PLACER COUNTY

AIR POLLUTION CONTROL DISTRICT

STAFF REPORT

RULE 233

BIOMASS BOILERS

PROPOSED AMENDMENTS

June 14, 2012

Staff Report – Rule 233, Biomass Boilers

Page 1 

June 14, 2012 

SUMMARY

Rule 233, Biomass Boilers, first adopted on October 6, 1994, was last amended on December 10, 

2009. The amendment was adopted by the California Air Resources Board (CARB) as a State 

Implementation Plan (SIP) revision and it was forwarded to U.S. Environmental Protection 

Agency (EPA) for approval by CARB on May 17, 2009. A formal limited approval and limited 

disapproval of the amended Rule was issued by EPA in the Federal Registry, Volume 77, Number 

12, on January 10, 2012. See attachment #1.

The limited approval means that EPA has determined that overall the rule improves the SIP and is 

largely consistent with the relevant Federal Clean Air Act (CAA) requirements but simultaneously 

issued a limited disapproval because it was their opinion that the NOx emission limits in Section 

301 do not represent current Reasonably Available Control Technology (RACT). 

The District proposes to amend Rule 233, Biomass Boilers, by adding an additional NOx 

limitation of 68 ppmv corrected to 12% CO2 twenty-four hour block average. This is being done 

solely to satisfy the limited disapproval by EPA and obtain approval into the SIP.

BACKGROUND

The Federal Clean Air Act, as amended in 1990, required adoption of source specific regulations 

for major sources of nitrogen oxides (NOx) pursuant to Sections 182(b)(2)(C) and 182 (f). These 

sections required the adoption of RACT rules. In addition, the California Clean Air Act transport 

mitigation provisions required the adoption of Best Available Retrofit Control Technology 

(BARCT) for sources compromising 75% of the actual NOx emission inventory in the District.

Biomass boilers were affected by this requirement. There are currently two facilities with 

biomass boilers in Placer County. Rio Bravo-Rocklin operates a fluidized bed biomass boiler and

Sierra Pacific Industries which operates a stoker biomass boiler. 

Rule 233, Biomass Boilers, was originally adopted on October 6, 1994 and subsequently 

approved in the SIP in 1996. 

The rule originally limited NOx emission to the least stringent of 115 ppmv corrected to 12% 

CO2 or 50% of the uncontrolled emission concentration in the boiler exhaust. The 115 ppmv 

limitation corresponded to the limitation in Sierra Pacific Industries Prevention of Significant 

Deterioration (PSD) permit issued by the EPA. This emission limitation reflected a determination 

by the EPA that the selective non-catalytic reduction system using ammonia injection to control 

NOx constituted Best Available Control Technology (BACT). 

At that time, this control technology and limitation was considered to represent RACT and 

BARCT which are less stringent requirements than BACT. 

NOx emissions are measured by a continuous emission monitoring system (CEMS) installed in 

the stack. The concentration is corrected, or normalized, to 12% CO2 so that one boiler may be 

compared to another. It is also corrected so that an operation cannot introduce additional outside 
Staff Report – Rule 233, Biomass Boilers

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June 14, 2012 

air into the boiler solely to lower the concentration. The correction is a simple calculation as 

follows: 

NOx corrected to 12% CO2 = NOx measured x 12% / CO2 % measured

The District amended Rule 233 to address startup and shutdown conditions. The October 11, 

2007, rule amendment was forwarded to the California Air Resources Board (CARB) for 

approval into the SIP. This was approved by CARB and forwarded to the EPA for approval. 

EPA declined to approve that amendment into the SIP saying it was inconsistent with federal 

regulation and policy. Their response was contained in an email in Attachment #1. The main 

objections were in two areas:

1. The 115 ppm limit for NOx does not apply during startup and shutdown. Instead mass 

emission limits in the Permit to Operate would apply. Although these limits were already 

in place in the both the District Permit to Operate and federal Title V, EPA requested that 

the limitations be listed in the Rule itself.

2. The amendment must provide a demonstration that both the length of time of the startups 

and shutdown and the emissions were minimized as much as technologically feasible.

In acknowledgement of EPA intention to disapprove the October 11, 2007, amendment the 

District requested the withdrawal of the amendment from SIP consideration in a letter dated 

October 14, 2008. 

The District subsequently proposed the following changes to address the EPA’s concerns. These 

changes were discussed at length with EPA. 

• A startup was defined as the period of time a unit is heated to the normal operating 

temperature, as specified by the manufacturer. A normal startup shall not exceed 24 hours. 

A curing startup shall not exceed 96 hours. 

• Section 301, Limitations, which addresses limitations during normal operation, was

changed to add a carbon monoxide (CO) limitation for each type of boiler. These 

limitations currently exist in the Permits to Operate for each facility.
Staff Report – Rule 233, Biomass Boilers

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June 14, 2012 

TABLE 1 - NOx and CO Emission Limitations

Type of Boiler NOx CO

Circulating Fluidized Bed 115

ppmv corrected to 12% 

CO2

(3 hour rolling average)

400

ppmv corrected to 12%

CO2

(3 hour rolling 

average)

Stoker 115

ppmv corrected to 12% 

CO2

(3 hour rolling average)

1000

ppmv corrected to 12%

CO2

(3 hour rolling 

average)

• To address EPA's concerns and attempt to make the amendment SIP approvable, this rule 

amendment included the mass emission limitations in pounds per hour as follows in 

Section 302, Startup and Shutdown Provisions. 

Table 2 Startup and Shutdown Emission Limitations

Type of Boiler NOx CO

Circulating Fluidized Bed 35

pounds per hour

(24 hour block average)

56

pounds per hour

(24 hour block average)

35

pounds per hour

(72 hour block average during 

curing of refractory)

56

pounds per hour

(72 hour block average 

during curing of refractory )

Stoker 37.6

pounds per hour

(3 hour rolling average)

170

pounds per hour

(3 hour rolling average)

These proposed rule amendments were discussed at length with EPA staff. General agreement 

was reached that the Rule would be SIP approvable. EPA staff never identified an issue with the 

ppm NOx limitation. The proposed rule was then adopted by the District Board on December 10, 

2009. 

Rule 233 was submitted to CARB for approval into the SIP. CARB agreed and forwarded to EPA 

for final approval into the SIP on May 17, 2010. 

In April of 2011, EPA contacted the District and indicated the agency had planned on approving 

Rule into the SIP but there had been objections from an environmental group, Earth Justice, to the 

SIP approval of San Joaquin Valley Unified Air Pollution Control District’s (SJVUAPCD) rule 

which has similar NOx limits for biomass boilers. As a result, EPA reconsidered its position and 

issued a limited approval and limited disapproval to SJVUAPCD. EPA indicated its intent to issue 

a limited approval and limited disapproval for Rule 233 unless the District could provide a counter 
Staff Report – Rule 233, Biomass Boilers

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June 14, 2012 

argument that our existing rule NOx limitation met current RACT. The Technical Support 

Document for EPA’s Notice of Rulemaking was provided to the District by EPA. 

A formal limited approval and limited disapproval of District Rule 233 was issued by EPA in the 

Federal Registry, Volume 77, Number 12, on January 10, 2012 (See Attachment #1). EPA 

indicated that the disapproval was based on their determination that the NOx limitation of 115 

parts per million by volume (ppmv) on a three-hour rolling average was not low enough to be 

considered current RACT. This was based on the fact that Yolo-Solano AQMD had adopted a rule 

which limits NOx emissions from a biomass boiler to 90 ppmv corrected to 3% O2 on a twentyfour hour average. Also, source test results show that the two regulated facilities in Placer County 

can achieve lower emission rates. There was no discussion of the fact that currently the Rule 233 

limit requires a significantly shorter time period (three-hour rolling average). The shorter the 

averaging period the more stringent a limit becomes.

EPAs technical support document (see Attachment #2) concludes that 90 ppmv corrected to 3% 

O2 twenty-four hour block average is approximately equal to 68 ppmv corrected to 12% CO2

twenty-four hour block average. EPA staff indicated that the calculation was made using the F 

Factors in EPA Test Method 19 along with the equations in EPA Test Method 3B. Note, 

calculation by the District staff found that 90 ppmv corrected to 3% O2 is approximately 64 ppmv 

corrected to 12% CO2. The staff report prepared by Yolo-Solano AQMD when adopting their 

biomass rule indicates 90 ppmv corrected to 3% O2 is approximately 70 ppmv corrected to 12% 

CO2. While the District was considering its response, SJVUAPCD revised its biomass boiler rule 

to 90 ppmv corrected to 3% O2 twenty-four hour block average in December of 2011. 

As mentioned previously, the District proposes to amend Rule 233, Biomass Boilers, by adding an 

additional NOx limitation of 68 ppmv corrected to 12% CO2 twenty-four hour block average. This

limit is the same as was recommended in the EPA technical support document, and between the 

values independently determined by District staff and Yolo-Solano staff. 

DISCUSSION OF PROPOSED RULE AMENDMENT

The District is required to revise Rule 233 and gain EPA SIP approval within eighteen (18) 

months, by July 20, 2013, or sanctions will be imposed. 

The District proposes to amend Rule 233, Biomass Boilers, by adding an additional NOx 

limitation of 68 ppmv corrected to 12% CO2 twenty-four hour block average. This is considered 

equivalent to and consistent with the NOx limitations for biomass boilers in other District Rules. 

This amendment is being proposed to satisfy the limited disapproval by EPA and obtain SIP 

approval. There will be no emission reductions from this amendment because the affected 

facilities have installed and are currently operating the ammonia injection air pollution control 

equipment needed to meet this limit.

The District proposes that the added NOx limit become effective on January 1, 2013, so that 

sources will have an opportunity to program the CEMS software to record and report on NOx 

twenty-four hour averages. This effective date is before the date when EPA’s sanctions might be 

considered, July 20, 2013. During this time the previously existing emission limits will continue to 

be effective. 
Staff Report – Rule 233, Biomass Boilers

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June 14, 2012 

Applicability:

No Change. 

Exemptions: 

Removed Section 104; Exemption for Rule 232, Biomass Suspension Boilers. The District 

recently removed Rule 232 from the District Rules and Regulations because there are no longer 

any boilers of this type in Placer County and the Rule had not been SIP approved. 

Definitions:

Added a definition of Block 24-Hour Average to clarify the newly added standard which is 

measured on this basis. 

Standards:

Added an additional NOx limitation of 68 ppmv corrected to 12% CO2 twenty-four hour block 

average in addition to the existing limitation of 115 ppmv corrected to 12% CO2 three-hour 

rolling average.

Administrative:

There are no changes to the Administrative Requirements.

Monitoring and Records:

Added references to require monitoring and recording the twenty-four hour block average. 

FINDINGS

FINDING DEFINITION REFERENCE

Authority The District is permitted or required 

to adopt, amend, or repeal the rule by 

a provision of law or a state or 

federal regulation.

California Health and Safety Code, 

Section 40702 and Section 41010; 

1990 Federal Clean Air Act, Section 

110(a) (2) (H) and Section 182(d).

Necessity The District has demonstrated that a 

need exists for the rule, or for its 

amendment or repeal.

It is necessary for the District to 

adopt this rule in order to fulfill the 

requirements of the Federal Clean 

Air Act Amendments of 1990 and 

seek SIP approval.

Clarity The rule is written or displayed so 

that its meaning can be easily 

understood by the persons directly 

affected by it.

There is no indication at this time 

that the rule is not written in such a 

manner that the person affected by 

the rule can easily understand it.

Consistency The rule is in harmony with, and not The District has found that the rule is 
Staff Report – Rule 233, Biomass Boilers

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June 14, 2012 

in conflict with or contradictory to, 

existing statutes, court decisions, or 

state or federal regulations.

consistent with existing state and 

federal guidelines.

Non-duplication The rule does not impose the same 

requirements as an existing state or 

federal regulation, unless the District 

finds that the requirements are 

necessary or proper to execute the 

powers and duties granted to, and 

imposed upon the District.

NSPS, Subpart Da and Db apply to 

these boilers but the requirements are 

less stringent than Rule 233.

Reference Any statute, court decision, or other 

provision of law that the District 

implements, interprets, or makes 

specific by adopting, amending, or 

repealing the rule. An example of 

this would be the 1988 EPA State 

Implementation Plan call to revise 

District rules.

This rule is being proposed because 

of the requirements of the Federal 

Clean Air Act Amendments of 1990.

SUMMARY 

This amendment has been proposed to address the limited disapproval from EPA and to make 

Rule 233, Biomass Boilers, SIP approvable. 

Attachments(s) #1: Federal Registry Notice

#2: EPA Technical Support Document for EPA’s Notice 

#3: Calculation of Equivalent Correction from % Oxygen vs. % Carbon Dioxide

#4: Proposed Rule 233, Biomass Boilers Strikeout Version 

 
ATTACHMENT #1

SUBJECT:

Federal Registry Notice





ATTACHMENT #2

SUBJECT:

EPA Technical Support Document







ATTACHMENT #3 

SUBJECT:

Calculations of % Oxygen vs. % Carbon Dioxide 

District Calculations

Comparing Theoretical Values at 3% O2 vs. 12% CO2

Using F Factors

Fo = (20.9-%O2)/%CO2

Fo = 0.209Fd / Fc

Fd = 9240 Wood

Fc = 1830 Wood

(Above F factors from EPA Method 19)

If %CO2= 12

Fo = (20.9-%O2)/%CO2 = (20.9 - %O2)/12 = .209 * 9,240 / 1,830

Fo = (20.9 - %O2) = 12 *.209 * 9,240 / 1830 = 12.663

Solving for O2

%O2 = 8.2367

NOx @ 3% O2 = (20.9% - 3 %)/(20.9 - %O2) x NOx at 12% CO2

NOx @ 3 % O2 = 1.4135 X NOx at 12% CO2

90@3% = 64 @ 12% CO2

(approximately)

Apparently, EPA used a F Factors other than the ones

in the above equations and solved for O2

%O2 = 7.38

NOx @ 3% O2 = (20.95% - 3 %)/(20.95 - %O2) x NOx at 12% CO2

NOx @ 3 % O2 = 1.3228 X NOx at 12% CO2

90@3%O2 = 68 @ 12% CO2

Yolo-Solano's staff report indicated that a typical biomass boiler ran at 

7 % O2 which they calculated as equivalent to 70 ppmv at 12% CO2.