Emergency Compression Ignition Engines (Diesel Engines)

I. Background

Emergency standby compression ignition engines operate as short-term temporary replacements for primary mechanical or electrical power during periods of fuel or energy curtailment, power outages, or while the primary power supply is under repair. In many cases, for example at hospitals, the installation of emergency engines is required by state law. In addition, a great majority of these engines are installed at non-major sources.

Emergency engines ordinarily operate for testing and maintenance only, which amounts to an annual operation of less than 50 hours per year. In addition, total annual operation of these engines including testing, maintenance and emergencies is limited to 200 hours per year. Emergency engines do not include units that produce power to be sold or otherwise supplied to the grid.

U.S. EPA has adopted manufacturer NO_x standards for all "non-road I.C. engines," which include portable engines that do not remain at a location for more than 12 consecutive months. These standards are similar to certification standards and vary in their effective dates based on the rated horsepower of the engine. The federal NO_x standards of 6.9 gr/bhp-hr and effective manufacture's date are shown in the attached table.

Prior A QMD Best Available Control Technology (BACT) guidance, as revised on April 10, 1998, provided emission limits for emergency engines of less than 750 hp based on federal nonroad standards for new engines. However, this did not take into account the need for a transitional period for engines purchased and installed prior to April 10, 1998, which do not meet the federal standards. Without transitional limits, compliance with BACT for these engines can generally only be achieved by replacement of the engine. Engines of 750 hp or greater installed prior to July 1, 2000, also need a transition period, because these engines generally do not meet nonroad engine standards that are now in effect.

This document addresses BACT standards based on the need for a transition period by establishing specific emission control requirements depending on the horsepower rating and installation date of the engine. (Please see the attached table.) It allows engines installed up to six months after the date that the nonroad manufacture standard went into effect for newly manufactured engines to meet separate control requirements. Since more recently manufactured engines are now widely and commercially available, transition limits for recently installed engines are not necessary.

In general, BACT is determined on a case-by-case basis. At this time, taking into account the emergency nature of these engines, their relatively low annual emissions, and the recent electrical energy shortages and potential power outages, BACT for the emergency I.C. engines shall be as noted below, and as shown in the attached table. However, on a case-by-case basis, and based on future available technologies BACT could be more stringent as determined by the Executive Officer.

A. All emergency standby engines subject to BACT shall be limited to a maximum of 50 hours per year for regular maintenance and testing as well as 200 hours per year total operation. In addition to maintenance and testing, these engines shall only operate during emergencies resulting in an interruption of service of the primary power supply or during a Stage II or III Electrical Emergency declared by the California Independent System Operator.

B. The following NO_x limits shall apply:

1. Engines greater than or equal to 50 hp, but less than 100 hp installed on or after July 1, 1998 shall meet 6.9 gr/bhp-hr or less.
2. Engines greater than or equal to 100 hp, but less than 175 hp installed on or after July 1, 1997 shall meet 6.9 gr/bhp-hr or less.
3. Engines greater than or equal to 175 hp, but less than 750 hp installed on or after July 1, 1996 shall meet 6.9 gr/bhp-hr or less.
4. Engines at 750 hp or greater installed on or after July 1, 2000 shall meet 6.9 gr/bhp-hr.
5. All other engines shall either meet a NO_x limit of 10 gr/bhp-hr or less, or the engine shall be turbocharged and the timing retarded
   4-degrees relative to standard timing. The 4-degree injection timing retard is not required where it can be demonstrated technologically infeasible to the satisfaction of the Executive Officer.
   

C. PM₁₀ shall be limited to 0.38 gr/bhp-hr or less.

The requirements in A, B, and C above shall be incorporated into the permits as permit conditions, along with any other appropriate permit conditions.

BACT Emission Limits for NOx for Emergency Diesel Engines

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This page updated: March 01, 2004
URL: http://www.aqmd.gov/news1/Generator_BACT.htm