MACT rule will have effect on stationary engines

Pipeline & Gas Journal, Oct, 2005 by Jay Holden

Many have heard of the current MACT (Maximum Achievable Control Technology) regulations, but they may be unaware of its impact. What does it mean? How will it affect us? The MACT rule affects many aspects of the stationary engine owner/operator--from environmental permitting to daily operations and recordkeeping.

The question is, who is affected, what engines are affected, what needs to be done and by when? This article is an introduction to MACT for existing and new reciprocating engines, explaining it from a high level, and providing answers to some of the questions above. This article does not address the gas turbines. Let's start with a little history.

MACT regulations are developed by the U.S. Environmental Protection Agency (EPA), and address air toxics emissions from specific equipment categories and industrial operation. The final rule, promulgated on Feb. 26, 2004 by the EPA, drives at reducing toxic air emissions from stationary engines found in pipeline compressor stations and other industrial facilities.

The goal is to reduce air pollutants such as formaldehyde, acetaldehyde, acrolein and methanol. These emissions are categorized as "Hazardous Air Pollutants" (HAPs) or air toxics. The MACT regulation requires emissions controls for certain engines, depending upon the engine type, facility size, and whether the engine is new or existing. EPA projects air toxics will be reduced nationally by 5,600 tons in the fifth year after the promulgation of the rule.

MACT Applicability

There are several steps to determine MACT applicability for your reciprocating engines:

1. Determine if your facility is considered a "Major Source." A major source facility is one that emits greater than 25 tons per year (TPY) of a combination of toxic air pollutants or greater than 10 TPY of any single constituent. For facilities that include engines, 10 TPY of formaldehyde emissions will typically be the emission that triggers classification as a major source. A facility that is designated a major source can avoid MACT by being re-categorized as a "synthetic minor" source if modifications are made to reduce the facility emissions below the major source threshold.

2. Determine if the specific engine in question has a site horsepower rating greater than 500.

4. Determine the category the engine falls under, for natural gas-fired engines:

a. 4-stroke rich burn (4SRB),

b. 4-stroke lean burn (4SLB),

c. 2-stroke lean burn (2SLB),

d. Emergency,

e. Limited Use. (1)

The engine must fall under one of these categories. For example, if the engine is a 4SRB that is a "Limited Use" engine, it then falls under the limited use category.

The 4SRB category is defined as an engine where the manufacturer's recommended air/fuel ratio setpoint divided by the stoichio-metric air/fuel ratio is less than or equal to 1.1. If there are no manufacturer's standards for the air/fuel ratio setpoint, the engine is considered a rich burn if the oxygen content in the exhaust is less than or equal to 2%. The 4SLB category is defined as a 4-stroke engine that is not a rich burn. The 2SLB category includes any engine that is 2-stroke cycle. MACT does not recognize 2-stroke rich burn engines.

Engines defined under the Emergency category are units that are operated in an emergency such as production of power for critical systems if local utility power is lost or for pumping of water in case of flood or fire. These engines may be operated for maintenance/readiness checks and for up to an additional 50 hours per year in other non-emergency situations. During an emergency, there is no operational time limit. An engine that would fall under the Limited Use category would be a unit that is operated less than 100 hours per year.

Now that we have determined what type of engine you have, we must identify which engines are subject to MACT requirements. Table 1.0 outlines which categories are subject to MACT. Note that the only existing units subject to MACT are 4SRB units.

No MACT Requirement

If an engine has "No MACT Requirement," nothing is required by the owner/operator. However, the burden of compliance is on the owner. It is recommended that the owner keep on hand documentation explaining why the particular unit is not subject to MACT.

For "Initial Notification" for emergency and limited use engines, the owner/operator is required to submit documentation to the EPA Region and/or delegated authority outlining the specifics of the unit/owner and also clearly state that the RICE is for limited or emergency use only, therefore not subject to the MACT requirements. Note that Initial Notification is also a requirement for units subject to Full MACT Requirements.

For the purpose of a MACT overview, we will focus on the "Full MACT Requirements" for a 4-stroke rich burn. We will briefly discuss the differences between the 4SRB, 4SLB and 2SLB following this section. The requirements for a 4SRB engine are broken into seven sections:

1. Emissions Limits

2. Emission Test Requirements

3. Operating Limits and Parameter Monitoring Requirements if using a NSCR catalyst