太阳能海水淡化的英文翻译

太阳能海水淡化的英文翻译 The development of a high flow seawater membrane Abstract Reverse osmosis (RO) technology has been used for the reduction of the salt content of water since the late 1960s. The RO membrane elements are available for a variety of desalination applications, treating water from sources ranging from seawater and brackish water to waste water for use in applications ranging from industrial and process water to drinking water. In recent years major advancements have been made in the flux and salt rejection capabilities of the membranes. It became apparent that a high flow seawater membrane element was needed particularly for cooler, lower salinity water and during the mid 1990s a product was developed to meet these needs. In 1999 high flow seawater elements, Koch Membrane Systems product Fluid Systems TM TFC1 2822HF-370 elements were installed in a new plant producing 5230 m3/d process and boiler feed water for EDIPOWER at Archi Marina San Filippo del Mela – Sicily, Italy. This paper is a case history describing the plant and looking at the performance of the membrane using Koch Membrane Systems NormPro1 to normalize the data. Keywords: Reverse osmosis; Seawater; High flow; Industrial water; Boiler feed; Normalisation 1. Introduction In 1990s the decision was taken in Italy to modify a number of the power stations,changing from coal fired to oil fired. For environmental reasons, there was also a requirement for a deSOx plant for flue gas scrubbing. The plant at San Filippo del Mela was one of those changed. Originally the plant had a demineraliser treating well water to provide boiler feed water. However the deSOx plant required additional process water and it was decided to use desalinated seawater to provide water for both the deSOx plant and for boiler feed replacing the demineraliser treating well water. Two process water qualities were required <1000 _S/cm for the deSOx and <20 _S/cm to feed the mixed beds for boiler feed. The available technologies were by thermal desalination or reverse osmosis. Partial two pass RO was chosen over thermal evaporators because of need of two qualities. And so the decision was made to build the two pass RO plant. Commissioning began in late 1999 and the RO went into service in early 2000. 2. Development of high flow seawater membrane The use of RO for desalination has grown rapidly since its commercialisation in the 1960s. The first thin film composite membranes [1] were introduced in the mid 1970s and the first seawater systems were built in the late 1970s [2]. The early plants consisted of two passes or partial two pass [3] as the seawater membrane had <99% rejection and could not achieve drinking water standards in one pass. Over the years improvements were made to increase both flux and rejection of the membranes [4] to allow production of low salinity water from one pass and in construction of the element to operate up to higher pressures [5] of 83 bar to allow higher recoveries and operation on high salinity water. However by the late 1990s a need was seen for a high flux seawater membrane for use on lower salinity seawater and at lower temperatures. This fitted the requirement at San Filippo del Mela, where the high flow seawater membrane could produce the process water for the deSOx plant and a partial second pass could produce the low salinity water to feed the mixed beds for the boiler feed water. In 1995 Fluid SystemsTM TFC1 high flow seawater membrane had started to be supplied for small elements used in yachts and this membrane worked very well for this application and had in fact ideal properties for an 8 inch element. The element construction was developed to give a high area and capability to operate up to 70 bar. This is achieved by using 28 mil spacer rather than 31 mil used in a standard area element and rather than the simplex permeate spacer used for the high pressure 82 bar elements, a thinner modified tricot is used, giving a membrane area of 370 ft2. The element was designated Fluid SystemsTM TFC1 2822HF-370. The first commercial production was in late 1999 for the San Filippo del Mela project and was one of the first 8 inch high flow seawater elements to be commercialised. 3. Description of plant 3.1. Pretreatment The seawater is drawn from an existing open intake 250 m out and at 15–20 m depth. The seawater is typically about 42,000 mg/l TDS and 57,000 _S/cm conductivity and temperature varies from about 12–27?C. The design analysis is given in Table 1. The seawater is dosed with sodium hypochlorite for disinfection and there is a facility to dose polyelectrolyte for coagulation. There are two stages of filtration. The first stage filtration is through continuous backwashing upflow gravity sand filters and the filtered water is collected in the filtered water storage tank. Table 1 Design seawater analysis Parameter mg/l Calcium 640 Magnesium 1446 Sodium 11440 Potassium 518 Strontium 7.5 Barium 0.005 Bicarbonate 183 Sulphate 3314 Chloride 24850 Silica 0.6 TDS 42300 Temperature(?C) 20 The filtered water is pumped through second stage multimedia pressure sand filters, with facility to dose additional coagulant if required. The filtered water is passed through UV sterilisers for further disinfection. Hydrochloric acid and antiscalant are dosed for scale control and sodium bisulphite is dosed for dechlorination. The final step is 5 _ cartridge filtration (Fig. 1). Fig. 1. Pretreatment P & ID. 3.2. RO trains The system is divided into three first pass trains of high flow seawater membrane elements And two second pass trains of high rejection low pressure brackish water membrane elements. Each first pass has a capacity of 72 m3/h and operates at 42% recovery. Each second pass has a capacity of 32.5 m3/h. First pass consists of a single array of 20 tubes with seven TFC1 2822HF-370 high flow seawater elements in each tube (Fig. 2). Part of the permeate goes for process water and has the facility to dose with sodium hydroxide for pH correction. Part goes to a storage tank and is pumped through cartridge filters into the second pass which consists of 3:1 array of 4 tubes with seven TFC1 8822HR-400 high rejection low pressure brackish water elements in each tube (Fig. 3 and Fig. 4). 4. Performance of plant The plant started up well. The paper focuses on the performance of the TFC1 2822HF-370 high flow seawater elements in the first pass. Train A operated for the longest time during the period and data from this train will be presented and analysed. Fig. 2. First pass RO trains A, B and C. During commissioning samples were taken which gave first pass permeate Total hardness of 16 mg/l as CaCO3 and Chloride of 170 mg/l, which was in line with anticipated values and the feed pressure settled to less than 60 bar which was better than anticipated. Once stabilised after commissioning the flux remained relatively constant for about 2 years, after that a decline can be seen. Fig. 3. Second pass RO. The graph shows the first pass relative normalised flux (A v) vs. time for the operating period (Fig. 5). The salt passage remained stable during the whole period. However permeate conductivity rises with temperature in the summer of 2004 the temperatures exceeded 30 ?C (much higher than design values) and the conductivity became too high. A row of tubes was taken off line to improve the quality by increasing the flux. The graph shows the first pass relative normalized salt passage (B v) vs time for the operating period (Fig. 6). The differential pressure rose slowly during the first two years, from about 0.8 bar to 1.9 bar, however in the last year rose more rapidly to 3.3 bar. The graph shows the first pass relative normalized differential pressure coefficient (DPCoeff) vs time for the operating period (Fig. 7). The flux decline together with the differential pressure increase shows that eventually significant fouling occurred. Records from 2002 show feed water SDI of 1–2 however by 2004 this had deteriorated to 4–5. This would explain the increase in fouling and element blockage. Despite regular cleaning the blinding of the membrane and the blockage of the element feed channel could not be fully reversed. Cleaning was initially at every 2–3 months and was later increased to every month. It was thought that a significant part of the fouling was attributable to biogrowth and this was addressed by starting to sanitise the elements. 5. Conclusion The first full commercial production of the Fluid SystemsTM TFC1 2822HF-370 elements performed very well on start up in 1999 and have continued to perform well over the 4 years to date. The client has been very satisfied with the performance. Fig. 4. RO P&ID. Fig. 5. Train A first pass relative normalised flux vs. time. Fig. 6. Train A first pass relative normalised salt passage vs. time. Fig. 7. Train A first pass relative normalised differential pressure coefficient vs. time. They were more open than anticipated operating at lower pressure however were able to produce the design quality and quantity of permeate from both passes. Despite the feed water eventually causing significant fouling, performance has been maintained with regular cleaning and little deterioration in quality occurred. Higher seawater temperatures meant some changes in operation and for that reason it is planned to change one train of elements this year. References [1] J.H. Sleigh and R.L. Truby, Development of commercial reverse osmosis spiral wound seawater desalting systems and IDEA Conference, Puerto Rico, 1975. [2] A. Al-Gholaikah, N. El-Ramly, I. Jamjoom and R. Seaton, TheWorld’s first large RO desalination plant at Jeddah. KSA. NWSIA J., 1997. [3] H. Beets and R.L. Truby, Seawater desalting using membranes — past, present and future. KAE NV Conference, Curacao, 1998. [4] P. Moss and J.M. de Lara y Gil, Desalination, 125 (1999) 17–23. [5] S. Cappos, W. Varnava and M. Silbernagel, Seawater desalination with advanced TFC RO membranes and IDA Conference, Abu Dhabi, 1995.