Theoretical and practical analysis of waste heat recovery system in off-season rainbow trout production

Accepted Manuscript Title: Theoretical and Practical Analysis of Waste Heat Recovery System in off-Season Rainbow Trout Production Author: Yousef Abbaspour-Gilandeh PII: DOI: Reference:

S0144-8609(18)30139-0 https://doi.org/10.1016/j.aquaeng.2019.02.001 AQUE 1985

To appear in:

Aquacultural Engineering

Received date: Revised date: Accepted date:

1 October 2018 14 February 2019 28 February 2019

Please cite this article as: Abbaspour-Gilandeh Y, Theoretical and Practical Analysis of Waste Heat Recovery System in off-Season Rainbow Trout Production, Aquacultural Engineering (2019), https://doi.org/10.1016/j.aquaeng.2019.02.001 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Theoretical and Practical Analysis of Waste Heat Recovery System in off-Season Rainbow Trout Production Yousef Abbaspour-Gilandeh

University of Mohaghegh Ardabili, Daneshgah Street, 56199-11367, Ardabil,

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[email protected]

Abstract

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The supply of heat for fish farms, especially during off-season production, is necessary for the establishment of commercial aquaculture. For this purpose, research was carried out on the supply of heating energy to a rainbow trout farm (cold water fish) using a waste heat recovery system in the city of Meshgin in Ardabil province. The study area has 20 indoor pools and 14 unguarded pools. The 14 pools that are in the indoor area, are used for this study. Seven pools of these 14 pools were at high altitude and other 7 pools were at low altitude. After collection of the temperature data for waste water ponds that had provided optimum temperature conditions in the off-season using geothermal fluid, three modes for waste heat recovery were designed according to the thermal, flow and physicochemical properties of the waste pond. In the first mode, the output of the first seven pools and the second seven pools were combined and the fluid flow rate reached to 24.92 L/sec. In the second mode, the output of the second seven pools (8.15 L/sec) was used to recover heat, and in the third case, the output of the first seven pools (at high-altitude pools and with the flow rate of 16.77 L/sec) was used to recover heat. After obtaining technical approval and determining the economic value of each component of the waste heat recovery circuit from specialized companies in Iran, the proposed systems were analyzed theoretically with COMSOL software. Because there was no equal rate of flow, velocity or geometry for comparison between the optimum state in the theoretical conditions of practice, the temperature differences between the input hot water and output cold water were used for all three modes of heat recovery. Technically, the results indicate that the second mode is best in both the theoretical and practical modes of the waste heat recovery circuit. The first mode recovery system had the smallest temperature difference between the hot water inlet and cold water outlet. Economically, the minimum cost of establishing a heat recovery system was for the second mode, with a decrease of 60.65% and 38.83% compared to the third and first modes, respectively. Considering technical and economic factors, the waste heat recovery system of the second mode was the most appropriate choice for the trout farm, both theoretically and practically. The first and third modes ranked next, respectively.

Keyword: Coldwater fish, Waste pond, Waste heat recovery, Technical-economic factors 1. Introduction

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Considering the increased population and the destruction of natural resources due to human pollution, food shortages are the greatest threat to human society. Therefore, the need for food, especially protein, is felt more than before. Statistics show that aquaculture production has the fastest growth among food producing sectors [13]. According to FAO forecasts, aquaculture will play an important role in the food supply, income, employment, foreign exchange and rural sustainable development in most countries in the future [20]. The global aquaculture production in 2009 was 15 million tons, which should increase to 64 million tons by 2025 [8]. In Iran, the only cultured species of cold-water fish is rainbow trout. With a production of 91519 tons, Iran comprises 12.57% of world production and is ranked first in Asia and second worldwide after Chile [6]. In 2012, Ardabil province ranked tenth (with 41 farms of 1776 total farm) in terms of the number of cold water fish farmed. In terms of area, it ranked 13th in the country (with an area of 27315 m2 compared to 2374719 m2). In terms of production, it ranked 13th in Iran with 2972 tons out of 10632 [11].

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The ideal temperature for rainbow trout (Salmo gairdneri) has been determined in both vertical and horizontal temperature gradients. No statistically significant difference was found between the preferred temperatures using the two methods. This suggests that the nature of the gradient plays a smaller role than generally believed in laboratory investigations of temperature preference [18]. Better control of the temperature of fish farm pools and the optimal growth of aquatic animals through the direct use of geothermal energy is one of the most common applications. For example, the best salmon growth occurs at 15.5°C. Therefore, by keeping the fish pool temperature constant in cold seasons using geothermal fluid it is possible to achieve optimal salmon growth in all seasons. The largest users of this method are Iceland, Georgia, Turkey and New Zealand [12, 19].

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Waste heat recovery (WHR) systems use the waste energy of a system. Generally, these systems use the energy of a hot environment that leaves the system to heat or pre-heat another environment. The lost energy is converted into useful energy for the system. Accordingly, the first task in heat recovery analysis is to estimate the energy consumption of the unit and the recyclable energy lost in the system [11]. Affective factors in the heat recovery system that alone play a determinative role in the success or failure of a heat recovery project include compatibility between source and demand, accessibility, distance between source and demand, form and condition of waste heat source, product quality, degree of upgrade required, regulatory aspects [2]. Many economic factors affect the use, selection and usefulness of technology and waste heat recovery equipment. These include system costs and waste heat recovery equipment, temperature constraints in waste heat sources, chemical compounds of waste heat sources and limits resulting from specific applications [1].

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The main types of heat exchangers that can be used to transfer energy from a geothermal fluid are plate and down-hole heat exchangers [17]. Plate heat exchangers are well suited for geothermal applications because they are made of non-corrosive materials, are easily cleaned, and can increase the load by adding a plate. They also have high efficiency, which is a valuable feature in the design of such systems. Because the temperatures of geothermal resources are often less than the temperature used in the design of conventional hot water heating systems, minimizing temperature loss in a heat exchanger is an important design goal. Materials for the plates of heat exchangers in direct use usually contain Buna-N or EPDM insulation and 316 or titanium plates [17].

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In the northwestern regions of Iran, about half of the year has temperatures that are not conducive to farming of cold water fish such as rainbow trout; thus, producers can only produce for four to six months of the year. In order to increase production and production efficiency and reduce production costs and increase revenue, the use of storage techniques and increasing the fluid temperature in the pools of these producers is necessary. One of the most effective techniques in this regard is the use of waste heat recovery systems, which use the waste energy from the installed system. These systems use the hot environment energy that leaves the system to heat or pre-heat another environment, turning lost energy into useful energy for the system.

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Because of the importance of aquatic animal production, especially of trout in Ardabil province of Iran during the cold season (off-season production) and the technical-economic aspects, the objective of the current study was to design and theoretically and practically analyze a waste heat recovery system from the waste pond of a typical trout farm. This farm was located in the city of Meshgin and uses direct geothermal fluid for heating fish pools.

2.1 Spatial and climatic conditions of study area

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2. Materials and Methods

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GPS and Google Earth software was used to determine the location and take aerial photos of the study site, respectively. The latitude, longitude and the height of the site is 38°17'59.72" N, 4°41'40.72" E and 1975 m, respectively. This area is south of Meshgin. An aerial view of the trout farm is shown in Figure 1. In order to estimate the average monthly temperature and monthly and seasonal rainfall of the study area, XY-Clima-Ardabil was used in the macro section of Microsoft Excel for observation and for climate and statistical maps of temperature and precipitation to determine the regional climate. Table 1 shows the upper, average and lower temperatures (monthly, seasonal, and yearly) of the study area.

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The estimated temperature table of the study site (Table 1) based on latitude and longitude and location height was estimated to determine the heat transfer factors. The lower limit of the region was considered to have the worst atmospheric conditions and temperature. The months of October, November, December, January, February, March, April and May had the minimum required temperatures that were below that for trout growth. Table 2 shows the upper, average and lower cumulative rainfall (monthly, seasonal, annual) of the study area.

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2.2 Dimensional characteristics of studied fish farm The study area has 20 indoor pools and 14 unguarded pools. The 14 pools that are in the indoor area, are used for the reproduction and rearing of fish and the six other pools are used to breed fish in the cold season (October to May). The plans and illustrations of the 20 covered indoor pools are shown in Figure 2. In all calculations of thermal factors, for the purpose of uniformity of estimations and comparisons, the pool dimensions were considered to be 2×18×1.5 m with a total volume of 54 m3. 2.3 System mechanisms (theoretical-practical foundations of the system) One effective factor in the design of waste heat recovery systems is the physicochemical quality of the recyclable water [1]. Water quality varies according to the water source (surface or underground) and the geographic features of the area. Water quality can also vary

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by season and even daily. Water quality is very effective for the optimal growth of fish; hence, it is important for producers and water quality parameters should be regularly measured and managed [21]. The physical and chemical properties of the water quality used in the pool are shown in Table 3.

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Every 4.5-5 h, the pool water is completely changed. About 10 L/sec of water flows constantly into each pool. The input fluid is added to the pool at a temperature of 4°C (the lower limit of the monthly pool water temperature) and at a rate of 10 L/sec. In order to reduce the occupied space and economize the waste heat recovery geometry, a plate exchanger with a maximum possible outlet temperature was used. The circulator pump and filter are designed and selected according to the specifications of the exchangers.

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The system has 14 raceway pools that are increased by geothermal fluid at the minimum desired temperature. The output of these pools is considered to be the hot side of the heat recovery circuit.

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Water in the system has an initial kinetic energy (kinetic energy due to gravity acceleration). As for rivers, the fluid moves in the pool. The input water rate for each tank is 10 L/sec.

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In addition to fluid physicochemical properties, a range of the lowest temperatures of the fluid inlet to the pools was used to calculate and design a retrograde system for waste heat recovery from the flow of the drainage pool. Table 4 shows the average monthly water temperature of the pool. Other characteristics of the features in the design of the heat exchanger circuit were as follows:

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Table 5 shows the temperature and flow characteristics of the waste ponds for fish farming pools covered by the direct use of geothermal energy. The cold and warm input temperatures were used to exchange heat in the waste heat recovery system. In order to design and select a filter, circulator pump and heat exchanger in accordance with the physical and mechanical conditions of the fluid for all three conditions, the required equipment was acquired from companies in Iran. After selecting the system circuit structure, the waste heat recovery geometry was designed and arranged based on the technical-economic characteristics presented by the companies. The three models are shown in Figures 3, 4, and 5 and in Tables 6, 7, and 8. In these models, all of the route, filter, pump and exchanger pipes were covered with rock wool to prevent environmental heat loss.

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In all three models, first, based on the fluid flow rate and the physical and chemical characteristics of the outlet fluid of the pools, the filter was selected (Figure 4) and then the heat exchangers were chosen. Finally, in order to generate kinetic energy of the fluid, the pumps were selected based on the input and output water and the available pressure in the circuit [4]. The differences between the pumps used in the three circuits was in terms of the discharge rate and the power needed to run the pumps. The pump type of 80-315 has a discharge rate of 90 m3/h and the power of 15 kw for the electromotor for pump starting up. Pump type of 50-315 has a discharge rate of 30 m3/h, and needs an electromotor power of 7.5 kW, while the pump type of 65-315 has a discharge rate of 61 m3/h and requires the power of 11 kW.

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2.4 Definitions of physical space of the system in COMSOL software

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In order to determine the geometry of the three systems using the theoretical models, the COMSOL Multiphysics 5.2a and CATIA ver. 5r21 were used [10]. Figure 6 shows the inlets and outlets of the fluid for both warm and cold sides of the exchangers. To analyze the exchanger element, the software was considered stationary. The shape of the element was designed in CATIA software for loading into COMSOL. After loading the shape of the element, the material was selected. Because the main of this study was heat transfer and laminar flow, the heat transfers and fluid flow modes were selected. The governing equations for heat transfer are: 𝜌𝐶𝑝 𝑈 × ∇𝑇 + ∇ × 𝑞 = 𝑄

(1)

𝑞 = −𝐾∇𝑇

(2)

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where 𝜌 = density (kg/m³), 𝐶𝑝 = heat capacity at constant pressure (J/(kg·K)), 𝑈 = speed of fluid (m/sec), 𝑇 = temperature (K), 𝑞 = convective heat transfer, 𝑄 = heat source, 𝐾 = heat transfer coefficient (W/m K). The governing equations for fluid flow are as follows: 2

(3)

∇ × (𝜌𝑈) = 0

(4)

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𝜌(𝑈 × ∇)𝑈 = ∇ × [−𝜌𝐿 + 𝜇(∇𝑢 + (∇𝑈 )𝑇 ) − 3 𝜇(∇ × 𝑈)𝐿] + 𝐹

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where 𝜇 = dynamic viscosity water (Pa·s) and 𝐹 = shear stress (L/sec).

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After determining the temperatures of the warm and cold sides, based on the type of fluid flow, the values of the warm and cold sides of the laminar fluid flow were also determined. The problem data was used to obtain the boundary conditions of the inlet rate, inlet mass flow rate and inlet pressure. Because there are common warm and cold water boundaries in the analyzed exchangers, the effects of heat transfer created within these boundaries are also considered. Four types of mesh were selected in the analysis and no significant changes were observed in the heat transfer generated in the converter. Therefore, to accelerate problem solving, in all stages of shape analysis, the mesh type selected was normal triangular. A total of 72,884 meshes with a volume of 0.009292 m3 were selected. Figure 7 shows the meshing specifications for all three waste heat recovery exchangers. After selecting the meshing, the problem was solved for all three exchangers.

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3. Results and Discussion Table 9 shows the results of the temperature difference between the theoretical and practical state. In theory, it is assumed that heat transfer is carried out only between warm and cold plates but, in practice, it is also due to heat transfer from the plates to the environment, which increases the heat transfer. Table 9 shows that heat transfer increased according to relation Q = m × c × ΔT as the temperature difference (ΔT) increased. It appears that the recovery circuit of the third mode with a warm water inlet (13.5°C) and cold water inlet (4°C) had a greater difference in temperature transfer on the cold side compared to the theoretical and practical modes, which is technically ideal. Because the inflow, speed and geometry are not

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identical for the three modes of waste heat recovery, the temperature difference between the warm water inlet and the cold water outlet for all three modes of waste heat recovery was used to compare the optimal mode of the exchangers.

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The lower the temperature difference between the warm water inlet and a cold water outlet, the more optimal will be the exchanger and waste heat recovery circuit. For this reason, the second mode of a waste heat recovery system, which has the smallest temperature difference in the practical (2.1°C) and theoretical (0.4°C) modes, is the optimal technical model. This represents higher heat transfer due to high flow velocity than the first and third modes. Because the inlet and outlet pipe diameters in the second mode are less than for the first and third modes, it decreased to half (2 instead of 4). Technically, the second mode is best for both the theoretical and practical aspects of the waste heat recovery circuit and the mass flow rate and temperature at the pump outlet are determined. It is assumed that the pump, filter and pipes of the route are insulated with adiabatic rock wool; thus, software analysis of the pump, filter and route pipes in this comparison have no value. Also, because the mass flow rates are different in all three modes of heat recovery, comparison of heat exchangers in the three different modes was not possible.

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Tables 6, 7, and 8 show that the highest cost of purchasing a heat recovery circuit is related to the third mode (US$ 42,836). The heat recovery circuit of the first mode (US$ 65,035), with a decrease of 35.87% is ranked second compared after the third mode. The heat recovery circuit of the second mode (US$ 25,590) decreased 60.65% and 38.83% compared to the third and first modes, respectively, and had the lowest heat recovery circuit cost.

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4. Conclusion

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1- Technically, the second mode is best in both the theoretical and practical modes of the waste heat recovery circuit. The first mode recovery system had the smallest temperature difference between the hot water inlet and cold water outlet.

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2- Economically, the minimum cost of establishing a heat recovery system was for the second mode, with a decrease of 60.65% and 38.83% compared to the third and first modes, respectively.

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3- In terms of the technical-economic factors, the waste heat recovery system of the second mode was the most appropriate choice for the trout farm, both theoretically and practically. The first and third modes ranked next, respectively.

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4- By installing and implementing the second mode of the heat recovery system, it was possible to increase the optimal growth temperature for trout in the studied farm. The growth temperature of the 14 study pools was provided by the use of geothermal fluid. Instead of the fluid entering at a flow rate of 8.15 L/sec with a temperature of 4°C, an output temperature of 9.3°C and 5 h of water circulation, the optimum growth temperature can be provided for more fish farming pools during off-season production by installing this thermal recovery system without changing the flow conditions and water flow, but by increasing the fluid inlet temperature to 7.2°C. 5- It is recommended that similar experiments could be carried out in other cold regions of the breeding fields and the optimal design and functional parameters should be considered. It

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is also suggested that the objectives of this research would be analyzed and evaluated for production in other cold water fishery products.

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References

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1- Anonymous, 2008. Waste Heat Recovery: Technology and Opportunities in U.S. Industry. Prepared by BCS, Incorporated. U.S Department of Energy . 2- Anonymous, 2010. Energy management series for industry, commerce, and institutions. Issued by the Energy Efficiency Division, Department of Energy, Mines and Resources, Ottawa, Canada. 3- Anonymous, 2018. Heat Exchanger-catalogues. TGT Co. . 4- Anonymous, 2017. Low pressure centrifugal pumps-catalogues. PUMPIRAN . 5- Anonymous. 2011. Heat Recovery. Razavi Khorasan Province of Gas Company. Research and Technology Affairs. National Iranian Gas Company. 6- Anonymous. 2012. The State of World Fisheries and Aquaculture 2012. Prepared by FAO. Fisheries and Aquaculture Department staff, under the coordination of a team. . 7- Anonymous. 2016. Introduction to Comsol (5.2a). © 1998–2016 COMSOL. Protected by U.S. Patents 7,519,518; 7,596,474; and 7,623,991. Patents pending. 8- Baniasad, M., Salami, J.A., Shiri, N., Yaghoubi, M. 2010. Investigating the production structure of trout culture farms in Tehran province. Journal of Agricultural Economics Research, 2 (1): 115-130. 9- Caramel, B.P., Moraes, M.A.B., Carmo, C.F., Vaz-dos-Santos, A.M., Tabata, Y.A., Osti, J.A.S., Ishikawa, C.M., Cerqueira, M.A.S. and Mercante, C.T.J. 2014. Water Quality Assessment of a Trout Farming Effluent, Bocaina, Brazil. Journal of Water Resource and Protection, 6, 909-915, http://dx.doi.org/10.4236/jwarp.2014.610086. 10- Cozzen, R., 2011. CATIA V5r21. Schroff Development Corporation. www.schroff.com. 11- Ebadzadeh, H., Ahmadi, K., Mohammadnia, A.S., Taghan, R.A., Moradi Islami, A., Abbasi, M. Yari, Sh. 2016. Agricultural Statistics of 2015 (Volume II). Ministry of Agriculture Jihad, Deputy Director of Planning and Economics, Center for Information and Communication Technology. 12- Fotouhi, M., and Nourollahi, Y., 2001. Principles of Geothermal Energy, Miad Publications, Tehran, p. 148. 13- Hasanpour, B., Ismail, M.M., Mohamed, Z. and Kamarulzaman, N.H., 2011. Factors affecting technical change of productivity growth in rainbow trout aquaculture in Iran. African Journal of Agriculture Research. 6(10): 2260-2272, https://doi.org/10.5897/AJAR10.467. 14- Hosseini, S.H., Sajjadi, M.M., Kamrani, E., Sourinejad, I., Ranjbar, H. 2013. Impact of rainbow trout (Oncorhynchus mykiss) farm effluents on water physico-chemical parameters of Ryjab River (Kermanshah province). J. Aquatic Ecology, 2 (4) :29-39. . 15- Macintyre, C.M. 2008. Water quality and welfare assessment on United Kingdom trout farms. Thesis Submitted for the Degree of Doctor of Philosophy. Institute of Aquaculture, University of Stirling. 16- Mahdinezhad, K., 2006. Water quality- Determination of pond water fish culture for the common cold and warm water fishes -Specification. Institute of Standards and Industrial Research of IRAN. No. 8726. 17- Maxwell, N., Rock, B.A., Brickman, H., Davis, R.L., Debes, G.C., Francis, C.A., Awson, C.N., Merdith, D.B., Thrasher, K.C., Tisdale, R.W. 2007. ASHRAE Handbook: Heating,

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Ventilating and Air Conditioning Applications (SI Edition): Geothermal Energy. ASHRAE. Chpter32, 1-30. 18- McCauley, R. W. and W. L. Pond. 1971. Temperature selection of rainbow trout (Salmo gairdneri) fingerlings in vertical and horizontal gradients. Journal of the Fisheries Research Board of Canada 28:1801-1804, https://doi.org/10.1139/f71-266. 19- Nazaripour, H., Fotouhi, S., and Poudineh, M.R. 2010. The need for revision of energy sources and the replacement of new energies (geothermal energy). The 4th International Conference of the Islamic World Geographers. 20- Salehi, H. 2002. The needs of research on aquaculture economics in Iran. Iranian Scientific Fisheries Journal, 4: 75-96, . 21- Summerfelt, R.C. 1998. Water quality considerations for aquaculture. Department of Animal Ecology. Iowa State University, .

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Figure 1. Aerial and interior images of trout farm used in this study.

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Figure 2. Farm plans and images of temperature test of geothermal fluid branches used in

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trout farming pond.

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Figure 3. Schematic of waste heat recovery circuit for three proposed modes.

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Figure 4. Schematic and technical-economic dimensions of T-filter proposed by water machinery company.

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Figure 5. Schematic dimensions of plate exchangers for three modes of waste heat recovery

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systems [3].

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Figure 6. Inlets and outlets of fluid for both cold and warm sides in theory analysis.

Figure 7. Specification of meshing for all three waste heat recovery exchangers. 14

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Table 1. Temperature of the study site (°C) (monthly, seasonal, and annual) Temperature (°C)

February

March

April

May

June

July

August

September

October

November

December

Spring

Summer

Autumn

Winter

Annual

Estimated upper limit

-0.1

-0.5

3.7

9.7

13.8

19.2

21.9

22.3

18.7

13.1

6.9

1.9

14.1

20.9

7.2

0.7

10.4

Estimated average

-2.2

-2.2

2.2

8.3

12.3

17.0

19.7

20.1

16.8

11.4

5.3

0.5

12.5

18.8

5.7

-0.7

9.1

Estimated lower limit

-4.2

-3.9

0.7

6.9

10.7

14.7

17.4

17.8

14.8

9.6

3.7

-0.9

10.9

16.8

4.2

-2.1

7.7

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January

Cumulative rainfall (mm)

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Table 2. Cumulative rainfall of study site (mm) (monthly, seasonal, and annual) February

March

April

May

June

July

August

September

October

November

December

Spring

Summer

Autumn

Winter

Annual

Estimated upper limit

42.8

50.5

46.2

62.2

66.6

23.7

23.9

28.7

25.9

33.9

42.1

35.9

148.5

77.5

105.5

132.6

402.2

Estimated average

34.9

38.1

36.5

42.7

44.0

18.3

15.5

16.0

18.2

25.0

33.1

26.8

105.0

49.7

85.0

109.5

349.1

Estimated lower limit

37.0

25.7

26.7

23.2

22.3

12.9

7.1

3.3

10.6

16.1

24.2

17.8

61.5

26.9

64.5

86.3

295.9

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January

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Table 3. Physical and chemical properties of cold water fish farming water [16], [15], [9], and [14] Index Temperature Oxygen Carbon dioxide

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Transparency (depth of vision) Total dissolved solids Electrical conductivity Total suspended solids Total alkalinity Total hardness Nitrite Nitrate Ammonia N-NH3 Orthophosphate Hydrogen sulfide Total iron

Proper range 9-17 °C 6-12 mg/L 15< mg/L 6.5-8 15-35 cm 200> mg/L µm hos>8000 mg/L<80 mg/L<20 mg/L>400 mg/L>0.02 2-5 mg/L mg/L>0.01 0.5-0.2 mg/L Zero mg/L >0.2

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Copper

0.1-0.005 mg/L

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Zinc

0.5-0.03 mg/L

19 20 21 22

Chlorine Mercury Cadmium PCB

mg/L>0.02 mg/L>0.05 3-0.4 mg/L 0.5 µg/L

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Observations Preferably 12-16°C Preferably, at least 70% oxygen saturation Preferably less

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pH

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Row 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

For cold-water fish, it should be transparent Usually between 500 and 600 mg/L Usually between 0.4 and 1.58 mg/L Usually between 150 and 200 mg/L It can be 0.1 Preferably less than 2 mg Can be 1.113 It should be zero, but also can be 0.28 The permissible amount of copper depends on water hardness. A hardness of 10 is 0.005, a hardness of 50 is 0.21, a hardness of 100 is 0.04 and a hardness of 300 is 0.122 Permissible amount of zinc depends on water hardness. A hardness of 10 is 0.03, a hardness of 50 is 0.2, a hardness of 100 is 0.3, and a hardness of 500 is 0.5

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Table 4. Monthly water temperature of pool water

October

November

December

January

February

March

April

May

11

9

7

4

4

4

5

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The average monthly lower limit of water pool temperature (°C)

Table 5. Specifications of temperature and outlet fluid discharge from pools for direct use of geothermal energy Fluid discharge (L/sec)

Flow volume (m3/h)

Minimum monthly temperature of input fluid (°C)

Outlet fluid temperature (°C)

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Pool outlet

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Design Modes

Combination of first and second modes

24.92

89.712

4

12

Second mode

Second seven pools

8.15

29.34

4

9.3

First seven pools

16.77

60.372

4

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First mode

Third mode

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Table 6. Technical-economic characteristics of circulator pump for three modes of waste heat recovery Head of operating point (m)

First

EN 80-315

EN 80-315

90

Second

EN 50-315

EN 50-315

30

Third

EN 65- 315

EN 65- 315

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Discharge of operating point (m3/h)

Power of proposed electromotor (kW)

Electromotor round (rpm)

Purchase fee (US$)

30

15

1450

7.5

1450

11

1450

30

30

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Modes of waste heat recovery circuit

Table 7. Technical-economic characteristics of the filter for three modes of waste heat recovery

Filter type

Mesh size(mm)

PN(bar)

Lace basket material

Dimensions (mm)

Weight(kg)

Purchase fee (US$)

First

DN 100 T type-

1

10

AISI 304

470×410×670

75

3293

Second

DN 50 T type-

1

10

AISI 304

330×300×470

45

2705

Third

DN 100 T type-

1

10

AISI 304

470×410×670

75

3293

A

CC E

Modes of waste heat recovery circuit

18

I N U SC R

Table 8. Technical-economic characteristics of plate heat exchangers for three modes of waste heat recovery Fluid (kg/h)

power(kW)

Plate material

Washer Material

First mode

388.6

SS316L

EPDM

89830

Second mode

109.9

SS316L

EPDM

29380

Third mode

514.6

SS316L

Warm side outlet

Cold side inlet

Cold side outlet

89825

12

7.1

4

8.9

4

30710

29377

9.3

6

4

7.2

2

17494

ED

60450

60448

13.5

8

44

9.5

44

55746

A

CC E

PT

EPDM

Warm side inlet

Input and output pipe size (in)

Cold side outlet and inlet

M

Warm side outlet and inlet

Operating temperature (°C)

A

Modes of waste heat recovery circuit

19

Purchase fee (US$)

I N U SC R

Table 9. Specifications of input speed and temperature difference between warm and cold water pipes in theoretical and practical modes of exchangers in waste heat recovery circuit Hot Side

Cold Side

Tin Hot (°C)

Tout Hot (°C)

12

4.99

First mode

Theoretical Practical

12

7.1

Second mode

Theoretical

9.3

4.28

Practical

9.3

Third mode

Theoretical

13.5

∆T0ut (°C)

M

2.11

Tin Cold (°C)

A

Modes of waste heat recovery circuit

Tout Cold (°C)

4.0

10.97

4.0

8.9

4.0

8.95

4.0

7.2

4.0

12.27

6.0

5.26

2.78

2.07

0.03

1.75

0.04

2.77

0.02

A

CC E

PT

Practical

ED

1.72

∆T0ut (C°)

Average speed U(m/s)

20