United States EPA-600/7-81-123a
Environmental Protection
Agency July 1981
oEPA Research and
Development
COMBUSTION MODIFICATION CONTROLS
FOR RESIDENTIAL AND COMMERCIAL
HEATING SYSTEMS
Volume I. Environmental Assessment
Prepared for
Office of Air Quality Planning and Standards
Prepared by
industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
systems; and integrated assessments of a wide range of energy-related environ-
mental issues.
EPA REVIEW NOTICE
This report has been reviewed by the participating Federal Agencies, and approved
for publication. Approval does not signify that the contents necessarily reflect
the views and policies of the Government, nor does mention of trade names or
commercial products constitute endorsement or recommendation for. use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/7-81-123a
July 1981
COMBUSTION MODIFICATION CONTROLS FOR RESIDENTIAL
AND COMMERCIAL HEATING SYSTEMS:
VOLUME I. ENVIRONMENTAL ASSESSMENT
By
C. Castaldini, R. A. Brown, and K. J. Lim
Acurex Corporation
Energy & Environmental Division
485 Clyde Avenue
Mountain View, California 94042
Contract 68-02-2160
Program Element EHE 624A
Prepared for
EPA Project Officer -- J. S. Bowen
EPA Deputy Project Officer -- R. E. Hall
Industrial Environmental Research Laboratory
Office of Environmental Engineering and Technology
Research Triangle Park, North Carolina 27711
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
WASHINGTON, DC 20460
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DISCLAIMER
This Final Report was furnished to the U.S. Environmental
Protection Agency by Acurex Corporation, Energy & Environmental Division,
Mountain View, California 94042, in partial fulfillment of
Contract No. 68-02-2160. The opinions, findings, and conclusions
expressed are those of the authors and not necessarily those of the
Environmental Protection Agency or of cooperating agencies. Mention of
company or product names is not to be considered as an endorsement by the
Environmental Protection Agency.
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PREFACE
This is one in a series of five process engineering reports
documented in the "Environmental Assessment of Stationary Source NOV
A
Combustion Modification Technologies" (NO EA). Specifically, this
A
report documents the environmental assessment of residential and
commercial heating systems with primary emphasis on NO combustion
A
controls for residential warm air furnaces. The NOV EA, a 36-month
A
program which began in July 1976, is sponsored by the Combustion Research
Branch of the Industrial and Environmental Research Laboratory of EPA
(IERL-RTP). The program has two main objectives: (1) to identify the
multimedia environmental impact of stationary combustion sources and NO
A
combustion modification controls applied to these sources, and (2) to
identify the most cost-effective, environmentally sound NO combustion
A
modification controls for attaining and maintaining current and projected
N02 air quality standards to the year 2000.
The NO EA is assessing the following combination of process
A
parameters and environmental impacts:
• Major fuel combustion stationary NOX sources: utility
boilers, industrial boilers, gas turbines, internal combustion
(1C) engines, and commmercial and residential warm air
furnaces. Other sources (including mobile and noncombustion)
will be considered only to the extent that they are needed to
determine the NO contribution from stationary combustion
A
sources.
• Conventional and alternate gaseous, liquid and solid fuels
• Combustion modification N0x controls with potential for
implementation to the year 2000; other controls (flue gas
cleaning, mobile controls) will be considered only to estimate
the future need for combustion modifications
-------
t Source effluent streams potentially affected by NO controls
/\
• Primary and secondary gaseous, liquid and solid pollutants
potentially affected by NOX controls
• Pollutant impacts on human health and terrestrial or aquatic
ecology
To achieve the objectives discussed above, the NOX EA program
approach is structured as shown schematically in Figure P-l. The two
major tasks are: Environmental Assessment and Process Engineering
(Task 85), and Systems Analysis (Task C). Each of these tasks is designed
to achieve one of the overall objectives of the NO EA program cited
/\
earlier. In Task B5, of which this report is a part, the environmental,
economic, and operational impacts of specific source/control combinations
are evaluated. On the basis of this assessment, the incremental
multimedia impacts from the use of combustion modification NO controls
/\
will be identified and ranked. Systems analysis in turn uses the results
of Task B5 to identify and rank the most effective source/control
combinations to comply, on a local basis, with the current N0? air
quality standards and projected N02 related standards.
As shown in Figure P-l, the key tasks supporting Tasks B5 and C are
Baseline Emissions Characterization (Task Bl), Evaluation of Emission
Impacts and Standards (Task B2), and Experimental Testing (Task B3). The
arrows in Figure P-l show the sequence of subtasks and the major
interactions among the tasks. The oval symbols identify the major outputs
of each task. The subtasks under each main task are shown on the figure
from the top to the bottom of the page in roughly the same order in which
they will be carried out.
As indicated above, this report is a part of the Process
Engineering and Environmental Assessment Task. The goal of this task is
to generate process evaluations and environmental assessments for specific
source/control combinations. These studies will be done in order of
descending priority. In the first year of the N0y EA, all the sources
/\
and controls involved in current and planned NOX control implementation
programs were investigated. The "Preliminary Environmental Assessment of
Combustion Modification Techniques" (Reference P-l) documented this effort
and established a priority ranking based on source emission impact and
iv
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NOV EA approach.
A
-------
potential for effective NO control, to be used in the current ongoing
^
detailed evaluation.
This report presents the assessment of combustion modification
NOX controls for the last source category to be treated, residential and
commercial heating systems. Other environmental assessment reports
documented are:
• Environmental Assessment of Utility Boiler Combustion
Modification NO Controls (Reference P-2)
/\
• Environmental Assessment of Industrial Boiler Combustion
Modification NOX Controls (Reference P-3)
• Environmental Assessment of Combustion Modification Controls
for Stationary Gas Turbines (Reference P-4)
• Environmental Assessment of Combustion Modification Controls
for Stationary Internal Combustion Engines (Reference P-5)
-------
REFERENCES FOR PREFACE
P-l. Mason, H. B., et al., "Preliminary Environmental Assessment of
Combustion Modification Techniques: Volume II. Technical
Results," EPA-600/7-77-119b, NTIS-PB 276 681/AS, October 1977.
P-2. Lim, K. J., et al., "Environmental Assessment of Utility Boiler
Combustion Mocfif i cat ion NOX Controls: Volume 1. Technical
Results; Volume II: Appendices," EPA-600/7-80-075a,b, April 1980.
P-3. Lim, K. J., jit al., "Industrial Boiler Combustion Modification
NOX Controls: "Volume I. Environmental Assessment,"
EPA-600/7-81-126a, July 1981.
P-4. Larkin, R., et al., "Combustion Modification Controls for
Stationary Gas Turbines: Volume I. Environmental Assessment,"
EPA-600/7/81-122a, July 1981.
P-5. Lips, H. I., et al., "Environmental Assessment of Combustion
Modification Controls for Stationary Internal Combustion Engines,"
EPA-600/7-81-127, July 1981.
VII
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TABLE OF CONTENTS
Section Page
Preface iii
1 EXECUTIVE SUMMARY 1-1
1.1 Overview of Residential and Commercial
Heating Systems 1-1
1.2 Emissions and Fuels 1-3
1.3 Status of Environmental Protection Alternatives. . 1-4
1.4 Environmental and Cost Impacts 1-11
1.5 Data Needs and Recommendations 1-17
2 INTRODUCTION 2-1
2.1 Background 2-1
2.2 Role of Residential and Commercial Heating
Systems 2-2
2.3 Objective of this Report 2-4
2.4 Organization of this Report 2-5
3 SOURCE CHARACTERIZATION 3-1
3.1 Equipment Types 3-1
3.1.1 Residential Units 3-3
3.1.2 Commercial Units 3-3
3.2 Furnace Design Practice 3-10
3.2.1 Residential Units 3-10
3.2.2 Commercial Systems 3-34
3.3 Areas of Environmental Concern 3-40
3.3.1 Stack Emissions 3-42
3.3.2 Leakage of Combustion Products 3-42
3.3.3 Solid Waste Streams 3-43
4 CHARACTERIZATION OF FUELS, PRODUCTS AND AIR
EMISSIONS 4-1
4.1 Summary of Sampling and Analytical Activities . . 4-1
4.2 Fuels 4-6
4.2.1 Gaseous Fuels 4-6
4.2.2 Liquid Fuels 4-7
4.2.3 Solid Fuels 4-12
4.3 Product Characterization 4-16
4.4 NOX Formation 4-17
ix
-------
TABLE OF CONTENTS (Continued)
Section
4.4.1 Thermal NOX Formation 4-17
4.4.2 Fuel NOX Formation 4-17
4.5 Emission Characterization 4-18
4.5.1 Nitric Oxide Emissions 4-23
4.5.2 Carbon Monoxide and Hydrocarbon Emissions . . . 4-23
4.5.3 Smoke and Particulate Emissions 4-24
4.5.4 Emission Factors and Emission Inventory .... 4-24
5 PERFORMANCE AND COST OF CONTROLS 5-1
5.1 Emission Control Alternatives for Gas-Fired
Residential Systems 5-1
5.1.1 Nitric Oxide Control 5-2
5.1.2 Carbon Monoxide and Unburned Hydrocarbon
Control 5-12
5.1.3 Cost and Energy Impact of Controls 5-14
5.2 Emission Control Alternatives for Oil-Fired
Residential Systems 5-15
5.2.1 Nitric Oxide Control 5-16
5.2.2 Carbon Monoxide and Unburned Hydrocarbon
Control 5-28
5.2.3 Smoke and Particulate Control 5-34
5.2.4 Cost and Energy Impact of Controls 5-37
5.3 Emission Control Alternatives for Solid
Fuel-Fired Residential Systems 5-39
5.4 Surmiary of Most Effective Control Alternatives
for Residential Systems 5-41
5.4.1 Gas-Fired Systems 5-41
5.4.2 Oil-Fired Systems 5-43
5.5 Emission Control Alternatives for Commercial
Systems 5.47
5.5.1 Commercial Heaters 5.47
5.5.2 Commercial Boilers 5_48
6 ENVIRONMENTAL ASSESSMENT 6-1
6.1 Environmental Impact Analysis 6-2
6.2 Source Analysis Model Evaluation 6-4
6.3 Environmental Impacts of NOX Controls
on Criteria Pollutants 6-8
-------
TABLE OF CONTENTS (Concluded)
Section Page
6.4 Operational and Cost Impacts of Controls 6-10
6.5 Data Base Evaluation and Needs 6-13
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LIST OF ILLUSTRATIONS
Figure Page
P-l NOX EA Approach v
2-1 Distribution of Stationary Anthropogenic NOX
Emissions for the Year 1977 (Controlled NOX
Levels) 2-3
3-1 Distribution of Residential and Commercial Heating
Systems 3-2
3-2 Gas-Fired Forced Air Furnaces 3-13
3-3 Gas-Fired Forced Air Downflow Furnace and Details of
Components 3-15
3-4 Oil-Fired Central Air Furnaces 3-19
3-5 Typical High Pressure Atomizing Gun Oil Burners .... 3-21
3-6 ABC Mite Burner with Flame Retention Head 3-25
3-7 Gas-Fired Hydronic Boiler 3-27
3-8 Oil-Fired Hydronic System 3-31
3-9 Residential Heater Stoker Assembly 3-33
3-10 Direct Gas-Fired Duct Heater and Line Burner
Assembly 3-36
3-11 Simplified Diagram of a Watertube Boiler 3-38
3-12 Simplified Diagram of a Firetube Boiler 3-38
3-13 Exposed-tube Vertical Boiler 3-40
4-1 Effect of API Gravity on Particulate Emissions .... 4-11
4-2 Effect of Free Swelling Index on Boiler Particulate
Emissions 4-14
4-3 Effect of Coal Volatile Content on Boiler
Particulate Emissions 4-15
4-4 Contribution of Nitrogen in Fuel Oil to Total NOX
Emissions from Commercial Boilers 4-18
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LIST OF ILLUSTRATIONS (Concluded)
Figure Page
4-5 General Trend of Smoke, Gaseous Emissions, and
Efficiency Versus Stoichiometric Ratio for a
Residential Oil Burner 4-19
4-6 Gaseous Emissions Characteristic for a Typical
Commercial Boiler as Influenced by Combustion Air
Setting 4-19
4-7 Temperature Rise Across an Oil-fired Warm Air
Furnace Heat Exchanger During a Typical Cycle 4-21
4-8 Characteristic Emissions of Oil Burners During
One Complete Cycle 4-22
5-1 General Arrangements of Screens for Gas-Fired
Residential Burners 5-3
5-2 Effect on NOX Emissions of Placing a Screen in the
Flame of a Meker Type Burner 5-4
5-3 Amana Heat Transfer Module (HTM) 5-7
5-4 Schematic of the Bratko Burner 5-9
5-5 Schematic Operating Cycle of a Pulse Combustion
Device 5-11
5-6 Effect of Air Adjustment on Gaseous Emissions for a
Typical Atmospheric Gas Burner 5-13
5-7 1 ml/s (gph) Optimum Low-Emission Residential
Oil Burner 5-19
5-8 Comparative NO Emissions for the Controlled Mixing
EPA/Rocketdyne Burner Heat as a Retrofit Device in
Two Warm-Air Furnaces 5-22
5-9 EPA Low-Emission Integrated Furnace Components .... 5-23
5-10 Schematic Illustration of the Blueray Head Assembly . . 5-26
5-11 Schematic of the M.A.N. Residential Oil-Fired
Rocketburner 5-28
5-12 Distribution of Smoke Emission for Residential
Units 5-35
5-13 Schematic of the Cross-Feed Combustion Design for
Coal-Fired Residential Furnaces 5-40
xm
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LIST OF TABLES
Table
1-1 Estimated 1977 Air Pollutant Emissions from Stationary
Fuel Combustion Sources with Heat Input Capacity Less
Than 2.9 MW (10 x 106 Btu/hr) 1-5
1-2 Performance Sunmary of Low-N0x Control Equipment for
Natural Gas-Fired Residential Heaters 1-7
1-3 Performance Surrrnary of Low-N0x Control Equipment
for Distillate Oil-Fired Residential Heaters 1-8
1-4 Performance Sumnary of Controls for Reduction of
Seasonal Combustible, Smoke and Particulate
Emissions from Oil-Fired Residential Heaters 1-12
1-5 Flue Gas Discharge Severities Greater Than 0.1 for the
Blueray Furnace and Conventional Oil-Fired Heaters . . 1-14
1-6 Cost Impact of NOX Control Alternatives 1-16
3-1 Population and Ranking of Domestic Heating Systems
By Type (1976) -- 1000 Units 3-4
3-2 Regional Distribution of Residential Heating
Equipment by Fuel (1976) ~ 1000 Units 3-5
3-3 Regional Distribution of Residential Heating
Equipment by Equipment Type (1976) — 1000 Units ... 3-6
3-4 Population of Boilers with Less Than 2.9 MW
(10 x 106 Btu/hr) Heat Input Capacity in Use in the
Industrial Sector -- 1977 Number of Units (Installed
Capacity MW) 3-8
3-5 Population of Boilers with Less Than 2.9 MW
(10 x 106 Btu/hr) Heat Input Capacity in Use in the
Industrial Sector — 1977 Number of Units (Installed
Capacity MW). . 3-9
3-6 Summary of Installed Capacities of Commercial and
Industrial Steam and Hot Water Units with Heat Input
Less Than 2.9 MW (10 x 106 Btu/hr) -- MW (Percent) . . 3-11
3-7 Typical Operating Conditions for a Warm Air
Gas-Fired Furnace: 29.3 kW (100,000 Btu/hr) 3-18
3-8 Typical Operating Conditions for Oil-Fired Central
Air Systems: 29.3 kW (100,000 Btu/hr) 3-24
3-9 Typical Operating Conditions for Oil- and Gas-Fired
Hot Water with 29.3 kW (100,000 Btu/hr) Heat Input. . . 3-30
xiv
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LIST OF TABLES (Concluded)
Table Page
3-10 Emission Streams from Residential and Commercial
Units 3-41
4-1 Summary of Major Sampling and Analytical Activities
on Residential and Commercial Heating Systems 4-2
4-2 Fuel Oil Designations and Typical Characteristics . . . 4-8
4-3 Estimated 1977 Air Pollutant Emissions of Industrial
Commercial and Residential Fuel Combustion Sources
With Heat Input Capacity Less Than 2.9 MW
(10 x 106 Btu/hr) 4-25
5-1 Effect on CO and NOX Emission of Placing Radiant
Screen in Burner Flame 5-3
5-2 Effect of a Radiating Screen From a Furnace Operated on
Cleveland Natural and Algerian LNG 5-5
5-3 Effect on Mean Emission of Identifying and Replacing
Residential Units in Poor Condition and Tuning .... 5-32
5-4 Performance Surmiary of Low NOX Control Equipment for
Natural Gas-Fired Residential Heaters 5-42
5-5 Performance Surmiary of Low-N0x Control Equipment for
Distillate Oil-Fired Residential Heaters 5-44
5-6 Performance Sumnary of Controls for Reduction of
Seasonal Combustible, Smoke, and Particulate Emissions
From Oil-Fired Residential Heaters 5-46
5-7 Combustion Modification NOX Controls for Oil- and
Gas-Fired Industrial Boilers 5-49
5-8 Combustion Modification NOX Controls for Stoker
Coal-Fired Industrial Boilers 5-51
6-1 Criteria Trace Elements and Organic Emissions from
Conventional and Low-N0x Furnaces 6-3
6-2 Flue Gas Discharge Severities Greater than 0.1 for the
Blueray Furnace and Conventional Oil-Fired Heaters . . 6-6
6-3 Environmental Impact of Most Effective NOX Control
Alternatives on Residential Space Heaters 6-9
6-4 Cost Impact of NOX Control Alternatives 6-12
xv
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SECTION 1
EXECUTIVE SUMMARY
With more NO controls being implemented in the field and
A
expanded control development anticipated for the future, there is
currently a need to: (1) ensure that the current and emerging control
techniques are technically and environmentally sound and compatible with
efficient and economical operation of systems to which they are applied,
and (2) ensure that the scope and timing of new control development
programs are adequate to allow stationary sources of NO to comply with
A
potential air quality standards. The residential and commercial heating
system environmental assessment helps to address these needs by evaluating
the operational, economic and environmental impacts from applying
combustion modification NO controls.
A
Residential warm air furnaces, the major source category dealt with
in this report, are the fifth largest contributors of man-made NO
A
emissions from stationary sources in the U.S. -- constituting about
2 percent of annual nationwide emissions. It is projected that their
contribution will remain significant through the year 2000
(Reference 1-1). Given this background and their potential for NO
A
control, residential and commercial heating systems were specified as a
major category to be studied under the N0x EA program.
1.1 OVERVIEW OF RESIDENTIAL AND COMMERCIAL HEATING SYSTEMS
The major domestic fuel combustion sources are central warm air
furnaces, room or direct heaters, residential hot water heaters, and steam
and hot water hydronic boilers for space and water heating. Minor sources
include stoves and fireplaces; these consume a relatively insignificant
quantity of fuel compared to other space heating equipment.
The primary fuels for residential heating are natural gas and
distillate oils (no. 1, kerosene, or no. 2 distillate). These fuels
-------
combined account for nearly 90 percent of all fuel burned for domestic
heating. Liquified petroleum gas, LPG (butane or propane), coal and wood
are also used, although in relatively small quantities. In 1976 LPG-fired
equipment account for about 6 percent of domestic heating equipment while
coal- and wood-fired units account for only 2 percent of the total
equipment population. Built-in electric residential heating systems have
become increasingly popular as domestic supply of clean fuels dwindles and
fuel costs increase. Electrical heaters in 1976 accounted for nearly
14 percent of residential heating equipment.
The primary fuels and equipment used for domestic heating show
significant regional variation. For example, the Northeast regions depend
primarily on oil-fired steam or hot water units while in all other
regions, natural gas-fired central warm air furnaces are the primary
equipment type for domestic space heating.
Combustion equipment in most residential heating systems is
similar. For natural gas-fired equipment the single port upshot or the
tubular multiport burners are the most common burner types. Natural gas-
fired warm air furnaces, room heaters, or hot water heaters often use a
pilot flame to ignite the burner automatically. Distillate oil-fired
residential heating systems generally use high pressure atomizing gun type
burners. Nearly all new oil-fired burners use the flame retention burner
head which promotes more efficient combustion.
Commercial heating systems can be divided into three general
categories: warm air unit heaters or space heaters, warm air furnaces or
duct heaters, and hot water or steam systems. The combustion system of
commercial warm air unit or space heaters and duct heaters is generally
similar to residential equipment, although there are a few unique
gas-fired designs. Warm air units and duct heaters are either direct or
indirect fired. Direct fired heaters use only clean gaseous fuels. These
units exhaust the combustion products directly into the heated space.
Indirect fired heaters use either gas or oil fuels and are vented to the
outdoors. These units, except for their larger capacity, are generally
similar to residential central warm air furnaces. Information on
equipment population and emissions from commercial space heaters is
limited.
1-2
-------
Hot water and steam systems in the commercial size capacity, here
defined in the range of 0.12 to 2.9 MW ((0.4 to 10) x 106 Btu/hr) heat
input capacity, include cast iron hydronic boilers and small firetube and
watertube boilers used in both the commercial and industrial sectors.
Cast iron hydronic boilers are also used in residential as well as
commercial applications. These units, which are common in the
Northeastern and Northcentral regions of the U.S., are primarily either
gas- or distillate oil-fired. Firetube and small watertube boilers used
for heating of large commercial plants and buildings are similar to the
smaller industrial boilers used to generate process steam. These boilers
are generally fired with gas, oil or less frequently stoker coal, and
account for about 25 percent of the installed capacity of steam and hot
water boilers with heat input capacity less then 2.9 MW (10 x 106
Btu/hr).
1.2 EMISSIONS AND FUELS
Because natural gas and distillate oil are the principal fuels used
in domestic and commercial heating systems, air pollutant emissions
represent the primary waste stream of environmental concern. Coal- and
wood-fired furnaces and stoves, however, also produce solid ash waste
streams. Although increasing in popularity due to the scarcity and high
cost of clean fuels, residential wood- and coal-fired systems account for
only 2 percent of all domestic heaters. Thus nationally, solid waste
streams from residential heating pose only a minor environmental concern
but are potentially significant when considered on a local or regional
basis. Commercial coal-fired watertube and firetube stokers are also the
source of solid waste streams. These units, which account for about
15 percent of the firetube and watertube population, could increase in
popularity with economic and political incentives for increased use of
domestic coal.
Flue gas stream composition from residential heating equipment
depends highly on the type of fuel burned, burner type, combustor
geometry, combustor material and operating characteristics. Natural gas-
fired equipment emits NO , carbon monoxide (CO) and unburned
/\
hydrocarbons (UHC). When distillate oil is used, particulate (smoke) and
small quantities of SOX are also emitted. NOX emissions are generally
1-3
-------
highest and CO, UHC and smoke are lowest when the heater operates at
design (tuned) and steady state conditions. S02 emissions are a
function of the sulfur content of the oil. SO,, control is primarily
achieved by using low sulfur oil.
NO is one of the primary pollutants of concern with residential
/\
gas- and oil-fired heaters. It is emitted in significant quantities, is
deleterious to human respiratory functions and acts as a key precursor to
photochemical smog. Carbon monoxide, UHC and smoke made up of carbon
particles or soot are products of incomplete combustion. These pollutants
are emitted in the largest quantity during ignition, and warm up and shut
off periods of a residential furnace heating cycle. Because domestic
heaters operate in a cyclic mode combustible emissions due to on-off
transients account for the majority of the total yearly emissions.
Control techniques for reducing combustible emissions often concentrate on
reducing the heater cycling frequency.
Table 1-1 summarizes 1977 emissions for stationary combustion
sources with heat input less than 2.9 MW (10 x 106 Btu/hr). These
sources include primarily residential and commercial heating systems as
well as small industrial boilers (Reference 1-2). Residential and
commercial heating systems contribute 56 and 28 percent respectively of
the total NO from these sources. These emissions are seasonal with
A
nearly all the total annual output occurring in the cold winter months;
during that period the impact of residential and commercial heating on
ground level ambient N02 concentration in urban areas can be significant
(References 1-3, 1-4).
1.3 STATUS OF ENVIRONMENTAL PROTECTION ALTERNATIVES
Emission control technology for residential and commercial
equipment is typically adapted to the specific fuel and burner type.
Because NOX emissions from either gas or distillate oil combustion are
primarily due to thermal NOX, control techniques are aimed at
controlling temperature or oxygen availability in the high temperature
flame region. Tables 1-2 and 1-3 summarize NOV control alternatives for
/\
residential heaters firing natural gas and distillate oil respectively.
These controls have been developed primarily for warm air furnaces;
however, the advanced burner and combustor redesign technology presented
1-4
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TABLE 1-1. ESTIMATED 1977 AIR POLLUTANT EMISSIONS FROM STATIONARY
FUEL COMBUSTION SOURCES WITH HEAT CAPACITY LESS THAN
2.9 MW (10 x 106 Btu/hr)a
Sector
Residential":
Residential
and Commercial
Equipment
Warm air central
furnaces
Warm air space
heaters
Miscellaneous
combustion
Steam and hot
water heaters
Fuel
Natural gas
Distillate
oil
Natural gas
Distillate
oil
Natural gas
Distillate
011
Natural gas
Distillate
oil
Residual oil
Coal
Total Capacity
MW (106 Btu/hr)
--
-
--
-
—
-
--
--
--
--
Fuelb
Consumption
EJ (Quads)
1.876C
(1.979)
1.354C
(1.428)
0.57C
(0.60)
0.42C
(0.44)
1.524C
(1.608)
0.926C
(0.977)
2. 1C
'(2.2)
1.4C
(1.5)
O.llc
(0.12)
0.043C
(0.045)
Air Pollutant Emissions Gg (103 tons)
NOX
65.7
(72.5)
33.8
(37.3)
19.9
(21.9)
10.5
(11.6)
53.3
(58.8)
27.4
(30.2)
82.8
(91.3)
77.9
(85.9)
17.5
(19.3)
7.1
(7.8)
CO
19.0
(20.9)
33.8
(37.3)
5.7
(6.3)
10.5
(11.6)
15.2
(16.8)
27.4
(30.2)
17.8
(19.6)
41.7
(46.0)
1.64
(1.81)
7.53
(8.30)
HC
6.40
(7.10)
6.40
(7.06)
1.94
(2.14)
1.97
(2.17)
5.20
(5.73)
5.15
(5.68)
4.76
(5.25)
13.4
(14.8)
2.74
(3.02)
2.12
(2.34)
Particulates
7.50
(8.27)
10.3
(11.4)
2.30
(2.54)
3.20
(3.53)
6.10
(6.73)
8.33
(9.19)
16.6
(18.3)
10.6
(11.7)
9.09
(10.0)
150.2
(165.6)
SOX
0.49
(0.54)
146
(161)
0.15
(0.17)
45.4
(50.1)
0.40
(0.44)
118.4
(130.6)
0.62
0.68
150.2
(165.6)
52.6
(58.0)
30.7
(33.8)
aBased on data from References 1-1, 1-2, and 1-5.
bEJ = 1018 Joules = 0.948 Quads = 0.948 x 1015 Btu
"-Fuel consumption for residential units was obtained from Department of Energy (Reference 1-5).
-------
TABLE 1-1. (Concluded)
Sector
Commercial
and Industrial
TOTAL
Equipment
Cast iron
boilers
Watertube
boilers
Firetube
boilers
AH equipment
Fuel
Natural gas
Distillate
oil
Residual oil
Coal
Natural gas
Distillate
oil
Residual oil
Coal
Natural gas
Distillate
oil
Residual
oil
Coal
All fuels
Total Capacity
W (106 Btu/hr)
143,520
(489,495)
33,730
(115,041)
53,790
(183,456)
31,590
(107,742)
5,770
(19,679)
4,490
(15,313)
5,240
(17.872)
1,900
(6,480)
79,090
(269,748)
31,530
(107,538)
48,200
(164,393)
14,420
(49,181)
--
Fuelb
Consumption
EJ (Quads)
1.8
(1.9)
0.35
(0.37.)
0.47
(0.50)
0.097
(1.0)
0.053
(0.056)
0.021
(0.023)
0.015
(0.016)
0.012
(0.013)
1.358
(1.433)
0.37
(0.39)
0.354
(0.374)
0.11
(0.116)
15.22
(16.97)
Air Pollutant Emissions Gg (10-' tons)
NOX
91.7
(101.1)
23.7
(26.1)
84.6
(93.3)
14.6
(16.1)
3.16
(3.5)
1.18
(1.3)
2.38
(2.6)
3.0
(3.3)
31.0
(34.2)
12.8
(14.1)
30.7
(33.9)
14.1
(15.6)
708.8
(781.6)
CO
35.3
(38.9)
0.56
(0.61)
0.66
(0.73)
21.3
(23.5)
1.06
(1.17)
0.06
(0.07)
0.02
(0.02)
0.91
(1.00)
15.2
(16.8)
0.34
(0.38)
0.29
(0.32)
5.40
(5.95)
261.4
(288.3)
HC
4.06
(4.48)
3.34
(3.68)
11.8
(13.8)
5.53
(6.10)
0.18
(0.20)
0.01
(0.01)
0.07
(0.08)
0.19
(0.21)
1.75
(1.93)
2.05
(2.26)
5.12
(5.65)
3.40
(3.75)
87.6
(96.6)
Particulates
6.88
(7.59)
4.18
(4.61)
13.2
(14.6)
314.3
(346.6)
0.05
(0.05)
0.18
(0.20)
0.42
(0.46)
23.5
(25.9)
3.02
(3.33)
2.57
(2.83)
5.73
(6.32)
130.0
(143.4)
728.3
(803.1)
*>x
0.53
(0.58)
37.6
(41.5)
225.6
(248.8)
110.6
(122.0)
0.02
(0.02)
3.27
(3.61)
6.70
(7.39)
16.0
(17.6)
0.23
(0.25)
18.7
(20.6)
92.1
(101.61)
91.8
(101.2)
1,148.1
(1,266.0)
-------
TABLE 1-2. PERFORMANCE SUMMARY OF LOW-NOX CONTROL EQUIPMENT FOR
NATURAL GAS-FIRED RESIDENTIAL HEATERS
Control
Conventional
Units
Radiant Screens
Secondary Air
Baffles
Surface Combus-
tion Burner
Amana (HTM)
Modulating
Furnace
Pulse
Comb us tor
Catalytic
Comb us tor
Average
Operating
Excess A1r
(percent)
40-120
40-120
60-80
10
NA
NA
NA
NA
Cyclic Pollutant Emissions
nq/J Heat Input
NV
28-45
15-18
22
7.5
7.7
25
10-20
<5
CO
8.6-25
6.4
14
5.5-9.6
26
NA
NA
NA
UHCb
3.3-33
NA
NA
NA
NA
NA
NA
NA
Steady State
Efficiency
(percent)
70
75
NA
NA
85
75
95
90
Cycle
Efficiency
(percent)
60-65
70
NA
NA
80
70
95
85
1978
Installed
Control
Cost
c
NA
NA
$100-$200
$100-$300
over
conventional
furnace
$50-$250
over con-
ventional
furnace
$300 -$600
$100-$250
Comments
Emission factors from References 1-6
and 1-7. Costs Include Installation
Emissions of CO and HC can Increase
significantly 1f screen 1s not placed
properly or deforms
Requires careful installation. Best
suited for single port upshot burners
Not commercially available. Still
under development
Commercially available design. Spark
Ignited thus requires no pilot
Furnace is essential ly derated. Thus
it requires longer operation to deliver
a given heat load
Currently being investigated by AGAL.
Efficiencies correspond to condensing
systems.
Still at the R&D stage. Efficiencies
correspond to condensing systems.
«Sum of NO + NO? reported as NO?
bl)nburned hydrocarbons calculated as methane (CH4)
cTyp1cal costs of uncontrolled unit $500-$800
NA « not available
-------
TABLE 1-3. PERFORMANCE SUMMARY OF LOW-NOX CONTROL EQUIPMENT
FOR DISTILLATE OIL-FIRED RESIDENTIAL HEATERS
Control
Conventional
Units
Flame Reten-
tion Burner
Head
Controlled
Mixing
Burner Head
by EPA/
Rocketdyne
Integrated
Furnace Sys-
tem by EPA/
Rocketdyne
Bluer ay
"blue flame"
Burner/Furnace
System
M.A.N.
Burner
Average
Operating
Excess air
(percent)
50-85
20-40
10-50
20-30
20
10-15
Cyclic Pollutant Emissions
ng/J Heat Input
Smoke
NOX CO UHCb Number Particulate
37-85 15-30 3.0-9.0 3.2 7.6-30
26-88 11-22 0.2-1.8 2.0 NA
34 13 0.7-1.0 <1.0 NA
19 20 1.2 <1.0 NA
10 4.5-7.5 1.5-2.5 zero NA
10-25 <30 NA <1.0 NA
Steady State
Efficiency
(percent)
75
80-83
also depends
on heat
exchanger
80
also depends
on heat
exchanger
84
84
85
Cycle
Efficiency
(percent)
65-70
NA
NA
74
74
NA
1978
Installed
Control
Cost
c
$52d
$43d
$250 over
conven-
tional
furnace
$100 over
conven-
tional
furnace
NA
Comments
Range in NOX emissions is
for residential systems not
equipped with flame reten-
tion burners (References 1-4
and 1-8). Emissions for
other pollutants are aver-
ages reported in
References 1-7 and 1-8.
If a new burner is needed as
well as a burner head, the
total cost would be $385.
Cost of mass produced burner
head only about $1.50. Com-
bustible emissions are
relatively low because hot
firebox was used.
Uses optimized burner head.
For new furnace installation
only. Combustible emissions
are higher than with burner
head because of quenching in
in air cooled firebox.
Recent cost estimate.
New installation only.
Furnace is commercially
available. Recent cost
estimate.
Both for -retrofit or new
installations. Not yet
commercially available 1n
U.S. Commercialization
expected in 1980.
I
00
aSum of NO and NOg reported as NO?
bUnburned hydrocarbons calculated as Methane
cTyp1cal costs of uncontrolled unit $650-$!,000
^Original costs reported for years other than 1978 were corrected for inflation
using Gross National Product (SNP) implicit price inflators (Reference 1-9)
NA — Not available
-------
in these tables could possibly be applied also to other domestic heating
equipment as well as some larger commercial installations.
For residential gas-fired heaters, the American Gas Association
Laboratories (AGAL) developed radiant screens and secondary air baffles
capable of average NO reductions of 58 and 20 percent respectively.
/\
However, these controls may find little application because of
installation and performance problems highlighted by the Gas Appliance
Manufacturer Association (GAMA). Two advanced NO control alternatives
A
are the Bratko surface combustor and the Amana Heat Transfer Module
(HTM). In these concepts, the radiation from the combustion zone
maintains a lower temperature of the combustion products and thus lower
NOX production while maintaining good efficiency and low CO levels.
NO emissions from both the Bratko and Amana burners are approximately
A
80 percent below levels of conventional warm air furnaces. Between the
two, the Amana is the only commercially available unit and its cost to the
consumer is generally $100 to $300 above that of a conventional furnace.
The modulating furnace system produces a cooler flame by altering
the burner firing rate to respond to heating costs instead of cycling on
and off. N0x reductions of about 40 percent have been reported. AGAL
is currently investigating pulse combustion for residential heating using
a condensing exhaust gas system. Preliminary NO emissions have been
A
reported in the 19 to 20 ng/J range. Commercialization of the pulse
combustor residential heating system is expected in 1981. Catalysts
promoting combustion of fuel at low temperature offer potential for very
low NO emissions while maintaining good combustion efficiency.
A
Research groups and trade organizations are investigating the commercial
feasibility of catalytic combustion for residential warm air and hot water
systems burning natural gas. Performance and emission data for these
systems have not yet been published; however, N0x emissions are expected
to be very low.
Residential oil-fired heaters are forced draft fired and therefore
more readily modified for reduced emissions and increased efficiencies
than natural draft gas-fired heaters. Early work involved the development
of the flame retention oil burner. These units produce lower CO, UHC and
smoke emissions and operate on excess air lower than previous conventional
1-9
-------
oil burner designs. In some particular designs the flame retention
devices also lower NO emissions by 20 to 40 percent. Furthermore, they
/\
stay tuned longer and thus maintain low combustible emission levels
(Reference 1-6). These units are now the primary residential oil burners
sold.
As part of their combustion research program, the EPA has supported
low-NO high efficiency residential burner development since 1971.
A
Under one program, Rocketdyne developed a controlled mixing burner head
for retrofit and new applications on domestic heaters. It was estimated
that widespread application of the relatively inexpensive burner head
device would be effective in reducing NO by 20 percent and increase
efficiency by 5 percent on the average for each retrofitted furnace.
Recently the burner has been integrated with an "optimum"* low emission
high efficiency warm air furnace. NOV emissions have been reduced by 65
A
to 70 percent and steady state efficiencies have been increased by
10 percent over those of conventional designs. The EPA program emphasized
the necessity to match the firebox, burner and heat exchanger design to
achieve low-NOx emissions while also maintaining low levels of CO, UHC
and smoke.
Both the Blueray "blue flame" and the M.A.N. burners use
aerodynamic flue gas recirculation to achieve a blue flame with distillate
fuel oil. These burners thus achieve reduced flame temperature, dilution
of the oxygen concentration in the near-burner zone and rapid vaporization
of the fuel prior to ignition. These conditions result in low NO
A
emissions on the order of 15 to 40 ppm corrected at zero percent excess
air, representing NOX reductions of 50 to 80 percent. Theoretically,
these burner concepts could be scaled up to larger commercial sizes. The
Blueray furnace system is currently the only commercially available low-
NO system in the U.S. for oil-fired residential use.
A
Control techniques aimed at reducing seasonal pollutant emissions
from residential heating systems through improved fuel economy and general
terminology used by Rocketdyne to characterize the final design capable
of achieving program goals.
1-10
-------
reduced equipment usage are listed in Table 1-4. Replacement of wornout
furnaces, tuning and changes in thermostat anticipator setting represent
the most effective control techniques with overall combustible emission
reductions ranging from 16 to 65 percent for CO, 3 to 87 percent for UHC,
59 percent for smoke, and 17 to 33 percent for particulates. Installation
of delayed action solenoid valves and reduced firing capacity through
minor modification or installation of a new flame retention burner are
effective in reducing excessive smoke emissions during furnace start-up
and shut-down periods. Reported average smoke reductions range from 24 to
82 percent. In general, all these techniques result in fuel savings
sometimes as high as 39 percent in addition to lowering combustible
emissions.
Application of control technology to commercial heating equipment
is very limited. Theoretically, the flame quenching and surface
combustion concepts investigated for gas-fired residential equipment could
also apply to commercial heaters burning natural gas. Similarly,
low-NO burner designs for distillate oil firing or optimum air-fuel
/\
mixing concepts could possibly be scaled up to the larger commercial
equipment.
NOX control technology from the gas- and oil-fired industrial
boiler source category include low-NO burners, staged combustion, flue
A
gas recirculation, load reduction and low excess air operation. These
techniques could possibly be applicable to commercial size boilers of
similar design. Low-N0x burners represent the most attractive control
alternative for this boiler size category. Some U.S. companies are
currently working on new burner design concepts, primarily for oil-fired
boilers. Most of these efforts, however, have been oriented toward
industrial (2.9 to 73.3 MW heat input) size boilers.
1.4 ENVIRONMENTAL AND COST IMPACTS
As a part of the NOV EA program, a Blueray low-NOv high-
A A
efficiency residential furnace was tested in the field to quantify the
environmental impact of low-NOx residential systems. Results from these
tests were then compared with those from another program in which seven
conventional oil-fired residential heaters (five warm air and two hot
water) using high pressure atomizing burners were field tested.
1-11
-------
TABLE 1-4. PERFORMANCE SUMMARY OF CONTROLS FOR REDUCTION OF SEASONAL
COMBUSTIBLE, SMOKE AND PARTICULATE EMISSIONS FROM OIL-FIRED
RESIDENTIAL HEATERS
Control
Replacement of worn-out
units
Tuning and scheduled
seasonal maintenance
Delayed action solenoid
valves
Reduced excessive firing
capacity with conven-
tional burner
Reduced excessive
firing capacity with new
retention burner
Installation of positive
chimney dampers
Change In thermostat
anticipator setting
Overnight thermostat
cut -back (3-5K)
Percent Reduction (Average)
CO UHC Smoke Partlculates
(65) (87) NC* (17)
(16) (3.0) (59) (7.0)
NA NA 60-90 NA
(80)
(14) NA 10-38 (3.7)
(24)
(14) NA 80-85 (3.7)
(82)
2.0-19 NA NA 2.3-17
(11) (10)
41-45 NA NA 31-33
(43) (33)
9.1-27 NA NA 12-24
(17) (15)
Percent
Improvement
In Fuel Saving
NAb
1.7 percent
average efficiency
Increase
NA
5.6-2.5
(14)
14-39
(30)
3-9
0-2
7-15
1978
Installed
Control
Cost
$650-J1000C
for new warm
air furnaces
$38-$60c
$43C
$52<:
$385C
$200C
Minimal
Minimal
Comments
Nine percent of the existing resi-
dential heaters were found in need
of replacement. Recent cost
estimates.
Tuning results is an increase in
efficiency for some units and a
decrease in efficiency for others.
Smoke emission reduction primarily
during start-up and shut-down.
Installation of flame retention
head cone plus modifications to
reduce firing capacity by about
36 percent. -
Installation of new lower capacity
burner with flame retention head
retention head. Firing capacity
reduced by 43 percent.
Large variation In pollutant
slon reduction due to changes
In furnace cycle frequency.
Recent cost estimate.
Very effective for residential
units with high cyclic frequency.
Cost does not take Into account
improved home insulation which
might be necessary with thermostat
cut-back.
I
no
»NC ' No change
bNA - Not available
cCosts for material and labor are typical of New England area. Original costs reported
for years other than 1978 were corrected for inflation using Gross National Product (GNP)
implicit price inflators (Reference 1-9)
-------
In general, the Blueray unit showed decreases of criteria and
noncriteria pollutants when compared with conventional heaters. For
cyclic operation, particulate, S03, and trace elements were 70 to
80 percent lower for the Blueray low-NOv furnace. However, total
A
organic emissions from the Blueray unit were about five times higher than
the average emissions from the seven conventional heaters. Switching from
continuous to cyclic operation, NO emissions from the Blueray furnace
A
decreased because of lower N0x during transient furnace operation.
Particulates and trace element emissions generally remained unchanged.
Emissions of Fe, Ni and possibly Cr, Mn, and Mo decreased significantly
when switched to cyclic operations. However, trace element results need
verification since sample contamination from steel metal surfaces was
suspected.
A rapid screening of potentially hazardous emissions from the
Blueray furnace and conventional oil-fired heaters was performed using the
Source Analysis Model (SAM IA) (Reference 1-10). For the purpose of
screening pollutant emissions data to identify species requiring further
study, a Discharge Severity (DS) is calculated using SAM IA procedures.
DS is defined as the ratio of a pollutant species discharge concentration
to that species' Discharge Multimedia Environmental Goal (DMEG). The DMEG
value represents a threshold, or "allowable" discharge concentration of a
pollutant, above which adverse health or ecological effects may occur.
When DS exceeds unity, more refined chemical analysis may be required to
quantity specific compounds present.
Table 1-5 lists discharge severities for those species with DS
greater than 0.1. The DS for NO was significantly lower for the
A
Blueray furnace, decreasing from a value of about 5 for conventional units
(representing potential environmental hazard), to less than 1.0 for the
low-NO unit. Of the trace elements, Cr and Ni emissions present the
/\
greatest potential hazard; in all cases their DS is a sizeable fraction of
total stream DS. However, measured levels of these metals may be an
artifact of the stream sampling methodology. The flue gas sampling trains
in both the conventional furnace test program and the NO EA contained
J\
many stainless steel components. Thus, some of the reported Cr and Ni
1-13
-------
TABLE 1-5. FLUE GAS DISCHARGE SEVERITIES GREATER THAN 0.1 FOR THE
BLUERAY FURNACE AND CONVENTIONAL OIL-FIRED HEATERS
Pollutant
NOX
SO 2
SO 3
CO
Arsenic (As)
Calcium (Cd)
Chromium (Cr)
Cobalt (Co)
Copper (Cu)
Iron (Fe)
Lead (Pb)
Nickel (Ni)
Thallium (Th)
Amines
Carboxylic acid
Total Stream DS
Blue ray Furnace ,
(Reference 1-11)
Continuous
Operation
0.86
1.6
0.15
0.17
0.23
0.17
85
0.14
0.075
0.42
0.14
4.5
0.37
NFC
0.20
95.7
Cyclic
Operation
0.60
2.1
0.77
1.1
0.27
0.11
5.5
0.11
0.055
0.046
0.14
0.73
0.41
NFC
2.3
1 5. 5
Conventional Furnace
(Reference 1-12)
Cyclic
Operation
4.73
6.3a
4.5
0.3a
0.60
0.85
22
NDb
0.60
0.011
0.21
15
NDb
1.6
NFC
59.0
aPollutant not measured in test program,
DS calculated from AP-42 emission factors:
S02, 106 ng/J; CO, 15 ng/J
"ND: Species not analyzed for
CNF: None found
NOX, 55 ng/J;
1-14
-------
could have come from the sampling train itself rather than being a
significant component of the flue gas.
For both types of units SO,, emissions were flagged and emissions
of certain organic categories had DS values greater than 1. For the
conventional units amines were flagged as being of potential concern; for
the Blueray unit carboxylic acids would be of potential concern under
cyclic operation. The DS for NO exceeds 1 for conventional units, but
A
is less than 1 for the low-NOx Blueray unit under both continuous and
cyclic operations.
In summary, flue gas stream Total Discharge Severity (TDS) for
typical conventional units appears to fall between the TDS for the
low-NO unit under cyclic (normal) operation and that for both the
A
low-NO unit under continuous operation. If Cr and Ni are removed from
A
the TDS calculations, adjusted TDSs of 32.7, 5.3, and 18.3 result for the
conventional, Blueray continuous, and Blueray cyclic data, respectively.
Thus, if measured Cr and Ni indeed comes from the sampling train, then the
low NO unit's TDS under both cyclic and continuous operation is lower
X
than that of the conventional units. This suggests that using the Blueray
design to control NO from oil-fired heating units is environmentally
A
sound.
Table 1-6 summarizes estimated cost data for the most effective
NO control alternatives for residential heating systems. As indicated,
A
retrofit of the controlled mixing burner head (EPA/Rocketdyne) for
residential oil-fired warm air furnaces represents the most cost-effective
alternative to achieve a NO emission level of about 45 ng/J of useful
/\
heat. Surface combustion, pulse combustor and catalytic burner for
gas-fired units and the Rocketdyne developed technologies for oil-fuel
units are not commercially available. The payback periods listed in the
table are estimates based on the time required to recover the money spent
for the initial investment of installing NO control equipment. Since
J\
all of these control alternatives bring about an increase in thermal
efficiency, and thus fuel savings, the initial investment cost is often
recouped over a one year or less time period.
1-15
-------
TABLE 1-6. COST IMPACT OF NOX CONTROL ALTERNATIVES
Control
Amana (HTM) Furnace
Modulating Furnace
Surface Combustion
Burner (Infrared Bratko
type)
Pulse Combustion
Burnerb
Catalytic Combustion
Burner0
Flame Retention Burner
Head
Flame Retention Burner
EPA/Rocketdyne Burner
Head
EPA/Rocketdyne Furnace
Bluer ay Furnace
Fuel
Natural Gas
Natural Gas
Natural Gas
Natural Gas
Natural Gas
Distillate Oil
Distillate Oil
Distillate Oil
Distillate Oil
Distillate Oil
Achievable NOX Level
ng/J Useful Heat
12
(390 ng/m3 fuel)
35
(920 ng/m3 fuel)
12
(380 ng/m3 gas)
21
(683 ng/m-3 gas)
Estimate 5
(163 ng/m3 gas)
50
(1.8 g/kg fuel)
50
(1.8 g/kg fuel)
45
(1.6 g/kg fuel)
29
(0.7 g/kg/fuel)
20
(0.7 g/kg fuel)
1978
Incremental
Investment Cost
J100-J300 over cost of
conventional furnace
$50-$250 over cost of
conventional furnace
J100-J200 over cost of
conventional furnace/
heater
$300-$600 over cost of
conventional furnace/
heater
$150-$250 over cost of
conventional furnace/
heater
$52 — retrofit
including installation
$385 — retrofit of
reduced capacity burner
$43 — retrofit
including installation
$250 over cost of
conventional furnace
$100 over cost of
conventional furnace
Cost Effectiveness
$/ng/Ja
1.7-5.2
1.4-7.0
1.7-3.4
6.1-12.2
2.3-3.9
2.6
12.8
1.3
4.2
1.7
Payback Period Based
on Annual Fuel Bill
of $500
1-3 years
1-3.8 years
3.5-8.0
1.7-3.5
1.4-2.3
Less than 1 year
3.5 years
Less than 1 year
2.5 years
1 year
aBased on uncontrolled NOX emissions of 70 ng/J heat output for natural gas-fired heaters and 80 ng/J heat output
for distillate oil-fired heaters. Cost-effectveness is based of the differential investment cost of the control.
''Based on installation of a condensing system where seasonal efficiencies can be as high as 95 percent.
-------
1.5 DATA NEEDS AND RECOMMENDATIONS
A modest amount of information has been gathered on emissions from
residential space heating equipment. In addition, control alternatives
for N0x and combustible pollutants have also been investigated. Some
low-NOx and high efficiency furnace designs are commercially available,
while other equally effective designs are either at final demonstration
stages or await commercialization. Performance tests on these improved
heating designs are being gathered through EPA sponsored field and
laboratory programs. These and other test programs will aid in further
documenting the performance, reliability of these advanced controls and
quantifying their impact on other pollutant emissions.
Cost data on N0x control alternatives for residential heating
systems were generally sparse and imprecise. This lack of definitive cost
data prevented a detailed economic impact assessment of widespread
implementation of control alternatives. As advanced controls become
available, future EA programs should quantify the cost impact of NO
A
control implementation to achieve specific level of controls.
Investigative efforts on NOY control alternatives for commercial
A
size steam and hot water boilers burning gas or oil is also scarce. While
it can be speculated that some boiler designs lend themselves to NO
A
control techniques developed for industrial size boilers, little
experimental data exist to confirm this. Low-NO burner technology for
A
heat input capacities in the size range of 0.1 to 2.9 MW (0.4 to 10 x
10 Btu/hr) shows promise based on advanced burner technology developed
for both residential units on the small side and industrial units on the
larger side.
NO control technology for solid-fuel-fired residential and
A
commercial equipment, is also very limited. Past and on-going test
programs have mainly dealt with quantifying the pollutant levels and
identifying equipment operating parameters and fuel characteristics which
have some impact on these levels. Primary pollutants of interest for this
category of equipment have been particulate and smoke emissions as well as
levels of unburned hydrocarbons, toxic elements and polycyclic organic
matter (POM). The simplicity of the solid-fuel-fired equipment, whether
coal- or wood-fired, often does not permit extensive modifications of
1-17
-------
existing equipment or operating procedures to reduce NO levels.
A
Investigative efforts in this area should continue to determine potential
NO control technology applicable to new unit design while still
A
concentrating on reducing the impact of other criteria and noncriteria
pollutant emissions.
1-18
-------
REFERENCES FOR SECTION 1
1-1. Water!and, L. R., et al., "Environmental Assessment of Stationary
Source NOX Control Technologies -- Final Report," Acurex Draft
Final Report, EPA Contract 68-02-2160, Acurex Corp., Mountain View,
CA, April 1980.
1-2. Devitt, T., et al., "The Population and Characterization of
Industrial/Commercial Boilers," EPA 600/7-79-178a, NTIS
PB-80-150881, August 1979.
1-3. Howekamp, D. P., "Flame Retention -- Effects on Air Pollution,"
U.S. Department of Health, Education and Welfare, presented at the
Ninth Annual Convention of National Oil Fuel Institute, Atlantic
City, New Jersey, June 1970.
1 Hall, R. E., et al., "Study of Air Pollutant Emissions from
Residential Heating Systems," EPA-650/2-74-003, NTIS-PB 229 697,
January 1974.
1-5. Personal communication with Charles Allen, Department of Energy
Information Administration (EIA), Washington, D.C., on preliminary
data from Annual Report to Congress, May 1, 1979.
1-6. Brookman, G. T., and W. Kalika, "Measuring the Environmental Impact
of Domestic Gas-Fired Heating Systems," in the Proceedings of the
67th Annual Meeting, Air Pollution Control Association, June 1974.
1-7. U.S. Environmental Protection Agency, "Compilation of Air Pollution
Emission Factors, Second Edition With Supplements," EPA AP-42,
Research Triangle Park, North Carolina, 1972-1977.
1-8. Barrett, R. E., et al., "Field Investigation of Emissions from
Combustion Equipment for Space Heating," EPA-R2-084a, (API
Publication 4180) NTIS-PB 223 148, June 1973.
1-9. "Statistical Abstracts of the United States -1978," U.S.
Department of Commerce, 99th Annual Edition, Section 15,
pp 480-485, September 1978.
1-10. Shalit, L. M., and K. J. Wolfe, "SAM/IA: A Rapid Screening Method
for Environmental Assessment of Fossil Energy Process Effluents,"
EPA-600/7-78-015, NTIS-PB 277 088, February 1978.
1-11. Higginbotham, E. B., "Combustion Modification Controls for
Residential and Commercial Heating Systems: Volume II. Oil-fired
Residential Furnace Field Test," EPA-600/7-81-123b, July 1981.
1-12. Surprenant, N. F., et al., "Emission Assessment of Conventional
Stationary Combustion Systems: Volumn 1. Gas- and Oil-Fired
Residential Heating Sources," EPA-600/7-79-029b, NTIS-PB 298-494,
May 1979.
1-19
-------
SECTION 2
INTRODUCTION
This report assesses the operational, economic, and environmental
impacts from applying combustion modification NO controls to
A
residential and commercial combustion equipment with heat input capacity
less than 2.9 MW (10 x 106 Btu/hr). With more NOX controls being
implemented in the field and expanded control development anticipated for
the future, there is currently a need to: (1) ensure that the current and
emerging control techniques are technically and environmentally sound, and
compatible with efficient and economical operation of systems to which
they are applied, and (2) ensure that the scope and timing of new control
development programs are adequate to allow stationary sources of NO to
/\
comply with potential air quality standards. The NO EA program
addresses these needs by (1) identifying the incremental multimedia
environmental impacts of combustion modification controls, and
(2) identifying the most cost-effective source/control combinations to
achieve ambient N02 standards.
2.1 BACKGROUND
Since the 1970 Clean Air Act Amendments, techniques have been
developed and implemented that reduce NOX emissions by a moderate amount
(30 to 60"percent) for a variety of stationary source/fuel combinations.
In 1971, EPA set NSPS for large steam generators burning gas, oil, and
coal (except lignite). Recently, more stringent standards for utility
boilers burning bituminous and subbituminous coals have been promulgated,
along with new standards for lignite fired utility boilers. In addition,
NSPS have been proposed for stationary gas turbines reciprocating internal
combustion engines and are under study for industrial steam generators.
Local standards also have been set, primarily for new and existing large
steam generators and gas turbines, as parts of State Implementation Plans
in several areas with NOX problems.
2-1
-------
Because of the relaxation of mobile standards, coupled with the
continuing growth rate of stationary sources, NO control for stationary
sources has become more important for maintaining air quality. Thus more
stringent controls than current and impending NSPS provide will be
required. To meet these standards the preferred approach is to control
new sources by using low-NO redesigns.
2.2 ROLE OF RESIDENTIAL AND COMMERCIAL HEATING SYSTEMS
This source category includes warm air furnaces and hot water
heaters for home heating, and small commercial hot water or steam boilers
for plant heating and air conditioning. Home heating equipment consume
the largest quantity of fuel within this source category. In 1977,
domestic space and water heaters alone consumed about 8 EJ* or
approximately 20 percent of the total U.S. energy used by stationary
combustion sources (Reference 2-1). Commercial boilers with heat input
capacity less than 2.9 MW (10 x 10 Btu/hr) consumed approximately an
additional 4.15 EJ, or about 10 percent of total U.S. fuel consumption for
stationary combustion sources.
Residential combustion equipment warm air furnaces, steam and hot
water heaters and warm air space heaters (combined) is the fifth largest
contributor of NO emissions in the U.S. Figure 2-1 shows that warm air
/\
central furnaces are responsible for 14 percent of NOV emissions from
x /-
all sources with heat input capacity less than 2.9 MW (10 x 10 Btu/hr)
or about 0.9 percent of total NO ; steam and hot water heaters
A
contributed 26.1 percent or 1.8 percent of total NO ; while warm air
^
space heaters contributed another 4.3 percent, or 0.3 percent of total
NO (updated from Reference 2-3). Steam and hot water boilers
y\
(firetubes, watertubes, and cast iron) with a capacity less than 2.9 MW
(10 x 10 Btu/hr), used in both commercial and industrial sectors,
contributed about another 3.0 percent to the total NO emissions.
J\
The impact of residential and commercial heating systems on ambient
NO levels is much more severe than these low percentage points
X
indicate. The seasonal use pattern, low stack heights and wide
geographical distribution of residential and commercial heating systems
*Does not include about 2 EJ of electricity also used for residential
heating.
2-2
-------
Conmerdal and residential
<2.9 MW (10 x 106) Btu/hr) 6.8%
Incineration 0.4J
Noncombustlon 1.9%
Gas turbines 2.0'
Others (fugitive) 4.U
Irdustrial nrocess heaters 4.1%
Industrial and commercial boilers
>2.9 MW (>10 x 10b Btu/hr) 9.71
Reciprocating
1C engines
18.9%
Total from ill sources: 10.5 Tg/yr (11.6 » 106 tons/yr
Warm air space heaters 4.3'.
Miscellaneous cot*ust1on" 11.4%
Firetube boilers \2.K
Uitertube boilers 1.41
Ham air
central
furnaces 14.0%
Steam and hot
water heaters
26.
Total from all sources with capacity less than 2.9 MW
(10 x 106 Btu/hr): 0.709 Tg/yr (0.781 x 106 tons/vr)
'includes coolinq and air conditioning
Figure 2-1.
Distribution of stationary anthropogenic NOX emissions for
the year 1977 (controlled NOX levels) (Reference 2-2).
2-3
-------
are often the cause of high NCL ambient levels in populated urban
areas, the contribution of these sources often exceeds that of other
stationary or transportation sources during the "heating season"
(References 2-4 and 2-5). With the increasig number of homes and
commercial buildings requiring heating and air combustion systems will
continue to be a problem unless adequate controls are developed. The
problem may be aggravated as fuels such as residual oils or stoker coal
which show a propensity for higher NO formation, becomes more
A
attractive in the face of shortages and higher prices of natural gas and
distillate oils normally used for home and commercial heating.
Given this background and their potential for NOX control,
residential and commercial heating systems were selected as a major source
category to be studied under the NO EA program. The "Preliminary
/\
Environmental Assessment of Combustion Modification Techniques"
(Reference 2-5) concluded that modifying combustion process conditions is
the most effective and widely used technique for achieving 20 to
70 percent reduction in oxides of nitrogen. Nearly all current NO
/\
control applications use combustion modifications. Other approaches, such
as treating postcombustion flue gas, are generally not considered feasible
for application on small residential and commercial heating systems.
2.3 OBJECTIVE OF THIS REPORT
This report evaluates and compares the important environmental and
process engineering aspects of available or emerging combustion
modification techniques for residential and commercial heating systems
with special emphasis on central warm air furnaces. Subobjectives of this
evaluation are:
• Evaluate control impact on total multimedia emissions
t Identify the effect of control application on equipment
performance and identify potential problem areas
• Estimate the economics of control implementation
• Estimate the limits of control achievable for the significant
sources as fuels
• Identify research and development and/or testing needs to
optimize combustion modification techniques and to upgrade
their assessment
2-4
-------
2.4 ORGANIZATION OF THIS REPORT
The components of the environmental assessment reported here are as
follows:
• Characterize the source category with regard to equipment,
fuels and emissions (Section 3)
• Review pollutant formation mechanisms and relate fuels to their
emissions potential (Section 4)
• Evaluate the performance of current and developing NO
/\
control techniques available for implementation (Section 5)
• Estimate the capital and operating costs, including energy
impacts of implementing NO control (Section 5)
rt
e Evaluate the environmental impact of NO controls through the
/\
analysis of incremental emissions (Section 6)
e Assess the total impact of NO controls on ambient air,
/\
economics, energy and operations and maintenance of the
residential equipment, thereby evaluating the effectiveness of
current and emerging control technology (Section 6).
With some exceptions due to the nature of the subject treated, the
reporting format conforms to the "Environmental Assessment Report"
guidelines developed by EPA's Industrial Environmental Research Laboratory
for disseminating results of EPA's environmental assessment program.
2-5
-------
REFERENCES FOR SECTION 2
2-1. Personal communication with C. Allen, Department of Energy,
Washington, D.C., on preliminary data from Energy Information
Administration (EIA) Annual Report to Congress, May 1, 1979.
2-2. Waterland, L. R., et al^, "Environmental Assessment of Stationary
Source NOX Control Technologies ~ Final Report," Acurex Draft
Final Report FR-80-57/EE, EPA Contract 68-02-2160, Acurex Corp.,
Mountain View, CA, September 1979.
2-3. Salvesen, K. G., et al., "Emissions Characterization of Stationary
NOX Sources, EPA-60077^78-120a, NTIS-PB 284 520, October 1977.
2-4. Howekamp, D.P., "Flame Retention — Effects on Air Pollution," U.S.
Department of Health, Education and Welfare, presented at the Ninth
Annual Convention of National Oil Fuel Institute, Atlantic City,
N.J., June 1970.
2-5. Hall, R. E., et aj_., "Study of Air Pollutant Emissions from
Residential Heating Systems," EPA-650/2-74-003, NTIS-PB 229 697,
January 1974.
2-6. Mason, H.B., et al., "Preliminary Environmental Assessment of
Combustion ModTfication Techniques, Volume II, Technical Results,"
EPA-600/7-77-1196, NTIS-PB 276 681/AS, October 1977.
2-6
-------
SECTION 3
SOURCE CHARACTERIZATION
This section characterizes space heating combustion sources with
heat input capacity less than 2.9 MW (10 x 106 Btu/hr). This size
category covers steam and hot water systems and warm air furnaces in both
the residential and commercial sectors. In addition, it includes process
steam or hot water units in the industrial sector with capacity less than
2.9 MW (10 x 10 Btu/hr). Equipment types, population and installed
capacity, current design practice, and areas of environmental concern are
identified and discussed.
3.1 EQUIPMENT TYPES
Figure 3-1 summarizes the types of residential and commercial
combustion equipment used for space heating. For this report the
distinction between residential and commercial units is arbitrarily set at
0.1 MW (400,000 Btu/hr) heat input capacity, although, warm air furnaces,
space heaters, and hot water or steam units below this firing rate are
also used in commercial establishments. Units with capacity above 0.1 MW
(400,000 Btu/hr) are rarely found in single family residential dwellings.
Figure 3-1 indicates that there are four generic equipment types --
(1) room heaters or direct vent heaters used for domestic warm air, (2)
space or unit heaters only used for commercial direct heating, (3) warm
air furnaces used for both residential and commercial heating, and (4) hot
water or steam systems also used for domestic and commercial heating.
Warm air room heaters or direct vent heaters are single room heaters which
may be mounted in the wall, floor or from the ceiling. Warm air furnaces
are central air units delivering warm air to a number of rooms. In many
cases, especially in commercial systems the warm air heating system is
integral with a central air conditioning system. Space or unit heaters
are used solely for commercial heating, exhausting hot combustion products
3-1
-------
co
Residential
<0.12 MW (<0.4 x 106 Btu/hr)
Commercial
0.12-2.9 MW
(0.4 -10 x 106 Btu/hr)
Room or
heaters
Warm air
furnaces
— Steam or hot
water boilers
heaters
_ Wall un
— Miscell
Natural
forced
— Cast ir
>— Steel
r— Coil
— Steel
its
nits
aneous
and
draft
on
I— Rooftop heaters
-Warm air space or—I
unit heaters
'— Unit heaters
.Warm air.
furnaces
t
Direct
Indirect
I—Cast iron
—Hot water
and steam boilers3
•Firetube
1—Water tube
Natural gas, distillate oil
Natural gas
Natural gas, distillate oil
Natural gas, distillate oil
Natural gas, distillate oil, coal
Natural gas, distillate oil, coal
Natural gas, distillate oil
Natural gas, distillate oil,
residual oil, coal
Natural gas, distillate oil
Natural gas, distillate oil
Natural gas
Natural gas, distillate oil
Natural gas, distillate oil,
residual oil, coal
Natural gas, distillate oil,
residual oil, coal
Natural gas, distillate oil,
residual oil, coal
aAlso found in the industrial sector.
Figure 3-1. Distribution of residential and commercial heating systems.
-------
directly into the space being heated. Finally, hot water or steam
systems, may be utilized for either space heating or for process hot water
or steam. The following sections present the population distribution of
these commercial and residential units by fuel, equipment type, and region.
3.1.1 Residential Units
Table 3-1 lists domestic heating populations based on 1976 U.S.
Census data by equipment type and fuel (Reference 3-1). The Census data
indicate that central warm air furnaces are the most common residential
combustion equipment accounting for nearly 53 percent of the entire
population. Natural gas is currently the principle house heating fuel
accounting for about 56 percent of total fuel used. Oil and kerosene rank
second as sources of energy with about 22 percent, while electricity,
which has recently grown in popularity, in 1976 accounted for nearly
14 percent of the total energy used.
Table 3-2 lists the distribution of residential equipment by fuel
type for the four U.S. Census Regions. In the Northeast Region, a higher
percentage of fuel oil is consumed than other fuels, whereas in all other
regions natural gas is the predominant domestic fuel. Equipment
distribution also varies regionally (Table 3-3). In the Northeast Region,
steam or hot water systems comprise the highest percentage of all
residential equipment types. This indicates that, although gas-fired warm
air systems dominate nationally, oil-fired hot water or steam units can be
significant air pollution contributors on a regional basis.
3.1.2 Commercial Units
With the exception of the hot water or steam boilers below 2.9 MW
(10 x 10 Btu/hr) firing capacity, no compilation of user statistics or
sales was found for commercial size space heating equipment. However,
discussion with manufacturers revealed the following:
• There are both gas-fired and oil-fired unit heaters and warm
air furnaces or duct heaters in the commercial size range
designated in this report, 0.1 to 2.9 MW (0.4 to 10 x 106 Btu/hr)
t Although there are a few unique gas-fired designs, in general
the combustion systems of commercial heating equipment is
similar in design to the residential equipment
3-3
-------
TABLE 3-1. POPULATION AND RANKING OF DOMESTIC HEATING SYSTEMS BY TYPE (1976) -- 1000 UNITS
CO
-p.
Heating Equipment
Harm Air Furnace
Steam or Hot Water
Floor, Wall or Pipeless
Furnace
Room Heater wtth Flue
Room Heaters w/o Flue
Built-in Electric Units
Others (Fireplaces,
Stoves)
Total
Natural Gas
25,042
(34.1)a
5,308
(7.2)
5,471
(7.4)
2,767
(3.8)
2,331
(3.2)
--
300
(0.4)
41,219
(56.0)
Bottled or
Liquified
Petroleum Gas
1,961
(2.7)
112
(0.2)
503
(0.7)
636
(0.9)
938
(1.3)
--
90
(0.1)
4,240
(5.8)
Oil or Kerosene
6,729
(9.1)
7,987
(10.9)
422
(0.6)
1,183
(1.6)
68
(0.1)
—
62
(0.1)
16,451
(22.4)
Electricity
4,877
(6.6)
--
--
--
--
4,794
(6.5)
479
(0.7)
10,150
(13.8)
Other Fuel
179
(0.2)
192
(0.3)
22
—
--
--
1,090
(1.5)
1,483
(2.0)
Total
38,787
(52.7)
13,598
(18.5)
6,417
(8.7)
4,586
(6.2)
3,337
(4.5)
4,794
(6.5)
2,021
(2.7)
73,543
(100)
aPercent of total systems given in parenthesis.
-------
TABLE 3-2. REGIONAL DISTRIBUTION OF RESIDENTIAL HEATING
EQUIPMENT BY FUEL (1976) -- 1000 UNITS
Fuel
Natural Gas
Bottled or
Liquified
Petroleum Gas
Oil, or
Kerosene
Electricity
Coal, Coke
Other,
incl. Wood
Total
Northeast
6,140
(8.4)a
125
(0.2)
9,161
(12.5)
846
(1.1)
162
(0.2)
101
(0.1)
16,535
(22.5)
Northcentral
13,803
(18.8)
1,337
(1.8)
3,004
(4.1)
1,366
(1.9)
102
(0.1)
105
(0.1)
19,717
(26.8)
South
11,449
(15.6)
2,367
(3.2)
3,488
(4.7)
5,498
(7.5)
193
(0.3)
588
(0.8)
23,583
(32.1)
West
9,826
(13.4)
411
(0.6)
798
(1.1)
2,441
(3.3)
28
(0.04)
204
(0.3)
13,708
(18.6)
Total
41,219
(56.0)
4,240
(5.8)
16,451
(22.4)
10,151
(13.8)
485
(0.7)
988
(1.4)
73,543
(100)
aPercent of total systems given in parenthesis.
Northeast
3-5
-------
TABLE 3-3. REGIONAL DISTRIBUTION OF RESIDENTIAL HEATING
EQUIPMENT BY FUEL (1976) — 1000 UNITS
Equipment
Warm Air
Furnaces
Steam or Hot
Water
Floor, Wall
or Pipeless
Furnace
Room Heater
with Flue
Room Heater
without Flue
Built-in
Elect. Units
Others (Fire-
places, Stoves)
Total
Northeast
5,984
(8.1)a
8,923
(12.1)
174
(0.2)
521
(0.7)
51
(0.1)
733
(1.0)
148
(0.2)
16,534
(22.5)
Northcentral
13,782
(18.7)
3,068
(4.2)
556
(0.8)
1,220
(1.7)
52
(0.1)
899
(1.2)
140
(0.2)
19,717
(26.8)
South
11,922
16.2)
1,070
(1.5)
2,365
(3.2)
2,049
(2.8)
3,112
(4.2)
1,674
(2.3)
1,390
(1.9)
23,582
(32.1)
West
7,100
(9.6)
538
(0.7)
3,321
(4.5)
796
(1.1)
122
(0.2)
1,488
(2.0)
344
(0.5)
13,709
(18.6)
Total
38,788
(52.7)
13,599
(18.5)
6,416
(8.7)
4,586
(6.2)
3,337
(4.5)
4,794
(6.5)
2,022
(2.7)
73,542
(100)
aPercent of total systems given in parenthesis.
Northeast
3-6
-------
• The majority of unit heaters are gas-fired and some of these
are "infrared type" burners where surface combustion occurs on
a refractory grid
t Warm air heaters are either indirect gas-or-oil-fired similar
to the residential units or direct gas-fired where the
combustion gases are mixed with the air being heated. This
heated air may be used for space heating or for drying.
t Indirect fired warm air heaters are either larger versions of
residential design or duct heaters. Duct heaters are usually
part of a central air conditioning system or roof top climate
control system.
• Rooftop gas-fired central air systems are often utilized in
commercial buildings. In more severe climates and high-rise
buildings a central boiler, either gas- or oil-fired, is
utilized.
Three types of burner systems are commonly used in commercial space
heating equipment; these are:
a The atmospheric gas-fired single port, ribbon or multiport
burner
• The retention head distillate oil-fired power burner
• The direct gas-fired duct burner
The first two designs are similar to those used for residential systems.
These burner systems will be discussed with regard to their pollution
impact and control potential in the following sections of this report.
Steam and hot water units with heat input capacity below 2.9 MW
(10 x 10 Btu/hr) can be found in both the commercial as well as the
industrial sector. These units can be divided into three general
equipment types -- watertubes, firetubes, and cast iron boilers. A
recent population distribution of these commercial size boilers has been
published by Devitt, et aiK, (Reference 3-2). Tables 3-4 and 3-5 list
respectively the 1977 commercial and industrial population and installed
-capacity for the various types of boilers within this size category.
In the commercial sector (Table 3-4), cast iron boilers account for
over 90 percent of all installed steam or hot water units. Nearly 66
percent of these units have heat input less than 0.1 MW (400,000 Btu/hr).
Firetube boilers are the second most numerous boiler type accounting for
3-7
-------
TABLE 3-4. POPULATION OF BOILERS WITH <2.9 MW (10 x 106 Btu/hr)
HEAT INPUT CAPACITY IN USE IN COMMERCIAL SECTOR —
1977 NUMBER OF UNITS (INSTALLED CAPACITY MW)
Equipment
Type
Watertube
Watertube
Total
Firetube
Firetube
Total
Cast Iron
Cast Iron
Total
All Equip-
ment Types
Size Range MW
(106 Btu)
£0.1 (0.4)
0.1-0.4
(0.4-1.5)
0.4-2.9
(1.5-10)
<0.1-2.9
0.4-10)
£0.1 (0.4)
0.1-0.4
(0.4-1.5)
0.4-2.9
(1.5-10)
0.1-2.9
TO. 4-10)
<0.1 (0.4)
0.1-0.4
(0.4-1.5)
0.4-2.9
(1.5-10)
<0.1-2.9
TO. 4-10)
<0.1-2.9
TO. 4-10)
Stoker
Coal
—
392
(no)
630
(955)
1,022
(1,065)
—
13,459
(3,940)
2,866
(4,830)
16,325
(8,770)
90 , 630
(4,810)
37,408
(9,840)
15,826
(10,610)
143,864
(25,260)
161,211
(35,095)
Residual
Oil5
—
399
(140)
772
(1,160)
1,171
(1,300)
—
15,731
(4,610)
5,163
(8,310)
20,894
(12,920)
162,855
(12,010)
57,291
(12,860)
19,428
(18,140)
239,574
(43,010)
261,639
(57,230)
Distillate
Oil*
—
1,552
(550)
1,183
(1,380)
2,735
(1,930)
—
16,001
(4,690)
5,636
(9,070)
21,637
(13,760)
102,266
(7,530)
35,983
(8,090)
12,196
(11,370)
150,445
(26,990)
174,817
(42,680)
Natural
Gas5
—
893
(310)
723
(985)
1,616
(1,295)
—
30,889
(9,050)
6,715
(10,920)
37,604
(19,970)
421,033
(30,970)
175,055
(40,260)
51,221
(43,570)
647,309
(114,800)
686,529
(136,065)
Total
—
3,236
(1,110)
3,308
(4,480)
6,544
(5,590)
—
76,080
(22,290)
20,380
(33,130)
96,460
(55,420)
776,784
(55,320)
305,737
(71,050)
98,671
(83,690)
1,181,192
(210,060)
1,284,196
(271,070)
aA number of boilers have dual gas/oil firing capability. Units are
listed here by the primary fuel burned.
3-8
-------
TABLE 3-5. POPULATION OF BOILERS WITH <2.9 MW (10 x TO6 Btu/hr
HEAT INPUT CAPACITY IN USE IN THE INDUSTRIAL SECTOR
1977 NUMBER OF UNITS (INSTALLED CAPACITY MW)
Equipment
Type
Water-tube
Watertube
Total
Firetube
Firetube
Total
Cast Iron
Cast Iron
Total
All Equip-
ment Types
Size Range MW
(106 Btu)
<0.1 (0.4)
0.1-0.4
(0.4-1.5)
0.4-2.9
(1.5-10)
<0.1-2.9
(04-1.0)
<0.1 (0.4)
0.1-0.4
(0.4-1.5)
0.4-2.9
(1.5-10)
<0.1-2.9
(0.4-10)
£0.1 (0.4)
0.1-0.4
(0.4-1.5)
0.4-2.9
(1.5-10)
<0.1-2.9
(0.4-10)
<0.1-2.9
(0.4-10)
Stoker
Coal
—
168
(50)
515
(785)
683
(835)
—
5,768
(1,690)
2,344
(3,956)
8,112
(5,650)
22,657
(1,200)
9,352
(2,460)
3,956
(2,670)
35,965
(6,330)
44,760
(12,815)
Residual
Oil3
—
774
(270)
2,443
(3,670)
3,217
(3,940)
—
30,536
(8,960)
16,348
(26,320)
46,884
(35,280)
40,714
(3,020)
14,323
(3,220)
4,857
(4,540)
59,894
(10,780)
109,995
(50,000)
Distillate
Oil*
—
1,376
(480)
1,775
(2,080)
3,151
(2,560)
—
14,190
(4,160)
8,453
(13,610)
22,643
(17,770)
25,567
(1,880)
8,996
(2,020)
3,049
(2,840)
37,612
(6,740)
63,406
(27,070)
Natural
Gas3
--
1,521
(540)
2,893
(3,935)
4,414
(4,475)
--
52,594
(15,420)
26,862
(43,700)
79,456
(59,120)
105,258
(7,740)
43,764
(10,080)
12,805
(10,900)
161,827
(28,720)
245,697
(92,315)
Total
--
3,839
(1,340)
7,626
(10,470)
11,465
(11,810)
—
103,088
(30,230)
54,007
(87,590)
157,095
(117,820)
194,196
(13,840)
76,435
(17,780)
24,667
(20,950)
295,298
(52,570)
463,858
(182,200)
aA number of boilers have dual gas/oil firing capability. Units are
listed here by the primary fuel burned.
3-9
-------
7.3 percent of all commercial units below 2.9 MW (10 x 10 Btu/hr) heat
input capacity. In the industrial sector (Table 3-5), cast iron boilers
account for 64 percent of all boilers less than 2.9 MW, while firetubes
account for 34 percent. The total 1977 installed heat input capacity of
steam and hot water boilers from Tables 3-4 and 3-5 is summarized in
Table 3-6. Nearly half of the capacity is provided by natural gas-fired
units. Residual oil accounts for nearly one-fourth the capacity and is
the second most common fuel used.
The burner assembly of most gas- and oil-fired equipment normally
consists of the single power burner designs. However, there are some
atmospheric type gas burners installed on the small size equipment such as
small cast iron boilers. The majority of the stoker coal units are
underfed.
3.2 FURNACE DESIGN PRACTICE
This section reviews the current design practice of units
identified in the previous section. Central air and hot water units are
discussed in the residential section. For the commercial sector, the
various hot water and steam boiler designs as well as some warm air
cabinet, rooftop and duct heaters are discussed.
3.2.1 Residential Units
The primary space heating systems in use today include gas- and
oil-fired warm air central furnaces, and gas- and oil-fired hot water or
steam units, also referred to as hydronic systems. Additionally, the
residential sector also includes a great number of smaller floor, room and
direct vent heater designs, usually gas-fired. The combustion systems on
these units are very similar to the gas-fired warm air furnaces.
3.2.1.1 Gas-Fired Central Air Furnaces
Figures 3-2 and 3-3 show typical gas-fired forced central air
furnaces which account for the single largest equipment category*. There
are three basic forced air configurations; "high-boy" (up-flow or
down-flow), "lo-boy" and horizontal. Typically, for an upflow unit the
*In the past, there were also a considerable number of gravity or natural
draft gas-and oil-fired central air systems. These have fallen out of
favor due to the rather large ducts and furnace volume required and the
higher cost.
3-10
-------
TABLE 3-6. SUMMARY OF INSTALLED CAPACITIES OF COMMERCIAL AND INDUSTRIAL
STEAM AND HOT WATER UNITS WITH HEAT INPUT LESS THAN 2.9 MW
(10 x 106 Btu/hr) -- MW (PERCENT)
Equipment
Type
Watertube
Firetube
Cast Iron
Total
Stoker
Coal
1,900
(0.41)
14,420
(3.18)
31,590
(6.97)
47,910
(10.6)
Residual
Oila
5,240
(1.14)
48,200
(10.62)
53,790
(11-9)
107,230
(23.7)
Distillate
Oil3
4,490
(0.99)
31,530
(6.96)
33,730
(7.44)
69,750
(15.4)
Natural
Gasa
5,770
(1.27)
79,090
(17.5)
143,520
(31.7)
228,380
(50.4)
Total
17,400
(3.8)
173,240
(38.2)
262,630
(57.9)
453,270
(100)
aBoilers are listed by the primary fuel burned. A large number of
units have dual gas/oil fuel burning capability.
3-11
-------
(£-£ aDuaja^ay) saoeuun^ uie paauo^ pa.nj.-se9 -g-j;
co
r—
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-------
CO
I
UNIVERSAL SLOTTED PORT STEEL
BURNER
Burns Natural And Liquefied Petroleum
Gases. Stainless Steel Head,
HEAT EXCHANGER
UNIQUE PATENTED DRAFT DIVERTER
Figure 3-3.
Gas-fired forced air downflow furnace and
details of components (Reference 3-3).
-------
recirculating room air enters the bottom or side of the unit, flows
through the main circulating fan, then to the heat exchanger and usually
out the top to the distribution ducting. The gas burners are usually
naturally aspirated consisting of venturi three to five primary air
shutter and burner ports (single port, ribbon or drilled or formed
multiport). The primary air is drawn into the venturi by the expanding
natural gas and premixes with the gas prior to ignition. The primary
air/fuel ratio can be controlled through the shutter valves at each
venturi. After the mixture exits the ports it is ignited by a standing
gas pilot or electronic ignitor. Secondary air to complete the combustion
reaction enters from the furnace through its secondary air openings and
passes around the burners to complete the combustion reaction. The
combustion products flow upward through a parallel flow heat exchanger and
exit into a collector box or draft diverter. The draft diverters dilute
the flue gas stream, prevent downdrafts from blowing out the pilot, and
isolate the burner from changes in vent draft. Typical operating
conditions are listed in Table 3-7.
Several comments concerning the data of Table 3-7 should be noted.
The wide range in excess air levels is due to variations in installation
and meterological conditions. The combustion chamber pressures are quite
low due to the naturally aspirated design. Consequently, the flue gas
flow area is quite large to avoid excessive pressure drop. The low
velocity associated with this area results in a fairly low hot side heat
transfer coefficient and consequently fairly large surface areas. The
furnace relies on the stack to create sufficient draft to draw the
secondary air through the furnace. Manufacturers design practice shows
that stack temperatures below 422 K (300°F) can yield insufficient draft
for the burners and cause condensation in the stack.
3.2.1.2 Oil-Fired Central Air Furnaces
Figure 3-4 shows three common oil-fired forced air furnaces. From
the outside these furnaces appear very similar to the gas-fired units and
-are now being made with overall volumes comparable to gas-fired units.
The main difference between the two furnace types is burner design. Most
oil-fired burners use pressurized combustion air which mixes with atomized
distillate oil as it leaves the nozzle. The gun type oil burner, pictured
in Figure 3-5, consists of a combustion air blower, motor, damper, fuel
3-17
-------
TABLE 3-7. TYPICAL OPERATING CONDITIONS FOR A WARM AIR
GAS-FIRED FURNACE: 29.3 kW (100,000 Btu/hr)a
Recirculating Air Flowrate 0.38-0.57 W/m3/s (800-1200 SCFM)
Combustion Excess Air: 40-120%
Flue Exit Diameter: 0.089-0.13 m (3.5-5.0 in)
Heat Exchanger Area: 1.9-2.4 m2 (20-25 ft2)
Overall Heat Transfer Coefficient: 11-17 W/m2-K
(2-3 Btu/hr-ft2-°F)
Exit Flue Gas Temperature (Before Draft Diverter): 505-616 K
(450-6500p)
Draft Diverter Dilution Air Flow Percent of Flue: 20-50%
Combustion Chamber Pressure: +50 Pa (_+ 0.2 in. H20)
Temperature Rise on Air Side: 39-55 K (70-100°F)
Overall Steady State Efficiency:15 75-80%
aData is compiled from discusion with manufacturers and from References
3-4, 3-5, 3-6, 3-7, and 3-8.
bNew furnace must meet American National Standards Institute (ANSI)
standards of 75 percent.
3-18
-------
00
I
Figure 3-4. Oil-fired central air furnaces (Reference 3-3)
-------
Figure 3-5.
Typical high pressure atomizing gun oil burners
(Reference 3-3).
3-21
-------
pump, ignition system, main air tube and swirlers, or retention head and
fuel nozzle(s). The fuel flowrate is controlled by the size of the
orifice in the oil nozzle, while the total air flowrate is controlled by
the blower and damper. The proper air/fuel ratio is adjusted using the
damper until minimum CO and smoke levels are achieved. Typical operating
conditions of oil-fired residential furnaces are summarized in Table 3-8.
The burner is usually mounted in a refractory or refractory felt
lined combustion chamber which is cooled by the recirculating room air.
From the combustion chamber the flue gases pass through a gas-to-air heat
exchanger and finally out the stack. Generally there is no draft diverter
in the flue because a forced draft system is used and there is no pilot
flame. The burner blower may supply the full pressure to exhaust the flue
from the stack or it may rely partially on the buoyancy forces downstream
of the furnace.
In recent years the flame retention head burner has become the
primary burner design sold. Several types are available with residential
burner manufacturers. One design is shown in Figure 3-6. These units
usually produce a more stable, compact, and intense flame and will stay in
tune (low CO and smoke) longer than previous conventional designs. This
flame retention head produces a stable flame by forming recirculation
zones in the wake of the flame retention plate. Some swirl is also
imparted to the airflow with some burner designs. Oil spray nozzles are
pressure atomized often producing a hollow or solid cone spray with a
spray angle from 50 to 80 degrees depending on the burner and firebox
design. Tuning for low emissions and high efficiency consists of cleaning
the burner and nozzle of any deposits (or replacing the nozzle), adjusting
the spark ignitors for optimum spark, and adjusting the air damper for
minimum CO, smoke and excess air.
The design of the oil-fired burner and heating system is quite
empirical and relies on prototype development, experience and testing.
Efficiency and standards for construction are set by Underwriters
-Laboratory and the American National Standards Institute (ANSI).
3.2.1.3 Gas-Fired Hot Water Units
Figure 3-7 shows a typical gas-fired hot water or hydronic heater.
New units are usually more expensive than forced air systems and therefore
are now being made in the larger capacities of 0.38 MW (130,000 Btu/hr)
3-23
-------
TABLE 3-8. TYPICAL OPERATING CONDITIONS FOR OIL-FIRED CENTRAL
AIR SYSTEMS: 29.3 kW (100,000 Btu/hr)
Typical Operating Conditions
Recirculating Air Flow: 0.38-0.57 Nm3/s (800-1200 SCFM)
Combustion Excess Air: 50-85%
Flue Exit Diameter: 0.13-0.18 m (5.0-7.0 in)
Heat Exchanger Area: 1.9-2.8 m2 (20-30 ft2)
Overall Heat Transfer Coefficient: 11-17 W/m2-K
(2-3 Btu/hr-ft2-°p)
Exit Flue Gas Temperature: 533-589 K (500-600°F)
Combustion Chamber Pressure: 12.5-50 Pa (0.05-0.2 in H20)
Temperature Rise on Air Side: 42-44 K (75-80°F)
Overall Steady Efficiency: 75-80%
3-24
-------
ELECTRODES
AIR TUBE
CHOKE
Figure 3-6. ABC Mite burner with flame retention head (Reference 3-9)
3-25
-------
galvanized and baked
ename! jacketi
massive bronze headers—
easily removable
comer sealed & interlocked
combustion chamber
high velocity water flow
100% copper
and bronze waterways
heat exchanger
inspection panel
baffles
1" integral-finned
copper tubing
modulating valve
totally enclosed
automatic controls
removable door for access to
slide out burner drawer
'precision titanium-
stainless steel burners
. '.'if-, '•'•'. ••
Figure 3-7. Gas-fired hydronic boiler (Reference 3-3)
3-27
-------
and above. However, old residential units are still quite prevalent in
the Northeastern and Northcentral regions of the U.S. The gas systems on
the new units are quite similar to the central air furnace utilizing the
naturally aspirated burners. Heat transfer area is governed by the gas
side transfer coefficient which is once again limited by the pressure drop
requirements of the naturally aspirated burners. Typical operating and
design conditions for both oil and gas systems are given in Table 3-9.
3.2.1.4 Oil-Fired Hot Water Units
Figure 3-8 shows the oil-fired hot water system. Again, although
quite prevalent in older homes in the Northeast and Northcentral States,
they are generally more costly than warm air systems and are often
manufactured in larger size ranges for new sales. These units are similar
in some respects to the oil-fired warm air central furnaces in that they
often employ a refractory lined combustion chamber followed by the heat
exchange surface.
3.2.1.5 Stoker Coal-Fired Hot Water and Warm Air Units
Most of the few existing stoker coal-fired residential systems are
underfed stoker units. A typical stoker is pictured in Figure 3-9. The
coal feed tube delivers the coal to the combustion chamber and also
supplies the combustion air. At the end of the feed screw, the coal
enters a cast iron chamber or retort where the coal is devolatized. The
retort is surrounded by a wind box that supplies combustion air to the
fuel bed through slotted holes called tuyeres. In some units, the tuyeres
rotate to help break up clinkers and push ash to the outside. Air is
supplied by the combustion air blower located under the coal hopper. The
airflow is controlled by a damper on the inlet or outlet of the combustion
air fan. Ash and clinkers are periodically removed from the outer edge of
the fuel bed with a shovel. This material raises to the surface as the
coal is fed from underneath the bed. The best coal type for a given
design depends on the design of the firebox, retort and air tuyeres.
Frequently, a given furnace is adopted to only a limited range of coal
."types.
The combustion gases pass upward either to water circulating
through a boiler or to a heat exchanger to heat recirculated room air.
These heat exchanger designs are similar to those used with oil or gas
3-29
-------
TABLE 3-9. TYPICAL OPERATING CONDITIONS FOR OIL- AND GAS-FIRED HOT
WATER BOILER WITH 29.3 kW (100,000 Btu/hr) HEAT INPUT
Gas Oil
Recirculating Water Flows, m3/hr (gpm): 0.68-3.4 0.68-3.4
(3-15) (3-15)
Excess Air, percent: 20-100 30-100
Flue Exit Diameter, m (inches): 0.09-0.13 0.09-0.13
(3.5-5) (3.5-5)
Exit Flue Gas Temp, K (°F) 505-588 477-588
Upsteam Draft Diverter: (450-600) (400-600)
Exit Flue Gas Temp, K (°F) 422-477 422-477
(Downstream Draft Diverter): (300-400) (300-400)
Combustion Chamber Pressure, Pa (in H20): 12.5-50 50
(0.05-0.2) (0.2)
Temperature Rise on Water Side, K (°F) 5.6-22 5.6-22
(10-40) (10-40)
Overall Steady State Efficiency, percent: 75-80 75-80
3-30
-------
HYDRO-WALL DESIGN
TOP CLEAN-OUT OPENINGS
Figure 3-8. Oil-fired hydronic system (Reference 3-3)
3-31
-------
TOP VIEW
SIDE VIEW
1. HOPPER
2. ELECTRIC MOTOR
3. TRANSMISSION
4. COAL FEED TUBE
5. FEED WORM
6. RETORT
7. RETORT AIR CHAMBER
8. COMBUSTION CHAMBER
9. WIND BOX AND TUYERES
Figure 3-9. Residential heater stoker assembly (Reference 3-10),
3-33
-------
except the combustion gas velocities are lower via larger exchange surface
spacing to prevent accumulation of ash.
Both the warm air or hot water systems use a barometric damper to
control draft through the fuel bed. When the stack is at negative
pressure the barometric damper allows room air to enter the exhaust
stack. From an emission perspective this is beneficial because the
naturally induced air entering the stack dilutes the stack CO and unburned
hydrocarbons which occur during transient operation.
3.2.2 Commercial Systems
The major commercial sources include gas-fired warm air systems and
gas-, oil-, and coal-fired hot water or steam systems. As noted earlier
some hot water and steam systems are also used for industrial process
steam. The sections that follow review the current design practice for
the types of units that are most popular in the commercial sector.
3.2.2.1 Warm Air Heaters
The four major types of warm air heating systems in the commercial
sector are:
t Packaged units
« Rooftop units packaged as part of central air conditioning
e Duct heaters which are also generally part of a central air
conditioning system
• Unit heaters
The packaged type units are scaled-up versions of the residential system.
They include the burner and controls, gas to air heat exchanger, air
circulation fan, draft diverter and cabinet. There is no appreciable
difference in the burner design and operation other than there may be more
flue gas distribution tubes for better heat transfer.
Rooftop heaters use either the atmospheric gas-fired combustion
system or a power gas- or oil-fired burner. The atmospheric gas burners
are identical to the burners used in residential systems-incorporating the
primary air venturi, gas distribution tubes and a gas to air heat
exchanger. Power or pressurized burners in the rooftop units are either
gas- or oil-fired. The gas burner is forced draft with a combustion air
blower, spark ignitor, fuel delivery system, and some sort of flame
retention device. The gas burner will usually fire into a large
cylindrical steel combustion chamber and the combustion gases pass through
3-34
-------
a tubular heat exchanger. In this case a draft diverter is not used. In
other power burner designs the fuel and air is premixed and distributed to
a number of exit ports in ceramic blocks. These ceramic blocks act as
flame holders radiating heat to the heat exchanger surface. Little
information is available on the emission characteristics or the population
distribution of these commercial systems, especially in relation to the
variety of burner designs just described.
The third class of commercial space heating system is the duct
heater. These are of two classes -- direct fired and indirect fired. The
indirect fired units are placed in line in an air conditioning duct. The
majority of duct furnaces are naturally aspirated gas-fired units similar
in design to warm air furnaces. The direct fired duct heater or make-up
air heater as shown in Figure 3-10 usually includes the air fan that
supplies a portion of the total air for a commercial building. These are
exclusively natural gas-fired units and the products of combustion are
combined with the air circulated to the space being heated. The burners
are unique in that they are placed in the delivery air duct and the total
room air supply passes through the burners. The hole pattern in the
burner assembly allows for a slow mixing of this diluent air thus
preventing rapid quenching of the flame and high CO levels.
The unit heater is a variation of the indirect fired duct heater.
Unit heaters are self contained systems with a fan, burner and heat
exchanger. They usually are mounted from the ceiling to supply warm air
only to the room in which they are located. These heaters, although
usually gas-fired, may also be propane or oil-fired. One type of unit
heater design, usually natural gas-fired, operates by heating ceramic
elements which in turn radiate in the infrared wavelength range to the
object or area being heated. This type of heater is frequently used where
a very localized area requires heating. In the gas-fired unit the
combustion takes place at the surface of the ceramic tile. All the
combustion air is aspirated by the gas expansion similar to warm air
-furnace burners. No combustion air blower or air circulating fan is
required. The combustion products exit directly into the room but
pollutant levels are quite low because of nearly complete combustion at
the ceramic tile.
3-35
-------
Airflow Line
Burner
FAN
HEATH) AIR
Figure 3-10.
Direct gas-fired duct heater and line burner assembly
(Reference 3-11).
3-36
-------
3.2.2.2 Hot Water or Steam Systems
In the size range of 0.1 to 2.9 MW (0.4 to 10 x 106 Btu/hr) there
are over 10 different boiler designs adapted to be either gas- or, oil-,
or coal-fired. These designs can be grouped in three major categories:
watertube, firetubes, and cast iron boilers. Figures 3-11 and 3-12 show
schematics of watertube and firetube designs, respectively. Cast iron
hydronic designs are described in Section 3.3.1.3 for residential hot
water units; commercial or industrial cast iron units are of similar
design. Both commercial watertube and firetube designs are similar to the
small industrial size boiler designs which are assessed in another NO
/\
EA report (Reference 3-12). However, a brief description of firetube and
cast iron boilers, which represent over 95 percent of the installed
conmercial hot water or steam capacity, is given. There are four major
firetube boiler designs — scotch, horizontal return tube (HRT), firebox,
and vertical.
Scotch Firetube
This boiler design, developed over 30 years ago is the most popular
of the firetube boilers. Scotch firetube boilers are available in two-,
three-, or four pass units with the boiler and furnace contained in the
same shell. The heat input capacity for these units is normally less than
2.9 MW (10 x 10 Btu/hr). They account for almost 40 percent of total
firetube capacity in this size range, and can burn a variety of fossil
fuels. However, coal-fired units are not common because of slagging and
scaling problems.
Horizontal Return Tubular (HRT)
The HRT boiler and furnace is generally lined with brick. The
boiler, which is set horizontally, rests above the refractory brick
furnace. The HRT design accounts for about 11 percent of the installed
capacity in the size category less than 2.9 MW (10 x 10 Btu/hr). The
boiler comes with two-, three-, or four-passes and can burn all types of
fossil fuels. Coal is burned on a grate.
.Firebox
The firebox design employs two- or three-passes depending on
whether the boiler is the short or compact type. Similar to the Scotch
design, the furnace is steel encased, water jacketed, and internal to the
3-37
-------
-FURNACE
TO >
ATMOSPHERE
STACK
STEAM
,\X"WV
7LAME
WATER AND STEAM
BOILER
WATER
Figure 3-11. Simplified diagram of a watertube boiler (Reference 3-2)
TO
ATMOSPHERE
STEAM OUT
Figure 3-12. Simplified diagram of a firetube boiler (Reference 3-2),
3-38
-------
boiler. Firebox units are designed with heat input capacities as high as
5.8 MW (20 x 10 Btu/hr) and have an advantage of compactness and high
efficiency. Below 2.9 MW (10 x 106 Btu/hr) they account for almost 45
percent of the total installed firetube capacity.
Vertical
With the vertical design, the firetubes are vertical instead of
horizontal as with the other designs. The tubes can be either submerged
in water or partially exposed to steam. Figure 3-13 shows the partially
exposed tube design. Submerged tube designs have been abandoned because
of their tendency to leak. Capacities of these units are generally lower
than 0.75 MW (2.5 x 10 Btu/hr) and have a maximum efficiency of about
70 percent (Reference 3-2). These units comprise less than 5 percent of
total firetube capacity.
Coal-fired systems in the size category below 2.9 MW (10 x 105
Btu/hr) are all stoker or hand fed. Three designs of watertube and
firetube coal-fired stokers, are in use -- underfed, overfed, and spreader
stokers. Underfed stokers, account for about 80 percent of coal-fired
boilers with heat input below 2.9 MW (10 x 106 Btu/hr). These units
feed raw coal from below the fuel bed. Overfeed stokers account for
approximately 10 percent of coal-fired boiler capacity. They are less
popular because of higher cost, which is about twice that of an underfeed
stoker unit. Spreader stokers account for less than 10 percent of the
capacity in the commercial size range. The coal in the spreader stoker
burns partially in suspension. Combustion is completed on a moving or
stationary vibrating grate. Further details on the stoker designs are
given in the NO EA report on industrial boilers (Reference 3-12).
A
3.2.2.3 Cast Iron
The commercial cast iron boiler consists of an assembly of cast
iron sections with water or steam on one side and combustion gases on the
other. Frequently the cast iron surface is either ribbed or studded to
provide extended heat transfer surface area. The size of the boiler is
determined by the number of sections sandwiched together. Although these
units are more expensive than firetube boilers, they are also more
reliable, durable, and require less maintenance. As with residential
units they are usually naturally aspirated when fired with gas, or fitted
with a gun type oil burner.
3-39
-------
Figure 3-13. Exposed-tube vertical boiler (Reference 3-2).
With a gas-fired unit the entire bottom of the boiler is open to
allow combustion air to be drawn into the unit by the draft of the flue
gases. With oil firing, a firebox cavity is built into the unit and the
system is intended to be sealed. Design and construction of these units
are governed by ASME Boiler Code for pressurized vessels and are tested
and rated by the Hydronics Institute. The Hydronics Institute provides an
Industrial Boiler Rating (IBR) in accordance with minimum efficiency,
percent CCL, flue gas temperature, and smoke emissions.
3.3 AREAS OF ENVIRONMENTAL CONCERN
This section identifies areas of environmental concern for the
residential, commercial and industrial combustion equipment types with
heat input capacities of 0.1 to 2.9 MW (0.4-10 x 106 Btu/hr). Major
pollution streams identified here are then quantified in Section 4.
Table 3-10 sunmarizes pollution streams from these combustion units. As
indicated, combustion products exiting the stack constitute the major
environmental concern for all equipment types. For coal-fired equipment,
ash disposal is also an area of environmental concern due to quantities of
ash generated and some potentially toxic constituents in the ash. Leakage
3-40
-------
TABLE 3-10. EMISSION STREAMS FROM RESIDENTIAL AND COMMERCIAL UNITS
Emission Streams
Gas- and 01l-F1red Systems
Residential Commercial
Residential Residential & Commercial Hot Water
Warm A1r Hot Water Direct Fired and Steam
Furnace Heater Heater Boilers
Coal- and Wood-Fired Systems
Residential
Warm Air
Furnace
Commercial
Residential Hot Water
Hot Water and Steam
Heater Boiler
Remarks
Combustion products
from the stack
Major pollutants 1n the flue
gas Include NOX, HC, and
CO. In addition, part leu late
(smoke) and SOX when
burning oil or coal.
Combustion products
leakage Into heated
air
Combustion products leakage
across heat exchanger with
some older units. Some
leakage from ducts into
surrounding space also
possible.
Solid ash waste
disposal
Ash wastes to disposal site.
Potentially Teachable trace
elements In the ash. Major
concern with coal.
Combustion products
mixed with heated
air
Direct fired heaters are
primarily gas fired. Major
pollutants are NO,, CO,
and HC.
Fuel Supply
leakage
Leakage of gas and oil only
an accidental occurrence.
Coal dust as fugitive
emissions.
M — major pollutant stream
m — minor pollutant stream.
-------
of combustion products into habitated areas may occasionally cause
environmental concern with some older units. These three streams — stack
emission, combustion products leakage, and solid waste -- are briefly
discussed below.
3.3.1 Stack Emissions
Pollutant emission of NO , CO, and unburned hydrocarbons (UHC) in
A
varying concentrations are emitted from the stack along with H^O, C02,
N2, and oxygen for all fuels burned. Levels of sulfur and inorganic
compounds, negligible with natural gas and distillate oil combustion, are
significant when residual oil and coal are burned. Sulfur and ash in the
residual oil and coal convert to S02 emissions and particulate matter
respectively and exit with the flue gas. Air pollutant emissions from
coal are often emitted in greater quantity than emissions from gas and oil
combustion. Conversion of fuel bound nitrogen in the coal contributes to
emissions of NO , which are generally higher than those of units fired
A
with gas or oil. Also carbon monoxide as well as nonmethane hydrocarbon
emissions from coal are often higher than those from gas and oil
combustion.
The largest emission levels of CO, UHC, and smoke occur during
lightoff and shutdown periods. Because of the cyclic nature of most
heating systems, the furnace often never reaches equilibrium condition.
The CO, UHC, and smoke problem associated with cyclic operation is further
aggravated when the system is oversized. In such cases, cycle frequency
is usually higher with a correspondingly low on-period.
3.3.2 Leakage of Combustion Products
Leakage of the combustion products into the heated space may occur
in a number of areas in the furnace system. Of primary importance is the
possibility of leakage across the heat exchanger of a warm air furnace.
Many gas utilities will shut off the gas supply to a unit that has visible
cracks in the heat exchanger. Overall, unless residential heating
equipment is relatively old, leaks are not a serious environmental concern.
In a home installation the house air is usually recirculated from
the rooms to the furnace and back to the rooms. If there is leakage from
the furnace system potentially the air quality in the rooms would
deteriorate. However, usually there is sufficient make-up air in
buildings through leaks in windows, doors, etc., to prevent this problem.
3-42
-------
As greater emphasis is given to energy conservation and the sealing of
leaks into the house (air infiltration accounts for the largest load in
residential heating) attention should be paid to the air quality within
the home. Sufficient air must always be brought into the home for the
combustion process. In commercial systems frequently make-up air is
brought into a building so that a certain number of ambient air changes
per hour is maintained. Some commercial heating systems also rely on an
outside air supply for combustion.
3.3.3 Solid Waste Streams
The solid waste stream (although intermittent) in the form of
bottom ash clinkers is of environmental concern for coal-fired residential
and commercial size units. These clinkers usually find their way to a
refuse disposal site in urban areas where trace contaminants in the ash
can be leached out by rainfall. In rural areas they are usually buried or
disposed in a local waste disposal site where leaking can also occur.
3-43
-------
REFERENCES FOR SECTION 3
3-1- "General Housing Characteristics for the United States and Regions;
1976," U.S. Department of Commerce, Bureau of Census, Current
Housing Reports, Series H-150-76, Part A, U.S. G.P.O. Washington,
D.C. 1978.
3-2. Devitt, T. et al., "The Population and Characteristics of
Industrial/Commercial Boilers," EPA 600/7-79-178a,
NTIS-PB-80-150881, August 1979.
3-3. Brown, R. A., et al.. "Feasibility of a Heat and Emission Loss
Prevention System for Area Source Emissions," EPA-600/2-76-097,
NTIS-PB 253 945, April 1976.
3-4. "Gas Engineers Handbook," American Gas Association, Industrial
Press Inc., New York, NY, 1969.
3-5. "1972 ASHRAE Handbook of Fundamentals," American Society of
Heating, Refrigerating, and Air-Conditioning Engineers Inc., New
York, NY, 1972.
3-6. "1972 Equipment Volume/ASHRAE Guide and Data Book," American
Society of Heating, Refrigerating and Air-Conditioning Engineers
Inc., New York, NY, 1972.
3-7. Strock, C., and R. L. Koral, "Handbook of Air Conditioning,
Heating, and Ventilating," Industrial Press Inc., New York, NY,
Third Edition, 1965.
3-8. "Research on Effect of Ambient Pressures in Combustion Chambers of
Contemporary Appliances on Primary Air Injection and Oth.er Gas
Burner Operating Conditions," American Gas Association Committee on
Domestic Gas Research, Research Report No. 1080, Arlington, VA,
June 1947.
3-9. Hall, R. E., et al.. "A Study of Air Pollutant from Residential
Heating Systems," EPA-650/2-74-003, NTIS-PB 229 697, January 1974.
3-10. "Domestic Stokers, Hopper and Bin Feed by Will-Burt," Manufacturer
Brochure. Form W346-75-2M, The Will-Burt Co., Orrville, OH, 1975.
3-11. "Maxon -- Burner Equipment and Valves for Industry," Manufacturer
Brochure, Maxon Premix Burner Company, Inc., Muncie, Indiana,
August 1969.
3-12. Urn, K. J. et al., "Industrial Boiler Combustion Modification NOX
Control: Volume I. Environmental Assessment." EPA-600/7-81-126a,
July 1981.
3-44
-------
SECTION 4
CHARACTERIZATION OF FUELS, PRODUCTS AND AIR EMISSIONS
This section surmiarizes the physical and chemical characteristics
of fuels burned and waste streams (primarily flue gas) for residential and
commercial heating systems described in Section 3. A recent air pollutant
emission inventory is also presented for selected systems.
4.1 SUMMARY OF SAMPLING AND ANALYTICAL ACTIVITIES
Activities to quantify air pollution emissions and determine
control potential in residential/commercial heating have centered
primarily on residential heating furnaces and commercial steam and hot
water units. Less is known of the emissions of various commercial warm
air heating systems.
Table 4-1 surmiarizes major laboratory and field studies performed
on residential and commercial heating equipment. The table lists the
specific type of equipment tested, the organization performing and
sponsoring the work, the completion date of the study and the principal
pollutants sampled. Information on the emission controls investigated is
also listed. Major results of these studies will be reviewed in the
following sections of this report.
As the table indicates, the bulk of the sampling and analytical
activity for the gas-fired residential and commercial space heaters and
boilers has been sponsored by the EPA and by the American Gas Association
Laboratories (AGAL). Some work specific to oil-fired systems has been
jointly sponsored by the American Petroleum Institute (API) and the EPA.
Tests primarily related to energy consumption and conservation (with
limited emission data taken) were not included in this table. These tests
have been performed for the National Science Foundation (NSF), Federal
Energy Administration (FEA), and the Department of Energy (DOE).
4-1
-------
TABLE 4-1. SUWARY OF MAJOR SAMPLING AND ANALYTICAL ACTIVITIES
ON RESIDENTIAL AND COMMERCIAL HEATING SYSTEMS
-£»
I
General
Equipment
Category
Gas -Fired
Indirect Heating
Specific*
Equipment
Tested
SFB, FFB, FAF
FAF
HUB
FAF
FAF, HWB, VH
USH, HH
FAF, CIB, SFB,
FFB, WB
Organ ization
Performing Work
Battelle
Columbus Labs.
American Gas
Association (AGA)
The Research
Company (TRC)
American Gas
Association (AGA)
American Gas
Association (AGA)
Battelle
Columbus Labs.
Sponsoring
Organization
American Petroleum
Institute (API)
American Gas
Association (AGA)
American Gas
Association (AGA)
Gas Appliance
Manufacturers
Association (GAHA)
American Gas
Association (AGA)
American Petroleum
Institute (API)
and EPA
i
Completion
Date
1971
1975
1974
1978
1974
1973
Emissions FvaluatM
N0x
X
X
X
X
X
X
CO
X
X
X
X
-
X
X
HC
X
X
X
X
X
S0x
X
X
Part.
X
X
X
Smoke
X
X
Trace
f, 1 emen t s
Organ ics
i
Pollution
Controls
Tuning
Radiant
screens
secondary
air
baffles
None
None
Radiant
screens
secondary
air
baffles
and burner
mods
Tuning,
replace..
burner
Ref .
4-1
4-2
4-3
4-4
4-S
4-6
•Specific equipment tested
SFB = Scotch Firetube Boiler
FFB = Firebox Firetube Boiler
HWB = Hot Water Boiler
VH = Vented Heater
WS = Wood Stove
USH = Unvented Space Heater
WH - Wall Heater
WB = Watertube Boiler
BSFB = Bituminous Stoker Firetube Boiler
FP = Fireplace
FAF = Forced Air Furnace
CIB = Cast iron boiler
-------
TABLE 4-1. Continued
-P.
oo
General
Equipment
Category
Gas-Fired
Indirect Heating
(continued)
Gas-Fired
Direct Heating
Oil-Fired
Indirect Heating
Specific*
Equipment
Tes ted
FAF, HHB
FAF
UVH
FAF, HB, SFB,
FFB
Maxon Makeup Air
Burners
SFB, FFB, FAF
CIB, HWB, HH
FAF, HHB, HH,
SFB, FFB, CIB,
HB
Organization
Performing Work
EPA
Lawrence
Berkeley Labs.,
U.C.
The Research
Corp. (TRC)
TRW
IGT
Battelle
Columbus Labs.
Battelle
Columbus Labs.
-i
Sponsoring
Organization
EPA
ERDA (DOE)
EPA
EPA
Maxon
American Petroleum
Institute (API)
API and EPA
Completion
Date
1974
1976
1974
1979 -
Ongoing
1969
1971
1973
Emissions Evaluated
NO,
X
X
X
X
X
X
X
CO
X
X
X
X
X
X
X
HC
X
X
X
X
X
S°x
X
X
X
X
Part.
X
X
X
Smoke
X
X
X
X
Trace
E 1 emen t •;
X
Organics
X
Pollution
Controls
Burner
and
combust-
tion mods
None
None
None
None
None
Tuning,
Replace-
ment and
burner
mods.
Ref.
4-7
4-8
4-9
4-10
4-11
4-12
4-1
4-6
*Specific equipment tested
SFB = Scotch Firetube Boiler
FFB * Firebox Firetube Boiler
HHB = Hot Hater Boiler
VH = Vented Heater
WS * Hood Stove
USH = Unvented Space Heater
HH = Hal I Heater
HB = Hatertube Boiler
BSFB = Bituminous Stoker Firetube Boiler
FP = Fireplace
FAF = Forced Air Furnace
CIB = Cast iron boiler
-------
TABLE 4-1. Continued
General
Equipment
Category
Oil-Fired
Indirect Heating
(continued)
Specific*
Equipment
Tested
FAF. HWB
FAF
HWB
WH, FAF
FAF
FAF
FAF
SFB
Organization
Performing Work
EPA
U.S. Oept. of
H.E.W.
Langley Research
Center
Canadian Combus-
tion Research
Lab. (CCRL)
Rocketdyne Div.
Rockwell Inter-
national
Acurex
EPA
Sponsoring
Organ ization
EPA
NAPCA/EPA
NASA
Canada Centre
for Mineral and
Energy Technology
EPA
EPA
EPA
Completion
Date
1974
1970
1976
1978
1976 to
1979
1979
1975 to
1979
Emissions Evaluated
N0x
X
X
X
X
X
X
CO
X
X
X
X
X
X
HC
X
X
X
X
S0x
X
Part.
X
X
Smoke
X
X
X
X
X
Trace
Elements
X
X
Organics
X
X
Pollution
Controls Ref.
Burner & 4-7
combus-
tion mods.
Flame re-
tention
burner 4-13
None 4-14
Water-oil 4-15
emulsion
Burner & 4-16
furnace 4-17
develop- 4-18
ment 4-19
Low emis- 4-20
sion high
efficiency
furnace
Water- 4-21
oil 4-22
emulsion 4-23
I
-p>
*Specific equipment tested
SFB * Scotch Firetube Boiler
FFB = Firebox Firetube Boiler
HUB = Hot Water Boiler
VH = Vented Heater
WS = Wood Stove
USH = Unvented Space Heater
WH = Wall Heater
WB = Hatertube Boiler
BSFB = Bituminous Stoker Firetuhe Boile
FP = Fireplace
FAF = Forced Air Furnace
CIB = Cast iron boiler
-------
TABLE 4-1. Concluded
General
Equipment
Category
Oil-Hred
Indirect Heating
(continued)
Coal-Fired
Indirect Heating
Wood -Fired
Indirect Heating
Specific*
Equipment
Tes ted
FAF
FAF, KB
SFB, FFB
BSFB
FAF, HWB
FAF, HWB
WS, FP
WS
Organization
Performing Work
EPA
TRW
Battelle
Columbus Labs
Monsanto Research
Corporation
Battelle
Columbus Labs
Monsanto Research
Corporation
Battelle
Columbus Labs
Sponsoring
Organization
EPA
EPA
EPA
EPA
Bituminous Coal
Research (BCR)
EPA
EPA
Completion
Date
1980
1979 to
ongoing
1976
1978
1978
1980
Ongoing
Emissions Evaluated
NOX
X
X
X
X
X
X
CO
X
X
X
X
X
X
HC
X
X
X
X
X
S°x
X
X
X
X
X
X
Part.
X
X
X
X
X
X
Smoke
X
X
X
X
Trace
Elements
X
X
X
X
X
Organ ics
X
X
X
X
X
X
Pollution
Controls
None
None
Coal
Switching
None
Furnace
Develop-
ment
Tuning
Process
Modifi-
cations
Ref.
4-24
4-10
4-11
4-25
4-?6
'4.? 7
4-28
4-29
•Specific equipment tested
SFB = Scotch Firetube Boiler
FFB = Firebox Firetube Boiler
HWB = Hot Water Boiler
VH = Vented Heater
WS = Wood Stove
USH = Unvented Space Heater
WH = Hal! Heater
WB = Watertube Boiler
BSFB = Bituminous Stoker Firetube Boiler
FP = Fireplace
FAF = Forced Air Furnace
CIS = Cast iron boiler
-------
A large number of the test programs listed in Table 4-1 were
performed under laboratory conditions allowing for the monitoring of many
test parameters. Carbon monoxide (CO), unburned hydrocarbons (UHC),
NO , S(L, smoke, and filterable particulate matter were the principal
X c
pollutants of interest tested. Trace metals and organic emissions were
determined primarily with coal and wood combustion.
4.2 FUELS
Over 90 percent of residential furnaces and small commercial
heaters burn natural gas or distillate oil. Residual oils which require
heating for efficient atomization and combustion are generally burned in
the larger commercial equipment. Coal is still used in some residential
furnaces and hot water heaters. The increasing scarcity of the cleaner
gas and distillate oil fuels has renewed interest in coal and wood firing
for residential and commercial applications. However, economic and
environmental considerations still dictate the use of natural gas or
distillate oil as the primary fuels for the small residential systems.
4.2.1 Gaseous Fuels
Natural gas is the most common fuel for residential and conmercial
space heating and commercial hot water or steam production. Approximately
55 percent of the residential and comnercial equipment with heat input
less than 2.9 MW (10 x 106 Btu/hr) is fired with this fuel. Natural
gas, which is relatively clean burning and easy to handle, is the primary
fuel used for direct fired commercial heaters in which the combustion
products are mixed directly with heated air. However, some oil-fired
portable direct space heaters are being used commercially mainly for
construction jobs, garages, barns, etc.
Primary air pollutants emitted from gas-fired units include NO ,
/\
CO, and hydrocarbons. Particulate matter and sulfur oxides are generally
minimal and do not pose an environmental concern. Other gaseous fuels
used in the residential sector include bottle butane or propane, also
known as liquid petroleum gas (LPG). Nearly half of domestic LPG
-consumption is for warm air furnaces and steam and hot water hydronic
boilers.
The continuously rising cost of natural gas may in the future lead
to significant use of electric heat or alternate gaseous fuels for
residential and comnercial space heating. One such alternate fuel is the
4-6
-------
high Btu gas produced from the gasification of coal. High Btu gas, also
referred to as synthetic natural gas (SNG), is a pipeline quality gas
essentially identical in composition to natural gas. Thus, SNG can use
the same distribution and combustion system now being used for natural
gas. However, at present, there is no commercial high Btu gas plant
supplying pipeline networks carrying natural gas. The Lurgi methanation
process has been demonstrated to be the most technically feasible of all
high Btu gasification processes. However, high capital and operating
costs may preclude the commercial availability of this alternate gaseous
fuel until the late 1980's. In the meanwhile, as natural gas supplies
become increasingly scarce, it is possible that more industrial users will
be made to switch to alternate fuels to leave sufficient natural gas for
existing residential and commercial heating installations.
4.2.2 Liquid Fuels
Liquid fuels for residential heating are almost entirely distillate
oils, while commercial and industrial units in the size range of 0.1 to
2.9 M
oils.
2.9 MW (4 x 105 to 10 x 106 Btu/hr) burn both distillate and residual
There are various grades of fuel oil available today in the United
States. These oils are classified according to their physical
characteristics as shown in Table 4-2. Grades No. 1 and No. 2 are
distillate oils while Grades No. 5 through No. 6 are residual oils. The
table also describes low sulfur residual oil which is a fuel growing in
popularity, especially in those areas with stringent sulfur emission
regulations. Grade No. 4 oil can be either a distillate or a mixture of
distillate and residual oil (Reference 4-34). The No. 2 fuel oil accounts
for about 75 percent of the distillate fuel consumption in residential
heating systems. The remainder of the domestic oil demand is met with
No. 1 grade oil (Reference 4-35). Residual oil accounts for about
60 percent of all oil burned in commercial and industrial equipment with
heat input less than 2.9 MM (10 x 106 Btu/hr) (Reference 4-36).
Methanol and water-in-oil emulsions have also been investigated as
alternate liquid fuels for residential and commercial space heating
equipment. Methanol is currently produced from the synthesis of natural
gas. However, there is currently strong interest in methanol generation
4-7
-------
TABLE 4-2. FUEL OIL DESIGNATION AND TYPICAL CHARACTERISTICS
(Reference 4-30)
4=.
I
00
Grade*
No. 1
No. 2
No. 3
No. 4
No. 5 Light
No. 5 Heavy
No. 6
Low-Sulfur
Residb
Description and Application
Light distillate oil Intended for vapori-
zing pot-type burners. Seldom used for
pressure-type oil burners or comnercial
burners.
Medium distillate oil for general pur-
pose domestic and commercial heating
equipment.
Obsolete grade designation.
Heavy distillate oil that may contain
some residual oil. Suitable for firing
most commercial burners.
Light residual oil for commercial-
Industrial burners. Generally contains
a larger blended portion of distillate
oil than No. 5 Heavy. Usually requires
preheat for burning but not for handling.
Medium-viscosity residual fuel oil for
commercial-Industrial burners. Usually
requires preheat for burning.
High-viscosity grade of residual fuel
oil for the largest comnercial-
indjs trial burners with full preheating.
Sometimes referred to as "Bunker S".
Residual fuel oil for commercial-
industrial burners that is refined or
blended to meet local sulfur regulations
Preheating Requirement Viscosity Range
For Pumping
and Handling
No
No
-
Usually
Noc
Usually
Noc
Usually
Noc
Yes
Usually
Noc
For
Burning
No
No
-
Usually
Noc'd
Usually
Yesc
Yes
Yes
Usually
Yesc
Saybolt Universal
at 100°Fe
—
33-38 SSU
(35)
-
45-125 SSU
(80)
125-300 SSU
(200)
300-900 SSU
(550)
900-9000 SSU
(5000)
45-9000 SSU
Typical
API Gravity
Sec. at 60°Ff
42
35
-
19
IB
16
13
~~
'Grade numbers No. 1, No. 2, No. 4, No. 5 (light), No. 5 (heavy), and No. 6 are ASTM designations (Reference 4-31).
''"Low-sulfur resld" is a recent term used to describe residual oil grades recently shipped to meet local regulations;
it is essentially replacing No. 5 and No. 6 where sulfur regulations are 1n effect, for example, along the East
Coast. (The sulfur content of this grade of fuel oil is generally 1 percent, or less.) The viscosity of present
low-sulfur resid is in the range of No. 5 (Reference 4-32). (It is not clear what the viscosity of these fuels
may be in the future.)
cPreheating requirement depends on pour-point and viscosity in relation to climate.
^May require heating for burning when using mechanical atomization.
eViscosity limits specified by ASTM 0396-75 for number grade shown. Range for low-sulfur resid is estimated.
Average viscosity for U.S. refined fuels from ERDA Heating Oils Survey, 1975 (Reference 4-33) is shown in brackets
and is presented as a typical value.
fAverage API gravity for U.S. refined fuels from ERDA Heating Oils Survey, 1975 (Reference 4-33).
-------
from biomass. Combustion of methanol in an experimental hot wall furnace
produced approximately 75 percent less NO than distillate oil
/\
combustion (Reference 4-37).
Water-in-oil emulsions have been investigated as a means to
increase efficiency of residential furnaces as well as to reduce NO
^
emissions. NO emission levels from emulsions with approximately
/\
50 percent water in distillate oil by mass approached the levels obtained
from methanol combustion (Reference 4-38). The EPA program also tested
emulsions in one residential and one commercial unit using three
commercially available water/oil emulsifiers (References 4-21, 4-22, and
4-23). The laboratory study concluded that NO , smoke and particulate
A
mass are reduced while CO and HC were not significantly affected using up
to 32 percent water-in-oil emulsions. Efficiency dropped sharply when the
percentage of water in the emulsion exceeded 18 percent. NO reductions
/\
ranged from about 15 to 50 percent depending on the type of emulsifier and
source used. With water/residual oil emulsion tests, no significant
effects on NO, SOp, HC or CO emissions were reported (References 4-22
and 4-23). The little change in NO emissions compared to tests with
distillate oil was attributed to the ineffectiveness of water emulsion in
reducing fuel nitrogen conversion to NO Particulate mass emissions
«
decreased with increasing percent water in the residual oil (up to
30 percent water in oil was tested) (Reference 4-22). However, the total
amount of fine particulate emissions was found to increase
(Reference 4-23). Boiler efficiency changes varied from +1 to -7 percent
with excess air levels set at emission smoke limits for both oil only and
water-in-oil tests (Reference 4-23).
Recent studies on two residential heating systems showed that over
10 percent water content in the distillate oil is impractical because it
leads to increased CO emissions (Reference 4-15). Furthermore, the
increase in combustion efficiency with 10 percent water content was found
to be modest (less than 2.6 percent). This slight improvement in
efficiency does not warrant operating difficulties such as ignition
difficulties, pump failures, combustion instabilities and corrosion of
water-in-oil emulsions (Reference 4-15). These results agree with EPA
test results.
4-9
-------
4.2.2.1 Physical Properties
Viscosity is the primary physical property of fuel oils affecting
equipment operation and emissions. Viscous oils, No. 2 distillate and
higher grades need to be atomized to form small droplets which can mix
thoroughly with combustion air and burn efficiently and completely. The
energy required to break up the oil in these droplets depends on the
surface tension of the oil and the mean diameter of the desired droplet.
Viscous residual oils have higher surface tensions, thus requiring more
energy to achieve the same degree of atomization as a distillate oil.
This is accomplished by heating the fuel to about 350 K (206°F) for
No. 6 oil prior to atomization. In burners designed exclusively for
kerosene and No. 1 distillate oil, the oil is generally not atomized but
is prepared for burning solely by vaporization.
Three main methods of atomization are used in commercial
boilers — air, pressure and rotary atomization. Pressure atomization is
used in about half of all commercial boilers, while air and rotary
atomization methods are evenly divided among the remaining burner types
(Reference 4-6). Steam atomization, which is prevalent with residual oil
combustion, is not common in the small commercial size boilers.
The high-pressure atomizing gun oil burner is the most widely used
residential heater distillate oil burner, accounting for over 90 percent
of the total population (Reference 4-6). Low pressure and vertical rotary
atomized burners are two other types of distillate oil-fired burners for
residential heating.
Fuel oil viscosity and atomization methods have a significant
effect on particulate and smoke emissions. A recent study of emissions
from commercial hot water and steam boilers indicated that combustion of
the heavier, more viscous fuels (i.e., lower API gravity) yielded higher
emissions of smoke and filterable particulates under baseline operating
conditions (Reference 4-39), as Figure 4-1 indicates. The heavier fuels
also tend to have higher ash content, however the ash was found to be only
partially responsible for the increase in particulate emissions.
Heavy viscous oils are also higher in molecular weight and have a
lower percentage of hydrogen; they tend to form coke, especially with
cyclic burner operation. This characteristic of residual oils makes for
increased burner maintenance to clean carbon deposits. Carbon coking on
4-10
-------
12.0
£(100)
en
o
o
o
0>
to
13
O
•M
S_
D-
O)
JO
J_
o>
9.0
(75)
6.0
(50)
3.0
(25)
No4
Fuel Oil Grades
No6
10 15 20 25 30 35 40
API Gravity
Figure 4-1. Effect of API gravity on parti oil ate emissions
(Reference 4-39).
the oil gun tip can lead to insufficient fuel-air mixing and consequent
emissions of particulate and soot.
4.2.2.2 Chemical Properties
Sulfur and nitrogen concentrations in the fuel oil affect emissions
of SO and NO respectively. Essentially all of the sulfur in the
^ "
fuel oil converts to gaseous SOp and SO., during combustion. However,
only 40 to 60 percent of the nitrogen in residual fuel oil is generally
converted to NO (Reference 4-37). For low nitrogen content distillate
oil the conversion can be as high as 100 percent. Heavier oils often
"contain more nitrogen and sulfur than distillate oils, contributing to
higher NO and SO emission levels.
Certain constituents (impurities) present in most fuel oils are
noncombustible and form residual ash. Most fuel oil ash results from
4-11
-------
contaminants present in the crude oil, with a minor fraction due to
contamination occuring during handling or refining. Heavier fuels contain
the most ash. The composition of fuel ash, particularly from residual
oils, may include trace elements. Some of these elements are toxic and
may adhere to aerosols emitted with combustion products. Distillate No. 2
oil contains very little ash and trace elements as compared with No. 6
residual oil. Because residential or commercial sources have generally
low stack heights, the ground level concentration of these toxic elements
in the immediate area of a residential or commercial heating plant burning
residual oils may be significant.
In a study by the Langley Research Center on a commercial heating
plant burning residual oil, it was found that toxic trace elements, Zn,
Mo, Ag, Pb, and to a lesser extent Cd, tended to concentrate on small
aerosols in the inhalable size range (Reference 4-14). The study
concluded that combustion of residual oils in commercial heating equipment
could cause toxic element concentration in the vicinity of the plant to be
above safety levels established by the National Institute for Occupational
Safety and Health (NIOSH). Therefore, either higher stacks for improved
dispersion of these aerosols or combustion of cleaner distillate oils
would be necessary to maintain low ambient trace element concentration.
4.2.3 Solid Fuels
Coal and wood are the principal solid fuels burned in combustion
equipment with heat input capacity less than 2.9 MW (10 x 10 Btu/hr).
Coal-fired warm air and hot water units represent only about 1 percent of
the total residential heating equipment installed in 1976 (Reference 4-40).
Coal for residential heating is either stoker or hand fed. In the
commercial size sector, coal is more widely used contributing nearly
12 percent of the total installed commercial steam and hot water capacity
(Reference 4-36). Coal combusted in this size category is all stoker
fed. Combustor designs allow the use of a variety of coals. However,
bituminous and anthracite are the primary coal types burned.
Equipment population statistics for wood-fired heaters and
commercial boilers are not readily available. Two recent EPA test
programs characterized emissions from wood-fired stoves and fireplaces.
In addition control variables which affect these emissions were identified
and investigated to the extent that they could be varied (References 4-28
4-12
-------
and 4-29). The residential wood combustion source category will be
reviewed separately in a subsequent effort of the NO EA program.
With the increasing scarcity and escalating cost of clean fuels,
coal is being reconsidered as contributing a larger share of the fuel
supply for commercial as well as residential space heating. Additionally,
existing advanced designs of residential coal-fired equipment allow for a
relatively automatic combustion of coal. However, the air pollution
impact of widespread coal-fired residential heating will certainly be
significant. Under adverse meteorological conditions, the air quality in
residential areas heated with coal is expected to degrade significantly to
the point that National Ambient Air Quality Standards (NAAQS) could be
exceeded solely due to the residential equipment (Reference 4-41).
The following subsections highlight some of the physical and
chemical characteristics of coal which affect emissions and equipment
operation.
4.2.3.1 Physical Properties
Test results of two EPA-sponsored studies on coal combustion in
residential size stokers indicate that physical properties of coals were
the main parameters affecting the composition and quantity of air
pollutants (References 4-25 and 4-26). Stoker operation and on-off
cycling did not prove as significant on air pollutant emissions as did the
varying physical properties of the coals tested.
The free swelling index, volatile content, and coal size are the
primary coal properties that affect the emissions of particulates, smoke
and polynuclear organic material (POM). The effect of coal ash content on
these emissions was found to be of secondary importance.
The free swelling index is a measure of the caking property of
coals. High volatile bituminuous coals have high free swelling index and
thus, they tend to cake on stoker bed and form large clinkers. These
clinkers do not permit a uniform distribution of combustion air which
leads to higher emissions of particulate (smoke), CO, hydrocarbons and POM.
Figure 4-2 shows the effect of the free swelling index on
particulate emissions measured in two test programs on residential stoker-
fed heaters. Anthracite and western subbituminous coals with free
swelling indices less than 1 did not cake, permitting a more uniform air
4-13
-------
c
o
^ 6.0
8.0
(16.0)
_ 7.0
(14.0)
6.0
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o
i—
£ 5.0
"- (10.0)
c
10 4.0
? (8-0)
ce
«r
o.
o
CO
3.0
(6.0)
2.0
(4.0)
1.0
(2.0)
35". to 40% COAL VOLATILE CONTENT
22',, COAL VOLATILE CONTENT
WESTERN SUBBITIMINOUS COAL
WESTERN SUBBITIMINOUS COAL (Ref.
BATTELLE STUDY, EASTERN BITUMINOUS COAL 4-25)
BATTELLE STUDY, WESTERN SUBBITUMINOUS COAL (Ref.
BATTELLE STUDY, ANTHRASITE (Ref. 4-22) 4'25)
I I I I I 1
0123456 78
Free swelling index of coal
Figure 4-2. Effect of free swelling index on boiler particulate
emissions (Reference 4-26).
distribution throughout the bed. Particulate emissions averaged 10 to 30
percent of particulate emission levels from bituminous coals.
The high volatile content of bituminous coal also tended to produce
high levels of particulate, smoke, and POM emissions during tests on
residential units. POM levels were highest during the "off" portion of
the cycle when the low bed temperature and lack of combustion air did not
permit combustion of tars released from the coal bed. Figure 4-3 shows
the effect of volatile content on particulate emissions. Anthracite,
shown in Figure 4-2, with a volatile content of about 4 percent registered
the lowest particulate emissions, 0.15 g/kg coal (0.3 Ib/ton coal). High
volatile bituminous coals emitted the highest particulate levels. High
particulate emissions were also accompanied by higher smoke and POM
emissions. Coal size and ash content have a less pronounced effect on
_particulate, smoke and POM emission from residential size heaters.
However, a large amount of fines in the coal tended to increase
particulate emissions during the "on" cycle. This was attributed to the
combustion air carrying the light particles to the flue.
4-14
-------
8.0
(16.0)
> 7.0
£(14.0)
(12.0)
LJ
«I
CZ.
S
5.0
vlO.O)
4.0
(8.0)
3.0
(6.0)
2.0
(4.0)
1.0
(2.0)
o
CD
Free swelling
Index 5.7-1/2
Free swelling
Index = <1
• WESTERN SUBBITUMINOUS COAL
• WESTERN SUBBITUMINOUS COAL
A BATTELLE STUDY, EASTERN BITTUMINOUS COAL
V BATTELLE STUDY, WESTERN SUBBITUMINOUS COAL
(Ref. 4-25)
(Ref.4-25)
H f-
I
I
20
25 30 35
VOLATILE CONTENT OF COAL, %
40
45
Figure 4-3. Effect of coal volatile content on boiler particulate
emissions (Reference 4-26).
These emission levels indicate that anthracite is the most
desirable coal type for residential and small commercial heating
equipment. However, availability of anthracite is limited, while
bituminous coal is much more abundant and is indigenous to many eastern
states. Western subbituminous coals and processed lignitic (smokeless)
coals were investigated as alternatives to the combustion of bituminous
coals in residential furnaces and boilers. As indicated in Figures 4-2
and 4-3 these coals have generally lower free swelling indices but, except
for the smokeless coal, also have about the same amount of volatile matter
as bituminous coals. Overall, subbituminous coals were found to be less
polluting than bituminous coals and thus, in the absence of anthracite,
are more desirable as fuels for residential and commercial heating
equipment (Reference 4-23).
4.2.3.2 Chemical Properties
Coal contains a significant amount of elemental metals of which a
-portion are released to the atmosphere during combustion. The rest is
removed from the boiler with the bottom ash. De Angel is and Reznik
reported that in general less than 10 percent of trace metal species in
4-15
-------
the coal find their way to the atmosphere through the stack, however high
volatile mercury and selenium in the flue gas measured over 50 percent of
that introduced with the coal (Reference 4-25). In another study,
Surprenant, et^ aj^, reported that at least 1 percent of the less volatile
trace metallic elements were released to the atmosphere from residential
units (Reference 4-42). These trace elements generally include lead,
cadmium, arsenic, selenium and zinc, all of which are of significant
environmental concern. Mercury, which is highly volatile, leaves the
boiler in vapor form.
Trace elements remaining in the bottom ash also constitute an
environmental concern. Some of these elements, aluminum, calcium, barium,
sodium, silicon and strontium, are leached by rainfall and can enter
potable water supplies.
With wood combustion in residential stoves and fireplaces, high
resin content combined with high moisture content of unseasoned (green)
pine wood was attributed with high particulate, condensible organic and
polycyclic organic material (POM) emissions compared with combustion of
drier and harder woods (Reference 4-28). Resinous material content and
chemical composition of soft woods, such as pine, may then have a direct
impact on the organic emission characteristics from wood combustion in
residential systems.
4.3 PRODUCT CHARACTERIZATION
The principal products of residential and commercial combustion
equipment are warm air, hot water or steam. Warm air furnaces and hot
water boilers are generally smaller than 0.1 MW (400,000 Btu/hr) heat
input capacity. Steam units are a more popular equipment category with
heat capacity above 0.4 MW (1.5 x 106 Btu/hr). For warm air
applications, hot water or steam can be used as an intermediate fluid to
exchange heat with a forced air circulating system. Steam from small
commercial size units is also used in industrial process plants.
As discussed in Section 3, direct warm air systems exhaust the flue
gas directly into the heated air for maximum thermal efficiency. Direct
heating, however, has the disadvantages of creating increased ambient
levels of NOX, CO and HC in the space being heated. These indoor areas
require good ventilation which then reduces the effectiveness of the
direct heating system.
4-16
-------
4.4 N0¥ FORMATION
/\
Two mechanisms have been identified as responsible for NO
formation during the combustion process: thermal NO formation and fuel
J\
NO formation. The following subsections surrmarize these formation
/\
concepts. A more extensive discussion is given in Reference 4-43.
4.4.1 Thermal NO Formation
Thermal NO results from the thermal fixation of molecular
^
nitrogen and oxygen in the combustion air. The detailed chemical
mechanism by which molecular nitrogen in the combustion air is converted
to nitric oxide is not fully understood. In practical combustion
equipment, particularly for liquid or solid fuels, the kinetics of the
N2~^2 system are coupled to the kinetics of hydrocarbon oxidation and
both are influenced, if not dominated, by effects of turbulent mixing in
the flame zone. It is, however, generally accepted that thermal NO
/\
forms at high temperatures in an excess of 0^. For natural gas and
light distillate oil firing, nearly all NO emissions result from
n
thermal fixation. With residual oil and coal the contribution from fuel-
bound nitrogen can be significant and may even predominate.
4-4.2 Fuel NO Formation
~~~/\
Fuel NO derives from the oxidation of the organically bound
/\
nitrogen present in certain fuels such as residual and distillate oils.
Fuel NO emissions are dependent on the nitrogen content of the fuel as
/\
well as on combustion conditions. Fuel NO formation is strongly
A
affected by the rate of mixing of the fuel and airstream in general, and
by local oxygen concentration in particular.
Fortunately, with high nitrogen fuels only a portion of the fuel
bound nitrogen is converted to NO . Barrett and Locklin investigated
/\
the contribution of fuel N to total NO emissions from oil-fired
^
commercial boilers (Reference 4-39). Their results are summarized in
Figure 4-4. As indicated, the contribution of thermal NO to total
/\
NO emissions is approximately 100 ppm. Total NO emissions steadily
X *
increase as the nitrogen content of the fuel increases. However, the
fractional conversion of fuel nitrogen decreases as the fuel nitrogen
content increases. Commonly reported conversion rates range from 40 to
60 percent for residual oils and to nearly 100 percent for distillate oils
(very low nitrogen content).
4-17
-------
450
400
350
1
|300
250
I 200
o
a 150
in"
,|
8 too
E
ui
0X 50
Symbols denote different
boilers
N
0.6
l I I I
O.I 02 0.3 04
Nitrogen in Fuel.percent
0.5
Figure 4-4. Contribution of nitrogen in fuel oil to total NOX emissions
from commercial boilers (Reference 4-39).
Fuel nitrogen conversion to NO when burning coal can range from
A
20 to 60 percent depending on the coal type and percent nitrogen in the
fuel (Reference 4-44). In addition, this conversion is highly dependent
on the fuel-air ratio. Since coal in commercial and residential equipment
is generally burned in stokers with high excess air levels, conversion of
fuel nitrogen to NO is high.
4.5 EMISSION CHARACTERIZATION
Emissions from natural gas-fired residential and commercial
combustion sources include primarily NO. CO and HC. When fuel oil or
A
-coal is burned, smoke, particulate and S0x are also emitted. The levels
of NOX, CO and HC from oil and coal combustion are usually higher than
'those from gas combustion. Figures 4-5 and 4-6 illustrate general trends
of steady-state smoke and gaseous emissions from oil-fired residential
heaters and commercial boilers, respectively, as they are influenced by
4-18
-------
2.00
1.50
. 1.00
i
0.50
0.00
Optimum settlna for minimum |
emissions and maximum
efficiency
-20
20 40 60 80 100 120 140
Excess air, %
16 11 12
10
C02, *
Figure 4-5. General trend of smoke, gaseous emissions, and efficiency
versus stoichiometric ratio for a residential oil burner
(Reference 4-7).
14
Figure 4-6.
• 10 12
Ptrctnt C0t in Flut Got
Gaseous emissions characteristic for a typical commercial
boiler as influenced by combustion air setting
(Reference 4-45).
4-19
-------
combustion air settings. For both equipment types the operating setting
corresponding to lowest emissions of CO, HC, and smoke coincides with high
NO levels. As the excess air is reduced from the theoretical setting,
A
concentrations of CO, HC and smoke increase because of lack of oxygen in
the flame and reduced turbulent mixing which leads to incomplete
combustion. At very high excess air levels, these emissions can also
increase due to the excessive combustion air which cools the flame also
resulting in incomplete combustion.
One of the major factors contributing to high combustible
emissions, particularly in domestic burners, is the transient operating
mode. The on-off cycle is a dominant characteristic of warm air furnaces,
and its importance as a cause of increased emissions has been well
documented (References 4-6 and 4-7). A typical furnace cycle is shown in
Figure 4-7. The burner is ignited at a point off the chart and, after a
minute or so, the blower starts circulating air over the heat exchanger.
Four minutes later the burner flame is extinguished, and about 5 minutes
after that the blower stops. Investigations on a model residential
heating system indicated that the sizeable peak emissions measured during
ignition and shutdown can account for most of the total combustible
emissions. Figure 4-8 shows qualitative emission traces from an oil
burner during a typical cycle. CO and HC emissions peak at ignition and
shutoff. HC concentration drops to insignificant levels between the
peaks, while CO emissions tend to flatten out at a measurable level.
Parti cul ate emissions continuously taper off after the ign it ion-induced
peak, whereas NO emissions first rise rapidly for a short period and then
continue to rise at a more moderate rate as the combustion chamber
temperature increases. The operating time of most domestic burners
seemingly is not long enough for NO to reach equilibrium levels.
The transient emissions are caused mainly by variations in the
combustion chamber temperature. At ignition, a cold refractory will not
assist complete combustion and, therefore, peaks of CO, HC, and smoke can
-occur. In addition to the cold refractory, wear and tear of the oil pump
can cause poor shut-off performance, hence high smoke and combustible
emissions. This problem can be minimized by the use of solenoid valves in
the fuel tube (delayed on-instant off), the placement of this valve nearer
to the burner tip, and the use of smaller diameter tubes.
4-20
-------
Fire
stops
Area represents
unused heat
Extrapolated
to zero
temperature
rise
Blower time in minutes
Figure 4-7.
Temperature rise across an oil-fired warm air furnace
heat exchanger during a typical cycle.
4-21
-------
Filterable
Participate
NO
Burner
On
I I
Burner
,0ff
Time
Time
HC
Burner
On
I 1
Burner
Off
CO
Burner
Off
Tine *
Time -
Figure 4-8.
Characteristic emissions of oil burners during
one complete cycle (Reference 4-7).
4-22
-------
In general, with the exception of SO emissions which depend
/\
entirely on the sulfur content of the fuel, all other criteria pollutants
are primarily a function of burner nozzle type, combustion chamber shape
and material, and operating practice. The following subsections highlight
some of these parameters and how each affects the various criteria
pollutant emissions.
4.5.1 Nitric Oxide Emissions
Nitric oxide production from fuel oil combustion is highest in high
temperature turbulent diffusion flames rich in excess oxygen. NO
A
emissions from residential heaters, which burn primarily natural gas and
distillate oil that is relatively low in fuel nitrogen content, are due to
thermal NO . The oxidation of molecular nitrogen in the combustion air
depends on residence time and temperature. The higher temperatures and
long residence times promote production of thermal NO. Fuel/air ratios
have less effect on thermal NO production than on fuel nitrogen
conversion, which is highly affected by excess oxygen availability during
pyrolysis of fuel nitrogen compounds.
4.5.2 Carbon Monoxide and Hydrocarbon Emissions
Both CO and HC are products of incomplete combustion. Steady-state
and cyclic combustible emissions in small residential and commercial
sources have been attributed to excessive firing rate (or input rate) and
lack of scheduled maintenance. A field survey concluded that a large
majority of oil-fired residential heating systems have an excessive firing
rate which leads to high stack losses and reduced seasonal efficiency
(Reference 4-46). Oversized residential heaters cycle more frequently
because the heating load is met quickly and the furnace shuts down.
During the ignition and shutdown periods, emissions of CO and HC are high
because of flame quenching from the cold wall. A reduction in burner
capacity (i.e., lower firing rate) reduces these emissions significantly
and increases the overall cycle efficiency of the units. Residential
burner performance can usually degrade with time; if so, the furnace emits
-umeccessarily high levels of combustible CO and HC. Improper burner
adjustment may cause flame impingement or reduced stoichiometry which lead
to incomplete combustion. Scheduled burner maintenance by skilled
servicemen remedies this problem.
4-23
-------
4.5.3 Smoke and Particulate Emissions
Smoke and particulates from oil-fired residential and commercial
units consist primarily of carbon participate (soot) which is a product of
incomplete combustion. These emissions increase with short furnace
residence time and cold wall furnace effect. Short furnace residence time
is characteristic of small size combustion chambers of conventional
residential heaters. Larger fireboxes can help reduce particulate
emissions by as much as one-fourth (Reference 4-7). Combustion chambers
of domestic oil burners are usually made of hard refractory, ceramic felt
material or steel. The temperature of a refractory lined chamber reaches
steady state with combustion gases faster and retain the heat longer than
steel chambers. Therefore, residential oil burners with ceramic lined
chambers emit lower particulate and smoke than do steel chambers. During
the time in which chamber temperature is low, however, excess air levels
must be increased to counteract the poor combustion due to low
temperature. Since it has not been practical to allow for altering the
amount of excess air during a heating cycle, the initial high air level is
maintained throughout, resulting in low thermal efficiency.
4.5.4 Emission Factors and Emission Inventory
Emission factors together with fuel consumption were used to
calculate total 1977 emissions from combustion sources having heat input
capacity less than 2.9 MW (10 x 106 Btu/hr) (Reference 4-47). As
discussed earlier, this site category also includes a significant number
of boiler equipment used in industry in addition to those used for
residential and commercial heating. Fuel consumption and emissions in
Table 4-3 are presented by end use. As indicated, fuel consumption data
for residential systems were obtained directly from the Department of
Energy (Reference 4-48). Fuel consumption for the industrial and
commercial sources with heat input capacity less than 2.9 MW (10 x 106
Btu/hr) was calculated using equipment installed capacity and load factors
estimated in a recent EPA-sponsored study (Reference 4-36).
Gas- and distillate oil-fired residential systems contributed the
most to total NO emissions from these sources. This is due to the fuel
A
'consumption for residential heating which accounted for nearly 65 percent
of the total fuel consumption.
4-24
-------
TABLE 4-3. ESTIMATED 1977 AIR POLLUTANT EMISSIONS FROM STATIONARY
FUEL COMBUSTION SOURCES WITH HEAT CAPACITY LESS THAN
2.9 MW (10 x 106 8tu/hr)a
Sector
Residential0
Residential
and Commercial
Equipment
Harm air central
furnaces
Harm air space
heaters
Miscellaneous
combustion
Steam and hot
water heaters
Fuel
Natural gas
Distillate
oil
Natural gas
Distillate
oil
Natural gas
Distillate
oil
Natural gas
Distillate
oil
Residual oil
Coal
Total Capacity
MW (106 Btu/hr)
--
-
--
--
--
-
--
-
-
--
Fuelb
Consumption
EJ (Quads)
1.876C
(1.979)
1.354C
(1.428)
0.57C
(0.60)
0.42C
(0.44)
1.524C
(1.608)
0.926C
(0.977)
2. 1C
(2.2)
1.4C
(1.5)
0.11C
(0.12)
0.043C
(0.045)
Air Pollutant Emissions Gg (103 tons)
NO,
65.7
(??. 5)
33.8
(37.3)
19.9
(21.9)
10.5
(H-6)
53.3
(58.8)
27.4
(30.2)
82.8
(91.3)
77.9
(85. 9)
17.5
(19.3)
7.1
(7.8)
CO
19.0
(20.9)
33.8
(37.3)
5.7
(6.3)
10.5
(11.6)
15.2
(16.8)
27.4
(30.2)
17.8
(19.6)
41.7
(46.0)
1.64
(1.81)
7.53
(8.30)
HC
6.40
(7.10)
6.40
(7.06)
1.94
(2.14)
1.97
(2.17)
5.20
(5.73)
5.15
(5.68)
4.76
(5.25)
13.4
(14.8)
2.74
(3.02)
2.12
(2.34)
Particulates
7.50
(8.27)
10.3
(H-4)
2.30
(2.54)
3.20
(3.53)
6.10
(6.73)
8.33
(9.19)
16.6
(18.3)
10.6
(11.7)
9.09
(10.0)
150.2
(165.6)
so,
0.49
(0.54)
146
(161)
0.15
(0.17)
45.4
(50.1)
0.40
(0.44)
118.4
(130.6)
0.62
0.68
150.2
(165.6)
52.6
(58.0)
30.7
(33.8)
ro
en
"Based on data from References 4-36, 4-47, and 4-48.
bEJ * 1018 Joules = 0.948 Quads * 0.948 x 10lb Btu
cFuel consumption for residential units was obtained from Department of Energy (Reference 4-48).
-------
TABLE 4-3. (Concluded)
Sector
Commercial
and Industrial
TOTAL
Equipment
Cast Iron
boilers
Hatertube
boilers
Flretube
boilers
All equipment
Fuel
Natural gas
Distillate
oil
Residual oil
CM!
Natural gas
Distillate
oil
Residual oil
Coal
Natural gas
Distillate
oil
Residual
oil
Coal
All fuels
Total Capacity
»l (106 Btu/hr)
143,520
(489,495)
33,730
(115.041)
53,790
(183,456)
31,590
(107,742)
5,770
(19,679)
4.490
(15,313)
5,240
(17,872)
1,900
(6,480)
79,090
(269,748)
31,530
(107,538)
48.200
(164,393)
14,420
(49.181)
--
Fuelb
Consumption
EJ (Quads)
1.8
(1.9)
0.35
(0.37)
0.47
(0.50)
0.097
(1.0)
0.053
(0.056)
0.021
(0.023)
0.015
(0.016)
0.012
(0.013)
1.358
(1.433)
0.37
(0.39)
0.354
(0.374)
0.11
(0.116)
15.22
(16.97)
Air Pollutant Emissions Gg (103 tons)
NO,
91.7
(101.1)
23.7
(26.1)
84.6
(93.3)
14.6
(16.1)
3.16
(3.5)
1.18
(1.3)
2.38
(2.6)
3.0
(3.3)
31.0
(34.2)
12.8
(14.1)
30.7
(33.9)
14.1
(15.6)
708.8
(781.6)
CO
35.3
(38.9)
0.56
(0.61)
0.66
(0.73)
21.3
(23.5)
1.06
(1.17)
0.06
(0.07)
0.02
(0.02)
0.91
(1.00)
15.2
(16.8)
0.34
(0.38)
0.29
(0.32)
5.40
(5.95)
261.4
(288.3)
HC
4.06
(4.18)
3.34
(3.68)
11.8
(13.8)
5.53
(6.10)
0.18
(0.20)
0.01
(0.01)
0.07
(0.08)
0.19
(0.21)
1.75
(1.93)
2.05
(2.26)
5.12
(5.65)
3.40
(3.75)
87.6
(96.6)
Partlculates
6.88
(7.59)
4.18
(4.61)
13.2
(14.6)
314.3
(346.6)
0.05
(0.05) -
0.18
(0.20)
0.42
(0.46)
23.5
(25.9)
3.02
(3.33)
2.57
(2.83)
5.73
(6.32)
130.0
(143.4)
728.3
(803.1)
SOX
0.53
(0.58)
37.6
(41.5)
225.6
(248.8)
110.6
(122.0)
0.02
(0.02)
3.27
(3.61)
6.70
(7.39)
16.0
(17.6)
0.23
(0.25)
18.7
(20.6)
92.1
(101.61)
91.8
(101.2)
1,148.1
(l,26fi.O)
ro
-------
REFERENCES FOR SECTION 4
4-1. Levy, A., et al., "A Field Investigation of Emissions From Fuel Oil
Combustion For Space Heating," American Petroleum Institute
Publication 4099, November 1971.
4-2. Thrasher, W. H., and D. W. De Werth, "Evaluation of the Pollutant
Emissions From Gas-Fired Forced Air Furnaces," American Gas
Association Research Report No. 1503, May 1975.
4-3. Brookman, G. T., and Kalika, P. W., "Measuring The Environmental
Impact of Domestic Gas-Fired Heating Systems," presented at the
67th Annual Meeting of the Air Pollution Control Associati
(APCA), Denver, Colorado, June 1974.
4-4. "NOX Emissions of Seven Furnaces Predominant in the California
Area," Report by the American Gas Association Laboratories (AGAL)
to the Gas Appliance Manufacturers Association (GAMA) in response
to the California imposed Model Rule, August 1978.
4-5. De Werth, D. W., and R. L. Himmel, "An Investigation of Emissions
From Domestic Natural Gas-Fired Appliances," presented at the 67th
Annual Meeting of the Air Pollution Control Association (APCA),
Denver, Colorado, June 1974.
4-6. Barrett R. E., et al., "Field Investigation of Emissions From
Combustion Equipment For Space Heating," EPA-R2-73-084a (API
Publication 4180), NTIS-PB 223 148, June 1973.
4-7. Hall, R. E., et al., "A Study of Air Pollutant Emissions From
Residential Heating" Systems," EPA-650/2-74-003, NTIS-PB 229 697,
January 1974.
4-8. Hollowell, C. D., et al., "Combustion-Generated Indoor Air
Pollution I. FielTMeasurements 8/75 - 10/75," LBL-4416, UC-11,
TID-4500-R63, January 1976.
4-9. Cote, W. A., et al., "A Study of Indoor Air Quality,"
EPA-650/4-74-M2, NTIS-PB 238 556, September 1974.
4-10. Surprenant, N. F., et al., "Emission Assessment of Conventional
Stationary Combustion Systems: Volume 1. Gas- and Oil-Fired
Residential Heating Sources," EPA-600/7-79-029b, NTIS-PB 298-494,
May 1979.
4-11. Personal communication with Don Price, TRW Inc., Redondo Beach, CA,
August 16, 1979.
4-27
-------
4-12. Hama, G. M., "Report of Test For Carbon Monoxide and Other
Contaminants on a Maxon Premix Series RG-IV Airflow Burner,"
Certification Tests by the American Board of Industrial Hygiene,
Akron, OH, January 1969.
4-13. Howekamp, D. P., "Flame Retention — Effects on Air Pollution,"
U.S. Department of Health, Education and Welfare, presented at the
Ninth Annual Convention of National Oil Fuel Institute, Atlantic
City, New Jersey, June 1970.
4-14. Singh, J. J., ert a/L_, "An Investigation of Size-Dependent
Concentration of Trace Elements in Aerosols Emitted From the
Oil-Fired Heating Plants," NASA Technical Memorandum TMX-3401,
Norfolk, VA, July 1976.
4-15. Whaley, H., et a!., "Energy Conservation and Emissions From Two
Residential "Furnaces Using an Emulsified Water-in-Oil Fuel,"
Presented at the 71st Annual Meeting of the Air Pollution Control
Association (APCA), Houston, Texas, June 1978.
4-16. Combs, L. P- and A. S. Okuda, "Commercial Feasibility of an Optimum
Residential Oil Burner Head," EPA-600/2-76-256, NTIS-PB 259 912,
September 1976.
4-17. Combs, L. P. and A. S. Okuda, "Residential Oil Furnace System
Optimization Phase II," EPA-600/2-77-028, NTIS-PB 264 202,
January 1977.
4-18. Okuda, A. S. and L. P. Combs, "Field Verification of Low-Emission
Integrated Residential Furnaces," in the Proceedings of the Third
Stationary Source Combustion Symposium, EPA-600/7-79-050a,
NTIS-PB 292 539, February 1979.
4-19. Okuda, A. S. and L. P. Combs, "Design Optimization and Field
Verification of an Integrated Residential Furnace Phase 1,"
EPA-600/7-79-037a, NTIS-PB 294 293, February 1979.
4-20. Higginbotham, E. B., "Combustion Modification Controls for
Residential and Commercial Heating Systems: Volume II. Oil-fired
Residential Furnace Field Test," EPA-600/7-81-123b, July 1981.
4-21. Hall, R. E., "The Effect of Water/Distillate Oil Emulsions on
Pollutants and Efficiency of Residential and Commercial Heating
Systems," Presented at the 68th Annual Meeting of the Air Pollution
Control Association, Boston, MA, June 1975.
4-22. Hall, R. E., "The Effect of Water/Residual Oil Emulsion on Air
Pollutant Emissions and Efficiency of Commercial Boilers," ASME
Publication 75-WA/APC-l, July 1975.
4-28
-------
4-23. Beard, J. T. and Robert E. Hall, "Performance and Air Pollutant
Emissions of an Experimental Water/Residual Oil Emulsion Burner in
a Commercial Boiler," EPA Draft Report, Research Triangle Park,
North Carolina, September 1979.
4-24. Personal Conmunication with Robert E. Hall, U.S. EPA, Research
Triangle Park, North Carolina, May 27, 1980.
4-25. Giammar, R. D., et al_., "Emissions From Residential and Small
Commercial Stoker-Coal-Fired Boilers Under Smokeless Operation,"
EPA-600/7-76-029, NTIS-PB 263 891, October 1976.
4-26. De Angelis, D. G. and R. B. Reznik, "Source Assessment: Coal-Fired
Residential Combustion Equipment Field Tests, June 1977,"
EPA-600/2-78-004o, NTIS-PB 283 699, June 1978.
4-27. Engdahl, R. B., "Cross-Feed Combustion For Clean Burning of Solid
Fuels For Residences," Presented at the 71st Annual Meeting of the
Air Pollution Control Association (APCA), Houston, Texas, June 1978.
4-28. De Angelis, D. G., et al_., "Preliminary Characterization of
Emissions from Wood-Fired Residential Combustion Equipment,"
EPA-600/7-80-040, NTIS-PB 80-182066, March 1980.
4-29. Personal comnunication with Robert Hall, U.S. EPA, Research
Triangle Park, NC, November 25, 1980.
4-30. Locklin, D. W. and R. E. Barrett, "Guidelines for Burner
Adjustments of Commercial Oil-Fired Boilers," EPA-600/2-76-088,
NTIS-PB 251 911, March 1976.
4-31. "Specifications for Fuel Oils," ASTM D-396-75, ASTM Standards for
Petroleum Products (Part 17), American Society for Testing and
Materials, Philadelphia, PA, 1975.
4-32. Siegmund, C. W., "Low-Sulfur Fuels are Pifferent," Hydrocarbon
Processing. Vol. 49, No. 2, pp. 89-95, February 19775".
4-33. Shelton, E. M., "Burner Fuel Oils," Bartlesville Energy Research
Center, BERC/PPS-75/2, Bartlesville, OK, August 1975.
4-34. Schmidt, P. F., "Knowing How Oil Behavior Makes For Better
Operation," Power, Vol. 118, No. 10, p. 28, October 1975.
4-35. Offen, G. R., et al^, "Control of Particulate Matter From Oil
Burners and Boilers," EPA-450/3-76-005, NTIS-PB 285 495, April 1976.
4-36. Devitt, T., et aj^, "The Population and Characterization of
Industrial/Conroercial Boilers," EPA 600/7-79-178a,
NTIS-PB/80-150881, August 1979.
4-29
-------
4-37. Martin, G. B., "Evaluation of NOX Emission Characteristics of
Alcohol Fuels in Stationary Combustion Systems," Presented at the
Joint Meeting, Western and Central States Sections, The Combustion
Institute, San Antonio, Texas, April 1975.
4-38. Martin, 6. B., "Environmental Considerations in the Use of
Alternate Clean Fuels in Stationary Combustion Processes," in
Symposium Proceedings: Environmental Aspects of Fuel Conversion
Technology (May 1974, St. Louis, MI), EPA-650/2-74-118.
NTIS-PB 233 304/AB, October 1974.
4-39. Barrett, R. E., and D. W. Locklin, "Field Investigation of
Emissions From Commercial Boilers," Presented at the 69th Annual
Meeting of the Air Pollution Control Association (APCA), Portland,
Oregon, June 1976.
4-40. "General Housing Characteristics for the United States and Regions;
1976," U.S. Department of Commerce, Bureau of Census, Current
Housing Reports, Series H-150-76. Part A, U.S. G.P.O.,
Washington, DC, 1978.
4-41. Weber, R. C., "Impact on Local Air Quality From Coal-Fired
Residential Furnaces," Presented at the 71st Annual Meeting of the
Air Pollution Control Association, Houston, Texas, June 1978.
4-42. Surprenant, N., et aJL, "Final Report, Volume II: Preliminary
Emissions Assessment of Conventional Stationary Combustion
Systems," EPA Contract 68-02-1316, Task Order II, GCA Corp.,
Bedford, MASS, March 1976.
4-43. Mason, H. B., et al., "Preliminary Environmental Assessment of
Combustion Modification Techniques. Volume II, Technical Results,"
EPA-600/7-77-119b, NTIS-PB 276/AS, October 1977.
4-44. "Air Quality and Stationary Source Emission Control," U.S. Senate,
Committee on Public Works, Serial No. 94-4, March 1975.
4-45. Locklin, D. W. and R. E. Barrett, "Guidelines for Burner
Adjustments of Conrnercial Oil-Fired Boilers," EPA-600/2-76-088,
NTIS-PB 251 911, March 1976.
4-46. Bonne, U., et al_., "Effect of Reducing Excess Firing Rate on the
Seasonal Efficiency of 26 Boston Oil-Fired Heating Systems,"
Presented at Conference on Efficiency of HVAC Equipment and
Component II, Purdue University, Indiana, April 1975.
4-47. Waterland, L. R., et al., "Environmental Assessment of Stationary
Source NOX ControlTecFnologies -- Final Report," Acurex Draft
Final Report FR-80-57/EE, EPA Contract No. 68-02-2160, Acurex
Corp., Mountain View, CA,.April 1980.
4-48. Personal conmunication with Charles Allen of the Department of
Energy, Washington, DC, on preliminary data from EIA Annual Report
to Congress, May 1, 1979.
4-30
-------
SECTION 5
PERFORMANCE AID COST OF CONTROLS
This section discusses the performance and cost of various control
options applicable to gas-, oil-, and coal-fired residential systems.
Controls for each of these equipment categories are discussed in three
separate sections according to the fuel burned. Control technology
developed specifically for NO emission reduction are also highlighted
^
and discussed separately from controls specifically developed for other
pollutants. Published costs and energy considerations of these controls
are also summarized for each fuel category. All costs are in 1978 dollars
unless otherwise indicated. Discussion of emission control technology for
commercial steam and hot water boilers is limited because of lack of
investigative efforts in this area. However, technology transfer from the
small industrial boiler sector is discussed.
5.1 EMISSION CONTROL ALTERNATIVES FOR GAS-FIRED RESIDENTIAL SYSTEMS
NO emission control techniques for gas-fired residential furnaces
/\
have been investigated since the early 1970's by the American Gas
Association Laboratories (AGAL), the Gas Appliance Manufacturers Association
(GAMA), and the EPA. Early work by AGAL quantified the variation of NO ,
^
CO, and hydrocarbon emissions from gas-fired residential units according to
burner type and firebox design. This work showed that multiport gas burners
were found to emit approximately 25 percent higher NO than single port
rt
burners (Reference .5-1). This was attributed to a compact, intense flame
front with the multiport burners which promotes NO formation. Single
n
port burners have larger burner flame volumes which result in fewer high
intensity temperature regions to promote NO formation (Reference 5-2).
A
Some observations were also made by AGAL on the effect of primary air
setting (primary aeration) and heat exchanger material on NO emissions.
^
These effects were generally found to be less important than burner design
(Reference 5-1).
5-1
-------
5.1.1 Nitric Oxide Control
Because NO emissions from combustion of natural gas are from
A
thermal NO formation, control techniques are aimed at controlling flame
temperature, residence time, and oxygen availability at the high temperature
flame region. Five major NO control options have been identified for
^
residential gas-fired warm air furnaces and hydronic boilers. These control
options are:
t Radiant screens
t Secondary air baffles
• Modulating combustion cycle
t Heat transfer module (HTM)
• Surface combustion burner (Bratko type)
• Catalytic combustors
The following subsections discuss the NO reduction performance,
n
applicability and cost of each of these control options.
5.1.1.1 Radiant Screens
Himmel and De Werth of AGA originally reported that infrared gas
burners emit lower nitric oxides than conventional type burners (Reference 5-2),
Incandescent radiant screens in a natural gas flame tend to approach the
level of infrared burners by radiating heat to the surroundings and
cooling the flame. An inverted "V" screen was placed above the tubular
multiport burner and extended the length of the burner. For a single port
upshot burner, a circular screen was placed around the burner. Both
arrangements are illustrated schematically in Figure 5-1.
Table 5-1 summarizes the performance of radiant screens on three
warm air furnaces. As shown, the NO was reduced from 36 to 76 percent
rt
with an average reduction of 58 percent. The radiant screen performance
was more significant with tubular multiport burners. Similar results were
obtained in other warm air furnaces when burners were modified by
installation of radiant screens. In general, this control technique was
also found to increase steady-state furnace efficiency slightly due to
increased flame and burner radiation.
AGAL, however, warns that the radiant screen concept, although
workable, needs further investigation to assess its durability in the
flame, its potential deterioration or deformation and overall safety.
Some concerns were also published in a recent GAMA report in response to
5-2
-------
Inverted "v"
screen (extends the
length of the burner)
Cross-sectional
view of tubular
burner
Flame
diverter
Burner
(a)
For multiport tubular burner
(b)
For single port upshot burner
Figure 5-1. General arrangements of screens for gas-fired residential
burners (based on illustrations from Reference 5-1).
TABLE 5-1. EFFECT ON CO AND NOX EMISSION OF PLACING RADIANT SCREEN
IN BURNER FLAME (Reference 5-1)
Unit Sample C02
Percent
FAF 23 — Tubul
No Screen
Screen
FAF 25 -- Tubul
No Screen
Screen
FAF 9 — Single
No Screen
Screen
ar Multiport
8.50
8.30
ar Multiport
7.70
7.75
Port Upshot
4.05
4.05
Flue Gas Concentration
ppm, (0% 02)
CO NO N02 NOX
14
15
8
11
with
15
44
104.9
23.4
76.7
21.5
0
1.6
3.7
3.4
104.9
25.0
80.5
24.9
NOX
Percent
Change
-76%
-69%
Flame Spreader
61.3
37.3
1.6
3.0
62.9
40.3
-36%
FAF = Forced Air Furnace
5-3
-------
the recommendations by the California Air Resources Board (CARB) for the
potential commercial application of radiant screens to control NOX from
warm air furnaces (References 5-3 and 5-4). Some of the potential
problems presented by GAMA included sensitivity of performance to screen
location, effect on CO emissions, and deterioration.
The screen design and location in or around the burner are critical
to its performance. Figure 5-2 illustrates how NOX reductions can
drastically vary with location of the screen. This sensitivity precludes
retrofit application to existing units unless they are made by skilled
service appliance personnel. GAMA also indicated that CO emissions can
increase significantly with the application of screens, even with furnace
manufacturer-suggested air settings. Furthermore, if these air settings
were to become misadjusted during installation or servicing, unacceptable
CO emissions would result. Test results by GAMA summarized in Table 5-2
show that CO increased above 1000 ppm with natural gas and a liquified
natural gas. With regard to screen durability it is expected that the
cycling operation of the residential equipment would impose numerous
thermal shocks to the screens which could eventually deform or break.
Screen deterioration could lead to loss in performance and/or excessive CO
and HC emissions.
60
55
I 5°
£ 40
35
No Screen
2.5
5.0
7.5
10.0 on
1.0 2.0 3.0
Portion of screen tbove Meker Burner Port
4.0 In.
Figure 5-2.
Effect on NOX emissions of placing a screen in the flame
of a Meker Type burner (Reference 5-3).
5-4
-------
TABLE 5-2. EFFECT OF A RADIATING SCREEN FROM A FURNACE OPERATED ON
CLEVELAND NATURAL AND ALGERIAN LNG (Reference 5-3)
Test Conditions
A -- Unmodified Burners
— Manufacturer's recommended setting
— "Hard" flame setting
~ "Soft" flame setting
B — Inverted "V" 10 x 10 mesh inconel
screen added to burners with manu-
facturers suggested air shutter
setting
C ~ Same as "B" except air shutters
wide open (hard flame)
D -- Same as "B" except air shutters
closed (soft flame)
Steady State Flue Gas
Concentration, ppm Air Free
Cleveland
Natural Gas
NOX
70
72
63
31
33
36
CO
10
109
693
30
1000+
1000+
Algerian Gas
NOX
65
—
--
28
28
32
CO
10
--
--
480
1000+
1000+
5.1.1.2 Secondary Air Baffles
The effect of the secondary air baffle is to control secondary
airflow into the flame front. Decreasing excess oxygen availability at
peak temperatures with reductions in secondary airflow was found to reduce
NO emissions on the order of 10 to 40 percent (Reference 5-1).
However, NO reductions without increases in CO emissions were generally
/\
limited to about 15 percent. The effect of the secondary air baffle was
found to be sensitive to its geometry and positioning with respect to the
burner port. Therefore, concerns expressed by GAMA with this technique
are similar to those pointed out for the radiant screen control option.
5-5
-------
Furthermore, it is not clear whether the secondary air baffles can be
applied to all types of residential burner designs.
5.1.1.3 Modulating Furnace
The modulating furnace also tested by AGAL is a commercially
available residential heater design. The furnace differs from
conventional units in that the firing rate is altered to respond to the
heating load demand instead of cycling on and off. In this manner, the
furnace is essentially derated, yielding a cooler flame which apparently
leads to lower NO emissions. The reported NO emission factor for
x /-X
this furnace design is 24.9 ng/J.(0.058 lb/10 Btu) (Reference 5-1).
This corresponds to about a 40 percent reduction from emission levels of
conventional furnaces.
GAMA indicated that this reduction in N0¥ mass emission achieved
/\
with the modulating furnace was due to the single-port inshot burner type
used originally rather than the reduced heat input rate as indicated by
AGAL (Reference 5-3). However, it can be speculated that elimination of
the on-off cycle should reduce combustible emissions because CO and UHC
emission peaks characteristic of ignition and shutdown would decrease.
However, no emission data are available to substantiate this hypothesis.
5.1.1.4 Heat Transfer Module (HTM)
The HTM by Amana shown in Figure 5-3 has been commercially
available for about 6 years. The design includes a perforated burner
located in the center. The natural gas mixes with air through the many
holes of the burner and burns at the burner surface. The heat is
transferred to an intermediate glycol solution in small tubes imbedded in
a close fitted fin arrangement surrounding the burner. The glycol then
transfers heat to room air. The HTM is used for both heating and air
conditioning and is designed for outdoor installations. One additional
important feature of the HTM furnace is the lack of a pilot. The flame is
spark ignited instead of using a pilot flame. Thus seasonal fuel
consumption is reduced compared with pilot ignition furnaces. NO
emissions reported by AGAL averaged 7.74 ng/J.(0.018 lb/106 Btu) which
corresponds to an emission reduction of about 80 percent from conventional
•warm air furnace design (Reference 5-1).
5-6
-------
The I Exclusive
Here's how it works:
Gas (natural or propane) Is pulled front
the gas valve by the combustion blower
into the HTM* HearBsetia«gef-burner.
The burner Is only 4* high x 2" 1n-
diameter,
A spark plug ignites the gas ami air
mixture in the burner. No wasteful, both-
ersome pilot light. Wind does not affect
its operation,
•A flame probe monitors the bower to
five proof of combustion, If combustion
doesn't'lake-pjaee, the ffam® probe wlH*
close the gas vaive within 15 seconds.
The stainless steel burner provides 9000
tiny fiames which produce extremely
hot ffoe gases.
These 0830$ passing through the por-
ous matrix create high turbulence to
produce rapid heat transfer. Exclusive
porous matrix is made up of thousands
"Of copper coated steel ball® fused to-
v..;:C3)
gether to perform the function of heat
exchange,
(§} The solution (50% water and 50% eth-
ylene glycol to, prevent freezing) carry-
ing tubes embedded in the matrix pick
up the heat and transfer the hot solu-
tion, moving at 4,7 feet per second,
through the HTM* Heat Exchanger.
(7) A limit control monitors the tempera-
ture of the solution. And, if it rises above
design temperatures, it shuts down the
system.
($} You get 7% -10% more usable heat
than industry standards (depending on
the firing rate) from the gas burned be-
cause of less heat loss through the flue.
{9} The heater keeps the temperature of
the HTM* Heat Exchanger above sur-
rounding temperature at ail times, so it
remains dry and untarnished by atmos-
pheric moisture.
Figure 5-3. Amana Heat Transfer Module (HTM)
5-7
-------
Recently, the HTM combustor has been tested by the Southern
California Gas Company. Preliminary results indicate that the Amana
design might not be capable of the 80 percent NO reduction reported by
A
AGAL. Follow-up measurements are scheduled for the near future to verify
the validity of this new finding (Reference 5-5).
5.1.1.5 Surface Combustion Burner
A schematic of the surface combustion burner by Bratko is
illustrated in Figure 5-4. This burner employs surface combustion of
premixed natural gas and air on a refractory porous material. The burner
becomes incandescent and radiates heat to an air-cooled firebox. In this
manner, the combustion zone is maintained below about 1,250 K
(1,790°F). NO emissions of about 7 ng/J (0.016 lb/106 Btu),
A
corresponding to over 80 percent reduction, have been reported with a
prototype furnace using the surface combustor (Reference 5-6). The
furnace maintains steady-state thermal efficiencies of 80 percent or more
by operating with only 10 percent excess air.
TOCONVECTIVE HEAT EXCHANGER
/VWWV
I I! ! ! I
COOLING AIR
Figure 5-4. Schematic of the Bratko Burner (Reference 5-6),
5-9
-------
The refractory surface combustion concept is not a new one. In
fact, some commercial direct fired heaters use this refractory burner
(refer to Section 3.2.2 for discussion). NO emissions data from those
^
commercial units are, however, not available.
5.1.1.6 Pulse Combustors
The concept of pulse combustion has been known since the turn of
the century. This concept, illustrated in Figure 5-5, involves combustion
in a chamber fitted at one end with mechanical flapper valves and at the
other end with an open exhaust pipe. The fuel (natural gas, propane or
light distillate) is introduced with the air through the flapper valves.
The mixture entering the chamber is ignited with an electric spark plug.
the resulting pressure of combustion closes the flapper valves and forces
the product gases through the exhaust pipe. The exhaust products leaving
the chamber in time create a negative pressure, which causes the valves to
open, in a manner similar to an internal combustion engine, thus repeating
the cycle. The most extensive application of pulse combustion was in the
German VI "buzz bomb" during World War II.
Application of the mechanical valved pulse combustor for home
heating has been studied since the early 1950's. The simplicity of
construction, compactness, and self-powered characteristic of this burner
are attractive advantages over conventional residential burners. However,
although a hydronic system using pulse combustion was commerically offered
over two decades ago, there are no marketed systems in use today
(Reference 5-7). AGAL is currently investigating pulse combustion for
residential heating using a condensing exhaust gas system. Preliminary
N0x emissions from pulse combustion of Cleveland natural gas range
between 19 and 20 ng/J (0.044 and 0.047 lb/106 Btu) (Reference 5-8).
Commercialization of a pulse combustor residential heating system is
expected in 1981 (Reference 5-8).
5.1.1.7 Catalytic Combustors
Catalytic residential combustors offer potential for very low-NO
^
emissions while maintaining good combustion efficiency (Reference 5-7).
The catalytic agent, usually in the precious metal family, promotes
combustion of the fuel at low temperatures in the range of 755 to 1,366 K
(900 to 2,000°F.). At these low temperatures, thermal NO formation is
n
significantly reduced.. Large amounts of combustion air are, however,
5-10
-------
AIR
GAS
AIR
SPARK PLUG
COMBUSTION CHAMBER
y, ,. \
Hi! :•:-:; \
V.-'W' •'.":•.
.. v--
TAILPIPE
•FLAPPER VALVES
A. STARTING OPERATION
B. EXHAUST PHASE CINLET CLOSED)
CAS
EXHAUST
PRODUCTS
AIR
C. INTAKE PHASE (INLET OPEN)
Figure 5-5. Schematic operating cycle of a pulse combustion device.
5-11
-------
required with catalytic combustors. The use of a condensing residential
system, in which the latent heat of water vaporization is recovered by
condensing the exhaust gas, is a viable option for minimizing heat losses
due to high excess air levels. Catalytic combustors are not commercially
available. However, research groups and trade organizations are now
investigating its commercial feasibility for residential warm air and hot
water systems burning natural gas. Performance and emission data for
these systems have not yet been published.
5.1.2 Carbon Monoxide and Unburned Hydrocarbon Control
Gas-fired heating appliances and commercial boilers emit some level
of CO and hydrocarbons during steady-state combustion. These levels are
generally low for well adjusted (tuned) gas burners. AGA Laboratories
reported an average CO emission level of about 8 ppm on an air-free basis
for forced air furnaces and 4 to 70 ppm for hot water and steam boilers
equipped with atmospheric gas burners. Aliphatic aldehydes expressed as
formaldehyde (HCHO) generally averaged less than 1 ppm (Reference 5-1).
The well adjusted or tuned condition of residential furnaces and
heaters equipped with atmospheric gas-fired burners can degrade with
extended use in dirty environments. The low CO blue flame, characteristic
of a tuned condition, will tend to eventually change with poor
housekeeping or long time between service. The blue flame changes to a
yellow-tip flame which is indicative of high CO emissions. AGA1 indicated
that yellow-tip gas flames, which occur during high input rates and low
primary air aeration, can be the cause of CO emissions of 200 ppm and
above (Reference 5-1).
The only practical control option available to reduce CO and other
combustible emissions from untuned atmospheric gas burners is to provide a
yearly service by skilled service personnel. During regularly scheduled
service calls, the excess combustion air, which is the primary control
variable, can be set at a correct operating range. Guidelines for
minimizing air pollution and maintaining high efficiency for gas-fired
furnaces, developed by Battelle and AGAL,. were recently published by EPA
(References 5-9 and 5-10), Figure 5-6 illustrates that the normal excess
air level for well adjusted gas-fired heaters falls between 40 and
90 percent. Excess air settings much above 40 percent will unnecessarily
reduce furnace efficiency due to more sensible heat being carried to the
5-12
-------
u
8
s
&
Incr»o»ing Combustion Air
60 40 20 6
Air Deficiency, percent
120
Excess Combustion Air, percent
9.7 8.5/^,7.3/^6.5^ 5.8
*— CO,, percent (noturoi gos)
10.7 9.8 8.5 7.6 6.7
«— C02, percent (LP Gos)
Figure 5-6.
Effect of air adjustment on gaseous emissions for a
typical atmospheric gas burner (Reference 5-9).
5-13
-------
stack. Reduced furnace efficiency has an adverse effect on overall mass
emissions because more fuel is burned and thus more pollutants are
generated for a given amount of heat delivered . Maximum furnace
efficiency for conventional equipment is limited to about 85 percent due
to high stack gas temperatures necessary to avoid flue gas condensation.
Typical factory adjusted residential furnaces have approximately 75 to
80 percent furnace efficiency at steady-state conditions.
As indicated in Section 4, CO and HC emissions occurring during
furnace ignition and shutdown operation can account for most of these
emissions. Therefore, one method of reducing CO and HC is to reduce the
frequency of furnace cycling. This can be accomplished by reducing the
firing rate of gas burners. Lower firing rates necessitate longer
furnace-on periods in order to deliver a given amount of heat.
Consequently, this reduces the number of on-off cycles over an entire
heating season. Reduced firing rate (or "derating") also increases the
residence time of combustion products in the firebox which tends to reduce
steady- state combustible emissions. Reduced firing rate for existing
furnaces can be accomplished by replacement of the existing burner orifice
with smaller capacity orifices. Derating can accelerate furnace corrosion
due to increased condensation during cyclic operation. This aspect can
become a practical limitation to derating existing units. For new units,
it is desirable to match closely the capacity of the furnace to the heat
load requirements of the residence. Residential heating systems in the
past have generally been oversized.
5.1.3 Cost and Energy Impact of Controls
Pending further verification of the performance of the Amana HTM,
this burner design is presently considered the best available NO
/\
control technology for gas-fired residential and commercial heaters. The
low-NOx emission concept of the HTM design can be utilized for other
furnace types according to Amana (Reference 5-4). An estimate for initial
investment of about $1,000,000 has been reported by Amana for retooling to
produce low-NO furnaces capable of meeting NO levels of 12 ng/J
(\ ^
(0.028 lb/10 Btu). Annualized cost spread over 20 years to the
consumer was reported at approximately $17 per furnace, or a cost
effectiveness of $1.80 per kilogram ($0.80 per pound) of NO reduced
A
(Reference 5-4). A more recent estimate for capital cost indicates that
5-14
-------
the HTM would cost approximately $100 more to the consumer than a
conventional warm air and air conditioning unit of comparable size
(Reference 5-11).
The incremental equipment cost for a new modulating warm air
furnace has been reported in the range of $50 to $250 (References 5-4 and
5-7). Ranges in incremental costs of pulse combustion burner and
catalytic burners have been estimated by Putnam, et a!.. at $300 to $600
and $150 to $250, respectively, for applications in flue gas condensing
systems. The incremental cost of a radiant burner (surface combustion)
was estimated to be $100 to 200 above that of a comparable noncondensing
system (1979) (Reference 5-7). Because both the pulse and surface
combustors and catalytic burner for domestic gas-fired heating are not
commercially available, these cost estimates are considered preliminary.
A yearly service call to readjust residential furnaces for low
smoke, CO and HC emissions and high efficiency was estimated at $33 to $55
(1976) for oil-fired units (References 5-12 and 5-13). This cost, which
is based on estimated labor for nozzle cleaning or replacement, filter
changes and excess air adjustment would be slightly less for gas-fired
furnaces.
Since both the Amana and Bratko burner designs maintain good
combustion efficiency at low excess air levels it is expected that NO
/\
reductions with these controls also contribute to a reduction in energy
requirement for residential heating systems. While control of combustible
emissions with burner servicing may increase energy requirements slightly
through increases in excess air setting, the overall energy impact of CO
and HC emission control for existing residential space heating equipment
is considered minimal.
5.2 EMISSION CONTROL ALTERNATIVES FOR OIL-FIRED RESIDENTIAL SYSTEMS
Oil-fired residential and commercial heating systems emit NO ,
/\
HC, and CO as well as particulates and smoke. Emission levels of these
pollutants are generally higher than those from gas-fired units. Air
pollutant control efforts for oil-fired residential equipment have been
directed at controlling combustible emissions, smoke and particulate
'(soot) as well as NO through advanced burner and firebox design and
A
improved maintenance procedures. NO controls which did not maintain
5-15
-------
low smoke and hydrocarbon emissions were generally not viewed by
investigators as reasonable alternatives.
This section discusses control alternatives to reduce these
pollutants for distillate oil-fired residential heating systems and
commercial size boilers burning distillate or residual oil. Emphasis is
placed on NO control technology for residential furnaces; however,
/\
control technology for other criteria pollutants and NOX control
techniques for commercial size hot water or steam boilers are also
discussed.
5.2.1 Nitric Oxide Control
NO control technology development for residential oil-fired
units was initially sponsored by the EPA and the American Petroleum
Institute (API) (Reference 5-14). Control alternatives developed since
these early studies include primarily new burner and firebox designs. The
most promising control alternatives for residential heaters include:
• Flame retention burners
t Controlled mixing burner head
• Integral furnace design using controlled mixing burner head
• Blueray burner
• M.A.N. burner
With the exception of the controlled mixing head and integral furnace
design, all other controls are commercially available or nearly so. The
controlled mixing burner head and furnace are undergoing field tests to
ascertain their performance, reliability and environmental impact. These
controls are discussed in the following subsections.
NO control technology for commercial size hot water or steam
A
boilers is less advanced than for residential systems. However, several
control alternatives investigated for small industrial boilers during
recent EPA sponsored field studies (References 5-15, 5-16 and 5-17) may be
applicable to the commercial-size units of the same design. For example,
the commercial size firetubes are very similar to the small packaged
industrial size firetubes. NO control techniques that have been
A
investigated for industrial firetube boilers include (References 5-15
'through 5-18):
• Low excess air (LEA)
t Flue gas recircu1 ation (FGR)
5-16
-------
• Staged combustion air (SCA)
t Low-NO burners (LNB)
A
Although F6R and SCA are very effective in reducing NOV, both
y\
techniques may be either technically impractical or too costly for
application on small commercial units. These boilers are generally
operated unattended with heat loads changing frequently. A low NO
A
burner for application on packaged boilers with heat input capacity of
less than 2.9 MW (10 x 10 Btu/hr) is currently under development
(Reference 5-19). Another LNB, developed and currently being field tested
by TRW Corporation, may be the most feasible alternative for significant
NO reductions for these units. However, the TRW LNB development has
fi
been limited to burner capacity above 2.9 MW (10 x 10° Btu/hr). TRW
representatives indicate that if a market for NO control for commercial
/\
steam and hot water boilers develops, TRW may then investigate the
potential for scaling down the industrial size burner to a commercial unit
with heat-input capacity as low as 0.15 MW (0.5 x 106 Btu/hr)
(Reference 5-20). Additional information on combustion modification NO
controls for small industrial package boilers with potential application
to commercial size boilers is given in References 5-21 and 5-22.
5.2.1.1 Flame Retention Burners
The flame retention burner head has been commercially available for
some time. Residential burners using flame retention devices accounted
for over 10 percent of the oil-fired burner designs for space heating
equipment in 1972 (Reference 5-23) and essentially all small burners
currently installed with new furnaces and boilers are flame retention
types. These devices in the form of plates, grids or cones produce a high
swirling flow which holds the flame at the retention ring. Local
recirculation zones reduce smoke emissions and allow for operation at low
excess air levels.
Laboratory experiments have shown that most flame retention burners
increase NO emissions (References 5-12 and 5-23). In a study on the
effect of burner type on emissions from a residential warm air furnace,
Hall reported NO emissions from a conventional high pressure atomizing
fi
burner at 37 ng/J as N02 (0.09 lb/10 Btu). Ten commercially
available flame retention burners were tested in the same furnace,
5-17
-------
producing NOX emissions in the range 26 to 59 ng/J as N02 (0.06 to
0.14 lb/106 Btu) (Reference 5-12). Only the ABC Mite burner model
illustrated in Figure 3-6 (see Section 3) was found to reduce NOX by
about 30 percent, from 37 to 26 ng/J, while also reducing smoke emissions
from a Bacharach number of 2.9 to 2.0 (Reference 5-12). During a field
investigation of residential systems, Barrett, et al., reported NOX
emissions from conventional burner systems, in "as-found" conditions, in
the range of 47 to 85 ng/J as N02 (0.11 to 0.20 lb/106 Btu). NOX
emissions from domestic heating systems equipped with flame retention
burners ranged between 48 and 88 ng/J as N02 (0.11 to 0.21 lb/106 Btu)
(Reference 5-23).
In general, most flame retention devices are desirable for all
conventional high pressure atomizing gun burners because they allow for
operation at low excess air levels and stay tuned longer. These two
characteristics improve furnace efficiency and reduce overall emissions
through reduced fuel consumption.
5.2.1.2 Controlled Mixing Burner Head
A controlled mixing burner head for retrofit application to
residential oil heating equipment was developed by Rocketdyne Division of
Rockwell International under EPA sponsorship (Reference 5-24). The
principal characteristics of this burner head are: (1) no flame retention
device, (2) choke diameter related quantitatively to the firing rate, and
(3) oversize internal peripheral vanes oriented at 25 degrees relative to
the blast tube axis (Reference 5-25). The choke diameter was attributed
to reducing N0x by promoting a uniform one-dimensional (plug) flow while
the internal vanes maintained low carbonaceous pollutant emissions at low
excess air operation. Figure 5-7 illustrates the details of this, burner
design.
Results of laboratory studies indicated that the controlled mixing
burner head design is feasible for commercialization and could be
retrofitted on existing residential space-heating equipment which
presently use conventional high pressure atomized oil burners. Sheet
metal stamping was found to be the best fabrication method for commercial
production of the burner head. The burners were found to operate
successfully with long life potential. NOX reduction capability was
5-18
-------
(a) External View
5DZ21-8/6/73-S1
(b) Optimum 1 al/s
Burner Head
5DZ21-8/6/73-S1A
Figure 5-7. 1 ml/s (gph) controlled mixing low-emission
residential oil burner (Reference 5-25).
5-19
-------
Investigated by testing two commercially available warm air furnaces
retrofitted with the EPA/Rocketdyne burner head. Results of the tests are
illustrated in Figure 5-8. Based on these data, Combs and Okuda estimated
that retrofit of this burner head design would reduce NO emissions by
A^
20 percent with potential increases in season-averaged thermal efficiency
as high as 5 percent (Reference 5-25).
5.2.1.3 Integral Furnace Design With Controlled Mixing Burner Head
Although appreciable NO reductions (20 percent) were achieved
/\
with the controlled mixing burner head, minimum NO emissions
J\
necessitated optimization of the entire furnace system. Under the same
EPA furnace development program, Rocketdyne developed a cylindrical
combustor to be used with the low-NO burner to produce a low emission
/\
integral furnace design. A NO emission level of 0.5 g/kg (1.0 Ib/ton)
fi
or about 11 ng/J (0.03 1b/10° Btu) heat input was set as the emission
goal for the program (Reference 5-25). The main features of the combustor
design needed to achieve this level were identified as follows
(Reference 5-26):
t Removal of approximately 20 percent of the heat input from the
firebox based on the higher heating value of the oil
• An inside combustor diameter of 0.28 m (11 inches) or greater
for a 1.05 ml of oil/s (1.0 gph)
• Long combustion chamber length for long residence time to
prevent formation of combustible emissions at low excess air
levels
The overall system utilizing the EPA/Rocketdyne combustor and
burner head plus additional energy saving features, is illustrated in
Figure 5-9. As shown, an air-cooled finned firebox was selected. The
figure also highlights other important features. Most important are the
controlled mixing (labelled optimum in the figure) burner head for
low-NO emissions at low excess air and the standby draft control used
A
to reduce energy losses during furnace "off" cycle. During laboratory
tests the prototype furnace reduced NO emissions by 65 to 70 percent to
A
about 0.63 g/kg (1.26 Ib/ton) level, short of the original program goal.
Steady-state and cyclical efficiencies averaged nearly 85 and 75 percent
respectively (Reference 5-26).
5-21
-------
Smoke < 1
Smoke > 1
W1ll1«mson Burner Head
Commercial Proto-
type Optimum Head
1.5
StolcMometHc Ratio
A. Williamson 1166-15 Furnace System
I
J.D
2.5
2n
1 5
i
/
-
i
^ Ci
\
^
'
/
1
irrle
k
S*—
^»«
\
S
I
T 1 i
Smoke * 1
Smoke >_ 1
p Bur
•ner »
-*x
^
•py»|
OptlRM
!
cad
*^
^^>
:1a1
n Hea
X
*roto
it
1
«v
type
1.0 1.5 I.
Sto1ch1owtr1c Ratio
B. Carrier 58HV-156 Furnace System
Figure 5-8. Comparative NO emissions for the controlled mixing
EPA/Rocketdyne burner head as a retrofit device in
two warm-air furnaces (Reference 5-26).
5-22
-------
Y1
ro
u>
SEALED COMBUSTION AIR SYSTEM
STANDBY DRAFT CONTROL
COMBUSTION AIR FILTER
QUIET PULSE FREE STATOR
OPTIMUM BURNER HEAD
AIR COOLED FINNED FIREBOX
Figure 5-9. EPA low-emission integrated furnace components
(Reference 5-28).
-------
Recently six units based on this prototype design were installed in
eastern U.S. residences and operated during the 1977-78 heating season.
During reported tests, NOX emissions were measured at 0.65 g/kg
(1.30 Ib/ton) of fuel burned. This NO level corresponds to an average
/\
reduction of 65 percent from levels measured with conventional furnace
designs. Steady-state and cyclical efficiencies averaged 84 and
74 percent respectively and, in general, did not degrade over the heating
season (Reference 5-29). These high efficiencies translated to
18.5 percent fuel savings when compared to the two prior heating seasons.
A second field test program is under way to assess the reliability of the
system and supplement the existing data base.
5.2.1.4 Blueray Burner
In 1973, the Blueray System Incorporated, Jericho, New York,
patented a low emission high efficiency oil-fired warm air furnace (U.S.
Patent No. 3,741,166). The Blueray furnace uses a new burner design which
produces a soft, even blue flame instead of the conventional orange-yellow
flame. Figure 5-10 illustrates a schematic of the Blueray burner
assembly. Combustion gases representing about 50 percent of the
stoichiometric air requirement are recirculated to produce smoke-free,
blue flame combustion at low excess air. Most luminous soot particles are
eliminated during the reburning. Because the blue flame burner is matched
to the combustion volume to obtain the desired recirculation pattern, the
Blueray system is available only as a burner-furnace package. Retrofit to
existing furnaces is not practical. The "blue flame" burner is sold in
warm air furnaces in two firing ranges, 0.63 to 0.79 ml/s (0.60 to
0.75 gph).
Nitric oxide emissions from a 0.79 ml/s (0.75 gph) furnace were
measured at between 25 and 35 ppm or about 0.41 g/kg (0.82 Ib/ton) of fuel
oil burned. CO emissions from the same furnace were 15 to 25 ppm and UHC
3 to 5 ppm, while smoke emissions were nearly zero (Reference 5-30). In
addition to the low-NO operation, the Blueray furnace operates at high
^
steady-state efficiency averaging 83 to 84.5 percent. The furnace
compactness and low operating noise are also desirable features.
In 1974, Underwriters Laboratory (UL) certified the 0.63 and
0.79 ml/s (0.6 to 0.75 gph) furnace as meeting the UL and ANSI standards.
Since then over one thousand furnaces have been installed in many eastern
5-25
-------
Vapon
Zone
Electrodes I "
Oil Spray
Combustion Zone
Supply
Air Supply
Flame
Front
Burner Blast
Tube
Recirculated
Products of
Combustion
Figure 5-10.
Schematic illustration of the Blueray head assembly
(Reference 5-30).
5-26
-------
states. Recently, under the current NO Control Environmental
A
Assessment (NOX EA) program, one such furnace was field tested
(Reference 5-31). Nitric oxides, CO and UHC emissions were measured
during continuous and cyclical operation. Cycles consisted of 10 minutes
on and 10 minutes off periods. Pollutant emissions in ppm measured with
20 percent excess air are listed below:
Cyclical Continuous
Operation Operation
NO, average 11 16
NO, peak 16 16
CO, average 160 25
CO, peak 2,000 25
UHC, average 23 0
UHC, peak 390 0
Cyclic NO emissions (11 ppm uncorrected) correspond to about 0.35 g/kg
(0.70 Ib/ton) of fuel burned and are lower than those reported in
Reference 5-30. Section 6 presents trace elements and organic emission
data also obtained during the NO EA test program on the Blueray
/\
furnace. These data are then compared with recently published test data
obtained by TRW for conventional distillate oil-fired residential furnaces
5.2.1.5 M.A.N. Burner
The M.A.N. burner was developed and licensed by the German Research
and Testing Laboratory for Air and Space Travel. Figure 5-11 illustrates
a schematic of the burner. Hot combustion gases are recirculated to
achieve complete combustion in a manner similar to the Blueray system.
The main difference between the two burners is that the Blueray burner
uses an "external" gas recirculation system which requires an air tight
combustion chamber to prevent air leaks. The M.A.N. burner, however,
recirculates the hot combustion gases internally within the blast tube.
This design feature may permit retrofit installation of the burner on
existing warm air furnaces.
The M.A.N. burner, which is commercially available in Europe in
firing capacities ranging from 0.53 to 0.80 ml/s (0.5 to 0.75 gph) is
being tested at the EPA Industrial Environmental Research Laboratory
5-27
-------
Seal
Oil [
Damper
Mixing
Pipe
Burner
Pipe
Figure 5-11. Schematic of the M.A.N. residential oil-fired
rocketburner (Reference 5-32).
(IERL) (Reference 5-33). Manufacturer estimates of NO emissions range
/\
from less than 20 to 50 ppm. Lowest NOX emissions are obtained with an
air-cooled blast tube. Reported CO emissions are less than 100 ppm and
smoke Bacharch number less than 1.0 (Reference 5-33).
5.2.2 Carbon Monoxide and Unburned Hydrocarbon Control
Emissions of CO and UHC from residential space heating equipment
are primarily a function of fuel consumption, cycle frequency, and excess
air levels. In general, CO and UHC emission reduction can be accomplished
by: (1) reducing fuel consumption with increased overall system
efficiency or reduced heat demand, (2) reducing the number of on-off
cycles which cause combustible emission peaks, and (3) assuring proper
normal excess air setting with tuning and scheduled burner maintenance.
The following subsections describe the implementation of these control
approaches and review published performance data.
5.2.2.1 Reduction in Fuel Consumption
Increased steady-state and cyclical thermal efficiency for
residential oil-fired heaters can best be achieved with integrated burner
and combustor system design. Advanced concepts such as the flame
5-28
-------
retention burner and the Blueray or EPA/Rocketdyne furnace design increase
steady-state efficiency primarily by achieving complete combustion at low
excess air. This increases efficiency by 5 to 10 percentage points
compared to conventional furnaces (Reference 5-26). Overall seasonal
emissions are reduced proportionally to the fuel saving.
Reduction in fuel consumption can also be accomplished by
installing energy saving devices such as chimney or duct dampers. These
devices increase cyclical furnace efficiency by reducing heat loss during
the standby portion of the heating cycle. Standby heat losses are caused
by cooling of the combustor by natural draft air circulation. During a
field study performed in Canada, chimney dampers reduced seasonal CO
emissions from two warm air furnaces by 2.4 and 19 percent, respectively
(Reference 5-34). The difference in performance between the two sources
was caused by variation in cycling frequency.
A third and most straightforward method of reducing fuel
consumption and thus CO and UHC emissions, is to turn down the thermostat
or increase thermostat anticipator settings. Overnight thermostat cut-
back by 3 to 5 K (5 to 9°F) reduced seasonal CO emissions by 9 to
27 percent (Reference 5-34). The relative performance of reduction in
fuel consumption on seasonal CO and UHC emissions depends highly on the
number of cycles the residential furnace or boiler undergoes. Furnaces
with a high cycle frequency have much higher combustible emissions than
those furnaces which are cycled less frequently. Thus, reduction in fuel
consumption is less effective in reducing seasonal CO emissions from
furnaces which cycle frequently during the entire heating season
(Reference 5-34).
5.2.2.2 Reduced Cycle Frequency
Reduced firing rate capacity and changes in thermostat anticipator
setting are the principal methods to reduce the cycling frequency of
residential heating systems. Reduced firing rate causes the furnace to
operate for longer periods to meet load requirements. Changes in
thermostat anticipator setting can result in a wider temperature "window"
in which the furnace is on and thus reduces furnace cycle frequency. To
achieve this increase in temperature window, the anticipator setting is
either increased or decreased depending on the thermostat wiring
arrangement. Both methods of reduced firing rate and change in
5-29
-------
anticipator setting independently reduce the number of times the burner is
ignited and shut off, thus reducing overall CO and UHC emissions over an
entire heating season. Furthermore, overall furnace heating fuel
efficiency to the home is increased.
Existing oil-fired residential heating systems are generally
oversized with respect to the residential load demand. A recent study of
26 residential systems (six forced warm air, 16 hot water, and four steam
or heat transfer fluid) in the Boston area by Bonne et a!., revealed that
the excess capacity of these residential oil burners averaged 147 percent
(i.e., 247 percent of design capacity) (Reference 5-35). Twelve oil-fired
burners had a minimum capacity in the range of 1.05 to 1.42 ml/s (1 to
1.35 gph) and 14 others had a capacity of greater than 1.42 ml/s
(1.35 gph) (Reference 5-36). When a reduction in firing rate of these
units was attempted by reducing the size of oil nozzles 28 percent,
however, an increase in excess air of about 37 percent was found necessary
to prevent excess smoke emissions. Soot formation was promoted by reduced
atomization efficiency with the smaller nozzles. Also smaller burners
tend to become plugged after short operating periods. Overall, Bonne, e_t
al., concluded that, even when accounting for the negative aspects of
retrofitting smaller capacity wastes on existing oversized units (such as
increased excess air, increased electrical energy consumption by the
blower motor, oil pump and system recirculating fan/pump due to longer
on-times, and higher furnace infiltration losses due to increased air flow
through the stack draft diverter), the net result was a modest decrease in
seasonal fuel consumption and cost for space heating by 5.2 and
3.7 percent, respectively (Reference 5-36).
Janssen, et al., investigated the feasibility of a thermal aerosol
generator as a residential oil burner which could operate efficiently at
firing rates reduced to as low as 0.42 ml/s (0.4 gph) while using an
excess capacity nozzle in the range of 0.89 to 1.31 ml/s (0.85 to
1.25 gph). Reducing the oil flow instead of using smaller 0.42 ml/s
(0.4 gph) capacity pressure atomizing nozzle eliminates the potential
plugging problem of very small capacity nozzles (Reference 5-37). In the
thermal aerosol burner the distillate oil was heated to over 373 K
(212°F). The use of heated oil improves atomization (i.e., smaller oil
drops and thus better fuel air mixing), at low pressure and reduced firing
5-30
-------
rate. The thermal aerosol oil burner achieved good atomization with low
CO and UHC emissions at 0.42 ml/s (0.4 gph) oil flowrate (representing a
53 to 68 percent nozzle capacity reduction) and low excess air. Heating
the fuel was also found to lower emissions during start-up. Fuel oil
heated to 423 K (302°F) produced zero smoke in less than 1.5 minutes
after ignition (Reference 5-37). During most tests, NO emissions also
decreased with increasing fuel oil temperature and pressure.
In another study, Hayden e_t al., reduced the firing rate on one
furnace, thus reducing seasonal number of cycles from 3,400 the previous
season to 3,301 during the test season. Seasonal CO emissions were
reduced 14.2 percent (Reference 5-34) with approximately 9 percent of this
reduction attributable to fuel savings. Reducing the cycling frequency
also generally significantly improves the overall furnace efficiency.
"Off" cycle heat losses due to the buoyancy induced drafts in the stack
and combustion system are reduced due to the fewer numbers of standby
periods. When Katzman and Monat reduced the firing rate of 18 oil-fired
residential heating systems by 36 percent, the resulting average increase
in seasonal efficiency was 14 percent (Reference 5-38). Overall seasonal
mass emissions are generally reduced through a reduction in fuel
consumption.
Increased thermostat anticipator setting showed a dramatic effect
on cycling frequency and seasonal CO emissions during tests on oil-fired
residential heaters (Reference 5-34). Two hot water hydronic systems with
unusually high cyclic frequency (approximately 11 to 22 thousand cycles
per season) were tested with an increased anticipator setting of the
Honeywell thermostats. The total number of cycles decreased an average of
55 percent. CO was reduced over 40 percent when compared to total
seasonal emissions of the previous heating season. These dramatic CO
emission reductions are indicative of the importance of combustible
emissions during cyclic operation.
5.2.2.3 Burner Tuning and Maintenance
Several investigators have shown that CO and UHC emissions can be
reduced significantly by adjusting or tuning existing burners, and by
replacing worn-out burner components or entire furnaces. One team of
investigators studied the emissions from 33 residential oil-fired units
during the 1970 to 1972 heating season (Reference 5-23). Pollutant
5-31
-------
emissions were measured in the "as found" condition and after tuning. The
procedure for tuning included:
• Cleaning and adjusting the ignition electrodes
• Cleaning the blast tube and blower shell
• Cleaning or replacing the nozzles
• Cleaning or replacing the oil filter
0 Sealing air leaks at the inspection door, around the blast tube
or at other easily accessible locations
t Changing the draft regulation setting
Three of the 33 units tested were found to be in such poor condition that
they had to be replaced.
Table 5-3 summarizes the reductions in mean pollutant emissions
that could be accomplished by identifying and replacing the units
obviously in poor condition and by tuning the remaining units.
Combustible emissions were reduced substantially only by replacing the
three furnaces found in poor condition. Actual tuning added only
3 percent reduction for UHC and 16 percent for CO. Barrett, et a!., also
showed that overall thermal efficiency for the units tested increased
1.7 percent on the average (Reference 5-23).
TABLE 5-3. EFFECT ON MEAN EMISSION OF IDENTIFYING AND REPLACING RESIDENTIAL
UNITS IN POOR CONDITION AND TUNING (Reference 5-23)
Pollutant
Smoke
CO
HC
N0x
Filterable Partic-
ulate
Reduction in Emissions, percent
Step 1
Replacements of
Worn-Out Units
65
87
No Change
17
Step 2
Replacement of Worn-
out Units and Tuning
of Remaining Units
59
81
90
No Change
24
Improvement
Due Only to
Tuning
59
16
3
0
7
5-32
-------
As indicated in Table 5-3, tuning has essentially no effect on NO
emissions except for the indirect reduction due to increased thermal
efficiency and hence reduced fuel consumption. Tuning was found to be most
effective for smoke emissions. The overall dramatic reduction in emissions
accomplished simply by replacing 9 percent of the units tested indicates that
unnecessary combustible pollutants are emitted from old furnaces with worn-out
or damaged burners. Hall, et^ aj_._, and Barrett, e_t aj_._, estimated that 9 to
30 percent of existing oil-fired residential burners are worn out and in need
of replacement (References 5-12 and 5-23). Lifetime of an oil-fired
residential furnace averages 15 years (Reference 5-13).
In addition to reducing CO and UHC emissions through burner tune up, an
annual maintenance program is suggested for low emissions and maximum thermal
efficiency throughout each heating season (Reference 5-12). Performance of
residential oil-fired heaters and, to some extent, commercial boilers
deteriorates with time. The decrease in performance if unchecked, can lead to
very poor operation. As much as 10 percent efficiency drop has been measured
over a period of 10 weeks on one experimental furnace (Reference 5-12). One
reason is that some of the soot which is formed during inefficient operation
adheres to the heat transfer surface. Soot accumulation will eventually lead
to reduction in heat transfer, higher stack temperatures, and increased
emissions due to increased fuel usage.
EPA Guidelines for tuning and maintenance of oil-fired residential and
commercial heating systems recommend the following (References 5-39 and 5-40):
t Inspect fuel oil nozzle; clean or replace if necessary
t Replace or install in-line oil filter
• Clean heat transfer surfaces of soot or other deposits
t Seal air leaks
• Set fuel oil pressure to manufacturer's recommendations
t Set fuel oil temperature to provide manufacturer's recommended
viscosity (only for large commercial units burning other than
distillate oils)
• Assure timely shut-off of fuel flow and proper ignition without
excessive emissions
• Set excess air to recommended COo levels without incurring
excessive CO or smoke emissions
5-33
-------
These maintenance procedures performed by skilled service personnel
will ensure that residential and commercial oil-fired heaters and boilers do
not cause unnecessary combustible emissions and that high thermal efficiency
of the unit is maintained.
5.2.3 Smoke and Particulate Control
Essentially all oil-fired residential heating units are fired with
No. 2 distillate oil. Particulate emissions from the burning of this grade of
oil are usually small compared with those from units fired with residual oil.
High smoke or particulate readings with distillate are mostly due to improper
air-to-fuel ratios, improper draft, worn-out burner components, or poor burner
and combustion chamber design.
As with CO and UHC control, an effective and practical technique to
reduce particulate and smoke emissions from residential oil burners is to keep
them well maintained. Significant improvements can also be obtained through
the use of new, well designed burners and combustion chambers. Also, energy
saving devices which improve steady-state efficiency and reduce cyclic
frequency reduce seasonal particulate and smoke emissions indirectly through
reduced fuel consumption.
In general, those controls discussed in the previous section for CO and
UHC emissions are also effective in reducing smoke and particulates from
residential heaters. In addition, delayed action solenoid oil valves have
been tested successfully to reduce smoke emissions during start-up and
shut-down periods when carbonaceous emissions are highest. This control is
discussed in Section 5.2.3.4.
5.2.3.1 Burner Tuning and Maintenance
In Battelle's tests of residential and commercial heating units
(Reference 5-23), tuning of the serviceable units reduced the mean values of
the Bacharach Number considerably. Results of these tests for smoke emissions
are summarized in Figure 5-12. The mean Bacharach Number was 3.2 for the "as
found" condition. After tuning, the mean smoke number was reduced 59 percent
to 1.3 (see Table 5-3). Moreover, after tuning, all of the serviceable units
could have complied with a standard of Bacharach No. 3 and nearly 90 percent
could have even complied with a level of 2. Reduction in emissions of
filterable particulate attributed to tuning averaged 7 percent. The guidelines
for tuning and maintenance discussed in the previous section are also valid
for control of smoke and particulate emissions.
5-34
-------
i-
o>
ID
4
As-found •
Tuned ©
Mean Values
• - As Found
Tuned
°
GO
OOOQOOOO
40 60
Percent
80
TOO
Figure 5-12.
Distribution of smoke emission for residential units
(Reference 5-23).
5-35
-------
5.2.3.2 Burners and Combustion Chamber Redesign
Advanced low-NO burners for residential oil-fired heaters are
also capable of operating at low excess air with essentially smoke-free
flue gas. These burner designs rely on optimal choices for swirl over
velocity to obtain the desired turbulence level and residence time
(EPA/Rocketdyne controlled mixing burner). In addition, many use either
internal or external flue gas recirculation for complete burnout (Blueray
and M.A.N. burners). Flame retention devices which produce a more stable,
compact and intense flame have also been demonstrated to reduce smoke and
particulate emissions. In one study, one type of flame retention burner
emitted less smoke than the conventional unit (average Bacharach Number of
1.2 for the retention head versus 2.9 for the others) (Reference 5-12). A
set of field test results also showed that smoke and particulate were
lower for retention head burners than for conventional designs. Smoke
emissions were reduced 26 percent and filterable particulate emissions
were reduced 50 percent on the average (Reference 5-23).
5.2.3.3 Reduced Fuel Consumption and Reduced Cycle Frequency
As indicated in the discussion for CO and UHC control, reduced fuel
consumption can be accomplished by a variety of methods. Installation of
chimney or duct dampers reduced fuel consumption by 3 to 9 percent on two
warm-air furnaces, decreasing seasonal particulate emissions from 2.2 to
17.2 percent. Overnight reductions in thermostat settings of 3 to 5 K (5
to 9°F) reduces seasonal fuel consumption by 7 to 15 percent and
decreased particulate emissions by about 12 to 24 percent (Reference
5-34). Increased thermostat anticipator (resulting in longer on-times
reduced fuel consumption marginally, but the particulate emission
reductions were significant — 32 to 33 percent -- primarily caused by a
reduction in cyclic frequency of warm-air furnaces tested
(Reference 5-34). Reduced firing rate resulted in seasonal particulate
emission reductions of only about 4 percent. These were caused by a
9 percent reduction in fuel oil consumed and a 3 percent reduction in
cycling frequency (Reference 5-34).
5.2.3.4 Delayed Action Solenoid Valve
Katzman and Weitzman found that the installation of delayed action
solenoid valves reduced the average smoke number from 6.3 to 2.3 during
furnace startup and 8.3 to 0.7 during shutdown periods (Reference 5-13).
5-36
-------
During start up, the solenoid delayed the opening of the oil valve until the
burner air blower had reached full speed. This prevented the poor startup
performance caused by insufficient combustion air and mixing. During shut
down, the delayed oil valve closed off immediately providing a clean flame cut
off. Without the valve, the speed of the blower generally decreased to
approximately 900 rpm (25 percent of capacity) before the oil flow was
actually shut off. Smoke emissions during start up and shut off periods
without the delayed oil valve ranged from Bacharach numbers of 5 to 9
(Reference 5-13).
5.2.4 Cost and Energy Impact of Controls
Reported control costs for oil-fired residential heating systems vary
significantly according to the type of control and application. For example,
the 1976 retrofit costs of NO controls ranged from about $38 for the burner
A
head developed by Rocketdyne to about $339 for a reduced capacity
high-efficiency flame retention burner. More recent differential costs of a
new low-NO furnace, such as the Blueray or the Rocketdyne unit, range from
/\
about $100 to $250 over the cost of a conventional furnace.
Although inflation has increased the cost of these controls over the
past few years since 1976, the cost of fuel oil has also risen even more
dramatically than the average rate of inflation has. Therefore, the energy
saving associated with most retrofit controls and new low-emission
high-efficiency furnaces is such that the initial investment is often
recovered within the first two heating seasons.
The volume production cost of the burner head by Rocketdyne was
estimated to be only $1.50 (Reference 5-25). Including the installation cost,
the total investment in 1976 was estimated at about $38 per burner. Since the
burner head increases seasonal efficiency by about 5 percent on the average,
the payback period should be rather short (i.e., generally less than a year).
As discussed in Section 5.2.1.1, retrofit of flame retention cone heads
on existing high pressure gun atomizing oil burners was determined to be
feasible. The cost and energy savings of retrofit installation of one flame
retention head with a new nozzle rated at lower firing capacity was also
estimated. The average 1976 investment cost was estimated to be $45 on the
5-37
-------
average and the energy savings would amount to approximately $110 for a
payback period of less than 1 year (Reference 5-13).
The cost to retrofit a new flame retention burner with a reduced
firing capacity was estimated to require an initial investment of $339 in
1976 (Reference 5-13). Accounting for inflation, this cost would increase
to about $385 in 1978. However, the annual fuel oil saving was estimated
to average 2009 liters (531 gallons) when compared to fuel oil
consumptions of existing low-efficiency furnaces (Reference 5-13).
Considering that the cost of home heating oil in 1978 was approximately
$0.20/1 ($0.80/gal) annual savings would amount to about $400. Therefore,
the payback period for the reduced capacity flame retention burner would
be approximately 1 year.
Rocketdyne, along with EPA, has applied for a patent for the new
furnace system discussed in Section 5.3.1.2. The incremental equipment
cost of this furnace compared with a conventional warm-air heater was
recently estimated to be about $250 (Reference 5-41). Assuming an annual
heating oil bill of $1,000 per household and considering the reported
savings in fuel consumption of about 18 percent, the payback period for
this initial investment is less than 2 years.
The Blueray furnace, equipped with the "blue flame" low-NO
/\
recirculating burner is commercially available with over one-thousand
units already in place. The cost of the Blueray furnace was estimated to
be about $100 more than the cost of a conventional warm air heating system
(Reference 5-42). This differential investment would generally be
recovered in less than a year.
No cost information is available for the M.A.N. burner. Foreign
manufacturers are planning to introduce this burner design in the U.S.
Recently the burner has undergone tests at EPA laboratories. Commercial
availability is expected in 1980 (Reference 5-43).
Tuning of a residential oil-fired furnace for low emissions and
high thermal efficiency was estimated to cost $33 to $55 (1976) based on
the labor cost estimates by Katzman and Weitzman for installation of flame
retention cones and nozzles and adjustment of combustion air flow
(Reference 5-13). Since unit efficiency generally increases with tuning,
this initial cost is offset by savings in fuel consumption. Manufacturers
and service organizations recommend that residential heaters be serviced
5-38
-------
once a year, preferably at the beginning of the heating season
(Reference 5-12).
Various other control techniques primarily aimed at reducing oil
consumption for residential heating and improving seasonal thermal
efficiency can be easily implemented by the homeowner. Change of
thermostat anticipator setting if adjusted by the homeowner and manual
overnight thermostat cut-back require no cost and reduce energy
consumption plus reduce overall emissions. Installation of positive stack
dampers requires some initial investment cost. The recently reported cost
of installed automatic chimney dampers is $200 — $120 for the damper
(Reference 5-44). Thus, it can be estimated that the payback period for
this energy saving device could also be relatively short.
In general, all air pollutant control techniques improve unit
thermal efficiency as well as reduce seasonal NO and combustible
emissions. For this reason, the initial investment required for new
burners, furnaces or scheduled tuning can in many cases be compensated
with reductions in fuel oil consumption which translate to savings for the
homeowner.
5.3 EMISSION CONTROL ALTERNATIVES FOR SOLID FUEL-FIRED RESIDENTIAL SYSTEMS
Solid fuel-fired residential and commercial systems include
hand-fired and stoker-fired systems plus some wood-fired stoves, furnaces,
and boilers. Residential stokers are hopper fed or bin fed if equipped
with a mechanical underfeed system. Larger commercial stokers can be of
the overfeed, underfeed and spreader type. However, underfeed types are
most common. Wood-fired residential furnaces are essentially all
hand-fired.
NO emission control techniques for residential coal- and
A
wood-fired heaters and boilers have not been widely investigated,
primarily because of the declining use of this equipment type in the
past. Also, small coal-fired equipment is not amenable to extensive
modifications to control NO emissions. Excess air and overfire air
/\
injection in some units are the only feasible control alternatives which
have some impact on the overall NO emissions. Wood heating has
A
experienced a recent revival, and is the subject of a separate NOX EA
review to be published at a later date.
5-39
-------
Excess air reduction in residential coal-fired equipment is very
limited due to increases in carbonaceous emissions. Overfire air
injection, only available with larger commercial size stokers, is only
moderately effective in reducing NO . Overfire air which is generally
J\
used to control smoke and HC emissions from volatile coal combustion was
found to be effective in achieving smokeless operation with some coals
containing 20 percent or more volatile matter (Reference 5-45).
The emphasis of emission control from residential coal-fired
equipment has been placed on reducing smoke and other carbonaceous
pollutants. As discussed in Section 4, the combustion of high volatile
bituminous coals in small residential systems produces high smoke and
particulate emissions. A bituminous coal-fired furnace originally
developed in the 1940's was investigated in a program to identify clean
burning solid fuel-fired furnaces for residences. This furnace developed
for Bituminous Coal Research, (BCR) Inc. uses a cross-feed principle of
burning in which both the coal and combustion air move downward to the
"hearth" or cross-fed portion of the fuel bed. Figure 5-13 illustrates a
new coal-fired furnace/boiler based on the BCR design. This furnace can
operate with 60 to 65 thermal efficiency and low smoke emission. This
concept is applicable to boilers and space heating stoves as well as
furnaces and can also burn wood or saw dust (Reference 5-47).
Nntntk
Figure 5-13.
Schematic of the cross-feed combustion design for
coal-fired residential furnaces (Reference 5-46).
5-40
-------
Control techniques for wood-fired residential heaters have not been
developed to any great extent. Since long term gas and oil supplies will
continue to dwindle, wood represents a possible alternative to coal burning
in home furnaces and residential and commercial boilers. Recently, however,
the EPA has sponsored two test programs to quantify emissions and identify
potential control options for wood burning appliances (Reference 5-48). In
the first test program Monsanto tested two air tight stoves (one baffled and
the other unbaffled) plus one fireplace for criteria pollutant, trace element
and organics. In the second program, which is just underway, Battelle is to
identify equipment and operating parameters which affect emissions. In
addition, the program will assess which of these parameters can be safely
varied to reduce emissions.
5.4 SUMMARY OF MOST EFFECTIVE CONTROL ALTERNATIVES FOR RESIDENTIAL SYSTEMS
In general, little of the NO control technology discussed
A
earlier for gas- and oil-fired residential and commercial systems has been
implemented in the field. Most emission control work for residential
heaters has centered around tuning and maintenance of existing equipment
or installation of new more efficient equipment for reduced fuel
consumption and minimum visible emissions. Tuning usually reduces CO, HC,
and particulates (smoke), however, without much effect on NO
/\
emissions. New furnace concepts utilize advanced burner designs which
allow for efficient operation at low excess air. Some of these burners
are also capable of low-NO emissions.
J\
The following discussion summarizes the performance and cost of
control techniques specifically aimed at reducing NO emissions from
A
residential heaters. Based on performance, commercial availability, and
cost, the best available NO control techniques are identified.
A
Performance and cost of combustible emission controls for residential
heaters are also summarized.
5.4.1 Gas-Fired Systems
Table 5-4 summarizes the performance of NO control equipment for
A
natural gas-fired residential heaters. Baseline uncontrolled emission
factors for the three major pollutants emitted from these sources are also
presented. Additionally, steady-state and cycle efficiencies of baseline
or "as found" residential units and controlled residential units are also
5-41
-------
TABLE 5-4. PERFORMANCE SUMMARY OF LOW-NOX CONTROL EQUIPMENT FOR NATURAL GAS-FIRED RESIDENTIAL HEATERS
ro
Control
Conventional
Units
Radiant Screens
Secondary A1r
Baffles
Surface Combus-
tion Burner
Amana (HTM)
Modulating
Furnace
Pulse C ambus tor
Catalytic
Comb us tor
Average
Operating
Excess Air
(percent)
40-120
40-120
60-80
10
NA
NA
NA
NA
Cyclic Pollutant Emissions
ng/J heat input
NOX
28-45
15-18
22
7.5
7.7
25
19-20
<5
CO
8.6-25
6.4
14
5.5-9.6
26
NA
NA
NA
UHCb
3.3-33
NA
NA
NA
NA
NA
NA
NA
Steady State
Efficiency
(percent)
70
75
NA
NA
85
75
95
90
Cycle
Efficiency
(percent)
60-65
70
NA
NA
80
70
95
85
1978
Installed
Control
Cost
c
NA
NA
J100-J200
J100-J300
over
conventional
furnace
J50-J250
over con-
ventional
furnace
J300-J600
J150-J2SO
C Dements
Emission factors from References
5-49 and 5-50. Costs include
Installation.
Emissions of CO and HC can increase
significantly If screen is not
placed properly or deforms.
Requires careful Installation. Best
suited for single port upshot
burners.
Not commercially available. Still
under development.
Commercially available design.
Spark ignited thus requires no
pilot.
Furnace Is essentially derated.
Thus it requires longer operation
to deliver a given heat load.
furnace
Currently being investigated by
A6AL. Efficiencies correspond to
flue gas condensing systems.
Still at the R&O stage. Efficiencies
correspond to flue gas condensing
systems.
of NO + NO? reported as NO?
bUnburned hydrocarbons calculated as methane (CH4)
CTypical costs of uncontrolled unit $500-$800
dNA = not available.
-------
presented to highlight the general improvement in thermal performance with
any of the NO controls investigated.
/\
The Amana HTM and Bratko burner designs represent the most
effective control alternatives for gas-fired residential units. Reported
NOX reductions are generally greater than 80 percent accompanied by
increases in thermal efficiencies of about 10 to 15 percent. However,
recent tests with the Amana HTM combustor have not resulted in NO
x
reduction efficiencies of 80 percent as previously reported by AGA. New
tests have been scheduled (Reference 5-5).
The Amana furnace is the only commercially available unit. It is
generally used for combined heating and air conditioning of residences and
small commercial buildings. The cost to the consumer of an Amana heater
is 20 to 40 percent more than the cost for a comparable unit. No known
plans are under way to commercialize the Bratko burner.
Pulse combustion in a residential system has been reported to emit
19 to 20 ng N02/J (0.044 to 0.047 lb/106 Btu) (Reference 5-8). The
incremental cost of a pulse combustion burner was estimated in the range
of $300 to $600 for a condensing system with a seasonal efficiency of
95 percent (Reference 5-7). A catalytic burner also with a condensing
system and a seasonal efficiency of 85 percent was estimated to range
between $100 and $250 over the cost of conventional equipment
(Reference 5-7). Both pulse and catalytic combustion for domestic heating
are, however, not commercially available.
5.4.2 Oil-Fired Systems
Table 5-5 summarizes performance and cost of control equipment for
residential distillate oil-fired heating equipment. These controls were
primarily designed for warm air furnaces, however, the new burner/firebox
technology of these systems may be applicable to residential hot water
heaters or hydronic boilers.
The range in baseline NO emissions reflect data reported by
/\
Barrett, et al., (Reference 5-23) and Hall (Reference 5-12) for nonflame
retention type burners. Barrett, et al., suggested an average NO
6
emission factor of 55 ng/J as NO,, (0.13 lb/10 Btu) for hot water and
warm air systems utilizing both conventional and flame retention burners
(Reference 5-23). This emission factor compares to 61 ng/J as NOo
(0.14 lb/106 Btu) estimated by the EPA (Reference 5-50).
5-43
-------
TABLE 5-5. PERFORMANCE SUMMARY OF LOW-NOX CONTROL EQUIPMENT FOR DISTILLATE OIL-FIRED RESIDENTIAL HEATERS
Control
Conventional
Units
Flame Reten-
tion Burner
Head
Controlled
Mixing Burner
Head by EPA/
Rocketdyne
Integrated
Furnace Sys-
tem by EPA/
Rocketdyne
Blueray
"blue flame"
Bumer/Fumace
System
H.A.N.
Burner
Average
Operatin g
Excess air
(percent)
50-85
20-40
10-50
20-30
20
10-15
Cyclic Pollutant Emissions
ng/J heat input
a
NO/
37-85
26-88
34
19
10
10-25
CO
15-30
11-22
13
20
4.5-7.5
less than
30
UHCb
3.0-9.0
0.2-1.8
0.7-1.0
1.2
1.5-2.5
NA
Smoke
Number
3.2
2.0
less
than
1.0
less
than
1.0
zero
less
than
1.0
Particulate
7.6-30
NA
NA
NA
NA
NA
Steady State
Efficiency
(percent)
75
80-83
80
84
84
85
Cycle
Efficiency
(percent)
65-70
NA
NA
74
74
NA
1978
Instal led
Control
Cost
c
$52e
$436
$250 over
conven-
tional
furnace
$100 over
conven-
tional
furnace
NA
Comments
Range in NOX emissions is for residen-
tial systems not equipped with flame
retention burners References 5-12 and
5-23). Emissions for all other pollut-
ants are averages reported in References
5-23 and 5-50.
If new burner is needed as well as a
burner head, the total cost would be
$385. Cost is for 1978-79 heating season.
Cost of mass produced burner head only
about $1.50. Combustible emissions
are relatively low because hot firebox
was used.
Uses optimized burner head. For new
furnace installation only. Combustible
emissions are higher than with burner
head because of quenching in air cooled
firebox. Recent cost estimate.
New Installation only. Furnace Is
commercially available. Recent cost
estimate.
Both for retrofit or new installations.
Not yet commercially available in U.S.
Commercialization expected In 1980.
Ul
I
of NO and N02 reported as NO?
bUnburned hydrocarbons calculated as methane (CH/j)
^Typical costs of uncontrolled unit $650-$!,000
NA = Not available.
eOriginal costs reported for years other than 1978 were corrected for inflection
using Gross National Product (GNP) implicit price deflectors (Reference 5-51).
-------
The most effective N0x controls for new residential oil burning
is to use the Rocketdyne/EPA furnace system, the Blueray "blue flame"
furnace and the M.A.N. burner. Average NO emission reductions with
J\
these controls range from 65 to about 80 percent depending on which
uncontrolled emission level is considered (i.e., 55 ng/J from Reference
5-23 or 61 ng/J from Reference 5-50). Both the flame retention and
Rocketdyne/EPA controlled mixing burner head are desirable features for
retrofitting existing furnaces because they also allow for more efficient
furnace operation with lower combustible and smoke emissions. The
controlled mixing burner head results in a modest NO reduction of
X
20 percent. Although most flame retention head burners produce high NO
A
emissions, a few result in some decrease in NO from baseline levels.
The Blueray furnace is the only equipment available commercially in
the U.S. The M.A.N. burner is commercially available only in Europe.
However, this low-NOx advanced burner is expected to enter the U.S.
market in less than 1 year. The range in NO emissions for the M.A.N.
A
burner reflects test data reported for two firing configurations. The
lower emission factor was obtained with an air cooled blast tube while the
high emission factor is for an uncooled blast tube. The M.A.N. warm air
furnace system utilizes a cooled blast tube and firebox for low-NO
emissions and high heat transfer efficiency. The M.A.N. burner is an
attractive control technique because it may be applicable to existing
units.
The Rocketdyne/EPA warm air furnace is still undergoing field tests
to further demonstrate its reliability and improved performance.
Presently, however, Rocketdyne has no immediate plans to market the
optimized furnace design. As Table 5-6 indicates, CO, UHC, and smoke
emissions are equally reduced with any of the N0x control equipment
available. Similarly, thermal efficiencies are improved reducing fuel
consumption and seasonal pollutant emissions. Due primarily to its
commercial availability and low incremental cost, the Blueray furnace is
considered the best available technology for new distillate oil-fired
residential warm air furnaces.
Table 5-6 summarizes the various control techniques available for
CO, UHC, smoke and particulate emission reduction from existing warm air
furnaces, water heaters, or hydronic boilers burning distillate oil.
5-45
-------
TABLE 5-6. PERFORMANCE SUMMARY OF CONTROLS FOR REDUCTION OF SEASONAL COMBUSTIBLE, SMOKE AND
PARTICULATE EMISSIONS FROM OIL-FIRED RESIDENTIAL HEATERS
en
t
en
Control
Replacement of worn-out
units
Tuning and scheduled
seasonal maintenance
Dela>ed action solenoid
valves
Reduced excessive firing
capacity with conven-
tional burner
Reduced excessive
firing capacity with new
retention burner
Installation of positive
chimney dampers
Increased thermostat
anticipator setting
Overnight thermostat
cut-back (3-5K)
Percent Reduction (Average)
CO
(65)
(16)
NA
(14)
(14)
2.0-19
(11)
41-45
(43)
9.1-27
(17)
UHC
(87)
(3.0)
NA
NA
NA
NA
NA
NA
Smoke
NCa
(59)
60-90
(80)
10-38
(24)
80-85
(82)
NA
NA
NA
Particulates
(17)
(7.0)
NA
(3.7)
(3.7)
2.2-17
(10)
31-33
(33)
12-24
(15)
Percent
Improvement
in Fuel Saving
NAb
1 .7 percent aver-
age efficiency
increase
NA
5.6-2.5
(14)
14-39
(30)
3-9
0-2
7-15
1978
Installed
Control
Cost
$650-1000C
for new warm
air furnaces
$38-60c
J43C
$52C
J385C
J20QC
Minimal
Minimal
Comments
Nine percent of the existing residen-
tial heaters were found 1n need of
replacement. Recent cost estimates.
Tuning results in an Increase In effi-
ciency for some units and a decrease
1n efficiency for others.
Smoke emission reduction primarily
during start-up and shut-down.
Installation of flame retention head
cone plus modifications to reduce
firing capacity by about 36 percent.
Installation of new lower capacity
burner with flame retention head.
Firing capacity reduced by 43 percent.
Large variation In pollutant emission
reduction due to changes In furnace
cycle frequency. Recent cost estimates
Very effective for residential
units with high cyclic efficiency
Cost does not take Into account
improved home insulation which might be
necessary with thermostat cut-back.
*NC = No change
bNA = Not available
cCosts for material and labor are typical of New England area. Original costs reported for years other than
1978 were corrected for inflation using Gross National Product (GNP) implicit price inflectors (Reference 5-51)
Parenthesis indicate arithmetic averages
-------
Again, the data in this table reflects primarily emissions data from warm
air furnaces but these controls are equally applicable to other
residential heating equipment.
The first two techniques listed, replacement and tuning with
scheduled maintenance of existing furnaces, are aimed at reducing
combustible and smoke emissions and increasing system efficiency. These
controls have essentially no effect on NO emissions. However, CO, and
/\
UHC emissions are significantly reduced just by replacing worn-out units.
Smoke emissions are reduced significantly by tuning the equipment on a
yearly basis. This indicates that most of the yearly combustible and
smoke emissions from oil-fired residential heaters are caused by very old
units in need of replacement or units in need of maintenance or tuning.
Delayed action solenoid oil valves reduce smoke emissions during start up
and shut down periods when smoke as well as CO and UHC emissions are
h i gh es t.
The remaining control alternatives indirectly achieve a yearly
reduction in NO emissions firstly, through reduced equipment usage and
/\
secondly, through improved fuel efficiency. However, these controls are
aimed primarily at lowering seasonal combustible emissions and reducing
yearly fuel consumption. Reduced excessive firing capacity and change in
thermostat anticipator setting to increase furnace on-time lower
combustible emissions by reducing cyclic frequency of the furnace. These
controls lowered CO emissions by 14 to 43 percent respectively and smoke
24 and 82 percent primarily by reducing seasonal number of on-off cycles.
In general, these alternative control techniques are very effective
in reducing the annual combustible and smoke emissions from residential
oil-fired furnaces. With the exception of reducing excessive firing
capacity which might cause some operational problems with nozzle plugging,
all control alternatives are available to the consumer. Because all
reduce fuel consumption through improved efficiency or directly by
reducing equipment usage, there are some cost benefits as well as
environmental benefits associated with these controls.
5.5 EMISSION CONTROL ALTERNATIVES FOR COMMERCIAL SYSTEMS
5.5.1 Commercial Heaters
Application of control technology to commercial heating equipment
is very limited. No information was found for low emission systems in
5-47
-------
indirect gas-fired equipment although there is a strong interest in high
efficiency appliances which implies lowest excess air and complete
combustion. Compared to residential gas-fired equipment, a greater
percentage of commercial warm air heaters or duct heaters utilize a forced
combustion air burner as opposed to a naturally aspirated burner. These
power burners usually have greater flexibility for excess air control
while maintaining low CO and UHC emissions.
Theoretically, the flame quenching and surface combustor concepts
of the gas-fired residential burners could be implemented for commercial
systems. For oil-fired equipment, the EPA/Rocketdyne residential burner
head design implementing 25 degree air swirler vanes combined with optimum
choke diameter (varying as the 0.4 power of the oil flow) was found to
minimize NO emissions from burners with oil flow capacity as high as
J\
12.6 ml/s (12 gph). NO emissions with this burner design were
A
generally 25 to 50 percent lower than those from commercially available
burners with or without flame-retention devices and operating under
similar conditions (Reference 5-52).
Combustible emission controls listed in Table 5-6 could also be
applied to commercial space heating equipment. For example, reducing
firing rate would be a viable alternative for commercial heating systems
where the demand is strongly cyclic. Additionally, increased thermostat
anticipator setting or overnight thermostat cut-back could reduce annual
emissions by amounts equal to those obtained for residential units.
5.5.2 Commercial Boilers
Commercial or small industrial boilers are mostly single burner
packaged firetubes. NO control techniques for small firetubes with
fi
heat input capacities less than 2.9 MW (10 x 10 Btu/hr) have not been
widely investigated. However, the similarity in equipment design between
the small firetubes and the larger industrial size firetubes may allow
application of similar combustion modification control techniques.
Control techniques investigated for industrial boilers which may be
applicable to the small commercial firetube units are listed in
Table 5-7. Although N0x reductions represent controlled levels achieved
with both industrial firetubes and watertube designs, as well as field
erected and packaged boilers, it may be possible that these NO
A
reductions could also be achieved with small commercial firetubes.
5-48
-------
TABLE 5-7.
COMBUSTION MODIFICATION NOX CONTROLS FOR OIL- AND GAS-FIRED INDUSTRIAL BOILERS (Reference 5-22)
1 Control
Technique
None
Low Excess A1r
(LEA)
Staged
Combustion Air
Flue Gas
Recirculatlon
(FGR)
Flue Gas
Recirculatlon
plus staged
combustion
Load Reduction
(LR)
Low-N0x
Burners (LNB)
Description of
Technique
Baseline
Reduction of combus-
tion air
Fuel rich firing
burners with secon-
dary combustion air
ports
Reclrculation of
portion of flue gas
to burners
Combined techniques
of FGR and staged
combustion
Reduction of air and
fuel flow to all
burners in service
New burner designs
with controlled air/
fuel mixing and in-
creased heat dis-
sipation
Effectiveness of Control (Percent NOX Reduction)
Residual
67-362 ng/J
0-28; 11 average
or 10 ng/J/* 02
reduction
20-50
15-30
25-53
33% decrease to
25% increase
20-50
Distillate
011
45-107 ng/J
0-24; 11 average
or 10 ng/J/% 02
reduction
17-44
58-73
73-77
31* decrease to
17% increase
20-50
Natural
Gas
29-28 ng/J
71% decrease
to 85% in-
crease (10%
average
reduction)
5-46
48-86
Up to 76
32% decrease
to 82% in-
crease (10%
average
reduction
20-50
Range of
Application
Average excess 02
measured 5.8 percent
Generally excess 0?
can be reduced to 2.5%
representing a 3% drop
from baseline
70-90% burner stoi-
chiometries can be
used with proper
Installation of
secondary air ports
Up to 25-30% of flue
gas recycled. Can be
implemented on all
design types
Max. FGR rates set at
25% for distillate oil
and 20% for residual
oil
Applicable to all
boiler types and sizes.
Load can be reduced to
25% of max. Better Im-
plemented with improved
firebox design
New burners generally
applicable to all
boilers. More specific
Information needed
Comments
Emissions are from firetube and
watertube boilers not equipped
with preheaters.
Added benefits Included
increase in boiler efficiency.
Limited by increase 1n CO, HC,
and smoke emissions
Best implemented on new units.
Retrofit is probably not feasible
for most units. Generally
less effective for gas-fired
units. Doubtful application.
Best suited for new units. Costly
to retrofit. Possible flame In-
stability at high FGR rates. Most
effective on watertube units
Retrofit may not be feasible.
Best implemmented on new units.
Doubtful application of staged
combustion.
Technique not effective when It
necessitates an increase in excess
0;> levels, LR possible imple-
mented in new designs as reduced
combustion Intensity (enlarged
furnace plan area)
Specific emissions data from
industrial and commercial boilers
equipped with LNB are lacking
UD
-------
Available control alternatives include low excess air, flue gas
recirculation and load reduction. Low excess air is the only control
technique generally in use with boilers in this size category. Low-NO
burners, if developed, could be the most cost-effective NO control
technique besides LEA operation.
Table 5-8 summarizes NOX control techniques which have been
investigated for industrial stoker coal-fired boilers. These controls
could also be potentially applicable to commercial size stokers. However,
as indicated, NO reduction performance data are very limited for
commercial boiler equipment in the size category of less than 2.9 MW
(10 x 10 Btu/hr) heat input capacity.
5-50
-------
TABLE 5-8. COMBUSTION MODIFICATION NO CONTROLS FOR STOKER COAL-FIRED
INDUSTRIAL BOILERS (Reference 5-22)
en
i
en
Control
Technique
None
Low Excess
Air (LEA)
Staged
Combustion
(LEA + OFA)
Reduced Load
Description of
Technique
Baseline
Reduction of airflow
under stoker bed
Reduction of under
grate airflow and
increase of overfire
airflow
Reduction of coal and
air feed to the
stoker
Effectiveness of
Control (Percent
NOX Reduction)
150 ng/J
5-25
5-25
Varies from 49X
decrease to 25X
increase in NOX
(average 15X
decrease)
Range of
Application
Excess 0? measured
6.6-9.4X
Excess 02 limited
to 5-6X minimum
Excess 02 limited
5% minimum. Most
stokers have OFA
ports as smoke
control devices
but may need better
airflow control for
NOX reduction
Has been used down
to 25X load
Comments
Emissions are underfeed stokers
characteristic of low capacity
stoker-fed boilers.
Danger of overheating grate,
clinker formation, corrosion,
and high CO emissions
Need research to determine
optimal location and orienta-
tion of OFA ports for NOX
emission control. Overheating
grate, corrosion and high CO
emission can occur if under
grate airflow is reduced below
acceptable level as in LEA
Only for stokers that can
reduce load without increasing
excess air. Not a desirable
technique because of loss in
boiler efficiency
-------
REFERENCES FOR SECTION 5
5-1. Thrasher, W. H. and D. W. De Werth, "Evaluation of the Pollutant
Emissions from Gas-Fired Forced Air Furnaces," AGA Laboratories
Research Report No. 1503, Cleveland, OH, May 1975.
5-2. Himmel, R. L. and D. W. De Werth, "Evaluation of the Pollutant
Emissions from Gas-Fired Ranges," AGA Laboratories Research Report
No. 1492, Cleveland, OH, September 1974.
5-3. "NOX Emissions of Seven Furnaces Predominant in the California Area,"
Report by AGA to GAMA in response to the proposed CARB Model Rule,
Arlington, VA, August 1978.
5-4. Grandy, D. M. and T. Beutenmuller, "Proposed Model Rule for the Control
of Oxides of Nitrogen Emissions from New Gas-Fired Fan Type Central
Furnaces," State of California Air Resources Board, Sacramento, CA,
March 1978.
5-5. Personal communication with Douglas Grandy, California Air Resources
Board, Sacramento, CA, August 16, 1979.
5-6. Martin, G. B., "Evaluation of a Prototype Surface Combustion Furnace,"
in the Proceedings of the Second Stationary Source Combustion
Symposium, Volume III, EPA-6QO/7-77-073c, NTIS-PB 271 757, July 1977.
5-7. Putnam, A. A., et a!., "Survey of Available Technology for Improvement
of Gas-Fired Residential Heating Equipment," Battelle Columbus
Laboratories Final Report for Brookhaven National Laboratories,
BNL51067, Upton, New York, August 1979.
5-8. Personal communication with Bob L. Himmel, American Gas Association
Laboratories, Cleveland, Ohio, May 27, 1980.
5-9. De Werth, D. W., et al., "Guidelines for Adjustment of Atmospheric Gas
Burners for Residential and Commercial Space Heating and Water
Heating," EPA-600/8-79-005, NTIS-PB 290 777, February 1979.
5-10. Locklin, D. W., et aj^, "Guidelines for Adjustment of Residential Gas
Burners for Low Emission and Good Efficiency," in the Proceedings of
the Third Stationary Source Combustion Symposium, Volume I,
EPA-600/7-79-050a, NTIS-PB 292 539, February 1979.
5-11. Personal communication with Chuck Mueller, Amana Inc., Amana, 10,
April 14, 1979.
5-12. Hall, R. E., et al.. "Study of Air Pollutant Emissions from Residential
Heating Systems," EPA-650/2-74-003, NTIS-PB 229 697, January 1974.
5-52
-------
5-13. Katzman, L., and D. Weitzman, "A Study to Evaluate the Effect of
Reducing Firing Rates on Residential Oil Burner Installations," Walden
Research Report for the U.S. DOE under Contract No. 6-35738, Walden
Corp., Wilmington, Mass., January 1976.
5-14. Hall, R. E., "Status of EPA's Residential Space Heating Research
Program — 1976," ASME Publication 76-WA/Fu-4, August 1976.
5-15. Cato, G. A., et al., "Field Testing: Application of Combustion
Modifications to Control Pollutant Emissions from Industrial Boilers --
Phase I," EPA-600/2-74-078a, NTIS-PB 238 920/AS, October 1974.
5-16. Cato, G. A., et al., "Field Testing: Application of Combustion
ModificationsToTontrol Pollutant Emissions from Industrial Boilers —
Phase II," EPA-600/2-76-086a, NTIS-PB 253 500/AS, April 1976.
5-17. Carter, W. A., et al., "Emission Reduction on Two Industrial Boilers
with Major CombustTon Modifications," EPA 600/7-78-099a, NTIS-PB 283
109, June 1978.
5-18. Heap, M. P., et al., "Reduction of Nitrogen Oxide Emissions from Field
Operating Pacl
-------
5-26. Combs, L. P., and A. S. Okuda, "Design Criteria for Reducing Pollutant
Emissions and Fuel Consumption by Residential Oil-Fired Combustors,"
Paper 76-WA/Fu-10, Presented at the 97th ASME Winter Annual Meeting,
New York, NY, 1976.
5-27. Combs, L. P., and A. S. Okuda, "Residential Oil Furnace System
Optimization -- Phase I," EPA-600/2-76-038, NTIS-PB 250 878, February
1976.
5-28. Combs, L. P., and A. S. Okuda, "Residential Oil Furance System
Optimization — Phase II," EPA-600/2-77-028, NTIS-PB 264 202, January
1977.
5-29. Okuda, A. S., and L. P. Combs, "Field Verification of Low-Emission
Integrated Residential Furnaces," in The Proceedings of the Third
Stationary Source Combustion Symposium, Volume I, EPA-600/7-79-050a,
NTIS-PB 292 539, February 1979.
5-30. "The Blueray System," Fueloil & Oil Heat, Vol. 36, No. J5, pp 42-44, May
1977.
5-31. Higginbotham, E. B., ^t ^1_., "Combustion Modification Controls for
Residential and Commercial Heating Systems: Volume II. Oil-fired
Residential Furnace Field Tests," EPA-600/7-81-123b, July 1981.
5-32. M.A.N. sales brochure -- translated.
5-33. Personal communication with R. E. Hall, Industrial Environmental
Research Laboratory, EPA, Research Triangle Park, NC, June 13, 1979.
5-34. Hayden, A. C. S., et al., "Emissions and Energy Conservation in
Residential Oil Heating," Air Pollution Control Assocation, Vol. ^8,
No. 7_, pp. 669-672, July 1978.
5-35. Bonne, U., ejt aK_, "Effect of Reducing Excess Firing Rate on Seasonal
Efficiency of 26 Boston Oil-Fired Heating Systems," Conference on
Efficiency of HVAC Equipment and Components II, Purdue University,
Indiana, April 12-15, 1975.
5-36. Bonne, U., et^ £]_._, "Analysis of New England Oil Burner Data. Effect of
Reducing Excess Firing Rate on Seasonal Efficiency," Honeywell Final
Report to the National Bureau of Standards, U.S. Department of
Commerce, Washington, D.C., August 1975.
5-37. Janssen, J. E., £t &]_._, "Study of a Thermal Aerosol Oil Burner," EPA
600/7-77-108, NTIS-PB 277 438, September 1977.
5-38.
Katzman L., and J. P. Monat, "Field Study of Energy Efficiency
Improvements on Residential Oil Heating Installations," Paper
No. 78-49-5, presented at the 71st Annual APCA Meeting, Houston, Texas,
June 1978.
5-54
-------
5-39. Locklin, D. W. and R. E. Barrett, "Guidelines for Residential
Oil-Burner Adjustments," EPA 600/2-75-069a, NTIS-PB 248 292,
October 1975.
5-40. Locklin, D. W. and R. E. Barrett, "Guidelines for Burner Adjustment of
Commercial Oil-Fired Boilers," EPA 600/2-76-088, NTIS-PB 251 919, March
1976.
5-41. Personal communication with Allen Okuda, Rockwell International,
Los Angeles, California, March 26, 1979.
5-42. Personal communication with R. Lippiatt, Blueray System Inc., New York,
NY, March 12, 1979.
5-43. Personal communication with Karl Klatt, M.A.N. Representative Karlson
Blueburner Systems Ltd., Abbotsford, British Columbia, Canada, March
12, 1979.
5-44. Personal communication with A.C.S. Hayden, Canadian Department of
Energy, Ottawa, Canada, August 31, 1979.
5-45. Giammar, R. D., et al., "Emissions From Residential and Small
Commercial Stoker-Coal-Fired Boilers Under Smokeless Operation,"
EPA-600/7-76-029, NTIS-PB 263 891, October 1976.
5-46. Field, A. A., "European Trends in Space Heating," Heating, Piping, Air
Conditioning, Vol. 46, No. 3, pp. 75-80, March 1973"
5-47. Engdahl, R. B., "Cross-Feed Combustion for Clean Burning of Solid Fuels
for Residences," Presented at the 71st Annual Meeting of the Air
Pollution Control Association, Houston, Texas, June 1978.
5-48. Personal communication, with John Milliken, Industrial Environmental
Research Laboratory, EPA, June 15, 1979.
5-49. Brookman, G. T., and W. Kalika, "Measuring the Environmental Impact of
Domestic Gas-Fired Heating Systems, in the Proceedings of the 67th
Annual Meeting, Air Pollution Control Association, June 1974.
5-50. "Compilation of Air Pollution Emission Factors," U.S. Environmental
Protection Agency, Office of Air Quality Planning and Standards,
Publication AP-42, NTIS-PB 275 525, April 1973 and supplements and
No. 3 NTIS-PB 235 736, July 1974, and No. 6, NTIS-PB 254 274, April
1976.
5-51. Statistical Abstract of the United States -- 1978, U.S. Department of
Commerce, 99th Annual Edition, Section 15, Pg. 480-485, September 1978.
5-52. Dickerson, R. A., and A. S. Okuda, "Pollutant Formation and Emission
from No. 2 Distillate Oil Combustion," presented at the 66th Annual
AIChE Meeting, Philadelphia, Pennsylvania, November 1973.
5-55
-------
SECTION 6
ENVIRONMENTAL ASSESSMENT
The majority of residential and commercial heating systems burn
natural gas and fuel oil; thus the primary environmental impact of these
sources is on ambient air quality. Solid waste streams come from
residential and commercial wood- or coal-fired equipment, but these units
constitute a very small portion of the total number of existing
residential and commercial heating equipment. This may change, however,
due to the recent increase in wood burning equipment throughout the U.S.
Although, residential warm air furnaces and commercial hot water or steam
boilers contributed each approximately 2.0 percent of the total manmade
NO emissions in 1977, their impact on ambient NO levels in urban
X X
areas is more significant than these percentages indicate
(Reference 6-1). The seasonal usage pattern, the low stack heights and
spatial density are the principal factors which contribute to a
disproportionate impact of residential and commercial heating systems on
ground level ambient N0? concentration during the cold winter season.
The main focus of this section will be on assessing the environmental
impact of NO emissions control for residential and commercial heating
/\
systems on ambient air pollutant levels.
The environmental assessment begins with a discussion of results
from a recent field test to quantify multimedia emissions from a Blueray
low-NO high-efficiency residential warm air furnace. This furnace is
/\
considered best available NOX control technology for domestic oil-fired
control warm air furnaces. The assessment then discusses ambient air
impacts of the other NO controls identified in Section 5. The
operational, maintenance, and cost impacts of these controls are then
summarized followed by an evaluation of data base and future needs.
6-1
-------
6.1 ENVIRONMENTAL IMPACT ANALYSIS
Table 6-1 sunroarizes level 1 analysis results of exhaust emissions
from a Blueray low-NO high- efficiency home furnace in the field. This
/\
furnace was recently tested as a part of the NO EA program to quantify
^
the environmental impact of low-NO residential systems
n
(Reference 6-2). Table 6-1 also summarizes air pollutants from five
conventional (uncontrolled) oil-fired residential warm air furnaces and
two oil-fired hot water heaters tested in another EPA sponsored test
program (Reference 6-3). As indicated, for the Blueray unit two furnace
operating conditions were investigated; continuous operation and a
10-minutes on/10-minutes off cyclic operation. Tests performed on the
conventional oil-fired units were mostly with 50-minutes on/10-minutes off
cycles. However, two oil-fired systems were also tested with a 10-minute
on/20-minute off cycle to study the effect of cycle mode on organic
emissions.
Although emissions for any one pollutant vary significantly between
test programs and test conditions, several trends are evident from the
data in Table 6-1. For example, for the Blueray furnace CO, HC and organic
emissions (POM) increased when the furnace operation cycled. The
contribution of combustible emissions during ignition and shutoff periods
is clearly evident here. The average NO emissions decreased in the
A
cyclic operating mode primarily due to lower combustor temperatures.
Trace elements and particulate emissions generally remained unchanged when
the furnace was switched to cyclic operation. However, emissions of Fe,
Ni, and possibly Cr, Mn, and Mo were noticeably higher for continuous
furnace operations. The higher concentrations of these trace elements
during continuous firing may be partly attributed to deterioration of iron
and steel surfaces internal to the furnace and partly to contamination of
samples during sampling and analysis. Sulfur oxides (SOp and SO.,)
emissions from the Blueray furnace are questionable because a sulfur
balance analysis indicated only 30 to 40 percent conversion of fuel sulfur
to oxides.
For conventional furnaces, total organic emissions were about
20 percent higher than those from the Blueray unit operating
intermittently. In addition, particulate emissions were higher for the
6-2
-------
TABLE 6-1. CRITERIA TRACE ELEMENTS AND ORGANIC EMISSIONS FROM
CONVENTIONAL AND LOW-NOX OIL-FIRED HEATERS
Conventional
Pollutant
Part
SO?
S03
NOX
CO
Smoke
HC
Organic
Aluminum
Antimony
Arsenic
Barium
Beryllium
Bismuth
Boron
Cadmium
Calcium
Chromium
Cobalt
Copper
Iron
Lead
Magnesium
Manganese
Mercury
Molybdenum
Nickel
Potassium
Selenium
Tellurium
Thalli urn
Tin
Titanium
Vanadium
Zinc
Emissions
Cyclic
Heaters3
Test Method
and
Measurement Operation,
ng/Jb Techniques
3.1
—
5.9
—
--
1.0
—
9.2
0.25
0.0057
0.0015
0.016
—
—
0.011
0.45
0.029
--
0.16
0.14
0.042
0.21
—
0.0012
—
0.29
0.23
—
—
—
0.0029
0.11
SSMS
ND
CC
ND
ND
—
ND
GC/MS
SSMS
SSMS, AAS
SSMS, AAS
SSMS
ND
ND
ND
SSMS
SSMS
SSMS
ND
SSMS
SSMS
SSMS
SSMS
ND
AAS
ND
SSMS
SSMS
ND
ND
ND
ND
ND
SSMS
SSMS
Blueray Low-N0x Furnace
Emissions
Emissions --
Continuous Cyclic
Operation
ng/Jb
0.87-1.32
26.9
0.2
10
9
—
0
0.38
—
< 0.0005
< 0.0006
< 0.011
<1.54 x
< 0.0008
< 0.0039
< 0.0022
--
< 0.1 104
< 0.0088
0.0191
0.542
< 0.027
—
< 0.0152
<0.0054
< 0.0144
< 0.0882
—
<0.0030
< 0.0009
< 0.0482
< 0.0009
< 0.0033
0.0008
0.0042
, Operation,
ng/Jb
0.82-1.30
35.5
1.0
7
59
—
5
7.63
—
< 0.0006
< 0.0007
< 0.0147
106 <1.79 x 105
< 0.0008
< 0.0130
< 0.0014
—
< 0.0072
< 0.0074
0.0149
0.0594
< 0.0278
—
< 0.0033
< 0.0039
< 0.0046
< 0.0139
—
<0.0023
< 0.0010
<0.0533
< 0.0012
<0.0013
< 0.0014
0.0037
Test method
and
Measurement
Techniques
SASS -- Method 5
EPA Method 8
EPA Method 8
Chemi luminescent
NDIR
ND
FID
GC
ND
AAS
AAS
AAS
ND
AAS
Colorimetric
AAS
ND
AAS
AAS
AAS
AAS
AAS
ND
AAS
ND
MS
AAS
ND
AAS
AAS
AAS
AAS
AAS
AAS
AAS
Average of five warm air furnaces and two hot water heaters
all using conventional high pressure burners
bng/J on a heat input basis
SASS = Source Assessment Stack Sampler modified
CC = Controlled Condensation, a Goksoyr-Ross procedure
SSMS = Spark Source Mass Spectroscopy
GC/MS = Gas Chromatography/Mass Spectroscopy
ND - Not determined
AAS = Atomic Absorption Spectrometry
NDIR = Nondispersive Infrared Analyzer (continuous monitoring)
FID * Flame lonization Detector (continuous monitoring)
6-3
-------
conventional units. These observations substantiate that the low-NO
A
unit is also a high-efficiency unit.
Trace element emissions between the two test programs showed few
significant differences. These results indicate that trace element
emissions are not generally increased when using the Blueray furnace
compared to conventional heating equipment.
Trace element measurements were performed primarily using the Spark
Source Mass Spectroscopy (SSMS) for the conventional heaters, while Atomic
Absorption Spectrometry (AAS) was predominantly used for the Blueray
furnace. Because of the low level of mineral matter in the distillate
fuel oil and the small amount of particulate matter collected, several
trace elements were present below detectable levels (indicated by the "<"
sign) when using the AAS analytical method during the Blueray tests. SSMS
analysis of mineral matter in the distillate fuel oil burned in the
conventional heaters indicated that for over 50 percent of the elements,
stack emissions were below 70 percent of levels entering the heaters.
This finding may indicate some retention of fuel oil mineral matter in
residential heating equipment.
6.2 SOURCE ANALYSIS MODEL EVALUATION
To help quantify the environmental impact of a low-NO
A
residential furnace a Source Analysis Model, SAM IA (Reference 6-4), was
applied to the flue gas data from the fifth Blueray unit tested in the
NO EA program. IERL and the conventional units tested by GCA have been
/\
developing a series of Source Analysis Models to compare emission data to
environmental objectives, termed Multimedia Environmental Goals (MEGs)
(Reference 6-5). The model selected for the level of detail obtained from
the Blueray tests was SAM IA, designed for rapid screening purposes. As
such, it includes no treatment of pollutant transport or formation. Goal
comparisons employ threshold effluent stream concentration goals, termed
Discharge Multimedia Environmental Goals (DMEGs).
For the purposes of screening pollutant emissons data to identify
species requiring further study, a Discharge Severity (DS) is defined as
follows:
n<- _ Concentration of Pollutant i in Effluent Stream
i DMEG of Pollutant i
6-4
-------
The DMEG value, the threshold effluent concentration, is the
maximum pollutant concentration considered safe for occupational
exposure. When DS exceeds unity, more refined chemical analysis may be
required to quantify specific compounds present.
To compare waste stream potential hazards, a Weighted Discharge
Severity (WDS) is defined as follows:
WDS = (^ DS^ x Mass Flow Rate,
where the Discharge Severity is summed over all species analyzed. The WDS
is an indicator of output of hazardous pollutants and can be used to rank
the needs for controls for waste streams. It can also be used as a
preliminary measure of how well a pollutant control, say a combustion
modification NO control, reduces the overall environmental hazard of
A
the source. An extensive exposition of SAM IA and list of DMEGs are
presented in Reference 6-4 and will not be repeated here.
SAM IA was used to evaluate the emissions data in Table 6-1. Since
the model requires effluent concentrations on a mass per volume basis, the
emission factors in Table 6-1 were converted to concentrations at a
furnace discharge vent assuming a flue gas dilutive to 17 percent 0,,.
This Op level was the average roof vent level reported in Reference 6-3.
Table 6-2 lists discharge severities for those species with DS greater
than 0.1. In calculating DS for NO , S09, and CO for the conventional
A £_
furnace emission factors taken from AP-42 (Reference 6-5) were used, since
field tests reported in Reference 6-3 did not measure these pollutants.
The data in Table 6-2 led to several conclusions. First, DS values
for trace elements between the units are quite comparable as expected
based on trace elements emission results presented in Table 6-1. Of the
trace elements Cr and Ni emissions present the greatest potential hazard
in all cases. However, measured levels of these metals may be an artifact
of the stream sampling methodology. The flue gas sampling trains in both
the conventional furnace test program and the NO EA contained many
A
stainless steel components. Thus, some of the reported Cr and Ni could
have come from the sampling train itself rather than being a significant
component of the flue gas.
For both types of units S02 emissions were flagged and emissions
of certain organic categories had DS values greater than 1. For the
6-5
-------
TABLE 6-2. FLUE GAS DISCHARGE SEVERITIES GREATER THAN 0.1 FOR THE
BLUERAY FURNACE AND CONVENTIONAL OIL-FIRED HEATERS
Pollutant
NOX
S02
so3
CO
Arsenic (As)
Cadmium (Cd)
Chromium (Cr)
Cobalt (Co)
Copper (Cu)
Iron (Fe)
Lead (Pb)
Nickel (Ni)
Thallium (Tl)
Amines
Carboxylic acid
Total Stream DS
Blueray Furnace Conventional Furnace
(Reference 6-2) (Reference 6-3)
Continuous
Operation
0.86
1.6
0.15
0.17
0.23
0.17
85
0.14
0.075
0.42
0.14
4.5
0.37
NFC
0.20
95.7
Cyclic
Operation
0.60
2.1
0.77
1.1
0.27
0.11
5.5
0.11
0.055
0.046
0.14
0.73
0.41
NFC
2.3
15.5
Cylic Operation
4.73
6.3a
4.5
0.30a
0.60
0.85
22
NDb
0.60
0.011
0.21
15
NDb
1.6
—
59.0
aPollutant not measured in test program, DS calculated from AP-42
emission factors: NOX; 55 ng/J; S02J 100 ng/J; CO; 15 ng/J
^ND: Species not analyzed for
CNF: None found
6-6
-------
conventional units amines were flagged as being of potential concern; for
the Blueray unit carboxylic acids would be of potential concern under
cyclic operation. The DS for NO exceeds 1 for conventional units, but
/\
is less than 1 for the low-NO Blueray unit under both continuous and
A
cyclic operations.
In sunrnary, flue gas stream Total Discharge Severity (TDS) for
typical conventional units appears to fall between the TDS for the
low-NO unit under cyclic (normal) operation and that for the low-NO
X X
unit under continuous operation. If Cr and Ni are removed from the TDS
calculations, adjusted TDSs of 22, 6.2, and 9.3 result for the
conventional, Blueray continuous, and Blueray cyclic data respectively.
Thus, if measured Cr and Ni indeed comes from the sampling train, then the
low-NO unit's TDS under both cyclic and continuous operation is lower
A
than that of the conventional units. This suggests that using the Blueray
design
sound.
design to control NO from oil-fired heating units is environmentally
A
Of the flue gas species, S0? had the largest DS value. Its
potential hazard was lower for the low-NO unit than for the
A
conventional units (based on an AP-42 emission factor for conventional
units), however, this is most likely due to poor sulfur emissions test
results for the Blueray unit and fuel composition changes, rather than a
consequence of low-NO design. SO, emissions were also flagged as of
X o
concern for the conventional units. The fuel sulfur to SO., conversion
for two conventional domestic heaters was reported to range between 2.1
and 6.5 percent (Reference 6-3). This relatively high conversion rate for
distillate oil combustion was attributed to high combustion excess air
levels (Reference 6-3). The DS for S03 is lower for the low-NOx unit
(again, probably uncertain due to Blueray test results as well as fuel
composition effects).
The DS for NO was significantly lower for the Blueray furnace,
A
decreasing from a value of about five for conventional units (representing
potential environmental hazard), to less than one for the low-NO unit.
A
Finally, the flue gas stream total DS for the low-NO unit under
A
cyclic (or "normal") operation was lower than that for conventional units,
6-7
-------
due in part to significant NO reductions. However, the Blueray furnace
A
DS under continuous operation was higher, due largely to significantly
increased Cr emissions.
6.3 ENVIRONMENTAL IMPACTS OF NO CONTROLS ON CRITERIA POLLUTANTS
A
With the exception of radiant screens and secondary air baffles for
natural gas-fired residential burners the NO control techniques for
A
either gas-fired or oil-fired residential heaters have essentially no
adverse impact on other criteria and total organic pollutants. On the
contrary, some of the low-NO high-efficiency combustor designs such as
A
the Blueray and the M.A.N. burners, assure low combustible emissions by
recirculating the combustion products. The flue gas recirculation of the
Blueray combustor results in very low CO, UHC and smoke emissions even at
relatively low excess air operation. The low excess air also improves
thermal efficiency and reduces seasonal fuel consumption. Other effective
NO controls such as the EPA/Rocketdyne furnace, the M.A.N. burner for
A
fuel oil and the Amana HTM for natural gas are also effective in reducing
combustible emissions while significantly lowering NO
A
Table 6-3 summarizes the level of NO control achievable with
A
most effective control alternatives for both gas- and distillate oil-fired
residential heaters. Control alternatives which are far from
commercialization have not been included. The data indicate that the
flame retention burner head, for example, could be used to achieve a NO
standard for distillate oil-fired warm air furnaces of 40 ng/J heat input
or approximately 50 ng/J of useful heat. For more stringent NO
A
standards for oil-fired heaters the EPA/Rocketdyne burner head and the
Blueray design can achieve 35 and 15 ng/J on a heat input basis (11.5 and
4.9 lb/1000 gal of oil) respectively. For natural gas-fired heaters the
modulating furnace and the Amana HTM combustor could achieve NO
standards of 25 and 10 ng/J on a heat input basis (920 and 390 ng/m3 of
gas) respectively.
With the exception of the South Coast Air Quality Management
District (SCAQMD) in Southern California, there are no promulgated
regulations governing NO emissions from residential heaters. Rule 1111
A
of the SCAQMD states that all natural gas-fired residential warm air
furnaces for stationary residences sold after January 1, 1984, must not
6-8
-------
TABLE 6-3. ENVIRONMENTAL IMPACT OF MOST EFFECTIVE NOX CONTROL
ALTERNATIVES ON RESIDENTIAL SPACE HEATERS
Emission Level
ng/J Heat
Input
40b
35
19
15
25
10
ng/J Heat
Output or
Useful Heat
50
45
29
20
35
12
Fuel
Distillate oil
Distillate oil
Distillate oil
Distillate oil
Natural gas
Natural Gas
Best Control
Alternative
Flame retention
burner head
EPA/Rocketdyne
burner head
EPA/Rocketdyne
furnace
Blueray Furnace
H.A.N. Burner
Modulating furnace
Amana HTM Combustor
Environmetal
Impact3
Percent Change
in Emissions
CO UHC Smoke
-47 -78 -38
-57 -80 -78
-33 -73 -90
-80 -56 -100
N/A N/A -70
N/A N/A
N/A N/A
Application
R — Retrofit
N - New
N, R
N, R
N
N
N, R
N
N
»Percent reductions are based on baseline NOX emissions data reported
in Reference 6-6 and average controlled levels reported in Section 5
of this report.
lowest NOX level measured from a flame retention burner (Reference 6-7).
6-9
-------
exceed 40 ng/J of useful heat (the thermal heat output of a system).
Brookman and Kalika measured uncontrolled NO levels from existing gas-
A
fired heaters at about 60 ng/J of heat input (Reference 6-6). This
emission level translates to about 85 ng/J of useful heat for a furnace
cycle efficiency of 70 percent. Thus the SCAQMD Rule 1111 requires more
than 50 percent NO reduction from uncontrolled levels. As indicated in
/\
Table 6-3, both the modulating furnace and the HTM combustor can meet this
regulation. Furthermore, the commercial development of the Bratko burner
could in the near future add one more control alternative capable of
meeting stringent NO regulations for natural gas-fired heaters.
/\
Table 6-3 also shows the effect of NO controls on other criteria
/\
pollutants. As indicated, there are substantial reductions of combustible
emissions from distillate oil-fired space heaters for each of the NOX
control alternatives listed. These percent reductions were calculated
using the cyclic emission levels suggested by Barrett ejt a!. as being
representative of existing residential oil-fired heaters (Reference 6-8).
These suggested uncontrolled combustible emissions, however, account for
equipment in need of tuning. Therefore, tuning, maintenance and other
controls discussed in Section 5 (see Table 5-7) could also reduce these
combustible emissions lowering the percent reductions of Table 6-3
substantially. However, it can be generalized that selected most
effective NO control alternatives also reduce overall seasonal
J\
combustible emissions as well as lowering NO .
6.4 OPERATIONAL AND COST IMPACTS OF CONTROLS
NO controls listed in Table 6-3 for both natural gas and
/\
distillate oil-fired residential heaters not only reduce NO and
A
combustible emissions but often bring about an improvement in equipment
operating performance. For example for oil-fired equipment, both the
Blueray and the EPA/Rocketdyne furnace design have shown an improvement in
seasonal thermal efficiency of at least 10 percent above that of
conventional warm air furnaces. The Blueray furnace shows no loss in
performance and maintains minimum smoke and combustible emissions
(Reference 6-9). Similarly, the recently developed EPA/Rocketdyne furnace
has demonstrated relatively steady performance over an average field test
period of 2 months (Reference 6-10). Furthermore, representatives of the
6-10
-------
M.A.N. burner claim that the thermal efficiency and overall performance of
their system does not deteriorate thus the burner does not require yearly
servicing as do conventional oil- fired residential heaters
(Reference 6-11). However, field tests have not yet been performed to
verify these claims.
Table 6-4 lists the cost data available for the NO control
A
alternatives discussed throughout this report for residential heating
systems. Since no cost data are available on the M.A.N. burner either for
a retrofit or new installation this control has not been listed. As
indicated, retrofit of the optimized burner head for residential oil-fired
warm air furnaces represents the most cost-effective alternative to
achieve a NO emission level of about 45 ng/J of useful heat. The
A
payback period for the initial investment of $43 is estimated at less than
one year. Retrofit of the flame retention burner head to achieve NO
A
emissions of about 50 ng/J of useful heat from existing furnaces is the
second most effective control alternative for this level of control.
Payback period is also estimated at less than one year. For a stringent
NO emission control level of about 20 ng/J of useful heat for new oil-
A
fired heaters the Blueray "blue flame" furnace is the most cost-effective
as well as the only commercially available alternative.
The payback periods listed in Table 6-4 are estimates based on the
time required to recover the money spent for the initial investment of
installing NO control equipment. Since all these control alternatives
A
bring about an increase in thermal efficiency, and thus fuel savings, the
control is often paid for with the fuel cost savings cunmulated over a
time period less than a year. It should also be pointed out that for new
equipment installed in new homes the cost of the furnace is generally
included with that of the house. The incremental cost of the furnace is
then annualized over the mortgage period of the house (i.e., 20 to 30
years). For example, the estimated $100 incremental cost of a Blueray
furnace would be annualized to about $11 per year for a 20 year mortgage
at 9.25 percent interest. It can be seen that the annual fuel savings,
$100 for a typical oil bill of $500/year (Reference 6-9) would more than
compensate for the $11 increase in annual mortgage rate.
6-11
-------
TABLE 6-4. COST IMPACT OF NOX CONTROL ALTERNATIVES
I
I—•
ro
Control
Amana (HTM) Furnace
Modulating Furnace
Surface Combustion
Burner (Infrared Bratko
type)
Pulse Combustion
Burner0
Catalytic Combustion
Burner0
Flame Retention Burner
Head
Flame Retention Burner
EPA/Rocketdyne Burner
Head
EPA/Rocketdyne Furnace
Blueray Furnace
Fuel
Natural Gas
Natural Gas
Natural Gas
Natural Gas
Natural Gas
Distillate Oil
Distillate Oil
Distillate Oil
Distillate Oil
Distillate Oil
Achievable NOX Level
ng/J Useful Heat
12,
(390 ng/m3gas)
35
(920 ng/m3 gas)
12
(39 ng/mj gas)
21
(683 ng/m3 gas)
Estimated
(163 ng/m3 gas)
50
(1.8 g/kg fuel)
50
(1.8 g/kg fuel)
45
(1.6 g/kg fuel)
29
(0.9 g/kg/fuel)
20
(0.7 g/kg fuel)
1978
Incremental
Investment Cost
$100-$300 over cost
of conventional furnace
$50-$250 over cost
of conventional furnace
$100- $200 over cost of
conventional furnace/
heater
$300-$600 over cost of
conventional furnace/
heater
$150-$250 over cost of
conventional furnace/
heater
152 - retrofit
including installation
$385 — retrofit of
reduced capacity burner
$43 — retrofit
including installation
$250 over cost of
conventional furnace
$100 over cost of
conventional furnace
Cost Effectiveness
$/(ng/J)a
1.7-5.2
1.4-7.0
1.7-3.4
6.1-12.2
2.3-3.9
2.6
12.8
1.3
4.2
1.7
Payback Period
Based on Annual
Fuel Bill of $500
1-3 years
1-3.8 years
3.5-8.0 years
1.7-3.5 years
1.4-2.3 years
Less than 1 year
3.5 years
Less than 1 year
2.5 years
1 year
aBased on uncontrolled NOX emissions of 70 ng/J heat output for natural gas-fired heaters and 80 ng/J heat output
for distillate oil-fired heaters. Cost-effectiveness is based on the differential investment cost of the control.
°Based on Installation on a condensing system where seasonal efficiencies can be as high as 95 percent.
-------
6.5 DATA BASE EVALUATION AND NEEDS
The review of published papers on residential and commercial
heating systems conducted in this study has revealed a substantial amount
of criteria emissions data for gas- and oil-fired residential heaters.
Recently, noncriteria pollutants (trace elements and organics) have also
been measured. Residential equipment has been extensively characterized
and inventories are well documented. In addition, few control
alternatives for NO and combustible pollutants have also been
/\
investigated. Some low-NO and high-efficiency furnace designs are
A
commercially available, while other equally or more effective designs are
either in final demonstration stages or await commercialization.
Performance data on these improved heating equipment designs are being
gathered through EPA sponsored field and laboratory programs. These and
other test programs will aid in further documenting the performance,
reliability of these advanced sources and quantifying their impact on
other pollutant emissions.
This general availability of emissions and NO control technology
n
data for residential warm air furnaces is contrasted by the purity of
inventory and emission test data for commercial space heating equipment
with heat input generally less than 0.3 MW (106 Btu/hr).
These units include rooftop commercial heating equipment, both
indirect and direct fired, which are often combined with air conditioning
systems, and a number of indoor waters. The impact of these sources needs
to be identified through a detailed inventory of existing equipment and a
review of use patterns and fuel consumptions.
These commercial space heating sources could be substantial
contributors to ambient N0? concentrations during the cold season. With
the exception of the EPA/Rocketdyne low-NO burner head design for
J\
commercial size oil-fired burners little NO control technology has been
A
developed. Although combustion equipment in this source category is
generally similar to the residential equipment, the assumption that low
NO burner systems may be applicable to commercial units is only
A
speculative at present. Other low NO design concepts such as flue gas
A
recirculation as used in the Blueray furnace and M.A.N. burners can
probably be scaled up to commercial size equipment. In fact, the M.A.N.
6-13
-------
burner is being scaled up to 0.45 MW (1.5 x 106 Btu/hr). A unit is
being tested in W. Germany (Reference 6-11).
Information on NO control alternatives for commercial size steam
A
and hot water boilers burning gas or oil is also scarse. While it can be
speculated that some boiler designs lend themselves to N0x control
techniques investigated for industrial size boilers, little experimental
data exist to confirm this. Furthermore, low-NOx burner technology for
heat input capacities in the size range of 0.1 to 2.9 W (0.4 to 10 x
10 Btu/hr) show promise based on advanced burner technology developed
for both residential units on the small side and industrial units on the
large side. For example, the TRW oil-fired low-NOx burner
(Reference 6-12) with a capability of reducing NO up to 50 percent
/\
while increasing fuel efficiency is being demonstrated on industrial size
boilers. However, the low-NO design concept of this burner can
f\
apparently be scaled down to capacities less than 2.93 MW (10 x 10 Btu/hr),
Lack of regulatory incentives for commercial size boilers has suppressed
efforts in this area however.
In the area of solid fuel-fired residential and commercial
equipment NO technology is also very limited. Past and on-going test
A
programs have mainly dealt with quantifying the pollutant levels and
identifying equipment operating parameters and fuel characteristics which
have some impact on these levels. Primary pollutants of interest for this
category of equipment have been particulate and smoke emissions as well as
levels of organics, toxic elements and POM. Solid fuel fired equipment,
whether coal- or wood-fired, often does not permit extensive modifications
of equipment or operating procedures to reduce NO levels. Investigative
/\
efforts in this area should continue to determine potential NO control
/\
technology while still concentrating on reducing the impact of other
criteria and noncriteria pollutant emissions.
Cost data on NO control alternatives for residential heating
^
systems was generally not precise. This prevented a detailed economic
impact of widespread implementation of control alternatives. Future EA
programs should deal in more detail with cost impact of NO control
/\
devices to achieve specific levels of control. However, presently
available cost data indicate that the incremental cost of NO controls
6-14
-------
to the homeowner is often small (especially for new equipment) and
generally reversable within a short time through savings in fuel oil
consumptions.
6-15
-------
REFERENCES FOR SECTION 6
6-1 Waterland, L. R., et al.. "Environmental Assessment of Stationary
Source NOX Control Technologies — Final Report," Acurex Draft
Report, EPA Contract 68-02-2160, Acurex Corporation, Mountain View,
CA, September 1979.
6-2. Higginbotham, E. B. , "Combustion Modification Controls for
Residential and Commercial Heating Systems: Volume II. Oil-fired
Residential Furnace Field Tests " EPA-600/7-81-123b, July 1981.
6-3. Surprenant, N. F., et al.. "Emission Assessment of Conventional
Stationary Combustion Systems: Volume 1. Gas- and Oil-Fired
Residential Heating Sources", EPA-600/7-79-029b, NTIS-PB 298-494,
May 1979.
6-4. Shalit, L. M., and K.J. Wolfe, "SAM/IA: A Rapid Screening Method
for Environmental Assessment of Fossil Energy Process Effluents",
EPA-600/7-78-015, NTIS-PB177 088/AS, February 1978.
6-5. "Compilation of Air Pollutant Emission Factors, Third Edition,
Including Supplements 1-7", EPA Publication AP-42, NTIS PB 275-525,
October 1977.
6-6. Brookman, 6. T. and Kalika, W., "Measuring the Environmental Impact
of Domestic Gas-Fired Heating Systems," in the Proceedings of the
67th Annual Meeting, Air Pollution Control Association, June 1974.
6-7. Hall, R. E., et _aJL, "A Study of Air Pollutant Emissions from
Residential Heating Systems," EPA-650/2-74-003, NTIS PB-228 667,
January 1974.
6-8. Barrett, R. E., £t _al_., "Field Investigation of Emissions from
Combustion Equipment for Space Heating," EPA R2-0842 and API
Publication 418, June 1973.
6-9. "The Blueray Systems" Sales Brochures provided by Blueray Systems, -
Inc., Mineola, New York, October 1978.
6-10. Okuda, A. S. and Combs, L. P., "Field Verification of Low Emission
Integrated Residential Furnaces," in Proceedings of the Thi d
Stationary Source Combustion Symposium, Volume 1 EPA-600/7-78-050,
February 1979.
6-11. Personal communication with Karl Klatt, M.A.N. Representative,
Karl son, Scarborough, Ontario, Canada, March 13, 1979.
6-12. Personal Communications with R. R. Koppang, TRW Inc., Redondo
Beach, CA, March 12, 1979.
6-16
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-81-12 3a
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE Combustion Modification Controls for
Residential and Commercial Heating Systems: Volume
I. Environmental Assessment
5. REPORT DATE
July 1981
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
C. Castaldini, R. A. Brown, and K. J. Lim
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Acurex/Energy and Environmental Division
485 Clyde Avenue
Mountain View, California 94042
10. PROGRAM ELEMENT NO.
E HE 62 4 A
11. CONTRACT/GRANT NO.
68-02-2160
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Task Final; 6/78-9/79
14. SPONSORING AGENCY CODE
EPA/600/13
15. SUPPLEMENTARY NOTES JERL-RTP project officer is Joshua S. Bowen, Mail Drop 65,
919/541-2470.
16. ABSTRACT
repOrj- gjves an environmental assessment of combustion modification
techniques for residential and commercial heating systems , with respect to NOx con-
trol reduction effectiveness, operational impact, thermal efficiency impact, control
costs, and effect on emissions of pollutants other than NOx. Major equipment types
and design trends are reviewed, although emissions and control data for commercial
systems are very sparse. Natural gas and distillate oil are the principal fuels. NOx,
CO, unburned hydrocarbons, and (for oil firing) particulate are the primary pollu-
tants. For gas-fired residential systems, high radiative heat transfer burners have
been developed, which lower NOx emissions by about 80% without increasing emis-
sions of combustibles. For oil-fired residential systems, several new burner de-
signs, including integrated burner/furnace systems, have been developed, which
lower NOx by 20-85% and generally decrease CO, UHC, and particulate emissions.
Commercial application of these systems is very limited. Since the control tech-
niques generally increase thermal efficiency, the additional initial investment cost -
can often be recouped in a year. Field test data of a commercial, oil-fired, low-
NOx residential system indicate that the system poses less of an environmental
hazard than older conventional systems .
17.
KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
Pollution
Heating
Combustion Control
Nitrogen Oxides
Natural Gas
Fuel Oil
Assessments
18. DISTRIBUTION STATEMENT
b.lDENTIFIERS/OPEN ENDED TERMS
COSATl Field/Group
Pollution Control
Stationary Sources
Residential Systems
Commercial Systems
Combustion Modification
Environmental Assess-
ment
13 B
13H
21B
07B
21D
14B
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
189
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
-------
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
vVEPA
Research and Development
EPA-600/S7-81 -123 August 1982
Project Summary
Combustion Modification
Controls for Residential and
Commercial Heating Systems
C. Castaldini, K. J. Lim, and L. R. Waterland
This report provides an environ-
mental assessment of combustion
modification techniques for residential
and commercial heating systems. The
assessment evaluates NOX reduction
effectiveness, operational impact,
thermal efficiency impact, control
costs, and effects on pollutant emis-
sions other than NOX- Major equip-
ment types and design trends are
reviewed, although emissions and
control data for commercial systems
are very sparse. Natural gas and
distillate oil are the principal fuels.
NOx, CO, and unburned hydrocarbons
(and particulates for oil-firing) are the
primary pollutants. High radiative heat
transfer burners have been developed
for gas-fired residential systems,
lowering NOX emissions by about 80
percent without increasing emissions
of combustibles. For oil-fired resi-
dential systems, several new burner
designs (including integrated burner/
furnace systems) have been devel-
oped, lowering NO* by 20 to 85
percent and generally decreasing CO,
HC, and particulate emissions. Com-
mercial application of these systems is
very limited. No operational or main-
tenance problems are expected. Since
the control techniques generally
increase thermal efficiency, the addi-
tional initial investment cost will be
offset by operational savings. Field
test data from a commercially available
oil-fired low-NOx residential system
suggest that the system poses less of a
potential environmental hazard than a
conventional unit.
This Project Summary was devel-
oped by EPA's Industrial Environ-
mental Research Laboratory, Research
Triangle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
With the increasing extent of NOX
control application in the field, and
expanded INOX control development
anticipated for the future, there is
currently a need to ensure that: (1) the
current and emerging control tech-
niques are technically and environ-
mentally sound and compatible with
efficient and economical operation of
systems to which they are applied, and
(2) the scope and timing of new control
development programs are adequate to
allow stationary sources of NOX to
comply with potential air quality
standards. With these needs as back-
ground, EPA's Industrial Environmental
Research Laboratory, Research Triangle
Park (IERL-RTP) initiated the "Environ-
mental Assessment of Stationary Source
NOX Combustion Modification Tech-
nologies Program" (NOX EA) in 1976.
This program has two main objectives:
(1) to identify the multimedia environ-
mental impact of stationary combustion
sources and NOX combustibn modifica-
tion controls applied to these sources,
and (2) to identify the most cost-
effective, environmentally sound NOX
combustion modification controls for
attaining and maintaining current and
-------
projected NO2 air quality standards to
the year 2000.
The NOX EA's assessment activities
have placed primary emphasis on:
major stationary fuel combustion NOX
Sources (utility boilers, industrial boilers,
gas turbines, internal combustion
engines, and commercial and residential
heating systems); conventional gaseous,
liquid, and solid fuels burned in these
sources; and combustion modification
control applicable to these sources with
potential for implementation to the year
2000.
This report summarizes the environ-
mental assessment of combustion
modification controls for commercial
and residential heating systems. It
presents an outline of the environ-
mental, economic, and operational
impacts of applying combustion modi-
fication controls to this source category.
Results of a field test program aimed at
providing data to support the environ-
mental and operational impact evalua-
tion are also summarized.
Conclusions
Source Characterization
Figure 1 shows that commercial and
residential sources with a heat input
capacity <2.9 MW (<107 Btu/hr)
constitute the fourth largest NOX
emission category, contributing nearly
7 percent of the total NOX from all
stationary sources. Major fuel combus-
tion sources in the residential and
commercial category are central warm
air furnaces, room or direct heaters,
residential hot water heaters, and
steam and hot water hydronic boilers
used for space or water heating. Minor
sources include stoves and fireplaces;
these consume a relatively insignificant
quantity of fuel compared to other space
heating equipment. A breakdown of
1977 IMOx emissions from residential
and commercial sources indicates that
central warm air furnaces contributed
14 percent, steam and hot water
heaters 26.1 percent, and warm air
space heaters 4.3 percent of the total
NOX from the sources. A variety of
factors, including continuing demand
for new housing and fuel use trends,
will tend to increase NO* emissions
from residential heating systems. Thus,
given this trend and their potential for
NOx control, residential and commercial
heating systems represent a priority
source category for evaluation in the
NO, EA.
The primary fuels used for residential
heating are natural gas and distillate
Commercial and
residential 2.9 MW
(10 x 10* Btu/hr) 6.8%
Incineration 0.4%
Noncombustion 1.9%
Gas turbines 2.0%
Others (fugitive) 4.1%
Industrial process
heaters 4.1%
Industrial and commercial
boilers >2.9 MW
f>10x 10e Btu/hr) 9.7%
Reciprocating
1C engines
18.9%
Total from all sources: 10.5 Tg/yr (11.6 x JO6 ton/yr)
Warm air space heaters 4.3%
Warm air
central
furnaces 14.0%
Miscellaneous combustion* 17.4%
Firetube boilers 12.5%
Watertube boilers 1.4%
Steam and hot
water heaters
26.1%
Cast iron boilers
30.3 %
Total from all sources with capacity less than 2.9 MW
(WxW6 Btu/hr): 0.709 Tg/yr (0.781 x W6 tons/yr)
^Includes cooling and air conditioning
Figure 1. Distribution of stationary man-made sources of NOx
emissions for the year 1977 (controlled NOx levels.ffieference 1).
-------
oils (No. 1 and 2 distillate). These fuels
combined account for nearly 90 percent
of all fuel burned for domestic heating.
Liquefied petroleum gas(LPG-butane or
propane), coal, and wood are also used,
although in relatively small quantities.
In 1976, LPG-fired equipment accounted
for about 6 percent of domestic heating
equipment, while coal- and wood-fired
units accounted for only 2 percent.
Built-in, residential, electric heating
systems, including heat pumps, have
become increasingly popular as
domestic supply of clean fuels dwindles
and fuel costs increase. Electric heaters
in 1 976 accounted for nearly 14 percent
of residential heating equipment.
The primary fuels and equipment
types used for domestic heating show
significant regional variations. For
example, the Northeast depends pri-
marily on oil-fired steam or hot water
units, while in all other regions, natural-
gas-fired central warm air furnaces are
used primarily for domestic space
heating.
Combustion equipment designs for
most residential heating systems are
quite similar. For natural-gas-fired
equipment, the single-port upshot or
the tubular multiport burners are the
most common. Natural-gas-fired warm
air furnaces, room heaters, or hot water
heaters generally use a pilot flame to
ignite the burner automatically.
Distillate-oil-fired residential heating
systems generally use high-pressure
atomizing gun burners. Nearly all new
oil-fired burners use theflame retention
burner head which promotes more
efficient combustion.
Commercial heating systems can be
divided into three general categories:
warm air unit heaters or space heaters,
warm air furnaces or duct heaters, and
hot water or steam systems. The
combustion systems for commercial
warm air units (or space heaters) and
duct heaters are generally similar to
residential systems, although there are
a few unique commercial gas-fired
designs. Warm air units and duct
heaters are either direct or indirect
fired. Direct fired heaters use only clean
gaseous fuels, exhausting the combus-
tion products directly into the heated
space. Indirect fired heaters use either
gas or oil and are vented to the outdoors.
These units, except for their larger
capacity, are generally similar to
residential central warm air furnaces.
Hot water and steam systems in the
commercial size capacity, here defined
in the range of 0.12 - 2.9 MW[(0.4 -10)
x 106 Btu/hr] heat input capacity,
include cast iron hydronic boilers, and
small firetube and watertube boilers
used in both the commercial and
industrial sectors. Cast iron hydronic
boilers are also used in residential
applications. These units, common in
the Northeast and Northcentral regions
of the U.S., are primarily either gas- or
distillate-oil-fired. Firetube and small
watertube boilers used to heat large
commercial plants and buildings are
similar to the smaller industrial boilers
used to generate process steam. These
boilers are generally fired with gas, oil,
or (less frequently) stoker coal, and
account for about 25 percent of the
installed capacity of steam and hot
water boilers with heat input capacity
less than 2.9 MW (10 x 106 Btu/hr).
Source Emissions
Because natural gas and distillate oil
are the principal fuels used in residential
and commercial heating systems, air
pollutant emissions represent the
primary waste stream of environmental
concern. Coal- and wood-fired furnaces
and stoves, however, also produce ash
solid waste streams. Although increas-
ing in popularity due to the scarcity and
high cost of other fuels and electricity,
residential wood- and coal-fired systems
still account for only 2 percent of all
domestic heaters. Thus, nationally,
solid waste streams from residential
heating pose an insignificant environ-
mental concern. Commercial coal-fired
watertube and firetube stokers are also
the source of solid waste streams.
These units, which account for about 15
percent of the firetube and watertube
population, could increase in popularity
with economic and political incentives
for increased use of domestic coal.
Flue gas emissions from natural-gas-
fired residential and commercial com-
bustion sources include primarily NOX,
CO, and unburned hydrocarbons (HC).
When fuel oil or coal is burned, smoke,
paniculate, and S02 are also emitted.
The levels of NO,, CO, and HC from oil
and coal combustion are usually higher
than those from gas combustion. Figure
2 shows the general trends of steady-
state smoke and gaseous emissions
from oil-fired residential heaters as a
function of combustion air settings.
Commercial boilers show similar trends.
For both equipment types, the operating
setting corresponding to lowest emis-
sions of CO, HC, and smoke coincides
with high NOX levels. As the excessairis
reduced from the theoretical setting,
concentrations of CO, HC, and smoke
increase because of lack of oxygen in
the flame and reduced turbulent mixing
which leads to incomplete combustion.
At very high excess air levels, these
emissions can also increase due to the
excessive combustion air which cools
the flame, also resulting in incomplete
combustion.
A major factor contributing to high
combustible emissions, particularly in
residential burners, is the transient
operating mode. The on/off cycle is a
dominant characteristic of warm air
furnaces, and is quite important as a
cause of increased emissions. Figure 3
shows qualitative emission traces from
an oil burner during a typical cycle. CO
and HC emissions peak at ignition and
shutoff. HC concentration drops to
insignificant levels between the peaks,
while CO emissions tend to flatten out
at a measurable level. Particulate
emissions continuously taper off after
the ignition-induced peak, whereas NO
emissions first rise rapidly for a short
period and then continue to rise at a
more moderate rate as the combustion
chamber temperature increases. These
transient emissions are caused mainly
by variations in combustion chamber
temperature. At ignition, a cold re-
fractory will not assist complete com-
bustion; therefore, peaks of CO, HC, and
smoke can occur. In addition to the cold
refractory, wear and tear on the oil
pump causes poor shutoff performance
and (thus) high smoke and combustible
emissions.
In general, except for SO2 emissions
which depend entirely on the sulfur
content of the fuel, all other criteria
pollutant emissions are primarily a
function of burner nozzle type, combus-
tion chamber shape and material, and
operating practice.
Table 1 summarizes 1977 emissions
for stationary combustion sources with
heat input less than 2.9 MW (10 x 106
Btu/hr). These sources include pri-
marily residential and commercial
heating systems, as well as small
industrial boilers. Residential and
commercial heating systems contribute
56 and 28 percent, respectively, of the
total NOx from these sources. These
emissions are seasonal; nearly all the
total annual output occurs in the winter
months, during which the impact of
residential and commercial heating on
ground level ambient NOa concentra-
tion in urban areas can be significant.
-------
2.00-
7.50-
I
I
1.00—
-------
Filterable
Paniculate
NO
Burner
On
Burner
Off
I -\
Time
Time
HC
Burner
On
Burner
Off
|\
CO
Time —>•
Figure 3. Characteristic emissions of oil burners during one
complete cycle.
Time
levels. These units are now the primary
residential oil burners sold.
As part of its combustion research
program, EPA has supported low-NOx
high efficiency residential burner
development since 1971. Under one
program, Rocketdyne developed a
controlled-mixing burner head for
retrofit and new applications on
domestic heaters. It was estimated that
widespread application of the relatively
inexpensive burner head would be
effective in reducing NO* by 20 percent
and increase efficiency by 5 percent on
the average for each retrofitted furnace.
Recently the burner was integrated with
an "optimum"* low emission, high
•Terminology used bv Rocketdyne to characterize
the final design capable of achieving program goals
efficiency warm air furnace. NOX
emissions have been reduced by 65 to
70 percent, and steady state efficiencies
have been increased by as much as 10
percent over those of conventional
designs. The EPA program emphasized
the necessity to match the firebox,
burner, and heat exchanger design to
achieve low NO* emissions while also
maintaining low levels of CO, HC, and
smoke.
Both the Blueray "blue flame" and
the M.A.N. burners use aerodynamic
flue gas recirculation to achieve a blue
flame with distillate fuel oil. These
burners thus achieve reduced flame
temperature, reduced oxygen concen-
trations in the near-burner zone, and
rapid vaporization of the fuel prior to
ignition. These conditions result in low
NOX emissions on the order of 1 5 to 40
ppm corrected at zero percent excess
air, representing NOx reductions of 50 to
80 percent. Theoretically, these burners
could be scaled up to larger commercial
sizes. The Blueray furnace system is
currently the only commercially avail-
able low NOx system in the U.S. for oil-
fired residential use. The M.A.N. burner,
developed in West Germany, is marketed
in parts of Europe and Canada.
Techniques aimed at reducing sea-
sonal pollutant emissions from resi-
dential heating systems are also ef-
fective in delivering improved fuel
economy and generally reduced equip-
ment use. Replacement of wornout
furnaces, tuning, and changes in
thermostat anticipator settings are the
most effective emission reduction tech-
niques, with overall combustible emis-
sion reductions ranging from 1 6 to 65
percent for CO, 3 to 87 percent for HC,
59 percent for smoke, and 17 to 33 per-
cent for particulates. Installation of de-
layed action solenoid valves and re-
duced firing capacity through minor
modification or installation of a new
flame retention burner are effective in
reducing excessive smoke emissions
during furnace start-up and shutdown.
Reported average smoke reductions
range from 24 to 82 percent. In general,
all these techniques result in fuel sav-
ings, sometimes as high as 39 percent,
in addition to lowering combustible
emissions.
Application of control technology to
commercial heating equipment is very
limited. Theoretically, the flame
quenching and surface combustion
concepts investigated for gas-fired
residential equipment could also apply
to commercial heaters burning natural
gas. Similarly, low-NOx burner designs
for distillate oil firing or optimum
air/fuel mixing concepts could possibly
be scaled up to the larger commercial
equipment.
NOx control technology from gas- and
oil-fired industrial boilers include low-
NOx burners, staged combustion, flue
gas recirculation, load reduction, and
low excess air operation. These tech-
niques could possibly apply to com-
mercial size boilers of similar design.
Low-NOx burners are the most attractive
control alternative for this boiler size.
Some U.S. companies are currently
working on new burner designs,
primarily for oil-fired boilers. Most of
these efforts, however, have been
-------
Table 1. Estimated 1977 Air Pollutant Emissions from Stationary Fuel Combustion Sources with Heat Capacity Less than
2.9 MW(W x 10e Btu/hr)
r , Air Pollutant Emissions Gg (103 tons)
Fuer
Sector
Residential
Residential
and Commercial
Commercial
and Industrial
Total
Equipment
Warm air central
furnaces
Warm air space
heaters
Miscellaneous
combustion
Steam and hot
water heaters
Cast iron
boilers
Watertube
boilers
Firetube
boilers
All equipment
Fuel
Natural gas
Distillate
oil
Natural gas
Distillate
oil
Natural gas
Distillate
oil
Natural gas
Distillate
oil
Residual oil
Coal
Natural gas
Distillate
oil
Residual oil
Coal
Natural gas
Distillate
oil
Residual oil
Coal
Natural gas
Distillate
oil
Residual
oil
Coal
All fuels
Total Capacity,
MW I106 Btu/hrj
—
—
_
_
143,520
1489,495)
33,730
(115,041)
53,790
(183,456)
31,590
(107,742)
5,770
119,679)
4,490
(15,313)
5,240
(17,872)
1,900
(6.480)
79,090
(269,748)
31,530
(107,538)
48.200
(164,393)
14.420
(49,181)
—
Consumption
EJ (Quads)
1.876
(1.979)
1.354
(1.428)
0.57
(0.60)
0.42
(0.44)
1.524
(1.608)
0.926
(0.977)
2.1
(2.2)
1.4
(1.5)
0.11
(0.12)
0.043
(0.045)
1.8
(1.9)
0.35
(0.37)
0.47
(0.50)
0.097
(1.0)
0.053
(0.056)
0.021
(0.023)
0.015
(0.016)
0.012
(0.013)
1.358
(1.433)
0.37
(0.39)
0.354
(0.374)
0.11
(0.116)
15.22
(16.97)
/VOx
65.7
(72.5)
33.8
(37.3)
19.9
(21.9)
10.5
(11.6)
53.3
(58.8)
27.4
(30.2)
82.8
(91.3)
77.9
(85.9)
17.5
(19.3)
7.1
(7.8)
91.7
(101.1)
23.7
(26. 1)
84.6
(93.3)
14.6
(16.1)
3.16
(3.5)
1.18
(1.3)
2.38
(2.6)
3.0
(3.3)
31.0
(34.2)
12.8
(14.1)
30.7
(33.9)
14.1
(15.6)
708.8
(781.6)
CO
19.0
(20.9)
33.8
(37.3)
5.7
(6.3)
10.5
(11.6)
15.2
(16.8)
27.4
(30.2)
17.8
(19.6)
41.7
(46.0)
1.64
(1.81)
7.53
(8.30)
35.3
(38.9)
0.56
(0.61)
0.66
(0.73)
21.3
(23.5)
1.06
11.17)
0.06
(0.07)
0.02
(0.02)
0.91
(1.00)
15.2
(16.8)
0.34
(0.38)
0.29
(0.32)
5.40
(5.95)
261.4
(288.3)
HC
6.40
(7. 10)
6.40
(7.06)
1.94
(2. 14)
1.97
(2.17)
5.20
(5.73)
5.15
(5.68)
4.76
(5.25)
13.4
(14.8)
2.74
(3.02)
2.12
(2.34)
4.06
(4.48)
3.34
(3.68)
11.8
(13.8)
5.53
(6. 10)
0.18
(0.20)
0.01
(0.01)
0.07
(0.08)
0.19
(0.21)
1.75
(1-93)
2.05
(2.26)
5.12
(5.65)
3.40
(3.75)
87.6
(96.6)
Particulates 6'CA
7.50
(8.27)
70.3
(11.4)
2.30
(2.54)
3.20
(3.53)
6.10
(6.73)
8.33
(9. 19)
16.6
(18.3)
10.6
(11.7)
9.09
(10.0)
150.2
(165.6)
6.88
(7.59)
4.18
(4.61)
13.2
(14.6)
314.3
(346.6)
0.05
(0.05)
0.18
(0.20)
0.42
(0.46)
23.5
(25.9)
3.02
(3.33)
2.57
(2.83)
5.73
(6.32)
130.0
(143.4)
728.3
(803. 1)
0.49
(0.54)
146
(161)
0.15
(0.17)
45.4
(50. 1)
0.40
(0.44)
118.4
(130.6)
0.62
0.68
150.2
(165.6)
52.6
(58.0)
30.7
(33.8)
0.53
(0.58)
37.6
(41.5)
225.6
(248.8)
110.6
(122.0)
0.02
(0.02)
3.27
(3.61)
6.70
(7.39)
16.0
(17.6)
0.23
(0.25)
18.7
(20.6)
92.1
(101.61)
91.8
(101.2)
1,148.1
(1,266.0)
BEJ = W'a Joules = 0.948 Quads = 0.948 x W's Btu
oriented toward industrial (2.9 to 73.3
MW heat input) size boilers.
Cost of Control
Table 4 summarizes estimated costs
for the most effective NOX control
alternatives for residential heating
systems. As indicated, retrofit of the
controlled mixing burner head for
residential oil-fired warmairfurnaces is
the most cost-effective alternative to
achieve a NOX emissions level of about
45 ng/J of useful heat. Cost-effective-
ness of other alternatives for oil-fired
warm air furnaces is generally com-
parable, falling in the $1 to $4 ng/J
range. Similarly, for gas-fired warm air
furnaces, both the Amana HTM furnace
-------
Table 2. Performance Summary of Low-NO* Control Equipment f
Average Cyclic Pollutant Emissions,
Operating ng/J heat input Steady State
FyrR.tn A ir Fffiripnry
Control percent /V0xa CO UHCb percent
Baseline 40-120 28-45 8.6-25 3.3-33 70
Radiant screens 40-120 15-18 6.4 NA 75
Secondary air 60-80 22 14 NA NA
baffles
Bratko Surface 10 7.5 5.5-9.6 NA NA
combustion burner
Amana (HTM/ NA 7.7 26 NA 85
Modulating NA 25 NA NA 75
furnace
Pulse NA 10-20 NA NA 95
Combustor
Catalytic NA <5 NA NA 90
Combustor
or Natural Gas-Fired Residential Heaters
1978
Cycle Installed
Efficiency, Control
percent Cost Comments
60-65 ($500-S800f
70 NA
NA NA
NA S100-$200
80 $100 -$300
over
conventional
furnace
70 S50-S250
over con-
ventional
furnace
95 S300-S600
85 $100 -$250
Costs include installation
Emissions of CO and HC can increase
significantly if screen is not placed
properly or deforms
Requires careful installation. Best
suited for single-port upshot burners
Not commercially available. Still
under development
Commercially available design. Spark
ignited, thus requires no pilot
Furnace is essentially derated. Thus
it requires longer operation to deliver
a given heat load
Currently being investigated by AGAL
Efficiencies correspond to condensing
systems.
Still at the R&D stage. Efficiencies
correspond to condensing systems.
aSum of NO + /VO2 reported as NO?
tiUnburned hydrocarbons calculated as methane
^Typical costs of uncontrolled unit
NA not available
Table 3. Performance Summary of Low-NO* Control Equipment for Distillate-Oil-Fired Residential Heaters
Cyclic Pollutant Emissions,
A verage
Excess A ir.
Control percent NO"
Baseline 50-85 37-85
Flame Reten- 20-40 26-88
tion Burner
Head
Controlled 10-50 34
Mixing Burner
Head by EPA/
Rocketdyne
Integrated 20-30 19
Furnace Sys-
tem by EPA/
Rocketdyne
Blueray 20 10
"blue flame"
Burner/ Furnace
System
M.A.N. 10-15 10-25
Burner
ng/ j neat input
Steady State
Smoke Efficiency,
CO UHC" Number Paniculate percent
15-30 3.0-9.0 32 7.6-30 75
11-22 0.2- J 8 2.0 NA 80-83
also depends
on heat
exchanger
13 0.7-1.0 0.5-0.9 NA 80
also depends
on heat
exchanger
20 1.2 0.32 NA 84
4.5-7.5 1.5-2.5 zero NA 84
30 NA 10 NA 85
1978
Cycle Installed
Efficiency, Control
percent Cost
65-70 ($650-
$1000f
NA $52
NA $43
74 $250 over
conven-
tional
furnace
74 $100 over
conven-
tional
furnace
NA NA
Comments
Range in NO, emissions is
for resident/a! systems not
equipped with flame retention
burners Emissions for other
pollutants are averages
If a new burner is needed as well
as a burner head, the total cost
would be $385.
Cost of mass produced burner head
only about $1 .50. Combustible
emissions are relatively low because
hot firebox was used.
Uses optimized burner head.
For new furnace installation
only. Combustible emissions are
higher than with burner head
because of quenching in an air
cooled firebox. Recent cost estimate.
New installation only.
Furnace is commercially
available. Recent cost estimate.
Both for retrofit or new
installations. Not yet
commercially available in U.S.
Commercialization expected
in 1982.
"Sum of NO and NOi reported as NO2
"Unburned hydrocarbons calculated as methane !CHt)
"Typical costs of uncontrolled unit
-------
Table 4. Cost Impact of NO* Control Alternatives
Control
Amana (HTMI Furnace
Modulating Furnace
Surface Combustion
Burner (Infrared Bratko)
Pulse Combustion
Burner0
Catalytic Combustion
Burner"
Flame Retention
Burner Head
Flame Retention
Burner
EPA/Rocketdyne
Burner Head
EPA/Rocketdyne
Furnace
Bluer ay Furnace
Fuel
Natural Gas
Natural Gas
Natural Gas
Natural Gas
Natural Gas
Distillate Oil
Distillate Oil
Distillate Oil
Distillate Oil
Distillate Oil
Achievable /VOX Level,
ng/J useful heat
12
1390 ng/m3 fuel)
35
{920 ng/m3 fuel)
12
(390 ng/m3 fuel)
21
(683 ng/m3 fuel)
Estimated 5
(163 ng/m3 fuel)
50
(1.8 g/ kg fuel)
50
(1.8 g/kg fuel)
45
(1.6 g/kg fuel)
29
(0. 7 g/kg fuel)
20
(0.7 g/kg fuel)
1978
Incremental
Investment Cost
$100-$300 over cost of
conventional furnace
$50-$250 over cost of
conventional furnace
$100 -$200 over cost of
conventional furnace/
heater
$300-$600 over cost of
conventional furnace/
heater
$150-$250 over cost of
conventional furnace/
heater
$52— retrofit
including installation
$385— retrofit of
reduced capacity burner
$43— retrofit
including installation
$250 over cost of
conventional furnace
$100 over cost of
conventional furnace
Cost Effectiveness.
$/ng/J*
1.7-5.2
1.4-7.0
1.7-3.4
6.1-12.2
2.3-3.9
2.6
12.8
1.3
4.2
1.7
Payback Period Based
on Annual Fuel Bill
of $500, years
1-3
1-3.8
3.5-8.0
1.7-3.5
1.4-2.3
Less than 1
3.5
Less than 1
2.5
1
a Based on uncontrolled /VOX emissions of 70 ng/J heat output for natural-gas-fired heaters and 80 ng/J heat output for distillate-oil-fired heaters.
Cost effectiveness is based on the differential investment cost of the control.
"Based on installation of a condensing system where seasonal efficiencies can be as high as 95 percent.
and the modulating furnace are com-
parably cost-effective, in the $1 to $7
ng/J range. Surface combustor, pulse
combustor, and catalytic burner for gas-
fired units and the Rocketdyne devel-
oped techniques for oil-fired units are
not commercially available. The pay-
back periods listed in the table, are
estimates based on the time required to
recover the money spent for the initial
investment of installing NOX control
equipment. Since all these control
alternatives increase thermal efficiency,
and thus fuel savings, the initial
investment cost is often recouped in 1
year or less.
Incremental Emissions Due
to Controls
To assess the effects of a low-NOx
burner/furnace design on the incre-
mental emissions of pollutant species
other than NOX from a residential heat-
ing unit, an oil-fired Blueray low-NO*,
high-efficiency home furnace was field
tested. The unit was in a Medford, LI,
NY, residence and had been in service
about 1 year. The model tested fired
distillate fuel oil at 0.63 mg/s (0.6
gal./hr) and had a rated heat input of
24.6k J/s (84,000 Btu/hr). The program
involved testing in two modes of oper-
ation: continuous and cyclic (10 mi-
nutes on and 10 minutes off). The cyclic
mode is more representative of typical
operation. Sampling and analysis of the
flue gas stream, using slightly modified
Environmental Assessment Level 1
procedures, were performed (Reference
2). Detailed test results are reported in
Volume II of the full report summarized
here.
Table 5 shows average flue gas
composition data for the two tests. In
the cycling test, there were peaks in the
CO and HC emissions at the start and
end of each period of operation. This
initial peak is included in the average
concentration noted. Start-up peak
emissions averaged 2000 ppm for CO
and 400 ppm for HC. The NOx levels
started at zero and, toward the end of
the firing cycle, reached 1 6 ppm which
was the average valuefor the continuous
firing test. Average NO, emissions were
also very low in both cyclic and con-
tinuous operation. Paniculate emis-
sions were very low and did not vary
from continuous to cyclic operation.
Organic emissions increased substan-
tially for cyclic operation. Liquid column
chromatographic, infrared, and low
resolution mass spectrometric analyses
of the samples showed that, for both
cyclic and continuous operation, the
samples contained primarily aliphatic
hydrocarbons, with some aromatics and
carboxylic acids.
Table 6 summarizes flue gas emission
data, including those for trace element
Table 5. Flue Gas Composition:
Blueray Unit
Component Cyclic Continuous
NO*ng/J asNQt
ppm, dry
SOa, ng/J
SO3, ng/J
UHC, ng/J as CHt
ppm, dry
CO, ppm dry
COi, % dry
Oz. % dry
Paniculate, ng/J
Total OC7)
Organics, /jg/m3
6.6
11
35.5
1.0
5.0
23
160
12.9
4.0
1.30
2.63 xW
JO
16
26.9
0.2
0
0
25
13.1
3.8
1.32
1,300
8
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Table 6. Flue Gas Composition (ug/dscm).' Residential Warm air Furnaces
Element
/VOx
S02
S03
CO
Antimony
Arsenic
Barium
Beryllium
Bismuth
Boron
Cadmium
Chromium
Cobalt
Copper
Iron
Lead
Manganese
Mercury
Molybdenum
Nickel
Selenium
Tellurium
Thallium
Tin
Titanium
Vanadium
Zinc
Organics f>C7)
Bluer ay
Cyclic
5.4 x 103
2.7 x 104
770
4.5 x 104
<0.46
<0.54
<11
<0.014
<0.62
<10
<1.1
<5.5
<5.7
11
46
<21
<2.5
<3.0
<3.5
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Table 7. Flue Gas Discharge Severity: Oil-Fired Residential Warm Air Furnaces
Discharge Severity
Component
Cr
Ni
Alkylhalides
SO2
A/OX
S03
Amines
Carboxylic acids
CO
Total stream
MEG
Category
68
76
2
53
47
53
JO
8
42
Conventional
Cyclic
22
15
13
6.3a
4.7*
4.5
1.6
—
0.30a
59.0
Blueray
Continuous
85
4.5
—
1.6
0.86
0.15
—
0.20
0.77
95.7
Blueray
Cyclic
5.5
0.73
—
2.1
0.60
0.77
—
2.3
1.1
15.5
* Not measured; DS based on AP-42 emission factor s.
Performance test data on these im-
proved designs are being gathered in
EPA sponsored field and laboratory
programs. These and other test pro-
grams will aid in further documenting
the performance and reliability of these
advanced controls and quantifying their
impact on other pollutant emissions.
Cost data on NOX control alternatives
for residential heating systems are
generally sparse and imprecise. This
lack of definitive cost data prevented a
detailed economic impact assessment
of widespread implementation of control
alternatives. As advanced controls
become available, future studies should
quantify the cost impact of NOxcontrol
implementation to achieve specific
levels of control.
Information on NOX control alter-
natives for commercial size steam and
hot water boilers burning gas or oil is
also scarce. While it can be speculated
that some boiler designs lend them-
selves to NOx control techniques devel-
oped for industrial size boilers, little
experimental data exist to confirm this.
Low-NOx burner technology for heat
input capacities in the size range of 0.1
to 2.9 MW (0.4 to 10 x 10s Btu/hr)
shows promise based on advanced
burner technology developed for both
residential units on the small side and
industrial units on the larger side, but
definitive demonstration is needed.
NOx control alternatives for solid-
fuel-fired residential and commercial
equipment have also seen very limited
study. Past and on-going test programs
have mainly dealt with quantifying the
pollutant levels and identifying equip-
ment operating parameters and fuel
characteristics which have some impact
on these levels. Primary pollutants of
interest for this category of equipment
have been paniculate and smoke
emissions as well as levels of unburned
HC, toxic elements, and polycyclic
organic matter (POM). The simplicity of
the solid-fuel-fired equipment, whether
coal- or wood-fired, often does not
permit extensive modification of existing
equipment or operating procedures to
reduce NOx levels. Investigative efforts
in this area should continuetodetermine
potential NOx control technology appli-
cable to new unit design, while still
concentrating on reducing the impact of
other criteria and noncriteria pollutant
emissions.
References
1. Waterland, L.R., et al., "Environ-
mental Assessment of Stationary
Source NOX Control Technologies:
Final Report," Acurex Draft Final
Report FR-80-57/EE (IERL-RTP-
1279), EPA Contract 68-02-2160,
Acurex Corp., Mountain View, CA,
April 1980.
2. Lentzen, D.E., et al., "IERL-RTP
Procedures Manual: Level 1 Envi-
ronmental Assessment (Second
Edition)," EPA-600/7-78-201 (NTIS
PB293795), Industrial Environ-
mental Research Laboratory, Re-
search Triangle Park, NC, October
1978.
3. Surpenant, N.F., et al., "Emissions
Assessment of Conventional Sta-
tionary Combustion Systems; Volume
I: Gas- and Oil-fired Residential
Heating Sources," EPA-600/7-79-
029b (NTIS PB298494), Industrial
Environmental Research Laboratory,
Research Triangle Park, NC May
1979.
4. Schalit, L.M., and K.J. Wolfe,
"SAM/IA: A Rapid Screening Meth-
od for Environmental Assessment
of Fossil Energy Process Effluents,"
EPA-600/7-78-015 (NTIS PB277088),
Industrial Environmental Research
Laboratory, Research Triangle Park,
NC, February 1978.
10
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C. Castaldini, K. J. Urn, and L R. Water land are with Acurex Corporation,
Mountain View, CA 94042.
J. S. Bowen is the EPA Project Officer (see below).
The complete report consists of two volumes, entitled "Combustion Modification
Controls for Residential and Commercial Heating Systems,"
"Volume I. Environmental Assessment," (Order No. PB 82-231 168; Cost.
$16.50, subject to change)
"Volume II. Oil-Fired Residential Furnace Field Test," {Order No. PB 82-231
176; Cost: $10.50, subject to change)
The above reports will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
11
. 5. GOVERNMENT PRINTING OFFICE: 1982/559-092/0481
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