STAFF REPORT

Rule 3.21

Industrial, Institutional, and Commercial Boilers, Steam Generators, and 

Process Heaters

Date of Release: March 14, 2006

Schedule of Meetings

Rule 3.21Workshop: April 20, 2006

Public Hearing: June 5, 2006
STAFF REPORT 

Industrial, Institutional and Commercial Boilers, Steam Generators, and Process Heaters

Date of Release: March 14, 2006

Scheduled Date of FRAQMD Adoption: June 5, 2006

Feather River AQMD, 938 14th Street,

Marysville, California 95901

Contents Page 

Executive Summary.................................................................................................1

1. Purpose...............................................................................................................1

2. Background ........................................................................................................1

3. Legal Mandate....................................................................................................2

4. Proposed Rule Requirements.............................................................................2

5. Socioeconomic Impact.......................................................................................3

6. Effectiveness of Control Measures....................................................................3

7. Estimated Cost Impact .......................................................................................5

8. Environmental Review and Compliance ...........................................................6

9. Required Findings..............................................................................................7

...........................................

Attachment A. Rule Analysis

Attachment B. Public Notice

Attachment C. Comments and Responses
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STAFF REPORT

Executive Summary

Feather River Air Quality Management District (District) is a Bi-County district that administers local, 

state and federal air quality management programs for Yuba and Sutter Counties. Under the provisions 

of the California Clean Air Act (CCAA) of 1988, Yuba County and the northern portion of Sutter County

have been designated as “moderate” non-attainment areas for failing to meet the state ozone standard. 

The southern portion of Sutter County is designated as “serious” non-attainment for failing to meet the 

state ozone standard. 

Ozone is formed when volatile organic compounds (VOC) react with nitrogen oxides (NOx) in the 

presence of sunlight, and is one component of “smog”. Ozone is a strong irritant that attacks the 

respiratory system, leading to damage of lung tissues. Exposure to ozone aggravates asthma, bronchitis 

and other respiratory diseases, as well as cardiovascular diseases. Reductions in the NOx and VOC is 

necessary to attain and maintain the state ambient air quality standard for ozone.

The 2003 Air Quality Attainment Plan requires the Northern Sacramento Valley Air Basin (NSVAB) to 

adopt rules and regulations deemed necessary to attain and maintain the state ambient air quality 

standard for criteria pollutants at the earliest practical date. Rule 3.21, Industrial, Institutional, and 

Commercial Boilers, Steam Generators, and Process Heaters has been developed to fulfill the 

commitment made by the District and to help attain the state ambient air quality standards for ozone. 

1.0 Purpose:

The purpose of Rule 3.21 is to limit NOx emissions from boilers, steam generators, and process heaters 

with rated heat inputs greater than or equal to one (1) million Btu per hour (MMBtu/hr). 

2.0 Background:

The main function of boilers, steam generators, and process heaters are to transfer heat to water, which

will eventually form steam. Each unit creates heat through combustion, which is an exothermic reaction 

between a fuel (liquid, gaseous, or solid) and air. Some final products of combustion include oxides of 

nitrogen, carbon monoxide, volatile organic compounds (VOC) and fine particulate matter (PM-10) and 

are discharged into the atmosphere. Oxides of nitrogen and volatile organic compounds are recognized as 

precursors to ground-level ozone formation, and reductions in NOx and VOC are necessary to attain and 

maintain the state ambient air quality standard for ozone.

Rule 3.21, Industrial, Institutional and Commercial Boilers, Steam Generators, and Process Heater, 

regulates the NOx emissions of any unit defined in this rule. This rule applies to all boilers, steam 

generators, and process heaters used in industrial, institutional, and commercial operations that operate

within the boundaries of the Yuba and Sutter Counties. 

Staff proposed to adopt Rule 3.21 to achieve reasonable emission reductions from boilers, steam 

generators, and process heaters to help attain the state ambient air quality standard for ozone. The 

proposed rule will also be consistent among the NSVAB Districts, where emission standards are based 

on the CARB’s Determination for Reasonable Available Control Technology (RACT) and Best 
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Available Retrofit Control Technology (BARCT) for Industrial, Institutional and Commercial Boilers, 

Steam Generators, and Process Heaters. 

3.0 Legal Mandate:

State Mandates: Yuba County and the northern area of Sutter County is designated as “moderate” nonattainment for the state ozone standard. The southern area of Sutter County, also know as Sacramento 

Federal Non-attainment Area (SFNA), is designated “serious” non-attainment for the state ozone 

standard. The California Clean Air Act (CCAA) requires areas designated as non-attainment for ozone 

to adopt control measures required in Section 40918 & 40919 of California Health and Safety Code

(CH&S). CH&S Code, Section 40918 requires the District to adopt a control measure that will use 

reasonable available control technology (RACT) for all existing stationary sources in the “moderate” 

non-attainment area. CH&S Code, Section 40919 requires the District to adopt a control measure that 

will use Best Available Retrofit Control Technology for all existing stationary source in the “serious” 

non-attainment area. The CCAA also requires the District to develop a plan to achieve California’s 

ambient air quality standard by the earliest practical date (CH&S Code Section 40913).

All Feasible Measures Requirements: California Health and Safety Code Section 40914 requires the 

District’s plan to demonstrate that the plan includes “every feasible measure" to control emissions. 

Accordingly, the District must adopt an effective control measures to limit NOx emissions from boilers, 

steam generators and process heaters. The District has evaluated the standards in the rule against similar 

requirements recently adopted by other districts. The District has determined that the standards are 

feasible requirements and have been achieved in practice. 

4.0 Proposed Rule Requirements:

4.1 Standards

Rule 3.21 applies to all boilers, steam generators, process heaters used in industrial, institutional, 

and commercial operations that operate within the boundaries of the District. One year from the 

rule’s date of adoption, all boilers, steam generators and process heater shall meet the following 

standards: 

4.1.a Units with a rated heat input greater than or equal to 5 million Btu per hour and 

annual heat inputs greater than or equal to 90,000 therms shall demonstrate 

compliance with Reasonable Available Control Technology (RACT) or Best 

Available Retrofit Control Technology (BARCT) emission limitations according to 

area of designation and fuel type, as shown in Table 1, Emission Limits. The 

proposed RACT/BARCT emission limits are required by the CH&S, Section 40918 

and 40919. All new units must comply with District Rule 10.1, New Source Review. 

4.1.b Units rated greater than or equal to 5 MMBtu/hr with a heat input of less than 90,000 

therms and units rated less than 5 MMBtu/hr but greater than or equal to 1 

MMBtu/hr must provide to the District a list of all units operating within the District 

boundaries and select an option from either operating the unit at 3% oxygen 

concentration, tuning units with satisfactory results or meeting specific emission 

limits.
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Table 1. Emission Limits

Type of Fuel Used

Only Gaseous Fuel 

Firing Units

Gaseous & Non-Gaseous 

Fuel Co-Firing Firing 

Units

Non-Gaseous 

Firing Units

North 

Portion of 

FRAQMD 

Emission 

Limits

0.08 lbs/MMBTU

or

70 ppmv

*Heat Input Weighted 

Average Fuel Limits

0.15 lbs/MMBTU

or

115 ppmv

SFNA 

Portion of 

FRAQMD 

Emission 

Limits

0.036 lbs/MMBTU

or

30 ppmv

*Heat Input Weighted 

Average Fuel Limits

0.052 lbs/MMBTU

or

40 ppmv

4.2 Applicability and Exemptions

Rule 3.21 applies to boilers, steam generators, and process heaters having heat input capacities 

greater than or equal to 1 million Btu per hour (MMBtu/hr), used in all industrial, institutional, 

and commercial operations: This rule shall not apply to the following:

4.2.a Any unit with a rated heat input capacity less than 1 million Btu per hour. 

4.2.b Any unit that does not meet the definition of a boiler, steam generator or process 

heater

Rule 3.21 exempts the following units:

4.2.c Any unit with rated heat input greater than or equal to 1 MMBtu/hr but less than 5 

MMBtu/hr willing to accept a permit condition that restricts operation to less than 

90,000 therms per year of annual heat input.

5.0 Socioeconomic Impact:

Yuba and Sutter counties have a combined population less than 500,000 persons. The Required 

Assessment in subsection (d) of the California Health and Safety Code (Section 40728.5) states, “This 

section does not apply to any district with a population of less than 500,000 persons”. A socioeconomic 

impact analysis is not required.

6.0 Effectiveness of Control Measures:

The reduction of NOx emissions from process equipment, such as boilers and heaters, can be 

accomplished through pre and/or post combustion modifications. The application of a specific technique 

will depend on the type of boiler, the characteristic of its primary fuel, and method of firing. Some 
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controls have seen limited application, whereas certain boilers have little or no flexibility for 

modification of combustion conditions because of method of firing, size, or operating practices. 

The formation of NOx is governed primarily by the chemically-bound nitrogen content of the fuel, the 

oxygen concentration of the flame, the temperature of the flame, and the length of time for which the 

combustion gases are held at the flame temperature. The NOx emissions may then be emitted to the 

atmosphere along with other products of combustion in the flue gas. NOx emissions can be reduced 

either by limiting NOx formation during fuel combustion using control measures such as Low NOx 

Burners or Flue Gas Recirculation, or by reducing NOx emissions from the exhaust flue gas by 

retrofitting the unit with Selective Catalytic Reduction or Selective Non-Catalytic Reduction. The 

control measures are described below. 

1. Low NOx Burners (LNB)

Low NOx Burners utilize one or a combination of control technologies (i.e., low excess air, fuel 

and/or air staged combustion, combustion product recirculation) in the design of the burner to 

reduce NOx emissions. Low excess air minimizes the amount of excess oxygen for combustion 

and thus reducing the number of oxygen atoms available to react with nitrogen to form NOx. 

Staged combustion can achieve lower NOx emissions by dividing the combustion process into a 

number of stages in which air/fuel ratio varies to reduce NOx formation. 

There are two types of staged combustion: staged air combustion and staged fuel combustion. 

Staged air combustion involves controlling the formation of NOx by introducing in stages the 

total amount of air required for combustion. A portion of the air is used to form a fuel-rich 

primary combustion zone in which all of the fuel is partially burned. Some heat from this 

incomplete combustion is transferred to the boiler tubes before the completion of combustion. 

Combustion is completed with the injection of the remainder of the combustion air in a 

secondary burnout zone downstream of the fuel-rich primary zone. Because some heat is 

transferred prior to the completion of combustion, temperatures are lower with staged air 

combustion than with conventional combustion. Lower temperature reduces NOx formation. 

Staged fuel combustion involves controlling NOx formation by introducing in stages the amount 

of fuel required for combustion. In the primary combustion zone the burners are operated or 

fired with only a portion of the fuel; however, all of the required combustion air is added. 

Because there is a high level of excess air, the combustion temperature is lowered and the NOx 

formation reduced. In the secondary combustion zone, the remainder of the fuel is injected at 

high pressure and velocity into the combustion chamber which further reduces the combustion 

temperature and the partial pressure of oxygen in the secondary combustion zone. This situation 

retards the formation for NOx because of the decreased temperature and availability of oxygen, 

while producing desirable results. 

Low NOx Burners reduce temperature and the formation of NOx. Low NOx Burners are 

applicable to most gas-fired and oil-fired units. The control effectiveness ranges from 10 to 55 

percent for gas-fired units and low-nitrogen oil units. 

2. Flue Gas Recirculation (FGR)
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Flue Gas Recirculation for NOx control consists of extracting a portion of the flue gas from the 

economizer outlet and returning it to the furnace, admitting the flue gas through the furnace 

windbox. Flue gas recirculation lowers the bulk furnace gas temperature and reduces oxygen 

concentration in the combustion zone. 

The retrofit installation of FGR consists of adding a fan, ductwork, dampers, and controls as well 

as possibly having to increase existing fan horsepower due to increased draft loss. 

Flue Gas Recirculation is an effective control technique for both gas-fired and distillate oil-fired 

units. The control effectiveness of the FGR ranges from 60 to 70 percent for gas-fired unit and 

low-nitrogen oil units.

3. Selective Non-Catalytic Reduction (SNCR)

Selective Non-catalytic Reduction is a post-combustion control measure or after-treatment 

device. SNCR reduces NOx through injecting ammonia or urea into a specific temperature zone 

of the flue gas. The injected ammonia or urea reacts with nitrogen oxides to produce nitrogen and 

water vapor. Because the SNCR is highly dependent on the temperature, ranges between 1400oF 

to 2000oF, ammonia or urea in injected into the flue gas at a point in the system where the 

temperature is within the required range. If the temperature is below 1600oF, chemical enhancers 

such as hydrogen may be required to help the reaction. If the temperature is above 2000oF, the 

ammonia or urea tends to react with any available oxygen to form NO. The ammonia injection 

point is usually located upstream of the convection section as flue gas leaves the furnace. 

With SNCR, it is very important to control the excess un-reacted ammonia. The excess ammonia 

could react with other combustion by-product and form ammonia salts. Un-reacted ammonia 

may also pass through the system and into the atmosphere. The ammonia salts and un-reacted 

ammonia are sometimes visible in the plume from the stack. This is known as an ammonia slip. 

And due its environmental impact, it is restricted by this rule to not emit ammonia emissions in 

excess of 20 ppmv at dry stack conditions adjusted to 3% oxygen into the atmosphere from any 

control device. The control effectiveness of the SNCR ranges up to 90 percent.

4. Selective Catalytic Reduction (SCR)

A Selective Catalytic Reduction unit is a post-combustion control measure and is operated

similar to a SNCR. SCR injects ammonia to reduce NOx. Instead of injection in specific 

temperature zone, SCR inject ammonia into the flue gas over a catalyst bed. The catalyst bed 

allows the reaction to reduce NOx at a temperature range from 500oF to 850oF. The injected 

ammonia creates reducing atmosphere, where the rich ammonia environment strips the oxygen 

from the nitric oxide leaving nitrogen gas. 

Similar to SNCR, the ammonia slip is regulated by this rule to not emit ammonia emissions in 

excess of 20 ppmv at dry stack conditions adjusted to 3% oxygen into the atmosphere from any 

control device. The control effectiveness of the SCR unit ranges up to 90 percent.
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7.0 Estimated Cost Impact:

The proposed Rule 3.21 will require all units subject to this rule, to install additional equipment such as 

operational tracking devices and/or emission control devices. The proposed rule will also require 

compliance testing to show compliance with the required emission standards or permit conditions. A 

summary of the estimated cost for equipment and testing is shown below in Table 2.

After one year of the date of adoption of the proposed rule, all units subject to this rule or to the usage

exemption of this rule, shall install either a non-resettable hour meter or a fuel flow totalizing meter to 

track the annual usage of each unit. The District anticipates most owners or operators will chose to 

install a non-resettable hour meter, which will cost about $400. 

For each unit to be in compliance with rule 3.21, the facility must show that the unit operates at its 

optimal performance and/or meet the emissions requirement. For units less than 5 MMBtu/hr but greater 

than 1 MMBtu and units equal to or greater than 5 MMBtu/hr but has a heat input less than 90,000 

therms, the facility must operate at its optimal design where it is required to be tuned, set up an oxygen 

trim system or operate at 3% oxygen level of concentration. The District expects most facilities to tune 

the unit(s) to meet the requirements in the proposed rule. Tune-ups are about $600 for each unit by a 

qualified technician. For units rated greater than 5 MMBtu/hr and an annual heat input greater than or 

equal to 90,000 therms, the facilities are expected to meet emission requirements for its designated area. 

Most units can achieve the emission standards by retrofitting the unit with a Low NOx Burner and/or a 

Flue Gas Recirculation. The estimated cost to retrofit a unit ranges from $65,000 to $442,000, which 

depends greatly on the type of retrofit and the size of the boiler. 

Furthermore, to show compliance on a continual basis, the proposed rule requires the facility to 

demonstrate in accordance with the compliance schedule and depending on the maximum unit capacity, 

each unit is either properly tuned or source tested. Tune-ups are required annually, and source tests are 

required once every two years or every 8,760 hours of operation, whichever occurs more frequently. A 

source test, not including District observation and review, is about $1,500 to $2,000 per source test. 

Table 2. Summary of Estimated Cost

Equipment Cost (dollars)

Non-resettable Hour Meter 

Fuel Flow Meter

Oxygen Trim System 

Equipment Retrofit 

 Low-NOx Burner

 Flue Gas Recirculation

 Selective Catalytic Reduction

 Selective Non-Catalytic Reduction

Replace Unit 

$ 400

$ 1,500

$ 15,000 to $ 22,000

$ 65,000 to $442,000

$135,000 to $750,000

Testing

Annual Tune-up

Source Test 

$ 600 per boiler 

$1,500 to $2,000 per test
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8.0 Environmental Review and Compliance:

The adoption of rule 3.21 is categorically exempt from the California Environmental Quality Act 

(CEQA) under Sections 15307 and 15308 of the State CEQA Guidelines and no exceptions to these 

exemptions apply. This exemption is allowed when the rule will help improve air quality in Yuba and 

Sutter County. California Public Resources Code (Section 21159) requires an environmental analysis of 

the reasonably foreseeable methods of compliance. The District has concluded that no reasonably 

foreseeable adverse environmental impacts will be caused by adoption of the proposed rule.

9.0 Required Findings:

The California Health and Safety Code, Division 26, Air Resources, requires local Districts to comply 

with a rule adoption protocol as set forth in Section 40727 of the Code. This section has been revised 

through legislative mandate to contain 6 findings that the District must make when developing, 

amending, or repealing a rule. These findings and their definitions are listed in the following table.

Table 3. Required Findings

FINDING DEFINITION REFERENCE

Authority A district shall adopt rules and regulations 

and do such acts as may be necessary or 

proper to execute the powers and duties 

granted to, and imposed upon, the district by 

this division and other statutory provisions

California Health and Safety Code, Sections 

40000, 40001, and 40702 are provisions of 

law that provide air districts with the 

authority to adopt these proposed rules.

Necessity The District has demonstrated that a need 

for the rule, or for rule amendment or 

repeal.

It is necessary for districts to adopt these 

amendments to comply with state law and to 

ensure consistency with neighboring air 

districts.

Clarity The rule is written or displayed so that its 

meaning can easily be understood by the 

persons directly affected by it

There is no indication, at this time, that the 

proposed rules are written in such a manner 

that it can not be easily understood by 

persons affected by the rule.

Consistency This rule is in harmony with, and not in 

conflict with or contradictory to, existing 

statutes, court decisions, or State or federal 

regulations.

These rules are consistent with applicable 

statutory requirements.

NonDuplicationThe rule does not impose the same 

requirements as an existing State or federal 

regulation, unless the District finds that the 

requirements are necessary and proper to 

execute the powers and duties granted to, 

and imposed upon, the district

The proposed rule does not impose 

requirements that duplicate existing laws or 

regulations.

Reference Any statute, court decision, or other 

provision of law that the district 

implements, interprets, or makes specific by 

adopting, amending, or repealing a 

regulation.

The proposed rule has been developed to 

meet the requirements of the 2003 State 

Implementation Plan.
ATTACHMENT A

Rule Analysis
ATTACHMENT B

Public Notice
ATTACHMENT C

Comments and Responses