# Water and Energy Efficiency Improvement of Steel Wire Manufacturing by Circuit Modelling and Optimisation

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## Abstract

**:**

## 1. Introduction

^{3}, in which 85% corresponds to water cooling [13].

## 2. Model Assembling

#### 2.1. Circuit Description

_{input}

_{,RM}) is determined by:

_{RMinput}= Q

_{1}× ρ

_{w}× c

_{pw}× (T

_{RMinlet}− T

_{RMoutlet})

_{1}and Q

_{2}corresponds to the water flowrate of the main and secondary circuit respectively (Table 2). The density of the water (ρ

_{w}) corresponds to 999 kg/m

^{3}and the specific heat (c

_{pw}) to 4.186 kJ/kg°C. The T

_{inlet_RM}is determined by:

_{1}× ρ

_{W}× C

_{P,w}× (T

_{in,1}− T

_{out,1}) = Q

_{2}× ρ

_{W}× C

_{P,w}× (T

_{in,2}− T

_{out,2})

_{out,1}= T

_{RMinlet}

#### 2.2. Design and Assembling of IWC Model

#### 2.2.1. Tank Model

_{0}(volume of the fluid when the level is at reference zero height), A (cross section of the free surface) and y

_{0}(height of “zero-level”). The model also requires the input parameters ymin and ymax, which should be appropriate to avoid underflow or overflow of the tank. The pressure at the inlet and outlet ports accounts for the ambient pressure and the static head due to the level, while the pressure at the inlet port corresponds to the ambient pressure.

#### 2.2.2. Pump Model

#### 2.2.3. Pipe Model

_{e}= 24,300). Moreover, for the total head losses the minor losses are also considered. The minor losses consist of the local pressure drop (Equation (5)) due to sudden or gradual expansion or contraction, the presence of bends, elbows, tees and valves (open or partially closed).

_{L}is determined according to tabulated values for each type of local pressure drop [15].

#### 2.2.4. Filter Model

#### 2.2.5. Cooling Tower Model

_{CTinlet}) and outlet (T

_{CToutlet}) ports of the water stream, there is also an outlet port for the electric power consumption of the fan (powerConsumption).

#### 2.2.6. Rolling Mill

_{RMoutlet}).

#### 2.2.7. System and Time Tables

## 3. Model Validation

_{CTinlet}and T

_{CToutlet}) and the water outlet temperature of the rolling mills (T

_{RMoutlet}). The outputs of the numerical results for these parameters are presented from Figure 3, Figure 4 and Figure 5.

## 4. Sensitivity Analysis

## 5. Identification of Improvement Measures

_{2}impact which are the primary aspect that industrials consider regarding energy efficiency.

#### 5.1. Variable Speed Drives (VSD) in Pumps

#### 5.2. Refurbishment of Pumps

#### 5.3. Change of Filters

#### 5.4. Change of Electric Motors of the Pumps

#### 5.5. VSD in the Cooling Tower Fans

## 6. Definition of Optimization Methodology

_{CWT}) reaches more than 0.5 °C relatively to the target value (22.1 °C). From this, the constraint is defined as a requirement of not exceeding 0.5 °C of the temperature at the cold water tank. This allows to maintain the cooled water temperature close to the required in the cooling process.

_{PG}

_{1}, n

_{PG}

_{2}and n

_{PG}

_{3}), cooling tower fans (n

_{CT}) and the hydraulic and mechanical efficiencies of the pumps (designated by η

_{hydr}and η

_{mech}, respectively) as well as the pressure drop in the filters. Table 7 summarizes the objective functions, decision variables and constraints of the optimisation problems.

## 7. Techno-Economic Evaluation

_{op}the annual operational time, C the electricity cost per energy unit and P

_{nom}and P

_{opt}the power at initial conditions and optimized conditions, respectively:

_{op}× C

_{elec}× (P

_{nom}− P

_{opt})

_{IE}

_{1}and η

_{IE}

_{1}correspond to the pump power and its overall efficiency at initial conditions of a standard efficiency motor E1. While P

_{IE}

_{3}and η

_{IE}

_{3}correspond to the pump power and its overall efficiency of a premium efficiency motor IE3.

_{nom}and η

_{nom}designate, the power of a pump and its overall efficiency at initial conditions respectively; P

_{opt}and η

_{opt}correspond to the power of a pump and its mechanical efficiency, respectively, by the installation of VSD’s and i to the numeral designation of a load regime:

## 8. Discussion

^{3}/h for the pump group 3. From the simulation, it was observed that required the cooling load was achieved for a flowrate of 555 m

^{3}/h. Taking into account that average annual water consumption per inhabitant in Germany in 2016 was 45 m

^{3}[26] the water savings could meet the needs of 6601 inhabitants.

## 9. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## Nomenclature

Index | |

1 | Main Circuit |

2 | Secondary Circuit |

air | Air |

CT | Cooling Tower |

CWT | Cold Water Tank |

elec | Electricity |

G | Group |

i | Load regime |

in | Inlet |

IE1 | IE1 Standard Efficiency Motors Installed |

IE3 | IE3 Premium Efficiency Motors Installed |

L | Minor Losses |

nom | Nominal conditions |

out | Outlet |

opt | Optimised conditions |

op | Operational |

RM | Rolling mill |

S | Saturated Air |

VSD | Variable Speed Drives Installed |

w | Water |

filter | filter |

Abbreviations | |

Baseline | Operational conditions for nominal pump motor and fans speed |

EEM | Energy Efficiency Improvement Measure |

ELC | Electric Energy Consumption |

IWC | Industrial Water Circuits |

Measured | Measured plant data |

RTD | Resistance thermometer |

VSD | Variable Speed Drive |

Parameters | |

C_{P,w} | Water heat capacity (kJ °C^{−1} kg^{−1}) |

C_{elec} | Cost of electricity (€/kWh) |

D | Pipe diameter (m) |

ELC | Energy Consumption (MWh/year) |

f | Darcy friction factor |

g | Gravitic acceleration (m s^{−2}) |

H | Enthalpy (J/kg) |

k | Overall heat mass transfer coefficient (kg m^{−2} s^{−1}) |

K_{L} | Coefficient of Minor Losses |

L | Pipe length (m) |

n | Rotational Speed (rpm) |

P | Power (kW) |

Q | Water flowrate (m^{3}/s) |

Q_{M} | Water mass flowrate (kg/s) |

R_{e} | Reynolds Number |

Savings | Economic Savings (€/year) |

S | Cooling tower surface of packing (m^{2}) |

T | Water temperature (°C) |

t_{op} | Operational Time (h/year) |

Z | Depth of a vertical pipe (m) |

ΔP | Pipe pressure drop (Pa) |

ρ_{w} | Water density (kg/m^{3}) |

η_{hydr} | Hydraulic efficiency |

η_{mech} | Mechanical efficiency |

## References

- Hoekstra, A.Y.; Mekonnen, M.M. The Water Footprint in Humanity. Proc. Natl. Acad. Sci. USA
**2012**, 109, 3232–3237. Available online: https://doi.org/10.1073/pnas.1109936109 (accessed on 18 December 2018). [CrossRef] - Banerjee, R.; Cong, Y.; Gielen, D.; Jannuzzi, G.; Maréchal, F.; McKane, A.T.; Rosen, M.A.; van Es, D.; Worrell, E. Chapter 8—Energy End-Use: Industry. In Global Energy Assessment—Toward a Sustainable Future; Cambridge University Press: Cambridge, UK; New York, NY, USA; The International Institute for Applied Systems Analysis: Laxenburg, Austria, 2012; pp. 513–574. [Google Scholar]
- Eurostat. Eurostat Statistics Explained, Water Use in Industry. 2014. Available online: http://ec.europa.eu/eurostat/statisticsexplained/index.php/Archive:Water_use_in_industry (accessed on 26 July 2018).
- Eurostat. Eurostat Statistics Explained, Consumption of Energy. 2017. Available online: http://ec.europa.eu/eurostat/statistics-explained/index.php/Consumption_of_energy (accessed on 26 July 2018).
- Tolvanen, J. LCC approach for big motor-driven systems savings. World Pumps
**2008**, 2008, 24–27. Available online: https://doi.org/10.1016/S0262-1762(08)70314-6 (accessed on 26 July 2018). [CrossRef] - Almeida, A.T.; Fonseca, P.; Bertoldi, P. Energy-efficient motor systems in the industrial and in the services sectors in the European Union: Characterisation, potentials, barriers and policies. Energy
**2013**, 28, 673–690. Available online: https://doi.org/10.1016/S0360-5442(02)00160-3 (accessed on 26 July 2018). [CrossRef] - EUR-Lex. Directive 2012/27/EU of the European Parliament and of the Council of 25 October 2012 on Energy Efficiency, Amending Directives 2009/125/EC and 2010/30/EU and Repealing Directives 2004/8/EC and 2006/32/EC Text with EEA Relevance. Official Journal of the European Union. Available online: http://data.europa.eu/eli/dir/2012/27/oj (accessed on 18 December 2018).
- EUR-Lex. Commission Regulation (EU) No 547/2012 of 25 June 2012 Implementing Directive 2009/125/EC of the European Parliament and of the Council with Regard to Ecodesign Requirements for Water Pumps. Official Journal of the European Union. Available online: http://data.europa.eu/eli/reg/2012/547/oj (accessed on 26 December 2018).
- European Commission. Europe 2020 Strategy. 2016. Available online: https://ec.europa.eu/info/business-economy-euro/economic-and-fiscal-policy-coordination/eu-economic-governance-monitoring-prevention-correction/european-semester/framework/europe-2020-strategy_en (accessed on 26 July 2018).
- WaterWatt. Improvement of Energy Efficiency in Industrial Water Circuits Using Gamification for Online Self-Assessment, Benchmarking and Economic Decision Support. Funded under: H2020-EU. Available online: https://www.waterwatt.eu/index.php?page=about-project (accessed on 26 July 2018).
- Cabrera, E.; Gómez, E.; Espert, V.; Cabrera, E., Jr. Strategies to improve the energy efficiency of pressurized water systems. Procedia Eng.
**2017**, 186, 294–302. Available online: https://doi.org/10.1016/j.proeng.2017.03.248 (accessed on 18 December 2018). [CrossRef] - Eurostat. Energy Balances, Energy Data. Available online: http://ec.europa.eu/eurostat/web/energy/data/energy-balances (accessed on 26 July 2018).
- Statistisches Bundesamt. Nichtöffentliche Wasserversorgung und nichtöffentliche Abwasserentsorgung; Fachserie 19, Reihe 2.2; Statistisches Bundesamt: Wiesbaden, Germany, 2013.
- Politecnico di Milano. ThermoPower Home Page. 2009. Available online: http://home.deib.polimi.it/casella/thermopower/help/ThermoPower.html/ (accessed on 28 September 2018).
- Çengel, Y.A.; Cimbala, J.M. Fluid Mechanics: Fundamentals and Applications, 2nd ed.; McGraw Hill: New York, NY, USA, 2010. [Google Scholar]
- Shah, P.; Tailor, N. Merkel’s Method for designing induced draft cooling tower. J. Impact Factor
**2015**, 6, 63–70. Available online: https://www.researchgate.net/publication/299411018_MERKEL’S_METHOD_FOR_DESIGNING_INDUCED_DRAFT_COOLING_TOWER (accessed on 18 December 2018). - Fernandes, M.C.; Matos, H.A.; Nunes, C.P.; Cabrita, J.C.; Cabrita, I.; Martins, P.; Cardoso, C.; Partidário, P.; Gomes, P. Medidas Transversais de Eficiência Energética Para a Indústria, 1st ed.; Tecnico Lisboa: Lisbon, Portugal, 2016; pp. 31–52. ISBN 978-972-8268-41-1. [Google Scholar]
- GAMBICA—Automation, Instrumentation and Control Laboratory Technology. Variable Speed Driven Pumps—Best Practice Guide; BPMA: West Bromwich, UK, 2003. [Google Scholar]
- IMechE—Institution of Mechanical Engineers. Pumping Cost Savings in the Water Supply Industry; Fluid Machinery Committee of the Power Industries Division: London, UK, 1989. [Google Scholar]
- ADENE. Cursos de Utilização Racional de Energia—Eficiência Energética na Indústria; ADENE: Gaia, Portugal, 2014. [Google Scholar]
- Almeida, A.T.; Ferreira, F.J.T.E.; Bock, D. Technical and economical considerations in the apllication of Variable-Speed Drives with Electric Motor Systems. IEEE Trans. Ind. Appl.
**2005**, 41, 188–199. Available online: https://ieeexplore.ieee.org/document/1388677/ (accessed on 26 July 2018). [CrossRef] - Viljoen, J.H.; Muller, C.J.; Craig, I.K. Dynamic modelling of induced draft cooling towers with parallel heat exchangers, pumps and cooling water network. J. Process Control
**2018**, 68, 34–51. Available online: https://doi.org/10.1016/j.jprocont.2018.04.005 (accessed on 26 July 2018). [CrossRef] - ERSE—Entidade Reguladora dos Serviços Energéticos. Preços das Tarifas Transitórias de Venda a Clientes Finais em Portugal Continental em 2018; Eletricidade, Tarifas e Preços. Tarifas Reguladas em 2017. Available online: http://www.erse.pt/pt/electricidade/tarifaseprecos/2017/Paginas/TtransVCFPortugalcont2017.aspx (accessed on 26 July 2018).
- Siemens Industry. SIMOTICS Low-Voltage Motors; Type Series 1LA, 1LE, 1LG, 1LL, 1LP, 1MA, 1MB, 1PC, 1PP, 1PQ, Frame Sizes 63 to 450, Power Range 0.09 to 1250 kW, Price List D 81.1 P; Siemens Industry: Munich, Germany, 2015. [Google Scholar]
- ABB Group. ACS55, ACS150, ACS310, ACS355, ACS550, 2014. Conversores de Frequência Para Controlo Preciso do Motor e Poupança Energética; Tabela de Preços; ABB: Zürich, Switzerland, 2014. [Google Scholar]
- Statista. Entwicklung des Wasserverbrauchs pro Kopf und Tag in Deutschland in den Jahren 1990 bis 2016. Available online: https://de.statista.com/statistik/daten/studie/12353/umfrage/wasserverbrauch-pro-einwohner-und-tag-seit-1990/ (accessed on 26 July 2018).

**Figure 2.**Diagram of the circuit of a steel wire processing plant in OpenModelica (Legend: (1) Pump Group 1, (2) Hot Rolling Mills, (3) Cyclone Tank, (4) Pump Groups 2, (5) Pipes from pumps to filters, (6) Sand Filters, (7) Pipes from filters to tank, (8) Pump Group 3, (9) Pipes from pumps to cooling towers, (10) Cooling Towers, (11) Cold Water Tank, (12) Reference System).

**Figure 3.**Numerical and measured pump power (

**a**) pump group 1, (

**b**) pump group 2 and (

**c**) pump group 3.

**Figure 7.**Influence of rotational speed of the pump motors on the water temperature of the cold water.

**Figure 8.**Influence of rotational speed of the cooling tower fans (nCT) on the water temperature of the cold water tank (T).

Annual Operational Time (h/year) | 6600 | ||

Main Circuit Nominal Flow rate (m^{3}/h) | 1000 | ||

Secondary Circuit Nominal Flow rate (m^{3}/h) | 1200 | ||

Main Circuit Operational Flow Rate (m^{3}/h) | 900 | ||

Secondary Circuit Operational Flow Rate (m^{3}/h) | 900 | ||

Latitude of the Plant | 51°36′ N | ||

Main circuit | Pump Group 1 | Nominal Flow rate (m^{3}/h) | 500 |

Nominal Head (m) | 48 | ||

Motor Velocity (rpm) | 1450 | ||

Motor Efficiency (%) | 90 | ||

Design Power (kW) | 110 | ||

Running Power (kW) | 90 | ||

Rolling Mill Pipe | Diameter (m) | 0.5 | |

Length (m) | 200 | ||

Pressure Drop (bar) | 4.6 | ||

Outlet Temperature (°C)—T_{in}_{,1} | 24.5 | ||

Pump Group 2 | Nominal Flow rate (m^{3}/h) | 500 | |

Nominal Head (m) | 48 | ||

Motor Velocity (rpm) | 1450 | ||

Motor Efficiency (%) | 90 | ||

Design Power (kW) | 110 | ||

Running Power (kW) | 90 | ||

Cyclone Tank | Area (m^{2}) | 45 | |

Height of water (m) | 2 | ||

Pipe (Pump Group 2 to Sand Filters) | Diameter (m) | 0.5 | |

Length (m) | 200 | ||

Pressure Drop (bar) | 3.1837 | ||

Sand Filters | Nominal Pressure Loss (bar) | 1.3 | |

Area (m^{2}) | 78.5 | ||

Diameter (m) | 5 | ||

Pipe (Sand Filters to Cold Water Tank) | Diameter (m) | 0.5 | |

Length (m) | 20 | ||

Pressure Drop (bar) | 0.3184 | ||

Secondary circuit | Pump Group 3 | Nominal Flow rate (m^{3}/h) | 600 |

Nominal Head (m) | 47.5 | ||

Motor Velocity (rpm) | 1450 | ||

Motor Efficiency (%) | 90 | ||

Design Power (kW) | 110 | ||

Running Power (kW) | 104 | ||

Cooling Towers | Motor Velocity (rpm) | 1500 | |

Installed Power (kW) | 22 | ||

Inlet Temperature (°C)—T_{out}_{,2} | 22 | ||

Outlet Temperature (°C)—T_{in}_{,2} | 20 | ||

Ambient Temperature (°C) | 11 | ||

Wet-bulb Temperature (°C) | 8 | ||

Pipe (Cold Water Tank to Cooling Towers) | Diameter (m) | 0.5 | |

Length (m) | 7 | ||

Pressure Drop (bar) | 3.96 | ||

Main and Secondary circuit | Cold Water Tank | Area (m^{2}) | 75 |

Height of water (m) | 1 | ||

Additional pipe parameters | Material | Stainless Steel | |

Roughness (mm) | 0.015 | ||

R_{e} | 24300 | ||

Friction Factor | 0.025 |

Parameter | Results |
---|---|

q_{input}_{,RM} (kW) | 1380 |

T_{RMinlet} (°C) | 22.1 |

Measurement | Flowrate | Temperature | Pressure | Power |
---|---|---|---|---|

Range | 0.03 to 82 ft/s | −238 to +1040 °F | 0 to 100 psi | 10 W to 10 GW |

Resolution | 0.15% of reading ±0.03 ft/s | 0.01 K | 2 psi | ±1% ± 0.3% of nominal power |

Accuracy | ±1.6% of reading ±0.03 ft/s | ±0.01% of reading ±0.03 K | 3/2/3% of reading | 0.01 kW |

Parameter | Deviation (%) |
---|---|

Power of Pump Group 1 (Pump_1) | 0.74 |

Power of Pump Group 2 (Pump_4) | 0.77 |

Power of Pump Group 3 (Pump_8) | 1.56 |

Inlet Temperature of Cooling Tower (T_{CTinlet}) | 2.62 |

Outlet Temperature of Cooling Tower (T_{CToutlet}) | 4.75 |

Outlet Temperature (T_{RMoutlet}) | 3.29 |

Scenario | Pump Groups 1 and 2 Rotational Speed (nPG1 and nPG2) | Pump Group 3 Rotational Speed (nPG3) |
---|---|---|

1 | 1444 | 1401 |

2 | 1413 | 1434 |

3 | 1408 | 1373 |

4 | 1405 | 1342 |

5 | 1372 | 1328 |

6 | 1418 | 1401 |

7 | 1411 | 1392 |

8 | 1350 | 1350 |

9 | 1442 | 1403 |

10 | 1341 | 1400 |

Scenario | Cooling Towers Fans Rotational Speed (nCT) |
---|---|

1 | 1392.48 |

2 | 1350.50 |

3 | 1190.55 |

Objective Functions | Decision Variables | Constraints |
---|---|---|

min (ELC_{PG}_{1} + ELC_{PG}_{2} + ELC_{PG}_{3} + ELC_{CT}) | n_{PG}_{1} | T_{CWT} (n_{nom}) − T_{CWT} (n) < 0.5 °C |

n_{PG}_{2} | ||

n_{PG}_{3} | ||

n_{CT} | ||

η_{hydr} | ||

η_{mech} | ||

ΔP_{filter} |

Improvement Measure | Annual Energy Savings (MWh/year) | Share of Energy Savings | Investment Cost (€) | Payback (Years) |
---|---|---|---|---|

(i.1) Couple VSD in pump group 1 | 231.74 | 19% | 21,622 | 1.0 |

(i.2) Couple VSD in pump group 2 | 231.05 | 19% | 21,622 | 1.0 |

(i.3) Couple VSD in pump group 3 | 266.24 | 20% | 21,622 | 0.9 |

(ii) Refurbishment of the pumps | 524.18 | 12% | 436 | 0.01 |

(i.1) and (ii) in pump group 1 | 400.60 | 29% | 21,786 | 0.6 |

(i.2) and (ii) in pump group 2 | 399.83 | 29% | 21,786 | 0.6 |

(i.3) and (ii) in pump group 3 | 452.77 | 29% | 21,786 | 0.5 |

(iii) Change filters (1.3 bar to 0.5 bar) | 146.67 | 4% | 42,196 | 3.1 |

(iv) Change motors to high-efficiency (IE3) | 212.46 | 6% | 134,916 | 6.9 |

(i.1) and (iv) in pump group 1 | 286.51 | 24% | 66,594 | 2.5 |

(i.2) and (iv) in pump group 2 | 285.84 | 24% | 66,594 | 2.5 |

(i.3) and (iv) in pump group 3 | 327.86 | 24% | 66,594 | 2.2 |

(v) Couple VSD in fans | 157.40 | 27% | 14,872 | 1.0 |

Improvement Measure | Savings in Water Consumption (m^{3}/h) | Share of Water Savings (%) |
---|---|---|

(i.1) Couple VSD in pump group 1 | 35 | 7.5 |

(i.2) Couple VSD in pump group 2 | ||

(i.3) Couple VSD in pump group 3 | 45 | |

Total | 80 |

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## Share and Cite

**MDPI and ACS Style**

Iten, M.; Oliveira, M.; Costa, D.; Michels, J.
Water and Energy Efficiency Improvement of Steel Wire Manufacturing by Circuit Modelling and Optimisation. *Energies* **2019**, *12*, 223.
https://doi.org/10.3390/en12020223

**AMA Style**

Iten M, Oliveira M, Costa D, Michels J.
Water and Energy Efficiency Improvement of Steel Wire Manufacturing by Circuit Modelling and Optimisation. *Energies*. 2019; 12(2):223.
https://doi.org/10.3390/en12020223

**Chicago/Turabian Style**

Iten, Muriel, Miguel Oliveira, Diogo Costa, and Jochen Michels.
2019. "Water and Energy Efficiency Improvement of Steel Wire Manufacturing by Circuit Modelling and Optimisation" *Energies* 12, no. 2: 223.
https://doi.org/10.3390/en12020223