturing Sectors, EPA Sector Strategies Division, 

March 2007. 

29 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

Exhibit 14: Primary Fuel Inputs as Fraction of Total Energy Supply for the Cement 

Industry in 2002 (fuel use only)

Coal Other Net Electricity Natural Gas Coke & Breeze 

58% 23% 11% 5% 2% 

Source: Energy Trends in Selected Manufacturing Sectors, EPA Sector Strategies Division, March 

2007, based on DOE/EIA Manufacturing Energy Consumption Survey, 2002 Data Tables. Totals may 

not add to 100 percent due to rounding. 

Net electricity provides a rough approximation for purchased power and includes purchased 

electricity, transfers in, and generation from noncombustible renewables, and excludes electricity 

transferred out or sold.

Air Emissions 

The largest emission source within cement plants is the kiln operation, which includes the feed 

system, preheater or precalciner (for preheater/precalciner kiln systems), the fuel firing 

system(s), the actual kiln, and the clinker cooling and transport system. The kiln generates NOx, 

SO2, CO, and hydrocarbon emissions. NOx emissions are from the combustion of fuels to dry, 

calcine, and clinker the raw materials. The emissions of CO, SO2 and hydrocarbons are 

primarily derived from organic and pyretic sulfur in the raw materials. Sources of particulate 

emissions include raw material storage, grinding and blending, clinker production, finish 

grinding, and packaging. 

b. Location 

There were 114 cement plants located in 37 states in 2005. Regionally, cement production was 

concentrated in six states – California, Texas, Pennsylvania, Michigan, Missouri, and Alabama – 

which accounted for approximately one-half of U.S. production.45 Exhibit 15 below presents the 

location of cement plants in relation to nonattainment and maintenance areas for the current 8-

hour ozone NAAQS, as of October 2007.46 47 Exhibit 16 presents the location of cement plants 

in relation to counties violating the current 24-hour PM2.5 NAAQS, based on 2004-06 

monitoring data.48 While these exhibits indicate that a number of cement plants are located in 

or near areas that currently violate the short-term standards for ozone or PM2.5, it should be 

noted that many of these areas are projected to attain the standards in the near term while other 

areas are at risk of violating the standards in the future. It should also be emphasized that 

source-specific factors, including process-level emissions, stack parameters, topography, 

meteorology and air chemistry, would need to be taken into account when assessing the air 

quality impact of any individual facility or sector on local or regional air quality problems. 

 

45 See Cement Profile in Sector Strategies Performance Report 2006, U.S. EPA Sector Strategies 

Division, available at www.epa.gov/sectors/performance.html. 46 The locations of cement plants were obtained from PIS Plant Directory, U.S. Cement Plants, December 

2002. Data on nonattainment and maintenance areas for the current 8-hour ozone NAAQS were 

obtained from EPA’s Green Book: Nonattainment Status for Each County by Year, October 2007, 

available at http://www.epa.gov/oar/oaqps/greenbk/map8hrnm.html and 

http://www.epa.gov/oar/oaqps/greenbk/anay.html.

47 EPA proposed tightening the 8-hour ozone NAAQS on July 11, 2007. See: 

http://www.epa.gov/air/ozonepollution/pdfs/20070711_proposal_fr.pdf. 

48 The locations of cement plants were obtained from PIS Plant Directory, U.S. Cement Plants, December 

2002. Data on counties violating the current 24-hour PM2.5 NAAQS were obtained from EPA’s Air 

Quality System (AQS) as of July 11, 2007, available at http://www.epa.gov/airtrends/values.html. 

30 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

Exhibit 15: Location of Cement Plants in Relation to 

8-Hour Ozone Nonattainment and Maintenance Areas 

Sources: Cement plant locations obtained from PIS Plant Directory, U.S. Cement Plants, December 

2002. Nonattainment and maintenance areas for the current 8-hour ozone NAAQS obtained from 

EPA’s Green Book: Nonattainment Status for Each County by Year, October 2007. 

Exhibit 16: Location of Cement Plants in Relation to 

Counties Violating the 24-Hour PM2.5 NAAQS 

Sources: Cement plant locations obtained from PIS Plant Directory, U.S. Cement Plants, December 

2002. Counties violating the current 24-hour PM2.5 NAAQS (based on 2004-06 monitoring data) 

obtained from EPA’s Air Quality System (AQS) as of July 11, 2007. 

31 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

c. Potential Episodic Control Measures 

We focused our analysis on four categories of potential episodic control measures for the 

cement sector: 

• Fuel switching; 

• Low-cost retrofits and enhanced use of existing control equipment; 

• Scheduling changes; and 

• Combustion reoptimization. 

i. Fuel switching 

We analyzed three potential short-term fuel switching opportunities: (a) increasing the use of tire 

derived fuel (TDF); (b) partially replacing coal with used oil, waste solvents or other alternative 

liquid fuels; and (c) partially replacing coal with natural gas. 

Increasing TDF usage 

According to industry experts, burning TDF at cement kilns by means of mid-kiln injection can 

reduce NOx emissions by as much as 20 to 40 percent.49 Moreover, TDF can be stored easily 

by most cement plants in closed trailers onsite. Hence, we considered whether there was any 

potential to increase TDF usage rates on an episodic basis to reduce NOx emissions and help 

communities meet their ozone and/or PM2.5 attainment goals. 

Currently, about 25 percent of the kilns in the U.S. are configured to use TDF as an alternative 

fuel source. These kilns typically burn anywhere between 10 and 20 percent of their total fuel in 

TDF, with the upper limit determined through existing permit requirements. Most of these kilns, 

however, appear to use TDF below their maximum permitted levels, as well as below their 

physical TDF burning capacities, due to cost and availability considerations. Hence, these kilns 

have some potential for increasing their TDF feed rates. 

Most industry analysts agreed, however, that because of the complex chemistry of the kiln 

operation, making short-term changes to the TDF feed rates could have a negative impact on 

the clinker chemical composition and may require other changes in the production process. In 

addition, kilns typically operate under “steady-state” conditions, and short-term deviations due to 

changes in the fuel mix can make them less efficient, thereby requiring more energy to operate 

at the optimum level. Short-term changes in the fuel mix can also cause kiln upsets. Additional 

energy consumption or a kiln upset could result in a corresponding increase in air emissions 

which could undermine or erode the emission reduction benefits associated with greater TDF 

usage. 

Moreover, some analysts believed that the NOx emission reduction resulting from each 

incremental unit of TDF burned in a kiln is likely to be less than the reduction that resulted from 

the previous unit of TDF burned (that is, the relationship between increased use of TDF and its 

associated emission reduction benefit may be nonlinear with diminishing returns). Increasing 

TDF burn rates from current levels could, therefore, give rise to less than proportional 

 

49 See also SCAQMD Expects Tires to Reduce NOx Emissions, available at 

www.wbcsd.ch/web/projects/cement/tf2/tires.pdf.

32 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

reductions in NOx emissions, making the additional TDF consumption less useful as an episodic 

pollution control strategy.50 

Switching from coal to used oil or solvents 

Another short-term fuel switching option that we investigated involves the introduction of a 

limited quantity of used oil, waste solvent or other alternative liquid fuel to replace existing coal 

used in a kiln. 

Most analysts thought it might be possible to replace 5 to 15 percent of the coal burned in a kiln 

with used oil without significantly altering the steady-state chemistry in the kiln. A switch from 

coal to used oil of this magnitude could potentially produce significant incremental NOx 

reductions – particularly if the first displaced units of coal yield a disproportionate NOx emission 

reduction benefit. A fuel switch of this magnitude could also yield some incremental SO2 

emission reductions. Similar emission reductions may also be achievable by displacing a 

limited amount of the coal burned in a kiln with waste solvents or tar. The introduction of waste 

solvents, tar or other alternative liquid fuels could, however, trigger the need for lengthy and 

contentious permit revisions, and it could be difficult to justify such revisions where the fuels in 

question would only be used for short intervals. For this reason, used oil may be a better 

candidate for fuel switching as part of an episodic control strategy, particularly in cases where a 

cement plant is already set up and permitted to burn used oil and has one or more dormant oil 

tanks. 

Switching from coal to natural gas 

A final short-term fuel switching option we considered was to partially replace the coal burned in 

precalciners with natural gas. According to industry analysts, typically 50-60 percent of the fuel 

consumed by cement plants with precalciner kilns is burned in the precalciner, and coal is the 

predominant fuel utilized. Unlike the kiln itself, where switching from coal to natural gas would 

likely increase NOx emissions, displacing some of the coal burned in the precalciner with 

natural gas would be expected to yield NOx emission reductions. However, the coal used in 

different precalciners may contain different amounts of nitrogen (generating NOx after 

combustion), and so this fuel switching option may be of limited utility as a NOx reduction 

strategy at facilities that already burn coal with relatively low nitrogen content.51 

A major concern expressed by industry analysts regarding this fuel switching strategy was that 

replacing a large percentage of the coal burned in a precalciner with natural gas could alter the 

chemical composition of the clinker (e.g., by reducing the coal ash content), thereby raising 

quality concerns regarding the final product. It may, however, be possible to replace coal with 

natural gas on a more limited basis without raising product quality concerns. This requires 

further analysis.

 

50 One option that appears to be worth considering is to increase the number of kilns that are permitted to 

burn TDF. Technically, this seemed to be a viable option, especially for the preheater/precalciner kilns, 

most of which are currently not permitted to burn TDF. While permitting more kilns to burn TDF cannot be 

considered an episodic control strategy, this strategy may hold promise for the ultimate goal of pollution 

reduction in nonattainment areas. 

51 An alternative to replacing coal with natural gas could be to replace coal with liquid petroleum gas 

(LPG), which would be easier to store onsite than natural gas. While most analysts we spoke with did not 

raise any immediate concerns with this type of fuel switch, further studies need to be conducted to 

determine its viability.

33 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

Industry analysts noted that given the high price of natural gas, switching from coal to natural 

gas on a continuous basis would be prohibitively expensive. However, since this strategy 

involves only short-term substitution of a limited portion of the coal used in the precalciner, and 

since it would require very low capital expenditures, it may prove to be more cost-effective than 

other available alternatives. However, site-specific costs, access to natural gas supplies and 

other facility-specific factors would need to be taken into consideration in order to determine 

whether this can be a viable episodic control strategy. 

Summary: Fuel Switching 

Overall, large scale fuel switching measures to reduce emissions from cement kilns on an episodic basis 

seem to have little potential. 

• The biggest concern expressed by industry analysts was the importance of maintaining the steadystate nature of kiln operations which minimizes kiln upsets and related emission increases, and the 

optimum fuel mix to drive kiln efficiency. 

• A related concern was that the quality of the final product was dependent on the complex chemistry 

inside the kiln; changing fuels on short notice may alter the chemical composition of the final product. 

Our discussions with industry analysts did, however, indicate there may be potential to replace a limited 

portion (e.g., 5 to 15 percent) of the coal burned in a cement kiln with used oil, and a limited portion of the 

coal burned in a precalciner with natural gas. These relatively small scale fuel switches could potentially 

yield additional SO2 and NOx reductions without disrupting the steady-state production process or the 

chemistry in the kiln, although the magnitude of the pollution reductions would need to be analyzed to 

determine their significance. These options require further analysis. 

ii. Low-cost retrofits and enhanced use of existing control equipment 

Another set of episodic control measures we considered entails the use of pollution control 

equipment, such as post-combustion control technologies. Although most pollution control 

retrofits require significant capital expenditure for installation, there are some that have relatively 

low installation costs but higher O&M costs. Such low-capital, high O&M retrofits may be costeffective to operate for short time periods during an episodic event. Similarly, where control 

technologies are already deployed, it may be possible to run them more aggressively for short 

intervals, or in other ways that would not be feasible or cost-effective on a continuous basis. 

• One control technology that seemed promising from the standpoint of achieving further 

short-term NOx reductions was Selective Non-Catalytic Reduction (SNCR). 52 

• Another promising control option from the standpoint of achieving further short-term SO2

reductions was the use of lime injection techniques, including micro-fine lime addition. 

SNCR for NOx Control 

Analysts felt that SNCR may hold some promise as an episodic control strategy for reducing 

NOx emissions from preheater/precalciner kilns in the cement industry. SNCR technology has 

been in use for many years. To date, however, fewer than ten cement plants have installed an 

SNCR system. While there are indications that some state and local air quality regulators may 

 

52 Another NOx control technology that might be viable for the cement sector is gas reburn. Industry 

analysts pointed out there is no data on gas reburn in the cement sector. However, because gas reburn 

may be a viable strategy for episodic NOx reductions in other sectors, it warrants further study with 

respect to the cement sector as well. 

34 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

be considering the imposition of SNCR control requirements where further NOx emission 

reductions are needed to achieve air quality goals, the limiting factor to date has been the cost 

of implementing these systems. 

According to industry analysts and technology vendors, the cost of purchasing and installing an 

SNCR system may be on the order of $1 million for a typical mid-sized kiln. However, for most 

large applications such as cement kilns, the majority of the total annualized cost associated with 

an SNCR system is for the reagent used (urea or aqueous ammonia). Therefore, the cost 

burden associated with installing and operating an SNCR system could be reduced significantly 

under an episodic control program. For example, it might be possible to reduce the total cost 

burden of an SNCR system by 50 percent or more where the system is installed and run at an 

intermediate control level on a continuous basis and then ramped up to full capacity on days 

with high air pollution concentrations. Even greater cost reductions may be possible where the 

system is kept on standby and used only on days with high air pollution concentrations. 

A major concern expressed by industry analysts was that once an SNCR system is installed and 

available for use as part of an episodic control program, regulators and/or community activists 

may demand that it be run at full capacity on a continuous basis. Further analysis of the costs 

of this option and other site-specific considerations is required. 

For those cement plants that have already installed an SNCR system, an alternative strategy 

may be to increase their utilization rates for short time periods when high air pollution 

concentrations occur. Although we were not able to conclusively determine whether there is 

room for increased utilization at facilities with existing SNCR systems, this strategy may warrant 

further exploration with regulators, plant managers and equipment vendors. 

Lime injection for SO2 Control 

Cement plants may have the ability to use lime injection to get additional cost-effective SO2

removal on a short-term basis. Since most cement plants using a preheater or precalciner 

system already have spray cooling and conditioning towers, the additional costs associated with 

lime injection would be less than for wet or long dry kilns. Further research is needed to 

determine the extent to which lime injection could achieve further SO2 reductions on an episodic 

basis, and the cost of implementing this approach. Site-specific factors would need to be taken 

into consideration as well. 

Micro-fine lime addition for SO2 Control 

Micro-fine lime addition involves the use of a very fine grind lime to absorb SO2 in the exhaust 

stream of a kiln. The micro-fine lime is converted into a slurry (water suspension of lime) and 

injected into the water that is used in a spray cooling and conditioning tower that is connected to 

a bag house or ESP. The capital costs for retrofitting a cement plant to use micro-fine lime 

addition could be relatively small where a facility already has a spray cooling and conditioning 

tower in place, as is the case with most preheater/precalciner kilns. There would, however, be 

some capital costs to purchase and install equipment needed to store the micro-fine lime 

reagent onsite and for other equipment modifications. However, the major cost associated with 

micro-fine lime addition is the relatively high cost of the reagent itself, which makes it unsuitable 

for use as a continuous control strategy for cement kilns. 

Evidence of micro-fine lime addition’s use in the cement industry is limited, with its use to date 

restricted to precalciner kilns. Its primary function has been either to serve as a backup SO2

control measure, e.g., to meet permit limits during short periods when the raw mill is not in 

operation, or to address detached plume/plume opacity issues created by condensing ammonia 

35 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

salts. When the raw mill is operating it serves as a de facto scrubber capable of removing as 

much as 80 to 90 percent or more of the SO2. (Similar SO2 removal efficiencies are typical with 

the operation of other types of kilns.) Nonetheless, our discussions with industry analysts 

indicated there might be opportunities to use micro-fine lime addition to achieve additional SO2

reductions at precalciner kilns even when the raw mill is operating, as well as at other types of 

kilns. According to its manufacturer, micro-fine lime addition could be expected to further reduce 

SO2 emissions from cement plants by 50 to 75 percent. This technology should be evaluated 

further to determine its viability and cost as an episodic control measure. 

Summary: Low Cost Retrofits and Enhanced Use of Existing Control Equipment 

Most analysts agreed that installing an SNCR system on preheater/precalciner kilns may have promise as 

an episodic control strategy for reducing NOx emissions and warrants further research. Because of the 

relatively low installation costs and the limited use of reagent, installing and using SNCR systems as part 

of an episodic control program may be a cost-effective strategy for preheater/precalciner kilns in this 

industry. 

For those cement plants that have already installed an SNCR system, an alternative strategy may be to 

increase their utilization rates for short time periods during an episodic event. Although we were not able 

to conclusively determine whether there is room for increased utilization at facilities with existing SNCR 

systems, this strategy may warrant further exploration. 

The use of lime injection or micro-fine lime addition to achieve additional SO2 reductions at cement kilns 

should also be evaluated further to determine their viability and costs as episodic control strategies. 

iii. Scheduling changes 

We considered two types of short-term scheduling changes for the cement industry: 

• First, we considered short-term changes in the clinker production schedule that could be 

undertaken to achieve additional emission reductions on a limited number of days when 

high air pollution concentrations occur. An example of such a schedule change is the 

curtailment of kiln operations for short periods. 

• The second type of scheduling change relates to cement manufacturing activities that are 

ancillary to, and independent of, the actual clinker production process. 

Changes to the clinker production schedule 

Industry analysts indicated that while kiln operations could be curtailed on short notice (e.g., by 

slowing the rotation of the kiln to reduce its production rate), cement plants, which have been 

operating near full capacity in recent years, may be unable to make up the foregone production. 

Moreover, kilns that operate at optimum efficiency generally have the lowest emissions intensity 

(i.e., emissions per unit of clinker produced). Therefore, short-term changes to the optimum 

production rate can be counter-productive to emission reduction goals, eroding the short-term 

emission reduction benefits resulting from a slowdown while increasing the plant’s total annual 

emissions. 

Scheduling changes related to ancillary activities 

Activities that are ancillary to the operation of a cement kiln include quarrying, running the 

finishing mill and bagging/loading the finished product. In addition to their direct emissions 

impact, these ancillary activities require electricity, and most cement kilns depend on gridsupplied electricity for these activities. Therefore, episodic control measures that curtail these 

36 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

operations for short periods of time can provide secondary emission reductions by temporarily 

reducing demand for electricity. 

• Defer quarrying activities: Quarrying activities at cement plants can potentially be deferred 

to reduce PM and NOx emissions from diesel equipment, as well as the demand for gridsupplied electricity, on days with high air pollution concentrations. According to industry 

analysts, some facilities already conduct quarrying activities at night (for example, in 

response to interruptible electricity contracts, or to take advantage of cheaper off-peak 

electricity rates), and there may be additional opportunities to defer quarrying activities until 

nighttime hours as an episodic control measure. Other facilities may be able to curtail 

daytime quarrying activities when high air pollution concentrations occur by using existing 

stockpiles. These relatively low-cost strategies could be particularly useful on high electricity 

demand days when electric utilities may rely on relatively high emitting generating units in 

order to meet peak-day demand. Curtailing peak-day electricity consumption, or shifting 

that consumption from daytime to nighttime (when lower-emitting generating capacity is 

available and the resultant emissions may have less ozone or PM2.5 forming impact), could 

provide significant air quality benefits. 

• Defer operation of finishing mill: The finishing mill uses the clinker generated by the kiln 

to produce the finished product sold to buyers. Finishing mills require electricity, and there 

is evidence that some mills run at night to take advantage of cheaper off-peak electricity 

rates, and others operate under interruptible electricity contracts so that they can be 

temporarily halted when there is a surge in electricity demand. Thus, some cement plants 

may be able to defer running the finishing mill in order to reduce electricity demand when 

high air pollution concentrations occur. As discussed above, this strategy could be 

particularly useful on high electricity demand days when electric utilities may rely on very 

high-emitting generating units in order to meet peak-day demand. The extent to which 

operations at a finishing mill can be deferred depends, however, on the facility’s storage 

capacity and the extent to which the mill has excess grinding capacity to make up the lost 

production. 

• Defer bagging/loading: Another ancillary activity that we considered with regard to shortterm schedule changes relates to plant bagging and bulk loading processes. Changes in 

bagging and bulk loading schedules have the potential to defer electrical demand to off-peak 

hours, along with emissions from the operation of diesel trucks and equipment. However, 

according to industry analysts, many cement plants are set up to provide round-the-clock 

cement loading services to their customers. Since most customers rely on their own trucks 

and may not have the flexibility to defer deliveries, these plants need to load vehicles on a 

continuous basis as they arrive. In other cases, loading at night may create noise related 

problems with trucks traveling through residential neighborhoods. For these reasons, 

scheduling changes pertaining to bulk loading operations do not appear to hold promise as 

episodic control measures. However, industry analysts indicated that most facilities have 

some inventory of bagged product, and this may allow for short-term deferral of bagging 

operations on days with high air pollution concentrations. Nonetheless, there are indications 

that bagging operations account for only a small portion of a cement plant’s overall 

emissions. 

 

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EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

Summary: Scheduling Changes 

Our discussions with industry analysts indicated there may be opportunities to implement short-term 

scheduling changes in certain ancillary activities without significant disruptions to kiln operations or facility 

production schedules. For example, some cement plants may be able to defer quarrying activities and/or 

operation of the finishing mill on days with high air pollution concentrations. Most plants already have the 

infrastructure to stockpile some quantity of raw materials or finished products. Thus, rescheduling these 

ancillary activities for limited time periods may be feasible, if given up to 24-hours advance notice. 

iv. Combustion reoptimization 

 

We also considered the following potential short-term combustion reoptimization techniques 

with regard to their ability to achieve incremental NOx emission reductions from the cement 

industry on days when high air pollution concentrations occur: 

• Kiln operational control adjustments (such as controlling flame temperature or oxygen 

content). 

• Cement kiln dust (CKD) recirculation and/or flue gas recirculation. 

Combustion reoptimization techniques seem to hold little promise as an episodic control 

strategy for the cement sector. Most cement kilns, particularly in ozone nonattainment areas, 

already use sophisticated computerized control systems with combustion controls optimized for 

maximum kiln efficiency and product quality. And because cement kilns are heavily dependent 

on their steady-state performance for optimum operational efficiency, most analysts suggested 

there would be little room to reoptimize these systems on a short-term basis to obtain significant 

emission reduction benefits. Any short-term changes may actually reduce kiln efficiency and 

increase the emissions intensity of kiln operations.53 

Summary: Combustion Reoptimization 

Industry analysts believe that most kilns are currently optimized; any short-term modifications would likely 

reduce operational efficiency and could potentially increase emissions.

 

53 One area that may need further evaluation is to determine whether there is a tradeoff potential in 

emission reduction goals through combustion reoptimization. For example, there appear to be ways to 

reoptimize kiln operations to further reduce NOx emissions for short intervals when high concentrations of 

ozone and PM2.5 occur at the cost of increasing CO emissions during those time periods. 

38 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

d. Opportunity Assessment of Potential Episodic Control Options 

Exhibit 17 summarizes the potential viability of the four primary options for further reducing 

emissions on days with high air pollution concentrations. 

Exhibit 17: Opportunity Assessment – Cement 

Option Viability as Possible Episodic Control Measure 

Fuel switching 

Unlikely – Fuel switching on a large scale 

Promising – Small scale displacement of coal with other fuels in the kiln 

or precalciner (for NOx reductions) 

Low cost retrofits and 

enhanced use of existing 

control equipment 

Promising – SNCR for preheater/precalciner kilns (for NOx reductions) 

Possible – Micro-fine lime addition for facilities with spray cooling and 

conditioning towers (for SO2 reductions) 

Scheduling changes 

Promising – For ancillary activities, such as deferring quarrying and/or 

running the finishing mill (to reduce direct emissions and electricity 

demand) 

Combustion reoptimization Unlikely 

39 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

IV. Implications for Other Sectors 

Although our primary focus in this study has been on three selected industry sectors–pulp and 

paper, iron and steel, and cement–some of the episodic control measures explored here may be 

applicable to other sectors as well. This section of the report assesses the implications of our 

findings for emission sources in other industry sectors. 

a. Implications for Industrial Boilers 

Episodic control measures applicable to industrial boilers in the pulp and paper sector, or iron 

and steel sector, may also be applicable to boilers in other manufacturing sectors. Exhibit 18 

below shows the distribution of industrial boilers, by size, across major manufacturing sectors. 

Exhibit 18: Industrial Boiler Inventory – Boiler Capacity 

(Number of Boiler Units in Parenthesis)

Boiler 

Capacity 

(MMBtu/ 

hr input) 

Food Pulp & 

Paper Chemicals Petroleum Refining Metals 

Other 

Manufactur

ing 

Total 

31,070 4,105 28,660 1,255 7,505 29,710 102,305 

< 10 

(6570) (820) (6,720) (260) (1,850) (7,275) (23,495) 

64,970 24,490 81,690 6,670 19,405 80,585 277,810 

10-50 

(3,070) (1,080) (3,370) (260) (920) (3.680) (12,380) 

37,885 36,665 64,970 18,390 22,585 62,630 243,125 

50-100 

(570) (530) (950) (260) (330) (930) (3,570) 

47,950 81,500 86,840 30,480 17,775 62,790 327,335 

100-250 

(330) (540) (590) (200) (110) (440) (2,210) 

27,860 229,590 150,915 114,720 45,365 47,760 616,210 

>250 

(70) (490) (350) (220) (120) (110) (1,360) 

209,735 376,350 413,075 171,515 112,635 283,475 1,566,785 

Total 

(10,610) (3,460) (11,980) (1,200) (3,330) (12,435) (43,015) 

Source: ICF/EEA Boiler study for ORNL. 

As is evident from Exhibit 18, the chemical industry accounts for more than a quarter of the 

boilers used in all manufacturing sectors, in terms of total capacity, total number of units, and 

total number of large units (i.e., over 250 MMBtu/hr input). Use of industrial boilers in the food 

industry (consisting of 13 percent of total capacity, 25 percent of the total number of units, and 5 

percent of the total number of large units) and petroleum refining industry (consisting of 11 

percent of total capacity, 3 percent of the total number of units and 16 percent of the total 

number of large units), also make these industries particularly important candidates for the 

40 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

consideration of episodic control strategies where such strategies can help address air quality 

problems. 

While there are sector-specific (and indeed, facility-specific) issues to analyze further, this 

section provides a general overview of a number of control measures that might have broad 

applicability to industrial boilers. Each of these potential measures is discussed in more detail in 

one or more of the preceding sections, including a more complete discussion of potential 

limitations and concerns. 

i. SO2 control measures 

Our discussions with regulatory experts and industry analysts indicated there is a large 

population of industrial boilers that do not currently employ any SO2 controls technologies. 

Boilers, including large boilers that pre-date the New Source Performance Standards for 

industrial boilers that came into effect in 1986, typically have no federal requirements for SO2

control (although they may be subject to state-level requirements or consent decrees that 

require the use of control technology or low sulfur coal). 

In situations where further SO2 reductions are needed to address short-term air quality problems 

(e.g., violations of the 24-hour PM2.5 standard), but where installing a packed tower scrubber or 

other continuous SO2 control device is not technically or economically feasible, facilities may be 

able to install a lime injection system to temporarily achieve additional SO2 emission reductions 

on short notice as part of an episodic control strategy. For example, boilers that use a 

baghouse or ESP for PM control could intermittently inject lime powder into the duct that carries 

exhaust gases from the boiler to the baghouse or ESP to obtain further SO2 reductions on a 

short-term basis. Boilers that do not have post-combustion SO2 controls may also be able to 

reduce SO2 emissions by switching to natural gas or a low-sulfur coal for limited periods of time, 

where those fuels are not currently being utilized. 

In addition, industrial boilers that have been retrofitted with SO2 control devices may have the 

ability to increase the control efficiencies of those devices, or to switch to a lower sulfur fuel, for 

short periods of time in certain situations. 

ii. NOx control measures 

SNCR systems may hold some promise as a short-term episodic control measure for reducing 

NOx emissions from industrial boilers in many industry sectors. SNCR technology has been in 

use for many years. However, in most sectors, its use has been limited to boilers that are 

subject to new source control requirements. While there are indications that some state and 

local air quality regulators may be considering the imposition of SNCR control requirements on 

existing industrial boilers in some industries, in situations where further emission reductions are 

needed to achieve air quality goals, the limiting factor to date has been the cost of installing and 

operating this technology. 

According to industry analysts and technology vendors, the cost of purchasing and installing an 

SNCR system may be on the order of $1 million for a large industrial boiler. However, for most 

large boiler applications, the majority of the total annualized cost associated with an SNCR 

system may be for the reagent used (urea or aqueous ammonia). Therefore, the cost burden 

associated with installing and operating an SNCR system could be reduced significantly under 

an episodic control program. For example, in some situations it might be possible to reduce the 

total cost burden of an SNCR system by 50 percent or more if the system were installed and run 

41 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

at an intermediate control level on a continuous basis, and then ramped up to full capacity on 

days with high air pollution concentrations. The cost burden could be further reduced if the 

SNCR system were kept on standby and used only on days with high air pollution 

concentrations. 

Another NOx control technology that might be used as part of an episodic control program is 

gas reburn. According to industry analysts and EPA experts, many industrial boilers have 

access to natural gas for use as a backup or starter fuel. For these boilers, limited capital 

expenditures would be required to install additional burner(s) and duct work to tie the burners to 

the gas supply. The majority of the cost would be for the additional natural gas needed to 

operate the technology. Because under an episodic control program the reburn technology 

would be used only on a limited number of days each year, the system may not be cost 

prohibitive even under the current scenario of high gas prices. 

Finally, some industrial boilers may also have the ability to switch to fuels with lower nitrogen 

content or flame temperatures for short periods of time to achieve additional NOx emission 

reductions when high air pollution concentrations occur. 

iii. PM control measures 

Because of the history of regulatory requirements for PM abatement, the vast majority of 

industrial boilers appear to be controlled for primary PM. Most large boilers currently use 

baghouses, ESPs or venturi scrubbers for PM control purposes. While the industry analysts we 

spoke with were uncertain about how much opportunity there may be to increase the control 

efficiencies of these devices on a short-term basis, they felt there might be some situations in 

which this could be accomplished. For example, in some cases it may be possible to increase 

the voltage in an ESP in order to increase its PM control efficiency for short time periods. In 

addition, some boilers may be able to further reduce their PM emissions on a short-term basis 

by switching to a lower emitting fuel. 

b. Implications for Other Industrial Sources 

As with industrial boilers, some of the episodic control measures applicable to other units and 

processes within the three selected industries may be applicable to similar units or processes in 

other industries as well. Examples include fuel switching at furnaces and process heaters, 

installation of low capital cost retrofits, enhanced use of existing control equipment, and certain 

scheduling changes. Some sectors may also be able to provide additional, sector-specific 

opportunities for reducing emissions on an episodic basis. For example, in the course of our 

research we learned that a number of chemical facilities in the Gulf Coast region defer routine 

maintenance activities on high ozone days as part of local ozone action programs. Perhaps the 

most significant of the deferred maintenance activities relates to planned shutdowns. When 

shutting down a chemical plant for routine maintenance, facility operators typically need to flare 

off some of the VOCs from process vessels, and this can be a major short-term emission 

source.54 Hence, the deferral of planned shutdowns at chemical facilities on high ozone days 

can avoid emission spikes at times when they would be most detrimental. 

 

54 A recent study of the Houston-Galveston area suggests that flaring is a major source of highly reactive 

VOCs from point sources in the area and, therefore, a potential major contributor to violations of the 8-

hour ambient air quality standard for ozone. See Murphy, C.F. and D. T. Allen, “Hydrocarbon Emissions 

from Industrial Release Events in the Houston-Galveston Area and their Impact on Ozone Formation,” 

Atmospheric Environment, 39, 3785-3798 (2005). 

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EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

c. Implications for Electric Utilities 

Several episodic control measures explored in this analysis involve the rescheduling of 

industrial processes that use large amounts of grid-supplied electricity (e.g., quarrying activities 

and finishing mill operations at cement plants, and melting operations at steel mini mills), to 

times when they are less likely to exacerbate air quality problems. Other industry sectors may 

have similar opportunities to temporarily halt, curtail or defer processes that use large amounts 

of grid-supplied electricity, as part of an episodic control program. These measures could be 

particularly useful on high electricity demand days when electric utilities may rely on very high 

emitting generating units in order to meet peak electricity demand. Reducing electricity demand 

from industrial sources on high electricity demand days, or shifting that demand from daytime to 

nighttime hours (when lower-emitting generating capacity is available and the resultant 

emissions may have less ozone or PM2.5 forming impact), could provide significant air quality 

benefits. 

In addition to taking advantage of efforts by industrial sources to reschedule electricity-intensive 

operations, electric utilities may have the ability to employ other episodic control measures to 

reduce NOx, SO2 and/or PM emissions on days when high air pollution concentrations occur. A 

number of such measures may be possible and warrant further research, including fuel 

switching strategies, dispatching strategies, installation of low capital cost retrofits, and 

enhanced use of existing control equipment. 

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3. Summary of Findings & Next Steps 

As EPA, states, communities and other stakeholders consider the potential role that episodic 

control measures could play in attaining and maintaining air quality standards for ozone and 

PM2.5, one challenge will be to determine what measures can be viably and cost-effectively 

implemented by industrial sources on an episodic basis. This analysis identifies and 

preliminarily assesses a potential set of episodic control measures based on a review of 

literature and discussions with industry experts. In order to put some bounds on the research, 

we choose three industry sectors to serve as case studies for this analysis – pulp and paper, 

iron and steel, and cement. These sectors, however, are in no way an exhaustive list of sectors 

where episodic control measures may potentially be employed. Indeed, a number episodic 

control measures were identified in the course of this research that could have broad application 

to emission sources in other industries. 

I. Findings 

a. Episodic Control Measures Exist for the Three Selected Sectors 

This study finds that there are a number of potential episodic control measures available for 

each of the three sectors analyzed. Further exploration of these measures is warranted to 

determine the extent to which they would provide net emission reductions, and to more fully 

assess the technical, cost, and operational impacts of the various measures on individual 

facilities. 

• All three sectors possess some fuel switching capabilities and may be able to shift to lower 

emitting fuels to reduce NOx, SO2, and/or PM on an intermittent basis for short periods of 

time. The manner and extent to which short-term fuel switching could be employed, 

however, varies from sector to sector. Since facilities typically select their fuels so as to 

minimize production costs and meet other operational objectives, switching to more 

expensive fuels on a continuous basis would be untenable for many facilities. However, 

because fuel switching under an episodic control program would only be invoked on a 

limited number of days each year, the total incremental costs may be within acceptable 

levels for many facilities. 

• Installation of low capital cost retrofit technologies, such as selective non-catalytic reduction 

(SNCR) and gas reburn (for NOx control), and lime injection (for SO2 control) appears to 

hold promise in the context of an episodic control program. Although the high O&M costs 

associated with these retrofit technologies (e.g., due to the significant consumption of 

reagent or natural gas) may make them cost prohibitive for use on a continuous basis at 

many facilities, they may be suitable for use at some facilities as an episodic control 

measure. 

• Opportunities may exist to modify – and thereby enhance – the use of existing pollution 

control equipment on a temporary basis to control for additional pollutants (i.e., in addition to 

the main pollutant(s) these controls are intended for). For example, many industrial boilers 

and furnaces have venturi scrubbers. These scrubbers are generally installed as PM control 

devices but may also remove some SO2 from the exhaust stream of the combustion unit. 

Some industry analysts and regulatory experts believe there may be an opportunity to 

enhance the SO2 removal efficiency of venturi scrubbers in some situations by adding alkali 

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EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

reagent. This may be technically feasible and economical where a unit already has such a 

device and is able to obtain significant incremental SO2 reductions on a short-term basis 

with the addition of the reagent. 

• Opportunities may also exist to run existing pollution control devices more aggressively for 

short intervals to achieve incremental emission reductions. Some industry analysts thought 

that in some cases it might be possible to temporarily increase the control efficiency of a 

variety of NOx, SO2, and PM control systems on days when high air pollution concentrations 

occur and where, for cost or other reasons, existing permit conditions do not require these 

control devices to be utilized at their maximum performance levels. 

 

• While temporary shutdowns and curtailments that could disrupt core production processes 

were generally deemed inadvisable, there may be opportunities to curtail certain operations 

or rearrange production schedules on a short-term basis to move high emitting processes to 

times when they are less likely to exacerbate air quality problems. For example, because 

steel mini mill operation is generally batch in nature, some mini mills may be able to 

reschedule melting operations from daytime to nighttime hours to reduce VOC and NOx 

emissions, as well as electrical demand, during critical daylight hours when ozone formation 

is likely to occur. There may also be opportunities to defer certain ancillary activities at 

cement plants, such as quarrying activities and finishing mill operations, to reduce emissions 

as well as electrical demand on a short-term basis. 

• Changing the dispatch of boilers at large pulp and paper mills with excess boiler capacity 

appears to be a feasible episodic control strategy in some instances. 

• Additionally, there may also be other sector-specific episodic control opportunities, such as 

increasing the use of cogeneration units in the pulp and paper sector, which require further 

exploration. 

• Episodic control measures related to combustion reoptimization techniques appeared less 

viable for the selected industry sectors. Most facilities in these sectors use sophisticated 

computer controlled equipment on highly inter-connected and synchronized production 

processes. Industry experts seemed reluctant to entertain the idea of altering the already 

optimized processes, as they might make the processes less efficient and/or more polluting. 

b. Episodic Control Measures Also Exist for Other Industrial Sources 

While this study has focused primarily on facilities in the pulp and paper, iron and steel, and 

cement manufacturing industries, our research and information gathering indicates that a wide 

variety of episodic control measures may be available for use by other industrial sources as 

well. 

• A number of the episodic control measures that are applicable to industrial boilers in the 

pulp and paper sector, or the iron and steel sector, may also be broadly applicable to boilers 

in other industry sectors. For example, some industrial boilers in other industries may be 

able to install low capital cost retrofit technologies (such as SNCR or gas reburn for NOx 

control, or lime injection for SO2 control), to reduce boiler emissions on a short-term basis. 

Other boilers may be able to temporarily reduce emissions by switching to a lower emitting 

fuel for limited periods of time. In addition, some boilers that have already been retrofitted 

with control devices may have the ability to increase the control efficiencies of those devices 

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by modifying their operation (e.g., adding reagent to a venturi scrubber) or running them 

more aggressively for short time intervals (e.g., increasing voltage in an ESP). 

• As with industrial boilers, a number of the episodic control measures that are applicable to 

other units and industrial processes in the three selected industries may be applicable to 

similar units or processes in other industries as well. Examples include fuel switching at 

furnaces and process heaters, installation of low capital cost retrofits, enhanced use of 

existing control equipment, and certain scheduling changes. Some sectors may also be 

able to provide additional, sector-specific opportunities for achieving emission reductions on 

an episodic basis. 

• Several of the episodic control measures examined in this report involve the rescheduling of 

electricity-intensive industrial processes to times when they are less likely to exacerbate air 

quality problems. Other industry sectors may have similar opportunities to temporarily halt, 

curtail or defer electricity-intensive processes as part of an episodic control program. These 

measures could be especially helpful on high electricity demand days when electric utilities 

may rely on very high emitting generating units in order to meet peak-day demand for 

electricity. Reducing peak-day electricity consumption, or shifting that consumption from 

daytime to nighttime hours (when lower-emitting generating capacity is available and the 

resultant emissions may have less ozone or PM2.5 forming impact), could provide 

significant air quality benefits. Electric utilities may also have the ability to employ a variety 

of other episodic control measures to reduce NOx, SO2 and/or PM emissions on days with 

high air pollution concentrations. 

Industry analysts and regulatory experts emphasized that because of the inherent differences 

between facilities within a sector (as well as between sectors), generalized solutions for all 

facilities within a sector are unlikely to be effective. Episodic control measures need to be 

assessed on a plant-by-plant basis to determine their technical feasibility, practicality and costeffectiveness. 

II. Next Steps 

This report is intended to provide a preliminary assessment of the wide array of episodic control 

measures that may be available to industrial sources. The potential measures identified in this 

report should be studied further as EPA, states, communities, and other stakeholders consider 

the potential role that episodic control measures could play in helping to meet ozone and PM2.5 

air quality goals. A number of refinements to this analysis and additional research activities are 

recommended below to help EPA and other stakeholders more fully evaluate the potential 

contribution of episodic control measures. 

• This analysis focuses primarily on three industry sectors – pulp and paper, iron and steel, 

and cement. While it also provides a cursory assessment of the potential applicability of 

episodic control measures to industrial sources outside of these sectors, further analysis 

with respect to other industry sectors is needed. 

• To better assess the technical feasibility, emission reduction potential and cost of 

prospective episodic control measures, it will be necessary to conduct detailed engineering 

and cost analyses of specific measures. Because of the heterogeneity across facilities 

within a sector, as well as across sectors, these analyses will need to take into account site46 
EPISODIC AIR POLLUTION CONTROL MEASURES JANUARY 2008

specific and process-level emissions, as well as other source-specific considerations at 

individual facilities. 

• In order to more fully assess the business and operational impacts of potential episodic 

control measures, it will be necessary to hold additional discussions with industry 

representatives and technical consultants. 

• Because the ambient impact of episodic control measures is likely to be spatially 

differentiated, location-specific air quality modeling will be necessary to determine the actual 

contribution that short-term emission reductions from any particular industrial source or 

sector would make in solving local and/or regional air quality problems. 

• In order to evaluate the potential utility of episodic control measures it will be necessary to 

review state-of-the-art practices pertaining to the prediction of ozone and PM2.5 episodes. 

The effectiveness of episodic control measures would in part depend on the degree of prior 

notice that can be provided to plant operators, which is in turn a function of the ability of 

regulatory agencies and/or other institutions to predict air pollution episodes. Certain 

strategies may be technologically feasible and cost-effective, but may not be good 

candidates to implement if adequate prior notice cannot be provided to the affected facilities. 

• Another key step in the further exploration of episodic control strategies is to quantify the 

cost-effectiveness of these strategies on a dollar-per-ton of pollutant removed basis. Our 

discussions with industry analysts indicated that this is a major unknown, because episodic 

strategies for industrial sources have traditionally been overlooked in the air pollution control 

literature. It must be emphasized, however, that comparisons to cost-per-ton estimates 

based on continuous control programs would provide an erroneous picture, as the 

acceptable cost-effectiveness range for an episodic control program is likely to be 

substantially higher than the corresponding range for a continuous program. Thus, a better 

understanding of the range of cost-effectiveness values that could be appropriate given the 

benefits of an episodic control program needs to be carefully developed. 

• A number of critical policy questions will also need to be addressed before episodic control 

measures can be systematically implemented. For example, how should these measures 

be integrated with continuous and seasonal control measures as part of an air quality 

management plan, and how might this vary based on the attainment status of an area? 

Should episodic control measures be mandated by regulation, negotiated as part of the 

permitting process, or pursued by individual facilities on a purely voluntary basis? What 

types of monitoring, record-keeping and reporting provisions should be required to ensure 

that episodic emission reductions are quantifiable and/or enforceable? 

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Appendix: 

Examples of Reactions by Industrial Sectors to the 

California Outages of 2001 and 2005 

This Appendix discusses the challenges associated with unscheduled shutdowns in the pulp 

and paper, iron and steel, and petroleum refining industries due to the rolling blackouts that 

occurred in California in 2001 and 2005. 

In large plants including pulp, paperboard, and paper mills, iron and steel mills, and petroleum 

refineries, the operations of their major processes and ancillary equipment are intertwined and 

synchronized. An unscheduled stoppage of a process or equipment could cost substantial 

revenue losses to a plant because it not only stops the operation of the process or equipment, 

but could also cause the breakdown of other units linked to the original unit. As such, the 

reliability of each process or piece of equipment has to be high. To maintain the reliability of 

equipment or entire production operations, industrial plants schedule regular maintenance of 

their equipment and processes. Some of these maintenance activities could require a stoppage 

of the entire plant’s operation or the shutdown of particular units or groups of units in the plant. 

The stoppage schedule is designed as far in advance as possible to ensure worker safety, 

sufficient labor resources, minimal revenue loss, and equipment integrity upon the resumption of 

plant/equipment operations. 

During the rolling blackouts in California in 2001 and again in 2005, manufacturing facilities 

were adamant that they should be informed well in advance and even asked for exemptions 

from blackouts. Industries were concerned that blackouts could be extremely costly (due to loss 

of revenue) and could also compromise worker safety. Petroleum refiners in California cited 

that refiners could not resume operations with just a simple flick of a switch. Petroleum 

refineries claimed that an hour-long shutdown could lead to a 2-3 day restart since tanks must 

be drained and heating units must be brought back to temperature. Also, refiners already try to 

follow a well-choreographed schedule of maintenance outages to ensure optimal operations in 

their plants, so that an unscheduled stoppage could put the maintenance schedule in disarray. 

A possible unacceptable result of an unscheduled refinery shutdown or curtailment is the loss of 

gasoline/diesel fuel supply in the market, and as such could lead to an increase in 

gasoline/diesel fuel prices. Historically, refinery outages have generally been scheduled when 

markets are not tight (during non-summer season), and they therefore have had little or no 

measurable impact on monthly average prices. However, a government program that requires 

refiners to shutdown during the summer ozone season associated with peak gasoline demand, 

could result in a loss of gasoline/diesel supply in the market and a corresponding increase in 

fuel prices. 

For the iron and steel industry, the implementation of a stoppage should differentiate between 

the integrated mill and the mini mill. An integrated steel mill is comparable to a petroleum 

refinery in the complexity of its processes and equipment. As such, an unplanned stoppage 

could also cause substantial costs apart from risks to worker safety. For instance, an 

unplanned shutdown of the blast furnace results not only in production losses but risks making 

the blast furnace unusable because of the iron solidifying in the blast furnace’ air tuyeres. The 

cost to rebuild a blast furnace is estimated at approximately $100 million. 

For mini mills, which use electric arc furnaces, it is possible to consider not a stoppage but a 

rescheduling of operations. During the California rolling blackouts, some mini mills with 

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interruptible power contracts switched to firm contracts with their power suppliers because the 

power curtailments were too costly. Others rescheduled their melting operations to off-peak 

hours to enjoy the cheaper electricity rates during those times and still allow for the interruptible 

contract to continue. Note that a rescheduling to off-peak hours for the mini mills is a possibility 

because the operation is generally batch in nature. 

Pulp, paper, and paperboard mills, like integrated steel mills and petroleum refiners, have a 

complex system of continuous operations that are well-synchronized. An unscheduled 

stoppage could be very expensive for the company. Paper mills have many large boilers and 

their start-ups require several hours. Several hours of lost production could be costly for a 

paper company. It could also cost the reduction of equipment reliability and lower product 

quality. 

Paper mills, integrated steel mills, and refiners may also be large cogenerators and a number of 

them are Qualifying Facilities (QF). QFs are essential to the balancing of the power grid and so 

a shutdown of an industrial QF could cause demand-supply imbalance as well. 

Another commonality among these industries is that they are capital-intensive so that 

maximizing the utilization of their assets is essential to their profitability. Also, these companies 

have substantial contracts with labor, their suppliers and their customers, and unmet obligations 

due to unscheduled stoppages of their operations could also have legal implications. 

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