RESEARCH ARTICLE Micro-generation of energy - Loures Case Study

Tânia Caladoa, Helena M. Ramosb aMaster student of Civil Engineering at Instituto Superior Técnico, Technical University of Lisbon, Lisbon, Portugal; bPhd. Professor in Civil Engineering

Department and CEHIDRO, Instituto Superior Técnico, Technical University of Lisbon, Lisbon, Portugal

ABSTRACT: The energy crises and the high consumption of resources leads to the discovery of new alternative energy sources, new production methods of energy and convert those we already use to become more efficient. In this paper we plan to use the excess energy of a water distribution system by the use of pumps as turbines. The pressure in water distribution systems is controlled by devices such as pressure reduction valves (PRV) that allow the excess energy escape from the system. Thus, it’s possible to replace the PRV by micro turbines and then produce electrical energy. This hypothesis is applied in two water distribution systems in the area of Loures, in Portugal. With the data given by the Loures City Services and using the EPANET model it is possible to obtain the principle hydraulic parameters of the two networks. The turbo machine theory allows the evaluation of which hydraulic machine is more suitable to apply in this project. It’s made an assessment of the machine performance by the Portuguese Legislation and the dynamic response of transient regime. This study is finished with an economical study for the energy production capability in these water distribution systems.

Key-words: micro production of energy, water distribution systems, pressure reduction valves (PRV), EPANET, pump as turbines (PAT), water hammer, economic analysis.

1. INTRODUCTION

We’ve been seeing a few major energy crises in the past years. In all of them, the countries with high dependence of energy struggle to balance their economies. Since the main energy sources are oil and coal, the high prices due to wars or political incidences, show the world the necessity to find new alternative energy sources. Also the carbon emissions, a result from our progress, brought a new environment conscience that enforces the use of renewable energy. The Figure 1 shows the main primary energy sources used by Portugal until the year of 2011. The energy dependency rate for Portugal is 79,4% in the year 2012 (ADENE, 2014). In order to contribute for the reduction of this dependency this study promotes the creation of a micro-generation of energy. In water distribution systems it’s possible to create electrical energy replacing the pressure reducing valves (PRV) by micro turbines (RAMOS, 2004) In this paper we want to promote a green energy, with no carbon emissions and transform the water distribution systems more efficient and sustainable.

2. WATER DISTRIBUTION SYSTEMS

The development of the water distribution systems comes from ancient civilizations. They created structures that now-a-days are seen as monuments that people identify and relate to them. Because of the modern away of life, the conditions of health and hygiene, lead to a higher water demand. These systems had to change to follow and serve the population needs. The water comes from a natural or artificial reservoir; it’s treated and saved in smaller reservoirs. Then it is distributed to the population. In the first case the system is characterized for having high pressures, and in the second low pressures. The Portuguese Legislation ensures the quality of the water distribution service establishing criteria for the flow velocity in the pipes and the pressure.

The flow velocity must not exceed the following expression, V = 0,127 D0,4 (1)

where V is the maximum velocity limit (m/s) and D the diameter (mm). The minimum flow velocity in the system is 0,3 m/s. For the pressure, the maximum value for service or static The next expression gives the pressure criteria,

H = 100 + 40 n (2) where H is the pressure (kPa) and n the number of floors. The maximum value of pressure for static and service state is 600 kPa and minimum is 100 kPa. This study is made with the Loures City Services, who provide the data for two water distribution systems in Lisbon district. Loures City Services provides water to 349 603 people, in a total area of intervention of 195 km2. The length of his network is 4600 km with a capacity of 98730 m3 (SML, 2012). Although the economic crises in Portugal this services have invested in the quality of their service. They have been repairing pipes, reservoirs and installing auto-controlled devices allowing them to control more efficiently the water. The water losses are a real problem in this network, representing 39% of the total acquire water (Table 1).

Figure 1 – Main primary energy sources for Portugal (IEA, 2014)

1

Figure 2 – (A) Milharada and (B) Património plants and networks

Table 1 – Evolution of the acquire water by Loures City Services (SML, 2013)

Water (m3)

2011 2012 2013

Acquire 28 873 344 28 878 382 27 526 429

Paid 18 055 040 17 038 248 16 804 577

Non-Paid 10 818 304 11 840 134 10 721 852

The two networks are from residential areas, one, called Milharada which is a typical suburb area with houses surrounded by green areas (Figure 2A), and the second it’s a urban area with high buildings called Património (Figure 2B). These networks have been provided because the existence of a Pressure Reducing Valve installed in their system, also identified in Figure 2. For this study Loures City Services also provided the local elevation, flow measured at the PRV and inlet and outlet pressure on the PRV.

3. HIDROMECHANIC EQUIPMENT

There are many devices that can be applied in water systems, helping ensure the quality of the service. One device used to control the pressure is a Pressure Reducing Valve (PRV). This valve controls and stabilizes the pressure by increasing the head loss when the outlet pressure is higher than the set value (RAMOS, 2004). This leads to an energy dissipation that can be harvest to produce electric energy. For the several factors that contribute for water losses, the most easy to manage its pressure. (RAMOS et al., 1998) End the PRV is the main equipment used to control pressure. There are three ways for a PRV behavior: in the first the PRV it is active, when the pressure outlet it is higher than the set value, the valve closes increasing the head loss; in the second, the valve is passive open, when the inlet pressure is lower than the minimum established

value, the valve opens decreasing the head loss; and the third, the valve is passive closed, when the outlet pressure is higher than the inlet pressure, the behavior of the PRV is alike a retention valve. (RAMOS, 2004) Using PRV in water distribution systems allows creating sector where the pressure and flow is controlled, called Control and Measurement Areas (CMA). These areas give the possibility for a more efficient control of the water losses. Accordantly with GOMES (2011) this is not a way for direct control, but an instrument that can be used for detection and rapid response. For the outcome of the PRV becomes efficient it must be installed in strategic places. There are many studies for the valve right location. ARAUJO et al., (2006) make an investigation take in two steps: in the first, they use Genetic Algorithms to identify the number and the location of valves for the optimum control of pressure, minimizing water losses: in the second they adjust the opening for several valves. The authors could define alternative scenarios for the valve location and conclude that a higher number of valves don’t necessary leads to a better solution. The installation of this device usually requires the construction of a “by-pass” and the valve is put between two section valves. The set value it is defined by the operator adjusting the spring in the valve. In Table 2 is presented the main proprieties of the PRV installed in the study networks.

Table 2 – Proprieties of the PRV in the study networks

Milharada Património

Pinlet (bar) 7,3 10

Poutlet (bar) 3,8 5,5

Diameter (mm) 150 125

ID Location (-) 208063 203929

A

B

2

Since the aim of this study is to produce electrical energy, the principal energy converters had to be study. This equipment converts pressure energy and kinetic energy into electric energy. The main turbines applied in water systems are divided in two groups: action or impulse turbines and reaction turbines. In the first group we have Pelton turbines and in the second Francis and Kaplan turbines. The difference between these two groups is the state of pressure flow. In Pelton turbines the flow that passes through it at atmospheric pressure. The flow enters in the central and by the injectors is shoot at the buckets wheel. This makes the wheel spin and creates the kinetic energy. The turbine can lose his efficiency if the water jet is not correctly directed to the buckets. So the main challenge when constructing a Pelton turbine is his wheel. Reaction turbines such Francis and Kaplan turbines have a different configurations. The Francis turbine can work efficiently for a high range of head and flow. Otherwise Kaplan turbines are adapted for high flow rate with low heads. This type of propeller turbine has the advantage to have variable vanes that adjust to the flow. The work of a turbine is defined by the characterisc curves that relate with the flow, head, power and torque for a rotational speed and wheel diameter. With this curves it’s possible to trace equal efficiency lines, “hill diagram”. With the combination of new political and environmental policies and a high cost of energy lead to a search of new energy sources. Pump as Turbines (PAT) became viable because they require low investment, maintenance and repairing costs, giving reasonable efficiency. From the economic point of view a PAT installation with power between 5 - 500 kW should give investment return in 2 or 3 years. The main issue of this hydraulic machine is that the supplier doesn’t provide the characteristic curves working as a turbine (DERAKHSHAN et al., 2007). Pumps as turbines comparatively to the conventional turbines don’t have any flow control device, which means that when applied in networks with variable flow it’s not possible to maintain its efficiency. Finding the best efficiency point (BEP) of a PAT has been the focus of many studies. Because losses by turbulence and friction the BEP of a PAT when working in pumping mode is not equal when working in turbine mode. (RODRIGOS et al., 2003) studied water mass displacement finding that 30% of the total losses are in the spiral case and 40% in the impellor.

There has been made some theoretical and experimental studies to predict PAT performance. Some are based in the BEP and others in the specific speed ns. The relations between the BEP in pumping mode and in turbine mode are presented by correcting factor in relation to the flow and head (Figure 3).

ℎ =𝐻𝐻𝑡𝑡𝐻𝐻𝑝𝑝

𝑞𝑞 =𝑄𝑄𝑡𝑡𝑄𝑄𝑝𝑝

(3)

Where, h is the Head correction factor and q the Flow correction factor. RAMOS et al., (2000) based on Sutter parameters prove that independently of the motor or generator used the energy production it will always be feasible with a right choice of PAT. RAMOS et al., (2005) studied the hydraulic behavior (steady and transient states) between a system a PRV and PAT in the water network. In the steady state the behavior of this two devices are similar. Although the transient response has some differences such as the PRV produces higher overpressure values. (DERAKHSHAN et al., 2007) made an theoretical analysis to obtain the BEP of industrial PAT using a method called “Area Ratio”. Later they develop two equations to evaluate the PAT characristic curves based on BEP. The conclusion of this study PAT with high specific speeds need low flow rates and heads to reach high efficiencies. RAMOS et al., (2008) identified the best points for energy production in Valongo water network developing a PAT solution with that became profitable after 5 years, depending on the production point. Recently is use CFD (Computational Fluid Dynamics) to predict the PAT performance (SIMÃO et al., 2010) NAUTIYAL et al., (2011) has realized that the BEP of a PAT in turbine mode is 8,53% lower than the BEP in pumping mode. CARAVETTA et al., (2012) proposed a method called “Variable Strategic Operation” which allows identifying the efficiency curves that maximize the PAT energy production. The main PAT hydraulic characteristic it’s the hydraulic power (Ph), that is obtain by using the specific weight fluid (γ), the discharge (Q), and the net head (H),

𝑃𝑃𝐻𝐻 = 𝛾𝛾𝑄𝑄𝑡𝑡𝐻𝐻𝑢𝑢 (4)

The mechanical power is calculated by Torque (M), impeller rotational speed, fluid mass density (ρ), discharge, and free-vortex constant are used to calculate the engine or mechanical power (Pe), by using:

𝑃𝑃𝑒𝑒 = 𝑀𝑀 ∙ 𝜔𝜔 = 𝜌𝜌 ∙ 𝑄𝑄 ∙ 𝑘𝑘 ∙ 𝜔𝜔 (5)

Figure 3 - Development of PAT performance prediction methods (NAUTIYAL et al., 2010)

3

The efficiency (η) is obtained using the electric power and the hydraulic power

𝜂𝜂 =𝑃𝑃𝑒𝑒𝑃𝑃ℎ

(6)

The theory of the hydraulic similarity consists in three essential laws: geometric similarity, kinematic similarity and dynamic similarity. They can be defined as: geometric similarity, the dimension of the turbine cannot be reduced to a smaller scale which can induce scale effects in the prototype; kinematic similarity, the triangle of speeds is equivalent in the inlet and outlet and dynamic similarity the polygon of forces must be similar both in the prototype as in the model (QUINTELA, 2007).

𝑁𝑁𝑁𝑁′

=𝑄𝑄𝑄𝑄′

�𝑁𝑁𝑁𝑁′�2

=𝐻𝐻𝐻𝐻′

�𝑁𝑁𝑁𝑁′�3

=𝑃𝑃ℎ𝑃𝑃ℎ′

(7)

Specific speed of a turbine gives the geometrical proportion of a similar turbine to a known turbine is defined by:

𝑛𝑛𝑠𝑠 = 𝑛𝑛𝑃𝑃1/2

𝐻𝐻5/4(8)

In a turbine performance It must be defined two characteristic curves; the first corresponding to N=0, standstill curve, in which values of flow and head lower than this curve don’t produce torque; and in the second, M=0, shows the values from which the torque isn’t transmitted to the shaft (Figure 4)

Figure 4 – Turbine characteristic curves (KSB, 2005)

4. HIDRAULIC SIMULATION WITH EPANET MODEL

The technological progress allowed the development of computational models that are used in every research and science field. These models let the engineer simulate several scenarios base on the network hydraulic behavior. So when project is done these computational models help on the choice of the best decision. On this study were used two types of models. On the first step is used the EPANET model to calibrate the networks provided by Loures City Services. The EPANET model was created in 1993 by the United States Environment Protect Agency. Twenty years have passed and is still a model with high percentage of users, because his results are trustful and is license free. One of the advantages of this model is to do dynamic simulations, producing graphics and tables about the hydraulic parameters evolution. Based on the two next equations it is possible to obtain the hydraulic pressure, head and quality in the nodes and flow, velocity and head loss in the pipes.

�𝑎𝑎𝑖𝑖𝑖𝑖𝑄𝑄𝑖𝑖

𝑁𝑁𝑁𝑁𝑁𝑁𝑖𝑖

𝑁𝑁=1

+ 𝐷𝐷𝑀𝑀𝑖𝑖 = 0

𝐻𝐻𝑖𝑖 − 𝐻𝐻𝑘𝑘 = 𝑟𝑟𝑖𝑖𝑄𝑄𝑖𝑖�𝑄𝑄𝑖𝑖�𝑛𝑛−1

(9)

Where, H is the net head (m), Q the flow (l/s), DMi the demand in the node I (l/s) and NPj the number of pipes. These equations are resolved by the “Gradient Method” with the resolution propose by Todini and Pilati algorithm (Rossman, 2000). The base-demand was obtain by considering the demand directly proportional to the fiction length and is defined in the node plus the elevation. There were made two types of simulations: one with the flow media given by the Loures City Services and the second, based on flow values that will induce a more profitable energy making. The time for the simulation was set to 24H and the time step 1h. For both networks a time demand was defined accordantly to the flow in the PRV. Considering the variable flow and the inlet and outlet pressure in the PRV, the two networks are calibrated (Figure 5). The simulation results shown very reliable values, with correlation factors above 0,96 in the two cases. This model allows obtaining the installation curve for each network.

Figure 5 –Calibration of the networks: A – Milharada and B – Património

A B

4

5. PAT APPLICATION IN THE NETWORKS

Based on the hydraulic characteristics of the two networks, it was needed to find a PAT able to produce energy for low flow rates. This will influence the results, which could be better if the flow rate was higher. Thus, there were available two PAT, the Multitec 32-2.1 and the Etanorm 32-161.1 both from the KSB manufacturer. The PAT performance is evaluated by the Portuguese Legislation in each network.

MILHARADA In this case is applied the Multitec 32-2.1. This multicellular machine is made by more than one runner placed in series, increasing the PAT performance. The manufacturer provided de characteristic curves for the pump and turbine mode for a diameter of 142 mm (Figura 6)

Figure 6 – Characteristic Curve and Efficiency Curve for Multitec 32 – 2.1

It is possible to calculate de BEP of the PAT in turbine mode (Table 3)

Table 3 – BEP point of Multitec in Milharada

Q H0 PH PE 𝜼𝜼 N ns [l/s] [m] [kW] [kW] [-] [rpm] [m.kW] 4.44 58 2.5 1.56 0.631 1520 11.86

Based on the theory of the hydraulic similarity it was possible to calculate the characteristic curves for different rotational speeds (Figure 7). It is possible to visualize that increasing the rotational speed the head value increases too. Using analytic relations the electric power PE, and hydraulic power PH are calculated. Therefor the efficiency of the PAT can easily be obtain and construct the hill diagram (Figure 8).

Figure 8 - Hill diagram: Bairro da Milharada.

The best efficiency obtain was for the rotational speed of 1750 rpm with a value of 64%. To find the working point for this case is done the intersection of the hill diagram with the installation curve, obtain in the EPANET model. This intersection will cross the efficiency curves and generate two working points (Figure 9).

Figure 7 – Characteristic Curves for different rotational speed

5

Figure 9 – Working Point of a PAT (RAMOS et al., 2000a)

In the EPANET model, the PRV are substitute by Generic Valves (VG) and it is attributed the head loss curve. This head loss curve corresponds to the characteristic curve of the turbine (Figure 10).

Figure 10 – Introducton of the head loss curve in the EPANET model

The simulation was made for the high demand hour corresponding to 12:00H (Figure 11).

Figure 11 – Pressure results for the higher demand, 12:00H: a) PRV and b) PAT

The service pressure for this network by the Portuguese Legislation is 20 m. We can see that all of the networks are highly overpressure. The application of the PAT takes the pressure to more soothed values, accordantly to the law. This will relief the pipes and reducing the volume of water losses that might occur. The velocities don’t overcome the maximum velocity imposed by law. The Figure 12 presents the installation proposal in the local, where the PRV works complementary with the PAT.

Figure 12 – Installation proposal in Milharada

PATRIMÓNIO The struggle to find a PAT adequate for the flow conditions leed to create two scenarios in order to seize all of the flow and head available:

- Scenario A – two PAT in series for Q = Q0 and H = H0/2; - Scenario B – one PAT for Q = Q0 and H = H0.

Scenario A In this case were utilized two PATs in series Etanorm 160.1-32 with a diameter of 176 mm. The manufacture provided the characteristic curves for the PAT in turbine mode (Figure 13). Accordantly with the characteristic curves was calculated the turbine BEP (Table 1)

Table 4 – BEP of Etanorm 160.1-32 Q H0 PH PE 𝜼𝜼 N ns

[l/s] [m] [W] [W] [-] [rpm] [m.kW] 4.4 22.1 0.95 0.49 0.47 1520 21.04

It was made the same methodology for obtaining the work point of the turbine.

a) b)

6

Figure 13 – Characteristic curves and efficiency curve for Etanorm

Using analytic relations the electric power PE, and hydraulic power PH

are calculated. Therefor the efficiency of the PAT can obtain and construct the hill diagram. The working point for this case study is given by the intersection between the installation curve and the hill diagram (Figure 14).

Figure 14 – Hill diagram of Etanorm

Applying the turbine curve for the rotational speed of 1520 rpm as a curve of head loss, we can simulate its performance. The results are for the period of higher demand, corresponding to 7:00H, to the actual state, with a PRV, and considering a PAT. By the Portuguese law the service pressure in this network should be 45m. As we can see in Figure 15, the PAT installation allows the pressure to drop to lower values but it still maintains the quality service. The velocity in the pipes doesn’t pass the maximum velocity regulated by the Portuguese law.

Figure 16 – Installation proposal for Scenario A

The Figure 16 presents the installation proposal by the author for Scenario A.

Scenario B In this network is apply the PAT Multitec (Figure 6). The turbine curve which originates the work point it is put as a generic valve in the EPANET model (Figure 17). In the high demand hour the influence area of the installation of a Multitec is well notable in Figure 18. The pressure drops to values inferior to those calculated in the Portuguese legislation. The problems with high pressure, above 60 m, are observed in all networks. For the lower consumption hours the PAT must work complementarity with the PRV. In this way there are no harmful effects in the network because of the high pressure. The installation of a PAT in these water distribution systems can maintain the quality and level of service.

Figure 15 – Pressure results for the higher demand, Scenario A 07:00H: a) PRV and b) PAT

a) b)

7

Figure 17 – Work Point for Scenario B

b)

Figure 19 – Pressure results for the higher demand, Scenario B 07:00H: a) PRV

and b) PAT 6. HIDRODYNAMIC BEHAVIOR AND SECURITY

In a pressurized system, any type of maneuver causes a variation of flow and velocity that will create a pressure wave. The velocity of this wave depends on the properties of both the fluid and pipe walls and it is measured by:

𝑐𝑐 =�𝜀𝜀𝜌𝜌

�1 + 𝜀𝜀𝐸𝐸𝛼𝛼𝐷𝐷𝑒𝑒

(10)

where ε is the volumetric elasticity of the fluid; ρ the density of the fluid; E the Young’s modulus of elasticity of the pipe wall; e the thickness of the pipe’s wall. To obtain the maximum overpressure during a maneuver we can use some simplified formulas. These formulas can be applied, considering the time of the maneuver. Considering the water hammer as periodic phenomenon his phase period is given by:

𝑇𝑇𝐸𝐸 = 2𝐿𝐿𝑐𝑐

(11)

where, L is the pipe length and c the wave velocity. When the time of maneuver is higher than the phase period, we are in a presence of a slow maneuver; in the other side it’s called a fast maneuver. For fast maneuver we applied the Frisel-Joukowky formula:

∆𝐻𝐻𝑖𝑖 =𝑐𝑐𝑐𝑐𝑔𝑔

(12)

where V is the flow velocity initial steady state flow. For slow maneuver extreme pressures estimated utilizing the Michaud formula:

∆𝐻𝐻𝑖𝑖 =2𝐿𝐿𝑐𝑐𝑔𝑔𝑡𝑡𝑓𝑓

(13)

For the evaluation of the overspeed effect in a turbogenerator, the author (RAMOS, 2000) presents the relative overpressure values as a function of the turbine specific speed, Ns, and the relations Tw/ Tm e Tc/ TE

Figure 20 - Relative overpressure induced by the turbine overspeed and guide vane closure (RAMOS, 2000)

a)

8

Figure 18 - Instalation proposal Scenario B

The start-up time of rotating masses, Tm (s), is defined based on:

𝑇𝑇𝑚𝑚 =𝑊𝑊𝐷𝐷2𝑁𝑁2

3575𝑃𝑃× 10−3 (14)

𝑊𝑊𝐷𝐷2 = 4𝑔𝑔𝑔𝑔 where n0 (rpm) is the nominal runner speed, P0 the reference power (kW) and WD2=4gI (N.m2). The hydraulic inertia time constant,Tw, is defined by the following equation:

𝑇𝑇𝑤𝑤 =𝐿𝐿 𝑈𝑈0𝑔𝑔 𝐻𝐻0

(15)

With the help of the computational model HAMMER the overpressure due to closure of the valve and turbine overspeed were calculated. The results are shown a upstream of the PAT. For the closure of the valve:

Figure 21 – Graphic results for the closure of valve

In this maneuver the calculation of the overpressure were made by the formulas of Michaud or Joukowky depending if is a fast or slower maneuver. The analytical results are shown in Table 5. The graphical results for introducing the torque moment, with a annulation period equal to the period of the closure valve.

Figure 22 – Graphic results for the turbine overspeed

In the graphics it is possible to see two pic pressure points. The first pressure pic is due to the flow cut by the turbine overspeed, and the second by the closure of the valve. In the first pic it is calculated de velocity variation to obtain the overpressure proposed by Joukowky (Table 5).

For the evaluation of the overspeed effect in a turbogenerator proposed by RAMOS, (2000), we obtain an overpressure increment around 28%.

Figure 23 - Calculation of relative overpressure

MIL

HARA

DA

PATR

IMÓN

IO –

SCE

NARI

O A

PATR

IMÓN

IO –

SCE

NARI

O B

MIL

HARA

DA

PATR

IMÓN

IO –

SCE

NARI

O A

PATR

IMÓN

IO –

SCE

NARI

O B

9

Table 5 – Analytical Results for the simulation

7. ENERGY PRODUCTION AND ECONOMIC ANALYSIS.

Every energy production study must be joined with an economic analysis in order to evaluate it is feasibility. Cost and benefit analysis becomes a powerful decision tool. The energetic assessment in a water network depends on daily demand law (RAMOS et al., 1999). Knowing the daily demand law it can be defined the usable flow for produced energy. The total energy produced is obtain by:

𝐸𝐸 = �(𝑃𝑃𝑢𝑢∆𝑡𝑡) (16)

Where the Pu (kW) is power and ∆t is the usable hours. The profitability of the project is given by the assessment between the costs such as the PAT itself, pipes, valves and the civil construction and the profit generated by sales of electricity. The costs are divided in four parts: implantation costs; operational costs; maintenance costs and spare parts costs. The profit generated was calculated based on a sensitivity analyses on the selling price of energy: 0.11, 0.125 and 0.15 €/kWh The Net Actual Value (NAV) is the sum of the yearly cash flows (CF), with the value of money updated yearly taking in account an correction factor (C). By cash flow is defined by sum of all the profits and expenses of a year.

𝑁𝑁𝑁𝑁𝑐𝑐 = �𝐶𝐶𝐶𝐶𝑘𝑘

(1 + 𝐶𝐶)𝑘𝑘

𝑁𝑁

(17) 𝑘𝑘 =0

If the NAV is positive, the project is economically viable, since the profits exceed the costs. If it is negative, the project will suffer with an economic loss. Other indicators for the viability are indicated, such as the Internal Rate of Return (IRR) which translates to maximum interest of the investment. Or the Benefit/Cost Rate. In the Milharada case the option considered to seize the most energy is the PAT for 3,0 l/s which runs for 13 hours a day, generating 529 W (Figure 24).

Figure 24 –Milharada exploration study

Considering the prices for selling energy it was made a sensibility análisis for the time of outcome (Table 6).

Table 6 – Economics analysis for Milharada

Despite some positive results the IRR values are smaller than some correction factors, meaning that in this case the project isn’t economically viable. The combination for low flow rate and efficiency don’t allow to provide some good results. In the Quinta do Património case it was considered two options. In the Scenario A is used two PATs in series for a flow of 4,4 l/s which runs for 17 hours a day, generating 466 W (Figure 25).

0.0

1.0

2.0

3.0

4.0

1 3 5 7 9 11 13 15 17 19 21 23

Q

Qpe

10

Figure 25 – Património exploration study, Scenario AUsing the various selling prices and the total production in a year is made the economic analysis (Table 7).

Table 7 – Economics analysis for Património Scenario A

The value for these parameters are very sensitive to the selling price of energy. Although it has positive value, the time for the payback in some cases is still very high. In Scenario B it was installed the multicellular PAT for 4,0 l/s which runs for 18 hours a day, generating 992 W (Figure 25).

Figure 26 – Património exploration study, Scenario B

Establish the flow for production of energy the economic analysis is made for the variation of the selling price of energy (Table 8).

Table 8– Quinta do Património Case – Economics analysis – Option B

This scenario B is the most benefic and optimistic of them all. The payback times are still a little high but it shows the capability for projects of this type.

CONCLUSION

The world high energetic dependency leads countries, especially those without natural reserves of fossil Fuels, to search for new alternative ways of producing energy. This study seeks to determine the hydraulic and economic viability of an installation of Pump As Turbine (PAT) in the two water distribution systems in Loures. The seek for turbomachines that were better adapted to the network conditions lead to only one manufacturer, the KSB. Which for this case they have two PATs that fit the conditions. The manufacturer supplied the PATs for booth modes (turbine and pump). Based on the theory of similarity of turbomachines were built new curves for different rotational speed and efficiency hill diagrams. On both case studies, the use of a PAT is an advantage, because it can control better the pressures and also produce electrical energy. The pressures are controlled by the characteristic curve of the PAT and change with the flow, so on high flow situation this corresponds to an also high head loss. The high pressures, above the regulatory, are regulated by the complementary PRV in all networks, when the PAT can’t control those values because there’s no demand, especially in the hours of less flow. So the PAT installation can maintain the same level of service. The transient state is associated to variations of pressure and velocity that can generate very high instantaneous pressures putting in danger the network. The analysis with simplified formulas allows to obtain similar values from those obtain in the computational model. The valve close maneuver is the one that generates the higher overpressures and that the simplified formulas of Michaud and Joukowsky provide values very close to the ones from the model. The low flow on the studied networks and the low efficiencies of the turbo machines are the conditioning factors on energy production. Despite the elevated payback time in the economic analysis developing this study has the highest interest on micro hydric application, regarding sustainability and improvement on network efficiency.

REFERENCES

ARAUJO, LS., RAMOS, H., COELHO, S.T. 2004. Localização óptima de

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