Understanding emission compliance: the new design/specify caveat

When it comes to ever-changing emission regulations, understanding the rules that apply to your specific application is a good place to start.


Stationary engine source applications such as gensets and fire pumps are facing increasingly stringent emission regulations created and implemented by the U.S. Environmental Protection Agency (EPA) as well as state and local air authorities.

Specifiers of equipment must understand the applicable emissions regulations that apply to their application and account for the various design and maintenance considerations that must be included for proper use and care of the product. Understanding the process by which emission laws are enacted can help specifiers determine if their projects must comply with additional requirements.

U.S. emission laws

In 1970 Congress passed the Clean Air Act. This law defines EPA’s responsibilities for protecting and improving U.S. air quality and the ozone layer. Individual states and local air districts are responsible for creating state implementation plans (SIPs) to maintain or improve their overall air quality.

A geographic area with air quality that is cleaner than the primary standard is called an attainment area, whereas an area that does not meet the primary standard is called a nonattainment area. Exceeding National Ambient Air Quality Standards (NAAQS) for one of six pollutants yields an EPA nonattainment designation for individual states and, more specifically, the local areas within the state that exceed EPA standards.

Nonattainment designations trigger enhanced SIP requirements to bring air quality within NAAQS standards. States and the local jurisdictions in designated nonattainment areas are forced to adopt stringent SIP requirements or risk losing federal highway funds along with possible federal government intervention. The more serious the nonattainment rating, the more likely states and local air jurisdictions are to create and implement emission regulations that trickle all the way down to stationary engine sources.

The impact of emissions regulations are felt all the way through the supply chain. Engine manufacturers are struggling with Tier 4 emissions requirements, which are stringent enough to force the use of aftertreatment devices. Equipment manufacturers must redesign their footprints to accommodate the extra emissions devices and pay between 25% and 40% more per engine for Tier 4 versus an equivalent Tier 3 engine creating the same amount of horsepower.

Enforcement of emission regulations is slowly working its way to combined liability. Combined liability means that agencies are taking enforcement actions against the installing contractor and the end user who hired the contractor. Typically, the end user is unaware of these rules and regulations, which leaves plenty of blame for the design engineer or application specifier.

Although U.S. emission requirements for stationary emergency engines pale in comparison to what is in store for continuous-use engines in on- and off-highway applications, some state and local air authorities are creating regulatory requirements that will force stationary emergency source engines to meet or exceed emission levels lower than those currently required by the EPA. These requirements may include limited hours of use (including restrictions on testing), stringent reporting requirements, emission aftertreatment devices, or all of these. Emission aftertreatment devices are of particular concern in stationary source applications because they pose new operational requirements, require prebuild design reviews, and create potential service and maintenance issues.

New specifier caveat

Because of these increasingly stringent regulations, there is a new caveat for the design and specification processes: emissions compliance. Due diligence must be completed early to avoid costly mistakes—both from the design/build aspect and from the end-user perspective.

To understand the rules and regulations that apply to your specific application, start with location, location, location. Access the U.S. EPA website and follow the links associated with the geographical area of your project. Also review EPA’s Reciprocating Internal Combustion Engine, National Emission Standards Hazardous Air Pollutants regulations (RICE NESHAP) now in effect for stationary engine sources operated in both emergency and nonemergency situations. Compliance requirements differ depending on hours of operation. Consult with the EPA or an emissions consultant to determine what category your stationary source fits into (www.epa.gov/airtoxics/rice/ricepg.html).

Next, check with the local air authority having jurisdiction for the geographical area of your particular project. This may require some Internet research and several phone calls on your part to get to the right agency. Failing that, contact local equipment vendors and ask for the contact information for the appropriate local air jurisdiction. The local vendor should have experience dealing with other customers who have already gone through the regulatory process or know whom to speak with at the local level.

Instead of relying solely on the advice of the vendor, speak directly to a representative for the air district. Communicating directly with the authority having jurisdiction ensures that you have all the relevant details that affect your project.

Extreme emission regulations

California has the most aggressive emission reduction SIPs by far. The California Air Resources Board, working with local air districts, has adopted emission regulations on many internal combustion and spark ignition engines. These rules can also apply to stationary sources used exclusively for emergency situations.

The Southern California Air Quality Management District is preparing to amend Rule 1470. This rule applies to new and in-use stationary diesel-fueled internal combustion and other compression ignition engines including prime and emergency standby engines. The amended rule would require further particulate matter (PM) reductions for stationary emergency diesel-engine sources greater than 50 hp within the district.

In most cases, the PM requirements for emergency engines will be stringent enough to force the use of an aftertreatment device such as a diesel particulate filter. This rule affects stationary emergency engine sources within 100 meters of a school or sensitive receptor. A sensitive receptor is any residence including private homes, condominiums, apartments, and living quarters; schools including preschools and daycare centers; and healthcare facilities such as hospitals and retirement or nursing homes. Sensitive receptors also include long-term care hospitals, hospices, prisons, and dormitories or similar live-in housing.

This is a good example of an air district in a nonattainment area taking extreme measures by regulating emergency engine sources that are primarily in essential services applications. In situations such as these, diesel particulate filters (DPFs) are used to reduce the amount of PM by 85% or more. Diesel exhaust PM has been identified as a toxic air contaminant based on its potential to cause cancer or premature death. PM and oxides of nitrogen (NOX) are the two major air contaminants that most emission-reduction regulations target (see Figure 1).

Figure 1: Catalytic reduction is another type of diesel genset aftertreatment and is typically used to reduce NOX emissions.Courtesy: DCL America Inc.


Accommodating aftertreatment in design

Engine exhaust aftertreatment is also commonly referred to as best available control technology (BACT). Accommodating aftertreatment affects size and accessibility (see Figure 2). BACT—specifically DPF—requires more room for installation and creates a tremendous amount of heat to regenerate itself. Filter regeneration can best be compared to an oven in self-cleaning mode.

Typically, regeneration can be achieved passively or actively. Passive regeneration uses exhaust heat to create an oxidation process hot enough to essentially clean the filter. Passive regeneration is typically used in applications where the engine duty cycle is predictable and constant for a specific period of time and the exhaust remains at a specific temperature.

Figure 2: In this application, indoor stationary engines have externally mounted DPFs. Mounting aftertreatment solutions externally minimizes size and accessibility constraints. Courtesy: DCL America Inc.

Stationary emergency sources such as backup generators and engine-driven fire pumps typically do not meet this criteria. If a particulate filter cannot regenerate properly, it can become plugged, causing enough back pressure to cause the engine to shut down. Also, a type of “flash over” can occur, where too much PM is oxidized at the same time, effectively igniting the filter.

Active regeneration can be achieved at lower exhaust temperatures because it uses an independent ignition source to create the oxidation process. When the filter needs to regenerate, either a combustible liquid such as diesel fuel or an electrical charge is used to trigger the oxidation process. This is a much more common approach to regeneration in stationary emergency standby applications. The Manufacturers of Emissions Controls Association provides more information on emission control devices and how they work.

Manufacturers and installers use back-pressure calculations for the specific target engine to correctly size the DPF for the application. The physical size and amount of heat generated by these filters make installation a tricky proposition. Since installation is different for each stationary source, attention to this detail is vital in avoiding long-term issues after installation.

Aftertreatment devices require periodic service. In some cases, the filtration system must be removed for additional cleaning. Ash must be removed from DPFs—a process known as de-ashing. In some states, the ash from DPFs is considered hazardous material and must be handled accordingly. Access for safe DPF removal must be accommodated to avoid exposing the technician to hazardous material, or to avoid possible fines for mishandling.

Specifying a stationary engine source means understanding the entire emission compliance process. As emission standards continue to evolve, so does the technology used to meet it.

Not only are emissions standards constantly evolving, so is the technology used to comply with them. Taking time to understand the emission requirements for your next project can save time and money in the long run—as well as help the environment.

Rasmussen is president and founder of Emissions Guru Inc., a company that provides emission-compliance consulting and testing services for engine manufacturers, OEMs, emerging emission control technology companies, and equipment owners.

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