Document ID: EPA-HQ-OW-2008-0667-0647
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2011-04-20T04:00Z

MEMORANDUM

Tetra Tech, Inc.
10306 Eaton Place, Suite 340
Fairfax, VA 22030
phone	703-385-6000
fax	703-385-6007

TO:			Paul Shriner and Jan Matuszko, EPA
FROM:		John Sunda, SAIC and Kelly Meadows, Tetra Tech
DATE: 		April 17, 2009

SUBJECT:	Modular Cooling Tower Technology and Costs

Closed-cycle cooling (in the form of cooling towers) is one form of flow reduction.  However, in estimating compliance costs associated with closed-cycle cooling, EPA has typically only considered permanently-built onsite structures with concrete cold water basins.  Closed-cycle cooling may also be achieved through the use of modular cooling towers.  Modular cooling towers are portable cooling units that can supplement or even replace once-through cooling water flows at electric generators and other significant users of cooling water.  While this alternative technology offers a number of benefits over permanent cooling towers and could significantly reduce facility downtime, EPA does not presently have enough information to assess the widespread applicability of this technology.

Typical Modular Tower System

Much of the technical information below was obtained through correspondence with Blue Stream Services, which has partnered with the modular tower manufacturer Varitech Equipment Company.  The services provided by the vendors primarily involve short-term and long-term rentals, especially for systems that may require use during only a portion of the year.

System Operation

Modular cooling towers are typically used in either a helper mode or a recirculating mode.  In the recirculating mode, hot water can be withdrawn directly from the hot water discharge channel, cooled and then returned to the intake channel upstream of the intake pumps or in the intake pump well.  The modular tower system can recirculate all or only a portion of the total cooling system flow requirements.  To recirculate all of the flow, the modular cooling tower pumping rate is matched to the associated condenser cooling water pumping rate through the use of float controls in the intake channel.

System Set-Up

The simplest installation is to withdraw water from the facility's effluent channel and pump the water through the towers, where it then flows by gravity to the existing intake channels or cooling water pump wells.  The upstream portion of the intake can then be blocked off so that the existing recirculation pumps remain functional while intake construction occurs.  Other engineering solutions for cooling water pump and piping configurations are possible.  In some cases, there may be challenges in finding a suitable path for the placement of the temporary cooling water recirculation pipes, but engineering solutions should be available in most circumstances.

Modular towers can be installed while the plant is in operation and can be operated on an as-needed basis.  The installation can be done quickly; once the units are trucked in-place, it takes approximately one day per unit to complete the installation.  This allows modular towers to be used as a temporary source of cooling water during the period when an intake must be shut down, such as allowing for the retrofit of 316(b) compliance technology.

The Varitech units are transported to the site on a truck trailer bed.  In earlier designs prior to this one, the modular units either remained on the truck trailer or were removed using a crane.  One advantage of the newer Varitech units is that they can be trucked onsite, jacked up so that the truck trailer can move out, and then the tower height can be adjusted using built-in legs that are easily leveled.  No crane is necessary, thus reducing mobilization and demobilization costs.  These towers require very little site preparation as long as the site is moderately level.

System Design

The basic modular cooling tower configuration uses PVC pipes running along the ground to and from the towers, skid-mounted pumping units that pump water through the towers, and the tower units themselves.  The vendor typically provides all the necessary equipment, including pumps, piping, control system, electrical cable and transformers.  The vendor can also provide all necessary services, including engineering design, mobilization/installation, contract operation and maintenance, and removal/demobilization.  In short, the vendor can provide all necessary equipment and services with the exception of permitting activities.  In many respects, operation and maintenance activities for modular towers will be similar to those for permanent towers, except that these tasks would be performed by the vendor.  One benefit of modular towers is that it will be easier to perform maintenance on the modular units while maintaining generation at near full capacity, since the temporary loss of the flow from one unit at a time represents only a small component of total cooling water flow.

In the past, large portable towers generally ranged in size from 500 ton to 2,000 ton capacities.  Recently, however, Varitech has begun manufacturing portable 3,000 ton units capable of handling up to 10,000 gpm of cooling water.  A typical design flow for these units is 10 MGD or 6,945 gpm (Blue Stream 2008b).  These units are the largest portable units available and provide the most efficient use of available space.  

With the use of multiple side-by-side tower units, a cooling system of any size capacity can be assembled.  For example, Blue Stream recently worked on a system for the 2,600 MW Cumberland Plant in Cumberland City, Tennessee, operated by the TVA (see below).  This plant requires cooling tower flow capacity of 500,000 gpm.  In this case, the towers have been installed in a helper tower configuration to eliminate the need to derate (reduce plant generation) during summer source water low-flow conditions that have been exacerbated by recent drought.

The specifications for the 3,000 ton units are:

      Flow Range:		5,000  -  10,000 gpm
      Design Flow:		6,945 gpm (10 MGD)
      Tower Width:		12 ft
      Tower Length:		50 ft
      Tower Height:		15 ft excluding ground clearance
      Fans:			20 direct drive at 15 Hp each
      Fan Energy Req.:	300 Hp
      Shipping Weight:	56,000 lbs
      Operating Weight:	88,000 lbs
      Source: Varitech 2008.

The towers are constructed of fiberglass-reinforced plastic, stainless steel, and PVC components to prevent corrosion.  The towers contain high efficiency cellular sheet PVC drift eliminators.

System Requirements

The system requirements are available space for placement of the towers and a route for the piping from the warm water discharge channel to the towers and then from the tower cold water outlet to the intake channel.  Each unit is 12 ft wide by 50 ft long and requires a side clearance of 12 ft between units placed side-by side and 24 to 36 ft between rows to allow for proper air circulation (Blue Stream 2008b).  The result is that, for each 10 MGD of design flow volume, an area of approximately 2,000 sq ft including the side clearance is required.  Looking at the tower footprint alone, these 3000 ton units can cool 11.6 gpm/sq ft.  The footprint size of the permanent cooling towers derived using the EPRI cost methodology (as described in Chapter 8 of the TDD) indicates they cool only 3.4 gpm/sq ft.  Thus, the modular towers are more compact and should require less space.  The reason for this is the higher fan energy requirement (see discussion below) and high efficiency design of the units and fill material.  

Assuming that the total side clearance for both sides for permanent cooling towers is equal to the tower width, a similarly sized permanent cooling tower would require about 4,000 sq ft.  The difference in space requirements may be somewhat less than the factor of 2 that is implied by the above estimates, since the smaller modular units will have plumes that may be more prone to recirculation, especially if they are placed in arrays of multiple rows and close together using minimum clearance.  A 10,000 gpm skid-mounted pump requires a space of 6 ft by 6 ft (Blue Stream 2008a).

Another system requirement is a power source.  The fan energy requirements for modular towers are about 50% higher than the fan energy requirements estimated using EPRI's methodology for a similar design flow.  The higher fan energy is part of the modular tower design that allows for the towers to be more compact, taking up less space than permanent towers.

A comparison of the total pump and fan energy requirements reported by the vendor to estimates derived from EPRI's methodology indicates that the modular towers may require about 70% more electrical energy than equivalent permanent towers to operate.  That means that pumping energy requirements may also be higher for modular towers.  This may be due to the fact that modular towers use multiple pumps and pipes that are smaller in size than those used in permanent towers.  The use of smaller pipes and pumps tends to result in greater friction losses and less efficient pump operation. 

Non-Water Quality Impacts

In general, non-water quality impacts (e.g., noise, drift, water consumption, plume) should be similar for both modular and permanent cooling towers.

Example Installations

The largest example facility provided by the vendor is the 2,600 MW Cumberland Plant in Cumberland City Tennessee (operated by the TVA).  The facility's design intake flow (DIF) is over 2 billion gallons per day (BGD).  This plant operates the towers in a helper mode due to problems with low river flow, which have led to problems in meeting the facility's 316(a) discharge limits.

Another facility is the 370 MW WS Lee Steam Station in Anderson County, South Carolina (operated by Duke Energy).  The facility recently purchased modular towers and is using them in a recirculating mode to reduce intake flow volume.  Existing permanent cooling towers already located onsite are operated in as helper towers; the new modular towers are operated in a recirculating mode during the summer because the river level drops too far.  The modular tower recirculating flow volume is approximately 100,000 gpm, which is close to the facility's actually intake flow (AIF).   So during the summer, the facility routes the helper tower effluent to the modular towers, recirculating the water back to the intake and thus running water through two sets of towers. 

System Costs

Table 1 below presents the rental costs and total energy requirements for modular towers (as supplied by the vendor).  These costs require a minimum rental period of four months per year but facilities are only charged for the period the towers remain in use in excess of 4 months each year after that (i.e., beyond the minimum 4 month rental, a facility is only charged for time the towers are in use; if they are idle, there is no additional fee).  The rental costs include the tower units, pumps, piping, controls, and maintenance.  These costs do not include items such as site preparation, freight, installation labor, electrical supply equipment, electricity to operate the pumps and fans, or system removal labor and freight (Blue Stream 2008b).  The vendor noted that since the clients are power companies, they usually provide the electrical supply components using their own resources.
                                  Table 1.  

Cost of Modular Towers Compared to Permanent Towers

For comparison, Table 1 also includes the capital and O&M costs and the energy requirements for a permanent cooling tower system, as derived from the EPRI methodology.  A present-value calculation using an interest rate of 5% and the assumption that the towers will operate for four months per year indicates that the break-even time period is about 14 years (see below for a detailed discussion).  This means that if the modular towers are used for 4 months or less each year, they will be more economical than permanent towers if they are needed for a period of less than 14 years.  If the duration of tower operation is extended to 12 months/year, the break-even time period is less than four years.  The break-even calculation takes into consideration the costs presented in Tables 1 though 4 below (including estimated cost of energy requirements), but assumes that the non-power O&M costs for permanent towers (Table 1, Column 7  --  EPRI O&M) are the same for both 4 and 12 months of operation.  The energy costs are a large component of O&M costs.  For permanent towers operated continuously throughout the year, energy requirements can represent up to 90% of total O&M costs.  The results of the break-even analysis demonstrate that modular towers may be more financially advantageous for facilities that require flow reduction for only a portion of the year and for facilities in which the cooling tower technology will not be needed for the full service-life of permanent towers constructed onsite.

Estimation of Costs for Temporary Use During Construction Downtime  

The temporary installation of modular cooling towers is an available technology option for minimizing construction downtime costs.  This approach also has the added benefit of maintaining generating capacity at baseload plants which may be important in regions or time periods where extended facility downtime would be detrimental to maintaining reliable generation.  Below is an estimate of the costs for a typical temporary rental tower installation.  For each facility with an estimated net downtime period (due to installing a compliance technology as a result of the proposed rule), the equations below can be used to estimate the cost of this downtime technology option.  These costs can then be compared to the lost generation costs of shutting down the generating units.  EPA could then identify the facilities that could benefit economically from employing this option and adjust the downtime costs accordingly.
 
Each project will have a minimum cost associated with installation and demobilization costs plus rental costs (minimum four months for Blue Stream).  The decision to utilize modular towers to reduce downtime costs will be somewhat dependent on whether the estimated lost generation costs for the net downtime period exceeds the total cost for tower rental by a large enough margin to make it economically worthwhile.  Lost generation costs will also be dependent on both the downtime duration and facility's capacity utilization rate (CUR) during the downtime period.  Due to the installation and minimum rental period costs, this technology will likely be more attractive to facilities that expect longer downtime requirements and a high CUR during the outage.  The decision to use temporary cooling towers may not be limited to just economic considerations for the facility, as the need to maintain minimum regional generating capacity and the cost of replacement power generation may also factor into the decision. 

Table 2 presents the estimated one-time installation and demobilization costs that are not covered by the vendor rental costs.  The total costs apply to all applications regardless of duration.  The shipping, installation, power supply, demobilization, and other costs not covered by the vendor fees are derived using the assumptions below:

 Freight  -  transportation costs per tower (each way) is $6,000 including shipping of towers and ancillary equipment.
 Installation labor  -  installation time of one day per tower is assumed to require six persons for two 8-hr shifts per tower.
 Demobilization labor - same as for installation.
 Labor Rate - $50/hr ($38/hr in 2002 adjusted for inflation to 2009).
 Site Preparation - assumed as $4,000 per unit (estimate based on BPJ).
 Electrical hookup  -  material and labor cost is assumed to be $20,000 per unit (estimate based on BPJ).
 Allowance  -  additional costs equal to 50% of total for above items (freight, labor, site preparation, and electrical) to account for all other costs.
 Power  -  cost estimate for power to operate pumps and fans are based on a CUR of 85% and an average wholesale power cost of $65/Mwh.

                                    Table 2
                                       

Table 3 presents the tower rental costs based on the data in Tables 1 and 2 and includes the total costs for a rental duration of up to 16 weeks, the weekly rental costs for periods exceeding 16 weeks, and power costs which are shown separately.  Note that the tower rental costs already include tower O&M for labor and materials, with the exception of the cost of power to operate pumps and fans. 

                                    Table 3
                                       

The total downtime for all cost modules ranges from <4 weeks to 15 weeks, with the exception of installing cooling towers at nuclear facilities which has a relatively high downtime value of 32 weeks.  In the 2004 Phase II rule, the total downtime values were converted to net downtime by subtracting 4 weeks of routine maintenance downtime. A second possible approach to consider downtime is to use facility-specific data to calculate facility-specific estimated routine maintenance durations ranging from 1 to 8 weeks.  Using this approach, the calculated net downtime periods for any facility could range from 0 to 14 weeks.  Since both of these approaches would yield outages that are less than the minimum four-month (16 weeks) rental period, the minimum cost will apply to most technology modules at non-nuclear facilities.  The only variable cost is the power to operate the pumps and fans.  

The costs shown in Table 3 were plotted against the recirculating flow rate and the data were fitted to straight lines.  Table 4 presents cost estimation equations derived from this data.  Equations for O&M costs for pump and fan energy are presented in both megawatts at full capacity and in dollars per week assuming that the energy usage will be 85% of full capacity over the operating period and the average wholesale cost of electricity is $65/Mwh. 

                                    Table 4
                                       

Additional Cost Information

The rental fee is charged only for the months the towers are used; the equipment can stay onsite the remainder of the year at no extra charge.  Thus, installation/demobilization costs can be amortized over the entire rental contract period.  As a result, modular cooling towers are often rented for periods of several years or more.  Another benefit is that rental towers can be financed through the facility's operating budget, thus avoiding the time-consuming planning and approval requirements for such a major capital expenditure as a cooling tower.

Modular towers may be capable of producing colder water than permanent cooling towers, which in turn could offset a portion of the extra power requirements through a reduction in the turbine efficiency energy penalty.  The vendor stated that the modular towers had an approach of 7 to 10 F, while the EPRI documentation specified an approach of 10 F for permanent towers (Blue Stream 2009).  The approach is the difference between the temperature of the cold water exiting the tower and the wet bulb temperature of the air and thus, towers with lower approach values will produce colder water.  The modular tower cited here is designed to be efficient and compact and accomplishes this, in part, by using a higher fan power and thus may produce colder water. 

Cooling towers can be designed with different approach values, generally ranging from 5 to 15 F with 10 F being a typical design value.  In general, a tower with a lower approach will cost more and in the case of permanent towers will be larger in size.  The 316(b) Phase I Rule based cooling tower costs on a vendor-supplied tower sizing factor of $30/gpm for a cooling tower with an approach of 10 F and a sizing factor of $50/gpm for a tower with an approach of 5 F.  (USEPA 2000)  Thus, based on these sizing factors, it is estimated that a reduction of the approach from 10 F to 5 F would result in an increase in capital costs for a permanent tower of approximately 67%.  

It is estimated that a 1.0 C reduction in the cooling water temperature can decrease the heat rate of a thermal power plant by 5 Kcal/KWh.  (National Productivity Council of India (NPCI) 2009)  Using this factor, a coal-fired plant with a heat rate of 9,000 BTU/KWh (thermal efficiency = 37.9%) would increase its output by 0.12% for each 1.0 F reduction in cooling water temperature during warmer periods of the years.  Another analysis of a theoretical pressurized water nuclear reactor predicted that an increase in cooling water temperature by 1.0 C would decrease output by 0.45%. (Durmayaz and Sogut 2006)  This is equivalent to a change in output of 0.25% for a 1.0 F change in cooling water temperature, or roughly double the NPCI-based estimate.  Note that an approach of 5 F is generally considered the lower limit for tower design, due to the fact that the tower size will increase exponentially as the approach decreases, resulting in greatly diminishing returns in terms of performance versus costs.
 
The quality of the water being circulated through the towers (e.g., concentration of suspended of solids) may affect the type of tower fill that can be used, which can in turn affect the efficiency of the tower and the approach value.  The modular towers use a film fill that is more susceptible to plugging and fouling than splash fill.  Film fills come in different designs that can be tailored to the water quality.  If the water contains solids or is susceptible to biofouling that could plug the smaller holes/channels, then a fill with larger holes/channels must be used, which will reduce the efficiency of the tower.

Applicability for 316(b)

Modular cooling tower systems would be most useful for projects requiring a temporary source of cooling water during major repairs or construction at existing once-through intakes and cooling tower systems, such as during the downtime associated with retrofitting a new intake technology or closed-cycle cooling system (although there are limitations on the latter, as discussed below).  The modular towers would be available to those facilities with sufficient space for the towers and where the existing cooling water pumps and pump wells or intake channels can be blocked off (see Figure 1).  Modular towers require somewhat less space than permanent towers and, since the modular cooling towers consist of many individual units, they can also be placed in configurations that allow for efficient use of available space, including space that might not otherwise be useful for conventional multi-cell cooling towers. 

Potential Sites for Modular Towers

Modular towers may provide a significant reduction in downtime and the associated costs at some facilities.  In some cases, especially those where the interruption period is fairly long or if the facility is a baseload facility, the downtime costs (due to lost generation) can be much higher than the tower rental costs, resulting in substantial overall savings for the project when modular cooling towers are used.  As described in Chapter 8 of the Technical Development Document (TDD), EPA estimated that 100% of normal generating revenue will be lost during net construction downtime; however, in cases where modular towers are compatible with site conditions, this is likely an overestimate for facilities with long downtime periods, since it does not consider modular towers as an available cost-saving option.  The actual downtime costs would simply be the modular cooling tower rental costs for the period, including mobilization/demobilization costs.

Modular cooling towers are also useful at facilities that are subject to periodic interruptions or reductions in the quantity of water withdrawn for cooling purposes, and can be a cost-effective option for facilities that require supplemental cooling or flow reduction for only a portion of the year.

Limitations on Applicability

This technology is most appropriate for compliance technologies that involve major modifications to the intake structure or relocation of the intake inlet.  There are limitations regarding the use of modular cooling towers at nuclear facilities and in conjunction with the installation of new cooling towers.

At nuclear plants, the service water may be pumped from a combined service water and condenser cooling water intake, or it may be from a separate intake.  Nuclear facilities have more stringent safety requirements for the service water system than for the condenser cooling water system.  The service water system is considered part of the emergency and safety system, which has very rigorous certification requirements regarding the manufacturing, installation, and maintenance of each component.  Obtaining certification for a new technology can be a rather involved process with no guarantee that the technology will become certified.  

During intake construction downtime, the intake no longer functions as a cooling water source and thus, when modular towers are used during construction downtime to replace this cooling water, they become the sole source.  For this reason, it is unlikely that modular towers would be considered for situations where they would become at any time during plant operation the sole source of cooling water for the service water system at a nuclear facility.  

At nuclear facilities where the condenser cooling water has a separate intake, the installation of modular towers would still be required to meet rigorous seismic and fire control requirements.  Even if these requirements were met, there may be a perception of modular towers as a "temporary technology" that could influence the Nuclear Regulatory Agency's decision to permit such a technology application.  

For the reasons discussed above, modular towers are not likely to be used as an alternate cooling water source to keep a nuclear plant operating during construction activities.  It may, however, be possible to use them in situations where they function as an alternate source of cooling water where once-though operation can be maintained as a backup, provided the technology can meet the technical requirements.

For facilities installing new (permanent) cooling towers, modular towers are also unlikely to prove useful.  In order for modular towers to be used as an alternate source of cooling water during the construction downtime, space must be available for the towers and piping for both the permanent and modular towers.  This essentially doubles the space required; most facilities would be unlikely to have this much available space.

Implications for EPA's Engineering Costs

One difficulty of incorporating this potential construction cost-saving option into the compliance technology economic analysis is that there is insufficient information to determine for which facilities and construction projects this technology would be viable.  The primary obstacle that may limit the technology viability is the availability of sufficient space to place the modular cooling towers.  However, this technology should be viable for more facilities than conventional permanent cooling towers because modular towers require somewhat less space and also allow for more flexibility in the placement of individual units, including the availability of alternatives such as placing some or all of the units on barges.  Conventional cooling towers are generally too large to be installed on floating barges.  

In general, limitations on the availability of sufficient space for modular towers will be greatest at facilities that are located in higher density urban areas, where there is insufficient available space within the plant property boundaries as well as there being no undeveloped land adjacent to the plant that could be purchased and used for siting cooling towers.  

Also, the elevation of the available land is an important consideration.  Optimal locations for cooling towers should be at elevations that are not much higher than those of the generating unit condensers to ensure that pumping costs are economically acceptable.
 
Summary of Advantages and Disadvantages

The advantages and disadvantages of modular cooling towers (as compared to permanent cooling towers) are summarized below.

Advantages include:

          Can be more economical than permanent towers where requirements for use are temporary or seasonal
          Can be installed quickly
          Can be installed with minimal site preparation
          Can be installed without use of explosives that might be necessary for permanent tower concrete basins
          May be available to more facilities because they require less space than conventional cooling towers
          Can be installed in almost any configuration
          Can be installed on barges
          Can be used to provide temporary supply of cooling when existing intake is being modified
          Rental cost includes equipment maintenance and repair
          Can be paid for using facility operating budget

Disadvantages include:

          Economic benefit over permanent towers diminishes or disappears as period of use per year or number of years in use increase
          Energy requirements (and thus operating costs) are higher than for permanent towers

Analysis

The CUR at which the plant would have otherwise been operating during the downtime is an important factor in determining whether the lost generation cost would be high enough to justify using this technology option during construction downtime.  To analyze how capacity utilization could affect this decision, the lost generation costs and total tower rental costs were calculated and then compared for different CUR values and different net downtime durations in weeks.  The typical generating capacity associated with each recirculating flow rate was calculated using the average cooling water requirement of 707 gpm per MW.  Lost revenue was assumed to be $45/Mwh, based on an assumed wholesale value of $65/Mwh minus an assumed fuel cost of $20/Mwh.  The tower costs and lost generation costs were then calculated for different downtime durations in weeks and CUR values in increments of 10%.  The data were then reviewed to determine the minimum number of weeks for assumed CUR values at which the lost generation cost exceeded the tower rental costs. 

Using an assumed value for cooling water requirements of 707 gpm/MW, a facility requiring 400 MGD of recirculating cooling water (last row in Tables 1-3) would generate approximately 400 MW of electricity at full power.  Lost generation costs for the loss of 400 MW of electric power generation are estimated to be approximate $18,000/hr using the assumed value for lost revenue of $45/ MWh.  This is equivalent to a loss of $2.4 million dollars per week if the capacity utilization rate (CUR) is 80%.  Using this example, at $65/MWh, a reduction in the approach of 1.0 F (increase in efficiency of 0.12%) will increase revenue by $3,120/hr or $419,000 per week at 80% CUR. 

Table 5 presents the results of the analysis and indicates that the use of temporary cooling towers to reduce downtime costs will not likely be cost-effective for construction projects with net downtime durations of less than 6 weeks for facilities with a high CUR during the downtime period.  Nor would temporary towers be economical for facilities with CUR values of <40% for the range of estimated construction downtime durations for most of the technology cost modules considered by EPA.  Since most facilities would likely schedule the construction downtime to coincide with a period of time where power demand is lower, the CUR during the downtime period will likely be lower than the annual average CUR for the plant.

                                    Table 5
                                       

Table 6 presents a comparison of estimated downtime costs for a 400 MW and a 1000 MW power plant, assuming two different capacity utilization rates:  one for a baseload plant (80%) and one for an intermediate load plant (60%).  The net downtimes are based on EPA estimates for cost modules 4, 7, 12, and 14, and are associated with relocation of intakes to a submerged offshore location.  These net downtimes are the net values after subtracting out a four-week concurrent scheduled maintenance downtime event.  Table 6 shows that downtime cost for longer durations can be reduced substantially by use of modular towers, especially at baseload facilities.  The last column is the break-even point for these examples, similar to that shown in Table 5. 

                                    Table 6
                  Comparison of Estimated Downtime Costs for
                  Use of Modular Tower Versus Plant Shut Down
                                       

As an example of the potential benefits of a lower tower design approach value, if the example 400 MW facility in row one of Table 5 is used along with the 0.12% (output increase /1.0 F) factor described above, the effect of reducing the cold water temperature by 1.0 F would be to increase plant revenue by up to $3,800,000 for the nine-week period if this were to occur during a period of continuously elevated air temperatures.  Note that the benefit of increased generating efficiency is only available during periods when the wet bulb temperature is high enough to result in a turbine back-pressure that is well above the design back-pressure of the turbine.  

Conclusions

In summary, modular towers are a technology that offers a potentially significant reduction in facility downtime related to compliance with the proposed rule.  Facilities that are able to install the modular towers may actually face no downtime at all, which would eliminate a significant component of the costs of the proposed rule and replace it with the smaller, temporary cost of modular tower rentals.  (See the Environmental and Economics Benefit Analysis for a discussion of the role of downtime costs in EPA's estimation of national economic impacts.)  However, EPA is not able to estimate how many facilities would be able to employ these modular towers, nor has it attempted to estimate the overall cost savings of using them.  As a result, EPA has not adjusted its national cost estimates to include the use of modular cooling towers.
References

Blue Stream Inc., Richard Brister.  Telephone contact record by John Sunda, SAIC.  Regarding technical requirements and costs of modular cooling towers.  May 30, 2008a.

Blue Stream Inc. Email from Richard Brister to John Sunda, SAIC.  Re:  Request for Modular Cooling Tower Cost Information In Support of EPA 316(b) Rule.  May 30, 2008b.

Blue Stream Inc.  "Estimated Cooling Cost Chart" (attachment to May 30, 2008 email from Richard Brister to John Sunda, SAIC).

Blue Stream Inc., Richard Brister.  Telephone contact record by John Sunda, SAIC.  Regarding technical requirements and costs of modular cooling towers.  June 10, 2008c.

Blue Stream Inc., Richard Brister.  Telephone contact record by John Sunda, SAIC.  Regarding modular tower energy requirements and approach.  March 25, 2009.

Durmayaz, Ahmet and Sogut, Oguz.  Influence of Cooling Water Temperature on the Efficiency of Pressurized-Water Reactor Nuclear-Power Plant.  International Journal of Energy Research.  Vol. 30 No. 10. pp 799-810.  2006.

National Productivity Council of India (NPCI).  Guide Book 3  -  Energy Efficiency in Electric Utilities.  Chapter 7  -  Cooling Towers.  No Date.  Accessed on March 25, 2009 at website:  http://www.em-ea.org/Guide%20Books/book-3/Chapter%203.7%20Cooling%20Tower.pdf. 

EPA.  316(b) Phase I  -  Proposed Rule.  Economic and Engineering Analyses of the Proposed Rule.  Appendix A.  August 2000.

EPRI.  Tower Calculation Worksheet.  September 17, 2007.

Varitech Equipment Company.  Fact Sheet:  VTECT-ID3000 Portable Cooling Tower (equipment specifications).  Accessed on May 30, 2008 at website:  http://www.rentalcoolingtowers.com/product-specifications.htm

Figure 1. Intake Canal with Sheet Pile Wall, Forming a Closed Loop System

Figure 2. Example of Flexible Configuration