EC

/R Incorporated Providing Environmental Technical Support Since 1989

501 Eastowne Drive, Suite 325 y Chapel Hill, North Carolina 27514 

Telephone: (919) 484-0222 y Fax: (919) 484-0122 

 

MEMORANDUM 

DATE: February 5, 2010 

SUBJECT: Subcategorization of Existing Stationary CI RICE 

FROM: Bradley Nelson and Tanya Parise, EC/R, Inc. 

 

TO: Melanie King, EPA OAQPS/SPPD/ESG 

1.0 PURPOSE 

The purpose of this memorandum is to document the subcategorization of existing 

stationary compression ignition (CI) reciprocating internal combustion engines (RICE). Section 

112 of the Clean Air Act (CAA) allows the EPA to establish subcategories among a group of 

sources in cases where there are differences in the design, operation, and consequently the 

emissions. In addition, the application of control devices may differ among the population of 

sources. 

2.0 INTRODUCTION

The EPA is developing a regulation affecting existing stationary CI RICE located at 

major sources and area sources of hazardous air pollutants (HAP) emissions that will address 

toxic air emissions from these engines. The development of subcategories in this rulemaking is 

similar to that of the promulgated standards for stationary RICE greater than 500 HP located at 

major sources of HAP emissions due to inherent similarities between the engines. These source 

distinctions are based on criteria that differentiate existing sources in terms of technical 

feasibility or applicability of emission control or testing methodology. Technical criteria which 

are related to technical feasibility or applicability of emission controls may include differences 

in: 

1) Emission characteristics (exhaust flow parameters, pollutant concentrations), 

2) Mode of operation (type of fuel used, idle/maximum), and 

3) Size or capacity of source (engine capacity, production rate). 

 

Existing stationary RICE are present in a variety of makes, models, and sizes and burn a 

variety of liquid and gaseous fuels. Existing CI stationary RICE generally burn diesel fuel. 

Engine design and operation characteristics, size and fuel type are the key factors that affect 
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HAP emissions and the viability of controls. Subcategories for stationary RICE were established 

to incorporate factors that may affect the HAP emissions from stationary RICE and/or the 

applicability of control techniques or testing methodologies. Existing CI stationary RICE is 

itself a subcategory of the broader category of stationary RICE. The reasons for this initial 

subcategorization have been explained in the previous rules and in documentation supporting the 

proposal for this rule. 

3.0 SUBCATEGORIZATION 

Section 112 of the CAA allows the EPA to establish subcategories among a group of 

sources. These subcategories are based on criteria that differentiate sources in terms of technical 

feasibility or applicability of emissions control or testing methodology. The selected 

subcategories are necessary in order to capture the differences which could affect the emissions 

of HAP from these CI engines. For the final rule, EPA has determined that the following 

subcategories are necessary in order to capture the differences between different types of 

stationary CI engines: 

• Emergency CI Engines; 

• Non-emergency CI Engines <100 HP; 

• Non-emergency CI Engines 100≤HP≤300; 

• Non-emergency CI Engines 300<HP≤ 500; 

• Non-emergency CI Engines >500 HP; 

• Black Start CI Engines; and 

• CI Engines Located at Area Sources in Rural Areas of Alaska not accessible by 

FAHS. 

Mode of Operation

 EPA has found it appropriate to distinguish between emergency and non-emergency CI 

engines in order to account for differences between the modes of operation of these engines. The 

following describe some of the factors that necessitate having a separate subcategory for 

emergency CI engines: 

• Limited and unexpected operation, 

• Operation often only for maintenance or testing purposes, 

• Low emissions on an annual basis, and 

• Less effective catalytic control 

Stationary emergency engines are used when electric power from the local utility is interrupted 

or becomes unreliable. The duration of the power outages is entirely beyond the control of the 

source, and, when they do occur (except in the case of a major catastrophe) they rarely last more 

than a few hours, often only a few minutes. Emergency engines are in some cases only operated 

for the purpose of maintenance and readiness testing. Information published by the California 

Air Resources Board based on a survey of emergency engine operation indicated that emergency 

engines are on average operated about 30 hours per year. Maintenance and testing requirements 

may be conducted on a regular basis, but may be brief in length, e.g., the National Fire Protection 
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Association requires 30 minutes per week (27 hours per year) to maintain and test emergency 

engines. Stationary emergency engine emissions are low on an annual basis due to minimal 

operation and add-on catalytic control devices effective in reducing HAP from stationary engines 

may not be as effective due to the short operating time and may not reach the required exhaust 

temperatures needed for proper catalytic conversion and reduction of HAP. Testing of 

emergency engines is also impractical and may not be feasible because of minimal operation 

time. For these reasons, it is necessary to establish a subcategory for stationary emergency 

engines. 

EPA has also determined that black start engines, whose only purpose is to start up a 

combustion turbine, require a separate subcategory based on their unique and limited operation. 

According to information received during the public comment period, black start engines 

typically operate no more than 10 minutes at a time and only operate during emergencies or 

during periods of high demand (see for example EPA-HQ-OAR-2008-0708-0088 and 0129). 

The short time of operation makes testing of black start engines using the required procedures 

impracticable. The limited operating time also makes applying aftertreatment to black start 

engines not effective because oxidation catalysts do not become efficient until adequate 

temperatures are reached. In order to reach operating temperatures sufficient for effective HAP 

destruction, an engine is typically required to operate for at least 20 to 30 minutes. Information 

submitted to EPA by the Engine Manufacturers Association (EMA) indicate that reaching a 

catalyst inlet temperature of around 250°C, which is, based on the information submitted by 

EMA, the temperature at which a 70 percent CO reduction occurs, may take more than 20 

minutes. Consequently, a black start engine that normally operates less than 10 minutes would 

not reach temperature levels adequate for effective HAP removal. 

Size or capacity of source

 EPA has found it appropriate to make a size distinction between emergency and nonemergency CI engines in order to account for differences between engines of different capacity. 

EPA has decided to subcategorize stationary non-emergency CI engines less than 100 HP. 

Further study by EPA of these engines found that measurement of emissions from these engines 

is not practicable due to technological and economic limitations. Because the exhaust pipe of 

these engines have a very small diameter and length, extensive retrofit of the exhaust system 

would be required to prepare the engine for testing. The cost of the exhaust system retrofit and 

the testing itself would exceed the capital cost of the engine. 

 In addition, EPA has decided to subcategorize stationary non-emergency CI engines 

between 100 HP and 300 HP, between 300 HP and 500 HP, and those above 500 HP for the final 

rule, in order to account for different operating characteristics and emissions. Smaller size 

stationary CI engines tend to be more similar to mobile source engines as compared to larger size 

stationary CI engines. Stationary CI engines that are smaller are also typically employed in 

various different applications. Also, HAP emissions on a mass-basis are less from engines that 

are smaller and the application of controls may not be as cost effective. Finally, smaller engines 

are more likely to be operated by small business owners and for agricultural purposes. 

Therefore, EPA believes that it is appropriate to subcategorize these engines. 
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Location

EPA has found it necessary to create a subcategory for stationary CI area source engines 

that are located in remote areas of Alaska that are not accessible by the Federal Aid Highway 

System (FAHS). Numerous rural communities in Alaska are not accessible by the FAHS and 

rely on stationary diesel engines and fuel for electricity. In addition to reliance on stationary 

diesel engines and fuel for electricity, communities are scattered over long distances in remote 

areas and are not connected to population centers by road or power grid, some of which can only 

be reached by air. Engines in these locations experience some of the most severe arctic 

environments in the United States. Transportation of diesel fuel to these areas is dependent on 

weather and communities typically pay some of the highest prices for fuel in the United States. 

Stationary engines located in rural areas of Alaska have different fuel storage and use logistics 

and higher operating and compliance costs. Therefore, special consideration is required in order 

to properly address these engines, which face challenges that are not typically experienced by 

other area sources in the rest of the country.