At present 2 billion people in 80 countries of the world live in regions with a severe shortage of potable water. Water consumption in 9 countries exceeds the speed of its replenishment. 6 from 7 East-African countries and all 5 countries of south coast of Mediterranean Sea live in deficiency of fresh water. 3 billion people in 48 countries will face such problem within 2025 year. In some regions excess of water demand over its recovery is more than 160%. Subterranean waters as the soil itself recover very slowly: about 1% a year. For past 150 years quantity of potable water per person became 4 times less. In some regions exceeding of consumption over recovery comes up to 16 %. Irrigation is vital for production of food in the world. Irrigable soils take abt. 16 % of the world fertile lands. In the meanwhile, irrigation is accompanied by the loss of soils due to pickling and swamping (abt. 1 % per year). India, Pakistan, Egypt, Mexico, Australia and USA have already to deal with this problem. In 25 years 30 % of fertile soils will be lost, and in 50 years – a half of irrigable soils.
Thus, the problem of fresh water replenishment becomes more vital. A lot of projects are being developed today for increase of fresh water resources, including Arctic ice transportation, icebergs haulage, distilling plants construction. Water desalination is a way of water treatment for reduction of dissolved salt concentration up to the level (usually up to 1g/litre) at which water becomes suitable for potable and domestic use. Deficiency of potable water can be closed by distillation of salt (with salinity more than 10 g/litre) and brackish (2-10 g/litre) oceanic, sea and ground waters, resources of which make 98% of all water on Earth. Shortage of fresh water can be eliminated by industrial pumping through pipelines or channels from the regions with excess supply of it. When fresh water sources are located far enough, salt- water distillation at site will cost less than fresh water pumping. At water consumption rate up to 1000 m3 a day salt water distillation in situ is more advantageous than water supply for a distance more than 40-50 km, and at water consumption rate of 100 000 m3 a day it is more advantageous than fresh water supply for a distance of 150-200 km and more. The world demand for desalinating of sea water increases constantly, especially from the part of countries with deserts, and island states. During the last 10 years world capacities for desalinating of sea water have increased from 13.2 Mill m3 in 1990 to 20 Mill m3 in 2000. 12,5 thousands of desalinating plants in 120 countries are operating worldwide. Nevertheless, these plants can provide only for 1 % of worldwide water supply.
Nowadays evaporator (distillation) desalination systems are the most prevalent for water desalting. At present distilling plants of a new, third generation – with horizontal-tube film evaporators – are under development in Russia. Area of application of these covers not only sea water desalting, but recovery of desalted makeup water for boilers and steam generators at heat and nuclear power plants as well as treatment of mineralised industrial waste waters.
Another type of distilling plants under consideration is desalinating plants using Reverse Osmosis technology. RO process for water purification has been used from early 60-s. Nonorganic substances are removed by RO membrane well enough. Depending on the type of membrane used (cellulose acetate of thin-film composite membrane), purification efficiency reaches 85%-98% for majority of nonorganic elements. RO membrane also removes organic substances from water. Organic substances with molar weight of more than 100-200 are removed fully and ones of less weight can permeate through the membrane in minor quantities. A large size of viruses and bacteria actually excludes possibility of their permeation through the membrane. Evaporator plants used so far are very energy-intensive, that argue for RO technology on which our project is based. Thus, average price of water treatment by traditional plants grew from 0,45 up to 1,8 EURO/m3 lately.
Comparative analysis of distilling desalinating plant and reverse osmosis desalinating plant usage
Having decided in favour of the Reverse Osmosis technology, we have studied preliminary list of possible suppliers of such equipment. Using RO plant of «Lifestream» make we can reach the following parameters: 1 plant productivity – 1000 m3/day; power consumption – 0,2 kW/m3; overall dimensions: 12,2х2,4х2.4 m. Price of 1 plant is USD 656 000. Uralchimmash can manufacture desalinating plants with capacity 700m3/hour. The cost of such a unit is abt. USD 9Mill. Steam consumption is 62 t/h, el power consumption – 670 kW/h. Power consumption per 1m3 of water is 1,05 kW. Overall dimensions of the unit is 24.2 x 24 x 24 metres. After design works units with more capacity can be produced.
MARINE DESALINATING PLANT Main particulars Lengh over all 65,50 m Breadth (moulded)16,90 m Draught 3,00 m Main engine power 7100 kW Deadweight3200 t
We have developed a project of floating distilling plant for salt and sea water desalination with salt load up to 41 g/l. The plant produces 400 000 m3 of fresh water a day with salinity of no more than 500 mg/l (salt content is in conformity with international standards). The plant can be placed either in naturally protected waters (fjord, gulf, and lagoon) or under protection of water- development facilities. The depth at site should be at least 5 m at low tide. Anchoring system of the plant assures normal operation at moderate sea and wind speeds up to 40 m/sec. The plant is a floating construction equipped with the distilling and power plants. It has the following dimensions: Maximum length65,5 m Breadth16,9 m Depth4,5 m Draughtabout 3,0 m Total displacement3200 tons Dimensions of the plant have been determined with consideration for installation of water distilling units, power plant equipment and auxiliary equipment and systems. The processing plant of the floating distilling plant consists of the following: water intake system, distillation units and potable water treatment system. For providing plant auxiliary in transit to the work location, during stay without power supply from the shore and for providing the plant with steam three reserve diesel generators (one of which is stand-by) are intended. Electric power is 3 x 2370 kW, voltage – 400V, frequency – 50 Hz. The stipulated fuel storage in the tanks on board the plant can provide its work within 30 days. The plant is equipped with all necessary ship systems: Firefighting systems: Water firefighting system CO2 firefighting system Stationary foam firefighting units Bilge systems Ballast-drainage system Sewage system Domestic fresh water system Ventilation system
We have elaborated the program of construction of such plant at our shipyard. Cost of construction of one RO-module will make about USD 57 million. Construction time of the plant at Baltiysky Zavod JSC will make 1,5 years. The capacity of such plant is 14,600,000 tonnes per year, and its life time of the plant is estimated as 20 years. Consumption of water for domestic needs makes about 500 litres a day in metropolises. Using such floating distilling plant with productivity 40000 m3/day will provide domestic demand for water of a city with population not less than 80 000 people. Baltiysky Zavod JSC is certified in accordance with ISO 9000 International Standards and has been attested by the leading Classification societies, so it can build such plants not only for domestic owner, but also worldwide.