Tier 4i Emissions

Experts answer questions about EPA Tier 4i emissions regulations and generator operating procedures.

By Consulting-Specifying Engineer webcast with MTU Onsite Energy September 3, 2010

The U.S. Environmental Protection Agency’s Tier 4 Interim emissions regulations are scheduled to go into effect in 2011, but some facility owners, engineers, and power system operators still have questions about how the complex regulations will affect them. While it has been the responsibility of the genset manufacturers to make sure that Tier-certified generator products are available to customers on the timetable established by the EPA, customers still have questions about purchasing, installing, and operating EPA-certified power systems.

This fact was made clear during a March 4, 2010, webinar entitled “The Future of Emissions Regulations: Tier 4i and Beyond.” It was sponsored by Consulting-Specifying Engineer magazine and MTU Onsite Energy. Hosted by Michael Ivanovich, previous editor of Consulting-Specifying Engineer, the webcast featured four industry experts from MTU Onsite Energy: Christine Ueno, manager of regulatory compliance; Dwight Wells, regional sales manager; Brian Ponstein, applications engineer for power generation; and Suzanne Seivright, government affairs coordinator, Valley Power Systems, a large California-based MTU distributor.

After an initial presentation by the panel that summarized the upcoming Tier 4i regulations and the technology being used to comply with the new rules, webinar participants e-mailed questions that centered on specific topic areas. These included:

  • Basic definitions of stationary emergency, prime, and continuous power systems and how EPA regulations apply to each
  • How the Tier 4i regulations apply to various applications or regions (such as California)
  • Retrofitting of existing or currently non-compliant gensets
  • Details concerning the operation of selective catalytic reduction (SCR) systems used to control nitrogen oxides (NOx).

Basic Definitions

Part of the confusion surrounding the Tier 4i standards is that gensets used strictly for emergency standby are exempt from Tier 4i and only have to comply with Tier 2 or Tier 3 (depending on the engine’s horsepower). This exception generated many questions.

Q: Can you clarify the difference between emergency standby-, prime-, and continuous-rated gensets as they relate to Tier 4i?

A: An emergency standby generator is an auxiliary power system that only supplies power to a facility when normal utility power is unavailable due to an outage. These generators are exempt from the regulations of Tier 4i and Tier 4 as long as they are used for emergency power only and operate less than 100 hours per year for testing and maintenance. There is no limit on operating hours when being used for emergency power.

A prime-rated genset is one that provides onsite electric power to a facility not served by regular utility power. The prime-rated genset is intended by the manufacturer to supply a varying load for a specified number of hours each year. Since the generator is not intended as an emergency standby power supply, new prime-rated gensets manufactured after Jan. 1, 2011, must comply with EPA Tier 4i regulations.

A continuous-rated genset is intended by the manufacturer to supply power to a facility not served by normal utility power at a constant load for an unlimited number of hours per year. Continuous-rated gensets manufactured after Jan. 1, 2011, must comply with EPA Tier 4i.

Q: Can a prime-rated genset be considered exempt from Tier 4i if it is used only as an emergency standby power supply?

A: After Jan. 1, 2011, if a facility purchases a prime-rated genset, it will come equipped with SCR aftertreatment that will meet Tier 4i. If it is an existing prime-rated genset, it will be treated the same as all other existing gensets.

Q: Does an emergency standby genset running for “storm abatement” qualify for the EPA exemption?

A: Since the generator is running when normal utility power is available (but might fail during a current storm), it would not generally qualify for the emergency standby exemption from Tier 4i. However, there is a new provision that will be coming out of EPA in mid-2010 that will allow an emergency standby generator to run up to 50 hours per year for non-emergency, non-maintenance operation that would include storm abatement for hospitals and other critical facilities. This ruling is intended for data centers in particular, where the generators need to be used for certain types of UPS maintenance. The facility operators do not want the UPS to be connected to the utility during UPS maintenance, so they will run it on generator power. This exclusion is one that the engineering community has requested to allow additional time to make those maintenance checks that are not related to the engine-generator itself. As long as the generator still meets all the criteria for an emergency standby power supply and generator testing is limited to 100 hours per year, facility operators can use a Tier 2 or Tier 3 genset.

Q: EPA regulations state that if a facility with an emergency standby system has “financial arrangements” with a local utility, the genset is not exempt from Tier 4i. What are examples of “financial arrangements”?

A: If an owner-operator gets financial consideration from the utility because the facility has an emergency standby system on its property that could be used during peak demand periods or brownouts, that would be a “financial arrangement.” In any instance where the utility contracts for the use of a private genset to supply power for load shedding or during a brownout, the power system would no longer be considered exempt from Tier 4i.

Tier 4i Regulations

A number of questions related to when the Tier 4i regulations become effective and how they are applied to certain operational situations.

Q: Does the Jan. 1, 2011, date for Tier 4i compliance apply to the date the genset is sold or the date the system is commissioned?

A: The effective date for Tier 4i refers to the date that the engine is manufactured, not when the genset is built. However, any stationary engine has to be installed and commissioned within two years of any change in emission standards to remain compliant. Otherwise, the unit will have to be exported out of the US. “Installed” means bolted to the earth and ready to be started up. This provision is listed in Part 60.6214 of the EPA regulations. For example, an engine manufactured on Dec. 31, 2010, that meets the 2010 Tier 2 or Tier 3 standard would have to be installed and operational by Dec. 31, 2012, in order to be compliant. In California, local air districts have a different permitting process, and the issuance of the permit becomes the milestone date for application of the EPA rule.

Q: Is California the only state that has “control boards” with more stringent regulations than the EPA?

A: No, both New York and Texas have more stringent regulations than the EPA. Other states are adopting more stringent NOx standards as well – especially if they have urban “non-attainment” areas where ozone levels tend to exceed EPA regulations. NOx is a precursor to ozone.

Q: When should we start specifying Tier 4i engines?

A: Any installation of prime or continuous duty that is going to be permitted in 2011 and beyond should be specified for Tier 4i right now. Facilities installing an emergency standby power system in California right now should be specifying a Tier 2 or Tier 3 with aftertreatment to meet the BACT (best available control technology) requirements of the local air district. As a manufacturer, MTU Onsite Energy is starting to see specifications now – especially in data centers – asking for options for Tier 4i or Tier 2 plus third-party aftertreatment for emergency standby. The milestone date for applying the rule is when you actually submit for permits.

Q: After 2011, will manufacturers be required to label emergency generators with a specific label stating how the genset can and cannot be used?

A: Yes, there are specific labelling requirements for all engines, including emergency generators. The label will state that the engine is certified to the stationary engine requirement, but it will not list what limitations are on that engine. However, the owner’s manual will describe the operating limitations. Also, the permit for the power system will clearly state its operating parameters.

Q: How do the 2011 EPA rules apply to trailer-mounted gensets? And is there any advantage to using mobile gensets to supply emergency power?

A: Any genset on wheels is mobile; therefore, it will have to meet the mobile standards, whether it’s for emergency power or not. So, no, there is no particular advantage to using mobile gensets to supply emergency power. In general, mobile emergency engines are governed under Part 1039 of the EPA regulations and would, therefore, have to meet Tier 4i standards. However, outside of California, a wheeled genset onsite for more than 12 months is considered to be a stationary engine and, at that point, exempt from Tier 4i if it meets the definition of emergency engine.  

In California, portable equipment is regulated by two different agencies. One is the local air district, which requires the genset to remain within the jurisdiction of that local air district. Or, it can be permitted through the California Air Resources Board (CARB). However, CARB says that a portable genset cannot exceed 12 months at any one location.  

Q: Will SCR-DPF combination systems be sold separately so that existing installations can be made to comply with the new Tier 4 standards?

A: As a manufacturer, MTU Onsite Energy will not be offering aftertreatment packages for retrofits. Local MTU distributors will have access to third-party providers for this type of equipment. However, if a genset is retrofitted with an aftertreatment system in the field, it may be compliant with emissions regulations but not “EPA certified.” Once a genset is sold, it is not possible to “certify” it to a current standard as required by EPA. An engine can only be EPA certified by the manufacturer during manufacturing. Compliance usually requires testing by a local entity, but EPA compliant and EPA certified are not the same thing.

SCR Operation

SCR after-treatment will be the major technology used by MTU Onsite Energy to make gensets compliant with Tier 4i after 2011. It reduces the amount of NOx in diesel exhaust by up to 90 percent by injecting diesel emissions fluid (DEF – also known as aqueous urea) into the exhaust stream. The DEF contains ammonia, which reacts with the NOx in the presence of a catalyst to convert NOx into harmless nitrogen, carbon dioxide and water vapor. Following are questions about SCR operation.

Q: How long does it take for a genset to come up to temperature so that the SCR unit will operate properly?  

A: How fast the SCR reaches operating temperature depends on ambient conditions and load. If the offline diesel engine is kept is warm with a coolant heater, then diesels with SCR can heat up in 10 to15 minutes for most large engines. This will take longer in cold climates, but load is the major factor and the key factor to be considered in the design. This is one reason that SCR aftertreatment is not required for emergency standby gensets and wouldn’t necessarily be helpful in meeting emissions standards as a retrofit. Emergency gensets rarely run long enough to get an SCR system up to operating temperature.

Q: What is the shelf life of DEF?

A: The shelf life of DEF is directly related to the ambient storage temperature. At room temperature or a little colder, it will last at least a year. DEF suppliers have graphs that illustrate the shelf life and they are probably available online. The American Petroleum Institute (API) has a new DEF standard, and MTU Onsite Energy recommends that everyone purchase DEF that meets the API standard because it will have the best quality and the longer shelf life.

Q: What is the projected durability of an SCR unit on a genset?

A: We don’t know if this is true for all genset manufacturers, but MTU Onsite Energy’s factory-installed SCR equipment is designed to last for the life of the engine until overhaul.

Q: What are the rules concerning low-sulfur diesel fuel and aftertreatment?

A: The sulfur content of diesel fuel is directly related to emissions, and ultra-low-sulfur diesel fuel (ULSD) that is coming out will help reduce overall emissions. While sulfur in diesel fuel does not harm the operation of SCR, high sulfur in the exhaust will foul the catalysts in a diesel particulate filter (DPF). So, when DPF is used, ULSD (< 15 ppm sulfur) will be necessary to protect the catalysts.

Q: Does the use of biofuels affect the levels of NOx and PM?

A: Yes, changing the fuel will definitely change what comes out of the exhaust. Biofuels tend to produce slightly more NOx in the exhaust than straight diesel fuel, but this depends on the amount of biofuel in the blend. Check with your engine manufacturer regarding recommendations about biofuels.

In conclusion, compliance with the new EPA regulations is dependent on the timing of the unit’s manufacturing date, the installation of the generator set and the type of application (emergency standby, prime power, peak shaving, etc.).  Consult with the generator set’s manufacturer or distributor, the responsible specifying engineer or local permitting agencies if you have additional questions.

To view the full webcast on-demand, visit www.csemag.com/webcasts