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Overview of the cost of desalinated water and costing methodologies
Desalination 205 (2007) 340–353
Overview of the cost of desalinated water and costing methodologies K.V. Reddy, N. Ghaffour* Middle East Desalination Research Center (MEDRC) PO Box 21, Al-Khuwair, PC. 133, Muscat, Sultanate of Oman Tel: þ968 695 351; Fax: þ968 697107, email: [email protected] Received 9 February 2006; accepted 6 March 2006
Abstract In the last decade desalination has been considered as a solution for potable water needs only for specific water scarcity countries having cheap fuel. Now, desalination is extensively used, even where it was unthinkable twenty years back, due to reduction in desalination cost. The cost reduction is due to new developments and improvements in desalination technologies, particularly in RO technology. The RO is a well accepted technology due to recent increase in energy prices and takes up a major share in worldwide market. But, it is not able to achieve its proper share in the Arabian Gulf market due to difficult seawater composition and extensive historical use of thermal desalination. But RO still has potential in hybrid systems in the Arabian Gulf to account for seasonal and night to day fluctuations in the demand for power and water. There is a need for an accurate methodology for evaluation of desalination costs to help in selection of appropriate technology suitable for a specific location, for process design and other requirements. However, existing methodologies and software packages do not account for all the parameters that contribute for desalting cost and their accuracy is limited to specific conditions. This paper presents an overview of the trends in desalination costs for major desalination technologies like Multi Stage Flash, Multi Effect Distillation and Reverse Osmosis and review of costing methodologies. Keywords: Desalination costing; Costing softwares; Cost trends; Technologies developments
*Corresponding author. Presented at EuroMed 2006 conference on Desalination Strategies in South Mediterranean Countries: Cooperation between Mediterranean Countries of Europe and the Southern Rim of the Mediterranean. Sponsored by the European Desalination Society and the University of Montpellier II, Montpellier, France, 21-25 May 2006 0011-9164/07/$– See front matter 2007 Elsevier B.V. All rights reserved
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1. Introduction The cost of desalination is decreasing in recent times due to the developments in desalination technologies and desalination is now able to successfully compete with conventional water resources for potable water supplies. However, the cost of desalination is site-specific, mostly based on the quality of the feed water available at the selected site. It is thus essential to select an appropriate desalination technology that produces desalinated water at a low cost for any site under consideration. Most desalination plants in the Arabian Gulf region are co-generation type, producing both power and water. The power and water demand ratio varies considerably in different seasons. To cope with such situation, hybrid desalination systems are generally suitable and in recent plants such a concept has been used. Right costing methodologies for both desalination and power plants, are thus required to select appropriate combinations and capacities of co-generation hybrid desalination configurations. Prices of fossil fuels have increased considerably during the last five years and the same trend may continue. In future, the use of nuclear or renewable energy for desalination may be cost-effective. Since there are many types of nuclear power generation reactors and renewable energy sources, cost estimations for many combinations of energy sources and the desalination process for any particular site will be required to evolve from economical configurations. The above requirements necessitate the need for an accurate methodology/software that evaluates the cost of desalinated water produced by each technology for the site-specific conditions to help in selecting a suitable technology for that specific location. However, existing methodologies and software
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packages do not account for all the cost parameters and their accuracy is limited to specific conditions. Reliable desalination cost data is required for policy makers, planners, consultants, plant suppliers, process engineers and researchers. Policy makers, planners and consultants need the cost data for conducting feasibility studies for the selection of appropriate technologies, process engineers to optimize the process configuration and equipment sizing for minimizing the cost of production and researchers for developing new technologies and improving the existing ones. The aim of the present paper is to give an overview of the trends in desalination costs, costing methodologies for different desalination technologies, with emphasis on Multi Stage Flash (MSF), Multi Effect Distillation (MED) and Reverse Osmosis (RO), which are the major desalination technologies that are used for seawater desalination. 2. Trends in desalination costs The earliest interest in desalination was to produce fresh water for boiler and for drinking purpose on ships. Vapor compression units were first used in naval vessels powered by diesel engines in 1940. The MSF process was invented in 1950 by Silver. Reverse Osmosis phenomenon was discovered in 18th century but the breakthrough occurred in 1950 with the invention of cellulose acetate membranes. The Electrodialysis membrane was discovered in 1950. The MED technology was adopted for desalination in 1900 which has been in extensive use in the chemical industry. By the Second World War, hundreds of mobile MED and vapor compression desalination units were in use. But the cost of desalinated water was US$0.5 per m3 for the
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prevailing low fuel prices of 10–20 US$/ton. It was considered very high at that time. The Office of Saline Water was established in 1952 with initial funding of US$2 million, which was later increased to US$160 million for desalination research. Since then, tremendous interest was shown by both government and private sectors in desalination research, which led to the introduction of ED technology in 1952, freezing desalination and RO in 1954. A MSF unit of 0.05 MGD for seawater desalination was demonstrated for the US Navy in 1954. The first commercial MSF unit of 0.5 MGD was built at Shuwaikh in Kuwait later in 1957. Since 1960, MSF process became highly popular and many commercial plants were built worldwide using this technology during the last four decades, particularly in the Arabian Gulf. During this period, many national programs were initiated to study and evaluate the use of nuclear energy in desalination by Office of Saline Water, International Atomic Energy Agency and Oak Ridge National Laboratory. ED was modified to current Electrodialysis Reversal (EDR) and accepted as a commercial process during this period. In 1966 a spiral wound RO process of 0.05 MGD capacity was demonstrated. By the 1970s, improved MSF, MED, VC, ED and RO were available for commercial production and many desalination plants were built worldwide using these technologies. The total desalination capacity by all processes contracted till 2005 is 53.69 million m3/day. The contracted capacity was low, with a meager 110,000 m3/day, in the first
ten years from 1950. But it picked up gradually and increased exponentially with more than 50% during 2000–2005. The contracted capacity figures from 1950 to 2005 are given in Table 1 [1]. The cost of desalinated water produced by these technologies in 1970 was high and various organizations continued their efforts to reduce the desalination cost. Considerable decrease in the desalination costs of these technologies took place in the last four decades and, presently, desalinated water cost reached about US$0.5 per m3. These low costs are contributing to narrow the gap between conventional water supplies and desalinated water even for the non-water stressed countries. The unit water cost comparisons were made by Sommariva as in Fig. 1 [2]. In many countries in the Middle East, identified as geographical area A in the figure, price concepts are not applicable, as natural resources are so limited that life and industry would not be sustainable without desalination. Geographical areas B and C are for regions that over exploit the natural resources and regions with abundant natural resources respectively. 2.1. Multi stage flash Even though MSF is thermodynamically inefficient, large numbers of plants were installed world over, in particular in the Arabian Gulf countries, because of its reliability. Since MSF is mostly used for desalination of seawater, the data for seawater desalination is only considered. The total contracted capacity of all MSF plants worldwide till 2005 is
Table 1 Contracted capacity of all desalination plants world-wide Duration 3
Contracted Capacity (Million m /day)
1950–59
1960–69
1970–79
1980–89
1990–99
2000–05
Total
0.11
0.89
5.12
8.04
12.56
26.97
53.69
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K.V. Reddy, N. Ghaffour / Desalination 205 (2007) 340–353 Water value area A Water cost/value (US$/M3)
1.6
no cost criteria applicable
1.4
Water cost from desalination
1.2 1 Breakeven points
0.8 0.6
Water cost from re-use
0.4
Water value area B
0.2 0 1994
Water value area C 1996
1998
2000
2002
2004
Year
Fig. 1. Trends in desalination and conventional water costs. [2]
17 million m3/day with about 32% of the total desalination capacity. The contracted capacity of MSF desalination plants is given in Table 2 [1]. The first MSF plant was contracted in 1957 and the contracted capacity 1957–59 was only 27,000 m3/day. In the next decade, 1960–69, it was only 694,000 m3/day. But it increased considerably to about 20% of the total contracted capacity during 1970–79 and about the same percentage increase continued till 1999. The growth was steep in the last five years with a contracted capacity of 6.396 million m3/day. The cost of water produced by MSF was high in 1960 but many improvements took place later in the process design. Though the basic concept of the process has not changed till today, the top brine temperature was gradually increased to 112 C with the availability of better anti-scalants and newer materials of construction. This led to the
reduction of cost of desalination, particularly in the investment cost. Operating costs also decreased to some extent due to improvements in the process performance. The actual investment costs of some of the MSF installations world over in the last four decades as provided by Wangnick [1], are plotted by the authors in Fig. 2. It is clear from this figure, that the data is very much scattered and mostly clustered around investment cost of 1000–2000 US$/m3/day up to 1990 and around 1000–1500 US$/m3/day after 1995. This indicates that in spite of inflation, the investment cost reduced marginally over a period of time. Zhou and Tol [3] calculated the annual amortized capital costs with annual discount rate of 8% and a plant life of 25 years using the investment cost data reported in Wangnick Report 17. Since operating costs are not included in the Wangnick data, they assumed that the total cost comprises 40%
Table 2 Contracted capacity of all MSF desalination plants world-wide Duration
1950–59
1960–69
1970–79
1980–89
1990–99
2000–05
Total
Contracted Capacity (Million m3/day)
0.027
0.694
3.213
3.546
3.124
6.396
17.00
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K.V. Reddy, N. Ghaffour / Desalination 205 (2007) 340–353 4000 US$ per cubic meter per day
3500 3000 2500 2000 1500 1000 500 0 1965
1970
1975
1980
1985
1990
1995
2000
2005
2010
Year
Fig. 2. Investment cost of MSF per m3/day capacity over years.
capital cost for interest and depreciation on the investment and 60% for running costs. The load factor was assumed as 90%. They adjusted all Wangnick reported costs according to the United States Consumer Price Index with 1995 as base year. The unit water costs thus calculated are plotted by them in Fig. 3. It is clear from Fig. 3 that over 40 years the unit water costs of MSF decreased by a factor of 10. The main contributor for such reduction is due to about 50% reduction in the installation costs despite the increased cost of raw materials by 40% and the labor
cost increase by more than 100%. The main factors for such reduction are the following: Severe competition among MSF plant contractors and from RO plant suppliers forced the contractors to propose improvements/deviations to the technical specifications of MSF plants and implementation of such suggestions led to the reduction in the installation costs. The other contributor is engaging subcontractors from Far Eastern countries who had developed technical skills, instead of engaging subcontractors on a regional/national basis.
Unit cost ($/m3)
12.0
9.0
6.0
3.0
0.0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Year
Fig. 3. Unit water cost by MSF process over years. [3]
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The feedback from earlier projects helped in improving the process and equipment design of the MSF process. These improvements are specifically related to the increase in unit capacity of MSF plants over the years, 2–3 MGD in 1960– 70, 2–5 in 1971–80, 3–7.5 in 1981–90, 3.5–12 in 1991–00 and 7–20 after 2000. The use of Duplex steel instead of AISI 316, 316L and 316Ti reduced the cost. Duplex steel is cheap, has better mechanical properties and higher corrosion resistance than AISI 316, 316L and 316Ti, which were being used earlier. The use of thinnest titanium tubes in place of wellknown copper nickel alloy for heat transfer tubes also contributed to the reduction in the investment cost. The relaxation of stringent specifications by users with respect to fouling factors, distiller hydraulic test pressures, distillate purity, brine load, construction material specifications, heat exchange tube thickness, bypass on control valves, removable water boxes and redundancy of equipment and instrumentation helped the contractor to arrive at appropriate options which led to the reduction in the investment cost. The BOOT contract specifications, which changed from technical to functional, has allowed the contractor to further optimize the plant and helped in reducing the cost. Increased top brine temperature from 90 to 112 C over the last 10 years helped in improving the performance of the MSF plant and also contributed to the reduction of unit water cost.
The above improvements helped in reducing the unit water cost produced by MSF to less than US$1.0 per m3. Unit water cost depends on the investment cost and operating cost. The investment cost of MSF plants is
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about US$900 per m3/day capacity based on the average value of the contracted plant in the Middle East in the last years [4]. The share of operation cost in the unit water cost will be 55–60% depending on the cost of capital, plant life assumed and on energy cost. Recently Borsani and Rebagliati [4] estimated the unit water cost at US$0.52 per m3 for MSF for Middle East conditions. This unit water cost may be on the lower side. Their costs are compared with Wade [5] in Table 3. The total cost according to Wade is 1.044 US$/m3. Presently, the unit water cost could be between these two values, but may be closer to that given by Wade. The components of operating costs and their contributions are compared in Table 4. It is interesting to note that they are considerably different. The cost of chemicals reported by Sommariva [2] is on the high side. Similarly, the cost of personnel and spares reported by Borsani and Rebagliati [4] are on the low side. 2.2. Multi effect distillation Multi effect distillation is thermo-dynamically a more efficient process compared to MSF. The performance ratio is directly proportional to the number of effects unlike for the MSF. But it has some scaling problems compared to MSF. Small capacity MED plants were built since 1900 in ships. But the first land-based MED desalination plant was built in 1930 in Saudi Arabia. The total contracted capacity of MED without vapor compression by the end of 2005 was only 1.175 million m3/day, which is much less than that of MSF. The contracted capacities in each decade from 1950 to 2005 are given in Table 5 [1]. The contracted capacity was roughly constant around 20% after 1970. Most of the MED
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Table 3 Typical unit water cost comparison Desalination
Wade
Borsani and Rebagliati
Production capacity (m3/day) Number of units/trains Performance ratio Top brine temperature Number of stages Heat consumption, MJ/m3 Power consumption, kWh/m3 Load factor, % Energy cost, US$/GJ Power cost, US$/kWh Plant life, years Discount rate, % Amortization, % Capital cost, US$ in million Distillers installed Seawater intake and out fall Foundations and building Financing during construction Engineering and consultancy Total capital cost Operating Cost in US$/m3 Heat energy Electrical energy Operation and maintenance Spares Chemicals Sub-total operating cost Capital charges in US$/m3 (Total capital cost/ production capacity) Total in US$/m3
31,822 1 8.0
205,000 3 8.5 112 19
290 3.6 90 1.5 0.03 25 8 9.37
0.03 20 7 10.59
34.5 2.8 5.6 4.3 4.3 51.4
180
0.242 0.109 0.126 0.082 0.024 0.583 0.461
0.136 0.119
0.032 0.287 0.233
1.044
0.52
plants are small or medium size unit capacity. The largest MED unit capacity is only 5 MGD compared to 17 MGD of MSF. There are two types of commercial vapor compression desalination plants: thermal vapor compression and mechanical vapor compression. MED technology is used in vapor compression plants, particularly in thermal vapor compression. Since MED with mechanical vapor compression has not much effect on the specific power consumption, only single effect is generally used. On the other hand, MED with thermal vapor compression decreases the specific energy consumption and most of the recent MED plants are coupled with thermal vapor compression. The contracted total capacities of mechanical and thermal vapor compression plants are 504,358 and 1,455,433 m3/day respectively. It was attempted to plot the actual investment cost data given by Wangnick for MED plants against contracted year as was done in the MSF case. But it was not possible to get any trend correlation due to the limited data and different plant sizes and specifications. However, from the data reported in the literature, the cost reduction trend over years is similar to MSF with improvements in similar parameters as discussed below. Most of the MED plants built till 1970 were for brackish or river water desalination
Table 4 Comparison of operating cost contributions Component
Thermal Energy Electrical Energy Chemicals Personnel & Spare parts
% contribution Borsani and Rebagliati
Wade
Sommariva
46 40 9 5
42 19 4 35
38 14 30 18
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K.V. Reddy, N. Ghaffour / Desalination 205 (2007) 340–353 Table 5 Contracted capacity of all MED desalination plants worldwide Duration
1950–59
1960–69
1970–79
1980–89
1990–99
2000–05
Total
Contracted Capacity (Million m3/day)
0.083
0.108
0.292
0.242
0.239
0.207
1.175
and they used submerged tubes with unit capacities of 1 MGD or less due to scaling problems with seawater desalination. Heat transfer coefficients were low in submerged tube evaporators and hence vertical and horizontal tube falling film evaporators were introduced to improve the heat transfer coefficient. Higher heat transfer coefficients in the falling film allowed in reducing the top brine temperature to less than 70 C, which helped in reducing the scaling problems. The first large capacity MED plant for seawater desalination with 3.5 MGD capacity and vertical tube evaporator was built in Kazakhstan in 1964 and similar plants were built later in 1966, 1967, 1968 and 1970 in the same country. Since horizontal tube falling film evaporators have higher heat transfer coefficients compared to vertical tube evaporators for large scale applications, they became popular in the industry. Horizontal tube falling film MED of 0.1 MGD for seawater desalination was first built in Belgium in 1970. Large scale MED of 4.5 MGD with horizontal tube evaporator was built in Israel at Ashdod in 1980. In the last ten years, many developments took place in MED with respect to coupling of thermal vapor compression with MED, use of improved horizontal tube falling film evaporation, stabilization of low temperature operation, use of aluminum for heat transfer tubes resulting in realization of modern MED plants and reduction of unit water costs. Modern MED plants are reliable, matured and have better performance than MSF even for the harsh Gulf water
conditions. This led to the construction of 2 MED units of 5 MGD unit capacity in 1999 at Layyah in Sharjah. They have also opened the way for its application for large BOT projects in the Gulf Region, as e.g. Taweelah A1 where its high reliability is fully manifested. Many large-scale MED plants of 6 MGD with thermal vapor compression were built in UAE at Ajman in 2003, at Al-Nakheel in 2003 and at Ras Al-Khaimah in 2003. An excellent review of the performance of some of the operating MED plants is reported by Al-Shammiri and Safari [6]. Increase in unit capacity, increase in heat transfer coefficients with horizontal tube evaporators and use of appropriate materials for low temperature operation have considerably reduced the unit cost of desalinated water using MED. The unit water cost of MED was always lower than MSF after the introduction of falling film evaporation and this further decreased after the integration with thermal vapor compression, or heat pump. The unit water cost of the recent MED plants is 0.55–0.7, which is less than for MSF and very close to RO. The capital cost is about US$850 per m3/day capacity and energy consumption is less than MSF. 2.3. Reverse osmosis The RO desalination was commercialized much later than MSF and MED. The first commercial brackish water RO plant with spiral wound membrane was contracted to build at Kashima in Japan in 1969 to cater to the water needs of a power plant. After 6
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years in 1975, a seawater RO plant of 1500 m3/day capacity was contracted to build at Al-Kharj in Saudi Arabia. The total contracted capacity of RO plants by the end of 2005 reached 23.36 million cubic meters per day, which is the highest capacity compared to any other process. But the seawater desalination share is only 9.611 million cubic meters per day. The contracted total capacity and contracted seawater desalination capacity from 1950 to 2005 are given in Table 6 [1]. It is clear from the values given in Table 6 that the total and seawater RO capacity have grown fast in the last 30 years and it has exponentially increased for both total and seawater RO capacity in the last five years with 50% growth in the total capacity and 70% in seawater RO capacity. In Fig. 4, actual investment cost of seawater RO plants given by Wangnick is
plotted by authors against contracted year. The investment cost data is more scattered before 1995. After 1995, it is more clustered between 500 and 1000 US$ per m3/day capacity. This indicates that the investment costs decreased in the last ten years. With the same assumptions as were made in MSF for calculating unit water cost, Zhou and Tol [3] calculated the unit water cost for RO and plotted them in Fig. 5. The unit water cost decreased considerably over the years and at about 0.5 US$/m3, it is presently lowest of all the processes. There are many developments over the last three decades that contributed to the reduction of unit water cost of RO desalination, particularly membrane module performance and reduction in energy consumption. The performance of the membrane modules improved with respect to increased salt rejec-
Table 6 Contracted capacity of RO desalination plants worldwide Duration Total Seawater
US$ per cubic meter per day capacity
Contracted Capacity Million m3/day
1950–59
1960–69
1970–79
1980–89
1990–99
2000–05
Total
– –
0.016 –
1.241 0.48
3.168 0.577
7.227 2.162
11.713 6.824
23.365 9.611
4000 3500 3000 2500 2000 1500 1000 500 0 1975
1980
1985
1990 1995 Year
2000
2005
Fig. 4. Investment cost of seawater RO plant per m3/day capacity over years.
2010
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Unit cost ($/m3)
5.0 4.0 3.0 2.0 1.0 0.0 1965
1970
1975
1980
1985 Year
1990
1995
2000
2005
Fig. 5. Unit water cost by RO over years. [3]
tion, increased surface area per unit volume, increased flux, improved membrane life, capacity to work at high pressure and also decrease in membrane cost. The recovery ratio increased considerably over the years due to improved salt rejection. The recovery ratio for seawater desalination was about 25% in 1980s and it increased to 35% in 1990s. Currently it is about 45% and it will be more if 2nd stage is included. Improved recovery facilitated a decrease in the investment cost and also operating costs. The capital cost reduction is due to a reduction in RO trains and intake system sizes. The operating cost reduction is due to a reduction in usage of chemicals and pumping energy. The surface areas per unit volume increased considerably with the introduction of hollow fine fiber modules and spiral wound modules. The increase in surface area per unit volume and increase in flux contributed to the reduction of investment cost. Improved membrane life and capacity to work at high pressure also helped in reducing the operating cost. The membrane costs should increase due to inflation over a period of time. But they have fallen down by 86% between 1990 and
2005, which contributed considerably for unit water cost reduction. Recently the specific energy consumption has been considerably decreased with the introduction of better energy recovery system from reject brine such ERI (Energy Recovery Inc.) or DWEER (Dual Work Exchanger Energy Recovery). The developments in various parameters of RO as desalination presented by Sommariva [2] are given in Fig. 6. Apart from improvements in RO technology, increase in plant capacity also contributed to the reduction in unit water cost. The magnitude of the respective costs due to improvements in the membranes and increase in plant capacity are difficult to measure since they have both taken place simultaneously. The plant capacity increased by a factor of 10 between 1995 and 2005. As in the case of thermal desalination, competition among the plant suppliers, subcontractors, membrane suppliers also contributed to the reduction in unit water cost. The investment cost of recent seawater RO desalination plants is about US$800 per m3/ day capacity. In order to have a better idea of the latest cost figures, the data reported by Dreizin [7] for Ashkelon seawater RO
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K.V. Reddy, N. Ghaffour / Desalination 205 (2007) 340–353 10.00 Cost Productivity Recip.SP Life Energy
9.00 Unit Improvements
8.00 7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 1980
1985
1990
1995
2005
2010
Year
Fig. 6. Membrane improvements over years. [2]
desalination plant and calculated by Borsani and Rebagliati [4] for Arabian Gulf conditions are given in Table 7. 3. Review of desalination costing methodologies In the 1960s only MSF was available for commercial application and the bidding process would normally call for an investment cost proposal with performance data. In the Table 7 The average total water price of Ashkelon RO plant US$/m3 Cost Item
Ashkelon
Borsani and Rebagliati
Base fixed price Base variable price Energy Membranes Filters Chemical Post treatment Others Sub total Base total water price
0.311
0.22
0.134 0.28 0.005 0.21 0.009 0.17 0.214 0.525
0.148
0.078
0.446
1970s there were other desalination technologies in the market and there was a need for better evaluation process for their merits based on the cost analysis. However, only investment cost and performance were used for comparison and evaluation. Recognizing the importance of various factors at play, in 1972 Office of Saline Water issued a Desalting Handbook For Planners that included a chapter on factors influencing the process selection and water cost, including a format for calculating capital cost and total cost of water. Larson and Leitner prepared an updated report for the Office of Water Research and Technology in 1979, which contained comparison of MSF, MED and RO in a standard format. This report was updated again in 1982 and it received favorable reviews. But even in 1981 these standard formats were not used for evaluating project bids and total cost of water was not an important criterion. A workshop on production cost of water was held in 1989 in Bahrain, which generated interest for a computer software program that included a tool for preliminary
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engineering design to each process along with the evaluation method for calculating the capital and total cost based on the latest standards. In 1991, Leitner and Associates in cooperation with International Desalination Association developed two software packages for this purpose; one for seawater desalination and other one for brackish water desalination. The seawater desalting costs program of Leitner calculates design parameters like heat transfer surface area required for MSF, MED and TC/MED and number of membranes modules for seawater RO and also calculates operation performance data like required power, steam and chemicals. These calculations are simple and are devoid of any rigorous methods. The program evaluates the capital and the total cost of desalinated water. The Brackish water desalting costs program also performs similar calculations for RO and ED using the input data for brackish water desalination. International Atomic Energy Agency (IAEA) issued in 1989 a software program called ‘‘Desalination Economic Evaluation Program’’ Version 1 called DEEP 1.0, which is useful for preliminary economic evaluation for different combinations of various energy sources of fossil and nuclear power plants with different desalination processes [8]. It contains desalination models for MSF, MED, RO and possible hybrid combinations. It includes power models for five nuclear reactors, three nuclear steam power plants, super heated steam boilers for coal, oil or gas; an open cycle gas turbine; a combined cycle gas turbine; a diesel, used as a poweronly plant and a boiler (steam or hot water), used as a heat-only plant. Steam extraction/ condensing turbine models are assumed both for nuclear and fossil energy options. This package is continuously updated and Version 2.2 is in the market. Work is in progress for
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releasing Version 3. The developments in new versions include advanced gas turbine designs and a new generation of nuclear power plants of the small and medium type. The desalination technology developments include improved thermal designs, increased energy efficiency and a new generation of high-performance membranes. The new version also includes a lost shaft work calculation for steam extraction configurations in a form similar to the one used for backpressure systems. Available performance correlations and cost data will also be included to reflect new developments in technology. DEEP is a spreadsheet tool that enables side-by-side comparison of a large number of design alternatives, which help in identifying the lowest cost options for water and/or power production at a specific location. It calculates process performance and costs based on a combination of user defined and built-in input data. The main components of the DEEP program are input data, performance calculations of the energy source and the desalination plant, cost calculation, economic evaluation and output results. The MSF and MED process performance is based on estimating the gain/output ratio, which is a function of the available temperature range and the number of stages. Whereas, the performance of RO is based on the recovery ratio, salt rejection and permeate flux depend primarily on membrane characteristics and feed properties, mainly salinity, temperature and pressure. The feed flows and energy requirements are then determined based on calculated gain/output ratio or recovery ratio. Based on the required water production capacity, an estimate of the number of thermal or membrane units of pre-defined capacities is obtained. Distillation energy costs are estimated based on lost shaft work. For RO systems, energy costs are represented by electricity consumption and
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pumping power costs are estimated accordingly. A total cost estimate is then calculated, which includes investment costs, energy costs as well as operation and maintenance costs. Another well known computer software program, WTCost, was developed by the US Bureau of Reclamation and I. Moch & Associates for evaluation and comparison of water treatment processes that employ reverse osmosis/nanofiltration, electro-dialysis, microfiltration/ultrafiltration, and ion exchange [9]. This project was sponsored by the American Membrane Technology Association. It uses flexible cost indexes and adjustable inputs and includes cost equations for estimating different pre and post-treatment unit operations such as media filtration; coagulation and flocculation with powdered activated carbon, alum, ferric chloride, ferrous sulfate, or polyelectrolyte; disinfection by chlorine, monochloramine, ozone, and ultraviolet light; lime/soda softening; electrical operations including energy recovery; and chemical consumptions and intake and outfall infrastructures. A number of default water compositions are included. Labor and supervision, membrane replacements, amortization rates, and tanks, piping, and instrumentation are also included, which permits calculation of plant capital requirements and operating and maintenance costs. 4. Conclusions It is clear from the costing data presented for various desalination processes in the previous sections and from other sources in the literature that the selection of costing parameters, costing procedures and costs figures are not consistent. However, it is true that the cost of desalination has considerably decreased over the last three decades and desalination technologies, particularly RO, may compete soon with conventional water
supplies for potable purposes even in the nonwater stressed regions. The cost reduction has a good correlation with increase in desalination capacity and growth rate in the last four decades. This has been discussed in the paper in detail. The total desalinated water cost comprises capital and operating costs and they are specific to location, feed water components and composition, energy cost, other cost parameters and the method selected for costing. The cost figures reported in different sources thus vary considerably. The parameters that contributed to the reduction in cost are discussed in clear detail in this paper rather than just providing large data of costs reported. Therefore, each component cost and total water cost serve the purpose of knowing the range rather than the absolute values. This situation demands the necessity to identify and specify the parameters that will contribute to the desalination cost and develop procedures for the estimation of desalinated water cost of any plant. There are many methods and software packages reported in the literature for costing desalinated water. They are either, methods and software packages of private organizations such as consultants and plant suppliers or publicly available methods and software packages. The parameters that are considered and the methodology adopted in private software packages are proprietary. There are some software packages developed by membrane suppliers, which are publicly available for use but details are not available, whereas the details of publicly available software packages discussed in the previous section are in the open domain. The accuracy of the costs estimated by these packages will be in the range 30% according to the American Association of Cost Engineers. Furthermore, these packages do not consider all the
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equipment and site parameters. For example, for MSF plant steam requirement in the Leitner methodology considers heat transfer coefficients whereas the DEEP consider the Gain Output Ratio. WTCost package is more rigorous than Leitner and DEEP software packages but it includes only membrane processes, but not thermal. Presently, they are working to include thermal processes in WTCost package. These packages are normally applied only for feasibility studies but not for project budgeting. Even for the feasibility studies, the accuracy of the costs estimated by these packages is not sufficient. Inclusion of thermoeconomics in the costing packages may improve the accuracy of the results. These packages should also account for the reliability and long term operating costs, and means to project reliable forecasts, leading to lower total cost of water to cater to the needs of latest BOO or BOOT contracts. Realizing the importance of desalination costing, Middle East Desalination Research Center organized an international conference on desalination costing in December 2004 in Cyprus with the aim of formulating generally accepted procedures for costing with the hope that, in the end, a standard procedure would possibly emerge that would be globally approved. However, due to the vastness of the endeavor the conference only allowed limited review of desalination technologies, existing cost models, desalination project boundary conditions, planning issues and case studies. The Center has further plans
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for standardizing procedures for desalinated water costing and for producing a costing software package that could be made available to the desalination community. References [1] K. Wangnick, IDA Worldwide Desalting Plants Inventory Report No. 18, International Desalination Association, 2004. [2] C. Sommariva, Desalination Management and Economics, Sponsored by Mott MacDonald and published by Faversham House Group, UK. [3] Y. Zhou and R.S.J. Tol, Implications of desalination to water resources in China – an economic perspective, Desalination, 164(2004) 225–240. [4] R. Borsani and S. Rebagliati, Fundamentals and costing of MSF desalination plants and comparison with other technologies, Desalination, 182(2005) 29–37. [5] N.M. Wade, Distillation plant development and cost updates, Desalination, 136(2001) 3–12. [6] M. Al-Shammiri and M. Safari, Multi-effect distillation plants: state of the art, Desalination, 126(1999) 45–59. [7] Y. Dreizin, Ashkelon seawater desalination project – off-taker’s self costs, supplied water costs, total costs and benefits, Desalination, 190(2006) 104–116. [8] M. Methnani, Recent model developments for the desalination economic evaluation program, IDA World Congress on desalination and water reuse, SP05–031, Singapore, 2005 [9] I. Moch Jr., William R Querns and Darlene Steward, Capital and operating costs CD ROM for all commercial desalination processes, IDA World Congress on desalination and water reuse, SP05–180, Singapore, 2005
Overview of the cost of desalinated water and costing methodologies K.V. Reddy, N. Ghaffour* Middle East Desalination Research Center (MEDRC) PO Box 21, Al-Khuwair, PC. 133, Muscat, Sultanate of Oman Tel: þ968 695 351; Fax: þ968 697107, email: [email protected] Received 9 February 2006; accepted 6 March 2006
Abstract In the last decade desalination has been considered as a solution for potable water needs only for specific water scarcity countries having cheap fuel. Now, desalination is extensively used, even where it was unthinkable twenty years back, due to reduction in desalination cost. The cost reduction is due to new developments and improvements in desalination technologies, particularly in RO technology. The RO is a well accepted technology due to recent increase in energy prices and takes up a major share in worldwide market. But, it is not able to achieve its proper share in the Arabian Gulf market due to difficult seawater composition and extensive historical use of thermal desalination. But RO still has potential in hybrid systems in the Arabian Gulf to account for seasonal and night to day fluctuations in the demand for power and water. There is a need for an accurate methodology for evaluation of desalination costs to help in selection of appropriate technology suitable for a specific location, for process design and other requirements. However, existing methodologies and software packages do not account for all the parameters that contribute for desalting cost and their accuracy is limited to specific conditions. This paper presents an overview of the trends in desalination costs for major desalination technologies like Multi Stage Flash, Multi Effect Distillation and Reverse Osmosis and review of costing methodologies. Keywords: Desalination costing; Costing softwares; Cost trends; Technologies developments
*Corresponding author. Presented at EuroMed 2006 conference on Desalination Strategies in South Mediterranean Countries: Cooperation between Mediterranean Countries of Europe and the Southern Rim of the Mediterranean. Sponsored by the European Desalination Society and the University of Montpellier II, Montpellier, France, 21-25 May 2006 0011-9164/07/$– See front matter 2007 Elsevier B.V. All rights reserved
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1. Introduction The cost of desalination is decreasing in recent times due to the developments in desalination technologies and desalination is now able to successfully compete with conventional water resources for potable water supplies. However, the cost of desalination is site-specific, mostly based on the quality of the feed water available at the selected site. It is thus essential to select an appropriate desalination technology that produces desalinated water at a low cost for any site under consideration. Most desalination plants in the Arabian Gulf region are co-generation type, producing both power and water. The power and water demand ratio varies considerably in different seasons. To cope with such situation, hybrid desalination systems are generally suitable and in recent plants such a concept has been used. Right costing methodologies for both desalination and power plants, are thus required to select appropriate combinations and capacities of co-generation hybrid desalination configurations. Prices of fossil fuels have increased considerably during the last five years and the same trend may continue. In future, the use of nuclear or renewable energy for desalination may be cost-effective. Since there are many types of nuclear power generation reactors and renewable energy sources, cost estimations for many combinations of energy sources and the desalination process for any particular site will be required to evolve from economical configurations. The above requirements necessitate the need for an accurate methodology/software that evaluates the cost of desalinated water produced by each technology for the site-specific conditions to help in selecting a suitable technology for that specific location. However, existing methodologies and software
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packages do not account for all the cost parameters and their accuracy is limited to specific conditions. Reliable desalination cost data is required for policy makers, planners, consultants, plant suppliers, process engineers and researchers. Policy makers, planners and consultants need the cost data for conducting feasibility studies for the selection of appropriate technologies, process engineers to optimize the process configuration and equipment sizing for minimizing the cost of production and researchers for developing new technologies and improving the existing ones. The aim of the present paper is to give an overview of the trends in desalination costs, costing methodologies for different desalination technologies, with emphasis on Multi Stage Flash (MSF), Multi Effect Distillation (MED) and Reverse Osmosis (RO), which are the major desalination technologies that are used for seawater desalination. 2. Trends in desalination costs The earliest interest in desalination was to produce fresh water for boiler and for drinking purpose on ships. Vapor compression units were first used in naval vessels powered by diesel engines in 1940. The MSF process was invented in 1950 by Silver. Reverse Osmosis phenomenon was discovered in 18th century but the breakthrough occurred in 1950 with the invention of cellulose acetate membranes. The Electrodialysis membrane was discovered in 1950. The MED technology was adopted for desalination in 1900 which has been in extensive use in the chemical industry. By the Second World War, hundreds of mobile MED and vapor compression desalination units were in use. But the cost of desalinated water was US$0.5 per m3 for the
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prevailing low fuel prices of 10–20 US$/ton. It was considered very high at that time. The Office of Saline Water was established in 1952 with initial funding of US$2 million, which was later increased to US$160 million for desalination research. Since then, tremendous interest was shown by both government and private sectors in desalination research, which led to the introduction of ED technology in 1952, freezing desalination and RO in 1954. A MSF unit of 0.05 MGD for seawater desalination was demonstrated for the US Navy in 1954. The first commercial MSF unit of 0.5 MGD was built at Shuwaikh in Kuwait later in 1957. Since 1960, MSF process became highly popular and many commercial plants were built worldwide using this technology during the last four decades, particularly in the Arabian Gulf. During this period, many national programs were initiated to study and evaluate the use of nuclear energy in desalination by Office of Saline Water, International Atomic Energy Agency and Oak Ridge National Laboratory. ED was modified to current Electrodialysis Reversal (EDR) and accepted as a commercial process during this period. In 1966 a spiral wound RO process of 0.05 MGD capacity was demonstrated. By the 1970s, improved MSF, MED, VC, ED and RO were available for commercial production and many desalination plants were built worldwide using these technologies. The total desalination capacity by all processes contracted till 2005 is 53.69 million m3/day. The contracted capacity was low, with a meager 110,000 m3/day, in the first
ten years from 1950. But it picked up gradually and increased exponentially with more than 50% during 2000–2005. The contracted capacity figures from 1950 to 2005 are given in Table 1 [1]. The cost of desalinated water produced by these technologies in 1970 was high and various organizations continued their efforts to reduce the desalination cost. Considerable decrease in the desalination costs of these technologies took place in the last four decades and, presently, desalinated water cost reached about US$0.5 per m3. These low costs are contributing to narrow the gap between conventional water supplies and desalinated water even for the non-water stressed countries. The unit water cost comparisons were made by Sommariva as in Fig. 1 [2]. In many countries in the Middle East, identified as geographical area A in the figure, price concepts are not applicable, as natural resources are so limited that life and industry would not be sustainable without desalination. Geographical areas B and C are for regions that over exploit the natural resources and regions with abundant natural resources respectively. 2.1. Multi stage flash Even though MSF is thermodynamically inefficient, large numbers of plants were installed world over, in particular in the Arabian Gulf countries, because of its reliability. Since MSF is mostly used for desalination of seawater, the data for seawater desalination is only considered. The total contracted capacity of all MSF plants worldwide till 2005 is
Table 1 Contracted capacity of all desalination plants world-wide Duration 3
Contracted Capacity (Million m /day)
1950–59
1960–69
1970–79
1980–89
1990–99
2000–05
Total
0.11
0.89
5.12
8.04
12.56
26.97
53.69
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K.V. Reddy, N. Ghaffour / Desalination 205 (2007) 340–353 Water value area A Water cost/value (US$/M3)
1.6
no cost criteria applicable
1.4
Water cost from desalination
1.2 1 Breakeven points
0.8 0.6
Water cost from re-use
0.4
Water value area B
0.2 0 1994
Water value area C 1996
1998
2000
2002
2004
Year
Fig. 1. Trends in desalination and conventional water costs. [2]
17 million m3/day with about 32% of the total desalination capacity. The contracted capacity of MSF desalination plants is given in Table 2 [1]. The first MSF plant was contracted in 1957 and the contracted capacity 1957–59 was only 27,000 m3/day. In the next decade, 1960–69, it was only 694,000 m3/day. But it increased considerably to about 20% of the total contracted capacity during 1970–79 and about the same percentage increase continued till 1999. The growth was steep in the last five years with a contracted capacity of 6.396 million m3/day. The cost of water produced by MSF was high in 1960 but many improvements took place later in the process design. Though the basic concept of the process has not changed till today, the top brine temperature was gradually increased to 112 C with the availability of better anti-scalants and newer materials of construction. This led to the
reduction of cost of desalination, particularly in the investment cost. Operating costs also decreased to some extent due to improvements in the process performance. The actual investment costs of some of the MSF installations world over in the last four decades as provided by Wangnick [1], are plotted by the authors in Fig. 2. It is clear from this figure, that the data is very much scattered and mostly clustered around investment cost of 1000–2000 US$/m3/day up to 1990 and around 1000–1500 US$/m3/day after 1995. This indicates that in spite of inflation, the investment cost reduced marginally over a period of time. Zhou and Tol [3] calculated the annual amortized capital costs with annual discount rate of 8% and a plant life of 25 years using the investment cost data reported in Wangnick Report 17. Since operating costs are not included in the Wangnick data, they assumed that the total cost comprises 40%
Table 2 Contracted capacity of all MSF desalination plants world-wide Duration
1950–59
1960–69
1970–79
1980–89
1990–99
2000–05
Total
Contracted Capacity (Million m3/day)
0.027
0.694
3.213
3.546
3.124
6.396
17.00
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3500 3000 2500 2000 1500 1000 500 0 1965
1970
1975
1980
1985
1990
1995
2000
2005
2010
Year
Fig. 2. Investment cost of MSF per m3/day capacity over years.
capital cost for interest and depreciation on the investment and 60% for running costs. The load factor was assumed as 90%. They adjusted all Wangnick reported costs according to the United States Consumer Price Index with 1995 as base year. The unit water costs thus calculated are plotted by them in Fig. 3. It is clear from Fig. 3 that over 40 years the unit water costs of MSF decreased by a factor of 10. The main contributor for such reduction is due to about 50% reduction in the installation costs despite the increased cost of raw materials by 40% and the labor
cost increase by more than 100%. The main factors for such reduction are the following: Severe competition among MSF plant contractors and from RO plant suppliers forced the contractors to propose improvements/deviations to the technical specifications of MSF plants and implementation of such suggestions led to the reduction in the installation costs. The other contributor is engaging subcontractors from Far Eastern countries who had developed technical skills, instead of engaging subcontractors on a regional/national basis.
Unit cost ($/m3)
12.0
9.0
6.0
3.0
0.0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Year
Fig. 3. Unit water cost by MSF process over years. [3]
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The feedback from earlier projects helped in improving the process and equipment design of the MSF process. These improvements are specifically related to the increase in unit capacity of MSF plants over the years, 2–3 MGD in 1960– 70, 2–5 in 1971–80, 3–7.5 in 1981–90, 3.5–12 in 1991–00 and 7–20 after 2000. The use of Duplex steel instead of AISI 316, 316L and 316Ti reduced the cost. Duplex steel is cheap, has better mechanical properties and higher corrosion resistance than AISI 316, 316L and 316Ti, which were being used earlier. The use of thinnest titanium tubes in place of wellknown copper nickel alloy for heat transfer tubes also contributed to the reduction in the investment cost. The relaxation of stringent specifications by users with respect to fouling factors, distiller hydraulic test pressures, distillate purity, brine load, construction material specifications, heat exchange tube thickness, bypass on control valves, removable water boxes and redundancy of equipment and instrumentation helped the contractor to arrive at appropriate options which led to the reduction in the investment cost. The BOOT contract specifications, which changed from technical to functional, has allowed the contractor to further optimize the plant and helped in reducing the cost. Increased top brine temperature from 90 to 112 C over the last 10 years helped in improving the performance of the MSF plant and also contributed to the reduction of unit water cost.
The above improvements helped in reducing the unit water cost produced by MSF to less than US$1.0 per m3. Unit water cost depends on the investment cost and operating cost. The investment cost of MSF plants is
345
about US$900 per m3/day capacity based on the average value of the contracted plant in the Middle East in the last years [4]. The share of operation cost in the unit water cost will be 55–60% depending on the cost of capital, plant life assumed and on energy cost. Recently Borsani and Rebagliati [4] estimated the unit water cost at US$0.52 per m3 for MSF for Middle East conditions. This unit water cost may be on the lower side. Their costs are compared with Wade [5] in Table 3. The total cost according to Wade is 1.044 US$/m3. Presently, the unit water cost could be between these two values, but may be closer to that given by Wade. The components of operating costs and their contributions are compared in Table 4. It is interesting to note that they are considerably different. The cost of chemicals reported by Sommariva [2] is on the high side. Similarly, the cost of personnel and spares reported by Borsani and Rebagliati [4] are on the low side. 2.2. Multi effect distillation Multi effect distillation is thermo-dynamically a more efficient process compared to MSF. The performance ratio is directly proportional to the number of effects unlike for the MSF. But it has some scaling problems compared to MSF. Small capacity MED plants were built since 1900 in ships. But the first land-based MED desalination plant was built in 1930 in Saudi Arabia. The total contracted capacity of MED without vapor compression by the end of 2005 was only 1.175 million m3/day, which is much less than that of MSF. The contracted capacities in each decade from 1950 to 2005 are given in Table 5 [1]. The contracted capacity was roughly constant around 20% after 1970. Most of the MED
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Table 3 Typical unit water cost comparison Desalination
Wade
Borsani and Rebagliati
Production capacity (m3/day) Number of units/trains Performance ratio Top brine temperature Number of stages Heat consumption, MJ/m3 Power consumption, kWh/m3 Load factor, % Energy cost, US$/GJ Power cost, US$/kWh Plant life, years Discount rate, % Amortization, % Capital cost, US$ in million Distillers installed Seawater intake and out fall Foundations and building Financing during construction Engineering and consultancy Total capital cost Operating Cost in US$/m3 Heat energy Electrical energy Operation and maintenance Spares Chemicals Sub-total operating cost Capital charges in US$/m3 (Total capital cost/ production capacity) Total in US$/m3
31,822 1 8.0
205,000 3 8.5 112 19
290 3.6 90 1.5 0.03 25 8 9.37
0.03 20 7 10.59
34.5 2.8 5.6 4.3 4.3 51.4
180
0.242 0.109 0.126 0.082 0.024 0.583 0.461
0.136 0.119
0.032 0.287 0.233
1.044
0.52
plants are small or medium size unit capacity. The largest MED unit capacity is only 5 MGD compared to 17 MGD of MSF. There are two types of commercial vapor compression desalination plants: thermal vapor compression and mechanical vapor compression. MED technology is used in vapor compression plants, particularly in thermal vapor compression. Since MED with mechanical vapor compression has not much effect on the specific power consumption, only single effect is generally used. On the other hand, MED with thermal vapor compression decreases the specific energy consumption and most of the recent MED plants are coupled with thermal vapor compression. The contracted total capacities of mechanical and thermal vapor compression plants are 504,358 and 1,455,433 m3/day respectively. It was attempted to plot the actual investment cost data given by Wangnick for MED plants against contracted year as was done in the MSF case. But it was not possible to get any trend correlation due to the limited data and different plant sizes and specifications. However, from the data reported in the literature, the cost reduction trend over years is similar to MSF with improvements in similar parameters as discussed below. Most of the MED plants built till 1970 were for brackish or river water desalination
Table 4 Comparison of operating cost contributions Component
Thermal Energy Electrical Energy Chemicals Personnel & Spare parts
% contribution Borsani and Rebagliati
Wade
Sommariva
46 40 9 5
42 19 4 35
38 14 30 18
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K.V. Reddy, N. Ghaffour / Desalination 205 (2007) 340–353 Table 5 Contracted capacity of all MED desalination plants worldwide Duration
1950–59
1960–69
1970–79
1980–89
1990–99
2000–05
Total
Contracted Capacity (Million m3/day)
0.083
0.108
0.292
0.242
0.239
0.207
1.175
and they used submerged tubes with unit capacities of 1 MGD or less due to scaling problems with seawater desalination. Heat transfer coefficients were low in submerged tube evaporators and hence vertical and horizontal tube falling film evaporators were introduced to improve the heat transfer coefficient. Higher heat transfer coefficients in the falling film allowed in reducing the top brine temperature to less than 70 C, which helped in reducing the scaling problems. The first large capacity MED plant for seawater desalination with 3.5 MGD capacity and vertical tube evaporator was built in Kazakhstan in 1964 and similar plants were built later in 1966, 1967, 1968 and 1970 in the same country. Since horizontal tube falling film evaporators have higher heat transfer coefficients compared to vertical tube evaporators for large scale applications, they became popular in the industry. Horizontal tube falling film MED of 0.1 MGD for seawater desalination was first built in Belgium in 1970. Large scale MED of 4.5 MGD with horizontal tube evaporator was built in Israel at Ashdod in 1980. In the last ten years, many developments took place in MED with respect to coupling of thermal vapor compression with MED, use of improved horizontal tube falling film evaporation, stabilization of low temperature operation, use of aluminum for heat transfer tubes resulting in realization of modern MED plants and reduction of unit water costs. Modern MED plants are reliable, matured and have better performance than MSF even for the harsh Gulf water
conditions. This led to the construction of 2 MED units of 5 MGD unit capacity in 1999 at Layyah in Sharjah. They have also opened the way for its application for large BOT projects in the Gulf Region, as e.g. Taweelah A1 where its high reliability is fully manifested. Many large-scale MED plants of 6 MGD with thermal vapor compression were built in UAE at Ajman in 2003, at Al-Nakheel in 2003 and at Ras Al-Khaimah in 2003. An excellent review of the performance of some of the operating MED plants is reported by Al-Shammiri and Safari [6]. Increase in unit capacity, increase in heat transfer coefficients with horizontal tube evaporators and use of appropriate materials for low temperature operation have considerably reduced the unit cost of desalinated water using MED. The unit water cost of MED was always lower than MSF after the introduction of falling film evaporation and this further decreased after the integration with thermal vapor compression, or heat pump. The unit water cost of the recent MED plants is 0.55–0.7, which is less than for MSF and very close to RO. The capital cost is about US$850 per m3/day capacity and energy consumption is less than MSF. 2.3. Reverse osmosis The RO desalination was commercialized much later than MSF and MED. The first commercial brackish water RO plant with spiral wound membrane was contracted to build at Kashima in Japan in 1969 to cater to the water needs of a power plant. After 6
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years in 1975, a seawater RO plant of 1500 m3/day capacity was contracted to build at Al-Kharj in Saudi Arabia. The total contracted capacity of RO plants by the end of 2005 reached 23.36 million cubic meters per day, which is the highest capacity compared to any other process. But the seawater desalination share is only 9.611 million cubic meters per day. The contracted total capacity and contracted seawater desalination capacity from 1950 to 2005 are given in Table 6 [1]. It is clear from the values given in Table 6 that the total and seawater RO capacity have grown fast in the last 30 years and it has exponentially increased for both total and seawater RO capacity in the last five years with 50% growth in the total capacity and 70% in seawater RO capacity. In Fig. 4, actual investment cost of seawater RO plants given by Wangnick is
plotted by authors against contracted year. The investment cost data is more scattered before 1995. After 1995, it is more clustered between 500 and 1000 US$ per m3/day capacity. This indicates that the investment costs decreased in the last ten years. With the same assumptions as were made in MSF for calculating unit water cost, Zhou and Tol [3] calculated the unit water cost for RO and plotted them in Fig. 5. The unit water cost decreased considerably over the years and at about 0.5 US$/m3, it is presently lowest of all the processes. There are many developments over the last three decades that contributed to the reduction of unit water cost of RO desalination, particularly membrane module performance and reduction in energy consumption. The performance of the membrane modules improved with respect to increased salt rejec-
Table 6 Contracted capacity of RO desalination plants worldwide Duration Total Seawater
US$ per cubic meter per day capacity
Contracted Capacity Million m3/day
1950–59
1960–69
1970–79
1980–89
1990–99
2000–05
Total
– –
0.016 –
1.241 0.48
3.168 0.577
7.227 2.162
11.713 6.824
23.365 9.611
4000 3500 3000 2500 2000 1500 1000 500 0 1975
1980
1985
1990 1995 Year
2000
2005
Fig. 4. Investment cost of seawater RO plant per m3/day capacity over years.
2010
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K.V. Reddy, N. Ghaffour / Desalination 205 (2007) 340–353 6.0 BRACK RIVER SEA PURE WASTE
Unit cost ($/m3)
5.0 4.0 3.0 2.0 1.0 0.0 1965
1970
1975
1980
1985 Year
1990
1995
2000
2005
Fig. 5. Unit water cost by RO over years. [3]
tion, increased surface area per unit volume, increased flux, improved membrane life, capacity to work at high pressure and also decrease in membrane cost. The recovery ratio increased considerably over the years due to improved salt rejection. The recovery ratio for seawater desalination was about 25% in 1980s and it increased to 35% in 1990s. Currently it is about 45% and it will be more if 2nd stage is included. Improved recovery facilitated a decrease in the investment cost and also operating costs. The capital cost reduction is due to a reduction in RO trains and intake system sizes. The operating cost reduction is due to a reduction in usage of chemicals and pumping energy. The surface areas per unit volume increased considerably with the introduction of hollow fine fiber modules and spiral wound modules. The increase in surface area per unit volume and increase in flux contributed to the reduction of investment cost. Improved membrane life and capacity to work at high pressure also helped in reducing the operating cost. The membrane costs should increase due to inflation over a period of time. But they have fallen down by 86% between 1990 and
2005, which contributed considerably for unit water cost reduction. Recently the specific energy consumption has been considerably decreased with the introduction of better energy recovery system from reject brine such ERI (Energy Recovery Inc.) or DWEER (Dual Work Exchanger Energy Recovery). The developments in various parameters of RO as desalination presented by Sommariva [2] are given in Fig. 6. Apart from improvements in RO technology, increase in plant capacity also contributed to the reduction in unit water cost. The magnitude of the respective costs due to improvements in the membranes and increase in plant capacity are difficult to measure since they have both taken place simultaneously. The plant capacity increased by a factor of 10 between 1995 and 2005. As in the case of thermal desalination, competition among the plant suppliers, subcontractors, membrane suppliers also contributed to the reduction in unit water cost. The investment cost of recent seawater RO desalination plants is about US$800 per m3/ day capacity. In order to have a better idea of the latest cost figures, the data reported by Dreizin [7] for Ashkelon seawater RO
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K.V. Reddy, N. Ghaffour / Desalination 205 (2007) 340–353 10.00 Cost Productivity Recip.SP Life Energy
9.00 Unit Improvements
8.00 7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 1980
1985
1990
1995
2005
2010
Year
Fig. 6. Membrane improvements over years. [2]
desalination plant and calculated by Borsani and Rebagliati [4] for Arabian Gulf conditions are given in Table 7. 3. Review of desalination costing methodologies In the 1960s only MSF was available for commercial application and the bidding process would normally call for an investment cost proposal with performance data. In the Table 7 The average total water price of Ashkelon RO plant US$/m3 Cost Item
Ashkelon
Borsani and Rebagliati
Base fixed price Base variable price Energy Membranes Filters Chemical Post treatment Others Sub total Base total water price
0.311
0.22
0.134 0.28 0.005 0.21 0.009 0.17 0.214 0.525
0.148
0.078
0.446
1970s there were other desalination technologies in the market and there was a need for better evaluation process for their merits based on the cost analysis. However, only investment cost and performance were used for comparison and evaluation. Recognizing the importance of various factors at play, in 1972 Office of Saline Water issued a Desalting Handbook For Planners that included a chapter on factors influencing the process selection and water cost, including a format for calculating capital cost and total cost of water. Larson and Leitner prepared an updated report for the Office of Water Research and Technology in 1979, which contained comparison of MSF, MED and RO in a standard format. This report was updated again in 1982 and it received favorable reviews. But even in 1981 these standard formats were not used for evaluating project bids and total cost of water was not an important criterion. A workshop on production cost of water was held in 1989 in Bahrain, which generated interest for a computer software program that included a tool for preliminary
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engineering design to each process along with the evaluation method for calculating the capital and total cost based on the latest standards. In 1991, Leitner and Associates in cooperation with International Desalination Association developed two software packages for this purpose; one for seawater desalination and other one for brackish water desalination. The seawater desalting costs program of Leitner calculates design parameters like heat transfer surface area required for MSF, MED and TC/MED and number of membranes modules for seawater RO and also calculates operation performance data like required power, steam and chemicals. These calculations are simple and are devoid of any rigorous methods. The program evaluates the capital and the total cost of desalinated water. The Brackish water desalting costs program also performs similar calculations for RO and ED using the input data for brackish water desalination. International Atomic Energy Agency (IAEA) issued in 1989 a software program called ‘‘Desalination Economic Evaluation Program’’ Version 1 called DEEP 1.0, which is useful for preliminary economic evaluation for different combinations of various energy sources of fossil and nuclear power plants with different desalination processes [8]. It contains desalination models for MSF, MED, RO and possible hybrid combinations. It includes power models for five nuclear reactors, three nuclear steam power plants, super heated steam boilers for coal, oil or gas; an open cycle gas turbine; a combined cycle gas turbine; a diesel, used as a poweronly plant and a boiler (steam or hot water), used as a heat-only plant. Steam extraction/ condensing turbine models are assumed both for nuclear and fossil energy options. This package is continuously updated and Version 2.2 is in the market. Work is in progress for
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releasing Version 3. The developments in new versions include advanced gas turbine designs and a new generation of nuclear power plants of the small and medium type. The desalination technology developments include improved thermal designs, increased energy efficiency and a new generation of high-performance membranes. The new version also includes a lost shaft work calculation for steam extraction configurations in a form similar to the one used for backpressure systems. Available performance correlations and cost data will also be included to reflect new developments in technology. DEEP is a spreadsheet tool that enables side-by-side comparison of a large number of design alternatives, which help in identifying the lowest cost options for water and/or power production at a specific location. It calculates process performance and costs based on a combination of user defined and built-in input data. The main components of the DEEP program are input data, performance calculations of the energy source and the desalination plant, cost calculation, economic evaluation and output results. The MSF and MED process performance is based on estimating the gain/output ratio, which is a function of the available temperature range and the number of stages. Whereas, the performance of RO is based on the recovery ratio, salt rejection and permeate flux depend primarily on membrane characteristics and feed properties, mainly salinity, temperature and pressure. The feed flows and energy requirements are then determined based on calculated gain/output ratio or recovery ratio. Based on the required water production capacity, an estimate of the number of thermal or membrane units of pre-defined capacities is obtained. Distillation energy costs are estimated based on lost shaft work. For RO systems, energy costs are represented by electricity consumption and
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pumping power costs are estimated accordingly. A total cost estimate is then calculated, which includes investment costs, energy costs as well as operation and maintenance costs. Another well known computer software program, WTCost, was developed by the US Bureau of Reclamation and I. Moch & Associates for evaluation and comparison of water treatment processes that employ reverse osmosis/nanofiltration, electro-dialysis, microfiltration/ultrafiltration, and ion exchange [9]. This project was sponsored by the American Membrane Technology Association. It uses flexible cost indexes and adjustable inputs and includes cost equations for estimating different pre and post-treatment unit operations such as media filtration; coagulation and flocculation with powdered activated carbon, alum, ferric chloride, ferrous sulfate, or polyelectrolyte; disinfection by chlorine, monochloramine, ozone, and ultraviolet light; lime/soda softening; electrical operations including energy recovery; and chemical consumptions and intake and outfall infrastructures. A number of default water compositions are included. Labor and supervision, membrane replacements, amortization rates, and tanks, piping, and instrumentation are also included, which permits calculation of plant capital requirements and operating and maintenance costs. 4. Conclusions It is clear from the costing data presented for various desalination processes in the previous sections and from other sources in the literature that the selection of costing parameters, costing procedures and costs figures are not consistent. However, it is true that the cost of desalination has considerably decreased over the last three decades and desalination technologies, particularly RO, may compete soon with conventional water
supplies for potable purposes even in the nonwater stressed regions. The cost reduction has a good correlation with increase in desalination capacity and growth rate in the last four decades. This has been discussed in the paper in detail. The total desalinated water cost comprises capital and operating costs and they are specific to location, feed water components and composition, energy cost, other cost parameters and the method selected for costing. The cost figures reported in different sources thus vary considerably. The parameters that contributed to the reduction in cost are discussed in clear detail in this paper rather than just providing large data of costs reported. Therefore, each component cost and total water cost serve the purpose of knowing the range rather than the absolute values. This situation demands the necessity to identify and specify the parameters that will contribute to the desalination cost and develop procedures for the estimation of desalinated water cost of any plant. There are many methods and software packages reported in the literature for costing desalinated water. They are either, methods and software packages of private organizations such as consultants and plant suppliers or publicly available methods and software packages. The parameters that are considered and the methodology adopted in private software packages are proprietary. There are some software packages developed by membrane suppliers, which are publicly available for use but details are not available, whereas the details of publicly available software packages discussed in the previous section are in the open domain. The accuracy of the costs estimated by these packages will be in the range 30% according to the American Association of Cost Engineers. Furthermore, these packages do not consider all the
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equipment and site parameters. For example, for MSF plant steam requirement in the Leitner methodology considers heat transfer coefficients whereas the DEEP consider the Gain Output Ratio. WTCost package is more rigorous than Leitner and DEEP software packages but it includes only membrane processes, but not thermal. Presently, they are working to include thermal processes in WTCost package. These packages are normally applied only for feasibility studies but not for project budgeting. Even for the feasibility studies, the accuracy of the costs estimated by these packages is not sufficient. Inclusion of thermoeconomics in the costing packages may improve the accuracy of the results. These packages should also account for the reliability and long term operating costs, and means to project reliable forecasts, leading to lower total cost of water to cater to the needs of latest BOO or BOOT contracts. Realizing the importance of desalination costing, Middle East Desalination Research Center organized an international conference on desalination costing in December 2004 in Cyprus with the aim of formulating generally accepted procedures for costing with the hope that, in the end, a standard procedure would possibly emerge that would be globally approved. However, due to the vastness of the endeavor the conference only allowed limited review of desalination technologies, existing cost models, desalination project boundary conditions, planning issues and case studies. The Center has further plans
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for standardizing procedures for desalinated water costing and for producing a costing software package that could be made available to the desalination community. References [1] K. Wangnick, IDA Worldwide Desalting Plants Inventory Report No. 18, International Desalination Association, 2004. [2] C. Sommariva, Desalination Management and Economics, Sponsored by Mott MacDonald and published by Faversham House Group, UK. [3] Y. Zhou and R.S.J. Tol, Implications of desalination to water resources in China – an economic perspective, Desalination, 164(2004) 225–240. [4] R. Borsani and S. Rebagliati, Fundamentals and costing of MSF desalination plants and comparison with other technologies, Desalination, 182(2005) 29–37. [5] N.M. Wade, Distillation plant development and cost updates, Desalination, 136(2001) 3–12. [6] M. Al-Shammiri and M. Safari, Multi-effect distillation plants: state of the art, Desalination, 126(1999) 45–59. [7] Y. Dreizin, Ashkelon seawater desalination project – off-taker’s self costs, supplied water costs, total costs and benefits, Desalination, 190(2006) 104–116. [8] M. Methnani, Recent model developments for the desalination economic evaluation program, IDA World Congress on desalination and water reuse, SP05–031, Singapore, 2005 [9] I. Moch Jr., William R Querns and Darlene Steward, Capital and operating costs CD ROM for all commercial desalination processes, IDA World Congress on desalination and water reuse, SP05–180, Singapore, 2005