Document ID: EPA-HQ-OAR-2008-0708-0326
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2010-02-22T05:00Z

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
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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 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 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 non-emergency 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.

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.