20 years Evolution of Desalination Costs in Spain

Transcription

1 Abstract 20 years Evolution of Desalination Costs in Spain Jose A. Medina San Juan. Cedex Desalination is being used in Spain since late 60 ties, when the first MSF desalination plant was installed in the island of Lanzarote, Canary Islands. Since then more than 900 desalination plants, in capacities ranging from as low as 150 m3/day up to m3/day, have been constructed and operated in the country. Along this time, technological changes have been decisive for desalination in the country, and if at the beginning only isolated areas were supposed to be covered with non conventional resources, the advent of new technologies and the improvement year after year of them, has completely moved the panorama of desalination, making it more available to sectors where a few years before it would be an unbelievable option. This change came with the rise of the RO membrane market that unlike distillation, made the technology less dependent on steam, fuel and other energetic resources in which the country lacking. The new RO technology has a lower investment cost than steam dependent systems, and is more efficient from the energetic point of view. This has opened the way to the experienced Spanish water treatment companies that came into the market, increasing the competition and reducing as much as possible overall and specific costs of production. The roll played by the Spanish Ministry of Public Works, now Environment, to drive this tendency has been very important. Their management and control of the construction and first two years of operation of the big seawater desalination plants has provided the opportunity to improve and developed the design technology as well as the operation management, with the main goal to reduce energetic costs. An overview of the desalination costs in the country during the last 20 years is being presented in the paper and a detailed description of main issues that has made to change the landmark of the different desalination plants built. Regarding desalination costs, every plant is different, and differences in water intake, capacity, design, capacity of enlargement or other issues, influence them; so that more than a strict cost, a range of costs has to be given when planning the construction of a desalination plant. 294

2 Introduction Cost of desalination is determinant for the expansion of these technologies worldwide, especially in countries where the lack of water in quality and quantity is not accompanied by incomes allowing payment for them. The cost of desalinated water has to be considered in order to study its possibilities to use in different sectors and areas, and to try to cut down to broaden its use. Spain, with a tradition of over 40 years of using desalination, since the seventies, when MSF was the only technology reliable, started with desalination only for urban purposes, to supply water to cities, in isolated areas where no other alternative resources where available. Though a few years before, a small plant, installed in a boat was used in the island of Lanzarote, it could be said that the first important plant started its construction in 1967 in the island of Gran Canaria Las Palmas I, a dual plant with a capacity of m3/day, went into stream in As energy was needed as well at that time, this plant was a complementary one to supply electricity to the island. The operation and maintenance of the MSF plant and the power plant associated were connected and it was difficult to separate costs between the two facilities. If power consumption could be an index, that plant with a GOR of 6 was using steam from the heaters of the dual ( MW) plant equivalent to 22 kwh/m 3. It took 10 years to bring into stream the second plant, Las Palmas II, a single MSF facility of m 3 /day capacity with a GOR of 7. More efficient than the one before, this plant reduced its power consumption to an equivalent of 18 kwh/m 3. The plant imported the steam from an external plant that if useful at the beginning, it became unavailable as the prices of fuel started rising at the end of the eighties. It is still able to be used nowadays, though its production has gone down to m 3 /day, thereby reducing its operation to emergency situations. Figures collected from those days showed prices of production really high, even at full capacities. Evolution of desalination costs Though evaporation has improved since that time, the improvements have not been enough to reduce costs to such levels to allow to be used broadly, and if we analyze the Spanish trends of desalination, no other MSF plant has been built in the country since then. Years later small VC desalination units where installed with a continuous reduction in power consumption (electricity in these systems). The last of these units were installed in 1993, with a capacity of 1,500 m 3 /day and being the most efficient of all, its process consumption (compressor) was not lower of 9 kwh/m 3. It was not possible to increase the efficiency of the compressors and to enlarge the capacity of the units. Since 1990, RO plants where processing water with less than 6 kwh/m 3 and capacity of racks surpassed 5,000 m 3 /day. This last unit stopped its production 5 years later for economic reasons, not technical, as a new RO desalination plant of m 3 /day of the same budget started its operation. The introduction of RO (1987 in Lanzarote), opened the way to the expansion of desalination, as up to then not a real reduction in production costs had been demonstrated. 295

3 Nevertheless it took a few years for further reductions in costs. If we study the growth of seawater desalination in Spain, it was not until the 1996 when desalination started expanding its use that, from domestic move to industry (in small units) and to the agriculture. Total costs of desalinated seawater Many parameters are influencing those costs as: Size and site of the desalination plant Seawater Product water salinity required Technology ad equipments selected Design Water intake It could be said that the cost of desalinated water is different in every facility since any of them was made to different design its operating conditions could be quite different For any desalination plant two flows of cost have to be considered. Investment Costs In which are incorporated the value of Soil site Project Licences Civil works Equipments The recovery of this capital is made through the repayments according with interest rates and period of time establish for every project. Operation and maintenance Costs Two different costs have to be considered: Fix costs: Determined by local building costs for infrastructure, permits, and other local requirements Variable costs: Depending of the operating conditions of the desalination plant Fix Labour Civil works maintenance Equipment maintenance Variable Power consumption Chemical Membranes replacement Cartouch replacement Others 296

4 Investment Costs From all referred components the construction of the desalination plant is the most important, not only site conditions for civil works itself but for its changes of equipment needed. The size of the plant has an important influence for the economy of scale, but the design could as well influence investment (recovery, trains,etc). Table 1: Investment costs Size in m 3 /day Water Eu/m 3.day Water < ,46 Brackish ,38 Brackish ,34 Brackish ,29 Brackish > ,25 Brackish < Sea 961, Sea 856, Sea 751, Sea 661, Sea 611, Sea 588, Sea 525,89 > Sea 506,35 Though any desalination plant can have especial characteristics and depending on the intake, local conditions, etc, it can be summarized, at least in Spain that the average costs related with the size are as indicated. How do these investments influence the cost of desalinated water? The repayment depends on rate and period to be considered, but it deserves to be considered that in the European Union, rates could be assured at relative low percents (in this moment around 4 %), financial risks are very reduced and private and public capitals compete in the scenario. Another important consideration for a bank financial, are repayment periods and consequently life of the equipment that has to be considered. The desalination plant has to be separated between civil works and equipments whose investment, period of amortizing and maintenance are different. Most of desalination plants are into these ranges of investment costs: Table 2: Budget Seawater Brackish water Civil works 20% 10% Equipments 80% 90% Amortizing periods are as follow: Table 3: Amortizing Period Seawater Brackish Water Civil Works 30 years 20 years Equipments 15 years 10 years 297

5 A 25 years period for the whole investment could be reasonable. Depending of investment and yearly rates, repayment of the investment costs could average: Table 4: Repayment Seawater Brackish Water Yearly rates Euros/m 3 Euros/m 3 4% 0,1208 a 0,2296 0,0138 a 0,0252 5% 0,1304 a 0,2476 0,0144 a 0,0264 6% 0,1400 a 0,2662 0,0150 a 0,0276 7% 0,1503 a 0,2855 0,0162 a 0,0294 Fixed Operating Costs Hand labour To guaranty a continuous and trouble free operation of a desalination plant, a minimum of workers is necessary. The size of the desalination plant has an influence in such cost; number of people needed and their costs are as follows: Table 5: Labour costs Plant capacity No. of persons Euros/m 3 m 3 /year m 3 /day , , , , , , , , Maintenance Costs for civil works and equipments Maintenance cost is considered as percentages of the investment and could vary between 1 and 1.5% for civil works and 2 to 2.5 % for mechanical and electrical equipments. Variable Operating Costs Power Consumption (electricity) It accounts for the most important of the costs and has to include the production of water and its pumping to a tank located in the desalination plants. If further impulsion is needed it has to be considered as well. It is composed of two different consumptions: Water abstraction (from the intake to the desalination plan) Desalination process itself For normal recoveries between 35 and 45 %, and distances between the location of the desalination plant and the intake it could vary between 0,5 y 0,7 kwh/m

6 Reverse Osmosis process: Large desalination plants with Pelton wheels as energy recovery devise: 3.1 to 3.3 kwh/m 3 Medium and small systems with Pelton wheel: 3.4 to 4 kwh/m 3 Desalination plants with pressure exchange vessels as energy recovery devices: 2.3 to 2.6 kwh/m 3 Small power consumption involved in the plant: dosing pumps and lighting: 0.1 to 0.15 kwh/m 3 If desalinated water has to be delivered outside the plant, the total consumption has to be increased between 0.3 and 0.6 kwh/m 3,for regular distances and heights, going to 1 kwh/m 3 and up in special situations. The electricity tariff could be important and depend mainly on the power contracted (size of the plant). Other Variable Costs According with the physico-chemical composition of the seawater and the type of intake (open or beachwells) Table 6: Variable costs Variable costs euros/m3 Chemicals 0,018 a 0,054 Membrane replacements 0,018 a 0,036 Cartouch replacements 0,0018 a 0,0042 Others 0,018 Average structure of RO seawater desalination costs. With all these figures we can establish for seawater desalination, as an average, the following costs in percentage. As can be seen, repayment and energy costs account for similar proportions and are close to 299

7 40% each, so that most important reductions in costs of seawater desalination mayl come from these two components. Conclusions Regarding investment costs, the tendency is to increase the size of the desalination plant, though other drawbacks can derive from that. In power consumption, the introduction of energy recovery devices, started in 1,986 with Francis turbines coupled to high pressure pumps, the second stage came with the use of two generation of Pelton wheels, starting in 1,996, and finally the pressure exchange vessels or the increase in the recovery of the system through the use of booster pumps in a second stage. Regarding the power consumption the reduction experienced in Spain, and its influence in the final cost of desalinated water could be seen in table 7: Table 7: Evolution of power consumption and seawater desalination costs in Spain Year KWh/m 3 Euros/m 3 Remarks MSF MSF VC VC VC RO RO RO RO RO RO RO RO RO RO Finally, since the start up of Las Palmas III (1.999), at that time the largest plant worldwide, variation in other items happened as follows: Items Yearly increase Ten years period Hand labour 3 4 % 44 % Electricity (tariff) % 29 % Chemicals % 14 % On the other side, membranes showed cost reduction of 50 %. 300