Emergy Cost Benefit: Comparison of a Cooling Tower vs. an ...€¦ · environmental cost of a cooling tower versus an ecologically-engineered substitute, the algal turf scrubber (e.g.,

66

Emergy Cost Benefit: Comparison of a Cooling Tower vs. an Algal

Turf Scrubber for Reduction of Thermal Waste

Elliott Campbell, Patrick Kangas, Mark Ross

ABSTRACT

In 1974 H.T. Odum evaluated the energy cost of a thermal plume in an estuary, as a result of nuclear

power plant effluent, on the environment (Odum, 1974). He compared this cost to the cost of constructing

and running a cooling tower that would reduce the temperature of the effluent to ambient conditions. He

found that the energy cost of the cooling tower was roughly an order of magnitude greater than the

energy cost to the estuary and recommended against the use of cooling towers, stating that unnecessary

energy use was a detrimental cost to society. We adapted the 1974 study from proto-environmental

accounting to current emergy standards and specific to the Peach Bottom nuclear power plant in Fulton,

PA. The emergy cost of construction and maintenance of a cooling tower was compared to that of an

algal turf scrubber (ATS) large enough to perform the same function. Algal turf scrubbers were designed

to help address the eutrophication of the Chesapeake Bay; algae are periodically harvested from the

ATS to remove nutrients from the system and add dissolved oxygen. When heated water is used to operate

an ATS a cooling effect is an added benefit. In an ATS warm effluent from the discharge canal of the

power plant is pumped to a raised point and flows down a flume, stimulating the growth of algae. Based

on preliminary data from the ATS at the Peach Bottom plant, temperature was reduced between 1 and

2° C per 100 m. We found that ATS’s can perform the same reduction of temperature as cooling towers

at a lower emergy cost; they will also provide the ancillary benefits of oxygenating and reducing

nutrients in the effluent. Optimization of resource use and net societal benefits were at the core of

Odum’s work. If ATS were available in 1974, this work shows that he would likely have recommended

their construction over cooling tower use.

INTRODUCTION

In the mid-1970s H. T. Odum published an early emergy synthesis calculation of mitigation of

thermal pollution from a nuclear power plant by comparing the total energetic cost of a traditional

cooling tower versus direct discharge into an estuary Odum, 1974, 1975). His early methodology adjusts

for energy quality using fossil fuel equivalence. His later work establishes the renewable emergy

baseline, showing that all extant energy on earth can be traced back to the renewable inputs of sun, tide

and deep heat. The comparison calculation showed that the cooling tower had a much higher total cost

on the overall environment than direct discharge, suggesting that the cooling tower was a poor

investment by society and thus should not be built. However, nearly 40 years later regulators are still

requiring that power plants utilize cooling towers to treat their thermal wastes.

In this study we assume that the thermal waste must be treated and we compare the total

environmental cost of a cooling tower versus an ecologically-engineered substitute, the algal turf

scrubber (e.g., the “green cooling tower”) using environmental accounting.

H. T. Odum’s Study of Thermal Pollution

Odum developed his original emergy synthesis of thermal pollution during a long-term study of the

environmental impact of the Crystal River Nuclear Power Plant on the central Gulf Coast of Florida. He

evaluated the alternatives of either building a cooling tower to reduce the elevated temperature effluent

from the nuclear power plant to a lower point where stress would not be placed on the estuary vs. direct

discharge into the estuary without cooling. A cooling tower transfers waste heat to the atmosphere

through evaporative cooling (heat is lost when a portion of the water evaporates). In the typical

hyperboloid cooling tower evaluated here air enters through the bottom of the tower and cools the warm

waste water, with cooler water then flowing out the bottom of the tower and warmer, elevated moisture

content, air rising from the top of the tower. The density difference between the cold entering air and the

warm exiting air results in a natural draft that causes the air flow through the column. In the 1975 paper

the heated effluent was assumed to cause complete inhibition of biological processes over 1 square mile

of the estuary, although this is a gross overestimate as the 1974 study cites data showing no statistical

difference in species diversity or production between the affected estuary and reference conditions to the

north and south. Studies in California, Brazil and China have found that introduction of elevated

temperature water has caused significant changes in species diversity and abundance, suggesting that the

effect is ecosystem specific (Schiel 2004, Teixeira 2009, Wang 2011). The investment ratio shown in

Figure 1 was used to illustrate that the cooling tower cost the greater environmental-economic system

more emergy (in fossil fuel equivalents) than it saved in avoided impact to the estuarine metabolism of

the coastal zone impacted by thermal discharge. Odum used this calculation as an example that “well-

meaning environmental technology may turn out to be energy-intensive and a poor expenditure of the

conservation dollar” (Odum, 1975).

Figure 1. H.T. Odum’s Original Diagram showing the societal choice between disposing of high

temperature power plant effluent in the estuary vs. cooling the water via a cooling tower. The energy

cost of a cooling tower is nearly 100 times more than the energy cost of stress on the estuarine ecosystem

The Algal Turf Scrubber (ATS)™ Technology ™The algal turf scrubber is trade-marked by the Hydromentia Corporation of Ocala, Florida.

An algal turf scrubber is an ecologically-engineered system utilizing controlled algal growth for

water quality improvement. Algae are grown attached to a screen in a basin of shallow, flowing water.

The algae is harvested and removed from the system either once per week or once every two weeks,

dependent on growth rate. Water quality improvement occurs 1) through removal of nutrients as algae

grow and are subsequently harvested from the system and 2) through the addition of dissolved oxygen

from algal photosynthesis. Furthermore, the algal biomass produced in water quality improvement is a

potentially valuable byproduct of the system. Uses of the algal biomass include feedstocks for anaerobic

digestion, fertilizer, or biofuels.

The Algal Turf Scrubber as a Cooling Tower Substitute

When heated water is used to grow algae, the ATS can serve as a substitute for a traditional cooling

tower, which we term the “green cooling tower” (Figure 2). Heat is dissipated to the atmosphere as

water flows through the ATS. Thus, the ATS improves water quality with mitigation of thermal

pollution, as it does with mitigation of nutrient pollution. In our field studies, at the Exelon Corporation’s

Peach Bottom Nuclear Power Plant in southeastern Pennsylvania, an ATS is observed to dissipate at

least 1° C per 100 meter of length under typical operation conditions. Based on the observation that ATS

technology has the ability to replicate the performance of a cooling tower in reducing effluent

temperature, the objectives of this study were to evaluate the sustainability of replacing a cooling tower

with an ATS with the ability to process commensurate amounts of effluent using emergy analysis.

Figure 2. Energy Systems Language diagram of how an ATS functions to cool power plant effluent, as

well as remove nutrients from the system.

METHODS

This research uses Odum (1974) and Odum (1975) comparing the energy costs of a cooling tower

to direct discharge into the adjacent estuary as a blue print, but we updated the study in the following

ways: 1) We compare the emergy cost of a cooling tower to the emergy cost of constructing an algal turf

scrubber to perform the same reduction in water temperature 2) We use current emergy methodology

(inclusion of labor, services, and materials, transformities are calculated on the 15.83E24 global

renewable emergy baseline) 3) Units are solar emjoules rather than fossil fuel equivalents.

The cooling tower at Peach Bottom nuclear power plant cools the water discharged from the plant

7.6° C when in operation. We designed a potential ATS that would perform this same reduction in

temperature for the same amount of water. The cooling tower processes 4000 gallons per minute (gpm),

or 1030 cubic meters per minute (m3pm). To process the same amount of water and perform the same

cooling function the ATS would need to be 27 ha (68 acres) with dimensions of 183 m wide by 1500 m

long. We approximate a temperature reduction of 0.5°C per 100 m of length. This is a conservative

estimate as pilot studies show a more rapid decrease of temperature but this estimate should make up for

potential diminishing returns with ATS length and a higher gpm projection for the theoretical ATS. The

cooling tower at Peach Bottom is only run approximately three months in the summer (93 days) and

inputs for both the cooling tower and ATS are for this time period. Materials and construction labor are

prorated over the life time of the constructions, assumed to be 20 years for both the ATS and cooling

tower.

Data for the inputs to the ATS were identical to the necessary inputs to a pilot ATS at the Bridgetown

site on the Maryland Eastern Shore, but scaled for a 27.4 ha system. With many inputs (HDPE, plastic

etc), this was a linear relationship but with some inputs (the pump, resulting electricity input) allowing

for an economy of scale. It was assumed the ATS would use larger pumps than the pilot system with a

resulting decrease in electricity demand per unit of water pumped. Assumptions based on experience

were made for the labor necessary to construct and maintain the ATS (see footnotes for Table 1). The

mass of the cooling tower and pump were obtained from the engineering data and specifications put out

by the manufacturer (Marley AV Series Cooling Tower). Information regarding construction and

maintenance of the cooling tower was obtained from the Exelon Corporation (Mark Ross, personal

communication).

RESULTS

The results of an emergy synthesis of a Cooling Tower (Marley, Class 600 Crossflow) and a 27 ha

Algal Turf Scrubber are displayed in Table 1. Electricity is the largest input for both the cooling tower

and ATS; comprising 85% of the cooling tower and 90% of the ATS total purchased inputs (Figure 3).

Construction labor comprises a larger percentage of the total for the cooling tower vs. the ATS, while

the opposite is true for maintenance labor. In total, the purchased inputs are 40% larger for the cooling

tower than for the ATS.

The calculated indices are more favorable for the ATS (it has a lower Investment Ratio, higher Yield

Ratio, a lower ratio of Nonrenewable/Renewable, and a slightly lower empower density). The last ratio

(the emergy invested in the cooling tower to the emergy invested in the ATS) is perhaps the most

important finding of our research. This index shows that the emergy invested in the cooling tower is 1.7

times that invested in the ATS, for the same service to be performed (Figure 4).

Note

Algal Turf Scrubber,

Item Unit

Data

(units/yr)

Unit Solar

Emergy

(sej/unit)

Solar

Emergy

(E16 sej/yr)

Em$ Value

(2000 $/yr)

Cooling Tower,

ItemUnit

Data

(units/yr)

Unit

Solar

Emergy

(sej/unit)

Solar

Emergy

(E16

sej/yr)

Em$ Value

(2000 $/yr)

RENEWABLE RESOURCES

1 Sun J 1.28E+15 1.00E+00 0.13 0.5 18 Sun J 1.88E+13 1 0.002 0.007

2 water J 6.81E+14 8.10E+04 5517 19,565,472 19 water J 6.81E+14 8.10E+04 5517 19,565,472

OPERATIONAL INPUTS

3 Screen g 1.31E+07 2.71E+09 4 12,571 20 Cooling Tower, mass g 1.39E+08 5.91E+09 82 291,744

4 Electricity J 2.02E+13 1.74E+05 352 1,247,405 21 Lift Motor, 1400 HP g 8.88E+06 1.47E+10 13 46,277

5 HDPE Liner System g 2.09E+07 8.85E+09 19 65,718 22 Electricity J 3.24E+13 1.74E+05 564 1,999,149

6 PVC Pipe g 2.69E+05 9.86E+09 0.3 942 23

Cooling Tower

Construc. Cost $ 3.83E+05 2.82E+12 108 383,333

7 Concrete g 1.35E+07 2.12E+09 3 10,143 24 Construction Labor hour 2.73E+09 3.36E+08 91 324,267

8 Pumps g 1.15E+06 1.47E+10 2 6,003 25 Maintenance Labor hour 1.74E+08 3.36E+08 6 20,753

9 Construction Labor J 4.98E+08 1.90E+08 9 33,633

10 Maintenance Labor J 3.56E+09 1.90E+08 68 240,235

Sum of purchased inputs 388 1,376,414 Sum of purchased inputs 659 2,337,171

5906 20,942,341 6177 21,902,643

Output Output

11 N removed g 7.68E+06 2.36E+10 18 64,253 26 Treated water J 6.68E+14 9.25E+04 6177 21,902,649

12 P removed g 7.68E+05 2.15E+10 2 5,854 27 Water Vapor J 1.36E+13 4.53E+06 6177 21,902,649

13 Algae J 5.35E+12 3.00E+03 2 5,696 28 temperature J 4.43E+15 1.49E+03 659 2,337,171

14 Treated water J 6.81E+14 8.67E+04 5906 20,942,341 29 temperature °C 7.60E+00 8.67E+17 659 2,337,171

15 O2 Added g 6.89E+11 5.77E+06 398 1,410,666

16 temperature J 4.39E+15 8.84E+02 388 1,376,414

17 temperature °C 7.60E+00 5.11E+17 388 1,376,414

Total Yield (N+P+O2+Water+Temp) 7.11E+19 sej Total Yield J (Water + Temp) 6.84E+19 sej

INDICES, calculated

Name of Index Expression Quantity, ATS Quantity, Cooling Tower

Investment Ratio (P + S)/(N + R) 0.08 0.16

Yield Ratio Y/(P + S) 16.3 7.91

Nonrenewable/Renewable (N + P)/R 0.08 0.16

Empower Density sej/ha/yr 2.15E+18 6.18E+19

(P+S)CT/(P+S)ATS 1.70

Table 1: Comparison of Emergy Evaluation of an Algal Turf Scrubber, 68 acres with a Cooling Tower Marley, Class 600, Crossflow, over 1 year

Ratio of Cooling Tower Investment to ATS

Investment

Figure 3. Emergy spectrum of the inputs to a 27 ha ATS and a Cooling tower, calibrated to treat 1030

m3 per minute for 93 days, decreasing the temperature 7.6° C.

The algal turf scrubber provides a number of services not provided by the cooling tower (Figure 5).

The ATS alters the incoming water flow by removing nitrogen and phosphorus and adding O2. These

services add 8.16x10^18 sej, or 2.89 million emdollars yr-1, of value to the thermal reduction service the

ATS is providing (valued at 1.4 million emdollars yr-1). These results are over the 93 day functioning

period for the cooling tower. This is the peak period for algae production so it cannot be assumed the

results would increase linearly if the ATS were running year round, but it can be assumed that these

values would be significantly higher, as preliminary results from our research have shown that algae can

be grown year-round in elevated temperature power plant effluent.

Figure 4. Choice between Cooling Tower and ATS. Society is faced with the choice of investing 3.9x1018

sej (1.4 million em$/yr) in an ATS or 6.6x1018sej (2.3 million em$/yr) in a cooling tower to perform the

same service, the treatment of 5.5x1019 sej of water with elevated above the ambient temperature in the

Susquehanna River.

DISCUSSION

The results of the emergy syntheses of a 27 ha ATS and a Marley Series cooling tower, show that

the ATS requires 40% less emergy to perform the same service as the cooling tower. The additional

benefits provided by the ATS increase the quality of the water discharged, removing nitrogen,

phosphorus and adding oxygen. When these ancillary benefits are considered the ATS is adding twice

the benefits that the cooling tower provides (only thermal waste treatment). This is the effective cost to

society of treating thermal waste with cooling towers rather than algal turf scrubbers. Eutrophication in

the Chesapeake Bay (of which the Susquehanna River is the primary water source, contributing 50% of

the total freshwater input, Chesapeake Bay Program, 2013) and the resulting instances of plankton

blooms and anoxic zones are major problems (Chesapeake Bay Program, 2013). This makes the ancillary

benefit of water quality improvement the ATS provides particularly attractive. Burgeoning nutrient

markets in the Chesapeake Bay watershed (PDEP, 2013) and potential exploitation of algae biomass for

fertilizers or biofuels (Borowitz, et al. 2013) may make the ATS an even more financially feasible option.

Locating ATS’s near power plants is mutually beneficial as thermal waste is treated and the higher

temperature waters allow the ATS to function (grow algae) year round so higher total nutrient removal

is achieved, facilitating watersheds meeting Total Maximum Daily Load (TMDL) goals and, ultimately,

reducing the nutrient load on the Bay. Thus, a “win-win” scenario is created.

A potential benefit of the ATS over the cooling tower is that the ATS may have less evaporative

water loss, allowing a larger percentage of the river water extracted available to be returned to the river.

However, we did not have a good estimate of the evaporative loss from the ATS and only a rough

estimate for the cooling tower. This would be a valuable comparison for future research.

Figure 5. Products of the cooling tower and the ATS. The emergy of the treated water and temperature

are higher for the cooling tower because the purchased inputs are higher for the cooling tower. In this

case higher emergy value is not indicative of quality, but indicates that a larger amount of emergy is

necessary for the thermal waste processing of the water.

A significant caveat to the ATS technology is the high areal footprint necessary. The cooling tower

has a footprint of approximately 1 ha while the ATS would require 27 ha. The land would need to be

adjacent to the water body to minimize pumping costs. A potential negative effect of installing a large

ATS would be the possible loss of natural areas that would be cleared for ATS installation. Ideally, an

ATS would be put on already impacted lands. The cost of acquiring land may be a significant limiting

factor. A cost comparison of the ATS and cooling tower is forthcoming, but preliminary work indicates

that the ATS would be favorable in this respect.

CONCLUSION

H.T. Odum demonstrated that cooling towers were thermodynamically a losing proposition more

than 40 years ago and our research continues this theme, indicating that ATS technology cool thermal

waste with lower financial input and also provide benefits that cooling towers do not provide. Based on

the Peach Bottom Nuclear Power Plant and an experimental ATS using data from a study on the

Maryland Eastern Shore, a 27 hectares (68 acres) ATS would be required to provide the equivalent

amount of heat dissipation as provided by the cooling tower. A comparison of the total emergy inputs

indicates a 40% lower cost for the ATS substitute (green cooling tower) compared to the conventional

cooling tower. In addition, the ATS provides ancillary benefits (water quality improvement and biomass

production); these benefits are valued at approximately 2.9 million em$. In Odum’s original work he

concludes that direct discharge of untreated effluent was preferable to lowering the effluents temperature

through a cooling tower. It may be that direct discharge would be preferable to using an ATS for

treatment as well, but further work studying the downstream effects of the ancillary benefits should be

done before this conclusion can be made. However, this research indicates that Algal Turf Scrubbers are

a potentially more sustainable alternative for meeting regulatory requirements for dissipating waste heat

from power plants.

REFERENCES

Borowitzka, Michael A.; Moheimani, Navid R. (Eds.). 2013. Algae for Biofuels and Energy. Series:

Developments in Applied Phycology, Vol. 5. 288 pp

Buranakarn, Vorasun. 1998. Evaluation of Recycling and Reuse of Building Materials Using the Emergy

Analysis Method. PhD Dissertation, University of Florida, Gainesville, FL

Campbell, D.E. 2012a. Emergy of the global biogeochemical cycles of biologically active elements.

Proceedings of the 7th biennial Emergy Conference, Gainesville, FL

Campbell, D.E. 2012b. Emergy of the occupations. Proceedings of the 7th biennial Emergy Conference,

Gainesville, FL

Campbell, D.E. and Brandt-Williams, S. Unpub. Maryland State Emergy Analysis. United States

Environmental Protection Agency (USEPA).

Daniel E. Campbell and HongFang Lu. 2010. The Emergy Basis for Formal Education in the United

States. Proceedings of the 6th Biennial Emergy Conference, Gainesville FL

Campbell,D.E. and Andrew Ohrt. 2009. Environmental Accounting Using Emergy: Evaluation of

Minnesota. United States Environmental Protection Agency (USEPA) Document 600/R-09/002

Chesapeake Bay Program. 2013. Facts and Figures.

http://www.chesapeakebay.net/discover/bay101/facts

Cohen, M.J., Sweeney, S., Brown, M.T. 2007. Computing the Unit Emergy Value of Crustal Elements.

Pp 16.1-16.11. Emergy Synthesis 4: Theory and Applications of the Emergy Methodology. Center

for Environmental Policy, University of Florida, Gainesville

Odum, H.T., 1996, Environmental Accounting: Emergy and Environmental Decision Making, John

Wiley & Sons, New York, 370 pp.

Odum, H.T. 1974. Energy cost-benefit models for evaluating thermal plumes. In, Gibbons and Sharitz

(eds.) Thermal Ecology: Proceedings of a symposium held at Augusta, GA. U.S. Atomic Energy

Commission. Pp. 628-648.

Odum, H.T. 1975. Energy Cost Benefit Approach to Evaluating Power Plant Alternatives. 9pp

Odum, H.T., W. Kemp, M. Sell, W. Boynton and M. Lehman. 1977. Energy analysis and the coupling

of man and estuaries. In Environmental Management, Vol. 1, No. 4. Springer-Verlag, NY. pp. 297-

315.

Pennsylvania Department of Environmental Protection. 2013. Nutrient Trading.

http://www.portal.state.pa.us/portal/server.pt/community/nutrient_trading/21451

Schiel, David, Steinbeck, John, Foster, Michael. 2004. TEN YEARS OF INDUCED OCEAN

WARMING CAUSES COMPREHENSIVE CHANGES IN MARINE BENTHIC

COMMUNITIES. Ecology 85(7) pp. 183301839

Teixeira, T.P., Neves, L.M., Araujo, F.G. 2009. Effects of a nuclear power plant thermal discharge on

habitat complexity and fish community structure in Ilha Grande Bay, Brazil. Marine Environmental

Research. Vol. 68 189-195.

You-Shao Wang (2011). Effects of the Operating Nuclear Power Plant on Marine Ecology and

Environment - A Case Study of Daya Bay in China, Nuclear Power - Deployment, Operation and

Sustainability, Dr. Pavel Tsvetkov (Ed.), ISBN: 978-953-307-474-0, InTech, Available from:

http://www.intechopen.com/books/nuclear-power-deployment-operation-and-

sustainability/effects-of-the-operating-nuclear-power-plant-on-marine-ecology-and-environment-

a-case-study-of-daya-

APPENDIX

Footnotes to Table 1

1 Sun, J

Annual energy = (Avg. Total Annual Insolation J/yr)(Area)(1-albedo)

Insolation:

5.06E+09 J/m2/y

(calculated using solar

constant of 2 Langleys/sec

and integrating over changing

surface area for one year,

latitude 27N, longitude 82W)

Area: 68 acre

Area: 2.75E+05 m2

Albedo: 0.08

Annual energy: 1.28E+15 J

Emergy per unit input = 1 sej/J (Odum 1996)

2 Water, J

flow rate

6.18E+04

m^3 per

hour

operation hours per year 2232 hours/year

Annual energy: m^3/hour*hours/year*1e6g/m^3*4.94J/g

grams 1.38E+14 grams


Emergy per unit input = 8.10E+04 sej/J

temperature change 7.6 °C (Odum 1996)

joules= °C temperature change/gram water* grams water *4.19J/g

= 4.39E+15 J/yr 3 Screen

area of screen 6.54E+07 ft^2

mass= 6.54E+07 grams

assume 5 year lifespane 1.31E+07 g

Emergy per unit input = 2.71E+09 sej/g Odum et al, 1987

4 Electricity, J

2 pumps/acre

18.5 kw

http://zhenxingpump.en.alibab

a.com/product/464765032-

210333851/api

_610_centrifugal_pump.html

Energy Content = KW*3.6E6 J/KWh*2232 hrs/yr

KW for all pumps: 2516 kw

Annual energy over: 2.02E+13 J

Emergy per unit input = 1.74E+05 sej/J (Odum 1996), P 305

5 HDPE Liner System

Amount of HDPE plastic = 4.19E+08 g

assume 20 year lifetime 2.09E+07 g

Emergy per unit input = 8.85E+09 sej/g Buranakarn (1993), emergy

evaluation of

HDPE

6 PVC Pipe

Amount of pipe = 5.39E+06 g


Emergy per unit input = 9.86E+09 sej/g Buranakarn (1993), emergy

evaluation of

PVC

7 Concrete

mass 2.70E+08 g


2.12E+09 sej/g Buranakarn (1993)

5.72E+17 sej 8 Pumps

mass per 1000 gpm pump

1.27E+05 g/pump

http://www.ebay.com/itm/

Ruhrpumpen-CPP21-6x4x8-

Single-Stage-Centrifugal-

Pump-1-000-GPM-

140627992636#shId

2 pumps per acre

1.73E+07 g/acre

assume 15 year lifetime 1.15E+06

specific emergy 1.47E+10 sej/g Cohen et al, 2007

2.54E+17 sej/acre 9 Construction Labor, J

(3 employees)*(14 days)*(45$/hour)

Energy (J) = (man-hr)*((2500kcal consumed/day)/24 hr)

*(4186 J/Kcal)

$/yr: 10080

$/yr: 10080 $

Emergy per unit input = 1.90E+12 sej/$

Energy = 9.96E+09 J

assume 20 year lifetime 4.98E+08

Emergy per unit input = 1.90E+08 sej/J Campbell, 2010

10 Maintenance Labor (2 workers)(2 hours/week)(30 weeks per year)

120

hours per

year


*(4186 J/Kcal)

3.56E+09 J/yr

transformity 1.90E+08 sej/J Campbell, 2010

11 Yield-Nitrogen Removed 0.03 g N/g dry weight Algae

7.68E+06 g N per 93 days

2.36E+10 sej/g Campbell, 2007

7.08E+08 sej N/yr 12 Yield- Phosphorus

Removed

0.003 P per g dry weight algae

7.68E+05 g P per 93

days

2.15E+10 sej/g Campbell, 2007

13 Yield - Algae

10 g/m^2/day

Algae Yield= g/m^2/day*area*93 days

= 2.56E+08 g

Energy content = g of biomass*5kcal/g*4184 J/kcal

Product in Joules 5.35E+12 J/93 days

transformity= 3000 sej/J

14 Yield-Treated Water 6.81E+14 j of water input

total emergy, ATS= 5.91E+19 sej

transformity= sej of system/j treated water

= 8.67E+04 sej/J calculated

15 Yield-Oxygen Added

Increase of 0.01 Dissolved Oxygen

= mass H20 *50% of time where production is >respiration *1% O2

increase 6.89E+11 grams O2 over 1 year

transformity 5.77E+06 Campbell, D.E. 2012

16 Temperature, joules

°C temperature change/gram water* grams water *4.19J/g

= 4.39E+15 J/yr 17 Temperature °C 7.6 °C

Transformity, °C 5.11E+17 sej/C Calculated

Transformity, J 8.84E+02 sej/j Calculated

18 Sun, J

Annual energy = (Avg. Total Annual Insolation J/yr)(Area)(1-albedo)

Insolation:

5.06E+09 J/m2/yr

(calculated using solar

constant of 2 Langleys/sec

and integrating over changing

surface area for one year,

latitude 27N, longitude 82W)

Area: 1 acre

Area: 4.05E+03 m2

Albedo: 0.08 (NASAeosweb 2002)


Emergy per unit input = 1 sej/J Odum 1996

19 Water, J see footnote 2 20 Cooling Tower

mass

253.11 mt

http://www.surplus-used-

equipment.com/media/9585/a

v-ts-08.pdf 11.00 modules

2.78E+09 grams

assume 20 year replacement

time

1.39E+08

specific emergy 5.91E+09 sej/gram Odum, 1996

21 motor, 40 HP

6.66E+07 g

http://www.surplus-used-

equipment.com/media/9585/a

v-ts- 08.pdf

assume 15 year replacement

time

4.44E+06

specific emergy 1.47E+10 sej/g Odum, 1996

22 electricity 100000 kwh/day

1 kwh= 3600000 joules

3.6E+11 j/day

energy= joules/day*93 days of operation

= 3.24E+13 J

Transformity 1.74E+05 sej/J

23 Cooling Tower Cost 7.67E+06 $/year of construction

Annualized, Assume 20 year

lifetime

3.83E+05 $/year

24 Construction Labor 2.50E+06 $

Assume $20 per hour 1.25E+05 hours

Assume 20 year lifetime 6.25E+03 hours/year


*(4186 J/Kcal)

Energy = 2.73E+09 J


25 Maintenance Labor 400 hours


*(4186 J/Kcal)

Energy = 1.74E+08 J


26 Treated Water = input to the tower-evaporative loss

= 6.68E+14 J/yr

transformity 9.25E+04 sej/j calculated

27 Water Vapor 2% lost to evaporation

water lost= m^3/hour*hours/year*1e6g/m^3*4.94J/g*2% lost

8.78E+13 J/yr

transformity 4.53E+06 sej/j calculated

28 Temperature, J

designed heat rejection, per

hour

2.02E+09 BTU/hr

loss per year= BTU/hr*24hr/day*93days/yr*1055J/BTU

= 4.74E+15 J/yr

transformity 1.49E+03 calculated

29 Temperature, °C 7.67 deg C

transformity 8.67E+17 sej/ deg C calculated

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Emergy Cost Benefit: Comparison of a Cooling Tower vs. an ...€¦ · environmental cost of a cooling tower versus an ecologically-engineered substitute, the algal turf scrubber (e.g.,