1、 STD.AWWA M30-ENGL 1995 H 0783350 0509194 1bT Precoat F i 1 trat i on AWWA MANUAL M30 Second Edition American Water Works Association FO:Epl STDOAWWA M30-ENGL 2995 = 0783350 0509295 OTb W MANUAL OF WATER SUPPLY PRACTICES - M30, Second Edition Precoat Filtration Copyright O 1988, 1995 American Water
2、Works Association All rights reserved. No part of this publicat.ion may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information or retrieval system, except in the form of brief excerpts or quotations for review purposes,
3、without the written permission of the publisher. Editor: Phillip Murray Project Manager: Kathleen A. Faller Printed in the United States of America American Water Works Association 6666 West Quincy Avenue Denver, CO 80235 ISBN 0-89867-787-4 11 Printed on recycled paper STD-AWWA M30-ENGL 1775 0783350
4、 0507396 T32 Contents Foreword, v Chapter 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . History, 1 Description, 1 1 Chapter 2 Applications and Economic Considerations . . . . . . . . . . . 7 Source Water Quality Considerations, 7 Economic Considerations, 11 Chapter 3 Fil
5、ter Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Filter Vessel Design, 15 Filter Element Design, 19 Filter Septum Design, 20 Hydraulics, 22 Filtration Rate, 22 Design Capacity, 23 Chapter 4 Filter Media. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Media Types and
6、 Grades, 25 Precoating, 26 Body-feed, 28 Filter Media Storage, 30 25 Chapter 5 Spent Cake Removal andResiduals Handling . . . . . . . . . 31 Spent Cake Removal and Cleaning Methods, 31 Sludge and Waste Handling, 32 Chapter 6 Operation, Process Control, and Monitoring . . . . . . . . . . 35 Operating
7、 Adjustments, 35 Process Control, 36 Monitoring, 37 Emergency Controls, 38 Maintenance, 38 Record Keeping, 39 Chapter 7 Auxiliary Equipment and Safety . . . . . . . . . . . . . . . . . 41 Auxiliary Equipment, 41 Safety, 42 Glossary, 45 Sources of Information, 47 Index, 49 . 111 STD.AWWA M30-ENGL 399
8、5 0783350 0509397 979 Foreword The first edition of AWWA Manual M30, Precoat Filtration, published in 1988, was prepared by the Precoat Filtration Subcommittee of the Coagulation Gary S. Logsdon; James L. Ris; and Alan Wirsig. Regulations stemming from the 1986 amendments to the Safe Drinking Water
9、Act, specifically the Surface Water Treatment Rule, sparked a renewed interest in filtration techniques, including precoat filtration. The Coagulation the pressure cannot be used for filter operation. Air or dissolved gases that come out of solution because of a decrease in pressure across the filte
10、r cake and septum and are transported by the water (outgassing) may have an adverse effect on the filter cake. Outgassing tends to disrupt the integrity of 15 Previous page is blank STD-AWWA M30-ENGL 1995 W 0783350 0509212 TO5 16 PRECOAT FILTRATION Filter Overflow Filter Element Shell Weir With Slee
11、ve - Effluent Courtesy of Westfail Manufacturing Company. Figure 3-1 Vacuum diatomite (DE) filter element flow diagram Courtesy of Wesffaii Manufacturing Company. Figure 3-2 Vacuum diatomite filter STD.AWWA M30-ENGL 2995 0783350 0509233 942 m Outlet Inlet - FILTER DESIGN 17 the filter media on the s
12、eptum. Special care should be taken to eliminate any air being pulled into source water through pump glands or nonflooded filter-media slurry eductors. The amount of gas coming out of solution is directly related to the dissolved gas concentration, water temperature, and vacuum. Pressure Filters In
13、pressure filters, a filter feed pump or influent gravity flow produces higher-than- atmospheric pressure on the inlet (upstream) side of the filter, forcing liquid through the filter media cake. Large pressure drops across the filter are theoretically possible (limited only by the strength of the fi
14、lter shell and the filter elements and septa), but the maximum economic differential pressure drop is generally limited to 30-40 psi. Qpically, a higher pressure drop across a pressure filter will yield longer cycles and will remove more suspended solids per pound of filter media than with vacuum fi
15、lters. Increased pumping costs for differential pressures much greater than 30-40 psi, however, usually offset savings in filter media costs. Several types of pressure filtration vessels have been developed. Figures 3-3 through 3-6 depict some of the possible configurations. Space considerations may
16、 favor the selection of one filter vessel configuration over others for a particular application. Any vessel selected should meet the following construction criteria. Pressure filter housings should be made of corrosion-resistant materials or should be lined or coated with protective materials that
17、will last for many years. American Water Works Association (AWWA) standards for coating and lining tanks and water pipelines should be used as guidelines when specifying the coating and lining for precoat filtration facilities. Stainless steel should be considered for maximum service life. Vessels s
18、hould be fabricated to ensure good construction and adequate strength in accordance with the American Society of Mechanical Engineers Boiler and , Air Vent and Gauge Reprinted with permission of Celite Corporation. Figure 3-3 Horizontal tank pressure leaf filter - rotating leaf STD-AWWA M30-ENGL 199
19、5 m 0783350 0509234 888 18 PRECOAT FILTRATION fi AirVent Sluice c Filtrate , inlet + rate Reprinted with permission of Celite Corporation. Figure 34 Vertical tank pressure leaf filter Filtrate Reprinted with permission of Celite Corporation. Figure 3-5 Horizontal tank pressure filter -vertical leaf
20、STD-AWWA fl30-ENGL 1995 W 0783350 O509235 7/11 FILTER DESIGN 19 Reprinted with permission of Celite Corporation. Figure 3-6 Tubular pressure filter Pressure Vessel Code, Section VIII, or other guidelines. High-pressure relief should be provided. Vessel design should provide for full access for inspe
21、ction and maintenance operations. One or more illuminated sight ports should be installed in the shell to permit visual observation of the filter during operation. Access to internal areas of the filters may be achieved through quick-opening heads that allow the vessel to be opened within minutes (s
22、ee Figures 3-3 and 3-4). Pressure vessels are also designed with fixed heads and retracting shells to permit immediate access to all of the septa (see Figure 3-5). Before inspection, pressure tubular filters generally require bolt removal and some piping disassembly, as well as a hoisting facility t
23、o remove the filter head and the tube sheet (see Figure 3-6). Suitable lifting devices should be provided, either over or alongside filters, to assist in the removal and disassembly of internal elements of the filter for maintenance. Piping, wiring, and auxiliary equipment should be arranged to faci
24、litate normal operations and maintenance work. FILTER ELEMENT DESIGN The following basic criteria must be incorporated into element design: firm support for the filter media cake 0 adequate drainage area inside the element so that the filtered water can easily exit from the element 0 proper construc
25、tion of the septum to provide clear openings of proper size so that the filter media forms strong, stable “bridges” over the openings capability of septum material to maintain the integrity of the weave pattern to prevent distortion of opening size or shape with continued use 0 corrosion-resistant c
26、onstruction materials fl30-ENGL 1995 O783350 0509216 650 20 PRECOAT FILTRATION Rectangular Leaf Circular Leaf Flat Filter Elements Tubular Filter Element Figure 3-7 Typical filter elements Filter elements may be either flat or tubular (Figure 3-7). Flat elements, often referred to as leaves, may be
27、rectangular or round. Tubular elements are available in several different cross-sectional shapes but are generally round. Tubular elements, which are always oriented vertically in vertical tanks, require sufficient headroom for disassembly and routine maintenance. Flat leaf elements used in pressure
28、 filters are generally mounted vertically in horizontal or vertical tanks and discharge filtered water through a bottom nozzle into the filter discharge manifold. Flat leaf elements in vacuum filters are also generally mounted vertically, but they discharge filtered water through a top nozzle into a
29、 discharge manifold located near the top of the filter box. This arrangement permits escape of any displaced air or gas. The internal construction of flat leaf elements can vary widely, depending on the intended service, but elements intended for water service will usually incorporate a drainage mem
30、ber to provide strength and rigidity as well as free drainage area (Figure 3-8). The septum material overlays the drainage member. It usually consists of either tightly woven stainless-steel wire mesh or a tightly fitted bag made from monofilament polypropylene weave. A frame member around the perim
31、eter of the leaf provides additional drainage as well as strength (Figure 3-9). Tubular element construction varies widely, but it usually includes a drainage supporting member of perforated metal or well screen wire overlaid by a septum of stainless-steel wire or wire mesh. Cylindrical elements mad
32、e of flexible woven wire; synthetic mesh; or a porous, ceramic, heat-treated material are available. FILTER SEPTUM DESIGN The filter cake forms on and is supported by the septum. The size of the clear openings in the septum must be small enough for the precoat media to form and maintain stable bridg
33、es across the openings. A clear opening of 0.005 in. (about 125 pm) or less in one direction is desirable. In stainless steel, a 24 x 110 Dutch-weave wire mesh has been successfully used with the grades of precoat media found in water filtration. An air permeability rating of 70-100 scfm/ft2 at a pr
34、essure drop of 0.018 psi (0.5 in. of water) in association with clear openings of 0.005 in. indicates a satisfactory septum material. Finer mesh septum material may be desirable if finer grades of filter media are required. For example, a 50 x 250 wire mesh having a 60-pm retention is available. STD
35、-AWWA M30-ENGL 2995 0783350 0509237 597 FILTER DESIGN 21 w Reprinted with permission of Celite Corporation. Figure 3-8 Typical construction of a flat leaf filter element b 37 in. 1 fi Bottom View Upper Element Support Bar 30-ft2 Filter Area - Cloth Sleeve Over Septum support Lower Element , Support
36、Bar Courtesy of Westfall Manufacturing Company. Figure 3-9 Typical construction of vacuum DE leaf filter element STD-AUWA M30-ENGL 1995 m 0783350 0509238 423 m 22 PRECOAT FILTRATION The finer mesh screen exhibits a higher pressure drop than the 24 x 110 Dutch-weave wire mesh noted previously. Where
37、possible, evaluations of different mesh screens should be included in pilot studies. The septum should be firmly supported so that it does not yield, flex, or become distorted as the differential pressure drop increases during the filter cycle. If the septum yields or gives as pressure increases, th
38、e filter media bridges may slowly break down. When this occurs, small amounts of filter media may enter the finished water, increasing turbidity. It is also important for the septum to allow any particles that have passed through the filter media also to pass through the septum itself, or else the s
39、eptum will become plugged and require cleaning. A septum made of monofilament material having uniform, consistent opening sizes resists plugging better than multifilament materials or those that depend on labyrinth passageways to retain the filter media. HYDRAULICS. A basic criterion in design is to
40、 ensure adequate flow velocities within piping and filters to transport the source water and filter media particles to all parts of the filter. This is particularly important when the system is operating at minimum design flow. For most filters, sufficient upward velocity should be maintained to kee
41、p particles in suspension and moving. All filter media and dirt particles should become lodged on the element rather than on the bottom of the filter. Appropriate flow distribution or baffling within the filter vessel should be provided to distribute flow evenly and to prevent short circuiting or sc
42、ouring of the filter media cake during filter operations. Proper spacing of the filter elements is necessary to provide for cake accumulation, to permit adequate cleaning, and to maintain good hydraulics within the filter. The drainage characteristics of the filter vessel are important for filter sy
43、stems in which the spent filter media cake is washed away from the septum and removed from the filter vessel as a slurry. The filter vessel drain should be large enough to discharge the water slurry quickly. The bottom of the vessel should slope to the drain, or the vessel should be equipped with in
44、ternal flush headers to move all of the solids to the drain. Clean water flush nozzles should also be provided so that the interior of the vessel can be flushed clean of all solids. Any solids remaining in the filter vessel after cleaning could be resuspended and deposited on the clean septum during
45、 the next precoat cycle, leading to eventual plugging of the septum. FILTRATION RATE As described previously, filtration rate is defined in terms of the volume of liquid that passes through a given area of filter in a specific time. The rate used for design purposes is most frequently an economic ju
46、dgment based on a number of factors. In the past, a typical filtration rate of 1.0 gpm/ft2 has been used for design; however, studies involving full-scale equipment have shown filtration rates of up to 3.0 gpm/ft2 to be most frequently used in treatment plants. The actual filtration rate in service
47、may need to be varied because of normal variations in demand for water. It is important, however, that the filters not be designed for direct operation according to system demand. Increases or decreases in filtration rate within practical limits do not significantly affect the quality of the finishe
48、d water, so long as the needed changes are made slowly to avoid hydraulic shock to the developing filter cake. Most of the source water particulates are removed STD-AWWA M30-ENGL 1995 0783350 0509239 3bT = FILTER DESIGN 23 on or near the surface of the filter cake, and removed materials are not norm
49、ally dislodged by gradual rate changes. Any filtration rate change should include a gradual change in the rate of body-feed to maintain the body-feed proportion to the filtration rate. DESIGN CAPACITY The size of the filters and the auxiliary pumps and piping can be determined based on the desired total design capacity. For preliminary design purposes, a common filtration rate for sizing precoat filters for potable water is 1.0 gpm/ft2. It is essential to carry out suitable field pilot studies to determine the actual design criteri
