1. No category

Cost Estimation Briefing for Large
Seawater Reverse Osmosis Facilities in Spain
José Díaz-Caneja and Manuel Fariñas
PRIDESA, Ramón Rubial nº 2, 48950 Erandio, Spain
Tel. +34 94 60 50 700; Fax + 34 94 46 76 406
Email: [email protected]
Abstract
The Spanish desalination market is currently one of the largest and most experienced ones for
RO, due to the high water demand in the Mediterranean Coast of Spain, driven by the
seasonal variations in population because of the tourism and the intensive agriculture. This
reason, jointly with the water scarcity in the area, has obliged Spain to develop a large number
of RO facilities, for supplying fresh water in this large part of the country. In addition, the
Canary and Balearic Islands are also areas in which RO desalination has a very important role
as a drinking water supply.
The purpose of this document is to show estimation for the cost of producing desalinated
water in the Spanish market. It provides breakdown of the desalinated water cost in Spain,
based on the data gathered form PRIDESA’s experience on several large size, new RO
facilities, and specifically from 3 of the largest and latest RO plants tendered in the country.
Data has been collected from plants with a production flow between 65 and 170 MLD (14 to
37,5 MIGD), with different characteristics, as the raw water intake system, trains sizes, etc,
that allows having three different case scenarios and an average result.
Finally, this result shows that the desalination costs, which in the near past have been
considered as a solution only for very specific areas in which the availability of fresh water
was reduced, nowadays can be considered as an alternative to the traditional sources, with the
advantage of the reliability and independency from external factors.
1. Introduction
For over 30 years, Spain has been developing cost-effective and sustainable solutions using
reverse osmosis desalination as one of its strategies for addressing the country’s
water resource challenges. Over that period, an industry has evolved, breeding companies that
have accumulated a wealth of knowledge and experience in the research, design, construction,
operation and maintenance of desalination plants. PRIDESA has been at the heart of this
process, having pioneered a number of innovations and contributed to Spain becoming a
world leader in reverse osmosis desalination. Just as the Middle East is acknowledged as
leading the world in thermal desalination technology, Spain now holds the same status in the
field of membrane desalination.
This maturity in the Spanish desal market has driven to have the possibility to achieve lower
cost in the process that have made RO desalination a real alternative to the traditional water
supply resources.
The required investment to build a desalination facility logically depends on its size, but not
in a direct way. Even being modular, the specific investment for these facilities (required
investment per m3/day production) decreases as the size of the plant increases, which means
that the scale factor plays a relevant role in the investment calculations.
121
Nowadays, municipal plants size’s are continuously increasing due to the cost saving
associated to large scale facilities, however, some relevant cost variations depend on the
adopted options for any given plant size.
The options likely to generate such variations in relation to the standard cost are the
following:
Sea water Abstraction system
Due to the huge seawater volume required to operate large desalination plants, we must
consider the adoption of surface water intakes instead of coastal abstraction boreholes, since
the required number of these and the surface involved would be too large. Once decided, the
surface water intake may be done in two different ways:
Channel Intake
Underwater penstock
It is obvious that the investment required for either option differs greatly, the underwater
penstock being usually the most expensive, especially when the sea bottom near the site is
rocky or has strong undercurrents.
Pre-treatment
Pre-treatment requirements may be more or less complex and, therefore, more or less costly,
depending on water pollution. In general, we try to deal with the best possible quality water
by choosing the best abstraction methods and location for each case. Having said this, there
are some cases in which this situation is not possible, requiring more systems that are more
sophisticated, which, logically, results in an increase of the cost of the mentioned
pretreatment.
Reverse Osmosis
Depending on raw water characteristics and product water requirements, the design of the RO
process can vary substantially. In high salinity waters with high quality requirements, product
water can require more than one RO pass with the associated cost increase.
Energy recovery devices have improved its efficiency, although the newest systems, while
achieving better recovery figures, normally have a higher CAPEX cost, so the selected system
must be evaluated depending on the O&M requirements, in order to achieve the lowest total
(CAPEX + OPEX) cost.
Polishing treatment
R. O. desalinated water is corrosive and poor in calcium and bicarbonate and it may not be
directly suitable, neither for drinking nor for irrigations purposes, before conditioning.
When we want to use desalinated water for human consumption, we shall have to:
Increase its calcium contents to make the water harder, giving it a better taste, reducing
at the same time its corroding power.
Increase its bicarbonate contents to render the water less corrosive while stabilizing its
pH.
Ensure disinfection (absence of all pathogen agents)
Calcium, as lime slurry, CO2 gas to react with the lime to form calcium bicarbonate and
chlorine as sodium hypochlorite for disinfection, are added to all desalinated water that is
going to be used for human supply.
122
When the water is to be used for irrigation, we shall only need to add calcium as lime slurry to
it.
Although the polishing treatment is different for municipal or agricultural purposes, the
required investment variation between both is not very significant, but its operation costs is,
since the required CO2 dosage for human supply water is high and so is its cost.
Product water external pumping
Once conditioned, desalinated water must be pumped out to the network. Seawater
desalination plants are usually located as close as possible to the coast in order to minimize
the environmental risks related to dealing with sea water and reject brine.
On the other hand, it is best to build desalination plants as close as possible to the point where
the product water is going to be consumed in order to minimize the transfer infrastructure and,
therefore, the required investment. However, this option is not always possible. Sometimes,
locating a desalination plant near coastal cities with a harbour may mean working with highly
polluted water, which is neither technically advisable nor economically profitable.
Of course, the longer the required transfer infrastructure is, the greater the investment will be
and vice versa.
Brine disposal
Brine reject from a desalination plant represents its most relevant environmental drawback
when it cannot be adequately dispersed into the sea. Therefore, it is most important to make
sure that the brine mixes rapidly with the remaining seawater to avoid all potential
environmental risks.
There are different available techniques to dispel the brine into the sea which application
depends on the type of coast where the plant is located (rocky, sandy, etc.), on the local sea
movements and on the shape and slope of the sea bottom, etc.
Choosing one of the available dispelling techniques may represent a major investment
variation factor.
Electricity
Seawater desalination plants are intensive power consuming installations requiring the
presence of a large electric line nearby.
If such infrastructure is not already available, it will have to be installed in order to bring the
necessary power to the plant. In this case, the required investment will be severely affected as
well.
Civil works
The civil works involved in the construction of water desalination facilities is usually very
conventional. The building housing the equipment and membranes is usually made of
prefabricated concrete to reduce corrosion risks, since the handled fluids (sea water and reject
brine) are extraordinarily aggressive.
Civil works variations (more detailed finishing, architecture, etc.) do not usually represent any
relevant investment variations. However, any shore works related to the need to gain some
land from the sea or to protect the site from waves beating, does represent a significant
investment
increase.
123
REFERENCIAL PROJECTS
1.1.
Carboneras S.W.R.O. facility
Figure 1: Air view of Carboneras seawater desalination plant
Source: PRIDESA
Figure 2: Air view of Carboneras seawater desalination plant
Source: PRIDESA
124
Table 1: General features of Carboneras Sea Water Desalination Plant Source: PRIDESA
Desalinated water flow ........................................................ 120.000m3/day
(42,9 hm3/year)
Abstraction type ................................................................... Open
Abstraction means
......................................................... Sub-marine penstock (2 Uts)
Number of lines .................................................................... 12 Uts.
Flow per line ........................................................................ 10.000 m3/day
Work conversion ................................................................. 45%
Power recovery system......................................................... Pelton turbines
Reject brine disposal system ................................................ Mixed with the nearby Power
Plant refrigeration water
Site altitude........................................................................... + 10,00 m
Desalinated water delivery altitude ...................................... + 65,00 m
Installed power .................................................................... 30 MVA
Specific power consumption ................................................ 4,08 kWh/m3
Electric power branching ..................................................... Substation next to Power Plant
Award budget ...................................................................... 79,9 million €
(VAT included, April 2.000)
Special features of this desalination facility are as follows:
Open type seawater abstraction using two submarine penstocks.
Brine dispersion problem solved with the minimum cost by mixing the brine with the
refrigeration water from a nearby power station.
Electric power taken from a nearby sub-station close to the Power Plant, although a new
sub-station had to be built next to the desalination plant.
Pelton turbines reject power recovery.
The absence of sufficient available flat land to build the desalination plant demanded
huge mountainside excavations, as may be seen in figure 2.
The total plant cost, including absolutely every item (price revisions, modifications and final
settlement), even costs not considered in the awarded budget as for example, works direction,
Public Authorities cooperation, the land cost and environmental impact assessment , etc.,
rose to 105 million € (VAT included).
The investment cost per m3/day desalinated water was:
or
SAN PEDRO DEL PINATAR S.W.R.O. FACILITY
The next case we shall see is San Pedro del Pinatar Sea Water Desalination Plant which image
under construction may be seen in figure 3. This plant’s singular characteristics deserve
special consideration.
This desalination plant was conceived to be later extended by several stages. The entire
infrastructure for the first extension has already been executed.
All it needs to increase its production is the addition of the necessary membranes and
pumping equipment. The next extension would consist in doubling the plant’s capacity.
The most outstanding characteristics of this facility are shown in table 2.
125
Figure 3: Air view of San Pedro del Pinatar (Murcia) Desalination Plant site under
construction Source: PRIDESA
Table 2: San Pedro del Pinatar (Murcia) Desalination Plant main characteristics Source: PRIDESA
Items
Desalinated water flow
(m3/day)
Annual product flow(hm3)
Abstraction type
Abstraction method
Number of lines (Uts.)
Flow per line (m3/day)
Conversion (%)
Energy recovery system
Reject brine disposal
system
Initial
Conditions
1st. extension
2nd. extension
65.000
85.000
170.000
23
Horizontal well
Horizontal drain
9
7.225
45
30,2
Horizontal well
Horizontal drain
10
8.500
53
Pelton Turbine
Pelton Turbine
60,4
Horizontal well
Horizontal drain
20
8.500
53
Pelton Turbine/
Hyperbaric Chamber
Sub-marine
outfall with
diffusers
+4,00
Sub-marine
outfall with
diffusers
+4,00
Site altitude (m)
Product water delivery
+86,00
+86,00
altitude (m)
Installed power (MVA)
30
30
Specific power
4,25
4,30
consumption kWh/m3
Power branching
5 Km. away line
5 Km. away line
(*)
Total budget
64,7
81,6
(VAT included; million €)
(*) The prices include revisions, modifications and final settlement
126
Sub-marine outfall
with diffusers
+4,00
+86,00
30
4,30
5 Km. away line
139,7
This desalination plant is rather singular, both as regards its initial conditions and its first
extension, which explains the high investment required for every m3/day of desalinated water
produced by it.
The plant’s most outstanding features in its original conception (65.000 m3/day initial
production) were:
Seawater abstraction system based on a very new technique consisting in raw water
abstraction through horizontal wells demanding a very limited available surface (100 x
15 m2).
The seawater intake is located far away from the desalination plant (about 1,7 Km.). Its
pipe runs along some urban areas where the street pavement had to be lifted. Directed
horizontal drilling was used for part of its layout.
The abstraction infrastructure (intake collector, boosting pipe, etc.) was dimensioned for
a 170.000 m3/day future extension.
Land purchase included the necessary space for a future extension.
A second stage with booster pumps will be added in subsequent extensions to increase
the plant’s conversion rate from 45 to 53%, as was planned from the beginning.
Power branching and a sub-station for a second extension are already installed and high
tension electric cables have been buried along 4 kms to comply with environmental
regulations.
Desalinated water is pumped from a tank within the plant to a second 65.000 m3
capacity, +86,00 elevation general tank 7,5 Km. away. Both tanks and the boosting pipe
are included in the initial costs estimation.
The environmental assessment declaration demanded that the reject brine disposal
outflow should be located 5,1 Km away from the coast, using a sub-marine outfall, to
preserve the valuable Posidonia Oceanica fields in the area (see fig. 4). This factor
represented a significant cost increase.
Figure 4: Posidonia Oceanica view at el Mojón beach (San Pedro del Pinatar)
Source: PRIDESA
Considering the singular requirements related to the preservation of the Posidonia, the proper
procedure to calculate the investment required to produce each m3/day of desalinated water,
would be to base the calculations on the final estimated capacity of the plant (170.000
m3/day), including all the necessary costs for a very complex facility.
The investment repercussion per m3/day desalinated water would be:
127
Pridesa’s tender for a 140 MLD S.W.R.O. facility
Other desalination plant we shall consider is one of the latest large-scale projects tendered in
Spain. This plant’s execution project is awaiting approval now. The most relevant features of
one of the options for this desalination plant may be seen in table 3.
Table 3: General characteristics of one of the solutions considered for Campo de Cartagena
Sea Water Desalination Plant.
Desalinated water flow ........................................................ 140.000 m3/day
(50 hm3/year)
Abstraction type ................................................................... Open
Abstraction means ................................................................ Sub-marine penstock (2 Uts.)
Number of lines .................................................................... 7 Uts
Flow per line ........................................................................ 20.000 m3/day
Conversion .......................................................................... 45%
Power recovery system ........................................................ hyperbaric chambers
Reject brine disposal system ................................................ Sea outfall with diffusers
Desalination site altitude ...................................................... + 35,00 m
Treated Water delivery altitude............................................ + 35,00 m
Installed power .................................................................... 25 MVA
Specific power consumption ................................................ 3,13 kWh/m3
Electric power branching ..................................................... Underground high-tension line
coming from a sub-station (2 / 3
Km)
Award budget ...................................................................... 71,9 million €
(VAT included,
February 2.002)
This plant differs from the formers in that it does not have any outstanding characteristics
demanding any significant additional investment, for which reason it may be considered as a
standard plant for its capacity.
This plant’s only singularity is not related to the required investment, although it does affect
the specific power demands, as we shall see. Incorporating the most up to date energy
recovery system in the market -hyperbaric chambers-, serves to reduce the plant’s specific
power consumption to the minimum possible.
The reason why this plant is cheaper than Carboneras although its production is higher and
despite the fact that it was awarded later, is due to two main reasons:
It does not incorporate any basic infrastructures for any future extensions.
It has fewer, higher capacity production lines, which makes the costs cheaper.
The initial investment recovery per m3/day desalinated water would be:
71.900.000
140.000
3
513,6 € / m / día
3
1,44 € / hm año
But this is only a tender price and tender prices often have a tendency to increase due to
various possible complications related, either to environmental impact difficulties, problems
with foundations or others, as well as layout modifications (access roads, pipes, etc.) and price
revision increases. According to our experience with other works of similar characteristics,
128
although smaller, the maximum increase should be less than 1,3 times the tender budget (10%
for final settlement and 10% for modifications, plus 10% for price revision). The maximum
repercussion would be, therefore, as follows:
1,3 x 513,5 = 667,6 €/m3 day (111.000 Ptas/m3 day) = 1,87 €/m3 year
2. Cost Structure
Desalinated water cost structure is as follows:
C
O
S
T
S
Fix costs
Variable costs
2.1.
Amortization
Operation staff
Power Connection
Maintenance
Miscellaneous
Chemicals
Conservation and Maintenance
Electric Power Consumption
Membrane replacements
Fix costs
2.1.1. Investment & Amortization
Having in mind the previous data, required CAPEX for producing desalinated water can be
summarized as follows:
Table 4: Investment required for building a large seawater desalination plant (VAT included)
Source: PRIDESA
Required investment
(Euros)
Cheapest
Average
Dearest
Per m3/day
Per m3/year
668
740
875
1,87
2,06
2,44
Amortization calculations
In order to calculate the desalinated water cost per m3 in relation to the invested capital, we
must compound the required investment at a given interest rate, during a period equal to the
estimated life of the plant. The annual amortization rate would, therefore, be:
Where:
I = Investment
n = number of amortization years
i = interest rate
129
The annual sum obtained is divided into the number of m3desalinated water produced during
one year to obtain the amortization sum.
This calculation method implies that:
The residual value of the plant will be zero at the end of the amortization period.
The plant will produce the same number of m3-desalinated water every year (as an
average).
Amortization period
It was thought until recently that the technological evolution might render a desalination plant
obsolete within a relatively short period, for which reason its amortization period should
coincide with its expected technological life.
However, the case of Las Palmas III (36.000 m3/day originally) and Sureste de Gran Canaria
(33.000 m3/day) seawater desalination plants have shown quite the contrary.
The first of the two was started in October 1.989, 15 years ago now, and it has been
technologically updated without any difficulties nor any additional cost until now, since the
investment required to implement all technological updating was financed with the economies
generated in the production costs by the innovation itself, even leaving a surplus for other
investments.
The same thing happened to Gran Canaria desalination plant, which has undergone three
different technological innovations in its 10 year of existence, without increasing its water
price, because all the required and additional works were financed with the savings accrued
per m3 of desalinated water production as consequence of the introduction of the new
technologies themselves.
Due to the high quality, corrosion resistant, materials used for sea water desalination plants
construction (super-duplex type stainless steel, split chamber pumps, concrete buildings, etc.),
it seems that the amortization period for these plants should be estimated as 25 years
minimum.
If, as it seems to be, future technological innovations can only be related to certain
improvements of the membranes that would result in reducing work pressure, considering
longer amortization periods for sea water desalinations plants does not seem unrealistic.
In order to confirm the amortization rates variations in relation to the facilities estimated life
for the purpose of comparing the obtained data with the river water transfer project costs in
equal conditions, the amortization rate will be calculated for 15, 20, 25 and 30 years.
Interest rates
When considering what interest rate we should apply, we must distinguish between the rates
applied to the State and the rates applied to private firms.
For the State, it is reasonable to consider an interest rate that is equal to the interest applied to
the 30 years bonds plus 0,25%.
In any case, in order to analyze the amortization sensitivity versus interest rate variations, we
shall consider 3, 4, 5, 6 y 7% rates.
Amortization costs
Considering the parameters given in the above paragraphs, table 5 shows the necessary annual
contribution per 1 million Euros, according to different interest rates and different
amortization times.
130
Table 5: Annual quota per 1 million Euros amortization
Interest rates
(%)
3
4
5
6
7
Amortization years
20
25
67.216
57.428
73.582
64.012
80.243
70.952
87.185
78.227
94.393
85.811
15
83.767
89.941
96.342
102.963
109.795
30
51.019
57.830
65.051
72.649
80.586
Figure 5 shows the above data as a graphic.
Annual quote evolution for amortizating € 1 million
Annual quote ( Euros )
120,000
100,000
3%
80,000
4%
60,000
5%
6%
40,000
7%
20,000
15
20
25
30
Amortization period (years)
Figure 5: Quota evolution for € 1 million amortization
Tables 6, 7 and 8 show desalinated water amortization costs per m3, VAT included.
Table 6: Desalinated water amortization cost per m3 (C€/m3) LOWEST investment
Source: PRIDESA
Interest Rates
(%)
3
4
5
6
7
15
15,66
16,82
18,02
19,25
20,53
Amortization years
20
25
12,57
10,74
13,76
11,97
15,01
13,27
16,30
14,63
17,65
16,05
131
30
9,54
10,81
12,16
13,59
15,07
Table 7: Desalinated water amortization cost per m3 (C€/m3) AVERAGE investment
Source: PRIDESA
Interest rates
(%)
3
4
5
6
7
Amortization years
20
25
13,85
11,83
15,16
13,19
16,53
14,62
17,96
16,11
19,44
17,68
15
17,26
18,53
19,85
21,21
22,62
30
10,51
11,91
13,40
14,97
16,60
Table 8: Desalinated water amortization cost per m3 (C€/m3) HIGHEST investment
Source: PRIDESA
Interest rate
(%)
3
4
5
6
7
Amortization years
20
25
16,40
14,01
17,95
15,62
19,58
17,31
21,27
19,09
23,03
20,94
15
20,44
21,95
23,51
25,12
26,79
30
12,45
14,11
15,87
17,73
19,66
Operation staff
For large desalination plants, the number of operation staff is practically unrelated to the
plants production capacity. The number of staff required to operate 140. m3/day (50
hm3/year) desalination plant is shown in figure 6.
!
!"
#
!$
! $%
&#
(# ) ! # ! *
!$
# ' $ %
#$
'# $
$# $
Figure 6: Required staff to operate a large desalination plant graphic
(1) Head of Plant
(1) Maintenance Master
(1) Clerck
(1) Analyst
(1) Mechanic journeyman
(1) Electrical and instrument journeyman
(1) Polyester journeyman
(1) Civil works journeyman
(5) Operators
(5) Assistants
Total : 18 people
132
#
!$
Office cleaning is usually entrusted to an external specialized firm. The average staff costs,
including clearing operations, may be around 560.000 €/year.
Considering an average 140.000 m3/day (50 hm3/year) production, the staff cost per m3 is:
+
,
, +
2.1.2. Connection to grid cost
Water desalination plants operate on a full time basis, that is, 100% capacity every day of the
year, except for the 7 to 15 days needed for general revision (transformers, pipes and pumps
clearing and maintenance), once a year.
In these circumstances, the best option, in Spain, is to subscribe an electric power rate giving
access to a six period basis supply.
Since the subscribed power depends on the desalination plant specific power consumption, its
cost will depend on:
The plant specific power consumption
Its branching tension.
Assuming that the desalination plant has an up to date design, and that the supply tension
ranges between 36 and 72,5 kV (normal for this type of plants), we might choose the rate 6.2
which, according to 2004 prices, would represent an annual connection cost of 570.089,88 €,
VAT not included.
The repercussion of this item in every m3-desalinated water, would be:
,
2.1.3. Fix maintenance costs
Certain maintenance operations must always be performed whether the desalination plant is in
operation or not.
Civil works maintenance (painting, slight damage fixing… etc.).
Gardening
Pipes and surrounding spaces checking
Machines painting
Transformation centre maintenance
The annual cost of these operations for a plant of the above capacity is around 144.000 €/year.
Its repercussion per m3-desalinated water would be:
,
2.1.4. Miscellaneous
Fix costs for miscellaneous items usually include the following:
Work clothes.
Health and safety equipment (gloves, helmets, auriculars, glasses, etc.).
Office furniture, equipment and materials.
Telephone and ADSL bills, photocopy machine, etc.
Vehicles: 2 vans and fuel for transport to workshops
Vehicles maintenance
133
Vehicles Insurance
Desalination plant insurance (all risk insurance for materials and machines damage)
Licenses, taxes and permits
Fungible laboratory materials
The most relevant of the above items in terms of cost is the insurance, including machinery
damage. Its present cost for a 50 hm3/year plant is around 240.000 €/year.
This item’s repercussion per m3-desalinated water would be:
,
2.2.
Variable costs
2.2.1. Reagents cost
The chemicals normally used in desalination plants may be classified in various large groups:
Pre-treatment chemicals for surface water catchments are shown in table 9.
Table 9: Pre-treatment reagentsSource: PRIDESA
Type
Sulphuric acid (98%)
Sodium Hypochlorite (120
g Cl2/l)
Ferric Chloride (40%)
Polyelectrolyte
Sodium bisulphite
Dispersant
Purpose
pH Control
Sea water disinfection
Coagulant
Coagulation aid
Oxidants Neutralization
To prevent membrane fouling
Approximate
dosage
(g/m3 desalinated
water)
45 – 55
20 – 35
12,5 – 20
1–2
10 – 20
1-4
The mentioned reagents and dosage may vary according to the water intake method and to
raw water quality.
The reagents used to condition desalinated water vary depending on the final water use,
whether for drinking or for irrigation.
The least favourable scenario from the point of view of cost is when the water is going to
be used for urban supply. The reagents required in this case are shown in table 10.
Table 10: Polishing treatment reagents (Urban supply water) Source: PRIDESA
Approximate
dosage
Reagents
Purpose
3
(g/m desalinated
water)
Promotes product water reCarbon dioxide CO2
35 - 60
mineralization
pH correction and Langelier index
Calcium hydroxide (98 %)
45 - 70
control
Sodium hypochlorite
supply water disinfection
5
(120 g Cl2/l)
134
Dosage varies according to temperature and depends on whether the water will be mixed
with water of different precedence before distribution, or not.
The chemicals used to clean the membranes and the cleaning frequency depends on the
intake water quality.
The most commonly used reagents to deal with an open seawater intake system are:
Caustic soda
Dodecyl sodium sulphate
Sodium Laurilsulphate
Sodium triphosphate
Bi-sodium phosphate
Na4 EDTA
Peracetic acid
The chemicals used to treat the effluent are:
Coagulant
Polyelectrolyte
Lime
Sulphuric acid
Dosage and frequency also depend on seawater quality, reagents demands increasing as the
water quality gets worse and vice-versa.
For a conventional plant dealing with relatively clear, pollution free water, and reagents costs
may be approximately as shown in table 11.
Table 11: Approximate annual reagents costsSource: PRIDESA
Annual costs
Reagents
(€)
Pre-treatment
1.000.000
Conditioning
500.000
Membrane cleaning
60.000
Effluents treatment
30.000
Total
1.590.000
The repercussion of these costs per m3-desalinated water is:
,
2.2.2.
The expected life of the different elements in a desalination plant and their duration depends
on a correct maintenance program in three aspects:
Predictive maintenance
Preventive maintenance
Corrective maintenance
The annual costs of the variable part of maintenance vary during the life of each plant. As an
average, we may assume the data given in table 12.
135
Table 12: Annual maintenance costs. Applicable rate to the different items of equipment
Source: PRIDESA
Item
Applicable Rate
0,8
4,3
1,5
4,5
3,0
4,2
4,3
0,3
Containers and tanks
Rotating mechanic equipment
Machinery drive mechanic equipment
Instrumentation
Pipes, valves and accessories
Centrifugal pumps
Electricity
Civil works
According to these data, the annual maintenance cost for a 50 hm3/year desalination plant
would be around 1.100.000 €.
Its repercussion per m3-desalinated water would be:
,
2.2.3. Electric power
2.2.3.1.
Specific power consumption
Each of the mentioned desalination plants specific power consumption is shown in table 13.
Table 13: Large desalination plants specific power consumption (kWh/m3) Source: PRIDESA
Stages
Abstraction
and
treatment
Desalination (R.O.)
pre-
Plants
Case 2
0,57
Case 1
0,63
Case 3
0,45
3,10
3,19
2,56
Leakage and miscellaneous
0,12
0,14
0,12
Total within the plant
3,85
3,90
3,13
External pumping
0,23
0,40
--
Total
4,08
4,30
3,13
As we can see, there are no absolute specific consumption coincidences, the reason being that
consumption depends on the following:
On production racks size
The larger the production lines and the global capacity of each plant, the lower its specific
power consumption is. This is clearly seen when comparing 10.000 m3/day Carboneras’
racks plant with 7.225/8.500 m3/day desalination (R.O.) San Pedro del Pinatar plant.
On sea water abstraction type
There may be significant differences within the open intake modality, depending on the
abstraction type and head loss adopted.
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On the recovery system
The use of hyperbaric chambers reduces the plant’s specific power consumption in 0,4 – 0,5
kWh/m3 in relation to Pelton turbines. If we compare the data shown for case 3 (hyper-baric
chambers for 20.000 m3/day per line) with Case 1 (Pelton turbines for 10.000 m3/day per line)
we shall see that the combined effect of hyper-baric chambers with large scale production
lines results in 0,54 kWh/m3 power savings.
On raw water temperature fluctuations
The higher the seawater temperature is, the lower will be the work pressure and the specific
power consumption.
On location
When a desalination site is either very far from the intake point, or very elevated in relation to
sea level, the specific power consumption will increase.
On outwards pumping pressure
The pressure required for the pumps to boost desalinated water to the storage or distribution
systems depends on altitude, on distance and on the size of pumps.
In order to calculate specific desalination power requirements, it seems clear that we should
proceed in two steps:
The first step will be to calculate the specific power consumption required to
produce water.
The second step will be to calculate the specific power required to transfer
the product water to a point located at a given distance and at a given
elevation in relation to sea level.
a) Specific power consumption within the plant
As we have seen in the three chosen examples, specific power consumption within a
desalination plant ranges between 3,13 and 3,90 kWh/m3.
High pressure pumping equipment is already well tested for lines producing 10.000 m3/day
using Pelton turbines.
According to Case 3, it seems conservative enough to suppose that, in the near future, the
specific power consumption at the edge of the sea ( +5,00 m altitude) will be 3,13 kWh/m3.
b) Specific power required to transfer water to a different point
The additional power needed will depend on the delivery point location, altitude and distance.
From empirical studies, an approximate figure for the specific power consumption of
transferring water to a point located 25 Km away and 50 m of altitude would be around 0,67
kWh/ m3
2.2.3.2.
The annual connection to the grid cost for the mentioned plant, at 2004 prices, is:
7.945.256,91 € (VAT not included).
The repercussion of this per m3-desalinated water, within the plant, would be:
,
- .-/ 0- 1 23 4-/ 56
178
01
+
-13
3
137
-39 /5 -31 -,1-43 & #
2
2.2.4.
Membranes replacement rate depends largely on raw water quality and on the efficiency of
the applied pre-treatment.
When the raw water quality is poor and the applied pre-treatment does not improve it in a
significant way, the membranes will need frequent washing, which will result in shortening
their lives.
In general, we may say that for a properly operated open seawater intake plant, the annual
membrane replacement rate will range between 10 and 15%, which represents an average 2,7
C€/m3.
3. TOTAL DESALINATED WATER COSTS PER m3
3.1.
Without amortization
The cost per m3-desalinated water, within the plant, without amortization or VAT, is shown in
table 14.
Table 14: Desalinated water cost per m3 within the plant, before amortization
Source: PRIDESA
Cost per m3
Costs
Items
(C€)
Operation staff
1.12
Contracted power quote
1.14
Fix
Maintenance
0.29
Miscellaneous
0.48
Chemicals
3.18
Conservation and maintenance
2.20
Variable
Electric power
15.89
Membrane replacement
2.70
Total cost
27.00
3.2.
Total
As was already said, the amortization sum will depend on the interest rate, on the
amortization period and, of course, on the invested sum.
For an average investment sum, with a 25 years amortization period, at 4.0% interest rate,
which seems reasonable when dealing with the State on a long term basis, the amortization
sum would be 13,19 C€/m3, VAT included. (See Table 7)
Therefore, the total desalinated water cost per m3 within the plant, for 50 hm3/year, VAT
included, would be:
13,19 + 1,07 x 27,00 = 42,08 C€/m3
If a private firm with a concession formula operates a plant, general expenses and industrial
profit margins would increase the above sum. Considering this figure could be about 12% +
6% = 18%, the final cost (VAT included) would be:
(13,19 + 1,07 x (27,00 x 1,18) = 47,28 C€/m3
Figures 7 & 8 show the percentual cost for fix and variable and for each cost item:
138
EPC Amortization
29%
Fix Costs
8%
Variable Costs
63%
Figure 7: Fix Cost ( EPC Amort. + Others Fix Costs) Vs Variable Cost Graphic
Source: PRIDESA
Operation Staff
3%
Contracted
Power Quote
3%
Maintenance-Fix
1%
Miscellaneous
1%
EPC
Amortization
28%
Chemicals
9%
Membrane
Replacement
7%
Electric Power
Comsumption
42%
Figure 8: Itemized percentual costs graphic
Source: PRIDESA
139
Conservation &
Maintenace-Var
6%
4. CONCLUSSIONS
Having in mind all the previous data, we can obtain the following conclusions:
The new large scale RO desalination facilities to be designed in the near
future, featuring pressure exchangers as energy recovery devices will
produce desalinated water with an energy specific consumption of about 3,03,2 kWh / m3 (water at the desalinated water tank in the facility)
Regarding the percentual split of costs, amortization plus energy is about
73% of the total cost, so these are the items to low for achieving significant
reduction in the desalinated water cost.
In Spain, energy costs could be lowered if a CCGT Power Plant would be
exclusively dedicated to the RO facility power supply due to the constant
rate at which it could run and the lower amortization period this implies,
therefore energy costs would be lower
Fewer and larger RO trains results in a lower initial investment and therefore
in a reduction on its amortization
Total cost of desalinated water, including every item, taxes, etc., is lower
than € 0,50 per m3 (water at the desalinated water tank in the facility)
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