Production of Drinking and Service Water from Brackish and Sea Water

Transcription

1 Production of Drinking and Service Water from Brackish and Sea Water The Process of Membrane Filtration In many regions, the first stage in the production of drinking or service water is to pump water directly from the sea, groundwater wells near the coast or brackish water. This untreated water must then be treated and there are different processes and combinations of processes for this purpose. One reliable method of treating water is, for example, by means of membrane filtration. With this method, very small particles are retained by a membrane and filtered out (retentate). The membrane consists of a thin, fine-porous wall which can filter practically all particles above a certain size. Smaller particles can pass through unhindered and without loss and can thereby be selected (permeate). The water is generally forced or drawn through the filter membrane. In this way, the retained particles or molecules accumulate on the membrane and are concentrated to form a filter cake. The pressure-driven membrane filtration consists of the following basic processes: Microfiltration (MF): filtration of solid particles or colloid particles above a certain diameter Ultrafiltration (UF): filtration of macromolecules above a certain molecular weight Nanofiltration (NF): filtration of nano-range particles Reverse osmosis (RO): filtration of dissolved molecules or ions Membrane process Microfiltration µm Ultrafiltration kda Nanofiltration 1 kda 200 Da Reverse osmosis < 200 Da Composition Zooplankton Phytoplankton Bacteria Suspended particles Macromolecules Viruses Colloids Organic compounds Multivalent ions Ions Required pressure differential 0.1 to 2 bar 0.1 to 5 bar 3 to 20 bar 10 to 100 bar

2 Pre-Filtration Prior to Membrane Systems Water treatment processes generally consist of several stages which must be specially coordinated with one another. For reliable water desalination by means of a pressure-driven membrane process, optimised pre-treatment of the untreated water is an important prerequisite. The pre-treatment is generally the most important step in a multi-stage water treatment process as it can strongly affect the economic efficiency of the membrane filtration downstream. Short lifetimes of the filters and membranes installed downstream, high maintenance costs and high energy consumption due to the high content of turbid particles, suspended solids, colloids and also to a certain extent, organic matter, escalate the costs and have a negative effect on process reliability. Direct sea water extraction NF / RO Pretreatment Posttreatment Brackish / groundwater wells The first stage in the pre-treatment generally consists of coarse particle filtration. During this stage coarse particles which are present in the untreated water, and which could penetrate the system, are removed. Screens, strainers or coarse filters ranging in size from 1 to 5 mm are used. In the next stage the untreated water is further pre-treated to achieve the required feed water quality for the membrane filtration downstream. After the membrane filtration, a post-treatment may be required (e.g. disinfection). Depending on the water quality required, the process stages are adapted to suit the particular requirements of the consumer as well as the actual quality of the untreated water. HYDAC Process Technology is engaged in the pre-treatment of saltwater prior to membrane systems. The AutoFilt RF3 or TwistFlow Strainer TFS, for example, can be used as part of the pre-treatment process. The following examples show that the pre-treatment process can consist of very different process stages.

3 Model 1 Cost reductions on sea water desalination systems are predominantly made through well-engineered pre-treatment processes as these have a lasting effect on the subsequent membrane processes. With the following typical process the pre-treatment essentially consists of the combination of coarse screens, back-flushing filters and cartridge filters. Sea water, Brackish water Posttreatment Pretreatment RO Pretreatment Drinking water / Service water coarse screen AutoFilt RF3 static mixer cartridge filter scale inhibitor 5-15 µm This treatment process is explained in further detail in a case study on page 7. Model 2 In certain cases, the RF3 can also be installed before sand filters where these are used for water treatment. However, since a sand filter is a depth filter which, when operated correctly, can filter out contaminants to a few micrometers nominal, it must be decided on an individual basis to what extent a back-flushing filter can relieve the sand filter. Sea water, brackish water Posttreatment RO Drinking water / service water coarse screen AutoFilt RF3 static mixer sand filter carbon filter static mixer cartridge filter chlorine-containing flocculant polyelectrolyte scale inhibitor

4 Model 3 Membrane processes are also used increasingly in pre-treatment. Here microfiltration or ultrafiltration membranes are used to clean the untreated water to the condition required before undergoing reverse osmosis. Seawater, brackish water Posttreatment Pretreatment RO microfiltration Drinking water / service water coarse screen AutoFilt RF3 ultrafiltration scale inhibitor and/ or With such pre-treatment processes pre-filtration is particularly necessary for microfiltration or ultrafiltration. The RF3 or TFS can be used here to relieve the microfiltration or ultrafiltration and increase the operating reliability of the process. Other Possible Models The pre-treatment processes for the production of drinking and service water are varied and individual. Despite this, in many cases the RF3 and other HYDAC filters, such as the TFS, can make an important contribution towards reducing operating costs and increasing operational reliability The following table shows a selection from the extensive HYDAC filter range from which individual pre-treatment solutions can be created. Other optional models are available on request. Posttreatment Pretreatment RO PRFS TFS RF3 / RF4 PMRF Connection DN 50 to DN 700 NW 1 to DN 100 DN 50 to DN 900 G 1 to DN 200 Flow rate up to 6,000 m³/h up to 120 m³/h up to 10,000 m³/h up to 1,200 m³/h Pressure up to 16 bar up to 16 bar up to 16 bar up to 40 bar Filtration rating 25 to 3,000 µm 200 to 3,000 µm 25 to 3,000 µm 1 to 90 µm

5 AutoFilt RF3 The automatic back-flushing filter Autofilt RF3 is a self-cleaning system for filtering solid particles from low-viscosity fluids. Special features: Isokinetic filtering and back-flushing due to conical filter elements Fewer back-flushing cycles Lower loss of back-flushing fluid Pulse-aided back-flushing Low back-flushing quantities due to cyclic control Compact dimensions with high filtration performance and low pressure drop Variable filter isometry User-selectable control parameters Static sealing Ready-to-operate unit Advantages of the RF3 Extends the lifetime of downstream filters Reduces maintenance costs Reduces energy consumption Increases process reliability by successfully removing the sand particles before the membrane filtration process Space-saving installation Flexible construction Self-cleaning, robust stainless steel filter elements No recurring additional costs Can be retrofitted Economical

6 AutoFilt TFS The Autofilt TwistFlow Strainer TFS is a hybrid system consisting of a centrifugal separator and an inline filter. Special features: TFS - 1 G1 (DN 25) 2 8 m 3 /h TFS - 2 DN m 3 /h TFS - 3 DN m 3 /h Process reliability - not affected by fluctuations in operating pressure, flow rate or consistency of the fluid Specific filtration rating consistently high filtrate quality Suitable for high and fluctuating levels of contamination No other fluids required to clean the filter element Pre-filtration of solid particles of a higher density filter area can take a higher load Low pressure drop Application even at low operating pressure Robust construction, no moving internal parts no spare parts required Space-saving installation Adaptation to flow rates several TFS can be combined on one skid Cost-effective, economical and reliable TFS-2 Cutaway Model Advantages of the TFS Increase in process reliability during pretreatment prior to membrane systems Extension in the service life of the downstream filter Reduction in maintenance costs Reduction in energy consumption Space-saving installation Flexible design Self-cleaning, robust stainless steel filter elements No recurring additional costs Can be retrofitted Economical Cost-effective TFS-2 Filter Skid Filtration Cleaning Phase Phase

7 HYDAC Inline Filters HYDAC inline filters are suitable for continuous and discontinuous filtration of solid particles from water. To avoid interruptions to operation during element change, change-over filters are ideal since one housing is filtering whilst the other is in reserve. A wide range of designs and filter materials ensures optimum adaptation to the particular filtration task and process conditions and provides effective filtration of all types of solid particles. Special features: Temperatures up to 400 C Pressures up to 1,000 bar Filtration ratings of 1 µm (absolute) up to 10 mm Flow rates up to 6,000 m³/h Advantages of Inline Filters Long service life due to large filtration areas Filter materials with a high contamination retention capacity Low pressure drops due to flow-optimised designs Compact, easy-to-operate filter housing Very economical as most filter elements are cleanable Consistently high quality to ISO 9001 Stable design

8 Case Study: Using the RF3 Prior to Cartridge Filters In many water treatment plants where drinking water is produced from brackish water, a treatment process consisting of pre-treatment using fine filtration and downstream reverse osmosis is often employed. The main aim of the study was, therefore, to test and evaluate an automatic backflushing filter Autofilt RF3 in the pre-treatment stage when producing drinking water from brackish and sea water. The study revealed that the backflushing filter is ideally suited to protecting the cartridge filters. The particle contaminants which consisted of fine sand, could be continuously removed from the untreated water which meant that the fine filter cartridges had a considerably longer service life. Retrofitting the backflushing filter in the water treatment plant demonstrated the economic and technical advantages of this concept. Advantages Extends the service life of the cartridge filter elements to several months Reduces maintenance costs and energy consumption Increases process reliability by successfully removing the sand particles prior to the reverse osmosis process Furthermore, it was demonstrated that retrofitting the HYDAC Autofilt RF3 into an existing system is not difficult due to its space-saving, flexible design. In addition, the self-cleaning, robust stainless steel filter elements mean that there are no recurring additional costs. In the meantime, this design has now been successfully implemented in a number of other water treatment plants which had similar problems with fine sand contaminants. p [bar] 0.7 Replacement of the cartridge filter elements without RF3 with RF time [month] Comparison showing increase in differential pressure across the cartridge filter elements both with and without an RF3.

9 Suppliers of Sea Water Desalination Systems System supplier total capacity (m³/d) IONICS US 3,368,000 VEOLIA SIDEM FR 2,248,000 FISIA IT 2,240,000 DOOSAN KR 2,020,000 WEIR TECHNA GB 1,470,000 MHI/SASA KURA JP 1,450,000 ONDEO FR 1,180,000 HITACHI ZOSEN JP 885,000 ENVIROGENICS US 810,000 KURITA JP 780,000 SASAKURA JP 780,000 NOMURA JP 780,000 ISHIKAWAJIMA JP 706,000 VATECH WABAG AT 670,000 VEOLIA US 660,000 IDE IL 615,000 SNAM PROGETTI IT 580,000 HYDRANAUTICS US 560,000 VEOLIA ARABIA SA 520,000 MITSUBISHI JP 502,000 PRIDESA ES 500,000 CADAGUA ES 440,000 ADVANCED EWT US 440,000 ANSALDO IT 436,000 USSR SU 405,000 OTID IDE OTV IL 395,000 MEMBRANE SYST US 380,000 FLUID SYSTEMS US 365,000 EMCO US 352,000 MITSUI JP 346,000 AQUA CHEM US 345,000 ORGANO JP 329,000 INIMA ES 306,000 HYDROPRO US 287,000

10 Suppliers of Membrane Systems System supplier total capacity (m 3 /d) HYDRANAUTICS US 3,215,000 DOW FILMTEC US 2,130,000 DUPONT US 2,080,000 IONICS US 1,430,000 TORAY JP 1,110,000 KOCH FLUID SYSTEMS US 1,050,000 TOYOBO JP 425,000 KURITA JP 425,000 NITTO JP 333,000 SIDMAS SA 240,000 DESALINATION US 190,000 DOW US 135,000

11 Filter Information Further details on the HYDAC PROCESS TECHNOLOGY products presented here can be found in the following brochures and catalogues. D Brochure RF3 D Brochure RF4 D Brochure TFS D Brochure Inline filters D Catalogue Datasheet RF3 D Catalogue Datasheet RF4 D Catalogue Datasheet TFS D Catalogue Datasheet PRFS D Catalogue Datasheet RFSD D Catalogue Datasheet PMRF D Catalogue Datasheet PMRFD D Complete Product Catalogue HYDAC Process Technology GmbH Industriegebiet Grube König Am Wrangelflöz 1 D Neunkirchen Phone: +49/6897/ Fax: +49/6897/ prozesstechnik@hydac.com