Upload
hoanghanh
View
219
Download
1
Embed Size (px)
Citation preview
Artículo: COMEII-15025
I CONGRESO NACIONAL COMEII 2015
Reunión Anual de Riego y Drenaje
Jiutepec, Morelos, México, 23 y 24 de noviembre
EVALUACIÓN EXPERIMENTAL DE UN SISTEMA NF-PV DESTINADO PARA
APLICACIONES DE RIEGO AGRÍCOLA
Ulises Dehesa Carrasco1; José Javier Ramírez Luna2
1CONACYT Research Fellow, Instituto Mexicano de Tecnología del Agua, Paseo
Cuauhnáhuac 8532, Col. Progreso, C.P. 62550, Jiutepec, Morelos, México. 2 Instituto Mexicano de Tecnología del Agua, Paseo Cuauhnáhuac 8532, Col. Progreso, C.P.
62550, Jiutepec, Morelos, México.
Resumen
La desalinización con energía solar representa una solución atractiva para aplicaciones de
riego agrícola en zonas remotas, especialmente en cuencas endorreicas donde los
compuestos presentes, tales cómo sulfatos, exceden los límites máximos permisibles para
aplicaciones de riego. En éste trabajo se presenta un estudio experimental de un sistema de
desalinización de Nano filtración (NF) con paneles fotovoltaicos (PV) que opera sin
almacenamiento eléctrico. Con el fin de evaluar el rendimiento del sistema, diferentes
concentraciones de S04 fueron analizados. El experimento se llevó a cabo a cielo abierto
bajo diferentes condiciones de radiación solar. Con base en los resultados experimentales,
la calidad del permeado obtenido satisfice los estándares de la Ley Federal de Derechos en
Materia de Agua. Sin embargo, la concentración inicial y el ensuciamiento del sistema de
pre-tratamiento juegan un papel importante en el rendimiento del sistema. Se observó una
disminución de permeado de 7 lpm cuando la concentración inicial aumenta de 525 mg / l
a 2,539 mg / l. Esta disminución representa cerca del 2 kWh / m3 de consumo de energía. El
consumo máximo de energía probado fue 3,4 kWh / m3 con una concentración de 2,539 mg
/ l. Se observó una producción de permeado que oscila entre 2,16 a 4,08 m3 / d, por lo que
es posible irrigar entre 1 y 2 hectáreas de cultivos.
Palabras clave: Desalinización solar, riego agrícola, aplicaciones de la NF.
I Congreso Nacional COMEII 2015, Jiutepec, Morelos, México, 23 y 24 de noviembre
2
ABSTRACT
Desalination driven with solar energy represent an appealing solution for agricultural
irrigation in remote areas. In this work, an experimental study of a NF-PV desalination
system without electric storage is presented. In order to evaluate the performance of the
system, different salt concentrations (mainly SO4-2) was tested. The experiment was
conducted at open sky under varying solar radiation conditions. Based on experimental
result, the quality of permeated obtained satisfice the standards of Mexican norm for
irrigation. However, the initial concentration and fouling play an important role in the
performance of the system. Was observed a decrement of permeated of 7 lpm going from
525 mg/l to 2539 mg/l. This decrement represent close of the 2 kWh/m3 of energy
consumption. The maximum energy consumption tested was 3,4 kWh/m3 with a
concentration of 2539 mg/l. Was observed a production of 2,16 – 4,8 m3/d, making it
possible to irrigate between 1 and 2 hectares of crops.
Keywords: Solar Desalination, agricultural irrigation, applications of NF.
1. Introduction
The limited water resources are a real challenge for the actual status of agriculture in the
world. The most important drivers for water scarcity are: growing water demands as the
population increases, economic development, and the increase water per capita
consumption [1]. Experts in the field agree that the production of food locally represents a
strategic policy for undeveloped countries [2]
In Latin America, in particular the north of Mexico, exist large tracts of land that are
potentially productive for crops or pasture management. However, these lands are not
exploited because the available groundwater has not the water-quality necessary for
agriculture applications [3]. Mainly because the limit maximum permissible of some type
of salt, so as, S04-2 are exceeded by 400% as previously was reported by [4]. Without other
water sources, brackish groundwater is used directly to irrigate the crops. However, this
practice reduces the performance of agricultural production and causes a negative impact
on the soil surface by the salt deposition [2].
Desalination of brackish groundwater (BW) is an alternative that has been employed to
increase the availability of water, and indirectly reduce the negative impact of
contamination of the soil by salt. The quantity and water quality needed for irrigation is
defined depending on the crop and soil characteristics [2]. The water for irrigation is
classified based on established standards, the most important are: electrical conductivity
(EC), total dissolved solids concentration (TDS), sodium risk (as function of the sodium
absorption ratio (SAR)), the potential of hydrogen (pH) and the cations (Ca2+, Mg2+, Na+,
K+) and anions concentration (HCO32-, Cl-, SO42-, CO32-, and NO3).
I Congreso Nacional COMEII 2015, Jiutepec, Morelos, México, 23 y 24 de noviembre
3
Desalination for agriculture applications is often thought as an unprofitable process,
mainly because this is an expensive method (e.i 40-45% of the total cost) [5]. However, in
recent years this perception is changing [2],[6]-[7] . Some countries such as Spain, Israel
and United Arab Emirates have increased the volume of desalination water for agriculture
irrigation [8]. The reverse osmosis (RO) is the technology with major presence in market
desalination for large or small applications [2],[8].
Nanofiltration (NF) has been used as one part of the solution for pre-treatment in RO
desalination. The NF membrane is used to remove particles with diameters greater than 2
nm such as sulfates, which negatively affect the useful life of the RO membranes. The NF
membrane do not prevent entirely the flow of salt through the membrane; monovalent
compounds present in the mixture can cross. The presence of these compounds in
permeate flow can be beneficial for the crops, because some of this compounds are
required for the plant growth appropriately; provided that the maximum permissible
limits, stabilized in standardized norm, are not exceed [5].
An NF system works with lower pressures than RO, in consequence the specific energy
consumption is lower. This characteristics allow design and build less robust systems
where solar energy with photovoltaic panels is very attractive especially for small-scale
applications in remote areas [9].
The NF desalination process couplet with solar photovoltaic (NF-PV), has been reported
previously in literature [11],[13]. IEA-ETSAP and IRENA, publication demonstrated the
feasibility of NF-FV, for treating water in isolated places for human consumption [11]. The
results showed that this systems can be used for small scale irrigation. Richards et al.,
reported a study of desalination by an hybrid membrane configuration (NF,UF and RO).
The specific energy consumption ranged from 2 – 8 kWh per 1 m3 of disinfected and
desalinated drinking water. Ghermandi A. and Massalem R. studied the advantages of NF
membranes instead of RO membrane in the production of irrigation water. Based on the
simulation of the performance of a solar-assisted pilot plant, the energy consumption by
the proposed system was 40% lower than conventional reverse osmosis desalination,
reducing in 34% the currently abstracted groundwater volumes, and increasing in 18% the
total biomass production of the irrigated crops [5].
Recently, Jasson et al.[4], carried out an experimental study about alternative treatment
brackish water for irrigation using a NF-FV system. The study was focused in
understanding the behavior of the system, keeping constant the amount of sulfate in the
influent (1863 mg/l) which affect mainly the water quality. Authors report a production
average of 3.2 m3 / day with 6.3 solar peak hr, allowing cultivation in the region of study,
up to 15 tons of tomatoes to a rate of 35 kg / m3. Zarzo D. et al. published the Spanish
experience in desalination for agriculture applications. The authors concluded that the
desalinated water can be more expensive than water from other origins but this depends
I Congreso Nacional COMEII 2015, Jiutepec, Morelos, México, 23 y 24 de noviembre
4
on many factors. However, many agricultural products can support the price of
desalinated water without a great impact on the overall price [2] [7].
Application of desalination with PV assisted as previously was described, commonly uses
a batteries support system for the storage of the photovoltaic electric energy that is on its
turn transformed in AC for powering the pumping system. However, the electricity
supplied by PV system can be used directly to energize the pump of the NF system
producing permeate only during the sunlight hours and storing the desalinated water
instead of the electric energy.
The aim of the present study is to evaluate the performance of the NF-PV desalination
system as function of exogenous variable. The electricity supplied by PV system is used
directly to energize the driven pump of the NF system, without battery support. The
system was evaluated as function of energy consumption, recovery rate and quality of the
effluent, considering the exogenous variables as irradiance and the salt concentration in
the influent. The effect of pressure drop in the system by fouling in the pretreatment filters
are discussed.
2. Materials and methods.
a) NF-PV System
In Fig. 1 the scheme of the experimental device is shown. The system is integrated by one
micro filter used for pretreatment of the influent, a stage of Nanofiltration modules (NF),
photovoltaic solar cell (PV) and pumping system. The NF stage is composed by four NF
polyamide membranes (ESNA1-LF-4040 model) connected in parallel configuration,
providing an equivalent area of 30.6 m2. The prototype was designed to operate with a
nominal capacity of permeate close to 12 l / min with a supply of brackish water of 60 l /
min. The electric supply was provided by a photovoltaic plant with a nominal power of
1.92 kW integrated by eight polycrystalline silicon modules of 240 W each module which
supplies power to a submersible centrifugal pump, model SQFlex 16 SQF-10. The coupling
of the PV plant with the pump system was direct (without battery support) and controlled
only with an on-off switch.
I Congreso Nacional COMEII 2015, Jiutepec, Morelos, México, 23 y 24 de noviembre
5
Fig. 1. Schematic diagram of the NF-PV system
b) Methodology
The experiment was carried out under laboratory conditions using a solution with high
content of SO4 -2 as influent. In order to evaluate the system performance, four different
concentrations of the influent were tested. The nominal values of concentrations was 525
mg/L, 1170 mg/L, 1750 mg/L and 2539 mg/L respectively. In each test the concentration
was kept constant while solar radiation was a free parameter whit a variation along the
solar day in a range of 300-1000 w/m2. The irradiation was measured over the plane of the
PV solar cell with a Kipp & Zone pyranometer of first class with an uncertainty of ± 1.0%.
In order to calculate the power supplied by PV plant the voltage and electrical current
was directly measured with a 34972A Data Acquisition. The volumetric flow was
measured using an AQF-600-105 flow meter with resolution of 0.25 l / min and the
pressure through Ashcroft G2 pressure transducers were installed on the input and output
ports of the system.
The evaluation of the system consisted in determine the removing effectiveness of SO4-2,
the specific energy consumption, the permeate recovery rate and quality of permeate for
fertigation. The removal efficiency of SO4-2 was determined under conditions of sunny and
cloudy days with a relation of the SDT of the influent and the permeate stream.
The energy consumption was defined as the ratio of permeate flow and the electric power
supplied to the pumping system according to equation 1.
(1)
I Congreso Nacional COMEII 2015, Jiutepec, Morelos, México, 23 y 24 de noviembre
6
Where represent the average permeate flow in the time as function of solar
radiation, and is the average electric power supplied to the pumping system in
the same time.
The quality of permeate for fertigation was evaluated as function of the following
parameters: EC, TDS, PH and SAR. The SAR is evaluated with the content of sodium
cations, calcium and magnesium according the equation 2, as was reported by [3],[12].
(2)
3. Analysis and discussion of results.
The experiment focused in the behavior of the NF-PV desalination unit as function of the
influent concentration and solar irradiation. Four sets of experiments were carried out for
this purpose. In each set, the concentration of influent was kept constant, varying only the
irradiance along the solar day in a range from 300 to1000 w/m2. The fixed nominal
influent concentration corresponding to the four sets were 525 mg / L, 1170 mg / L, 1750
mg / L and 2539 mg / L respectively. As mentioned above, each reported data point
corresponds to an average over 3000 measurements, during a 500 min period. The
experiment results are discussed in below.
a) Water quality
In order to quantify the water quality the pH, EC and SDT was measured. In each set, the
measurement were carrying out at the start, middle and end of the test. The concentration
remained with a maximum standard deviations of ±10 mg / L (± 19.9 µS/cm). The
experimental result is shown in table 1.
I Congreso Nacional COMEII 2015, Jiutepec, Morelos, México, 23 y 24 de noviembre
7
Table 1: Evaluation of water quality
Test pH CE (µS/cm)
SDT
(mg/L) T (°C)
A 8.54 1105 525 30.8
1 B 8.55 1217 565 31
C 8.53 154 85 30.9
A 8.45 2330 1170 29.7
2 B 8.42 2630 1320 29.7
C 8.38 350 180 29.7
A 8.37 3490 1750 28
3 B 8.35 4100 2050 28
C 8.31 320 160 28
A 8.1 4885 2539 25.2
4 B 8.1 5759 3003 25.2
C 8.1 281 96 25.2
Influent (A), Effluent (B) and permeated (C)
Based on experiment observations, the "fouling” in pre-treatment filters, have an
important effect on the water quality. The suspended solids eventually can saturate the
filters. Consequently, the effective working pressure are drastically reduced as show in the
Fig, 2.
Fig, 2. Effect of fouling in the pre-treatment filter on the hydraulic head loss. A dirty filter
respect to a new one.
I Congreso Nacional COMEII 2015, Jiutepec, Morelos, México, 23 y 24 de noviembre
8
A typical maintenance of the system consists in changing the pre-treatment filter with a
new one. This modification led to an increment in the inlet pressure on to NF membrane.
The NF membranes do not avoid entirely the flow of salt, monovalent compounds present
in the mixture cross through to the membrane. Water and salt have different rates of mass
transfer across to NF membrane, it allows the "rejection” phenomenon. As the working
pressure increases, the rate of water transfer increase also without changing the flow rate
of the salt. In consequence, the permeation of the salt through the membrane was lower as
is show in the experiment four (table 1).
The sulfates remotion effectiveness, based on CE measurement, can be expressed as
× 100 (3)
Where represents the amount of salts rejected and , the influent
concentration. It can be observed that the highest efficiency (94%) was obtained in the test
4th. The results are presented in Table 2.
Table 2: Efficiency of sulfate remotion
Influent
(µS/cm) Permeate Efficiency %
Test 1 1,105 154.5 86
Test 2 2,330 350 85
Test 3 3,490 320 90.8
Test 4 4,885 281 94.2
In order to quantify the amount of sulfates and chlorides, a detailed study for test 4 was
conducted. According with NMX-AA-073-SCFI-2001 (Mexican standard) were determined
chlorides and with NMX-AA-074-1981 (Mexican standard) was used for the sulfates.
Considering the NMX-AA-051-SCFI-2001 and flame method, the elements useful for the
SAR was obtained. The results are presented in Table 3.
Table 3 Determination of chlorides, sulfates and SAR
Test
chlorides
(mg/L)
sulfates
(mg/L) Ca Mg Na SAR
A 48.4 2491 344.503 220.927 53.074 0.549
4 B 52.5 2951 433.81 236.645 62.575 0.631
C 19.4 76.3 12.955 11.579 12.56 0.611
I Congreso Nacional COMEII 2015, Jiutepec, Morelos, México, 23 y 24 de noviembre
9
b) Solar system
The experimental tests runs were conducted under conditions of sunny and cloudy days.
During experimental tests the voltage provided by the photovoltaic panels was kept at an
average of 217.4 volts. The graph of Fig. 3 shows a typical day of test.
Fig. 3. Solar radiation on PV level (primary axis) and volts provide by panel (secondary
axis)
Figure 4 shows the power required by the system relative to the incident solar radiation. A
linear dependence is observed. However, scattering effects were due to the radiation
dispersed by cloudiness and the effects of tilt PV system.
I Congreso Nacional COMEII 2015, Jiutepec, Morelos, México, 23 y 24 de noviembre
10
Fig. 4. Power supplied to system as a function of solar radiation. The test correspond to
one day of sparsely cloudiness.
c) NF system
Permeate flow rate is affected inversely with the influent concentration. This is a
characteristic of the NF systems. Figure 5 shows the permeate production with respect to
the initial concentration. Based on the experimental results, the production of permeate
relative to the supply pressure has a linear trend. Further, the concentration inversely
affects permeate production. Observe that the increase of 525 mg / L to 2539 (mg / L)
production experienced a decline close to 7 lpm which affects the energy consumption of
the system.
I Congreso Nacional COMEII 2015, Jiutepec, Morelos, México, 23 y 24 de noviembre
11
Fig. 5. Production of permeate as a function of the feed pressure.
Fig. 6 shows power consumption per unit of permeate volume. It can be observed that the
power consumption is a linear function to influent concentration: higher sulfates
concentration requires higher energy consumption. The maximum consumption was 3.4
Kwh/m3. In previous works, has been reported consumption between 0.5-4 kWh / m3 [11] .
I Congreso Nacional COMEII 2015, Jiutepec, Morelos, México, 23 y 24 de noviembre
12
Figura 6 Energy consumption for deferent influent concentration
The direct coupled configuration of the NF-PV was established by irrigation requirements.
As a general rule, the crops should be irrigated when the irradiance is low, in order to
reduce losses of water by vaporization and minimize plant stress. In this context, instead
of accumulating electric energy in batteries for later use, treated water during the day can
be stored in elevated tanks. In fact, is cheaper store water in tanks that accumulate energy
in a batteries. The NF-PV system produce from of 2.16 - 4.8 m3/d, making it possible to
irrigate between 1 and 2 hectares of crops.
4. Conclusion
An experimental study of a NF-PV desalination system without electrical storage support
was presented. Experiments were carried out for different influent concentration and solar
radiation. Based on experiment observation, the quality of permeated obtained satisfice
the standards of Mexican norm for irrigation. The permeate production is affected
inversed to influent concentration. In fact, was observed a decrement of permeated of 7
lpm going from 525 mg/l to 2539 mg/l. The fouling have an important effect on the
production, was observed a hydraulic head loss maximum of 20.9 m H20. The energy
consumption is affected stronger by the initial concentration as well as fouling in the
pretreatment filters. Concern to energy consumption the maximum value was 3.4 Kwh/m3
with a concentration of 2539 mg/l. The NF-PV system produce from of 2.16 - 4.8 m3/d,
making it possible to irrigate between 1 and 2 hectares of crops.
I Congreso Nacional COMEII 2015, Jiutepec, Morelos, México, 23 y 24 de noviembre
13
Acknowledgement
The authors appreciate the partial support by “1772 Cátedras CONACYT-Mexico” project.
U. Dehesa-Carrasco wishes to thanks J.J. Quiñones Aguilar and E. Delgado-Quezada for
technical support.
Reference
[1] Shaffer D. L., Yin Yip N., Gilron J., Elimelech M., Seawater desalination for agriculture
by integrated forward and reverse osmosis: Improved product water quality for
potentially less energy, Journal of Membrane Science 415–416 (2012) 1–8.
[2] Zarzo D.,Campos E., Terrero P., Spanish experience in desalination for agriculture,
Desalination and Water Treatment, 1944-3994/1944-3986 2012 Desalination
Publications.
[3] Carrera-Villacrés D.V., Crisanto-Perrazo T., Ortega-Escobar H., Ramírez-Garcia J.,
Salinidad cuantitativa y cualitativa del sistema hidrográfico Santa María-Río verde,
México, Tecnología y ciencias del agua, Vol. 6, 2015, pp 69-82.
[4] Flores-Prieto J.J., Ramírez-Luna J.J., Calderón-Mólgora C., Delgado-Quezada, E.,
Morales-García A.J., Tratamiento de agua salobre mediante nanofiltración solar a baja
presión para irrigación, Tecnología y ciencias del agua, (2015).
[5] Ghermandi A., Messalem R. The advantages of NF desalination of brackish water for
sustainable irrigation: The case of the Arava Valley in Israel, Desalination and Water
Treatment, 10 (2009) 101–107
[6] Garcia C., Molina F., Zarzo D., 7 year operation of a BWRO plant with raw water from
a coastal aquifer for agricultural irrigation, Desalin. Water Treat. 31 (2011) 331–338.
[7] Veza J.M., Water desalination for agricultural applications, Chapter in Water
Desalination for agricultural Applications,Proceedings of the FAO Expert
Consultation on Water Desali- nation for Agriculture Applications, 26–27 April,
Rome, 2004.
[8] Birnhack L., Shlesinger N., Lahav O., A cost effective method for improving the
quality of inland desalinated brackish water destined for agricultural irrigation,
Desalination 262 (2010) 152–160.
[9] Richards, B. S. and Schafer, A. I., Photovoltaic-powered desalination system for
remote Australian communities, Renewable Energy, Vol. 28, 2003, pp. 2013-2022.
I Congreso Nacional COMEII 2015, Jiutepec, Morelos, México, 23 y 24 de noviembre
14
[10] Koyuncu, I., Yazgan, M., Topacik D., and Sarikaya, H. Z., Evaluation of the low
pressure RO and NF membranes for an alternative treatment of Buyukcekmece Lake
Water Science and Technology: Water Supply © IWA Publishing, Vol 1, No1, 2001, pp
107-115.
[11] IEA-ETSAP and IRENA, Water desalination using renewable energy, Technology
Brief I12 – March 2012.
[12] Silva, J.T., Montocayo R., Ochoa S., Estrada F., Cruz-Cárdenaz G., Escalera C.,
Villalpando F., Nava J., Calidad química del agua subterránea y superficial de la
cuenca del rio Duero, Michoacán. Water Technology and Sciences, Vol. IV, No. 5,
2013, pp. 127-144.
[13] Ludwig, H., Energy consumption of reverse osmosis seawater desalination —
possibilities for its optimization in design and operation of SWRO plants, Desalination
and Water Treatment, Vol. 13, 2010, pp. 13–25.
[14] HRAYSHAT E. S., Brackish water desalination by a standalone reverse osmosis
desalination unit powered by photovoltaic solar energy, Renewable Energy, Vol. 33,
2008, pp.1784-1790.
[15] MAC-HARG, J. P., Energy Optimization of Brackish Groundwater Reverse Osmosis
Desalination, Final Report for Contract Number 08048308452011; Texas Water
Development Board, 2011, pp. 25.