FROM: Jeff Coburn, RTI International

TO: Brenda Shine, EPA/OAQPS

FOR: EPA Docket No. EPA-HQ-OAR-2011-0002

DATE: July 12, 2011

SUBJECT: Technology Review for Heat Exchange Systems

1. Purpose

This memorandum documents the technology review for heat exchange systems. It reviews control alternatives and estimates the costs a nd environmental impacts for the alternatives identified.

2. Legislative Background

The Clean Air Act (CAA) requires EPA to review promulgated standards periodically to ensure new source performance standards (NSPS) and na tional emissions standards for hazardous air pollutants (NESHAP) reflect advances in emissi ons reduction technology. Specifically, Section 112(d)(6) of the Clean Air Act (CAA) states that “[t]he Administrator shall re view, and revise as necessary (taking into account de velopments in practices, proce sses, and control technologies), emission standards promulgated und er this section no less often th an every 8 years.” Similarly, Section 111(b)(1)(B) requires EPA to review NSPS for a given source category every 8 years, and, if appropriate, revise such standards. To facilitate these required re views, EPA is evaluating key emission sources that exist across severa l source categories to provide a consistent framework when evaluating the emissions from these key sources for a particular source category. This memorandum documents one such t echnology review for heat exchange systems.

3. Introduction

Heat exchangers are devices or coll ections of devices used to transf er heat from process fluids to another fluid (typically air or wa ter) without intentional direct c ontact of the process fluid with the cooling fluid ( i.e. , non-contact heat exchanger). The focus of this technology memorandum is on water-cooled heat exchangers. The term “heat exchange system” is used in this memorandum to refer collectively to water-cooled heat exchangers and the associated cooling water handling system. There are two types of heat exchange sy stems: closed-loop recirculation systems and once-through systems. Closed-loop recirculation systems are marked by the use of a cooling tower to cool the heated water leavi ng the heat exchanger and then return the newly cooled water to the heat exchanger for reuse. For closed-loop recirculat ion systems, the heat exchange system consists of a cooling tower, all heat exchangers that are serviced by that cooling tower, and all water lines to and from the heat exchanger(s). Once-through systems typically useTechnical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

2 river or pond water as the influe nt cooling fluid to the heat ex changers, and the heated water leaving the heat exchangers is then discharged from the facility. For once-through systems, the heat exchange system consists of one or more heat exchangers servicing an individual process unit and all water lines to and fr om the heat exchanger(s).

At times, the heat exchanger’s internal tubing material can corrode or crack, allowing some process fluids to mix or become entrained with the cooling water. Pollutants in the process fluids may subsequently be released from the c ooling water into the atmosphere when the water is exposed to air ( e.g. , in a cooling tower fo r closed-loop systems or trenches/ponds in a oncethrough system). This technology memorandum specifically considers methods to reduce emissions from cooling water that has unintentiona lly contacted a process fluid within in a heat exchanger. Note that intenti onal direct contact of water with process fluids results in the formation of a wastewater, which is not covered in this technology memorandum.

4. Description of Emission Releases

Once-through heat exchange syst ems generally transport the c ooling water leaving the heat exchangers in open sewer lines or trenches to a holding pond to allow the water to cool prior to discharge. Fugitive air emissions of polluta nts from the water may occur along the transport lines and from the surface of the holding pond or receiving water body. So me facilities may use a spray in the holding pond to help cool the water, but this also increases water contact with the air and therefore the potential fo r air emissions. Emissions from once-through heat exchange systems are similar to releases from wastewater treatment units and are fugitive in nature. The emissions occur via volatilization at the air-liquid inte rface within the trans port lines or in the surface impoundments. Not all pollutants will be emitted from the cooling water to the same extent. Highly volatile compounds ( i.e. , those with high Henry’s Law constants) are expected to be nearly completely released from the coo ling water while only a small fraction of the less volatile compounds are emitted; the remainder of the less volatile compounds would remain in the water through the collection and holding units.

It is costly to completely cover these once-throu gh cooling water sources to prevent air releases. Furthermore, covering these units would only serv e to suppress the volatile emissions that would be released later from the receiving water body. It would be very costly to build a treatment system for the cooling water which would not actu ally need treatment excep t for the small period of time a leak at the heat exchanger might exist. That is, it is not generall y feasible to prescribe or enforce a standard of performance because the pollutant or pollutants are not emitted through a conveyance designed and constructed to emit or capture such pollutant(s) and that the application of a measurement methodology, whic h would require such a conveyance to be installed, is not generally feas ible in light of the technolog ical and economic limitations.

Closed-loop heat exchange systems typically use cl osed piping to transport the water to and from the cooling tower. Emissions from closed-loop heat exchange systems occur primarily at the cooling tower, as this is gene rally the only point for exposure of the cooling water with the atmosphere. Cooling towers may be designed as either natural draft or mechanical draft. Natural draft cooling towers are large hyperbolic st ructures (often associat ed with nuclear power plants) that use natural convection of warmed ai r to create air flow across the water, thereby cooling the water. Mechanical dr aft cooling towers use large fans to force air through or acrossTechnical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

3 the cooling water to cool the water. Figure 1 shows a typical mechanical, induced-draft industrial cooling tower. The cooling towers are designed to have a high surface area for airwater contact for the purposes of cooling the wa ter. Most industrial cooling towers have multiple exhaust fans that are used to draw am bient air through water that is cascading down the outer-portion of the tower; the air is then e xhausted from very short, wide fan openings at multiple locations across the top of the cooling tower. Emissions can also occur across the openings at the sides of cooling towers as wind blows across the unit. Em issions occur primarily due to volatilization of light organics from the wa ter. A small fraction of the recirculating water may become entrained in the exhausted air and le ave the cooling tower as a water mist. This water mist is commonly referred to as “drift” or “drift losses.” All po llutants contained in the water mist, including low volatility compounds, can be released to the atmosphere via the cooling tower drift.

Figure 1. An induced-draft industrial cooling tower.

Although emissions from closed-loop systems are expected to be released primarily in the exhaust air from the cooling towers, it is not gene rally feasible to prescribe or enforce a standard of performance because the pollutant or po llutants are not emitted through a conveyance designed and constructed to emit or capture such pollutant(s) and that the application of a measurement methodology, which would require su ch a conveyance to be installed, is not feasible due to technological and economic limitations . First, not all of the emissions occur from the exhaust gas fans at the top of the cooling tower; fugitive releases can also occur through openings along the side or bottom of the cooling tower. To capture all of the emissions would require that the whole cooling tower be enclosed. This is not practical or technically feasible considering the size of the cooling towers and th e volume of gas that would be required to be handled within the enclosure system and consid ering the heat transfer requirements of theTechnical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

4 cooling tower. While it may be technically feas ible to install ducts on each exhaust fan to capture and route the primary exhaus t gas to a single stack for poten tial treatment and/or release, such an installation still suffers from techni cal and economic limitations. Such a proposed capture and exhaust stack would still have to be very large due to the size of the physical dimensions of the cooling towers, the volume of air exhausted, and the need to transport the exhaust air away from the cooling tower (oth erwise, the stack itself will reduce the cooling efficiency of the cooling tower, leading to pro cess operation issues for the heat exchanger served by the cooling tower). Given the large exhaust volumes and the high moisture content of the exhaust, routine measurements that provide th e necessary detection limits needed to identify typical heat exchanger leaks are not available. Furthermore, such a capture system would not capture all of the emissions from the cooling tower.

Based on the nature of the emission releases fr om heat exchange systems (both once-through and closed-loop systems as described above), it is ge nerally not feasible to prescribe or enforce a standard of performance for heat exchange systems. Specifically, the application of a measurement methodology, which would require a conveyance designed and constructed to emit or capture the emissions from the heat exchange syst em to be installed, is not feasible in light of the technological and economic lim itations associated with atmo spheric releases from heat exchange systems.

Differences in emissions from once-through h eat exchange systems and closed-loop heat exchange systems were evaluated using emissi on models. This evaluation was completed because direct emission measurements are not available for these sources (due to the measurement method limitations just discu ssed). Wastewater emission models ( e.g. , using mass transfer correlations) can be us ed to predict the releases from the open cooling water sources used in a once-through heat exchange system. Although the emissions will vary based on the design and operation of the cooling water collec tion and holding units in once-through systems, highly volatile compounds are projected to be ne arly 100 percent emitted from the cooling water while only a small fraction of low volatility compounds will be released. These results are similar to modeling results for th e releases projected for cooling towers used in closed-loop heat exchange systems. Again, emissions from the cooling tower can vary based on the air-liquid flow ratio and mass transfer efficiency. Given th e uncertainty and variabili ty of emissions from these sources, the emissions potential for bot h once-through and closed -loop heat exchange systems are expected to be essentially equivalent.

5. Identification of Control Alternatives

Since it is not feasible to prescribe or enfor ce a standard of performance for heat exchange systems, design, equipment, work practice, a nd operational standards for reducing emissions from heat exchange systems were identified and evaluated.

Potential Equipment Design and Operational Standards

As the heat exchange systems evaluated in this memorandum are designed as non-contact systems, any contact that does occur happens as a result of an unintentional equipment failure that results in a leak of the process fluid into the cooling water. No construction material was identified that, in all cases, could not unint entionally leak. Certain design or operationalTechnical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

5 conditions were identified that would effectively reduce or eliminate the leak from the heat exchanger from contaminating the cooling water and subsequently be emitted. A brief description of these design and operational conditions follows:

• Heat exchangers where the cooling water pre ssure significantly exc eeds the process fluid
pressure . For these heat exchangers, if a crack in the heat exchanger occurs, water will leak into the process fluid rather than the process fluid leaking into the cooling water. Note that there will be a pressure drop acr oss the heat exchanger for both the water and process fluid, and most heat exchangers opera te with countercurrent flow. The process fluid inlet side of the heat exchanger, which will be the location of the maximum process fluid pressure within the heat exchanger, will also be the water outlet side of the heat exchanger (location of minimum water pressu re within the heat exchanger). It is conceivable that a leak into the cooling water can still o ccur even though the inlet water pressure exceeds the inlet fluid pressure. Ther efore, it is necessary to specify that the minimum cooling water pressure at any poi nt within the heat exchanger exceeds the maximum process fluid pressure within the he at exchanger. Typical language used in previous rules for heat exchangers describe th ese heat exchangers as those that “operate with the minimum pressure on the cooli ng water side at least 35 kilopascals [ i.e.

, 5.0 pounds per square inch absolute (psia)] greater than the maximum pressure on the process side.”

• Heat exchangers that employ an inert (not vol atile) intervening coo ling fluid between the process and the cooling water and isolates the cooling water from the process fluid . The intervening fluid must remain enclosed a nd cannot be sent through a cooling tower or otherwise allowed routine c ontact with the atmosphere; otherwise, emissions would simply be transferred from the cooling wate r release points to the intervening fluid release points. Provisions would be need ed for draining the in tervening fluid for maintenance purposes. One could conceive of a situation in which a leak develops between the process fluid and a second leak develops between the intervening fluid and the cooling water. If this occurs, and the process flui d pressure exceeds the water pressure, the intervening process fluid chamber would become filled with process fluid and the process fluid would leak into the c ooling water. Thus, while a heat exchanger designed to use an intervening fluid is much less likely to leak (because two leaks would have to occur) than a heat exchanger that doe s not employ an intervening fluid, this type of design does not necessarily guarantee that process fluid leaks that contaminate the cooling liquid will never occur.

The question arises: should these design and operational alternativ es be required for all new or modified sources? As process fl uid pressures are dictated by process operational conditions, and many chemical processes operate at elevated pre ssure, it is impractical to require the cooling water supply to operate at a pre ssure exceeding the process fluid pr essures in all cases. Typical industrial water supply systems operate at a of 30 to 100 psi gauge pressure (psig). If the process fluid is at a high pressure, co mmonly available water supply syst ems could not supply cooling water at these same high pressures. Additionally , the heat exchanger housing would have to be designed to handle these high pressu res. It would be cost-prohi bitive and energy intensive to require heat exchanger water pressures to exceed process fluid pressures in all applications.Technical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

6 The use of an intervening process fluid requires a specially designed pro cess heater. It would generally be impossible to retrofit a process heater to use an intervening fluid without completely replacing the heat exchanger. This would be a cost-prohibitive requirement for existing heat exchange systems. New installations could be de signed to use an intervening fluid; however, the use of an intervening fluid generally reduces the heat transfer effici ency of the heat exchanger, so there are additional costs associat ed with using an intervening fluid because the heat exchangers would be larger when using an intervening flui d. It is beyond the scope of this evaluation to determine the precise costs associated with requir ing the use of an intervening fluid, as this can vary significantly by size and ope rational needs of a specific heat exchanger. Also, it is difficult to quantify the emission reductions achieved by such an application because there are no data to determine how often these systems do eventually leak. However, the fact that such systems could eventually develop leaks in to the cooling water would sugge st that monito ring to identify incidence of leaks may still be needed. Therefore, a facility would have to undergo significant costs to design and install a heat exchanger w ith an intervening flui d, and still incur ongoing costs to monitor for leaks. As described pres ently, a monitoring and repair program to identify leaks is effective at reducing emissions from heat exchange systems. While it is not possible to develop a quantitative cost-effec tiveness value for a requirement to use an intervening fluid in new heat exchanger installations, the additional costs associated with such a requirement do not appear to be reasonable considering the limite d emission reductions that would be achieved beyond the implementation of a monitoring and repair program to identify leaks. In fact, in most cases, it would be extremely expensive to implem ent with little to no emission reductions. While the use of an intervening fluid may be evaluated in more detail for specific source categories, particularly for heat exchangers handling proces s fluids that are highly toxic or corrosive ( e.g. , hydrogen fluoride), it appears that, fo r typical heat exchanger system s, the use of an intervening fluid in new or existing heat exch angers is not practical, taking into consideration the cost of achieving limited emission reductions (beyond th ose achieved through a monitoring and repair program) and considering the e nvironmental and energy impact s of such a requirement.

Potential Monitoring Alternatives

A variety of different work prac tices were identified as potential emission reduction measures for heat exchange systems. These work practices can be loosely grouped as visual inspections, surrogate monitoring, water sampling and anal ysis, and stripping column air analysis.

Visual inspections have been used by several facilities. For heat exchangers servicing a gaseous process fluid, gas entering the cooling water will coll ect in these high points in the line. If these locations have a site glass, visual inspections can be used to identify these leaks. For oncethrough cooling systems, the owner or operato r can visually inspect the holding pond for a visible organic sheen. The presen ce of an organic sheen indicates that a heat exchanger is likely to be leaking. Visual inspections are expected to be able to identify very large leaks, but they will not be able to identify leaks that do not exceed solubility limits of the cooling water.

Surrogate monitoring methods include monitoring of chemical usage rates ( e.g. , chlorine, hypochlorite, or bromine usage rate s), monitoring of free chlorine in the cooling water, and monitoring of the oxidation/reducti on potential of the cooling water. When a leak of a degradable organic pollutant occurs, the added organic matte r in the cooling water causesTechnical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

7 increased microbial growth. The oxidation/reducti on potential or free ch lorine concentration may be used to monitor for microbial growth (Suslow, 2004). When microbial growth is found, disinfectant chemical use rates are increased to control the biological grow th. Microbial growth in the heat exchanger will reduce the heat tran sfer efficiency and ma y cause plugging of the water tubes. Consequently, esse ntially every closed-l oop heat exchange system is monitored for microbial growth. Several consecutive days of increased biological growth or increased disinfectant chemical use rates w ould indicate a leak has occurred. Since surrogate monitoring is commonly performed on a daily or per shift freq uency, these methods should be able to detect leaks fairly quickly. However, there may be lag period between the initiation of the leak and significant microbial growth, so there may be some delay between the first occurrence of the leak and a change in the surrogate monitoring level. For this same reason, surrogate monitoring may not be able to identify leaks in once-through sy stems even if monitoring is used to control microbial growth from the source water used in the system. Surrogate monitoring methods can detect leaks that do not exceed wa ter solubility limits, so these methods should be more sensitive than visual inspections. However, as there is commonly some background level of microbial growth and disinfectant use, surrogate monitori ng methods generally are not sensitive enough to identify smaller heat exchanger leaks. Base d on the available data, monitoring of surrogate parameters will only detect relatively large l eaks and could miss leaks that would generate significant organic emissions (Corsi et al., 2004).

Water sampling methods include total hydrocarbon (THC), total organic carbon (TOC), or speciated chemical analysis. Common industrial water supply can have TOC concentrations of 1 to 5 parts per million by weight (ppmw). Cons equently, THC or TOC monitoring may be able to identify an increase in THC or TOC of 1 ppmw by monitoring before and after the heat exchanger, but are generally not sensitive enough to identify smaller leaks. Using knowledge of the process fluid, analysis of speci fic pollutants can be used to iden tify a leak. For example, for an ethylene unit, monitoring for et hylene in the cooling water leav ing the heat exchanger can be used to identify a leak. By targeting a specific chemical or limited set of chemicals, very low water detection limits can be achieved; common de tection limits are approximately 10 to 20 parts per billion by weight (ppbw). For very volatil e compounds, the direct water concentration and flow rate can be used to estimate the emissi ons from the heat exchange system by assuming 100 percent of the pollutant will be emitted. For less volatile compounds in closed-loop heat exchange systems, the concentration of semi-vol atile compounds can slowly build-up within the recirculated cooling water, because not all of the compound will be emitted from the cooling tower. For these compounds, direct water sa mpling of the cooling wa ter leaving the heat exchanger may be able to identify very small leak s, but this concentration may not correlate with the actual emissions from the system (when a ssuming 100 percent emissions). Sampling can be performed before and after the c ooling tower (which is the same as monitoring before and after a heat exchanger or set of heat exchangers) to get a better estimate of the actual emissions or leak rate, but this tends to re duce the sensitivity of the method. For example, if the concentration of a cresol builds up to 200 ppbw, it may be difficult to detect a change in concentration across the heat exchanger of 20 ppbw even though the detec tion limit for cresol may be less than 20 ppbw. Nevertheless, the elevated concentrations of cr esol provide reasonable evidence that a leak exists. It may be reasonable to compare the conc entrations in the cooling water leaving the heat exchanger with the source water used in a once- through system or the water used as make-up inTechnical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

8 a closed-loop system to ensure that any elevated concentrations are due to a leak in the heat exchanger rather than background water contamination.

The modified El Paso method (TCEQ, 2003) uses a dynamic or flow-through system for air stripping a sample of the water and analyzing the resultant off-gases for volatile organic compounds (VOC) using a common flame ionization detector (FID) analyzer. This method was originally developed for use by El Paso Products Company in the early 1970s for cooling tower water characterization, and it has been the popular monitoring choice in Texas for many years. The modified El Paso method helps to overcome potential losses of hi ghly volatile components during water sampling. Also, based on the liquid and air flow rates used in the modified El Paso method, the air concentration detection limit of approximately 1 ppm by volume (ppmv) (as methane) corresponds to a wate r concentration of approximate ly 15 ppbw. Therefore, the modified El Paso method provides similar detecti on limits as speciated water analysis. It also simulates, to some extent, the losses that might occur from the cooling water, so leaks of semivolatile compounds that are not eas ily stripped from the cooling water in the cooling tower are also not fully stripped in th e stripping column. While the stripping column may not exactly simulate the stripping efficiency of the specifi c cooling tower being mon itored within the heat exchange system, the stripping column provides a reasonable proxy of the air emissions from the heat exchange system.

Leak Repair Considerations

Regardless of the monitoring method used, once a l eak is identified, it must be repaired or isolated to prevent the process fluid from contam inating the cooling water. Many industrial heat exchangers use a shell and tube design, where the process fluid is in the tubes with the cooling water flow in the shell. If the specific tube th at is leaking can be iden tified, that tube can be plugged, thereby preventing the proc ess fluid from flowing through that tube and isolating the leaking section of the heat exchanger. This procedure diminishes the effective area for heat exchange, thereby reducing the overall efficiency of the heat exchanger bundle. Depending on the age of the heat exchanger and the number of tubes that have been blocked already, the heat exchanger bundle may need to be replaced. In some installations, the leaking heat exchanger bundle can be isolated, removed fr om service, and replaced wit hout interruption of the process served by the heat exchanger. However, there ca n be installations where a heat exchange system may not have excess capacity to allow one bundl e to be removed without shutting down the process unit.

It takes time to identify the prec ise location of a leak and affect its repair. Some heat exchange systems may include multiple heat exchanger b undles from different processes. Speciated chemical analysis is typically used as a fingerp rint to identify which pr ocess fluid is leaking, thereby identifying the likely proc ess unit associated with the lea k. However, it takes additional monitoring to identify which heat exchanger bundle is leaking, and additional time to identify the specific tube that has the leak. Plugging a tube can be done fa irly quickly, but it may take additional time to obtain parts needed if the heat exchanger bundle must be replaced. The repair should be accomplished as soon as practical, and in most cases, this will take no longer than 45 days. For specially sized or designed heat exchangers, there may be instances where the necessary equipment may take several months to obtain. Under this ci rcumstance, it may beTechnical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

9 reasonable to allow the repair to be delayed until the part can be obtained. Most special order parts can be obtained within 90 da ys of an order, so a total re pair time of 120 days should be sufficient to locate the leak, order the parts, and complete the repa ir. Delay of repairs may also be reasonable for small leaks that can only be repaired if the proce ss unit is shut down. Requiring the unit to shut down sp ecifically for the repair may ge nerate more emissions than would occur by delaying repair. Also, requiring the unit to shut down c ould result in significant lost revenue, which could (potentially) make the requirement for immediate repair very costly.

6. Costs of Monitoring Alternatives

This section describes the costs associated with various work practice monitoring alternatives. Costs were not developed for specific equipment de sign or operational alte rnatives because these costs can vary widely by application and are expe cted to be very high in most applications. While these equipment design or operational altern atives can be very expensive, there may be instances where they can be considered. For exam ple, if a certain source category has units that only operate at low pressures, it may be reasonable, at least for ne w sources, to require that the water-side pressure exceed the process fluid pressu re at all points in th e heat exchanger. The equipment or design alternatives id entified in Section 5 should be evaluated for a specific source category to determine if, based on the operational characteristics of the processes and the hazards associated with the pollutants contained in the pr ocess fluids, these alternatives are economically viable or needed to reduce risks associat ed with potential pollutant releases.

General manufacturing industry sect or labor rates (May 2009 dollars) were used to develop the costs for labor-related requirements for the different work practice monitoring alternatives described in Section 5. These costs were based on mean hourly labor rates and were developed for different labor classes (tech nical, managerial, administrativ e, maintenance, and operating labor classes). The hourly labor rates were bur dened with fringe benefits and overhead to calculate the loaded hourly labor ra te for each labor class. The labor classes used in the analysis and the loaded hourly labor ra te calculated for each labor class are summarized in Table 1

.Technical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

10 Table 1. Summary of 2009 Hourly Labor Rates

Labor Class (A) Mean hourly labor rate 1 ($/hr) (B) Fringe benefit loading

rate I

Overhead and profit rate (D = A x B x C)

Loaded wage rate ($/hr) 1. Professional specialty and Technical (SOC Code: 17-2081) 39.53 1.5 1.4 83.01
2. Executive, administrative and managerial (SOC Code: 11-9041) 57.80 1.5 1.4 121.38
3. Administrative support, including clerical (SOC Code: 43-0000) 17.31 1.5 1.4 36.35

4. Installation, Maintenance, and Repair (SOC Code: 49-0000) 22.08 1.5 1.4 46.37
5. Plant and System Operators, All (SOC Code: 51-8099) 22.72 1.5 1.4 47.71

1 Labor rates as reported by U.S. Department of Labor, Bur eau of Labor Statistics (U.S. DOL, 2010). Labor rates for

May 2009 for general manufacturing industry sector: 2-digit NAICS code 31 through 33 ( http://stats.bls.gov/oes/oes_dl.htm accessed in December 2010).

Visual Inspections and Surrogate Monitoring Costs

For the most part, visual inspecti ons and/or surrogate monitoring is already widely used in nearly all industrial cooling water applic ations. As such, there are li mited costs associated with a requirement to perform visual inspections and/ or surrogate monitoring. The primary additional cost associated with such a regulatory program would be the development of a quality assurance (QA) plan to document the inspections/monitoring procedures, the baseline monitoring value or acceptable range, and the parameter values that would trigger corrective action ( i.e. , indicate a leak that must be repaired). Thus, no addi tional equipment is assumed to be needed to implement visual inspections or surrogate monitoring, and only minimal labor costs would be incurred for QA plan development, recordkeeping, and reporting.

Table 2 summarizes the costs associated with a visual inspections a nd surrogate monitoring program. The cost of developing a QA plan is expect ed to be a one-year cost per facility; if there are multiple heat exchange systems at the facility , the cost per heat exchange system would be the total QA plan cost divided by the number of heat exchange systems affected by the rule. It is assumed that the QA plan has a useful life of 5 years when annualizing these costs. The 6 hours for recordkeeping are based on an additional minute per day to record the results of the visual inspections and surrogate monitoring (beyond th ose routinely required by the facility).Technical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

11 Table 2. Summary of Costs Associ ated with Surrogate Monitoring

Activity/Requirement Number of labor hours by labor class per year for activity/requirement

Total Cost ($)TechnicalManagerialAdministrativeOperators

QA plan (1 st year cost only) 10 1 2 0 1,024 Recordkeeping 0 0 0 6 286 Reporting (assumes semi-annual reporting) 4 0.4 0.8 0 410

Water Sampling Monitoring Costs

Water sampling costs are dependent on the partic ular analytical method used and, for speciated organic analysis, the number of compounds that must be analytica lly determined. TOC analysis costs range from $50-75 per sample, and speciat ed chemical analysis via EPA Method 601/602 costs approximately $250/sample (based on on-line price lists: Analytical Laboratories, Inc., http://analyticallaboratories.com/page.cfm?pageid=90 ; Analytical Resources, Inc., http://arilabs.com/portal/ downloads/ARI_price_list.pdf ; Environmental Testing Inc., http://www.eti-lab.com/files/Price.pdf ). Since most cooling water can have fairly significant and potentially variable TOC concentrations, both in let and outlet samples from the heat exchanger may be needed to identify a leak. Traditionally, this “delta” concentration is determined using triplicate analysis at each samp ling location, requiring six samples total. Therefore, costs of typical TOC sampling can range from $300 to $450 per event. As such, TOC water sampling costs approximately the same or even more than speciated water sampling using only one sample of the cooling water after the heat exchanger. Of course, if a delta c oncentration were needed from the speciated organic monitoring, speciated organic monitoring would cost more than TOC monitoring, but if the speciated or ganic analysis can be correctly targeted, a single concentration analysis should be adequate.

Like the surrogate monitoring approach, a QA plan will need to be developed for water sampling monitoring. Because these types of water sample s must be collected in specific ways and may require different sampling locations than those used for routine sampling used to control disinfectant addition. Therefore, additional hours are projected for this task compared to the surrogate monitoring QA plan. The cost of deve loping a QA plan is expected to be a one-year cost per facility; if there are multiple heat exchan ge systems at the facility, the cost per heat exchange system would be the total QA plan cost divided by the number of heat exchange systems affected by the rule. It is assumed that the QA plan has a useful life of 5 years when annualizing these costs. Labor time is also re quired to collect the samples for each sampling event and for recordk eeping and reporting. Table 3 provides the labor estimates for a water sampling monitoring program. As the annual cost of a water sampling program is dependent on the number of sampling events, the costs in Tabl e 3 are provided per sample or sampling event (except for the QA plan as discussed previously and reporting costs, wh ich are per periodic reporting event) so that the costs can be scaled for diffe rent monitoring frequencies.Technical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

12 Table 3. Summary Costs Associated with Water Sampling Monitoring

Activity/Requirement Number of labor hours by labor class per year for activity/requirement

Total Cost ($)TechnicalManagerialAdminis-trativeOperators

QA plan (1 st year cost only) 32 2 4 0 3,045 TOC analysis costs/sample 60 Method 301/302 analysis costs/sample 250 Sample express shipping cost/event 30 Sample shipping & results review labor/event 0.5 0 0.5 0 60 Single sample collection labor/event 0 0 0 1 48 Triplicate in-out sample collection labor/event 0 0 0 1.5 72 Recordkeeping labor/event 0 0 0 0.25 12 Reporting labor/reporting event 2 0.2 0.4 0 205 Example costs for quarterly Method 301/302 sampling with semiannual reporting for single heat exchange system First year costs [QA plan + 4×(sampling+ship ping+analysis+recording)+2×reporting] 5,055 Subsequent year costs [4×(sampling+shippi ng+analysis+recording)+2×reporting] 2,010 Average annualized costs [CRF 1 ×QA plan + subsequent year costs] 2,750

1 CRF = capital recovery factor = 0.2439 based on 5 year life and 7 percent annual interest.

Modified El Paso Monitoring Costs

Stripping columns can be purchased for use by the facility personne l or the facility can hire a contractor to come to the f acility and perform the strippi ng column (modified El Paso) monitoring without the facility purchasing th e equipment. The decision to purchase the equipment will depend on the number of sampling ev ents required to be performed each year. Stripping column equipment costs and testing f ees were obtained from a testing contractor (Boudreaux, 2010). These costs as well as other costs associated with a periodic modified El Paso monitoring program are summarized in Table 4 . As with a water sampling program, the annual costs for a modified El Paso monito ring program are dependent on the number of sampling events per year (which is dependent on both the number of heat exchange systems that must be monitored and the monitoring frequency) . As such, many of the costs in Table 4 are provided per monitoring event so that the co sts can be scaled for different monitoring frequencies.Technical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

13 Table 4. Summary Costs Associated with Modified El Paso Monitoring

Activity/Requirement Number of labor hours by labor class per year for activity/requirement

Total Cost ($)TechnicalManagerialAdminis-trativeOperators

QA plan (1 st year cost only) 32 2 4 0 3,045 Stripping column 3,850 FID analyzer 10,000 Contracted analysis, first or single event 680 Contracted analysis, 2nd or 3rd locations/event 1 195 In-house sampling/monitoring event 0 0 0 3 143 Recordkeeping/monitoring event 0 0 0 0.25 12 Technical review of results/monitoring event 0.5 0 0 0 42 Training/training event (annual) 2 0 0 6 450 Reporting/reporting event 2 0.2 0.4 0 205 Example costs for quarterly in-house El Paso monitoring with semiannual reporting for single heat exchange system First year costs [QA plan + stripping column+ FID analyzer + 4×(in-house sampling+recording+tech review)+ 2×reporting + training] 18,545
Subsequent year costs [4×(sampling+recor ding+review)+2×reporting+training] 1,650 Average annualized costs [CRF 2 ×(QA plan+column+analyzer) + su bsequent year costs] 5,770

1 Sampling of 4 or more heat exchange systems is not ex pected to be completed within 1 day, so additional lodging

expenses would be incurred, which are not included in the model. Purchasing an in-house system is comparable to contract sampling and is the assumed option when 4 locations or more are required to be monitored.

2 CRF = capital recovery factor = 0.2439 based on 5 year life and 7 percent annual interest.

Like the surrogate and water sampling monitoring approach, a QA plan will need to be developed for modified El Paso monitoring. Th e costs of developing th e QA plan for using the modified El Paso method are expected to be similar to the costs of developing a QA plan for water sampling; the costs are “one-time” per facility, but are expected have a useful life of 5 years when annualizing these costs. Similarly, if a stripping column is purchased, it is assumed that one system will be purchased for the facility and the equipment is expected to have a useful life of 5 years. While costs are provided separately for the FID analyzer (because some facilities have available FID analyzers), all stripping colu mns are assumed to be purchased with a new FID analyzer. It is estimated to take 3 hours per sampling event to set-up, run, then clean the stripping column to prepare it fo r re-use. Additionally, annual tr aining is assumed to be needed to properly implement this monitoring method in- house; these costs are per facility rather than per heat exchange system.

The modified El Paso method can be set up to run continuously for continuous monitoring of the heat exchange system. For th is option, the equipment costs for the stripping column and FIDTechnical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

14 analyzer would be incurred per heat exchange syst em rather than per facility. A shelter would be needed to house the stripping column system fo r a continuous application; the costs of such a shelter were estimated to be $10,000 per heat exch ange system. Daily checks of the continuous monitoring system would also be needed to ensu re the system is opera ting correctly; 0.5 operator hours per day were estimated for these daily checks.

Annualized Costs of Alternative Monitoring Programs

The total annualized costs of water sampling a nd modified El Paso monitoring programs at different monitoring frequencies were estimated ba sed on the costs presented in Tables 3 and 4. As the cost to perform triplicate inlet-outlet TOC sampling is essentially identical to the cost of performing a single speciated orga nic analysis, only the cost for a water sampling program using a single sample for speciated organic analysis per sampling event are presented here. These same costs apply for the TOC sampling approach . For modified El Paso monitoring, it is assumed the facility would elect to purchase a stripping column and FI D analyzer and perform in-house monitoring when the total annualized co sts for in-house monitoring was less than the costs for contracted services. For the annual monitoring frequency option, annual reporting was assumed. For all other monito ring frequencies, semi-annual reporting was assumed to be required. Table 5 presents the costs of key options a ssuming there is only one heat exchange system present at the facility. Table 6 presents similar costs pe r monitored heat exchange system when 2 monitored heat exchange rs are present at the facility.

Table 5. Summary of Monitoring Costs as a F unction of Monitoring Frequencies with One Monitored Heat Exchange System at the Facility

Monitoring Method Capital and 1x Costs Annualized Capital

Cost Annual Operating

Costs Total Annualized Costs Sample Events

per Year Water sampling $ 3,045 $ 743 $ 604 $ 1,347 1 El Paso - contracted out $ 3,045 $ 743 $ 947 $ 1,690 1 El Paso - buying system $ 16,895 $ 4,120 $ 854 $ 4,974 1 Water sampling $ 3,045 $ 743 $ 2,007 $ 2,750 4 El Paso - contracted out $ 3,045 $ 743 $ 3,316 $ 4,059 4 El Paso - buying system $ 16,895 $ 4,120 $ 1,648 $ 5,769 4 Water sampling $ 3,045 $ 743 $ 5,202 $ 5,944 12 El Paso - contracted out $ 3,045 $ 743 $ 9,089 $ 9,831 12 El Paso - buying system $ 16,895 $ 4,120 $ 3,221 $ 7,341 12 Water sampling $ 3,045 $ 743 $ 21,174 $ 21,917 52 El Paso - contracted out $ 3,045 $ 743 $ 37,949 $ 38,691 52 El Paso - buying system $ 16,895 $ 4,120 $ 11,084 $ 15,204 52 El Paso - continuous $ 26,895 $ 6,559 $ 9,569 $ 16,129 8760Technical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

15 Table 6. Summary of Monitoring Costs per Heat Exchange System as a Function of Monitoring Frequencies when Two Monitored Heat Exchange System are Present at the Facility

Monitoring Method Capital and 1x Costs Annualized Capital

Cost Annual Operating

Costs Total Annualized Costs Sample Events

per Year Water sampling $ 1,522 $ 371 $ 604 $ 975 1 El Paso - contracted out $ 1,522 $ 371 $ 705 $ 1,076 1 El Paso - buying system $ 8,447 $ 2,060 $ 628 $ 2,688 1 Water sampling $ 1,522 $ 371 $ 2,007 $ 2,378 4 El Paso - contracted out $ 1,522 $ 371 $ 2,346 $ 2,718 4 El Paso - buying system $ 8,447 $ 2,060 $ 1,422 $ 3,482 4 Water sampling $ 1,522 $ 371 $ 5,202 $ 5,573 12 El Paso - contracted out $ 1,522 $ 371 $ 6,179 $ 6,550 12 El Paso - buying system $ 8,447 $ 2,060 $ 2,995 $ 5,055 12 Water sampling $ 1,522 $ 371 $ 21,174 $ 21,546 52 El Paso - contracted out $ 1,522 $ 371 $ 25,339 $ 25,710 52 El Paso - buying system $ 8,447 $ 2,060 $ 10,857 $ 12,918 52 El Paso - continuous $ 25,372 $ 6,188 $ 9,343 $ 15,531 8760

Similar cost tables to Tables 5 and 6 can be deve loped for facilities with three or more monitored heat exchange systems. Note that the monito ring cost per monitored heat exchange system decreases as the number of monitore d heat exchange systems at the facility increases. Also note that in-house modified El Paso monitoring becomes the most economical alternative as the monitoring frequency increases to monthly. Wh en there are three or more monitored heat exchange systems present at th e facility, the cost of quarterly in-house modified El Paso monitoring is comparable to the cost of quart erly water sampling or contracted El Paso monitoring services.

7. Costs of Implementing Repairs

The cost of implementing repairs includes the cost of pinpointing the precis e heat exchanger that is leaking and repairing or isolating the leak. A detailed chemical analysis of the cooling water (or the purge gas when using the modified El Pa so method) can be used to pinpoint the leak when different processes may be serviced by the same heat exchange system. Although this may not always be needed ( e.g. , if only one process is serviced by the heat exchange system), a flat analytical cost of $400 was assumed to be in curred each time a leak was detected.

Most of the repairs are expected to be perfor med by plugging a specific heat exchanger tube. No attempt was made to develop costs of replacing th e heat exchanger. It is assumed that a heat exchanger that is leaking to the extent that it need s to be replaced is eff ectively at the end of its useful life, so the cost of replacing the heat exchanger is an operational cost that would beTechnical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

16 incurred by the facility as a result of routin e maintenance and equipment replacement and it is not attributable to the work pr actice standard. However, all ot her corrective acti ons taken by the facility to repair or isolate the leak are included in the costs of implementing repairs. Table 7 presents the costs estimated for the average leak requiring repair.

Table 7. Summary Costs Associated with Leak Repair

Activity/Requirement Number of labor hours by labor class per year for activity/requirement Total Cost ($) Operator Maintenance Labor for finding and repairing leak 20 40 2,809 “Fingerprint” speciated sample analysis 400 Material costs for repair (assumed to equal costs for labor) 2,809

Total Repair Costs (per event) 6,018

8. Impact Estimates for Heat Exchange Systems

Impact Model for Heat Exchange Systems

The emission reductions achieved by a monito ring and repair program will depend on the monitoring frequency (how quickly a leak is identified), the size threshold of the leaks that must be repaired, and the water usage ra te (for once-through systems) or recirculation rate (for closedloop systems). To evaluate different monitoring and repair program requirements, a spreadsheet impact model was developed to estimate the cost and emission reductions achieved from the implementation of a monitoring and repair progr am. The impact model assesses the cost and emission reductions for four different sizes of heat exchange systems based on the water use or recirculation rates as follows: 5,000 gall ons per minute (gpm); 15,000 gpm; 40,000 gpm; and 110,000 gpm.

An important, but uncertain, factor that affects the baseline emi ssion estimates (and therefore the potential emission reductions that can be achieved) is the distribu tion of heat exchange system leaks prior to the implementation of the monitori ng and repair program. For each model heat exchanger, six different model l eak concentrations were used to assess the impacts of a given monitoring and repair pr ogram as presented in Table 8 . Except for the lowest model leak, each model leak interval was designed to cover a factor of 5 difference in concentration ranges. Each of these leak concentration was assigned an ini tial leak frequency, which is also provided in Table 8. From these initial assumptions, the ba seline emissions for each model heat exchanger can be calculated.Technical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

17 Table 8. Model Leak Concentration Va lues and Initial Leak Distribution

Description of Representative Leak Interval Model Leak Concentration in Cooling Water (ppbw) Initial Leak Frequency Distribution No detectable leaks (0 to 5 ppbw) 1 0.45 Leaks from >5 to 25 ppbw 10 0.25 Leaks from >25 to 125 ppbw 50 0.15 Leaks from >125 to 600 ppbw 250 0.10 Leaks from >625 to 3,000 ppbw 1,200 0.04 Leaks greater than 3,000 ppbw 6,000 0.01

Implementation of a leak monitori ng and repair program is expected to alter the distribution of leaks in subsequent years. This pattern has been observed in the implementation of leak detection and repair (LDAR) pr ograms for equipment leaks (Parri sh et al., 2007). The leak frequency after implementation of the monitori ng and repair program was estimated from the initial leak frequency distribu tion, the leak threshold for the monitoring program, and a “leak reduction factor.” The original frequency of l eaks larger than the leak repair threshold is multiplied by this leak reduction factor to calcula te the subsequent leak frequency in Year 2 and later years. For example, using a leak reduction factor of 0.10 and an initial leak frequency of 0.04 ( i.e. , for 1,200 ppbw model leak concentration), th e subsequent leak frequency would be 0.004 (0.1×0.04). If a leak reduction factor of 0.3 is used, then th e subsequent leak frequency would be 0.012 (0.3×0.04). The cumulative leak fr equency distribution must add up to 1, so the leak frequency of leaks less than the leak repair threshold must be increased when the frequency of leaks greater than th e leak repair threshold is reduced. It was assumed that the relative distribution of leaks less than th e leak repair threshold remained the same as in the initial leak frequency distribution, but the magnitude of each leak frequency less than the repair threshold was scaled-up so that the sum of all leak freque ncies (including those above the repair threshold) equals 1. Note that the subsequent leak fr equency is applied per annual period and not per monitoring period. For example, a subsequent leak frequency of 0.012 for a model leak concentration would imply that 1.2 percent of heat exchange systems would develop a leak represented by that model leak concentration at some point during the year. Thus, the subsequent year (annual) leak fr equency distribution is independe nt of the monitoring frequency, and only varies based on the leak threshold.

The sensitivity of the impact estimates on the le ak reduction factor select ed was evaluated using leak reduction factors of 0.10 and 0.30 (see Annex A – Sensitivity Analysis ). The lower (0.10) leak reduction factor resulted in only a 5 percent increase in the projected emissions reductions; however, the lower (0.10) leak reduction factor also resulted in lower implementation costs (because fewer repairs are required in subsequent years and more recovery credits are earned). Therefore, while the emission re ductions estimated by the impact s model do not appear to be highly sensitive to this parameter, this parame ter can be significant wh en evaluating the overall cost-effectiveness of a given monitoring option. A leak reduction factor of 0.3 is recommended for most analyses, and should provide a rela tively conservative estimate of the emission reductions and costs associated with a monitoring and repair option.Technical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

18 Although each model concentration was envisioned to represent a range of concentrations, the model logic only evaluates the actual value of the model leak concentr ation with the repair threshold of the monitoring program. Therefor e, the 50 ppbw model l eak concentration may include a 100 ppbw leak concentration based on th e representative concentration range (from 25 ppbw to 125 ppbw as shown in Table 8), but since 50 ppbw is less than the 100 ppbw leak repair threshold, the 50 ppbw model leak would not trigger a required repa ir based on the logic used in the impact model. A repair of the model leak occurs when that model leak concentration equals or exceeds the repair threshold.

Although the monitoring frequency does not impact the annual leak frequency distribution, it does determine how quickly a l eak will be discovered. After the implementation of the monitoring and repair program, a new leak is assu med to exist for half the monitoring frequency plus the time it takes to effect repair. For most leaks, repairs are completed 45 days after the leak monitoring event that identified th e leak (the maximum time period allowed for leak repair when criteria for delay of repair are not met). For re pairs that can be delaye d, repairs are assumed to be completed 120 days after the leak monitoring event that identified th e leak. While some repairs may be delayed for more than 120 days, this value represents the maximum delay period for repairs delayed due constraint s on the availability of parts, equipment, or personnel. The exact proportion of repairs that will be delayed is difficult to assess. Model analyses were performed at delay of repair factors of 20 and 50 percent ( i.e. , 20 percent or 50 percent of all leaks below the delay of repair threshold were delayed; see Annex A – Sensitivity Analysis ). Since all leaks are eventually repaired, the repa ir costs are not affected by the number of leaks for which repair is delayed. The emissions re ductions dropped by only 1 percent when using a 50 percent delay of repair factor . While this also causes a 1 percent change in the recovery credits, the overall model is not ve ry sensitive to this parameter. A delay of repair factor of 0.5 (50 percent) is recommended for most he at exchange system model analyses.

The monitoring costs as presented in Section 6 appl y to each heat exchange system regardless of the model leak concentration or assumed leak fr equency. As noted in Section 6, the monitoring cost per heat exchange system of implementi ng a monitoring program becomes less when more than one heat exchange system is present at the facility. Most of the costs presented in this section are based on the costs determined for a si ngle heat exchange system at the facility; costs per heat exchanger would be lower if multiple he at exchange systems are present at a typical facility. For heat exchangers with model leak concentrations exceeding the repair threshold, the repair costs (presented previously in Table 7) are also added to the monitoring costs to get a total program cost for that model heat exchange syst em/leak concentration combination. The impacts of all model leak concentrations for a given mode l heat exchange system are weighted by their distribution frequency to determine an average cost per model heat exchange system for the monitoring and repair program.

Process fluid that leaks into the cooling water is product lost from the industrial process. Repairing the leak results in a ne t product recovery credit because produ ct not lost as a result of a repaired leak can be sold; therefore, the mon itoring costs are offset, to some extent, by the increased product sales. The product recovery cr edit is a function of th e value of the process fluid. For this analysis, a product recovery cred it of $500 per ton of orga nic pollutant emissions reduced was used to account for the recovery of lost product fluid when the repair is fixed. ForTechnical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

19 most chemical applications, it is expected that the recovery credit will be approximately in this range. For example, organics recovered in a petroleum refinery are expected to be approximately $1.75/gallon, based on average crud e and gasoline spot prices (based on September 7, 2007 OGJ crack spread spot prices of $74.96/bbl ($1.78/gal) for brent crude and $87.04/bbl ($2.08/gal) for product value per barrel; re ported in Oil and Gas Journal, September 17, 2007, p. 90). Assuming an average petroleum refi nery process stream specific gravity of 0.75, the recovery credit is $560 per ton organic emissions reduced.

Impact Model Results for Alternativ e Monitoring and Repair Programs

It is anticipated that the primary variables of a monitoring and repair program would be the monitoring frequency and the leak repair threshold. While some monitoring methods may not be capable of identifying leaks at a certain leak threshold, any monito ring method can be used in the program if the method can reliably identify leaks at the repair threshold. As the cost of water sampling is similar to the cost of modified El Pa so monitoring (using the lower of contracted or in-house monitoring), the model evaluations develope d for this section assumed that modified El Paso monitoring would be used. This assumption is not intended to suggest that modified El Paso monitoring is preferred over water sampling; this assumption is used to provide a common data set with which to evaluate the affects of monitoring frequency and re pair thresholds. For each model heat exchanger, program costs we re developed for an array of monitoring frequencies ranging from annua l to continuous for four di fferent leak thresholds. Table 9 summarizes the parameters used in the analysis.

Table 9. Model Input Parameters used to A ssess Relative Importance of Leak Threshold Concentrations and Monitoring Frequency
Model Input Parameter Value and Units Number of heat exchange systems at the facility 1 Monitoring frequency Varies, options are: annually; quarterly; monthly; weekly; and continuously (hourly) Leak repair threshold /delay of repair threshold Varies, option combinations are: 1,000/5,000 ppbw; 80/800 ppbw; 40/800 ppbw; and 10/800 ppbw
Leak reduction factor 0.3 Repair time for normal leak events 45 days Repair time for delayed repairs 120 days Fraction of detected leaks less than the delay of repair threshold that are delayed 0.50

Organic recovery credit $500/ton

Figures 2, 3, 4, and 5 provide the results of the model impacts for 5,000 gallon per minute (gpm), 15,000 gpm, 40,000 gpm, and 110,000 gpm model heat exchan ge systems, respectively.Technical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

20 $

‐ $2,000 $4,000 $6,000 $8,000 $10,000 $12,000 $14,000 $16,000 $18,000

‐ 0.50 1.00 1.50 2.00 Emission Reductions (tpy per model HE system)



## 5,000 GPM HE System

Annual
Quarterly
Monthly
Weekly

Continuous

Figure 2. Impact results for 5,000 gpm model he at exchange (HE) system using the model parameters in Table 9.

$

‐ $2,000 $4,000 $6,000 $8,000 $10,000 $12,000 $14,000 $16,000 $18,000

‐ 1.00 2.00 3.00 4.00 5.00 Emission Reductions (tpy per model HE system) 

## 15,000 GPM HE System

Annual
Quarterly
Monthly
Weekly

Continuous

Figure 3. Impact results for 15,000 gpm model he at exchange (HE) system using the model parameters in Table 9.Technical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

21 $(4,000) $(2,000) $

‐ $2,000 $4,000 $6,000 $8,000 $10,000 $12,000 $14,000

‐ 2.00 4.00 6.00 8.00 10.00 12.00 14.00

Emission Reductions (tpy per model HE system) 

## 40,000 GPM HE System

Annual
Quarterly
Monthly
Weekly

Continuous

Figure 4. Impact results for 40,000 gpm model he at exchange (HE) system using the model parameters in Table 9.

$(12,000) $(10,000)

$(8,000) $(6,000) $(4,000) $(2,000) $

‐ $2,000 $4,000 $6,000

‐ 5.00 10.00 15.00 20.00 25.00 30.00 35.00

Emission Reductions (tpy per model HE system) 

## 110,000 GPM HE System

Annual

Quarterly

Monthly

Weekly

Continuous

Figure 5. Impact results for 110,000 gpm mode l heat exchange (HE) system using the model parameters in Table 9.Technical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

22 The most cost-effective monitoring programs are represented by those at the bottom and right side of the graphs in Figures 1 through 4. Opti ons in the middle of the graphs are inefficient because they have higher costs but achieve less emission reductions than other monitoring programs. It is evident from the graphs presen ted in Figures 1 through 4 that lowering the leak definition (moving to the right fo r programs marked by the same-c olored symbol) is generally more cost-efficient than increasing the monitori ng frequency (shifts acro ss different-colored symbols). Based on the model inputs in Table 9, quarterly sampling with a leak definition of 40 ppbw in the water (or 3.1 ppmv in the El Paso stripping column air steam) provides essentially identical emission reduc tions (within the uncertainty of the model) at lower cost than monthly sampling with a leak defi nition of 80 ppbw in the water (o r 6.2 ppmv in stripping air). Although even lower leak definition repair thre sholds may prove cost-effective for certain applications, it is important that the leak threshol d be a factor of 2 or 3 times greater than the analytical detection limit. Otherwise, it could be difficult or impossible to conclude that a leak does not exist because the repair threshold is at or below the analytical detection limit. For typical FID gas analyzers, detecti on limits of 1 ppmv in the air ar e typical. As such, a stripping air concentration of 3.1 ppmv or ganics (as methane), which corresponds with 40 ppbw organics as methane in the cooling water, would be consid ered the lowest repair threshold level that can be routinely assessed using the modified El Pa so method. The 40 ppbw also appears to be a reasonable minimum leak defini tion repair threshold based on typical speciated organic analytical test methods. For select process str eams or pollutants, it may be possible to achieve lower detection limits on a routine basis. In this case, a 10 ppbw or lower repair threshold should be considered (in addition to a 40 ppbw repair threshold) as one of the control options.

It is also clear from Figures 1 through 4 that a given mon itoring and repair program option is more cost-effective for larger heat exchange sy stems. For example, the 40,000 gpm model heat exchanger shows a net savings for annual monitori ng options and a small savings or break even costs for the quarterly monitoring options, wh ile the 110,000 gpm model h eat exchanger shows a net savings for annual, quarterly, and monthly monitoring options. Therefore, it may be appropriate to have different m onitoring frequencies for different-s ized heat exchange systems. The size-range selected for the different thre sholds will depend predominately on the typical number of heat exchange systems present at a facility within a give n source category and the recovery credit (value of the product stream).

Based on Figures 1 through 4, and assuming 40 ppbw is the minimal quantifiable leak concentration, “optimal” monitoring options appe ar to include: annual at 80/800 ppbw; annual at 40/800 ppbw; quarterly at 40/800 ppbw; and monthly at 40/800 ppbw. The weekly or continuous monitoring frequency op tions greatly increase the co st of the monitoring program without significantly reducing th e emissions compared to monthl y monitoring for the model heat exchange systems evaluated in this analysis. For the single heat exchange system scenario (upper-end cost scenario), Table 10 provides detailed cost information for these “optimal” monitoring options.Technical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

23 Table 10. Detailed Results from Op tion Cost-Effectiveness Evaluation 1

Leak Repair /Delay Threshold

(ppbw) Monitoring Frequency Model HE System

Size (gpm) Capital and 1x Costs

($) Annualized Cost w/o Recovery

Credits ($/yr) Annualized Cost w/ recovery credits ($/yr) VOC Emission Reduction (tons/yr) CostEffect ($/tons) Incremental Cost-Effect

($/tons) 5,000 gpm model heat exchange (HE) system

80/800 annual 5,000 $3,045 $2,087 $1,569 1.03 $1,517

40/800 annual 5,000 $3,045 $2,484 $1,937 1.09 $1,770 $6,172 40/800 quarterly 5,000 $3,045 $4,853 $4,179 1.35 $3,099 $8,820 40/800 monthly 5,000 $16,895 $8,136 $7,433 1.41 $5,290 $57,599 15,000 gpm model heat exchange (HE) system

80/800 annual 15,000 $3,045 $2,087 $535 3.10 $172 40/800 annual 15,000 $3,045 $2,484 $843 3.28 $257 $1,724 40/800 quarterly 15,000 $3,045 $4,853 $2,831 4.05 $700 $2,607 40/800 monthly 15,000 $16,895 $8,136 $6,028 4.22 $1,430 $18,866 40,000 gpm model heat exchange (HE) system

80/800 annual 40,000 $3,045 $2,087 $(2,052) 8.28 $(248) 40/800 annual 40,000 $3,045 $2,484 $(1,893) 8.75 $(216) $334 40/800 quarterly 40,000 $3,045 $4,853 $(541) 10.79 $(50) $665 40/800 monthly 40,000 $16,895 $8,136 $2,515 11.24 $224 $6,762 110,000 gpm model heat exchange (HE) system

80/800 annual 110,000 $3,045 $2,087 $ (9,296) 22.77 $(408) 40/800 annual 110,000 $3,045 $2,484 $ (9,554) 24.08 $(397) $ (197) 40/800 quarterly 110,000 $3,045 $4,853 $ (9,981) 29.67 $(336) $(76) 40/800 monthly 110,000 $16,895 $8,136 $ (7,320) 30.91 $(237) $2,146

1 Impacts based on single heat exchange system and model input parameters summarized in Table 9.

Considerations of Very Small Heat Exchange Systems (“Sample Coolers”)

As seen in Figures 1 through 4 and Table 10, the larger the heat ex change system, the more costeffective it is to monitor and repair leaks. C onversely, as the cooling water flow rates become smaller, it becomes less cost-effective to monitor a nd repair leaks. Logic dictates that, at some flow level, the potential emissi on reductions achieved do not jus tify the costs of the monitoring program. While this lower flow limit is unlik ely to apply to conven tional industrial heat exchange systems, small water cooling systems used to collect process samples or used in conjunction with monitoring equipment (“sample cool ers”) are expected to meet the definition of a once-through heat exchange system, and these may have very low flow rates. The impacts model was used to evaluate a potential applicabil ity flow limit for a given heat exchange system monitoring program. Model heat exchange syst em flow rates of 1, 10, 100, and 1,000 gpm were assessed in this analysis. The monitoring cost s developed for the impacts model are directly applicable to any heat exchange system; the re pair costs developed for the impacts model are potentially different. For these sample coolers, direct replacement of th e leaking cooler is the expected repair scenario. It was assumed that the repair costs for a leaking heat exchanger provided a reasonable estimate of the sample cooler replacement cost. As new equipment is expected to have a lower likelihood of leaking, a leak reduction factor of 0.1 was used for this analysis. The baseline leak distribution was also adjusted upward because these “sampleTechnical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

24 coolers” are not expected to be monitored for bi ologicals (or other potentia l leak indicators) as regularly as conventional industrial heat exchan ge systems are monitored. The high model leak concentrations (model leaks of 1.2 and 6 ppmw) were each assumed to represent 10 percent of the sample coolers. The moderate model leak concentrations (model leaks of 250 and 50 ppbw) were each assumed to represent 15 percent of the sample coolers. Even with a relatively high frequency of leaks, the cost-effectiveness of a nnual or quarterly monitoring generally exceeded $10,000 per ton VOC reduced for heat exchange syst ems with cooling water flow rates at or under 100 gpm. While there are uncertainties as sociated with applying the heat exchange impacts model for “sample coolers,” this analysis suggests that routine he at exchange monitoring programs should not apply to very small heat exchange systems or “sample coolers.” Furthermore, the analysis suggests that a reasona ble flow rate threshold for excluding “sample coolers” would be a heat exchange system with cooling water flow rate of 100 gpm or less.

9. Application of Impact Model for a Specific Source Category

This section provides an exampl e of how to use the heat exch ange system impacts model to determine impacts for a specific source category. The heat exchange system impacts model is provided in a Microsoft ExcelTM workbook. This section contains numerous references to specific sheets or cells within the workbook; it may be useful to have the workbook (or “impacts model”) open for easy reference as you read this section.

Step 1 . Revise the labor rates for the specific indu stry, if desired. The heat exchange system impacts model includes labor rates (in May 2009 dollars) for general ma nufacturing industry sector (2-digit NAICS code 31 to 33) in the “l abor rates” sheet within the impacts model. Industry-specific labor rates are available from the Bureau of Labor Stat istics (BLS) (U.S. DOL, 2010) for specific NAICS codes. For the NAICS code associated with the specific source category, the mean hourly labor rates for the specified SOC C ode Numbers specified in the model can be found and entered into the spread sheet. The new values should be entered in shaded cells (Cells I3 to I7 of sheet “labor rates”). If desired, the fringe be nefits loading factor and overhead and profit rate can be adjusted in the corresponding cells in columns C and D.

Step 2 . Determine the number of heat exchange systems per facility for which to estimate facility costs (per heat exchange system). Th e monitoring costs are calculated in the “Cost by monitoring method” sheet. As discussed previous ly, the cost per heat exchange system is a function of the number of heat exchange systems that will need to be monitored at a specific facility. The number of heat exchange systems should be ente red in the yellow-highlighted Cell I9 in the “Cost by monito ring method” sheet. There are five monitoring frequencies evaluated in the macro: four pe riodic frequencies specified in th e green highlighted cells (Cells R9 to R12) in the “Cost by monitoring method” sheet and a continuous monitoring option. If desired, the periodic monitoring fr equencies in Cells R9 to R12 can be adjusted to evaluate different monitoring frequencies than those pre-loaded in the spread sheet. In general, no other edits should be made to this sheet. 1 Run the macro provided by pushing the “Generate Control_Options Costs” button to automatically calculate an array of costs for different monitoring frequencies and store the results for further use in the “Control_Options” sheet.

1 If additional edits to the costing assumptions are deemed necessary ( i.e. , hours required for training, reporting, or other elements), these should be made prior to running the “Generate Control_Option Costs” macro.Technical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

25 Step 3 (Optional) . Review the table starting at Cell B9 in the “Control_Options” sheet. After running the “Generate Control_Options Costs” macro, costs for the various control options (monitoring frequencies) will be generated and stor ed in this table. The “Control_Options” sheet also houses the repair cost estimates. The t op 30 rows of the “Control_Options” sheet are used in the “Cost by HEsize” sheet for projecting the impacts per model h eat exchange system. If you choose to do so, you can use subsequent rows in the “Control_Options” sh eet to store costs for previously evaluated sets of runs. One advant age of using the general manufacturing labor rates is that several cost tables are already developed and stored in this sheet; however, with the macro, these costs can be easily and quickly updated, so most users will find this step
unnecessary.
Step 4 . The next step in the process is to evalua te the specific options in the “Cost by HEsize” sheet. There is a drop down selection for the monitoring method and frequency in Row 10, and yellow-highlighted input selections for the leak definition (in terms of water concentration), delay of leak threshold concentration, leak redu ction factor (“Reduct_Fact or”), fraction of leaks that below the delay-of-repair threshold that ar e delayed (“Fr_Delayed”), and the VOC credit. The results of the model analysis are summarized on a per heat exchange system level for four different model heat exchange system wa ter circulation sizes: 5,000 gpm; 15,000 gpm; 40,000 gpm; and 110,000 gpm. The macro “Generate Imp act Results Summary” allows the evaluation of using modified El Paso monitoring at all frequencies included in the current “Control_Options” table. These results will be in the placed in the “Results_temp” sheet. The macro will automatically highlight the results range which can then be copied into one of the three “Results_#” sheets (where # = 1, 2, or 3) . The “Results_#” sheets are used to save the specific model run results for further analysis. Th e selected range from the “Results_temp” sheet would be copied to Cell B1, I1, P1, or W1 in one of the “Results_#” sheets as appropriate.

Step 5 . Repeat Step 4 as needed for different mo del run evaluations for a given model plant ( i.e.

, a given number of heat exchange systems at a fac ility). Each “Results_# ” sheet is designed to hold results for 4 different model runs. The model runs in a given sheet can be used to evaluate the effect of different leak definitions or the impact of different model assumptions ( e.g. , different leak reduction factors or differences in fraction of leaks for whic h delay of repair is used). Graphs are provided to illustrate the re sults of the different mode l runs for each of the four model heat exchange system s (see Rows 77-98). It is anticip ated that the results for any given sheet will only alter the yellow highlighted in Cells D11:G13 of the “Cost by HEsize” sheet. The results output by the macro will incl ude these inputs (along with the number of heat exchange systems per facility) for documentati on of the run results. The results summary does not store the initial leak distribution ( i.e. , the yellow highlighted in Cells M11:M16 of the “Cost by HEsize” sheet). If the initial leak distribution is varied ac ross these runs, the leak distribution should also be saved to docum ent these inputs as well.

Step 6 . Repeat Steps 2 through 5 as need ed for different model plants ( i.e. , to develop impacts for different numbers of heat exchange systems per facility). It is likely that the impacts for a specific industry may entail developing costs for a variety of model plant sizes or complexities, which may require costs to be eval uated for several different number s of heat exchange systems. For example, evaluation of three different model facilities may be desired for different facility complexities: a simple model facility with one heat exchange system to be monitored; aTechnical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

26 moderately complex facility with two heat exchange systems to be monitored; a complex facility with four heat exchange systems to be monitore d. Steps 2 through 5 would have to be repeated of each of these model plants. The three “Res ults_#” sheets were originally designed to house impact results for three different model plants , with each sheet repres enting the results for a given model plant. However, you could alternat ively use one results sh eet to house the results for a specific set of model inputs (leak definition and repair threshold), and use the four columns to house the results for different mo del plants. If this second option is used, the graphs included in the “Results_#” sheets at Row 80 will be meaningless, but it may be easier to quickly copy the selected results to the “NW_Impacts” sh eet for calculation of nationwide impacts.

Step 7 . Assign a nationwide number of heat excha nge systems that can be represented by each model heat exchange system / model plant co mbination. The costs and emission reductions presented are per heat exchange system. By multiplying the costs and emission reductions by the number of heat exchange systems, nationwide impacts are developed for the source category. The “NW_Impacts” sheet provides a means to ca lculate the number of heat exchange systems represented by each model heat exchange system / model plant combination for up to four model plants. The inputs needed for these calculations ar e the total number of heat exchange systems in the source category and the rela tive distribution of heat exch ange systems by size and model plant. Note: the number of the number of h eat exchange systems used for each model plant combination is rounded to whole numbers for the impact calculations, so there may be a slight difference in the number of heat exchangers calcul ated in Cell F32 and the total number of heat exchange system input in Cell G5 due to rounding.

Step 8 . Identify the specific control options for evaluation to calculate the nationwide impacts and enter those results in the “NW_Impacts” sh eet (see Cell J32). As noted previously, if a single sheet contains output for th e different model plants, it may expedite the manual process of transferring selected results to the “NW_Impacts” sheet (but the graphs in the “Results_#” sheets will be of little value). Once the impacts for th e selected control options are entered (or copied) into the “NW_Impacts” sheet, the sheet will au tomatically calculate the nationwide impacts in the final results table.

10. References

Boudreaux, W. 2010. E-mail with attachment from Wayne Boudreaux, En RUD Resources, Inc., to Cindy Wang Hancy, RTI International. “CWT Estimate.” November 2, 2010.

Corsi, R, et.al. 2004. Assessment of Selected Leak Detect ion, Sampling, Testing, Measurement and Monitoring Methods for Estimating Emi ssions of Highly Reactive Volatile Organic Compounds from Industrial Cooling Waters . University of Texas at Austin for TCEQ. September 2004. Docket Item No. EPA-HQ-OAR-2003-0146-0004.

Lucas, B. 2008. Memorandum from B. Lucas, EPA/ SPPD, to Project Docket File (EPA Docket No. EPA-HQ-OAR-2003-0146). Cooling Towers: Contro l Alternatives and Impact Estimates . October 30, 2008.

Parrish, K., D. Randall, and J. Coburn. 2007. Memorandum from Kristin Parrish, David Randall, and Jeff Coburn, RTI International, to Karen Rackley, EPA/SPPD. Final ImpactsTechnical Memorandum – Technology Re view for Heat Exchange Systems July 12, 2011

27 Analysis for Regulatory Options for Equipm ent Leaks of VOC in Petroleum Refineries

. October 30, 2007. Docket It em No. EPA-HQ-OAR-2006-0699-0089.

Texas Commission on Environmen tal Quality (TCEQ). 2003. Sampling Procedures Manual, Appendix P: Air Stripping Method (Modified El Paso Method) fo r Determination of Volatile Organic Compound Emissions from Water Sources

.
Suslow, Trevor V. 2004. Oxidation-Reduction Potential (ORP) for Water Disinfection Monitoring, Control, and Documentation . University of California, Davis; Division of Agriculture and Natural Resources; P ublication 8149. ISBN 978-1-60107-319-8.

U.S. Department of Labor (DOL), Bureau of Labor Statistics. 2010. Occupational Employment Statistics: May 2009 Employment and Wage Estimates

. http://stats.bls.gov/oes/current/oessrci.htm ; Last accessed in December 2010.

## Technology Review for Heat Exchange Systems Annex A – Sensitivity Analysis

An impacts model was developed to estimate th e emission reductions achieved and the costs incurred for different monitoring options for heat exchange system. Th e output of the model depends, to some extent, on some of the assumptions used in the model. This Annex presents the results of various impact model runs for a heat exchange system with a cooling water flow rate of 40,000 gallon per minute (gpm) for four different monitoring options:

1. Quarterly monitoring with a leak definiti on of 80 parts per billion by weight (ppbw) strippable organics in the cooling water.

2. Quarterly monitoring with a leak definiti on of 40 ppbw strippable organics.

3. Monthly monitoring with a leak definiti on of 80 ppbw strippable organics.

4. Monthly monitoring with a leak definiti on of 40 ppbw strippable organics.

The model itself helps to account fo r different sized heat exchange systems, different number of heat exchange systems at a given facility th at require monitoring, and different monitoring frequencies and different action thresholds. There ar e other underlying assu mptions within the model that are generally fixed, and the purpose of this analysis is to assess the sensitivity of the model to these fixed assumptions. Table A-1 summarizes some of the basic default parameters for the impacts model.

The time allowed for repair or for delayed repair is generally specified as part of the monitoring requirements, and these are, for the most part, li mited by the time required to identify the specific tube or heat exchanger bundle th at is leaking, order necessary pa rts (if needed), and isolate and repair the leak. Similarly, the organic recovery credit can generally be determined for a given source category based on the product value of the process fluid lost as a result of the leak. Consequently, this sensitivity analysis focuse s on the “leak reduction factor” and on the fraction of leaks for which repair can be delayed.

Table A-1. Heat Exchange System Impact Model Input Parameters

Model Input Parameter Value and Units
Leak reduction factor 0.3 Repair time for normal leak events 45 days Repair time for delayed repairs 120 days Fraction of detected leaks less than the delay of repair threshold that are delayed 0.50
Organic recovery credit $500/tonTechnology Review for Heat Exchange Syst ems: Annex A – Sensitivity Analysis

A-2 Typically, when a facility implements a leak detection a nd repair program ( e.g. , for equipment leaks), the number of leaks a bove the repair threshold is reduced in subsequent monitoring events, which causes a shift in the leak distribu tion for subsequent monitoring events. A “leak reduction factor” is applied to the portion of the initial leak distribution for l eaks above the repair threshold to account for this phenomenon. A leak reduction factor of 0.3 is suggested for use in the heat exchange impacts model based on engineering judgment; th is would reduce the probability of a leak at levels above the leak repair threshold in subsequent years to 30 percent of the leaks in the baseline year. For the sensitivity analysis, the results of using this default leak reduction factor are compared to alternative le ak reduction factors of 0.1 and 0.5 for the model heat exchange system and for different monitoring options. Table A-2 summarizes the results of this analysis in terms of em issions reductions and costs.

The fraction of leaks for which delay can be repair ed is another uncertain input parameter. For units that operate contin uously with minimal downtime, the fraction of leaks that may be delayed may be higher than for batch systems or pr ocesses that run conti nuously but for shorter durations. The fraction of leaks that may be dela yed may be dependent on the age of the process equipment as well. Older equipment may be more likely to need significant repair or replacement, whereas newer equipment may only need to plug a single tube in the heat exchanger. The suggested default value for the fr action of leaks that can be delayed is 0.5; for this sensitivity analysis, delay fractions of 0.2 and 0.8 were also investigated. Table A-3 summarizes the results of these impact model runs.

Table A-2. Sensitivity Analys is for Leak Reduction Factor 1

Leak Reduction

Factor Capital and 1x Costs ($) Annualized Cost w/o Recovery Credits ($/yr) Annualized Cost w/ recovery credits ($/yr) VOC Emission Reduction

(tons/yr) CostEffectiveness ($/ton) Quarterly Monitoring with a Leak Action Level of 80 ppbw
0.1 $3,045 $4,312 $(1,027) 10.68 $(96)

0.3 $3,045 $4,456 $ (646) 10.20 $(63)

0.5 $3,045 $4,601 $(264) 9.73 $(27) Quarterly Monitoring with a Leak Action Level of 40 ppbw
0.1 $3,045 $4,565 $(1,089) 11.31 $(96)

0.3 $3,045 $4,853 $ (541) 10.79 $(50)

0.5 $3,045 $5,142 $7 10.27 $1 Monthly Monitoring with a Leak Action Level of 80 ppbw
0.1 $16,895 $7,594 $2,119 10.95 $194

0.3 $16,895 $7,738 $2,423 10.63 $228

0.5 $16,895 $7,883 $2,726 10.31 $264 Monthly Monitoring with a Leak Action Level of 40 ppbw
0.1 $16,895 $7,847 $2,049 11.59 $177

0.3 $16,895 $8,136 $2,515 11.24 $224

0.5 $16,895 $8,424 $2,981 10.89 $274

1 Impacts based on single 40,000 gpm heat exchange syst em with a delay of repair threshold of 800 ppbw.Technology Review for Heat Exchange Syst ems: Annex A – Sensitivity Analysis

A-3 Table A-3. Sensitivity Analysis for Fracti on of Leak for Which Repair is Delayed 1

Fraction Delayed Repair Capital and 1x Costs ($) Annualized Cost w/o Recovery Credits ($/yr) Annualized Cost w/ recovery credits ($/yr) VOC Emission Reduction

(tons/yr) CostEffectiveness ($/ton) Quarterly Monitoring with a Leak Action Level of 80 ppbw
0.2 $3,045 $4,456 $ (675) 10.26 $ (66)

0.5 $3,045 $4,456 $ (646) 10.20 $ (63)

0.8 $3,045 $4,456 $ (616) 10.14 $ (61) Quarterly Monitoring with a Leak Action Level of 40 ppbw
0.2 $3,045 $4,853 $ (580) 10.87 $ (53)

0.5 $3,045 $4,853 $ (541) 10.79 $ (50)

0.8 $3,045 $4,853 $ (502) 10.71 $ (47) Monthly Monitoring with a Leak Action Level of 80 ppbw
0.2 $ 16,895 $7,738 $2,393 10.69 $ 224

0.5 $ 16,895 $7,738 $2,423 10.63 $ 228

0.8 $ 16,895 $7,738 $2,452 10.57 $ 232 Monthly Monitoring with a Leak Action Level of 40 ppbw
0.2 $ 16,895 $8,136 $2,477 11.32 $ 219

0.5 $ 16,895 $8,136 $2,515 11.24 $ 224

0.8 $ 16,895 $8,136 $2,554 11.16 $ 229

1 Impacts based on single 40,000 gpm heat exchange syst em with a delay of repair threshold of 800 ppbw.

Reviewing the results presented in Tables A-2 an d A-3, a few factors are not eworthy. First, it is clear that the model is not very sensitive to the assumed fraction of leaks for which delay of repair is allowed. Using 0.5 as the base case fo r the “fraction of delaye d repair,” altering the fraction of delayed repair causes less than a 0.1 percent change in th e emission results. For example, for quarterly sampling at a leak acti on level of 40 ppbw, the change in emissions is 0.08 tons/yr, or 0.08/10.79 = 0.7 percent. The lack of sensitivity to the fraction of delayed repair is due, in part, to the assumption in the impacts model that the delay will be for 120 days. This time period is based on a delay associated with ordering necessary equipment or scheduling specialists. Longer delays may be allowed for re pairs that require a pr ocess shutdown, but these should be a limited number of cases, and they will also be limited to leaks that do not get significantly larger over time. Long delay of repairs are not likely because a leak is likely to get worse with time and trigger the delay of repair threshold, so that the re pair can no longer be delayed.

The model is more sensitive to the “leak reduction factor.” Using 0.3 as the base case for the leak reduction factor, altering th e leak reduction factor causes a 3 to 5 percent change in the emission results, with the 5 percent change associ ated with the quarterly monitoring alternatives and the 3 percent change associ ated with the monthly monitori ng alternatives. It is also interesting to note that these different degrees of sensitivity could impact what monitoring provisions achieve the greatest emission reducti on. For most options considered, quarterly monitoring at a leak action le vel of 40 ppbw provides more emission reduction than monthlyTechnology Review for Heat Exchange Syst ems: Annex A – Sensitivity Analysis

A-4 monitoring at a leak action leve l of 80 ppbw; however, at a leak reduction factor of 0.5, monthly monitoring at a leak action level of 80 ppbw is projected to achi eve slightly greater emissions reductions than quarterly monitoring at a leak ac tion level of 40 ppbw. Thes e results suggest that these two monitoring options ac hieve essentially equivalent emission reductions within the uncertainty of the analysis. Th e leak reduction factor also imp acts the costs of the monitoring program (more than just the magnitude of the recove ry credit), with higher costs (associated with more repairs) at higher leak re duction factors, so the cost-effec tiveness of an overall monitoring option is much more significantly impacted by the se lected leak reduction factor than the fraction of delayed repair.

The total emission reductions achieved by a monitoring program will be very sensitive to the leak initial leak distribu tion, particularly the propor tion of larger leaks. However, most decisions are made based on incremental differences be tween monitoring options rather than total reductions achieved by any given option. For the incremental costs between control options, the initial distribution is less important than how that distribution is affected by the monitoring program itself. Thus, it is anticipated that the leak reduction factor will be as important as (or more important than) the initial distribution when evaluating the incremental cost-effectiveness of an option, and it is this incremental assessment that is most important when selecting a monitoring option.

Table A-4 provides some of the same data as Table A-2, but shows the incremental costeffectiveness for two similar options (in this case , quarterly monitoring at leak action levels of 40 and 80 ppbw). The incremental emission reduc tions varied from 0.54 to 0.63 tons per year (tons/yr) and exhibited an uncertainty of approximately ± 8 pe rcent. Altering the leak reduction factor also altered th e incremental cost-effectiveness of these options by approximately ± $300/ton.

Table A-4. Effect of Leak Reduction Factor on Incremental Impacts 1

Monitoring Frequency and Leak Action Level Capital and 1x Costs ($) Annualized Cost w/o Recovery Credits ($/yr) Annualized Cost w/ recovery credits ($/yr) VOC Emission Reduction

(tons/yr) CostEffectiveness ($/ton)
Leak Reduction Factor of 0.1 Quarterly, 80 ppbw $3,045 $4,312 $(1,027) 10.68 $(96) Quarterly, 40 ppbw $3,045 $4,565 $(1,089) 11.31 $(96)
Difference $0 $253 $(62) 0.63 $(98)
Leak Reduction Factor of 0.3 Quarterly, 80 ppbw $3,045 $4,456 $ (646) 10.20 $(63) Quarterly, 40 ppbw $3,045 $4,853 $ (541) 10.79 $(50)
Difference $0 $397 $105 0.59 $178
Leak Reduction Factor of 0.5 Quarterly, 80 ppbw $3,045 $4,601 $(264) 9.73 $(27) Quarterly, 40 ppbw $3,045 $5,142 $7 10.27 $1
Difference $0 $541 $271 0.54 $502

1 Impacts based on single 40,000 gpm heat exchange syst em with a delay of repair threshold of 800 ppbw.