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Jan-2010

Monitoring heat exchange systems

Anticipating final federal standards, the cooling tower monitoring programs at two refineries have been beneficial in estimating VOC emissions from the towers

Loree Fields URS Corporation
Jason Bradford Marathon Petroleum Company

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Article Summary

In January 2009, the Refinery Maximum Achievable Control Technology (MACT) I residual risk amendments were finalised, but not published. The Environmental Protection Agency (EPA) has now moved forward with issuing a new, separate final rule to directly add requirements for heat exchange systems to the Refinery MACT I regulations at 40 CFR 63, Subpart CC. On 28 October 2009, the federal heat exchange standards were promulgated via publication in the Federal Register. These standards require all refineries to monitor heat exchange systems in organic Hazardous Air Pollutant (HAP) service. The MACT standards are designed to address the HAP emissions that will occur during malfunctions (leaks) of heat exchange systems.

Refineries in the Houston/Galveston area have been monitor-ing emissions from cooling towers in Highly Reactive Volatile Organic Compound (HRVOC) service, according to the Texas Commission on Environmental Quality (TCEQ) regulations instituted in 2003. This article summarises the new federal monitoring requirements and presents examples of cooling tower monitoring programs at two Mara-thon Oil Corporation refineries: the Texas City refinery, which conducts monitoring as required by the TCEQ regulations as well as per the refinery air permit requirements; and the Robinson, Illinois, refinery, which conducts monitoring per the refinery air permit requirements.

The finalised Refinery MACT 
I residual risk amendments 
included: storage tank provisions; requirements for heat exchange systems, including cooling towers; as well as some regulatory clarifications and cross-references. However, the amendments were not published in the Federal Register prior to the issuance of the 20 January 2009 memorandum from the White House Chief of Staff stating that no proposed or final regulations should be sent to the Office of the Federal Register for publication until the regulations have been reviewed and approved by the new Administration.

Summary of the new federal requirements 
The regulated heat exchange systems are heat exchange systems that cool process fluids containing 
5 wt% or greater of total organic HAPs, as listed in Table 1 
of 40 CFR 63, Subpart CC. Systems that meet this criterion are designated as “in organic HAP service”. The heat exchange standards are designed to address the HAP emissions that will occur during malfunctions (leaks) of heat exchange systems. Therefore, the federal regulatory requirements apply at all times, including during periods of start-up and shutdown of refinery equipment.

For existing sources (refinery sites that commenced construction or reconstruction prior to 18 August 1995) and for new sources 
that commenced construction or reconstruction between 18 August 1995 and 4 September 2007, monitoring of heat exchange 
systems in organic HAP service must begin within 36 months after publication of the standards in the Federal Register (ie, no later than 29 October 2012). For new sources 
that commenced construction or reconstruction after 4 September 2007, monitoring of heat exchange systems in organic HAP service is required upon start-up or by 28 October 2009, whichever is later.

Monitoring requirements 
A heat exchange system is defined as: “A device or series of devices used to transfer heat from process fluids to water without intentional direct contact of the process fluid with the water (ie, non-contact heat exchanger) and to transport and/or cool the water in a closed-loop recirculation system (cooling tower system) or a once-through system (eg, river or pond water).” The com-ponents of a closed-loop recirculation system include heat exchangers, water lines to and from the heat exchangers and cooling towers. A typical closed-loop recirculation system is shown in Figure 1.

Cooling water is to be sampled monthly and analysed for volatile organic compound (VOC) content using the TCEQ’s Modified El Paso Method (Revision No 1, January 2003). Samples can be collected at:
• The cooling water effluent of each heat exchanger in organic HAP service
• Branch points combining several heat exchanger effluent lines
• From the combined stream influent to the cooling tower, prior to exposure of the influent stream to the air.

The Modified El Paso Method uses a sampling train with a small-scale air stripper. After the air passes through the cooling water, the gas stream is routed through a water knockout container. Then the total strippable VOC concentration (as methane) in the stripping gas is measured using a flame ionisation detector.

Leak repair requirements 
A leak is defined as a total strippable VOC concentration (as methane) in the stripping gas of:
• 3.1 parts per million by volume (ppmv) or greater for heat exchange systems at new sources
• 6.2 ppmv or greater for heat exchange systems at existing sources.

Any leak that is detected during a sampling event is to be repaired within 45 days of the event. Delay of repair is allowed until the next shutdown if the repair requires that a process unit be shut down and the leak rate is less than 62 ppmv. Delay of repair is allowed for up to 120 days if critical parts or personnel are not available and the leak rate is less than 62 ppmv. During the delay 
of repair time frame, monthly monitoring must continue. If the monitoring results show a leak rate greater than or equal to 62 ppmv, the leak must be repaired within 30 days of the monitoring event.

Exemptions
The requirements of the new federal heat exchange system standards do not apply to a heat exchange system that does not contain any heat exchangers in organic HAP service. A heat exchange system that is in organic HAP service is exempt from the monitoring and leak repair requirements if:
• The pressure of the cooling water side of the exchanger is at least 35 kilopascals (5.1 psi) greater than the pressure of the process fluid side, or
• There is an intervening cooling fluid containing less than 5 wt% total HAPs, which isolates the cooling water from the process 
fluid, and this intervening fluid is not sent to a cooling tower or discharged.  


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